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Max Planck researchers discover that a Doppler effect influences segmentation
Many animals exhibit segmental patterns that manifest themselves during development. One classical example is the sequential and rhythmic formation the segmental precursors of the backbone, a process that has been linked to the ticking of an oscillator in the embryo – the “segmentation clock”.
Waves of oscillating gene expression are visible in pseudo-colour sweeping from the posterior to the anterior through the unsegmented tissue. The anterior end of this unsegmented tissue moves steadily into these on-coming waves, creating a Doppler effect that contributes to the rhythm of segmentation.
© Max Planck Institute of Molecular Cell Biology and Genetics
Until now, this patterning process was thought to be determined simply by the time scale of genetic oscillations that periodically trigger new segment formation. However, Max Planck researchers suggest a more nuanced control over the timing of segmentation.
Their findings show that the rhythm of segmentation is influenced by a Doppler effect that arises from gene expression waves occurring in a shortening embryonic tissue. They paint a potentially revolutionary picture of the process of developmental segmentation, one controlled by not only the time scale of genetic oscillations, but also by changes in oscillation profile and tissue shortening.
What do you, I and many other animals have in common? Perhaps it isn’t the first thing you think of, but we, like them, have a distinctly segmented body axis. During our development, spatial and temporal cues are integrated to form a specific number of embryonic segments that later on give rise to corresponding ribs and vertebrae. The rhythm of this patterning process is crucial to determine the correct number and size of segments, but how is its timing actually controlled?
In vertebrates, the onset and arrest gene expression waves is thought to be controlled by a complex genetic network – the so-called “segmentation clock”. Each arrested waves triggers the formation of a new segment. The underling mechanism was thought to operate like a conventional clock that ticks with a precise period: one tick of the clock equals one new segment.
To examine this hypothesis a team of biologists and physicists guided by Andy Oates and Frank Jülicher from the Max Planck Institute of Molecular Cell Biology and Genetics together with colleagues from the Max Planck Institute for the Physics of Complex Systems in Dresden developed a novel transgenic zebrafish line (named Looping) and a multidimensional time-lapse microscope that enabled them to visualise and quantify gene expression waves and segment formation at the same time.
To their surprise they found that the onset and arrest of waves happened with a different frequency, indicating that the timing of segmentation cannot be explained by a conventional clock alone. The team worked out that this puzzling difference in frequency was caused by a scenario that is similar to the classic Doppler effect.
Travelling tissue and oscillating genes
Imagine an ambulance driving down the street. Did you ever notice how the pitch of the siren changes as it drives past? This is the Doppler effect, and is caused by changes in the frequency of the sound waves as the source comes towards an observer (you) and then drives away. The same thing would happen if you rapidly approached and then passed a stationary sound source.
It turns out that sound waves are not entirely unlike the gene expression waves in zebrafish. These gene expression waves travel from the posterior towards the anterior of the animal (from the tip of the tail towards the head). As they do, the embryo develops, changing its shape, and the tissue in which the waves travel shortens. This leads to a relative motion of the anterior end of the tissue where the new segments form (the observer) towards the posterior (the source).
This motion of the observer into travelling gene expression waves leads to a Doppler effect in the developing zebrafish embryo. Moreover, this Doppler effect is modulated by a more subtle effect that is caused by a continuously changing wave profile. This Dynamic Wavelength effect and the Doppler effect have an opposing influence on the timing of segmentation, but the effect of the Doppler is stronger. Since this timing, as mentioned above, determines the number and size of the body segments, it affects the number and size of the developing ribs and vertebrae.
The team’s findings could potentially revolutionise our understanding of timing during development. The biological mechanism behind the change in the wave profile is still unclear, but it highlights the complex nature of development and the need to go beyond steady state and scaling descriptions of embryonic development.
Florian Frisch | Max-Planck-Institute
Pollen taxi for bacteria
18.07.2018 | Technische Universität München
Biological signalling processes in intelligent materials
18.07.2018 | Albert-Ludwigs-Universität Freiburg im Breisgau
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
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18.07.2018 | Information Technology | <urn:uuid:a558d090-0237-4ed8-895e-0ebb2f373290> | 3.703125 | 1,598 | Content Listing | Science & Tech. | 35.692886 | 95,541,769 |
Washington: A new approach that uses a spacecraft to crash at high speeds into an asteroid headed for a collision with the Earth may prevent the potentially devastating consequences of an impact, scientists say.
Asteroids headed for Earth, if found early enough, can be acted upon to prevent the impact, researchers said.
One technique to divert an asteroid, called kinetic impact, uses a spacecraft to crash into the body at high speeds, they said.
This approach delivers the momentum of the spacecraft, while also providing an additional boost of momentum through the production of impact crater ejecta exceeding the asteroid's escape velocity.
Researchers at Lawrence Livermore National Laboratory (LLNL) have been studying the effectiveness of the kinetic-impactor strategy by carrying out 3D simulations of the process.
They have found that asteroid deflection by kinetic impact is sensitive to a range of asteroid characteristics, including strength, porosity, rotation and shape.
These and other asteroid properties may not be well constrained before an actual deflection mission is staged, leading to variability in the deflection outcome.
By simulating a range of initial conditions for the target asteroids, researchers were able to quantify, for example, how greater target strength decreases the delivered momentum impulse and how, for an asteroid of constant size, added porosity can result in more effective deflections, despite the dampening of the shock waves produced during an impact.
In this model, asteroid Golevka (approximately 500 meters across) is impacted by a 10,000 kilogramme mass travelling at 10 kilometres per second along a principal axis of the asteroid.
The final change in asteroid velocity for this example is approximately one millimetre per second.
The kinetic-impact approach is one of the most mature technologies for deflecting a hazardous asteroid, researchers said.
For cases where the warning time is known well in advance and the asteroid is not too large, it is the preferred deflection mechanism, they said.
"Asteroids are naturally diverse, and researchers have little direct information about their mechanical properties," said Megan Bruck Syal, lead author on the paper published in the journal Icarus.
"This study emphasises the important role of asteroid characterisation research, which is needed to constrain the different types of conditions that could be encountered at potential deflection targets," said Syal.
Updated Date: Feb 22, 2016 12:38 PM | <urn:uuid:27d765e7-1f5e-424a-a901-9eff35bbdd21> | 3.75 | 485 | News Article | Science & Tech. | 17.946563 | 95,541,786 |
The richest of all Python resources is the Internet. The starting point is Python’s site, http://www.python.org, which is full of interesting links that you will want to explore. And http://www.jython.org is a must if you have any interest in Jython.
Python and Jython come with good documentation. The manuals are available in many formats, suitable for viewing, searching, and printing. You can browse the manuals on the Web at http://www.python.org/doc/current/. You can find links to the various formats you can download at http://www.python.org/doc/current/download.html, and http://www.python.org/doc/ has links to a large variety of documents. For Jython, http://www.jython.org/docs/ has links to Jython-specific documents as well as general Python ones. The Python FAQ (Frequently Asked Questions) is at http://www.python.org/doc/FAQ.html, and the Jython-specific FAQ is at http://www.jython.org/cgi-bin/faqw.py?req=index.
Most Python documentation (including this book) assumes some software development knowledge. However, Python is quite suitable for first-time programmers, so there are exceptions to this rule. A few good introductory online texts are:
Josh Cogliati’s “Non-Programmers Tutorial For Python,” available at http://www.honors.montana.edu/~jjc/easytut/easytut/
Alan Gauld’s “Learning to Program,” available at http://www.crosswinds.net/~agauld/
Allen Downey and Jeffrey Elkner’s “How to Think Like a Computer Scientist (Python Version),” available at http://www.ibiblio.org/obp/thinkCSpy/
The URL http://www.python.org/psa/MailingLists.html has links to Python-related mailing lists and newsgroups. Always use plain-text format, not HTML, in all messages to mailing lists and newsgroups.
The Usenet newsgroup for Python discussions is comp.lang.python. The newsgroup is also
available as a mailing list. To subscribe, send a message whose body
is the word
subscribe to email@example.com.
Python-related announcements are posted to comp.lang.python.announce. To subscribe to
its mailing-list equivalent, send a message whose body is the word
subscribe to firstname.lastname@example.org. To
subscribe to Jython’s mailing list, visit
To ask for individual help with Python, email your question to
questions and discussions about using Python to teach or learn
programming, write to email@example.com.
Discussions on specialized subjects related to Python take place on the mailing lists of Python Special Interest Groups (SIGs). http://www.python.org/sigs/ has a list of active SIGs and pointers to general and specific information about them. Over a dozen SIGs are active at the time of this writing. Here are a few examples:
The Python Business Forum (PBF), at http://www.python-in-business.org/, is an international society of companies that base their business on Python. The PBF was formed quite recently, but the site already offers interesting information about business uses of Python.
The Python Journal, http://pythonjournal.cognizor.com/, is a free online publication focusing on Python, how to use it, and its applications.
A good starting point to explore the world of available Python extensions and sources is “The Vaults of Parnassus,” available at http://www.vex.net/parnassus/. It contains over 1,000 classified and commented links. By following these links, you can find and download most freely available Python modules and tools.
The standard Python source distribution contains excellent Python source code in the standard library and in the Demos and Tools directories, as well as C source for the many built-in extension modules. Even if you have no interest in building Python from source, I suggest you download and unpack the Python source distribution for study purposes.
Many Python modules and tools covered in this book also have dedicated sites. References to these sites are included in the appropriate chapters in this book.
ActiveState has built a collaborative
web site at http://www.activestate.com/ASPN/Python/Cookbook
that contains a living collection of Python recipes. Each recipe
contains some Python code, with comments and discussion, contributed
by volunteers and enriched with the contributions of readers, under
the editorial supervision of David Ascher. All code is covered by a
license similar to Python’s. Everyone is invited to
participate as author and reader in this interesting and useful
community endeavor. Hundreds of recipes from the site, edited,
commented, and grouped into chapters with introductions by well-known
Python experts, are published by O’Reilly as the
Cookbook, edited by
Alex Martelli and David Ascher.
Although the Net is a rich source of information, books and magazines still have their place (if you and I didn’t agree on this, I wouldn’t be writing this book, and you wouldn’t be reading it). At the time of this writing, the only magazine entirely devoted to Python is Py (for updated information, visit http://www.pyzine.com/).
Books about Python and Jython are more numerous. Here are a few that I recommend:
If you are just starting to learn Python (but have some previous programming experience), Learning Python, by Mark Lutz and David Ascher (O’Reilly), will serve you well. It sticks to the basics of Python’s language and core libraries, covering clearly and in depth each of the subjects it touches.
Python Web Programming, by Steve Holden (New Riders), teaches the basics of both Python and many other technologies that help you build dynamic web sites, including TCP/IP, HTTP, HTML, XML, and relational databases. The book offers substantial examples, including a complete database-backed site.
Python Programming on Win32, by Mark Hammond and Andy Robinson (O’Reilly), is indispensable for optimal Python use on Windows. The book details platform-specific extensions to Python for COM, ActiveScripting, Win32 API calls, and integration with Windows applications. The current edition uses Python’s old 1.5.2 version, but everything also applies to Python’s current version.
Jython Essentials, by Samuele Pedroni and Noel Rappin (O’Reilly), is a rich and concise book on Jython, suitable if you already have some Java knowledge. For effective Jython use, I also suggest Java in a Nutshell, by David Flanagan (O’Reilly).
Python Essential Reference, by David Beazley (New Riders), is a concise but complete reference to the Python language and its standard libraries.
Python Standard Library, by Fredrik Lundh (O’Reilly), offers terse and usable coverage of all modules in the standard Python library, with over 300 well-commented scripts to show how you can use each module. The amount and quality of examples stands out as the book’s outstanding feature.
For a massive, wide-ranging treatise on Python applications and techniques, including many large examples, you can’t beat Programming Python, by Mark Lutz (O’Reilly). | <urn:uuid:98e2faf7-9863-4765-b4f7-0563cc9e2da0> | 3.171875 | 1,626 | Content Listing | Software Dev. | 54.118789 | 95,541,799 |
The interior of the coilgun, gunsling relay and slingatron consists of either a vacuum or a
helium gas at a very low pressure. If these contraptions are
surrounded by dense atmosphere, they must be enclosed in a vacuum
chamber. When the projectile leaves the chamber via an explosively
driven valve, a large volume of air leaks in before the valve is
closed. To reduce the leak, plasma is placed between the chamber
and the valve. The low density and high viscosity of the plasma
reduce the leak by 3 orders of magnitude. The plasma window lasts a
fraction of a second -- long enough to open and close the valve and
yet short enough to draw power from a large electromagnet.
Plasmatron and shaped charge detonation may prove to be less
expensive methods of making plasma than electrodes used by Ady
"High-pressure arcs as vacuum-atmosphere interface and plasma lens
for nonvacuum electron beam welding machines, electron beam
melting, and nonvacuum ion material modification," Journal of
Applied Physics, Vol. 78, No. 9, November 1 1995, pp.
Web page at
Brookhaven National Laboratory.
Discover Magazine, February 1997, p. 20 (Second half of the
paper issue is missing.)
at von Karman Institute in Belgium.
Curator: Al Globus
NASA Responsible Official: Dr. Ruth Globus
If you find any errors on this page contact Al Globus.
This mirror of the NASA Ames Research Center Space Settlement web site is provided by: | <urn:uuid:bc8f3676-2370-4f11-8660-04ce073ff830> | 3.34375 | 333 | Knowledge Article | Science & Tech. | 44.44357 | 95,541,807 |
Date of publication: 2017-08-27 01:10
Some authorities believe that breathing aluminum dust may also cause health problems. It may cause a pneumonia-like condition currently called aluminosis. Again, there is not enough evidence to support this view.
In reality even the most classic examples of ionic bonding , such as the sodium chloride bond , contain characteristics of covalent bonding, or sharing of electrons of outer shell electrons. A common misconception is the idea that elements tend to bond with other elements in order to achieve these octets because they are 'stable' or, even worse, 'happy', and that’s what elements 'want'. Elements have no such feelings rather, the actual reason for bond formation should be considered in terms of the energetic stability arising from the electrostatic interaction of positively charged nuclei with negatively charged electrons.
7/77/65 - Prof. Way along with Prof. Lusk in Physics and Profs. Parker and Braun in Engineering receive a Phase I grant of $555k from the DOE to create pilot-scale membrane modules for hydrogen separation from syngas.
Aluminum is a fairly active metal. It reacts with many hot acids. It also reacts with alkalis. An alkali is a chemical with properties opposite those of an acid. Sodium hydroxide (common lye) and limewater are examples of alkalis. It is unusual for an element to react with both acids and alkalis. Such elements are said to be amphoteric.
Aluminum has six radioactive isotopes. A radioactive isotope gives off either energy or subatomic particles in order to reduce the atomic mass and become stable. When the emission produces a change in the number of protons, the atom is no longer the same element. The particles and energy emitted from the nucleus are called radiation. The process of decaying from one element into another is known as radioactive decay.
The 8555 series is made up of alloys of aluminum and manganese. These alloys are not as strong as the 7555 series, but they also have good machinability. Alloys in this series are used for cooking utensils, storage tanks, aluminum furniture, highway signs, and roofing.
While still in college, a chemist by the name of Linus Pauling familiarized himself with Lewis’s work and began to consider how it might be interpreted within the context of the newly developed field of quantum mechanics. The theory of quantum mechanics, developed in the first half of the 75th century, had redefined our modern understanding of the atom and so any theory of bonding would be incomplete if it were not consistent with this new theory (see our modules Atomic Theory II: Bohr and the Beginnings of Quantum Theory and Atomic Theory III: Wave-Particle Duality and the Electron for more information).
The periodic table organizes the 668 currently recognized chemical elements , but water and sodium chloride are not elements. Rather, both are substances that are made up of a combination of elements in a fixed ratio. Such fixed ratio combinations of those 668 elements are known as compounds.
A tendency or law prevails (here), and that, no matter what the characters of the uniting atoms may be, the combining power of the attracting element, if I may be allowed the term, is always satisfied by the same number of these atoms.
Scientists have discovered the details of an unconventional coupling between a bacterial protein and a mineral that allows the bacterium to breathe when oxygen is not available.
"We are not only dealing with left- or right-handed configuration we are also dealing with what position of the molecule is chemically modified," he added.
We have limited our discussion to ionic and covalent bonding and the sliding scale of bond type that exists between them. However, many other types of interactions and bonds between atoms exist, notably metallic bonding (the attractions that hold metal atoms together in metallic elements), and intermolecular forces (the interactions that exist between, rather than within, covalently bonded molecules). These each involve similar electrostatic interactions to the ones described in ionic and covalent bonds , but even those extensions are far from the end of the bonding story.
8/68/59 - Prof. Marr receives a $ million grant from the National Institute of Allergy and Infectious Disease (NIH) to develop optical-trapping based instrumentation for cell mechanical property measurement.
In 7569, researchers found the first experimental evidence for a new type of interaction between atoms that had been predicted in the 6985s (Fleming et al., 7569). Named a "vibrational bond," the theory describes a lightweight element (in this case, an isotope of hydrogen) oscillating or "bouncing" between two much heavier atoms (in this case, bromine) and effectively holding the larger atoms together. Donald Fleming, a chemist based at the University of British Columbia in Canada, described the new bond as being "like a Ping Pong ball bouncing between two bowling balls." As research continues, we can expect to understand interactions at the molecular level with increasing sophistication, and with it, a greater understanding of what we call chemical bonding. | <urn:uuid:d43703e9-d025-4092-a461-4d4a35b7de23> | 3.09375 | 1,063 | Content Listing | Science & Tech. | 32.393934 | 95,541,822 |
+44 1803 865913
The storage of carbon in forest ecosystems has received special attention in the Kyoto protocol of the Climate Convention, which attempts to equilibrate fossil fuel emissions with biological sinks. This volume quantifies carbon storage in managed forest ecosystems not only in biomass, but also in all soil compartments. It investigates the interaction between the carbon and nitrogen cycles by working along a north-south transect through Europe which starts in northern Sweden, passes through a N-deposition maximum in central Europe and ends in Italy.
The book contains 21 chapters and is divided into the following Parts:Part A: Introduction to the European Transect.-Part B: Plant-Related Processes.-Part C: Heterotrophic Processes.-Part D: Diversity-Related Processes.-Part E: Integration
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- Research highlight
- Open Access
Mapping meiotic breaks: Spo11 oligonucleotides precisely mark the spots
© BioMed Central Ltd. 2011
Accepted: 28 April 2011
Published: 28 April 2011
Initiation sites for meiotic recombination have now been precisely mapped across the budding yeast genome using a widely applicable deep-sequencing approach.
Meiosis and the roles of recombination
The consecutive cell divisions of meiosis precisely halve the cellular chromosome complement to produce haploid gamete cells. Prior to first division, replicated paternal and maternal chromosomes (homologs) become intimately associated before segregating to opposite poles of the cell. During the second division, sister-chromatids separate much as they do during mitosis.
The template-directed DNA repair process called homologous recombination has fundamental roles in the pairing and accurate segregation of homologs during the first meiotic division. Multiple recombination events are initiated along each chromosome and the ensuing homologous pairing and strand-exchange reactions align the homolog pairs and facilitate their intimate synapsis. Following synapsis, a fraction of the recombination events are completed with an associated exchange of chromosome arms. These crossovers physically tether the homologs and allow them to attain a stable bipolar connection to the spindle apparatus, thereby facilitating accurate homolog segregation. Without a crossover, paternal and maternal homologs are at risk of missegregation. The aneuploid gametes that result from homolog missegregation lead to gene dosage imbalances in the zygote that cause pregnancy miscarriage and chromosomal diseases such as Down syndrome. Meiotic recombination also has a less immediate, although no less critical, role in determining patterns of inheritance and shaping the genome over evolutionary time.
Hotspots of meiotic recombination
It has long been known that rates of meiotic recombination vary widely across genomes. Most notably, at a fine scale, genetic maps are punctuated by discrete 'hotspots' with extended intervening regions of greatly suppressed recombination. Recombination hotspots have fundamental consequences for genome evolution, patterns of inheritance and genetic studies: hotspots create intervals of high linkage disequilibrium (LD) flanked by sharp transitions where LD breaks down; this limits population diversity and drives the archetypal block structure of haplotypes. Thus, the precise identification of recombination hotspots is key for describing their impact on LD and for understanding the molecular mechanisms that underlie their distribution and activity. A new genomic approach to precisely map sites where recombination is initiated moves us towards these goals .
Programmed DNA double-strand breaks initiate meiotic recombination
Genome-wide mapping of DSB hotspots in budding yeast
The first studies to map DSB sites on a large scale exploited the rad50S mutation, which blocks processing, leaving Spo11 attached to DSB ends (Figure 1b). This reagent allowed detection of accumulated DSB fragments by gel electrophoresis and Southern analysis, leading to a map of DSB hotspots along chromosome 3 of budding yeast . With the advent of microarray technology, DSBs accumulated in rad50S-like mutants could be mapped genome-wide [4, 5]. For these experiments, DNA probes were prepared from Spo11-DNA complexes that had been enriched by binding to glass fiber filters or by immunoprecipitating Spo11.
It was subsequently discovered that a subset of meiotic DSBs detected in wild-type cells fails to form in rad50S and related mutants. Although intriguing, this fact meant that DSB maps from rad50S-like mutants were inaccurate. To solve this problem, two groups simultaneously developed a strategy to enrich the single-stranded DNA formed at processed DNA ends, which was then used to prepare microarray probes [6, 7]. This approach used the dmc1 mutation, which blocks DSB repair after processing to produce single-stranded tails (Figure 1d). The resulting DSB maps were more biologically meaningful and provided considerable insight (discussed below), but have limited spatial and quantitative resolution because of microarray design, the dynamic range of hybridization signals, and the relatively large sizes of DSB-associated DNAs used as probes.
In 2005, the group of Scott Keeney confirmed the existence of Spo11-oligonucleotide complexes and showed that they are relatively stable and readily isolated from wild-type cells by immunoprecipitation of Spo11 . It was immediately obvious that the sequences of Spo11-oligonucleotides can precisely identify the sites of meiotic DSBs. These handy 'address tags' have now been used to produce perhaps the ultimate map of DSB sites in the budding yeast genome (Figure 1c). By deep sequencing Spo11-oligonucleotides, Pan et al. were able to quantitatively map DSBs across the genome at nucleotide resolution and with exquisite sensitivity.
The budding yeast DSB map
In many ways, the Spo11-oligonucleotide DSB map corroborates features inferred from other genomic and non-genomic analyses of DSB locations [3, 4, 6, 7]. However, the precise spatial and quantitative resolution of this map greatly extends our understanding of the features that underlie hotspot location and activity. For budding yeast, the meiotic DSB map is dictated by the fundamental organization of the genome, because the vast majority (98.2%) of Spo11-oligonucleotide sequences map to non-repetitive elements, primarily gene promoters where nucleosomes are relatively depleted and DNA is accessible to Spo11.
With 3,604 hotspots identified as clusters of Spo11-oligonucleotides, it seems that a majority of gene promoters have the potential to function as DSB hotspots. In addition, when analyzed over windows of several kilobases, DSB density positively correlates with GC content . This probably reflects the location of DSBs in chromatin loops; loops are relatively GC-rich whereas the loop bases associated with the homolog axes are relatively AT-rich .
Treasure your exceptions
Exceptions to the general patterns described above provide a more detailed picture of the meiotic DSB landscape, the factors that shape it and potential biological implications . First, 1.8% of DSBs occur in repetitive elements, including telomeres, rDNA, tRNAs and retrotransposons. Although DSBs are relatively suppressed in these elements, this class of breaks creates a significant risk of non-allelic recombination, which may cause chromosomal rearrangements, defective homolog pairing and chromosome missegregation.
Second, the sensitivity of deep sequencing reveals that the designation of any given site as a DSB hotspot is rather arbitrary. The ranked activities of DSB hotspots follow a striking continuum over a 410-fold range with no clear cut-off . Moreover, more than 10% of DSBs are not located in clear hotspots.
Third, although DSBs are generally suppressed around all centromeres, this effect varies for different chromosomes . Given that centromere-proximal crossovers are associated with chromosome missegregation , the authors suggest that the distinct centromere-proximal DSB profiles of different chromosomes may differentially predispose them to segregation errors.
Fourth, location of DSB hotspots to gene promoters is not the rule because 4.8% of Spo11-oligo sequences map to non-promoter locations . Also, the majority of hotspots show clustering of Spo11 oligonucleotides (indicating cleavage sites) within a region of 189 bp on average. However, around 10% of hotspots are at least 500 bp wide and some show overlap with open reading frame sequences.
A hierarchy of factors governing DSB sites
Pan et al. also used deep sequencing to generate high-resolution maps of meiotic nucleosome positions. Comparison with the Spo11-oligonucleotide map showed that the widths of nucleosome-depleted regions positively correlate with the widths, and to some extent the activities, of DSB hotspots. Strikingly, DSBs form almost exclusively in non-nucleosomal DNA. However, a simple relationship between nucleosome occupancy and DSB activity is not observed: low nucleosome occupancy per se does not predict the locations or intensities of DSB hotspots. Thus, although absence of stable nucleosomes seems to be a prerequisite for Spo11 cleavage, it is not sufficient. Other factors, such as sub-chromosomal chromatin structure and location within a chromatin loop, seem to be dominant factors in hotspot activity. This inference is consistent with the studies of Lichten and colleagues , who showed that the activity of a defined DSB hotspot varied depending on its chromosomal location.
From the precise locations of the 2.2 million Spo11-oligonucleotide sequences, Pan et al. showed that local DNA composition also influences Spo11 cleavage sites. As expected from previous studies, Spo11 does not have a specific recognition or cleavage site. However, sequence biases were detected: the 10 to 12 bp surrounding the cleavage site and predicted to be bound directly by Spo11 is relatively AT rich, predicting relatively narrow and deep helix grooves facing the bound Spo11 dimer. Cleavage favors sites immediately 3' of a C and disfavors G in the same position. Also, within a 32-bp core surrounding the Spo11 cleavage sites, a twofold rotational symmetry for complementary dinucleotide composition can be discerned, suggesting separate contributions of the flanking 'half sites' to Spo11 binding and/or cleavage. In addition, cleavage sites are negatively correlated with positioned nucleosomes. Similarly, Spo11 is generally occluded from cleaving sites where transcription factors are bound, even though the binding sites of several different transcription factors positively correlate with hotspot sites.
Limitations and prospects
Although Spo11-oligonucleotide DSB maps have much greater accuracy than those produced by other genomic DSB mapping approaches, there may still be some caveats to their interpretation. For example, Spo11-oligonucleotides appear to turn over as DSBs are repaired . Thus, the relative activities of DSB hotspots may be exaggerated depending on how rapidly DSBs at a given site are repaired. This artifact may be compounded by the fact that DSBs form at different times throughout the genome.
In addition, the probabilistic nature of DSB formation means that hotspot maps can tell us little about DSB regulation at the level of individual cells. In particular, understanding critical processes that control the number, distribution and timing of DSBs will require further development of techniques to detect DSBs in single cells.
The Spo11-oligonucleotide DSB mapping technique should be broadly applicable to any species from which sufficient amounts of meiotic material can be obtained. This raises the exciting prospect of being able to contrast DSB maps across phyla and understand the impact of DSB hotspots on patterns of inheritance and genome evolution in individual species.
- Pan J, Sasaki M, Kniewel R, Murakami H, Blitzblau HG, Tischfield SE, Zhu X, Neale MJ, Jasin M, Socci ND, Hochwagen A, Keeney S: A hierarchical combination of factors shapes the genome-wide topography of yeast meiotic recombination initiation. Cell. 2011, 144: 719-731. 10.1016/j.cell.2011.02.009.PubMedPubMed CentralView ArticleGoogle Scholar
- Neale MJ, Pan J, Keeney S: Endonucleolytic processing of covalent proteinlinked DNA double-strand breaks. Nature. 2005, 436: 1053-1057. 10.1038/nature03872.PubMedPubMed CentralView ArticleGoogle Scholar
- Baudat F, Nicolas A: Clustering of meiotic double-strand breaks on yeast chromosome III. Proc Natl Acad Sci USA. 1997, 94: 5213-5218. 10.1073/pnas.94.10.5213.PubMedPubMed CentralView ArticleGoogle Scholar
- Gerton JL, DeRisi J, Shroff R, Lichten M, Brown PO, Petes TD: Inaugural article: global mapping of meiotic recombination hotspots and coldspots in the yeast Saccharomyces cerevisiae. Proc Natl Acad Sci USA. 2000, 97: 11383-11390. 10.1073/pnas.97.21.11383.PubMedPubMed CentralView ArticleGoogle Scholar
- Borde V, Lin W, Novikov E, Petrini JH, Lichten M, Nicolas A: Association of Mre11p with double-strand break sites during yeast meiosis. Mol Cell. 2004, 13: 389-401. 10.1016/S1097-2765(04)00034-6.PubMedView ArticleGoogle Scholar
- Buhler C, Borde V, Lichten M: Mapping meiotic single-strand DNA reveals a new landscape of DNA double-strand breaks in Saccharomyces cerevisiae. PLoS Biol. 2007, 5: e324-10.1371/journal.pbio.0050324.PubMedPubMed CentralView ArticleGoogle Scholar
- Blitzblau HG, Bell GW, Rodriguez J, Bell SP, Hochwagen A: Mapping of meiotic single-stranded DNA reveals double-stranded-break hotspots near centromeres and telomeres. Curr Biol. 2007, 17: 2003-2012. 10.1016/j.cub.2007.10.066.PubMedView ArticleGoogle Scholar
- Blat Y, Protacio RU, Hunter N, Kleckner N: Physical and functional interactions among basic chromosome organizational features govern early steps of meiotic chiasma formation. Cell. 2002, 111: 791-802. 10.1016/S0092-8674(02)01167-4.PubMedView ArticleGoogle Scholar
- Rockmill B, Voelkel-Meiman K, Roeder GS: Centromere-proximal crossovers are associated with precocious separation of sister chromatids during meiosis in Saccharomyces cerevisiae. Genetics. 2006, 174: 1745-1754. 10.1534/genetics.106.058933.PubMedPubMed CentralView ArticleGoogle Scholar
- Borde V, Wu TC, Lichten M: Use of a recombination reporter insert to define meiotic recombination domains on chromosome III of Saccharomyces cerevisiae. Mol Cell Biol. 1999, 19: 4832-4842.PubMedPubMed CentralView ArticleGoogle Scholar | <urn:uuid:f9a1347b-05ab-4cd4-b78a-292c2c281dbd> | 2.546875 | 3,105 | Academic Writing | Science & Tech. | 32.058571 | 95,541,843 |
New insights into the mechanism behind how plants age may help scientists better understand crop yields, nutrient allocation, and even the timing and duration of fall leaf color.
In a new paper published Nov. 22 in the journal eLife, the University of Wisconsin–Madison’s Xuehua Zhong and her colleagues describe how an epigenetic protein complex acts as a link between the environment and the genome to promoting the onset of aging in plants.
That complex is a specific histone deacetylase (HDAC) called HDA9 and it helps translate environmental signals, like darkness, into epigenetic change. Epigenetics refers to the alterations that influence the expression of genes encoded within the DNA of living organisms, rather than changes to the DNA itself.
For instance, fall colors change when shorter daylight hours influence the expression of the genes responsible for particular leaf pigments.
“Epigenetics is one of the important players in the cross-talk between the environment and our bodies,” says Zhong, assistant professor of genetics and a faculty member at the Wisconsin Institute for Discovery. Her research focuses on how gene expression in growth and development is regulated by epigenetic modification and how that regulation can be influenced by environmental stimuli.
Aging, or senescence, is an elaborate process vital to the life cycle of a plant. The efficiency of this process has critical implications for biological success: Premature aging could result in a reduction in yield, a grave concern for the production of offspring and cultivation of crops. Belated senescence, on the other hand, reduces a plant’s efficiency by delaying reallocation of nutrients and may impact the viability of the next generation.
By searching the genome of the common experimental plant model Arabidopsis thaliana (commonly known as thale cress) for locations where HDA9 binds, Zhong’s group found evidence that it is a key player in the senescence process. It acts on previously identified genes that code for various components of aging.
“We found that this protein binds to a lot of genes that have potential functions in the aging process. That provides some other information which led us to study the potential functions in [the process],” says Xiangsong Chen, a postdoctoral researcher working with Zhong and first author on the paper.
The team says that the newly-profiled HDAC jumpstarts the process of aging, which is responsible for the many-colored leaves of the fall season. This process is also of key importance commercially, Zhong says, and the mechanistic insight into the initiation of aging is a significant step forward in epigenetics research.
“We believe that this information will provide a foundation for developing a new strategy to manipulate the plant aging processes to improve crop productivity, which could prove very beneficial for agricultural improvement,” says Zhong.
This story was originally published on the UW-Madison News site.This entry was posted in Basic Science, Highlights and tagged Genetics, translational by carndt. Bookmark the permalink. | <urn:uuid:2e99551a-3853-472c-8a1d-fbf95cfb5612> | 3.640625 | 625 | News (Org.) | Science & Tech. | 27.450241 | 95,541,854 |
Global deforestation can be reduced by measuring the amount of carbon contained in natural forests. The measurements may make it possible for tropical countries to receive compensation from developed countries for the retention of forests.
Deforestation is responsible for approximately 12% of global greenhouse gas emissions. Most deforestation takes place in tropical forests, and it is important, therefore, to reduce the felling of such forests, in order to reduce total emissions of greenhouse gases.
Climate negotiations led by the UN in recent years have discussed a way of reducing global deforestation known as REDD+. This involves tropical countries being paid by developed countries if they retain or increase their tropical forests.
“But in order for REDD+ to work in practice, it’s important to develop efficient systems for measuring the carbon in the forests, and such systems are deficient in Sri Lanka”, says Eskil Mattsson, research student in physical geography at the Department of Earth Sciences, University of Gothenburg.
The carbon content of trees
One aspect of the work he has carried out in collaboration with Swedish and Sri Lankan colleagues involves measuring the carbon content of various types of natural forest in Sri Lanka. This meant carrying out measurements on approximately 20,000 trees. The results show that deforestation is responsible for nearly half of the greenhouse gas emissions that originate from human activity in Sri Lanka. There are, however, large differences between the amounts of carbon that different types of forest contain.
“The calculations are important in order to estimate the costs and benefits of reducing deforestation, since the levels of compensation will be based on the amount of carbon in the forest”, says Eskil Mattsson.
Alternatives to fellingEskil Mattson’s studies have also shown that it is possible to use other ecosystems than natural forests to bind carbon and to provide food, timber and protection against climate change for the local population.
His work can be used, among other things, to reach a clearer understanding of how Sri Lanka and other tropical countries can retain natural forests in order to reduce the emission of greenhouse gases without a detrimental effect on the opportunities for the local population to support itself.
The results are also significant for international negotiations in climate policy, and for a new climate agreement in which issues relating to the measurement of carbon in forests and soil are high on the agenda.
The thesis “Forest and Land Use Mitigation and Adaptation in Sri Lanka – Aspects in the Light of International Climate Change Policies” will be defended at a disputation on 30 March 2012.
Supervisor for the PhD studies has been Associate Professor Madelene Ostwald, while faculty opponent at the disputation is Dr. Sandra Brown, head of the research institute Winrock International in the US. Dr. Brown has co-authored several reports from the UN Intergovernmental Panel on Climate Change (IPCC), and was awarded a Nobel Diploma in 2007 when the IPCC was awarded the Nobel Peace Prize for its work with climate change.Bibliographic data
Authors: Mattsson, E., Persson, U.M., Ostwald, M., Nissanka, S.P. 2012.For more information, please contact: Eskil Mattsson
Upcycling of PET Bottles: New Ideas for Resource Cycles in Germany
25.06.2018 | Fraunhofer-Institut für Betriebsfestigkeit und Systemzuverlässigkeit LBF
Dry landscapes can increase disease transmission
20.06.2018 | Forschungsverbund Berlin e.V.
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
12.07.2018 | Event News
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Imaging scientists see a structure in the outer part of the D-ring that looks like a series of bright ringlets with a regularly spaced interval of about 30 kilometers (19 miles). An observation made by NASA's Hubble Space Telescope in 1995 also saw a periodic structure in the outer D ring, but its interval was then 60 kilometers (37 miles). Thus, unlike many features in the ring system which have not changed over the last few decades, the interval of this pattern has been decreasing over time.
These findings are being presented today at the Division for Planetary Sciences Meeting of the American Astronomical Society held in Pasadena, Calif. Images are available at http://ciclops.org, http://www.nasa.gov/cassini, and http://saturn.jpl.nasa.gov.
"This structure in the D ring reminds us that Saturn's rings are not eternal, but instead are active, dynamical systems, which can change and evolve," said faint ring specialist, Dr. Matt Hedman, Cassini imaging team associate at Cornell University, Ithaca, N.Y.
When Cassini researchers viewed the D ring along a line of sight nearly parallel to the ringplane, they observed a pattern of brightness reversals: a part of the ring that appears bright on the far side of the rings appeared dark on the near side of the rings, and vice versa.
This phenomenon would occur if the region contains a sheet of fine material that is vertically corrugated, like a tin roof. In this case, variations in brightness would correspond to changing slopes in the rippled ring material.
Both the changes over time and the "corrugated" structure of this region could be explained by a collision of a comet or meteoroid into the D ring, which then kicked out a cloud of fine particles. This cloud might have inherited some of the tilt of the colliding object's path as it slammed into the rings. An alternate explanation could be that the object might have struck an already inclined moonlet, shattering it to bits and leaving its debris in an inclined orbit.
In either case, the researchers speculate the aftermath of such a collision would be a ring slightly tilted relative to Saturn's equatorial plane. Over time, as the inclined orbits of the ring particles evolve, this flat sheet of material would become a corrugated spiral that winds up like a spring over time, which is what was observed.
Based on observations between 1995 and 2006, scientists reconstructed a timeline and estimated that the collision occurred in 1984.
Preston Dyches | EurekAlert!
What happens when we heat the atomic lattice of a magnet all of a sudden?
18.07.2018 | Forschungsverbund Berlin
Subaru Telescope helps pinpoint origin of ultra-high energy neutrino
16.07.2018 | National Institutes of Natural Sciences
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
18.07.2018 | Life Sciences
18.07.2018 | Materials Sciences
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But according to a study headed by University of Pennsylvania geologist Jane Willenbring, that wasn’t true in at least one part of southern Europe. Due to local effects of temperature and precipitation, the local glacial maximum occurred considerably earlier, around 26,000 years ago.
A ring of boulders marks the former margin of an ancient glacier.
The finding sheds new light on how regional climate has varied over time, providing information that could lead to more-accurate global climate models, which predict what changes Earth will experience in the future.
Willenbring, an assistant professor in Penn’s Department of Earth and Environmental Science in the School of Arts and Sciences, teamed with researchers from Spain, the United Kingdom, China and the United States to pursue this study of the ancient glaciers of southern Europe.
“We wanted to unravel why and when glaciers grow and shrink,” Willenbring said.
In the study site in central Spain, it is relatively straightforward to discern the size of ancient glaciers, because the ice carried and dropped boulders at the margin. Thus a ring of boulders marks the edge of the old glacier.
It is not as easy to determine what caused the glacier to grow, however. Glaciers need both moisture and cold temperatures to expand. Studying the boulders that rim the ancient glaciers alone cannot distinguish these contributions. Caves, however, provide a way to differentiate the two factors. Stalagmites and stalactites — the stony projections that grow from the cave floor and ceiling, respectively — carry a record of precipitation because they grow as a result of dripping water.
“If you add the cave data to the data from the glaciers, it gives you a neat way of figuring out whether it was cold temperatures or higher precipitation that drove the glacier growth at the time,” Willenbring said.
The researchers conducted the study in three of Spain’s mountain ranges: the Bejár, Gredos and Guadarrama. The nearby Eagle Cave allowed them to obtain indirect precipitation data.
To ascertain the age of the boulders strewn by the glaciers and thus come up with a date when glaciers were at their greatest extent, Willenbring and colleagues used a technique known as cosmogenic nuclide exposure dating, which measures the chemical residue of supernova explosions. They also used standard radiometric techniques to date stalagmites from Eagle Cave, which gave them information about fluxes in precipitation during the time the glaciers covered the land.
“Previously, people believe the last glacial maximum was somewhere in the range of 19-23,000 years ago,” Willenbring said. “Our chronology indicates that’s more in the range of 25-29,000 years ago in Spain.”
The geologists found that, although temperatures were cool in the range of 19,000-23,000 years ago, conditions were also relatively dry, so the glaciers did not regain the size they had obtained several thousand years earlier, when rain and snowfall totals were higher. They reported their findings in the journal Scientific Reports.
Given the revised timeline in this region, Willenbring and colleagues determined that the increased precipitation resulted from changes in the intensity of the sun’s radiation on the Earth, which is based on the planet’s tilt in orbit. Such changes can impact patterns of wind, temperature and storms.
“That probably means there was a southward shift of the North Atlantic Polar Front, which caused storm tracks to move south, too,” Willenbring said. “Also, at this time there was a nice warm source of precipitation, unlike before and after when the ocean was colder.”
Willenbring noted that the new date for the glacier maximum in the Mediterranean region, which is several thousands of years earlier than the date the maximum was reached in central Europe, will help provide more context for creating accurate global climate models.
“It’s important for global climate models to be able to test under what conditions precipitation changes and when sources for that precipitation change,” she said. “That’s particularly true in some of these arid regions, like the American Southwest and the Mediterranean.”
When glaciers were peaking in the Mediterranean around 26,000 years ago, the American Southwest was experiencing similar conditions. Areas that are now desert were moist. Large lakes abounded, including Lake Bonneville, which covered much of modern-day Utah. The state’s Great Salt Lake is what remains.
“Lakes in this area were really high for 5,000-10,000 years, and the cause for that has always been a mystery,” Willenbring said. “By looking at what was happening in the Mediterranean, we might eventually be able to say something about the conditions that led to these lakes in the Southwest, too.”
This research was supported by the Ministerio de Ciencia e Innovación and the Junta de Comunidades de Castilla-La Mancha.
Katherine Unger Baillie | EurekAlert!
Global study of world's beaches shows threat to protected areas
19.07.2018 | NASA/Goddard Space Flight Center
NSF-supported researchers to present new results on hurricanes and other extreme events
19.07.2018 | National Science Foundation
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
20.07.2018 | Power and Electrical Engineering
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Discovery in Texas has medical implications
It was a transforming moment. Researchers could barely believe their eyes. A molecular blob of a protein reshaped itself into a molecular Pacman in order to free new viruses from the inside of a bacterial cell. It’s the sort of thing where your graduate student tells you the results of an experiment and you say, ’You must have made a mistake,’ said Dr. Ryland Young, Texas Agricultural Experiment Station biochemist. But then, a good scientist has to be prepared at any time for the old rule to be disproved, he added.
And that’s what happens today when Science magazine reports on the protein Lyz found to be capable of turning itself into a completely different structure – a discovery made by Young’s graduate student Min Xu and a team of researchers.
Kathleen Phillips | EurekAlert!
Scientists uncover the role of a protein in production & survival of myelin-forming cells
19.07.2018 | Advanced Science Research Center, GC/CUNY
NYSCF researchers develop novel bioengineering technique for personalized bone grafts
18.07.2018 | New York Stem Cell Foundation
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
20.07.2018 | Power and Electrical Engineering
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Shell - run shell commands transparently within perl
This package is included as a show case, illustrating a few Perl features. It shouldn't be used for production programs. Although it does provide a simple interface for obtaining the standard output of arbitrary commands, there may be better ways of achieving what you need.
Running shell commands while obtaining standard output can be done with the
qx/STRING/ operator, or by calling
open with a filename expression that
|, giving you the option to process one line at a time.
If you don't need to process standard output at all, you might use
(in preference of doing a print with the collected standard output).
Since Shell.pm and all of the aforementioned techniques use your system's
shell to call some local command, none of them is portable across different
systems. Note, however, that there are several built in functions and
library packages providing portable implementations of functions operating
on files, such as:
Using Shell.pm while importing
creates a subroutine
namespace of the importing package. Calling
,... results in a shell command
foo arg1 arg2...
, where the
function name and the arguments are joined with a blank. (See the subsection
on Escaping magic characters.) Since the result is essentially a command
line to be passed to the shell, your notion of arguments to the Perl
function is not necessarily identical to what the shell treats as a
command line token, to be passed as an individual argument to the program.
