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Since the 1990s, there has been an ongoing debate whether computer operating systems that use GNU software and the Linux kernel should be referred to as "GNU/Linux" or "Linux" systems. [ 1 ]
Proponents of the term Linux argue that it is far more commonly used by the public and media [ 2 ] [ 3 ] and that it serves as a generic term for systems that combine that kernel with software from multiple other sources, [ 4 ] while proponents of the term GNU/Linux note that GNU alone would be just as good a name for GNU variants which combine the GNU operating system software with software from other sources. [ 5 ]
The term GNU/Linux is promoted by the Free Software Foundation (FSF) and its founder Richard Stallman . Their reasoning is that the operating system is seen as a modified version of the GNU operating system. Linux as a kernel is just a part of an operating system, whereas the whole operating system is basically the GNU system. [ 6 ] [ 7 ] Several distributions of operating systems containing the Linux kernel use the name that the FSF prefers, such as Debian , [ 8 ] Trisquel [ 9 ] and Parabola GNU/Linux-libre . [ 10 ] Others claim that GNU/Linux is a useful name to make a distinction between those and Linux distributions such as Android and Alpine Linux .
In 1983, Richard Stallman , founder of the Free Software Foundation , set forth plans of a complete Unix-like operating system , called GNU , composed entirely of free software . In September of that year, Stallman published a manifesto in Dr. Dobb's Journal detailing his new project publicly, outlining his vision of free software . [ 11 ] [ 12 ] Software development work began in January 1984. By 1991, the GNU mid-level portions of the operating system were almost complete, and the upper level could be supplied by the X Window System , but the lower level ( kernel , device drivers, system-level utilities and daemons ) was still mostly lacking.
The kernel officially developed by GNU was called GNU Hurd . The Hurd followed an ambitious microkernel design, which proved unexpectedly difficult to implement early on. However, in 1991, Linus Torvalds independently released the first version of the Linux kernel. Early Linux developers ported GNU code, including the GNU C Compiler , to run with Linux, while the free software community adopted the use of the Linux kernel as the missing kernel for the GNU operating system. This work filled the remaining gaps in providing a completely free operating system. [ 7 ]
Over the next few years, several suggestions arose for naming operating systems using the Linux kernel and GNU components. In 1992, the Yggdrasil Linux distribution adopted the name "Linux/GNU/ X ". In Usenet and mailing-list discussions, one can find usages of "GNU/Linux" as early as 1992, [ 13 ] and of "GNU+Linux" as early as 1993. [ 14 ] The Debian project, which was at one time sponsored by the Free Software Foundation , switched to calling its product "Debian GNU/Linux" in early 1994. [ 3 ] [ 15 ] [ 16 ] [ 17 ] This change followed a request by Richard Stallman (who initially proposed "LiGNUx," but suggested "GNU/Linux" instead after hearing complaints about the awkwardness of the former term). [ 18 ] GNU's June 1994 Bulletin described "Linux" as a "free Unix system for 386 machines" (with "many of the utilities and libraries" from GNU), [ 19 ] but the January 1995 Bulletin switched to the term "GNU/Linux" instead. [ 20 ]
Stallman's and the FSF's efforts to include "GNU" in the name started around 1994, but were reportedly mostly via private communications (such as the above-mentioned request to Debian) until 1996. [ 21 ] [ 22 ] In May 1996, Stallman released Emacs 19.31 with the Autoconf system target "linux" changed to "lignux" (shortly thereafter changed to "linux-gnu" in emacs 19.32), [ 23 ] [ 7 ] and included an essay "Linux and the GNU system" [ 24 ] suggesting that people use the terms "Linux-based GNU system" (or "GNU/Linux system" or "Lignux" for short). He later used "GNU/Linux" exclusively, and the essay was superseded by Stallman's 1997 essay, "Linux and the GNU System". [ 6 ]
Modern free software and open-source software operating systems are composed of software by many different authors, including the Linux kernel developers, the GNU project, and other vendors such as those behind the X Window System . Desktop and server-based distributions use GNU software such as the GNU C Library (glibc), GNU Core Utilities (coreutils), GNU Compiler Collection , GNU Binutils , GNU gzip , GNU tar , GNU gettext , GNU grep , GNU awk , GNU sed , GNU Findutils , gnupg , libgcrypt , gnutls , GRUB , GNU readline , GNU ncurses , and the Bash shell.
In a 2002 analysis of the source code for Red Hat Linux 7.1, a typical Linux distribution , the total size of the packages from the GNU project was found to be much larger than the Linux kernel. [ 25 ] Later, a 2011 analysis of the Ubuntu distribution's "Natty" release main repository found that 8% to 13% of it consisted of GNU components (the range depending on whether GNOME is considered part of GNU), while only 6% is taken by the Linux kernel (9% when including its direct dependencies). [ 26 ] Determining exactly what constitutes the "operating system" per se is a matter of continuing debate. [ 1 ]
On the other hand, some embedded systems , such as handheld devices and smartphones (like Google's Android ), residential gateways (routers), and Voice over IP devices, are engineered with space efficiency in mind and use a Linux kernel with few or no components of GNU, due to perceived issues surrounding bloat , and impeded performance. [ 27 ] A system running μClinux is likely to substitute uClibc for glibc, and BusyBox for coreutils. Google's Linux-based Android operating system does not use any GNU components or libraries, using Google's own BSD -based Bionic C library in place of glibc. The FSF agrees that "GNU/Linux" is not an appropriate name for these systems. [ 28 ] [ 29 ] [ 30 ]
There are also systems that use a GNU userspace and/or C library on top of a non-Linux kernel, for example Debian GNU/Hurd (GNU userland on the GNU kernel) [ 31 ] or Debian GNU/kFreeBSD (which uses the GNU coreutils and C library with the kernel from FreeBSD ). [ 32 ]
The FSF justifies the name "GNU/Linux" primarily on the grounds that the GNU project was specifically developing a complete system, of which they argue that the Linux kernel filled one of the final gaps; [ 33 ] the large number of GNU components and GNU source code used in such systems is a secondary argument:
So if you were going to pick a name for the system based on who wrote the programs in the system, the most appropriate single choice would be GNU . But we don't think that is the right way to consider the question. The GNU Project was not, is not, a project to develop specific software packages. [...] Many people have made major contributions to the free software in the system, and they all deserve credit. But the reason it is an integrated system—and not just a collection of useful programs—is because the GNU Project set out to make it one. We made a list of the programs needed to make a complete free system, and we systematically wrote, or found people to write, everything on the list.
Other arguments include that the name "GNU/Linux" recognizes the role that the free-software movement played in building modern free and open source software communities , [ 28 ] that the GNU project played a larger role in developing packages and software for GNU/Linux or Linux distributions , [ 6 ] [ 7 ] and that using the word "Linux" to refer to the Linux kernel, the operating system and entire distributions of software leads to confusion on the differences about the three. Because of this confusion, legal threats and public relations campaigns apparently directed against the kernel, such as those launched by the SCO Group or the Alexis de Tocqueville Institution (AdTI), have been misinterpreted by many commentators who assume that the whole operating system is being targeted. SCO and the AdTI have even been accused of deliberately exploiting this confusion. [ 34 ] [ 35 ] [ 36 ]
Regarding suggestions that renaming efforts stem from egotism or personal pique, Stallman has responded that his interest is not in giving credit to himself but to the GNU Project: "Some people think that it's because I want my ego to be fed. Of course, I'm not asking you to call it 'Stallmanix'." [ 37 ] In response to another common suggestion that many people have contributed to the system and that a short name cannot credit all of them, the FSF has argued that this cannot justify calling the system "Linux", since they believe that the GNU project's contribution was ultimately greater than that of the Linux kernel in these related systems. [ 7 ] [ 26 ]
In 2010, Stallman stated that naming is not simply a matter of giving equal mention to the GNU Project, saying that because the system is more widely referred as "Linux", people tend to "think it's all Linux, that it was all started by Mr. Torvalds in 1991, and they think it all comes from his vision of life, and that's the really bad problem." [ 38 ]
Ariadne Conill , the developer and security chair of Alpine Linux , has stated that in her opinion GNU/Linux is the correct name when referring to Linux distributions that are based on glibc and coreutils , such as Debian and Fedora Linux . This can be contrasted to other Linux distributions such as Alpine, which instead uses musl as its C library and BusyBox to provide core functionality. [ 39 ]
Proponents of naming the operating systems "Linux" state that "Linux" is used far more often than "GNU/Linux". [ 2 ] [ 3 ]
Eric S. Raymond writes (in the "Linux" entry of the Jargon File ):
Some people object that the name "Linux" should be used to refer only to the kernel, not the entire operating system. This claim is a proxy for an underlying territorial dispute; people who insist on the term GNU/Linux want the FSF to get most of the credit for Linux because [Stallman] and friends wrote many of its user-level tools. Neither this theory nor the term GNU/Linux has gained more than minority acceptance.
When Linus Torvalds was asked in the documentary Revolution OS whether the name "GNU/Linux" was justified, he replied:
Well, I think it's justified, but it's justified if you actually make a GNU distribution of Linux ... the same way that I think that "Red Hat Linux" is fine, or "SUSE Linux" or "Debian Linux", because if you actually make your own distribution of Linux, you get to name the thing, but calling Linux in general "GNU Linux" I think is just ridiculous. [ 40 ] [ 41 ]
An earlier comment by Torvalds on the naming controversy was:
Umm, this discussion has gone on quite long enough, thank you very much. It doesn't really matter what people call Linux, as long as credit is given where credit is due (on both sides). Personally, I'll very much continue to call it "Linux", ...
The GNU people tried calling it GNU/Linux, and that's ok. It's certainly no worse a name than "Linux Pro" or "Red Hat Linux" or
"Slackware Linux" ...
Lignux is just a punny name—I think Linux/GNU or GNU/Linux is a bit more "professional" ... [ 42 ]
The name "GNU/Linux," particularly when using Stallman's preferred pronunciation, has been criticized for its perceived clumsiness and verbosity, [ 43 ] [ 44 ] a factor that Torvalds has cited as the downfall of operating systems such as 386BSD . [ 45 ]
The Linux Journal speculated that Stallman's advocacy of the combined name stems from frustration that "Linus got the glory for what [Stallman] wanted to do." [ 46 ]
Others have suggested that, regardless of the merits, Stallman's persistence in what sometimes seems a lost cause makes him and GNU look bad. For example, Larry McVoy (author of BitKeeper , once used to manage Linux kernel development) opined that "claiming credit only makes one look foolish and greedy". [ 47 ]
Many users and vendors who prefer the name "Linux," such as Jim Gettys , one of the original developers of the X Window System , point to the inclusion of non-GNU, non-kernel tools, such as KDE , LibreOffice , and Firefox , in end-user operating systems based on the Linux kernel:
There are lots of people on this bus; I don't hear a clamor of support that GNU is more essential than many of the other components; can't take a wheel away, and end up with a functional vehicle, or an engine, or the seats. I recommend you be happy we have a bus. [ 48 ] | https://en.wikipedia.org/wiki/GNU/Linux_naming_controversy |
GNU Multiple Precision Arithmetic Library ( GMP ) is a free library for arbitrary-precision arithmetic , operating on signed integers , rational numbers , and floating-point numbers . [ 4 ] There are no practical limits to the precision except the ones implied by the available memory (operands may be of up to 2 32 −1 bits on 32-bit machines and 2 37 bits on 64-bit machines). [ 5 ] [ 6 ] GMP has a rich set of functions, and the functions have a regular interface. The basic interface is for C , but wrappers exist for other languages, including Ada , C++ , C# , Julia , .NET , OCaml , Perl , PHP , Python , R , Ruby , and Rust . Prior to 2008, Kaffe , a Java virtual machine , used GMP to support Java built-in arbitrary precision arithmetic. [ 7 ] Shortly after, GMP support was added to GNU Classpath . [ 8 ]
The main target applications of GMP are cryptography applications and research, Internet security applications, and computer algebra systems .
GMP aims to be faster than any other bignum library for all operand sizes. Some important factors in doing this are:
The first GMP release was made in 1991. It is constantly developed and maintained. [ 9 ]
GMP is part of the GNU project (although its website being off gnu.org may cause confusion), and is distributed under the GNU Lesser General Public License (LGPL).
GMP is used for integer arithmetic in many computer algebra systems such as Mathematica [ 10 ] and Maple . [ 11 ] It is also used in the Computational Geometry Algorithms Library (CGAL).
GMP is needed to build the GNU Compiler Collection (GCC). [ 12 ]
Here is an example of C code showing the use of the GMP library to multiply and print large numbers:
This code calculates the value of 7612058254738945 × 9263591128439081.
Compiling and running this program gives this result. (The -lgmp flag is used if compiling on Unix-type systems.)
For comparison, one can write instead the following equivalent C++ program. (The -lgmpxx -lgmp flags are used if compiling on Unix-type systems.) | https://en.wikipedia.org/wiki/GNU_Multiple_Precision_Arithmetic_Library |
GNet is a simple network library. It is written in C , object-oriented, and built upon GLib . It is intended to be small, fast, easy-to-use,
and easy to port. The interface is similar to the interface for Java 's network library.
GNet has been ported to Linux , BSD , macOS , Solaris , HP-UX , and Windows . It may work on other flavors of Unix too.
According to the GNet reference below,
GNet is very soon (with the release of GLib 2.22.0) going to be deprecated and replaced by the newly added platform-independent network and socket abstraction layer in GLib/Gio
This computing article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/GNet |
The GOR method (short for Garnier–Osguthorpe–Robson) is an information theory -based method for the prediction of secondary structures in proteins . [ 1 ] It was developed in the late 1970s shortly after the simpler Chou–Fasman method . Like Chou–Fasman, the GOR method is based on probability parameters derived from empirical studies of known protein tertiary structures solved by X-ray crystallography . However, unlike Chou–Fasman, the GOR method takes into account not only the propensities of individual amino acids to form particular secondary structures, but also the conditional probability of the amino acid to form a secondary structure given that its immediate neighbors have already formed that structure. The method is therefore essentially Bayesian in its analysis. [ 2 ]
The GOR method analyzes sequences to predict alpha helix , beta sheet , turn , or random coil secondary structure at each position based on 17-amino-acid sequence windows. The original description of the method included four scoring matrices of size 17×20, where the columns correspond to the log-odds score, which reflects the probability of finding a given amino acid at each position in the 17-residue sequence. The four matrices reflect the probabilities of the central, ninth amino acid being in a helical, sheet, turn, or coil conformation. In subsequent revisions to the method, the turn matrix was eliminated due to the high variability of sequences in turn regions (particularly over such a large window). The method was considered as best requiring at least four contiguous residues to score as alpha helices to classify the region as helical, and at least two contiguous residues for a beta sheet. [ 3 ]
The mathematics and algorithm of the GOR method were based on an earlier series of studies by Robson and colleagues reported mainly in the Journal of Molecular Biology and The Biochemical Journal . [ 4 ] [ 5 ] The latter describes the information theoretic expansions in terms of conditional information measures. The use of the word "simple" in the title of the GOR paper reflected the fact that the above earlier methods provided proofs and techniques somewhat daunting by being rather unfamiliar in protein science in the early 1970s; even Bayes methods were then unfamiliar and controversial. An important feature of these early studies, which survived in the GOR method, was the treatment of the sparse protein sequence data of the early 1970s by expected information measures. That is, expectations on a Bayesian basis considering the distribution of plausible information measure values given the actual frequencies (numbers of observations). The expectation measures resulting from integration over this and similar distributions may now be seen as composed of "incomplete" or extended zeta functions, e.g. z(s,observed frequency) − z(s, expected frequency) with incomplete zeta function z(s, n) = 1 + (1/2) s + (1/3) s + (1/4) s + …. +(1/ n ) s . The GOR method used s=1. Also, in the GOR method and the earlier methods, the measure for the contrary state to e.g. helix H, i.e. ~H, was subtracted from that for H, and similarly for beta sheet, turns, and coil or loop. Thus the method can be seen as employing a zeta function estimate of log predictive odds. An adjustable decision constant could also be applied, which thus implies a decision theory approach; the GOR method allowed the option to use decision constants to optimize predictions for different classes of protein. The expected information measure used as a basis for the information expansion was less important by the time of publication of the GOR method because protein sequence data became more plentiful, at least for the terms considered at that time. Then, for s=1, the expression z(s,observed frequency) − z(s,expected frequency) approaches the natural logarithm of (observed frequency / expected frequency) as frequencies increase. However, this measure (including use of other values of s) remains important in later more general applications with high-dimensional data, where data for more complex terms in the information expansion are inevitably sparse. [ 6 ] | https://en.wikipedia.org/wiki/GOR_method |
The GP5 is a co-processor accelerator built to accelerate discrete belief propagation on factor graphs and other large-scale tensor product operations for machine learning. It is related to, and anticipated by a number of years, the Google Tensor Processing Unit
It is designed to run as a co-processor with another controller (such as a CPU (x86) or an ARM/MIPS/Tensilica core). It was developed as the culmination of DARPA's Analog Logic program [ 1 ]
The GP5 has a fairly exotic architecture, resembling neither a GPU nor a DSP, and leverages massive fine-grained and coarse-grained parallelism. It is deeply pipelined. The different algorithmic tasks involved in performing belief propagation updates are performed by independent, heterogeneous compute units. The performance of the chip is governed by the structure of the machine learning workload being evaluated. In typical cases, the GP5 is roughly 100 times faster and 100 times more energy efficient than a single core of a modern core i7 performing a comparable task. It is roughly 10 times faster and 1000 times more energy efficient than a state-of-the art GPU. It is roughly 1000 times faster and 10 times more energy efficient than a state-of-the-art ARM processor. It was benchmarked on typical machine learning and inference workloads that included protein side-chain folding, turbo error correction decoding, stereo vision, signal noise reduction, and others.
Analog Devices , Inc. acquired the intellectual property for the GP5 when it acquired Lyric Semiconductor, Inc. in 2011. | https://en.wikipedia.org/wiki/GP5_chip |
A GPCR oligomer is a protein complex that consists of a small number ( ὀλίγοι oligoi "a few", μέρος méros "part, piece, component") of G protein-coupled receptors (GPCRs). It is held together by covalent bonds or by intermolecular forces . The subunits within this complex are called protomers , while unconnected receptors are called monomers. Receptor homomers consist of identical protomers, while heteromers consist of different protomers.
Receptor homodimers – which consist of two identical GPCRs – are the simplest homomeric GPCR oligomers. Receptor heterodimers – which consist of two different GPCRs – are the simplest heteromeric GPCR oligomers.
The existence of receptor oligomers is a general phenomenon, whose discovery has superseded the prevailing paradigmatic concept of the function of receptors as plain monomers, and has far-reaching implications for the understanding of neurobiological diseases as well as for the development of drugs. [ 2 ] [ 3 ]
For a long time it was assumed that receptors transmitted their effects exclusively from their basic functional forms – as monomers. The first clue to the existence of GPCR oligomers goes back to 1975 when Robert Lefkowitz observed that β-adrenoceptors display negative binding cooperativity . [ 4 ] At the beginning of the 1980s, it was hypothesized, receptors could form larger complexes , the so-called mosaic form, [ 5 ] where two receptors may interact directly with each other. [ 6 ] Mass determination of β-adrenoceptors (1982) [ 7 ] and muscarinic receptors (1983), [ 8 ] supported the existence of homodimer or tetrameric complexes. In 1991, the phenomenon of receptor crosstalk was observed between adenosine A 2A (A2A) and dopamine D 2 receptor (DRD2) thus suggesting the formation of heteromers. [ 9 ] While initially thought to be a receptor heterodimer , a review from 2015 determined that the A2A-DRD2 heteromer is a heterotetramer composed of A2A and DRD2 homodimers (i.e., two adenosine A2A receptors and two dopamine D2 receptors). [ 10 ] Maggio and co-workers showed in 1993 the ability of the muscarinic M 3 receptor and α2C-adrenoceptor to heterodimerize. [ 11 ] The first direct evidence that GPCRs functioned as oligomers in vivo came from Overton and Blumer in 2000 by fluorescence resonance energy transfer ( FRET ) analysis of the α-factor receptor in the yeast Saccharomyces cerevisiae . [ 12 ] In 2005, further evidence was provided that receptor oligomerization plays a functional role in a living organism with regulatory implication. [ 13 ] The crystal structure of the CXCR4 dimer was published in 2010. [ 14 ]
GPCR oligomers consist of receptor dimers , trimers , tetramers , and complexes of higher order. These oligomers are entities with properties that can differ from those of the monomers in several ways. [ 15 ] The functional character of a receptor is dependent on its tertiary or quaternary structure. Within the complex protomers act as allosteric modulators of another. This has consequences for:
There are various methods to detect and observe GPCR oligomers. [ 16 ] [ 17 ] | https://en.wikipedia.org/wiki/GPCR_oligomer |
GPD Duo is a dual-screen AMD -powered laptop created by GamePad Digital (GPD), crowdfunded via Indiegogo . [ 1 ] [ 2 ] [ 3 ] It has two 13.3-inch OLED screens. [ 4 ] [ 5 ]
This computing article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/GPD_Duo |
GPM J1839−10 [ 1 ] is a potentially unique [ 2 ] ultra-long period magnetar [ 3 ] [ 4 ] located about 15,000 light-years away from Earth in the Scutum constellation , in the Milky Way . It was discovered by a team of scientists at Curtin University using the Murchison Widefield Array . [ 5 ] [ 6 ] Its unusual characteristics violate current theory and prompted a search of other radio telescope archives, including the Giant Metrewave Radio Telescope and the Very Large Array , which revealed evidence of the object dating back to 1988. [ 5 ] The signature of the object went unnoticed because scientists did not know to look for its unusual behavior. [ 5 ]
The current understanding of neutron stars is that below a certain rate of rotation, called "the death line", they cease emissions. Uniquely, not only does GPM J1839−10 have an extremely slow rotation of approximately twenty-two minutes, it emits bursts of radio waves lasting up to five minutes, for which there is currently no generally accepted explanation. [ 5 ] [ 4 ] [ 6 ] [ 7 ] [ 8 ]
This star -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/GPM_J1839−10 |
GPOPS-II (pronounced "GPOPS 2") is a general-purpose MATLAB software for solving continuous optimal control problems using hp-adaptive Gaussian quadrature collocation and sparse nonlinear programming. The acronym GPOPS stands for " G eneral P urpose OP timal Control S oftware", and the Roman numeral "II" refers to the fact that GPOPS-II is the second software of its type (that employs Gaussian quadrature integration).
GPOPS-II [ 3 ] is designed to solve multiple-phase optimal control problems of the following mathematical form (where P {\displaystyle P} is the number of phases):
It is important to note that the event constraints can contain any functions that relate information at the start and/or terminus of any phase (including relationships that include both static parameters and integrals) and that the phases themselves need not be sequential. It is noted that the approach to linking phases is based on well-known formulations in the literature. [ 4 ]
GPOPS-II uses a class of methods referred to as h p {\displaystyle hp} -adaptive Gaussian quadrature collocation where the collocation points are the nodes of a Gauss quadrature (in this case, the Legendre-Gauss-Radau [LGR] points). The mesh consists of intervals into which the total time interval t ( p ) ∈ [ t 0 ( p ) , t f ( p ) ] {\displaystyle t^{(p)}\in [t_{0}^{(p)},t_{f}^{(p)}]} in each phase is divided, and LGR collocation is performed in each interval. Because the mesh can be adapted such that both the degree of the polynomial used to approximate the state y ( p ) ( t ) {\displaystyle \mathbf {y} ^{(p)}(t)} and the width of each mesh interval can be different from interval to interval, the method is referred to as an h p {\displaystyle hp} -adaptive method (where " h {\displaystyle h} " refers to the width of each mesh interval, while " p {\displaystyle p} " refers to the polynomial degree in each mesh interval). The LGR collocation method has been developed rigorously in Refs., [ 5 ] [ 6 ] [ 7 ] while h p {\displaystyle hp} -adaptive mesh refinement methods based on the LGR collocation method can be found in Refs., . [ 8 ] [ 9 ] [ 10 ] [ 11 ]
The development of GPOPS-II began in 2007. The code development name for the software was OptimalPrime , but was changed to GPOPS-II in late 2012 in order to keep with the lineage of the original version of GPOPS [ 12 ] which implemented global collocation using the Gauss pseudospectral method . The development of GPOPS-II continues today, with improvements that include the open-source algorithmic differentiation package ADiGator [ 13 ] and continued development of h p {\displaystyle hp} -adaptive mesh refinement methods for optimal control.
GPOPS-II has been used extensively throughout the world both in academia and industry. Published academic research where GPOPS-II has been used includes Refs. [ 14 ] [ 15 ] [ 16 ] where the software has been used in applications such as performance optimization of Formula One race cars, Ref. [ 17 ] where the software has been used for minimum-time optimization of low-thrust orbital transfers, Ref. [ 18 ] where the software has been used for human performance in cycling, Ref. [ 19 ] where the software has been used for soft lunar landing, and Ref. [ 20 ] where the software has been used to optimize the motion of a bipedal robot. | https://en.wikipedia.org/wiki/GPOPS-II |
The GPS-aided GEO augmented navigation ( GAGAN ) is an implementation of a regional satellite-based augmentation system (SBAS) by the Government of India . [ 2 ] It is a system to improve the accuracy of a GNSS receiver by providing reference signals. [ 3 ] The Airports Authority of India (AAI)'s efforts towards implementation of operational SBAS can be viewed as the first step towards introduction of modern communication, navigation and surveillance / air traffic management system over the Indian airspace . [ 4 ]
The project has established 15 Indian Reference Stations (INRES), 2 Indian Master Control Centre (INMCC) and 3 Indian Land Uplink Station (INLUS) and installation of all associated software and communication links. [ 5 ] It will be able to help pilots to navigate in the Indian airspace by an accuracy of 3 m (9.8 ft) and will be helpful for landing aircraft in marginal weather and difficult approaches like Mangalore International and Kushok Bakula Rimpochee airports. [ 6 ]
The ₹ 774 crore (US$92 million) project was deployed in three phases through 2008 by the Airports Authority of India with the help of the Indian Space Research Organisation 's (ISRO) technology and space support. [ 7 ] The goal is to provide navigation system for all phases of flight over the Indian airspace and in the adjoining area. It is applicable to safety-to-life operations, and meets the performance requirements of international civil aviation regulatory bodies. [ 8 ]
The space component became available after the launch of the GAGAN payload on the GSAT-8 communication satellite, which was successfully launched. This payload was also part of the GSAT-4 satellite that was lost when the Geosynchronous Satellite Launch Vehicle (GSLV) failed during launch in April 2010. A final system acceptance test was conducted during June 2012 followed by system certification during July 2013. [ 7 ]
All aircraft being registered in India after 1 July 2021 are mandated to be outfitted with GAGAN equipment. [ 9 ] The first aircraft to land using GAGAN system was an ATR-72 aircraft of IndiGo . The landing was carried out 29 April 2022 in Kishangarh Airport , Rajasthan . [ 10 ]
In 2024, reports suggested that all the new aircraft that were ordered by Air India and IndiGo will be equipped with GAGAN systems whereas many of the turboprop aircraft in India like ATR-72 and De Havilland Canada Dash 8 . The GAGAN systems will be primarily operationalised in smaller airports lacking instrument landing system (ILS) whereas larger airports with ILS will keep it as a backup option in case of non availability of such infrastructures. [ 11 ]
The first phase of the system was the GAGAN-TDS (Technology Demonstration System). TDS was successfully completed during 2007 by installing eight Indian Reference Stations (INRESs) at eight Indian airports and linked to the Master Control Centre (MCC) located near Bengaluru . Preliminary system acceptance testing has been successfully completed in December 2010. [ 7 ] The ground segment for GAGAN, which has been put up by the Raytheon, has fifteen reference stations scattered across the country. Two mission control centres, along with associated uplink stations, have been set up at Kundalahalli in Bengaluru. One more control centre and uplink station were expected to be established at Bengaluru and Delhi. As a part of the programme, a network of eighteen total electron content (TEC) monitoring stations were installed at various locations in India to study and analyse the behaviour of the ionosphere over the Indian region. The FSAT (Final System Acceptance Test) for GAGAN-TDS was completed on 14-15th August, 2007 using the signal-in-space (SIS) from INMARSAT-4 F1 . [ 12 ]
GAGAN's TDS signal in space provides a 3 m (9.8 ft) accuracy as against the requirement of 7.6 m (25 ft). Flight inspection of GAGAN signal is being carried out at Calicut International , Rajiv Gandhi International , Dr. Babasaheb Ambedkar International and Kempegowda International airports and the results have been satisfactory so far. [ when? ]
One essential component of the GAGAN project is the study of the ionospheric behaviour over the Indian region. This has been specially taken up in view of the uncertain nature of the behaviour of the ionosphere in the region. The ion content in the airspace increases with the increase of solar activities and peaks at around 2 pm IST . The study will lead to the optimisation of the algorithms for the ionospheric corrections in the region. [ 13 ]
To study the ionospheric behaviour more effectively over entire Indian airspace, Indian universities and research and development labs, which are involved in the development of regional based ionotropic model for GAGAN, have suggested nine more TEC stations. [ 4 ]
According to a report, however, told the problems faced due to this can be eliminated by using "dual-frequency multi-constellation (DFMC) GAGAN approach". [ 13 ]
To begin implementing a satellite-based augmentation system over the Indian airspace, Wide Area Augmentation System (WAAS) codes for L1 frequency and L5 frequency were obtained from the United States Air Force and the United States Department of Defense in November 2001 and March 2005. [ 4 ] United States defence contractor Raytheon has taken part in the project to establish the required systems. The system will uses: [ 6 ]
There are two operational satellites excluding one as a backup [ 8 ] [ 14 ]
GAGAN is now in operational phase and is compatible with other SBAS systems such as the Wide Area Augmentation System (WAAS), the European Geostationary Navigation Overlay Service (EGNOS) and the MTSAT Satellite Augmentation System (MSAS) and will provide seamless air navigation service across regional boundaries. [ 15 ] While the ground segment consists of fifteen reference stations and a master control centre, which will have sub systems such as data communication network, SBAS correction and verification system, operations and maintenance system, performance monitoring display and payload simulator, Indian land uplinking stations will have dish antenna assembly. The space segment will consist of one geo-navigation transponder.
A GAGAN-based flight management system will be able to save time and money of operators by controlling climb, descent, and engine performance profiles. The utilization of operator-preferred trajectories will increase, leading to increased efficiency and flexibility from the FMS. It will enhance access to airports and airspace in any weather conditions and enhance compliance with environmental and obstacle clearance requirements. By establishing more exact terminal area procedures with parallel routes and environmentally optimized airspace corridors, it will also improve reliability and decrease delays. [ citation needed ]
The first GAGAN transmitter was integrated into the GSAT-4 geostationary satellite, and had a goal of being operational in 2008. [ 16 ] [ 17 ] Following a series of delays, GSAT-4 was launched on 15 April 2010, however it failed to reach orbit after the third stage of the Geosynchronous Satellite Launch Vehicle Mk.II that was carrying it malfunctioned. [ 18 ]
In 2009, Raytheon had won an $82 million contract. It was mainly dedicated to modernise Indian air navigation system. [ 19 ] The vice president of Command and Control Systems, Raytheon Network Centric Systems, Andy Zogg commented:
GAGAN will be the world's most advanced air navigation system and further reinforces India's leadership in the forefront of air navigation. GAGAN will greatly improve safety, reduce congestion and enhance communications to meet India's growing air traffic management needs [ 19 ]
In 2012, the Defence Research and Development Organisation (DRDO) received a "miniaturised version" of the device with all the features from Global Positioning Systems (GPS) and global navigation satellite systems (GNSS). The module weighing just 17 g (0.60 oz), can be used in multiple platforms ranging from aircraft (e.g. winged or rotor-craft) to small boats, ships. Reportedly, it can also assist "survey applications". It is a cost-efficient device and can be of "tremendous" civilian use. The navigation output is composed of GPS, GLONASS and GPS+GLONASS position, speed and time data. According to a statement released by the DRDO, G3oM is a state-of-the-art technology receiver, integrating Indian GAGAN as well as both global positioning system and GLONASS systems. [ 20 ]
According to Deccan chronicle:
G. Satheesh Reddy , associate director of the city-based Research Centre Imarat , said the product is bringing about a quantum leap in the area of GNSS technology and has paved the way for highly miniaturised GNSS systems for the future. [ 20 ]
On 30 December 2012, the Directorate General of Civil Aviation (DGCA), India provisionally certified the GPS-aided geo-augmented navigation (GAGAN) system to RNP0.1 (required navigation performance, 0.1 nautical miles [0.19 km; 0.12 mi]) service level. The certification enabled aircraft fitted with SBAS equipment to use GAGAN signal in space for navigation purposes. [ 21 ]
The Indian government has stated that it intends to use the experience of creating the GAGAN system to enable the creation of an autonomous regional navigation system called the I ndian R egional N avigation S atellite S ystem (IRNSS), operationally known as NavIC (acronym for Nav igation with I ndian C onstellation). [ 22 ]
IRNSS-1
Indian regional navigational satellite system (IRNSS)-1, the first of the seven satellites of the Indian Regional Navigation Satellite System constellation, carries a navigation payload and a C-band ranging transponder. The spacecraft employs an optimised I-1K structure with a power handling capability of around 1660W and a lift off mass of 1,425 kg (3,142 lb), and is designed for a nominal mission life of 10 years. The first satellite of IRNSS constellation was launched onboard Polar Satellite Launch Vehicle (PSLV) (C22) on 1 July 2012. While the full constellation was planned to be realised during 2014 time frame, launch of subsequent satellites was delayed. [ citation needed ]
Currently all seven satellites are in orbit but in 2017 it was announced that all three rubidium based atomic clocks on board IRNSS-1A had failed, mirroring similar failures in the Galileo constellation. The first failure occurred in July 2016, following which two other clocks also failed. This rendered the satellite somewhat redundant and required replacement. Although the satellite still performs other functions, the data is coarse, and thus cannot be used for accurate measurements. ISRO plans to replace it with IRNSS-1H in July or August 2017.
Two more clocks in the navigational system had started showing signs of abnormality, thereby taking the total number of failed clocks to five.
As a precaution to extend the operational life of navigation satellite, ISRO is running only one rubidium atomic clock instead of two in the remaining six satellites. Each satellite has three clocks, therefore a total of 27 clocks for all satellites in the system (including standby satellites). The clocks of both IRNSS and GALILEO were supplied by SpectraTime. ISRO replaced the atomic clocks in two standby NavIC satellites. The setback comes at a time when IRNSS is yet to start commercial operations.
Karnataka Forest Department has used GAGAN to build a new, accurate and publicly available satellite based database of its forestlands. This is a followup to the Supreme Court directive to states to update and put up their respective forest maps. The geospatial database of forestlands pilot has used data from the Cartosat-2 satellite. The maps are meant to rid authorities of ambiguities related to forest boundaries and give clarity to forest administrators, revenue officials as also the public, according to R.K. Srivastava, chief conservator of forests (headquarters). [ 23 ]
The Indian National Centre for Ocean Information Services (INCOIS) along with AAI has launched a new satellite-based GEMINI (Gagan Enabled Mariner's Instrument for Navigation and Information) system that will alert deep-sea fishermen of upcoming disasters. The GEMINI app on the cellphone decodes the signals from GEMINI device and alerts the user on imminent threats like cyclones, high waves, strong winds along with PFZ and search and rescue mission.
Various Indian manufactured missiles including the BrahMos will use GAGAN for guidance. [ 24 ] | https://en.wikipedia.org/wiki/GPS-aided_GEO_augmented_navigation |
A location-based game (also called location-enabled game , geolocation-based game , or simply geo game ) is a type of game in which the gameplay evolves and progresses via a player's real world location. Location-based games must provide some mechanism to allow the player to report their location, usually with GPS . Many location-based video games are video games that run on a mobile phone , using its GPS capability.
“Urban games” or “street games” are typically multiplayer location-based games played using city streets and built up urban environments. Various mobile devices can be used to play location-based games. These games have been referred to as “location-based mobile games,” [ 1 ] merging the concept of location-based games and mobile games .
Location based-games can be digital or physical in nature. For example, Geocaching is an outdoor recreational activity in which participants use a Global Positioning System (GPS) receiver or mobile device and other navigational techniques to hide and seek containers. In contrast, games such as Pokémon Go are fully contained in digital devices with very little to no interaction or effect on the physical world.
Some location-based games that are video games have used embedded mobile technologies such as near field communication , Bluetooth and UWB . Such video games have also commonly used augmented reality to create an immersive experience. Games such as Pokémon Go and Ingress also use an Image Linked Map (ILM) interface, where approved geotagged locations appear on a stylized map generated based on GPS data for the user to interact with. [ 2 ]
Early location-based video games typically used SMS as a medium and located players using cellular network 's control plane locating requiring no additional capabilities from the user's device. [ 3 ]
Location-based games may induce learning, with researchers having observed that these activities produce learning that is social, experiential and situated. [ 4 ] It supports learning in Geography and other subjects including environmental education . Learning, however, is related to the objectives of the game designers. In a survey of location-based games, (Avouris & Yiannoutsou, 2012) [ 5 ] it was observed that in terms of the main objective, these games may be categorized as ludic (e.g., games that are created for fun), pedagogic, (e.g., games created mainly for learning), and hybrid, (e.g., games with mixed objectives). The ludic group, are to a large extent action oriented, involving either shooting, action or treasure hunt type of activities. These are weakly related to a narrative and a virtual world.
The role-playing version of these games have a higher learning potential, which has been confirmed by studies on students using location based games for learning. [ 6 ] On the other hand, the social interaction that takes place and skills related to strategic decisions, observation, planning and physical activity are the main characteristics of this strand in terms of learning. The pedagogic group of games involve participatory simulators, situated language learning and educational action games. Finally, the hybrid games are mostly museum location-based games and mobile fiction, or city fiction.
In a paper titled "Death by Pokémon GO ", researchers at Purdue University ’s Krannert School of Management claim the game caused "a disproportionate increase in vehicular crashes and associated vehicular damage, personal injuries, and fatalities in the vicinity of locations, called PokéStops, where users can play the game while driving." [ 7 ] Using data from one municipality, the paper extrapolates what that might mean nationwide and concluded "the increase in crashes attributable to the introduction of Pokémon GO is 145,632 with an associated increase in the number of injuries of 29,370 and an associated increase in the number of fatalities of 256 over the period of 6 July 2016, through 30 November 2016." The authors extrapolated the cost of those crashes and fatalities at between $2 billion and $7.3bn for the same period.
The nature of location-based gaming may mean that certain real-world locations will be visited by higher-than-normal numbers of people who are playing the game, which generally has been received favorably by nearby attractions or local businesses. However, these games may generate activity at locations that are privately-owned or have access limits, or otherwise cause undesirable congestion.
Pokémon Go notably has several publicized events of players being drawn to inappropriate locations for the game, requiring the developer to manually remove these areas from the game. [ 8 ] [ 9 ] [ 10 ] In one of the first legal challenges for location-based gaming, a Federal District court ruled that a Wisconsin county ordinance to require game developers of such location-based games to get appropriate permits to allow locations in the county's public park systems was likely unconstitutional. While the county had felt there was no First Amendment rights involved due to how locations were generated in-game, the Federal judge disagreed. [ 11 ]
The interaction of location-bound games with property law is largely undefined. [ 12 ] [ 13 ] Several models have been analysed for how this interaction may be resolved in a common law context: an extension of real property rights to also cover augmentations on or near the property with a strong notion of trespassing , forbidding augmentations unless allowed by the owner; an ' open range ' system, where augmentations are allowed unless forbidden by the owner; and a ' freedom to roam ' system, where real property owners have no control over non-disruptive augmentations. [ 14 ]
One issue experienced during the Pokémon Go craze was the game's players disturbing owners of private property while visiting nearby location-bound augmentations. The terms of service of Pokémon Go explicitly disclaim responsibility for players' actions, which may limit (but may not totally extinguish) the liability of its producer, Niantic , in the event of a player trespassing while playing the game: by Niantic's argument, the player is the one committing the trespass, while Niantic has merely engaged in permissible free speech . A theory advanced in lawsuits brought against Niantic is that their placement of game elements in places that will lead to trespass or an exceptionally large flux of visitors can constitute nuisance , despite each individual trespass or visit only being tenuously caused by Niantic. [ 15 ] [ 16 ] [ 17 ]
Another claim raised against Niantic is that the placement of profitable game elements on land without permission of the land's owners is unjust enrichment . [ 18 ] More hypothetically, a property may be augmented with advertising or disagreeable content against its owner's wishes. [ 19 ] Under American law, these situations are unlikely to be seen as a violation of real property rights by courts without an expansion of those rights to include augmented reality (similarly to how English common law came to recognise air rights ). [ 18 ]
Some attempts at legislative regulation have been made in the United States. Milwaukee County, Wisconsin , attempted to regulate location-based games played in its parks, requiring prior issuance of a permit, [ 20 ] but this was criticised on free speech grounds by a federal judge; [ 21 ] and Illinois considered mandating a notice and take down procedure for location-bound augmentations. [ 22 ]
Japan is the world's biggest market for consumer spending on location-based titles like Pokémon Go and Dragon Quest Walk , having generated over $620 million in 2023 which is equal to 50% of the global revenue. [ 23 ] By comparison, the United States is the second largest market for this genre spending over $380 million on the top five games. South Korea's spending on its top five came in at less than $16 million. [ 24 ] | https://en.wikipedia.org/wiki/GPS-based_game |
GPS/INS is the use of GPS satellite signals to correct or calibrate a solution from an inertial navigation system (INS). The method is applicable for any GNSS /INS system.
The GPS gives an absolute drift-free position value that can be used to reset the INS solution or can be blended with it by use of a mathematical algorithm, such as a Kalman filter . The angular orientation of the unit can be inferred from the series of position updates from the GPS. The change in the error in position relative to the GPS can be used to estimate the unknown angle error.
The benefits of using GPS with an INS are that the INS may be calibrated by the GPS signals and that the INS can provide position and angle updates at a quicker rate than GPS. For high dynamic vehicles, such as missiles and aircraft, INS fills in the gaps between GPS positions. Additionally, GPS may lose its signal and the INS can continue to compute the position and angle during the period of lost GPS signal. The two systems are complementary and are often employed together. [ 1 ]
GPS/INS is commonly used on aircraft for navigation purposes. Using GPS/INS allows for smoother position and velocity estimates that can be provided at a sampling rate faster than the GPS receiver. This also allows for accurate estimation of the aircraft attitude (roll, pitch, and yaw) [ citation needed ] angles. In general, GPS/INS sensor fusion is a nonlinear filtering problem, which is commonly approached using the extended Kalman filter (EKF) [ 2 ] or the unscented Kalman filter (UKF). [ 3 ] The use of these two filters for GPS/INS has been compared in various sources, [ 4 ] [ 5 ] [ 6 ] [ 7 ] [ 8 ] [ 9 ] [ 10 ] including a detailed sensitivity analysis. [ 11 ] The EKF uses an analytical linearization approach using Jacobian matrices to linearize the system, while the UKF uses a statistical linearization approach called the unscented transform which uses a set of deterministically selected points to handle the nonlinearity. The UKF requires the calculation of a matrix square root of the state error covariance matrix , which is used to determine the spread of the sigma points for the unscented transform. There are various ways to calculate the matrix square root, which have been presented and compared within GPS/INS application. [ 12 ] From this work it is recommended to use the Cholesky decomposition method.
In addition to aircraft applications, GPS/INS has also been studied for automobile applications such as autonomous navigation, [ 13 ] [ 14 ] vehicle dynamics control, [ 15 ] or sideslip, roll, and tire cornering stiffness estimation. [ 16 ] [ 17 ] Integrating inertial navigation systems with high-precision GNSS technologies, such as real-time kinematic (RTK) and precise point positioning (PPP), enhances the accuracy of autonomous vehicle navigation by providing high-precision localization. [ 18 ] | https://en.wikipedia.org/wiki/GPS/INS |
GPS Block IIF , or GPS IIF is an interim class of GPS (satellite) which were used to bridge the gap between previous Navstar Global Positioning System generations until the GPS Block III satellites became operational. They were built by Boeing , operated by the United States Air Force , and launched by the United Launch Alliance (ULA) using Evolved Expendable Launch Vehicles (EELV). [ 2 ] They are the final component of the Block II GPS constellation to be launched. On 5 February 2016, the final Block IIF satellite was successfully launched, completing the series.
The spacecraft have a mass of 1,633 kg (3,600 lb) and a design life of 12 years. Like earlier GPS satellites, Block IIF spacecraft operate in semi-synchronous medium Earth orbits , with an altitude of approximately 20,460 km (12,710 mi), and an orbital period of twelve hours.
The satellites supplement and partially replace the GPS Block IIA satellites that were launched between 1990 and 1997 with a design life of 7.5 years. [ 3 ] The final satellite of the Block IIA series was decommissioned on 09 October 2019. [ 4 ] The operational constellation now includes Block IIR, IIRM, IIF and III variants.
Because the Evolved Expendable Launch Vehicles are more powerful than the Delta II , which was used to orbit earlier Block II GPS satellites, they can place the satellites directly into their operational orbits. As a result, Block IIF satellites do not carry apogee kick motors . The original contract for Block IIF, signed in 1996, called for 33 spacecraft. This was later reduced to 12, and program delays and technical problems pushed the first launch from 2006 to 2010. [ 5 ]
Overall, 12 GPS Block IIF satellites were launched, all of which are currently operational: | https://en.wikipedia.org/wiki/GPS_Block_IIF |
GPS Block III (previously Block IIIA ) consists of the first ten GPS III satellites , which are used to keep the Navstar Global Positioning System operational. Lockheed Martin designed, developed and manufactured the GPS III Non-Flight Satellite Testbed (GNST) and all ten Block III satellites. [ 5 ] The first satellite in the series was launched in December 2018. [ 6 ] [ 7 ] [ 8 ]
The United States' Global Positioning System (GPS) reached Full Operational Capability on 17 July 1995, [ 9 ] completing its original design goals. Advances in technology and new demands on the existing system led to the effort to modernize the GPS system. In 2000, the U.S. Congress authorized the effort, referred to as GPS III .
The project involves new ground stations and new satellites, with additional navigation signals for both civilian and military users, and aims to improve the accuracy and availability for all users.
Raytheon was awarded the Next Generation GPS Operational Control System (OCX) contract on 25 February 2010. [ 10 ]
The first satellite in the series was projected to launch in 2014, [ 11 ] but significant delays [ 12 ] pushed the launch to December 2018. [ 6 ] [ 13 ] The tenth and final GPS Block III launch is projected in FY2026. [ 14 ]
Block III satellites use Lockheed Martin's A2100M satellite bus structure. The propellant and pressurant tanks are manufactured by Orbital ATK from lightweight, high-strength composite materials. [ 15 ] Each satellite will carry eight deployable JIB antennas designed and manufactured by Northrop Grumman Astro Aerospace [ 16 ]
Already delayed significantly beyond the first satellite's planned 2014 launch, [ 11 ] on 27 April 2016, SpaceX , in Hawthorne, California , was awarded a US$82.7 million firm-fixed-price contract for launch services to deliver a GPS III satellite to its intended orbit. The contract included launch vehicle production, mission integration, and launch operations for a GPS III mission, to be performed in Hawthorne, California; Cape Canaveral Air Force Station , Florida ; and McGregor, Texas . [ 17 ] In December 2016, the Director of the U.S. Air Force's Global Positioning Systems Directorate announced the first satellite would launch in the spring of 2018. [ 18 ] In March 2017, the U.S. General Accounting Office stated "Technical issues with both the GPS III satellite and the OCX Block 0 launch control and checkout system have combined to place the planned March 2018 launch date for the first GPS III satellite at risk". [ 19 ] The delays were caused by a number of factors, primarily due to issues found in the navigation payload. [ 12 ] [ 20 ] Further launch date slippages were caused by the need for additional testing and validation of a SpaceX Falcon 9 rocket which ultimately launched the satellite on 23 December 2018. [ 21 ] [ 22 ] On 22 August 2019, the second GPS III satellite was launched aboard a Delta IV rocket. [ 23 ]
On 21 September 2016, the U.S. Air Force exercised a US$395 million contract option with Lockheed Martin for the ninth and tenth Block III space vehicles, expected to be available for launch by 2022. [ 24 ]
7 of 10 GPS Block III satellites have been launched, and all 7 are currently operational, with 1 undergoing preparations for launch.
One of the first announcements was the addition of a new civilian-use signal to be transmitted on a frequency other than the L1 frequency used for the existing GPS Coarse Acquisition (C/A) signal. Ultimately, this became known as the L2C signal because it is broadcast on the L2 frequency (1227.6 MHz). It can be transmitted by all block IIR-M and later design satellites. The original plan stated that until the new OCX (Block 1) system is in place, the signal would consist of a default message ("Type 0") that contains no navigational data. [ 42 ] OCX Block 1 with the L2C navigation data was scheduled to enter service in February 2016, [ 43 ] [ 44 ] but was delayed until 2022 or later. [ 45 ]
As a result of OCX delays, the L2C signal was decoupled from the OCX deployment schedule. All satellites capable of transmitting the L2C signal (all GPS satellites launched since 2005) began broadcasting pre-operational civil navigation (CNAV) messages in April 2014, and in December 2014 the U.S. Air Force started transmitting CNAV uploads on a daily basis. [ 42 ] [ 46 ] The L2C signal will be considered fully operational after it is being broadcast by at least 24 space vehicles, projected to happen in 2023. [ 42 ] As of October 2017, L2C was being broadcast from 19 satellites; by June 2022 there were 24 satellites broadcasting this signal. [ 42 ] The L2C signal is tasked with providing improved accuracy of navigation, providing an easy-to-track signal, and acting as a redundant signal in case of localized interference.
The immediate effect of having two civilian frequencies being transmitted from one satellite is the ability to directly measure, and therefore remove, the ionospheric delay error for that satellite. Without such a measurement, a GPS receiver must use a generic model or receive ionospheric corrections from another source (such as a Satellite Based Augmentation System ). Advances in technology for the GPS satellites and the GPS receivers have made ionospheric delay the largest source of error in the C/A signal. A receiver capable of performing this measurement is referred to as a dual frequency receiver. Its technical characteristics are:
It is defined in IS-GPS-200. [ 47 ]
A major component of the modernization process, a new military signal called M-code was designed to further improve the anti-jamming and secure access of the military GPS signals. The M-code is transmitted in the same L1 and L2 frequencies already in use by the previous military code, the P(Y) code. The new signal is shaped to place most of its energy at the edges (away from the existing P(Y) and C/A carriers). Unlike the P(Y) code, the M-code is designed to be autonomous, meaning that users can calculate their positions using only the M-code signal. P(Y) code receivers must typically first lock onto the C/A code and then transfer to lock onto the P(Y) code.
In a major departure from previous GPS designs, the M-code is intended to be broadcast from a high-gain directional antenna , in addition to a wide angle (full Earth) antenna. The directional antenna's signal, termed a spot beam , is intended to be aimed at a specific region (i.e., several hundred kilometers in diameter) and increase the local signal strength by 20 dB (10× voltage field strength, 100× power). A side effect of having two antennas is that, for receivers inside the spot beam, the GPS satellite will appear as two GPS signals occupying the same position.
While the full-Earth M-code signal is available on the Block IIR-M satellites, the spot beam antennas will not be available until the Block III satellites are deployed. Like the other new GPS signals, M-code is dependent on OCX—specifically Block 2—which was scheduled to enter service in October 2016, [ 44 ] [ 48 ] but which was delayed until 2022, [ 49 ] and that initial date did not reflect the two year first satellite launch delays expected by the GAO. [ 50 ] [ 51 ]
Other M-code characteristics are:
Safety of Life is a civilian-use signal, broadcast on the L5 frequency (1176.45 MHz). In 2009, a WAAS satellite sent the initial L5 signal test transmissions. SVN-62 , the first GPS block IIF satellite, continuously broadcast the L5 signal starting on 28 June 2010.
As a result of schedule delays to the GPS III control segment, the L5 signal was decoupled from the OCX deployment schedule. All satellites capable of transmitting the L5 signal (all GPS satellites launched since May 2010) [ 52 ] began broadcasting pre-operational civil navigation (CNAV) messages in April 2014, and in December 2014 the Air Force started transmitting CNAV uploads on a daily basis. [ 53 ] The L5 signal will be considered fully operational once at least 24 space vehicles are broadcasting the signal, currently projected to happen in 2027. [ 52 ]
As of 10 July 2023, L5 is being broadcast from 17 satellites, after the removal of the block IIF, SVM-63. [ 54 ]
WRC-2000 added a space signal component to this aeronautical band so the aviation community can manage interference to L5 more effectively than L2. It is defined in IS-GPS-705. [ 55 ]
L1C is a civilian-use signal, to be broadcast on the same L1 frequency (1575.42 MHz) that contains the C/A signal used by all current GPS users.
L1C broadcasting started when GPS III Control Segment (OCX) Block 1 becomes operational, scheduled for 2022. [ 45 ] [ 18 ] The L1C signal will reach full operational status when being broadcast from at least 24 GPS Block III satellites, projected for the late 2020s. [ 56 ]
It is defined in IS-GPS-800. [ 57 ]
Increased signal power at the Earth's surface:
Researchers from The Aerospace Corporation confirmed that the most efficient means to generate the high-power M-code signal would entail a departure from full-Earth coverage, characteristic of all the user downlink signals up until that point. Instead, a high-gain antenna would be used to produce a directional spot beam several hundred kilometers in diameter. Originally, this proposal was considered as a retrofit to the planned Block IIF satellites. Upon closer inspection, program managers realized that the addition of a large deployable antenna, combined with the changes that would be needed in the operational control segment, presented too great a challenge for the then existing system design. [ 58 ]
The GPS Operational Control Segment (OCS), consisting of a worldwide network of satellite operations centers, ground antennas and monitoring stations, provides Command and Control (C2) capabilities for GPS Block II satellites. [ 62 ] The latest update to the GPS OCS, Architectural Evolution Plan 7.5, was operationally accepted in 2019. [ 63 ]
In 2010, the United States Air Force announced plans to develop a modern control segment, a critical part of the GPS modernization initiative. OCS will continue to serve as the ground control system of record until the new system, Next Generation GPS Operational Control System (OCX), is fully developed and functional. [ 64 ]
OCX features are being delivered to the United States Air Force in three separate phases, known as "blocks". [ 65 ] The OCX blocks are numbered zero through two. With each block delivered, OCX gains additional functionality.
In June 2016, the U.S. Air Force formally notified Congress the OCX program's projected program costs had risen above US$4.25 billion, thus exceeding baseline cost estimates of US$3.4 billion by 25%, also known as a critical Nunn-McCurdy breach. Factors leading to the breach include "inadequate systems engineering at program inception", and "the complexity of cybersecurity requirements on OCX". [ 66 ] In October 2016, the Department of Defense formally certified the program, a necessary step to allow development to continue after a critical breach. [ 67 ]
In July 2021, all OCX monitor station installations had been completed. [ 68 ] OCX monitoring stations are expected to transition to operations in "early 2023," and the U.S. Space Force hopes to complete operational acceptance for all of OCX in 2027. [ 68 ]
OCX Block 0 provides the minimum subset of full OCX capabilities necessary to support launch and early on-orbit spacecraft bus checkout on GPS III space vehicles. [ 18 ]
Block 0 completed two cybersecurity testing events in April and May 2018 with no new vulnerabilities found. [ 69 ]
In June 2018, Block 0 had its third successful integrated launch rehearsal with GPS III. [ 69 ]
The U.S. Air Force accepted the delivery of OCX Block 0 in November 2017, and is used it to prepare for the first GPS launch in December 2018. [ 70 ]
As of May 2022, OCX Block 0 has successfully supported the launch and checkout of GPS III SV 01–05. [ 71 ]
OCX Block 1 is an upgrade to OCX Block 0, at which time the OCX system achieves Initial Operating Capability (IOC). Once Block 1 is deployed, OCX will for the first time be able to command and control both Block II and Block III GPS satellites, as well as support the ability to begin broadcasting the civilian L1C signal. [ 18 ]
In November 2016, the GAO reported that OCX Block 1 had become the primary cause for delay in activating the GPS III PNT mission. [ 72 ]
Block 1 completed the final iteration of Critical Design Review (CDR) in September 2018. [ 69 ] Software development on Block 1 is scheduled to complete in 2019, after which the Block 1 software will undergo 2.5 years of system testing. [ 69 ]
OCX Block 2 upgrades OCX with the advanced M-code features for military users and the ability to monitor performance of the civilian signals. [ 65 ] In March 2017, the contractor rephased its OCX delivery schedule so that Block 2 will now be delivered to the Air Force concurrently with Block 1. [ 73 ] In July 2017, an additional nine months delay to the schedule was announced. According to the July 2017 program schedule, OCX will be delivered to the U.S. Air Force in April 2022. [ 49 ]
OCX Block 3F upgrades OCX with the ability to perform Launch & Checkout for Block IIIF satellites. [ 74 ] [ 68 ] Block IIIF satellites are expected to start launching in 2026.
The OCX Block 3F contract, valued at $228 million, was awarded to Raytheon Intelligence and Space on 30 April 2021. [ 75 ]
GPS III Contingency Operations ("COps") is an update to the GPS Operational Control Segment, allowing OCS to provide Block IIF Position, Navigation, and Timing (PNT) features from GPS III satellites. [ 18 ] The Contingency Operations effort enables GPS III satellites to participate in the GPS constellation, albeit in a limited fashion, without having to wait until OCX Block 1 becomes operational (scheduled for 2022).