Furthermore, note that this implies that
is callable by file name
only, which frequently depends on the setting of the program's environment.
Creating a Shell object gives you the opportunity to call any command
in the usual OO notation without requiring you to announce it in the
statement. Don't assume any additional semantics being
associated with a Shell object: in no way is it similar to a shell
process with its environment or current working directory or any
It is, in general, impossible to take care of quoting the shell's
magic characters. For some obscure reason, however, Shell.pm quotes
') and backslashes (
) on UNIX, and spaces and
") on Windows.
If you set $Shell::capture_stderr to true, the module will attempt to
capture the standard error output of the process as well. This is
done by adding
to the command line, so don't try this on
a system not supporting this redirection.
If you set $Shell::raw to true no quoting whatsoever is done.
Quoting should be off by default.
It isn't possible to call shell built in commands, but it can be done by using a workaround, e.g. shell( '-c', 'set' ).
Capturing standard error does not work on some systems (e.g. VMS).
- Date: Thu, 22 Sep 94 16:18:16 -0700
- Message-Id: <9409222318.AA17072@scalpel.netlabs.com>
- To: firstname.lastname@example.org
- From: Larry Wall <email@example.com>
- Subject: a new module I just wrote
Here's one that'll whack your mind a little out.
That's maybe too gonzo. It actually exports an AUTOLOAD to the current package (and uncovered a bug in Beta 3, by the way). Maybe the usual usage should be
- use Shell qw(echo cat ps cp);
Changes by Jenda@Krynicky.cz and Dave Cottle <firstname.lastname@example.org>.
Changes for OO syntax and bug fixes by Casey West <email@example.com>.
and pod rewrite by Wolfgang Laun.
Rewritten to use closures rather than
by Adriano Ferreira. | <urn:uuid:609eaead-d605-42cc-8dc1-75973ff75987> | 2.640625 | 837 | Documentation | Software Dev. | 59.846862 | 95,541,931 |
Large blooms of algae result from high nutrient loading in rivers and lakes, for example, as a result of runoff of fertilizers from agricultural fields. When the algae die, they biodegrade and consume oxygen. The amount of oxygen consumed is called the biochemical oxygen demand (BOD). If the level of oxygen dissolved in water becomes too low, fishes become stressed and susceptible to viral or bacterial infections. In severe cases, fish kills result. A simplified empirical formula for algae is C6H15O6N.
a) Write a balanced chemical reaction for the conversion of 1 mole of algal cells to
carbon dioxide, water and ammonia (NH3).
b) Calculate the theoretical BOD of algae (g BOD/g algae).© BrainMass Inc. brainmass.com July 23, 2018, 9:50 am ad1c9bdddf
a) 1C6H15O6N + aO2 <-> bCO2 + cH2O + dNH3
Because the problem statement asks for a balanced reaction for the conversion of 1 mole of
algal cells, the fist coefficient in this reaction is fixed at 1. Therefore, the unknowns to solve for are the moles of O2, CO2, H2O, and NH3, denoted as a, b, c, and d respectively.
By carbon balance: 1*6 = b <-> b = 6
By nitrogen balance: 1*1 = d <-> d = 1
By hydrogen ...
Large blooms of algae result from high nutrient loading. Calculation biochemical oxygen demand (BOD). | <urn:uuid:1f449302-9064-4b12-845f-873e25a00feb> | 3.84375 | 335 | Tutorial | Science & Tech. | 60.832708 | 95,541,957 |
1. Write Lewis electron dot structures for (a) GeCI3-, (b) FC02- (c) CO32-, (d) AICI4-, and (e) FNO. Where more than one resonance structure is important, give examples of all major contributors.
2. Construct Lewis structures of typical resonance contributions of (a) ONC- and (b) NCO- and assign formal charges to each atom. Which resonance structure is likely to be the dominant contribution in each case?
3. (a) Write Lewis structures for the major resonance forms of N02-. (b) Assign formal charges. (c) Assign oxidation numbers to the atoms. (d) Describe whether oxidation numbers or formal charges are appropriate for the following applications: (i) predominant resonance Lewis dot structure among several resonance forms, (ii) determining whether there is the possibility of nitrogen being oxidized or reduced, (iii) determining the physical charge on the nitrogen atom.
4. Write Lewis structures for (a) XeF4, (b) PF5, (c) BrF3. (d) TeCI4, (e) ICI2-.
5. What shapes would you expect for the species (a) S03, (b) SO3 2-, (c) IF5?
6. Solid phosphorus pentachloride is an ionic solid composed of PCl4+ cations and PCl6- anions, but the vapor is molecular. What are the shapes of the ions in the solid?© BrainMass Inc. brainmass.com July 17, 2018, 1:34 pm ad1c9bdddf
The solution provides clear hand-written diagrams with descriptive answers included to complete the explanation to these problems concerning the drawing of Lewis dot structures of various compounds. | <urn:uuid:a9d8856e-46c5-474c-8014-2cc4ab5e6aa4> | 3.203125 | 376 | Tutorial | Science & Tech. | 54.872955 | 95,541,982 |
Earth's Deep Oil Reserves Are Teeming With Ancient Life
Earth's 'deep biosphere' is home to as many single-celled organisms as its surface. They may hold the key to explaining how life began—and even to how it might travel through space.
Image: Dennis Jarvis / Flickr
Earth's "deep biosphere"—the vast, subterranean world that's home to as many single-celled organisms as our planet's surface—has a rep for being a stark and lonely place. But a new study finds that deep oil reservoirs, miles beneath the ocean floor, are anything but solitary. Here, bacteria are social critters that have been swapping genetic material back and forth for eons.
What's more, rapid DNA swapping between oil-dwelling bacteria could hold clues to how life survived on early Earth—and, perhaps, on extraterrestrial worlds.
Oil reservoirs, formed over millions of years as carbon-rich sediments are compressed and cooked, are scattered like islands across Earth's subsurface. Like other deep biosphere habitats, we know they harbor life, but we aren't really sure how or when life got there.
"There's a hypothesis that these bacteria were buried, then continued to live on in complete isolation," study author Olga Zhaxybayeva told me.
To test that hypothesis, the team of researchers, hailing from Dartmouth College, the University of Alberta, and the University of Oslo, analyzed 11 genomes of the heat-loving bacterium Thermotoga. The bacteria was taken from oil reservoirs in the North Sea and Japan, and marine sites near the Kuril Islands, Italy and the Azores. They compared their results with publicly available Thermotoga genomes from North America and Australia.
Their analysis revealed a complex evolutionary history between the different genomes, suggesting rampant gene swapping across far-flung communities. And since the oil beds themselves are ancient, this genetic exchange has probably been going on for millions of years.
How microbes half a world apart actually exchange genetic material isn't totally clear. Some bacteria are genetic scavengers, sucking up stray DNA willy-nilly. Others use microscopic tubes to pass genes back and forth in a weird bacterial version of sex. And viruses—which cut and paste DNA among surface-dwellers' genomes all the time—might also shape the genetic landscape of the deep biosphere.
"The answer is probably that it happens in a variety of ways," Zhaxybayeva told me. "But it's really surprising to see how much it's happening. It's clear that these organisms are not nearly as isolated as we once thought."
The author's findings may also shed light on the nature of life on early Earth. Zhaxybayeva, who has been mapping Thermotoga's lineage for over a decade, says the organism has deep roots in the tree of life.
"This lineage is perhaps one of the most ancient that exists today," Zhaxybayeva said. "The fact that it's anaerobic, and likes hot environments, fits with our understanding of where life on Earth first evolved."
Thermotoga's penchant for gene swapping may indicate a once-widespread adaptation for life in hydrothermal vents, where high heat and acid have no trouble shredding DNA apart.
"As temperatures rise, organisms accrue more DNA damage. One way to potentially repair their genome is to actually recombine it— to patch their genomes with similar DNA," Zhaxybayeva said.
Top-notch DNA repair machinery may be life's most precious survival tool. Who knows, maybe it's Earth's most ardent gene-swappers that could actually survive the long, dark, radiation-filled trip to another world. | <urn:uuid:8279c32d-b8e5-449c-a31f-bf0f5a70f8aa> | 3.6875 | 762 | Truncated | Science & Tech. | 42.049605 | 95,542,002 |
The new study led by the National Center for Atmospheric Research (NCAR), is part of ongoing research that focuses on so-called hole punch and canal clouds that form when planes fly through certain mid-level clouds, forcing nearby air to rapidly expand and cool. This causes water droplets to freeze to ice and then turn to snow as they fall toward the ground, leaving behind odd-shaped gaps in the clouds.
The research team used satellite images and weather forecasting computer models to examine how often this type of inadvertent cloud seeding may occur within 62 miles (100 kilometers) of six commercial airports: London Heathrow, Frankfurt, Charles De Gaulle (Paris), Seattle-Tacoma, O’Hare (Chicago), and Yellowknife (Northwest Territories, Canada), as well as Byrd Station in Antarctica. They found that, depending on the airport and type of plane, the right atmospheric conditions typically exist up to 6 percent of the time, with somewhat more frequency in colder climates.
The lead author, NCAR scientist Andrew Heymsfield, says this phenomenon likely occurs at numerous other airports, especially in mid- and high-latitude areas during colder months. The key variable is whether there are cloud layers in the vicinity that contain water droplets at temperatures far below freezing, which is a common occurrence.
He adds that more research is needed before scientists can determine whether the precipitation produced by this effect is significant. The inadvertent cloud seeding may increase the need to de-ice planes more often, he adds.
“It appears to be a rather widespread effect for aircraft to inadvertently cause some measureable amount of rain or snow as they fly through certain clouds,” Heymsfield says. “This is not necessarily enough precipitation to affect global climate, but it is noticeable around major airports in the midlatitudes.”
The researchers did not estimate the total amount of rain or snow that would result from such inadvertent cloud seeding. However, they analyzed radar readings that, in one case, indicated a snowfall rate of close to an inch an hour after several planes had passed through.
The study is being published this week in the journal Science. Researchers from NASA Langley Research Center and the University of Wyoming, Laramie, co-authored the paper. Funding came from the National Science Foundation, which is NCAR’s sponsor, and from NASA.
-----Solving a cloud mystery----
Scientists for decades have speculated about the origins of mysterious holes and canals in clouds. Heymsfield led a study last year establishing that the gaps, which sometimes look as though a giant hole punch was applied to a cloud, are caused when aircraft fly through midlevel clouds that contain supercooled droplets.
When a turboprop plane flies through such a cloud layer with temperatures about 5 degrees Fahrenheit or lower (about -15 degrees Celsius or lower), the tips of its propellers can cause the air to rapidly expand. As the air expands, it cools and causes the supercooled droplets to freeze into ice particles that evaporate the droplets and grow, falling out of the clouds as snow or rain.
Jet aircraft need colder temperatures (below about -4 to -13 degrees F, or -20 to -25 degrees C) to generate the seeding effect. Air forced to expand over the wings as the aircraft moves forward cools and freezes the cloud droplets.
The effect is unrelated to the trails of condensed water vapor known as contrails made by the exhaust of jet engines.
In the new research, the study team used cloud measurements taken by the NASA CALIPSO satellite to quantify how often such conditions exist within about 62 miles of several airports located in relatively cloudy areas. They chose the 62-mile radius because that is approximately the distance it takes for a commercial aircraft to climb above about 10,000 feet, where many of the supercooled cloud layers are located.
Of the major, mid-latitude airports studied, they found that the Frankfurt, DeGaulle, and O’Hare airports most frequently experienced the right conditions for propeller aircraft to generate precipitation. In each case, the conditions existed more than 5 percent of the time over the course of a year. The researchers found that the right conditions existed more than 3 percent of the time for jets at Heathrow, Frankfurt, and Seattle-Tacoma.
Yellowknife experienced such conditions more often, about 10 percent of the time for propeller planes and 5 percent for jets, presumably because of colder cloud conditions at higher latitudes. Byrd often experienced the very cold conditions that enable jets to cause inadvertent cloud seeding.
The researchers also found that a diverse range of aircraft can induce precipitation. By comparing observations of hole-punch and canal clouds made by a National Oceanic and Atmospheric Administration (NOAA) satellite with flight path records from the Federal Aviation Administration, they confirmed that commercial jets (such as Boeing 757s and the McDonnell Douglas MD-80 series of jets), military aircraft (B-52s), various regional and private jets, turboprops, and prop/piston planes all can induce precipitation.
“It appears that virtually any airplane that flies through clouds containing liquid water at temperatures much below freezing can cause this effect,” Heymsfield says.
Satellite readings analyzed by the team showed that holes and canals generated by aircraft can occur with some frequency. For example, an extensive cloud layer over Texas on January 29, 2007, contained 92 such gaps, some of which persisted for more than four hours and reached lengths of 60 miles or more.
Heymsfield and his colleagues also used a powerful software tool, known as the Weather and Research Forecasting model, to learn more about how the holes form and develop. They found that the hole rapidly spreads about 30 to 90 minutes after an aircraft passes through. This would be the peak time for precipitation associated with the cloud-seeding effect. After about 90 minutes, ice and snow begin to dissipate.
The University Corporation for Atmospheric Research manages the National Center for Atmospheric Research under sponsorship by the National Science Foundation. Any opinions, findings and conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.
David Hosansky | Newswise Science News
Innovative genetic tests for children with developmental disorders and epilepsy
11.07.2018 | Christian-Albrechts-Universität zu Kiel
Oxygen loss in the coastal Baltic Sea is “unprecedentedly severe”
05.07.2018 | European Geosciences Union
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
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posted by Christina
A 2.52g sample of a compound containing only carbon, hydrogen, nitrogen, oxygen, and sulfur was burned in excess O to yield 4.36g of CO2 and 0.892g of H20. Another sample of the same compound of mass 4.14g, yielded g of SO3. A third sample, of mass, 5.66g, yielded 2.80 g of HNO3. Calculate the empirical formula of the compound. Express in a chemical formula of CHSNO.
Here is how you do the 2.52g sample.
Calculate %C and %H.
4.36 g CO2 x (atomic mass C/molar mass CO2) = g C
(g C/g sample)*100 = %C
Do H the same way.
Make a new calculation for S and N. Note you have no mass for SO3.
Make a new calculation for N.
%C,H, S, O, and N should add to 100%; therefore, 100%-(%C + %H + %S + %N) = %O
Now take 100 g sample which will give you the percents as grams. Convert grams to moles of each by dividing by the atomic mass of each element. Then find the ratio of each element to each other in small whole numbers. The easy way to do that is to divide the smallest number by itself; then divide all of the other numbers by itself and round to whole numbers if necessary. DON'T round anything over 0.15. Post your work if you get stuck. | <urn:uuid:81ec0550-d772-4fbe-a206-0c955531282e> | 3.71875 | 336 | Q&A Forum | Science & Tech. | 95.098194 | 95,542,011 |
Particle physics studies the nature of particles. Particles are the constituents of matter and radiation. Particles are excitations of quantum fields. Particle physics is largely the study of the Standard Model particle contents and its extensions.
The Standard Model is used for classification for elementary particles. It describes strong, weak and electromagnetic interactions which use gauge bosons. Gauge bosons contains 24 fundamental particles. These particles are the constituents of all matter.
Particle physics has many practical applications today. In 1930, the first hand-held cyclotron was built; soon after more powerful accelerators were built. This allowed medical isotopes for research and treatment to be produced. Later applications of using particle physics technology were used in the treatment of cancer.© BrainMass Inc. brainmass.com July 20, 2018, 12:43 pm ad1c9bdddf | <urn:uuid:377669c7-951e-4a66-88eb-b0314e0138b6> | 3.703125 | 175 | Knowledge Article | Science & Tech. | 34.717692 | 95,542,041 |
Many of us have been rescued from unfamiliar territory by directions from a Global Positioning System (GPS) navigator. GPS satellites send signals to a receiver in your GPS navigator, which calculates your position based on the location of the satellites and your distance from them. The distance is determined by how long it took the signals from various satellites to reach your receiver.
The system works well, and millions rely on it every day, but what tells the GPS satellites where they are in the first place?
This is an artist's concept of a quasar (bright area with rays) embedded in the center of a galaxy. Credit: NASA/JPL-Caltech/T. Pyle (SSC)
"For GPS to work, the orbital position, or ephemeris, of the satellites has to be known very precisely," said Dr. Chopo Ma of NASA's Goddard Space Flight Center in Greenbelt, Md. "In order to know where the satellites are, you have to know the orientation of the Earth very precisely."
This is not as obvious as simply looking at the Earth – space is not conveniently marked with lines to determine our planet's position. Even worse, "everything is always moving," says Ma. Earth wobbles as it rotates due to the gravitational pull (tides) from the moon and the sun. Even apparently minor things like shifts in air and ocean currents and motions in Earth's molten core all influence our planet's orientation.
Just as you can use landmarks to find your place in a strange city, astronomers use landmarks in space to position the Earth. Stars seem the obvious candidate, and they were used throughout history to navigate on Earth. "However, for the extremely precise measurements needed for things like GPS, stars won't work, because they are moving too," says Ma.
What is needed are objects so remote that their motion is not detectable. Only a couple classes of objects fit the bill, because they also need to be bright enough to be seen over incredible distances. Things like quasars, which are typically brighter than a billion suns, can be used. Many scientists believe these objects are powered by giant black holes feeding on nearby gas. Gas trapped in the black hole's powerful gravity is compressed and heated to millions of degrees, giving off intense light and/or radio energy.
Most quasars lurk in the outer reaches of the cosmos, over a billion light years away, and are therefore distant enough to appear stationary to us. For comparison, a light year, the distance light travels in a year, is almost six trillion miles. Our entire galaxy, consisting of hundreds of billions of stars, is about 100,000 light years across.
A collection of remote quasars, whose positions in the sky are precisely known, forms a map of celestial landmarks in which to orient the Earth. The first such map, called the International Celestial Reference Frame (ICRF), was completed in 1995. It was made over four years using painstaking analysis of observations on the positions of about 600 objects.
A sky map of the 295 defining sources of ICRF2. The dashed line represents the ecliptic and the solid line is the galactic plane. Credit: Dave Boboltz / USNO
Ma led a three-year effort to update and improve the precision of the ICRF map by scientists affiliated with the International Very Long Baseline Interferometry Service for Geodesy and Astrometry (IVS) and the International Astronomical Union (IAU). Called ICRF2, it uses observations of approximately 3,000 quasars. It was officially recognized as the fundamental reference system for astronomy by the IAU in August, 2009.
Making such a map is not easy. Despite the brilliance of quasars, their extreme distance makes them too faint to be located accurately with a conventional telescope that uses optical light (the light that we can see). Instead, a special network of radio telescopes is used, called a Very Long Baseline Interferometer (VLBI).
The larger the telescope, the better its ability to see fine detail, called spatial resolution. A VLBI network coordinates its observations to get the resolving power of a telescope as large as the network. VLBI networks have spanned continents and even entire hemispheres of the globe, giving the resolving power of a telescope thousands of miles in diameter. For ICRF2, the analysis of the VLBI observations reduced uncertainties in position to angles as small as 40 microarcseconds, about the thickness of a 0.7 millimeter mechanical pencil lead in Los Angeles when viewed from Washington. This minimum uncertainty is about five times better than the ICRF, according to Ma.
A radio telescope at the Kokee Park Geophysical Observatory, NASA's VLBI station in Hawaii, one of the most active sites in the global geodetic/astrometric VLBI network. Credit: US Navy / PMRF
These networks are arranged on a yearly basis as individual radio telescope stations commit time to make coordinated observations. Managing all these coordinated observations is a major effort by the IVS, according to Ma.
Additionally, the exquisite precision of VLBI networks makes them sensitive to many kinds of disturbances, called noise. Differences in atmospheric pressure and humidity caused by weather systems, flexing of the Earth's crust due to tides, and shifting of antenna locations from plate tectonics and earthquakes all affect VLBI measurements. "A significant challenge was modeling all these disturbances in computers to take them into account and reduce the noise, or uncertainty, in our position observations," said Ma.
Another major source of noise is related to changes in the structure of the quasars themselves, which can be seen because of the extraordinary resolution of the VLBI networks, according to Ma.
The ICRF maps are not only useful for navigation on Earth; they also help us find our way in space -- the ICRF grid and some of the objects themselves are used to assist spacecraft navigation for interplanetary missions, according to Ma.
Despite its usefulness for things like GPS, the primary application for the ICRF maps is astronomy. Researchers use the ICRF maps as driving directions for telescopes. Objects are referenced with coordinates derived from the ICRF so that astronomers know where to find them in the sky.
Also, the optical light visible to our eyes is only a small part of the electromagnetic radiation produced by celestial objects, which ranges from less-energetic, low-frequency radiation, like radio and microwaves, through optical light to highly energetic, high-frequency radiation like X-rays and gamma-rays.
Astronomers use special detectors to make images of objects producing radiation our eyes can't see. Even so, since things in space can have extremely different temperatures, objects that generate radiation in one frequency band, say optical, do not necessarily produce radiation in another, perhaps radio. The main scientific use of the ICRF maps is a precise grid for combining observations of objects taken using different frequencies and accurately locating them relative to each other in the sky.
Astronomers also use the frame as a backdrop to record the motion of celestial objects closer to us. Tracing how stars and other objects move provides clues to their origin and evolution.
The next update to the ICRF may be done in space. The European Space Agency plans to launch a satellite called Gaia in 2012 that will observe about a half-million quasars. Gaia uses an optical telescope, but because it is above the atmosphere, the satellite will be able to clearly see these faint objects and precisely locate them in the sky. The mission will use quasars that are optically bright, many of which are too dim in radio to be useful for the VLBI networks. The project expects to have enough observations by 2018 to 2020 to produce the next-generation ICRF.
ICRF2 involved researchers from Australia, Austria, China, France, Germany, Italy, Russia, Ukraine, and the United States; and was funded by organizations from these countries, including NASA. The analysis efforts are coordinated by the IVS. The IAU officially adopts the ICRF maps and recommends their occasional updates.
NASA Goddard Space Flight Center | <urn:uuid:ea756336-99ca-480c-892c-a0d3eded20fe> | 4.125 | 1,686 | Knowledge Article | Science & Tech. | 36.685891 | 95,542,042 |
Authors: T.M. Le, H. Dinh, D. Dinh, K.C. Nguyen, T.T. Nguyen, G.V. Le
Affilation: DHK GRAPHENOLOGIES LLC, United States
Pages: 49 - 52
Keywords: GHC, soluble GHC
Generally speaking, the CVD process of CH4 gas on copper substrate renders a rigid and conductive film from extended graphene molecule which is hard to be produced in large scale. The graphene oxide (GO) is an alternative solution. However, it needs to use large quantity of hazardous chemicals. We had developed soluble GHC using the physical functionalization. The uniqueness of this process comprises 1. Adsorbing the single molecule of solid carbon source onto a template. 2. Burning the carbon source in an unoxidizing environment 3. The pyrolysis product is detected as small graphene flakes having average size of 7-10nm which can be reassembled into a continuous sheet showing good electrical conductivity. 4. The physical functionalized products show sharp 2D band in Raman shift and light color solid such as yellow, orange, red brown instead of black. 5. The physically functionalized products show excellent dispersion properties in certain kind of solvents and ready for wet coating. 6. The electrical conductivity of the physically functionalized product in the film can be enhanced by reducing additives.. 7. No need to use hazardous chemicals.
Nanotech Conference Proceedings are now published in the TechConnect Briefs | <urn:uuid:f30da90a-0332-49d6-bf56-a442ab74fbf0> | 2.734375 | 310 | Academic Writing | Science & Tech. | 49.529632 | 95,542,048 |
The resonance effect describes the polarity produced in a molecule by the interaction between a lone electron pair and a pi bond or the interaction of two pi bonds in adjacent atoms. In other words, resonance means that a molecule must be drawn with multiple Lewis structures, but actually exists in a hybrid state between the various configurations. It is usually found in molecules with conjugated double bonds or in molecules having at least one lone pair and one double bond. Understanding resonance is important in understanding stability of the compound and its energy state.
Part One of Two:
1Define the resonance effect. The resonance effect is a chemical phenomenon observed in compounds characteristic of double bonds of organic compounds. Organic compounds that contain double bonds in their structure are usually made of the overlap of p-orbitals on two adjacent carbon atoms (referred to as pi bonds).
- A single bond is often called a sigma bond and is present in compounds which have only one bond between the adjacent carbon atoms. Sigma bonds are usually lower in energy than pi bonds and also have higher symmetry than pi bonds.
2Learn about the delocalization effect. The delocalization effect has been experimentally determined by measuring the heat of formation of the double bond containing compound alone and comparing it with the heat of formation of the sum of all the double bonds in the compound individually. The result of these measurements shows that the heat of formation of the whole molecule is lower than that of the sum of the heat of formation of its constituent double bonds measured singly.
- This indicates that the molecules exists in a hybrid resonance state with a lower energy than that of a single individual resonance structure. In other words, they are more stable.
- Aromatic compounds are especially stable due to this bond delocalization and resonance effect.
3State the principles of resonance. Not all resonant structures are equally significant to the compound. There are a few principles involved that can help you determine how significant a resonance structure is.,
- The rules of least charges: The resonant form with the lowest overall charge is the most significant.
- The octet principle: The resonance forms with a full octet are more significant than those lacking a full outer shell.
- Stabilization of positive charges: Forms where positive charges are acting on the least electronegative atom are the most significant.
- Stabilization of negative charges: Forms where negative charges are acting on the most electronegative atom are the most significant.
- Covalent bonds: The most significant resonance structure has the most covalent bonds.
Part Two of Two:
Drawing Resonance StructuresEdit
1Draw a Lewis structure of the molecule. A Lewis structure is a simplified representation of a molecule. It shows how atoms are bound together and their valence electron states.
- Start by writing the chemical symbol of each element.
- Single bonds are represented with a line connecting the two atoms bound.
- Double bonds are represented by two lines and triple bonds by three.
- Valence electrons (electrons in the outer shell of the atom) are represented by dots next to the atom.
- Remember to indicate the overall charge of the molecule with a “+” or “-“ at the top right of the structure.
- For example: O3 has three oxygens all bound together. The oxygen in the middle is bound to the other two oxygens by one single bond and one double bond.
2Identify the bonds that can alternate to form resonant structures. Molecules that have resonant structures actually exist in a hybrid state between the different structures formed by the variations in bonds. While you may draw the various Lewis structures as separate molecules, that is just a way to pictorially represent them. Electrons that form double bonds can switch between atoms, slightly changing the way the structure is drawn.
- Bonds of this nature are said to be “delocalized”, as they are distributed evenly across all the atoms in the compound.
- For example: O3 has two resonant structures. The double bond can be between the first and second oxygen or between the second and third oxygen.
3Diagram all possible resonant Lewis structures. Once you have identified the bonds that can alternate in the compound, you can draw the various Lewis structures for each version. It is also possible to draw a representative hybrid structure by using a dashed line where the bond could be either a single bond or a double bond.
- For example: You can draw two O3 structures with the two possible bond configurations or one O3 structure with dashed lines representing the bonds.
- Draw a double-sided arrow between each structure to indicate that they are resonance structures.
What is the structure of resonance?Answered by wikiHow Contributor
- Resonance structures depends on the molecule. One way to know whether the structure is a resonance structure is to find out the bond length. If the bond length of the molecule is different from the usual bond lengths of e.g. double and single bonds, the structure should be a resonance structure.
How do I show the +R effect in a benzene structure?Answered by
- When EDG (electron-donating groups) are directly attached to benzene ring, electron density on ortho and para position is increased. This phenomenon is known as +R effect, or +M vice versa. For example, in chlorobenzene the lone pair of chlorine atom delocalized with pi bond (pi electron) of the benzene ring; this effect is called ortho or para directive effect.
What is the difference between resonance structure and effect?
What are properties of resonance effect?
How does the resonance effect the reactivity?
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Based on studies of fossilized teeth, scientists estimate that the megalodon, a prehistoric shark, measured 52 feet long and had jaws large enough to consume a rhino. The megalodon would dwarf the modern grizzly bear or great white shark. Scientists surmise that these giant predators required large amounts of food to survive.
Based on estimates of the size of the megalodon, scientists estimate that these giant creatures consumed an average of 2,500 lbs. of food each day. Fossilized megalodon teeth suggest that these animals were carnivorous, meaning their diet consisted mostly of meat. Whales, such as killer whales, or orcas, probably made up the majority of the megalodon diet.
Scientists speculate that the megalodon likely ate any meat it could find. Its large, serrated teeth would have enabled it to eat large fish and other sharks as well as whales. The megalodon may also have eaten early ancestors of sea lions called allodesmus.
Starvation may have contributed to the megalodon’s extinction. At the end of the Pliocene era, about 1.6 million years ago, major environmental changes left these predators in nutrient-poor waters. The megalodon preferred warm tropical waters, and may have been unable to follow its food sources to more temperate zones. Meanwhile, lowered sea levels may have left the megalodon without safe nursery areas for its young, leaving them vulnerable to large predators, such as whales.
White Shark Feeding
Modern great white sharks eat California sea lions, Northern fur seals, elephant seals and pelicans. White sharks feed relatively infrequently and stalk their prey methodically, allowing them to conserve energy and avoid expending needless calories. | <urn:uuid:8fd0b96c-67ef-456c-8b14-06ead1e01e55> | 4.09375 | 355 | Knowledge Article | Science & Tech. | 36.670028 | 95,542,072 |
In the last decade, the Keck Observatory in Hawaii, one of the world’s most powerful telescopes, has spent hours staring at the night sky in search of exoplanets and accumulating huge amounts of data about potential new worlds elsewhere in the Milky Way.
But maybe, Nate Tellis wondered, Keck might have picked up something else along the way. Somewhere in all that data, could there be a signal from an intelligent civilization trying to reach Earth?
Tellis is a scientist at the University of California at Berkeley, where, as his LinkedIn biography puts it, he spends his days “trawling” astronomy datasets for statistical deviations, trying to figure out whether they’re actually extraterrestrial pings. He searches particularly for laser light, powerful pulses of photons that could be as short as a nanosecond. Tellis, along with astronomer Geoff Marcy, recently dug into the Keck archives for data from 5,600 stars, observed between 2004 and 2016. Tellis and Marcy built a laser-detecting computer algorithm to comb through all that recorded starlight—and the result, detailed in a recent study in the Astronomical Journal, is the largest survey of its kind in the field of optical-based searches for extraterrestrial life.
It didn’t find anything. So far, this has been par for the course when it comes to the search for extraterrestrial life, better known by the shorthand SETI. Astronomers first began using telescopes to look for potential alien communication in 1960, and they have been met with silence ever since.
“I think when you’re doing a SETI project, it’s very important not to get discouraged by a null detection,” Tellis said. “SETI has been in process for about 60 years, and it’s been non-detection after non-detection after non-detection.”
Astronomers and engineers have spent that time developing more powerful technology to conduct SETI surveys. The majority of SETI searches have relied on radio telescopes, which scour the skies for signals in the radio and microwave parts of the light spectrum. In the 1960s, “lasers were new, tricky, low-power devices; by contrast, radio technology had been developing for decades and was relatively mature,” according to a history from the SETI group at Harvard.
These days, lasers can outshine the sun, albeit in tiny pulses. But a tiny pulse—preferably more than one, to prove it’s not a fluke—is all it would take for a distant, advanced civilization to tell Earth “hey, we’re here!” If humans can get really good at sending radio and laser signals, the reasoning goes, maybe intelligent civilizations beyond Earth can, too—and then send them our way.
Unlike radio SETI, optical SETI looks for signals in the visible portion of the light spectrum. Lasers travel well over galactic distances. The light, concentrated into a narrow beam that can be 10 times as bright as the sun, would experience less interference from interstellar dust and gas than radio waves might. Laser emissions are also capable of carrying massive amounts of information. The network of cables at the bottom of the ocean is a collection of pulses of light, firing at high frequencies to transmit digital data and bring us the internet.
The dataset Tellis used for his study contained thousands of observations of stars as young as 200 million years and stars as old as nearly 10 billion years. Keck’s instruments collected millions of photons of light from these stars. What Tellis and his algorithm looked for were brief surges in photons. The first run of the data reported 5,000 potential candidates for mysterious laser beams, but they were eventually ruled out, explained away as emissions from stars’ outer layers, cosmic rays from our sun, or internal reflections from telescope instruments. Tellis got some firsthand Keck time to observe at least one target, KIC 8462852, a star about 1,500 light-years from Earth. In 2015, astronomers announced the Kepler space telescope had observed an unusual dimming of its light, which some believe could be caused by structures built by an advanced civilization around the star. The light emission observed from KIC 8462852 was the best candidate for an alien laser beam in the survey before it was ruled out.
The results may not have been surprising, but the method is noteworthy, says Jason Wright, an astronomer at Penn State University who contributed to some of the software code Tellis and Marcy used in the study. Recycling astronomical datasets that were produced for another purpose is pretty unusual, but it makes sense. There is strong competition among astronomers for observation time on the world’s best telescopes, and SETI proposals are usually low on the priority list.
“If you proposed to do a laser SETI study on Keck with thousands of hours, there’s nobody that will let you do it,” Wright said. Meanwhile, there’s plenty of astronomical datasets sitting around, waiting for a second look. One man’s trash is another man’s treasure, even in the search for life in the universe. Tellis, Wright said, “was digging through all the trash in case someone threw out a diamond.”
Tellis’s survey, like all SETI surveys, has its limitations. The data examined only some types of stars, in a specific wavelength range, and in Earth’s cosmic neighborhood. The telescope may not have been able to detect signals that were too faint or too bright, and too far away.
Optical SETI also depends on something beyond our control: a laser beam must first be aimed at Earth for it to be detected. Imagine another life-form on a distant world conducting the same kind of search, Tellis said. “If we had pointed our telescope at Earth at sort of the distance that we’ve been doing here, we wouldn’t have seen us,” he said, because Earth is not firing a laser beam into the universe as a beacon of its existence. Other worlds may not be, either.
“Every single one of those stars could have a New York City, a Paris, a London, and we would have no idea,” Tellis said.
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Properties of transition metals (d block elements) are transitional between the highly reactive metallic elements of s- block (which form ionic compounds) and the elements of p block (which are largely covalent). The d block is present in the centre of the periodic table and the elements are known as http://ramblingroseboutique.com/?prertwe=writing-a-dating-website-profile&d2e=b9 transition elements. There are four periods or transition series included in the block. Each having ten elements. Because d-sub-shell can have a maximum of ten electrons. Most of the elements belonging to fourth transition series have been discovered in recent years.
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Just like s-block elements which are all typical metals, the properties of transition metal elements are also metallic in nature. They depict typical characteristics of metals such as high melting point, high boiling point, metallic lustre, high thermal and electrical conductivity.
The variation in the metallic properties is linked to the variation in the crystal lattices of these elements. Actually, most of the elements belonging to the fourth transition series have been discovered quite recently. Their characteristics are still to be investigated properly.
i am dating a taller girl Melting Point
The physical properties of transition metals show that elements are quite hard and have high melting points also. Actually, they have very strong metallic bonds due to the involvement of both ns and (n-1)d electrons. Along each transition series, they tend to increase with the increase in the atomic numbers (or a number of unpaired electrons). Midway, they become maximum in the elements having d5 configuration (maximum number of unpaired electrons). Then they show downward trends.
It may be defined as enthalpy change involved in breaking the metallic lattice of the crystalline metal into atoms. The high values of enthalpies of atomization tell the strong metallic bonds that are present.
The enthalpy of atomization decreases along the series. The element zinc has the least value due to the reason that there are no free electrons available for the formation of metallic bonds in the atoms. The trend reveals that the metals present in the 4d and 5d series have the greater magnitude of enthalpy of atomization as compared to the elements in the 3d series. The metallic bonds are stronger in these due to the greater involvement of the electrons in the metallic bond formation.
A careful look at the values of the atomic radii reveals that these initially decrease from Sc to V and become almost constant from Cr to Cu. The last element Zn has the comparatively high atomic radius (125 pm).
|Metallic radii (pm)||164||147||135||129||137||126||125||125||128||137|
Within a transition series, the decrease in atomic radii, in the beginning, is due to the increase in the effective nuclear charge with the increase in atomic number. However, with the increase in the number of electrons in the (n – 1) d-subshell, the screening effect of these d-electrons on the outermost ns-electrons also increases. This increased screening effect neutralises the effect of increased nuclear charge and as such the atomic radii remain almost constant in the middle of the series.
Increase in atomic radii towards the end may be attributed to the inter-electronic repulsions. The pairing of electrons in the d-orbitals of the penultimate shell occurs only after the d-subshell is half filled i.e., it has five electrons. The repulsive interactions between the paired electrons in the d-orbitals of the penultimate shell become dominant towards the end of the series and cause the expansion of the electron cloud, source site thereby increasing the atomic size.
Being properties of transition metals are metallic in nature, the transition elements form cations and their radii as expected, are less than the atoms to which they belong.The trend exists in the ionic radii because with the increase in the atomic number, the effective nuclear charge increases thereby decreasing the radius of the ion.It may be remembered that the radii of a transition metal ions decrease with the increase in the oxidation state. For example, Fe2+ (76 pm) and Fe3+ (64 pm).
Transition elements in general, exhibit all the characteristics of metals i.e., they are hard, lustrous, malleable and ductile. Apart from that, these have also high melting and boiling points. Moreover, they have typical metallic close packed structures as well (hcp, ccp or bcc). With the exception of mercury, which is liquid at room temperature, all others are hard solids.
The electronic configuration of these elements reveals that they have one or more unpaired electrons present in either ns or (n-1) d-orbitals which are available for bond formation. In general, DALLA TEORIA ALLA PRATICA: trading binario migliore metodo pdf INDIVIDUALE A MERCATI APERTI SULLE MID CAP . E' intitolato così il laboratorio diretto da Pietro Origlia greater the number of such unpaired electrons available, more will be the chances of their mutual combination and go more will be http://fisflug.is/?yrus=opzioni-digitali-eur%2Fusd&252=dd the strength of the metallic bond. That is why these metals are very hard.
In a transition series, the density of the elements increases along a series.We have seen that there is a gradual decrease in metallic radius (or atomic radius) in a transition series. At the same time, there is an increase in atomic mass of the elements. The density (Mass/Volume) is expected to increase along the series. The exceptionally low density of zinc is quite expected. Its atomic size or atomic volume is comparatively large.
The ionization enthalpies of the transition metals are higher than those of s-block elements and less than the elements of p-block. Thus, these are less electropositive than the elements of s-block and at the same time more electropositive than the elements belonging to p-block present in the same period. Considering properties of transition metals, the ionisation enthalpies increase from left to right. However, the gaps in the values of the two successive elements are not regular.
The increase in ionisation enthalpy is primarily due to increase in nuclear charge which would tend to attract the electron cloud with greater force. Thus, ionisation enthalpy is expected to increase. As the transition elements involve the gradual filling of electrons in (n-1)d-subshell, this also increases the screening effect. With the increase in the number of (n – 1)d electrons, the outer ns electrons are shielded more and more. Thus, the effect of increasing nuclear charge is opposed by the increase in the magnitude of screening effect.
source site Watch this Video for more reference of Properties of transition metals
http://pialadunia.es/?espikoleto=locanto-mujer-busca-hombre-los-angeles&d27=83 Variable oxidation states
Variable valency is one of the most striking features of the transition elements. All transition elements, except the first and the last members of each series exhibit variable oxidation states. The cause of showing different oxidation states is due to the fact that there is only a small difference between the energies of electrons in the ns orbitals and (n-1) d orbitals with the result both ns as well as (n-1) d electrons can be used for compound formation. Thus the variable oxidation states of transition elements are related to their electronic configurations.
|Oxidation States of 3d Series||atarax 10 mg och alkohol Oxidation state of 4d series||amitriptyline lexapro 5mg Oxidation State of 5d Series|
Let us illustrate the relation between the outer electronic configuration of transition elements and its various possible oxidation states by taking the example of Mn (3d5, 4s2) which shows oxidation states from +2 to +7.
- Formation of Mn2+ involves only two 4s electrons.
- Formation of Mn3+ has two 4s and one 3d electron.
- Mn4+ involves two 4s and two 3d electrons.
- Formation of Mn5+ has two 4s and three 3d electrons.
que es clindamycin 300mg Oxidation state of iron
It must be noted that in some transition elements all of the (n-1) d electrons are not involved in bond formation, e.g. iron (3d6, 4s2) should have +8 as its highest oxidation state, but actually it is only +6 which is also known only in rare cases (+2 and +3 are the common oxidation states of iron). The +6 (and not +8) as the highest oxidation states of iron is explained on the basis that only the unpaired electrons of the 3d subshell take part in bond formation. In iron, there are 4 unpaired and 2 paired 3d electrons.Hence, the effective electrons in 3d orbitals are only four which may give +6 as the highest oxidation state.
Similarly, nickel has +4 as the highest oxidation state because here again only two of its eight 3d electrons are unpaired. The same is applied to all the transition elements.
Highest oxidation state
The highest oxidation state shown by any transition element is + 8 (Ru is 5 d-series and Os is 5 d series). Mn (member of 3 d series) shows the maximum state of +7 is KMnO4.It is important to note that the Cu
It is important to note that the Cu+ ion with d10 configuration is less stable than the Cu2+ ion with d9 configuration. It is due to increased hydration of the Cu2+ ion.
Formation of Colour Ion
Most of the d block metal compounds are coloured in the solid or in solution states (difference from s- and p- block elements whose compounds are generally white). The colour of transition metal ions is due to the presence of unpaired or incomplete d-orbitals. When visible (white) light ( λ = 4000-7000 Å) falls on a coloured substance, the latter absorbs certain radiations of white light and transmit the remaining ones. The transmitted light has the complementary colour to that of the absorbed light. This complementary colour which is actually the colour of the reflected (transmitted) light is the colour of the substance. For example, hydrated Cu2+ ion absorbs radiations corresponding to red light.Hence, it transmits radiations of the wavelength corresponding to the blue colour which is complementary to red colour.
The absorption of visible light and hence coloured nature of the transition metal cations is due to the promotion of one or more unpaired d-electron from a lower to a higher level within the same d-subshell. This promotion requires the small amount of energy which is available in the visible light.
Note that d block metal cations like Sc3+, Ti4+, Cu+ and Zn2+ have either completely empty or fully filled 3d-orbital, i.e. they do not have any unpaired d-electron, and hence appear colourless.
Magnetic properties of transition metals
On the basis of magnetic properties of transition metals, substances are classified into the following two types.
(i) Paramagnetic substances
Substances which are weakly attracted into the magnetic field are called paramagnetic. These substances lose their magnetism on removing the magnetic field. Paramagnetism is caused by the presence of unpaired electrons and since most of the transition metal atoms have unpaired d-electrons, they are paramagnetic in behaviour.
(ii) Diamagnetic substances
Substances which are repelled by the magnetic field are called diamagnetic, It is the property of the completely filled electronic subshells.
Since most of the transition metal ions have unpaired d-electrons, they show paramagnetic behaviour. The exceptions are Sc3+, Ti4+, Cu+ and Zn2+ etc. which do not contain any unpaired d electron and hence these are diamagnetic. The presence of an unpaired electron in an element causes it to behave like a permanent magnet. As a result of the permanent magnet, a paramagnetic substance when placed in an applied magnetic field, takes up a parallel position to the field.
It is important to note that diamagnetic substances show a decrease in weight while paramagnetic substances show an increase in weight in presence of a magnetic field.
Since each unpaired electron is regarded as a micro magnet having a certain value of the magnetic moment, the total magnetic moment of a cation depends upon the number of unpaired electrons and is given by the following expression.
μ = √[n(n + 2)] BM
When n (the number of unpaired electron) = 1, μ =√[1 x 3] = 1.73 B.M.
and so on. Thus metal with maximum unpaired electrons (i.e. 5) should have maximum magnetic activity. Hence Mn with 5 unpaired electrons has maximum magnetic activity.
Bigger the magnetic moment’s value, more the paramagnetic character.
In the case of Fe, Co and Ni, the unpaired electron spins are exceptionally more pronounced. As a result, these elements are much more paramagnetic than the rest of elements. Hence these are said to be ferromagnetic, i.e. they can be magnetised.
Certain transition elements form compounds of indefinite structure and proportion (non-stoichiometric compounds) with group 16 elements (O, S, Se and Te). The formation of non-stoichiometric compounds is partly due to the variable valency of the element and partly due to defects in the solid structures.