The United States Space Force awarded the US$96 million Contingency Operations contract in February 2016. [ 76 ] Contingency Ops was operationally accepted by in April 2020. [ 63 ] | https://en.wikipedia.org/wiki/GPS_Block_III |
GPS Block IIIF , or GPS III Follow On (GPS IIIF) , is the second set of GPS Block III satellites, consisting of up to 22 space vehicles. The United States Air Force began the GPS Block IIIF acquisition effort in 2016. [ 7 ] On 14 September 2018, a manufacturing contract with options worth up to $7.2 billion was awarded to Lockheed Martin. [ 8 ] [ 9 ] The 22 satellites in Block IIIF are projected to start launching in 2027, with launches estimated to last through at least 2037. [ 5 ] [ 6 ] [ 10 ]
Engineering efforts for Block IIIF satellites began upon contract award in 2016—a full 16 years after the government approved entry into the initial modernization efforts for GPS III in 2000. [ 7 ] [ 11 ] As a result, GPS Block IIIF introduces a number of improvements and novel capabilities compared to all previous GPS satellite blocks.
Block IIIF satellites host a redesigned U.S. Nuclear Detonation Detection System (USNDS) capability that is both smaller and lighter than previous systems. [ 11 ]
The USNDS is a worldwide system of space-based sensors and ground processing equipment designed to detect, identify, locate, characterize, and report nuclear detonations in the Earth's atmosphere and in space. [ 12 ]
GPS IIIF satellites are the first to feature a 100% digital navigation payload. [ 13 ]
The fully-digital navigation payload introduced by Block IIIF (SV11+) produces improved accuracy, better reliability, and stronger signals compared to the 70% digital navigation payload used by GPS Block III (SV01-SV10). [ 14 ] [ 15 ]
GPS IIIF-03 and beyond (GPS III SV13+) will incorporate the Lockheed Martin LM2100 Combat Bus, an improvement on the LM2100M bus used in GPS III SV01 through SV12. The LM2100 Combat Bus provides improved resilience to cyber attacks, as well as improved spacecraft power, propulsion, and electronics. [ 16 ] [ 2 ]
GPS IIIF satellites will be the first GPS satellites to host an Energetic Charged Particle (ECP) sensor payload. [ 6 ]
In March 2015, the U.S. Secretary of the Air Force enacted policy mandating all new Air Force satellite programs must include ECP sensors. [ 17 ] Aggregating ECP data from multiple satellites allows for enhanced space domain awareness , enabling improved detection of space weather effects as well as differentiation between anomalies induced by hostile activity, the natural environment, or other non-hostile causes. [ 18 ] [ 6 ] [ 19 ]
GPS IIIF will be the first GPS satellite block to have all space vehicles participate in the Cospas-Sarsat system. The Cospas-Sarsat system is an international collection of satellites spanning low-earth, medium-earth, and geostationary orbit satellites which all listen for 406 MHz distress signals generated by beacons on earth. Satellites relay distress signals to ground stations to initiate timely emergency response efforts. [ 20 ]
Adding laser retro-reflector arrays (LRAs) to all GPS IIIF Space Vehicles allows GPS monitoring stations on earth equipped with laser rangefinding equipment to determine much more precise 3D locations for every GPS IIIF satellite. This improves the ability of the GPS system to provide more accurate time/position fixes to GPS receivers. Estimates are that as more GPS satellites host LRAs, the location accuracy will improve from one meter achievable today to one centimeter accuracy, an improvement of several orders of magnitude. [ 21 ]
Block IIIF will be compliant with the Unified S-Band (USB) capabilities, allowing for consolidation of radio frequencies used for telemetry, tracking, and commanding of Block IIIF satellites. [ 22 ] [ 11 ]
Regional Military Protection (RMP) is an anti-jamming technology for military GPS consumers. RMP involves directing a massively-amplified spot beam which only includes military GPS signals over a small geographic area. US/allied military GPS receivers located within the RMP spot beam's signal footprint are significantly more difficult for adversaries to jam due to the extremely-amplified signal strength in the area. [ 16 ]
GPS IIIF-03 and newer satellites (GPS III SV13+) will incorporate Lockheed-Martin's LM2100 Combat Bus. [ 2 ] Satellites based on the Combat Bus are capable of hosting the "Augmentation System Port Interface" (ASPIN), an interface that allows for future on-orbit servicing and upgrade opportunities. [ 16 ] [ 23 ]
The first GPS Block IIIF satellite is planned to launch in 2027. [ 24 ] The first three launches have been contracted.
Note: none of the navigation signals that GPS Block IIIF satellites transmit are new in Block IIIF; all signals were first supported in previous generation (Block I, Block II, or Block III) GPS satellites.
GPS IIIF is an evolution of GPS III , which uses the A2100 bus as its core. The new models use the modernized LM2100 bus along with a fully digital navigation payload from L3Harris , a significant upgrade from the previous 70% digital payload used in GPS III. [ 35 ] [ 36 ] [ 37 ]
An upgraded version known as the LM2100 Combat Bus will be used starting with the third service vehicle. It will enable on-orbit servicing at a later date, which may include hardware upgrades, component replacement, or refuelling. [ 38 ] [ 39 ]
Medium Earth Orbit Search and Rescue (MEOSAR) payloads are being provided by the Canadian government on behalf of the Canadian Armed Forces . The time it takes to detect and locate a distress signal will be reduced from an hour to five minutes, along with greatly improved accuracy in locating a distress beacon. [ 40 ] [ 41 ]
Laser Retroreflector Arrays (LRAs) will be built by the United States Naval Research Lab . This is a passive reflector system that improves accuracy and provides better ephemeris data. The National Geospatial-Intelligence Agency (NGA) will fund the integration costs of the LRA.
Other significant enhancements include: unified S-Band (USB) interface compliance, integration of hosted payloads including a redesigned United States Nuclear Detonation (NUDET) Detection System (USNDS) payload, Energetic Charged Particles (ECP) sensor, and Regional Military Protection (RMP) capabilities that provide the ability to deliver high-power regional Military Code (M-Code) signals in specific areas of intended effect. [ 42 ]
The U.S. Air Force has identified four "technology insertion points" for GPS Block IIIF. [ 43 ] These four points are the only four times during the block's lifecycle where new capabilities will be allowed to be introduced to Block IIIF satellites.
The U.S. Air Force employed a two-phase competitive bid acquisition process for the GPS Block IIIF satellites.
On 5 May 2016, the U.S. Air Force awarded three Phase One Production Readiness Feasibility Assessment contracts for GPS III Space Vehicles (SV's) 11+, one each to Boeing Network and Space Systems , Lockheed Martin Space Systems Company, and Northrop Grumman Aerospace Systems. [ 9 ] [ 49 ] The phase one contracts were worth up to six million dollars each. [ 50 ] During the phase one effort, both Boeing and Northrop Grumman demonstrated working navigation payloads. [ 51 ]
On 19 April 2017, the U.S. Air Force Space Command announced the start of the second phase of its acquisition strategy with the publication of a special notice for an "Industry Day" for companies planning on bidding for the contract to manufacture GPS III vehicles 11+. [ 50 ] During the Industry Day event, the Air Force shared the tentative acquisition strategy which it will use to evaluate proposals, then solicited feedback from potential bidders.
In July 2017, the Deputy Director of the U.S. Air Force GPS Directorate stated the acquisition strategy for GPS Block IIIF would be to award the manufacturing contracts for all 22 Block IIIF satellites to the same contractor. [ 43 ]
In November 2017, the Deputy Director of the U.S. Air Force's GPS Directorate announced the name of the second tranche of GPS III satellites was "GPS Block IIIF". [ 52 ]
Also in November 2017, it was announced that development of the fully digital navigation payload for GPS Block IIIF satellites had completed. [ 53 ] The Block IIIA program schedule was delayed multiple times due to issues with the navigation payload. [ 54 ] [ 55 ]
While the Air Force originally expected to publish the formal Request For Proposals (RFP) for GPS Block IIIF production in September 2017, it was not released until 13 February 2018. [ 56 ] The RFP was for a firm-fixed price (FFP) contract for a single company to manufacture all 22 space vehicles. All three participants from phase one (Boeing, Lockheed Martin, and Northrop Grumman) were believed to be likely to submit proposals. [ 50 ] The government held a pre-proposal conference in El Segundo, California , to be held on 15 March 2018 for potential bidders to ask the Air Force questions about the solicitation. The submission deadline for proposals was 16 April 2018. [ 57 ]
The bid status of companies who participated in phase one, in alphabetical order:
On 14 September 2018, the Air Force awarded a manufacturing contract with options worth up to US$7.2 billion to Lockheed Martin. [ 8 ]
GPS Block IIIF's ground control system of record will be the same used for GPS Block III , the Next Generation GPS Operational Control System (OCX).
In order to be able to command and control Block IIIF satellites, in April 2021 the U.S. Space Force awarded a $228 million contract to Raytheon Intelligence and Space called OCX Block 3F, which builds on the existing OCX Block 2 system and adds the ability to perform Launch and Checkout of Block IIIF satellites. [ 60 ] [ 61 ]
OCX Block 3F delivery was expected in July 2025, with operational acceptance expected in late 2027. [ 61 ] [ 62 ] | https://en.wikipedia.org/wiki/GPS_Block_IIIF |
GPS Exchange Format ( GPX ) is an XML schema designed as a common GPS data format for software applications. It can be used to describe waypoints , tracks , and routes. It is an open format [ 2 ] and can be used without the need to pay license fees. Location data (and optionally elevation, time, and other information) is stored in tags and can be interchanged between GPS devices and software. Common software applications for the data include viewing tracks projected onto various map sources, annotating maps, and geotagging photographs based on the time they were taken.
A GPX file's main components are waypoints , routes , and tracks :
Note that the XML tags enclosing each waypoint of a route or track segment are called rtept and trkpt, respectively, while the tag for the basic waypoint element is wpt. Despite this difference in name, they all hold the same data type called wptType.
In addition to the above, GPX files can also contain additional data. The minimum properties for a GPX file are latitude and longitude for every single point. Some vendors, such as Humminbird and Garmin , use extensions to the GPX format for recording street address, phone number, business category, air temperature, depth of water, and other parameters. [ 4 ] [ 5 ]
Latitude and longitude are expressed in decimal degrees , and elevation in meters, both using the WGS 84 datum . [ 6 ] Dates and times are expressed in Coordinated Universal Time (UTC) using ISO 8601 format. [ 1 ]
The document below is a sample GPX file which contains three waypoints which correspond to the locations of the German, Swiss, and Austrian parliaments. | https://en.wikipedia.org/wiki/GPS_Exchange_Format |
GPS animal tracking is a process whereby biologists , scientific researchers, or conservation agencies can remotely observe relatively fine-scale movement or migratory patterns in a free-ranging wild animal using the Global Positioning System (GPS) and optional environmental sensors or automated data-retrieval technologies such as Argos satellite uplink, mobile data telephony or GPRS and a range of analytical software tools. [ 1 ]
A GPS tracking device will generally record and store location data at a predetermined interval or on interrupt by an environmental sensor. These data may be held pending recovery of the device or relayed to a central data store or internet-connected computer using an embedded cellular ( GPRS ), radio , or satellite modem. The animal's location can then be plotted against a map or chart in near real-time or, when analysing the track later, using a GIS package or custom software.
GPS tracking devices may also be attached to domestic animals , such as pets , pedigree livestock and working dogs .
Some owners use these collars for geofencing of their pets. [ 2 ]
GPS wildlife tracking can place additional constraints on size and weight and may not allow for post-deployment recharging or replacement of batteries or correction of attachment.
As well as allowing in-depth study of animal behaviour and migration, the high-resolution tracks available from a GPS-enabled system can potentially allow for tighter control of animal-borne communicable diseases such as the H5N1 strain of avian influenza . [ 3 ]
Collar attachment is the primary technique where the subject has a suitable body type and behaviour. Tracking collars are typically used on the animal's neck (assuming the head has a larger circumference than the neck) [ 4 ] but also on a limb, perhaps around an ankle. Suitable animals for neck attachment include primates, large cats, some bears, etc. Limb attachment works well in animals such as kiwi , where the foot is much larger than the ankle. [ citation needed ]
Harness attachments may be used when collar attachment is unsuitable, such as for animals whose neck diameter may exceed that of the head. Examples of this type of animal may include pigs, Tasmanian devils , etc. [ citation needed ] Large, long-necked birds such as the greylag goose may also need to be fitted with a harness to prevent the removal of the tag by the subject. [ 5 ]
Direct attachment is used on animals where a collar cannot be used, such as birds, reptiles, and marine mammals .
In the case of birds, the GPS unit must be very lightweight to avoid interfering with the bird's ability to fly or swim. The device is usually attached by gluing or, for short deployments, taping [ 6 ] to the bird. The unit will then naturally fall off when the bird subsequently moults.
In the case of reptiles such as crocodiles and turtles , gluing the unit onto the animal's skin or carapace using epoxy (or similar material) is the most common method and minimises discomfort. [ 7 ]
In deployments on marine mammals such as phocids or otariids , the device would be glued to the fur and fall off during the annual moult . Units used with turtles or marine animals have to resist the corrosive effects of seawater and be waterproof to pressures of up to 200bar. [ citation needed ]
Other applications include rhinoceros tracking, for which a hole may be drilled in the animal's horn and a device implanted. [ citation needed ] Compared to other methods, implanted transmitters may suffer from a reduced range as the large mass of the animal's body can absorb some transmitted power. [ citation needed ]
There are also GPS implants for large snakes, such as ones offered by Telemetry Solutions .
Duty Cycle Scheduling - GPS devices typically record data about the animal's exact location and store readings at pre-set intervals known as duty cycles. By setting the interval between readings, the researcher can determine the device's lifespan - persistent readings drain battery power more rapidly. In contrast, longer intervals between readings might provide lower resolution over a more extended deployment. [ 8 ]
Release Timers - Some devices can be programmed to drop off at a set time/date rather than requiring recapture and manual retrieval. Some may also be fitted with a low-power radio receiver allowing a remote signal to trigger the automatic release. [ citation needed ]
Locational data provided by GPS devices can be displayed using Geographic information system (GIS) packages such as the open-source GRASS or plotted and prepared for display on the World Wide Web using packages such as Generic Mapping Tools (GMT) , FollowDem (developed by Ecrins National Park to track ibex) or Maptool .
Statistical software such as R can be used to display and examine data and may reveal behavioural patterns or trends.
GPS tracking devices have been linked to an Argos Platform Transmitter Terminal (PTT), enabling them to transmit data via the Argos System, a scientific satellite system that has been in use since 1978. Users can download their data directly from Argos via telnet and process the raw data to extract their transmitted information. [ 9 ]
Where satellite uplink fails due to antenna damage, it may be possible to intercept the underpowered transmission locally using a satellite uplink receiver. [ 10 ]
GPS location data can be transmitted via the GSM mobile/cell phone network, using SMS messages or internet protocols over a GPRS session. [ 11 ] The EPASTO GPS is dedicated to following and locating cows.
GPS data may be transmitted via short-range radio signals and decoded using a custom receiver. [ citation needed ]
It was believed that GPS collars used on animals affected their behavior. This theory was tested on elephants that lived in a zoo in the United States. They studied how the elephants behaved with and without the collars simultaneously for both scenarios and saw no change in behavior. [ 12 ]
A study was done with mantled howler monkeys to see if GPS Ball and Chain collars affected the monkeys behavior. The study involved observing a group of collared and uncollared female howler monkeys. There was no significant difference in the collared and uncollared behavior, but when the study was over, it was discovered that the monkeys had injuries. The collars had caused damage to the necks of the monkeys; one had minor scratches and some swelling, while four other monkeys had deep cuts from the collar. Two of the monkeys with the lacerations had their tissue healing over the collar. [ 13 ]
There is a need for Internet-enabled tracking collars for animals to be designed with a multiple-year lifespan to avoid interference with the animals. Satellite tracking devices are deployed in ultra-remote areas. To preserve battery power, the device only powers on when required. GSM or cellular technology is widely deployed where connectivity is available - however, GSM is also highly intensive on battery power. Devices, like Airtag from Apple, either have a large battery or are only powered on when required, and may need to be constantly recharged. [ 14 ]
Sigfox or LoRa are new technologies powering the Internet of Things connectivity. These technologies are beginning to be deployed in remote areas due to their ease of deployment and incredibly long range. The advantages of these technologies for an animal tracking collar are that the device form size can be minimised, and the battery life is considerably extended. Sigfox has already covered large parts of the Kruger National Park in South Africa, allowing rangers to track smaller forms of wildlife better. [ 15 ] | https://en.wikipedia.org/wiki/GPS_animal_tracking |
A GPS buoy is a buoy equipped with a GPS receiver . [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] It is used for sea level and research search-and-rescue operations, among other applications.
This geodesy -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/GPS_buoy |
GPS drawing , also known as GPS art , is a method of drawing where an artist uses a Global Positioning System (GPS) device and follows a pre-planned route to create a large-scale picture or pattern. The .GPX data file recorded during the drawing process is then visualised, usually overlaying it as a line on a map of the area. Artists usually run or cycle the route—while cars, vans, boats and aeroplanes are utilized to create larger pieces.
The first known GPS drawing was made by Reid Stowe in 1999. "Voyage of the Turtle" is an ocean sized drawing with a 5,500 mile circumference in the Atlantic made using a sailboat. The GPS data was recorded in logbooks and was therefore very low resolution. [ 1 ]
In 2000, after the US Military GPS satellite signals were opened up to the public, [ 2 ] artists Jeremy Wood and Hugh Pryor were able to use a newly available GPS tracker to record their movements. To display their drawings Hugh Pryor wrote a computer program which convented the GPX data into a single line to be shown on screen or to be turned into an image file. [ 3 ] With these tools in place GPS drawing as distinct artform was able to develop.
GPS artists can spend many hours finding a certain image or text hidden in a map or can sometimes simply see an existing image in a map due to pareidolia . In many cities and towns the road layout and landscape restricts the routes available so artists have to find creative ways to show their pictures or characters. In cities where there is a strong grid pattern 8-bit -style or pixelated images can be created of almost any object or shape. Many artists will create paper or digital maps of their route to follow on their journey.
Several websites have arisen (including RouteDoodle.com and GPSArtify.com) to aid in the planning process.
There are many approaches to GPS drawing which an artist can choose depending on their means of travel and the landscape around them.
One style uses only pre-existing roads, paths, trails, etc. This can make it more challenging to find a route and plan the artwork. Working on pre-existing routes can make navigation easier, and the artwork is more likely to reflect the original plan. This is how the majority of GPS drawings are made.
In freehand GPS drawing, an artist creates a shape on open ground, air, or water without following existing paths. This means the artist has to watch their progress in real time on their GPS device. Artists can run or cycle over open ground such as parks, fields, and car parks. Artists in cars and other motor vehicles can draw shapes on large open areas such as deserts, airfields, and beaches. Almost all artworks created by aircraft and watercraft use this technique as they are not restricted by human and physical geography . Freehand GPS drawing opens unlimited possibilities but without waypoints and existing routes it is very easy to lose track of your progress and make mistakes.
By pausing the GPS device and restarting it at different locations an artist is able to draw straight lines across the map in a similar way to a connect the dots puzzle. This means the artist can draw over the built environment and over physical barriers such as rivers and hills.
Some artists add extra images or lines to the map after they have created the route. They can simply add googly eyes to an animal or face or go further and add lines and other features which help viewers see what they have drawn. Other times an artist will show a photo or other image alongside their drawing if it is not clear at first glance what has been drawn.
Artists can collaborate with each other or members of the public to create larger images, visualisations, collages and even GPS animations from multiple GPX files or routes images. GPS devices can also be given to people or attached to vehicles which are tracked as they go about normal life or take part in specific activities and the GPX data is then visualised.
In the freestyle method of GPS drawing, the path followed by the GPS receiver is random or semi random following set of pre determined rules. [ 4 ]
Burbing – a term derived from the word suburb – is the practice of cycling every road in a suburb and tracking this on GPS to create an intricate pattern. [ 5 ] One of the first examples of burbing was created by cyclist Christian Lloyd in 2014. [ 5 ] Burbing became a more widespread trend during the COVID-19 pandemic , when wider travel was restricted . [ 6 ]
Most people use a route mapping app or other service to display their drawing online and to share on social media. Popular apps include Strava, Map My Run, and Garmin. Many artists also import their route into Google Maps , OpenStreetMap , Viewranger, and other map services before capturing the image to display and share. This gives the artist the option of expanding and cropping the image, orienting it another way, or tilting the map to add perspective. Some artists use false color maps with contrasting colors for their route to create vivid images.
Artist Jeremy Wood often displays his drawings without a showing any map underneath. He is able to do this as the drawings are so detailed you can see the shape of the built environment or landscape in the lines. One work, "Traverse Me", maps out the University of Warwick campus and includes the map title, other text and images, a compass, scale, and date signature. It was made by walking 238 miles over 17 days. [ 7 ]
In 1999, Reid Stowe was probably the first artist to employ waypoints on a GPS-verified journey in order to render a large-scale art object. [ 8 ] This work of GPS art, representing a baby sea turtle (1900 miles long and 1400 miles wide, with a perimeter of 5,500 miles), was performed with a two-masted schooner during the Voyage of the Sea Turtle. [ 9 ] [ 10 ] [ 11 ] He made two more large GPS-verified drawings on his 1000-day voyage . [ 12 ]
The idea was first implemented on land by artists Hugh Pryor and Jeremy Wood, whose work includes a 13-mile wide fish in Oxfordshire , spiders with legs 21 miles long in Port Meadow, Oxford , [ 13 ] and "the world's biggest "IF'" with a total length is 537 km, and the height of the drawing in typographic units is 319,334,400 points . [ 13 ] Typical computer fonts at standard resolutions are between 8 and 12 points.
The largest text written using a GPS device was "PEACE on Earth (60,794.07km)" in 2015 created by Yassan. This was created by travelling around the entire globe by plane. Yassan also made headlines by proposing to his girlfriend with "Marry Me" [ 14 ] a 7,163.7 km route covering most of Japan.
In 2018 artist Nathan Rae created a #WeLoveManchester piece as part of the commemorations of the Manchester Arena Bombing . [ 15 ]
One of the most prolific GPS artists is the artist known as WallyGPX who, as of October 2018, has created over 500 pieces of GPS art. He uses pencil and paper to plan the routes around his home city of Baltimore which he then creates by bicycle. | https://en.wikipedia.org/wiki/GPS_drawing |
Since the Global Positioning System (GPS) was introduced in the late 1980s there have been many attempts to integrate it into a navigation-assistance system for blind and visually impaired people.
RightHear was first released in December 2015. It uses data from OpenStreetMap alongside their own databases and with this information, RightHear provides their users with multilingual audio-descriptions of the environment, indoors and outdoors.
RightHear main features are as follow:
Corsair is a GPS for pedestrians. It allows you to discover places around you and take you there. A new way of guidance has been developed by using the smartphone's vibration feature to indicate the direction to follow. This solution is particularly useful for people with visual impairments.
Cydalion is a navigation aid for people with visual impairments for Tango -enabled devices. Cydalion detects objects (including their height), offers custom sounds, and has a personalized user interface.
Candle is an open-source navigation app hosted on Github using OpenStreetMap, designed for the visually impaired. It features VoicePins for personalized location annotations, an 'Explore Near Me' function for discovering nearby points of interest, comprehensive Google_TalkBack support, and a feedback-enabled compass. The app also includes a feature to set compass directions to specific locations, aiding in navigation.
Lazarillo is based on Google Maps, OpenStreetMap and Foursquare alongside they own databases and with this information, Lazarillo collects the necessary data about the surroundings of the user to support the following features: [ 1 ]
Was designed in France to compensate for the limitations of traditional GPS and smartphone applications for the blind and visually impaired . [ citation needed ] The fruit of 8 years of research in collaboration with the CNRS, ANGEO is the only device capable of discretely, reliably guiding you when crossing areas where GPS satellites are masked. [ citation needed ]
When Apple introduced the iPhone 3GS in 2009, it was the first ever touch screen device accessible to the blind. iOS device usage has steadily increased among the blind and visually impaired population and numerous GPS apps targeting this user group have been developed since. [ 2 ]
Ariadne GPS, developed by Luca Giovanni Ciaffoni, was released in June 2011 and was one of the first GPS apps specifically designed for blind and visually impaired users. It is based on Google map data and has the following features:
BlindSquare is developed by MIPsoft and was first released in May 2012. It uses data from Foursquare and OpenStreetMap and offers a large feature set covering the needs of blind and visually impaired travelers. [ 3 ] It is based on Foursquare, OpenStreetMap, and Apple Maps data and supports the following features:
iMove has been developed by EveryWare Technologies and was first released in January 2013. It is unique, because it lets users record sound clips and associate them with saved locations. iMove offers the following features:
MyWay Classic was first released in January 2012 and is developed by the Swis Federation of the Blind. It has evolved into an app with a large set of features covering the needs of blind and visually impaired travelers. It uses OpenStreetMap data and includes the following features:
Seeing Assistant move is developed by Transition Technologies S.A. and was first released in March 2013. It is the only GPS app designed for blind and visually impaired people that lets the user operate the app through predefined speech commands. It is based on OpenStreetMap and supports the following features:
Sendero Seeing Eye GPS is developed by the Sendero Group in collaboration with several organizations for the blind (Seeing Eye, RNIB, Guide Dogs NSW ACT) and was first released in July 2013. The Seeing Eye GPS is a fully accessible turn-by-turn GPS iPhone app developed by Sendero Group. It has all the normal navigation features plus features unique to blind users, such as simple menu structure, automatic announcements of intersections and points of interest, and routes for both pedestrian and vehicle with heads-up announcements for approaching turns.
It uses Foursquare and Google Places for points of interest and Google Maps for street info. [ 4 ]
Seeing Eye is not available globally and is offered under various names:
The Sendero apps include the following features:
ViaOpta Nav is developed by Novartis Pharmaceuticals Corporation and was first released in August 2014. It is available for both IOS and Android devices. It is the only GPS app targeting blind and visually impaired users that offers the possibility to search for accessibility information for example information about intersections, tactile paving, and audible traffic signals. Although OpenStreetMap supports respective categories, this information is not very widely available yet in the map data itself.
ViaOpta Nav uses Apple Maps (on iOS devices) and Google Maps (on Android devices) for address retrieval, and OpenStreetMap for route calculation, intersection information, and public points of interest. ViaOpta Nav supports the following main features:
The Loadstone project is developing an open source software for satellite navigation for blind and visually impaired users. The software is free and runs currently on many different Nokia devices with the S60 platform under all versions of the Symbian operating system. A GPS receiver must be connected to the cell phone by Bluetooth . Many blind people around the world are using Nokia cell phones because there are two screen reader products for the S60 Symbian platform; Talks from Nuance Communications and Mobile Speak from the Spanish company Code Factory. This makes these devices accessible by output of synthetic speech and also allow the use of third-party software, such as Loadstone GPS.
The Loadstone developers, who are blind, are from Vancouver, Glasgow, and Amsterdam. Many users from around the world have contributed improvement proposals as they know exactly what functionality helps to increase their pedestrian mobility. Monty Lilburn and Shawn Kirkpatrick started the project in 2004. After the first development successes, they made it public in May 2006. Since then, other volunteers have found their way to this project of global self-help. The program is under the GNU General Public License (GPL), and was financed entirely by the private developers and by donations of users. This product provides blind people with more independence from the trading policy and prices of the few global vendors of accessible satellite navigation solutions.
In large rural regions and developing or newly industrializing countries, nearly no exact map data is available in common map databases. As such, the Loadstone software provides users an option to create and store their own waypoints for navigation and share them with others. The Loadstone community is working on importing coordinates from free sources, such as the OpenStreetMap project. In addition they are searching for a sponsor of licenses for commercial map data , such as is offered by the company Tele Atlas . The other major supplier is Navteq , which belongs to Nokia.
Lodestone is the name of a natural magnetic iron that was used throughout history in the manufacturing of compasses. Sighted owners of S60 devices can use Loadstone for leisure-time activities geocaching . [ citation needed ]
LoroDux was a project by Fachhochschule Hannover . Like in Loadstone the user is led by direction and distance information. The text on the screen is read out by a screenreader. Vibration-Only navigation is possible. Data can be imported from the OpenStreetMap project. The development is discontinued because the team prefers to use Java on Android for the future. [ citation needed ]
Mobile Geo is Code Factory's GPS navigation software for Windows Mobile-based Smartphones, Pocket PC phones and personal digital assistants (PDAs). Powered by GPS and mapping technology from the Sendero Group, Mobile Geo is the first solution specifically designed to serve as a navigation aid for people with a visual impairment which works with a wide range of mainstream mobile devices. Though it is a separately licensed product, Mobile Geo is seamlessly [ citation needed ] integrated with Code Factory's popular screen readers – Mobile Speak for Pocket PCs and Mobile Speak for Windows Mobile Smartphones. [ citation needed ]
Developed in Sweden and available since 2022. The system consists of a high precision GPS module connected to your smartphone and earphones that signals that the blind person stays along a pre-recorded digital path. Used for walking, running, skiing etc. outside without a companion.
The Victor Trekker, designed and manufactured by HumanWare (previously known as VisuAide), was launched in March 2003. It is a personal digital assistant ( PDA ) application operating on a Dell Axim 50/51 or later replaced by HP IPAQ 2490B Pocket PC , adapted for the blind and visually impaired with talking menus, talking maps, and GPS information. Fully portable (weight 600g), it offered features enabling a blind person to determine position, create routes and receive information on navigating to a destination. It also provided search functions for an exhaustive database of point of interests, such as restaurants, hotels, etc.
The PDA's touch screen is made accessible by a tactile keypad with buttons that is held in place with an elastic strap.
It is fully upgradeable, so it can expand to accommodate new hardware platforms and more detailed geographic information.
Trekker and Maestro, which is the first off-the-shelf accessible PDA based on Windows Mobile Pocket PC, are integrated and available since May 2005.
The Trekker is no longer sold by Humanware; the successor "Trekker Breeze" is a standalone unit. The software has fewer features than the original Trekker. [ citation needed ]
The Trekker Breeze is standalone hardware. Routes need to be recorded before they can be used. POIs are supported.
The BrailleNote GPS device is developed by Sendero Group, LLC, and Pulse Data International, now called HumanWare, in 2002. It is like a combination of a personal digital assistant, Map-quest software and a mechanical voice.
With a receiver about the size of a small cell phone, the BrailleNote GPS utilizes the GPS network to pinpoint a traveler's position on earth and nearby points of interest. The BrailleNote receives radio signals from satellites to chart the location of users and direct them to their destination with spoken information from the speech synthesizer . The system uses satellites to triangulate the carrier's position, much like a ship finding its location at sea.
Users can record points of interest such as local restaurants or any other location into the PDA's database. Afterward, they can use keyboard commands on the unit's keyboard to direct themselves to a specific point of interest.
The French company Kapsys offers a navigation system without a display, that works with speech input and output, called Kapten.
It was originally developed for cyclists but soon became a favourite in blind communities because of its low price compared to other accessible navigation solutions. Later versions took feedback about accessibility into account.
The Trinetra project aims to develop cost-effective, independence-enhancing technologies to benefit blind people. One such system addresses accessibility concerns of blind people using public transportation systems. Using GPS receivers and staggered Infrared sensors, information is relayed to a centralized fleet management server via a cellular modem. Blind people, using common text-to-speech enabled cell phones can query estimated time of arrival, locality, and current bus capacity using a web browser .
Trinetra, spearheaded by Professor Priya Narasimhan, is an ongoing project at the Electrical and Computer Engineering department of Carnegie Mellon University . Additional research topics include item-level UPC and RFID identification while grocery shopping and indoor navigation in retail settings. [ citation needed ]
MoBIC means Mobility of Blind and Elderly people Interacting with Computers , which was carried out from 1994 to 1996 supported by the Commission of the European Union . It was developing a route planning system which is designed to allow a blind person access to information from many sources such as bus and train timetables as well as electronic maps of the locality. The planning system helps blind people to study and plan their routes in advance, indoors.
With the addition of devices to give the precise current position and orientation of the blind pedestrian, the system could then be used outdoors. The outdoor positioning system is based on signals and satellites which give the longitude and latitude to within a metre; the computer converts this data to a position on an electronic map of locality. The output from the system is in the form of spoken messages.
Drishti is a wireless pedestrian navigation system. It integrates several technologies including wearable computers, voice recognition and synthesis, wireless networks, geographic information system (GIS) and GPS. It augments contextual information to the visually impaired and computed optimized routes based on user preference, temporal constraints (e.g. traffic congestion), and dynamic obstacles (e.g. ongoing ground work, road blockade for special events). [ citation needed ]
The system constantly guides the blind user to navigate based on static and dynamic data. Environmental conditions and landmark information queries from a spatial database along their route are provided on the fly through detailed explanatory voice cues. The system also provides capability for the user to add intelligence, as perceived by the blind user, to the central server hosting the spatial database.
In 1985, Jack Loomis, a professor of psychology at the University of California, Santa Barbara , came up with the idea of a GPS-based navigation system for the visually impaired. A short unpublished paper (Loomis, 1985) [ full citation needed ] outlined the concept and detailed some ideas for implementation, including the idea of a virtual sound interface. Loomis directed the project for over 20 years, in collaboration with Reginald Golledge (1937–2009), Professor of Geography at UCSB, and Roberta Klatzky , Professor of Psychology (now at Carnegie Mellon University). Their combination of development and applied research was supported by three multi-year grants from the National Eye Institute (NEI) and another multi-year consortium grant from the National Institute on Disability and Rehabilitation Research (NIDRR), headed by Michael May of Sendero Group. In 1993, the UCSB group first publicly demonstrated the Personal Guidance System (PGS) using a bulky prototype carried in a backpack. Since then, they created several versions of the PGS, one of which was carried in a small pack worn at the waist. Their project mostly focused on the user interface and the resulting research has defined the legacy of the project. As indicated earlier in this entry, several wearable systems are now commercially available. These systems provide verbal guidance and environmental information via speech and braille displays. But just as drivers and pilots want pictorial information from their navigation systems, survey research by the UCSB group has shown that visually impaired people often want direct perceptual information about the environment. Most of their R&D has dealt with several types of "spatial display", with researchers Jim Marston and Nicholas Giudice contributing to the recent efforts. The first is a virtual acoustic display, which provides auditory information to the user via earphones (as proposed in the 1985 concept paper). With this display, the user hears important environmental locations, such as turn points along the route and points of interest. The labels of these locations are converted to synthetic speech and then displayed using auditory direction and distance cues, such that the spoken labels appear in the auditory space of the user. A second type of display, which the group calls a "haptic pointer interface", was inspired by the hand-held receiver used in the Talking Signs© system of remote signage. The user holds a small wand, to which are attached an electronic compass and a small loudspeaker or vibrator. When the hand is pointing toward some location represented in the computer database, the user hears a tone or feels a vibration. Supplementary verbal information can be provided by synthetic speech. The user moves toward the desired location by aligning the body with the hand while maintaining the "on-course" auditory or vibratory signal. Other variants of the pointer interface involve putting the compass on the body or head and turning the body or head until the on-course signal is perceived. Six published route-guidance studies indicate that spatial displays provide effective route guidance, entail less cognitive load than speech interfaces, and are generally preferred by visually impaired users. [ citation needed ]
Prof. W. Balachandran is the pioneer and the head of GPS research group at Brunel University . He and his research team are pursuing research on navigation system for blind and visually impaired people. The system is based on the integration of state of the art current technologies, including high-accuracy GPS positioning, GIS, electronic compass and wireless digital video transmission (remote vision) facility with an accuracy of 3~4m. It provides an automated guidance using the information from daily updated digital map datasets e.g. roadworks. If required the remote guidance of visually impaired pedestrians by a sighted human guide using the information from the digital map and from the remote video image provides flexibility.
The difficulties encountered include the availability of up to date information and what information to offer including the navigation protocol . Levels of functionality have been created to tailor the information to the user's requirements.
NOPPA navigation and guidance system was designed to offer public transport passenger and route information using GPS technology for the visually impaired. This was a three-year (2002~2004) project in VTT Industrial Systems in Finland. The system provides an unbroken trip chain for a pedestrian using buses, commuter trains and trams in three neighbor cities' area. It is based on an information server concept, which has user-centered and task oriented approach for solving information needs of special needs groups.
In the system, the Information Server is an interpreter between the user and Internet information systems. It collects, filters and integrates information from different sources and delivers results to the user. The server handles speech recognition and functions requiring either heavy calculations or data transfer. The data transfer between the server and the client is minimized. The user terminal holds speech synthesis and most of route guidance.
NOPPA can currently offer basic route planning and navigation services in Finland. In practice, map data can have outdated information or inaccuracies, positioning can be unavailable or inaccurate, or wireless data transmission is not always available.
NAVIG is a multidisciplinary project, with fundamental and applied aspects. The main objective is to increase the autonomy of blind people in their navigation capabilities. Reaching a destination while avoiding obstacles is one of the most difficult issue that blind individuals have to face.
Achieving autonomous navigation will be pursued indoor and outdoor, in known and unknown environments. The project consortium is composed by two research centers in computer sciences specialized in human-machine interaction (IRIT) for handicapped people and in auditory perception, spatial cognition, sound design and augmented reality (LIMSI). Another research center is specialized in human and computer vision (CERCO), and two industrial partners are active in artificial vision (Spikenet Technology) and in pedestrian geolocalisation (Navocap). The last member of the consortium is an educational research center for the visually impaired (CESDV – IJA, Institute of Blind Youth). [ citation needed ]
TANIA is a project founded at the University of Stuttgart , Germany. The hardware is based on GPS and RFID. It allows navigation for blind and deafblind persons with step accuracy. It only works where special maps have been created for the system. [ 5 ]
Wayfinder Access was a GPS solution from the Swedish company Wayfinder Systems AB. This application for Symbian phones was designed especially to work with screen readers, such as Mobile Speak from Code Factory or TALKS from Nuance Communications and offers text-to-speech technology. It is able to take the special needs of the blind and visually impaired into consideration. Symbian screen reader software offers more than just the reading of the application's screens, but also supports braille devices.
Highlights of Wayfinder Access include, but are not limited to:
The Wayfinder Access Service was shut down in 2011 after the company was taken over by Vodafone. | https://en.wikipedia.org/wiki/GPS_for_the_visually_impaired |
GPS when applied in the earthmoving industry can be a viable asset to contractors and increase the overall efficiency of the job. Since GPS satellite positioning information is free to the public, it allows for everyone to take advantage of its uses. Heavy equipment manufacturers, in conjunction with GPS guidance system manufacturers, have been co-developing GPS guidance systems for heavy equipment since the late 1990s. These systems allow the equipment operator to use GPS position data to make decisions based on actual grade and design features. Some heavy equipment guidance systems can even operate the machine's implements automatically from a set design that was created for the particular jobsite. GPS guidance systems can have tolerances as small as two to three centimeters making them extremely accurate compared to relying on the operator's skill level. Since the machine's GPS system has the ability to know when it is off the design grade, this can reduce surveying and material costs required for a specific job.
GPS Technology was officially introduced as a guidance system for earthmoving machines in the late 1990s. Since this time, many manufacturers of earthmoving equipment now offer GPS and other guidance systems, as a factory option. Many companies exist that also sell GPS guidance systems for the earthmoving industry as a retrofit option. The two main companies for heavy equipment guidance systems are Trimble and Topcon . In April 2002, Trimble and Caterpillar Inc. began a joint venture known as Caterpillar Trimble Controls Technology LLC (CTCT). "The joint venture develops machine control products that use site design information combined with accurate positioning technology to automatically control dozer blades and other machine tools". [ 1 ] Though aftermarket kits were available from various companies to retrofit an existing machine for GPS guidance, Caterpillar Inc. was the first heavy equipment manufacturer to offer GPS guidance systems as a factory option from the dealer called an ARO (Attachment Ready Option). [ 2 ] John Deere soon followed with their own version of ARO called "Integrated Grade Control" in 2006 on many Track-Type Tractors (TTT) and Motorgraders (MG). [ 3 ]
While there are various GPS systems currently used in the heavy equipment industry, they can typically be categorized as either "indicate only" or "fully automatic". [ 4 ] Both systems can utilize one or two GPS receivers. Using only one GPS receiver limits how the guidance system can orient the machine's position in respect to the site design. Using two GPS receivers gives the guidance system two points of position allowing it to calculate what angle the machine is on relative to the site plan. The following describes "indicate only" and "fully automatic" in more detail.
Indicate only uses GPS positioning information as a guide to the operator. Depending on the system used, the machine position can be displayed over the specific design site that was created for the earthmoving project. This system relies on the operator to steer and move the machine's implements in order to match the site's design. Indicate only systems are typically cheaper and less complicated since they do not require hardware to tap into the machine's implement control systems . Indicate only systems typically utilize a single GPS receiver mounted on the machine itself and can use an angle sensor to calculate the machine's slope. Accuracy of these systems depends on if the site has a base station that can relay site specific corrections. If the site does not have a base station, indicate only systems can just use satellite information, however, the accuracy is usually in the one to two meter range.Utilizing a base station allows for site specific corrections to be transmitted to the machine, increasing the accuracy through Real Time Kinematics [ 5 ] (RTK). Site specific corrections can increase the accuracy of an indicate only system to be around two to three centimeters. Machines that typically use indicate only consist of Soil Compactors (SC), Track-Type Tractors (TTT), and Motor Graders (MG). The use of a base station really depends on the accuracy requirements of the project. Some projects such as clearing overburden at a mine site with a TTT, may not need two to three centimeter accuracy while as grading a road base with a MG does.
Fully automatic systems allow the ability of the machine's implements to be controlled by the GPS guidance system. This is typically used in the fine grading applications where precise levels of material need to be moved on a predetermined design or grade. The advantages to this system is due to the accuracy that can be achieved with GPS and RTK, but requires an onsite base station. These systems can use either one or two GPS receivers and are mounted on the machine's blade. The more advanced systems use two receivers since it allows the machine to be controlled in a three-dimensional design. Fully automatic systems require the GPS guidance system to be integrated in the machine's implement controls. Some manufacturers sell the machine with these controls already integrated into the machine as an option. Aftermarket kits are available that can retrofit your existing machine to fully automatic control, but requires the GPS system to interface with the machine's implement controls. This is typically done one of two ways. If the machine's implements are controlled using electric over hydraulic (EH), the GPS system can input lever commands in parallel with the machine's implement lever. The output from the GPS system is interpreted by the machine's electronic control module as a lever command given by the operator and moves the implements accordingly. The second method for integrating GPS in the machine's implement controls is by adding a second pilot hydraulic valve in parallel with the machine's pilot hydraulic valve. This second valve is controlled by the GPS system and moves the implement valve according to the system design and blade location. Types of machines that use fully automatic GPS systems include TTT and MG.
The key to successfully using GPS in the earthmoving industry is having an accurate site design. The site design, typically created by an engineering firm, can be imported from the original design file into the machine's GPS display. Most GPS guidance systems also have the ability to allow the operator to define a specific grade elevation or grade angle without a specific design. The following describes common machine applications that utilize GPS guidance systems.
Track-Type Tractors
TTT are an extremely popular machine platform for GPS guidance systems specifically in the smaller sized models that are used for fine grading. Caterpillar Inc. and John Deere both offer fully automatic integrated GPS as an option from the factory on some of these models. One example of GPS being used on a TTT would be on a road project.
Motorgraders are another popular machine platform since they also perform fine grading activities that can benefit from the GPS accuracy. Caterpillar Inc. and John Deere also offer some models with integrated GPS.
Hydraulic excavators are just beginning to be integrated using GPS technology and are typically indicate only. Excavators use GPS technology in conjunction with angle sensors integrated in the machine's boom, stick, and bucket. This allows the operator to see how deep they are digging by comparing the actual bucket location to the site design on the GPS display.
In recent years, Komatsu has released excavators offering semi-automatic functions. With these functions, the machine will automatically raise the boom and bucket to maintain the predetermined design grade. These machines also offer an auto stop function, preventing the bucket and boom function from lower beyond the predetermined design grade. https://www.youtube.com/watch?v=X0ELceB420I
Scrapers use GPS technology and are typically indicate only. The GPS antenna is typically mounted on the bowl of the scraper and allows the operator to compare the depth of the cut versus the site plan. This takes a lot of the ambiguity out of moving large amounts of material.
GPS technology is applied in both trash compactors and soil compactors. Typical systems record where the compactor has been in order to create a map of the area's compaction. Usually the display has various colors that indicate that the machine has compacted the area.
GPS systems typically have a high initial cost of around $100,000 per machine. When used properly GPS on average can increase productivity by as much as 30% over traditional methods. There is also cost reduction of material (since less is needed) because such high accuracy can be achieved. Some construction projects even require the use of GPS since it can bring down the overall cost of the project due to its efficiency advantages. Some GPS systems allow the user to switch systems to other machines making this tool very versatile. The contractor must plan for greater efficiency, since increasing one aspect of the job by 30% may not increase the overall efficiency, since another area may not be able to keep up. "If you do everything right and boost overall productivity say 30 percent, you’re going to have to line up 30 percent more work in the future or send crews home early". [ 4 ]
GPS is extremely versatile in the earthmoving industry, but it does have its limitations. GPS satellite signals can only be received in a non obstructed view of the sky with the exception of clouds. If a contractor wanted to perform grade work in preparation for a concrete floor within a building, for example, the roof would block the view to the GPS satellites, preventing the system from working. Working too close to a structure can also obstruct the machine's view of the sky creating dead zones. High-voltage power-lines can also create dead zones when working underneath them. GPS satellite coverage can also be weaker during certain parts of the day lowering the number of satellites the machine's system can use. This all depends on the geographical location and time of day. Improvements in GPS technology and the addition of GLONASS (Russian GNSS Satellites) satellites have reduced this issue. As mentioned earlier, in order to increase the overall accuracy of GPS you have to purchase and use a base station, which adds additional cost.
GPS continues to be integrated in the construction industry and soon will be an industry standard . Autonomous cars that utilize GPS are currently being developed, and someday the earthmoving industry could incorporate such features. Already, new machines are coming equipped with GPS integrated from the factory. The possibilities are endless and who knows what other practical uses for GPS in the earthmoving industries will be discovered.
The first user-oriented web resource for prospective 3D machine control users was created in 2010. The Kellogg Report [ 6 ] publicized a detailed comparison of the major systems available on the market, evaluating more than 200 system features. The report continues to be updated as the technology evolves. | https://en.wikipedia.org/wiki/GPS_in_the_earthmoving_industry |
GPS jamming is an act of overwhelming satellite navigation receivers with powerful radio signals that drown out the signals from GPS satellites , rendering the receiver unable to calculate its position or time accurately. [ 1 ] Such jamming can disrupt various GPS -dependent devices, from vehicle and aircraft navigation systems to precision agriculture and mobile phone networks . [ 1 ] In civil aviation , GPS jamming can disrupt ADS-B transmission. GPS jamming is a particular type of GNSS interference .
Under ITU rules, countries are obliged to eliminate harmful interference through GPS jamming and spoofing , but the ITU lacks effective enforcement measures. [ 2 ] The ICAO legal framework requires that countries should implement appropriate prevention and mitigation of GPS jamming and spoofing. [ 2 ] Under the ICAO's Montreal Convention , countries shall make GPS jamming and spoofing punishable. [ 2 ] In the United States, the operation, marketing, or sale of any GPS jamming equipment is prohibited under federal law. [ 3 ]
GPS jamming may be used by countries when conducting military exercises and drills, but under IATA recommendations they should recognize the harmful impact of such jamming to civil aviation and exercise utmost caution. In civil aviation, Eurocontrol outlined two major hotspots of GPS jamming: Eastern Turkish airspace to Iraq, Iran, Armenia (extending to Armenia–Azerbaijan border ) and Southern Cypriot airspace towards Egypt, Lebanon and Israel. [ 4 ]
Following Russian invasion of Ukraine , Russia used GPS jamming to support its military activity and in an effort to harass NATO nations . In December 2022 and January 2023, GPS jamming was noted in northern Poland, southern Sweden, southeastern Finland, Estonia and Latvia. [ 5 ] [ better source needed ] In April 2023, Russia, to counter Ukrainian drone attacks, deployed GPS jamming in 15 of its regions, including Ivanovo , Vladimir , Yaroslavl , Ryazan , Kaluga and Tver Oblast that surround Moscow . GPS-guided Ukrainian drones frequently target infrastructure and residential areas in Moscow and Moscow Oblast. [ citation needed ]
GPS jamming is seen as not as insidious as GPS spoofing . It has been encountered on long-haul flights (particularly to Russia) and airline pilots are able to counter such jamming. [ 6 ] Flickering readings instantly reveal GPS jamming and there are multiple checklists to handle it. [ 6 ] | https://en.wikipedia.org/wiki/GPS_jamming |
GPS meteorology refers to the use of the effect of the atmosphere on the
propagation of the Global Positioning System's ( GPS ) radio signals to derive
information on the state of the (lower, neutral) atmosphere.
There are currently two main operational techniques in use in GPS meteorology:
GPS limb sounding from orbit, and GPS water vapour monitoring.
As a result, if it is possible to determine the total atmospheric delay by GPS,
one can subtract out the calculated contribution by the well-mixed "dry" gasses
from the measured air pressure at the surface, and obtain a measure for the
absolute water vapour content of the atmosphere, integrated from surface to
space. This is also referred to as "total precipitable water vapour".
What makes it possible to determine the total atmospheric delay, is its known
dependence of the zenith or elevation angle of the satellite. If z {\displaystyle z} is the zenith angle, the propagation path delay is proportional to 1 cos z {\displaystyle {\frac {1}{\cos z}}} . This unique signature makes it possible to solve
separately for the zenith delay in GPS computations also solving for
station coordinates and receiver clock delays.
Nowadays water vapour estimates are generated routinely in real time (latency
measured in hours) by permanent geodetic GPS networks existing in
many parts of the world.
Water vapour is a very important gas for meteorological and climatological
studies, because of the latent heat it carries in transport. Additionally
it is a powerful greenhouse gas. The GPS technique is especially valuable
because it measures absolute water vapour content or partial pressure
rather than relative humidity, which corresponds to water vapour contents that
are strongly dependent on the often not precisely known temperature.
One can receive on a low flying satellite the signals from the much higher
orbiting (20 000 km) GPS satellite constellation. As the low flying satellite
orbits the Earth in 1.5 hours, many of the GPS satellites will "rise" and "set"
during the time of the orbit. When they do, their signal will traverse the atmosphere.
A signal delay is produced which grows or decays exponentially with time, just
as the atmospheric density is an exponential function of height above the
Earth's surface. In fact, this so-called limb sounding technique allows
us to determine the scale height , the constant describing the steepness of
this atmospheric density decay. This makes the technique extremely valuable for
climatological studies, as the scale height is directly related to the
temperature in the upper atmosphere, where the limb sounding signals do their
sensing. The technique works best in the lower stratosphere and upper
troposphere; it breaks down close to the Earth surface especially in the
tropics, due to water vapour extinction.
Satellites involved in GPS limb sounding have been: METSAT, OERSTED (Danish),
and several others. | https://en.wikipedia.org/wiki/GPS_meteorology |
GPS satellite blocks are the various production generations of the Global Positioning System (GPS) used for satellite navigation . The first satellite in the system, Navstar 1, was launched by the United States Air Force on 22 February 1978. [ 1 ] The GPS satellite constellation is now operated by the 2nd Navigation Warfare Squadron (2 NWS) of Mission Delta 31 , United States Space Force .
The GPS satellites circle the Earth at an altitude of about 20,000 km (12,427 miles) and complete two full orbits every day. [ 2 ]
Rockwell International was awarded a contract in 1974 to build the first eight Block I satellites. In 1978, the contract was extended to build an additional three Block I satellites. Beginning with Navstar 1 in 1978, ten "Block I" GPS satellites were successfully launched. One satellite, "Navstar 7", was lost due to an unsuccessful launch on 18 December 1981. [ 3 ]
The Block I satellites were launched from Vandenberg Air Force Base using Atlas rockets that were converted intercontinental ballistic missiles . The satellites were built by Rockwell International at the same plant in Seal Beach, California where the S-II second stages of the Saturn V rockets were built. [ 4 ]
The Block I series consisted of the concept validation satellites and reflected various stages of system development. Lessons learned from the 10 satellites in the series were incorporated into the fully operational Block II series.
Dual solar arrays supplied over 400 watts of power, charging nickel–cadmium batteries for operations in Earth's shadow. S-band communications were used for control and telemetry, while an UHF channel provided cross-links between spacecraft. A hydrazine propulsion system was used for orbital correction. The payload included two L-band navigation signals at 1575.42 MHz (L1) and 1227.60 MHz (L2).
The final Block I launch was conducted on 9 October 1985, but the last Block I satellite was not taken out of service until 18 November 1995, well past its 5-year design life. [ 5 ]
The Block II satellites were the first full scale operational GPS satellites, designed to provide 14 days of operation without any contact from the control segment. The prime contractor was Rockwell International , which built a SVN 12 qualification vehicle after an amendment to the Block I contract. In 1983, the company was awarded an additional contract to build 28 Block II/IIA satellites.
Block II spacecraft were three-axis stabilized , with ground pointing using reaction wheels . Two solar arrays supplied 710 watts of power, while S-band communications were used for control and telemetry. A UHF channel was used for cross-links between spacecraft. A hydrazine propulsion system was used for orbital correction. The payload included two L-band GPS signals at 1575.42 MHz (L1) and 1227.60 MHz (L2). Each spacecraft carried two rubidium and two cesium clocks, as well as nuclear detonation detection sensors, leading to a mass of 1,660 kg (3,660 lb). [ 7 ]
The first of the nine satellites in the initial Block II series was launched on 14 February 1989; the last was launched on 1 October 1990. [ 8 ] The final satellite of the series to be taken out of service was decommissioned on 15 March 2007, well past its 7.5 year design life.
The Block IIA satellites were slightly improved versions of the Block II series, designed to provide 180 days of operation without contact from the control segment. However, the mass increased to 1,816 kg (4,004 lb). [ 9 ]
Nineteen satellites in the Block IIA series were launched, the first on 26 November 1990 and the last on 6 November 1997. Two of the satellites in this series, numbers 35 and 36, were equipped with laser retro-reflectors , allowing them to be tracked independently of their radio signals, providing unambiguous separation of clock and ephemeris errors. [ 10 ]
SVN-34 , the last Block IIA satellite, broadcast on the PRN 18 signal. [ 11 ] It was removed from service on 9 October 2019 but kept as an on-orbit spare until April 2020. [ 12 ] [ 13 ]
The Block IIR series are "replenishment" (replacement) satellites developed by Lockheed Martin . Each satellite weighs 2,030 kg (4,480 lb) at launch and 1,080 kg (2,380 lb) once on orbit. [ 14 ] The first attempted launch of a Block IIR satellite failed on 17 January 1997 when the Delta II rocket exploded 12 seconds into flight. The first successful launch was on 23 July 1997. Twelve satellites in the series were successfully launched. At least ten satellites in this block carried an experimental S-band payload for search and rescue , known as Distress Alerting Satellite System . [ 15 ] [ 16 ]
The Block IIR-M satellites include a new military signal and a more robust civil signal, known as L2C. [ 17 ] There are eight satellites in the Block IIR-M series, which were built by Lockheed Martin . [ 18 ] The first Block IIR-M satellite was launched on 26 September 2005. The final launch of a IIR-M was on 17 August 2009. [ 19 ]
The Block IIF series are "follow-on" satellites developed by Boeing. The satellite has a mass of 1,630 kg (3,590 lb) and a design life of 12 years. The first Block IIF space vehicle was launched in May 2010 on a Delta IV rocket. [ 20 ] The twelfth and final IIF launch was on 5 February 2016. [ 21 ]
GPS Block III is the first series of third-generation GPS satellites, incorporating new signals and broadcasting at higher power levels. In September 2016, the United States Air Force awarded Lockheed Martin a contract option for two more Block III satellites, setting the total number of GPS III satellites to ten. [ 22 ] On 23 December 2018, the first GPS III satellite was launched aboard a SpaceX Falcon 9 Full Thrust . On 22 August 2019, the second GPS III satellite was launched aboard a Delta IV. [ 23 ] The third GPS III satellite was launched on 30 June 2020, aboard a SpaceX Falcon 9 launch vehicle. [ 24 ] The fourth GPS III satellite launched on 5 November 2020, also aboard a Falcon 9. [ 25 ]
The Block IIIF series is the second set of GPS Block III satellites, which will consist of up to 22 space vehicles. [ 26 ] Block IIIF launches are expected to begin no earlier than 2026 and continue through 2034. [ 27 ] | https://en.wikipedia.org/wiki/GPS_satellite_blocks |
GPS sonobuoy or GPS intelligent buoy ( GIB ) are a type of inverted long-baseline (LBL) acoustic positioning devices where the transducers are installed on GPS -equipped sonobuoys that are either drifting or moored. [ 1 ] GIBs may be used in conjunction with an active underwater device (such as a pinger equipped torpedo), or with a passive acoustic sound source (such as an inert bomb striking the surface of the water). Typically the sound source or impact event is tracked or localized using a time of arrival (TOA) technique. [ 2 ] [ 3 ] Typically several GIBs are deployed over a given area of operation; with the total number determined by the size of the test area and the accuracy of the results desired. Different methods of GPS positioning may be used for positioning the array of GIBs, with accuracies of cm to meter level in realtime possible. [ 3 ]
Buoys are manufactured by the French company ACSA-underwater-GPS (subsidiary of the ALCEN group). Three off-the shelf products are available from the small portable GIB-Lite system to the large torpedo tracking GIB-FT, and including the medium-size, medium-range GIB-Plus system.