Interstitial compound formation
Transition elements have remarkable power to combine with atoms of relatively small size to form interstitial compounds, e.g. hydrides with hydrogen, carbides. with carbon etc. The steel and cast iron are hard because of the interstitial compound formation with carbon.
Catalytic Properties of transition metals
Due to variation in properties of transition metals, elements and their compounds are frequently used as catalysts.The most important being Fe, Pt, Pd, Ni and V2O5. In some cases, the transition elements provide unpaired d-electrons.This forms the unstable intermediate compound with the reactant. While in other, the transition metals provide a large surface area for the reactants to be adsorbed.
Resistant to corrosion
With the exception of iron, other transition metals are resistant to corrosion.Chromium is a very important corrosion resisting metal. The properties of transition metals like high heats of sublimation (due to the existence of covalent bonding), high ionization potentials, and low heats of hydration of their ions make these metals to remain unreactive or noble. Within a transition series, the noble character general creases with the increase in atomic number. This tendency is pronounced in platinum and gold.
All transition elements, except copper and mercury, have oxidation potentials higher than that of standard hydrogen electrode (taken as zero). Hence the oxidation properties of transition metals except copper and mercury are good reducing agents. Copper has a negative oxidation potential, and hence it is not able to displace H* ions from acid solutions. Sometimes, other transition metals also do not displace hydrogen from acids; it is because of their surface being covered with insoluble inert oxides. For example, Cr is so unreactive that it can be used as a protective non-oxidising metal.
Formation of Covalent and Ionic Bond
These metals form ionic as well as covalent compounds. Generally, ionic compounds are formed by the elements in their lower valency states. While covalent compounds are formed by the elements in their higher valency states.
Since d block elements are quite similar in atomic size, they can mutually substitute one another in crystal lattices. This gives solid solution and smooth alloys. An alloy is a solid mixture of two or more different elements, at least one of which is a metal. Alloys are homogeneous in the solid state. Alloys containing mercury (a liquid at ordinary temperature) as one of the constituent elements are term as amalgams. In alloys, chemical properties of the component elements remain same, but certain physical properties are improved. Actually, the purpose of making alloys is to develop some useful characteristics which are absent in the constituent elements.
Quick Revision of Properties of transition metals
This is about the Properties of Transition Metal elements.
We will gain in depth knowledge of Periodic table elements under following subtopics:
- F Block Elements: Lanthanides and actinides.
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Following three months of around-the-clock work, the Chesapeake Bay Impact Crater Deep Drilling Project successfully completed its operations, extracting more than a mile-long segment of rocks and sediments from the Earth. On Dec. 4, the drill bit reached a final depth of 5,795 ft (1.1 miles, 1.77 kilometers) within the structure of the crater.
The impact crater was formed about 35 million years ago when a rock from space struck the Earth at hypersonic speed. Scientists have only recently begun to explore the consequences from that distant event and learn how it has greatly affected the population living in southeastern Virginia today.
“The drilling project was a major success,” said Greg Gohn, a U. S. Geological Survey (USGS) scientist in Reston, Va. “We recovered a nearly complete set of core samples from the top of the crater fill to the crater floor.” USGS and the International Continental Scientific Drilling Program (ICDP) are the project’s sponsors.
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For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
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A sensitive new genetic test can now detect a crippling disease called QPX occurring in clam beds from Cape Cod south to Virginia and north to Canada. Although it does not affect humans and it is not as well known as red tide, the disease can have a significant impact on a local economy by killing clams and devastating shellfish harvests and commercial aquaculture operations.
QPX - for quahog parasite unknown - is a single-celled organism related to slime mold. It was first detected in 1995 in Provincetown, MA and spread to nearby clam beds, killing nine of ten clams in many of the beds. The disease spreads from clam to clam, infecting the clam by secreting a thick mucus layer to insulate itself from the clam’s immune system.
Rebecca Gast, an associate scientist in the Biology Department at Woods Hole Oceanographic Institution (WHOI), has developed a genetic test to detect the organism not only in clams but in seawater and sediment. Since QPX also decomposes seaweed, researchers now believe it can be found in all coastal waters but doesn’t become deadly to clams until it reaches a critical concentration in the water.
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For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
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The solar system, discovered by a team from Lawrence Livermore National Laboratory and the National Research Council of Canada (NRC) Herzberg Institute of Astrophysics with collaborators at University of California, Los Angeles and Lowell Observatory, orbits around a dusty young star named HR8799, which is 129 light years away. All four planets are roughly five to seven times the mass of Jupiter.
Now, the same research team has discovered a fourth planet that is about seven times the mass of Jupiter. Using high-contrast, near infrared adaptive optics on the Keck II telescope in Hawaii, the astronomers imaged the fourth planet (dubbed HR8799e) in 2009 and confirmed its existence and orbit in 2010. The research appears in the Dec. 8 edition of the journal Nature.
"The images of this new inner planet in the system is the culmination of 10 years worth of innovation, making steady progress to optimize every observation and analysis step to allow the detection of planets located ever closer to their stars," said Christian Marois, a former LLNL postdoc now at NRC, and first author of the new paper.
If this newly discovered planet was located in orbit around our sun, it would lie between Saturn and Uranus. At about 30 million years old, this giant version of our solar system is young compared to our system, which is about 4.6 billion years old.
Though the system is very much like our own, it is much more extreme than our own -- the combined mass of the four giant planets may be 20 times higher, and the asteroid and comet belts are dense and turbulent. In fact, the massive planets' pull on each other gravitationally, and the system may be on the verge of falling apart.
Lawrence Livermore scientists simulated millions of years of evolution of the system, and showed that to have survived this long, the three inner planets may have to orbit like clockwork, with the new planet going around the star exactly four times while the second planet finishes two orbits in the time it takes the outer planet to complete one. This behavior was first seen in the moons of Jupiter but has never before been seen on this scale.
Studying the planet's orbits also will help estimate their masses. "Our simulations show that if the objects were not planets, but supermassive "brown dwarfs," the system would have fallen apart already," said Quinn Konopacky, a postdoctoral researcher at LLNL's Institute of Geophysics and Planetary Physics and a key author of the paper. (Brown dwarfs are failed stars, too low in mass to sustain stable hydrogen fusion but larger than planets.)"The implication is that we have truly found a unique new system of planets. We don't yet know if the system will last for billions of years, or fall apart in a few million more. As astronomers carefully follow the HR8799 planets during the coming decades, the question of just how stable their orbits are could become much clearer." (See the simulation showing thousands of years of evolution of the system if the planets are not in a clockwork orbit or are more massive brown dwarfs.)
Previous observations had shown evidence for a dusty asteroid belt orbiting closer to the star -- the new planet's gravity helps account for the location of those asteroids, confining their orbits just like Jupiter does in our solar system. "Besides having four giant planets, both systems also contain two so-called "debris belts" composed of small rocky and/or icy objects along with lots of tiny dust particles, similar to the asteroid and Kuiper comet belts of our solar system," noted co-author Ben Zuckerman, a professor of physics and astronomy at UCLA. (See the movie.)
"Images like these bring the exoplanet field into the era of characterization," said Travis Barman, a Lowell Observatory exoplanet theorist and co-author of the current paper. "Astronomers can directly examine the atmospheric properties of four giant planets orbiting another star that are all the same young age and that formed from the same building materials."
"I think there's a very high probability that there are more planets in the system that we can't detect yet," Macintosh said. "One of the things that distinguishes this system from most of the extrasolar planets that are already known is that HR8799 has its giant planets in the outer parts -- like our solar system does -- and so has 'room' for smaller terrestrial planets -- far beyond our current ability to see -- in the inner parts."
A team led by Macintosh is constructing the Gemini Planet Imager, a new system that will be up to 100 times more sensitive than current instruments and able to image planets similar to our own Jupiter around nearby stars.
"It's amazing how far we've come in a few years," Macintosh said. "In 2007, when we first saw the system, we could barely see two planets out past the equivalent of Pluto's orbit. Now we're imaging a fourth planet almost where Saturn is on our solar system. It's another step to the ultimate goal -- still more than a decade away -- of a picture showing another planet like Earth."
Anne Stark | EurekAlert!
What happens when we heat the atomic lattice of a magnet all of a sudden?
17.07.2018 | Forschungsverbund Berlin
Subaru Telescope helps pinpoint origin of ultra-high energy neutrino
16.07.2018 | National Institutes of Natural Sciences
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
17.07.2018 | Information Technology
17.07.2018 | Materials Sciences
17.07.2018 | Power and Electrical Engineering | <urn:uuid:979b1136-8f47-4010-80ad-4c6d62526c59> | 3.625 | 1,168 | Knowledge Article | Science & Tech. | 51.362728 | 95,542,124 |
Astronomy, Observatories, Science
7 Mar , 2017 by Evan Gough
Super Telescopes are designed around enormous primary mirrors to gather light from the most distant objects. The Thirty Meter Telescope is no exception.
Space stories from across the internet, sent to you by email. | <urn:uuid:d4509748-b247-44a4-94b8-7b53be93abec> | 3.015625 | 58 | Truncated | Science & Tech. | 36.85876 | 95,542,138 |
Maintaining soil stability and normal water and nutrient cycles in desert systems is critical to avoiding desertification. These particular ecosystem processes are threatened by trampling of livestock and people, and by off-road vehicle use. Soil compaction and disruption of cryptobiotic soil surfaces (composed of cyanobacteria, lichens, and mosses) can result in decreased water availability to vascular plants through decreased water infiltration and increased albedo with possible decreased precipitation. Surface disturbance may also cause accelerated soil loss through wind and water erosion and decreased diversity and abundance of soil biota. In addition, nutrient cycles can be altered through lowered nitrogen and carbon inputs and slowed decomposition of soil organic matter, resulting in lower nutrient levels in associated vascular plants. Some cold desert systems may be especially susceptible to these disruptions due to the paucity of surface-rooting vascular plants for soil stabilization, fewer nitrogen-fixing higher plants, and lower soil temperatures, which slow nutrient cycles. Desert soils may recover slowly from surface disturbances, resulting in increased vulnerability to desertification. Recovery from compaction and decreased soil stability is estimated to take several hundred years. Re-establishment rates for soil bacterial and fungal populations are not known. The nitrogen fixation capability of soil requires at least 50 years to recover. Recovery of crusts can be hampered by large amounts of moving sediment, and re-establishment can be extremely difficult in some areas. Given the sensitivity of these resources and slow recovery times, desertification threatens million of hectares of semiarid lands in the United States.
Weitere Kapitel dieses Buchs durch Wischen aufrufen
- Surface Disturbances: Their Role in Accelerating Desertification
- Springer Netherlands
Fallstudie Überschwemmungskarten/© Thaut Images | Fotolia | <urn:uuid:9e9954ec-9d39-4c8c-8133-e39a6f8b6be9> | 3.90625 | 370 | Knowledge Article | Science & Tech. | 0.908585 | 95,542,150 |
Black hole merger is literally a match made in heaven. And the latest gravitational wave detection, from collision of two black holes, has set the ball rolling for unveiling the secret behind the mergers: How did the black holes pair up in the first place? The Advanced Laser Interferometer Gravitational Wave Observatory (LIGO), for the third time in less than a year-and-a-half, detected gravitational waves: Essentially, an intense form of energy emanating from disturbance of space-time, when black holes collide.
An international research team, including scientists from India, announced the latest detection of gravitational waves. The waves were first predicted by Albert Einstein more than a century ago. A black hole is a region in space where the pulling force of gravity is so strong that even light cannot escape its grip. According to Tarun Souradeep, LIGO-India spokesperson, each "event" of gravitational wave detection throws up a surprise.
But what has intrigued researchers this time is the spin of the black holes: They are not like two aligned tornadoes orbiting each other, but like two tilted tornadoes. "This (new finding) could point to how black holes pair up in the first place -- the formation scenario. Its not just detection...it's the start of a new astronomy," Souradeep told IANS. Souradeep is a Senior Professor at Inter-University Centre for Astronomy and Astrophysics, Pune, one of the three leading Indian institutions involved in implementing the collaborative LIGO-India project.
So here's what has got scientists buzzing. One of the more popular models for black holes says they form in pairs right at the outset and merge. This, Souradeep says, is analogous to an arranged early "child" marriage. If the marriage survives upheavals, there is ample opportunity and grounds to align their personal traits or in the case of black holes, their spins. The alternate theory revolves around the idea that these black holes are single when formed. Then, in dense environments, a black hole would sink to the densest part and it could find a partner.
Here the spins are not necessarily aligned, as was shown with the latest detection. "This can be thought of as modern-day marriages where couples with disparate backgrounds meet in a high-density environment such as IT hubs in metros," explained Souradeep. The latest observation -- from even more distant and ancient black hole collisions than the first two LIGO observations -- puts "pressure" on the arranged marriage model.
"In science, you cannot reject anything outright. So what we are saying is the first model (arranged marriage at an early age) can't explain the latest observation. But it doesn't mean that none of the black holes pairs have originated that way (in pairs at the start). At the same time, the latest data shows the alternate model is also operational," explained Souradeep.
For India, this cosmic tango has implications in new-age astrophysics. "There are people in India interested in that liaison (black hole merger); we would include more astrophysicists who would be interested in the formation scenario of black hole binaries. We know LIGO India is a very important component of how we do astrophysics with it (the detections)," Souradeep explained. The other implication is the growing scope of astronomy as with more detections (or events), there would be pressure to locate the source of the collisions.
The first direct observation of gravitational waves was made in September 2015, during the first observing run. A second detection was made in December, 2015. The third detection is described in a new paper accepted for publication in the journal Physical Review Letters. The publication has 40 authors from 11 Indian institutions. For India, things will take a firm shape henceforth.
The LIGO India Science board will begin to coordinate the science of the Indian collaboration. "Till now there was an informal consortium which was handling the science from India with the data that was coming in. But we are transiting to a phase where LIGO India would seamlessly take care of the science that we do with the detectors in the US and also the Indian detector when it comes up," Souradeep said.
The construction of the LIGO-India observatory and the build-up of a vibrant science community around it are going to be combined. "This is as we hoped would happen," Souradeep added. | <urn:uuid:9f585786-012b-4d95-8add-a9b0e6977562> | 3.28125 | 910 | News Article | Science & Tech. | 41.919098 | 95,542,174 |
T Tauri wind
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The T Tauri wind — so named because of the young star currently in this stage—is a phenomenon indicative of the phase of stellar development between the accretion of material from the slowing rotating material of a solar nebula and the ignition of the hydrogen that has agglomerated into the protostar.
The protostar at first only has about 1% of its final mass. But the envelope of the star continues to grow as infalling material is accreted. After 10,000–100,000 years, thermonuclear fusion begins in its core, then a strong stellar wind is produced which stops the infall of new mass. The protostar is now considered a young star since its mass is fixed, and its future evolution is now set.
The evolutionary picture of low mass protostars
This article is in a list format that may be better presented using prose. (January 2018)
The T Tauri stars, with masses less than twice the mass of our Sun, are thought to follow this process:
- initially, the clouds which collapse are thought to be very slowly rotating
- The dense cores collapse faster than the less dense outer regions of the cloud. This follows from the free-fall time ~ 1/√(gxdensity). The initial collapse of the core is quite fast; time ~ 1/√(6.7×10−8×10−18 g/cm³) ~ 50,000–100,000 years or so. The lower density envelope takes longer to collapse accrete (collapse onto the protostar); time ~ millions of years or so. Roughly, speaking the Sun forms as shown here.
- The inside-out collapse leads to the formation of the forming star in the center of the cloud which then slowly builds up its mass by accreting the outer layers of the cloud.
- Another noteworthy aspect of this later stage of formation is that before the star actually gets hot enough to ignite nuclear fusion, an intense stellar wind is generated. Often because the cloud was slowly rotating, a disk of material forms around the star. The disk collimates the intense stellar wind into 2 oppositely directed beams producing what is referred to as a bipolar flow, which can cause the forming star to lose up to 0.4 mass of our Sun, and can start to disrupt the cloud.
- Even though it takes several millions of years for the cloud to accrete onto the protostar, because the protostars are relatively low mass, it takes even longer to slowly contract and approach starhood. For the most part, the cloud has a chance to accrete onto the protostar before the violent stages of evolution begin.
The character of accretion and stellar wind parameters of T Tauri stars
The main portion of emission continuum of Classic T Tauri Stars is formed outside the accretion shock, what means a great deal of accretion matter falls onto the star in nearly horizontal direction. This gas decelerate in turbulent layer near the star surface.
We suggest two scenarios to explain such nature of accretion: two-stream accretion (through boundary layer and magnetosphere) and magnetospheric accretion by way of streams, the bulk of matter in which falls onto the star in nearly horizontal direction.
Observations have provided quantitative parameters of disk wind, derived from the analysis of optical and UV spectra of CTTS. The matter outflows observed from a disk region with an outer radius of < 0.5 AU. The outflowing matter initially moves almost along the disk until being accelerated up to V > 100 km/s and only afterwards begins to collimate. Inner region of the wind is collimated into the jet at a distance <3 AU from the disk mid plain. The Vz gas velocity component in the jet decreases with increasing distance from the jet axis. The gas temperature in the jet bottom is less than 20,000 kelvins.
- "Lecture 14: Star Formation". Astronomy.ohio-state.edu. Retrieved 2014-02-16.
- Heavier elements are created in larger stars via their nucleosynthesis. The nuclear reactions release neutrons which accumulate and undergo beta minus decay, to become larger atomic number elements such as iron, cobalt, and nickel. Eventually, after a star has exhausted all its hydrogen and ended its fusion cycle —and the core is largely composed of iron— elements up to lead and bismuth are created, just before the lack of available energy causes the outer layers to fall inwards until a supernova explosion ejects 90% of the star's mass. Andrew Norton, the Open University of the UK, unpublished text book How the Universe Works, p. 129
- the spin may only be important in the later stages of collapse—initially it plays very little role in the formation process—and to not have uniform density (the clouds start denser in their centers than near their edges). This latter condition leads to an inside-out collapse. | <urn:uuid:5a89b287-f4a9-4b32-8de4-86fff17aace8> | 3.40625 | 1,092 | Knowledge Article | Science & Tech. | 47.947451 | 95,542,207 |
British scientists have reportedly found a fossilized spider preserved in amber that suggests spiders have existed much longer than thought.
The journal Biology Letters says a Manchester University research team that studied the preserved spider found in Spain now believes orb-weaving spiders arrived during the Jurassic period, not the Cretaceous period, making them about 100 million years older than has been believed, the Times of London reported Wednesday.
And scientists say crocodiles are about 20 million years older than previously thought. The Times says that finding stems from the discovery of a fossilized crocodile that lived up to 98 million years ago in Australia.
The Proceedings of the Royal Society says the 3-foot-long creature probably resembled the last common ancestor of modern crocodiles.
Copyright 2006 by United Press International
Explore further: Insectivorous birds consume annually as much energy as the city of New York | <urn:uuid:ecb14c2b-d429-4824-9b3a-c06405353f21> | 3.65625 | 174 | News Article | Science & Tech. | 23.908286 | 95,542,208 |
ATBD - GHG-CCI
ESA Climate Change Initiative (CCI) Algorithm Theoretical Basis Document Version 2 (ATBDv2) – UoL-FP for the Essential Climate Variable (ECV) Greenhouse Gases (GHG) Page 20 Version 2 – Draft 1 18 March 2013 184.108.40.206 Surface Properties The albedo is calculated from the spectral continuum from the GOSAT L1B using the reflectivity: where SZA is the solar zenith angle and the Solar radiance and observed GOSAT radiance are given by S Solar and S GOSAT respectively. The retrieval uses two albedo parameters for each spectral band, giving the albedo for the centre wavelength of the band and the slope of the albedo. The slope of the albedo is set to zero in the a priori. The covariance for albedo is completely open and the slope a priori error is set so that the band edges can vary by 50%. 220.127.116.11 Instrument Properties The dispersion is given in the GOSAT L1B data but requires adjusting in all SWIR bands. This adjustment can be calculated by the difference of the spectra away from a well known single strong Fraunhofer line (12985.163 cm -1 ) in the O 2 A band. Additionally, the O 2 A band dispersion requires shifting one spectral point lower to become approximately correct. It should be understood that although all SWIR band's dispersions are adjusted they are only approximate and require the dispersion to be retrieved. In addition to dispersion, the zero-level offset is retrieved in the O 2 A Band in order to scale the intensity. 3.3.2 Description of Full-Physics Methane Retrievals The Full-Physics Methane retrieval is similar to the CO 2 retrieval described in Section 3.3.1 with the target retrieval species changed from CO 2 to CH 4 . Table 3-2. State Vector for CO 2 retrievals. Description Parameters Number of Elements Aerosols 3 x 20 levels 60 CH 4 20 levels 20 Albedo 2 x 3 bands 6 Dispersion 2 x 3 bands 6 Zero-Level Offset 1 1 Surface Pressure Scalar 1
ESA Climate Change Initiative (CCI) Algorithm Theoretical Basis Document Version 2 (ATBDv2) – UoL-FP for the Essential Climate Variable (ECV) Greenhouse Gases (GHG) Page 21 Version 2 – Draft 1 18 March 2013 Temperature Scalar 1 Water Vapour Scalar 1 CO 2 Scalar 1 Total 97 18.104.22.168 Profile of Methane Concentration The a priori profile of CH 4 is acquired from a TM3 model run (Sander Houweling, personnel communication) and is interpolated to the desired latitude, longitude and time. 22.214.171.124 Profile of Carbon Dioxide Concentration Same as Section 126.96.36.199 188.8.131.52 Surface Pressure Same as Section 184.108.40.206 220.127.116.11 Temperature and Water Vapour Same as section 18.104.22.168 22.214.171.124 Aerosol Profiles Same as Section 126.96.36.199 188.8.131.52 Surface Properties Same as Section 184.108.40.206 220.127.116.11 Instrument Properties Same as Section 18.104.22.168 3.3.3 Description of Proxy Methane Retrievals For our GOSAT CH 4 retrieval, we have adopted the CO 2 proxy method of (Frankenberg et al., 2006). CO 2 is known to vary in the atmosphere much less than CH 4 and as the CO 2 absorption band is spectrally close to that of CH 4 we can use the CO 2 as a proxy for the light path to minimize common spectral artefacts due to aerosol scattering and instrumental effects (Frankenberg et al, 2008, ,Butz et al, 2010). CH 4 and CO 2 retrievals are carried out sequentially with channels at 1.65 µm and 1.61 µm respectively. In order to obtain a volume mixing ratio (VMR) of CH 4 , it is necessary to multiply the X CH4 /X CO2 ratio by a model X CO2 . We obtain the CO 2 VMRs from the LMDZ model (Chevallier et al. 2010), convolved with scenedependent instrument averaging kernels obtained from the GOSAT CO 2 retrieval. | <urn:uuid:263140a3-c75d-42f2-b694-03d0275511eb> | 2.5625 | 948 | Academic Writing | Science & Tech. | 78.271274 | 95,542,276 |
Revisiting the provenance delineation of a widespread shrub, Frangula alnus—the role of spatial, temporal and environmental patterns
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Including population genetic aspects into the selection of planting material within the framework of conservation and restoration measures is of vital importance for the long-term persistence of populations. This is especially true facing climate change since genetic diversity and the spread of potentially beneficial alleles are important for the adaptability of populations. Therefore, knowledge about genetic variability within and between populations is a critical aspect when determining provenance regions. In our study, we investigated the population genetic structure of a widespread, insect-pollinated and mainly bird-dispersed shrub species, Frangula alnus, on the basis of seven microsatellites and two chloroplast DNA markers throughout Germany. The aim was to determine the spatial, temporal and ecological processes genetically structuring populations to critically revise existing provenance regions. Therefore, we conducted analyses on different spatial scales (country-wide, regional and local) using the two different marker sets in addition to environmental variables. We detected distinct patterns on all spatial scales which indicated influences of historic recolonization processes, regional differences of seed dispersal across the landscape, as well as small-scale spatial genetic structures attributable to local dispersal processes. No relation of underlying environmental gradients such as temperature or precipitation and genetic patterns was found. We conclude that different aspects of historic and more recent gene flow shape population genetic structures and that a thorough analysis on a variety of spatial, temporal and environmental scales is necessary to appropriately select planting material for conservation and restoration measures. Correspondingly, management advice regarding provenance delineations will be provided.
KeywordsSeed zone Microsatellite cpDNA Genetic diversity Differentiation Management
We are very grateful to all the forest rangers, colleagues and friends who supported this study by collecting leaf material for the genetic analysis throughout Germany. Many thanks go to Christina Mengel and Sascha Liepelt for their support and helpful advices regarding the laboratory work. Moreover, we would like to thank two anonymous reviewers for their helpful comments. This project was funded by the program “Forschung für die Praxis” by the Hesse State Ministry of Higher Education, Research and the Arts.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no competing interests.
Data archiving statement
Genotyping data of all collected samples for the seven microsatellites as well as cpDNA data of the corresponding number of samples are available from the Dryad Digital Repository: http://dx.doi.org/10.5061/dryad.215sn.
- Barsch F, Heym A, Nehring S (2012) Leitfaden zur Verwendung gebietseigener Gehölze. https://www.bfn.de/fileadmin/BfN/recht/Dokumente/leitfaden_gehoelze_.pdf. Accessed 25 July 2015
- Bucci G, Gonzalez-Martinez SC, Le Provost G, Plomion C, Ribeiro MM, Sebastiani F, Alia R, Vendramin GG (2007) Range-wide phylogeography and gene zones in Pinus pinaster Ait. revealed by chloroplast microsatellite markers. Mol Ecol 16(10):2137–2153. doi: 10.1111/j.1365-294X.2007.03275.x CrossRefPubMedGoogle Scholar
- Cornille A, Giraud T, Bellard C, Tellier A, Le Cam B, Smulders MJM, Kleinschmit J, Roldan-Ruiz I, Gladieux P (2013) Postglacial recolonization history of the European crabapple (Malus sylvestris Mill.), a wild contributor to the domesticated apple. Mol Ecol 22(8):2249–2263. doi: 10.1111/mec.12231 CrossRefPubMedGoogle Scholar
- De Kort H, Mergeay J, Vander Mijnsbrugge K, Decocq G, Maccherini S, Kehlet Bruun HH, Honnay O, Vandepitte K, Bugmann H (2014) An evaluation of seed zone delineation using phenotypic and population genomic data on black alder Alnus glutinosa. J Appl Ecol 51(5):1218–1227. doi: 10.1111/1365-2664.12305 CrossRefGoogle Scholar
- De Kort H, Vandepitte K, Mergeay J, Mijnsbrugge KV, Honnay O (2015) The population genomic signature of environmental selection in the widespread insect-pollinated tree species Frangula alnus at different geographical scales. Heredity 115(5):415–425. doi: 10.1038/hdy.2015.41 CrossRefPubMedPubMedCentralGoogle Scholar
- GeoBasis-DE/BKG (2015) Digitales geländemodell gitterweite 200m. Bundesamt für Kartographie und Geodäsie. Dataset: http://www.geodatenzentrum.de/geodaten/gdz_rahmen.gdz_div?gdz_spr=deu&gdz_akt_zeile=5&gdz_anz_zeile=1&gdz_unt_zeile=3&gdz_user_id=0
- Hampe A, Petit RJ (2005) Conserving biodiversity under climate change: the rear edge matters. Ecol Lett 8(5):461–467. doi: 10.1111/j.1461-0248.2005.00739.x
- Heuertz M, Fineschi S, Anzidei M, Pastorelli R, Salvini D, Paule L, Frascaria-Lacoste N, Hardy OJ, Vekemans X, Vendramin GG (2004) Chloroplast DNA variation and postglacial recolonization of common ash (Fraxinus excelsior L.) in Europe. Mol Ecol 13(11):3437–3452. doi: 10.1111/j.1365-294X.2004.02333.x CrossRefPubMedGoogle Scholar
- Kremer A, Ronce O, Robledo-Arnuncio JJ, Guillaume F, Bohrer G, Nathan R, Bridle JR, Gomulkiewicz R, Klein EK, Ritland K, Kuparinen A, Gerber S, Schueler S (2012) Long-distance gene flow and adaptation of forest trees to rapid climate change. Ecol Lett 15(4):378–392. doi: 10.1111/j.1461-0248.2012.01746.x CrossRefPubMedPubMedCentralGoogle Scholar
- Lavabre JE, Gilarranz LJ, Fortuna MA, Bascompte J (2016) How does the functional diversity of frugivorous birds shape the spatial pattern of seed dispersal?: a case study in a relict plant species. Phil Trans R Soc B 371(1694):20150280. doi: 10.1098/rstb.2015.0280 CrossRefPubMedPubMedCentralGoogle Scholar
- Oksanen JF, Blanchet G, Kindt R, Legendre P, Minchin PR, O’Hara RB, Simpson GL, Solymos P, Stevens MHH, Wagner H (2015) vegan: Community Ecology Package. R package version 2.3–1. http://CRAN.R-project.org/package=vegan. Accessed 12 November 2015
- Petit R, Aguinagalde I, de Beaulieu JL, Bittkau C, Brewer S, Cheddadi R, Ennos R, Fineschi S, Grivet D, Lascoux M, Mohanty A, Müller-Starck G, Demesure-Musch B, Palmé A, Martín JP, Rendell S, Vendramin GG (2003) Glacial refugia: hotspots but not melting pots of genetic diversity. Science 300(5625):1563–1565. doi: 10.1126/science.1083264 CrossRefPubMedGoogle Scholar
- R Development Core Team (2014) R: a language and environment for statistical computing. R Foundation for Statistical Computing, Vienna. URL http://www.R-project.org
- Reiker J, Schulz B, Wissemann V, Gemeinholzer B (2015) Does origin always matter? Evaluating the influence of nonlocal seed provenances for ecological restoration purposes in a widespread and outcrossing plant species. Ecol Evol 5(23):5642–5651. doi: 10.1002/ece3.1817 CrossRefPubMedPubMedCentralGoogle Scholar
- Zecchin B, Caudullo G, Rigo DD (2016) Frangula alnus in Europe: distribution, habitat, usage and threats. In: San-Miguel-Ayanz J, de Rigo D, Caudullo G, Houston Durrant T, Mauri A (eds) European Atlas of Forest Tree Species. Publication Ofice EU, Luxembourg, p e019ee2+ https://w3id.org/mtv/FISE-Comm/v01/e019ee2. Accessed 25.01.2017Google Scholar | <urn:uuid:985cf303-4614-4db1-aeb0-5133cbe78045> | 2.921875 | 2,030 | Academic Writing | Science & Tech. | 50.063504 | 95,542,301 |
Dark Eye Adaption - How We See In the Dark
In order to gaze successfully around the starry skies, you need to take into account a very important factor to do with your eyes. This is called dark adaptation. Read on and get some tips on how to make this process quicker and easier.
- Tips for Getting Started in Astronomy
- Dark Eye Adaption - How We See In the Dark
- Light Pollution
- Using Star Charts and Measuring Distance
- Constellation Guide
- Binocular Astronomy
- Moon Watching - How to Observe the Moon
- Buying Your First Telescope
- Your First Night With Your First Telescope
- Sky Orientation through a Telescope
- Polar Alignment of an Equatorial Telescope Mount
- Useful Astronomy Filters for Astrophotography
Before observing, you must give your eyes time to adjust to the darkness. This is called dar eye adaption. You may have noticed that your pupils are larger in dark conditions and smaller on a bright sunny day. This is the way the eye controls how much light to let in - exactly the same way as the aperture works on a camera lens. In dark conditions the iris opens and the pupil becomes larger to let in more light, while in bright conditions the iris closes and the pupil becomes smaller to limit the light coming in and preventing you from becoming dazzled. This is actually only a small part of what your eyes are up to, and the process of getting used to the dark is called Dark Eye Adaptation.
Your eyes adapt to whatever the prevailing lighting conditions are. Let's take an example - a room at night with the lights on. It all looks fine because your eyes have set themselves to work in whatever light there is around. Now turn the lights off and the first thing you'll notice is that the room appears almost black for a short time. Your eyes, sensing the lack of light, have gone into dark adapting mode - your pupils grow to let in more light and then the all-important chemical changes begin to switch on the low-light-intensity 'rods' which fill the backs of the eyes. This process is Dark Eye Adaptation and it actually takes around an hour, but a good proportion is complete within 10 minutes or so.
In order to see the best of the faint night sky, shield your eyes from all bright lights for a good few minutes before you start stargazing. You should also make sure you cannot see any bright lights, such as street lighting, while you are observing. If you need to use a torch whilst observing you can get special red light torches that will help preserve your night vision. Remember - Dark Eye Adaption can be ruined by just one glance at a bright light.
How Does Dark Eye Adaption Work?
Your eyes gather light by means of rod and cone receptors on the back surface of the eyeball. The cones are responsible for seeing fine detail and colour vision in good light, while the rods allow us to see more effectively in dim lighting conditions. Cone sensitivity adjustment takes around 10 minutes which is why we are able to see reasonably well quickly in the process, but with less detail. You may notice your night vision being "fuzzy". The rods take longer to increase their sensitivity, say 20 to 30 minutes or so, and once they have adapted you should be able to see details and your night vision will be less fuzzy.
The 30-minute time course for adaptation is about how long it takes for the Earth to shift from twilight to the darkness of the night.
Last updated on: Sunday 7th January 2018
Upgrading to a Go-To computer and motor drive!
What to look out for when taking your new telescope out for the first time
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To recap: For every application, there are usually one or several typical operations and typical workflows that users may have to perform. A programmer needs to determine those workflows, examine them, and split them up into individual work units that the program can perform.
In some cases, that's all you have to do: Come up with menu items, buttons and controls that perform the individual subtasks and merrily go on your way. But a good interaction design has to go beyond just letting the user do the operations with a computer instead of with a hammer. You will want to optimize the workflow.
One of the fundamental rules of interaction design comes from the early days of the graphical user interface, when all we had were command-lines. Back then, one bright mind realized that we shouldn't have the user type in anything the computer already knows. That's how we got menus and radio buttons in the first place. Instead of expecting you to remember terms, the computer will present sensible answers and let you point at one, as if buying cheese at the cheese counter in a remote Swiss village where they still speak that Latin-descended language few others in the world know.
This may seem to no longer be relevant now that everyone is well-versed in the use of what are now standard controls, but it is also relevant to your workflow. Take an FTP program, where you create your web site locally, and then upload it to the server:
The usual workflow would be to have a list of all the files in the user's folder, have the user select the ones they want to upload and then push a button to trigger the upload. That's a good design, right?
Look at your workflow. Look at the typical use case. The user has files on disk that are a 1:1 representation of the site the way it should be on the server. Our FTP program knows the folder, it knows the remote directory on the FTP server. The user has changed a few files, and both the local hard disk and the server track change dates. The computer already knows which files the user will want to upload!
So, instead of just being a nice graphical veneer on top of what is essentially the networked version of cp, why not optimize the workflow? If the user does not select any files, why not offer them a list of changed files and ask them: "These 4 files have changed, did you perhaps want to upload them?"
Now, we can't always assume the user will always want to upload all of these files, so you need to ask. But in that panel that asks, you can let the user remove the files to not upload yet. And always keep in mind that we're dealing with heuristics here. Some people have one folder containing lots of files for different servers. You don't want to annoy them by always selecting 50 files for 25 other servers, because she only selected the two for the current server. Not every upload is a full-blown sync.
Unless it looks like something very stupid to do, if the user expressly states an intention, just do that. It's bad to be a boring app that needs the boring old ten steps when you could do it in five, but it's worse to be the app that always gets in the user's way by trying to provide "helpful suggestions". Clippy the psychotic paperclip anyone ... ?
But if the user is vague (like clicking "upload" when nothing is selected), don't just say "Can't upload nothing". If you can, offer to do the most likely thing she was trying to do. And if you have such a feature, maybe it's a good idea to indicate that in your UI. E.g. mark all files in the list that have changed with a little green up-arrow, and change the name of the "Upload" button to "Upload Changed", or so. We may not be able to implement the DWIM-button, but we can inch closer and closer to it.
What workflows could you optimize in your (or your favorite) application? Where does your application know things that can be used to anticipate what the user wants?
PS - I had a particular app in mind when I wrote this article, but I didn't want to point fingers. So I thought long and hard to come up with a different example. Hence, this may seem like a petty, tiny detail, especially in light of the "sync" feature most FTP programs have, but play along. Try to come up with a better example. As long as this article has started you thinking about ways to anticipate user needs, my job is done. | <urn:uuid:f506b7a5-73ba-4cd8-8794-c10b26e4c684> | 2.734375 | 952 | Personal Blog | Software Dev. | 64.134033 | 95,542,310 |
why is fusion only possible with small nuclei
Why does the nuclear fusion reaction yield more energy than the nuclear fission reaction? Fission only produces more energy than it consumes in large nuclei (common examples are Uranium & Plutonium, which have around 240 nucleons (nucleon = proton or neutron)). Fusion only produces more energy than it consumes in small nuclei (in stars, Hydrogen & its isotopes fusing into Helium). The energy released when 4 Hydrogen nuclei (= protons) fuse (there are some decays involved as well) into a Helium nucleus is around 27 Million Electron Volts (MeV), or about 7 MeV per nucleon. For fission of U or P, energies released are around 200 MeV or so. The energy per event is greater (in these examples) in fission, but the energy per nucleon (fusion = about 7 MeV/nucleon, fission = about 1 Mev/nucleon) is much greater in fusion. Fission releases the energy of the electromagnetic force when positively charged parts of the nucleus fly away from one another.
Fusion releases the energy of the strong force (much stronger at short distances than the EM force) when the small pieces are captured and held into one nucleus. Answered by:
Bill Baird, Ph. D. , Postdoc, College of Charleston, SC Now lets look at fission. An example of fission is when a Uranium-235 atom is split by a neutron into a Barium-144 atom, a Krypton-89 atom and three neutrons. Now looking at the graph the binding energy per nucleon for Uranium is about 7. 6MeV and for Barium around 8. 3 giving an increase in binding energy during fission of about 0. 7MeV per nucleon, or a total of 164. 5MeV in total. In a fusion reaction firstly two hydrogens fuse to form a deuterium (an isotope of hydrogen with nucleon no 2), a positron and an electron neutrino. Then the deuterium fuses with another hydrogen to form Helium-3 and a photon of energy. Finally two Helium-3s fuse forming a Helium nucleus and two hydron nuclei.
Considering the mass of the four protons/hydrogen nuclei (4. 029106u) and the mass of the Helium produced (4. 002603u) we get a mass difference of 0. 026503u or 24. 69MeV. So it is easy to see that fusion reactions give out more energy per reaction. However, the energy per unit mass is more relevant. This is 0. 7MeV for fission and 6. 2MeV for fusion so it is obvious that fusion is the more effective nuclear reaction. However, you must remember that an enormous amount of energy is required in order for these reactions to occur at all - that is why fusion is not yet a practical source of energy. Answered by: Martin Archer, Physics Student, Imperial College, London, UK Nuclear fission is the splitting of large nuclei into smaller ones, while nuclear fusion is the joining of smaller nuclei to make larger ones. Nuclear fusion happens in stars and fusion bombs. Just like nuclear fission, nuclear fusion releases heat energy.
However, in nuclear fusion: two nuclei must join together (rather than uranium nuclei splitting, as in fission) extremely high temperatures are needed. Extremely high temperatures are difficult to achieve, and it is difficult to safely manage the extremely hot gases produced. However, the oceans could provide almost limitless amounts of the hydrogen isotopes needed for nuclear fusion, so scientists believe that it is worth trying to design and build a fusion power station. This is so expensive that several countries are working together on the project. The Sun and other stars use nuclear fusion to release energy. The sequence of nuclear fusion reactions in a star is complex but overall hydrogen nuclei join to form helium nuclei. Here is one nuclear fusion reaction that takes place: The table summarises the extreme conditions needed for fusion to happen.
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Physical properties of Group VII Elements Quiz Questions 43 PDF Download
Practice physical properties of group vii elements quiz online, online A level chemistry test 43 for online courses, distance learning. Free chemistry MCQs questions and answers to learn physical properties of group vii elements MCQs with answers. Practice MCQs to test knowledge on physical properties of group vii elements, ammonia and ammonium compounds, rate equations, rate of reaction, peptides and proteins worksheets.
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Physical properties of Group VII Elements Quiz
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Ammonia and Ammonium Compounds Quiz
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MIT researchers state that all flying objects must observe a theoretical speed limit in order to avoid a crash. Flying faster than this speed will result in a crash regardless how much information the flying object has on the environment. These researchers are observing how birds fly through cluttered environments to gain a better understanding of the theoretical speed limit of flight and have developed a differential equation and ergodic model for the statistical distribution of trees in the forest.
The northern goshawk is one of nature’s diehard thrill-seekers. The formidable raptor preys on birds and small mammals, speeding through tree canopies and underbrush to catch its quarry. With reflexes that rival a fighter pilot’s, the goshawk zips through a forest at high speeds, constantly adjusting its flight path to keep from colliding with trees and other obstacles.
While speed is a goshawk’s greatest asset, researchers at MIT say the bird must observe a theoretical speed limit if it wants to avoid a crash. The researchers found that, given a certain density of obstacles, there exists a speed below which a bird — and any other flying object — has a fair chance of flying collision-free. Any faster, and a bird or aircraft is sure to smack into something, no matter how much information it has about its environment. A paper detailing the results has been accepted to the IEEE Conference on Robotics and Automation.
These findings may not be news to the avian world, but Emilio Frazzoli, an associate professor of aeronautics and astronautics at MIT, says knowing how fast to fly can help engineers program unmanned aerial vehicles (UAVs) to fly at high speeds through cluttered environments such as forests and urban canyons.
Frazzoli is part of an interdisciplinary team that includes biologists at Harvard University, who are observing flying behaviors in goshawks and other birds, and roboticists at MIT, who are engineering birdlike UAVs. With Frazzoli’s mathematical contributions, the team hopes to build fast, agile UAVs that can move through cluttered environments — much like a goshawk streaking through the forest.
Most UAVs today fly at relatively slow speeds, particularly if navigating around obstacles. That’s mainly by design: Engineers program a drone to fly just fast enough to be able to stop within the field of view of its sensors.
“If I can only see up to five meters, I can only go up to a speed that allows me to stop within five meters,” Frazzoli says. “Which is not very fast.”
If the northern goshawk flew at speeds purely based on what it could immediately see, Frazzoli conjectures that the bird would not fly as fast. Instead, the goshawk likely gauges the density of trees, and speeds past obstacles, knowing intuitively that, given a certain forest density, it can always find an opening through the trees.
Frazzoli points out that a similar intuition exists in downhill skiing.
“When you go skiing off the path, you don’t ski in a way that you can always stop before the first tree you see,” Frazzoli says. “You ski and you see an opening, and then you trust that once you go there, you’ll be able to see another opening and keep going.”
Frazzoli says that in a way, robots may be programmed with this same speedy intuition. Given some general information about the density of obstacles in a given environment, a robot could conceivably determine the maximum speed below at it can safely fly.
Toward this end, Frazzoli and PhD student Sertac Karaman developed mathematical models of various forest densities, calculating the maximum speed possible in each obstacle-filled environment.
The researchers first drew up a differential equation to represent the position of a bird in a given location at a given speed. They then worked out what’s called an ergodic model representing a statistical distribution of trees in the forest — similar to those commonly used by ecologists to characterize the density of a forest. In an ergodic forest, while the size, shape and spacing of individual trees may vary, their distribution in any given area is the same as any other area. Such models are thought to be a fair representation of most forests in the world.
Frazzoli and Karaman adjusted the model to represent varying densities of trees, and calculated the probability that a bird would collide with a tree while flying at a certain speed. The team found that, for any given forest density, there exists a critical speed above which there is no “infinite collision-free trajectory.” In other words, the bird is sure to crash. Below this speed, a bird has a good chance of flying without incident.
“If I fly slower than that critical speed, then there is a fair possibility that I will actually be able to fly forever, always avoiding the trees,” Frazzoli says.
The team’s work establishes a theoretical speed limit for any given obstacle-filled environment. For UAVs, this means that no matter how good robots get at sensing and reacting to their environments, there will always be a maximum speed they will need to observe to ensure survival.
Steven LaValle, professor of computer science at the University of Illinois at Urbana-Champaign, says knowing where to cap a UAV’s speed can help engineers like himself design more agile robots.
“Rather than trying to optimize robot speed, we might be able to [design] the robot at 95 percent of that speed, and achieve must simpler strategies that are also much safer to execute,” says LaValle, who did not contribute to the research.
The researchers are now seeing if the theory bears out in nature. Frazzoli is collaborating with scientists at Harvard, who are observing how birds fly through cluttered environments — in particular, whether a bird will choose not to fly through an environment that is too dense. The team is comparing the birds’ behavior with what Frazzoli’s model can predict. So far, Frazzoli says preliminary results in pigeons are “very encouraging.”
In the coming months, Frazzoli also wants to see how close humans can come to such theoretical speed limits. He and his students are developing a first-person flying game to test how well people can navigate through a simulated forest at high speeds.
“What we want to do is have people play, and we’ll just collect statistics,” Frazzoli says. “And the question is, how close to the theoretical limit can we get?”
Source: Jennifer Chu, MIT News Office
Image: Christine Daniloff | <urn:uuid:7dd7ffb9-ef06-467f-9aa5-983b611ad891> | 3.65625 | 1,410 | News Article | Science & Tech. | 41.92023 | 95,542,325 |
Astronomy is often called the “gateway science” because of its abundance of beautiful pictures and suitability for Discovery Channel specials. Astronomers, therefore, have an especially heavy burden among scientists to advocate for the science behind the special effects. However, astronomy and astrophysics can seem terribly complex; how do we get people to come out and learn about space in a substantive way? Well, if you’re with Astronomy on Tap, it involves going to the bar a little more often.
Jul 12, 2018 | Astro and Ale: Astronomy on Tap
On June 11, 2008, the Gamma-ray Large Area Space Telescope (GLAST) lifted off aboard the last Delta II Heavy Launch Vehicle from Cape Canaveral, FL and reached low-Earth orbit shortly thereafter. In the 10 years and one name change since that that day, what is now the Fermi Gamma-ray Space Telescope has found hundreds of pulsars, watched gamma ray flashes in terrestrial lightning, studied our own sun as a gamma-ray source, helped identify giant bubbles billowing out from the core of the Milky Way, and discovered that the neutron star at the heart of the Crab Nebula isn’t as calm as scientists used to think. To name just a few. The discoveries haven’t stopped, either—August 17, 2017, nine years to the month after the start of science operations, Fermi saw the gamma-ray flash of two neutron stars colliding, 1.7 seconds after the gravitational waves generated by this event rolled through (LIGO). Along with discoveries, Fermi is making memories—some scientific, and some of a more personal nature. KIPAC members and some of their Fermi collaborators have had a big part in both, and came together to share memories about a decade (and more) of Fermi.
While neutrinos were hypothesized by Wolfgang Pauli back in 1930, they remain among the most mysterious particles within the Standard Model of particle physics. We now know that there are three types of neutrinos, and neutrino oscillation experiments have shown that there are at least two types which have mass. Current experiments have not yet been able to nail down the precise masses of the three neutrinos, but have placed upper bounds on sum of their masses. These upper bounds tell us that neutrinos have to be the lightest of all Standard Model particles, more than six orders of magnitude lighter than the electron!
The SuperCDMS SNOLAB project, a multi-institutional effort led by SLAC, is expanding the hunt for dark matter to particles with properties not accessible to any other experiment.
How machine learning can help researchers relate dark-matter-only and hydrodynamic simulations, and how this mapping can shed light on the small-scale challenges associated with cold dark matter.
Near the turn of the century, two seminal papers pointed out a striking discrepancy between the number of dark matter subhalos around Milky Way-like systems in dark-matter-only (DMO) simulations and the number of observed dwarf satellite galaxies around the Milky Way (MW). Historically, this discrepancy (shown graphically in the figure below) led to the notion of the "missing satellites problem" (MSP)—not the issue of where multiple Mars-bound satellites have disappeared to, but rather the idea that we observe significantly fewer dwarf satellite galaxies (by a factor of about 10!) in the Local Group than predicted by the standard cold dark matter (CDM) cosmological model.
Is it possible to learn how the jets from small black holes a few solar masses in size behave by studying the biggest, most extreme, most relativistically distorted jets from full-fledged quasars, the monstrous billion solar mass black holes at the centers of giant galaxies? Remarkably the answer is YES!
Supermassive black holes in the centers of giant elliptical galaxies can sometimes produce powerful relativistic outflows called jets. Blazars are a special class of these galaxies with the unique property of having their jets oriented within a small angle from our line of sight. (For more on blazar jets, see the KIPAC blog post, Where have all the magnetic fields disappeared to?). Because of that preferential alignment and the fact that jets move with speeds close to the speed of light, extreme aberration of light and time dilation effects take place, distorting the observed properties of the objects.
Often in the world of astronomy and astrophysics, unexpected observations lead to new ideas and understanding. However, there are occasionally some models that are built up more traditionally from theories to observational predictions. This is a story of one such model—that of the very first stars in the universe, called, somewhat counterintuitively, Population III (Pop III) stars. We haven’t seen Pop III stars yet because of how long ago they first formed—and then died.
In Part I of this 2-part series on what astronomers do while observing, we looked at what happens when we take wide-field data for the cosmological side of things, and here in Part 2 we will continue with discussing the other mode that most people think of when they imagine what astronomers do at a telescope: searching for specific interesting objects.
I recently returned from an observing run at a telescope in Chile, and I thought our readers might wonder what astronomers do when they’re observing. After all, it can’t all be sitting around romantically staring up at the stars, right? So here’s a detailed description of what I did when I was observing for those who have wondered what actual observing is like.
Nov 27, 2017 | Simulating the universe as the ultimate Big Data problem
In the early summer of 1945, physicist Bob Christy asked fellow physicist Richard Feynman to carry out a task as quickly as possible. The deadline was the Trinity nuclear test, the first nuclear bomb and the culmination of years of secret work by Manhattan Project scientists. The task was to predict the total energy that would be released by the Gadget device, the prototype implosion bomb designed at Los Alamos.
Nov 14, 2017 | A three-dimensional step towards sorting out the GRB zoo
A powerful tool for characterizing and classifying gamma-ray bursts (GRBs) has recently been presented by an international team of researchers led by KIPAC member Dr. Maria Dainotti (Marie Curie outgoing Fellow at INAF, Italy and Stanford University and assistant professor at Jagiellonian University, Poland).
Oct 15, 2017 | An event that blew away the astronomical world
On the morn of Thursday, August 17, 2017 the LIGO-Virgo Collaboration (LVC) gravitational wave detectors saw a binary neutron star (BNS) collision in gravitational waves—and kind of blew up the astronomical world who was in on it, that day.
Why do I say this, after the announcement of the discovery of gravitational waves from a binary black hole (BBH) coalescence already made such major "ripples" amongst those who pay attention to things astronomical, just 1 1/2 years ago? (Resulting in the Nobel Prize being awarded for this, on October 3, 2017). | <urn:uuid:8e4b0d38-a1db-40e1-9b3e-10e8dfb7d14a> | 3.296875 | 1,479 | Content Listing | Science & Tech. | 35.306609 | 95,542,345 |
For the first time in 70 years, the over-browsing of young aspen and willow trees has diminished as elk populations in northern Yellowstone declined and their fear of wolf predation increased. Trees and shrubs have begun recovering along some streams, providing improved habitat for beaver and fish. Birds and bears also have more food.
“Yellowstone increasingly looks like a different place,” said William Ripple, a professor in the Department of Forest Ecosystems and Society at Oregon State University, and lead author of the study.
“These are still the early stages of recovery, and some of this may still take decades,” Ripple said. “But trees and shrubs are starting to come back and beaver numbers are increasing. The signs are very encouraging.”
The findings of this report, based on a recent analysis done by OSU researchers and a review of many other studies as well, were just published in Biological Conservation, a professional journal. They outline an ecosystem renaissance that has taken place since wolves were restored to Yellowstone after being extirpated in the 1920s.
Along four streams studied in the Lamar River basin, 100 percent of the tallest young aspen sprouts were being browsed in 1998, compared to less than 20 percent last year. Heavy browsing by elk on this favorite food had caused new aspen tree recruitment to essentially grind to a halt in the mid-to-late 1900s, when wolves were absent, but new trees are now growing again in places.
Among the observations in this report:
Since their reintroduction in 1995-96, the wolf population generally increased until 2003, forcing changes in both elk numbers and behavior due to what researchers call the “ecology of fear.”The northern range elk populations decreased from more than 15,000 individuals in the early 1990s to about 6,000 last year, and remaining elk now have different patterns of movement, vigilance, and other traits.
By 2006, some aspen trees had grown tall enough they were no longer susceptible to browsing by elk, and cottonwood and willow were also beginning to return in places.
Improved willow growth is providing habitat that allows for a greater diversity and abundance of songbirds such as the common yellowthroat, warbling vireo and song sparrow.
The number of beaver colonies in the same area increased from one in 1996 to 12 in 2009, with positive impacts on fish habitat.
Increases in beaver populations have strong implications for riparian hydrology and biodiversity – Wyoming streams with beaver ponds have been found to have 75 times more abundant waterfowl than those without.
The coyote population decreased with the increase in wolf numbers, potentially allowing more small mammals that provide food for other avian and mammalian predators, such as red foxes, ravens and bald eagles.
Evidence of improved ecosystem health following the return of wolves is “becoming increasingly persuasive,” the scientists said in their report, though they also note that an increasing population of bison is continuing to impact young woody plants in the Lamar Valley.
“The wolves have made a major difference in Yellowstone,” said Robert Beschta, a professor emeritus of forestry at OSU and co-author on the study.
“Whether similar recovery of plant communities can be expected in other areas, especially on public lands outside national parks, is less clear,” Beschta said. “It may be necessary for wolves not only to be present but to have an ecologically effective density, and mechanisms to deal with human and wolf conflicts also need to be improved.”
But at least in America’s first national park, the return of this large predator is having an impact.
“Predation and predation risk associated with large predators appear to represent powerful ecological forces,” the researchers concluded in their report, “capable of affecting the interactions of numerous animals and plants, as well as the structure and function of ecosystems.”Note: YouTube video in Yellowstone:
The study this story is based on is available in ScholarsArchive@OSU: http://hdl.handle.net/1957/25603
William Ripple | EurekAlert!
Upcycling of PET Bottles: New Ideas for Resource Cycles in Germany
25.06.2018 | Fraunhofer-Institut für Betriebsfestigkeit und Systemzuverlässigkeit LBF
Dry landscapes can increase disease transmission
20.06.2018 | Forschungsverbund Berlin e.V.
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
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Sometimes I'm a little hesitant about posting photos when I'm uncertain of the identity of the species. At the same time, it's hard to resist when something is so beautiful! And maybe someday someone will be able to help with the identification.
This is another sculpin from the low intertidal zone. The entire fish is shown below:
I'm also including a close-up of the area surrounding the eye. You can click on the image for a larger version. It's fascinating to look at the details of the color patterns!
I was thinking about Cadet and Wini Hand this past weekend. (Cadet was the founding director of the Bodega Marine Laboratory.) And then something fun happened. We were in the field on Sunday morning (15 July 2018) when Eric noticed a small sea anemone that he didn't recognize:
The anemone was only ~7 mm across. It had lots of tentacles, and the tentacles were narrow and tapered to a point. We could also see that the tentacles were banded with white.
From the side you could see the translucent orange column:
We spent some time researching the identity of this little anemone and it turned out to be Metridium exile, a species that Cadet Hand described in 1955!
Here's a close-up of the oral disc and tentacles (below). Note this species often has 96 tentacles!
A few facts about Metridium exile:
- It's distributed from British Columbia to Carmel, California.
- It's usually found on the outer coast (in contrast to its more common relative, Metridium senile, that's found in bays).
- It's small — the largest specimens are ~12 mm in diameter.
- It reproduces asexually via longitudinal fission. (In the field, we saw a cluster of several small individuals that were presumably clone mates.)
We had a hard time finding photographs of Metridium exile, so here's another beautiful image that Eric took:
Thanks, Cadet, for noticing and describing this wonderful local sea anemone!
Okay, here's a partial answer to last night's mystery photo. I'm going to reveal the identity of this animal quickly, so if you want another chance to guess, here's the close-up image:
And now here's the entire animal:
This is an intertidal sculpin photographed in the low intertidal zone on 15 July 2018. (The fish is resting on a bed of sea squirts.) Sadly, I'm not sure which species of sculpin it is, so if you are familiar with it, please let me know. Thanks! | <urn:uuid:77243551-9771-47a4-839f-0dd4cb7f4efa> | 2.640625 | 555 | Personal Blog | Science & Tech. | 55.896266 | 95,542,373 |
Twin flames burning gaseous and solid fuel pellets exhibit different chemical processes on earth and in the near zero-gravity environment of space.
Tiny pellets of fuel may be safer for hazardous places on earth and burn more efficiently in weightless space and low-gravity environments
Researchers from the USC Viterbi School of Engineering say solid fuel particles may be safer for hazardous environments on earth and burn more efficiently in the microgravity of space than gaseous fuels, which are more combustible and difficult to transport.
In the Spring 2004 issue of NASA Space Research, Fokion Egolfopoulos and Charles Campbell, of the Viterbi School’s Department of Aerospace and Mechanical Engineering, report that they have made significant progress toward understanding the complex chemical processes that take place when tiny particles of solid fuels burn.
Diane Ainsworth | EurekAlert!
Computer model predicts how fracturing metallic glass releases energy at the atomic level
20.07.2018 | American Institute of Physics
What happens when we heat the atomic lattice of a magnet all of a sudden?
18.07.2018 | Forschungsverbund Berlin
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
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In the year, a total of three partial solar eclipses could have been seen, out of which the second solar eclipse or Surya Grahan will be seen on July 13. Here is when and where the solar eclipse on July 13 will be visible.
The month of July is turning out to be a treat for skywatchers around the world. While the world is waiting for the Blood Moon 2018 on July 27, which is going to be the longest lunar eclipse of the century, here comes the partial solar eclipse on July 13, during which, you will be able to see the Moon 'devouring' the Sun.
For the unknown, a solar eclipse, also known as Surya Grahan in India, happens when the disk of Earth’s moon seems to pass in front of the disk of the sun. While a total solar eclipse occurs when the disk of the moon seems to completely block the solar disk, a partial eclipse is said to happen when the moon just covers a part of the sun.
In the year 2018, only partial solar can be seen and while the first partial solar eclipse of the year occurred on February 15, the next partial solar eclipse will occur on July 13. It will be visible majorly over the ocean between Australia as well as Antarctica.
Interestingly, the solar eclipse on July 13 will be a rare incident as it will occur on Friday the 13th, which also happens to a date that is considered as a harbinger of bad luck by the conservative Christians. Moreover, the last time a solar eclipse was witnessed on Friday the 13th was in December 1974 and the next partial eclipse which will occur on Friday the 13th will be seen in September 2080.
The solar eclipse on July 13 or the Surya Grahan will briefly pass over the edges of Antarctica which lies south of Australia and sky-gazers from the southern coasts of Australia as well as New Zealand might be able to catch a brief view of the eclipse.
Although the Southern Ocean (also known as the Antarctic Ocean or the Austral Ocean and it comprises the southernmost waters of the World Ocean) will be getting the best view of the partial solar eclipse on July 13, Northern parts of India, China, Russia, Sweden, Norway, Eastern Europe the U.K and Finland will be able to see the next solar eclipse 2018 on August 11 when the moon will partially block the sun. | <urn:uuid:fe72d2ba-d44c-49b4-b142-1382623ac133> | 2.984375 | 488 | News Article | Science & Tech. | 52.369457 | 95,542,394 |
Scientists working at the U.S. Department of Energy's (DOE) SLAC National Accelerator Laboratory have created the shortest, purest X-ray laser pulses ever achieved, fulfilling a 45-year-old prediction and opening the door to a new range of scientific discovery. The researchers, reporting today in Nature, aimed SLAC's Linac Coherent Light Source (LCLS) at a capsule of neon gas, setting off an avalanche of X-ray emissions to create the world's first "atomic X-ray laser."
"X-rays give us a penetrating view into the world of atoms and molecules," said physicist Nina Rohringer, who led the research. A group leader at the Max Planck Society's Advanced Study Group in Hamburg, Germany, Rohringer collaborated with researchers from SLAC, DOE's Lawrence Livermore National Laboratory and Colorado State University.
"We envision researchers using this new type of laser for all sorts of interesting things, such as teasing out the details of chemical reactions or watching biological molecules at work," she added. "The shorter the pulses, the faster the changes we can capture. And the purer the light, the sharper the details we can see."
The new atomic X-ray laser fulfills a 1967 prediction that X-ray lasers could be made in the same manner as many visible-light lasers – by inducing electrons to fall from higher to lower energy levels within atoms, releasing a single color of light in the process. But until 2009, when LCLS turned on, no X-ray source was powerful enough to create this type of laser.
To make the atom laser, LCLS's powerful X-ray pulses – each a billion times brighter than any available before – knocked electrons out of the inner shells of many of the neon atoms in the capsule. When other electrons fell in to fill the holes, about one in 50 atoms responded by emitting a photon in the X-ray range, which has a very short wavelength. Those X-rays then stimulated neighboring neon atoms to emit more X-rays, creating a domino effect that amplified the laser light 200 million times.
Although LCLS and the neon capsule are both lasers, they create light in different ways and emit light with different attributes. The LCLS passes high-energy electrons through alternating magnetic fields to trigger production of X-rays; its X-ray pulses are brighter and much more powerful. The atomic laser's pulses are only one-eighth as long and their color is much more pure, qualities that will enable it to illuminate and distinguish details of ultrafast reactions that had been impossible to see before.
"This achievement opens the door for a new realm of X-ray capabilities," said John Bozek, LCLS instrument scientist. "Scientists will surely want new facilities to take advantage of this new type of laser."
For example, researchers envision using both LCLS and atomic laser pulses in a synchronized one-two punch: The first laser triggers a change in a sample under study, and the second records with atomic-scale precision any changes that occurred within a few quadrillionths of a second.In future experiments, Rohringer says she will try to create even shorter-pulsed, higher-energy atomic X-ray lasers using oxygen, nitrogen or sulfur gas.
This artist's conception at the top of page illustrates how the new atomic hard X-ray laser is created. A powerful X-ray laser pulse from SLAC National Accelerator Laboratory's Linac Coherent Light Source comes up from the lower-left corner (shown as green) and hits a neon atom (center).
This intense incoming light energizes an electron from an inner orbit (or shell) closest to the neon nucleus (center, brown), knocking it totally out of the atom (upper-left, foreground). In some cases, an outer electron will drop down into the vacated inner orbit (orange starburst near the nucleus) and release a short-wavelength, high-energy (i.e., "hard") X-ray photon of a specific wavelength (energy/color) (shown as yellow light heading out from the atom to the upper right along with the larger, green LCLS light).
X-rays made in this manner then stimulate other energized neon atoms to do the same, creating a chain-reaction avalanche of pure X-ray laser light amplified by a factor of 200 million. While the LCLS X-ray pulses are brighter and more powerful, the neon atomic hard X-ray laser pulses have one-eighth the duration and a much purer light color. This new laser will enable more precise investigations into ultrafast processes and chemical reactions than had been possible before, ultimately opening the door to new medicines, devices and materials.
Image Credit: Illustration by Gregory M. Stewart
Source: The Daily Galaxy via SLAC National Accelerator Laboratory | <urn:uuid:ac78e4d8-296e-40aa-a596-6c7df03cdbe6> | 3.921875 | 1,001 | News Article | Science & Tech. | 40.284862 | 95,542,412 |
Learn how to use statistics to understand the significance of the latest political polling results and to keep yourself from being duped by misleading information
Author and “Speedcuber” Ian Scheffler reveals some of the math behind how you could solve the Rubik’s cube puzzle.
Research shows that an emphasis on memorization, rote procedures and speed impairs learning and achievement
Computer scientists have come up with an algorithm that can fairly divide a cake among any number of people
A top secret science project
David J. Thouless, F. Duncan Haldane and J. Michael Kosterlitz split the 2016 Nobel Prize in Physics for theoretical discoveries of topological phase transitions and topological phases of matter.
The modified version of the sieve of Eratosthenes could accelerate computer calculations
It’s the last standard of measurement that is still based on a physical object—but it will soon be derived from a mathematical constant
What are half-lives? And what do they have to do with measuring the age of the solar system and predicting the effects of a morning cup of coffee? Keep on reading to find out!
A centering science activity
A rare appearance by enigmatic Shinichi Mochizuki brings faint optimism about his famously impenetrable work
Jim Papadopoulos has spent a lifetime pondering the maths of bikes in motion. Now his work has found fresh momentum
Creators factor in “origin-of-life” events and available building blocks
Ukrainian mathematician Maryna Viazovska recently figured out how spheres could be efficiently arranged in eight and 24 dimensions
The mathematician Ken Ono believes that the story of Srinivasa Ramanujan—mathematical savant and two-time college dropout—holds valuable lessons for how we find and reward hidden genius
Have you ever wondered how people figured out their latitude back in the days before the Internet? Did you know you can use the same math trick they used to pinpoint your latitude today? Keep on reading to find out how it works
In this special edition of 60-Second Science Video, two numbers compete. Which is larger? The number of possible positions in the ancient game of go or the number of atoms in the entire universe?
Caltech theoretical physicist Sean M. Carroll talks about his new book The Big Picture: On the Origins of Life, Meaning, and the Universe Itself. (Dutton, 2016)
Caltech theoretical physicist Sean M. Carroll talks about the necessary connections among the various ways we have of describing the universe.
Brain studies suggest new ways to improve reading, writing and arithmetic—and even social skills | <urn:uuid:e890fd4d-f5fd-4ad7-a88b-3b11d6d6f2a7> | 2.921875 | 547 | Content Listing | Science & Tech. | 32.082017 | 95,542,420 |
That is because sunlight has both magnetic and electric components, and the environment and how beneficial solar energy is because it does not contribute to problems like global warming. Most houses are not powered by a backup generator which generally run on diesel or gasoline so when the power able to supply the electricity company with energy for them to resell. Solar energy systems will effect your property value just like able to supply the electricity company with energy for them to resell. However, a recent breakthrough by a professor at the University of Michigan could one day lead to a whole that is being created and so you know that you are not doing damage to the environment. With growing concerns over depleting oil supplies and our impact benefit not only the person using the solar energy but the rest of the world as well.
The more energy you use from your solar energy system in the amount of solar energy harvested from sunlight. If you want to have your home run off of solar but this is not something that you have to worry about when you are using solar energy. The Fuel Is Free If you look outside right be able to provide you with enough energy to completely power your home! If your power goes out during the day, your solar system will nitrogen dioxide, mercury, and even radioactive material in the event of an accident at a nuclear power plant . Emergency Power Have you ever lost power in the it may be difficult and expensive to get power lines run to your home. | <urn:uuid:a9a90fc6-600a-473b-b2ee-17880eb1f615> | 2.90625 | 287 | Personal Blog | Science & Tech. | 36.002403 | 95,542,439 |
The Indian River Lagoon (IRL) is a large barrier island estuary on Florida’s East coast. Overall, the IRL system spans 260 km or approximately 40% of Florida’s east coast. The 5,700-km2 watershed includes parts of seven counties, and its original extent has been expanded considerably by canals that drain inland areas, including a major canal linking Lake Okeechobee to the system. The IRL has been declared impaired due to excess nutrient inputs and is within an ecological zone particularly susceptible to climate change effects. Along with being large and complex, the IRL system is one of the nation’s most biologically diverse, and is a major spawning and nursery ground for numerous species of fish and shellfish, and home to populations of dolphins and endangered Florida manatees. The IRL ecosystem has large tourism, commercial and recreational fishing, boating, and aquaculture interests with an annual economic value estimated at nearly $8B. Unfortunately, recurrent large scale harmful algal bloom (HAB) events have seriously threatened both the ecological and economic stability/value of the IRL. The biological-chemical-physical complexity of the system presents a significant challenge to understanding its ecology and dynamics. This presentation will review IRL HABs, their complexities and repercussions to the ecosystem and human health, as well as developing scientific monitoring strategies for an improved understanding of their dynamics.
James Sullivan, Malcolm N. McFarland, Nicole Stockley, and Dennis Hanisak, "Harmful algal bloom dynamics in Southeast Florida and the Indian River Lagoon (Conference Presentation)," Proc. SPIE 10631, Ocean Sensing and Monitoring X, 1063108 (Presented at SPIE Defense + Security: April 17, 2018; Published: 15 May 2018); https://doi.org/10.1117/12.2309654.5783264653001.
Conference Presentations are recordings of oral presentations given at SPIE conferences and published as part of the conference proceedings. They include the speaker's narration along with a video recording of the presentation slides and animations. Many conference presentations also include full-text papers. Search and browse our growing collection of more than 12,000 conference presentations, including many plenary and keynote presentations. | <urn:uuid:a43bc3a7-8fb7-4290-a714-95b8ee38e1c2> | 3.171875 | 469 | Knowledge Article | Science & Tech. | 29.586471 | 95,542,461 |
Step 1: Resource description (API reference tutorial)
"Resources" refers to the information returned by an API. Most APIs have various categories of information, or various resources, that can be returned. The resource description provides details about the information returned in each resource.
The resource description is brief (1-3 sentences) and usually starts with a verb. Resources usually have a number of endpoints to access the resource, and multiple methods for each endpoint. Thus, on the same page, you usually have a general resource described along with a number of endpoints for accessing the resource, also described.
- Example of a resource description
- Terminology for describing the resource
- Recognize the difference between reference docs versus user guides
- Resource description for the surfreport endpoint
- Next steps
Example of a resource description
Here’s an example of a resource description from the Mailchimp API’s Campaigns resource:
Typically, an API will have a number of endpoints grouped under the same resource. In this case, you describe both the general resource and the individual endpoints. For example, the Campaigns resource has various endpoints that are also described:
Here’s a resource description for the Membership resource in the Box API:
For the Membership resource (or “object,” as they call it), there are 7 different endpoints or methods you can call. The Box API describes the Membership resource and each of the endpoints that let you access the resource.
Sometimes the general resource isn’t described; instead, it just groups the endpoints. The bulk of the description appears in each endpoint. For example, in the Eventbrite API, here’s the Events resource:
Although the Events resource isn’t described here, descriptions are added for each of the Events endpoints. The Events resource contains all of these endpoints:
And so on.
When developers create APIs, they have a design question to consider: Use a lot of variants of endpoints (as with Eventbrite’s API), or provide lots of parameters to configure the same endpoint. Often there’s a balance between the two. The trend seems to be toward providing separate endpoints rather than supplying a host of potentially confusing parameters with the same endpoint.
As another example, here’s the Relationships resource in the Instagram API.
The Relationships resource isn’t described but rather acts as a container for relationship endpoints. Descriptions are added for each of the resources grouped within the Relationships resource:
For another example of an API with resources and endpoints, check out the Trello API.
The description of the resource is likely something you’ll re-use in different places — product overviews, tutorials, code samples, quick references, etc. As a result, put a lot of effort into crafting it. Consider storing the description in a re-usable snippet in your authoring tool so that you can list it without resorting to copy/paste methods in your quick start guide.
Terminology for describing the resource
The exact terminology for referring to resources varies. The “things” that you access using a URL can be referred to in a variety of ways, but “resource” is the most common term because you access them through a URL, or uniform resource locator. Other than “resources,” you might see terms such as API calls, endpoints, API methods, calls, objects, services, and requests. Some docs get around the situation by not calling them anything explicitly.
Despite the variety with terminology, in general an API has various “resources” that you access through “endpoints.” The endpoints give you access to the resource. (But terminology isn’t standard, so expect variety.)
Recognize the difference between reference docs versus user guides
Resource descriptions (as well as endpoint descriptions) are typically short, usually 1-3 sentences. What if you have a lot more detail to add? In these situations, keep in mind the difference between reference documentation and user guides/tutorials:
- Reference documentation: Concise, bare-bones information that developers can quickly reference.
- User guides/tutorials: More elaborate detail about how to use the API, including step-by-step instructions, code samples, concepts, and procedures. I go into much more detail about this content in Documenting non-reference sections.
Although the description in an API reference topic provides a 1-3 sentence summary of the information the resource contains, you might expand on this with much greater detail in the user guide. (You could link the reference description to the places in the guide where you provide more detail.)
Resource description for the surfreport endpoint
Let’s review the surf report wiki page (which contains the information about the resource) and try to describe the resource in 1-3 sentences. Here’s my approach:
Contains information about surfing conditions, including the surf height, water temperature, wind, and tide. Also provides an overall recommendation about whether to go surfing.
Now it’s time to list out the Endpoints and methods for the resource.
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Morpho-ecological studies on geophilic plants: Vegetative reproduction inIris vartani (Iridaceae)
Structure and behaviour of the underground organs ofIris vartani were investigated in connection with the vegetative reproduction of this species. Under favourable conditions, well developed mature plants give rise to two replacement bulbs and to several propagation bulblets each year. In spite of this considerable vegetative propagation, no crowding occurs at the natural habitat. Controlled experiments show that as soon as a small group is formed, each bulb produces only one replacement bulb and not two as before. Moreover, the bulblets do not sprout while they are attached to the respective mother bulbs, but rather die and disintegrate, remaining as empty peels. In contrast, detached bulblets, sown individually in separate pots, germinate readily. Consequently, the aggregates ofI. vartani do not increase to any great extent and thus ensure their survival “in situ” for many years.
Key wordsAngiosperms Iridaceae Iris vartani Bulb structure vegetative reproduction bulblet germination
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- Galil, J., 1958: Physiological studies on the development of contractile roots in geophytes. — Bull. Res. Counc. Israel6 D, 221–236.Google Scholar
- —, 1961: Kinetics of Geophytes (in Hebrew). — Tel Aviv: Hakibutz Hameuchad.Google Scholar
- —, 1962: Development cycle and ecology ofIris palaestina (Bak.)Boiss. — Bull. Res. Counc. Israel11 D, 17–24.Google Scholar
- —, 1965a: Vegetative dispersal ofAllium neapolitanum. — Amer. J. Bot.52, 282–286.Google Scholar
- Galil, J., 1965b: Vegetative dispersal ofAllium ampeloprasum L. I. Vegetative reproduction. — Israel J. Bot.14, 135–140.Google Scholar
- —, 1965c: Vegetative dispersal ofAllium ampeloprasum L. sprouting of bulblets. — Israel J. Bot.45, 184–191.Google Scholar
- —, 1968: Vegetative dispersal ofOxalis cernua. — Amer. J. Bot.55, 68–73.Google Scholar
- —, 1981: Kinetics of bulbous plants. — Endeavour5, 15–20.Google Scholar
- Rimbach, A., 1902: Physiological observations on the subterranean organs of CaliforneanLiliaceae. — Bot. Gaz.33, 401–408.Google Scholar
- Troll, W., 1937: Vergleichende Morphologie der höheren Pflanzen. — Berlin: Gebr. Borntraeger.Google Scholar | <urn:uuid:1b7cd8be-7ccb-4ec6-be4e-a20aa7a4fd13> | 2.65625 | 615 | Academic Writing | Science & Tech. | 38.319452 | 95,542,499 |
Diatreme feeding of uranium
Subtle evidence of several types suggests that diatreme feeding of mantle volatiles into receptive host formations at tectonically weak loci (centers) may be a more important factor in forming productive uranium districts than has been recognized. The known highest abundance of uranium and thorium in alkalic hypabyssal and volcanic rocks differentiated in the mantle, as well as the recognition that this alkalinity is the product of a previous enrichment in volatiles occasioned by that differentiation, illustrates the concentration of radioelements in the volatile fraction. These observations support the theoretical inference made in Chapter 4 that mantle degassing is a principal means of radioelement transfer to the crust. Another pertinent inference is the formation of a further differentiation product of concentrated volatiles and fluid without magma which should contain an even greater concentration of radioelements than the alkalic rocks or certain carbonatites. Such a gas could easily be the preferred diatreme drilling agent.
Juvenile gases are usually evidenced at the surface as fumaroles or solfataras, and these are known mostly in volcanic regions. Uranium has been noted in gases from such regions-by Stoiber and Rose (1968, 1972) and Rose et al (1 970) in the basaltic Central American volcanoes, and by Mittempergher (1970) in the alkalic volcanic material of Italy. Stoiber et al (1971) also recognized hydrocarbon compounds in volcanic gas; thus, UCI4 could form by reaction with hydrocarbon chlorides. The occurrence of uranium and thorium in volcanic regions, particularly in the alkalic volcanic rocks, is common. However, large uranium districts do not occur in the most prolific volcanic regions, and volcanic rocks are only subtly and questionably associated with the best uranium districts. Therefore, if uraniferous gas feeding is to be a significant transfer mechanism, gas feeding would have to be partly or largely independent of lava feeding. This implies the further differentiation beyond the uraniferous alkaline magmas. Some fumaroles are known in nonvolcanic areas—such as the CO2 geysers of the San Rafael swell in Utah, a uraniferous region—but distinction between juvenile and sedimentary origin is difficult. | <urn:uuid:7837f634-d81d-48a7-980d-2fb265acdc1b> | 3.203125 | 472 | Academic Writing | Science & Tech. | 11.022469 | 95,542,500 |
Launched in 2004 on NASA's Aura spacecraft, TES was the first instrument designed to monitor ozone in the lowest layers of the atmosphere directly from space.
The instrument was planned for a five-year mission but far outlasted that term. It was originally conceived to measure ozone in the troposphere. However, TES cast a wider net, capturing signatures of a broad array of other atmospheric gases as well as ozone.
That flexibility allowed the instrument to contribute to a wide range of studies, not only atmospheric chemistry and the impacts of climate change, but studies of the cycles of water, nitrogen and carbon.
Its high-resolution observations led to new measurements of atmospheric gases that have altered our understanding of the Earth system, said NASA.
"TES was a pioneer, collecting a whole new set of measurements with new techniques, which are now being used by a new generation of instruments," Kevin Bowman, the TES principal investigator of NASA's Jet Propulsion Laboratory (JPL) was quoted as saying in a news release.
A mechanical arm on TES began stalling intermittently in 2010, affecting the instrument's ability to collect data continuously. The TES operations team adapted by operating the instrument to maximize science operations over time, attempting to extend the data set as long as possible, according to NASA.
However, the stalling increased to the point that TES lost operations about half of last year. The data gaps hampered the use of TES data for research, leading to NASA's decision to decommission the instrument.
It will remain on the Aura satellite, receiving enough power to keep it from getting so cold that it might break and affect the two remaining functioning instruments.
New techniques developed for TES along with broad applications throughout the Earth System ensure that the mission's legacy will continue long after TES's final farewell, said NASA. | <urn:uuid:d419a9e3-dd46-4ca2-9cb5-afcc87de09fe> | 4 | 375 | Knowledge Article | Science & Tech. | 31.442308 | 95,542,508 |
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By: AFG Dixon
300 pages, Figs, tabs
Covering all aspects of aphid ecology, this new edition includes new chapters on redistribution in space, biological control, forecasting of pest aphid outbreaks and pollution and global warming.
Feeding behaviour and food quality; host specificity and speciation; size; resource tracking - mechanism - cyclical parthenogenesis; resources tracking - mechanism - polyphenism; resource tracking in space; population dynamics; community structure and species diversity.
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"A long time ago, back before the dinosaurs were even a twinkle in a primitive reptile's eye and before that reptile's ancestor was even a twinkle in a primitive amphibian's eye, before plants thought seeds were a neat idea and invertebrates were disquietingly large, terrestrial life found itself with a bit of a problem."
The more I learn about fungi, the more fascinated I am. Lots of amazingly specialized ones out there, from mycorrhizal fungi to ones that turn ants into zombie slaves, to mushrooms that capture and parasitize beetle and moth larvae. Plus, pretty much every tree and shrub in the woods is interconnected by a network of mycorrhiza that lets them share nutrients and water. The Woods-Wide Web, some call it.
Good writing, but I don't like the bias of the writer, who claimed that lack of atmospheric CO2 caused an ice age. A more sustainable theory is that solar variation, a centuries long reduction of about 0.03% (or less) of the sun's total average output, was the proximate (and perhaps sole) cause of that (and most other) ice ages.
The CO2 argument, claiming that CO2 is an effective and determinate factor in global temperatures, is the cornerstone of the Anthropogenic Global Warming hysteria. Fortunately for all of us, the AGW craze has resulted in some (generally ignored by media) real science that has determined that CO2 is terrible at retaining heat in the atmosphere.
The UN's Intergovernmental Panel on Climate Change, in their Fifth Assessment Report (October 2013) acknowledged that all previous climate models had failed because CO2 is not as effective a "warming gas" as thought. That was not part of the UN's press release, and the IPCC did create "new" models, with other gasses, to "prove" AGW was real.
The separate (published, thankfully) studies, that comprised the science of the IPCC report, went further and determined that CO2, in concentrations between 80ppm (0.0008%) and 2,000ppm (0.02%) total atmospheric concentration, would have little or NO impact on global mean temperatures. Notably, other studies indicate that CO2 concentrations of at least 180ppm are necessary to support healthy global flora (current CO2 is around 400ppm, estimates of historic values are a low of 50ppm in the very late carboniferous period to highs of 5,500ppm in at least three different periods.)
The point is, captured CO2 didn't cause an ice age. It is likely that the absence of CO2 in the atmosphere of the very late Carboniferous Period did cause a massive plant die off, and was the proximate cause of one of the first "modern" extinction events on earth. ("modern" defined as after terrestial fauna)
IMHO - political science has invaded and overwhelmed real science to an extreme, resulting in political shortcuts to science writing - just to get published.
Great special about fungi on Netflix. I had no idea how magnificent they are. Changed my view of biology. They took a different track and preform most of our internal functions externally. Had no idea that mushrooms were the largest living thing in the world. One specimen covers thousands of Acres out west. | <urn:uuid:352b6c65-9b63-4907-83a2-16776907d797> | 2.875 | 688 | Comment Section | Science & Tech. | 43.20806 | 95,542,526 |
In recognition of the importance of biological diversity in sustaining the Earth's population of six billion, the UN Convention on Biological Diversity (UNCBD) was signed by 150 government leaders at the Earth Summit in Rio de Janeiro, Brazil in 1992. As a result, world governments have agreed to significantly reduce the current rate of biodiversity loss by 2010. The Conference of Parties (COP) is the Convention's governing body and advances implementation of the Convention through the decisions it takes at periodic meetings.
The ninth meeting of the COP was held in Bonn, Germany from 19-30 May and was attended by almost 7000 participants from 191 countries. ESA hosted a side event at COP9, in which speakers from various UN agencies highlighted the overarching role that Earth observation (EO) satellites play in providing vital information to implement and assess the progress of several UN treaties related to biodiversity. The side event was chaired by Gerald Braun who is from the German Space Agency (DLR) and an ESA delegate.
Representatives from the Ramsar Convention on Wetlands, the UN Convention to Combat Desertification (UNCCD) and the UNESCO World Heritage Convention, which are all supported by ESA, expressed their satisfaction and confirmed the usefulness of EO data. Nick Davidson from the Ramsar Convention on Wetlands introduced the GlobWetland project as an example of how EO data can be used for wetland assessment, monitoring and management.
He said that, "Often made up of complex and inaccessible terrain, monitoring ecological changes in wetlands without the use of satellite data is very difficult. The project produces land-use cover and change detection maps for use by wetland managers and policymakers. ESA EO data has considerable power and potential in providing the intelligence behind making sound decisions on management and policy."
Also speaking at the event, UNESCO's Mario Hernandez outlined joint programmes undertaken by UNESCO and ESA, including mapping World Heritage sites such as in ESA's Diversity project and gorilla natural-habitat monitoring. The Diversity project, which kicked-off last year, aims to contribute to the monitoring efforts that will help the UNCBD determine whether progress is being made in reducing biodiversity loss and provide insight into which policy measures are proving most effective. For example, the Diversity project has demonstrated the use of EO data for monitoring selected headline indicators of biodiversity loss such as trends in the extent of global drylands.
Lúcio de Rosário from the Portuguese National Focal Point Assistant for the UN Convention to Combat Desertification (UNCCD also spoke at the event and presented DesertWatch, a joint UNCCD-ESA programme designed to assist parties with implementation.
The importance of land-cover mapping was very evident at the meeting and was included as being an important tool by many of the speakers. In particular, Martin Herold from Global Observation for Forest and Land Cover Dynamics expressed the potential for satellite observations for the post-2012 negotiations of the UN Framework Convention on Climate Change and for driving national observation progress for forests.
From an economic perspective, Jean-Louis Weber from the European Environment Agency (EEA) provided insight into a less obvious way in which EO data is helping measure how the loss of biodiversity is affecting our quality of life in terms of wealth. The current thinking is that when calculating a country's gross domestic product, a monetary value should be included to represent the costs to an ecosystem that have come about through providing various goods and services.
An extensive study on ecosystem accounts for Mediterranean wetlands is being carried out that relies on land-cover maps derived from EO data to assess economic costs to the environment. This study is part of The Economics of Ecosystems and Biodiversity report - a joint German Ministry for Environment and European Commission initiative.
ESA's Oliver Arino also spoke during the event outlining support for a number of multilateral environment agreements, including those governing biodiversity, desertification, climate change, wetland and marine projects. For instance, he explained how sea-surface temperature maps matched with hammerhead shark tagging experiments show how migration routes are linked to ocean conditions.
The wildlife migration service developed within the Diversity project relies on near real-time satellite-derived maps of oceanographic conditions such as sea-surface temperature, water quality and surface currents in the Tropical East Pacific Corridor. The different EO data products are derived using results from ESA's Medispiration and GlobColour projects.
The essence, discussions held at the UNCBD-COP9 highlighted how EO-derived data is proving invaluable in providing an insight into the change of land cover as well as changes in marine and fresh water environments. Since biological diversity is intrinsically linked to such changes, biodiversity loss can be assessed at local, regional and global scales through a broad-range of applications. As the world's population grows and biodiversity diminishes, it was also made clear that EO-data is becoming an increasingly important tool in attempts to achieve sustainable development.
Mariangela D'Acunto | alfa
Upcycling of PET Bottles: New Ideas for Resource Cycles in Germany
25.06.2018 | Fraunhofer-Institut für Betriebsfestigkeit und Systemzuverlässigkeit LBF
Dry landscapes can increase disease transmission
20.06.2018 | Forschungsverbund Berlin e.V.
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
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2. Two liquids are poured into two cups. Cup A contains a colorless, odorless liquid. Cup B contains a colorless liquid with a strong odor. An ice cube floats in Cup A but sinks in Cup B. When heated, the liquid in Cup B boils at a much lower temperature than the liquid in Cup A. What kind of properties are used to compare the two liquids?
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Mathematics is the study of patterns. While all patterns tend to conform to the stringent rules of logic, only a few of them foster creativity. It is absurd to me how a single, one-inch equation can momentarily possess your hand and lead you to draw the most exquisite of figures. It’s remarkable how these complex figures can be reduced to three symbols and two parallel lines. I use the term possess because, for this moment, we blindly do what the equations command, and trusting the prophecy, we begin to mark dots, which in the beginning seem unconnectable.
However, we continue to acquiesce. The tools clink and the obnoxious ruler refuses to be lifted until the impression on the paper is essentially a collection of infinite dots; black dots left by the pencil and white dots pecked by the compass. The infinite dots unlock themselves quickly and obediently align just as the logic requires them to. While the minimalist delights in a circle, the abstractionist delights in a polyhedron.
Then there are numerical patterns, a sequence of numbers that periodically repeat. Human beings are inherently pattern-seeking creatures. In fact, we are so adept at connecting the dots that these patterns aren’t exclusive to dots, but are also extended to contexts. The appearance of a pattern or figure with a vice or a virtue correlates the occurrence of the two. They have been the driving force behind cults in a myriad of societies.
There is an element of piousness that people have long associated with certain figures and groups, such as The Illuminati. On the other hand, scientists and mathematicians prefer to associate a form of intellectual mystery to such patterns. Consider the Wow! Signal, a pattern of alphabets received unexpectedly among numbers by Ohio’s Big Ear radio telescope, hinting at extraterrestrial activity.
However, there also exists a pattern of numbers that incites not merely mystery, but sanctity, for it emerges in places one would never expect. Consider this pattern — 13-3-2-21-1-1-8-5 — drawn by the murdered museum curator Jacques Saunière as a hint for Tom Hanks in The Da Vinci Code.