Use of GIBs for underwater tracking and weapon scoring have been in use by the US Navy since the early to mid 1990s. Early GIBs were created for broad ocean area weapons testing by modifying conventional Navy sonobuoys with small OEM-grade GPS receivers and deploying them from a helicopter or from P-3 Orion aircraft. [ 3 ] [ 4 ] The GPS data captured by the GIB was modulated over the analog VHF acoustic data stream using frequency-shift keying (FSK). This allows the GPS measurement data to be transmitted and received on legacy VHF sonobuoy receiver equipment. A drifting array of twelve or more GIBs would be deployed in a concentric circular array approximately 7 nm in diameter. Weapon strikes within the array emitted acoustic signatures that were captured by the GIBs and transmitted up to the orbiting aircraft. [ 3 ] Post-mission the GPS and acoustic data from the GIBs would be combined to determine an absolute coordinate for the impact location in WGS 84 coordinates. [ 3 ]
GIB type systems have been developed for a variety of specialized applications. An illustrative use of GIBs for underwater
positioning is the TARGT weapon scoring and training system [ 5 ] [ 6 ]
The system concept (Figure 1) utilizes an array eight to ten GIBs (Figure 2) moored in a 2 km by 2 km array. In the case of the TARGT GIB, the GPS and RF antennas are located on top of the sensor and the hydrophone , or underwater acoustic transducer , is located on the bottom. The device is approximately 6 ft tall and weighs 35 lbs.
Inert weapon releases from military aircraft strike the surface of the water within the array, emitting an acoustic signature
that is captured by each of the GIBs. Each GIB determines the precise time of the received signal and transmits this time to the deployment ship in near real time. A command and control system located on the deployment and recovery ship combines the GPS data and acoustic timing information to triangulate the impact location and determine the exact impact time in near realtime. Several methods may be used, the most common being a time difference of arrival (TDOA) least-squares solution algorithm. Post-mission data processing is performed to further refine the results, with two-dimensional positioning accuracies of 1 to 2 meters and impact timing accuracies of 1-2 milliseconds demonstrated. | https://en.wikipedia.org/wiki/GPS_sonobuoy |
A radio clock or radio-controlled clock (RCC), and often colloquially (and incorrectly [ 1 ] ) referred to as an " atomic clock ", is a type of quartz clock or watch that is automatically synchronized to a time code transmitted by a radio transmitter connected to a time standard such as an atomic clock. Such a clock may be synchronized to the time sent by a single transmitter, such as many national or regional time transmitters, or may use the multiple transmitters used by satellite navigation systems such as Global Positioning System . Such systems may be used to automatically set clocks or for any purpose where accurate time is needed. Radio clocks may include any feature available for a clock, such as alarm function, display of ambient temperature and humidity, broadcast radio reception, etc.
One common style of radio-controlled clock uses time signals transmitted by dedicated terrestrial longwave radio transmitters, which emit a time code that can be demodulated and displayed by the radio controlled clock. The radio controlled clock will contain an accurate time base oscillator to maintain timekeeping if the radio signal is momentarily unavailable. Other radio controlled clocks use the time signals transmitted by dedicated transmitters in the shortwave bands. Systems using dedicated time signal stations can achieve accuracy of a few tens of milliseconds.
GPS satellite receivers also internally generate accurate time information from the satellite signals. Dedicated GPS timing receivers are accurate to better than 1 microsecond; however, general-purpose or consumer grade GPS may have an offset of up to one second between the internally calculated time, which is much more accurate than 1 second, and the time displayed on the screen.
Other broadcast services may include timekeeping information of varying accuracy within their signals. Timepieces with Bluetooth radio support, ranging from watches with basic control of functionality via a mobile app to full smartwatches obtain time information from a connected phone , with no need to receive time signal broadcasts.
Radio clocks synchronized to a terrestrial time signal can usually achieve an accuracy within a hundredth of a second relative to the time standard, [ 1 ] generally limited by uncertainties and variability in radio propagation . Some timekeepers, particularly watches such as some Casio Wave Ceptors which are more likely than desk clocks to be used when travelling, can synchronise to any one of several different time signals transmitted in different regions.
Radio clocks depend on coded time signals from radio stations. The stations vary in broadcast frequency, in geographic location, and in how the signal is modulated to identify the current time. In general, each station has its own format for the time code.
07:30–01:00 UTC [ 14 ]
Descriptions
Many other countries can receive these signals ( JJY can sometimes be received in New Zealand, Western Australia, Tasmania, Southeast Asia, parts of Western Europe and the Pacific Northwest of North America at night), but success depends on the time of day, atmospheric conditions, and interference from intervening buildings. Reception is generally better if the clock is placed near a window facing the transmitter. There is also a propagation delay of approximately 1 ms for every 300 km (190 mi) the receiver is from the transmitter.
A number of manufacturers and retailers sell radio clocks that receive coded time signals from a radio station, which, in turn, derives the time from a true atomic clock.
One of the first radio clocks was offered by Heathkit in late 1983. Their model GC-1000 "Most Accurate Clock" received shortwave time signals from radio station WWV in Fort Collins, Colorado . It automatically switched between WWV's 5, 10, and 15 MHz frequencies to find the strongest signal as conditions changed through the day and year. It kept time during periods of poor reception with a quartz-crystal oscillator . This oscillator was disciplined, meaning that the microprocessor-based clock used the highly accurate time signal received from WWV to trim the crystal oscillator. The timekeeping between updates was thus considerably more accurate than the crystal alone could have achieved. Time down to the tenth of a second was shown on an LED display. The GC-1000 originally sold for US$250 in kit form and US$400 preassembled, and was considered impressive at the time. Heath Company was granted a patent for its design. [ 20 ] [ 21 ]
By 1990, engineers from German watchmaker Junghans had miniaturized this technology to fit into the case of a digital wristwatch. The following year the analog version Junghans MEGA with hands was launched.
In the 2000s (decade) radio-based "atomic clocks" became common in retail stores; as of 2010 prices start at around US$15 in many countries. [ 22 ] Clocks may have other features such as indoor thermometers and weather station functionality. These use signals transmitted by the appropriate transmitter for the country in which they are to be used. Depending upon signal strength they may require placement in a location with a relatively unobstructed path to the transmitter and need fair to good atmospheric conditions to successfully update the time. Inexpensive clocks keep track of the time between updates, or in their absence, with a non-disciplined quartz-crystal clock , with the accuracy typical of non-radio-controlled quartz timepieces. Some clocks include indicators to alert users to possible inaccuracy when synchronization has not been recently successful.
The United States National Institute of Standards and Technology (NIST) has published guidelines recommending that radio clock movements keep time between synchronizations to within ±0.5 seconds to keep time correct when rounded to the nearest second. [ 23 ] Some of these movements can keep time between synchronizations to within ±0.2 seconds by synchronizing more than once spread over a day. [ 24 ]
Timepieces with Bluetooth radio support, ranging from watches with basic control of functionality via a mobile app to full smartwatches [ 25 ] obtain time information from a connected phone , with no need to receive time signal broadcasts.
Many digital radio and digital television schemes also include provisions for time-code transmission.
A radio clock receiver may combine multiple time sources to improve its accuracy. This is what is done in satellite navigation systems such as the Global Positioning System , Galileo , and GLONASS . Satellite navigation systems have one or more caesium, rubidium or hydrogen maser atomic clocks on each satellite, referenced to a clock or clocks on the ground. Dedicated timing receivers can serve as local time standards, with a precision better than 50 ns. [ 27 ] [ 28 ] [ 29 ] [ 30 ] The recent revival and enhancement of LORAN , a land-based radio navigation system, will provide another multiple source time distribution system.
Many modern radio clocks use satellite navigation systems such as Global Positioning System to provide more accurate time than can be obtained from terrestrial radio stations. These GPS clocks combine time estimates from multiple satellite atomic clocks with error estimates maintained by a network of ground stations. Due to effects inherent in radio propagation and ionospheric spread and delay, GPS timing requires averaging of these phenomena over several periods. No GPS receiver directly computes time or frequency, rather they use GPS to discipline an oscillator that may range from a quartz crystal in a low-end navigation receiver, through oven-controlled crystal oscillators (OCXO) in specialized units, to atomic oscillators ( rubidium ) in some receivers used for synchronization in telecommunications . For this reason, these devices are technically referred to as GPS-disciplined oscillators .
GPS units intended primarily for time measurement as opposed to navigation can be set to assume the antenna position is fixed. In this mode, the device will average its position fixes. After approximately a day of operation, it will know its position to within a few meters. Once it has averaged its position, it can determine accurate time even if it can pick up signals from only one or two satellites.
GPS clocks provide the precise time needed for synchrophasor measurement of voltage and current on the commercial power grid to determine the health of the system. [ 31 ]
Although any satellite navigation receiver that is performing its primary navigational function must have an internal time reference accurate to a small fraction of a second, the displayed time is often not as precise as the internal clock. Most inexpensive navigation receivers have one CPU that is multitasking. The highest-priority task for the CPU is maintaining satellite lock—not updating the display. Multicore CPUs for navigation systems can only be found on high end products.
For serious precision timekeeping, a more specialized GPS device is needed. Some amateur astronomers, most notably those who time grazing lunar occultation events when the moon blocks the light from stars and planets, require the highest precision available for persons working outside large research institutions. The Web site of the International Occultation Timing Association [ 32 ] has detailed technical information about precision timekeeping for the amateur astronomer.
Various formats listed above include a flag indicating the status of daylight saving time (DST) in the home country of the transmitter. This signal is typically used by clocks to adjust the displayed time to meet user expectations. | https://en.wikipedia.org/wiki/GPS_timing |
A GPS tracking unit , geotracking unit , satellite tracking unit , or simply tracker is a navigation device normally on a vehicle, asset , person or animal that uses satellite navigation to determine its movement and determine its WGS84 UTM geographic position ( geotracking ) to determine its location. [ 1 ] Satellite tracking devices may send special satellite signals that are processed by a receiver.
Locations are stored in the tracking unit or transmitted to an Internet -connected device using the cellular network ( GSM / GPRS / CDMA / LTE or SMS ), radio , or satellite modem embedded in the unit or WiFi work worldwide.
GPS antenna size limits tracker size, often smaller than a half-dollar (diameter 30.61 mm). In 2020 tracking is a $2 billion business plus military-in the gulf war 10% or more targets used trackers. Virtually every cellphone tracks its movements.
Tracks can be map displayed in real time, using GPS tracking software and devices with GPS capability. [ 2 ]
A GPS "track me" essentially contains a GPS module that receives the GPS signal and calculates the coordinates. For data loggers, it contains large memory to store the coordinates. Data pushers additionally contain a GSM / GPRS / CDMA / LTE modem to transmit this information to a central computer either via SMS or GPRS in form of IP packets. Satellite-based GPS tracking units will operate anywhere on the globe using satellite technology such as GlobalStar or Iridium . They do not require a cellular connection.
There are three types of GPS trackers, though most GPS-equipped phones can work in any of these modes depending on the mobile applications installed:
GPS loggers log the position of the device at regular intervals in its internal memory. GPS loggers may have either a memory card slot, or internal flash memory card and a USB port. Some act as a USB flash drive , which allows downloading the track log data for further computer analysis. The track list or point of interest list may be in GPX , KML , NMEA or other format.
Most digital cameras save the time a photo was taken. Provided the camera clock is reasonably accurate or used GPS as its time source, this time can be correlated with GPS log data, to provide an accurate location. This can be added to the Exif metadata in the picture file. Cameras with a GPS receiver built in can directly produce such a geotagged photograph .
In some private investigation cases, data loggers are used to keep track of a target vehicle. The private investigator need not follow the target too closely, and always has a backup source of data.
A data pusher is the most common type of GPS tracking unit, used for asset tracking , personal tracking and vehicle tracking systems. Virtually every cell phone is in this mode per user agreement, even if shut off or disabled storing the data for future transmission.
Also known as a "GPS beacon", this kind of device push (i.e. "sends"), at regular intervals, the position of the device as well as other information like speed or altitude to a determined server , that can store and analyze the data instantly.
A GPS navigation device and a mobile phone sit side-by-side in the same box, powered by the same battery. At regular intervals, the phone sends a text message via SMS or GPRS, containing the data from the GPS receiver. Newer GPS-integrated smartphones running GPS tracking software can turn the phone into a data pusher (or logger) device. As of 2009, open source and proprietary applications are available for common Java ME enabled phones, iPhone , Android , Windows Mobile, and Symbian. [ 3 ] [ 4 ] [ 5 ]
Most 21st-century GPS trackers provide data "push" technology, enabling sophisticated GPS tracking in business environments, specifically organizations that employ a mobile workforce, such as a commercial fleet. Typical GPS tracking systems used in commercial fleet management have two core parts: location hardware (or tracking device) and tracking software. This combination is often referred to as an Automatic Vehicle Location system. The tracking device is most often hardwired installed in the vehicle, connected to the CAN-bus , ignition system switch, battery. It allows collection of extra data, which is later transferred to the GPS tracking server . There it is available for viewing, in most cases via a website accessed over the Internet, where fleet activity can be viewed live or historically using digital maps and reports.
GPS tracking systems used in commercial fleets are often configured to transmit location and telemetry input data at a set update rate or when an event (door open/close, auxiliary equipment on/off, geofence border cross) triggers the unit to transmit data. Live GPS tracking used in commercial fleets generally refers to systems that update regularly at one-minute, two-minute or five-minute intervals while the ignition status is on. Some tracking systems combine timed updates with heading change triggered updates.
GPS tracking solutions such as Telematics 2.0 , an IoT based telematics technology for the automotive industry, are being used by mainstream commercial auto insurance companies.
GPS data pullers are also known as "GPS transponders". Unlike data pushers that send the position of the devices at regular intervals ( push technology ), these devices are always on, and can be queried as often as required ( pull technology ). This technology is not in widespread use, but an example of this kind of device is a computer connected to the Internet and running gpsd .
These can often be used in the case where the location of the tracker will only need to be known occasionally (e.g. placed in property that may be stolen, or that does not have a constant source of energy to send data on a regular basis, like freight or containers.)
Data Pullers are coming into more common usage in the form of devices containing a GPS receiver and a cell phone which, when sent a special SMS message reply to the message with their location.
Covert GPS trackers contain the same electronics as regular GPS trackers but are constructed in such a way as to appear to be an everyday object. One use for covert GPS trackers is for power tool protection; these devices can be concealed within power tool boxes and traced if theft occurs.
The applications of GPS trackers include:
Solar Powered: the advantage of some solar powered units is that they have much more power over their lifetime than battery-powered units. This gives them the advantage of reporting their position and status much more often than battery units which need to conserve energy to extend their life. Some wireless solar-powered units, such as the RailRider can report more than 20,000 times per year and work indefinitely on solar power, eliminating the need to change batteries.
Aircraft can be tracked either by ADS-B (primarily airliners and General Aviation aircraft with ADS-B-out enabled transponder ), or by FLARM data packets picked up by a network of ground stations (primarily used by General Aviation aircraft, gliders and UAVs), both of which are data pushers. ADS-B is to be superseded by ADS-C, a data puller.
Animal monitoring ( GPS wildlife tracking ): when put on a wild animal (e.g. in a GPS collar ), it allows scientists to study the animal's activities and migration patterns. Vaginal implant transmitters mark the location where pregnant females give birth. [ 15 ] Animal tracking collars may also be put on domestic animals, to locate them in case they get lost. [ 16 ]
There are no Australian Federal Laws for surveillance and GPS tracker legality.
However, most states have statutes covering the use and restrictions of tracking devices used for surveillance.
The below states have formal statutes. At present, only Queensland and Tasmania do not have legislation.
In the United States, the use of GPS trackers by government authorities is limited by the Fourth Amendment to the United States Constitution . So police, for example, usually require a search warrant . [ 18 ] While police have placed GPS trackers in vehicles without a warrant, this usage was questioned in court in early 2009. [ 19 ] [ 20 ]
Use by private citizens is regulated in some states, such as California, where California Penal Code Section 637.7 states: (a) No person or entity in this state shall use an electronic tracking device to determine the location or movement of a person. (b) This section shall not apply when the registered owner, lesser, or lessee of a vehicle has consented to the use of the electronic tracking device with respect to that vehicle. (c) This section shall not apply to the lawful use of an electronic tracking device by a law enforcement agency. (d) As used in this section, "electronic tracking device" means any device attached to a vehicle or other movable thing that reveals its location or movement by transmission of electronic signals. (g) A violation of this section is a misdemeanor. (f) A violation of this section by a person, business, firm, company, association, partnership, or corporation licensed under Division 3 (commencing with Section 5000) of the Business and Professions Code shall constitute grounds for revocation of the license issued to that person, business, firm, company, association, partnership, or corporation, pursuant to the provisions that provide for the revocation of the license as set forth in Division 3 (commencing with Section 5000) of the Business and Professions Code. [ 21 ]
Note that 637.7 pertains to all electronic tracking devices, and does not differentiate between those that rely on GPS technology or not. As the laws catch up with the times, it is plausible that all 50 states will eventually enact laws similar to those of California. [ original research? ]
Other laws, like the common law invasion of privacy tort as well as state criminal wiretapping statutes (for example, the wiretapping statute of the Commonwealth of Massachusetts , which is extremely restrictive) potentially cover the use of GPS tracking devices by private citizens without consent of the individual being so tracked. Privacy can also be a problem when people use the devices to track the activities of a loved one. [ 22 ] GPS tracking devices have also been put on religious statues to track the whereabouts of the statue if stolen. [ 23 ]
In 2009, debate ensued over a Georgia proposal to outlaw hidden GPS tracking, with an exception for law enforcement officers but not for private investigators . See Georgia HB 16 - Electronic tracking device; location of person without consent (2009). [ 24 ] [ 25 ]
The law in the UK has not specifically addressed the use of GPS trackers, but several laws may affect the use of this technology as a surveillance tool.
Data Protection Act 1998
It is quite clear that if client instructions (written or digitally transmitted) that identify a person and a vehicle are combined with a tracker, the information gathered by the tracker becomes personal data as defined by the Data Protection Act 1998 . The document “What is personal data? – A quick reference guide” [ 26 ] published by the Information Commissioner's Office (ICO) makes clear that data identifying a living individual is personal data. If a living individual can be identified from the data, with or without additional information that may become available, is personal data.
Identifiability
An individual is 'identified' if distinguished from other members of a group. In most cases, an individual's name, together with some other information, will be sufficient to identify them, but a person can be identified even if their name is not known. Start by looking at the means available to identify an individual and the extent to which such means are readily available to you.
Does the data 'relate to' the identifiable living individual, whether in personal or family life, business or profession?
Relates to means: Data which identifies an individual, even without an associated name, may be personal data which is processed to learn or record something about that individual, or the processing of information that affects the individual. Therefore, data may 'relate to' an individual in several different ways.
Is the data 'obviously about a particular individual?
Data 'obviously about' an individual will include their medical history, criminal record, record of work, or their achievements in a sporting activity. Data that is not 'obviously about' a particular individual may include information about their activities. Data such as personal bank statements or itemised telephone bills will be personal data about the individual operating the account or contracting for telephone services. Where data is not 'obviously about' an identifiable individual it may be helpful to consider whether the data is being processed, or could easily be processed, to learn, record or decide something about an identifiable individual. Information may be personal data where the aim, or an incidental consequence, of the processing, is that one learns or records something about an identifiable individual, or the processing could affect an identifiable individual. Data from a Tracker would be to identify the individual or their activities. It is therefore personal data within the meaning of the Data Protection Act 1998.
Any individual who wishes to gather personal data must be registered with the Information Commissioner's Office (ICO) and have a DPA number. It is a criminal offense to process data and not have a DPA number. [ 27 ]
Trespass
It may be a civil trespass for an individual to deploy a tracker on another's car. But in the OSC's annual inspection, the OSC's Chief Surveillance Commissioner Sir Christopher Rose stated "putting an arm into a wheel arch or under the frame of a vehicle is straining the concept of trespass". [ 28 ]
However, entering a person's private land to deploy a tracker is clearly a trespass which is a civil tort.
Prevention of Harassment Act 1997
At times, the public misinterprets surveillance, in all its forms, as stalking. Whilst there is no specific legislation to address this kind of harassment, a long-term pattern of persistent and repeated efforts at contact with a particular victim is generally considered stalking.
The Protection of Freedoms Act 2012 created two new offenses of stalking by inserting new sections 2A and 4A into the PHA 1997. [ 29 ] The new offences which came into force on 25 November 2012, are not retrospective. Section 2A (3) of the PHA 1997 sets out examples of acts or omissions which, in particular circumstances, are ones associated with stalking. Examples are: following a person, watching or spying on them, or forcing contact with the victim through any means, including social media.
Such behavior curtails a victim's freedom, leaving them feeling that they constantly have to be careful. In many cases, the conduct might appear innocent (if considered in isolation), but when carried out repeatedly, so as to amount to a course of conduct, it may then cause significant alarm, harassment or distress to the victim.
The examples given in section 2A (3) are not an exhaustive list but an indication of the types of behavior that may be displayed in a stalking offense.
Stalking and harassment of another or others can include a range of offenses such as those under the Protection from Harassment Act 1997; the Offences Against the Person Act 1861 ; the Sexual Offences Act 2003 ; and the Malicious Communications Act 1988 .
Examples of the types of conduct often associated with stalking include direct communication; physical following; indirect contact through friends, colleagues, family or technology; or, other intrusions into the victim's privacy. The behavior curtails a victim's freedom, leaving them feeling that they constantly have to be careful.
If the subject of inquiry is aware of the tracking, then this may amount to harassment under the Prevention of Harassment Act 1997. There is a case at the Royal Courts of Justice where a private investigator is being sued under this act for the use of trackers. In December 2011, a Claim was brought against Richmond Day & Wilson Limited (First Defendant) and Bernard Matthews Limited (Second Defendant), Britain's leading Turkey Provider.
The case relates to the discovery of a tracking device found in August 2011 on a vehicle supposedly connected to Hillside Animal Sanctuary. [ 30 ]
Regulation of Investigatory Powers Act 2000
Property Interference: The Home Office published a document entitled "Covert Surveillance and Property Interference, Revised Code of Practice, Pursuant to section 71 of the Regulation of Investigatory Powers Act 2000" [ 31 ] where it suggests in Chapter 7, page 61 that;
General basis for lawful activity
7. 1 Authorizations under section 5 of the 1994 Act or Part III of the 1997 Act should be sought wherever members of the intelligence services, the police, the services police, Serious and Organised Crime Agency (SOCA), Scottish Crime and Drug Enforcement Agency (SCDEA), HM Revenue and Customs (HMRC) or Office of Fair Trading (OFT), or persons acting on their behalf, conduct entry on, or interference with, property or with wireless telegraphy that would be otherwise unlawful.
7. 2 For the purposes of this chapter, "property interference" shall be taken to include entry on, or interference with, property or with wireless telegraphy.
Example: The use of a surveillance device for providing information about the location of a vehicle may involve some physical interference with that vehicle as well as subsequent directed surveillance activity. Such an operation could be authorized by a combined authorization for property interference (under Part III of the 1997 Act) and, where appropriate, directed surveillance (under the 2000 Act). In this case, the necessity and proportionality of the property interference element of the authorization would need to be considered by the appropriate authorizing officer separately to the necessity and proportionality of obtaining private information by means of the directed surveillance.
This can be interpreted to mean that placing a tracker on a vehicle without the consent of the owner is illegal unless you obtain authorization from the Surveillance Commissionaire under the RIPA 2000 laws. Since a member of the public cannot obtain such authorizations, it is therefore illegal property interference.
Another interpretation is that it is illegal to do so if you are acting under the instruction of a public authority and you do not obtain authorization. The legislation makes no mention of property interference for anyone else.
Currently, there is no legislation in place that deals with the deployment of trackers in a criminal sense except RIPA 2000 and that RIPA 2000 only applies to those agencies and persons mentioned in it.
In August 2010, Brazilian company Unilever ran an unusual promotion where GPS trackers were placed in boxes of Omo laundry detergent. Teams would then track consumers who purchased the boxes of detergent to their homes where they would be awarded a prize for their purchase. The company also launched a website (in Portuguese) to show the approximate location of the winners' homes. [ 32 ] | https://en.wikipedia.org/wiki/GPS_tracking_unit |
A GPS watch is a device with integrated GPS receiver that is worn as a single unit strapped onto a wrist, in the manner of a bracelet . The watch can have other features and capabilities depending on its intended purpose and be a smartwatch . GPS watches are most often used for sports and fitness purposes. Many can connect to external sensors by the wireless ANT+ protocol, and/or to a computer by USB to transfer data and configuration. Common sensors used are heart rate monitors and footpods (running cadence and speed sensor). A footpod can be used to supplement or replace GPS data, such as providing treadmill speed and distance for the watch to log and share. Recharging by USB is commonplace.
The GPS watch is commonly a sport watch (a device used for sports and exercise in general rather than just GPS functionally). It may be designed for one particular sport or other purpose, or provide modes and features to suit several.
Examples of common purposes:
GPS watches may also be used to get the correct time. Examples of these include Seiko Astron, a few G-Shocks , and Citizen Satellite Wave. | https://en.wikipedia.org/wiki/GPS_watch |
The GPS week number rollover is a phenomenon that happens every 1,024 weeks, which is about 19.6 years. The Global Positioning System (GPS) broadcasts a date, including a week number counter that is stored in only ten binary digits , whose range is therefore 0–1,023. After 1,023, an integer overflow causes the internal value to roll over, changing to zero again. Software that is not coded to anticipate the rollover to zero may stop working or could be moved back in time by a multiple of approximately 20 years. GPS is not only used for positioning, but also for accurate time. Time is used to accurately synchronize payment operations, broadcasters, and mobile operators.
The first rollover took place midnight ( UTC ) August 21 to 22, 1999.
NavCen issued an advisory prior to the rollover stating that some devices would not tolerate the rollover. [ 1 ] Because of the relatively limited use of GPS during the 1999 rollover, disruption was minor.
The second rollover occurred on the night of April 6 to 7, 2019, when GPS Week 2,047, represented as 1,023 in the counter, advanced and rolled over to 0 within the counter. [ 2 ] The United States Department of Homeland Security , the International Civil Aviation Organization , and others issued a warning about this event.
Products known to have been affected by the 2019 rollover include Honeywell 's flight management and navigation software that caused delays for a KLM flight and cancellations for numerous flights in China because the technicians failed to patch the software. [ 3 ] Furthermore, the New York City Wireless Network (NYCWiN), a private network for New York City's municipal services, [ 4 ] crashed. [ 5 ] Other products that were affected by the rollover include cellphones that were sold in 2013 or earlier, [ 6 ] certain types of older Vaisala radiosonde groundstations, suspending launches at some stations for up to two weeks, [ 7 ] NOAA 's weather buoys, [ 8 ] many scientific instruments, [ 9 ] and consumer GPS navigation devices . [ 10 ]
Prior to return to normal standard time from daylight saving time during the morning of November 3, 2019, Apple issued a warning to owners of iPhone and iPad devices sold before 2012 to update or risk losing Internet connectivity. [ 11 ]
Some Furuno GPS models had an internal rollover on January 2, 2022. If the equipment was not updated with the latest software version, the equipment's date would no longer be displayed correctly. [ 12 ]
Honda and Acura cars manufactured between 2004 and 2012 containing GPS navigation systems incorrectly displayed the year 2022 as 2002, with a time offset by several minutes. This problem was due to an overflow on the GPS epoch. [ 13 ] [ 14 ]
All Porsche models with PCM2.1 are also affected according to bulletin #1904 released by Porsche on December 20, 2019.
The third rollover will occur between November 20 and 21, 2038. [ 15 ] This is unrelated to the Year 2038 problem , which will occur in January of that year.
The above rollovers are due to a ten-bit week number; the more recent CNAV protocol, successor to the original NAV protocol, uses thirteen-bit week numbers, which amounts to a 157-year cycle; therefore, using the same epoch of 1980, the first rollover will not be until 2137. [ 15 ] | https://en.wikipedia.org/wiki/GPS_week_number_rollover |
GPS·C ( GPS Correction ) was a Differential GPS data source for most of Canada maintained by the Canadian Active Control System, part of Natural Resources Canada . When used with an appropriate receiver, GPS·C improved real-time accuracy to about 1–2 meters, from a nominal 15 m accuracy.
Real-time data was collected at fourteen permanent ground stations spread across Canada, and forwarded to the central station, "NRC1", in Ottawa for processing.
Visiting the external webpage for this service on 2011-11-04, there is only a note saying that the service had been discontinued on 2011-04-01. There is a PDF link on that page to possible alternatives.
GPS·C information was broadcast Canada-wide on MSAT by the Canada-Wide DGPS Correction Service ( CDGPS ). CDGPS required a separate MSAT receiver, which output correction information in the RTCM format for input into any suitably equipped GPS receiver. The need for a separate receiver made it less cost-effective than solutions like WAAS or StarFire , which receive their correction information using the same antenna and receiver.
On April 9, 2010, it was announced that the service would be discontinued by March 31, 2011.
The service was decommissioned on March 31, 2011 and finally terminated on April 1, 2011, at 9:00 EDT. [ 2 ]
Download coordinates as: | https://en.wikipedia.org/wiki/GPS·C |
TechPowerUp GPU-Z (or just GPU-Z ) is a lightweight utility designed to provide information about video cards and GPUs . [ 2 ] The program displays the specifications of Graphics Processing Unit (often shortened to GPU) and its memory; also displays temperature, core frequency, memory frequency, GPU load and fan speeds. [ 3 ]
This program allows to view the following information of the video card:
This Microsoft Windows software -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/GPU-Z |
GRANK , or Global Rank is a ranking of the rarity of a species , and is a useful tool in determining conservation needs.
Global Ranks are derived from a consensus of various conservation data centres, natural heritage programmes, scientific experts and NatureServe .
They are based on the total number of known, extant populations worldwide, and to what degree they are threatened by destruction. Criteria also include securely protected populations, size of populations, and the ability of the species to persist. | https://en.wikipedia.org/wiki/GRANK |
GRAVES ( French : Grand Réseau Adapté à la Veille Spatiale ) is a French radar -based space surveillance system , akin to the United States Space Force Space Surveillance System . [ 1 ]
Using radar measurements, the French Air and Space Force is able to spot satellites orbiting the Earth and determine their orbit . The GRAVES system took 15 years to develop, and became operational in November, 2005. [ 2 ] GRAVES is also a contributing system to the European Space Agency 's Space Situational Awareness Programme (SSA). [ 3 ]
GRAVES is a bistatic radar system using Doppler and directional information to derive the orbits of the detected satellites. Its operating frequency is 143.050 MHz, with the transmitter being located on a decommissioned airfield near Broye-lès-Pesmes at 47°20′53″N 5°30′54″E / 47.3480°N 5.5151°E / 47.3480; 5.5151 and the receiver at a former missile site near Revest du Bion on the Plateau d'Albion at 44°04′17″N 5°32′05″E / 44.0715°N 5.5346°E / 44.0715; 5.5346 . Data processing and generation of satellite orbital elements is performed at the Balard Air Complex in Paris, 48°50′06″N 2°16′48″E / 48.835°N 2.280°E / 48.835; 2.280 . [ 4 ] | https://en.wikipedia.org/wiki/GRAVES_(system) |
GRAVITY is an instrument on the interferometer of the Very Large Telescope (VLTI). It either combines the light of the four Unit Telescopes (UT) or the smaller four Auxiliary Telescopes. The instrument works with adaptive optics and provides a resolution of 4 milliarcseconds (mas) and can measure the position of astronomical objects down to a few 10 microarcseconds (μas). [ 1 ] VLTI GRAVITY has a collecting area of 200 m 2 and the angular resolution of a 130 m telescope. [ 2 ]
GRAVITY was built by a consortium led by the Max Planck Institute for Extraterrestrial Physics . [ 3 ] Other partner institutes are from France , Germany , Portugal and the European Southern Observatory . [ 4 ] The first light images included the discovery that Theta1 Orionis F in the Trapezium Cluster is a binary. [ 3 ]
GRAVITY can operate in single-field mode or in dual-field mode. In the dual-field mode it can interfere two astronomical objects at the same time and acquire this way very accurate astrometry . The instrument data can also be used for K-band spectroscopy with tree spectral resolutions. GRAVITY has the following sub-components: [ 4 ]
The Beam Combining Instrument is the primary unit of GRAVITY. It performs acquisition and provides interferometric fringes . BCI is cryogenically cooled and located in the VLT-I laboratory. [ 4 ]
GRAVITY is mainly used to observe the stars orbiting the supermassive black hole Sagittarius A* [ 5 ] and the position of exoplanets and brown dwarfs around their host star. [ 6 ] [ 7 ] It is also used for other studies that require a high resolution, such as the study of circumstellar disks [ 8 ] and the study of AGNs . [ 9 ]
GRAVITY+ is the upgrade of GRAVITY, which will increase its sensitivity and increase its sky coverage. The upgrade is performed incrementally to reduce the disruption of astronomical observations. [ 10 ] [ 11 ] | https://en.wikipedia.org/wiki/GRAVITY_(Very_Large_Telescope) |
1AZE , 1BM2 , 1BMB , 1CJ1 , 1FHS , 1FYR , 1GCQ , 1GFC , 1GFD , 1GHU , 1GRI , 1IO6 , 1JYQ , 1JYR , 1JYU , 1QG1 , 1TZE , 1X0N , 1ZFP , 2AOA , 2AOB , 2H5K , 2HUW , 2VVK , 2VWF , 2W0Z , 3C7I , 3IMD , 3IMJ , 3IN7 , 3IN8 , 3KFJ , 3MXC , 3MXY , 3N7Y , 3N84 , 3N8M , 3OV1 , 3OVE , 3S8L , 3S8N , 3S8O , 2H46 , 3WA4 , 4P9V , 4P9Z , 5CDW
2885
14784
ENSG00000177885
ENSMUSG00000059923
P62993
Q60631
NM_203506 NM_002086
NM_008163 NM_001313936 NM_001313937
NP_002077 NP_987102
NP_001300865 NP_001300866 NP_032189
Growth factor receptor-bound protein 2 , also known as Grb2 , is an adaptor protein involved in signal transduction / cell communication . In humans, the GRB2 protein is encoded by the GRB2 gene . [ 5 ] [ 6 ]
The protein encoded by this gene binds receptors such as the epidermal growth factor receptor and contains one SH2 domain and two SH3 domains . Its two SH3 domains direct complex formation with proline -rich regions of other proteins, and its SH2 domain binds tyrosine phosphorylated sequences. This gene is similar to the sem-5 gene of Caenorhabditis elegans , which is involved in the signal transduction pathway. Two alternatively spliced transcript variants encoding different isoforms have been found for this gene. [ 7 ]
Grb2 is widely expressed and is essential for multiple cellular functions. Inhibition of Grb2 function impairs developmental processes in various organisms and blocks transformation and proliferation of various cell types. It is thus not surprising that targeted gene disruption of Grb2 in mice is lethal at an early embryonic stage. Grb2 is best known for its ability to link the epidermal growth factor receptor tyrosine kinase to the activation of Ras and its downstream kinases, ERK1,2 . Grb2 is composed of an SH2 domain flanked on each side by an SH3 domain . Grb2 has two closely related proteins with similar domain organizations, Gads and Grap . Gads and Grap are expressed specifically in hematopoietic cells and function in the coordination of tyrosine kinase mediated signal transduction .
The SH2 domain of Grb2 binds to phosphorylated tyrosine-containing peptides on receptors or scaffold proteins with a preference for pY-X-N-X, where X is generally a hydrophobic residue such as valine (see [1] ).
The N-terminal SH3 domain binds to proline-rich peptides and can bind to the Ras-guanine exchange factor SOS .
The C-terminal SH3 domain binds to peptides conforming to a P-X-I/L/V/-D/N-R-X-X-K-P motif that allows it to specifically bind to proteins such as Gab-1. [ 8 ]
Grb2 has been shown to interact with: | https://en.wikipedia.org/wiki/GRB2 |
GRB 100621A was a long gamma-ray burst observed on June 21, 2010, by the Swift spacecraft. [ 1 ] [ 2 ] It is the third brightest gamma-ray burst yet observed, after GRB 221009A and GRB 130427A . However when it was discovered, it was the brightest GRB in terms of X-ray brightness. [ 3 ] [ 4 ] GRB 100621A is approximately five billion light years from Earth .
This astronomy -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/GRB_100621A |
GRE Subject Biochemistry, Cell and Molecular Biology was a standardized exam provided by ETS ( Educational Testing Service ) that was discontinued in December 2016. It is a paper -based exam and there are no computer -based versions of it. ETS places this exam three times per year: once in April, once in October and once in November. Some graduate programs in the United States recommend taking this exam, while others require this exam score as a part of the application to their graduate programs . ETS sends a bulletin with a sample practice test to each candidate after registration for the exam. There are 180 questions within the biochemistry subject test.
Scores are scaled and then reported as a number between 200 and 990; however, in recent versions of the test, the maximum and minimum reported scores have been 760 (corresponding to the 99 percentile) and 320 (1 percentile) respectively. The mean score for all test takers from July, 2009, to July, 2012, was 526 with a standard deviation of 95. [ 7 ] After learning that test content from editions of the GRE® Biochemistry, Cell and Molecular Biology (BCM) Test has been compromised in Israel, ETS made the decision not to administer this test worldwide in 2016–17.
Since many students who apply to graduate programs in biochemistry do so during the first half of their fourth year, the scope of most questions is largely that of the first three years of a standard American undergraduate biochemistry curriculum. A sampling of test item content is given below: [ 2 ]
A Chemical and Physical Foundations
Thermodynamics and kinetics
Redox states
Water, pH, acid-base reactions and buffers
Solutions and equilibria
Solute-solvent interactions
Chemical interactions and bonding
Chemical reaction mechanisms
B Structural Biology: Structure, Assembly, Organization and Dynamics
Small molecules
Macromolecules (e.g., nucleic acids, polysaccharides, proteins and complex lipids)
Supramolecular complexes (e.g., membranes, ribosomes and multienzyme complexes)
C Catalysis and Binding
Enzyme reaction mechanisms and kinetics
Ligand-protein interaction (e.g., hormone receptors, substrates and effectors, transport proteins and antigen-antibody interactions)
D Major Metabolic Pathways
Carbon, nitrogen and sulfur assimilation
Anabolism
Catabolism
Synthesis and degradation of macromolecules
E Bioenergetics (including respiration and photosynthesis)
Energy transformations at the substrate level
Electron transport
Proton and chemical gradients
Energy coupling (e.g., phosphorylation and transport)
F Regulation and Integration of Metabolism
Covalent modification of enzymes
Allosteric regulation
Compartmentalization
Hormones
G Methods
Biophysical approaches (e.g., spectroscopy, x-ray, crystallography, mass spectroscopy)
Isotopes
Separation techniques (e.g., centrifugation, chromatography and electrophoresis)
Immunotechniques
Methods of importance to cellular biology, such as fluorescence probes (e.g., FRAP, FRET and GFP) and imaging, will be covered as appropriate within the context of the content below.
A. Cellular Compartments of Prokaryotes and Eukaryotes: Organization, Dynamics and Functions
Cellular membrane systems (e.g., structure and transport across membrane)
Nucleus (e.g., envelope and matrix)
Mitochondria and chloroplasts (e.g., biogenesis and evolution)
B. Cell Surface and Communication
Extracellular matrix (including cell walls)
Cell adhesion and junctions
Signal transduction
Receptor function
Excitable membrane systems
C. Cytoskeleton, Motility and Shape
Regulation of assembly and disassembly of filament systems
Motor function, regulation and diversity
D. Protein, Processing, Targeting and Turnover
Translocation across membranes
Posttranslational modification
Intracellular trafficking
Secretion and endocytosis
Protein turnover (e.g., proteosomes, lysosomes, damaged protein response)
E. Cell Division, Differentiation and Development
Cell cycle, mitosis and cytokinesis
Meiosis and gametogenesis
Fertilization and early embryonic development (including positional information, homeotic genes, tissue-specific expression, nuclear and cytoplasmic interactions, growth factors and induction, environment, stem cells and polarity)
A. Genetic Foundations
Mendelian and non-Mendelian inheritance
Transformation, transduction and conjugation
Recombination and complementation
Mutational analysis
Genetic mapping and linkage analysis
B. Chromatin and Chromosomes
Karyotypes
Translocations, inversions, deletions and duplications
Aneuploidy and polyploidy
Structure
Epigenetics
C. Genomics
Genome structure
Physical mapping
Repeated DNA and gene families
Gene identification
Transposable elements
Bioinformatics
Proteomics
Molecular evolution
D. Genome Maintenance
DNA replication
DNA damage and repair
DNA modification
DNA recombination and gene conversion
E. Gene Expression/Recombinant DNA Technology
The genetic code
Transcription/transcriptional profiling
RNA processing
Translation
F. Gene Regulation
Positive and negative control of the operon
Promoter recognition by RNA polymerases
Attenuation and antitermination
Cis-acting regulatory elements
Trans-acting regulatory factors
Gene rearrangements and amplifications
Small non-coding RNA (e.g., siRNA, microRNA)
G. Viruses
Genome replication and regulation
Virus assembly
Virus-host interactions
H. Methods
Restriction maps and PCR
Nucleic acid blotting and hybridization
DNA cloning in prokaryotes and eukaryotes
Sequencing and analysis
Protein-nucleic acid interaction
Transgenic organisms
Microarrays | https://en.wikipedia.org/wiki/GRE_Biochemistry,_Cell_and_Molecular_Biology_Test |
GS-NDG-9422 is a nebular dominated galaxy in the constellation Fornax that was discovered by NASA ’s James Webb Space Telescope . [ 1 ] [ 2 ] [ 3 ] Scientists assume that the galaxy's light comes mostly from superheated gas (more than 80 000 degrees Celsius). [ 4 ] [ 5 ] [ 3 ] [ 6 ]
This astronomy -related article is a stub . You can help Wikipedia by expanding it .
This physics -related article is a stub . You can help Wikipedia by expanding it .
This galaxy-related article is a stub . You can help Wikipedia by expanding it .
This nebula-related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/GS-NDG-9422 |
The GS1 Databar Coupon code has been in use in retail industry since the mid-1980s. At first, it was a UPC with system ID 5. Since UPCs cannot hold more than 12 digits, it required another barcode to hold additional information like offer code, expiration date and household ID numbers. Therefore, the code was often extended with an additional UCC/EAN 128 barcode. EAN 13 was sometimes used instead of UPC, and because it starts with 99, it was called the EAN 99 coupon barcode , and subsequently GS1 DataBar. After more than 20 years in use, there is now a need to encode more data for complex coupons, and to accommodate longer company IDs , so the traditional coupon code has become less efficient and sometimes not usable at all. [ 1 ]
Formerly known as Reduced Space Symbology (RSS-14), this family of barcodes includes:
All GS1 DataBar barcodes encode a GTIN-12 or GTIN-13 in a 14-digit data structure. In order to make the GTIN-12 or GTIN-13 a 14-digit data structure, a leading zero or zeros is filled to the left of the GTIN. GS1 DataBar Omnidirectional, GS1 DataBar Stacked Omnidirectional, GS1 DataBar Expanded, and GS1 DataBar Expanded Stacked have omnidirectional scanning capability. GS1 DataBar Truncated, GS1 DataBar Stacked and GS1 DataBar Limited can only be scanned by a linear hand held or imaging scanning device: they cannot be scanned by omnidirectional scanners and are intended to be read by handheld scanners.
GS1 DataBar Stacked Omnidirectional is designed to condense the GTIN information into a more compact and square barcode suitable for use on smaller packages (such as the label stickers on fresh produce).
GS1 DataBar Limited, GS1 DataBar Stacked and GS1 DataBar Truncated are designed for very small item identification and are mainly used in the healthcare industry . Each encodes a GTIN-12 or GTIN-13 in 14-digit data structure. Only GS1 DataBar Limited uses an indicator digit 1.
In addition to encoding Application Identifier (01) GTIN, GS1 DataBar Expanded and GS1 DataBar Expanded Stacked can encode additional GS1 Application Identifiers such as sell-by date , weight, and lot number. Each symbol has a capacity of up to 74 characters. These attributes can help in controlling shrinkage , optimizing product replenishment, and improving the traceability of a product at the point of sale. They are seeing increased use in manufacturers' coupons. Starting June 2011, GS1 Databar use is mandated for coupons and the use of UPC-A must be discontinued. [ 2 ]
In the United States, GS1 DataBar Coupon barcodes are often placed on grocery coupons issued by product manufacturers (so-called Manufacturer Coupons). These grocery coupons are typically used to advertise products by offering discounts to the consumer at the time of purchase. For example, a coupon may offer a $1.00 discount when the consumer purchases a specific brand and flavor of toothpaste.
During the early years of its use, many checkout registers systems could not read GS1 DataBar barcodes. Consequently, coupons would have both a GS1 DataBar coupon and a traditional UPC/EAN barcode coupon for older registers. Stores have upgraded their checkout systems, so now most coupons have only GS1 DataBar barcodes.
Because the size of the traditional UPC/EAN barcode is limited, a great deal of additional information often had to be entered manually at the time of purchase, and complex offers such as "buy a shampoo and conditioner, and get a hair gel free" were impossible to encode. The manual entry process generally delayed the purchase transaction and introduced errors, inconveniencing customers and raising costs for retailers. In addition, because GS1 has started assigning Company Prefixes that are more than 6 digits long, but UPC/EAN barcodes can only accommodate 6-digit prefixes, companies with prefixes longer than 6 digits cannot use the old system at all. [ 3 ]
In order to address these problems, GS1 came up with a new solution for coupon barcodes. Instead of using a UPC barcode with an Extended UCC/EAN part, it decided to use a single GS1 DataBar Expanded Stacked (formerly RSS Expanded Stacked) barcode. This barcode can hold up to 74 numeric digits or 41 alphanumeric characters, and can be encoded with multiple coupon-specific Application Identifiers such as expiration date, serial number , etc. [ 4 ]
GS1 laid out specific instructions detailing how to compose coupon data using the DataBar Expanded Stacked barcode symbology . The new standard was rolled out in two phases: first there was an interim phase where the UPC remained along with the expanded barcode for backward compatibility. This interim process started in 2007. By 2011, the final phase with stand alone Expanded Stacked barcodes went into effect, and as of June 30, 2015 the GS1 DataBar is the USA industry standard for coupons. [ 5 ]
Having coupon barcodes in a human-readable format is important when the barcode does not scan and manual entry is required. It is recommended that the GS1 Company Prefix and offer code, separated by a dash, is stated on top of Expanded Stacked barcode. Although OCR-B is widely used as a human readable font, any font that clearly states the human readable part will be sufficient. | https://en.wikipedia.org/wiki/GS1_DataBar_Coupon |
GS1 EDI is a set of global electronic messaging standards for business documents used in Electronic Data Interchange (EDI). The standards are developed and maintained by GS1 . [ 1 ] GS1 EDI is part of the overall GS1 system, fully integrated with other GS1 standards, increasing the speed and accuracy of the supply chain.
Examples of GS1 EDI standards [ 2 ] [ 3 ] include messages such as: Order, Despatch Advice (Shipping Notice), Invoice, Transport Instruction, etc.
The development and maintenance of all GS1 standards is based on a rigorous process called the Global Standard Management Process (GSMP). GS1 develops its global supply chain standards in partnership with the industries using them. Any organization can submit a request to modify the standard. Maintenance releases of GS1 EDI standards are typically published every two years, while code lists can be updated up to 4 times a year.
GS1 developed the following sets of complementary EDI standards:
These groups of standards are being implemented in parallel by various users, GS1 supports and maintains all of them.
GS1 EDI standards are designed to work together with other GS1 standards for the identification and labeling of goods, locations, parties and packages. This means that the information and product flows can be combined to provide business with tool enabling traceability, visibility and safety.
In EDI, it is essential to unambiguously identify products, services and parties involved in the transaction. In GS1 EDI standard messages, each product, party and location is identified by a unique GS1 identification key, [ 11 ] e.g.:
Using the GS1 ID Keys enables master data alignment between trading partners before any trading transaction takes place. This ensures data quality, eliminates errors and removes the need to send redundant information in electronic messages (such as product specifications, party addresses, etc.).
GS1 EDI standards are developed based on other global standards, such as:
User companies are involved in the development of GS1 standards, either directly or via industry associations, such as The Consumer Goods Forum . [ 12 ]
GS1 EDI standards are globally used by companies and organizations from different sectors and applied in various processes like Retail Up- and Downstream, [ 13 ] Transport and Warehouse Management, [ 14 ] [ 15 ] Healthcare, [ 16 ] [ 17 ] [ 18 ] Defense, Finance, Packaging (collaborative artwork development), Cash Handling, [ 19 ] public administration [ 20 ] and much more. [ 21 ] [ 22 ] | https://en.wikipedia.org/wiki/GS1_EDI |
Ground state depletion microscopy ( GSD microscopy ) is an implementation of the RESOLFT concept. The method was proposed in 1995 [ 1 ] and experimentally demonstrated in 2007. [ 2 ] It is the second concept to overcome the diffraction barrier in far-field optical microscopy published by Stefan Hell . Using nitrogen-vacancy centers in diamonds a resolution of up to 7.8 nm was achieved in 2009. [ 3 ] This is far below the diffraction limit (~200 nm).
In GSD microscopy, fluorescent markers are used. In one condition, the marker can freely be excited from ground state and returns spontaneously via emission of a fluorescence photon. However, if light of appropriate wavelength is additionally applied the dye can be excited to a long-lived dark state, i.e. a state where no fluorescence occurs. As long as the molecule is in the long-lived dark state (e.g. a triplet state ), it cannot be excited from the ground state. Switching between these two states (bright and dark) by applying light fulfills all preconditions for the RESOLFT concept and subwavelength scale imaging, and therefore images with very high resolution can be obtained. For successful implementation, GSD microscopy requires either special fluorophores with high triplet yield, [ 4 ] or removal of oxygen by use of various mounting media such as Mowiol or Vectashield. [ 2 ]
The implementation in a microscope is very similar to stimulated emission depletion microscopy , however it can operate with only one wavelength for excitation and depletion. Using an appropriate ring-like focal spot for the light that switches the molecules into the dark state, the fluorescence can be quenched at the outer part of the focal spot. Therefore, fluorescence only still takes place at the center of the microscope's focal spot and the spatial resolution is increased. | https://en.wikipedia.org/wiki/GSD_microscopy |
One of the experimental facilities at the German laboratory GSI Helmholtz Centre for Heavy Ion Research in Darmstadt is an Experimental Storage Ring (ESR) with electron cooling in which large numbers of highly charged radioactive ions can be stored for extended periods of time. [ 1 ] This facility provides the means to make precise measurements of their decay modes. The absence of most or all of the electrons in the ions simplifies theoretical treatments of their influence on the decay. Also, such a high degree of ionization is typical in stellar environments where such decays play an important role in nucleosynthesis . [ 2 ]
In 2007 an ESR experiment reported the observation of unexpected modulation in time of the rate of electron capture decays of highly ionized heavy atoms — 140 Pr 58+ , which have a lifetime of 3.39 min. Such findings were soon repeated by the same group, and were extended to include the decay of 142 Pm 60+ (lifetime 40.5 s). [ 3 ] The oscillations in decay rate had time periods near to 7 s and amplitudes of about 20%. Such a phenomenon had not been previously observed, and was difficult to understand. The experimental group considered it very improbable that the appearance of the phenomenon is due to a technical artefact because they report that their detection technique provides—during the whole observation time—complete and uninterrupted information upon the status of each stored ion.
As this type of weak decay involves the production of an electron neutrino , attempts at the time were made to relate the observed oscillations to neutrino oscillations , but this proposal was highly controversial. [ 4 ]
In 2013, a similar experimental group at the ESR now called the Two-Body-Weak-Decays Collaboration reported further observations of the phenomenon with measurements on 142 Pm 60+ with much higher precision in period and amplitude. The same period was observed, but the amplitude was only about a half of that previously seen. [ 5 ]
Moreover, a follow-up high-statistics study (2019) did not observe any time modulation: indicating the observed anomaly was purely statistical, with no physical origin. [ 6 ] | https://en.wikipedia.org/wiki/GSI_anomaly |
GTFS Realtime (also known as GTFS-rt ) is an extension to GTFS , in which public transport agencies share real-time vehicle locations, arrival time predictions, and alerts such as detours and cancellations via Protocol Buffers web server. [ 1 ]
Realtime location data is created continuously by an agency from automatic vehicle location (AVL) systems. Trip arrival times are computed using machine learning models that analyse historical positional data and timetables. [ 2 ]
The standard is used by public transport agencies globally, including the United States, Canada, most countries in the European Union, United Kingdom, Australia, New Zealand, and in Yokohama, Japan .
On 22 August 2011, a first version of GTFS-rt was released by Google. [ 3 ] This data was shown to Google Maps users. [ 4 ]
In July 2012, Google Maps began showing alerts from GTFS-rt. [ 5 ]
A proposal that was created on July 28, 2015 and merged on Aug 15, 2015 allowed the combination of several feed entity types into a single feed. [ 6 ] While the majority of agencies separate feed entity types (Vehicle Positions, Trips, and Alerts), some feeds are still joined.
On August 30, 2021, an experimental feed entity types, Shapes, was released. Shapes has the ability to update route shapes in real time to reflect detour, as route updates are either reflected by referencing an existing shape_id or by defining in real time a new shape as an encoded polyline.
In 2022, CalTrans' Integrated Travel Project began validating GTFS Schedule and Realtime feeds published by municipality and county public transport agencies within California. [ 7 ] Monthly reports are published on the errors in agency data, along with analysis of typical street speeds and traffic.
In September 2023, Swiftly and the app Transit proposed 2 additional feed entity types: Stop and Trip Modifications. These allow agencies to broadcast new detour paths of routes and new temporary stops. The change has been released to users in the Transit app across several agencies. On March 11, 2024, the proposal was merged and released by GTFS maintainers. [ 8 ]
The GTFS Realtime specification is defined by a .proto file hosted by Google. [ 9 ] Data is serialized into raw bytes by the server and then deserialized by a client. Officially supported GTFS-rt binding libraries have been built in .NET , Java , Javascript , Python , and Go . Unofficial libraries have been written in other languages, such as Rust .
There are currently three official feed types defined in the standard, TripUpdates, VehiclePositions, and Alerts. Shapes, Trip Modifications, and Stops are currently experimental.
Agencies supporting GTFS-Realtime typically provide separate urls for the three separate feed types, and may choose to only provide some of the feeds. Unlike GTFS Schedule zip files, many agencies may require developers to request an API key via email or a web form.
Developers then write programs to periodically fetch an agency's web API over HTTP , typically every few seconds to minutes. Agencies typically refresh data in frequencies ranging between 1 second to 1 minute. There is no standard for streaming GTFS Realtime data, also support is built in to allow for deletion of items from previous iterations.
In the GTFS Specification , a trip refers to an operator driving a fixed-route vehicle from the start of the route to the end. A new trip is started for when the vehicle turns around at the end of its route.
The Trip Update feed allows maps to show the departure or arrival times of vehicles, and allows routing algorithms to update their directions. [ 10 ]
This feed contains an array of Trip Updates. Each trip update enumerates a description of a trip (trip id, route id, start time and date, direction), last updated time, may include an associated vehicle number and route number, and contains an array of StopTimeUpdate . The StopTimeUpdate can define past, current, and future stop times, delays, and cancellations. The stop id references the GTFS Schedule feed the agency provides.
Vehicle Positions are sometimes shown on mapping applications to aid users in tracking the location of buses. [ 11 ] This feed contains an array of VehiclePositions . Like Trip Updates, each VehiclePosition can also contain a basic description of the trip, such as its trip id, start and stop times, route number, and relationship to the schedule. The VehiclePosition also contains the current latitude and longitude of the vehicle, and can also include bearing, odometer, and speed in m/s. Finally, it can also contain information on how crowded the bus is, known as occupancy status, and status of road congestion experienced by the vehicle.
Alerts can be shown to mapping application users to alert them of detours, cancellations, or other service changes. [ 12 ] This feed contains an array of Alerts. Alerts typically don't update as often as Vehicle Positions or Trip Updates. Each Alert stores the cause (such as labour strike or a mechanical fault) of an incident, along with its effect (reduced service, detour, stop cancellation, etc.). Alerts also contain detailed headers, descriptions, urls, images, and a list of routes or stops affected (known as the Informed Entity). Alerts specify their beginning and expiration times using "active periods". Alerts can be localised into several languages. | https://en.wikipedia.org/wiki/GTFS_Realtime |
GTPases are a large family of hydrolase enzymes that bind to the nucleotide guanosine triphosphate (GTP) and hydrolyze it to guanosine diphosphate (GDP) . [ 1 ] The GTP binding and hydrolysis takes place in the highly conserved P-loop "G domain", a protein domain common to many GTPases. [ 1 ]
GTPases function as molecular switches or timers in many fundamental cellular processes. [ 2 ]
Examples of these roles include:
GTPases are active when bound to GTP and inactive when bound to GDP. [ 2 ] [ 3 ] In the generalized receptor-transducer-effector signaling model of Martin Rodbell , signaling GTPases act as transducers to regulate the activity of effector proteins. [ 3 ] This inactive-active switch is due to conformational changes in the protein distinguishing these two forms, particularly of the "switch" regions that in the active state are able to make protein-protein contacts with partner proteins that alter the function of these effectors. [ 1 ]
Hydrolysis of GTP bound to an (active) G domain-GTPase leads to deactivation of the signaling/timer function of the enzyme. [ 2 ] [ 3 ] The hydrolysis of the third (γ) phosphate of GTP to create guanosine diphosphate (GDP) and P i , inorganic phosphate , occurs by the S N 2 mechanism (see nucleophilic substitution ) via a pentacoordinate transition state and is dependent on the presence of a magnesium ion Mg 2+ . [ 2 ] [ 3 ]
GTPase activity serves as the shutoff mechanism for the signaling roles of GTPases by returning the active, GTP-bound protein to the inactive, GDP-bound state. [ 2 ] [ 3 ] Most "GTPases" have functional GTPase activity, allowing them to remain active (that is, bound to GTP) only for a short time before deactivating themselves by converting bound GTP to bound GDP. [ 2 ] [ 3 ] However, many GTPases also use accessory proteins named GTPase-activating proteins or GAPs to accelerate their GTPase activity. This further limits the active lifetime of signaling GTPases. [ 4 ] Some GTPases have little to no intrinsic GTPase activity, and are entirely dependent on GAP proteins for deactivation (such as the ADP-ribosylation factor or ARF family of small GTP-binding proteins that are involved in vesicle-mediated transport within cells). [ 5 ]
To become activated, GTPases must bind to GTP. Since mechanisms to convert bound GDP directly into GTP are unknown, the inactive GTPases are induced to release bound GDP by the action of distinct regulatory proteins called guanine nucleotide exchange factors or GEFs. [ 2 ] [ 3 ] The nucleotide-free GTPase protein quickly rebinds GTP, which is in far excess in healthy cells over GDP, allowing the GTPase to enter the active conformation state and promote its effects on the cell. [ 2 ] [ 3 ] For many GTPases, activation of GEFs is the primary control mechanism in the stimulation of the GTPase signaling functions, although GAPs also play an important role. For heterotrimeric G proteins and many small GTP-binding proteins, GEF activity is stimulated by cell surface receptors in response to signals outside the cell (for heterotrimeric G proteins, the G protein-coupled receptors are themselves GEFs, while for receptor-activated small GTPases their GEFs are distinct from cell surface receptors).
Some GTPases also bind to accessory proteins called guanine nucleotide dissociation inhibitors or GDIs that stabilize the inactive, GDP-bound state. [ 6 ]
The amount of active GTPase can be changed in several ways:
In most GTPases, the specificity for the base guanine versus other nucleotides is imparted by the base-recognition motif, which has the consensus sequence [N/T]KXD. The following classification is based on shared features; some examples have mutations in the base-recognition motif that shift their substrate specificity, most commonly to ATP. [ 8 ]
The TRAFAC class of G domain proteins is named after the prototypical member, the translation factor G proteins. They play roles in translation, signal transduction, and cell motility. [ 8 ]
Multiple classical translation factor family GTPases play important roles in initiation , elongation and termination of protein biosynthesis . Sharing a similar mode of ribosome binding due to the β-EI domain following the GTPase, the most well-known members of the family are EF-1A / EF-Tu , EF-2 / EF-G , [ 9 ] and class 2 release factors . Other members include EF-4 (LepA), BipA (TypA), [ 10 ] SelB (bacterial selenocysteinyl-tRNA EF-Tu paralog), Tet ( tetracycline resistance by ribosomal protection), [ 11 ] and HBS1L (eukaryotic ribosome rescue protein similar to release factors).
The superfamily also includes the Bms1 family from yeast. [ 8 ]
Heterotrimeric G protein complexes are composed of three distinct protein subunits named alpha (α), beta (β) and gamma (γ) subunits . [ 12 ] The alpha subunits contain the GTP binding/GTPase domain flanked by long regulatory regions, while the beta and gamma subunits form a stable dimeric complex referred to as the beta-gamma complex . [ 13 ] When activated, a heterotrimeric G protein dissociates into activated, GTP-bound alpha subunit and separate beta-gamma subunit, each of which can perform distinct signaling roles. [ 2 ] [ 3 ] The α and γ subunit are modified by lipid anchors to increase their association with the inner leaflet of the plasma membrane. [ 14 ]
Heterotrimeric G proteins act as the transducers of G protein-coupled receptors , coupling receptor activation to downstream signaling effectors and second messengers . [ 2 ] [ 3 ] [ 15 ] In unstimulated cells, heterotrimeric G proteins are assembled as the GDP bound, inactive trimer (G α -GDP-G βγ complex). [ 2 ] [ 3 ] Upon receptor activation, the activated receptor intracellular domain acts as GEF to release GDP from the G protein complex and to promote binding of GTP in its place. [ 2 ] [ 3 ] The GTP-bound complex undergoes an activating conformation shift that dissociates it from the receptor and also breaks the complex into its component G protein alpha and beta-gamma subunit components. [ 2 ] [ 3 ] While these activated G protein subunits are now free to activate their effectors, the active receptor is likewise free to activate additional G proteins – this allows catalytic activation and amplification where one receptor may activate many G proteins. [ 2 ] [ 3 ]
G protein signaling is terminated by hydrolysis of bound GTP to bound GDP. [ 2 ] [ 3 ] This can occur through the intrinsic GTPase activity of the α subunit, or be accelerated by separate regulatory proteins that act as GTPase-activating proteins (GAPs), such as members of the Regulator of G protein signaling (RGS) family). [ 4 ] The speed of the hydrolysis reaction works as an internal clock limiting the length of the signal. Once G α is returned to being GDP bound, the two parts of the heterotrimer re-associate to the original, inactive state. [ 2 ] [ 3 ]
The heterotrimeric G proteins can be classified by sequence homology of the α unit and by their functional targets into four families: G s family, G i family, G q family and G 12 family. [ 12 ] Each of these G α protein families contains multiple members, such that the mammals have 16 distinct α -subunit genes. [ 12 ] The G β and G γ are likewise composed of many members, increasing heterotrimer structural and functional diversity. [ 12 ] Among the target molecules of the specific G proteins are the second messenger-generating enzymes adenylyl cyclase and phospholipase C , as well as various ion channels . [ 16 ]
Small GTPases function as monomers and have a molecular weight of about 21 kilodaltons that consists primarily of the GTPase domain. [ 17 ] They are also called small or monomeric guanine nucleotide-binding regulatory proteins, small or monomeric GTP-binding proteins, or small or monomeric G-proteins, and because they have significant homology with the first-identified such protein, named Ras , they are also referred to as Ras superfamily GTPases. Small GTPases generally serve as molecular switches and signal transducers for a wide variety of cellular signaling events, often involving membranes, vesicles or cytoskeleton. [ 18 ] [ 17 ] According to their primary amino acid sequences and biochemical properties, the many Ras superfamily small GTPases are further divided into five subfamilies with distinct functions: Ras , Rho ("Ras-homology"), Rab , Arf and Ran . [ 17 ] While many small GTPases are activated by their GEFs in response to intracellular signals emanating from cell surface receptors (particularly growth factor receptors ), regulatory GEFs for many other small GTPases are activated in response to intrinsic cell signals, not cell surface (external) signals.
This class is defined by loss of two beta-strands and additional N-terminal strands. Both namesakes of this superfamily, myosin and kinesin , have shifted to use ATP. [ 8 ]
See dynamin as a prototype for large monomeric GTPases.
Much of the SIMIBI class of GTPases is activated by dimerization. [ 8 ] Named after the signal recognition particle (SRP), MinD, and BioD, the class is involved in protein localization, chromosome partitioning, and membrane transport. Several members of this class, including MinD and Get3, has shifted in substrate specificity to become ATPases. [ 19 ]
For a discussion of Translocation factors and the role of GTP, see signal recognition particle (SRP).
While tubulin and related structural proteins also bind and hydrolyze GTP as part of their function to form intracellular tubules, these proteins utilize a distinct tubulin domain that is unrelated to the G domain used by signaling GTPases. [ 20 ]
There are also GTP-hydrolyzing proteins that use a P-loop from a superclass other than the G-domain-containing one. Examples include the NACHT proteins of its own superclass and McrB protein of the AAA+ superclass. [ 8 ] | https://en.wikipedia.org/wiki/GTPase |
GTx, Inc. was a pharmaceutical company working on drugs in the selective estrogen receptor modulator (SERM) and selective androgen receptor modulator (SARM) classes. Its drugs in development included enobosarm (ostarine) and GTx-758 .
The company was founded in Memphis in 1997 by Mitch Steiner and Marc S. Hanover. [ 1 ] The company was originally called Genotherapeutics, changed its name to GTx, Inc. in 2001, and reincorporated in Delaware in 2003. [ 1 ] The company licensed toremifene from Orion Corporation, and licensed andarine, enobosarm and prostarine from the University of Tennessee Research Foundation; the SARM compounds from Tennessee had been invented by Duane D Miller and James T Dalton, who later joined the company and served as Chief Scientific Officer. [ 1 ] The company held its IPO in February 2004. [ 2 ] [ 3 ]
In 2006 GTx signed a partnership with Ipsen to develop toremifene, a selective estrogen receptor modulator to prevent prostate cancer and to prevent bone loss in men with prostate cancer; the FDA rejected the application to market the drug for this use in 2009, and Ipsen terminated the arrangement in 2011. [ 4 ] [ 5 ] In 2012 GTx sold its rights to toremifene to ProStrakan, a subsidiary of Kyowa Hakko Kirin , for around $19 million, and terminated its agreement with Orion. [ 6 ]
By 2007 enobosarm was in a Phase II trial, and that year GTx signed an exclusive license agreement for its SARM program with Merck; Merck bought $30M in GtX stock, paid an upfront fee of $40M, and agreed to fund $15M in research over the next three years. The agreement also included royalties on any product brought to market and around $400M in biodollars . [ 7 ] The companies ended the deal in 2010. [ 8 ]
In August 2013 GTx announced that enobosarm had failed in two Phase III clinical trials to treat wasting in people with lung cancer. [ 9 ] In October 2013 the company laid off around 60% of its 88-person workforce, [ 10 ] and Steiner resigned 6 months later. [ 11 ] The company had invested around $35 million in the development of the drug. [ 11 ] The company said at that time that is planned to pursue approval of enobosarm in Europe; the company was also still developing GTx-758 for castration-resistant prostate cancer. [ 12 ]
In 2016 GTx began Phase II trials, to see if enosobarm might be effective to treat stress urinary incontinence in women. [ 13 ]
In June 2019, GTx combined with Oncternal Therapeutics in a reverse merger, with the resulting company operating under the name Oncternal Therapeutics, Inc. [ 14 ]
This biotechnology article is a stub . You can help Wikipedia by expanding it .
This article about a medical , pharmaceutical or biotechnological corporation or company is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/GTx_Incorporated |
GUIDE-Seq ( Genome-wide, Unbiased Identification of DSBs Enabled by Sequencing ) is a molecular biology technique that allows for the unbiased in vitro detection of off-target genome editing events in DNA caused by CRISPR/Cas9 as well as other RNA-guided nucleases in living cells. [ 1 ] Similar to LAM-PCR, it employs multiple PCRs to amplify regions of interest that contain a specific insert that preferentially integrates into double-stranded breaks. As gene therapy is an emerging field, GUIDE-Seq has gained traction as a cheap method to detect the off-target effects of potential therapeutics without needing whole genome sequencing. [ citation needed ]
Conceived to work in concert with next-gen sequencing platforms such as Illumina dye sequencing , GUIDE-Seq relies on the integration of a blunt, double-stranded oligodeoxynucleotide (dsODN) that has been phosphothioated on two of the phosphate linkages on the 5' end of both strands. [ 1 ] The dsODN cassette integrates into any site in the genome that contains a double-stranded break (DSB). [ 1 ] This means that along with the target and off-target sites that may exist as a result of the activity of a nuclease, the dsODN cassette will also integrate into any spurious sites in the genome that have a DSB. [ 1 ] This makes it critical to have a dsODN only condition that controls for errant and naturally occurring DSBs, and is required to use the GUIDE-seq bioinformatic pipeline. [ 1 ]
After integration of the dsODN cassette, genomic DNA (gDNA) is extracted from the cell culture and sheared to 500bp fragments via sonication. The resulting sheared gDNA undergoes end-repair and adapter ligation. From here, DNA specifically containing the dsODN insert is amplified via two rounds of polymerase chain reaction (PCR) that proceeds in a unidirectional manner starting from the primers that are complementary to the dsODN. This process allows for the reading of the adjacent sequences, both the sense and anti-sense strands, flanking the insert. The final product is a panoply of amplicons, describing the DSB distribution, containing indices for sample differentiation, p5 and p7 Illumina flow-cell adapters, and the sequences flanking the dsODN cassette. [ 1 ]
GUIDE-Seq is able to achieve detection of rare DSBs that occur with a 0.1% frequency, however this may be as a result of the limitations of next-generation sequencing platforms. The greater the depth of reads an instrument is able to achieve, the better it can detect rarer events. [ 1 ] Additionally, GUIDE-Seq is able to detect sites not predicted by the "in silico" methods which often will predict sites based on sequence similarity and percent mismatch. [ 1 ] There have been cases of GUIDE-Seq not detecting any off-targets for certain guide RNAs, suggesting that some RNA-guided nucleases may have no associated off-targets. [ 1 ] [ 2 ] GUIDE-Seq has been used to show that engineered variants of Cas9 can have reduced off-target effects. [ 3 ]
GUIDE-Seq has been shown to miss some off-targets, when compared to the genome-wide sequencing DIGENOME-Seq method, due to the nature of its targeting. [ 4 ] Another caveat is that GUIDE-Seq has been observed to generate slightly different off-target sites depending on the cell line. [ 1 ] This could be due to cell lines having different parental genetic origins, cell line specific mutations, or, in the case of some immortal cell lines such as K562s, having aneuploidy. This suggests that it would be pertinent for researchers to test multiple cell lines to validate efficacy and accuracy. [ 5 ] GUIDE-Seq cannot be used to identify off-targets in vivo. | https://en.wikipedia.org/wiki/GUIDE-Seq |
The GUS reporter system ( GUS : β-glucuronidase ) is a reporter gene system, particularly useful in plant molecular biology [ 1 ] and microbiology. [ 2 ] Several kinds of GUS reporter gene assay are available, depending on the substrate used. The term GUS staining refers to the most common of these, a histochemical technique.
The purpose of this technique is to analyze the activity of a gene transcription promoter (in terms of expression of a so-called reporter gene under the regulatory control of that promoter) either in a quantitative manner, involving some measure of activity, or qualitatively (on versus off) through visualization of its activity in different cells, tissues , or organs. The technique utilizes the uidA gene of Escherichia coli , which codes for the enzyme, β-glucuronidase ; [ 3 ] this enzyme, when incubated with specific colorless or non-fluorescent substrates , can convert them into stable colored or fluorescent products. [ 4 ] The presence of the GUS-induced color indicates where the gene has been actively expressed. In this way, strong promoter activity produces much staining and weak promoter activity produces less staining.
The uidA gene can also be fused to a gene of interest, creating a gene fusion . The insertion of the uidA gene will cause production of GUS, which can then be detected using various glucuronides as substrates. [ 4 ]
There are different possible glucuronides that can be used as substrates for the β-glucuronidase, depending on the type of detection needed ( histochemical , spectrophotometrical , fluorimetrical ). The most common substrate for GUS histochemical staining is 5-bromo-4-chloro-3-indolyl glucuronide ( X-Gluc ). X-Gluc is hydrolyzed by GUS into the product 5,5'-dibromo-4,4'-dichloro-indigo (diX-indigo). DiX-indigo will appear blue, and can be seen using light microscopy. [ 5 ] This process is analogous to hydrolysis of X-gal by Beta-galactosidase [ 5 ] to produce blue cells as is commonly practiced in bacterial reporter gene assays.
For other types of detection, common substrates are p-nitrophenyl β-D-glucuronide for the spectrophotometric assay and 4-methylumbelliferyl-beta-D-glucuronide (MUG) for the fluorimetric assay. [ 6 ]
The system was originally developed by Richard Anthony Jefferson during his Ph.D. at the University of Colorado at Boulder . [ 7 ] He adapted the technique for the use with plants as he worked in the Plant Breeding Institute of Cambridge , between 1985 and 1987. [ 1 ] Since then thousands of labs have used the system, making it one of the most widely used tools in plant molecular biology, as underlined by thousands of citations in scientific literature. [ 7 ]
An organism is suitable for a GUS assay if it lacks naturally occurring β-glucuronidase activity or if the activity is very low ( background activity). For this reason, the assay is not useful in most vertebrates and many molluscs . [ 6 ] Since there is no detectable GUS activity in higher plants , mosses , algae , ferns , fungi and most bacteria , [ 6 ] the assay is ideally suited for gene expression studies in these organisms, and considered the reporter gene of choice for in plant science.
The GUS assay does not require the presence of any cofactors or ions for function. Beta-glucuronidase can function through a wide range of pH values, and is fairly resistant to thermal inactivation. [ 8 ] However, GUS is susceptible to inhibition from certain heavy metal ions, such as Cu 2+ and Zn 2+ .
Additionally, the interpretation of the assay is limited by the movement of diX-indigo throughout the cell. DiX-indigo, can associate with lipids to diffuse far from the site of enzyme activity, which shows a lack of cytosolic localization and irregularity of substrate penetration. This can potentially lead to an incorrect interpretation of GUS protein localization. [ 9 ] Despite a lack of cellular localization, nuclear localization of GUS has been well observed. [ 10 ] GUS assays can be carried out in the presence of potassium ferricyanide to prevent the stain from diffusing. [ 5 ]
The GUS system is not the only available gene reporter system for the analysis of promoter activity. Other competing systems are based on e.g. luciferase , GFP , beta-galactosidase , chloramphenicol acetyltransferase (CAT), alkaline phosphatase . The use of one or the other system is mainly dependent on the organism of interest and the imaging and microscopy technologies available to the laboratories conducting the research.
The GUS assay, as well as other reporter gene systems, can be used for other kinds of studies other than the classical promoter activity assay. Reporter systems have been used for the determination of the efficiency of gene delivery systems, the intracellular localization of a gene product, the detection of protein-protein or protein-DNA interactions, the efficiency of translation initiation signals and the success of molecular cloning efforts. | https://en.wikipedia.org/wiki/GUS_reporter_system |
GVA Consultants was a Swedish marine and offshore engineering company specialising in the design of offshore structures , and semi-submersible platforms.
The experience of GVA as a marine engineering company stretches back more than 25 years. There is an even longer history of building ships of various types, semi-submersibles, jack-ups and offshore modules at the shipyard Götaverken Arendal AB where GVA is based. [ 1 ]
From the late 1970s the yard [ clarification needed ] focused mainly on the offshore industry. Thus, the company designed, constructed and delivered 14 semisubmersibles from its facilities in Gothenburg. Seven units of the GVA series have also been built by yards all over the world, in different sizes and for various requirements. The units built at the yard in Gothenburg were adapted for duties such as production, drilling, diving support and accommodation/service. The deliveries included six Pacesetter type units and eight GVA designs.
The shipyard closed down in 1989 and GVA Consultants AB was established from the shipyards technical departments. GVA started out as a small company focusing on engineering services and conceptual studies. [ citation needed ] The company grew considerably during the years when larger contracts such as Visund , Troll C , Åsgard B and Kristin Gas Field were awarded to them. The company has continued to grow and has taken on even larger projects such as the Thunder Horse and Atlantis oil fields.
In 2001, Halliburton KBR (KBR), formerly Kellogg Brown & Root acquired GVA Consultants AB from British Maritime Technology Ltd (BMT) for an undisclosed amount." [ 2 ] Halliburton KBR was the engineering and construction segment of Halliburton , the world's largest provider of products and services to the petroleum and energy industries.
GVA Consultant's range of products and services includes:
GVA was a subsidiary to KBR but operated as a fully independent company providing specialized design services. [ citation needed ] The owner KBR shut down GVA Consultants in 2016. | https://en.wikipedia.org/wiki/GVA_Consultants |
GW 190814 was a gravitational wave (GW) signal observed by the LIGO and Virgo detectors on 14 August 2019 at 21:10:39 UTC, [ 2 ] and having a signal-to-noise ratio of 25 in the three-detector network. [ 1 ] The signal was associated with the astronomical super event S190814bv , located 790 million light years away, in location area 18.5 deg 2 [ n 1 ] [ 1 ] [ 3 ] [ 4 ] towards Cetus or Sculptor . [ 5 ] [ 6 ] [ 7 ] [ 8 ] [ 9 ] [ 10 ] No optical counterpart was discovered despite an extensive search of the probability region. [ 11 ]
In June 2020, astronomers reported details of a compact binary merging, in the " mass gap " of cosmic collisions, of a first-ever 2.50–2.67 M ☉ "mystery object", either an extremely heavy neutron star (that was theorized not to exist) or a too-light black hole , with a 22.2–24.3 M ☉ black hole, that was detected as the gravitational wave GW190814. [ 1 ] [ 12 ]
"We don't know if this object is the heaviest known neutron star or the lightest known black hole, but either way it breaks a record."
The mass of the lighter component is estimated to be 2.6 times the mass of the Sun ( M ☉ ≈ 1.9891 × 10 30 kg ), placing it in the aforementioned mass gap between neutron stars and black holes. [ 1 ] [ 13 ] [ 14 ] [ 15 ] [ 16 ] [ 17 ]
Despite an intensive search, no optical counterpart to the gravitational wave was observed. The lack of emitted light could be consistent with either a situation in which a black hole entirely consumed a neutron star or the merger of two black holes. [ 14 ] | https://en.wikipedia.org/wiki/GW190814 |
GW501516 (also known as GW-501,516 , GW1516 , GSK-516 , cardarine , and on the black market as endurobol [ 1 ] ) is a PPARδ receptor agonist that was invented in a collaboration between Ligand Pharmaceuticals and GlaxoSmithKline in the 1990s. It entered into clinical development as a drug candidate for metabolic and cardiovascular diseases , but was abandoned in 2007 because animal testing showed that the drug caused cancer to develop rapidly in several organs. [ 2 ]
In 2007, research was published showing that high doses of GW501516 given to mice dramatically improved their physical performance; the work was widely discussed in popular media, and led to a black market for the drug candidate and to its abuse by athletes as a doping agent . The World Anti-Doping Agency (WADA) developed a test for GW501516 and other related chemicals and added them to the prohibited list in 2009; it has issued additional warnings to athletes that GW501516 is not safe.
GW501516 was initially discovered during a research collaboration between GSK and Ligand Pharmaceuticals that began in 1992. [ 3 ] The discovery of the compound was published in a 2001 issue of PNAS . [ 4 ] Oliver et al. reported that they used " combinatorial chemistry and structure-based drug design " to develop it. [ 5 ] One of the authors was the son of Leo Sternbach who discovered benzodiazepines in the 1960s. [ 6 ]
R & D Focus Drug News reported that GSK began phase I trials of the compound for the treatment of hyperlipidemia in 2000 [ 7 ] followed by phase I/II in 2002. [ 8 ] In 2003, Ligand Pharmaceuticals earned a $1 million payment as a result of GSK continuing phase I development. [ 9 ]
By 2007, GW501516 had completed two phase II clinical studies and other studies relating to obesity , diabetes , dyslipidemia , and cardiovascular disease , [ 10 ] [ 11 ] but GSK abandoned further development of the drug in 2007 for reasons which were not disclosed at the time. [ 12 ] It later emerged that the drug was discontinued because animal testing showed that the drug caused cancer to develop rapidly in several organs, at dosages of 3 mg/kg/day in both mice and rats. [ 2 ] [ 13 ] [ 14 ]
Ronald M. Evans 's laboratory purchased a sample of GW501516 and gave mice a much higher dose than had been used in GSK's experiments; they found that the compound dramatically increased the physical performance of the mice. [ 15 ] The work was published in 2007 in Cell and was widely reported in the popular press including The New York Times and The Wall Street Journal . [ 16 ]
Another human study (comparing cardarine with the PPARα agonist GW590735 and placebo) was published in 2021. [ 17 ]
Concerns were raised prior to the 2008 Beijing Olympics that GW501516 could be used by athletes as a performance-enhancing drug that was not currently controlled by regulations or detected by standard tests. One of the main researchers from the study on enhanced endurance consequently developed a urine test to detect the drug, and made it available to the International Olympic Committee . The World Anti-Doping Agency (WADA) developed a test for GW501516 and other related PPARδ modulators, [ 18 ] and added such drugs to the prohibited list in 2009. [ 19 ]
GW501516 has been promoted on bodybuilding and athletics websites [ 20 ] and by 2011 had already been available for some time on the black market . [ 1 ] [ 21 ] In 2011, it was reported to cost $1,000 for 10 g. [ 16 ] In 2012, WADA recategorised GW501516 from a gene doping compound to a "hormone and metabolic modulator". [ 22 ]
In 2013, WADA took the rare step of warning potential users of the compound of the possible health risks, stating that "clinical approval has not, and will not be given for this substance"; the New Scientist attributed the warning to the risks of the drug causing cancer. [ 20 ] [ 23 ]
A number of athletes have tested positive for GW501516. At the Vuelta Ciclista a Costa Rica in December 2012, four Costa Rican riders tested positive for GW501516. Three of them received two-year suspensions, while the fourth received 12 years as it was his second doping violation. [ 24 ] [ 25 ] [ 26 ] In April 2013, Russian cyclist Valery Kaykov was suspended by cycling's governing body UCI after having tested positive for GW501516. Kaykov's team RusVelo dismissed him immediately [ 27 ] and in May 2013, Venezuelan Miguel Ubeto was provisionally suspended by the Lampre team. [ 28 ] In February 2014, Russian race walker Elena Lashmanova tested positive for GW501516. [ 29 ] [ 30 ] In April 2019, American heavyweight boxer Jarrell Miller tested positive for GW501516 which caused his challenge for Anthony Joshua 's World Heavyweight titles to be cancelled. [ 31 ] In December 2020, Miller was suspended for 2 years for repeated violations. [ 32 ] In July 2022, the 2012 800 m Olympic silver medalist from Botswana, Nijel Amos tested positive for GW501516 and was provisionally suspended just days before the 2022 World Athletics Championships . [ 33 ] Surinam's Issam Asinga , who set the under-20 world track record in the men's 100 meters, was informed on Aug. 9, 2023 by the Athletics Integrity Unit that his July 18 drug test the prior month detected trace amounts of GW501516. Asinga has alleged in a suit filed in the Southern District of New York that Gatorade provided him with Gatorade Recovery Gummies at their awards ceremony one week earlier in Los Angeles tainted with GW501516. [ 34 ]
GW501516 is a selective agonist of the PPARδ receptor. [ 35 ] It displays high affinity (K i = 1 nM) and potency (EC 50 = 1 nM) for PPARδ with greater than 1,000-fold selectivity over PPARα and PPARγ . [ 5 ]
In rats, binding of GW501516 to PPARδ recruits the coactivator PGC-1α . The PPARδ/coactivator complex in turn upregulates the expression of proteins involved in energy expenditure. [ 36 ] Furthermore, in rats treated with GW501516, increased fatty acid metabolism in skeletal muscle and protection against diet-induced obesity and type II diabetes was observed. In obese rhesus monkeys, GW501516 increased high-density lipoprotein (HDL) and lowered very-low-density lipoprotein (VLDL). [ 36 ]
Activation of PPARδ is also believed to be the mechanism responsible for cancer induction. A 2018 study in finds that GW501516 enhances the growth of colitis -associated colorectal cancer by increasing inflammation and the expression of GLUT1 and SLC1A5 . [ 37 ] | https://en.wikipedia.org/wiki/GW501516 |
GYRO is a computational plasma physics code developed and maintained at General Atomics . It solves the 5-D coupled gyrokinetic -Maxwell equations using a combination of finite difference , finite element and spectral methods . Given plasma equilibrium data, GYRO can determine the rate of turbulent transport of particles, momentum and energy.
This plasma physics –related article is a stub . You can help Wikipedia by expanding it .
This article about physics software is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/GYRO |
In Combustion , G equation is a scalar G ( x , t ) {\displaystyle G(\mathbf {x} ,t)} field equation which describes the instantaneous flame position, introduced by Forman A. Williams in 1985 [ 1 ] [ 2 ] in the study of premixed turbulent combustion. The equation is derived based on the Level-set method . The equation was first studied by George H. Markstein , in a restrictive form for the burning velocity and not as a level set of a field. [ 3 ] [ 4 ] [ 5 ]
The G equation reads as [ 6 ] [ 7 ]
where
The flame location is given by G ( x , t ) = G o {\displaystyle G(\mathbf {x} ,t)=G_{o}} which can be defined arbitrarily such that G ( x , t ) > G o {\displaystyle G(\mathbf {x} ,t)>G_{o}} is the region of burnt gas and G ( x , t ) < G o {\displaystyle G(\mathbf {x} ,t)<G_{o}} is the region of unburnt gas. The normal vector to the flame, pointing towards the burnt gas, is n = ∇ G / | ∇ G | {\displaystyle \mathbf {n} =\nabla G/|\nabla G|} .
According to Matalon–Matkowsky–Clavin–Joulin theory , the burning velocity of the stretched flame , for small curvature and small strain, is given by
where
The G equation has an exact expression for a simple slot burner. Consider a two-dimensional planar slot burner of slot width b {\displaystyle b} . The premixed reactant mixture is fed through the slot from the bottom with a constant velocity v = ( 0 , U ) {\displaystyle \mathbf {v} =(0,U)} , where the coordinate ( x , y ) {\displaystyle (x,y)} is chosen such that x = 0 {\displaystyle x=0} lies at the center of the slot and y = 0 {\displaystyle y=0} lies at the location of the mouth of the slot. When the mixture is ignited, a premixed flame develops from the mouth of the slot to a certain height y = L {\displaystyle y=L} in the form of a two-dimensional wedge shape with a wedge angle α {\displaystyle \alpha } . For simplicity, let us assume S T = S L {\displaystyle S_{T}=S_{L}} , which is a good approximation except near the wedge corner where curvature effects will becomes important. In the steady case, the G equation reduces to
If a separation of the form G ( x , y ) = y + f ( x ) {\displaystyle G(x,y)=y+f(x)} is introduced, then the equation becomes
which upon integration gives
Without loss of generality choose the flame location to be at G ( x , y ) = G o = 0 {\displaystyle G(x,y)=G_{o}=0} . Since the flame is attached to the mouth of the slot | x | = b / 2 , y = 0 {\displaystyle |x|=b/2,\ y=0} , the boundary condition is G ( b / 2 , 0 ) = 0 {\displaystyle G(b/2,0)=0} , which can be used to evaluate the constant C {\displaystyle C} . Thus the scalar field is
At the flame tip, we have x = 0 , y = L , G = 0 {\displaystyle x=0,\ y=L,\ G=0} , which enable us to determine the flame height
and the flame angle α {\displaystyle \alpha } ,
Using the trigonometric identity tan 2 α = sin 2 α / ( 1 − sin 2 α ) {\displaystyle \tan ^{2}\alpha =\sin ^{2}\alpha /\left(1-\sin ^{2}\alpha \right)} , we have
In fact, the above formula is often used to determine the planar burning speed S L {\displaystyle S_{L}} , by measuring the wedge angle. | https://en.wikipedia.org/wiki/G_equation |
G proteins , also known as guanine nucleotide-binding proteins , are a family of proteins that act as molecular switches inside cells, and are involved in transmitting signals from a variety of stimuli outside a cell to its interior. Their activity is regulated by factors that control their ability to bind to and hydrolyze guanosine triphosphate (GTP) to guanosine diphosphate (GDP). When they are bound to GTP, they are 'on', and, when they are bound to GDP, they are 'off'. G proteins belong to the larger group of enzymes called GTPases .
There are two classes of G proteins. The first function as monomeric small GTPases (small G-proteins), while the second function as heterotrimeric G protein complexes . The latter class of complexes is made up of alpha (G α ), beta (G β ) and gamma (G γ ) subunits . [ 1 ] In addition, the beta and gamma subunits can form a stable dimeric complex referred to as the beta-gamma complex . [ 2 ]
Heterotrimeric G proteins located within the cell are activated by G protein-coupled receptors (GPCRs) that span the cell membrane . [ 3 ] Signaling molecules bind to a domain of the GPCR located outside the cell, and an intracellular GPCR domain then in turn activates a particular G protein. Some active-state GPCRs have also been shown to be "pre-coupled" with G proteins, whereas in other cases a collision coupling mechanism is thought to occur. [ 4 ] [ 5 ] [ 6 ] The G protein triggers a cascade of further signaling events that finally results in a change in cell function. G protein-coupled receptors and G proteins working together transmit signals from many hormones , neurotransmitters , and other signaling factors. [ 7 ] G proteins regulate metabolic enzymes , ion channels , transporter proteins , and other parts of the cell machinery, controlling transcription , motility , contractility , and secretion , which in turn regulate diverse systemic functions such as embryonic development , learning and memory, and homeostasis . [ 8 ]
G proteins were discovered in 1980 when Alfred G. Gilman and Martin Rodbell investigated stimulation of cells by adrenaline . They found that when adrenaline binds to a receptor, the receptor does not stimulate enzymes (inside the cell) directly. Instead, the receptor stimulates a G protein, which then stimulates an enzyme. An example is adenylate cyclase , which produces the second messenger cyclic AMP . [ 9 ] For this discovery, they won the 1994 Nobel Prize in Physiology or Medicine . [ 10 ]
Nobel prizes have been awarded for many aspects of signaling by G proteins and GPCRs. These include receptor antagonists , neurotransmitters , neurotransmitter reuptake , G protein-coupled receptors , G proteins, second messengers , the enzymes that trigger protein phosphorylation in response to cAMP , and consequent metabolic processes such as glycogenolysis .
Prominent examples include (in chronological order of awarding):
G proteins are important signal transducing molecules in cells. "Malfunction of GPCR [G Protein-Coupled Receptor] signaling pathways are involved in many diseases, such as diabetes , blindness, allergies, depression, cardiovascular defects, and certain forms of cancer . It is estimated that about 30% of the modern drugs' cellular targets are GPCRs." [ 15 ] The human genome encodes roughly 800 [ 16 ] G protein-coupled receptors , which detect photons of light, hormones, growth factors, drugs, and other endogenous ligands . Approximately 150 of the GPCRs found in the human genome still have unknown functions.
Whereas G proteins are activated by G protein-coupled receptors , they are inactivated by RGS proteins (for "Regulator of G protein signalling"). Receptors stimulate GTP binding (turning the G protein on). RGS proteins stimulate GTP hydrolysis (creating GDP, thus turning the G protein off).
All eukaryotes use G proteins for signaling and have evolved a large diversity of G proteins. For instance, humans encode 18 different G α proteins, 5 G β proteins, and 12 G γ proteins. [ 17 ]
G protein can refer to two distinct families of proteins. Heterotrimeric G proteins , sometimes referred to as the "large" G proteins, are activated by G protein-coupled receptors and are made up of alpha (α), beta (β), and gamma (γ) subunits . "Small" G proteins (20-25kDa) belong to the Ras superfamily of small GTPases . These proteins are homologous to the alpha (α) subunit found in heterotrimers, but are in fact monomeric, consisting of only a single unit. However, like their larger relatives, they also bind GTP and GDP and are involved in signal transduction .
Different types of heterotrimeric G proteins share a common mechanism. They are activated in response to a conformational change in the GPCR, exchanging GDP for GTP, and dissociating in order to activate other proteins in a particular signal transduction pathway. [ 18 ] The specific mechanisms, however, differ between protein types.
Receptor-activated G proteins are bound to the inner surface of the cell membrane . They consist of the G α and the tightly associated G βγ subunits.
There are four main families of G α subunits: Gα s (G stimulatory), Gα i (G inhibitory), Gα q/11 , and Gα 12/13 . [ 20 ] [ 21 ] They behave differently in the recognition of the effector molecule, but share a similar mechanism of activation.
When a ligand activates the G protein-coupled receptor , it induces a conformational change in the receptor that allows the receptor to function as a guanine nucleotide exchange factor (GEF) that exchanges GDP for GTP. The GTP (or GDP) is bound to the G α subunit in the traditional view of heterotrimeric GPCR activation. This exchange triggers the dissociation of the G α subunit (which is bound to GTP) from the G βγ dimer and the receptor as a whole. However, models which suggest molecular rearrangement, reorganization, and pre-complexing of effector molecules are beginning to be accepted. [ 4 ] [ 22 ] [ 23 ] Both G α -GTP and G βγ can then activate different signaling cascades (or second messenger pathways ) and effector proteins, while the receptor is able to activate the next G protein. [ 24 ]
The G α subunit will eventually hydrolyze the attached GTP to GDP by its inherent enzymatic activity, allowing it to re-associate with G βγ and starting a new cycle. A group of proteins called Regulator of G protein signalling (RGSs), act as GTPase-activating proteins (GAPs), are specific for G α subunits. These proteins accelerate the hydrolysis of GTP to GDP, thus terminating the transduced signal. In some cases, the effector itself may possess intrinsic GAP activity, which then can help deactivate the pathway. This is true in the case of phospholipase C -beta, which possesses GAP activity within its C-terminal region. This is an alternate form of regulation for the G α subunit. Such G α GAPs do not have catalytic residues (specific amino acid sequences) to activate the G α protein. They work instead by lowering the required activation energy for the reaction to take place. [ 25 ]
G αs activates the cAMP-dependent pathway by stimulating the production of cyclic AMP (cAMP) from ATP . This is accomplished by direct stimulation of the membrane-associated enzyme adenylate cyclase . cAMP can then act as a second messenger that goes on to interact with and activate protein kinase A (PKA). PKA can phosphorylate a myriad downstream targets.
The cAMP-dependent pathway is used as a signal transduction pathway for many hormones including:
G αi inhibits the production of cAMP from ATP.
e.g. somatostatin, prostaglandins
G αq/11 stimulates the membrane-bound phospholipase C beta, which then cleaves phosphatidylinositol 4,5-bisphosphate (PIP 2 ) into two second messengers, inositol trisphosphate (IP 3 ) and diacylglycerol (DAG). IP 3 induces calcium release from the endoplasmic reticulum . DAG activates protein kinase C .
The Inositol Phospholipid Dependent Pathway is used as a signal transduction pathway for many hormones including:
Small GTPases, also known as small G-proteins, bind GTP and GDP likewise, and are involved in signal transduction . These proteins are homologous to the alpha (α) subunit found in heterotrimers, but exist as monomers. They are small (20-kDa to 25-kDa) proteins that bind to guanosine triphosphate ( GTP ). This family of proteins is homologous to the Ras GTPases and is also called the Ras superfamily GTPases .
In order to associate with the inner leaflet of the plasma membrane, many G proteins and small GTPases are lipidated [ citation needed ] , that is, covalently modified with lipid extensions. They may be myristoylated , palmitoylated or prenylated . | https://en.wikipedia.org/wiki/G_protein |
G protein-coupled receptors ( GPCRs ), also known as seven-(pass)-transmembrane domain receptors , 7TM receptors , heptahelical receptors , serpentine receptors , and G protein-linked receptors ( GPLR ), form a large group of evolutionarily related proteins that are cell surface receptors that detect molecules outside the cell and activate cellular responses. They are coupled with G proteins . They pass through the cell membrane seven times in the form of six loops [ 2 ] (three extracellular loops interacting with ligand molecules, three intracellular loops interacting with G proteins, an N-terminal extracellular region and a C-terminal intracellular region [ 2 ] ) of amino acid residues , which is why they are sometimes referred to as seven-transmembrane receptors. [ 3 ] Ligands can bind either to the extracellular N-terminus and loops (e.g. glutamate receptors) or to the binding site within transmembrane helices ( rhodopsin -like family). They are all activated by agonists , although a spontaneous auto-activation of an empty receptor has also been observed. [ 3 ]
G protein-coupled receptors are found only in eukaryotes , including yeast , and choanoflagellates . [ 4 ] The ligands that bind and activate these receptors include light-sensitive compounds, odors , pheromones , hormones , and neurotransmitters . They vary in size from small molecules to peptides , to large proteins . G protein-coupled receptors are involved in many diseases.
There are two principal signal transduction pathways involving the G protein-coupled receptors:
When a ligand binds to the GPCR it causes a conformational change in the GPCR, which allows it to act as a guanine nucleotide exchange factor (GEF). The GPCR can then activate an associated G protein by exchanging the GDP bound to the G protein for a GTP . The G protein's α subunit, together with the bound GTP, can then dissociate from the β and γ subunits to further affect intracellular signaling proteins or target functional proteins directly depending on the α subunit type ( G αs , G αi/o , G αq/11 , G α12/13 ). [ 6 ] : 1160
GPCRs are an important drug target, and approximately 34% [ 7 ] of all Food and Drug Administration (FDA) approved drugs target 108 members of this family. The global sales volume for these drugs is estimated to be 180 billion US dollars as of 2018 [update] . [ 7 ] It is estimated that GPCRs are targets for about 50% of drugs currently on the market, mainly due to their involvement in signaling pathways related to many diseases i.e. mental, metabolic including endocrinological disorders, immunological including viral infections, cardiovascular, inflammatory, senses disorders, and cancer. The long ago discovered association between GPCRs and many endogenous and exogenous substances, resulting in e.g. analgesia, is another dynamically developing field of the pharmaceutical research. [ 3 ]
With the determination of the first structure of the complex between a G-protein coupled receptor (GPCR) and a G-protein trimer (Gαβγ) in 2011 a new chapter of GPCR research was opened for structural investigations of global switches with more than one protein being investigated. The previous breakthroughs involved determination of the crystal structure of the first GPCR, rhodopsin, in 2000 and the crystal structure of the first GPCR with a diffusible ligand (β 2 AR) in 2007. The way in which the seven transmembrane helices of a GPCR are arranged into a bundle was suspected based on the low-resolution model of frog rhodopsin from cryogenic electron microscopy studies of the two-dimensional crystals. The crystal structure of rhodopsin, that came up three years later, was not a surprise apart from the presence of an additional cytoplasmic helix H8 and a precise location of a loop covering retinal binding site. However, it provided a scaffold which was hoped to be a universal template for homology modeling and drug design for other GPCRs – a notion that proved to be too optimistic. [ citation needed ]
Results 7 years later were surprising because the crystallization of β 2 -adrenergic receptor (β 2 AR) with a diffusible ligand revealed quite a different shape of the receptor extracellular side than that of rhodopsin. This area is important because it is responsible for the ligand binding and is targeted by many drugs. Moreover, the ligand binding site was much more spacious than in the rhodopsin structure and was open to the exterior. In the other receptors crystallized shortly afterwards the binding side was even more easily accessible to the ligand. New structures complemented with biochemical investigations uncovered mechanisms of action of molecular switches which modulate the structure of the receptor leading to activation states for agonists or to complete or partial inactivation states for inverse agonists. [ 3 ]
The 2012 Nobel Prize in Chemistry was awarded to Brian Kobilka and Robert Lefkowitz for their work that was "crucial for understanding how G protein-coupled receptors function". [ 8 ] There have been at least seven other Nobel Prizes awarded for some aspect of G protein–mediated signaling. As of 2012, two of the top ten global best-selling drugs ( Advair Diskus and Abilify ) act by targeting G protein-coupled receptors. [ 9 ]
The exact size of the GPCR superfamily is unknown, but at least 831 different human genes (or about 4% of the entire protein-coding genome ) have been predicted to code for them from genome sequence analysis . [ 10 ] [ 11 ] Although numerous classification schemes have been proposed, the superfamily was classically divided into three main classes (A, B, and C) with no detectable shared sequence homology between classes. [ citation needed ]
The largest class by far is class A, which accounts for nearly 85% of the GPCR genes. Of class A GPCRs, over half of these are predicted to encode olfactory receptors , while the remaining receptors are liganded by known endogenous compounds or are classified as orphan receptors . Despite the lack of sequence homology between classes, all GPCRs have a common structure and mechanism of signal transduction . The very large rhodopsin A group has been further subdivided into 19 subgroups ( A1-A19 ). [ 12 ]
According to the classical A-F system, GPCRs can be grouped into six classes based on sequence homology and functional similarity: [ 13 ] [ 14 ] [ 15 ] [ 16 ]
More recently, an alternative classification system called GRAFS ( Glutamate , Rhodopsin , Adhesion , Frizzled / Taste2 , Secretin ) has been proposed for vertebrate GPCRs. [ 10 ] They correspond to classical classes C, A, B2, F, and B. [ 17 ]
An early study based on available DNA sequence suggested that the human genome encodes roughly 750 G protein-coupled receptors, [ 18 ] about 350 of which detect hormones, growth factors, and other endogenous ligands. Approximately 150 of the GPCRs found in the human genome have unknown functions.
Some web-servers [ 19 ] and bioinformatics prediction methods [ 20 ] [ 21 ] have been used for predicting the classification of GPCRs according to their amino acid sequence alone, by means of the pseudo amino acid composition approach.
GPCRs are involved in a wide variety of physiological processes. Some examples of their physiological roles include:
GPCRs are integral membrane proteins that possess seven membrane-spanning domains or transmembrane helices . [ 26 ] [ 27 ] The extracellular parts of the receptor can be glycosylated . These extracellular loops also contain two highly conserved cysteine residues that form disulfide bonds to stabilize the receptor structure. Some seven-transmembrane helix proteins ( channelrhodopsin ) that resemble GPCRs may contain ion channels, within their protein. [ citation needed ]
In 2000, the first crystal structure of a mammalian GPCR, that of bovine rhodopsin ( 1F88 ), was solved. [ 28 ] In 2007, the first structure of a human GPCR was solved [ 29 ] [ 1 ] [ 30 ] This human β 2 -adrenergic receptor GPCR structure proved highly similar to the bovine rhodopsin. The structures of activated or agonist-bound GPCRs have also been determined. [ 31 ] [ 32 ] [ 33 ] [ 34 ] These structures indicate how ligand binding at the extracellular side of a receptor leads to conformational changes in the cytoplasmic side of the receptor. The biggest change is an outward movement of the cytoplasmic part of the 5th and 6th transmembrane helix (TM5 and TM6). The structure of activated beta-2 adrenergic receptor in complex with G s confirmed that the Gα binds to a cavity created by this movement. [ 35 ]
GPCRs exhibit a similar structure to some other proteins with seven transmembrane domains , such as microbial rhodopsins and adiponectin receptors 1 and 2 ( ADIPOR1 and ADIPOR2 ). However, these 7TMH (7-transmembrane helices) receptors and channels do not associate with G proteins . In addition, ADIPOR1 and ADIPOR2 are oriented oppositely to GPCRs in the membrane (i.e. GPCRs usually have an extracellular N-terminus , cytoplasmic C-terminus , whereas ADIPORs are inverted). [ 36 ]
In terms of structure, GPCRs are characterized by an extracellular N-terminus , followed by seven transmembrane (7-TM) α-helices (TM-1 to TM-7) connected by three intracellular (IL-1 to IL-3) and three extracellular loops (EL-1 to EL-3), and finally an intracellular C-terminus . The GPCR arranges itself into a tertiary structure resembling a barrel, with the seven transmembrane helices forming a cavity within the plasma membrane that serves a ligand -binding domain that is often covered by EL-2. Ligands may also bind elsewhere, however, as is the case for bulkier ligands (e.g., proteins or large peptides ), which instead interact with the extracellular loops, or, as illustrated by the class C metabotropic glutamate receptors (mGluRs), the N-terminal tail. The class C GPCRs are distinguished by their large N-terminal tail, which also contains a ligand-binding domain. Upon glutamate-binding to an mGluR, the N-terminal tail undergoes a conformational change that leads to its interaction with the residues of the extracellular loops and TM domains. The eventual effect of all three types of agonist -induced activation is a change in the relative orientations of the TM helices (likened to a twisting motion) leading to a wider intracellular surface and "revelation" of residues of the intracellular helices and TM domains crucial to signal transduction function (i.e., G-protein coupling). Inverse agonists and antagonists may also bind to a number of different sites, but the eventual effect must be prevention of this TM helix reorientation. [ 3 ]
The structure of the N- and C-terminal tails of GPCRs may also serve important functions beyond ligand-binding. For example, The C-terminus of M 3 muscarinic receptors is sufficient, and the six-amino-acid polybasic (KKKRRK) domain in the C-terminus is necessary for its preassembly with G q proteins. [ 37 ] In particular, the C-terminus often contains serine (Ser) or threonine (Thr) residues that, when phosphorylated , increase the affinity of the intracellular surface for the binding of scaffolding proteins called β- arrestins (β-arr). [ 38 ] Once bound, β-arrestins both sterically prevent G-protein coupling and may recruit other proteins, leading to the creation of signaling complexes involved in extracellular-signal regulated kinase ( ERK ) pathway activation or receptor endocytosis (internalization). As the phosphorylation of these Ser and Thr residues often occurs as a result of GPCR activation, the β-arr-mediated G-protein-decoupling and internalization of GPCRs are important mechanisms of desensitization . [ 39 ] In addition, internalized "mega-complexes" consisting of a single GPCR, β-arr(in the tail conformation), [ 40 ] [ 41 ] and heterotrimeric G protein exist and may account for protein signaling from endosomes. [ 42 ] [ 43 ]
A final common structural theme among GPCRs is palmitoylation of one or more sites of the C-terminal tail or the intracellular loops. Palmitoylation is the covalent modification of cysteine (Cys) residues via addition of hydrophobic acyl groups , and has the effect of targeting the receptor to cholesterol - and sphingolipid -rich microdomains of the plasma membrane called lipid rafts . As many of the downstream transducer and effector molecules of GPCRs (including those involved in negative feedback pathways) are also targeted to lipid rafts, this has the effect of facilitating rapid receptor signaling. [ citation needed ]
GPCRs respond to extracellular signals mediated by a huge diversity of agonists, ranging from proteins to biogenic amines to protons , but all transduce this signal via a mechanism of G-protein coupling. This is made possible by a guanine -nucleotide exchange factor ( GEF ) domain primarily formed by a combination of IL-2 and IL-3 along with adjacent residues of the associated TM helices. [ citation needed ]
The G protein-coupled receptor is activated by an external signal in the form of a ligand or other signal mediator. This creates a conformational change in the receptor, causing activation of a G protein . Further effect depends on the type of G protein. G proteins are subsequently inactivated by GTPase activating proteins, known as RGS proteins . [ citation needed ]
GPCRs include one or more receptors for the following ligands:
sensory signal mediators (e.g., light and olfactory stimulatory molecules); adenosine , bombesin , bradykinin , endothelin , γ-aminobutyric acid ( GABA ), hepatocyte growth factor ( HGF ), melanocortins , neuropeptide Y , opioid peptides, opsins , somatostatin , GH , tachykinins , members of the vasoactive intestinal peptide family, and vasopressin ; biogenic amines (e.g., dopamine , epinephrine , norepinephrine , histamine , serotonin , and melatonin ); glutamate ( metabotropic effect); glucagon ; acetylcholine ( muscarinic effect); chemokines ; lipid mediators of inflammation (e.g., prostaglandins , prostanoids , platelet-activating factor , and leukotrienes );
peptide hormones (e.g., calcitonin , C5a anaphylatoxin , follicle-stimulating hormone [FSH], gonadotropin-releasing hormone [GnRH], neurokinin , thyrotropin-releasing hormone [TRH], and oxytocin );
and endocannabinoids .
GPCRs that act as receptors for stimuli that have not yet been identified are known as orphan receptors . [ citation needed ]
However, in contrast to other types of receptors that have been studied, wherein ligands bind externally to the membrane, the ligands of GPCRs typically bind within the transmembrane domain. However, protease-activated receptors are activated by cleavage of part of their extracellular domain. [ 45 ]
The transduction of the signal through the membrane by the receptor is not completely understood. It is known that in the inactive state, the GPCR is bound to a heterotrimeric G protein complex. Binding of an agonist to the GPCR results in a conformational change in the receptor that is transmitted to the bound G α subunit of the heterotrimeric G protein via protein domain dynamics . The activated G α subunit exchanges GTP in place of GDP which in turn triggers the dissociation of G α subunit from the G βγ dimer and from the receptor. The dissociated G α and G βγ subunits interact with other intracellular proteins to continue the signal transduction cascade while the freed GPCR is able to rebind to another heterotrimeric G protein to form a new complex that is ready to initiate another round of signal transduction. [ 46 ]
It is believed that a receptor molecule exists in a conformational equilibrium between active and inactive biophysical states. [ 47 ] The binding of ligands to the receptor may shift the equilibrium toward the active receptor states. Three types of ligands exist: Agonists are ligands that shift the equilibrium in favour of active states; inverse agonists are ligands that shift the equilibrium in favour of inactive states; and neutral antagonists are ligands that do not affect the equilibrium. It is not yet known how exactly the active and inactive states differ from each other. [ citation needed ]
When the receptor is inactive, the GEF domain may be bound to an also inactive α-subunit of a heterotrimeric G-protein . These "G-proteins" are a trimer of α, β, and γ subunits (known as Gα, Gβ, and Gγ, respectively) that is rendered inactive when reversibly bound to Guanosine diphosphate (GDP) (or, alternatively, no guanine nucleotide) but active when bound to guanosine triphosphate (GTP). Upon receptor activation, the GEF domain, in turn, allosterically activates the G-protein by facilitating the exchange of a molecule of GDP for GTP at the G-protein's α-subunit. The cell maintains a 10:1 ratio of cytosolic GTP:GDP so exchange for GTP is ensured. At this point, the subunits of the G-protein dissociate from the receptor, as well as each other, to yield a Gα-GTP monomer and a tightly interacting Gβγ dimer , which are now free to modulate the activity of other intracellular proteins. The extent to which they may diffuse , however, is limited due to the palmitoylation of Gα and the presence of an isoprenoid moiety that has been covalently added to the C-termini of Gγ. [ citation needed ]
Because Gα also has slow GTP→GDP hydrolysis capability, the inactive form of the α-subunit (Gα-GDP) is eventually regenerated, thus allowing reassociation with a Gβγ dimer to form the "resting" G-protein, which can again bind to a GPCR and await activation. The rate of GTP hydrolysis is often accelerated due to the actions of another family of allosteric modulating proteins called regulators of G-protein signaling , or RGS proteins, which are a type of GTPase-activating protein , or GAP. In fact, many of the primary effector proteins (e.g., adenylate cyclases ) that become activated/inactivated upon interaction with Gα-GTP also have GAP activity. Thus, even at this early stage in the process, GPCR-initiated signaling has the capacity for self-termination. [ citation needed ]
GPCRs downstream signals have been shown to possibly interact with integrin signals, such as FAK . [ 48 ] Integrin signaling will phosphorylate FAK, which can then decrease GPCR G αs activity.
If a receptor in an active state encounters a G protein , it may activate it. Some evidence suggests that receptors and G proteins are actually pre-coupled. [ 37 ] For example, binding of G proteins to receptors affects the receptor's affinity for ligands. Activated G proteins are bound to GTP .
Further signal transduction depends on the type of G protein. The enzyme adenylate cyclase is an example of a cellular protein that can be regulated by a G protein, in this case the G protein G s . Adenylate cyclase activity is activated when it binds to a subunit of the activated G protein. Activation of adenylate cyclase ends when the G protein returns to the GDP -bound state.
Adenylate cyclases (of which 9 membrane-bound and one cytosolic forms are known in humans) may also be activated or inhibited in other ways (e.g., Ca2+/ calmodulin binding), which can modify the activity of these enzymes in an additive or synergistic fashion along with the G proteins.
The signaling pathways activated through a GPCR are limited by the primary sequence and tertiary structure of the GPCR itself but ultimately determined by the particular conformation stabilized by a particular ligand , as well as the availability of transducer molecules. Currently, GPCRs are considered to utilize two primary types of transducers: G-proteins and β-arrestins . Because β-arr's have high affinity only to the phosphorylated form of most GPCRs (see above or below), the majority of signaling is ultimately dependent upon G-protein activation. However, the possibility for interaction does allow for G-protein-independent signaling to occur.
There are three main G-protein-mediated signaling pathways, mediated by four sub-classes of G-proteins distinguished from each other by sequence homology ( G αs , G αi/o , G αq/11 , and G α12/13 ). Each sub-class of G-protein consists of multiple proteins, each the product of multiple genes or splice variations that may imbue them with differences ranging from subtle to distinct with regard to signaling properties, but in general they appear reasonably grouped into four classes. Because the signal transducing properties of the various possible βγ combinations do not appear to radically differ from one another, these classes are defined according to the isoform of their α-subunit. [ 6 ] : 1163
While most GPCRs are capable of activating more than one Gα-subtype, they also show a preference for one subtype over another. When the subtype activated depends on the ligand that is bound to the GPCR, this is called functional selectivity (also known as agonist-directed trafficking, or conformation-specific agonism). However, the binding of any single particular agonist may also initiate activation of multiple different G-proteins, as it may be capable of stabilizing more than one conformation of the GPCR's GEF domain, even over the course of a single interaction. In addition, a conformation that preferably activates one isoform of Gα may activate another if the preferred is less available. Furthermore, feedback pathways may result in receptor modifications (e.g., phosphorylation) that alter the G-protein preference. Regardless of these various nuances, the GPCR's preferred coupling partner is usually defined according to the G-protein most obviously activated by the endogenous ligand under most physiological or experimental conditions.
The above descriptions ignore the effects of Gβγ –signalling, which can also be important, in particular in the case of activated G αi/o -coupled GPCRs. The primary effectors of Gβγ are various ion channels, such as G-protein-regulated inwardly rectifying K + channels (GIRKs), P / Q - and N-type voltage-gated Ca 2+ channels , as well as some isoforms of AC and PLC, along with some phosphoinositide-3-kinase (PI3K) isoforms.
Although they are classically thought of working only together, GPCRs may signal through G-protein-independent mechanisms, and heterotrimeric G-proteins may play functional roles independent of GPCRs. GPCRs may signal independently through many proteins already mentioned for their roles in G-protein-dependent signaling such as β-arrs , GRKs , and Srcs . Such signaling has been shown to be physiologically relevant, for example, β-arrestin signaling mediated by the chemokine receptor CXCR3 was necessary for full efficacy chemotaxis of activated T cells. [ 49 ] In addition, further scaffolding proteins involved in subcellular localization of GPCRs (e.g., PDZ-domain -containing proteins) may also act as signal transducers. Most often the effector is a member of the MAPK family.