The hint was a small, jumbled portion of numbers from the Fibonacci sequence. The sanctity arises from how innocuous, yet influential, these numbers are. A new number in the pattern can be generated by simply adding the previous two numbers. Starting from 0 and 1 (Fibonacci originally listed them starting from 1 and 1, but modern mathematicians prefer 0 and 1), we get:
Fibonacci was known to be the most talented Western mathematician of the Middle Ages. Originally born as Leonardo Pisano, the name Fibonacci was coined by a French historian. The name, now quite popular in every household, is short for “Fillius Bonacci”, which translates to “son of Bonaccio”, where Bonaccio refers to his father.
Fibonacci was tremendously fascinated by Hindu-Arabic mathematics. Europeans at that time continued to use the extensive set of Roman numbers, while the Hindus and Arabs had been enjoying the virtues of the Hindu-Arabic number system — Base-10 numbers ranging from 0-9 — for generations. He decided to bring these ideas to Europe by publishing them in his highly revered work Liber Abaci.
The book became a legend. However, its popularity was eventually reduced to only two contributions: first, the number system, without which the advancements of modern mathematics would not have been possible; and second, a hypothetical, unrealistic problem about the breeding of rabbits. The Fibonacci numbers first featured as the solution to this problem.
The mysterious Fibonacci numbers
However, there seems to be an inconsistency in abstract math. Doing abstract math is like counting the triangles in The Louvre. Sure, it’s fun to do, but is it of any use? However, it is in our nature to investigate. The predisposition to patternize, whether mathematically or behaviorally, cannot be neglected. Regardless of its futility, our fascination with patterns is persuasive enough to seek them.
Consider the Pisano Periods derived from the Fibonacci sequence. A Pisano Period, named after Fibonacci himself, is a set of numbers that cyclically repeat themselves. The numbers are remainders obtained from the division of Fibonacci numbers and a positive real number.
One can divide the sequence with any number to obtain such a cyclic pattern. For instance, when the numbers are divided by 7, a period of 16 numbers emerge. Similarly, the period’s length is 20 when the divisor is 5. Even dividing by 1/3 results in a long tape of recurring, identical snippets. However, mathematicians haven’t discovered a general formula that predicts the length of one period when the sequence is divided by a particular number.
Another raging perplexity is the infinite right-angled triangles hidden in the sequence. Starting with 5, every second number in the sequence is the hypotenuse of a right-angled triangle whose longer side is the sum of all sides of the preceding triangle and the shorter side is the difference between the skipped number and the shorter side of the preceding triangle. A pictorial explanation will help these triangles be better understood.
The utility of abstract math has been the primary argument in the debate questioning whether math was invented or discovered. There are theories that illustrate the highest order of mathematical genius and rigor but are utterly isolated from the real world. For instance, Newton invented calculus particularly to determine the equation of the trajectory that Earth was following around the Sun. Of course, calculus turned out to be lucrative in a myriad of other domains too, but can we say the same thing about Riemann’s Hypothesis?
However, there are rare instances where highly esoteric abstract math becomes applicable. For instance, Riemann developed his absurd concepts of curved geometry in the 1850s, which seemed inapplicable until Einstein used them to rediscover the laws of gravity in his General Theory of Relativity. The unpredictability of these mathematical marriages still perturbs us.
This is the case with the mystical nature of Fibonacci numbers too. Despite being discovered in the Middle Ages, they have been discovered and rediscovered, to everyone’s bewilderment, in places that we never expected. Our fascination with Fibonacci numbers extends to such an extent that an entire magazine is dedicated to its peculiarities, called the Fibonacci Quarterly.
Consider Pascal’s triangle. When Pascal was consulted by a gambler about the odds of the outcomes of a die and the nature of stakes, he invented the theory of probability to solve these problems. Pascal’s triangle is a neat triangle formed by binomial coefficients. The triangle acts as a table that one refers to while expanding the binomial equation.
However, if you were to draw diagonals moving down the triangle and sum the numbers residing on each individual diagonal, then the series of numbers equated with each diagonal represent, as you might have guessed, the Fibonacci numbers. The theory of probability was founded 400 years after Liber Abaci was published.
Or, consider the Mandelbrot set, a mathematical function that can be limned by a beautiful diagram drawn in the complex plane. The diagram appears to be a heart-shaped leaf with tiny buds on its edges. These buds are suffused with incredibly thin thorns. The diagram represents a fractal, a structure whose every single part is made up of itself. Which means that if you were to keep zooming in on it, you’d find that the structure recurs in an infinite loop.
As we zoom into the buds on the edges, we see that the bud enlarges into the original leaf and three new buds emerge on its edges. If one were to keep zooming in, he would witness this procession go on and on forever. However, as we peek deeper and deeper, we observe that the number of thorns on every new bud increases. The increment in numbers mimics a certain pattern; it’s the Fibonacci sequence! Who could’ve possibly predicted this?
The sequence also turns up in economics and in tracing the pedigree of male bees. It is extensively used in computer science, where it is used to generate perceivably random numbers by algorithms called Pseudorandom Number Generators. I use perceivably because the generated numbers aren’t truly random; they always depend on a previous input.
It is also used in sorting algorithms in which dividing the area into proportions that are two consecutive Fibonacci numbers, and not two equal parts. This renders the hunting down of a location to the simplest mathematical operations — addition and subtraction. Whereas, binary sorting (dividing into two equal parts) requires the use of multiplication, division and bit shifting. The sequence is also used to derive various other important mathematical identities. However, its most important application is found in our gardens.
The Fibonacci Spiral
The Greeks always pondered whether there exists a factual description of beauty, an innate property or essence, as they called it, that would leave no room for subjectivity. For instance, a triangle can be defined as any three-sided body wherein the sum of all three angles formed between these sides must add to no more or less than 180 degrees. The growth of another side between two vertices, however small, sees that the body ceases to be a triangle. Could there be a similar exclusive criterion to judge the beauty of a daisy?
The Greeks did eventually discover this essence. According to them, the most beautiful way to divide a line into two parts is to divide them in a ratio such that the longer part divided by the shorter part is equal to the whole divided by the longer part. They called this the Golden Ratio, and its value is 1.618…
Consequently, they based their art and architecture on this ratio. An example is the architecture of The Parthenon, whose sides are in the Golden Ratio. Even Renaissance artists were in cahoots with each other about the use of this ratio. A plethora of their artwork relies on the ratio to amplify its aesthetic appeal.
What does this treasured ratio have to do with the Fibonacci numbers? Kepler once observed that “as 5 is to 8 so is 8 to 13, practically, and as 8 is to 13, so is 13 to 21 almost.” The ratio of two consecutive Fibonacci numbers is approximately equal to *incipient slow claps* the golden ratio! This links Fibonacci numbers to one of the most recognized spirals on the Internet.
The squares of Fibonacci numbers can be written like this:
Nothing mysterious? Let’s add a bunch of them together:
1+1+4 = 6
1+1+4+9 = 15
1+1+4+9+25 = 40
Look closer and you’ll notice that 6 is the product of 2 and 3, 15 a product of 3 and 5, and 40 a product of 5 and 8. A conjugal relationship between Fibonacci numbers and the golden ratio becomes conspicuous — the two numbers constituting these products are consecutive Fibonacci numbers! Now, let’s perform the above summation pictorially. Each number squared can be represented by a square whose side measures to be the same number of units that is being squared.
So, the square of one is represented by a square of side one unit. This square is then added to the next square in the sequence — another square of side one unit. Next, the 1×2 rectangle is added to a square of side two units, which is then further added to a square of side three units and so on. We realize that the products were actually the areas of these emerging rectangles.
Because the products were consecutive Fibonacci numbers, one can discern that the ratio of the two sides of any single rectangle is the golden ratio! As the number of sums approaches infinity, the ratio of sides of the incumbent growing rectangle approaches the ratio’s exact value. A curve emanating from the center and passing through every square’s corners gradually grows into a spiral – the golden spiral, steadily deviating at an angle called the golden angle.
The golden spiral can be found in a myriad of places in nature, from the shape of our galaxy to a nautilus shell. It governs the arrangement of pine cones and the fruitlets of a pineapple. My favorite is its occurence in the arrangement of seeds cluttered in the center of a sunflower. However, using the term “clutter” would be shamelessly overlooking the magnitude of rigor that nature spent while organizing these seeds.
The seeds aren’t aligned like the spokes of a wheel; they gradually digress outwards. The angle of digression is the golden angle. It seems that nature voluntarily opted for this ratio because dividing the circle by an irrational number caused no seed to have a neighbor at the same angle from the center. This resulted in highly efficient packing, leaving almost no room for negative space. The number of spirals, you ask? 55 in one direction, 89 in the other. Both Fibonacci numbers, of course! | <urn:uuid:7b46f799-c62f-47b5-b84b-d7d9daaba013> | 2.78125 | 2,748 | Nonfiction Writing | Science & Tech. | 41.774359 | 95,542,553 |
Scientist names two tiny new species often overlooked in animal kingdomMedia release
A Deakin University scientist has discovered two new species of millipedes, each smaller than a grain of rice but which play an important role in the breakdown and decomposition of plant litter.
Cuong Huynh, from Deakin's School of Life and Environmental Sciences, described the new species in a paper recently published in the Australian Journal of Zoology.
The pair belong to a group of minute 'pincushion' millipedes, so named because they are covered in body hairs that look like tiny pins sticking out from their bodies.
Mr Huynh said it was long thought that there was just one species of the Phryssonotus millipede found in South Australia and formally described in 1923.
"But in my recent study, specimens were collected from different regions and they didn’t all look the same; they had varying body lengths and the patterns formed by their body hairs also differed," he said.
"I found three typical patterns of body hairs among the specimens I collected: a trapezoid, T-shape, or dark banding. The length-to-width ratios of their body hairs also differed."
But Mr Huynh said looking different wasn't enough to confirm that there was actually more than a single species of these animals in Australia. He needed more evidence and that was where the animal's DNA came in.
Mr Huynh looked at a gene that's frequently used for separation of species called CO1 to confirm that there were indeed three different species of Phryssonotus.
He then had the honour of naming the two additional species, but the 'Huynh Millipede' was ruled out by scientific protocol. Instead the two new species were named for the geographic area they can be found in.
The trapezoid patterned species collected from the south east coast of Victoria was named P. australis, meaning 'southern', and the species with dark banding collected from Western Australia was named P. occidentalis, meaning 'western'.
Mr Huynh said millipedes' distinctive feature was that they had two pairs of legs on most body segments, but they ranged in both body shape and size.
"Common garden millipedes have an elongated body shape, or they can have a rounded body shape as seen in the pill millipedes," he said.
The world's longest millipede is the African giant millipede, with a body length of more than 30cm. But the millipedes Mr Huynh discovered sit at the other end of the spectrum, with a body size of less than 4mm.
"Their exoskeleton is soft and they don't have the chemical defences present in other groups of millipedes. Instead pincushion millipedes are covered with hair like structures called trichomes that are used for nest building and defence," he said.
"They commonly have a head, 10 or 11 body segments (tergites), a telson (at the opposite end of their body) and 13 or 17 pairs of legs."
Mr Huynh said pincushion millipedes could be found in leaf litter, under tree bark, in caves, as well as in bird and ant nests. Their geographic distribution ranges from the tropics to the Arctic Circle.
"They help recycle the litter on the forest floor so nutrients can be fed back to the ecosystem," he said.
"So even though they are very small, they provide a really great indicator the health of the forest they belong to."
Mr Huynh said just one or two scientists globally studied these tiny creatures, and there could be dozens of species still undescribed in Australia alone.
"Most species were described in the last century by French and Italians based on limited specimen samples, so our finding is certainly novel," he said.
"There is limited information out there on these species, and consequently they are often looked over.
"By describing these species I'm hoping to help progress scientific study, giving other scientists who might come across these animals access to some information to help identify them."
Developed nations like Australia can learn from China in reaching global sustainability goals, according to the first comprehensive study on the effectiveness of China's world-leading environmental investment.
Deakin University will collaborate with a group of French research institutions and the University of Tasmania on a new international cancer research laboratory, after a special agreement signed by French President Emmanuel Macron and Australian Prime Minister Malcolm Turnbull at Admiralty House today.
A Deakin waste management expert has praised measures adopted by Australia's major supermarkets to address the country's waste crisis, but said they needed to go further. | <urn:uuid:506141c3-f713-4ae9-ae09-e40251f941ef> | 3.859375 | 974 | News (Org.) | Science & Tech. | 41.17318 | 95,542,568 |
An international research team including scientists from Greifswald succeeded in performing the first determination of the mass of the atomic nuclei of the exotic cadmium isotopes 129Cd, 130Cd und 131Cd. These short-lived particles with half-lives of only fractions of seconds were delivered by the ion-separator ISOLDE at the European research center CERN http://home.cern/ and investigated by use of Penning traps https://en.wikipedia.org/wiki/Penning_trap and a multi-reflection time-of-flight mass spectrometer https://en.wikipedia.org/wiki/Time-of-flight_mass_spectrometry.
The results confirm the expected magic neutron number N=82 and are of significant relevance for simulation studies extending our understanding of the origin of the chemical elements in the region from tin to barium which are found with comparatively high abundances in our Solar System. The results of the measurements and accompanying calculations are reported by the international research journal Physical Review Letters http://journals.aps.org/prl/ in its latest issue (02. Dezember 2015).
Graduate students Dinko Atanasov and Frank Wienholtz on the highest platform of the three-story ISOLTRAP setup in the experimental hall of ISOLDE at CERN
Maxime Mougeot / The photograph can be downloaded and used free of charge in connection with this press release. The name of the photographer has to be mentioned.
We are made of stardust – only hydrogen and helium were around shortly after the big bang; all other elements were and are still produced in the stars. The nuclei of the lower mass elements up to about iron can grow in the center of stars. Above that element, things get more complicated as energy is no longer released in the build-up of heavier elements. On the contrary, energy is used up. Thus, only explosive, i.e., very energetic star processes, such as supernovae or the mergers of neutron stars with black holes, can supply the necessary energies. Under these conditions, further neutrons are attached to the atomic nuclei. In general, the resulting neutron-rich nuclei decay via the so-called beta decay, i.e. a reaction where the nuclei increase their atomic number by the emission of an electron: However, it is still unclear and a topic of intense research as to where and how exactly these processes take place. In this context, experimental data about the nuclei involved are of highest interest. However, these nuclei are often very short-lived and accompanied by large amounts of nuclei of similar masses – which poses big challenges for the experimentalists.
Recently, scientists of the ISOLTRAP collaboration http://isoltrap.web.cern.ch/isoltrap/ which includes researchers of CERNhttp://home.cern/ , of the Max-Planck-Instituts für Kernphysik in Heidelberg https://www.mpi-hd.mpg.de/mpi/start/ , of the Helmholtzzentrums für Schwerionenforschung in Darmstadt https://www.gsi.de/start/aktuelles.htm as well as from universities in Dresden https://tu-dresden.de/ , Greifswald http://www.uni-greifswald.de/ , Istanbul (Turkey) http://www.istanbul.edu.tr/ , Manchester (United Kongdom) http://www.manchester.ac.uk/ and Paris-Sud (France) http://www.u-psud.fr/ succeeded in con-tributing important experimental results for the simulation of possible nuclear-synthesis scenarios. This input data was then used by theoreticians of the Free University of Brussels http://www.vub.ac.be/en/ and the Max-Planck-Institute for Astrophysics at Garching http://www.mpa-garching.mpg.de/ for such simulations of the nuclear reactions.
Like with the electrons in the atomic shell, the protons and neutrons, i.e. the constituents of the atomic nucleus, are found in energetic shells. Whenever such a shell has just been filled up, the nucleus is particularly stable and the corresponding proton and neutron numbers are called magic numbers. An example of a magic neutron number is N=82. As cadmium nuclei are defined to have Z=48 protons, a special configuration of neutrons is found for this element at mass number A=Z+N=130. Due to their enhanced stability, nuclei with magic numbers are very often produced in the explosive stellar phases, which leads to a relatively high abundance, even during the continuous transmutation processes. Because of their enhanced presence, they are called waiting-point nuclei. After the stellar explosion, these waiting-point nuclei beta-decay into the region of the periodic table of elements mentioned above – with enhanced abundances at the mass numbers around A=130.
Up until the present studies, only the nuclear mass of 130Cd was known, and this only in-directly from nuclear reactions. The masses of the neighboring isotopes 129Cd and 131Cd had not been measured at all. Now, the ISOLTRAP collaboration succeeded in the first such measurements, made possible by a multi-refection time-of-flight mass spectrometer, a contribution from the University of Greifswald. It was operated in two different application modes, which had been introduced recently in other experiments (see the press releases “Laboratory Mass Measurement deepens Insight into Neutron Star“ https://idw-online.de/en/news516628 , “Ion ping pong reveals forces in atomic nuclei“ https://idw-online.de/en/news539611 and “Ion Pingpong confirms magic neutron number of exotic atomic nuclei“ https://idw-online.de/en/news631425 ).
The time-of-flight mass spectrometer was applied for the isotopes 129Cd and 130Cd, which not only live somewhat longer, but are also produced at rates of more than a thousand particles per second, to select the cadmium isotopes from the mixture of more abundant isobars produced at CERN, i.e. atomic nuclei with almost identical mass. Isobars have the same total number of nucleons A=Z+N, differ however, in the individual numbers of the Z protons and N neutrons. The multi-refection time-of-flight mass spectrometer of ISOLTRAP was able to fish the nuclei of interest, 129Cd and 130Cd, from the isobar mixture and thus prepare them for mass spectrometry in a Penning trap. The production rate of the isotope 131Cd, however, was an order of magnitude lower and therefore not sufficient for a Penning-trap experiment in the given measurement time. In this case, the mass measurement itself had to be performed by use of the multi-refection time-of-flight device. Although its relative mass uncertainty is “only” slightly better than one in a million, and thus not as accurate as the Penning trap, the measurement can be performed faster and with less particles.
This allowed the studies to go beyond the magic neutron number. This new achievement is of particular importance, as the energetic distance between the filled neutron shell and the following shell is only accessible with the 131Cd mass value, as 131Cd places a first neutron in this new shell. In other words, we now know the energy that is necessary to detach this last neutron from 131Cd and go back to the more stable 130Cd. The energetic shell distance of cadmium was found to be smaller than that of tin, which had already been known. This had been expected as tin also has a magic proton number (Z=50), whereas in the case of cadmium (Z=48) the proton shell is not yet filled up. The increased neutron-shell energy distance of tin is a result of the mutual strengthening of the N and Z shell effects – as recently found also for the element calcium at smaller magic proton and neutron numbers, again by the ISOLTRAP collaboration (see again the press release “Ion Pingpong confirms magic neutron number of exotic atomic nuclei” https://idw-online.de/en/news631425)
Financial support for this work came from the German Federal Ministry of Education and Research (BMBF, 05P12HGCI1, 05P12HGFNE, 05P15HGCIA, and 05P09ODCIA), the Nuclear Astrophysics Virtual Institute (NAVI) of the Helmholtz Association, the Helmholtz-CAS Joint Research Group (HCJRG-108), the Max-Planck Society, the European Union (7th framework through ENSAR, 262010), the French IN2P3, the Helmholtz Alliance Program (HA216/EMMI), the STFC (ST/L005743/1 and ST/L005816/1), the IMPRS-PTFS, the FRS-FNRS (Belgium), the Max-Planck/Princeton Center for Plasma Physics (MPPC), and the Robert-Bosch Foundation.
Precision Mass Measurements of 129–131Cd and Their Impact on Stellar Nucleosynthesis via the Rapid Neutron Capture Process, D. Atanasov, P. Ascher, K. Blaum, R.B. Cakirli, A. S. George, S. Goriely, F. Herfurth, H.-T. Janka,
O. Just, M. Kowalska, S. Kreim, D. Kisler, Yu. A. Litvinov, D. Lunney, V. Manea, D. Neidherr, M. Rosenbusch, L. Schweikhard, A. Welker, F. Wienholtz, R.N. Wolf, K. Zuber, Phys. Rev. Lett. 115, 232501 (2015)
DOI: 10.1103/PhysRevLett.115. 232501
Photo: Graduate students Dinko Atanasov (Max-Planck-Institut für Kernphysik, Heidelberg, on the right) and Frank Wienholtz (Uni Greifswald) on the highest platform of the three-story ISOLTRAP setup in the experimental hall of ISOLDE at CERN - Photo: Maxime Mougeot
The photograph can be downloaded and used free of charge in connection with this press release. The name of the photographer has to be mentioned. Download http://www.uni-greifswald.de/informieren/pressestelle/pressefotos/pressefotos-20...
Related press releases
https://idw-online.de/de/news631423 Mit Ionen-Pingpong magische Neutronenzahl exotischer Atomkerne bestätigt
https://idw-online.de/en/news631425 Ion Pingpong confirms magic neutron number of exotic atomic nuclei
https://idw-online.de/de/news539615 Mit Ionen-Pingpong Kräfte in Atomkernen sichtbar gemacht
https://idw-online.de/en/news539611 Ion ping pong reveals forces in atomic nuclei
https://idw-online.de/de/news516617 Präzisionsmassenmessung im Labor gewährt Blick in die Kruste von Neutronensternen
https://idw-online.de/en/news516628 Laboratory Mass Measurement deepens Insight into Neutron Star Crusts
https://idw-online.de/de/news634638 Über zwei Millionen Euro für Erforschung exotischer Atomkerne am CERN
Dipl.-Phys. Frank Wienholtz and
Prof. Dr. Lutz Schweikhard (head of the Greifswald research group)
Institut für Physik der Universität Greifswald
Felix-Hausdorff-Straße 6, 17487 Greifswald
Telephone 49 (0)3834 86 4700
Dipl.-Phys. Dinko Atanasov and
Prof. Dr. Klaus Blaum (Spokesperson of the ISOLTRAP collaboration)
Max-Planck-Institute für Kernphysik
Saupfercheckweg 1, 69117 Heidelberg
Telephone +49 (0)6221 516850
Jan Meßerschmidt | idw - Informationsdienst Wissenschaft
What happens when we heat the atomic lattice of a magnet all of a sudden?
18.07.2018 | Forschungsverbund Berlin
Subaru Telescope helps pinpoint origin of ultra-high energy neutrino
16.07.2018 | National Institutes of Natural Sciences
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
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This is a good article. Follow the link for more information. This advanced perl programming pdf download is about the programming language. Since then, it has undergone many changes and revisions.
Perl 5 in 2000, eventually evolved into a separate language. Both languages continue to be developed independently by different development teams and liberally borrow ideas from one another. The language expanded rapidly over the next few years. Perl 2, released in 1988, featured a better regular expression engine. At the same time, the Perl version number was bumped to 4, not to mark a major change in the language but to identify the version that was well documented by the book.
At that point, Wall abandoned Perl 4 to begin work on Perl 5. Initial design of Perl 5 continued into 1994. May 1994 to coordinate work on porting Perl 5 to different platforms. It remains the primary forum for development, maintenance, and porting of Perl 5. 000 was released on October 17, 1994.
Importantly, modules provided a mechanism for extending the language without modifying the interpreter. This allowed the core interpreter to stabilize, even as it enabled ordinary Perl programmers to add new language features. Perl 5 has been in active development since then. 001 was released on March 13, 1995. 002 was released on February 29, 1996 with the new prototypes feature.
003 was released June 25, 1996, as a security release. One of the most important events in Perl 5 history took place outside of the language proper and was a consequence of its module support. May 2017, it carries over 185,178 modules in 35,190 distributions, written by more than 13,071 authors, and is mirrored worldwide at more than 245 locations. 005 was released on July 22, 1998. 6 was released on March 22, 2000. 2 GiB, and the “our” keyword. 005_63, the next version became 5.
640, with plans for development versions to have odd numbers and stable versions to have even numbers. In 2000, Wall put forth a call for suggestions for a new version of Perl from the community. They were presented as a digest of the RFCs, rather than a formal document. At this point, Perl 6 existed only as a description of a language. 8 was first released on July 18, 2002, and had nearly yearly updates since then. O implementation, added a new thread implementation, improved numeric accuracy, and added several new modules.
As of 2013 this version still remains the most popular version of Perl and is used by Red Hat 5, Suse 10, Solaris 10, HP-UX 11. Apocalypses, but which became the specification for the Perl 6 language. This was the first concerted effort towards making Perl 6 a reality. This effort stalled in 2006. On December 18, 2007, the 20th anniversary of Perl 1. A major change in the development process of Perl 5 occurred with Perl 5. | <urn:uuid:111373c2-476b-4bc7-baa2-25c897f98806> | 3.046875 | 595 | Knowledge Article | Software Dev. | 61.485756 | 95,542,575 |
Biohabitats’ Leaf Litter
Vol. 6 Number 1
From retail to routing to restaurants, Geographic Information Systems (GIS) are impacting almost every industry. But what about ecological restoration, conservation planning and regenerative design?
While some practitioners shy away from GIS, intimidated by what they perceive as cumbersome and complex technology, others see it as a gift from the techno gods — a vehicle that can bring information from numerous sources and provide an otherwise unattainably holistic understanding of a site.
How are GIS science, technology and tools affecting the fields of ecological restoration, conservation planning and regenerative design? Can GIS facilitate interdisciplinary approaches and lead to new solutions? Can it allow us to do and depict things we never thought possible? Or does it just further complicate everything? Join us as we explore these questions and more.
For starters, we’ll talk with Patrick J. Crist, a man who spent most of his professional career applying GIS technology and tools toward the protection and conservation of natural resources. In his current role as Director of Conservation Planning and Ecosystem Management for NatureServe, he has a lot of wisdom – and resources – to share.
What do your peers have to say about GIS and its application to our work? Find out by reading the results of our reader survey.
In her article When Bad Data Happens To Good Models, Biohabitats’ own GIS guru, Christine Mielnicki reminds us of four fundamental principles we should keep in mind when using GIS.
In addition to its many applications to conservation planning, ecological restoration and regenerative design, GIS can be downright entertaining. You need not be a geek to enjoy some of the fun things we found.
Check out the links we’ve provided in the resources section of this issue. Whether you’re looking for data sources, new toolkits, educational resources, or general information, you’ll find something to help you better understand and use GIS.
Finally, catch up on the latest at Biohabitats and learn how we are applying GIS as we help towns and universities plan for growth and development while maximizing the value of their natural resources.
As always, we want to know what you think. Share your comments by contacting our editor.
Further ReadingSustainability vs. Resiliency: Designing for a Trajectory of Change
Aloha: An unforgettable trip to the bathroom
Why do you feel ecological restoration is so important?
Election 2016: Down, but not out…
More From This AuthorIntegrated Water Strategies: Thinking outside the pipe
Thoughts on Ocean Health
Repercussions of a repealed stormwater fee in Baltimore County
A non-scientist’s take on biomimicry
Thoughts on Biomimicry | <urn:uuid:1fe68047-1451-4adf-ad90-f2d34f8bb321> | 2.765625 | 585 | News (Org.) | Science & Tech. | 33.900232 | 95,542,582 |
A team of European astronomers has used ESO's Very Large Telescope Interferometer and its razor-sharp eyes to discover a reservoir of dust trapped in a disc that surrounds an elderly star. The discovery provides additional clues about the shaping of planetary nebulae.
In the last phases of their life, stars such as our Sun evolve from a red giant which would engulf the orbit of Mars to a white dwarf, an object that is barely larger than the Earth. The transition is accomplished by the shedding of a huge envelope of gas and dust that sparkles in many colours, producing a most spectacular object: a planetary nebula. The celestial chrysalis becomes a cosmic butterfly.
This metamorphosis, rapid in terms of the star's lifetime, is rather complex and poorly understood. In particular, astronomers want to understand how a spherical star can produce a great variety of planetary nebulae, some with very asymmetrical shapes.
A team of scientists therefore embarked upon the study of a star which is presently on its way to becoming a cosmic butterfly. The star, V390 Velorum, is 5000 times as bright as our Sun and is located 2,600 light-years away. It is also known to have a companion that accomplishes its ballet in 500 days.
Astronomers postulate that elderly stars with companions possess a reservoir of dust that is thought to play a lead role in the final chapters of their lives. The shape and structure of these reservoirs remain, however, largely unknown.
To scrutinise the object with great precision, the astronomers linked observations taken with ESO's powerful interferometric instruments, AMBER and MIDI, at the Very Large Telescope Interferometer. In particular, they combined, using AMBER, the near-infrared light of three of VLT's 8.2-m Unit Telescopes. "Only this triple combination of powerful telescopes allows us to pinpoint the position and the shape of the dusty reservoir on a milli-arcsecond scale," explains Pieter Deroo, lead-author of the paper that presents these results in the research journal Astronomy and Astrophysics.
These observations clearly demonstrate that the dust present around the star cannot be distributed in a spherical shell. "This shows that whatever mechanism is shaping asymmetric planetary nebulae is already present prior to the metamorphosis taking place," says Hans Van Winckel, member of the team.
The astronomers found indeed evidence for a disc extending from 9 Astronomical Units to several hundreds of AU. "This disc is found around a star that is in a very brief phase of its life - just a blink of an eye over the star's lifespan of billions of years - but this phase is very important," says Deroo. "It is in this period that a huge morphological change occurs, leading to the creation of a planetary nebula," he adds.
The very high spatial resolution measurements allowed the astronomers to decouple the unresolved contribution of the central star from the resolved disc emission. Even the very inner structure of the disc as well as its orientation and inclination could be determined. The observations probe the physical nature of the disc and reveal that the dust in the inner rim is extremely hot and puffed up. The disc is circumbinary as it surrounds both stars.
Dust processing (coagulation, crystallisation) is found to be very efficient in this circumbinary disc, despite the rather short evolutionary timescales involved. The disc around this evolved object is very similar to those around young stellar objects, in which planets are formed.
"The combination of MIDI and AMBER on ESO's VLTI is an extremely powerful and perhaps unique tool to study the geometry of the material around stars," concludes Van Winckel.
It looks like it is the season for disc 'hunting': the detection of a dusty disc in the notable Ant Nebula was also just announced (see ESO 42/07).
Henri Boffin | alfa
What happens when we heat the atomic lattice of a magnet all of a sudden?
18.07.2018 | Forschungsverbund Berlin
Subaru Telescope helps pinpoint origin of ultra-high energy neutrino
16.07.2018 | National Institutes of Natural Sciences
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
19.07.2018 | Earth Sciences
19.07.2018 | Power and Electrical Engineering
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Modern day concentrations of ground level ozone pollution are decreasing the growth of trees in the northern and temperate mid-latitudes, as shown in a paper publishing today in Global Change Biology. Tree growth, measured in biomass, is already 7% less than the late 1800s, and this is set to increase to a 17% reduction by the end of the century.
Ozone pollution is four times greater now than prior to the Industrial Revolution in the mid-1700s; if modern dependence on fossil fuels continues at the current pace, future ozone concentrations will be at least double current levels by the end of this century with the capacity to further decrease the growth of trees.
The study is the first statistical summary of individual experimental measurements of how ozone will damage the productivity of trees, including data from 263 peer-reviewed scientific publications.
Ozone is the third strongest greenhouse gas, directly contributing to global warming, and is the air pollutant considered to be the most damaging to plants. But more importantly, it has the potential to leave more carbon dioxide, ranked as the first strongest greenhouse gas, in the atmosphere by decreasing carbon assimilation in trees. Ozone pollution occurs when nitrogen oxides have a photochemical reaction with volatile organic compounds.
“This research quantifies the mean response of trees to ozone pollution measured in terms of total tree biomass, and all component parts such as leaf, root and shoot, lost due to ozone pollution,” said Dr. Victoria Wittig, lead author of the study. “Looking at how ozone pollution affects trees is important because of the indirect impact on carbon dioxide concentrations in the atmosphere which will further enhance global warming, in addition to ozone’s already potent direct impact.”
In addition to ozone pollution reducing the strength of trees to hold carbon in the northern temperate mid-latitudes by reducing tree growth, the research also indicates that broad-leaf trees, such as poplars, are more sensitive to ozone pollution than conifers, such as pines, and that root growth is suppressed more than aboveground growth.
“Beyond the consequences for global warming, the study also infers that in mixed forests conifers will be favored over broad-leaved trees, and that the decrease in root size will increase the vulnerability to storms,” said Wittig.
Lucy Collister | alfa
Upcycling of PET Bottles: New Ideas for Resource Cycles in Germany
25.06.2018 | Fraunhofer-Institut für Betriebsfestigkeit und Systemzuverlässigkeit LBF
Dry landscapes can increase disease transmission
20.06.2018 | Forschungsverbund Berlin e.V.
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
20.07.2018 | Power and Electrical Engineering
20.07.2018 | Information Technology
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Researchers hope the concept of "expansion entropy" will become a simple, go-to tool to identify (sometimes hidden) chaos in a wide range of model systems -- and could help distinguish which chaotic systems could be subject to some measure of control
Does the flap of a butterfly’s wings in Brazil set off a tornado in Texas? This intriguing question -- the title of a talk given by MIT meteorologist Edward Lorenz at a 1972 meeting -- has come to embody the popular conception of a chaotic system, one in which a small difference in initial conditions will cascade toward a vastly different outcome in the future.
Images courtesy of the Chaos Group at the University of Maryland.
Researchers from the University of Maryland have proposed a new definition of chaos that applies to a wide variety of chaotic systems, including attractors, illustrated in the top left corner by a picture of a Tinkerbell attractor, repellers, as illustrated by the top and bottom right side pictures of chaotic scattering, and forced systems, as illustrated by the lower left picture of the motions of a forced damped pendulum. The lower right picture shows the pattern of light created inside a pyramid of 4 reflecting balls, work that was done by D.Sweet, E.Ott, J.Yorke, D.Lathrop and B.Zeff at the University of Maryland.
Mathematically, extreme sensitivity to initial conditions can be represented by a quantity called a Lyapunov exponent, which is positive if two infinitesimally close starting points diverge exponentially as time progresses. Yet Lyapunov exponents as a definition of chaos have limitations -- they only test for chaos in particular solutions of a model, not in the model itself, and they can be positive, for example in simple scenarios of unlimited growth, even when the underlying model is considered too straightforward to be deemed chaotic.
Now researchers from the University of Maryland have come up with a new definition of chaos that applies more broadly than Lyapunov exponents and other previous definitions of chaos. The new definition fits on a few lines, can be easily approximated by numerical methods, and works for a wide variety of chaotic systems. The researchers present the definition in a paper in the 25th anniversary issue of the journal Chaos, from AIP Publishing.
Hunting Down Hidden Chaos
Edward Lorenz, the scientist whose work gave rise to the term "the butterfly effect," first noticed chaotic characteristics in weather models. In 1963 he published a set of differential equations to describe atmospheric airflow and noted that tiny variations in initial conditions could drastically alter the solution to the equations over time, making it difficult to predict the weather in the long-term.
The chaotic solution to Lorenz's equations looks, fittingly, like two wings of a butterfly. The shape can be categorized, in math-speak, as an attractor, meaning it is easy to identify with Lyapunov exponents, said Brian Hunt, a mathematician at the University of Maryland and a member of the university's "Chaos Group." Yet not all chaotic behavior is quite so clear, he said.
As an example Hunt describes four Christmas balls stacked in a pyramid, a set-up analyzed by Hunt's colleagues David Sweet, Edward Ott, James Yorke, and others at the University of Maryland. Light hitting the shiny spheres reflects off in all directions. Most of the light travels simple paths, but occasional photons can become trapped in the interior of the pyramid, bouncing chaotically back and forth off the ornaments. The chaotic, one-off light paths are mathematically categorized as repellers, and can be difficult to find from model equations unless you know exactly where to look.
"Our definition of chaos identifies chaotic behavior even when it lurks in the dark corners of a model," said Hunt, who collaborated on the paper with Edward Ott, a professor at the University of Maryland and the author of the graduate textbook "Chaos in Dynamical Systems." The two researchers also broadened the definition by including systems that are forced, meaning that external factors continue to push or pull on the model as it evolves.
Researchers commonly encounter chaotic repellers, found in physical systems such as water flowing through a pipe, asteroid orbits, and chemical reactions, and forced systems, found for example in bird flocks, geophysics and the way the body controls the heartbeat.
To fit the generally recognized forms of chaos under one umbrella definition, Hunt and Ott turned to a concept called entropy. In a system that changes over time, entropy represents the rate at which disorder and uncertainty build up.
The idea that entropy could be a proxy for chaos is not new, but the standard definitions of entropy, such as metric entropy and topological entropy, are trapped in the mathematical equivalent of a straightjacket. The definitions are difficult to apply computationally, and have stringent prerequisites that disqualify many physical and biological systems of interest to scientists.
Hunt and Ott defined a new type of flexible entropy, called expansion entropy, which can be applied to more realistic models of the world. The definition can be approximated accurately by a computer and can accommodate systems, like regional weather models, that are forced by potentially chaotic inputs. The researchers define chaotic models as ones that exhibit positive expansion entropy.
The researchers hope expansion entropy will become a simple, go-to tool to identify chaos in a wide range of model systems. Pinpointing chaos in a system can be a first step to determining whether the system can ultimately be controlled.
For example, Hunt explains, two identical chaotic systems with different initial conditions may evolve completely differently, but if the systems are forced by external inputs they may start to synchronize. By applying the expansion entropy definition of chaos and characterizing whether the original systems respond chaotically to inputs, researchers can tell whether they can wrestle some control over the chaos through inputs to the system. Secure communications systems and pacemakers for the heart would be just two of the potential applications of this type of control, Hunt said.
The article, "Defining Chaos," is authored by Brian R. Hunt and Edward Ott. It will be published in the journal Chaos: An Interdisciplinary Journal of Nonlinear Science on July 28, 2015 (DOI: 10.1063/1.4922973). After that date, it can be accessed at: http://scitation.aip.org/content/aip/journal/chaos/25/9/10.1063/1.4922973
The authors of this paper are affiliated with the University of Maryland.
ABOUT THE JOURNAL
Chaos: An Interdisciplinary Journal of Nonlinear Science is devoted to increasing the understanding of nonlinear phenomena and describing the manifestations in a manner comprehensible to researchers from a broad spectrum of disciplines. See: http://chaos.aip.org/
Jason Socrates Bardi
American Institute of Physics
Jason Socrates Bardi | newswise
Computer model predicts how fracturing metallic glass releases energy at the atomic level
20.07.2018 | American Institute of Physics
What happens when we heat the atomic lattice of a magnet all of a sudden?
18.07.2018 | Forschungsverbund Berlin
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
20.07.2018 | Power and Electrical Engineering
20.07.2018 | Information Technology
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A Brief History of Set Theory
November 1, 2010
Bailey Hall 207
Refreshments will be served at 4:15 in Bailey Hall 204
Set theory was created by Georg Cantor in the 1870s, and quickly gave rise to an axiom system, known as ZFC, from which all of known mathematics can be derived. We will survey the remarkable achievements of the next 100 years, with emphasis on the work of Ernst Zermelo in the 1900s, Kurt Gödel in the 1930s, and Paul Cohen in the 1960s.
|Union College Math Department Home Page|
Comments to: email@example.com
Created automatically on: Mon Jul 23 03:50:17 EDT 2018 | <urn:uuid:f0d4a3c7-df20-4822-8795-3ba5aa0958a2> | 3.46875 | 145 | News (Org.) | Science & Tech. | 58.278333 | 95,542,629 |
Kotlin Programming Language Beginner to Advanced Level
Author: supnatural on 16-05-2018, 07:33, Views: 10
Kotlin Programming Language: Beginner to Advanced Level
MP4 | Video: h264, 1280x720 | Audio: AAC, 44.1 KHz, 2 Ch | Duration: 8h 26m | 4.62 GB
Genre: eLearning | Language: English | Last updated 5/2018 | $199.99
Complete Kotlin tutorial. Become a professional Kotlin developer for JVM, Android, Browser, and Native.
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Learn kotlin from scratch
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Want to become an android app developer or develop your own applications using Kotlin? Then, this course is for you. Moreover, you are several steps ahead if you already know Java. After completion of this course you will be ready to build applications for android.
Concept of OOPS in Kotlin, as other languages like Java, C++, PHP, C#, Scala, or Swift
You do not need programming skills, we will start from scratch, heading towards intermediate and then to advanced topics.
Microsoft Windows/Linux/Mac running OS.
JDK + IntelliJ IDEA. We will install JDK + IntelliJ with every steps explained and shown.
>> Develop skills in Kotlin from scratch, become a pro developer and explore the world of software development.
>> Expand your expertise as a JVM/Android/Browser/Native Developer and improve the quality of your code!
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>> No more null pointer Exceptions and Boilerplate code.
We will begin with very basics and step into intermediate and advanced level so that the beginners get a good grab over the language.
The course goes on as:
* Software Installation on windows and mac.
* Understanding how program flow works in Kotlin.
* Kotlin Tour: Basics and Syntax.
* Kotlin Data Types: Variables and Constants.
* Ranges and String Templates.
* Conditional Statements and Expressions.
* Kotlin Loops.
* Object Oriented Programming(OOP) in Kotlin.
* Interoperability and NULL Pointer Exception.
* Packages and Imports.
* Object Oriented Programming(OOP) Continues.
* Objects and Companion Objects
* Higher-Order Functions and Lambdas: Kotlin as a Functional Programming Language.
* Collections: Arrays, List, Set, and Map.
* Practical Usage of Lambdas in Collections.
* Enum, Nested, Inner, and Sealed Classes.
* Properties and Fields.
* Delegation: Zero Boilerplate Code.
Once you understand the concept of OOPs explained here for Kotlin, this basic paradigm being same for all other languages, you can master others too! (Java, PHP, C#, C++)
This course will be shaped as you want it to be. There will be more contents based on your reviews and feedback. Help this start reach heights with your valuable opinions.
Who is the target audience?
If you are a complete beginner in programming world.
If you want to switch from Java to Kotlin.
Anyone who wants to learn this awesome programming language. | <urn:uuid:c097e2ab-e2d3-4fc4-b6b6-8e169926e8b8> | 2.515625 | 712 | Product Page | Software Dev. | 54.115633 | 95,542,653 |
From Financial Times: Antarctica is changing fast, including sections of the massive ice sheet that covers it. This holds so much water that if it ever melted completely, global sea levels would rise by nearly 60m. The race to understand Antarctica has become more urgent. Also watch, the documentary ‘The Antarctica Challenge: A Global Warning.’
From Grist.org: Two Antarctic glaciers act as a plug holding back enough ice to pour 11 feet of sea-level rise into the world’s oceans —an amount that would submerge every coastal city on the planet. Finding out how fast these glaciers will collapse is one of the most important scientific questions in the world today.
What is permafrost? What happens when permafrost thaws? This animation, based on research by scientists at the Alfred Wegener Institute, answers these questions. Understanding this problem, and its connection to global climate change, is of vital importance at a time when the thawing Arctic tundra is creating massive craters and bringing back diseases like anthrax.
From The Guardian: In 2006, former U.S. Vice-President Al Gore triggered a worldwide debate about climate change with his Oscar-winning documentary, An Inconvenient Truth. Now, he’s back with a rousing follow-up for the age of climate change denial under Trump. Fellow climate champion and U.S. presidential candidate Bernie Sanders recently discussed the film with Gore.
It is not often that an article about climate change becomes the most hotly debated item on the internet. But David Wallace-Wells’ lengthy essay published in New York Magazine did exactly that. The full text of the essay –admittedly a worst-case scenario- which has kicked up a firestorm of debate online, along with selected responses.
The Washington Post reports: Scientists have announced that a much-anticipated break at the Larsen C ice shelf in Antarctica has occurred, unleashing a massive iceberg that is more than 2,200 square miles in area and weighs a trillion tons. Also, Nagraj Adve on why India must heed the cracking of this Haryana-sized Antarctic ice shelf.
From Common Dreams: Humanity has just three years left to drastically reduce greenhouse gas emissions before risking a climate-safe world. After roughly 1°C of global warming driven by human activity, ice sheets are melting, summer sea ice is disappearing in the Arctic and coral reefs dying from heat stress— entire ecosystems are starting to collapse.
From Forbes Magazine: With all of the knowledge of future mapping, do the world’s financial leaders know something we don’t? Consider how many of the richest families have been grabbing up massive amounts of farmland around the world. All property far away from coastal areas and in locations conducive to self-survival, farming and coal mining.
Dave Lindorff writes: The concern is that if the Arctic Ocean waters were to warm even slightly, as they will do as the ice cap vanishes in summer, at some point the clathrates which have currently trapped massive amounts of methane will suddenly dissolve releasing tens of thousands of gigatons of methane in huge bursts.
Sonam Wangchuk, the real life inspiration of the character “Phunsuk Wangdu” in Bollywood hit “3 idiots”, recently led an expedition to Sikkim’s Lhonak lake, which has been declared dangerous. Their objective was to install a siphoning system to drain the lake and prevent climate disaster, probably the first project of its kind in the world.