In the late 1990s, evidence began accumulating to suggest that some GPCRs are able to signal without G proteins. The ERK2 mitogen-activated protein kinase, a key signal transduction mediator downstream of receptor activation in many pathways, has been shown to be activated in response to cAMP-mediated receptor activation in the slime mold D. discoideum despite the absence of the associated G protein α- and β-subunits. [ 50 ]
In mammalian cells, the much-studied β 2 -adrenoceptor has been demonstrated to activate the ERK2 pathway after arrestin-mediated uncoupling of G-protein-mediated signaling. Therefore, it seems likely that some mechanisms previously believed related purely to receptor desensitisation are actually examples of receptors switching their signaling pathway, rather than simply being switched off.
In kidney cells, the bradykinin receptor B2 has been shown to interact directly with a protein tyrosine phosphatase. The presence of a tyrosine-phosphorylated ITIM (immunoreceptor tyrosine-based inhibitory motif) sequence in the B2 receptor is necessary to mediate this interaction and subsequently the antiproliferative effect of bradykinin. [ 51 ]
Although it is a relatively immature area of research, it appears that heterotrimeric G-proteins may also take part in non-GPCR signaling. There is evidence for roles as signal transducers in nearly all other types of receptor-mediated signaling, including integrins , receptor tyrosine kinases (RTKs), cytokine receptors ( JAK/STATs ), as well as modulation of various other "accessory" proteins such as GEFs , guanine-nucleotide dissociation inhibitors (GDIs) and protein phosphatases . There may even be specific proteins of these classes whose primary function is as part of GPCR-independent pathways, termed activators of G-protein signalling (AGS). Both the ubiquity of these interactions and the importance of Gα vs. Gβγ subunits to these processes are still unclear.
There are two principal signal transduction pathways involving the G protein-linked receptors : the cAMP signal pathway and the phosphatidylinositol signal pathway. [ 5 ]
The cAMP signal transduction contains five main characters: stimulative hormone receptor (Rs) or inhibitory hormone receptor (Ri); stimulative regulative G-protein (Gs) or inhibitory regulative G-protein (Gi); adenylyl cyclase ; protein kinase A (PKA); and cAMP phosphodiesterase .
Stimulative hormone receptor (Rs) is a receptor that can bind with stimulative signal molecules, while inhibitory hormone receptor (Ri) is a receptor that can bind with inhibitory signal molecules.
Stimulative regulative G-protein is a G-protein linked to stimulative hormone receptor (Rs), and its α subunit upon activation could stimulate the activity of an enzyme or other intracellular metabolism. On the contrary, inhibitory regulative G-protein is linked to an inhibitory hormone receptor, and its α subunit upon activation could inhibit the activity of an enzyme or other intracellular metabolism.
Adenylyl cyclase is a 12-transmembrane glycoprotein that catalyzes the conversion of ATP to cAMP with the help of cofactor Mg 2+ or Mn 2+ . The cAMP produced is a second messenger in cellular metabolism and is an allosteric activator of protein kinase A.
Protein kinase A is an important enzyme in cell metabolism due to its ability to regulate cell metabolism by phosphorylating specific committed enzymes in the metabolic pathway. It can also regulate specific gene expression, cellular secretion, and membrane permeability. The protein enzyme contains two catalytic subunits and two regulatory subunits. When there is no cAMP, the complex is inactive. When cAMP binds to the regulatory subunits, their conformation is altered, causing the dissociation of the regulatory subunits, which activates protein kinase A and allows further biological effects.
These signals then can be terminated by cAMP phosphodiesterase, which is an enzyme that degrades cAMP to 5'-AMP and inactivates protein kinase A.
In the phosphatidylinositol signal pathway, the extracellular signal molecule binds with the G-protein receptor (G q ) on the cell surface and activates phospholipase C , which is located on the plasma membrane . The lipase hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP2) into two second messengers: inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG). IP3 binds with the IP3 receptor in the membrane of the smooth endoplasmic reticulum and mitochondria to open Ca 2+ channels. DAG helps activate protein kinase C (PKC), which phosphorylates many other proteins, changing their catalytic activities, leading to cellular responses.
The effects of Ca 2+ are also remarkable: it cooperates with DAG in activating PKC and can activate the CaM kinase pathway, in which calcium-modulated protein calmodulin (CaM) binds Ca 2+ , undergoes a change in conformation, and activates CaM kinase II, which has unique ability to increase its binding affinity to CaM by autophosphorylation, making CaM unavailable for the activation of other enzymes. The kinase then phosphorylates target enzymes, regulating their activities. The two signal pathways are connected together by Ca 2+ -CaM, which is also a regulatory subunit of adenylyl cyclase and phosphodiesterase in the cAMP signal pathway.
GPCRs become desensitized when exposed to their ligand for a long period of time. There are two recognized forms of desensitization: 1) homologous desensitization , in which the activated GPCR is downregulated; and 2) heterologous desensitization , wherein the activated GPCR causes downregulation of a different GPCR. The key reaction of this downregulation is the phosphorylation of the intracellular (or cytoplasmic ) receptor domain by protein kinases .
Cyclic AMP-dependent protein kinases ( protein kinase A ) are activated by the signal chain coming from the G protein (that was activated by the receptor) via adenylate cyclase and cyclic AMP (cAMP). In a feedback mechanism , these activated kinases phosphorylate the receptor. The longer the receptor remains active the more kinases are activated and the more receptors are phosphorylated. In β 2 -adrenoceptors , this phosphorylation results in the switching of the coupling from the G s class of G-protein to the G i class. [ 52 ] cAMP-dependent PKA mediated phosphorylation can cause heterologous desensitisation in receptors other than those activated. [ 53 ]
The G protein-coupled receptor kinases (GRKs) are protein kinases that phosphorylate only active GPCRs. [ 54 ] G-protein-coupled receptor kinases (GRKs) are key modulators of G-protein-coupled receptor (GPCR) signaling. They constitute a family of seven mammalian serine-threonine protein kinases that phosphorylate agonist-bound receptor. GRKs-mediated receptor phosphorylation rapidly initiates profound impairment of receptor signaling and desensitization. Activity of GRKs and subcellular targeting is tightly regulated by interaction with receptor domains, G protein subunits, lipids, anchoring proteins and calcium-sensitive proteins. [ 55 ]
Phosphorylation of the receptor can have two consequences:
As mentioned above, G-proteins may terminate their own activation due to their intrinsic GTP→GDP hydrolysis capability. However, this reaction proceeds at a slow rate (≈0.02 times/sec) and, thus, it would take around 50 seconds for any single G-protein to deactivate if other factors did not come into play. Indeed, there are around 30 isoforms of RGS proteins that, when bound to Gα through their GAP domain , accelerate the hydrolysis rate to ≈30 times/sec. This 1500-fold increase in rate allows for the cell to respond to external signals with high speed, as well as spatial resolution due to limited amount of second messenger that can be generated and limited distance a G-protein can diffuse in 0.03 seconds. For the most part, the RGS proteins are promiscuous in their ability to deactivate G-proteins, while which RGS is involved in a given signaling pathway seems more determined by the tissue and GPCR involved than anything else. In addition, RGS proteins have the additional function of increasing the rate of GTP-GDP exchange at GPCRs, (i.e., as a sort of co-GEF) further contributing to the time resolution of GPCR signaling.
In addition, the GPCR may be desensitized itself. This can occur as:
Once β-arrestin is bound to a GPCR, it undergoes a conformational change allowing it to serve as a scaffolding protein for an adaptor complex termed AP-2 , which in turn recruits another protein called clathrin . If enough receptors in the local area recruit clathrin in this manner, they aggregate and the membrane buds inwardly as a result of interactions between the molecules of clathrin, in a process called opsonization . Once the pit has been pinched off the plasma membrane due to the actions of two other proteins called amphiphysin and dynamin , it is now an endocytic vesicle . At this point, the adapter molecules and clathrin have dissociated , and the receptor is either trafficked back to the plasma membrane or targeted to lysosomes for degradation .
At any point in this process, the β-arrestins may also recruit other proteins—such as the non-receptor tyrosine kinase (nRTK), c-SRC —which may activate ERK1/2 , or other mitogen-activated protein kinase (MAPK) signaling through, for example, phosphorylation of the small GTPase , Ras , or recruit the proteins of the ERK cascade directly (i.e., Raf-1 , MEK , ERK-1/2) at which point signaling is initiated due to their close proximity to one another. Another target of c-SRC are the dynamin molecules involved in endocytosis. Dynamins polymerize around the neck of an incoming vesicle, and their phosphorylation by c-SRC provides the energy necessary for the conformational change allowing the final "pinching off" from the membrane.
Receptor desensitization is mediated through a combination phosphorylation, β-arr binding, and endocytosis as described above. Downregulation occurs when endocytosed receptor is embedded in an endosome that is trafficked to merge with an organelle called a lysosome. Because lysosomal membranes are rich in proton pumps, their interiors have low pH (≈4.8 vs. the pH≈7.2 cytosol), which acts to denature the GPCRs. In addition, lysosomes contain many degradative enzymes , including proteases, which can function only at such low pH, and so the peptide bonds joining the residues of the GPCR together may be cleaved. Whether or not a given receptor is trafficked to a lysosome, detained in endosomes, or trafficked back to the plasma membrane depends on a variety of factors, including receptor type and magnitude of the signal.
GPCR regulation is additionally mediated by gene transcription factors. These factors can increase or decrease gene transcription and thus increase or decrease the generation of new receptors (up- or down-regulation) that travel to the cell membrane.
G-protein-coupled receptor oligomerisation is a widespread phenomenon. One of the best-studied examples is the metabotropic GABA B receptor . This so-called constitutive receptor is formed by heterodimerization of GABA B R1 and GABA B R2 subunits. Expression of the GABA B R1 without the GABA B R2 in heterologous systems leads to retention of the subunit in the endoplasmic reticulum . Expression of the GABA B R2 subunit alone, meanwhile, leads to surface expression of the subunit, although with no functional activity (i.e., the receptor does not bind agonist and cannot initiate a response following exposure to agonist). Expression of the two subunits together leads to plasma membrane expression of functional receptor. It has been shown that GABA B R2 binding to GABA B R1 causes masking of a retention signal [ 60 ] of functional receptors. [ 61 ]
Signal transduction mediated by the superfamily of GPCRs dates back to the origin of multicellularity . Mammalian-like GPCRs are found in fungi , and have been classified according to the GRAFS classification system based on GPCR fingerprints. [ 17 ] Identification of the superfamily members across the eukaryotic domain, and comparison of the family-specific motifs, have shown that the superfamily of GPCRs have a common origin. [ 62 ] Characteristic motifs indicate that three of the five GRAFS families, Rhodopsin , Adhesion , and Frizzled , evolved from the Dictyostelium discoideum cAMP receptors before the split of opisthokonts . Later, the Secretin family evolved from the Adhesion GPCR receptor family before the split of nematodes . [ 17 ] Insect GPCRs appear to be in their own group and Taste2 is identified as descending from Rhodopsin . [ 62 ] Note that the Secretin / Adhesion split is based on presumed function rather than signature, as the classical Class B (7tm_2, Pfam PF00002 ) is used to identify both in the studies. | https://en.wikipedia.org/wiki/G_protein-coupled_receptor |
Trimethylgallium , often abbreviated to TMG or TMGa , is the organogallium compound with the formula Ga(CH 3 ) 3 . It is a colorless, pyrophoric liquid. [ 1 ] Unlike trimethylaluminium , TMG adopts a monomeric structure. [ 2 ] When examined in detail, the monomeric units are clearly linked by multiple weak Ga---C interactions, reminiscent of the situation for trimethylindium . [ 3 ]
Two forms of TMG are typically investigated: Lewis base adducts or TMG itself. All are prepared by reactions of gallium trichloride with various methylating agents. When the methylation is conducted with methylmagnesium iodide in diethyl ether , the product is the poorly volatile diethyl ether adduct. As noted by TMG discoverers Kraus and Toonder in 1933, the ether ligand is not readily lost, although it may be displaced with liquid ammonia. [ 4 ] When the alkylation is conducted with methyl lithium in the presence of a tertiary phosphine the air-stable phosphine adduct is obtained:
Heating the solid phosphine adduct under vacuum liberates the base-free TMG: [ 1 ]
Other non-volatile bases have been described. [ 5 ] Other methylating agents for the synthesis of TMG include dimethylzinc and trimethylaluminium .
TMG is the preferred metalorganic source of gallium for metalorganic vapour phase epitaxy (MOVPE) of gallium-containing compound semiconductors , such as GaAs , GaN , GaP , GaSb , InGaAs , InGaN , AlGaInP , InGaP , AlInGaNP and Ga 2 O 3 . [ 6 ] These material are used in the production of LED lighting and semiconductors as a metalorganic chemical vapor deposition precursor. | https://en.wikipedia.org/wiki/Ga(CH3)3 |
Gallium acetate is a salt composed of a gallium atom tri cation and three acetate groups as anions where gallium exhibits the +3 oxidation state . It has a chemical formula of Ga(CH 3 COO) 3 although it can be informally referred to as GaAc [ dubious – discuss ] because Ac is an informal symbol for acetate. Gallium is moderately water-soluble and decomposes to gallium oxide when heated to around 70 °C . [ 2 ] Gallium acetate, like other acetate compounds, is a good precursor to ultra-pure compounds , catalysts and nanoscale materials. [ 2 ] Gallium acetate is being considered as a substitute in de-icing compounds like calcium chloride and magnesium chloride . [ 3 ]
Gallium acetate can be formed using a neutralization reaction ( acetic acid reacts with gallium oxide or gallium hydroxide ):
Gallium can also be refluxed in acetic acid for several weeks to produce gallium acetate. [ 4 ]
It can also be used in conjunction with acetylacetonate bis(thiosemicarbazone) to create radiogallium-acetylacetonate bis(thiosemicarbazone) complex. It can be used in tumor imaging. [ 5 ] | https://en.wikipedia.org/wiki/Ga(CH3COO)3 |
Gallium nitrate (brand name Ganite) is the gallium salt of nitric acid with the chemical formula Ga(NO 3 ) 3 . It is a drug used to treat symptomatic hypercalcemia secondary to cancer. It works by preventing the breakdown of bone through the inhibition of osteoclast activity, thus lowering the amount of free calcium in the blood. [ 1 ] [ 2 ] Gallium nitrate is also used to synthesize other gallium compounds.
Gallium (Ga) was discovered in 1875 by P.É. Lecoq de Boisbaudran. [ 3 ] In most of its compounds, gallium is found with an oxidation number of 3+. Gallium chemically behaves similarly to iron 3+ when forming a coordination complex . [ 4 ] That means gallium(III) and iron(III) are similar in similar coordination number , electrical charge, ion diameter and electron configuration .
Gallium atoms are bound to the phosphates of DNA at low gallium concentrations, forming a stable complex. [ 5 ] Gallium competes with magnesium in DNA binding, since its DNA affinity is 100 times higher than that of magnesium. No interactions have been found between the metal and DNA bases. [ 6 ] According to Hedley et al., gallium inhibits replicative DNA synthesis, the major gallium-specific target probably being ribonucleotide reductase . [ 6 ] In addition to that, it was reported by Chitambar that gallium binds to transferrin more strongly than iron. The transferrin gallium complex inhibits DNA synthesis by acting on the M2 subunit of ribonucleotide reductase. [ 7 ] Gallium(III) seems to act as an antagonist to the actions of several ions (Ca 2+ , Mg 2+ , Fe 2+ and Zn 2+ ) in processes of cellular metabolism . The action of gallium on bone metabolism decreases hypercalcemia associated with cancer. However, gallium is mostly found within the cell as a salt in lysosomes .
Gallium nitrate is commercially available as the hydrate. The nonahydrate may also be prepared by dissolving gallium in nitric acid, followed by recrystallization. [ 8 ] The structure of gallium nitrate nonahydrate has been determined by X-ray crystallography. [ 9 ]
GaN powder was synthesized using a direct current (DC) non-transferred arc plasma. [ 10 ]
Gallium nitrate injection is a clear, colorless, odorless, sterile solution of gallium nitrate, a hydrated nitrate salt of the group IIIa element, gallium. The stable, nonahydrate, Ga(NO 3 ) 3 •9H 2 O is a white, slightly hygroscopic, crystalline powder of molecular weight 417.87, that is readily soluble in water. Each mL of Ganite (gallium nitrate injection) contains gallium nitrate 25 mg (on an anhydrous basis) and sodium citrate dihydrate 28.75 mg. The solution may contain sodium hydroxide or hydrochloric acid for pH adjustment to 6.0-7.0. [ 11 ]
Use of higher doses of gallium nitrate than recommended may cause nausea , vomiting and increases risk of chronic kidney disease . In the case of overdose, serum calcium should be monitored, patients should receive vigorous hydration for 2–3 days and any further drug administrations should be discontinued. [ 11 ]
The action of gallium in gallium nitrate on bone metabolism decreases the hypercalcemia associated with cancer. Gallium inhibits osteoclastic activity and therefore decreases hydroxyapatite crystal formation [ citation needed ] , with adsorption of gallium onto the surfaces of hydroxyapatite crystals. [ 12 ] Also, the increased concentration of gallium in the bone leads to increasing the synthesis of collagen as well as the formation of the bone tissue inside the cell. It has been reported that a protracted infusion was effective against cancer-associated hypercalcemia. [ 13 ] Preliminary studies in bladder carcinoma , carcinoma of the urothelium and lymphomas are also promising. [ 14 ] Another interesting schedule of subcutaneous injection with low doses of gallium nitrate has been proposed, especially for the treatment of bone metastases , but the definitive results have not yet been published. [ 15 ]
Gallium nitrate can react with reducing agents to generate heat and products that may be gaseous. The products may themselves be capable of further reactions (such as combustion in the air). The chemical reduction of materials in this group can be rapid, but often requires initiation of heat, catalyst and addition of a solvent. Explosive mixtures of gallium nitrate with reducing agents often persist unchanged for long periods if initiation is prevented. Some inorganic oxidizing agents such as gallium nitrate are salts of metals that are soluble in water; dissolution dilutes but does not nullify the oxidizing power of such materials. Generally, inorganic oxidizing agents can react violently with active metals, cyanides , esters , and thiocyanates . [ 11 ]
Adverse renal effects have been reported in about 12.5% of patients treated with gallium nitrate. Two patients receiving gallium nitrate and one patient receiving calcitonin developed acute renal failure in a controlled trial of patients with cancer-related hypercalcemia. Also, it was reported that gallium nitrate should not be administered to patients with serum creatinine >2.5 mg/dL. [ 11 ]
In a controlled trial of patients, it was noticed a decrease in mean systolic and diastolic blood pressure after the treatment with gallium nitrate. The decrease in blood pressure was asymptomatic and did not require specific treatment. [ 11 ]
High doses of gallium nitrate were associated with anemia when used in treating patients for advanced cancer. In results, several patients have received red blood cell transfusions . [ 11 ] | https://en.wikipedia.org/wiki/Ga(NO3)3 |
Gallium(III) bromide ( Ga Br 3 ) is a chemical compound , and one of four gallium trihalides.
Gallium(III) bromide is, at room temperature and atmospheric pressure, a white, crystalline powder which reacts favorably and exothermically with water. [ 1 ] Solid gallium tribromide is stable at room temperature and can be found primarily in its dimeric form. [ 2 ] GaBr 3 can form an intermediate halide, Ga 2 Br 7; however, this is not as common as with GaCl 3 . It is a member of the gallium trihalide group and is similar to GaCl 3 , and GaI 3 , but not GaF 3 , in its preparation and uses. [ 2 ] GaBr 3 is a milder Lewis acid than AlBr 3 , and has more versatile chemistry due to the comparative ease of reducing gallium, but is more reactive than GaCl 3 . [ 3 ]
GaBr 3 is similar spectroscopically to aluminum, indium, and thallium trihalides excluding trifluorides. [ 4 ]
One method of preparing GaBr 3 is to heat elemental gallium in the presence of bromine liquid under vacuum. [ 5 ] Following the highly exothermic reaction, the mixture is allowed to rest and then subjected to various purifying steps. This method from the turn of the twentieth century remains a useful way of preparing GaBr 3. Historically, gallium was obtained by electrolysis of its hydroxide in solution of potassium hydroxide, however today it is obtained as a byproduct of aluminium and zinc production.
GaBr 3 can be synthesized by exposing gallium to bromine in an environment free of water, oxygen and grease. [ 5 ] [ 6 ] The result is a gas which must be crystallized in order to form bromide purchased by laboratories. Below is the equation:
The GaBr 3 monomer has trigonal planar geometry, but when it forms the dimer Ga 2 Br 6 the geometry around the gallium center distorts to become roughly tetrahedral. As a solid, GaBr 3 forms a monoclinic crystalline structure with a unit cell volume of 524.16 Å 3 . Additional specifications for this unit cell are as follows: a = 8.87 Å, b = 5.64 Å, c =11.01 Å, α = 90˚, β = 107.81˚, γ = 90˚. [ 7 ]
Gallium is the lightest group 13 metal with a filled d-shell, and has an electronic configuration of ([Ar] 3d 10 4s 2 4p 1 ) below the valence electrons that could take part in d-π bonding with ligands. The somewhat high oxidation state of Ga in Ga(III)Br 3 , low electronegativity, and high polarizability allow GaBr 3 to behave as a "soft acid" in terms of the Hard-Soft-Acid-Base (HSAB) theory . The Lewis acidity of all the gallium trihalides, GaBr 3 included, has been extensively studied thermodynamically, and the basicity of GaBr 3 has been established with a number of donors. [ 2 ]
GaBr 3 is capable of accepting an additional Br − ion or unevenly splitting its dimer to form [GaBr 4 ] − , a tetrahedral ion of which crystalline salts can be obtained. [ 2 ] [ 8 ] This ionic complex is further capable of binding to . The Br − ion can be just as easily substituted with a neutral ligand. Typically these neutral ligands, with form GaBr 3 L and sometimes GaBr 3 L 2 , will form a tetrahedral bipyramidal geometric structure with the Br in an equatorial position due to their large effective nuclear charge. [ 2 ] Additionally, GaBr 3 can be used as a catalyst in certain oxidative addition reactions.
GaBr 3 is used as a catalyst in organic synthesis, with similar mechanism to GaCl 3. However, due to its greater reactivity, it is sometimes disfavored because of the greater versatility of GaCl 3 . [ 2 ] GaBr 3 as well as other gallium trihalides and group 13 metal trihalides can be used as catalysts in the oxidative addition of organic compounds. It has been verified that the GaBr 3 dimer cleaves unevenly into [GaBr 4 ] − and [GaBr 2 ] + . [ 8 ] The entire mechanism is uncertain partly because intermediate states are not always stable enough for study, and partially because GaBr 3 is studied less frequently than GaCl 3 . Ga(III) itself is a useful Lewis acid for organic reactions because its full d-electron shell makes it able to accept variable numbers of ligands, but will readily give up ligands if conditions prove favorable. | https://en.wikipedia.org/wiki/Ga2Br6 |
Gallium(III) chloride is an inorganic chemical compound with the formula GaCl 3 which forms a monohydrate, GaCl 3 ·H 2 O. Solid gallium(III) chloride is a deliquescent white solid and exists as a dimer with the formula Ga 2 Cl 6 . [ 2 ] It is colourless and soluble in virtually all solvents, even alkanes, which is unusual for a metal halide. It is the main precursor to most derivatives of gallium and a reagent in organic synthesis . [ 3 ]
As a Lewis acid , GaCl 3 is milder than aluminium chloride . It is also easier to reduce than aluminium chloride. The coordination chemistry of Ga(III) and Fe(III) are similar, so gallium(III) chloride has been used as a diamagnetic analogue of ferric chloride .
Gallium(III) chloride can be prepared from the elements by heating gallium metal in a stream of chlorine at 200 °C and purifying the product by sublimation under vacuum. [ 4 ] [ 5 ]
It can also be prepared from by heating gallium oxide with thionyl chloride : [ 6 ]
Gallium metal reacts slowly with hydrochloric acid, producing hydrogen gas. [ 7 ] Evaporation of this solution produces the monohydrate. [ 8 ]
As a solid, it adopts a bitetrahedral structure with two bridging chlorides. Its structure resembles that of aluminium tribromide . In contrast AlCl 3 and InCl 3 feature contain 6 coordinate metal centers. As a consequence of its molecular nature and associated low lattice energy , gallium(III) chloride has a lower melting point vs the aluminium and indium trihalides. The formula of Ga 2 Cl 6 is often written as Ga 2 (μ-Cl) 2 Cl 4 . [ 1 ]
In the gas-phase, the dimeric (Ga 2 Cl 6 ) and trigonal planar monomeric (GaCl 3 ) are in a temperature-dependent equilibrium, with higher temperatures favoring the monomeric form. At 870 K, all gas-phase molecules are effectively in the monomeric form. [ 9 ]
In the monohydrate, the gallium is tetrahedrally coordinated with three chlorine molecules and one water molecule. [ 8 ]
Gallium(III) chloride is a diamagnetic and deliquescent colorless white solid that melts at 77.9 °C and boils at 201 °C without decomposition to the elements. This low melting point results from the fact that it forms discrete Ga 2 Cl 6 molecules in the solid state. Gallium(III) chloride dissolves in water with the release of heat to form a colorless solution, which when evaporated, produces a colorless monohydrate, which melts at 44.4 °C. [ 8 ] [ 10 ] [ 11 ]
Gallium is the lightest member of Group 13 to have a full d shell, (gallium has the electronic configuration [ Ar ] 3 d 10 4 s 2 4 p 1 ) below the valence electrons that could take part in d -π bonding with ligands.
The low oxidation state of Ga in Ga(III)Cl 3 , along with the low electronegativity and high polarisability , allow GaCl 3 to behave as a "soft acid" in terms of the HSAB theory . [ 12 ] The strength of the bonds between gallium halides and ligands have been extensively studied. What emerges is: [ 13 ]
With a chloride ion as ligand the tetrahedral GaCl 4 − ion is produced, the 6 coordinate GaCl 6 3− cannot be made. Compounds like KGa 2 Cl 7 that have a chloride bridged anion are known. [ 14 ] In a molten mixture of KCl and GaCl 3 , the following equilibrium exists:
When dissolved in water, gallium(III) chloride dissociates into the octahederal [Ga(H 2 O) 6 ] 3+ and Cl − ions forming an acidic solution, due to the hydrolysis of the hexaaquogallium(III) ion: [ 15 ]
In basic solution, it hydrolyzes to gallium(III) hydroxide , which redissolves with the addition of more hydroxide , possibly to form Ga(OH) 4 − . [ 15 ]
Gallium(III) chloride is a Lewis acid catalyst , such as in the Friedel–Crafts reaction , which is able to substitute more common lewis acids such as ferric chloride . Gallium complexes strongly with π-donors, especially silylethynes , producing a strongly electrophilic complex. These complexes are used as an alkylating agent for aromatic hydrocarbons. [ 3 ]
It is also used in carbogallation reactions of compounds with a carbon-carbon triple bond. It is also used as a catalyst in many organic reactions. [ 3 ]
It is a precursor to organogallium reagents . For example, trimethylgallium , an organogallium compound used in MOCVD to produce various gallium-containing semiconductors , is produced by the reaction of gallium(III) chloride with various alkylating agents, such as dimethylzinc , trimethylaluminium , or methylmagnesium iodide . [ 16 ] [ 17 ] [ 18 ]
Gallium(III) chloride is an intermediate in various gallium purification processes, where gallium(III) chloride is fractionally distilled or extracted from acid solutions. [ 7 ]
110 tons of gallium(III) chloride aqueous solution was used in the GALLEX and GNO experiments performed at Laboratori Nazionali del Gran Sasso in Italy to detect solar neutrinos . In these experiments, germanium -71 was produced by neutrino interactions with the isotope gallium-71 (which has a natural abundance of 40%), and the subsequent beta decays of germanium-71 were measured. [ 10 ] | https://en.wikipedia.org/wiki/Ga2Cl6 |
Gallium(III) iodide is the inorganic compound with the formula Ga I 3 . A yellow hygroscopic solid, it is the most common iodide of gallium. [ 3 ] In the chemical vapor transport method of growing crystals of gallium arsenide uses iodine as the transport agent. In the solid state, it exists as the dimer Ga 2 I 6 , with a diborane structure. [ 4 ] When vaporized, its forms GaI 3 molecules of D 3h symmetry where the Ga–I distance is 2.458 Angstroms . [ 5 ]
Gallium triiodide can be reduced with gallium metal to give a green-colored gallium(I) iodide . The nature of this species is unclear, but it is useful for the preparation of gallium(I) and gallium(II) compounds. [ 6 ] [ 7 ]
This inorganic compound –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Ga2I6 |
Gallium(III) oxide is an inorganic compound and ultra-wide-bandgap semiconductor with the formula Ga 2 O 3 . It is actively studied for applications in power electronics , phosphors , and gas sensing . [ 5 ] [ 6 ] [ 7 ] The compound has several polymorphs , of which the monoclinic β-phase is the most stable. The β-phase’s bandgap of 4.7–4.9 eV and large-area, native substrates make it a promising competitor to GaN and SiC -based power electronics applications and solar-blind UV photodetectors. [ 7 ] [ 8 ] The orthorhombic ĸ- Ga 2 O 3 is the second most stable polymorph. The ĸ-phase has shown instability of subsurface doping density under thermal exposure. [ 9 ] Ga 2 O 3 exhibits reduced thermal conductivity and electron mobility by an order of magnitude compared to GaN and SiC , but is predicted to be significantly more cost-effective due to being the only wide-bandgap material capable of being grown from melt. [ 7 ] [ 10 ] [ 11 ] β-Ga 2 O 3 is thought to be radiation-hard , which makes it promising for military and space applications. [ 12 ] [ 13 ]
Gallium trioxide is precipitated in hydrated form upon neutralization of acidic or basic solution of gallium salt. Also, it is formed on heating gallium in air or by thermally decomposing gallium nitrate at 200–250 °C.
Crystalline Ga 2 O 3 can occur in five polymorphs, α, β, γ, δ, and ε. Of these polymorphs β-Ga 2 O 3 is the most thermodynamically stable phase at standard temperature and pressure [ 14 ] while α-Ga 2 O 3 is the most stable polymorph under high pressures. [ 15 ]
Bulk substrates of β-Ga 2 O 3 can be produced, which is one of the major advantages of this material system. Bulk substrates can be produced in multiple orientations and by multiple techniques. [ 21 ] [ 22 ]
Gallium(III) trioxide is amphoteric . [ 26 ] It reacts with alkali metal oxides at high temperature to form, e.g., NaGaO 2 , and with Mg, Zn, Co, Ni, Cu oxides to form spinels , e.g., MgGa 2 O 4 . [ 27 ] It dissolves in strong alkali to form a solution of the gallate ion, Ga(OH) − 4 .
With HCl, it forms gallium trichloride GaCl 3 . [ 28 ]
It can be reduced to gallium suboxide (gallium(I) oxide) Ga 2 O by H 2 . [ 29 ] or by reaction with gallium metal: [ 30 ]
β-Ga 2 O 3 , with a melting point of 1900 °C, is the most stable crystalline modification. The oxide ions are in a distorted cubic closest packing arrangement, and the gallium (III) ions occupy distorted tetrahedral and octahedral sites, with Ga–O bond distances of 1.83 and 2.00 Å respectively. [ 31 ]
α-Ga 2 O 3 has the same structure ( corundum ) as α-Al 2 O 3 , wherein Ga ions are 6-coordinate. [ 32 ] [ 33 ]
γ-Ga 2 O 3 has a defect spinel structure similar to that of γ-Al 2 O 3 . [ 34 ]
ε-Ga 2 O 3 films deposited by metalorganic vapour-phase epitaxy show a columnar structure with orthorhombic crystal symmetry . Macroscopically, this structure is seen by X-ray crystallography as hexagonal close packed . [ 35 ]
κ-Ga 2 O 3 has an orthorhombic structure and forms with 120° twin domains, resulting in hexagonal symmetry which is often identified as ε-Ga 2 O 3 . [ 36 ]
(Corundum)
Gallium(III) oxide has been studied for usage as passive components in lasers, [ 43 ] phosphors, [ 5 ] and luminescent materials [ 44 ] as well as active components for gas sensors, [ 6 ] power diodes, [ 45 ] and power transistors. [ 46 ] [ 47 ] Since the first publication in January 2012 by the National Institute of Information and Communications Technology , in collaboration with Tamura Co., Ltd. and Koha Co., Ltd. of the world's first single-crystal gallium oxide (Ga 2 O 3 ) field-effect transistors , the predominant interest in gallium oxide is in the β-polymorph for power electronics . [ 48 ] [ 7 ]
Monoclinic β-Ga 2 O 3 has shown increasing performance since 2012 approaching state of the art GaN and SiC power devices. [ 7 ] β-Ga 2 O 3 Schottky diodes have exceeded breakdown voltages of 2400 V. [ 45 ] β-Ga 2 O 3 / NiO x p–n diodes have exhibited breakdown voltages over 1200 V. [ 49 ] β-Ga 2 O 3 MOSFETs have individually achieved figures of merits of f T of 27 GHz, [ 46 ] f MAX of 48 GHz, [ 47 ] and 5.4 MV/cm average breakdown field. [ 47 ] This field exceeds that which is possible in SiC or GaN.
ε-Ga 2 O 3 thin films deposited on sapphire show potential applications as solar-blind UV photodetector . [ 8 ] | https://en.wikipedia.org/wiki/Ga2O3 |
Gallium(III) sulfide , Ga 2 S 3 , is a compound of sulfur and gallium , that is a semiconductor that has applications in electronics and photonics .
There are four polymorphs , α (hexagonal), α' (monoclinic), β(hexagonal) and γ(cubic). The alpha form is yellow. The crystal structures are related to those of ZnS with gallium in tetrahedral positions. [ 3 ] [ 2 ] [ 4 ] The alpha and beta forms are isostructural with their aluminium analogues. [ 5 ] The similarity in crystal form of gamma- with sphalerite (zinc blende), ZnS is believed to explain the enrichment of gallium in sphalerite ores. [ 5 ]
Ga 2 S 3 can prepared by reacting the elements at high temperature or as a white solid by heating Ga in a stream of H 2 S at high temperature (950 °C). [ 2 ]
It may also prepared by a solid state reaction of GaCl 3 and Na 2 S . [ 5 ]
The method of production can determine the polymorphic form produced, the reaction of Ga(OH) 3 with H 2 S at different temperatures is reported to produce a different polymorph depending on the temperature, α- 1020 K, β- 820 K and γ- above 873 K [ 6 ]
Ga 2 S 3 decomposes at high temperature forming the non-stoichiometric sulfide, Ga 4 S x (4.8 < x < 5.2). [ 5 ] Ga 2 S 3 dissolves in aqueous acids and decomposes slowly in moist air forming H 2 S . [ 2 ]
Ga 2 S 3 dissolves in aqueous solutions of potassium sulfide , K 2 S to form K 8 Ga 4 S 10 containing the (Ga 4 S 10 ) 8− anion which has an adamantane , molecular P 4 O 10 structure. [ 5 ]
Ternary sulfides M I GaS 2 , M II Ga 2 S 4 and M III GaS 3 respectively have been of interest due to their unusual electrical properties and some of these can be prepared by reactions of Ga 2 S 3 with metal sulfides e.g. CdGa 2 S 4 :- [ 5 ]
Although by itself Ga 2 S 3 is not a glass former it can be reacted with rare earth sulfides to form glasses e.g. the reaction with lanthanum sulfide, La 2 S 3 , forms gallium lanthanum sulfide glass which has interesting optical properties and is a semiconductor. [ 7 ] | https://en.wikipedia.org/wiki/Ga2S3 |
Gallium(III) selenide ( Ga 2 Se 3 ) is a chemical compound . It has a defect sphalerite (cubic form of ZnS) structure. [ 1 ] It is a p-type semiconductor [ 2 ]
It can be formed by union of the elements. It hydrolyses slowly in water and quickly in mineral acids to form toxic hydrogen selenide gas. The reducing capabilities of the selenide ion make it vulnerable to oxidizing agents. It is advised therefore that it not come into contact with bases. [ citation needed ]
This inorganic compound –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Ga2Se3 |
Gallium(III) telluride ( Ga 2 Te 3 ) is a chemical compound classified as a metal telluride . At room temperature gallium(III) telluride is an odorless, black, brittle crystalline solid and is a semiconductor of the III-VI type that crystallizes in a lattice structure . [ 2 ]
Gallium(III) telluride is most commonly synthesized through the solid-state reaction of trimethylgallium and a telluride oxide complex under high temperatures. It is also possible to synthesize the compound by reacting elemental gallium and elemental tellurium at high temperatures. [ 3 ]
At room temperature, gallium(III) telluride is a black, odorless, brittle crystal. The compound crystallizes in a four-coordinate tetrahedral structure. [ 4 ] The crystal is not immediately reactive or flammable, though serious protective ware should be worn while handling this compound (see toxicity). Gallium(III) telluride has a melting point of 788 °C to 792 °C and is not soluble in water. [ 5 ]
Gallium(III) telluride is stable at room temperature. The compound is relatively unreactive, and there are no known materials with which it is incompatible. Gallium(III) telluride will over time emit telluride fumes and it naturally decomposes. There is no risk of hazardous polymerization .
The toxicological properties of gallium(III) telluride have not been thoroughly investigated. However elemental tellurium has relatively low toxicity. It is converted in the body to dimethyl telluride which imparts a garlic-like odor to the breath and sweat. Heavy exposures may, in addition, result in headache, drowsiness, metallic taste, loss of appetite, nausea, tremors, convulsions, and respiratory arrest. [ 5 ] Proper precautions should be taken when handling this compound, including lab goggles and safety gloves. This compound should be handled in a well ventilated area. [ 5 ]
Gallium(III) telluride is a p-type semiconductor of the III-VI type. [ 2 ] Currently its use in industry is relatively limited but further application are being explored, especially as its use in a thin film and for applications in laser diodes and solar cells . [ citation needed ]
The medical uses of gallium(III) telluride are still being investigated. [ 2 ]
Gallium(III) telluride has been used in the production of sputtering targets, used for semiconductor , chemical vapor deposition (CVD) and physical vapor deposition (PVD) display and optical applications. [ 6 ] High-purity gallium(III) telluride is commercially available in many crystalline and polycrystalline forms. [ 7 ] | https://en.wikipedia.org/wiki/Ga2Te3 |
Gallium arsenide ( GaAs ) is a III-V direct band gap semiconductor with a zinc blende crystal structure.
Gallium arsenide is used in the manufacture of devices such as microwave frequency integrated circuits , monolithic microwave integrated circuits , infrared light-emitting diodes , laser diodes , solar cells and optical windows. [ 6 ]
GaAs is often used as a substrate material for the epitaxial growth of other III-V semiconductors, including indium gallium arsenide , aluminum gallium arsenide and others.
Gallium arsenide was first synthesized and studied by Victor Goldschmidt in 1926 by passing arsenic vapors mixed with hydrogen over gallium(III) oxide at 600 °C. [ 7 ] [ 8 ] The semiconductor properties of GaAs and other III-V compounds were patented by Heinrich Welker at Siemens-Schuckert in 1951 [ 9 ] and described in a 1952 publication. [ 10 ] Commercial production of its monocrystals commenced in 1954, [ 11 ] and more studies followed in the 1950s. [ 12 ] First infrared LEDs were made in 1962. [ 11 ]
In the compound, gallium has a +3 oxidation state . Gallium arsenide single crystals can be prepared by three industrial processes: [ 6 ]
Alternative methods for producing films of GaAs include: [ 6 ] [ 14 ]
Oxidation of GaAs occurs in air, degrading performance of the semiconductor. The surface can be passivated by depositing a cubic gallium(II) sulfide layer using a tert-butyl gallium sulfide compound such as ( t BuGaS) 7 . [ 15 ]
In the presence of excess arsenic, GaAs boules grow with crystallographic defects ; specifically, arsenic antisite defects (an arsenic atom at a gallium atom site within the crystal lattice). The electronic properties of these defects (interacting with others) cause the Fermi level to be pinned to near the center of the band gap, so that this GaAs crystal has very low concentration of electrons and holes. This low carrier concentration is similar to an intrinsic (perfectly undoped) crystal, but much easier to achieve in practice. These crystals are called "semi-insulating", reflecting their high resistivity of 10 7 –10 9 Ω·cm (which is quite high for a semiconductor, but still much lower than a true insulator like glass). [ 16 ]
Wet etching of GaAs industrially uses an oxidizing agent such as hydrogen peroxide or bromine water, [ 17 ] and the same strategy has been described in a patent relating to processing scrap components containing GaAs where the Ga 3+ is complexed with a hydroxamic acid ("HA"), for example: [ 18 ]
This reaction produces arsenic acid . [ 19 ]
GaAs can be used for various transistor types: [ 20 ]
The HBT can be used in integrated injection logic (I 2 L).
The earliest GaAs logic gate used Buffered FET Logic (BFL). [ 20 ]
From c. 1975 to 1995 the main logic families used were: [ 20 ]
Some electronic properties of gallium arsenide are superior to those of silicon . It has a higher saturated electron velocity and higher electron mobility , allowing gallium arsenide transistors to function at frequencies in excess of 250 GHz. [ 22 ] GaAs devices are relatively insensitive to overheating, owing to their wider energy band gap, and they also tend to create less noise (disturbance in an electrical signal) in electronic circuits than silicon devices, especially at high frequencies. This is a result of higher carrier mobilities and lower resistive device parasitics. These superior properties are compelling reasons to use GaAs circuitry in mobile phones , satellite communications, microwave point-to-point links and higher frequency radar systems. It is also used in the manufacture of Gunn diodes for the generation of microwaves . [ citation needed ]
Another advantage of GaAs is that it has a direct band gap , which means that it can be used to absorb and emit light efficiently. Silicon has an indirect band gap and so is relatively poor at emitting light. [ citation needed ]
As a wide direct band gap material with resulting resistance to radiation damage, GaAs is an excellent material for outer space electronics and optical windows in high power applications. [ 22 ]
Because of its wide band gap, pure GaAs is highly resistive. Combined with a high dielectric constant , this property makes GaAs a very good substrate for integrated circuits and unlike Si provides natural isolation between devices and circuits. This has made it an ideal material for monolithic microwave integrated circuits (MMICs), where active and essential passive components can readily be produced on a single slice of GaAs.
One of the first GaAs microprocessors was developed in the early 1980s by the RCA Corporation and was considered for the Star Wars program of the United States Department of Defense . These processors were several times faster and several orders of magnitude more radiation resistant than their silicon counterparts, but were more expensive. [ 23 ] Other GaAs processors were implemented by the supercomputer vendors Cray Computer Corporation, Convex , and Alliant in an attempt to stay ahead of the ever-improving CMOS microprocessor. Cray eventually built one GaAs-based machine in the early 1990s, the Cray-3 , but the effort was not adequately capitalized, and the company filed for bankruptcy in 1995.
Complex layered structures of gallium arsenide in combination with aluminium arsenide (AlAs) or the alloy Al x Ga 1−x As can be grown using molecular-beam epitaxy (MBE) or using metalorganic vapor-phase epitaxy (MOVPE). Because GaAs and AlAs have almost the same lattice constant , the layers have very little induced strain , which allows them to be grown almost arbitrarily thick. This allows extremely high performance and high electron mobility HEMT transistors and other quantum well devices.
GaAs is used for monolithic radar power amplifiers (but GaN can be less susceptible to heat damage). [ 24 ]
Silicon has three major advantages over GaAs for integrated circuit manufacture. First, silicon is abundant and cheap to process in the form of silicate minerals. The economies of scale available to the silicon industry has also hindered the adoption of GaAs. [ citation needed ]
In addition, a Si crystal has a very stable structure and can be grown to very large diameter boules and processed with very good yields. It is also a fairly good thermal conductor, thus enabling very dense packing of transistors that need to get rid of their heat of operation, all very desirable for design and manufacturing of very large ICs . Such good mechanical characteristics also make it a suitable material for the rapidly developing field of nanoelectronics . Naturally, a GaAs surface cannot withstand the high temperatures needed for diffusion; however a viable and actively pursued alternative as of the 1980s was ion implantation. [ 25 ]
The second major advantage of Si is the existence of a native oxide ( silicon dioxide , SiO 2 ), which is used as an insulator . Silicon dioxide can be incorporated onto silicon circuits easily, and such layers are adherent to the underlying silicon. SiO 2 is not only a good insulator (with a band gap of 8.9 eV ), but the Si-SiO 2 interface can be easily engineered to have excellent electrical properties, most importantly low density of interface states. GaAs does not have a native oxide, does not easily support a stable adherent insulating layer, and does not possess the dielectric strength or surface passivating qualities of the Si-SiO 2 . [ 25 ]
Aluminum oxide (Al 2 O 3 ) has been extensively studied as a possible gate oxide for GaAs (as well as InGaAs ).
The third advantage of silicon is that it possesses a higher hole mobility compared to GaAs (500 versus 400 cm 2 V −1 s −1 ). [ 26 ] This high mobility allows the fabrication of higher-speed P-channel field-effect transistors , which are required for CMOS logic. Because they lack a fast CMOS structure, GaAs circuits must use logic styles which have much higher power consumption; this has made GaAs logic circuits unable to compete with silicon logic circuits.
For manufacturing solar cells, silicon has relatively low absorptivity for sunlight, meaning about 100 micrometers of Si is needed to absorb most sunlight. Such a layer is relatively robust and easy to handle. In contrast, the absorptivity of GaAs is so high that only a few micrometers of thickness are needed to absorb all of the light. Consequently, GaAs thin films must be supported on a substrate material. [ 27 ]
Silicon is a pure element, avoiding the problems of stoichiometric imbalance and thermal unmixing of GaAs. [ 28 ]
Silicon has a nearly perfect lattice; impurity density is very low and allows very small structures to be built (down to 5 nm in commercial production as of 2020 [ 29 ] ). In contrast, GaAs has a very high impurity density, [ 30 ] which makes it difficult to build integrated circuits with small structures, so the 500 nm process is a common process for GaAs. [ citation needed ]
Silicon has about three times the thermal conductivity of GaAs, with less risk of local overheating in high power devices. [ 24 ]
Gallium arsenide (GaAs) transistors are used in the RF power amplifiers for cell phones and wireless communicating. [ 31 ] GaAs wafers are used in laser diodes , photodetectors , and radio frequency (RF) amplifiers for mobile phones and base stations. [ 32 ] GaAs transistors are also integral to monolithic microwave integrated circuits (MMICs) , utilized in satellite communication and radar systems, as well as in low-noise amplifiers (LNAs) that enhance weak signals. [ 33 ] [ 34 ]
Gallium arsenide is an important semiconductor material for high-cost, high-efficiency solar cells and is used for single-crystalline thin-film solar cells and for multi-junction solar cells . [ 35 ]
The first known operational use of GaAs solar cells in space was for the Venera 3 mission, launched in 1965. The GaAs solar cells, manufactured by Kvant, were chosen because of their higher performance in high temperature environments. [ 36 ] GaAs cells were then used for the Lunokhod rovers for the same reason. [ citation needed ]
In 1970, the GaAs heterostructure solar cells were developed by the team led by Zhores Alferov in the USSR , [ 37 ] [ 38 ] [ 39 ] achieving much higher efficiencies. In the early 1980s, the efficiency of the best GaAs solar cells surpassed that of conventional, crystalline silicon -based solar cells. In the 1990s, GaAs solar cells took over from silicon as the cell type most commonly used for photovoltaic arrays for satellite applications. Later, dual- and triple-junction solar cells based on GaAs with germanium and indium gallium phosphide layers were developed as the basis of a triple-junction solar cell, which held a record efficiency of over 32% and can operate also with light as concentrated as 2,000 suns. This kind of solar cell powered the Mars Exploration Rovers Spirit and Opportunity , which explored Mars ' surface. Also many solar cars utilize GaAs in solar arrays, as did the Hubble Telescope. [ 40 ]
GaAs-based devices hold the world record for the highest-efficiency single-junction solar cell at 29.1% (as of 2019). This high efficiency is attributed to the extreme high quality GaAs epitaxial growth, surface passivation by the AlGaAs, [ 41 ] and the promotion of photon recycling by the thin film design. [ 42 ] GaAs-based photovoltaics are also responsible for the highest efficiency (as of 2022) of conversion of light to electricity, as researchers from the Fraunhofer Institute for Solar Energy Systems achieved a 68.9% efficiency when exposing a GaAs thin film photovoltaic cell to monochromatic laser light with a wavelength of 858 nanometers. [ 43 ]
Today, multi-junction GaAs cells have the highest efficiencies of existing photovoltaic cells and trajectories show that this is likely to continue to be the case for the foreseeable future. [ 44 ] In 2022, Rocket Lab unveiled a solar cell with 33.3% efficiency [ 45 ] based on inverted metamorphic multi-junction (IMM) technology. In IMM, the lattice-matched (same lattice parameters) materials are grown first, followed by mismatched materials. The top cell, GaInP, is grown first and lattice matched to the GaAs substrate, followed by a layer of either GaAs or GaInAs with a minimal mismatch, and the last layer has the greatest lattice mismatch. [ 46 ] After growth, the cell is mounted to a secondary handle and the GaAs substrate is removed. A main advantage of the IMM process is that the inverted growth according to lattice mismatch allows a path to higher cell efficiency.
Complex designs of Al x Ga 1−x As-GaAs devices using quantum wells can be sensitive to infrared radiation ( QWIP ).
GaAs diodes can be used for the detection of X-rays. [ 47 ]
Despite GaAs-based photovoltaics being the clear champions of efficiency for solar cells, they have relatively limited use in today's market. In both world electricity generation and world electricity generating capacity, solar electricity is growing faster than any other source of fuel (wind, hydro, biomass, and so on) for the last decade. [ 48 ] However, GaAs solar cells have not currently been adopted for widespread solar electricity generation. This is largely due to the cost of GaAs solar cells - in space applications, high performance is required and the corresponding high cost of the existing GaAs technologies is accepted. For example, GaAs-based photovoltaics show the best resistance to gamma radiation and high temperature fluctuations, which are of great importance for spacecraft. [ 49 ] But in comparison to other solar cells, III-V solar cells are two to three orders of magnitude more expensive than other technologies such as silicon-based solar cells. [ 50 ] The primary sources of this cost are the epitaxial growth costs and the substrate the cell is deposited on.
GaAs solar cells are most commonly fabricated utilizing epitaxial growth techniques such as metal-organic chemical vapor deposition (MOCVD) and hydride vapor phase epitaxy (HVPE). A significant reduction in costs for these methods would require improvements in tool costs, throughput, material costs, and manufacturing efficiency. [ 50 ] Increasing the deposition rate could reduce costs, but this cost reduction would be limited by the fixed times in other parts of the process such as cooling and heating. [ 50 ]
The substrate used to grow these solar cells is usually germanium or gallium arsenide which are notably expensive materials. One of the main pathways to reduce substrate costs is to reuse the substrate. An early method proposed to accomplish this is epitaxial lift-off (ELO), [ 51 ] but this method is time-consuming, somewhat dangerous (with its use of hydrofluoric acid ), and requires multiple post-processing steps. However, other methods have been proposed that use phosphide-based materials and hydrochloric acid to achieve ELO with surface passivation and minimal post- etching residues and allows for direct reuse of the GaAs substrate. [ 52 ] There is also preliminary evidence that spalling could be used to remove the substrate for reuse. [ 53 ] An alternative path to reduce substrate cost is to use cheaper materials, although materials for this application are not currently commercially available or developed. [ 50 ]
Yet another consideration to lower GaAs solar cell costs could be concentrator photovoltaics . Concentrators use lenses or parabolic mirrors to focus light onto a solar cell, and thus a smaller (and therefore less expensive) GaAs solar cell is needed to achieve the same results. [ 54 ] Concentrator systems have the highest efficiency of existing photovoltaics. [ 55 ]
So, technologies such as concentrator photovoltaics and methods in development to lower epitaxial growth and substrate costs could lead to a reduction in the cost of GaAs solar cells and forge a path for use in terrestrial applications.
GaAs has been used to produce near-infrared laser diodes since 1962. [ 56 ] It is often used in alloys with other semiconductor compounds for these applications.
N -type GaAs doped with silicon donor atoms (on Ga sites) and boron acceptor atoms (on As sites) responds to ionizing radiation by emitting scintillation photons. At cryogenic temperatures it is among the brightest scintillators known [ 57 ] [ 58 ] [ 59 ] and is a promising candidate for detecting rare electronic excitations from interacting dark matter, [ 60 ] due to the following six essential factors:
For this purpose an optical fiber tip of an optical fiber temperature sensor is equipped with a gallium arsenide crystal. Starting at a light wavelength of 850 nm GaAs becomes optically translucent. Since the spectral position of the band gap is temperature dependent, it shifts about 0.4 nm/K. The measurement device contains a light source and a device for the spectral detection of the band gap. With the changing of the band gap, (0.4 nm/K) an algorithm calculates the temperature (all 250 ms). [ 69 ]
GaAs may have applications in spintronics as it can be used instead of platinum in spin-charge converters and may be more tunable. [ 70 ]
The environment, health and safety aspects of gallium arsenide sources (such as trimethylgallium and arsine ) and industrial hygiene monitoring studies of metalorganic precursors have been reported. [ 71 ] California lists gallium arsenide as a carcinogen , [ 72 ] as do IARC and ECA , [ 73 ] and it is considered a known carcinogen in animals. [ 74 ] [ 75 ] On the other hand, a 2013 review (funded by industry) argued against these classifications, saying that when rats or mice inhale fine GaAs powders (as in previous studies), they get cancer from the resulting lung irritation and inflammation, rather than from a primary carcinogenic effect of the GaAs itself—and that, moreover, fine GaAs powders are unlikely to be created in the production or use of GaAs. [ 73 ] | https://en.wikipedia.org/wiki/GaAs |
Gallium(III) bromide ( Ga Br 3 ) is a chemical compound , and one of four gallium trihalides.
Gallium(III) bromide is, at room temperature and atmospheric pressure, a white, crystalline powder which reacts favorably and exothermically with water. [ 1 ] Solid gallium tribromide is stable at room temperature and can be found primarily in its dimeric form. [ 2 ] GaBr 3 can form an intermediate halide, Ga 2 Br 7; however, this is not as common as with GaCl 3 . It is a member of the gallium trihalide group and is similar to GaCl 3 , and GaI 3 , but not GaF 3 , in its preparation and uses. [ 2 ] GaBr 3 is a milder Lewis acid than AlBr 3 , and has more versatile chemistry due to the comparative ease of reducing gallium, but is more reactive than GaCl 3 . [ 3 ]
GaBr 3 is similar spectroscopically to aluminum, indium, and thallium trihalides excluding trifluorides. [ 4 ]
One method of preparing GaBr 3 is to heat elemental gallium in the presence of bromine liquid under vacuum. [ 5 ] Following the highly exothermic reaction, the mixture is allowed to rest and then subjected to various purifying steps. This method from the turn of the twentieth century remains a useful way of preparing GaBr 3. Historically, gallium was obtained by electrolysis of its hydroxide in solution of potassium hydroxide, however today it is obtained as a byproduct of aluminium and zinc production.
GaBr 3 can be synthesized by exposing gallium to bromine in an environment free of water, oxygen and grease. [ 5 ] [ 6 ] The result is a gas which must be crystallized in order to form bromide purchased by laboratories. Below is the equation:
The GaBr 3 monomer has trigonal planar geometry, but when it forms the dimer Ga 2 Br 6 the geometry around the gallium center distorts to become roughly tetrahedral. As a solid, GaBr 3 forms a monoclinic crystalline structure with a unit cell volume of 524.16 Å 3 . Additional specifications for this unit cell are as follows: a = 8.87 Å, b = 5.64 Å, c =11.01 Å, α = 90˚, β = 107.81˚, γ = 90˚. [ 7 ]
Gallium is the lightest group 13 metal with a filled d-shell, and has an electronic configuration of ([Ar] 3d 10 4s 2 4p 1 ) below the valence electrons that could take part in d-π bonding with ligands. The somewhat high oxidation state of Ga in Ga(III)Br 3 , low electronegativity, and high polarizability allow GaBr 3 to behave as a "soft acid" in terms of the Hard-Soft-Acid-Base (HSAB) theory . The Lewis acidity of all the gallium trihalides, GaBr 3 included, has been extensively studied thermodynamically, and the basicity of GaBr 3 has been established with a number of donors. [ 2 ]
GaBr 3 is capable of accepting an additional Br − ion or unevenly splitting its dimer to form [GaBr 4 ] − , a tetrahedral ion of which crystalline salts can be obtained. [ 2 ] [ 8 ] This ionic complex is further capable of binding to . The Br − ion can be just as easily substituted with a neutral ligand. Typically these neutral ligands, with form GaBr 3 L and sometimes GaBr 3 L 2 , will form a tetrahedral bipyramidal geometric structure with the Br in an equatorial position due to their large effective nuclear charge. [ 2 ] Additionally, GaBr 3 can be used as a catalyst in certain oxidative addition reactions.
GaBr 3 is used as a catalyst in organic synthesis, with similar mechanism to GaCl 3. However, due to its greater reactivity, it is sometimes disfavored because of the greater versatility of GaCl 3 . [ 2 ] GaBr 3 as well as other gallium trihalides and group 13 metal trihalides can be used as catalysts in the oxidative addition of organic compounds. It has been verified that the GaBr 3 dimer cleaves unevenly into [GaBr 4 ] − and [GaBr 2 ] + . [ 8 ] The entire mechanism is uncertain partly because intermediate states are not always stable enough for study, and partially because GaBr 3 is studied less frequently than GaCl 3 . Ga(III) itself is a useful Lewis acid for organic reactions because its full d-electron shell makes it able to accept variable numbers of ligands, but will readily give up ligands if conditions prove favorable. | https://en.wikipedia.org/wiki/GaBr3 |
Gallium(III) chloride is an inorganic chemical compound with the formula GaCl 3 which forms a monohydrate, GaCl 3 ·H 2 O. Solid gallium(III) chloride is a deliquescent white solid and exists as a dimer with the formula Ga 2 Cl 6 . [ 2 ] It is colourless and soluble in virtually all solvents, even alkanes, which is unusual for a metal halide. It is the main precursor to most derivatives of gallium and a reagent in organic synthesis . [ 3 ]
As a Lewis acid , GaCl 3 is milder than aluminium chloride . It is also easier to reduce than aluminium chloride. The coordination chemistry of Ga(III) and Fe(III) are similar, so gallium(III) chloride has been used as a diamagnetic analogue of ferric chloride .
Gallium(III) chloride can be prepared from the elements by heating gallium metal in a stream of chlorine at 200 °C and purifying the product by sublimation under vacuum. [ 4 ] [ 5 ]
It can also be prepared from by heating gallium oxide with thionyl chloride : [ 6 ]
Gallium metal reacts slowly with hydrochloric acid, producing hydrogen gas. [ 7 ] Evaporation of this solution produces the monohydrate. [ 8 ]
As a solid, it adopts a bitetrahedral structure with two bridging chlorides. Its structure resembles that of aluminium tribromide . In contrast AlCl 3 and InCl 3 feature contain 6 coordinate metal centers. As a consequence of its molecular nature and associated low lattice energy , gallium(III) chloride has a lower melting point vs the aluminium and indium trihalides. The formula of Ga 2 Cl 6 is often written as Ga 2 (μ-Cl) 2 Cl 4 . [ 1 ]
In the gas-phase, the dimeric (Ga 2 Cl 6 ) and trigonal planar monomeric (GaCl 3 ) are in a temperature-dependent equilibrium, with higher temperatures favoring the monomeric form. At 870 K, all gas-phase molecules are effectively in the monomeric form. [ 9 ]
In the monohydrate, the gallium is tetrahedrally coordinated with three chlorine molecules and one water molecule. [ 8 ]
Gallium(III) chloride is a diamagnetic and deliquescent colorless white solid that melts at 77.9 °C and boils at 201 °C without decomposition to the elements. This low melting point results from the fact that it forms discrete Ga 2 Cl 6 molecules in the solid state. Gallium(III) chloride dissolves in water with the release of heat to form a colorless solution, which when evaporated, produces a colorless monohydrate, which melts at 44.4 °C. [ 8 ] [ 10 ] [ 11 ]
Gallium is the lightest member of Group 13 to have a full d shell, (gallium has the electronic configuration [ Ar ] 3 d 10 4 s 2 4 p 1 ) below the valence electrons that could take part in d -π bonding with ligands.
The low oxidation state of Ga in Ga(III)Cl 3 , along with the low electronegativity and high polarisability , allow GaCl 3 to behave as a "soft acid" in terms of the HSAB theory . [ 12 ] The strength of the bonds between gallium halides and ligands have been extensively studied. What emerges is: [ 13 ]
With a chloride ion as ligand the tetrahedral GaCl 4 − ion is produced, the 6 coordinate GaCl 6 3− cannot be made. Compounds like KGa 2 Cl 7 that have a chloride bridged anion are known. [ 14 ] In a molten mixture of KCl and GaCl 3 , the following equilibrium exists:
When dissolved in water, gallium(III) chloride dissociates into the octahederal [Ga(H 2 O) 6 ] 3+ and Cl − ions forming an acidic solution, due to the hydrolysis of the hexaaquogallium(III) ion: [ 15 ]
In basic solution, it hydrolyzes to gallium(III) hydroxide , which redissolves with the addition of more hydroxide , possibly to form Ga(OH) 4 − . [ 15 ]
Gallium(III) chloride is a Lewis acid catalyst , such as in the Friedel–Crafts reaction , which is able to substitute more common lewis acids such as ferric chloride . Gallium complexes strongly with π-donors, especially silylethynes , producing a strongly electrophilic complex. These complexes are used as an alkylating agent for aromatic hydrocarbons. [ 3 ]
It is also used in carbogallation reactions of compounds with a carbon-carbon triple bond. It is also used as a catalyst in many organic reactions. [ 3 ]
It is a precursor to organogallium reagents . For example, trimethylgallium , an organogallium compound used in MOCVD to produce various gallium-containing semiconductors , is produced by the reaction of gallium(III) chloride with various alkylating agents, such as dimethylzinc , trimethylaluminium , or methylmagnesium iodide . [ 16 ] [ 17 ] [ 18 ]
Gallium(III) chloride is an intermediate in various gallium purification processes, where gallium(III) chloride is fractionally distilled or extracted from acid solutions. [ 7 ]
110 tons of gallium(III) chloride aqueous solution was used in the GALLEX and GNO experiments performed at Laboratori Nazionali del Gran Sasso in Italy to detect solar neutrinos . In these experiments, germanium -71 was produced by neutrino interactions with the isotope gallium-71 (which has a natural abundance of 40%), and the subsequent beta decays of germanium-71 were measured. [ 10 ] | https://en.wikipedia.org/wiki/GaCl3 |
Gallium(III) fluoride ( Ga F 3 ) is a chemical compound . It is a white solid that melts under pressure above 1000 °C but sublimes around 950 °C. It has the FeF 3 structure where the gallium atoms are 6-coordinate. [ 1 ] GaF 3 can be prepared by reacting F 2 or HF with Ga 2 O 3 or by thermal decomposition of (NH 4 ) 3 GaF 6 . [ 2 ] GaF 3 is virtually insoluble in water. [ 2 ] Solutions of GaF 3 in HF can be evaporated to form the trihydrate, GaF 3 ·3H 2 O, which on heating gives a hydrated form of GaF 2 (OH). [ 2 ] Gallium(III) fluoride reacts with mineral acids to form hydrofluoric acid .
This inorganic compound –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/GaF3 |
Gallium monoiodide is an inorganic gallium compound with the formula GaI or Ga 4 I 4 . It is a pale green solid and mixed valent gallium compound, which can contain gallium in the 0, +1, +2, and +3 oxidation states. It is used as a pathway for many gallium-based products. Unlike the gallium(I) halides first crystallographically characterized, [ 1 ] gallium monoiodide has a more facile synthesis allowing a synthetic route to many low-valent gallium compounds.
In 1990, Malcolm Green synthesized gallium monoiodide by the ultrasonication of liquid gallium metal with iodine in toluene yielding a pale green powder referred to as gallium monoiodide. [ 2 ] The chemical composition of gallium monoiodide was not determined until the early to mid-2010s despite its simple synthesis.
In 2012, the pale green gallium monoiodide was determined to be a combination of gallium metal and gallium(I,III) iodide , having the chemical composition [Ga 0 ] 2 [Ga + ][GaI 4 − ]. [ 3 ] However, in 2014, it was found that the incomplete reaction of gallium metal with iodine yielded gallium monoiodide with this chemical composition. Gallium monoiodide synthesized with longer reaction times for complete reaction had a different chemical composition [Ga 0 ] 2 [Ga + ] 2 [Ga 2 I 6 2- ]. [ 4 ]
The resultant gallium monoiodide is highly air sensitive, but stable under inert atmosphere conditions for up to a year at -35 ˚C. [ 4 ]
When gallium monoiodide was first produced, it was proposed that gallium monoiodide is a combination of gallium metal, Ga 2 I 3 and Ga 2 I 4 based on the characteristic Raman spectra of these constituents. [ 5 ] This hypothesis was confirmed as two variants of gallium monoiodide were determined to have the chemical compositions [Ga 0 ] 2 [Ga + ][GaI 4 − ], simplified as Ga 2 I 4 ·2Ga, and [Ga 0 ] 2 [Ga + ] 2 [Ga 2 I 6 2- ], simplified as Ga 2 I 3 ·Ga. [ 4 ] [ 3 ]
When the incompletely reacted product was probed by NMR spectroscopy , it showed the presence gallium metal. [ 3 ] When probed by 127 I NQR , [ 4 ] it showed the presence of Ga 2 I 4 and further confirms the [Ga 0 ] 2 [Ga + ][GaI 4 − ] assignment. [ 6 ] Raman spectroscopy has also confirmed this composition assignment. [ 4 ] [ 7 ] All of the evidence from other spectroscopic methods, and power x-ray diffraction patterns, validates the assignment of [Ga 0 ] 2 [Ga + ][GaI 4 − ] for the incompletely reacted gallium monoiodide variant.
When the completely reacted product was probed by 127 I NQR, it showed the presence of Ga 2 I 3 . [ 4 ] Raman spectroscopy has also confirmed this assignment, as it aligned with those from a Ga 4 I 6 reference. [ 4 ] [ 7 ] Finally, power x-ray diffraction supports that this gallium monoiodide variant matches that of characteristic Ga 2 I 3, which is different from that of GaI 2 . [ 4 ]
[Ga 0 ] 2 [Ga + ][GaI 4 − ] converts to [Ga 0 ] 2 [Ga + ] 2 [Ga 2 I 6 2- ] over time. [ 4 ]
Gallium monoiodide is used as a precursor for a variety of reactions, acting as a lewis acid and a reducing agent . Early-on, gallium monoiodide was shown to produce alkylgallium diiodides via oxidative addition by reacting liquid gallium metal and iodine in the presence of an alkyl iodide. [ 1 ] [ 2 ] [ 8 ] Since then, other organogallium complexes have been synthesized, as well as Lewis base adducts and gallium based clusters. [ 8 ]
Gallium monoiodide reacts with various monodentate Lewis bases to form Ga(II), Ga(III), or mixed valent compounds, as well as gallium-based dimers and trimers. For example, gallium monoiodide can react with primary, secondary, and tertiary amines , secondary or tertiary phosphines or ethers to form Ga(II)-Ga(II) dimers. [ 2 ] [ 8 ] [ 10 ] Gallium monoiodide can also react with triphenylphosphine (PPh 3 ) to form Ga(III)I 3 PPh 3 . [ 2 ] It also reacts with the less sterically hindered triethylphosphine (PEt 3 ) to form a Ga(II)-Ga(I)-Ga(II) mixed valent complex with datively coordinated PEt 3 ligands. [ 8 ] [ 10 ] These reactions are believed to be a disproportionation , as gallium metal is produced in these reactions. [ 9 ]
Gallium monoiodide reacts with triphenylstibine to produce an SbPh 3 fragment datively bonded to a GaPhI 2 fragment. [ 11 ] The difference in reactivity between PPh 3 and SbPh 3 , a heavy atom analogue of PPh 3 , can be attributed to a weaker Sb-C bond, allowing for transfer of a phenyl group from antimony to gallium. This suggests that gallium monoiodide can be used as a reducing agent as well. [ 8 ] [ 11 ]
N-heterocyclic carbenes reacts with gallium monoiodide to form a complex with a sterically hindered isopropyl ligand. [ 9 ] However, gallium monoiodide reacts with diazabutadienes and subsequent reduction by potassium metal to form Ga analogs of N-heterocyclic carbenes. [ 8 ] Other Ga-based carbenes can be produced from gallium monoiodide precursor using Li( NacNac ). [ 8 ]
Gallium monoiodide reacts with multidentate Lewis bases, such as bipyridine , phenyl-terpyridine, and bis(imino)pyridine ligands to form Ga(III) complexes. [ 8 ] [ 12 ] Crystallographically, the bipyridine derivative has a distorted octahedral geometry, with a Ga–N bond length of 2.063 Å. The phenyl-terpyridine derivative adopts a distorted trigonal bipyramidal geometry where the two equatorial Ga–N bonds (as drawn) are longer than the axial Ga-N bond, with 2.104 Å and 2.007(5) Å, respectively. The average Ga-N bond length (2.071 Å) is similar to that of a neutral GaCl 3 (terpy) Lewis base adduct (2.086 Å). [ 13 ] The bis(imino)pyridine derivative has a distorted square-based pyramidal geometry. Like for the phenyl-terpyridine derivative, the equatorial imino Ga-N bonds (2.203 Å) are longer than the axial pyridyl Ga-N bond (2.014(7) A˚). [ 12 ] Despite these similar reactivities and bond characteristics, when gallium monoiodide was reacted with imino-substituted pyridines (RN=C(H)Py), unique reactivity was observed. Reductive coupling of the imino-substituted pyridines formed diamido-digallium(III) complexes. [ 12 ] These reactions display the ability of gallium monoiodides to form new C-C bonds .
Gallium monoiodide can also be used as a precursor to form gallium-based heterocycles. Reactions with diazabutadienes , {RN=C(H)} 2 , forms monomers or dimers based on the substituents on the diazabutadienes. More sterically hindered substituents such as tert-butyl have resulted in the formation of gallium(II) dimers, whereas reactions with alkyl or aryl substituted diazabutadienes have formed Ga(III) monomers. [ 8 ] Gallium monoiodide can be reacted with phenyl-substituted 1,4-diazabuta-1,3-dienes to form a gallium heterocycle with a diazabutadiene monoanion. [ 14 ] EPR spectroscopy has revealed that the diazabutadiene fragment is a paramagnetic monoanionic species rather than an ene-diamido dianion or a neutral ligand. [ 14 ] Thus, gallium monoiodide undergoes a disproportionation reaction to form a gallium(III) complex with deposition of a gallium metal. [ 8 ] [ 14 ] Upon further reaction with a 1,4-dilithiated diazabutadiene, this gallium heterocycle forms a new complex with the diazabutadiene monoanion fragment datively bonded to the gallium center and an ene-diamido dianion covalently bonded to the Ga center. [ 14 ]
One very important reactivity of this gallium(III) heterocycle is its ability to access gallium analogues of N-heterocyclic carbenes upon reduction with potassium metal. [ 15 ] Although a gallium analogue of N-heterocyclic carbenes had been synthesized previously, [ 16 ] having access to heavier analogues of N-heterocylic carbenes from a synthetically more facile gallium monoiodide route has opened new avenues in coordination chemistry, such as access to new Ga-M bonds. [ 17 ] [ 18 ] [ 19 ]
Gallium monoiodide can also be used to access six-membered gallium(I) heterocycles that have parallels to gallium analogues of N-heterocyclic carbenes. These neutral gallium(I) heterocycles can be synthesized by reacting gallium monoiodide and Li[nacnac]. [ 18 ] [ 20 ]
Gallium monoiodide can easily be converted to half-sandwich complexes, (pentamethylcyclopentadienyl)gallium(I) and cyclopentadienylgallium. [ 21 ] (Pentamethylcyclopentadienyl)gallium(I) can be easily produced by reacting gallium monoiodide with a potassium salt of the desired ligand under toluene to avoid side products. [ 22 ] [ 8 ]
Cyclopentadienylgallium, which is less sterically hindered than (pentamethylcyclopentadienyl)gallium(I), can also be accessed using a gallium monoiodide. This ligand can be synthesized with a metathesis reaction of NaCp with gallium monoiodide. [ 23 ] This cyclopentadienylgallium ligand has been used to access a GaCp 2 I complex with datively bonded cyclopentadienylgallium. This complex showcases an uncommon donor-acceptor Ga-Ga bond. Cyclopentadienylgallium can also be used to access a Lewis acid B(C 6 F 5 ) 3 complex with a datively bonded cyclopentadienylgallium ligand. [ 23 ] For both of these two complexes, the (pentamethylcyclopentadienyl)gallium(I) analogues have been synthesized and x-ray crystallography has supported that, as expected, (pentamethylcyclopentadienyl)gallium(I) is a slightly stronger donor than cyclopentadienylgallium.
Like (pentamethylcyclopentadienyl)gallium(I), cyclopentadienylgallium can also coordinate to transition metal complexes such as Cr(CO) 5 (cyclooctene) or Co 2 (CO) 8 to yield CpGa–Cr(CO) 5 or (thf)GaCp{Co(CO) 4 } 2 . [ 24 ] For CpGa–Cr(CO) 5 , the Ga-Cr bond length (239.6 pm) is similar to that for a (pentamethylcyclopentadienyl)gallium(I) analogue (240.5 pm). For this complex, the trans effect is also observed, where the Cr-CO bond trans to the cyclopentadienylgallium ligand is contracted (186 pm) relative to the cis Cr-CO bonds (189.5 pm). While cyclopentadienylgallium can act as a terminal ligand similar to (pentamethylcyclopentadienyl)gallium(I), it was determined that cyclopentadienylgallium analogues react faster than their (pentamethylcyclopentadienyl)gallium(I) counterparts. This can be attributed to the lower steric bulk of cyclopentadienylgallium. [ 24 ]
Unlike reactivity with Cr(CO) 5 (cyclooctene), reactivities of (pentamethylcyclopentadienyl)gallium(I) and cyclopentadienylgallium with Co 2 (CO) 8 diverge significantly. [ 24 ] Dicobalt octacarbonyl , or Co 2 (CO) 8 , exists in various isomeric states. One such isomer contains two bridging CO ligands. When (pentamethylcyclopentadienyl)gallium(I) reacts with Co 2 (CO) 8 , two equivalents of CO gas are released, forming (CO) 3 Co[ μ 2 -( η 5 -GaCp*)] 2 -Co(CO) 3 . This is a derivative of the dicobalt octacarbonyl complex where the bridging CO moieties are replaced by bridging (pentamethylcyclopentadienyl)gallium(I) moieties. [ 25 ] On the other hand, cyclopentadienylgallium enables oxidative addition to Co 2 (CO) 8 to form (thf)GaCp{Co(CO) 4 } 2 , where gallium has sigma interactions to two Co(CO) 4 units. The average Ga–Co bond length is 248.5 pm and gallium is in a formally +3 oxidation state in this new complex. [ 25 ] Overall, straightforward synthesis of cyclopentadienylgallium from a gallium monoiodide precursor has many merits in expanding the scope of transition metal chemistry with lower valent species.
A variety of gallium clusters have also been synthesized from gallium monoiodide. [ 26 ] These clusters have often been isolated as salts with bulky silyl or germyl anions, such as [Si(SiMe 3 ) 3 ] − . [ 8 ] An example of an isolated gallium cluster is [Ga 9 {Si(SiMe 3 ) 3 } 6 ] − , which has a pentagonal bipyramidal polyhedral structure. It is synthesized by reacting gallium monoiodide with Li(thf) 3 Si(SiMe 3 ) 3 in toluene at -78 ˚C. [ 8 ] [ 27 ] This reaction has been shown to access a wide array of products, which may be attributed to the wide range of gallium monoiodide compositions that have been subsequently probed. Of these products, [Ga 9 {Si(SiMe 3 ) 3 } 6 ] − is especially unique because Ga was found to have a very low average oxidation state (0.56) and also because this cluster has fewer R substituents than polyhedron vertices. [ 27 ] Other clusters that been isolated via similar reaction pathways include [Ga 10 {Si(SiMe 3 ) 3 } 6 ], which is a conjuncto- polyhedral cluster , and a closo-silatetragallane anion, which contains three 2-electron-2-center and three 2-electron-3-center bonds . [ 8 ] [ 28 ] [ 29 ] Interestingly, this latter species can only be synthesized when sub-stoichiometric quantities of I 2 are utilized to access a "Ga 2 I 3 " intermediate species. [ 29 ] This is equivalent to reacting liquid gallium metal and iodine to pre-completion, which, as explained above, accesses the [Ga 0 ] 2 [Ga + ] 2 [Ga 2 I 6 2- ] variant of gallium monoiodide. This highlights the versatility of the gallium monoiodide precursor in accessing a wide range of gallium-based complexes.
Gallium monoiodide can also form cluster-type compounds with transition metals precursors. One example is the reaction between gallium monoiodide and (2,6-Pmp 2 C 6 H 3 ) 2 Co, (Pmp = C 6 Me 5 ), which yields a nido-type cluster. [ 30 ] This molecule is structurally similar to cubane , where the corners are metal and bridging iodine atoms, with one corner removed. This is a particularly unique Co-GaI cluster due to its unusual geometry for transition metal compounds containing heavy group 13 atoms such as gallium. The bond critical points and bond paths, as computed with QTAIM analysis, support that while there are Co-Ga bonds, there are no Ga-Ga bonds. [ 30 ]
Finally, gallium monoiodide has been able to form clusters with heavy gold atoms by acting as a reducing reagent when combined with (pentamethylcyclopentadienyl)gallium(I) and triphenylphosphine-gold complexes(i.e. AuI(PPh 3 ) or AuCl(PPh 3 )). [ 8 ] [ 32 ] This cluster contained the first crystallographically confirmed Ga-Au bonds, consisting of a Au 3 cluster ligated by Ga ligands. In addition, NBO analysis showed that the charge on the galliums within the (pentamethylcyclopentadienyl)gallium(I) ligands were much higher than the charge on the Au atoms and the charge on the gallium atoms within the GaI 2 motifs. This suggests that non-bridging Ga-Au bonds are highly polarized, whereas the μ-bridging Ga-Au bonds are more non-polar covalent in character. [ 32 ] | https://en.wikipedia.org/wiki/GaI |
Gallium(III) iodide is the inorganic compound with the formula Ga I 3 . A yellow hygroscopic solid, it is the most common iodide of gallium. [ 3 ] In the chemical vapor transport method of growing crystals of gallium arsenide uses iodine as the transport agent. In the solid state, it exists as the dimer Ga 2 I 6 , with a diborane structure. [ 4 ] When vaporized, its forms GaI 3 molecules of D 3h symmetry where the Ga–I distance is 2.458 Angstroms . [ 5 ]
Gallium triiodide can be reduced with gallium metal to give a green-colored gallium(I) iodide . The nature of this species is unclear, but it is useful for the preparation of gallium(I) and gallium(II) compounds. [ 6 ] [ 7 ]
This inorganic compound –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/GaI3 |
Gallium nitrate (brand name Ganite) is the gallium salt of nitric acid with the chemical formula Ga(NO 3 ) 3 . It is a drug used to treat symptomatic hypercalcemia secondary to cancer. It works by preventing the breakdown of bone through the inhibition of osteoclast activity, thus lowering the amount of free calcium in the blood. [ 1 ] [ 2 ] Gallium nitrate is also used to synthesize other gallium compounds.
Gallium (Ga) was discovered in 1875 by P.É. Lecoq de Boisbaudran. [ 3 ] In most of its compounds, gallium is found with an oxidation number of 3+. Gallium chemically behaves similarly to iron 3+ when forming a coordination complex . [ 4 ] That means gallium(III) and iron(III) are similar in similar coordination number , electrical charge, ion diameter and electron configuration .
Gallium atoms are bound to the phosphates of DNA at low gallium concentrations, forming a stable complex. [ 5 ] Gallium competes with magnesium in DNA binding, since its DNA affinity is 100 times higher than that of magnesium. No interactions have been found between the metal and DNA bases. [ 6 ] According to Hedley et al., gallium inhibits replicative DNA synthesis, the major gallium-specific target probably being ribonucleotide reductase . [ 6 ] In addition to that, it was reported by Chitambar that gallium binds to transferrin more strongly than iron. The transferrin gallium complex inhibits DNA synthesis by acting on the M2 subunit of ribonucleotide reductase. [ 7 ] Gallium(III) seems to act as an antagonist to the actions of several ions (Ca 2+ , Mg 2+ , Fe 2+ and Zn 2+ ) in processes of cellular metabolism . The action of gallium on bone metabolism decreases hypercalcemia associated with cancer. However, gallium is mostly found within the cell as a salt in lysosomes .
Gallium nitrate is commercially available as the hydrate. The nonahydrate may also be prepared by dissolving gallium in nitric acid, followed by recrystallization. [ 8 ] The structure of gallium nitrate nonahydrate has been determined by X-ray crystallography. [ 9 ]
GaN powder was synthesized using a direct current (DC) non-transferred arc plasma. [ 10 ]
Gallium nitrate injection is a clear, colorless, odorless, sterile solution of gallium nitrate, a hydrated nitrate salt of the group IIIa element, gallium. The stable, nonahydrate, Ga(NO 3 ) 3 •9H 2 O is a white, slightly hygroscopic, crystalline powder of molecular weight 417.87, that is readily soluble in water. Each mL of Ganite (gallium nitrate injection) contains gallium nitrate 25 mg (on an anhydrous basis) and sodium citrate dihydrate 28.75 mg. The solution may contain sodium hydroxide or hydrochloric acid for pH adjustment to 6.0-7.0. [ 11 ]
Use of higher doses of gallium nitrate than recommended may cause nausea , vomiting and increases risk of chronic kidney disease . In the case of overdose, serum calcium should be monitored, patients should receive vigorous hydration for 2–3 days and any further drug administrations should be discontinued. [ 11 ]
The action of gallium in gallium nitrate on bone metabolism decreases the hypercalcemia associated with cancer. Gallium inhibits osteoclastic activity and therefore decreases hydroxyapatite crystal formation [ citation needed ] , with adsorption of gallium onto the surfaces of hydroxyapatite crystals. [ 12 ] Also, the increased concentration of gallium in the bone leads to increasing the synthesis of collagen as well as the formation of the bone tissue inside the cell. It has been reported that a protracted infusion was effective against cancer-associated hypercalcemia. [ 13 ] Preliminary studies in bladder carcinoma , carcinoma of the urothelium and lymphomas are also promising. [ 14 ] Another interesting schedule of subcutaneous injection with low doses of gallium nitrate has been proposed, especially for the treatment of bone metastases , but the definitive results have not yet been published. [ 15 ]
Gallium nitrate can react with reducing agents to generate heat and products that may be gaseous. The products may themselves be capable of further reactions (such as combustion in the air). The chemical reduction of materials in this group can be rapid, but often requires initiation of heat, catalyst and addition of a solvent. Explosive mixtures of gallium nitrate with reducing agents often persist unchanged for long periods if initiation is prevented. Some inorganic oxidizing agents such as gallium nitrate are salts of metals that are soluble in water; dissolution dilutes but does not nullify the oxidizing power of such materials. Generally, inorganic oxidizing agents can react violently with active metals, cyanides , esters , and thiocyanates . [ 11 ]
Adverse renal effects have been reported in about 12.5% of patients treated with gallium nitrate. Two patients receiving gallium nitrate and one patient receiving calcitonin developed acute renal failure in a controlled trial of patients with cancer-related hypercalcemia. Also, it was reported that gallium nitrate should not be administered to patients with serum creatinine >2.5 mg/dL. [ 11 ]
In a controlled trial of patients, it was noticed a decrease in mean systolic and diastolic blood pressure after the treatment with gallium nitrate. The decrease in blood pressure was asymptomatic and did not require specific treatment. [ 11 ]
High doses of gallium nitrate were associated with anemia when used in treating patients for advanced cancer. In results, several patients have received red blood cell transfusions . [ 11 ] | https://en.wikipedia.org/wiki/GaN3O9 |
Gallium phosphate (GaPO 4 or gallium orthophosphate) is a colorless trigonal crystal with a hardness of 5.5 on the Mohs scale . GaPO 4 is isotypic with quartz , possessing very similar properties, but the silicon atoms are alternately substituted with gallium and phosphorus , thereby doubling the piezoelectric effect . GaPO 4 has many advantages over quartz for technical applications, like a higher electromechanical coupling coefficient in resonators , due to this doubling.
Contrary to quartz, GaPO 4 is not found in nature. Therefore, a hydrothermal process must be used to synthesize the crystal.
GaPO 4 possesses, in contrast to quartz, no α-β phase transition , thus the low temperature structure (structure like α-quartz) of GaPO 4 is stable up to 970°C, as are most of its other physical properties. Around 970°C another phase transition occurs which changes the low quartz structure into another structure similar with cristobalite .
The specific structure of GaPO 4 shows the arrangement of tetrahedrons consisting of GaO 4 and PO 4 that are slightly tilted. Because of the helical arrangement of these tetrahedrons, two modifications of GaPO 4 exist with different optical rotation ( left and right ).
GaPO 4 does not occur in nature; thus it must be grown synthetically. Presently, only one company in Austria produces these crystals commercially.
Pressure sensors based on quartz have to be cooled with water for applications at higher temperatures (above 300°C). Starting in 1994 it was possible to substitute these big sensors with miniaturized, non cooled ones, based on GaPO 4 .
Further exceptional properties of GaPO 4 for applications at high temperatures include its nearly temperature independent piezo effect and excellent electrical insulation up to 900°C. For bulk resonator applications, this crystal exhibits temperature compensated cuts of up to 500°C while having Q factors comparable with quartz. Due to these material properties, GaPO 4 is very suitable for piezoelectric pressure sensors at high temperatures and for high temperature microbalance . | https://en.wikipedia.org/wiki/GaPO4 |
Gallium(II) selenide ( Ga Se ) is a chemical compound . It has a hexagonal layer structure, similar to that of GaS . [ 1 ] It is a photoconductor, [ 2 ] a second harmonic generation crystal in nonlinear optics , [ 3 ] and has been used as a far-infrared conversion material [ 4 ] at 14–31 THz and above. [ 5 ]
It is said to have potential for optical applications [ 6 ] but the exploitation of this potential has been limited by the ability to readily grow single crystals [ 7 ] Gallium selenide crystals show great promise as a nonlinear optical material and as a photoconductor . Non-linear optical materials are used in the frequency conversion of laser light . Frequency conversion involves the shifting of the wavelength of a monochromatic source of light, usually laser light, to a higher or lower wavelength of light that cannot be produced from a conventional laser source.
Several methods of frequency conversion using non-linear optical materials exist. Second harmonic generation leads to doubling of the frequency of infrared carbon dioxide lasers . In optical parametric generation, the wavelength of light is doubled. Near-infrared solid-state lasers are usually used in optical parametric generations. [ 8 ]
One original problem with using gallium selenide in optics is that it is easily broken along cleavage lines and thus it can be hard to cut for practical application. It has been found, however, that doping the crystals with indium greatly enhances their structural strength and makes their application much more practical. [ 7 ] There remain, however, difficulties with crystal growth that must be overcome before gallium selenide crystals may become more widely used in optics.
Single layers of gallium selenide are dynamically stable two-dimensional semiconductors, in which the valence band has an inverted Mexican-hat shape, leading to a Lifshitz transition as the hole-doping is increased. [ 9 ]
The integration of gallium selenide into electronic devices has been hindered by its air sensitivity. Several approaches have been developed to encapsulate GaSe mono- and few-layers, leading to improved chemical stability and electronic mobility. [ 10 ] [ 11 ] [ 12 ]
Synthesis of GaSe nanoparticles is carried out by the reaction of GaMe 3 with trioctylphosphine selenium (TOPSe) in a high temperature solution of trioctylphosphine (TOP) and trioctylphosphine oxide (TOPO). [ 13 ]
A solution of 15 g TOPO and 5 mL TOP is heated to 150 °C overnight under nitrogen, removing any water that may be present in the original TOP solution. This initial TOP solution is vacuum distilled at 0.75 torr, taking the fraction from 204 °C to 235 °C. A TOPSe solution (12.5 mL TOP with 1.579 g TOPSe) is then added and the TOPO/TOP/TOPSe reaction mixture is heated to 278 °C. GaMe 3 (0.8 mL) dissolved in 7.5 mL distilled TOP is then injected. After injection, the temperature drops to 254 °C before stabilizing in the range of 266–268 °C after 10 minutes. GaSe nanoparticles then begin to form, and may be detected by a shoulder in the optical absorption spectrum in the 400–450 nm range. After this shoulder is observed, the reaction mixture is left to cool to room temperature to prevent further reaction. After synthesis and cooling, the reaction vessel is opened and extraction of the GaSe nanoparticle solution is accomplished by addition of methanol . The distribution of nanoparticles between the polar (methanol) and non-polar (TOP) phases depends on experimental conditions. If the mixture is very dry, nanoparticles partition into the methanol phase. If the nanoparticles are exposed to air or water, however, the particles become uncharged and become partitioned into the non-polar TOP phase. [ 13 ] | https://en.wikipedia.org/wiki/GaSe |
Gallium(II) telluride , GaTe, is a chemical compound of gallium and tellurium .
There is research interest in the structure and electronic properties of GaTe because of the possibility that it, or related compounds, may have applications in the electronics industry. Gallium telluride can be made by reacting the elements or by metal organic vapour deposition ( MOCVD ). [ 1 ]
GaTe produced from the elements has a monoclinic crystal structure. Each gallium atom is tetrahedrally coordinated by 3 tellurium and one gallium atom. The gallium-gallium bond length in the Ga 2 unit is 2.43 Angstrom. The structure consists of layers and can be formulated as Ga 2 4+ 2Te 2− . [ 2 ] The bonding within the layers is ionic-covalent and between the layers is predominantly van der Waals. GaTe is classified as a layered semiconductor (like GaSe and InSe which have similar structures). It is a direct band gap semiconductor with an energy of 1.65eV at room temperature. [ 3 ] A hexagonal form can be produced by low pressure metal organic vapour deposition ( MOCVD ) from alkyl gallium telluride cubane-type clusters e.g. from (t-butylGa( μ 3 -Te)) 4 . The core consists of a cube of eight atoms, four gallium, and four tellurium atoms. Each gallium has an attached t-butyl group and three adjacent tellurium atoms and each tellurium has three adjacent gallium atoms. The hexagonal form, which is closely related to the monoclinic form, containing Ga 2 4+ units, converts to the monoclinic form when annealed at 500 °C. [ 1 ]
Greenwood, Norman N. ; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann . ISBN 978-0-08-037941-8 .
This inorganic compound –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/GaTe |
The gab operon is responsible for the conversion of γ-aminobutyrate (GABA) to succinate . The gab operon comprises three structural genes – gabD , gabT and gabP – that encode for a succinate semialdehyde dehydrogenase, GABA transaminase and a GABA permease respectively. There is a regulatory gene csiR , downstream of the operon, that codes for a putative transcriptional repressor [ 1 ] and is activated when nitrogen is limiting.
The gab operon has been characterized in Escherichia coli and significant homologies for the enzymes have been found in organisms such as Saccharomyces cerevisiae , rats and humans. [ 2 ]
Limited nitrogen conditions activate the gab genes. The enzymes produced by these genes convert GABA to succinate, which then enters the TCA cycle, to be used as a source of energy. The gab operon is also known to contribute to polyamine homeostasis during nitrogen-limited growth and to maintain high internal glutamate concentrations under stress conditions. [ 3 ]
The gab operon consists of three structural genes:
The gabT gene encodes for GABA transaminase , an enzyme that catalyzes the conversion of GABA and 2-oxoglutarate into succinate semialdehyde and glutamate. Succinate semialdehyde is then oxidized into succinate by succinate semialdehyde dehydrogenase which is encoded by the gabP gene, thereby entering the TCA cycle as a usable source of energy. The gab operon contributes to homeostasis of polyamines such as putrescine , during nitrogen-limited growth. It is also known to maintain high internal glutamate concentrations under stress conditions.
The expression of genes in the operon is controlled by three differentially regulated promoters, [ 4 ] two of which are controlled by RpoS encoded sigma factor σ S .
The csiD promoter ( csiD p ) is essential for the expression of csiD (carbon starvation induced gene), ygaF and the gab genes. The csiD p is activated exclusively under carbon starvation conditions and stationary phase during which cAMP accumulates in high concentrations in the cell. The binding of cAMP to the cAMP receptor protein (CRP) causes CRP to bind tightly to a specific DNA site in the csiD p promoter, thus activating the transcription of genes downstream of the promoter.
The gabD p1 exerts an additional control over the gabDTP region. The gabD p1 is activated by σ S inducing conditions such as hyperosmotic and acidic shifts besides starvation and stationary phase. The gabD p2 promoter on the other hand, is σ 70 dependent and is activated under nitrogen limitation. In nitrogen limiting conditions, the nitrogen regulator Nac binds to a site located just upstream of the promoter expressing the gab genes. The gab genes upon activation produce enzymes that degrade GABA to succinate.
The presence of nitrogen activates the csiR gene located downstream of the gabP gene. The csiR gene encodes a protein that acts as a transcriptional repressor for csiD-ygaF-gab operon hence shutting off the GABA degradation pathway.
GABA degradation pathways exists in almost all eukaryotic organisms and takes place by the action of similar enzymes. Although, GABA in E.coli is predominantly used as an alternative source of energy through GABA degradation pathways, GABA in higher eukaryotic organisms acts as an inhibitory neurotransmitter and also as regulator of muscle tone. GABA degradation pathways in eukaryotes are responsible for the inactivation of GABA. | https://en.wikipedia.org/wiki/Gab_operon |
In mathematical logic and computer science , Gabbay's separation theorem , named after Dov Gabbay , states that any arbitrary temporal logic formula can be rewritten in a logically equivalent "past → future" form. I.e. the future becomes what must be satisfied. [ 1 ] This form can be used as execution rules; a MetateM program is a set of such rules. [ 2 ]
This mathematical logic -related article is a stub . You can help Wikipedia by expanding it .
This computer science article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Gabbay's_separation_theorem |
Gabedit is a graphical user interface to GAMESS (US) , Gaussian , MOLCAS , MOLPRO , MPQC , OpenMopac , PC GAMESS , ORCA and Q-Chem computational chemistry packages. | https://en.wikipedia.org/wiki/Gabedit |
A Gabriel's horn (also called Torricelli's trumpet ) is a type of geometric figure that has infinite surface area but finite volume . The name refers to the Christian tradition where the archangel Gabriel blows the horn to announce Judgment Day . The properties of this figure were first studied by Italian physicist and mathematician Evangelista Torricelli in the 17th century.
These colourful informal names and the allusion to religion came along later. [ 1 ] Torricelli's own name for it is to be found in the Latin title of his paper De solido hyperbolico acuto , written in 1643, a truncated acute hyperbolic solid , cut by a plane. [ 2 ] Volume 1, part 1 of his Opera geometrica published the following year included that paper and a second more orthodox (for the time) Archimedean proof of its theorem about the volume of a truncated acute hyperbolic solid. [ 2 ] [ 3 ] This name was used in mathematical dictionaries of the 18th century, including "Hyperbolicum Acutum" in Harris' 1704 dictionary and in Stone's 1726 one, and the French translation Solide Hyperbolique Aigu in d'Alembert's 1751 one. [ 1 ]
Although credited with primacy by his contemporaries, Torricelli was not the first to describe an infinitely long shape with a finite volume or area. [ 4 ] The work of Nicole Oresme in the 14th century had either been forgotten by, or was unknown to them. [ 4 ] Oresme had posited such things as an infinitely long shape constructed by subdividing two squares of finite total area 2 using a geometric series and rearranging the parts into a figure, infinitely long in one dimension, comprising a series of rectangles. [ 5 ]
Gabriel's horn is formed by taking the graph of y = 1 x , {\displaystyle y={\frac {1}{x}},} with the domain x ≥ 1 {\displaystyle x\geq 1} and rotating it in three dimensions about the x axis. The discovery was made using Cavalieri's principle before the invention of calculus , but today, calculus can be used to calculate the volume and surface area of the horn between x = 1 and x = a , where a > 1 . [ 6 ] Using integration (see Solid of revolution and Surface of revolution for details), it is possible to find the volume V and the surface area A : V = π ∫ 1 a ( 1 x ) 2 d x = π ( 1 − 1 a ) , {\displaystyle V=\pi \int _{1}^{a}\left({\frac {1}{x}}\right)^{2}\,\mathrm {d} x=\pi \left(1-{\frac {1}{a}}\right),} A = 2 π ∫ 1 a 1 x 1 + ( − 1 x 2 ) 2 d x > 2 π ∫ 1 a d x x = 2 π ⋅ [ ln x ] 1 a = 2 π ln a . {\displaystyle A=2\pi \int _{1}^{a}{\frac {1}{x}}{\sqrt {1+\left(-{\frac {1}{x^{2}}}\right)^{2}}}\,\mathrm {d} x>2\pi \int _{1}^{a}{\frac {\mathrm {d} x}{x}}=2\pi \cdot \left[\ln x\right]_{1}^{a}=2\pi \ln a.}
The value a can be as large as required, but it can be seen from the equation that the volume of the part of the horn between x = 1 and x = a will never exceed π ; however, it does gradually draw nearer to π as a increases. Mathematically, the volume approaches π as a approaches infinity. Using the limit notation of calculus, [ 7 ] lim a → ∞ V = lim a → ∞ π ( 1 − 1 a ) = π ⋅ lim a → ∞ ( 1 − 1 a ) = π . {\displaystyle \lim _{a\to \infty }V=\lim _{a\to \infty }\pi \left(1-{\frac {1}{a}}\right)=\pi \cdot \lim _{a\to \infty }\left(1-{\frac {1}{a}}\right)=\pi .}
The surface area formula above gives a lower bound for the area as 2 π times the natural logarithm of a . There is no upper bound for the natural logarithm of a , as a approaches infinity. That means, in this case, that the horn has an infinite surface area. That is to say, [ 7 ] lim a → ∞ A ≥ lim a → ∞ 2 π ln a = ∞ . {\displaystyle \lim _{a\to \infty }A\geq \lim _{a\to \infty }2\pi \ln a=\infty .}
Torricelli's original non-calculus proof used an object, slightly different to the aforegiven, that was constructed by truncating the acute hyperbolic solid with a plane perpendicular to the x axis and extending it from the opposite side of that plane with a cylinder of the same base. [ 8 ] Whereas the calculus method proceeds by setting the plane of truncation at x = 1 {\displaystyle x=1} and integrating along the x axis, Torricelli proceeded by calculating the volume of this compound solid (with the added cylinder) by summing the surface areas of a series of concentric right cylinders within it along the y axis and showing that this was equivalent to summing areas within another solid whose (finite) volume was known. [ 9 ]
In modern terminology this solid was created by constructing a surface of revolution of the function (for strictly positive b ) [ 9 ]
y = { 1 c , where 0 ≤ x ≤ b , 1 x , where b ≤ x . {\displaystyle \quad {}y={\begin{cases}{\dfrac {1}{c}},&{\text{where }}0\leq x\leq b,\\{\dfrac {1}{x}},&{\text{where }}b\leq x.\end{cases}}}
and Torricelli's theorem was that its volume is the same as the volume of the right cylinder with height 1 / b {\displaystyle 1/b} and radius 2 {\displaystyle {\sqrt {2}}} : [ 9 ] [ 8 ]
Theorem. An acute hyperbolic solid, infinitely long, cut by a plane [perpendicular] to the axis, together with the cylinder of the same base, is equal to that right cylinder of which the base is the latus versum (that is, the axis) of the hyperbola, and of which the altitude is equal to the radius of the basis of this acute body.
Torricelli showed that the volume of the solid could be derived from the surface areas of this series of concentric right cylinders whose radii were 1 / b ≥ r ≥ 0 {\displaystyle 1/b\geq r\geq 0} and heights h = 1 / r {\displaystyle h=1/r} . [ 9 ] Substituting in the formula for the surface areas of (just the sides of) these cylinders yields a constant surface area for all cylinders of 2 π r h = 2 π r × 1 / r = 2 π {\displaystyle 2\pi rh=2\pi r\times 1/r=2\pi } . [ 9 ] This is also the area of a circle of radius 2 , {\displaystyle {\sqrt {2}},} and the nested surfaces of the cylinders (filling the volume of the solid) are thus equivalent to the stacked areas of the circles of radius 2 {\displaystyle {\sqrt {2}}} stacked from 0 to 1 / b {\displaystyle 1/b} , and hence the volume of the aforementioned right cylinder, which is known to be V = π r 2 h = π ( 2 ) 2 × 1 / b = 2 π / b {\displaystyle V=\pi r^{2}h=\pi ({\sqrt {2}})^{2}\times 1/b=2\pi /b} : [ 9 ]
Propterea omnes simul superficies cylindricae, hoc est ipsum solidum acutum e b d {\displaystyle ebd} , una cum cylindro basis f e d c {\displaystyle fedc} , aequale erit omnibus circulis simul, hoc est cylindro a c g h {\displaystyle acgh} . Quod erat etc.
(Therefore all the surfaces of the cylinders taken together, that is the acute solid E B D {\displaystyle EBD} itself, is the same as the cylinder of base F E D C {\displaystyle FEDC} , which will be equal to all its circles taken together, that is to cylinder A C G H {\displaystyle ACGH} .)
(The volume of the added cylinder is of course V c = π r 2 × h = π ( 1 / b ) 2 × b = π / b {\displaystyle V_{c}=\pi r^{2}\times h=\pi (1/b)^{2}\times b=\pi /b} and thus the volume of the truncated acute hyperbolic solid alone is V s = V − V c = 2 π / b − π / b = π / b {\displaystyle V_{s}=V-V_{c}=2\pi /b-\pi /b=\pi /b} . If b = 1 {\displaystyle b=1} , as in the modern calculus derivation, V s = π {\displaystyle V_{s}=\pi } .)
In the Opera geometrica this is one of two proofs of the volume of the (truncated) acute hyperbolic solid. [ 3 ] The use of Cavalieri's indivisibles in this proof was controversial at the time and the result shocking (Torricelli later recording that Gilles de Roberval had attempted to disprove it); so when the Opera geometrica was published, the year after De solido hyperbolico acuto , Torricelli also supplied a second proof based upon orthodox Archimedean principles showing that the right cylinder (height 1 / b {\displaystyle 1/b} radius 2 {\displaystyle {\sqrt {2}}} ) was both upper and lower bound for the volume. [ 3 ] Ironically, this was an echo of Archimedes' own caution in supplying two proofs, mechanical and geometrical, in his Quadrature of the Parabola to Dositheus. [ 11 ]
When the properties of Gabriel's horn were discovered, the fact that the rotation of an infinitely large section of the xy plane about the x axis generates an object of finite volume was considered a paradox . While the section lying in the xy plane has an infinite area, any other section parallel to it has a finite area. Thus the volume, being calculated from the "weighted sum" of sections, is finite.
Another approach is to treat the solid as a stack of disks with diminishing radii . The sum of the radii produces a harmonic series that goes to infinity. However, the correct calculation is the sum of their squares. Every disk has a radius r = 1/ x and an area π r 2 or π/ x 2 . The series Σ 1/ x diverges , but the series Σ 1/ x 2 converges . In general, for any real ε > 0 , the series Σ 1/ x 1+ ε converges. (see Particular values of the Riemann zeta function for more detail on this result)
The apparent paradox formed part of a dispute over the nature of infinity involving many of the key thinkers of the time, including Thomas Hobbes , John Wallis , and Galileo Galilei . [ 12 ]
There is a similar phenomenon that applies to lengths and areas in the plane. The area between the curves 1/ x 2 and −1/ x 2 from 1 to infinity is finite, but the lengths of the two curves are clearly infinite.
In lecture 16 of his 1666 Lectiones , Isaac Barrow held that Torricelli's theorem had constrained Aristotle 's general dictum (from De Caelo book 1, part 6) that "there is no proportion between the finite and the infinite". [ 13 ] [ 14 ] Aristotle had himself, strictly speaking, been making a case for the impossibility of the physical existence of an infinite body rather than a case for its impossibility as a geometrical abstract. [ 13 ] Barrow had been adopting the contemporary 17th-century view that Aristotle's dictum and other geometrical axioms were (as he had said in lecture 7) from "some higher and universal science", underpinning both mathematics and physics. [ 15 ] Thus Torricelli's demonstration of an object with a relation between a finite (volume) and an infinite (area) contradicted this dictum, at least in part. [ 15 ] Barrow's explanation was that Aristotle's dictum still held, but only in a more limited fashion when comparing things of the same type, length with length, area with area, volume with volume, and so forth. [ 15 ] It did not hold when comparing things of two different genera (area with volume, for example) and thus an infinite area could be connected to a finite volume. [ 15 ]
Others used Torricelli's theorem to bolster their own philosophical claims, unrelated to mathematics from a modern viewpoint. [ 16 ] Ignace-Gaston Pardies in 1671 used the acute hyperbolic solid to argue that finite humans could comprehend the infinite, and proceeded to offer it as proof of the existences of God and immaterial souls. [ 16 ] [ 17 ] Since finite matter could not comprehend the infinite, Pardies argued, the fact that humans could comprehend this proof showed that humans must be more than matter, and have immaterial souls. [ 17 ] In contrast, Antoine Arnauld argued that because humans perceived a paradox here, human thought was limited in what it could comprehend, and thus is not up to the task of disproving divine, religious, truths. [ 16 ]
Hobbes' and Wallis' dispute was actually within the realm of mathematics: Wallis enthusiastically embracing the new concepts of infinity and indivisibles, proceeding to make further conclusions based upon Torricelli's work and to extend it to employ arithmetic rather than Torricelli's geometric arguments; and Hobbes claiming that since mathematics is derived from real world perceptions of finite things, "infinite" in mathematics can only mean "indefinite". [ 18 ] These led to strongly worded letters by each to the Royal Society and in Philosophical Transactions , Hobbes resorting to namecalling Wallis "mad" at one point. [ 19 ] In 1672 Hobbes tried to re-cast Torricelli's theorem as about a finite solid that was extended indefinitely , in an attempt to hold on to his contention that "natural light" (i.e. common sense) told us that an infinitely long thing must have an infinite volume. [ 19 ] This aligned with Hobbes' other assertions that the use of the idea of a zero-width line in geometry was erroneous, and that Cavalieri's idea of indivisibles was ill-founded. [ 20 ] Wallis argued that there existed geometrical shapes with finite area/volume but no centre of gravity based upon Torricelli, stating that understanding this required more of a command of geometry and logic "than M. Hobs [ sic ] is Master of". [ 21 ] He also restructured the arguments in arithmetical terms as the sums of arithmetic progressions , sequences of arithmetic infinitesimals rather than sequences of geometric indivisibles. [ 22 ]
Oresme had already demonstrated that an infinitely long shape can have a finite area where, as one dimension tends towards infinitely large, another dimension tends towards infinitely small. [ 23 ] In Barrow's own words "the infinite diminution of one dimension compensates for the infinite increase of the other", [ 23 ] in the case of the acute hyperbolic solid by the equation of the Apollonian hyperbola x y = 1 {\textstyle xy=1} . [ 24 ]
Since the horn has finite volume but infinite surface area, there is an apparent paradox that the horn could be filled with a finite quantity of paint and yet that paint would not be sufficient to coat its surface. [ 25 ] However, this paradox is again only an apparent paradox caused by an incomplete definition of "paint", or by using contradictory definitions of paint for the actions of filling and painting. [ 26 ]
One could be postulating a "mathematical" paint that is infinitely divisible (or can be infinitely thinned, or simply zero-width like the zero-width geometric lines that Hobbes took issue with) and capable of travelling at infinite speed, or a "physical" paint with the properties of paint in the real world. [ 26 ] With either one, the apparent paradox vanishes: [ 26 ]
With "mathematical" paint, it does not follow in the first place that an infinite surface area requires an infinite volume of paint, as infinite surface area times zero-thickness paint is indeterminate . [ 26 ]
With physical paint, painting the outside of the solid would require an infinite amount of paint because physical paint has a non-zero thickness. Torricelli's theorem does not talk about a layer of finite width on the outside of the solid, which in fact would have infinite volume. Thus there is no contradiction between infinite volume of paint and infinite surface area to cover. [ 26 ] It is also impossible to paint the interior of the solid, the finite volume of Torricelli's theorem, with physical paint, so no contradiction exists. [ 26 ] This is because physical paint can only fill an approximation of the volume of the solid. [ 27 ] [ 28 ] The molecules do not completely tile 3-dimensional space and leave gaps, and there is a point where the "throat" of the solid becomes too narrow for paint molecules to flow down. [ 26 ] [ 27 ]
Physical paint travels at a bounded speed and would take an infinite amount of time to flow down. [ 29 ] This also applies to "mathematical" paint of zero thickness if one does not additionally postulate it flowing at infinite speed. [ 29 ]
Other different postulates of "mathematical" paint, such as infinite-speed paint that gets thinner at a fast enough rate, remove the paradox too. For volume π {\displaystyle \pi } of paint, as the surface area to be covered A tends towards infinity, the thickness of the paint π / A {\displaystyle \pi /A} tends towards zero. [ 30 ] Like with the solid itself, the infinite increase of the surface area to be painted in one dimension is compensated by the infinite decrease in another dimension, the thickness of the paint.
"Gabriel's wedding cake" is a discrete version of Gabriel's horn, in which the continuous horn shape is approximated by an infinite series of cylinders, but shares the same overall properties as the continuous version; the name derives from the similarity to a multi-tiered wedding cake . It has been used as a teaching tool for students who are not yet familiar with calculus. [ 31 ] [ 32 ]
The converse of Torricelli's acute hyperbolic solid would be a surface of revolution that has a finite surface area but an infinite volume.
In response to Torricelli's theorem, after learning of it from Marin Mersenne , Christiaan Huygens and René-François de Sluse wrote letters to each other about extending the theorem to other infinitely long solids of revolution; which have been mistakenly identified as finding such a converse. [ 33 ]
Jan A. van Maanen, professor of mathematics at the University of Utrecht , reported in the 1990s that he once mis-stated in a conference at Kristiansand that de Sluse wrote to Huygens in 1658 that he had found such a shape: [ 34 ]
evi opera dedicator meansura vasculie, pondere non magni, quod interim helluo nullus ebibat
(I give the measurements of a drinking glass (or vase), that has a small weight, but that even the hardest drinker could not empty.)
to be told in response (by Tony Gardiner and Man-Keung Siu of the University of Hong Kong ) that any surface of rotation with a finite surface area would of necessity have a finite volume. [ 34 ]
Professor van Maanen realized that this was a misinterpretation of de Sluse's letter, and that what de Sluse was actually reporting that the solid "goblet" shape, formed by rotating the cissoid of Diocles and its asymptote about the y axis, had a finite volume (and hence "small weight") and enclosed a cavity of infinite volume. [ 35 ]
Huygens first showed that the area of the rotated two-dimensional shape (between the cissoid and its asymptote) was finite, calculating its area to be 3 times the area of the generating circle of the cissoid, and de Sluse applied Pappus's centroid theorem to show that the solid of revolution thus has finite volume, being a product of that finite area and the finite orbit of rotation. [ 35 ] The area being rotated is finite; de Sluse did not actually say anything about the surface area of the resultant rotated volume. [ 35 ]
Such a converse essentially cannot occur:
First, observe that f is bounded on D . For if lim x → a f ( x ) = ± ∞ {\displaystyle \lim _{x\to a}f(x)=\pm \infty } for some (possibly infinite) a , then there is an open neighbourhood of a on which the solid's surface area is infinite. Hence there is an M > 0 that bounds f on D : | f ( x ) | < M . {\displaystyle |f(x)|<M.}
The volume is then given by V = ∫ D f ( x ) ⋅ π f ( x ) d x ≤ ∫ D M 2 ⋅ 2 π f ( x ) d x ≤ M 2 ⋅ ∫ D 2 π f ( x ) 1 + f ′ ( x ) 2 d x = M 2 ⋅ S < ∞ . {\displaystyle {\begin{aligned}V&=\int _{D}f(x)\cdot \pi f(x)\,\mathrm {d} x\\&\leq \int _{D}{\frac {M}{2}}\cdot 2\pi f(x)\,\mathrm {d} x\\&\leq {\frac {M}{2}}\cdot \int _{D}2\pi f(x){\sqrt {1+f'(x)^{2}}}\,\mathrm {d} x={\frac {M}{2}}\cdot S<\infty .\end{aligned}}} | https://en.wikipedia.org/wiki/Gabriel's_horn |
The Gabriel synthesis is a chemical reaction that transforms primary alkyl halides into primary amines . Traditionally, the reaction uses potassium phthalimide . [ 1 ] [ 2 ] [ 3 ] The reaction is named after the German chemist Siegmund Gabriel . [ 4 ]
The Gabriel reaction has been generalized to include the alkylation of sulfonamides [ 5 ] and imides , followed by deprotection , to obtain amines (see Alternative Gabriel reagents ). [ 6 ] [ 7 ]
The alkylation of ammonia is often an unselective and inefficient route to amines. In the Gabriel method, phthalimide anion is employed as a surrogate of H 2 N − .
In this method, the sodium or potassium salt of phthalimide is N -alkylated with a primary alkyl halide to give the corresponding N -alkylphthalimide. [ 8 ] [ 9 ] [ 10 ]
Upon workup by acidic hydrolysis the primary amine is liberated as the amine salt. [ 11 ] Alternatively the workup may be via the Ing–Manske procedure , involving reaction with hydrazine . This method produces a precipitate of phthalhydrazide (C 6 H 4 (CO) 2 N 2 H 2 ) along with the primary amine:
Gabriel synthesis generally fails with secondary alkyl halides.
The first technique often produces low yields or side products. Separation of phthalhydrazide can be challenging. For these reasons, other methods for liberating the amine from the phthalimide have been developed. [ 12 ] Even with the use of the hydrazinolysis method, the Gabriel method suffers from relatively harsh conditions.
Many alternative reagents have been developed to complement the use of phthalimides. Most such reagents (e.g. the sodium salt of saccharin and di-tert-butyl-iminodicarboxylate ) are electronically similar to the phthalimide salts, consisting of imido nucleophiles . In terms of their advantages, these reagents hydrolyze more readily, extend the reactivity to secondary alkyl halides , and allow the production of secondary amines. [ 7 ] | https://en.wikipedia.org/wiki/Gabriel_synthesis |
The Gabriel–Colman rearrangement [ 1 ] is the chemical reaction of a saccharin or phthalimido ester with a strong base , such as an alkoxide , to form substituted isoquinolines . [ 2 ] First described in 1900 by chemists Siegmund Gabriel and James Colman, this rearrangement , a ring expansion , is seen to be general if there is an enolizable hydrogen on the group attached to the nitrogen , [ 3 ] since it is necessary for the nitrogen to abstract a hydrogen to form the carbanion that will close the ring. [ 4 ] As shown in the case of the general example below, X is either CO or SO 2 .