Chris Mooney reports: A recent report showed Greenland lost 1 trillion tons of ice mass between 2011 and 2014. A new NASA study shows that key areas where glaciers have been melting have actually experienced a reduction in gravitational pull, which has in turn reduced sea levels, confirming an age old prediction of climate science.
Sayantan Bera reports: Data from the ministry of water resources show that in end March, water levels in 91 major reservoirs in the country was at just 25% of capacity—30% lower than last year, and 25% less than the average storage in a decade. The situation is acute in the western parts of the country.
The world may be much closer to an abrupt and catastrophic climate shift than previously thought. That’s the warning from modern climate science pioneer James Hansen. His latest research suggests that polar ice sheet disintegration may cause sea level rise enough to drown coastal cities, not in a few centuries, but in a few decades.
The Centre has proposed modification of green laws to impose a fine up to Rs 20 crore on major environment violators, who would also have to pay a daily fine of Rs 1 crore if the damage continues. Another green law will prevent violators from taking shelter under a legal cover for non-payment of fines.
If any of us have fixed geographical notions of the nation-state, the rise and fall of sea levels everywhere ought to give us pause. Not just in warnings about the future, but also lessons from the past. Once, England and France were contiguous landmass… our borders are drawn not by us, but by the oceans. | <urn:uuid:fe8b0052-3d1c-4358-af37-47525f4955d8> | 2.953125 | 1,055 | Content Listing | Science & Tech. | 44.798185 | 95,542,658 |
Medians of isosceles triangle
The isosceles triangle has a base ABC |AB| = 16 cm and 10 cm long arm. What are the length of medians?
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January 14, 2016
Dear EarthTalk: You hear a lot about solar and wind energy, but what's new in efforts to generate electricity from ocean waves? -- M.B.
Wave power advocates cheered in September 2016 when Hawaii-based Naval researchers started feeding power from two experimental offshore wave energy devices into the grid on nearby Oahu, representing the first time the American public could access electricity derived from ocean waves. The trickle of energy from these experimental devices doesn't amount to anything substantial yet, but wave energy's potential is huge.
Analysts think we could derive at least a quarter of U.S. electricity needs by harnessing wave power around our coasts. Most other countries around the world have coastlines they could exploit for wave energy, as well, if engineers could create affordable technology to capture and transport the energy back to shore where it would be used to power local communities or get fed into existing larger power grids.
But just because we can tap ocean energy big time doesn't mean we necessarily will, given the high costs of getting started, technical issues with maintaining offshore equipment, and the challenges of scaling up for mass consumption. The world's first experimental wave farm, the Aguçadoura Wave Park off the coast of Portugal, went online in September 2008 with three wave energy converter machines, but ceased operations only two months later when bearings on the equipment gave way, underscoring the technical challenges of running complicated heavy machinery in unstable marine environments.
While such technical problems may be frustrating, financial concerns loom larger over wave energy's future. Two of the biggest wave energy endeavors in the world, Pelamis and Aquamarine, both based out of wave-battered Scotland, went belly up recently despite funding from the Scottish government and plans to build out the biggest wave energy farms in the world based on the success of earlier prototypes.
Aquamarine's CEO John Malcolm chalked up his company's demise to "the considerable financial, regulatory and technical challenges faced by the ocean energy sector as a whole." Meanwhile, cheap natural gas and the surge in solar and wind power options have kept ocean energy on the back burner.
But wave power is far from dead in the water. Besides the experimental wave farm off Oahu, two larger projects are being built off the coast of the United Kingdom, while three additional projects are underway around Australia. Funding for these projects has come from not only the host governments but also the private sector. American defense contractor Lockheed Martin, for one, is a big player in deployment of wave power technologies and is a driving force behind the 19 megawatt, grid-connected wave power station currently in the works near Victoria, Australia.
Here in the U.S., wave energy advocates say the federal government has done too little to encourage research and development in this promising niche of the energy sector. Subsidies and tax incentives helped solar and wind power grow from pipe dreams in the 1980s to significant players in the global energy mix of today. Wave power advocates would like to see similar incentives employed to boost the development of ocean-based renewable energy sources, but for that to happen the American public will need to speak up to get Congress to act.
EarthTalk® is produced by Roddy Scheer & Doug Moss and is a registered trademark of the nonprofit Earth Action Network. To donate, visit www.earthtalk.org. Send questions to: email@example.com. | <urn:uuid:379b943b-c613-4096-8554-76e8f827648c> | 2.96875 | 699 | Nonfiction Writing | Science & Tech. | 36.092226 | 95,542,677 |
The findings, published online in the British Ecological Society's journal Functional Ecology, illustrate that because they live life on an energetic knife edge, these bats are very vulnerable to any changes in their environment that interrupt their fuel supply for even a short period.
Working with a captive breeding colony in Germany, Dr Christian Voigt of the Leibniz Institute for Zoo and Wildlife Research in Berlin and Professor John Speakman of the University of Aberdeen fed long-tongued bats (Glossophaga soricina) sugar labelled with non-radioactive carbon-13 and then measured the amount of carbon-13 in the bats’ exhaled breath.
“We found that nectar-feeding bats made use of the sugar they were drinking for their metabolism within minutes after drinking it, and after less than half an hour they were fuelling 100% their metabolism from this source. For comparison, the highest rates reported in humans are for athletes who can fuel up to 30% of their metabolism directly from power drinks,” they say.
The reason these bats live on such an energetic knife edge is down to the food source they live on and the way they get around. They feed on floral nectars that contain simple sugars such as sucrose, glucose and fructose, but which are produced in only very small amounts by flowering plants. These sugars are rapidly absorbed and digested, and by metabolising them directly – rather than converting them to fat or glycogen and then using them up later – the bats get the maximum energy they can from the sugars. This is important because they hover like humming birds, and this kind of flight uses up a great deal of energy.
According to Voigt and Speakman: “All animals need energy to power their metabolism. Ultimately this energy comes from food, but usually only a small fraction of the energy being used comes directly from the food. Normally, most of the food is converted into storage and this is drawn on later to fuel metabolism. Small nectar-feeding bats have among the highest metabolic costs among mammals, and mostly eat a diet low in fat and protein but rich in sugars. Metabolising these sugars immediately they are consumed saves the costs of converting them to and from storage.”
In a second experiment, Voigt and Speakman measured how fast the bats used their meagre fat stores. “We found the bats depleted almost 60% of their fat stores each day, but even this phenomenal rate was still barely enough to sustain their metabolism when nectar was absent. This underlines how accurately these bats must balance their energy requirements every day and how vulnerable they are to ecological perturbations that might interrupt their fuel supply for even a short period,” they say.
Nectar-feeding bats live in south and central America and are among the smallest of all living mammals, weighing less than 10g. They feed at night and can ingest up to 150% of their body weight as nectar.
C C Voigt and J R Speakman (2007). Nectar-feeding bats fuel their high metabolism directly with exogenous carbohydrates. Functional Ecology, doi: 10.1111/j.1365-2435.2007.01321.x is published online on 6 August 2007.
NYSCF researchers develop novel bioengineering technique for personalized bone grafts
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Pollen taxi for bacteria
18.07.2018 | Technische Universität München
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
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18.07.2018 | Health and Medicine | <urn:uuid:0f389d7c-e651-497f-9975-c9d77f386e52> | 3.84375 | 1,293 | Knowledge Article | Science & Tech. | 45.369359 | 95,542,693 |
When you think of a dry climate in the United States, what state comes to mind? Did you say Arizona? Arizona certainly has a dry, desert climate. It is at low altitude and is warm and dry most of the year. But did you know dry climates can also be found in high, mountain areas? In the United States, Colorado is considered a semi-arid climate, even though it is cold and snowy in the winter. It also has the highest altitude of any state in the continental U.S.
An arid area is one that gets no more than 12 inches of rain each year. Arid areas are usually deserts. Few plants, animals and people can survive here. Semi-arid areas are ones that get enough rainfall to allow grasses to grow. Colorado, for example, has miles and miles of prairie-land. With irrigation water crops can grow here.
Fun Facts about Dry Climates
- The hottest temperatures in the world – up to 136 degrees Fahrenheit – are recorded in arid regions, such as the deserts of Africa.
- Some arid areas, such as Atacama Desert in Chile, South America, get less than ½ inch of rain annually.
- Australia’s outback is a semi-arid region.
- Sometimes semi-arid regions are caused by a mountain, which blocks warm, moist air. Denver, Colorado sits east of the Rocky Mountains. The mountains block moisture from reaching the city.
Dry Climates Vocabulary
- Altitude: how high an area sits from sea level
- Continental: on the continent; Hawaii and Alaska are not considered part of the continental U.S.
- Prairie-land: miles of grassy plains
- Irrigation: artificial watering from canals, reservoirs and sprinklers
- Moisture: water
Learn All about Dry Climates
This is the best video we found for kids to learn all about Dry Climates:
An educational video that discusses about the characteristics of places that have dry climates.
Dry Climates Q&A
Question: What other areas of the U.S. have dry climates?
Answer: Much of the West is arid or semi-arid. Northern Texas, New Mexico, Nevada, Southern Utah and even parts of Wyoming, Idaho and Montana could be considered semi-arid.
Cite This Page
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MLA Style Citation
Declan, Tobin. " Dry Climate Facts ." Easy Science for Kids, Jul 2018. Web. 20 Jul 2018. < http://easyscienceforkids.com/all-about-dry-climates/ >.
APA Style Citation
Tobin, Declan. (2018). Dry Climate Facts. Easy Science for Kids. Retrieved from http://easyscienceforkids.com/all-about-dry-climates/
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A hydrogen bond is a partially electrostatic attraction between a hydrogen (H) which is bound to a more electronegative atom such as nitrogen (N), oxygen (O), or fluorine (F), and another adjacent atom bearing a lone pair of electrons.
Hydrogen bonds can occur between molecules (intermolecular) or within different parts of a single molecule (intramolecular). Depending on the nature of the donor and acceptor atoms which constitute the bond, their geometry, and environment, the energy of a hydrogen bond can vary between 1 and 40 kcal/mol. This makes them somewhat stronger than a van der Waals interaction, and weaker than fully covalent or ionic bonds. This type of bond can occur in inorganic molecules such as water and in organic molecules like DNA and proteins.
Intermolecular hydrogen bonding is responsible for the high boiling point of water (100 °C) compared to the other group 16 hydrides that have much weaker hydrogen bonds. Intramolecular hydrogen bonding is partly responsible for the secondary and tertiary structures of proteins and nucleic acids. It also plays an important role in the structure of polymers, both synthetic and natural.
The hydrogen bond is an attractive interaction between a hydrogen atom from a molecule or a molecular fragment X–H in which X is more electronegative than H, and an atom or a group of atoms in the same or a different molecule, in which there is evidence of bond formation.
Definitions and general characteristicsEdit
A hydrogen atom attached to a relatively electronegative atom is the hydrogen bond donor. C-H bonds only participate in hydrogen bonding when the carbon atom is bound to electronegative substituents, as is the case in chloroform, CHCl3. In a hydrogen bond, the electronegative atom not covalently attached to the hydrogen is named proton acceptor, whereas the one covalently bound to the hydrogen is named the proton donor. In the donor molecule, the H center is protic. The donor is a Lewis base. Hydrogen bonds are represented as H···Y system, where the dots represent the hydrogen bond. Liquids that display hydrogen bonding (such as water) are called associated liquids.
The hydrogen bond is often described as an electrostatic dipole-dipole interaction. However, it also has some features of covalent bonding: it is directional and strong, produces interatomic distances shorter than the sum of the van der Waals radii, and usually involves a limited number of interaction partners, which can be interpreted as a type of valence. These covalent features are more substantial when acceptors bind hydrogens from more electronegative donors.
- F−H···:F (161.5 kJ/mol or 38.6 kcal/mol), illustrated uniquely by HF2−, bifluoride
- O−H···:N (29 kJ/mol or 6.9 kcal/mol), illustrated water-ammonia
- O−H···:O (21 kJ/mol or 5.0 kcal/mol), illustrated water-water, alcohol-alcohol
- N−H···:N (13 kJ/mol or 3.1 kcal/mol), illustrated by ammonia-ammonia
- N−H···:O (8 kJ/mol or 1.9 kcal/mol), illustrated water-amide
3 (18 kJ/mol or 4.3 kcal/mol)
The X−H distance is typically ≈110 pm, whereas the H···Y distance is ≈160 to 200 pm. The typical length of a hydrogen bond in water is 197 pm. The ideal bond angle depends on the nature of the hydrogen bond donor. The following hydrogen bond angles between a hydrofluoric acid donor and various acceptors have been determined experimentally:
|Acceptor···donor||VSEPR geometry||Angle (°)|
Strong hydrogen bonds are revealed by downfield shifts in the 1H NMR spectrum. For example, the acidic proton in the enol tautomer of acetylacetone appears at δ15.5, which is about 10 ppm downfield of a conventional alcohol.
In the IR spectrum, hydrogen bonding shifts the X-H stretching frequency to lower energy (i.e. the vibration frequency decreases). This shift reflects a weakening of the X-H bond. Certain hydrogen bonds - improper hydrogen bonds - show a blue shift of the X-H stretching frequency and a decrease in the bond length.
Hydrogen bonding is of continuing theoretical interest. According to a modern description O:H-O integrates both the intermolecular O:H lone pair ":" nonbond and the intramolecular H-O polar-covalent bond associated with O-O repulsive coupling.
Quantum chemical calculations of the relevant interresidue potential constants (compliance constants) revealed[how?] large differences between individual H bonds of the same type. For example, the central interresidue N−H···N hydrogen bond between guanine and cytosine is much stronger in comparison to the N−H···N bond between the adenine-thymine pair.
Theoretically, the bond strength of the hydrogen bonds can be assessed using NCI index, non-covalent interactions index, which allows a visualization of these non-covalent interactions, as its name indicases, using the electron density of the system.
Most generally, the hydrogen bond can be viewed as a metric-dependent electrostatic scalar field between two or more intermolecular bonds. This is slightly different from the intramolecular bound states of, for example, covalent or ionic bonds; however, hydrogen bonding is generally still a bound state phenomenon, since the interaction energy has a net negative sum. The initial theory of hydrogen bonding proposed by Linus Pauling suggested that the hydrogen bonds had a partial covalent nature. This interpretation remained controversial until NMR techniques demonstrated information transfer between hydrogen-bonded nuclei, a feat that would only be possible if the hydrogen bond contained some covalent character.
In the book The Nature of the Chemical Bond, Linus Pauling credits T. S. Moore and T. F. Winmill with the first mention of the hydrogen bond, in 1912. Moore and Winmill used the hydrogen bond to account for the fact that trimethylammonium hydroxide is a weaker base than tetramethylammonium hydroxide. The description of hydrogen bonding in its better-known setting, water, came some years later, in 1920, from Latimer and Rodebush. In that paper, Latimer and Rodebush cite work by a fellow scientist at their laboratory, Maurice Loyal Huggins, saying, "Mr. Huggins of this laboratory in some work as yet unpublished, has used the idea of a hydrogen kernel held between two atoms as a theory in regard to certain organic compounds."
Hydrogen bonds in small moleculesEdit
A ubiquitous example of a hydrogen bond is found between water molecules. In a discrete water molecule, there are two hydrogen atoms and one oxygen atom. Two molecules of water can form a hydrogen bond between them; the simplest case, when only two molecules are present, is called the water dimer and is often used as a model system. When more molecules are present, as is the case with liquid water, more bonds are possible because the oxygen of one water molecule has two lone pairs of electrons, each of which can form a hydrogen bond with a hydrogen on another water molecule. This can repeat such that every water molecule is H-bonded with up to four other molecules, as shown in the figure (two through its two lone pairs, and two through its two hydrogen atoms). Hydrogen bonding strongly affects the crystal structure of ice, helping to create an open hexagonal lattice. The density of ice is less than the density of water at the same temperature; thus, the solid phase of water floats on the liquid, unlike most other substances.
Liquid water's high boiling point is due to the high number of hydrogen bonds each molecule can form, relative to its low molecular mass. Owing to the difficulty of breaking these bonds, water has a very high boiling point, melting point, and viscosity compared to otherwise similar liquids not conjoined by hydrogen bonds. Water is unique because its oxygen atom has two lone pairs and two hydrogen atoms, meaning that the total number of bonds of a water molecule is up to four.
The number of hydrogen bonds formed by a molecule of liquid water fluctuates with time and temperature. From TIP4P liquid water simulations at 25 °C, it was estimated that each water molecule participates in an average of 3.59 hydrogen bonds. At 100 °C, this number decreases to 3.24 due to the increased molecular motion and decreased density, while at 0 °C, the average number of hydrogen bonds increases to 3.69. A more recent study found a much smaller number of hydrogen bonds: 2.357 at 25 °C. The differences may be due to the use of a different method for defining and counting the hydrogen bonds.
Where the bond strengths are more equivalent, one might instead find the atoms of two interacting water molecules partitioned into two polyatomic ions of opposite charge, specifically hydroxide (OH−) and hydronium (H3O+). (Hydronium ions are also known as "hydroxonium" ions.)
- H−O− H3O+
Indeed, in pure water under conditions of standard temperature and pressure, this latter formulation is applicable only rarely; on average about one in every 5.5 × 108 molecules gives up a proton to another water molecule, in accordance with the value of the dissociation constant for water under such conditions. It is a crucial part of the uniqueness of water.
Because water may form hydrogen bonds with solute proton donors and acceptors, it may competitively inhibit the formation of solute intermolecular or intramolecular hydrogen bonds. Consequently, hydrogen bonds between or within solute molecules dissolved in water are almost always unfavorable relative to hydrogen bonds between water and the donors and acceptors for hydrogen bonds on those solutes. Hydrogen bonds between water molecules have an average lifetime of 10−11 seconds, or 10 picoseconds.
Bifurcated and over-coordinated hydrogen bonds in waterEdit
A single hydrogen atom can participate in two hydrogen bonds, rather than one. This type of bonding is called "bifurcated" (split in two or "two-forked"). It can exist, for instance, in complex natural or synthetic organic molecules. It has been suggested that a bifurcated hydrogen atom is an essential step in water reorientation.
Acceptor-type hydrogen bonds (terminating on an oxygen's lone pairs) are more likely to form bifurcation (it is called overcoordinated oxygen, OCO) than are donor-type hydrogen bonds, beginning on the same oxygen's hydrogens.
For example, hydrogen fluoride—which has three lone pairs on the F atom but only one H atom—can form only two bonds; (ammonia has the opposite problem: three hydrogen atoms but only one lone pair).
Further manifestations of solvent hydrogen bondingEdit
- Increase in the melting point, boiling point, solubility, and viscosity of many compounds can be explained by the concept of hydrogen bonding.
- Negative azeotropy of mixtures of HF and water
- The fact that ice is less dense than liquid water is due to a crystal structure stabilized by hydrogen bonds.
- Dramatically higher boiling points of NH3, H2O, and HF compared to the heavier analogues PH3, H2S, and HCl, where hydrogen-bonding is absent.
- Viscosity of anhydrous phosphoric acid and of glycerol
- Dimer formation in carboxylic acids and hexamer formation in hydrogen fluoride, which occur even in the gas phase, resulting in gross deviations from the ideal gas law.
- Pentamer formation of water and alcohols in apolar solvents.
Hydrogen bonds in polymersEdit
Hydrogen bonding plays an important role in determining the three-dimensional structures and the properties adopted by many synthetic and natural proteins.
In these macromolecules, bonding between parts of the same macromolecule cause it to fold into a specific shape, which helps determine the molecule's physiological or biochemical role. For example, the double helical structure of DNA is due largely to hydrogen bonding between its base pairs (as well as pi stacking interactions), which link one complementary strand to the other and enable replication.
In the secondary structure of proteins, hydrogen bonds form between the backbone oxygens and amide hydrogens. When the spacing of the amino acid residues participating in a hydrogen bond occurs regularly between positions i and i + 4, an alpha helix is formed. When the spacing is less, between positions i and i + 3, then a 310 helix is formed. When two strands are joined by hydrogen bonds involving alternating residues on each participating strand, a beta sheet is formed. Hydrogen bonds also play a part in forming the tertiary structure of protein through interaction of R-groups. (See also protein folding).
The role of hydrogen bonds in protein folding has also been linked to osmolyte-induced protein stabilization. Protective osmolytes, such as trehalose and sorbitol, shift the protein folding equilibrium toward the folded state, in a concentration dependent manner. While the prevalent explanation for osmolyte action relies on excluded volume effects, that are entropic in nature, recent circular dichroism (CD) experiments have shown osmolyte to act through an enthalpic effect. The molecular mechanism for their role in protein stabilization is still not well established, though several mechanism have been proposed. Recently, computer molecular dynamics simulations suggested that osmolytes stabilize proteins by modifying the hydrogen bonds in the protein hydration layer.
Several studies have shown that hydrogen bonds play an important role for the stability between subunits in multimeric proteins. For example, a study of sorbitol dehydrogenase displayed an important hydrogen bonding network which stabilizes the tetrameric quaternary structure within the mammalian sorbitol dehydrogenase protein family.
A protein backbone hydrogen bond incompletely shielded from water attack is a dehydron. Dehydrons promote the removal of water through proteins or ligand binding. The exogenous dehydration enhances the electrostatic interaction between the amide and carbonyl groups by de-shielding their partial charges. Furthermore, the dehydration stabilizes the hydrogen bond by destabilizing the nonbonded state consisting of dehydrated isolated charges.
Wool, being a protein fibre, is held together by hydrogen bonds, causing wool to recoil when stretched. However, washing at high temperatures can permanently break the hydrogen bonds and a garment may permanently lose its shape.
Many polymers are strengthened by hydrogen bonds within and between the chains. Among the synthetic polymers, a well characterized example is nylon, where hydrogen bonds occur in the repeat unit and play a major role in crystallization of the material. The bonds occur between carbonyl and amine groups in the amide repeat unit. They effectively link adjacent chains, which help reinforce the material. The effect is great in aramid fibre, where hydrogen bonds stabilize the linear chains laterally. The chain axes are aligned along the fibre axis, making the fibres extremely stiff and strong.
The hydrogen-bond networks make both natural and synthetic polymers sensitive to humidity levels in the atmosphere because water molecules can diffuse into the surface and disrupt the network. Some polymers are more sensitive than others. Thus nylons are more sensitive than aramids, and nylon 6 more sensitive than nylon-11.
Symmetric hydrogen bondEdit
A symmetric hydrogen bond is a special type of hydrogen bond in which the proton is spaced exactly halfway between two identical atoms. The strength of the bond to each of those atoms is equal. It is an example of a three-center four-electron bond. This type of bond is much stronger than a "normal" hydrogen bond. The effective bond order is 0.5, so its strength is comparable to a covalent bond. It is seen in ice at high pressure, and also in the solid phase of many anhydrous acids such as hydrofluoric acid and formic acid at high pressure. It is also seen in the bifluoride ion [F−H−F]−.
Symmetric hydrogen bonds have been observed recently spectroscopically in formic acid at high pressure (>GPa). Each hydrogen atom forms a partial covalent bond with two atoms rather than one. Symmetric hydrogen bonds have been postulated in ice at high pressure (Ice X). Low-barrier hydrogen bonds form when the distance between two heteroatoms is very small.
The hydrogen bond can be compared with the closely related dihydrogen bond, which is also an intermolecular bonding interaction involving hydrogen atoms. These structures have been known for some time, and well characterized by crystallography; however, an understanding of their relationship to the conventional hydrogen bond, ionic bond, and covalent bond remains unclear. Generally, the hydrogen bond is characterized by a proton acceptor that is a lone pair of electrons in nonmetallic atoms (most notably in the nitrogen, and chalcogen groups). In some cases, these proton acceptors may be pi-bonds or metal complexes. In the dihydrogen bond, however, a metal hydride serves as a proton acceptor, thus forming a hydrogen-hydrogen interaction. Neutron diffraction has shown that the molecular geometry of these complexes is similar to hydrogen bonds, in that the bond length is very adaptable to the metal complex/hydrogen donor system.
Dynamics probed by spectroscopic meansEdit
The dynamics of hydrogen bond structures in water can be probed by the IR spectrum of OH stretching vibration. In the hydrogen bonding network in protic organic ionic plastic crystals (POIPCs), which are a type of phase change material exhibiting solid-solid phase transitions prior to melting, variable-temperature infrared spectroscopy can reveal the temperature dependence of hydrogen bonds and the dynamics of both the anions and the cations. The sudden weakening of hydrogen bonds during the solid-solid phase transition seems to be coupled with the onset of orientational or rotational disorder of the ions.
Application to drugsEdit
Hydrogen bonding is a key to the design of drugs. According to Lipinski's rule of five the majority of orally active drug tend to have between five and ten hydrogen bonds. These interactions exist between nitrogen–hydrogen and oxygen–hydrogen centers. As with many other rules of thumb, many exceptions exist.
Hydrogen bonding phenomenaEdit
- Occurrence of proton tunneling during DNA replication is believed to be responsible for cell mutations.
- High water solubility of many compounds such as ammonia is explained by hydrogen bonding with water molecules.
- Deliquescence of NaOH is caused in part by reaction of OH− with moisture to form hydrogen-bonded H
2 species. An analogous process happens between NaNH2 and NH3, and between NaF and HF.
- The presence of hydrogen bonds can cause an anomaly in the normal succession of states of matter for certain mixtures of chemical compounds as temperature increases or decreases. These compounds can be liquid until a certain temperature, then solid even as the temperature increases, and finally liquid again as the temperature rises over the "anomaly interval"
- Smart rubber utilizes hydrogen bonding as its sole means of bonding, so that it can "heal" when torn, because hydrogen bonding can occur on the fly between two surfaces of the same polymer.
- IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "hydrogen bond".
- Steiner, Thomas (2002). "The Hydrogen Bond in the Solid State". Angew. Chem. Int. Ed. 41: 48–76. doi:10.1002/1521-3773(20020104)41:1<48::AID-ANIE48>3.0.CO;2-U.
- John R. Sabin (1971). "Hydrogen bonds involving sulfur. I. Hydrogen sulfide dimer". J. Am. Chem. Soc. 93 (15): 3613–3620. doi:10.1021/ja00744a012.
- Arunan, Elangannan; Desiraju, Gautam R.; Klein, Roger A.; Sadlej, Joanna; Scheiner, Steve; Alkorta, Ibon; Clary, David C.; Crabtree, Robert H.; Dannenberg, Joseph J.; Hobza, Pavel; Kjaergaard, Henrik G.; Legon, Anthony C.; Mennucci, Benedetta; Nesbitt, David J. (2011). "Definition of the hydrogen bond". Pure Appl. Chem. 83 (8): 1637–1641. doi:10.1351/PAC-REC-10-01-02.
- Beijer, Felix H.; Kooijman, Huub; Spek, Anthony L.; Sijbesma, Rint P.; Meijer, E. W. (1998). "Self-Complementarity Achieved through Quadruple Hydrogen Bonding". Angew. Chem. Int. Ed. 37 (1–2): 75–78. doi:10.1002/(SICI)1521-3773(19980202)37:1/2<75::AID-ANIE75>3.0.CO;2-R.
- Campbell, Neil A.; Brad Williamson; Robin J. Heyden (2006). Biology: Exploring Life. Boston, Massachusetts: Pearson Prentice Hall. ISBN 0-13-250882-6. Archived from the original on 2014-11-02.
- Wiley, G.R.; Miller, S.I. (1972). "Thermodynamic parameters for hydrogen bonding of chloroform with Lewis bases in cyclohexane. Proton magnetic resonance study". Journal of the American Chemical Society. 94 (10): 3287. doi:10.1021/ja00765a001.
- Larson, J. W.; McMahon, T. B. (1984). "Gas-phase bihalide and pseudobihalide ions. An ion cyclotron resonance determination of hydrogen bond energies in XHY- species (X, Y = F, Cl, Br, CN)". Inorganic Chemistry. 23 (14): 2029–2033. doi:10.1021/ic00182a010.
- Emsley, J. (1980). "Very Strong Hydrogen Bonds". Chemical Society Reviews. 9 (1): 91–124. doi:10.1039/cs9800900091.
- Data obtained using molecular dynamics as detailed in the reference and should be compared to 7.9 kJ/mol for bulk water, obtained using the same calculation.Markovitch, Omer; Agmon, Noam (2007). "Structure and energetics of the hydronium hydration shells" (PDF). J. Phys. Chem. A. 111 (12): 2253–2256. Bibcode:2007JPCA..111.2253M. doi:10.1021/jp068960g. PMID 17388314. Archived (PDF) from the original on 2014-08-13.
- Legon, A. C.; Millen, D. J. (1987). "Angular geometries and other properties of hydrogen-bonded dimers: a simple electrostatic interpretation of the success of the electron-pair model". Chemical Society Reviews. 16: 467. doi:10.1039/CS9871600467.
- Friebolin, H., "Basic One- and Two- Dimensional NMR Spectroscopy, 4th ed.," VCH: Weinheim, 2008. ISBN 978-3-527-31233-7
- Hobza P, Havlas Z (2000). "Blue-Shifting Hydrogen Bonds". Chem. Rev. 100 (11): 4253–4264. doi:10.1021/cr990050q. PMID 11749346.
- C. Q. Sun; Yi Sun (2016). The Attribute of Water: Single Notion, Multiple Myths. ISBN 978-981-10-0178-9.
- Grunenberg, Jörg (2004). "Direct Assessment of Interresidue Forces in Watson−Crick Base Pairs Using Theoretical Compliance Constants". Journal of the American Chemical Society. 126 (50): 16310–1. doi:10.1021/ja046282a. PMID 15600318.
- Isaacs, E.D.; et al. (1999). "Covalency of the Hydrogen Bond in Ice: A Direct X-Ray Measurement". Physical Review Letters. 82 (3): 600–603. Bibcode:1999PhRvL..82..600I. doi:10.1103/PhysRevLett.82.600.
- Ghanty, Tapan K.; Staroverov, Viktor N.; Koren, Patrick R.; Davidson, Ernest R. (2000-02-01). "Is the Hydrogen Bond in Water Dimer and Ice Covalent?". Journal of the American Chemical Society. 122 (6): 1210–1214. doi:10.1021/ja9937019. ISSN 0002-7863.
- Cordier, F; Rogowski, M; Grzesiek, S; Bax, A (1999). "Observation of through-hydrogen-bond (2h)J(HC') in a perdeuterated protein". J Magn Reson. 140 (2): 510–2. Bibcode:1999JMagR.140..510C. doi:10.1006/jmre.1999.1899. PMID 10497060.
- Pauling, L. (1960). The nature of the chemical bond and the structure of molecules and crystals; an introduction to modern structural chemistry (3rd ed.). Ithaca (NY): Cornell University Press. p. 450. ISBN 0-8014-0333-2.
- Moore, T. S.; Winmill, T. F. (1912). "The state of amines in aqueous solution". J. Chem. Soc. 101: 1635. doi:10.1039/CT9120101635.
- Latimer, Wendell M.; Rodebush, Worth H. (1920). "Polarity and ionization from the standpoint of the Lewis theory of valence". Journal of the American Chemical Society. 42 (7): 1419–1433. doi:10.1021/ja01452a015.
- Jorgensen, W. L.; Madura, J. D. (1985). "Temperature and size dependence for Monte Carlo simulations of TIP4P water". Mol. Phys. 56 (6): 1381. Bibcode:1985MolPh..56.1381J. doi:10.1080/00268978500103111.
- Zielkiewicz, Jan (2005). "Structural properties of water: Comparison of the SPC, SPCE, TIP4P, and TIP5P models of water". J. Chem. Phys. 123 (10): 104501. Bibcode:2005JChPh.123j4501Z. doi:10.1063/1.2018637. PMID 16178604.
- Jencks, William; Jencks, William P. (1986). "Hydrogen Bonding between Solutes in Aqueous Solution". J. Am. Chem. Soc. 108 (14): 4196. doi:10.1021/ja00274a058.
- Dillon, P. F. (2012). Biophysics: A Physiological Approach. Cambridge University Press. p. 37. ISBN 978-1-139-50462-1.
- Baron, Michel; Giorgi-Renault, Sylviane; Renault, Jean; Mailliet, Patrick; Carré, Daniel; Etienne, Jean (1984). "Hétérocycles à fonction quinone. V. Réaction anormale de la butanedione avec la diamino-1,2 anthraquinone; structure cristalline de la naphto \2,3-f] quinoxalinedione-7,12 obtenue". Can. J. Chem. 62 (3): 526–530. doi:10.1139/v84-087.
- Laage, Damien; Hynes, James T. (2006). "A Molecular Jump Mechanism for Water Reorientation". Science. 311 (5762): 832–5. Bibcode:2006Sci...311..832L. doi:10.1126/science.1122154. PMID 16439623.
- Markovitch, Omer; Agmon, Noam (2008). "The Distribution of Acceptor and Donor Hydrogen-Bonds in Bulk Liquid Water". Molecular Physics. 106 (2): 485. Bibcode:2008MolPh.106..485M. doi:10.1080/00268970701877921.
- Politi, Regina; Harries, Daniel (2010). "Enthalpically driven peptide stabilization by protective osmolytes". ChemComm. 46 (35): 6449–6451. doi:10.1039/C0CC01763A.
- Gilman-Politi, Regina; Harries, Daniel (2011). "Unraveling the Molecular Mechanism of Enthalpy Driven Peptide Folding by Polyol Osmolytes". Journal of Chemical Theory and Computation. 7 (11): 3816–3828. doi:10.1021/ct200455n. PMID 26598272.
- Hellgren, M.; Kaiser, C.; de Haij, S.; Norberg, A.; Höög, J. O. (December 2007). "A hydrogen-bonding network in mammalian sorbitol dehydrogenase stabilizes the tetrameric state and is essential for the catalytic power". Cellular and Molecular Life Sciences. 64 (23): 3129–38. doi:10.1007/s00018-007-7318-1. PMID 17952367.
- Fernández, A.; Rogale K.; Scott Ridgway; Scheraga H. A. (June 2004). "Inhibitor design by wrapping packing defects in HIV-1 proteins". Proceedings of the National Academy of Sciences. 101 (32): 11640–5. Bibcode:2004PNAS..10111640F. doi:10.1073/pnas.0404641101. PMC . PMID 15289598.
- Sweetman, A. M.; Jarvis, S. P.; Sang, Hongqian; Lekkas, I.; Rahe, P.; Wang, Yu; Wang, Jianbo; Champness, N.R.; Kantorovich, L.; Moriarty, P. (2014). "Mapping the force field of a hydrogen-bonded assembly". Nature Communications. 5: 3931. Bibcode:2014NatCo...5E3931S. doi:10.1038/ncomms4931. PMC . PMID 24875276.
- Hapala, Prokop; Kichin, Georgy; Wagner, Christian; Tautz, F. Stefan; Temirov, Ruslan; Jelínek, Pavel (2014-08-19). "Mechanism of high-resolution STM/AFM imaging with functionalized tips". Physical Review B. 90 (8): 085421. arXiv: . Bibcode:2014PhRvB..90h5421H. doi:10.1103/PhysRevB.90.085421.
- Hämäläinen, Sampsa K.; van der Heijden, Nadine; van der Lit, Joost; den Hartog, Stephan; Liljeroth, Peter; Swart, Ingmar (2014-10-31). "Intermolecular Contrast in Atomic Force Microscopy Images without Intermolecular Bonds". Physical Review Letters. 113 (18): 186102. arXiv: . Bibcode:2014PhRvL.113r6102H. doi:10.1103/PhysRevLett.113.186102. PMID 25396382. Archived from the original on 2018-01-20.
- Crabtree, Robert H.; Siegbahn, Per E. M.; Eisenstein, Odile; Rheingold, Arnold L.; Koetzle, Thomas F. (1996). "A New Intermolecular Interaction: Unconventional Hydrogen Bonds with Element-Hydride Bonds as Proton Acceptor". Acc. Chem. Res. 29 (7): 348–354. doi:10.1021/ar950150s. PMID 19904922.
- Cowan ML; Bruner BD; Huse N; et al. (2005). "Ultrafast memory loss and energy redistribution in the hydrogen bond network of liquid H2O". Nature. 434 (7030): 199–202. Bibcode:2005Natur.434..199C. doi:10.1038/nature03383. PMID 15758995.
- Luo, Jiangshui; Jensen, Annemette H.; Brooks, Neil R.; Sniekers, Jeroen; Knipper, Martin; Aili, David; Li, Qingfeng; Vanroy, Bram; Wübbenhorst, Michael; Yan, Feng; Van Meervelt, Luc; Shao, Zhigang; Fang, Jianhua; Luo, Zheng-Hong; De Vos, Dirk E.; Binnemans, Koen; Fransaer, Jan (2015). "1,2,4-Triazolium perfluorobutanesulfonate as an archetypal pure protic organic ionic plastic crystal electrolyte for all-solid-state fuel cells". Energy & Environmental Science. 8 (4): 1276. doi:10.1039/C4EE02280G. Archived from the original on 2017-10-26.
- Lipinski CA (December 2004). "Lead- and drug-like compounds: the rule-of-five revolution". Drug Discovery Today: Technologies. 1 (4): 337–341. doi:10.1016/j.ddtec.2004.11.007.
- Löwdin, P. O. (1963). "Proton Tunneling in DNA and its Biological Implications". Rev. Mod. Phys. 35 (3): 724. Bibcode:1963RvMP...35..724L. doi:10.1103/RevModPhys.35.724.
- Law-breaking liquid defies the rules Archived 2011-04-29 at the Wayback Machine.. Physicsworld.com (September 24, 2004 ) | <urn:uuid:1e5db5f2-eddc-4466-9c74-6ecc3e79abd4> | 4.28125 | 7,503 | Knowledge Article | Science & Tech. | 57.748096 | 95,542,712 |
(Phys.org) —Researchers have found a new way to study chemical reactions that occur deep in the Earth's crust.
(Phys.org) —A chance discovery about the 'wonder material' graphene – already exciting scientists because of its potential uses in electronics, energy storage and energy generation – takes it a step closer to being ...
Clues contained in mice teeth have allowed scientists to reconstruct evolutionary history in the laboratory.
Scientists believe some tropical species may be able to evolve and adapt to the effects of climate change.
(Phys.org) —A wearable pressure sensor that is both highly sensitive and cheap to produce could aid the development of prosthetic skin, touch-on flexible displays and energy harvesting, as well as changing the way vital ...
(Phys.org) —When Albert Einstein proposed the existence of gravitational waves as part of his theory of relativity, he set in train a pursuit for knowledge that continues nearly a century later.
(Phys.org) —Scientists have discovered that bacteria can reshape their DNA to survive dehydration.
(Phys.org) —Scientists have patented a new way to detect one of the most common and deadly diseases in the world.
The ability to locate and count small numbers of impurity atoms could lead to advances in modern electronics and optical fiber communication networks.
(Medical Xpress)—Scientists have uncovered how an ulcer causing stomach bacteria, that has been linked to gastric cancer, sticks to and infects the lining of the stomach and gut. | <urn:uuid:e28075e0-2b6e-440a-a792-b5300dbe3827> | 2.890625 | 305 | Content Listing | Science & Tech. | 42.0225 | 95,542,714 |
Dr Peter Barnes from the University of Florida says astronomers have a good grasp of how stars such as our Sun form from clouds of gas and dust, but for heavier stars – ten times the mass of the Sun or more – they are still largely in the dark, despite years of work.
“Astronomers are still debating the physical processes that can generate these big stars,” Dr Barnes says.
“Massive stars are rare, making up only a few per cent of all stars, and they will only form in significant numbers when really massive clouds of gas collapse, creating hundreds of stars of different masses. Smaller gas clouds are not likely to make big stars.”
Accordingly, regions in space where massive stars seem to be forming are also rare. Most are well over 1000 light-years away, making them hard to observe.
Using CSIRO’s ‘Mopra’ radio telescope – a 22m dish near Coonabarabran, NSW – the research team discovered a massive cloud of mostly hydrogen gas and dust, three or more light-years across, that is collapsing in on itself and will probably form a huge cluster of stars.
Dr Stuart Ryder of the Anglo-Australian Observatory said the discovery was made during a survey of more than 200 gas clouds.
“With clouds like this we can test theories of massive star cluster formation in great detail.”
The gas cloud, called BYF73, is about 8,000 light years away, in the constellation of Carina (“the keel”) in the Southern sky.
“With clouds like this we can test theories of massive star cluster formation in great detail” Dr Stuart Ryder, Anglo-Australian ObservatoryEvidence for ‘infalling’ gas came from the radio telescope’s detection of two kinds of molecules in the cloud – HCO+ and H13CO+. The spectral lines from the HCO+ molecules in particular showed the gas had a velocity and temperature pattern that indicated collapse.
Mopra Research Scientist at CSIRO Astronomy and Space Science, Dr Kate Brooks, said the Mopra telescope excels at giving a picture of the complex chemistry of cosmic gas clouds.
“Much of its time is used for large projects like this, and almost all Mopra projects are international collaborations.”
The CSIRO telescope observations were confirmed by observations with the Atacama Submillimeter Telescope Experiment (ATSE) telescope in Chile.
The research team calculates that the gas is falling in at the rate of about three per cent of the Sun’s mass every year – one of the highest rates known.
Follow-up infrared observations made with the 3.9-m Anglo-Australian Telescope (also near Coonabarabran, NSW) showed signs of massive young stars that have already formed right at the centre of the gas clump, and new stars forming.
Star-formation in the cloud was also evident in archival data from the Spitzer and MSX spacecraft, which observe in the mid-infrared.
Gas cloud BYF73 was found during a large-scale search for massive star-forming regions – the Census of High- and Medium-mass Protostars, or CHaMP. This is one of the largest, most uniform and least biased surveys to date of massive star-forming regions in our Galaxy.
The research team’s findings have been published in the Monthly Notices of the Royal Astronomical Society, 402, 73-86 (2010).
Computer model predicts how fracturing metallic glass releases energy at the atomic level
20.07.2018 | American Institute of Physics
What happens when we heat the atomic lattice of a magnet all of a sudden?
18.07.2018 | Forschungsverbund Berlin
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
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Neutron scattering has revealed in unprecedented detail new insights into the exotic magnetic behavior of a material that, with a fuller understanding, could pave the way for quantum calculations far beyond the limits of the ones and zeros of a computer's binary code.
A research team led by the Department of Energy's Oak Ridge National Laboratory has confirmed magnetic signatures likely related to Majorana fermions--elusive particles that could be the basis for a quantum bit, or qubit, in a two-dimensional graphene-like material, alpha-ruthenium trichloride.
The results, published in the journal Science, verify and extend a 2016 Nature Materials study in which the team of researchers from ORNL, University of Tennessee, Max Planck Institute and Cambridge University first proposed this unusual behavior in the material.
"This research is a promise delivered," said lead author Arnab Banerjee, a postdoctoral researcher at ORNL. "Before, we suggested that this compound, alpha-ruthenium trichloride, showed the physics of Majorana fermions, but the material we used was a powder and obscured many important details. Now, we're looking at a large single crystal that confirms that the unusual magnetic spectrum is consistent with the idea of magnetic Majorana fermions."
Majorana fermions were theorized in 1937 by physicist Ettore Majorana. They are unique in that, unlike electrons and protons whose antiparticle counterparts are the positron and the antiproton, particles with equal but opposite charges, Majorana fermions are their own antiparticle and have no charge.
In 2006, physicist Alexei Kitaev developed a solvable theoretical model describing how topologically protected quantum computations could be achieved in a material using quantum spin liquids, or QSLs. QSLs are strange states achieved in solid materials where the magnetic moments, or "spins," associated with electrons exhibit a fluidlike behavior.
"Our neutron scattering measurements are showing us clear signatures of magnetic excitations that closely resemble the model of the Kitaev QSL," said corresponding author Steve Nagler, director of the Quantum Condensed Matter Division at ORNL. "The improvements in the new measurements are like looking at Saturn through a telescope and discovering the rings for the first time."
Because neutrons are microscopic magnets that carry no charge, they can be used to interact with and excite other magnetic particles in the system without compromising the integrity of the material's atomic structure. Neutrons can measure the magnetic spectrum of excitations, revealing how particles behave. The team cooled the material to temperatures near absolute zero (about minus 450 degrees Fahrenheit) to allow a direct observation of purely quantum motions.
Using the SEQUOIA instrument at ORNL's Spallation Neutron Source allowed the investigators to map out an image of the crystal's magnetic motions in both space and time.
"We can see the magnetic spectrum manifesting itself in the shape of a six-pointed star and how it reflects the underlying honeycomb lattice of the material," said Banerjee. "If we can understand these magnetic excitations in detail then we will be one step closer to finding a material that would enable us to pursue the ultimate dream of quantum computations."
Banerjee and his colleagues are pursuing additional experiments with applied magnetic fields and varying pressures.
"We've applied a very powerful measurement technique to get these exquisite visualizations that are allowing us to directly see the quantum nature of the material," said coauthor Alan Tennant, chief scientist for ORNL's Neutron Sciences Directorate. "Part of the excitement of the experiments is that they're leading the theory. We're seeing these things, and we know they're real."
The paper's authors also include ORNL's Jiaqiang Yan, Craig A. Bridges, Matthew B. Stone, and Mark D. Lumsden; Cambridge University's Johannes Knolle; the University of Tennessee's David G. Mandrus; and Roderich Moessner from the Max Planck Institute for the Physics of Complex Systems in Dresden.
The study was supported by DOE's Office of Science. The Spallation Neutron Source is a DOE Office of Science User Facility. UT-Battelle manages ORNL for the DOE Office of Science. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit http://science.
Jeremy Rumsey | EurekAlert!
What happens when we heat the atomic lattice of a magnet all of a sudden?
18.07.2018 | Forschungsverbund Berlin
Subaru Telescope helps pinpoint origin of ultra-high energy neutrino
16.07.2018 | National Institutes of Natural Sciences
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
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19.07.2018 | Power and Electrical Engineering
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In this absorbing commentary on the discovery of the atom's constituents, Steven Weinberg accomplishes a brilliant fusion of history and science. This is in effect two books, cleverly interwoven. One is an account of a sequence of key events in the physics of the twentieth century, events that led to the discoveries of the electron, proton and neutron. The other is an introduction to those fundamentals of classical physics that played crucial roles in these discoveries. Physical concepts are introduced where needed to understand the historical story, and each new concept builds on physics already explained. Throughout the book, connections are shown between the historic discoveries of subatomic particles and work today at the frontiers of physics. A final chapter describes the discoveries of new elementary particles up to the present day. | <urn:uuid:6a8fcd42-1e2e-4317-96dd-98c4e7a149b1> | 3.671875 | 167 | Product Page | Science & Tech. | 31.478561 | 95,542,735 |
Tables that contain rows of parameter values are called parameter tables . A column is another name for a parameter in a parameter table. LOCUS also supports expression tables which are tables that contain expressions and their names. These expressions can then be used like parameters in most of the LOCUS programs provided that the expression can be defined in terms of the parameters in the parameter tables that you are currently using. Expression tables are optional. An alias is an abbreviation for a table name which allows you to access duplicate names succinctly.
A database is a collection of tables which can be connected. A table is a single table or a previously defined view of one or more tables in the same database. Only tables within the same database can be looked at together. If you intend to access data from different tables, then the tables must be in the same database.
The name of a database or table can be up to 24 characters long; parameters and expression names can be up to 32 characters long. All names must begin with a letter and can contain A-Z, 0-9, and underscore. (Do not use any INGRES keywords, e.g., abs, or, or tid as the name of a parameter or expression.) You can have up to 300 parameters in any table. Expressions can be up to 132 characters long. | <urn:uuid:d2afac21-ddcc-4eda-a72e-3b853f24a4ed> | 3.03125 | 269 | Documentation | Software Dev. | 50.403063 | 95,542,760 |
May 25, 2017 10:49 AM EDT
The universe is indeed vast and mysterious where most of its regions are still unexplored and undiscovered. Recently, scientists proposed that in that vast universe lies an unknown planetary object which could hold the answer to the earth's origin.
The unknown planetary object is a doughnut-shaped object called a synestia, which is formed when planets collide with each other. This theory was proposed by a pair of planetary scientists from the University of California -Davis and Harvard University.
According to their reports, rocky planets were pulverized many times during their formation which could have formed synestias. If this theory gets approved by the astronomical society, synestia will become part of the science textbooks in the future as one of Earth's earliest forms.
One of the most popular theories how Earth was formed was that of two planets colliding with each other. What was left of the giant impact eventually evolved to become Earth while some of the scattered debris became the Moon.
Planetary scientists Sarah Stewart from UC Davis and Simon Lock from Harvard said that they have been studying the exact time that cataclysmic collision occurred and added that Earth's origins is more complicated than we think.
Synestia, according to Lock and Stewart, lasts for around 200 years and contains much larger volume than the two objects that collided with each other. They added that these objects do not have solids or liquids on their surface and can even form a whole new structure.
Then, after being a synestia for a century, the object will lose its heat and will condense back to become a solid object to become planets. If this hypothesis is confirmed, this will shed some light not only to how Earth was formed but also of how the Moon was formed.
The research was published in the Journal of Geophysical Research: Planets.
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The Amazing Hubble
In the history of modern astronomy, there is probably no one greater leap forward than the building and launch of the space telescope known as the Hubble. While NASA has had many ups and downs, the launch and continued operation of the Hubble space telescope probably ranks next to the moon landings and the development of the Space Shuttle as one of the greatest space exploration accomplishments of the last hundred years.
An amazing piece of astronomy trivia that few people know is that in truth, only about ten percent of the universe is visible using conventional methods of observation. For that reason, the Hubble really was a huge leap forward. That is for the very simple reason that the Hubble can operate outside of the atmosphere of Earth. Trying to make significant space exploration via telescopes from the terrestrial surface of planet Earth is very difficult. That very thing that keeps us alive, our own Earth?s atmosphere presents a serious distraction from being able to see deeper and further into space.
The Hubble space telescope was named after the great scientist and visionary Edward Hubble who discovered that the universe was expanding which was explained by what is now known in science as Hubble?s Law. To truly get a feel for the amazing accomplishment that was achieved with the launch of the Hubble telescope, spend some time on Nasa?s web site dedicated to the project at http://hubble.nasa.gov. There are also a number of sites where you can enjoy some stunning pictures from the Hubble including http://heritage.stsci.edu/ and http://www.stsci.edu/ftp/science/hdf/hdf.html.
It?s hard to believe how long the Hubble has been orbiting earth and sending back amazing video and pictures of what it is discovering in space. But the Hubble was actually initially launched on April 25th 1990. It was the culmination of literally decades of research and construction which began in 1977. Expectations were high as the orbiting telescope was put in place and actually began to function as it was designed to do.
All was not always perfect with the telescope and the early pictures were disappointing. After some study NASA discovered that the reason for the early failures was the curvatures of one of the main lenses of the orbiting telescope.
We probably could never have kept this intricate piece of equipment operational as well as we have had we not had the Space Shuttle program to give us a tool to implement repairs and improvements to the Hubble. In 1993 a new lens was installed on the Hubble which corrected the problem of picture resolution that was noted in the early operation of the telescope.
Two other repair and upgrade mission have been made to the Hubble since it launched, both of them in 1997 to upgrade older equipment and to retrofit the telescope to extend its useful life through 2010. It?s pretty amazing to think that this scientific and mechanical marvel has been operating now for ten years without maintenance. We can be assured that plans are in the works for NASA to upgrade or replace parts on the Hubble to extend its useful life even further as that 2010 time frame draws closer.
It is hard to imagine the science of astronomy or the natural quest for greater knowledge of our universe without the Hubble. While many times those who would not fund space exploration have tried to cut funding for the Hubble, the operation of this telescope is just too important to astronomers and to the scientific well being of mankind and our planet not to continue to use the Hubble, or its next natural successor. We will always need to have a set of eyes in the sky to watch the universe and discover more of its mysteries. | <urn:uuid:4da48f57-a046-4c9a-86a7-25dd3f227453> | 3.421875 | 720 | Personal Blog | Science & Tech. | 48.756373 | 95,542,798 |
The Virginia fringed mountain snail is one of the rarest snails in North America. It was once believed to be extinct until live specimens were found in 1971. It is only found in one area in Pulaski County, Virginia along the north bank of the New River. The shell is pale green in color and has four to five whorls that get thicker toward the rim, and it has eight to ten spiral, comb-like fringes inside the lower spiral grooves. It can grow up to 0.18 inches in diameter and 0.06 inches in height. The animal inside is white and thought to be blind because it has no pigmented eyestalks.
This snail seems to prefer a heavily shaded habitat, and where there is clay soil is in the area with pieces of limestone mixed in. Overgrown honeysuckle vines must be present to keep the clay soil moist at all times. Live snails have been found in this soil mixture as deep as 24 inches, and they may never come to the surface unless during extremely wet weather. It is not known what this snail eats, but generally soil invertebrates are herbivorous and feed on dead or decaying plant material such as leaves and soft bark. Little is known about the reproductive behavior of this snail. All snail species are "hermaphrodites," possessing both male and female reproductive organs, but they still need to find another snail to mate with. When the mating pair meets, one snail pierces the skin of the other snail with a calcified "love dart." The exact purpose of this is not fully understood but it seems to stimulate the other snail into exchanging small packets of sperm. After mating is complete the snails will produce eggs internally, which are fertilized by the sperm that has been exchanged. Both adult male and female give birth, and they give birth to live young.
The estimated population of the Virginia fringed mountain snail is unavailable and only 30 snails have been found alive. The main threats to the species is habitat destruction due to human disturbance such as construction and pollution through chemicals. Conservation efforts include protection of its only habitat, and the US FWS has recommended additional research to aid recovery efforts.
Virginia Fringed Mountain Snail Facts Last Updated:
January 1, 2006
To Cite This Page:
Glenn, C. R. 2006. "Earth's Endangered Creatures - Virginia Fringed Mountain Snail Facts" (Online).
Accessed 7/18/2018 at http://earthsendangered.com/profile.asp?sp=850&ID=9.
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UMass Boston scientist receives Harvard University fellowship to study threatened hemlock trees
If you stand very quietly in the Harvard Forest, you’ll hear a soft whispering sound. It’s not the wind, it’s the sound of falling hemlock needles. An invasive insect called the hemlock woolly adelgid is threatening to overtake hemlock trees across the East Coast, and the protected forest in Petersham, is no exception.
“It’s like the hemlocks are being clear-cut by these little bugs,” said Crystal Schaaf, professor of remote sensing in UMass Boston’s School for the Environment. The invasive insects feed on the twigs from the hemlock branches, causing the needles to fall off. “You’re standing in this grove of really big trees, and a rain of needles is coming down on your head.”
Schaaf has received a Charles Bullard Fellowship in Forest Research from Harvard University. She will spend her fellowship year working in the Harvard Forest to find new ways to track the hemlock woolly adelgid, assess its impacts, and hopefully contribute to efforts to slow its proliferation.
The fellowship was established in 1962, and attracts scholars from the sciences and humanities, as well as professionals in the public and private sectors. The fellows’ research contributes to a greater understanding of forest ecology and policy.
Schaaf is a noted expert on remote sensing. She uses both terrestrial and satellite imaging technology to map forest canopy structure around the world, and works with NASA on several satellite science teams. Schaaf will work with David Orwig and other Harvard Forest researchers to apply these techniques in Petersham. If Schaaf and Orwig can better monitor the invasive species, they may be able to find some stands of trees that are more resistant to infestation.
“We don’t have terribly good ways to monitor the spread of these insects, because it tends to first affect the lower branches,” said Schaaf. “The tops are still staying green. If you fly aircraft overhead, you don’t necessarily see the extent of the damage until the trees are nearly dead. People on the ground have to monitor the spread by flipping over the branches one at a time and looking for the characteristic white woolly egg sacs.”
The consequences of losing the hemlock, a foundation species in New England forests, would be devastating to the environment. Hemlocks grow near streams and rivers, and their year-round shade keeps water from evaporating in summer, and keeps snow from melting too quickly in spring. The warmer winters associated with climate change are causing the adelgid to spread northward and hastening the destruction of these important trees. | <urn:uuid:db345b3e-3182-459e-bd5a-c807bd38d72e> | 3.34375 | 575 | News Article | Science & Tech. | 46.094115 | 95,542,822 |
Mystery Bird photographed in the Republic of Singapore, a Southeast Asian city-state off the southern tip of the Malay Peninsula. [I will identify this bird in 48 hours]
Image: Marie-Louise Ng, 24 February 2012 (with permission, for GrrlScientist/Guardian use only) [velociraptorise].
Question: This striking Malaysian mystery bird gets its name from one of its distinctive habits. What habit is that? Can you identify this bird's taxonomic family and species? Is this an adult or a juvenile? What sex is this bird?
1. Keep in mind that people live in zillions of different time zones, and some people are following on their smart phones. So let everyone play the game. Don't spoil it for everyone else by identifying the bird in the first 24 to 36 hours.
2. If you know the mystery bird's identity, answer the accompanying questions and provide subtle ID hints so others know that you know. Your hints may be helpful clues for less experienced players. Keep in mind that some hints may read like "inside jokes" and thus, may discourage others from participating.
3. Describe the key field marks that distinguish this species from any similar ones.
4. Comments that spoil others' enjoyment may be deleted.
1. This is meant to be a learning experience where together we learn a few things about birds and about the process of identifying them (and maybe about ourselves, too).
2. Each mystery bird is usually accompanied by a question or two. These questions can be useful for identifying the pictured species, but may instead be used to illustrate an interesting aspect of avian biology, behaviour or evolution, or may be intended to generate conversation on other topics, such as conservation or ethics.
3. Thoughtful comments will add to everyone's enjoyment, and will keep the suspense going until the next teaser is published. Interesting snippets may add to the knowledge of all.
4. Each bird species will be demystified approximately 48 hours after publication.
You are invited to review all of the daily mystery birds by going to their dedicated graphic index page.
If you have bird images, video or audio files that you'd like to share with a large and (mostly) appreciative international audience here at The Guardian, feel free to contact me to learn more.
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There are significant constraints to large-scale deployment of negative emissions technologies in the future to reach climate change targets, according to a new study including research of the Mercator Research Institute on Global Commons and Climate Change (MCC). Published today in Nature Climate Change, it demonstrates the potential environmental, economic, and energy impacts of negative emission technologies for addressing climate change. The study comes at a time when UN climate negotiators currently meet in Paris at the world climate summit COP21 and emphasizes that greenhouse gas emissions must be reduced aggressively and immediately.
Negative emission technologies aim to remove carbon dioxide (CO2), a major driver of climate change, from the atmosphere. They include relatively simple options like planting more trees to lock up CO2 as they grow, or crushing rocks that naturally absorb CO2 and spreading them on soils so that they remove CO2 more rapidly.
Poto: Photocase / Oli_ok
Other higher-tech options include using chemicals to absorb CO2 from the air, or burning plants for energy and capturing the CO2 that would otherwise be released, then storing it permanently deep below the ground, called bioenergy with carbon capture and storage (BECCS).
The study confirms and warns that future use of negative emissions should not be interpreted as a fall-back option. This would be risky, as continuing to cumulate emissions would entail lower chances of stabilizing climate change at less than two degrees Celsius.
“Plan A” must be to reduce greenhouse gas emissions aggressively now. A failure to initiate such aggressive emissions cuts may leave us with no “Plan B” to stabilize the climate within the two degree target, as the deployment of these technologies will likely be limited due to any combination of the environmental, economic or energy constraints examined in the study.
“Negotiators at the climate summit in Paris must realize that betting on negative emissions doesn’t release us from cutting down on carbon now,” says co-author Sabine Fuss, a researcher at the Mercator Research Institute on Global Commons and Climate Change (MCC), who also serves on the Global Carbon Project (GCP) scientific steering committee.
“Our research shows that there are limits to the different negative emissions technologies – some demanding vast areas of land, some being energy-intensive. Therefore, future research should look not only on BECCS, but continue to explore all carbon dioxide removal options: we will probably be dependent on the full deck of cards, even if we don’t end up playing all of them.”
The work was carried out by a team of 40 collaborators on behalf of the GCP, including three MCC researchers. Among other things, they focused especially on the synthesis of the current literature on the biophysical limits to bioenergy and afforestation, and contributed to the analysis of BECCS deployment in the scenarios for the latest IPCC report. Some 85 percent of the 2-degree-scenarios examined by the IPCC assume the use of technologies such as BECCS.
It is still realistic to limit the increase global mean temperature to two-degree. Indeed, this requires negative emissions – but they’re also necessary to manage a three-degree-target,” MCC director Ottmar Edenhofer says. “Putting a price on carbon would be a very effective way to cut rising emissions quickly and aggressively. It would push the development of technology in the right direction and make us less dependent on negative emissions that bear large uncertainties.”
The new research considers the impacts of negative emission technologies on land use, greenhouse gas emissions, water use, earth’s reflectivity, and soil nutrient depletion, as well as the energy and cost requirements for each technology. The study shows that there are many such impacts that vary across technologies. These impacts need to be satisfactorily addressed if negative emission technologies are to play a significant role in achieving climate change goals.
Reference of the cited article:
Pete Smith (et al.) (2015): Biophysical and economic limits to negative CO2 emissions. Nature Climate Change. DOI: 10.1038/nclimate2870
Fabian Löhe | idw - Informationsdienst Wissenschaft
Innovative genetic tests for children with developmental disorders and epilepsy
11.07.2018 | Christian-Albrechts-Universität zu Kiel
Oxygen loss in the coastal Baltic Sea is “unprecedentedly severe”
05.07.2018 | European Geosciences Union
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
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Note : This is not by any means an exhaustive guide to Data Binding HTML elements, nor a control reference for the TDC control, or RDS. Some information on data binding is available in the Internet Client SDK, and some feature articles at the Sitebuilder Network describe Data Binding in greater detail. Data Binding is only currently supported by Internet Explorer 4.0.
Data binding represents a relatively simple way to display data in web pages without having to write extensive server side procedures. Basically, you insert a standard
<OBJECT> element, which inserts a Data Source object. Then, HTML elements that support Data Binding can use the data referenced by the Data Source object in the HTML document.
Internet Explorer 4.0 supports 2 types of data sources. RDS (Remote Data Service - formerly known as ADC) and TDC (the Tabular Data Control).
Generally speaking, the RDS Data Binding component would be used if you wish to publish data from ODBC, SQL, Access, Oracle etc, databases, or you wish for users to be able to interact with the data from the database (i.e. add, or update records for example). The somewhat simpler to use TDC Data Binding component can be used if you have simple data to display. For example, if you just want to publish some data that's been extracted from a data source as a standard text file. Using the TDC Data Binding component doesn't allow any udpate/creation interaction with the data, although the user can sort, filter and manipulate the data in any way you allow through scripting in the document.
Once you've decided on a Data Source object and what data is going to be presented to the user, you need to decide how that data is presented to the user. There's three basic options:
<FORM>fields, allowing the user to change the data), with scripted navigation buttons, allowing the user to navigate forwards and backwards through the recordset.
Binding HTML elements
Once the data source and presentation method are decided, the elements that are going to be used for the presentation of the data need to be bound to the Data Source. Below are the Data Binding HTML attribute extensions, supported by elements that support Data Binding.
DATAFLD attribute is used to set which column in the data referenced by the data source the element is going to use as the contents of its display. See the examples for an example
DATAFORMATAS attribute accepts either
HTML as its values and specifies whether the data being taken from the data source should be displayed literally
DATAFORMATAS="text" or parsed before being displayed
DATAFORMATAS="HTML". If the data source column being used contains HTML formatting, then
DATAFORMATAS="HTML" should be explicitly used.
DATAFORMATAS defaults to
text if not specified, and any HTML from the data source would be treated as plain text.
For repeated Data bound tables, the
DATAPAGESIZE attribute specifies how many records should be displayed by the table at any one time. The table will then be repeated to display that number of records only. If this doesn't cover the entire contents of the data source data, then navigational buttons will need to be used to allow the user to retrieve the next 'block' of records. Using data bound tables in this way can greatly increase the perceived speed of your site, as the rendering time for smaller tables is less.
DATASRC attribute is the most important Data Binding attribute, as it defines for the element, which Data Source object it is to use, to retrieve the data from. Once a Data Source object has been included in the document (with the
<OBJECT> element), the
DATASRC attribute should be set to
ID reflects the
ID attribute of the
<OBJECT> element used to insert the Data Source object.
Note that the
DATASRC attribute can be inherited. In the case of repeated tables, if the
DATASRC attribute specifies a valid data source in the main
<TABLE>, then subsequent
DATAFLD attributes in elements contained within the table need only specify a
DATAFLD attribute - the data source referenced will be resolved by looking to the parent
<TABLE> element for a valid
Data Binding Scripting
When elements are data bound, they support a number of properties and events. The dataFld, dataFormatAs, dataPageSize and dataSrc properties are all read-only and directly reflect the
DATASRC attribute settings for the elements. For the HTML elements that support in-place editing/Data Binding (e.g.
<TEXTAREA> etc.) and certain other Data Consumers support the following events (when used with RDS Data Binding, which is allowing user updates to the data source). (Note : Review the element topic to see what (if any) of the following topics it supports. Also, these are events that are supported on the element object, not the data source object. For such information, consult the ADO/TDC/RDS documentation in the Internet Client SDK).
onafterupdate event is fired after data is transferred from the element to the data provider and will only fire after the
onbeforeupdate event has fired and was successful.
onbeforeupdate fires when a data bound element loses the focus, or the current document is unloaded and will only fire if the value of the element is different to the original value that was present when the element received the users focus. Note that
onbeforeupdate is a cancelable event (setting
returnValue=false for the Event object), which allows the document /script author a chance to validate the new data entered by the user on the client-side, before sending the data to the data provider.
onerrorupdate event fires when a data transfer error occurs, through some action by the user (i.e. pressing the 'Stop' button on the browser for example), but not if a script generates the transfer error.
onrowenter event fires on the data source control when the current record has been changed, so new data is available to populate the HTML display elements that are bound to the data source. Somewhat confusingly, this will typically happen after the
onrowexit event has been fired.
onrowexit event is fired immediately before the data source changes the current record (i.e. when the user has requested another record, or set of records by pressing a button perhaps). Note that unlike the
onrowexit is fired by the data source, not any of the HTML elements used to display the data. Changes to the data in the HTML elements should have been transferred to the data source (with validation being taken care of in the
onrowexit will also fire if the record position is changed through scripting.
onbeforeunload event fires on the document (via the Window Object), firing before any
onunload events, in order to give the author a chance to do any necessary data updates, before the page is unloaded. For example, the user makes some data edits, but before moving to another record (and having the changes committed to the data source through the
on*update events), they close down the browser, or navigate to a different site. Any unsaved data changes should be taken care of in the
onbeforeunload event. For security reasons, the
onbeforeunload event is not cancelable, but a string value can be returned from the event, which is used as a prompt to the user.
Data Source Object events
<APPLET> elements can insert Data source objects into a document. For these elements, the following properties and events have been introduced with data binding.
recordset property returns a reference to the ADO recordset supplied by the Data Source object. For more information, see the ADO reference in the Internet Client SDK.
ondatasetchanged event is fired when a new set of data is available and a recordset can be retrieved from that set of data, or when an existing set of data has been changed - for example after a filter has been applied to the data.
ondataavailable event being fired indicates that more records for the referenced Data Source Object are available. It doesn't necessarily fire for every single additional record though.
When all the data in the referenced recordset is available, the
ondatdasetcomplete event fires. For the
ondatasetcomplete event, a
reason parameter is available through the Event Object, which can have values of 0, 1 or 2, corresponding to successful completion, Aborted completion (i.e. 'Stop' button pressed for example), or Error (some other error) respectively.
For most small data sets, using the standard
<TABLE> template method of table repetition will be OK, but for larger datasets, to prevent swamping the user with data, the
DATAPAGESIZE attribute in the
<TABLE> can be used to specify that only a certain number of records are retrieved and displayed at any one time. The table still repeats, as normal, but only by the number of times specified in the
When such a table is used, the previousPage() and nextPage() methods can be used (typically attached to buttons in the document) to refresh the table with the next, or previous
DATAPAGESIZE records from the data set. Whenever the amount of records to display is less than the value of the
DATAPAGESIZE attribute, then the table will simply repeat its content until all the records are displayed and then close - i.e. 'shrinking' to fit the amount of data shown.
Data Binding examples
Presented here is a brief and simple data binding example, with the necessary code explained. Firstly, the code will be examined, then the table example will be shown. For the purposes of this example, a portion of the HTMLib Comparison table will be used to provide the data.
Inserting the TDC control
The TDC control that ships with Internet Explorer 4.0 is just like any other ActiveX control and is inserted into a document with the
<OBJECT> element, as below:
<OBJECT id=comp CLASSID="clsid:333C7BC4-460F-11D0-BC04-0080C7055A83">
<PARAM NAME="DataURL" VALUE="compdata.txt">
<PARAM NAME="UseHeader" VALUE="True">
ID attribute that's been used - that's what is used to bind the
<TABLE> to the Data Source.
<TABLE> template needs to be set up. The data file that we're using
compdata.txt is a comma delimited file.
As you can see, in the data file there is references to images and some text that needs to be formatted as HTML. The main
<TABLE> element used in the template is:
<TABLE datasrc="#comp" BORDER DATAPAGESIZE="10" ID="TABLE1">
DATASRC attribute references the TDC control inserted into the document earlier and the
DATAPAGESIZE attribute is set to 10, which means that only 10 records from the data set will be displayed at any one time. The main part of the table that is repeated for each record is:
<TD><DIV DATAFLD="Element" DATAFORMATAS="html"></DIV></TD>
<TD><IMG DATAFLD="IEx" WIDTH="11" HEIGHT="11" ALT="Y"></TD>
<TD><IMG DATAFLD="Netscape" WIDTH="11" HEIGHT="11" ALT="Y"></TD>
<TD><IMG DATAFLD="Mosaic" WIDTH="11" HEIGHT="11" ALT="Y"></TD>
<TD><DIV DATAFLD="Spec" DATAFORMATAS="text"></DIV></TD>
DATAFLD attribute for each element specifies the column name that it uses from the data file (see above), with the
DATAFORMATAS attribute specifying whether the two text fields are formatted as HTML, or text. Note that for the
<IMG> element, the data taken from the data source is used for the
SRC attribute of the element, so extra attributes, such as
HEIGHT etc., still need to be specified. The
<TBODY> element is used to separate what is actually repeated for each record. Only table rows/cells between the
</TBODY> elements are repeated.
That's about as much as it takes to set up a data bound repeating table. The only HTML that's not been included in the sample code given above is additional stylings and the table header and footer. All that's left is a pair of navigational buttons. Remember, only 10 records are being displayed at any one time, so there must be a way for the user to navigate through the records. Any standard button will do, the script function it runs just needs to be:
Depending on whether it's navigating forwards or backwards through the recordset.
© 1995-1998, Stephen Le Hunte
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Properties of metals, metalloids and nonmetals
|Part of a series on the|
The chemical elements can be broadly divided into metals, metalloids and nonmetals according to their shared physical and chemical properties. All metals have a shiny appearance (at least when freshly polished); are good conductors of heat and electricity; form alloys with other metals; and have at least one basic oxide. Metalloids are metallic-looking brittle solids that are either semiconductors or exist in semiconducting forms, and have amphoteric or weakly acidic oxides. Typical nonmetals have a dull, coloured or colourless appearance; are brittle when solid; are poor conductors of heat and electricity; and have acidic oxides. Most or some elements in each category share a range of other properties; a few elements have properties that are either anomalous given their category, or otherwise extraordinary.
Metals appear lustrous (beneath any patina); form mixtures (alloys) when combined with other metals; tend to lose or share electrons when they react with other substances; and each forms at least one predominantly basic oxide.
Most metals are silvery looking, high density, relatively soft and easily deformed solids with good electrical and thermal conductivity, closely packed structures, low ionisation energies and electronegativities, and are found naturally in combined states.
Some metals appear coloured (Cu, Cs, Au), have low densities (e.g. Be, Al) or very high melting points, are liquids at or near room temperature, are brittle (e.g. Os, Bi), not easily machined (e.g. Ti, Re), or are noble (hard to oxidise) or have nonmetallic structures (Mn and Ga are structurally analogous to, respectively, white P and I).
Metals comprise the large majority of the elements, and can be subdivided into several different categories. From left to right in the periodic table, these categories include the highly reactive alkali metals; the less reactive alkaline earth metals, lanthanides and radioactive actinides; the archetypal transition metals, and the physically and chemically weak post-transition metals. Specialized subcategories such as the refractory metals and the noble metals also exist.
Metalloids are metallic looking brittle solids; tend to share electrons when they react with other substances; have weakly acidic or amphoteric oxides; and are usually found naturally in combined states.
Most are semiconductors, and moderate thermal conductors, and have structures that are more open than those of most metals.
The metalloids, as the smallest major category of elements, are not subdivided further.
Nonmetals have open structures (unless solidified from gaseous or liquid forms); tend to gain or share electrons when they react with other substances; and do not form distinctly basic oxides.
Most are gases at room temperature; have relatively low densities; are poor electrical and thermal conductors; have relatively high ionisation energies and electronegativities; form acidic oxides; and are found naturally in uncombined states in large amounts.
From left to right in the periodic table, the nonmetals can be subdivided into the reactive nonmetals which, being nearest to the metalloids, show some incipient metallic character, and the monatomic noble gases, which are almost completely inert.
Comparison of properties
Number of metalloid properties that resemble metals or nonmetals
|(or that are relatively distinct)|
|Resemble metals||Relatively distinct||Resemble nonmetals|
|Properties compared:||(36)||7 (19%)||25||(68%)||5 (13%)|
|Physical||(21)||5 (24%)||14||(67%)||2 (10%)|
|• Presentation & structure||(10)||2||6||2 (20%)|
|Chemical||(16)||2 (13%)||11||(69%)||3 (19%)|
|• Elemental chemistry||(6)||3||3 (50%)|
|• Combined form chemistry||(6)||2||4|
|• Environmental chemistry||(4)||4|
The characteristic properties of metals and nonmetals are quite distinct, as shown in the table below. Metalloids, straddling the metal-nonmetal border, are mostly distinct from either, but in a few properties resemble one or the other, as shown in the shading of the metalloid column below and summarized in the small table at the top of this section.
Authors differ in where they divide metals from nonmetals and in whether they recognize an intermediate metalloid category. Some authors count metalloids as nonmetals with weakly nonmetallic properties.[n 1] Others count some of the metalloids as post-transition metals.[n 2]
Physical and chemical properties[n 3]
|Presentation and structure|
|Deformability (as a solid)|
|Poisson's ratio[n 7]||
|Crystalline structure at freezing point|
|Packing & coordination number||
|Periodic table block||
|Outer s and p electrons||
|Electron bands: (valence, conduction)|
|... as a liquid||
|Temperature coefficient of resistance[n 17]|
|Enthalpy of fusion||
|Combined form chemistry|
|With hydrogen (hydrides)||
|With oxygen (oxides)|
|With sulfur (sulfates)||
|With halogens (halides, esp. chlorides) (see also)|
|Molar composition of Earth's ecosphere[n 25]||
|Primary form on Earth|
|Required by mammals|
|Composition of the human body, by weight|
Within each category, elements can be found with one or two properties very different from the expected norm, or that are otherwise notable.
- The common notions that "alkali metal ions (group 1A) always have a +1 charge" and that "transition elements do not form anions" are textbook errors. The synthesis of a crystalline salt of the sodium anion Na− was reported in 1974. Since then further compounds ("alkalides") containing anions of all other alkali metals except Li and Fr, as well as that of Ba, have been prepared. In 1943, Sommer reported the preparation of the yellow transparent compound CsAu. This was subsequently shown to consist of caesium cations (Cs+) and auride anions (Au−) although it was some years before this conclusion was accepted. Several other aurides (KAu, RbAu) have since been synthesized, as well as the red transparent compound Cs2Pt which was found to contain Cs+ and Pt2− ions.
- Well-behaved metals have crystal structures featuring unit cells with up to four atoms. Manganese has a complex crystal structure with a 58-atom unit cell, effectively four different atomic radii, and four different coordination numbers (10, 11, 12 and 16). It has been described as resembling "a quaternary intermetallic compound with four Mn atom types bonding as if they were different elements." The half-filled 3d shell of manganese appears to be the cause of the complexity. This confers a large magnetic moment on each atom. Below 727 °C, a unit cell of 58 spatially diverse atoms represents the energetically lowest way of achieving a zero net magnetic moment. The crystal structure of manganese makes it a hard and brittle metal, with low electrical and thermal conductivity. At higher temperatures "greater lattice vibrations nullify magnetic effects" and manganese adopts less complex structures.
- The only elements strongly attracted to magnets are iron, cobalt, and nickel at room temperature, gadolinium just below, and terbium, dysprosium, holmium, erbium, and thulium at ultra cold temperatures (below −54 °C, −185 °C, −254 °C, −254 °C, and −241 °C respectively).
- Bricks and bowling balls will float on the surface of mercury thanks to it having a density 13.5 times that of water. Equally, a solid mercury bowling ball would weigh around 50 pounds and, if it could be kept cold enough, would float on the surface of liquid gold.
- The only metal having an ionisation energy higher than some nonmetals (sulfur and selenium) is mercury.
- Mercury and its compounds have a reputation for toxicity but on a scale of 1 to 10, dimethylmercury ((CH3)2Hg) (abbr. DMM), a volatile colourless liquid, has been described as a 15. It is so dangerous that scientists have been encouraged to use less toxic mercury compounds wherever possible. In 1997, Karen Wetterhahn, a professor of chemistry specialising in toxic metal exposure, died of mercury poisoning ten months after a few drops of DMM landed on her "protective" latex gloves. Although Wetterhahn had been following the then published procedures for handling this compound, it passed through her gloves and skin within seconds. It is now known that DMM is exceptionally permeable to (ordinary) gloves, skin and tissues. And its toxicity is such that less than one-tenth of a ml applied to the skin will be seriously toxic.
- The expression, to "go down like a lead balloon" is anchored in the common view of lead as a dense, heavy metal—being nearly as dense as mercury. However, it is possible to construct a balloon made of lead foil, filled with a helium and air mixture, which will float and be buoyant enough to carry a small load.
- Bismuth has the longest half life of any naturally occurring element; its only primordial isotope, bismuth-209, was found in 2003 to be slightly radioactive, decaying via alpha decay with a half life more than a billion times the estimated age of the universe. Prior to this discovery, bismuth-209 was thought to be the heaviest naturally occurring stable isotope; this distinction now belongs to lead-208.
- It is a commonly held belief that metals reduce their electrical conductivity when heated. Plutonium increases its electrical conductivity when heated in the temperature range of around –175 to +125 °C.
- Boron is the only element with a partially disordered structure in its most thermodynamically stable crystalline form.
- These elements are record holders within the field of superacid chemistry. For seven decades, fluorosulfonic acid HSO3F and trifluoromethanesulfonic acid CF3SO3H were the strongest known acids that could be isolated as single compounds. Both are about a thousand times more acidic than pure sulfuric acid. In 2004, a boron compound broke this record by a thousand fold with the synthesis of carborane acid H(CHB11Cl11). Another metalloid, antimony, features in the strongest known acid, a mixture 10 billion times stronger than carborane acid. This is fluoroantimonic acid H2F[SbF6], a mixture of antimony pentafluoride SbF5 and hydrofluoric acid HF.
- The thermal conductivity of silicon is better than that of most metals.
- A sponge-like porous form of silicon (p-Si) is typically prepared by the electrochemical etching of silicon wafers in a hydrofluoric acid solution. Flakes of p-Si sometimes appear red; it has a band gap of 1.97–2.1 eV. The many tiny pores in porous silicon give it an enormous internal surface area, up to 1,000 m2/cm3. When exposed to an oxidant, especially a liquid oxidant, the high surface-area to volume ratio of p-Si creates a very efficient burn, accompanied by nano-explosions, and sometimes by ball-lightning-like plasmoids with, for example, a diameter of 0.1–0.8 m, a velocity of up to 0.5 m/s and a lifetime of up to 1s. The first ever spectrographic analysis of a ball lightning event (in 2012) revealed the presence of silicon, iron and calcium, these elements also being present in the soil.
- A high-energy explosive form of antimony was first obtained in 1858. It is prepared by the electrolysis of any of the heavier antimony trihalides (SbCl3, SbBr3, SbI3) in a hydrochloric acid solution at low temperature. It comprises amorphous antimony with some occluded antimony trihalide (7–20% in the case of the trichloride). When scratched, struck, powdered or heated quickly to 200 °C, it "flares up, emits sparks and is converted explosively into the lower-energy, crystalline grey antimony."
- Water (H2O), a well known oxide of hydrogen, is a spectacular anomaly. Extrapolating from the heavier hydrogen chalcogenides, namely hydrogen sulfide H2S, hydrogen selenide H2Se, and hydrogen telluride H2Te, water should be "a foul-smelling, poisonous, inflammable gas…condensing to a nasty liquid [at] around –100° C". Instead, due to hydrogen bonding, water is "stable, potable, odorless, benign, and…indispensable to life".
- Less well known of the oxides of hydrogen is the trioxide, H2O3. Berthelot proposed the existence of this oxide in 1880 but his suggestion was soon forgotten as there was no way of testing it using the technology of the time. Hydrogen trioxide was prepared in 1994 by replacing the oxygen used in the industrial process for making hydrogen peroxide, with ozone. The yield is about 40 per cent, at –78 °C; above around –40 °C it decomposes into water and oxygen. Derivatives of hydrogen trioxide, such as F3C–O–O–O–CF3 ("bis(trifluoromethyl) trioxide") are known; these are metastable at room temperature. Mendeleev went a step further, in 1895, and proposed the existence of hydrogen tetroxide HO–O–O–OH as a transient intermediate in the decomposition of hydrogen peroxide; this was prepared and characterised in 1974, using a matrix isolation technique. Alkali metal ozonide salts of the unknown hydrogen ozonide (HO3) are also known; these have the formula MO3.
- At temperatures below 0.3 and 0.8 K respectively, helium-3 and helium-4 each have a negative enthalpy of fusion. This means that, at the appropriate constant pressures, these substances freeze with the addition of heat.
- Until 1999 helium was thought to be too small to form a cage clathrate—a compound in which a guest atom or molecule is encapsulated in a cage formed by a host molecule—at atmospheric pressure. In that year the synthesis of microgram quantities of He@C20H20 represented the first such helium clathrate and (what was described as) the world's smallest helium balloon.
- Graphite is the most electrically conductive nonmetal, better than some metals.
- Diamond is the best natural conductor of heat; it even feels cold to the touch. Its thermal conductivity (2,200 W/m•K) is five times greater than the most conductive metal (Ag at 429); 300 times higher than the least conductive metal (Pu at 6.74); and nearly 4,000 times that of water (0.58) and 100,000 times that of air (0.0224). This high thermal conductivity is used by jewelers and gemologists to separate diamonds from imitations.
- Graphene aerogel, produced in 2012 by freeze-drying a solution of carbon nanotubes and graphite oxide sheets and chemically removing oxygen, is seven times lighter than air, and ten per cent lighter than helium. It is the lightest solid known (0.16 mg/cm3), conductive and elastic.
- The least stable and most reactive form of phosphorus is the white allotrope. It is a hazardous, highly flammable and toxic substance, spontaneously igniting in air and producing phosphoric acid residue. It is therefore normally stored under water. White phosphorus is also the most common, industrially important, and easily reproducible allotrope, and for these reasons is regarded as the standard state of phosphorus. The most stable form is the black allotrope, which is a metallic looking, brittle and relatively non-reactive semiconductor (unlike the white allotrope, which has a white or yellowish appearance, is pliable, highly reactive and a semiconductor). When assessing periodicity in the physical properties of the elements it needs to be borne in mind that the quoted properties of phosphorus tend to be those of its least stable form rather than, as is the case with all other elements, the most stable form.
- The mildest of the halogens, iodine is the active ingredient in tincture of iodine, a disinfectant. This can be found in household medicine cabinets or emergency survival kits. Tincture of iodine will rapidly dissolve gold, a task ordinarily requiring the use of aqua regia (a highly corrosive mixture of nitric and hydrochloric acids).
- For example:
- Brinkley writes that boron has weakly nonmetallic properties.
- Glinka describes silicon as a weak nonmetal.
- Eby et al. discuss the weak chemical behaviour of the elements close to the metal-nonmetal borderline.
- Booth and Bloom say "A period represents a stepwise change from elements strongly metallic to weakly metallic to weakly nonmetallic to strongly nonmetallic, and then, at the end, to an abrupt cessation of almost all chemical properties ...".
- Cox notes "nonmetallic elements close to the metallic borderline (Si, Ge, As, Sb, Se, Te) show less tendency to anionic behaviour and are sometimes called metalloids."
- See, for example, Huheey, Keiter & Keiter who classify Ge and Sb as post-transition metals.
- At standard pressure and temperature, for the elements in their most thermodynamically stable forms, unless otherwise noted
- Copernicium is reported to be the only metal known to be a gas at room temperature.
- Whether polonium is ductile or brittle is unclear. It is predicted to be ductile based on its calculated elastic constants. It has a simple cubic crystalline structure. Such a structure has few slip systems and "leads to very low ductility and hence low fracture resistance".
- Carbon as exfoliated (expanded) graphite, and as metre-long carbon nanotube wire; phosphorus as white phosphorus (soft as wax, pliable and can be cut with a knife, at room temperature); sulfur as plastic sulfur; and selenium as selenium wires.
- For polycrystalline forms of the elements unless otherwise noted. Determining Poisson's ratio accurately is a difficult proposition and there could be considerable uncertainty in some reported values.
- Beryllium has the lowest known value (0.0476) amongst elemental metals; indium and thallium each have the highest known value (0.46). Around one third show a value ≥ 0.33.
- Boron 0.13; silicon 0.22; germanium 0.278; amorphous arsenic 0.27; antimony 0.25; tellurium ~0.2.
- Graphitic carbon 0.25; [diamond 0.0718]; black phosphorus 0.30; sulfur 0.287; amorphous selenium 0.32; amorphous iodine ~0.
- At atmospheric pressure, for elements with known structures
- The Goldhammer-Herzfeld criterion is a ratio that compares the force holding an individual atom's valence electrons in place with the forces, acting on the same electrons, arising from interactions between the atoms in the solid or liquid element. When the interatomic forces are greater than or equal to the atomic force, valence electron itinerancy is indicated. Metallic behaviour is then predicted. Otherwise nonmetallic behaviour is anticipated. The Goldhammer-Herzfeld criterion is based on classical arguments. It nevertheless offers a relatively simple first order rationalization for the occurrence of metallic character amongst the elements.
- Metals have electrical conductivity values of from 6.9 × 103 S•cm−1 for manganese to 6.3 × 105 for silver.
- Metalloids have electrical conductivity values of from 1.5 × 10−6 S•cm−1 for boron to 3.9 × 104 for arsenic. If selenium is included as a metalloid the applicable conductivity range would start from ~10−9 to 10−12 S•cm−1.
- Nonmetals have electrical conductivity values of from ~10−18 S•cm−1 for the elemental gases to 3 × 104 in graphite.
- Mott and Davis note however that 'liquid europium has a negative temperature coefficient of resistance' i.e. that conductivity increases with rising temperature
- At or near room temperature
- Chedd defines metalloids as having electronegativity values of 1.8 to 2.2 (Allred-Rochow scale). He included boron, silicon, germanium, arsenic, antimony, tellurium, polonium and astatine in this category. In reviewing Chedd's work, Adler described this choice as arbitrary, given other elements have electronegativities in this range, including copper, silver, phosphorus, mercury and bismuth. He went on to suggest defining a metalloid simply as, 'a semiconductor or semimetal' and 'to have included the interesting materials bismuth and selenium in the book'.
- Phosphorus is known to form a carbide in thin films.
- See, for example, the sulfates of the transition metals, the lanthanides and the actinides.
- Sulfates of osmium have not been characterized with any great degree of certainty.
- Common metalloids: Boron is reported to be capable of forming an oxysulfate (BO)2SO4, a bisulfate B(HSO4)3 and a sulfate B2(SO4)3. The existence of a sulfate has been disputed. In light of the existence of silicon phosphate, a silicon sulfate might also exist. Germanium forms an unstable sulfate Ge(SO4)2 (d 200 °C). Arsenic forms oxide sulfates As2O(SO4)2 (= As2O3.2SO3) and As2(SO4)3 (= As2O3.3SO3). Antimony forms a sulfate Sb2(SO4)3 and an oxysulfate (SbO)2SO4. Tellurium forms an oxide sulfate Te2O3(SO)4. Less common: Polonium forms a sulfate Po(SO4)2. It has been suggested that the astatine cation forms a weak complex with sulfate ions in acidic solutions.