The reaction mechanism [ 5 ] [ 6 ] starts with an attack on the carbonyl group by a strong base, such as methoxide ion. The ring is then opened, forming an imide anion . This is then followed by a rapid isomerization of the imide anion to the carbanion. This is facilitated by the electron withdrawing effect of the substituent , which allows for greater stabilization of the adjacent carbanion with respect to the imide anion. The reaction is then completed when the methoxide is displaced by the ring closing, which results in a ring expansion. The rate determining step of this reaction is the attack of the carbanion on the carbomethoxy group.
The displacement of the methoxide is analogous to the displacement seen in the Dieckman condensation , as it is also a result of a ring closure.
Furthermore, tautomerization can occur on both of the carbonyl groups on the ring, with interconversion of the keto form to the enol form and the amide form to the imidic acid form.
The major application of the Gabriel–Colman rearrangement is in the formation of isoquinolines, due to the relatively high yield of the desired products. Therefore, studies in which either the product or an intermediate is an isoquinoline, the Gabriel–Colman rearrangement can be utilized. This reaction has been utilized in the production of intermediates for the synthesis of potential anti-inflammatory agents. [ 7 ] It has also been used in the study of phthalimide and saccharin derivatives as mechanism based inhibitors for three enzymes; the human leukocyte elastase , cathepsin G and proteinase 3 . [ 8 ] Phthalimide derivatives were seen to be inactive, while saccharin derivatives were seen to be fair inhibitors of these enzymes.
In a study [ 9 ] of the derivatives of 3-Oxo-1,2-benzoisothiazoline-2-acetic acid 1,1-dioxide, the Gabriel–Colman rearrangement was employed in the conversion of Isopropyl (1,1-dioxido-3-oxo-1,2-benzothiazol-2(3H)-yl)acetate to Isopropyl 4-hydroxy-2H-1,2-benzothiazine-3-carboxylate 1,1-dioxide, as shown above. This reaction has shown a percent yield of 85%.
In another study, [ 10 ] N-phthalimidoglycine ethyl ester was used to synthesize 4-hydroxyisoquinoline through use of a Gabriel–Colman rearrangement, as shown above. This reaction has shown a percent yield of 91%. The formation of this product was an important step in the study of the synthesis of 4,4′-functionalized 1,1′-biisoquinolines. | https://en.wikipedia.org/wiki/Gabriel–Colman_rearrangement |
The Growth Arrest and DNA Damage or gadd45 genes , including GADD45A (originally termed gadd45) GADD45B (originally termed MyD118), and GADD45G (originally termed CR6), are implicated as stress sensors that modulate the response of mammalian cells to genotoxic / physiological stress , and modulate tumor formation. Gadd45 proteins interact with other proteins implicated in stress responses, including PCNA , p21 , Cdc2 /CyclinB1, MEKK4 , and p38 kinase . [ 1 ] [ 2 ]
GADD45 proteins regulate differentiation at the two cell stage of embryogenesis , a key stage of zygotic genome activation . [ 3 ] GADD45 likely acts by promoting TET -mediated DNA demethylation leading to the induction of expression of genes necessary for zygote activation.
Overexpression of the GADD45 gene in the Drosophila melanogaster nervous system significantly increases longevity . [ 4 ] This longevity increase can be attributed to more efficient recognition and repair of spontaneous DNA damages generated by physiological processes and environmental factors.
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Gadd45 |
A gadget is a mechanical device or any ingenious article. [ 2 ] Gadgets are sometimes referred to as gizmos .
The etymology of the word is disputed. The word first appears as reference to an 18th-century tool in glassmaking that was developed as a spring pontil . [ 3 ] As stated in the glass dictionary published by the Corning Museum of Glass, a gadget is a "metal rod with a spring clip that grips the foot of a vessel and so avoids the use of a pontil". Gadgets were first used in the late 18th century. [ 4 ] According to the Oxford English Dictionary , there is anecdotal evidence for the use of "gadget" as a placeholder name for a technical item whose precise name one can't remember since the 1850s; with Robert Brown's 1886 book Spunyarn and Spindrift, A sailor boy's log of a voyage out and home in a China tea-clipper containing the earliest known usage in print. [ 5 ]
A widely circulated story holds that the word gadget was "invented" when Gaget, Gauthier & Cie, the company behind the repoussé construction of the Statue of Liberty (1886), made a small-scale version of the monument and named it after their firm; however this contradicts the evidence that the word was already used before in nautical circles, and the fact that it did not become popular, at least in the US, until after World War I. [ 5 ] Other sources cite a derivation from the French gâchette which has been applied to various pieces of a firing mechanism, or the French gagée , a small tool or accessory. [ 5 ]
The October 1918 issue of Notes and Queries contains a multi-article entry on the word "gadget" (12 S. iv. 187). H. Tapley-Soper of The City Library, Exeter , writes:
A discussion arose at the Plymouth meeting of the Devonshire Association in 1916 when it was suggested that this word should be recorded in the list of local verbal provincialisms. Several members dissented from its inclusion on the ground that it is in common use throughout the country; and a naval officer who was present said that it has for years been a popular expression in the service for a tool or implement, the exact name of which is unknown or has for the moment been forgotten. I have also frequently heard it applied by motor-cycle friends to the collection of fitments to be seen on motor cycles. 'His handle-bars are smothered in gadgets' refers to such things as speedometers, mirrors, levers, badges, mascots, &c., attached to the steering handles. The 'jigger' or short-rest used in billiards is also often called a 'gadget'; and the name has been applied by local platelayers to the 'gauge' used to test the accuracy of their work. In fact, to borrow from present-day Army slang, 'gadget' is applied to 'any old thing.' [ 6 ]
The usage of the term in military parlance extended beyond the navy. In the book Above the Battle by Vivian Drake, published in 1918 by D. Appleton & Co., of New York and London, being the memoirs of a pilot in the British Royal Flying Corps , there is the following passage: "Our ennui was occasionally relieved by new gadgets—'gadget' is the Flying Corps slang for invention! Some gadgets were good, some comic and some extraordinary." [ 7 ]
By the second half of the twentieth century, the term "gadget" had taken on the connotations of compactness and mobility. In the 1965 essay "The Great Gizmo" (a term used interchangeably with "gadget" throughout the essay), the architectural and design critic Reyner Banham defines the item as:
A characteristic class of US products––perhaps the most characteristic––is a small self-contained unit of high performance in relation to its size and cost, whose function is to transform some undifferentiated set of circumstances to a condition nearer human desires. The minimum of skills is required in its installation and use, and it is independent of any physical or social infrastructure beyond that by which it may be ordered from catalogue and delivered to its prospective user. A class of servants to human needs, these clip-on devices, these portable gadgets, have coloured American thought and action far more deeply––I suspect––than is commonly understood. [ 1 ]
The first atomic bomb was nicknamed the gadget by the Scientists of the Manhattan Project , tested at the Trinity site.
In the software industry, Gadget refers to computer programs that provide services without needing an independent application to be launched for each one, but instead run in an environment that manages multiple gadgets. There are several implementations based on existing software development techniques, like JavaScript , form input, and various image formats. Proprietary formats include Google Desktop , Google Gadgets , Microsoft Gadgets , the AmigaOS Workbench and dashboard software Apple Widgets .
The earliest [ citation needed ] documented use of the term gadget in context of software engineering was in 1985 by the developers of AmigaOS , the operating system of the Amiga computers ( intuition.library and also later gadtools.library ). It denotes what other technological traditions call GUI widget —a control element in graphical user interface . This naming convention remains in continuing use (as of 2008) since then.
The X11 [ 8 ] windows system 'Intrinsics' [ 9 ] also defines gadgets and their relationship to widgets (buttons, labels, etc.). The gadget was a windowless widget which was supposed to improve the performance of the application by reducing the memory load on the X server. A gadget would use the Window id of its parent widget and had no children of its own.
It is not known whether other software companies are explicitly drawing on that inspiration when featuring the word in names of their technologies or simply referring to the generic meaning. The word widget is older in this context. In the movie " Back to School " from 1986 by Alan Metter, there is a scene where an economics professor Dr. Barbay, wants to start for educational purposes a fictional company that produces "widgets: It's a fictional product." | https://en.wikipedia.org/wiki/Gadget |
Gadolinium is a chemical element ; it has symbol Gd and atomic number 64. It is a silvery-white metal when oxidation is removed. Gadolinium is a malleable and ductile rare-earth element . It reacts with atmospheric oxygen or moisture slowly to form a black coating. Gadolinium below its Curie point of 20 °C (68 °F) is ferromagnetic , with an attraction to a magnetic field higher than that of nickel . Above this temperature it is the most paramagnetic element. It is found in nature only in an oxidized form. When separated, it usually has impurities of the other rare earths because of their similar chemical properties.
Gadolinium was discovered in 1880 by Jean Charles de Marignac , who detected its oxide by using spectroscopy. It is named after the mineral gadolinite , one of the minerals in which gadolinium is found, itself named for the Finnish chemist Johan Gadolin . Pure gadolinium was first isolated by the chemist Félix Trombe in 1935.
Gadolinium possesses unusual metallurgical properties, to the extent that as little as 1% of gadolinium can significantly improve the workability and resistance to oxidation at high temperatures of iron, chromium , and related metals. Gadolinium as a metal or a salt absorbs neutrons and is, therefore, used sometimes for shielding in neutron radiography and in nuclear reactors .
Like most of the rare earths, gadolinium forms trivalent ions with fluorescent properties, and salts of gadolinium(III) are used as phosphors in various applications.
Gadolinium(III) ions in water-soluble salts are highly toxic to mammals. However, chelated gadolinium(III) compounds prevent the gadolinium(III) from being exposed to the organism, and the majority is excreted by healthy [ 9 ] kidneys before it can deposit in tissues. Because of its paramagnetic properties, solutions of chelated organic gadolinium complexes are used as intravenously administered gadolinium-based MRI contrast agents in medical magnetic resonance imaging .
The main uses of gadolinium, in addition to use as a contrast agent for MRI scans , are in nuclear reactors, in alloys, as a phosphor in medical imaging, as a gamma ray emitter, in electronic devices, in optical devices, and in superconductors.
Gadolinium is the eighth member of the lanthanide series. In the periodic table , it appears between the elements europium to its left and terbium to its right, and above the actinide curium . It is a silvery-white, malleable , ductile rare-earth element . Its 64 electrons are arranged in the configuration of [Xe]4f 7 5d 1 6s 2 , of which the ten 4f, 5d, and 6s electrons are valence .
Like most other metals in the lanthanide series, three electrons are usually available as valence electrons. The remaining 4f electrons are too strongly bound: this is because the 4f orbitals penetrate the most through the inert xenon core of electrons to the nucleus, followed by 5d and 6s, and this increases with higher ionic charge. Gadolinium crystallizes in the hexagonal close-packed α-form at room temperature. At temperatures above 1,235 °C (2,255 °F), it forms or transforms into its β-form, which has a body-centered cubic structure. [ 10 ]
The isotope gadolinium-157 has the highest thermal-neutron capture cross-section among any stable nuclide: about 259,000 barns . Only xenon-135 has a higher capture cross-section, about 2.0 million barns, but this isotope is radioactive . [ 11 ]
Gadolinium is believed to be ferromagnetic at temperatures below 20 °C (68 °F) [ 12 ] and is strongly paramagnetic above this temperature. In fact, at body temperature, gadolinium exhibits the greatest paramagnetic effect of any element. [ 13 ] There is evidence that gadolinium is a helical antiferromagnetic, rather than a ferromagnetic, below 20 °C (68 °F). [ 14 ] Gadolinium demonstrates a magnetocaloric effect whereby its temperature increases when it enters a magnetic field and decreases when it leaves the magnetic field. A significant magnetocaloric effect is observed at higher temperatures, up to about 300 kelvins , in the compounds Gd 5 (Si 1− x Ge x ) 4 . [ 15 ]
Individual gadolinium atoms can be isolated by encapsulating them into fullerene molecules, where they can be visualized with a transmission electron microscope . [ 16 ] Individual Gd atoms and small Gd clusters can be incorporated into carbon nanotubes . [ 17 ]
Gadolinium combines with most elements to form Gd(III) derivatives. It also combines with nitrogen, carbon, sulfur, phosphorus, boron, selenium, silicon, and arsenic at elevated temperatures, forming binary compounds. [ 18 ]
Unlike the other rare-earth elements, metallic gadolinium is relatively stable in dry air. However, it tarnishes quickly in moist air, forming a loosely-adhering gadolinium(III) oxide (Gd 2 O 3 ):
which spalls off, exposing more surface to oxidation.
Gadolinium is a strong reducing agent , which reduces oxides of several metals into their elements. Gadolinium is quite electropositive and reacts slowly with cold water and quite quickly with hot water to form gadolinium(III) hydroxide (Gd(OH) 3 ):
Gadolinium metal is attacked readily by dilute sulfuric acid to form solutions containing the colorless Gd(III) ions, which exist as [Gd(H 2 O) 9 ] 3+ complexes: [ 19 ]
In the great majority of its compounds, like many rare-earth metals , gadolinium adopts the oxidation state +3. However, gadolinium can be found on rare occasions in the 0, +1 and +2 oxidation states. All four trihalides are known. All are white, except for the iodide, which is yellow. Most commonly encountered of the halides is gadolinium(III) chloride (GdCl 3 ). The oxide dissolves in acids to give the salts, such as gadolinium(III) nitrate .
Gadolinium(III), like most lanthanide ions, forms complexes with high coordination numbers . This tendency is illustrated by the use of the chelating agent DOTA , an octa dentate ligand. Salts of [Gd(DOTA)] − are useful in magnetic resonance imaging . A variety of related chelate complexes have been developed, including gadodiamide .
Reduced gadolinium compounds are known, especially in the solid state. Gadolinium(II) halides are obtained by heating Gd(III) halides in presence of metallic Gd in tantalum containers. Gadolinium also forms the sesquichloride Gd 2 Cl 3 , which can be further reduced to GdCl by annealing at 800 °C (1,470 °F). This gadolinium(I) chloride forms platelets with layered graphite-like structure. [ 20 ]
Naturally occurring gadolinium is composed of six stable isotopes, 154 Gd, 155 Gd, 156 Gd, 157 Gd, 158 Gd and 160 Gd, and one radioisotope , 152 Gd, with the isotope 158 Gd being the most abundant (24.8% natural abundance ). The predicted double beta decay of 160 Gd has never been observed (an experimental lower limit on its half-life of more than 1.3×10 21 years has been measured [ 21 ] ).
Thirty-three radioisotopes of gadolinium have been observed, with the most stable being 152 Gd (naturally occurring), with a half-life of about 1.08×10 14 years, and 150 Gd, with a half-life of 1.79×10 6 years. All of the remaining radioactive isotopes have half-lives of less than 75 years. The majority of these have half-lives of less than 25 seconds. Gadolinium isotopes have four metastable isomers , with the most stable being 143m Gd ( t 1/2 = 110 seconds), 145m Gd ( t 1/2 = 85 seconds) and 141m Gd ( t 1/2 = 24.5 seconds).
The isotopes with atomic masses lower than the most abundant stable isotope, 158 Gd, primarily decay by electron capture to isotopes of europium . At higher atomic masses, the primary decay mode is beta decay , and the primary products are isotopes of terbium .
Gadolinium is named after the mineral gadolinite . Gadolinite was first chemically analyzed by the Finnish chemist Johan Gadolin in 1794. [ 22 ] [ 23 ] In 1802 German chemist Martin Klaproth gave gadolinite its name. [ 24 ] [ 10 ] In 1880, the Swiss chemist Jean Charles Galissard de Marignac observed the spectroscopic lines from gadolinium in samples of gadolinite (which actually contains relatively little gadolinium, but enough to show a spectrum) and in the separate mineral cerite . The latter mineral proved to contain far more of the element with the new spectral line. De Marignac eventually separated a mineral oxide from cerite, which he realized was the oxide of this new element. He designated the element with the provisional symbol Yα. The French chemist Paul-Émile Lecoq de Boisbaudran named the element "gadolinium" in 1886. [ 25 ] [ 26 ] [ 27 ] [ 28 ] The pure element was isolated in 1935 by Félix Trombe . [ 29 ]
Gadolinium is a constituent in many minerals, such as monazite and bastnäsite . The metal is too reactive to exist naturally. Paradoxically, as noted above, the mineral gadolinite actually contains only traces of this element. The abundance in the Earth's crust is about 6.2 mg/kg. [ 10 ] The main mining areas are in China, the US, Brazil, Sri Lanka, India, and Australia with reserves expected to exceed one million tonnes. World production of pure gadolinium is about 400 tonnes per year. The only known mineral with essential gadolinium, lepersonnite-(Gd) , is very rare. [ 30 ] [ 31 ]
Gadolinium is produced both from monazite and bastnäsite .
Gadolinium metal is obtained from its oxide or salts by heating it with calcium at 1,450 °C (2,640 °F) in an argon atmosphere. Sponge gadolinium can be produced by reducing molten GdCl 3 with an appropriate metal at temperatures below 1,312 °C (2,394 °F) (the melting point of Gd) at reduced pressure. [ 10 ]
Gadolinium has no large-scale applications, but it has a variety of specialized uses.
Because gadolinium has a high neutron cross-section, it is effective for use with neutron radiography and in shielding of nuclear reactors . It is used as a secondary, emergency shut-down measure in some nuclear reactors, particularly of the CANDU reactor type. [ 10 ] Gadolinium is used in nuclear marine propulsion systems as a burnable poison . The use of gadolinium in neutron capture therapy to target tumors has been investigated, and gadolinium-containing compounds have proven promising. [ 32 ]
Gadolinium possesses unusual metallurgic properties, with as little as 1% of gadolinium improving the workability of iron, chromium , and related alloys , and their resistance to high temperatures and oxidation . [ 33 ]
Gadolinium is paramagnetic at room temperature , with a ferromagnetic Curie point of 20 °C (68 °F). [ 12 ] Paramagnetic ions, such as gadolinium, increase nuclear spin relaxation rates, making gadolinium useful as a contrast agent for magnetic resonance imaging (MRI). Solutions of organic gadolinium complexes and gadolinium compounds are used as intravenous contrast agents to enhance images in medical and magnetic resonance angiography (MRA) procedures. Magnevist is the most widespread example. [ 34 ] [ 35 ] Nanotubes packed with gadolinium, called " gadonanotubes ", are 40 times more effective than the usual gadolinium contrast agent. [ 36 ] Traditional gadolinium-based contrast agents are un-targeted, generally distributing throughout the body after injection, but will not readily cross the intact blood–brain barrier . [ 37 ] Brain tumors , and other disorders that degrade the blood-brain barrier, allow these agents to penetrate into the brain and facilitate their detection by contrast-enhanced MRI . Similarly, delayed gadolinium-enhanced magnetic resonance imaging of cartilage uses an ionic compound agent, originally Magnevist , that is excluded from healthy cartilage based on electrostatic repulsion but will enter proteoglycan -depleted cartilage in diseases such as osteoarthritis . [ medical citation needed ]
Gadolinium is used as a phosphor in medical imaging. It is contained in the phosphor layer of X-ray detectors, suspended in a polymer matrix. Terbium - doped gadolinium oxysulfide (Gd 2 O 2 S:Tb) at the phosphor layer converts the X-rays released from the source into light. This material emits green light at 540 nm because of the presence of Tb 3+ , which is very useful for enhancing the imaging quality. The energy conversion of Gd is up to 20%, which means that one fifth of the X-ray energy striking the phosphor layer can be converted into visible photons. [ citation needed ] Gadolinium oxyorthosilicate (Gd 2 SiO 5 , GSO; usually doped by 0.1–1.0% of Ce ) is a single crystal that is used as a scintillator in medical imaging such as positron emission tomography , and for detecting neutrons. [ 38 ]
Gadolinium compounds were also used for making green phosphors for color TV tubes. [ 39 ]
Gadolinium-153 is produced in a nuclear reactor from elemental europium or enriched gadolinium targets. It has a half-life of 240 ± 10 days and emits gamma radiation with strong peaks at 41 keV and 102 keV. It is used in many quality-assurance applications, such as line sources and calibration phantoms, to ensure that nuclear-medicine imaging systems operate correctly and produce useful images of radioisotope distribution inside the patient. [ 40 ] It is also used as a gamma-ray source in X-ray absorption measurements and in bone density gauges for osteoporosis screening. [ citation needed ]
Gadolinium is used for making gadolinium yttrium garnet (Gd:Y 3 Al 5 O 12 ), which has microwave applications and is used in fabrication of various optical components and as substrate material for magneto-optical films. [ 41 ]
Gadolinium can also serve as an electrolyte in solid oxide fuel cells (SOFCs). Using gadolinium as a dopant for materials like cerium oxide (in the form of gadolinium-doped ceria ) gives an electrolyte having both high ionic conductivity and low operating temperatures.
Gadolinium is the standard reference material in the study of magnetic refrigeration near room temperature. [ 15 ] : 1528 Pure Gd itself exhibits a large magnetocaloric effect near its Curie temperature of 20 °C (68 °F), and this has sparked interest into producing Gd alloys having a larger effect and tunable Curie temperature. In Gd 5 (Si x Ge 1− x ) 4 , Si and Ge compositions can be varied to adjust the Curie temperature .
Gadolinium-based materials, such as Gd 5 (Si x Ge 1− x ) 4 , are currently the most promising materials, owing to their high Curie temperature and giant magneto-caloric effect.
Magnetic refrigeration could provide significant efficiency and environmental advantages over conventional refrigeration methods. [ 15 ]
Gadolinium barium copper oxide (GdBCO) is a superconductor [ 42 ] [ 43 ] [ 44 ] with applications in superconducting motors or generators such as in wind turbines. [ 45 ] It can be manufactured in the same way as the most widely researched cuprate high temperature superconductor, yttrium barium copper oxide (YBCO) and uses an analogous chemical composition (GdBa 2 Cu 3 O 7− δ ). [ 46 ] It was used in 2014 to set a new world record for the highest trapped magnetic field in a bulk high temperature superconductor , with a field of 17.6T being trapped within two GdBCO bulks. [ 47 ] [ 48 ]
Gadolinium is being investigated as a possible treatment for preventing lung tissue scarring in asthma . A positive effect has been observed in mice. [ 49 ]
Gadolinium is used for antineutrino detection in the Japanese Super-Kamiokande detector in order to sense supernova explosions. Low-energy neutrons that arise from antineutrino absorption by protons in the detector's ultrapure water are captured by gadolinium nuclei, which subsequently emit gamma rays that are detected as part of the antineutrino signature. [ 50 ]
Gadolinium gallium garnet (GGG, Gd 3 Ga 5 O 12 ) was used for imitation diamonds and for computer bubble memory . [ 51 ]
As a free ion, gadolinium is reported often to be highly toxic, but MRI contrast agents are chelated compounds and are considered safe enough to be used in most persons. The toxicity of free gadolinium ions in animals is due to interference with a number of calcium-ion channel dependent processes. The 50% lethal dose is about 0.34 mmol/kg (IV, mouse) [ 53 ] or 100–200 mg/kg. Toxicity studies in rodents show that chelation of gadolinium (which also improves its solubility) decreases its toxicity with regard to the free ion by a factor of 31 (i.e., the lethal dose for the Gd-chelate increases by 31 times). [ 54 ] [ 55 ] [ 56 ] It is believed therefore that clinical toxicity of gadolinium-based contrast agents (GBCAs [ 57 ] ) in humans will depend on the strength of the chelating agent; however this research is still not complete. [ when? ] About a dozen different Gd-chelated agents have been approved as MRI contrast agents around the world. [ 58 ] [ 59 ] [ 60 ]
Use of gadolinium-based contrast agents results in deposition of gadolinium in tissues of the brain, bone, skin, and other tissues in amounts that depend on kidney function , structure of the chelates (linear or macrocyclic) and the dose administered. [ 61 ] In patients with kidney failure, there is a risk of a rare but serious illness called nephrogenic systemic fibrosis (NSF) [ 62 ] that is caused by the use of gadolinium-based contrast agents. The disease resembles scleromyxedema and to some extent scleroderma . It may occur months after a contrast agent has been injected. Its association with gadolinium and not the carrier molecule is confirmed by its occurrence with various contrast materials in which gadolinium is carried by very different carrier molecules. Because of the risk of NSF, use of these agents is not recommended for any individual with end-stage kidney failure as they may require emergent dialysis.
Included in the current guidelines from the Canadian Association of Radiologists [ 63 ] are that dialysis patients should receive gadolinium agents only where essential and that they should receive dialysis after the exam. If a contrast-enhanced MRI must be performed on a dialysis patient, it is recommended that certain high-risk contrast agents be avoided but not that a lower dose be considered. [ 63 ] The American College of Radiology recommends that contrast-enhanced MRI examinations be performed as closely before dialysis as possible as a precautionary measure, although this has not been proven to reduce the likelihood of developing NSF. [ 64 ] The FDA recommends that potential for gadolinium retention be considered when choosing the type of GBCA used in patients requiring multiple lifetime doses, pregnant women, children, and patients with inflammatory conditions. [ 65 ]
Anaphylactoid reactions are rare, occurring in approximately 0.03–0.1%. [ 66 ]
Long-term environmental impacts of gadolinium contamination due to human usage are a topic of ongoing research. [ 67 ] [ 68 ]
Gadolinium has no known native biological role, but its compounds are used as research tools in biomedicine. Gd 3+ compounds are components of MRI contrast agents . [ 69 ] It is used in various ion channel electrophysiology experiments to block sodium leak channels and stretch activated ion channels. [ 70 ] Gadolinium has recently been used to measure the distance between two points in a protein via electron paramagnetic resonance , something that gadolinium is especially amenable to thanks to EPR sensitivity at w-band (95 GHz) frequencies. [ 71 ] | https://en.wikipedia.org/wiki/Gadolinium |
The gag-onc fusion protein [ 1 ] is a general term for a fusion protein formed from a group-specific antigen ('gag') gene and that of an oncogene ('onc'), a gene that plays a role in the development of a cancer. The name is also written as Gag-v-Onc , with "v" indicating that the Onc sequence resides in a viral genome. [ 1 ] Onc is a generic placeholder for a given specific oncogene, such as C-jun . (In the case of a fusion with C-jun, the resulting "gag-jun" protein is known alternatively as p65 ). [ 2 ]
Gag genes are part of a general architecture for retroviruses , viruses that replicate through reverse transcription , where the gag region of the genome encodes proteins that constitute the matrix, capsid and nucleocapsid of the mature virus particles. Like in HIV's replication cycle , these proteins are needed for viral budding from the host cell's plasma membrane, where the fully formed virions leave the cell to infect other cells. [ 3 ]
When a viral gene is introduced into the host cell and is sufficient to induce oncogenesis – the creation of cancerous cells – in the infected cell line, the gene is said to be a "viral transforming gene". [ 4 ] When this type of gene is translated to a protein, the protein is called a "transforming protein". Note that since the viral oncogenes originated from a host genome, the transformation event is different from transduction , which describes the process of introducing non-native genes to a host organism via a viral infection.
The Gag-v-Onc fusion protein from the Rous sarcoma virus illustrates the dual role that the fusion protein plays in the viral and host cellular life cycle. For example, the viral gene Src (as in "sarcoma") is not necessary for viral reproduction, but does affect virulence . Due to evidence [ 5 ] of conserved homology between the v-Src gene and its host (animal) genomes, and its non-essential status for viral reproduction, the v-Src gene is likely to have been acquired from a host genome and altered by subsequent mutations. [ 6 ] These subsequent mutations are responsible for the oncogenic capabilities of the virus, as the normal (host) version of the Src gene, c-Src promotes survival, angiogenesis , proliferation and invasion pathways. These native pathways are disrupted in the presence of the mutant Src gene (v-Src) such that oncogenesis becomes more likely for the infected host cells, since the v-Src gene is translated into a functionally distinct version of its host counterpart.
In the case of the murine leukemia viruses , a species of viruses capable of causing cancer in murines (mice), the viral life cycle can also be responsible for oncogenesis through a Gag-v-Onc fusion protein called "Mo-MuLV(src)", which is a Gag-v-Src protein capable of inducing oncogenesis in living mice. [ 7 ] | https://en.wikipedia.org/wiki/Gag-onc_fusion_protein |
Gag/pol translational readthrough site (or Retroviral readthrough element ) is a cis-regulatory element found in retroviruses. [ 1 ] The readthrough site facilitates the mechanism of translation readthrough of the stop codon at the gag-pol junction producing the gag and pol fusion protein in certain retroviruses .
Retroviruses whose gag and pol genes are in the same reading frame often depend upon approximately 5% read-through of the gag UAG termination codon to form the gag-pol polyprotein. This readthrough is usually dependent on a pseudoknot located eight nucleotides downstream of the stop codon (UAG). Sequence conservation is found in the second pseudoknot loop.
This genetics article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Gag/pol_translational_readthrough_site |
Gagik Shmavonyan ( Armenian : Գագիկ Շմավոնյան, [ 1 ] May 12, 1963) is Professor at National Polytechnic University of Armenia, [ 2 ] PhD in physics, D.Sc. in Engineering., [ 3 ] [ 4 ] [ 5 ] Consultant at Nanolabs (Philippines), Expert at Malta Council for Science and Technology, Science Fund of the Republic of Serbia, Cyprus Research Promotion Foundation, European Cooperation in Science and Technology (COST) and Science Committee of Armenia, as well as President/Founder of NanoHiTech Association.
He got his PhD in physics in 1996 and D.Sc in Engineering in 2009 at National Polytechnic University of Armenia. He did postdoc at National Taiwan University . He was an Invited/Visiting Professor/Scholar at the University of Hull , UK, Polytechnic of Milan, Como , Italy, University of Bremen , Germany, Free University Berlin , Germany, Trinity College Dublin , CRANN, Ireland, University of Santiago de Compostela , Spain, Institute of Nanoscience and Nanotechnology, National Center for Scientific Research "Demokritos" , Athens, Greece, University of Cergy-Pontoise , France, Eberhard Karls University of Tübingen, Germany. [ 6 ] | https://en.wikipedia.org/wiki/Gagik_Shmavonyan |
In mathematics , and in particular in mathematical analysis , the Gagliardo–Nirenberg interpolation inequality is a result in the theory of Sobolev spaces that relates the L p {\displaystyle L^{p}} -norms of different weak derivatives of a function through an interpolation inequality . The theorem is of particular importance in the framework of elliptic partial differential equations and was originally formulated by Emilio Gagliardo and Louis Nirenberg in 1958. The Gagliardo-Nirenberg inequality has found numerous applications in the investigation of nonlinear partial differential equations, and has been generalized to fractional Sobolev spaces by Haïm Brezis and Petru Mironescu in the late 2010s.
The Gagliardo-Nirenberg inequality was originally proposed by Emilio Gagliardo and Louis Nirenberg in two independent contributions during the International Congress of Mathematicians held in Edinburgh from August 14, 1958 through August 21, 1958. [ 1 ] [ 2 ] In the following year, both authors improved their results and published them independently. [ 3 ] [ 4 ] [ 5 ] Nonetheless, a complete proof of the inequality went missing in the literature for a long time. Indeed, to some extent, both original works of Gagliardo and Nirenberg do not contain a full and rigorous argument proving the result. For example, Nirenberg firstly included the inequality in a collection of lectures given in Pisa from September 1 to September 10, 1958. The transcription of the lectures was later published in 1959, and the author explicitly states only the main steps of the proof. [ 5 ] On the other hand, the proof of Gagliardo did not yield the result in full generality, i.e. for all possible values of the parameters appearing in the statement. [ 6 ] A detailed proof in the whole Euclidean space was published in 2021. [ 6 ]
From its original formulation, several mathematicians worked on proving and generalizing Gagliardo-Nirenberg type inequalities. The Italian mathematician Carlo Miranda developed a first generalization in 1963, [ 7 ] which was addressed and refined by Nirenberg later in 1966. [ 8 ] The investigation of Gagliardo-Nirenberg type inequalities continued in the following decades. For instance, a careful study on negative exponents has been carried out extending the work of Nirenberg in 2018, [ 9 ] while Brezis and Mironescu characterized in full generality the embeddings between Sobolev spaces extending the inequality to fractional orders. [ 10 ] [ 11 ]
For any extended real (i.e. possibly infinite) positive quantity 1 ≤ p ≤ + ∞ {\displaystyle 1\leq p\leq +\infty } and any integer k ≥ 1 {\displaystyle k\geq 1} , let L p ( R n ) {\displaystyle L^{p}(\mathbb {R} ^{n})} denote the usual L p {\displaystyle L^{p}} spaces , while W k , p ( R n ) {\displaystyle W^{k,p}(\mathbb {R} ^{n})} denotes the Sobolev space consisting of all real-valued functions in L p ( R n ) {\displaystyle L^{p}(\mathbb {R} ^{n})} such that all their weak derivatives up to order k {\displaystyle k} are also in L p ( R n ) {\displaystyle L^{p}(\mathbb {R} ^{n})} . Both families of spaces are intended to be endowed with their standard norms, namely: [ 12 ] ‖ u ‖ L p ( R n ) := { ( ∫ R n | u | p ) 1 p if p < + ∞ , e s s s u p R n | u | if p = + ∞ ; ‖ u ‖ W k , p ( R n ) := { ( ∑ | α | ≤ k ‖ D α u ‖ L p ( R n ) p ) 1 p if p < + ∞ , ∑ | α | ≤ k ‖ D α u ‖ L ∞ ( R n ) if p = + ∞ ; {\displaystyle \|u\|_{L^{p}(\mathbb {R} ^{n})}:={\begin{cases}\left(\displaystyle \int _{\mathbb {R} ^{n}}|u|^{p}\right)^{\frac {1}{p}}&\quad {\text{if }}p<+\infty ,\\{\underset {\mathbb {R} ^{n}}{\operatorname {ess\,sup} }}\,|u|&\quad {\text{if }}p=+\infty ;\end{cases}}\qquad \qquad \|u\|_{W^{k,p}(\mathbb {R} ^{n})}:={\begin{cases}\left(\displaystyle \sum _{|\alpha |\leq k}\|D^{\alpha }u\|_{L^{p}(\mathbb {R} ^{n})}^{p}\right)^{\frac {1}{p}}&\quad {\text{if }}p<+\infty ,\\\ \ \ \displaystyle \sum _{|\alpha |\leq k}\|D^{\alpha }u\|_{L^{\infty }(\mathbb {R} ^{n})}&\quad {\text{if }}p=+\infty ;\end{cases}}} where e s s s u p {\displaystyle \operatorname {ess\,sup} } stands for essential supremum . Above, for the sake of convenience, the same notation is used for scalar, vector and tensor-valued Lebesgue and Sobolev spaces.
The original version of the theorem, for functions defined on the whole Euclidean space R n {\displaystyle \mathbb {R} ^{n}} , can be stated as follows.
Theorem [ 13 ] (Gagliardo-Nirenberg) — Let 1 ≤ q ≤ + ∞ {\displaystyle 1\leq q\leq +\infty } be a positive extended real quantity. Let j {\displaystyle j} and m {\displaystyle m} be non-negative integers such that j < m {\displaystyle j<m} . Furthermore, let 1 ≤ r ≤ + ∞ {\displaystyle 1\leq r\leq +\infty } be a positive extended real quantity, p ≥ 1 {\displaystyle p\geq 1} be real and θ ∈ [ 0 , 1 ] {\displaystyle \theta \in [0,1]} such that the relations 1 p = j n + θ ( 1 r − m n ) + 1 − θ q , j m ≤ θ ≤ 1 {\displaystyle {\dfrac {1}{p}}={\dfrac {j}{n}}+\theta \left({\dfrac {1}{r}}-{\dfrac {m}{n}}\right)+{\dfrac {1-\theta }{q}},\qquad {\dfrac {j}{m}}\leq \theta \leq 1} hold. Then, ‖ D j u ‖ L p ( R n ) ≤ C ‖ D m u ‖ L r ( R n ) θ ‖ u ‖ L q ( R n ) 1 − θ {\displaystyle \|D^{j}u\|_{L^{p}(\mathbb {R} ^{n})}\leq C\|D^{m}u\|_{L^{r}(\mathbb {R} ^{n})}^{\theta }\|u\|_{L^{q}(\mathbb {R} ^{n})}^{1-\theta }} for any u ∈ L q ( R n ) {\displaystyle u\in L^{q}(\mathbb {R} ^{n})} such that D m u ∈ L r ( R n ) {\displaystyle D^{m}u\in L^{r}(\mathbb {R} ^{n})} , with two exceptional cases:
In any case, the constant C > 0 {\displaystyle C>0} depends on the parameters j , m , n , q , r , θ {\displaystyle j,\,m,\,n,\,q,\,r,\,\theta } , but not on u {\displaystyle u} .
Notice that the parameter p {\displaystyle p} is determined uniquely by all the other ones and usually assumed to be finite. [ 8 ] However, there are sharper formulations in which p = + ∞ {\displaystyle p=+\infty } is considered (but other values may be excluded, for example j = 0 {\displaystyle j=0} ). [ 9 ]
The Gagliardo-Nirenberg inequality generalizes a collection of well-known results in the field of functional analysis . Indeed, given a suitable choice of the seven parameters appearing in the statement of the theorem, one obtains several useful and recurring inequalities in the theory of partial differential equations:
A complete and detailed proof of the Gagliardo-Nirenberg inequality has been missing in literature for a long time since its first statements. Indeed, both original works of Gagliardo and Nirenberg lacked some details, or even presented only the main steps of the proof. [ 6 ]
The most delicate point concerns the limiting case θ = j m {\textstyle \theta ={\frac {j}{m}}} . In order to avoid the two exceptional cases, we further assume that r {\displaystyle r} is finite and that u ∈ W m , r ( R n ) {\displaystyle u\in W^{m,r}(\mathbb {R} ^{n})} , so in particular u ∈ L r ( R n ) {\displaystyle u\in L^{r}(\mathbb {R} ^{n})} . The core of the proof is based on two proofs by induction .
Throughout the proof, given j {\displaystyle j} and m {\displaystyle m} , we shall assume that θ = j m {\textstyle \theta ={\frac {j}{m}}} . A double induction argument is applied to the couple of integers ( j , m ) {\displaystyle (j,m)} , representing the orders of differentiation. The other parameters are constructed in such a way that they comply with the hypotheses of the theorem. As base case, we assume that the Gagliardo-Nirenberg inequality holds for j = 1 {\displaystyle j=1} and m = 2 {\displaystyle m=2} (hence θ = 1 2 {\textstyle \theta ={\frac {1}{2}}} ). Here, in order for the inequality to hold, the remaining parameters should satisfy 2 p = 1 r + 1 q , n ≥ 1. {\displaystyle {\dfrac {2}{p}}={\dfrac {1}{r}}+{\dfrac {1}{q}},\qquad n\geq 1.} The first induction step goes as follows. Assume the Gagliardo-Nirenberg inequality holds for some m = m ⋆ ∈ N {\displaystyle m=m^{\star }\in \mathbb {N} } strictly greater than 1 {\displaystyle 1} and j = 1 {\displaystyle j=1} (hence θ = 1 m ⋆ {\textstyle \theta ={\frac {1}{m^{\star }}}} ). We are going to prove that it also holds for m = m ⋆ + 1 {\displaystyle m=m^{\star }+1} and j = 1 {\displaystyle j=1} (with θ = 1 m ⋆ + 1 {\textstyle \theta ={\frac {1}{m^{\star }+1}}} ). To this end, the remaining parameters n , p , q , r {\displaystyle n,\,p,\,q,\,r} necessarily satisfy 1 p = 1 m ⋆ + 1 r + m ⋆ m ⋆ + 1 q , n ≥ 1. {\displaystyle {\dfrac {1}{p}}={\dfrac {\frac {1}{m^{\star }+1}}{r}}+{\dfrac {\frac {m^{\star }}{m^{\star }+1}}{q}},\qquad n\geq 1.} Fix them as such. Then, let s > 0 {\displaystyle s>0} be such that 2 p = 1 s + 1 q . {\displaystyle {\dfrac {2}{p}}={\dfrac {1}{s}}+{\dfrac {1}{q}}.} From the base case, we can infer that ‖ ∇ u ‖ L p ( R n ) ≤ C ‖ D 2 u ‖ L s ( R n ) 1 2 ‖ u ‖ L q ( R n ) 1 2 . {\displaystyle \|\nabla u\|_{L^{p}(\mathbb {R} ^{n})}\leq C\|D^{2}u\|_{L^{s}(\mathbb {R} ^{n})}^{\frac {1}{2}}\|u\|_{L^{q}(\mathbb {R} ^{n})}^{\frac {1}{2}}.} Now, from the two relations between the parameters, through some algebraic manipulations we arrive at 1 s = 1 m ⋆ r + m ⋆ − 1 m ⋆ p , n ≥ 1 , {\displaystyle {\dfrac {1}{s}}={\dfrac {\frac {1}{m^{\star }}}{r}}+{\dfrac {\frac {m^{\star }-1}{m^{\star }}}{p}},\qquad n\geq 1,} therefore the inequality with m = m ⋆ {\displaystyle m=m^{\star }} applied to ∇ u {\displaystyle \nabla u} implies ‖ D 2 u ‖ L s ( R n ) ≤ C ‖ D m ⋆ + 1 u ‖ L r ( R n ) 1 m ⋆ ‖ ∇ u ‖ L p ( R n ) m ⋆ − 1 m ⋆ . {\displaystyle \|D^{2}u\|_{L^{s}(\mathbb {R} ^{n})}\leq C\|D^{m^{\star }+1}u\|_{L^{r}(\mathbb {R} ^{n})}^{\frac {1}{m^{\star }}}\|\nabla u\|_{L^{p}(\mathbb {R} ^{n})}^{\frac {m^{\star }-1}{m^{\star }}}.} The two inequalities imply the sought Gagliardo-Nirenberg inequality, namely ‖ ∇ u ‖ L p ( R n ) ≤ C ‖ D m ⋆ + 1 u ‖ L r ( R n ) 1 m ⋆ + 1 ‖ u ‖ L q ( R n ) m ⋆ m ⋆ + 1 , {\displaystyle \|\nabla u\|_{L^{p}(\mathbb {R} ^{n})}\leq C\|D^{m^{\star }+1}u\|_{L^{r}(\mathbb {R} ^{n})}^{\frac {1}{m^{\star }+1}}\|u\|_{L^{q}(\mathbb {R} ^{n})}^{\frac {m^{\star }}{m^{\star }+1}},} The second induction step is similar, but allows j {\displaystyle j} to change. Assume the Gagliardo-Nirenberg inequality holds for some pair ( j ⋆ , m ⋆ ) ∈ N 2 {\displaystyle (j^{\star },m^{\star })\in \mathbb {N} ^{2}} with j ⋆ < m ⋆ {\displaystyle j^{\star }<m^{\star }} (hence θ = j ⋆ m ⋆ {\textstyle \theta ={\frac {j^{\star }}{m^{\star }}}} ). It is enough to prove that it also holds for m = m ⋆ + 1 {\displaystyle m=m^{\star }+1} and j = j ⋆ + 1 {\displaystyle j=j^{\star }+1} (with θ = j ⋆ + 1 m ⋆ + 1 {\textstyle \theta ={\frac {j^{\star }+1}{m^{\star }+1}}} ). Again, fix the parameters n , p , q , r {\displaystyle n,\,p,\,q,\,r} in such a way that 1 p = j ⋆ + 1 m ⋆ + 1 r + m ⋆ − j ⋆ m ⋆ + 1 q , n ≥ 1 , {\displaystyle {\dfrac {1}{p}}={\dfrac {\frac {j^{\star }+1}{m^{\star }+1}}{r}}+{\dfrac {\frac {m^{\star }-j^{\star }}{m^{\star }+1}}{q}},\qquad n\geq 1,} and let t {\displaystyle t} be such that 1 p = j ⋆ m ⋆ r + m ⋆ − j ⋆ m ⋆ t . {\displaystyle {\dfrac {1}{p}}={\dfrac {\frac {j^{\star }}{m^{\star }}}{r}}+{\dfrac {\frac {m^{\star }-j^{\star }}{m^{\star }}}{t}}.} The inequality with j = j ⋆ {\displaystyle j=j^{\star }} and m = m ⋆ {\displaystyle m=m^{\star }} applied to ∇ u {\displaystyle \nabla u} entails ‖ D j ⋆ + 1 u ‖ L p ( R n ) ≤ C ‖ D m ⋆ + 1 u ‖ L r ( R n ) j ⋆ m ⋆ ‖ ∇ u ‖ L t ( R n ) m ⋆ − j ⋆ m ⋆ . {\displaystyle \|D^{j^{\star }+1}u\|_{L^{p}(\mathbb {R} ^{n})}\leq C\|D^{m^{\star }+1}u\|_{L^{r}(\mathbb {R} ^{n})}^{\frac {j^{\star }}{m^{\star }}}\|\nabla u\|_{L^{t}(\mathbb {R} ^{n})}^{\frac {m^{\star }-j^{\star }}{m^{\star }}}.} Since, by the first induction step, we can assume the Gagliardo-Nirenberg inequality holds with m = j ⋆ + 1 {\displaystyle m=j^{\star }+1} and j = 1 {\displaystyle j=1} , we get ‖ ∇ u ‖ L t ( R n ) ≤ C ‖ D j ⋆ + 1 u ‖ L p ( R n ) 1 j ⋆ + 1 ‖ u ‖ L q ( R n ) j ⋆ j ⋆ + 1 . {\displaystyle \|\nabla u\|_{L^{t}(\mathbb {R} ^{n})}\leq C\|D^{j^{\star }+1}u\|_{L^{p}(\mathbb {R} ^{n})}^{\frac {1}{j^{\star }+1}}\|u\|_{L^{q}(\mathbb {R} ^{n})}^{\frac {j^{\star }}{j^{\star }+1}}.} The proof is completed by combining the two inequalities. In order to prove the base case, several technical lemmas are necessary, while the remaining values of θ {\displaystyle \theta } can be recovered by interpolation and a proof can be found, for instance, in the original work of Nirenberg. [ 5 ]
In many problems coming from the theory of partial differential equations, one has to deal with functions whose domain is not the whole Euclidean space R n {\displaystyle \mathbb {R} ^{n}} , but rather some given bounded, open and connected set Ω ⊂ R n . {\displaystyle \Omega \subset \mathbb {R} ^{n}.} In the following, we also assume that Ω {\displaystyle \Omega } has finite Lebesgue measure and satisfies the cone condition (among those are the widely used Lipschitz domains ). Both Gagliardo and Nirenberg found out that their theorem could be extended to this case adding a penalization term to the right hand side. Precisely,
Theorem [ 17 ] (Gagliardo-Nirenberg in bounded domains) — Let Ω ⊂ R n {\displaystyle \Omega \subset \mathbb {R} ^{n}} be a measurable, bounded, open and connected domain satisfying the cone condition. Let 1 ≤ q ≤ + ∞ {\displaystyle 1\leq q\leq +\infty } be a positive extended real quantity. Let j {\displaystyle j} and m {\displaystyle m} be non-negative integers such that j < m {\displaystyle j<m} . Furthermore, let 1 ≤ r ≤ + ∞ {\displaystyle 1\leq r\leq +\infty } be a positive extended real quantity, p ≥ 1 {\displaystyle p\geq 1} be real and θ ∈ [ 0 , 1 ] {\displaystyle \theta \in [0,1]} such that the relations 1 p = j n + θ ( 1 r − m n ) + 1 − θ q , j m ≤ θ ≤ 1 {\displaystyle {\dfrac {1}{p}}={\dfrac {j}{n}}+\theta \left({\dfrac {1}{r}}-{\dfrac {m}{n}}\right)+{\dfrac {1-\theta }{q}},\qquad {\dfrac {j}{m}}\leq \theta \leq 1} hold. Then, ‖ D j u ‖ L p ( Ω ) ≤ C ‖ D m u ‖ L r ( Ω ) θ ‖ u ‖ L q ( Ω ) 1 − θ + C ‖ u ‖ L σ ( Ω ) {\displaystyle \|D^{j}u\|_{L^{p}(\Omega )}\leq C\|D^{m}u\|_{L^{r}(\Omega )}^{\theta }\|u\|_{L^{q}(\Omega )}^{1-\theta }+C\|u\|_{L^{\sigma }(\Omega )}} where u ∈ L q ( Ω ) {\displaystyle u\in L^{q}(\Omega )} such that D m u ∈ L r ( Ω ) {\displaystyle D^{m}u\in L^{r}(\Omega )} and σ {\displaystyle \sigma } is arbitrary, with one exceptional case:
In any case, the constant C > 0 {\displaystyle C>0} depends on the parameters j , m , n , q , r , θ {\displaystyle j,\,m,\,n,\,q,\,r,\,\theta } , on the domain Ω {\displaystyle \Omega } , but not on u {\displaystyle u} .
The necessity of a different formulation with respect to the case Ω = R n {\displaystyle \Omega =\mathbb {R} ^{n}} is rather straightforward to prove. Indeed, since Ω {\displaystyle \Omega } has finite Lebesgue measure, any affine function belongs to L p ( Ω ) {\displaystyle L^{p}(\Omega )} for every p {\displaystyle p} (including p = + ∞ {\displaystyle p=+\infty } ). Of course, it holds much more: affine functions belong to C ∞ ( Ω ) {\displaystyle C^{\infty }(\Omega )} and all their derivatives of order greater than or equal to two are identically equal to zero in Ω {\displaystyle \Omega } . It can be easily seen that the Gagliardo-Nirenberg inequality for the case Ω = R n {\displaystyle \Omega =\mathbb {R} ^{n}} fails to be true for any non constant affine function, since a contradiction is immediately achieved when j = 1 {\displaystyle j=1} and m ≥ 2 {\displaystyle m\geq 2} , and therefore cannot hold in general for integrable functions defined on bounded domains.
That being said, under slightly stronger assumptions, it is possible to recast the theorem in such a way that the penalization term is "absorbed" in the first term at right hand side. Indeed, if u ∈ L q ( Ω ) ∩ W m , r ( Ω ) {\displaystyle u\in L^{q}(\Omega )\cap W^{m,r}(\Omega )} , then one can choose σ = min ( r , q ) {\displaystyle \sigma =\min(r,q)} and get ‖ D j u ‖ L p ( Ω ) ≤ C ‖ D m u ‖ L r ( Ω ) θ ‖ u ‖ L q ( Ω ) 1 − θ + C ‖ u ‖ L min ( r , q ) ( Ω ) θ ‖ u ‖ L min ( r , q ) ( Ω ) 1 − θ ≤ C ‖ u ‖ W m , r ( Ω ) θ ‖ u ‖ L q ( Ω ) 1 − θ . {\displaystyle {\begin{aligned}\|D^{j}u\|_{L^{p}(\Omega )}&\leq C\|D^{m}u\|_{L^{r}(\Omega )}^{\theta }\|u\|_{L^{q}(\Omega )}^{1-\theta }+C\|u\|_{L^{\min(r,q)}(\Omega )}^{\theta }\|u\|_{L^{\min(r,q)}(\Omega )}^{1-\theta }\\&\leq C\|u\|_{W^{m,r}(\Omega )}^{\theta }\|u\|_{L^{q}(\Omega )}^{1-\theta }.\end{aligned}}} This formulation has the advantage of recovering the structure of the theorem in the full Euclidean space, with the only caution that the Sobolev seminorm is replaced by the full W m , r {\displaystyle W^{m,r}} -norm. For this reason, the Gagliardo-Nirenberg inequality in bounded domains is commonly stated in this way. [ 18 ]
Finally, observe that the first exceptional case appearing in the statement of the Gagliardo-Nirenberg inequality for the whole space is no longer relevant in bounded domains, since for finite measure sets we have that L ∞ ( Ω ) ↪ L ρ ( Ω ) {\displaystyle L^{\infty }(\Omega )\hookrightarrow L^{\rho }(\Omega )} for any finite ρ ≥ 1. {\displaystyle \rho \geq 1.}
The problem of interpolating different Sobolev spaces has been solved in full generality by Haïm Brezis and Petru Mironescu in two works dated 2018 and 2019. [ 10 ] [ 11 ] Furthermore, their results do not depend on the dimension n {\displaystyle n} and allow real values of j {\displaystyle j} and m {\displaystyle m} , rather than integer. Here, Ω ⊂ R n {\displaystyle \Omega \subset \mathbb {R} ^{n}} is either the full space, a half-space or a bounded and Lipschitz domain. If s ∈ ( 0 , 1 ) {\displaystyle s\in (0,1)} and p ≥ 1 {\displaystyle p\geq 1} is an extended real quantity, the space W s , p ( Ω ) {\displaystyle W^{s,p}(\Omega )} is defined as follows W s , p ( Ω ) := { { u ∈ L p ( Ω ) : | u ( x ) − u ( y ) | | x − y | s + n p ∈ L p ( Ω × Ω ) } if p < + ∞ , { u ∈ L ∞ ( Ω ) : | u ( x ) − u ( y ) | | x − y | s ∈ L ∞ ( Ω × Ω ) } if p = + ∞ ; ‖ u ‖ W s , p ( Ω ) := { ( ‖ u ‖ L p ( Ω ) p + ∫ Ω ∫ Ω | u ( x ) − u ( y ) | p | x − y | n + s p ) 1 p if p < + ∞ , ‖ u ‖ L ∞ ( Ω ) + ‖ u ( x ) − u ( y ) ( x − y ) s ‖ L ∞ ( Ω × Ω ) if p = + ∞ ; {\displaystyle W^{s,p}(\Omega ):={\begin{cases}\left\{u\in L^{p}(\Omega ):{\dfrac {|u(x)-u(y)|}{|x-y|^{s+{\frac {n}{p}}}}}\in L^{p}(\Omega \times \Omega )\right\}&\quad {\text{if }}p<+\infty ,\\\left\{u\in L^{\infty }(\Omega ):{\dfrac {|u(x)-u(y)|}{|x-y|^{s}}}\in L^{\infty }(\Omega \times \Omega )\right\}&\quad {\text{if }}p=+\infty ;\\\end{cases}}\qquad \|u\|_{W^{s,p}(\Omega )}:={\begin{cases}\left(\|u\|_{L^{p}(\Omega )}^{p}+\displaystyle \int _{\Omega }\int _{\Omega }{\dfrac {|u(x)-u(y)|^{p}}{|x-y|^{n+sp}}}\right)^{\frac {1}{p}}&\quad {\text{if }}p<+\infty ,\\\|u\|_{L^{\infty }(\Omega )}+\left\|{\dfrac {u(x)-u(y)}{(x-y)^{s}}}\right\|_{L^{\infty }(\Omega \times \Omega )}&\quad {\text{if }}p=+\infty ;\end{cases}}} and if s ≥ 1 {\displaystyle s\geq 1} we set W s , p ( Ω ) := { u ∈ W ⌊ s ⌋ , p ( Ω ) : D ⌊ s ⌋ u ∈ W { s } , p ( Ω ) } , ‖ u ‖ W s , p ( Ω ) := { ( ‖ u ‖ L p ( Ω ) p + ‖ D ⌊ s ⌋ u ‖ W { s } , p ( Ω ) p ) 1 p if p < + ∞ , ‖ u ‖ L ∞ ( Ω ) + ‖ D ⌊ s ⌋ u ‖ W { s } , ∞ ( Ω ) if p = + ∞ ; {\displaystyle W^{s,p}(\Omega ):=\{u\in W^{\lfloor s\rfloor ,p}(\Omega ):D^{\lfloor s\rfloor }u\in W^{\{s\},p}(\Omega )\},\qquad \|u\|_{W^{s,p}(\Omega )}:={\begin{cases}\left(\|u\|_{L^{p}(\Omega )}^{p}+\|D^{\lfloor s\rfloor }u\|_{W^{\{s\},p}(\Omega )}^{p}\right)^{\frac {1}{p}}&\quad {\text{if }}p<+\infty ,\\\|u\|_{L^{\infty }(\Omega )}+\|D^{\lfloor s\rfloor }u\|_{W^{\{s\},\infty }(\Omega )}&\quad {\text{if }}p=+\infty ;\end{cases}}} where ⌊ s ⌋ {\displaystyle \lfloor s\rfloor } and { s } {\displaystyle \{s\}} denote the integer part and the fractional part of s {\displaystyle s} , respectively, i.e. s = ⌊ s ⌋ + { s } {\displaystyle s=\lfloor s\rfloor +\{s\}} . [ 19 ] In this definition, there is the understanding that W 0 , p ( Ω ) = L p ( Ω ) {\displaystyle W^{0,p}(\Omega )=L^{p}(\Omega )} , so that the usual Sobolev spaces are recovered whenever s {\displaystyle s} is a positive integer. These spaces are often referred to as fractional Sobolev spaces. A generalization of the Gagliardo-Nirenberg inequality to these spaces reads
Theorem [ 20 ] (Brezis-Mironescu) — Let Ω ⊂ R n {\displaystyle \Omega \subset \mathbb {R} ^{n}} be either the whole space, a half-space or a bounded Lipschitz domain. Let 1 ≤ p , p 1 , p 2 ≤ + ∞ {\displaystyle 1\leq p,\,p_{1},\,p_{2}\leq +\infty } be three positive extended real quantities and let s , s 1 , s 2 {\displaystyle s,\,s_{1},\,s_{2}} be non-negative real numbers. Furthermore, let θ ∈ ( 0 , 1 ) {\displaystyle \theta \in (0,1)} and assume that s 1 ≤ s 2 , s = θ s 1 + ( 1 − θ ) s 2 , 1 p = θ p 1 + 1 − θ p 2 {\displaystyle s_{1}\leq s_{2},\qquad s=\theta s_{1}+(1-\theta )s_{2},\qquad {\dfrac {1}{p}}={\dfrac {\theta }{p_{1}}}+{\dfrac {1-\theta }{p_{2}}}} hold. Then, ‖ u ‖ W s , p ( Ω ) ≤ C ‖ u ‖ W s 1 , p 1 ( Ω ) θ ‖ u ‖ W s 2 , p 2 ( Ω ) 1 − θ {\displaystyle \|u\|_{W^{s,p}(\Omega )}\leq C\|u\|_{W^{s_{1},p_{1}}(\Omega )}^{\theta }\|u\|_{W^{s_{2},p_{2}}(\Omega )}^{1-\theta }} for any u ∈ W s 1 , p 1 ( Ω ) ∩ W s 2 , p 2 ( Ω ) {\displaystyle u\in W^{s_{1},p_{1}}(\Omega )\cap W^{s_{2},p_{2}}(\Omega )} if and only if at least one of { s 2 ∈ N and s 2 ≥ 1 , p 2 = 1 , 0 < s 2 − s 1 ≤ 1 − 1 p 1 is false. {\displaystyle {\text{at least one of}}\quad {\begin{cases}s_{2}\in \mathbb {N} {\text{ and }}s_{2}\geq 1,\\p_{2}=1,\\0<s_{2}-s_{1}\leq 1-\displaystyle {\dfrac {1}{p_{1}}}\end{cases}}\quad {\text{is false.}}} The constant C > 0 {\displaystyle C>0} depends on the parameters p , p 1 , p 2 , s , s 1 , s 2 , θ {\displaystyle p,\,p_{1},\,p_{2},\,s,\,s_{1},\,s_{2},\,\theta } , on the domain Ω {\displaystyle \Omega } , but not on u {\displaystyle u} .
For example, the parameter choice p = 8 3 , p 1 = 2 , p 2 = 4 , s = 7 12 , s 1 = 1 2 , s 2 = 2 3 , θ = 1 2 {\displaystyle p={\dfrac {8}{3}},\quad p_{1}=2,\quad p_{2}=4,\quad s={\dfrac {7}{12}},\quad s_{1}={\dfrac {1}{2}},\quad s_{2}={\dfrac {2}{3}},\quad \theta ={\dfrac {1}{2}}} gives the estimate ‖ u ‖ W 7 12 , 8 3 ( Ω ) ≤ C ‖ u ‖ W 1 2 , 2 ( Ω ) 1 2 ‖ u ‖ W 2 3 , 4 ( Ω ) 1 2 . {\displaystyle \|u\|_{W^{{\frac {7}{12}},{\frac {8}{3}}}(\Omega )}\leq C\|u\|_{W^{{\frac {1}{2}},2}(\Omega )}^{\frac {1}{2}}\|u\|_{W^{{\frac {2}{3}},4}(\Omega )}^{\frac {1}{2}}.} The validity of the estimate is granted, for instance, from the fact that p 2 ≠ 1 {\displaystyle p_{2}\neq 1} . | https://en.wikipedia.org/wiki/Gagliardo–Nirenberg_interpolation_inequality |
Gaia was a space observatory of the European Space Agency (ESA) that was launched in 2013 and operated until March 2025. The spacecraft was designed for astrometry : measuring the positions, distances and motions of stars with unprecedented precision, [ 5 ] [ 6 ] and the positions of exoplanets by measuring attributes about the stars they orbit such as their apparent magnitude and color . [ 7 ] The mission aims to construct by far the largest and most precise 3D space catalog ever made, totalling approximately 1 billion astronomical objects , mainly stars, but also planets, comets, asteroids and quasars , among others. [ 8 ]
To study the precise position and motion of its target objects, the spacecraft monitored each of them about 70 times [ 9 ] over the five years of the nominal mission (2014–2019), and about as many during its extension. [ 10 ] [ 11 ] Due to its detectors not degrading as fast as initially expected, the mission was given an extension. [ 12 ] As of March 2023, the spacecraft had enough micro-propulsion fuel to operate until the second quarter of 2025. [ 13 ] Gaia targeted objects brighter than magnitude 20 in a broad photometric band that covered the extended visual range between near-UV and near infrared; [ 14 ] such objects represent approximately 1% of the Milky Way population. [ 9 ] Additionally, Gaia was expected to detect thousands to tens of thousands of Jupiter-sized exoplanets beyond the Solar System by using the astrometry method, [ 15 ] [ 16 ] 500,000 quasars outside this galaxy and tens of thousands of known and new asteroids and comets within the Solar System. [ 17 ] [ 18 ] [ 19 ]
On March 27, 2025, scientists at the ESA switched off Gaia after more than a decade of service, sending it into orbit around the sun and overwriting some of its onboard data. [ 20 ]
The Gaia mission continues to create a precise three-dimensional map of astronomical objects throughout the Milky Way and map their motions, which encode the origin and subsequent evolution of the Milky Way. The spectrophotometric measurements provide detailed physical properties of all stars observed, characterizing their luminosity , effective temperature , gravity and elemental composition. This massive stellar census is providing the basic observational data to analyze a wide range of important questions related to the origin, structure and evolutionary history of the Milky Way galaxy.
The successor to the Hipparcos mission (operational 1989–1993), Gaia is part of ESA's Horizon 2000+ long-term scientific program. Gaia was launched on 19 December 2013 by Arianespace using a Soyuz ST-B / Fregat-MT rocket flying from Kourou in French Guiana. [ 21 ] [ 22 ] The spacecraft currently operates in a Lissajous orbit around the Sun – Earth L 2 Lagrangian point . The science observation officially ended on 15 January 2025. [ 23 ]
The Gaia space telescope had its roots in ESA's Hipparcos mission (1989–1993). Its mission was proposed in October 1993 by Lennart Lindegren ( Lund Observatory , Lund University , Sweden) and Michael Perryman (ESA) in response to a call for proposals for ESA's Horizon Plus long-term scientific programme. It was adopted by ESA's Science Programme Committee as cornerstone mission number 6 on 13 October 2000, and the B2 phase of the project was authorised on 9 February 2006, with EADS Astrium taking responsibility for the hardware. The name "Gaia" was originally derived as an acronym for Global Astrometric Interferometer for Astrophysics . This reflected the optical technique of interferometry that was originally planned for use on the spacecraft. While the working method evolved during studies and the acronym is no longer applicable, the name Gaia remained to provide continuity with the project. [ 24 ]
The total cost of the mission is around €740 million (~ $1 billion), including the manufacture, launch and ground operations. [ 25 ] Gaia was completed two years behind schedule and 16% above its initial budget, mostly due to the difficulties encountered in polishing Gaia 's ten silicon carbide mirrors and assembling and testing the focal plane camera system. [ 26 ]
The Gaia space mission has the following objectives: [ 27 ] [ 28 ]
Gaia was launched by Arianespace , using a Soyuz ST-B rocket with a Fregat-MT upper stage, from the Ensemble de Lancement Soyouz at Kourou in French Guiana on 19 December 2013 at 09:12 UTC (06:12 local time). The satellite separated from the rocket's upper stage 43 minutes after launch at 09:54 UTC. [ 29 ] [ 30 ]
The craft headed towards the Sun–Earth Lagrange point L2 located approximately 1.5 million kilometres from Earth, arriving there 8 January 2014. [ 31 ] The L2 point provides the spacecraft with a very stable gravitational and thermal environment. There, it uses a Lissajous orbit that avoids blockage of the Sun by the Earth, which would limit the amount of solar energy the satellite could produce through its solar panels , as well as disturb the spacecraft's thermal equilibrium. After launch, a 10-metre-diameter sunshade was deployed. The sunshade always maintains a fixed 45 degree angle to the Sun, while precessing to scan the sky, thus keeping all telescope components cool and powering Gaia using solar panels on its surface. These factors and the materials used in its creation allow Gaia to function in conditions between -170 ° C and 70 ° C. [ 32 ]
The Gaia payload consists of three main instruments:
In order to maintain the fine pointing to focus on stars many light years away, the only moving parts are actuators to align the mirrors and the valves to fire the thrusters. It has no reaction wheels or gyroscopes. The spacecraft subsystems are mounted on a rigid silicon carbide [ 7 ] frame, which provides a stable structure that will not expand or contract due to temperature. Attitude control is provided by small cold gas thrusters that can output 1.5 micrograms of nitrogen per second.
The telemetric link with the satellite is about 3 Mbit/s on average, while the total content of the focal plane represents several Gbit/s . [ 35 ] Therefore, only a few dozen pixels around each object can be downlinked.
The design of the Gaia focal plane and instruments. Due to the spacecraft's rotation, images cross the focal plane array right-to-left at 60 arcseconds per second. [ 36 ]
Similar to its predecessor Hipparcos , but with a precision one hundred times greater, Gaia consists of two telescopes providing two observing directions with a fixed, wide angle of 106.5° between them. [ 37 ] The spacecraft rotates continuously around an axis perpendicular to the two telescopes' lines of sight, with a spin period of 6 hours. Thus, every 6 hours the spacecraft scans a great circle stripe approximately 0.7 degrees wide. The spin axis in turn has a slower precession across the sky: it maintains a fixed 45 degree angle to the Sun, but follows a cone around the Sun every 63 days, giving a cycloid-like path relative to the stars. Over the course of the mission, each star is scanned many times at various scan directions, providing interlocking measurements over the full sky.
The two key telescope properties are:
Each celestial object was observed on average about 70 times during the five years of the nominal mission, which has been extended to approximately ten years and will thus obtain twice as many observations. [ 41 ] These measurements will help determine the astrometric parameters of stars: two corresponding to the angular position of a given star on the sky, two for the derivatives of the star's position over time (motion) and lastly, the star's parallax from which distance can be calculated. The radial velocity of the brighter stars is measured by an integrated spectrometer observing the Doppler effect . Because of the physical constraints imposed by the Soyuz spacecraft, Gaia 's focal arrays could not be equipped with optimal radiation shielding, and ESA expected their performance to suffer somewhat toward the end of the initial five-year mission. Ground tests of the CCDs while they were subjected to radiation provided reassurance that the primary mission's objectives can be met. [ 42 ]
An atomic clock on board Gaia plays a crucial role in achieving the mission's primary objectives. Gaia rotates with angular velocity of 60"/sec or 0.6 microarcseconds in 10 nanoseconds. Therefore, in order to meet its positioning goals, Gaia must be able to record the exact time of observation to within nanoseconds. Furthermore, no systematic positioning errors over the rotational period of 6 hours should be introduced by the clock performance. For the timing error to be below 10 nanoseconds over each rotational period, the frequency stability of the on-board clock needs to be better than 10 −12 . The rubidium atomic clock aboard the Gaia spacecraft has a stability reaching ~ 10 −13 over each rotational period of 21600 seconds. [ 43 ]
Gaia' s measurements contribute to the creation and maintenance of a high-precision celestial reference frame, the Barycentric Celestial Reference System (BCRS) , which is essential for both astronomy and navigation. This reference frame serves as a fundamental grid for positioning celestial objects in the sky, aiding astronomers in various research endeavors. All observations, regardless of the actual positioning of the spacecraft, must be expressed in terms of this reference system. As a fully relativistic model, the influence of the gravitational field of the solar-system must be taken into account, including such factors as the gravitational light-bending due to the Sun, the major planets and the Moon. [ 44 ]
The expected accuracies of the final catalogue data have been calculated following in-orbit testing, taking into account the issues of stray light, degradation of the optics, and the basic angle instability. The best accuracies for parallax, position and proper motion are obtained for the brighter observed stars, apparent magnitudes 3–12. The standard deviation for these stars is expected to be 6.7 micro-arcseconds or better. For fainter stars, error levels increase, reaching 26.6 micro-arcseconds error in the parallax for 15th-magnitude stars, and several hundred micro-arcseconds for 20th-magnitude stars. [ 45 ] For comparison, the best parallax error levels from the new Hipparcos reduction are no better than 100 micro-arcseconds, with typical levels several times larger. [ 46 ]
In October 2013 ESA had to postpone Gaia 's original launch date, due to a precautionary replacement of two of Gaia 's transponders. These are used to generate timing signals for the downlink of science data. A problem with an identical transponder on a satellite already in orbit motivated their replacement and reverification once incorporated into Gaia . The rescheduled launch window was from 17 December 2013 to 5 January 2014, with Gaia slated for launch on 19 December. [ 47 ]
Gaia was successfully launched on 19 December 2013 at 09:12 UTC . [ 48 ] About three weeks after launch, on 8 January 2014, it reached its designated orbit around the Sun-Earth L2 Lagrange point (SEL2), [ 4 ] [ 49 ] about 1.5 million kilometers from Earth.
In 2015, the Pan-STARRS observatory discovered an object orbiting the Earth, which the Minor Planet Center catalogued as object 2015 HP 116 . It was soon found to be an accidental rediscovery of the Gaia spacecraft and the designation was promptly retracted. [ 50 ]
Shortly after launch, ESA revealed that Gaia suffers from a stray light problem. The problem was initially thought to be due to ice deposits reflecting some of the light diffracted around the edges of the sunshield into the telescope apertures and on towards the focal plane. [ 51 ] The actual source of the stray light was later identified as the fibers of the sunshield, protruding beyond the edges of the shield. [ 52 ] This results in a "degradation in science performance [which] will be relatively modest and mostly restricted to the faintest of Gaia 's one billion stars." Mitigation schemes were implemented [ 53 ] to improve performance. The degradation is more severe for the RVS spectrograph than for the astrometry measurements, because it spreads the light of the star onto a much larger number of detector pixels, each of which collects scattered light.
This kind of problem has some historical background. In 1985 on STS-51-F , the Space Shuttle Spacelab -2 mission, another astronomical mission hampered by stray debris was the Infrared Telescope (IRT), in which a piece of mylar insulation broke loose and floated into the line-of-sight of the telescope causing corrupted data. [ 54 ] The testing of stray-light and baffles is a noted part of space imaging instruments. [ 55 ]
In April 2024, a micrometeoroid hit and damaged Gaia's protective cover, creating "a little gap that allowed stray sunlight – around one billionth of the intensity of direct sunlight felt on Earth – to occasionally disrupt Gaia ’s very sensitive sensors". In May, the electronics of one of the CCDs failed, which caused a high rate of false detections. After that, the engineers refocused Gaia' s optics "for the final time". [ 56 ]
The testing and calibration phase, which started while Gaia was en route to SEL2 point, continued until the end of July 2014, [ 57 ] three months behind schedule due to unforeseen issues with stray light entering the detector. After the six-month commissioning period, the satellite started its nominal five-year period of scientific operations on 25 July 2014 using a special scanning mode that intensively scanned the region near the ecliptic poles ; on 21 August 2014 Gaia began using its normal scanning mode which provides more uniform coverage. [ 58 ]
Although it was originally planned to limit Gaia ' s observations to stars fainter than magnitude 5.7, tests carried out during the commissioning phase indicated that Gaia could autonomously identify stars as bright as magnitude 3. When Gaia entered regular scientific operations in July 2014, it was configured to routinely process stars in the magnitude range 3 – 20. [ 59 ] On the bright side of that limit, special operational procedures download raw scanning data for the remaining 230 stars brighter than magnitude 3; methods to reduce and analyse these data are being developed; and it is expected that there will be "complete sky coverage at the bright end" with standard errors of "a few dozen μas". [ 60 ]
On 30 August 2014, Gaia discovered its first supernova in another galaxy. [ 61 ] On 3 July 2015, a map of the Milky Way by star density was released, based on data from the spacecraft. [ 62 ] As of August 2016, "more than 50 billion focal plane transits, 110 billion photometric observations and 9.4 billion spectroscopic observations have been successfully processed." [ 63 ]
In 2018 the Gaia mission was extended to 2020, and in 2020 it was further extended through 2022, with an additional "indicative extension" extending through 2025. [ 64 ] [ 65 ] The limiting factor to further mission extensions is the supply of nitrogen for the cold gas thrusters of the micro-propulsion system. [ 66 ] The amount of dinitrogen tetroxide (NTO) and monomethylhydrazine (MMH) for the chemical propulsion subsystem on board might be enough to stabilize the spacecraft at L2 for several decades. Without the cold gas, though, the space craft can no longer be pointed on a microarcsecond scale.
In March 2023, the Gaia mission was extended through the second quarter of 2025, when the spacecraft was expected to run out of cold gas propellant. [ 13 ]
Gaia' s last targeted observation was done on 10 January 2025. [ 67 ] After several weeks of onboard technology tests, Gaia left its orbit near L 2 and was put into a heliocentric orbit away from Earth's sphere of influence . [ 68 ] After downlinking all remaining data to Earth, Gaia was decommissioned and passivated on 27 March 2025. [ 67 ] [ 69 ] The mission has since entered a post-operations phase to complete and publish the final Gaia Data Release, DR5, by the end of 2030. [ 13 ]
Several Gaia catalogues are released over the years each time with increasing amounts of information and better astrometry; the early releases also miss some stars, especially fainter stars located in dense star fields and members of close binary pairs. [ 70 ] The first data release, Gaia DR1, based on 14 months of observation was on 14 September 2016. [ 71 ] [ 72 ] [ 73 ] The data release includes "positions and ... magnitudes for 1.1 billion stars using only Gaia data; positions, parallaxes and proper motions for more than 2 million stars" based on a combination of Gaia and Tycho-2 data for those objects in both catalogues; "light curves and characteristics for about 3,000 variable stars; and positions and magnitudes for more than 2000 ... extragalactic sources used to define the celestial reference frame ". [ 70 ] [ 74 ] [ 75 ]
The second data release (DR2), which occurred on 25 April 2018, [ 8 ] [ 76 ] is based on 22 months of observations made between 25 July 2014 and 23 May 2016. It includes positions, parallaxes and proper motions for about 1.3 billion stars and positions of an additional 300 million stars in the magnitude range g = 3–20, [ 77 ] red and blue photometric data for about 1.1 billion stars and single colour photometry for an additional 400 million stars, and median radial velocities for about 7 million stars between magnitude 4 and 13. It also contains data for over 14,000 selected Solar System objects. [ 78 ] [ 79 ]
Due to uncertainties in the data pipeline, the third data release, based on 34 months of observations, was split into two parts so that data that was ready first, was released first. The first part, EDR3 ("Early Data Release 3"), consisting of improved positions, parallaxes and proper motions, was released on 3 December 2020. [ 80 ] The coordinates in EDR3 use a new version of the Gaia celestial reference frame ( Gaia –CRF3), based on observations of 1,614,173 extragalactic sources, [ 80 ] 2,269 of which were common to radio sources in the third revision of the International Celestial Reference Frame (ICRF3) . [ 81 ] Included is the Gaia Catalogue of Nearby Stars (GCNS), containing 331,312 stars within (nominally) 100 parsecs (330 light-years). [ 82 ] [ 83 ]
The full DR3, published on 13 June 2022, includes the EDR3 data plus Solar System data; variability information; results for non-single stars, for quasars, and for extended objects; astrophysical parameters; and a special data set, the Gaia Andromeda Photometric Survey (GAPS). [ 84 ]
The full data release for the five-year nominal mission, DR4, will include full astrometric, photometric and radial-velocity catalogues, variable-star and non-single-star solutions, source classifications plus multiple astrophysical parameters for stars, unresolved binaries, galaxies and quasars, an exo-planet list and epoch and transit data for all sources. Additional release(s) will take place depending on mission extensions. [ 70 ] Most measurements in DR4 are expected to be 1.7 times more precise than DR2; proper motions will be 4.5 times more precise. [ 85 ] DR4 is expected to be released no earlier than mid-2026. [ 70 ]
The final Gaia catalogue, DR5, will consist of all data collected during the lifespan of the mission. It will be 1.4 times more precise than DR4, while proper motions will be 2.8 times more precise than DR4. [ 85 ] It will be published no earlier than the end of 2030. [ 70 ] All data of all catalogues will be available in an online data base that is free to use.
An outreach application, Gaia Sky , has been developed to explore the galaxy in three dimensions using Gaia data. [ 86 ]
The overall data volume that was retrieved from the spacecraft during the nominal five-year mission at a compressed data rate of 1 Mbit/s is approximately 60 TB , amounting to about 200 TB of usable uncompressed data on the ground, stored in an InterSystems Caché database. The responsibility of the data processing, partly funded by ESA, is entrusted to a European consortium, the Data Processing and Analysis Consortium (DPAC), which was selected after its proposal to the ESA Announcement of Opportunity released in November 2006. DPAC's funding is provided by the participating countries and has been secured until the production of Gaia 's final catalogue. [ 88 ]
Gaia sends back data for about eight hours every day at about 5 Mbit/s. ESA's three 35-metre-diameter radio dishes of the ESTRACK network in Cebreros , Spain, Malargüe , Argentina and New Norcia , Australia, receive the data. [ 24 ]
In July 2017, the Gaia–ESO Survey reported using Gaia data to find double-, triple-, and quadruple- stars. Using advanced techniques they identified 342 binary candidates, 11 triple candidates, and 1 quadruple candidate. Nine of these had been identified by other means, thus confirming that the technique can correctly identify multiple star systems. [ 89 ] The possible quadruple star system is HD 74438 , which was, in a paper published in 2022, identified as a possible progenitor of a sub-Chandrasekhar Type Ia supernovae . [ 90 ]
In November 2017, scientists led by Davide Massari of the Kapteyn Astronomical Institute , University of Groningen , Netherlands released a paper [ 91 ] describing the characterization of proper motion (3D) within the Sculptor dwarf galaxy , and of that galaxy's trajectory through space and with respect to the Milky Way , using data from Gaia and the Hubble Space Telescope . Massari said, "With the precision achieved we can measure the yearly motion of a star on the sky which corresponds to less than the size of a pinhead on the Moon as seen from Earth." The data showed that Sculptor orbits the Milky Way in a highly elliptical orbit; it is currently near its closest approach at a distance of about 83.4 kiloparsecs (272,000 ly), but the orbit can take it out to around 222 kiloparsecs (720,000 ly) distant.
In October 2018, Leiden University astronomers were able to determine the orbits of 20 hyperrunaway star candidates from the DR2 dataset. Expecting to find a single star exiting the Milky Way , they instead found seven. More surprisingly, the team found that 13 hyperrunaway stars were instead approaching the Milky Way, possibly originating from as-of-yet unknown extragalactic sources. Alternatively, they could be halo stars to this galaxy, and further spectroscopic studies will help determine which scenario is more likely. [ 92 ] [ 93 ] Independent measurements have demonstrated that the greatest Gaia radial velocity among the hyperrunaway stars is contaminated by light from nearby bright stars in a crowded field and cast doubt on the high Gaia radial velocities of other hypervelocity stars. [ 94 ]
In late October 2018, the galactic population Gaia-Enceladus , the remains of a major merger with the defunct Enceladus dwarf, was discovered. [ 95 ] This system is associated with at least 13 globular clusters, and the creation of the Thick Disk of the Milky Way. It represents a significant merger about 10 billion years ago in the Milky Way Galaxy. [ 96 ]
In November 2018, the galaxy Antlia 2 was discovered. It is similar in size to the Large Magellanic Cloud , despite being 10,000 times fainter. Antlia 2 has the lowest surface brightness of any galaxy discovered. [ 97 ]
In December 2019 the star cluster Price-Whelan 1 was discovered. [ 98 ] The cluster belongs to the Magellanic Clouds and is located in the leading arm of these Dwarf Galaxies . The discovery suggests that the stream of gas extending from the Magellanic Clouds to the Milky Way is about half as far from the Milky Way as previously thought. [ 99 ]
The Radcliffe wave was discovered in data measured by Gaia , published in January 2020. [ 100 ] [ 101 ]
In November 2020, Gaia measured the acceleration of the solar system towards the galactic center as 0.23 nanometers/s 2 . [ 102 ] [ 103 ]
In March 2021, the European Space Agency announced that Gaia had identified a transiting exoplanet for the first time. The planet was discovered orbiting solar-type star Gaia EDR3 3026325426682637824. Following its initial discovery, the PEPSI spectrograph from the Large Binocular Telescope (LBT) in Arizona was used to confirm the discovery and categorise it as a Jovian planet, a gas planet composed of hydrogen and helium gas. [ 104 ] [ 105 ] In May 2022, the confirmation of this exoplanet, designated Gaia-1b , was formally published, along with a second planet, Gaia-2b . [ 106 ]
Based on its data, Gaia's Hertzsprung–Russell diagram (HR diagram) is one of the most accurate ones ever produced of the Milky Way Galaxy. [ 107 ]
Analysis of Gaia DR3 data in 2022 revealed a Sun-like star with the identifier Gaia DR3 4373465352415301632 orbiting a black hole , dubbed Gaia BH1 . At a distance of roughly 1,600 light-years (490 pc), it is the closest known black hole to Earth. [ 108 ] [ 109 ] Another system with a red giant orbiting a black hole, Gaia BH2 , was also discovered. [ 110 ]
In September 2023, radial velocity observations were used to confirm an exoplanet orbiting the star HIP 66074 that was first detected in Gaia DR3 astrometry data. This planet, known as HIP 66074 b or Gaia-3b, is the third Gaia exoplanet discovery to be confirmed and the first such discovery made using astrometry. [ 111 ] In addition, another exoplanet was discovered from a gravitational microlensing event observed by Gaia, Gaia22dkv . The host star is brighter than that of any exoplanet previously detected by microlensing, potentially making the planet detectable by radial velocity as well. [ 112 ]
In March 2024, Gaia discovered two streams of stars, named by researchers Shakti and Shiva, that formed more than 12 billion years ago. [ 113 ]
In 2025 a detailed 3D map of dust distribution within the Milky Way was constructed using data from Gaia and LAMOST spectral survey and machine learning. [ 114 ]
GaiaNIR (Gaia Near Infra-Red) is a proposed successor of Gaia in the near-infrared . [ 115 ] The mission would enlarge the current catalog with sources that are only (or better) visible in the near-infrared, at the cost of less precise measurements than an equivalent visible-light mission due to the broader diffraction pattern at longer wavelengths. It would at the same time improve the star parallax and particularly proper motion accuracy by revisiting the sources of the Gaia catalog. [ 116 ] One of the main challenges in building GaiaNIR is the low technology readiness level of near-infrared time delay and integration detectors but recent progress with Avalanche photodiode detectors (APDs) is overcoming this. In a 2017 ESA report two alternative concepts using conventional near-infrared detectors and de-spin mirrors were proposed but even without the development of NIR TDI detectors the technological challenge will likely increase the cost over an ESA M-class mission and might need shared cost with other space agencies. [ 116 ] One possible partnership with US institutions was proposed. [ 117 ] Since then the European Space Agency Science Programme Voyage 2050 has selected the theme of "Galactic Ecosystem with Astrometry in the Near-infrared" as one of two potential L-class missions to be implemented in the coming years thus boosting the chances for GaiaNIR which proposes exactly this. | https://en.wikipedia.org/wiki/Gaia_(spacecraft) |
Gain field encoding is a hypothesis about the internal storage and processing of limb motion in the brain. In the motor areas of the brain, there are neurons which collectively have the ability to store information regarding both limb positioning and velocity in relation to both the body (intrinsic) and the individual's external environment (extrinsic). [ 1 ] The input from these neurons is taken multiplicatively, forming what is referred to as a gain field . [ 2 ] The gain field works as a collection of internal models off of which the body can base its movements. The process of encoding and recalling these models is the basis of muscle memory .
Neuron involved in gain field encoding work multiplicatively, taking the input from several together to form the gain field. [ 2 ] It is this process that allows the complexity of motor control . Instead of simply encoding the motion of the limb in which a specific motion is desired, the multiplicative nature of the gain field ensures that the positioning of the rest of the body is taken in to consideration. This process allows for motor coordination of flexible bimanual actions as opposed to restricting the individual to unimanual motion. [ 3 ] For example, when considering the movement of both arms, the body calls upon gain field models for each arm in order to compensate for the mechanical interactions created by both.
Most gain field activity is based in the premotor cortex found in the frontal lobe anterior to the primary motor cortex , however it receives input from a variety of locations in the brain. [ 4 ] These incoming signals provide frame of reference information through the individual's senses. Further evidence suggests that the cerebellum and posterior parietal cortex (PPC) also play major functional roles in gain field encoding. [ 5 ] [ 6 ] The intrinsic and extrinsic properties of the gain field can be shown as products of the PPC. In Brodmann area 7 of the PPC, the positioning of objects with respect to the eyes is represented completely extrinsically with no input from the positioning of the body involved. [ 7 ] [ 8 ] This opposes the case of other parts of the PPC such as Brodmann area 5 which represents objects in relation to body defined coordinates. Due to the extrinsic and intrinsic properties of motor functioning, it is speculated that these types of signals are both taken multiplicatively to form the gain field. With input from each area, a three-dimensional representation of the objects in space can be arranged for use by the rest of the motor system .
Unsurprisingly lesions in the parietal cortex lead to deficiencies in an individual's spatial movements and coordination and, in some cases, hemineglect . These effects were widely variable from person to person and depending on the location of the lesion further hinting at the complicated nature of gain modulated neurons. [ 9 ]
One of the key components of gain-field encoding is the variability in the response amplitude of the action potentials from neurons. This variability, when independent of change in response selectivity, is called gain modulation. Gain Modulation takes place in many cortical areas and is believed to be a common mechanism of neuronal computation . [ 7 ] [ 10 ] It allows for the combination of different sensory and cognitive information. For example, neurons implicated in processing a part of the visual field see a gain in the response amplitude due to shifting focus to that part of the field of vision. Therefore, neurons that are gain modulated can represent multiple types of information. The multi-modal nature of these neurons makes them ideal for specific types of computations, mainly coordinate transformations . This creates the ability to think spatially , the main contributor to physical coordination.
The encoding of the neurons involved in the motor gain field follow the same gain modulation principles as most of the neurons within the brain. That is to say, when gain is increased, the connections between the neurons firing increase in strength leading to further gain if the neurons continue to receive stimulation. [ 11 ] This observation is why repetition of a particular set of motions is what leads to muscle memory.
One of the main results of gain-field encoding is the cognitive ability to manipulate different coordinate planes that are dealt with daily and adjust limb muscle movements accordingly. A good example of this is moving a pointer across a computer screen with a mouse. Depending on the relative location of the user's head to the computer screen as well as the angle at which the screen is being observed, the user's perspective of the screen will be very different. A mentally mapped grid of the screen appears much larger when the user is closer to the screen as opposed to further away, and it is the brain's ability to keep a consistent mental representation that gives people the ability to function under such dynamic conditions. [ 12 ]
The equation for the firing rate of a gain modulated neuron is a combination of the two types of information being transmitted to the neuron:
r = f ( x ) g ( y ) {\displaystyle r=f(x)g(y)}
where r {\displaystyle r} is the rate of fire, f ( x ) {\displaystyle f(x)} is a function of one type of information input and g ( y ) {\displaystyle g(y)} is another. For example, neural activity for the interaction between gaze direction and retinal image location is almost exactly multiplicative, where x {\displaystyle x} represents the location of a stimulus in retinal coordinates and y {\displaystyle y} represents gaze angle. The primary process by which this interaction can take place is speculated to be recurrent neural networks where neural connections form a directed cycle . [ 2 ] [ 7 ] Recurrent circuitry is abundant in cortical networks and reportedly plays a role in sustaining signals, signal amplification, and response selectivity. [ 13 ]
Early hypotheses of gain field encoding suggested that the gain field works as a model for motion additively. This would mean that if two limbs needed to move, models for each would be called separately but at the same time. However, more recent studies in which more complex motor movements are observed have found that the gain field is created multiplicatively in order to allow the body to adapt to the constantly changing frames of reference experienced in everyday life.
This multiplicative property is an effect of recurrent neural circuitry . A target neuron that takes only two types of direct input can only combine them additively. However mathematical models show that when also receiving recursive input from neighboring neurons, the resulting transformation to the target neurons firing rate is multiplicative. In this model, neurons with overlapping receptive fields excite each other, multiplying the strength. Likewise, neurons with non-overlapping receptive fields are inhibitory. [ 7 ] The result is a response curve that is a scaled representation of the simple additive model.
Observation of human developmental patterns also lend evidence toward this theory of gain-field encoding and gain modulation. Since arm movements are based on both intrinsic and extrinsic models, in order to build these connections one has to learn by self-generating movements and watching. By moving the arms to different parts of space and following with the eyes, the neurons form connections based on mechanical body movements as well as their positioning in an external space. Ideally this is done from every possible gaze angle and position available. This provides your brain with the proper translations by aligning the retinal (extrinsic) and body-centered (intrinsic) representations of space. It is not surprising that before babies develop motor control of their limbs, they tend to flail and watch their own limbs move. [ 14 ]
A similar effect is found when people track moving objects with their eyes. The changing retinal image is referenced with the muscle movements of the eye resulting in the same type of retinal/body-centered alignment. [ 15 ] This is one more process that helps the brain properly encode the relationships needed to deal with our changing perception, and also serves as a verification that the proper physical movements are being made.
A contrary hypothesis to gain field encoding involved implicating the neurons of the primary motor cortex (M1) in dynamic muscle movement. An investigation into area M1 shows that when an individual is asked to rotate an object, activation of the neurons in M1 thought to be controlling the motion happened instantaneously with muscle activation. This provides evidence for preliminary steps from higher motor areas communicating with area M1 by means of gain modulation. [ 16 ] | https://en.wikipedia.org/wiki/Gain-field_encoding |
In electromagnetics , an antenna's gain is a key performance parameter which combines the antenna 's directivity and radiation efficiency . The term power gain has been deprecated by IEEE. [ 1 ] In a transmitting antenna, the gain describes how well the antenna converts input power into radio waves headed in a specified direction. In a receiving antenna, the gain describes how well the antenna converts radio waves arriving from a specified direction into electrical power. When no direction is specified, gain is understood to refer to the peak value of the gain, the gain in the direction of the antenna's main lobe . A plot of the gain as a function of direction is called the antenna pattern or radiation pattern . It is not to be confused with directivity, which does not take an antenna's radiation efficiency into account.
Gain or 'absolute gain' is defined as "The ratio of the radiation intensity in a given direction to the radiation intensity that would be produced if the power accepted by the antenna were isotropically radiated". [ 1 ] Usually this ratio is expressed in decibels with respect to an isotropic radiator (dBi). An alternative definition compares the received power to the power received by a lossless half-wave dipole antenna , in which case the units are written as dBd . Since a lossless dipole antenna has a gain of 2.15 dBi, the relation between these units is G a i n ( d B d ) ≈ G a i n ( d B i ) − 2.15 {\displaystyle \mathrm {Gain(dBd)} \approx \mathrm {Gain(dBi)} -2.15} . For a given frequency, the antenna's effective area is proportional to the gain. An antenna's effective length is proportional to the square root of the antenna's gain for a particular frequency and radiation resistance . Due to reciprocity , the gain of any antenna when receiving is equal to its gain when transmitting.
Gain is a unitless measure that multiplies an antenna's radiation efficiency η {\displaystyle \eta } and directivity D : [ 1 ] [ 2 ] [ 3 ]
The radiation efficiency η {\displaystyle \eta } of an antenna is "The ratio of the total power radiated by an antenna to the net power accepted by the antenna from the connected transmitter." [ 1 ]
A transmitting antenna is supplied with power by a transmission line connecting the antenna to a radio transmitter . The power accepted by the antenna P O {\displaystyle P_{O}} is the power supplied to the antenna's terminals. Losses prior to the antenna terminals are accounted for by separate impedance mismatch factors which are therefore not included in the calculation of radiation efficiency.
Published numbers for antenna gain are almost always expressed in decibels (dB), a logarithmic scale. From the gain factor G, one finds the gain in decibels as:
Therefore, an antenna with a peak power gain of 5 would be said to have a gain of 7 dBi. dBi is used rather than just dB to emphasize that this is the gain according to the basic definition, in which the antenna is compared to an isotropic radiator.
When actual measurements of an antenna's gain are made by a laboratory, the field strength of the test antenna is measured when supplied with, say, 1 watt of transmitter power, at a certain distance. That field strength is compared to the field strength found using a so-called reference antenna at the same distance receiving the same power in order to determine the gain of the antenna under test. That ratio would be equal to G if the reference antenna were an isotropic radiator (irad).
However a true isotropic radiator cannot be built, so in practice a different antenna is used. This will often be a half-wave dipole, a very well understood and repeatable antenna that can be easily built for any frequency. The directive gain of a half-wave dipole with respect to the isotropic radiator is known to be 1.64 and it can be made nearly 100% efficient. Since the gain has been measured with respect to this reference antenna, the difference in the gain of the test antenna is often compared to that of the dipole. The gain relative to a dipole is thus often quoted and is denoted using dBd instead of dBi to avoid confusion. Therefore, in terms of the true gain (relative to an isotropic radiator) G , this figure for the gain is given by:
For instance, the above antenna with a gain G = 5 would have a gain with respect to a dipole of 5/1.64 ≈ 3.05, or in decibels one would call this 10 log(3.05) ≈ 4.84 dBd. In general:
Both dBi and dBd are in common use. When an antenna's maximum gain is specified in decibels (for instance, by a manufacturer) one must be certain as to whether this means the gain relative to an isotropic radiator or with respect to a dipole. If it specifies dBi or dBd then there is no ambiguity, but if only dB is specified then the fine print must be consulted. Either figure can be easily converted into the other using the above relationship.
When considering an antenna's directional pattern, gain with respect to a dipole does not imply a comparison of that antenna's gain in each direction to a dipole's gain in that direction. Rather, it is a comparison between the antenna's gain in each direction to the peak gain of the dipole (1.64). In any direction, therefore, such numbers are 2.15 dB smaller than the gain expressed in dBi.
Partial gain is calculated as power gain, but for a particular polarization . It is defined as the part of the radiation intensity U {\displaystyle U} corresponding to a given polarization, divided by the total radiation intensity of an isotropic antenna. [ 2 ]
The partial gains in the θ {\displaystyle \theta } and ϕ {\displaystyle \phi } components are expressed as
and
where U θ {\displaystyle U_{\theta }} and U ϕ {\displaystyle U_{\phi }} represent the radiation intensity in a given direction contained in their respective E {\displaystyle E} field component.
As a result of this definition, we can conclude that the total gain of an antenna is the sum of partial gains for any two orthogonal polarizations.
Suppose a lossless antenna has a radiation pattern given by:
Let us find the gain of such an antenna. First we find the peak radiation intensity of this antenna:
The total radiated power can be found by integrating over all directions:
Since the antenna is specified as being lossless the radiation efficiency is 1. The maximum gain is then equal to:
Expressed relative to the gain of a half-wave dipole we would find:
As an example, consider an antenna that radiates an electromagnetic wave whose electrical field has an amplitude E θ {\displaystyle \ E_{\theta }\ } at a distance r . {\displaystyle \ r\ .} That amplitude is given by:
where:
For a large distance r . {\displaystyle \ r\ .} The radiated wave can be considered locally as a plane wave. The intensity of an electromagnetic plane wave is:
where
and
If the resistive part of the series impedance of the antenna is R s , {\displaystyle \ {R_{s}}\ ,} the power fed to the antenna is 1 2 R s I 2 . {\displaystyle \scriptstyle {1 \over 2}{R_{s}I^{2}}\ .} The intensity of an isotropic antenna is the power so fed divided by the surface of the sphere of radius r :
The directive gain is:
For the commonly utilized half-wave dipole , the particular formulation works out to the following, including its decibel equivalency, expressed as dBi (decibels referenced to isotropic radiator):
Sometimes, the half-wave dipole is taken as a reference instead of the isotropic radiator. The gain is then given in dBd (decibels over dipole):
Realized gain differs from gain in that it is "reduced by its impedance mismatch factor." This mismatch induces losses above the dissipative losses described above; therefore, realized gain will always be less than gain. Gain may be expressed as absolute gain if further clarification is required to differentiate it from realized gain. [ 1 ]
Total radiated power (TRP) is the sum of all RF power radiated by the antenna when the source power is included in the measurement. TRP is expressed in watts or the corresponding logarithmic expressions, often dBm or dBW. [ 4 ]
When testing mobile devices, TRP can be measured while in close proximity of power-absorbing losses such as the body and hand of the user. [ 5 ]
The TRP can be used to determine body loss (BoL). The body loss is considered as the ratio of TRP measured in the presence of losses and TRP measured while in free space.
This article incorporates public domain material from Federal Standard 1037C . General Services Administration . Archived from the original on January 22, 2022. (in support of MIL-STD-188 ). | https://en.wikipedia.org/wiki/Gain_(antenna) |
In live sound mixing , gain before feedback ( GBF ) is a practical measure of how much a microphone can be amplified in a sound reinforcement system before causing audio feedback . In audiology , GBF is a measure of hearing aid performance. In both fields the amount of gain is measured in decibels at or just below the point at which the sound from the speaker driver re-enters the microphone and the system begins to ring or feed back. Potential acoustic gain ( PAG ) is a calculated figure representing gain that a system can support without feeding back. [ 1 ]
In live sound mixing, GBF is dependent on a wide variety of conditions: the pickup pattern (polar pattern) of the microphone, the frequency response of the microphone and of the rest of the sound system, the number of active microphones and loudspeakers, the acoustic conditions of the environment including reverberation and echo, and the relative positions of the microphones, the loudspeakers, the sound sources and the audience. Each doubling of the number of open microphones (NOM) reduces the PAG by 3 dB. [ 2 ]
Directional microphones are used in live sound to maximize GBF. Directional microphones with cardioid and hypercardioid pickup patterns are designed with reduced sensitivity to the rear (cardioid) or to an angle between the side and the rear (hypercardioid). [ 1 ] Such microphones are aimed such that their pickup pattern is weakest in the direction of the loudspeakers. This is especially useful in the presence of foldback monitors (stage wedges). Directional loudspeaker systems may also be used to increase GBF. [ 3 ] [ 4 ]
The distance from the sound source to the microphone is a critical element of GBF. Greater GBF is obtained with the performer closer to the microphone; an instance of the inverse-square law . If the performer reduces the distance to the microphone by half, the PAG is increased by 6 dB while the environmental sounds remain relatively the same. [ 3 ] [ 1 ]
The sound system operator can use equalization to change the frequency response of a microphone or loudspeakers system to increase GBF. The frequency which first begins ringing or feeding back is identified by the operator, and a notch or parametric filter is engaged to reduce the overall level of that frequency. [ 3 ] This process is repeated several times to identify and reduce the level of further feedback frequencies. [ 5 ] A graphic equalizer can be used for the same purpose but with somewhat less precision. Automatic feedback suppressors automate and speed the process of identifying and reducing feedback frequencies. [ 6 ] A small amount of pitch shift applied to the signal can increase GBF, as can the addition of a few milliseconds of straight delay . The latter will increase the number of feedback frequencies while reducing the frequency range within which they occur, but it will slow the rate at which feedback grows. In practice, adding straight delay to a signal improves GBF. [ 6 ]
A hearing aid incorporates a miniature microphone and a very small speaker driver, and various conditions may increase or decrease the amount of gain that can be applied to the microphone signal before feedback. A well-fitted hearing aid has more GBF than one that is loose. The shape of the earmold is a factor, with larger and heavier designs capable of delivering greater GBF. Hearing aid designs deliver gain in increasing steps depending on the severity of the patient's hearing loss; the range spans from 10 to 65 dB of gain. To prevent feedback with the highest amounts of gain, such designs require the tightest-fitting earmolds with no venting, and the deepest penetration of the ear canal to place the speaker driver as close as practical to the eardrum . [ 7 ] | https://en.wikipedia.org/wiki/Gain_before_feedback |
Gain compression is a reduction in differential or slope gain caused by nonlinearity of the transfer function of an amplifying device [ 1 ] for large-signal inputs.
When overdriving an amplifier beyond its the linear range, gain compression will occur [ 1 ] due to nonlinear circuit characteristics. The output of large amplitude inputs will be less than expected than using the small signals gain of the amplifier, such that an increase in input will not be matched by a proportional increase in output. Gain compression is the difference between the ideal linear power transfer curve and the real circuit's power transfer curve.
An important gain compression parameter is the OP1dB , which is the power input that results in a 1 dB compression of the output power (OP), corresponding to a gain ratio of 10 - 1 ⁄ 10 = 79.4%.
Harmonic distortion results from nonlinear transfer curves. And once an amplifier's maximum amplitude is reached, signals will be clipped , resulting in even stronger harmonic distortion.
Nonlinearity may be caused by heat due to power dissipation. Also, a transistor's operating point may move with temperature.
Gain compression is relevant in any system with a wide dynamic range , such as audio or RF . It is more common in tube circuits than transistor circuits, due to topology differences, possibly causing the differences in audio performance called " valve sound ". The front-end RF amps of radio receivers are particularly susceptible to this phenomenon when overloaded by a strong unwanted signal. [ 1 ]
A tube radio or tube amplifier will increase in volume to a point, and then as the input signal extends beyond the linear range of the device, the effective gain is reduced, altering the shape of the waveform. The effect is also present in transistor circuits. The extent of the effect depends on the topology of the amplifier.
Gain compression in RF amplifiers is similar to soft clipping. However, in narrowband systems, the effect looks more like gain compression simply because the harmonics are filtered out after amplification. Many data sheets for RF amplifiers list gain compression rather than distortion figures because it's easier to measure and is more important than distortion figures in nonlinear RF amplifiers.
In wideband and low- frequency systems, the nonlinear effects are readily visible, e.g. the output is clipped . To see the same thing at 1 GHz , an oscilloscope with a bandwidth of at least 10 GHz is needed. Observing with a spectrum analyzer , the fundamental compressed and the harmonics picking up.
A low-noise RF amplifier , if fed by a directional antenna to a consumer 900 MHz receiver, should improve the transmission range. It works, but the receiver may also pick up a couple of UHF stations around 700 MHz.
For example, if channel 54 is transmitting 6 MW of AM , FM , and PM , the RF front end, expecting −80 dBm , would be grossly overloaded and generate mixing products. This is a typical effect of gain compression.
Power compression is a form of gain compression that takes place in loudspeaker voice coils when they heat up and increase their resistance . This causes less power to be drawn from the amplifier and a reduction in sound pressure level .
Dynamic range compression is a more general term that typically refers to intentional compression, and may be done in the digital realm or analog realm. Automatic gain control circuits are intentionally designed to actively change the overall gain in response to the level of the input, resulting in a transfer function that may vary over time. Gain compression on the other hand is a consequence of analog amplifier circuit non-linearities that are generally undesired. | https://en.wikipedia.org/wiki/Gain_compression |
In control theory , gain scheduling is an approach to control of nonlinear systems that uses a family of linear controllers , each of which provides satisfactory control for a different operating point of the system.
One or more observable variables, called the scheduling variables , are used to determine what operating region the system is currently in and to enable the appropriate linear controller. For example, in an aircraft flight control system , the altitude and Mach number might be the scheduling variables, with different linear controller parameters available (and automatically plugged into the controller) for various combinations of these two variables. In brief, gain scheduling is a control design approach that constructs a nonlinear controller for a nonlinear plant by patching together a collection of linear controllers.
A relatively large scope state of the art about gain scheduling has been published in (Survey of Gain-Scheduling Analysis & Design, D.J.Leith, WE.Leithead). [ 1 ]
Recently, new methodologies using Machine learning, such as Adaptive control based on Artificial Neural Networks (ANN) and Reinforcement Learning , [ 2 ] [ 3 ] [ 4 ] have been studied. | https://en.wikipedia.org/wiki/Gain_scheduling |
Gajim / ɡ ɛ ˈ ʒ iː m / [ 4 ] is an instant messaging client for the XMPP protocol which uses the GTK toolkit. The name Gajim is a recursive acronym for Gajim's a jabber instant messenger . Gajim runs on Linux , BSD , macOS , and Microsoft Windows . Released under the GPL-3.0-only license, Gajim is free software . A 2009 round-up of similar software on Tom's Hardware found version 0.12.1 "the lightest and fastest jabber IM client". [ 5 ]
Gajim aims to be an easy to use and fully-featured XMPP client. Gajim uses GTK (PyGObject) as GUI library, which makes it cross-platform compatible. Some of its features:
Gajim is available in Basque, Bulgarian, Chinese, Croatian, Czech, English, Esperanto, French, German, Italian, Norwegian (Bokmål), Polish, Russian, Spanish, Slovak, Swedish, Ukrainian and others. [ 3 ]
Gajim supports various third-party plugins ( official list ).
Reviews | https://en.wikipedia.org/wiki/Gajim |
The Gajski–Kuhn chart (or Y diagram ) depicts the different perspectives in VLSI hardware design . [ 1 ] Mostly, it is used for the development of integrated circuits . Daniel Gajski and Robert Kuhn developed it in 1983. In 1985, Robert Walker and Donald Thomas refined it.
According to this model, the development of hardware is perceived within three domains that are depicted as three axis and produce a Y. Along these axis, the abstraction levels that describe the degree of abstraction. The outer shells are generalisations, the inner ones refinements of the same subject.
The issue in hardware development is most often a top-down design problem. This is perceived by the three domains of behaviour, structure, and the layout that goes top-down to more detailed abstraction levels. The designer can select one of the perspectives and then switch from one view to another. Generally, the design process is not following a specific sequence in this diagram. | https://en.wikipedia.org/wiki/Gajski–Kuhn_chart |
Gal's accurate tables is a method devised by Shmuel Gal to provide accurate values of special functions using a lookup table and interpolation . It is a fast and efficient method for generating values of functions like the exponential or the trigonometric functions to within last-bit
accuracy for almost all argument values without using extended precision arithmetic.
The main idea in Gal's accurate tables is a different tabulation for the special function being computed. Commonly, the range is divided into several subranges, each with precomputed values and correction formulae. To compute the function, look up the closest point and compute a correction as a function of the distance.
Gal's idea is to not precompute equally spaced values, but rather to perturb the points x so that both x and f ( x ) are very nearly exactly representable in the chosen numeric format. By searching approximately 1000 values on either side of the desired value x , a value can be found such that f ( x ) can be represented with less than ±1/2000 bit of rounding error . If the correction is also computed to ±1/2000 bit of accuracy (which does not require extra floating-point precision as long as the correction is less than 1/2000 the magnitude of the stored value f ( x ), and the computed correction is more than ±1/1000 of a bit away from exactly half a bit (the difficult rounding case), then it is known whether the exact function value should be rounded up or down.
The technique provides an efficient way to compute the function value to within ±1/1000 least-significant bit, i.e. 10 extra bits of precision. If this approximation is more than ±1/1000 of a bit away from exactly midway between two representable values (which happens 99.8% of the time), then the correctly rounded result is clear.
Combined with an extended-precision fallback algorithm, this can compute the correctly rounded result in very reasonable average time. In 2/1000 (0.2%) of the time, such a higher-precision evaluation is required to resolve the rounding uncertainty, but this is infrequent enough that it has little effect on the average calculation time.
The problem of generating function values which are accurate to the last bit is known as the table-maker's dilemma . | https://en.wikipedia.org/wiki/Gal's_accurate_tables |
The gal operon is a prokaryotic operon , which encodes enzymes necessary for galactose metabolism . [ 1 ] Repression of gene expression for this operon works via binding of repressor molecules to two operators. These repressors dimerize, creating a loop in the DNA. The loop as well as hindrance from the external operator prevent RNA polymerase from binding to the promoter, and thus prevent transcription . [ 2 ] Additionally, since the metabolism of galactose in the cell is involved in both anabolic and catabolic pathways, a novel regulatory system using two promoters for differential repression has been identified and characterized within the context of the gal operon.
The gal operon of E. coli consists of 4 structural genes: galE (epimerase), galT (galactose transferase), galK (galactokinase), and galM (mutarotase) which are transcribed from two overlapping promoters, PG1 (+1) and PG2 (-5), upstream from galE . [ 3 ] GalE encodes for an epimerase that converts UDP-glucose into UDP-galactose. This is required for the formation of UDP-galactose for cell wall biosynthesis , in particular the cell wall component lipopolysaccharide, even when cells are not using galactose as a carbon/energy source. [ 4 ] GalT encodes for the protein galactosyltransferase which catalyzes the transfer of a galactose sugar to an acceptor, forming a glycosidic bond. [ 5 ] GalK encodes for a kinase that phosphorylates α-D-galactose to galactose 1-phosphate . [ 6 ] Lastly, galM catalyzes the conversion of β-D-galactose to α-D-galactose as the first step in galactose metabolism. [ 7 ]
The gal operon contains two operators , O E (for external) and O I (for internal). The former is just upstream of the promoter , and the latter is just after the galE gene (the first gene in the operon). These operators bind the repressor, GalR, which is encoded from outside the operator region. For this repressor protein to function properly, the operon also contains a histone binding site to facilitate this process. [ 8 ]
An additional site, known as the activating site, is found following the external operator, but upstream of PG2. This site serves as the binding region for the cAMP-CRP complex, which modulates the activity of the promoters and thus, gene expression. [ 9 ]
The unlinked galR gene encodes the repressor for this system. A tetrameric GalR repressor binds to 2 operators, one located at +55 and one located at -60 relative to the PG1 start site. Looping of the DNA blocks the access of RNA polymerase to promoters and/or inhibits formation of the open complex. This looping requires the presence of the histone-like protein, HU to facilitate the formation of the structure and allow for proper repression. [ 8 ] When GalR binds as a dimer to the -60 site only, the promoter PG2 is activated, not repressed, allowing basal levels of GalE to be produced. In this state, the PG1 promoter is inactivated through interactions with the alpha subunit of RNA polymerase. [ 2 ] Activity of this repressor protein is controlled based on the levels of D-galactose in the cell. Increased levels of this sugar inhibit the activity of the repressor by binding allosterically, resulting in a conformational change of the protein, which suppresses its interactions with RNA polymerase and DNA. [ 10 ] This induces the activity of the operon, which will increase the rate of galactose metabolism.
The gal operon is also controlled by CRP-cAMP, similarly to the lac operon. CRP-cAMP binds to the -35 region, promoting transcription from PG1 but inhibiting transcription from PG2. This is accomplished due to the location of the activation sequence. When CRP-cAMP binds the activating sequence, it blocks RNA polymerase from establishing an open complex with PG2, but enhances a closed complex with RNA polymerase at PG1. This represses the activity of the PG2 promoter, and increases the activity of the PG1 promoter. [ 9 ] When cells are grown in glucose , basal level transcription occurs from PG2. | https://en.wikipedia.org/wiki/Gal_operon |
Galactan ( galactosan ) is a polysaccharide consisting of polymerized galactose . [ 1 ] In general, galactans in natural sources contain a core of galactose units connected by α(1→3) or α(1→6), with structures containing other monosaccharides as side-chains. [ 2 ]
Galactan derived from Anogeissus latifolia is primarily α(1→6), but galactan from acacia trees is primarily α(1→3). [ 3 ]
Halymenia durvillei is a red seaweed (algae) that produces a sulfated galactan. [ 4 ] Several other algae species also contain galactans. [ 5 ] Including Carpopeltis F.Schmitz, 1895 . [ 6 ]
Galactan is found in the side chains of rhamnogalacturonan I (RG-I) and is needed for gel formation in the cell walls of organisms. [ 7 ] It was observed there was less of the gelling characteristic (as well as the polymeric chains being more likely to degrade) when fewer galactans were present in the polymeric side chains. [ 7 ] [ 8 ] | https://en.wikipedia.org/wiki/Galactan |
Galactic Bridges and Tails is a computer animation film created in 1972 by astrophysicists Alar Toomre and Juri Toomre . The brothers created the film as a teaching aid to accompany their 1972 landmark research paper of the same name, published in The Astrophysical Journal , which described galaxy collisions and galaxy mergers . [ 1 ]
The Toomre film contains both 2D and 3D computer graphics simulations of colliding galaxies. The animations are time-lapses that compress billions of years into just a few minutes. Written in the FORTRAN programming language, the simulations sent character and vector information to a CRT-based ASCII character film recorder. The film recorder exposed multiple frames of 16mm film to create the final animated film. [ 2 ]
In 2007, filmmaker Michael Lauter worked with the Toomre brothers to digitally restore the 16mm original film and create a new HD video (1080p24) digital master. [ 2 ]
Massachusetts-based MathWorks created a Simulink model titled Spiral Galaxy Formation Simulation for use within their MATLAB programming environment. The company states that their computer animation model was inspired by the original Galactic Bridges and Tails paper and film. [ 3 ] | https://en.wikipedia.org/wiki/Galactic_Bridges_and_Tails |
The Galactic Center GeV Excess ( GCE ) is an unexpected surplus of gamma-ray radiation in the center of the Milky Way Galaxy. This spherical source of radiation was first detected in 2009 [ 1 ] [ 2 ] by the Fermi Gamma-ray Space Telescope and is unexplained by direct observation. [ 3 ] Two percent of the gamma ray radiation in a 30° radius circle around the Galactic Center is attributed to the GCE. As of 2020 [update] , this excessive (and diffused) gamma-ray radiation is not well understood by astronomers. [ 4 ] [ 5 ] [ 6 ] [ 7 ]
Some astronomers argue that self-annihilating dark matter (which is not otherwise known to radiate) may be the cause of the GCE, while others prefer a population of pulsars (which have not been observed) as the source. [ 8 ] [ 3 ]
Astronomers have suggested that self-annihilating dark matter may be a dominant contributor to the GCE, based on analysis using non-Poissonian template fitting statistical methods, [ 5 ] wavelet methods, [ 7 ] and studies by other astronomers may support this idea. [ 9 ] [ 10 ] More recently, in August 2020, other astronomers have reported that self-annihilating dark matter may not be the explanation for the GCE after all. [ 11 ] [ 12 ] Other hypotheses include ties to a yet unseen population of millisecond pulsars [ 13 ] [ 14 ] or young pulsars, burst events, the stellar population of the galactic bulge , [ 15 ] or the Milky Way's central supermassive black hole . [ 16 ] | https://en.wikipedia.org/wiki/Galactic_Center_GeV_excess |
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