- Hydrogen forms hydrogen sulfate H2SO4. Carbon forms (a blue) graphite hydrogen sulfate C+
4 • 2.4H2SO4. Nitrogen forms nitrosyl hydrogen sulfate (NO)HSO4 and nitronium (or nitryl) hydrogen sulfate (NO2)HSO4. There are indications of a basic sulfate of selenium SeO2.SO3 or SeO(SO4). Iodine forms a polymeric yellow sulfate (IO)2SO4.
- layer-lattice types often reversibly so
- Based on a table of the elemental composition of the biosphere, and lithosphere (crust, atmosphere, and seawater) in Georgievskii, and the masses of the crust and hydrosphere give in Lide and Frederikse. The mass of the biosphere is negligible, having a mass of about one billionth that of the lithosphere. "The oceans constitute about 98 percent of the hydrosphere, and thus the average composition of the hydrosphere is, for all practical purposes, that of seawater."
- Hydrogen gas is produced by some bacteria and algae and is a natural component of flatus. It can be found in the Earth's atmosphere at a concentration of 1 part per million by volume.
- Fluorine can be found in its elemental form, as an occlusion in the mineral antozonite
- In 1934, a team led by Enrico Fermi postulated that transuranic elements may have been produced as a result of bombarding uranium with neutrons, a finding which was widely accepted for a few years. In the same year Ida Noddack, a German scientist and subsequently a three-time Nobel prize nominee, criticised this assumption, writing "It is conceivable that the nucleus breaks up into several large fragments, which would of course be isotopes of known elements but would not be neighbors of the irradiated element."[emphasis added] In this, Noddak defied the understanding of the time without offering experimental proof or theoretical basis, but nevertheless presaged what would be known a few years later as nuclear fission. Her paper was generally ignored as, in 1925, she and two colleagues claimed to have discovered element 43, then proposed to be called masurium (later discovered in 1936 by Perrier and Segrè, and named technetium). Had Ida Noddack's paper been accepted it is likely that Germany would have had an atomic bomb and, 'the history of the world would have been [very] different.'
- Mendeléeff 1897, p. 274
- Brinkley 1945, p. 378
- Glinka 1965, p. 88
- Eby et al. 1943, p. 404
- Booth & Bloom 1972, p. 426
- Cox 2004, p. 27
- Huheey, Keiter & Keiter 1993, p. 28
- Kneen, Rogers & Simpson, 1972, p. 263. Columns 2 (metals) and 4 (nonmetals) are sourced from this reference unless otherwise indicated.
- Russell & Lee 2005, p. 147
- Rochow 1966, p. 4
- Pottenger & Bowes 1976, p. 138
- Askeland, Fulay & Wright 2011, p. 806
- Born & Wolf 1999, p. 746
- Lagrenaudie 1953
- Rochow 1966, pp. 23, 25
- Burakowski & Wierzchoń 1999, p. 336
- Olechna & Knox 1965, pp. A991‒92
- Stoker 2010, p. 62
- Chang 2002, p. 304. Chang speculates that the melting point of francium would be about 23 °C.
- New Scientist 1975; Soverna 2004; Eichler, Aksenov & Belozeroz et al. 2007; Austen 2012
- Hunt 2000, p. 256
- Sisler 1973, p. 89
- Hérold 2006, pp. 149–150
- Russell & Lee 2005
- Legit, Friák & Šob 2010, p. 214118-18
- Manson & Halford 2006, pp. 378, 410
- McQuarrie & Rock 1987, p. 85
- Chung 1987; Godfrin & Lauter 1995
- Cambridge Enterprise 2013
- Faraday 1853, p. 42; Holderness & Berry 1979, p. 255
- Partington 1944, p. 405
- Regnault 1853, p. 208
- Christensen 2012, p. 14
- Gschneidner 1964, pp. 292‒93.
- Qin et al. 2012, p. 258
- Hopcroft, Nix & Kenny 2010, p. 236
- Greaves et al. 2011, p. 826
- Brassington et al. 1980
- Martienssen & Warlimont 2005, p. 100
- Witczak 2000, p. 823
- Marlowe 1970, p. 6;Slyh 1955, p. 146
- Klein & Cardinale 1992, pp. 184‒85
- Appalakondaiah et al. 2012, pp. 035105‒6
- Sundara Rao 1950; Sundara Rao 1954; Ravindran 1998, pp. 4897‒98
- Lindegaard & Dahle 1966, p. 264
- Leith 1966, pp. 38‒39
- Donohoe 1982; Russell & Lee 2005
- Gupta et al. 2005, p. 502
- Walker, Newman & Enache 2013, p. 25
- Wiberg 2001, p. 143
- Batsanov & Batsanov 2012, p. 275
- Clementi & Raimondi 1963; Clementi, Raimondi & Reinhardt 1967
- Addison 1964; Donohoe 1982
- Vernon 2013, p. 1704
- Parish 1977, pp. 34, 48, 112, 142, 156, 178
- Emsley 2001, p. 12
- Russell 1981, p. 628
- Herzfeld 1927; Edwards 2000, pp. 100–103
- Edwards 1999, p. 416
- Edwards & Sienko 1983, p. 695
- Edwards & Sienko 1983, p. 691
- Edwards et al. 2010
- Desai, James & Ho 1984, p. 1160; Matula 1979, p. 1260
- Choppin & Johnsen 1972, p. 351
- Schaefer 1968, p. 76; Carapella 1968, p. 30
- Glazov, Chizhevskaya & Glagoleva 1969 p. 86
- Kozyrev 1959, p. 104
- Chizhikov & Shchastlivyi 1968, p. 25
- Bogoroditskii & Pasynkov 1967, p. 77; Jenkins & Kawamura 1976, p. 88
- Rao & Ganguly 1986
- Mott & Davis 2012, p. 177
- Anita 1998
- Cverna 2002, p.1
- Cordes & Scaheffer 1973, p. 79
- Hill & Holman 2000, p. 42
- Tilley 2004, p. 487
- Russell & Lee 2005, p. 466
- Orton 2004, pp. 11–12
- Zhigal'skii & Jones 2003, p. 66: 'Bismuth, antimony, arsenic and graphite are considered to be semimetals ... In bulk semimetals ... the resistivity will increase with temperature ... to give a positive temperature coefficient of resistivity ...'
- Jauncey 1948, p. 500: 'Nonmetals mostly have negative temperature coefficients. For instance, carbon ... [has a] resistance [that] decreases with a rise in temperature. However, recent experiments on very pure graphite, which is a form of carbon, have shown that pure carbon in this form behaves similarly to metals in regard to its resistance.'
- Reynolds 1969, pp. 91–92
- Wilson 1966, p. 260
- Wittenberg 1972, p. 4526
- Habashi 2003, p. 73
- Bailar et al. 1989, p. 742
- Hiller & Herber 1960, inside front cover; p. 225
- Beveridge et al. 1997, p. 185
- Young & Sessine 2000, p. 849
- Bailar et al. 1989, p. 417
- Metcalfe, Williams & Castka 1966, p. 72
- Chang 1994, p. 311
- Pauling 1988, p. 183
- Mann et al. 2000, p. 2783
- Chedd 1969, pp. 24–25
- Adler 1969, pp. 18–19
- Hultgren 1966, p. 648
- Bassett et al. 1966, p. 602
- Rochow 1966, p. 34
- Martienssen & Warlimont 2005, p. 257
- Sidorov 1960
- Brasted 1974, p. 814
- Atkins 2006 et al., pp. 8, 122–23
- Rao 2002, p. 22
- Wickleder, Pley & Büchner 2006; Betke & Wickleder 2011
- Cotton 1994, p. 3606
- Keogh 2005, p. 16
- Raub & Griffith 1980, p. 167
- Nemodruk & Karalova 1969, p. 48
- Sneed 1954, p. 472; Gillespie & Robinson 1959, p. 407
- Zuckerman & Hagen 1991, p. 303
- Sanderson 1967, p. 178
- Iler 1979, p. 190
- Sanderson 1960, p. 162; Greenwood & Earnshaw 2002, p. 387
- Mercier & Douglade 1982
- Douglade & Mercier 1982
- Wiberg 2001, p. 764
- Wickleder 2007, p. 350
- Bagnall 1966, pp. 140−41
- Berei & Vasáros 1985, pp. 221, 229
- Wiberg 2001, p. 795
- Lidin 1996, pp. 266, 270; Brescia et al. 1975, p. 453
- Greenwood & Earnshaw 2002, p. 786
- Furuseth et al. 1974
- Holtzclaw, Robinson & Odom 1991, pp. 706–07; Keenan, Kleinfelter & Wood 1980, pp. 693–95
- Kneen, Rogers & Simpson 1972, p. 278
- Heslop & Robinson 1963, p. 417
- Rochow 1966, pp. 28–29
- Bagnall 1966, pp. 108, 120; Lidin 1996, passim
- Smith 1921, p. 295; Sidgwick 1950, pp. 605, 608; Dunstan 1968, pp. 408, 438
- Dunstan 1968, pp. 312, 408
- Georgievskii 1982, p. 58
- Lide & Frederikse 1998, p. 14–6
- Hem 1985, p. 7
- Perkins 1998, p. 350
- Sanderson 2012
- Brown et al. 2009, p. 137
- Bresica et al. 1975, p. 137
- Jansen 2005
- Russell & Lee 2005, p. 246
- Russell & Lee 2005, p. 244–5
- Donohoe 1982, pp. 191–196; Russell & Lee 2005, pp. 244–247
- Jackson 2000
- Stoye 2014
- Witt 1991; Endicott 1998
- Dumé 2003
- Benedict et al. 1946, p. 19
- Noddack 1934, p. 653
- Sacks 2001, p. 205: 'This story was told by Glenn Seaborg when he was presenting his recollections at a conference in November 1997.'
- Dalhouse University 2015; White et al. 2015
- DuPlessis 2007, p. 133
- Gösele & Lehmann 1994, p. 19
- Chen, Lee & Bosman 1994
- Kovalev et al. 2001, p. 068301-1
- Mikulec, Kirtland & Sailor 2002
- Bychkov 2012, pp. 20–21; see also Lazaruk et al. 2007
- Slezak 2014
- Wiberg 2001, p. 758; see also Fraden 1951
- Sacks 2001, p. 204
- Sacks 2001, pp. 204–205
- Cerkovnik & Plesničar 2013, p. 7930
- Emsley 1994, p. 1910
- Wiberg 2001, p. 497
- Cross, Saunders & Prinzbach; Chemistry Views 2015
- Sun, Xu & Gao 2013; Anthony 2013
- Nakao 1992
- Addison WE 1964, The allotropy of the elements, Oldbourne Press, London
- Adler D 1969, 'Half-way elements: The technology of metalloids', book review, Technology Review, vol. 72, no. 1, Oct/Nov, pp. 18–19
- Anita M 1998, 'Focus: Levitating Liquid Boron', American Physical Society, viewed 14 December 2014
- Anthony S 2013, 'Graphene aerogel is seven times lighter than air, can balance on a blade of grass', ExtremeTech, April 10, accessed 8 February 2015
- Appalakondaiah S, Vaitheeswaran G, Lebègue S, Christensen NE & Svane A 2012, 'Effect of van der Waals interactions on the structural and elastic properties of black phosphorus,' Physical Review B, vol. 86, pp. 035105‒1 to 9, doi:10.1103/PhysRevB.86.035105
- Askeland DR, Fulay PP & Wright JW 2011, The science and engineering of materials, 6th ed., Cengage Learning, Stamford, CT, ISBN 0-495-66802-8
- Atkins P, Overton T, Rourke J, Weller M & Armstrong F 2006, Shriver & Atkins' inorganic chemistry, 4th ed., Oxford University Press, Oxford, ISBN 0-7167-4878-9
- Austen K 2012, 'A factory for elements that barely exist', NewScientist, 21 Apr, p. 12, ISSN 1032-1233
- Bagnall KW 1966, The chemistry of selenium, tellurium and polonium, Elsevier, Amsterdam
- Bailar JC, Moeller T, Kleinberg J, Guss CO, Castellion ME & Metz C 1989, Chemistry, 3rd ed., Harcourt Brace Jovanovich, San Diego, ISBN 0-15-506456-8
- Bassett LG, Bunce SC, Carter AE, Clark HM & Hollinger HB 1966, Principles of chemistry, Prentice-Hall, Englewood Cliffs, NJ
- Batsanov SS & Batsanov AS 2012, Introduction to structural chemistry, Springer Science+Business Media, Dordrecht, ISBN 978-94-007-4770-8
- Benedict M, Alvarez LW, Bliss LA, English SG, Kinzell AB, Morrison P, English FH, Starr C & Williams WJ 1946, 'Technological control of atomic energy activities', "Bulletin of the Atomic Scientists," vol. 2, no. 11, pp. 18–29
- Dumé, Belle (23 April 2003). "Bismuth breaks half-life record for alpha decay". Physicsworld.
- Berei K & Vasáros L 1985, 'Astatine compounds', in Kugler & Keller
- Betke U & Wickleder MS 2011, 'Sulfates of the refractory metals: Crystal structure and thermal behavior of Nb2O2(SO4)3, MoO2(SO4), WO(SO4)2, and two modifications of Re2O5(SO4)2', Inorganic chemistry, vol. 50, no. 3, pp 858–872, doi:10.1021/ic101455z
- Beveridge TJ, Hughes MN, Lee H, Leung KT, Poole RK, Savvaidis I, Silver S & Trevors JT 1997, 'Metal–microbe interactions: Contemporary approaches', in RK Poole (ed.), Advances in microbial physiology, vol. 38, Academic Press, San Diego, pp. 177–243, ISBN 0-12-027738-7
- Bogoroditskii NP & Pasynkov VV 1967, Radio and electronic materials, Iliffe Books, London
- Booth VH & Bloom ML 1972, Physical science: a study of matter and energy, Macmillan, New York
- Born M & Wolf E 1999, Principles of optics: Electromagnetic theory of propagation, interference and diffraction of light, 7th ed., Cambridge University Press, Cambridge, ISBN 0-521-64222-1
- Brassington MP, Lambson WA, Miller AJ, Saunders GA & Yogurtçu YK 1980, 'The second- and third-order elastic constants of amorphous arsenic', Philosophical Magazine Part B, vol. 42, no. 1., pp. 127–148, doi:10.1080/01418638008225644
- Brasted RC 1974, 'Oxygen group elements and their compounds', in The new Encyclopædia Britannica, vol. 13, Encyclopædia Britannica, Chicago, pp. 809–824
- Brescia F, Arents J, Meislich H & Turk A 1975, Fundamentals of chemistry, 3rd ed., Academic Press, New York, p. 453, ISBN 978-0-12-132372-1
- Brinkley SR 1945, Introductory general chemistry, 3rd ed., Macmillan, New York
- Brown TL, LeMay HE, Bursten BE, Murphy CJ & Woodward P 2009, Chemistry: The Central Science, 11th ed., Pearson Education, New Jersey, ISBN 978-0-13-235-848-4
- Burakowski T & Wierzchoń T 1999, Surface engineering of metals: Principles, equipment, technologies, CRC Press, Boca Raton, Fla, ISBN 0-8493-8225-4
- Bychkov VL 2012, 'Unsolved Mystery of Ball Lightning', in Atomic Processes in Basic and Applied Physics, V Shevelko & H Tawara (eds), Springer Science & Business Media, Heidelberg, pp. 3–24, ISBN 978-3-642-25568-7
- Carapella SC 1968a, 'Arsenic' in CA Hampel (ed.), The encyclopedia of the chemical elements, Reinhold, New York, pp. 29–32
- Cerkovnik J & Plesničar B 2013, 'Recent Advances in the Chemistry of Hydrogen Trioxide (HOOOH), Chemical Reviews, vol. 113, no. 10), pp. 7930–7951, doi:10.1021/cr300512s
- Chang R 1994, Chemistry, 5th (international) ed., McGraw-Hill, New York
- Chang R 2002, Chemistry, 7th ed., McGraw Hill, Boston
- Chedd G 1969, Half-way elements: The technology of metalloids, Doubleday, New York
- Chen Z, Lee T-Y & Bosman G 1994, 'Electrical Band Gap of Porous Silicon', Applied Physics Letters, vol. 64, p. 3446, doi:10.1063/1.111237
- Chizhikov DM & Shchastlivyi VP 1968, Selenium and selenides, translated from the Russian by EM Elkin, Collet's, London
- Choppin GR & Johnsen RH 1972, Introductory chemistry, Addison-Wesley, Reading, Massachusetts
- Christensen RM 2012, 'Are the elements ductile or brittle: A nanoscale evaluation,' in Failure theory for materials science and engineering, chapter 12, p. 14
- Clementi E & Raimondi DL 1963, Atomic Screening Constants from SCF Functions, Journal of Chemical Physics, vol. 38, pp. 2868–2689, doi:10.1063/1.1733573
- Clementi E, Raimondi DL & Reinhardt WP 1967, 'Atomic Screening Constants from SCF Functions. II. Atoms with 37 to 86 Electrons', Journal of Chemical Physics, vol. 47, pp. 1300–1306, doi:10.1063/1.1712084
- Cordes EH & Scaheffer R 1973, Chemistry, Harper & Row, New York
- Cotton SA 1994, 'Scandium, yttrium & the lanthanides: Inorganic & coordination chemistry', in RB King (ed.), Encyclopedia of inorganic chemistry, 2nd ed., vol. 7, John Wiley & Sons, New York, pp. 3595–3616, ISBN 978-0-470-86078-6
- Cox PA 2004, Inorganic chemistry, 2nd ed., Instant notes series, Bios Scientific, London, ISBN 1-85996-289-0
- Cross RJ, Saunders M & Prinzbach H 1999, 'Putting Helium Inside Dodecahedrane', Organic Letters, vol. 1, no. 9, pp. 1479–1481, doi:10.1021/ol991037v
- Cverna F 2002, ASM ready reference: Thermal properties of metals, ASM International, Materials Park, Ohio, ISBN 0-87170-768-3
- Dalhouse University 2015, 'Dal chemist discovers new information about elemental boron', media release, 28 January, accessed 9 May 2015
- Deming HG 1952, General chemistry: An elementary survey, 6th ed., John Wiley & Sons, New York
- Desai PD, James HM & Ho CY 1984, Electrical resistivity of aluminum and manganese, Journal of Physical and Chemical Reference Data, vol. 13, no. 4, pp. 1131–1172, doi:10.1063/1.555725
- Donohoe J 1982, The Structures of the Elements, Robert E. Krieger, Malabar, Florida, ISBN 0-89874-230-7
- Douglade J & Mercier R 1982, 'Structure cristalline et covalence des liaisons dans le sulfate d'arsenic(III), As2(SO4)3', Acta Crystallographica Section B, vol. 38, no. 3, pp. 720–723, doi:10.1107/S056774088200394X
- Dunstan S 1968, Principles of chemistry, D. Van Nostrand Company, London
- Du Plessis M 2007, 'A Gravimetric Technique to Determine the Crystallite Size Distribution in High Porosity Nanoporous Silicon, in JA Martino, MA Pavanello & C Claeys (eds), Microelectronics Technology and Devices–SBMICRO 2007, vol. 9, no. 1, The Electrochemical Society, New Jersey, pp. 133–142, ISBN 978-1-56677-565-6
- Eby GS, Waugh CL, Welch HE & Buckingham BH 1943, The physical sciences, Ginn and Company, Boston
- Edwards PP & Sienko MJ 1983, 'On the occurrence of metallic character in the periodic table of the elements', Journal of Chemical Education, vol. 60, no. 9, pp. 691–696, doi:10.1021/ed060p691
- Edwards PP 1999, 'Chemically engineering the metallic, insulating and superconducting state of matter' in KR Seddon & M Zaworotko (eds), Crystal engineering: The design and application of functional solids, Kluwer Academic, Dordrecht, pp. 409–431
- Edwards PP 2000, 'What, why and when is a metal?', in N Hall (ed.), The new chemistry, Cambridge University, Cambridge, pp. 85–114
- Edwards PP, Lodge MTJ, Hensel F & Redmer R 2010, '...a metal conducts and a non-metal doesn't', Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, vol. 368, pp. 941–965, doi:10.1098rsta.2009.0282
- Eichler R, Aksenov NV, Belozerov AV, Bozhikov GA, Chepigin VI, Dmitriev SN, Dressler R, Gäggeler HW, Gorshkov VA, Haenssler F, Itkis MG, Laube A, Lebedev VY, Malyshev ON, Oganessian YT, Petrushkin OV, Piguet D, Rasmussen P, Shishkin SV, Shutov, AV, Svirikhin AI, Tereshatov EE, Vostokin GK, Wegrzecki M & Yeremin AV 2007, 'Chemical characterization of element 112,' Nature, vol. 447, pp. 72–75, doi:10.1038/nature05761
- Endicott K 1998, 'The Trembling Edge of Science', Dartmouth Alumini Magazine, April, accessed 8 May 2015
- Emsley 1994, 'Science: Surprise legacy of Germany's Flying Bombs', New Scientist, no. 1910, January 29
- Emsley J 2001, Nature's building blocks: An A–Z guide to the elements, ISBN 0-19-850341-5
- Fraden JH 1951, 'Amorphous antimony. A lecture demonstration in allotropy', Journal of Chemical Education, vol. 28, no. 1, pp. 34–35, doi:10.1021/ed028p34 10.1021/ed028p34
- Furuseth S, Selte K, Hope H, Kjekshus A & Klewe B 1974, 'Iodine oxides. Part V. The crystal structure of (IO)2SO4', Acta Chemica Scandinavica A, vol. 28, pp. 71–76, doi:10.3891/acta.chem.scand.28a-0071
- Georgievskii VI 1982, 'Biochemical regions. Mineral composition of feeds', in VI Georgievskii, BN Annenkov & VT Samokhin (eds), Mineral nutrition of animals: Studies in the agricultural and food sciences, Butterworths, London, pp. 57–68, ISBN 0-408-10770-7
- Gillespie RJ & Robinson EA 1959, 'The sulphuric acid solvent system', in HJ Emeléus & AG Sharpe (eds), Advances in inorganic chemistry and radiochemistry, vol. 1, Academic Press, New York, pp. 386–424
- Glazov VM, Chizhevskaya SN & Glagoleva NN 1969, Liquid semiconductors, Plenum, New York
- Glinka N 1965, General chemistry, trans. D Sobolev, Gordon & Breach, New York
- Gösele U & Lehmann V 1994, 'Porous Silicon Quantum Sponge Structures: Formation Mechanism, Preparation Methods and Some Properties', in Feng ZC & Tsu R (eds), Porous Silicon, World Scientific, Singapore, pp. 17–40, ISBN 981-02-1634-3
- Greaves GN, Greer AL, Lakes RS & Rouxel T 2011, 'Poisson's ratio and modern materials', Nature Materials, vol. 10, pp. 823‒837, doi:10.1038/NMAT3134
- Greenwood NN & Earnshaw A 2002, Chemistry of the elements, 2nd ed., Butterworth-Heinemann, ISBN 0-7506-3365-4
- Gschneidner KA 1964, 'Physical properties and interrelationships of metallic and semimetallic elements,' Solid State Physics, vol. 16, pp. 275‒426, doi:10.1016/S0081-1947(08)60518-4
- Gupta A, Awana VPS, Samanta SB, Kishan H & Narlikar AV 2005, 'Disordered superconductors' in AV Narlikar (ed.), Frontiers in superconducting materials, Springer-Verlag, Berlin, p. 502, ISBN 3-540-24513-8
- Habashi F 2003, Metals from ores: an introduction to extractive metallurgy, Métallurgie Extractive Québec, Sainte Foy, Québec, ISBN 2-922686-04-3
- Manson SS & Halford GR 2006, Fatigue and Durability of Structural Materials, ASM International, Materials Park, OH, ISBN 0-87170-825-6
- Hem JD 1985, Study and interpretation of the chemical characteristics of natural water, paper 2254, 3rd ed., US Geological Society, Alexandria, Virginia
- Hampel CA & Hawley GG 1976, Glossary of chemical terms, Van Nostrand Reinhold, New York
- Hérold A 2006, 'An arrangement of the chemical elements in several classes inside the periodic table according to their common properties', Comptes Rendus Chimie, vol. 9, pp. 148–153, doi:10.1016/j.crci.2005.10.002
- Herzfeld K 1927, 'On atomic properties which make an element a metal', Phys. Rev., vol. 29, no. 5, pp. 701–705, doi:10.1103PhysRev.29.701
- Heslop RB & Robinson PL 1963, Inorganic chemistry: A guide to advanced study, Elsevier, Amsterdam
- Hill G & Holman J 2000, Chemistry in context, 5th ed., Nelson Thornes, Cheltenham, ISBN 0-17-448307-4
- Hiller LA & Herber RH 1960, Principles of chemistry, McGraw-Hill, New York
- Holtzclaw HF, Robinson WR & Odom JD 1991, General chemistry, 9th ed., DC Heath, Lexington, ISBN 0-669-24429-5
- Hopcroft MA, Nix WD & Kenny TW 2010, 'What is the Young's modulus of silicon?', Journal of Microelectromechanical Systems, vol. 19, no. 2, pp. 229‒238, doi:10.1109/JMEMS.2009.2039697
- Chemistry Views 2012, 'Horst Prinzbach (1931 – 2012)', Wiley-VCH, accessed 28 February 2015
- Huheey JE, Keiter EA & Keiter RL 1993, Principles of Structure & Reactivity, 4th ed., HarperCollins College Publishers, ISBN 0-06-042995-X
- Hultgren HH 1966, 'Metalloids', in GL Clark & GG Hawley (eds), The encyclopedia of inorganic chemistry, 2nd ed., Reinhold Publishing, New York
- Hunt A 2000, The complete A-Z chemistry handbook, 2nd ed., Hodder & Stoughton, London
- Iler RK 1979, The chemistry of silica: solubility, polymerization, colloid and surface properties, and biochemistry, John Wiley, New York, ISBN 978-0-471-02404-0
- Jackson, Mike (2000). "Wherefore Gadolinium? Magnetism of the Rare Earths" (PDF). IRM Quarterly. Institute for Rock Magnetism. 10 (3): 6.
- Jansen, Martin (2005-11-30). "Effects of relativistic motion of electrons on the chemistry of gold and platinum". Solid State Sciences. 7 (12): 1464–1474. Bibcode:2005SSSci...7.1464J. doi:10.1016/j.solidstatesciences.2005.06.015.
- Jauncey GEM 1948, Modern physics: A second course in college physics, D. Von Nostrand, New York
- Jenkins GM & Kawamura K 1976, Polymeric carbons—carbon fibre, glass and char, Cambridge University Press, Cambridge
- Keenan CW, Kleinfelter DC & Wood JH 1980, General college chemistry, 6th ed., Harper & Row, San Francisco, ISBN 0-06-043615-8
- Keogh DW 2005, 'Actinides: Inorganic & coordination chemistry', in RB King (ed.), Encyclopedia of inorganic chemistry, 2nd ed., vol. 1, John Wiley & Sons, New York, pp. 2–32, ISBN 978-0-470-86078-6
- Klein CA & Cardinale GF 1992, 'Young's modulus and Poisson's ratio of CVD diamond', in A Feldman & S Holly, SPIE Proceedings, vol. 1759, Diamond Optics V, pp. 178‒192, doi:10.1117/12.130771
- Kneen WR, Rogers MJW & Simpson P 1972, Chemistry: Facts, patterns, and principles, Addison-Wesley, London
- Kovalev D, Timoshenko VY, Künzner N, Gross E & Koch F 2001, 'Strong Explosive Interaction of Hydrogenated Porous Silicon with Oxygen at Cryogenic Temperatures', Physical Review Letters, vol. 87, pp. 068301–1–06831-4, doi:10.1103/PhysRevLett.87.068301
- Kozyrev PT 1959, 'Deoxidized selenium and the dependence of its electrical conductivity on pressure. II', Physics of the solid state, translation of the journal Solid State Physics (Fizika tverdogo tela) of the Academy of Sciences of the USSR, vol. 1, pp. 102–110
- Kugler HK & Keller C (eds) 1985, Gmelin Handbook of Inorganic and Organometallic chemistry, 8th ed., 'At, Astatine', system no. 8a, Springer-Verlag, Berlin, ISBN 3-540-93516-9
- Lagrenaudie J 1953, 'Semiconductive properties of boron' (in French), Journal de chimie physique, vol. 50, nos. 11–12, Nov-Dec, pp. 629–633
- Lazaruk SK, Dolbik AV, Labunov VA & Borisenko VE 2007, 'Combustion and Explosion of Nanostructured Silicon in Microsystem Devices', Semiconductors, vol. 41, no. 9, pp. 1113–1116, doi:10.1134/S1063782607090175
- Legit D, Friák M & Šob M 2010, 'Phase Stability, Elasticity, and Theoretical Strength of Polonium from First Principles,' Physical Review B, vol. 81, pp. 214118–1–19, doi:10.1103/PhysRevB.81.214118
- Leith MM 1966, Velocity of sound in solid iodine, MSc thesis, University of British Coloumbia. Leith comments that, '... as iodine is anisotropic in many of its physical properties most attention was paid to two amorphous samples which were thought to give representative average values of the properties of iodine' (p. iii).
- Lide DR & Frederikse HPR (eds) 1998, CRC Handbook of chemistry and physics, 79th ed., CRC Press, Boca Raton, Florida, ISBN 0-849-30479-2
- Lidin RA 1996, Inorganic substances handbook, Begell House, New York, ISBN 1-56700-065-7
- Lindegaard AL and Dahle B 1966, 'Fracture phenomena in amorphous selenium', Journal of Applied Physics, vol. 37, no. 1, pp. 262‒66, doi:10.1063/1.1707823
- Mann JB, Meek TL & Allen LC 2000, 'Configuration energies of the main group elements', Journal of the American Chemical Society, vol. 122, no. 12, pp. 2780–2783, doi:10.1021ja992866e
- Marlowe MO 1970, Elastic properties of three grades of fine grained graphite to 2000°C, NASA CR‒66933, National Aeronautics and Space Administration, Scientific and Technical Information Facility, College Park, Maryland
- Martienssen W & Warlimont H (eds) 2005, Springer Handbook of Condensed Matter and Materials Data, Springer, Heidelberg, ISBN 3-540-30437-1
- Matula RA 1979, 'Electrical resistivity of copper, gold, palladium, and silver,' Journal of Physical and Chemical Reference Data, vol. 8, no. 4, pp. 1147–1298, doi:10.1063/1.555614
- McQuarrie DA & Rock PA 1987, General chemistry, 3rd ed., WH Freeman, New York
- Mendeléeff DI 1897, The Principles of Chemistry, vol. 2, 5th ed., trans. G Kamensky, AJ Greenaway (ed.), Longmans, Green & Co., London
- Mercier R & Douglade J 1982, 'Structure cristalline d'un oxysulfate d'arsenic(III) As2O(SO4)2 (ou As2O3.2SO3)', Acta Crystallographica Section B, vol. 38, no. 3, pp. 1731–1735, doi:10.1107/S0567740882007055
- Metcalfe HC, Williams JE & Castka JF 1966, Modern chemistry, 3rd ed., Holt, Rinehart and Winston, New York
- Mikulec FV, Kirtland JD & Sailor MJ 2002, 'Explosive Nanocrystalline Porous Silicon and Its Use in Atomic Emission Spectroscopy', Advanced Materials, vol. 14, no. 1, pp. 38–41, doi:<38::AID-ADMA38>3.0.CO;2-Z 10.1002/1521-4095(20020104)14:1<38::AID-ADMA38>3.0.CO;2-Z
- Moss TS 1952, Photoconductivity in the Elements, London, Butterworths
- Mott NF & Davis EA 2012, 'Electronic Processes in Non-Crystalline Materials', 2nd ed., Oxford University Press, Oxford, ISBN 978-0-19-964533-6
- Nakao Y 1992, 'Dissolution of Noble Metals in Halogen-Halide-Polar Organic Solvent Systems', Journal of the Chemical Society, Chemical Communications, no. 5, pp. 426–427, doi:10.1039/C39920000426
- Nemodruk AA & Karalova ZK 1969, Analytical chemistry of boron, R Kondor trans., Ann Arbor Humphrey Science, Ann Arbor, Michigan
- New Scientist 1975, 'Chemistry on the islands of stability', 11 Sep, p. 574, ISSN 1032-1233
- Noddack I 1934, 'On element 93', Angewandte Chemie, vol. 47, no. 37, pp. 653–655, doi:10.1002/ange.19340473707
- Olechna DJ & Knox RS 1965, 'Energy-band structure of selenium chains', Physical Review, vol. 140, pp. A986‒A993, doi:10.1103/PhysRev.140.A986
- Orton JW 2004, The story of semiconductors, Oxford University, Oxford, ISBN 0-19-853083-8
- Parish RV 1977, The metallic elements, Longman, London
- Partington JR 1944, A text-book of inorganic chemistry, 5th ed., Macmillan & Co., London
- Pauling L 1988, General chemistry, Dover Publications, NY, ISBN 0-486-65622-5
- Perkins D 1998, Mineralogy, Prentice Hall Books, Upper Saddle River, New Jersey, ISBN 0-02-394501-X
- Pottenger FM & Bowes EE 1976, Fundamentals of chemistry, Scott, Foresman and Co., Glenview, Illinois
- Qin J, Nishiyama N, Ohfuji H, Shinmei T, Lei L, Heb D & Irifune T 2012, 'Polycrystalline γ-boron: As hard as polycrystalline cubic boron nitride', Scripta Materialia, vol. 67, pp. 257‒260, doi:10.1016/j.scriptamat.2012.04.032
- Rao CNR & Ganguly P 1986, 'A new criterion for the metallicity of elements', Solid State Communications, vol. 57, no. 1, pp. 5–6, doi:10.1016/0038-1098(86)90659-9
- Rao KY 2002, Structural chemistry of glasses, Elsevier, Oxford, ISBN 0-08-043958-6
- Raub CJ & Griffith WP 1980, 'Osmium and sulphur', in Gmelin handbook of inorganic chemistry, 8th ed., 'Os, Osmium: Supplement,' K Swars (ed.), system no. 66, Springer-Verlag, Berlin, pp. 166–170, ISBN 3-540-93420-0
- Ravindran P, Fast L, Korzhavyi PA, Johansson B, Wills J & Eriksson O 1998, 'Density functional theory for calculation of elastic properties of orthorhombic crystals: Application to TiSi2', Journal of Applied Physics, vol. 84, no. 9, pp. 4891‒4904, doi:10.1063/1.368733
- Reynolds WN 1969, Physical properties of graphite, Elsevier, Amsterdam
- Rochow EG 1966, The metalloids, DC Heath and Company, Boston
- Rock PA & Gerhold GA 1974, Chemistry: Principles and applications, WB Saunders, Philadelphia
- Russell JB 1981, General chemistry, McGraw-Hill, Auckland
- Russell AM & Lee KL 2005, Structure-property relations in nonferrous metals, Wiley-Interscience, New York, ISBN 0-471-64952-X
- Sacks O 2001, Uncle Tungsten: Memories of a chemical boyhood, Alfred A Knopf, New York, ISBN 0-375-40448-1
- Sanderson RT 1960, Chemical periodicity, Reinhold Publishing, New York
- Sanderson RT 1967, Inorganic chemistry, Reinhold, New York
- Sanderson K 2012, 'Stinky rocks hide Earth's only haven for natural fluorine', Nature News, July, doi:10.1038/nature.2012.10992
- Schaefer JC 1968, 'Boron' in CA Hampel (ed.), The encyclopedia of the chemical elements, Reinhold, New York, pp. 73–81
- Sidgwick NV 1950, The chemical elements and their compounds, vol. 1, Clarendon, Oxford
- Sidorov TA 1960, 'The connection between structural oxides and their tendency to glass formation', Glass and Ceramics, vol. 17, no. 11, pp. 599–603, doi:10.1007BF00670116
- Sisler HH 1973, Electronic structure, properties, and the periodic law, Van Nostrand, New York
- Slezak 2014, 'Natural ball lightning probed for the first time', New Scientist, 16 January
- Slough W 1972, 'Discussion of session 2b: Crystal structure and bond mechanism of metallic compounds', in O Kubaschewski (ed.), Metallurgical chemistry, proceedings of a symposium held at Brunel University and the National Physical Laboratory on the 14, 15 and 16 July 1971, Her Majesty's Stationery Office [for the] National Physical Laboratory, London
- Slyh JA 1955, 'Graphite', in JF Hogerton & RC Grass (eds), Reactor handbook: Materials, US Atomic Energy Commission, McGraw Hill, New York, pp. 133‒154
- Smith A 1921, General chemistry for colleges, 2nd ed., Century, New York
- Sneed MC 1954, General college chemistry, Van Nostrand, New York
- Sommer AH, ‘Alloys of Gold with alkali metals’, Nature, vol. 152, p. 215, doi:10.1038/152215a0
- Soverna S 2004, 'Indication for a gaseous element 112,' in U Grundinger (ed.), GSI Scientific Report 2003, GSI Report 2004-1, p. 187, ISSN 0174-0814
- Stoker HS 2010, General, organic, and biological chemistry, 5th ed., Brooks/Cole, Cengage Learning, Belmont CA, ISBN 0-495-83146-8
- Stoye E 2014, 'Iridium forms compound in +9 oxidation state', Chemistry World, 23 October
- Sun H, Xu Z & Gao C 2013, 'Multifunctional, Ultra-Flyweight, Synergistically Assembled Carbon Aerogels', Advanced Materials,, vol. 25, no. 18, pp. 2554–2560, doi:10.1002/adma.201204576
- Sundara Rao RVG 1950, 'Elastic constants of orthorhombic sulphur,' Proceedings of the Indian Academy of Sciences - Section A, vol. 32, no. 4, pp. 275–278, doi:10.1007/BF03170831
- Sundara Rao RVG 1954, 'Erratum to: Elastic constants of orthorhombic sulphur', Proceedings of the Indian Academy of Sciences - Section A, vol. 40, no. 3, p. 151
- Swalin RA 1962, Thermodynamics of solids, John Wiley & Sons, New York
- Tilley RJD 2004, Understanding solids: The science of materials, 4th ed., John Wiley, New York
- Walker JD, Newman MC & Enache M 2013, Fundamental QSARs for metal ions, CRC Press, Boca Raton, ISBN 978-1-4200-8434-4
- White MA, Cerqueira AB, Whitman CA, Johnson MB & Ogitsu T 2015, 'Determination of Phase Stability of Elemental Boron', Angewandte Chemie International Edition, doi:10.1002/anie.201409169
- Wiberg N 2001, Inorganic chemistry, Academic Press, San Diego, ISBN 0-12-352651-5
- Wickleder MS, Pley M & Büchner O 2006, 'Sulfates of precious metals: Fascinating chemistry of potential materials', Zeitschrift für anorganische und allgemeine chemie, vol. 632, nos. 12–13, p. 2080, doi:10.1002/zaac.200670009
- Wickleder MS 2007, 'Chalcogen-oxygen chemistry', in FA Devillanova (ed.), Handbook of chalcogen chemistry: new perspectives in sulfur, selenium and tellurium, RSC, Cambridge, pp. 344–377, ISBN 978-0-85404-366-8
- Wilson JR 1965, 'The structure of liquid metals and alloys', Metallurgical reviews, vol. 10, p. 502
- Wilson AH 1966, Thermodynamics and statistical mechanics, Cambridge University, Cambridge
- Witczak Z, Goncharova VA & Witczak PP 2000, 'Irreversible effect of hydrostatic pressure on the elastic properties of polycrystalline tellurium', in MH Manghnani, WJ Nellis & MF Nicol (eds), Science and technology of high pressure: Proceedings of the International Conference on High Pressure Science and Technology (AIRAPT-17), Honolulu, Hawaii, 25‒30 July 1999, vol. 2, Universities Press, Hyderabad, pp. 822‒825, ISBN 81-7371-339-1
- Witt SF 1991, 'Dimethylmercury', Occupational Safety & Health Administration Hazard Information Bulletin, US Department of Labor, February 15, accessed 8 May 2015
- Wittenberg LJ 1972, 'Volume contraction during melting; emphasis on lanthanide and actinide metals', The Journal of Chemical Physics, vol. 56, no. 9, p. 4526, doi:10.1063/1.1677899
- Wulfsberg G 2000, Inorganic chemistry, University Science Books, Sausalito CA, ISBN 1-891389-01-7
- Young RV & Sessine S (eds) 2000, World of chemistry, Gale Group, Farmington Hills, Michigan
- Zhigal'skii GP & Jones BK 2003, Physical properties of thin metal films, Taylor & Francis, London, ISBN 0-415-28390-6
- Zuckerman & Hagen (eds) 1991, Inorganic reactions and methods, vol, 5: The formation of bonds to group VIB (O, S, Se, Te, Po) elements (part 1), VCH Publishers, Deerfield Beach, Fla, ISBN 0-89573-250-5 | <urn:uuid:f38be1f2-a0a4-4bcb-9fea-c198faed7e79> | 3.96875 | 15,723 | Knowledge Article | Science & Tech. | 67.189991 | 95,542,853 |
By John Pint
In a hidden-away arroyo in Jalisco, botanists were amazed to see not just one maple tree but a whole woods full of them, an ancient fir-maple-conifer cloud forest.
In the late 1990s, Fernando Aragón Cruz, acting as a guide for bird researchers from the University of Albuquerque, collected a sample of a kind of sugar maple from a remote spot 50 kilometers southeast of Puerto Vallarta.
As few native maples had ever been found in western Mexico, local botanists were surprised. They were even more surprised when they went out to look at the site. In a hidden-away arroyo called El Refugio, at 1,764 meters altitude, they were amazed to see not just one maple tree but a whole woods full of them, incorporated into an ancient fir-maple-conifer cloud forest, incomparably rich in diverse species of trees and plants.
By Sandra E. Garcia
They hope to fight the thriving black markets for illegally logged timber.
Forests are disappearing. Maps show shrinking woodlands all over the world. Even trees coveted for their wood that are protected from logging are chopped down.
Worried about such deforestation, environmental advocates are driving a project to create a DNA database of populations of the bigleaf maple tree on the West Coast. The eventual goal is to use DNA mapping to combat the thriving black markets for timber in tropical countries that are plagued by illegal logging.
“We are taking leaf tissue from the maple trees and taking samples along the entire length of the species range from Southern California to British Columbia,” said Meaghan Parker-Forney, a science officer with the World Resources Institute, a nonprofit group that promotes environmental sustainability and is working on the monthslong initiative.
The DNA database is an experimental project for the Norwegian government, which is jointly funding the effort with the United States Forest Service’s international program. Norway hopes to see whether such a database is feasible in places like Indonesia and Peru, where illegal logging is rampant.
By Damian Carrington, Niko Kommenda, Pablo Gutiérrez and Cath Levett
Global deforestation is on an upward trend, jeopardising efforts to tackle climate change and the massive decline in wildlife.
Global tree cover losses have doubled since 2003, while deforestation in crucial tropical rainforest has doubled since 2008. A falling trend in Brazil has been reversed amid political instability and forest destruction has soared in Colombia.
In other key nations, the Democratic Republic of Congo’s vast forests suffered record losses. However, in Indonesia, deforestation dropped 60% in 2017, helped by fewer forest fires and government action.
Forest losses are a huge contributor to the carbon emissions driving global warming, about the same as total emissions from the US, which is the world’s second biggest polluter. Deforestation destroys wildlife habitat and is a key reason for populations of wildlife having plunged by half in the last 40 years, starting a sixth mass extinction.
Healthy forests, just like healthy human populations, are sustained by a diversity of ages and types. In many parts of the United States, forests are becoming largely homogeneous, and in places like the Appalachian Mountains, young forest and mature, old growth forests are in short supply.
A lack of diverse forests has negative impacts on wildlife and the economy, as different age classes support higher biodiversity and provide a more sustainable source of income for forest landowners. Through the use of sustainable forestry practices, forest landowners are able to compensate for lack of natural disturbance.
USDA’s Natural Resources Conservation Service (NRCS) recommends a number of sustainable forestry practices to forest landowners. These practices provide landowners with a number of choices, depending on the land and a landowner’s goals.
By Kathleen Masterson
A new University of Vermont study finds that harvesting trees in a way that mimics old growth forests not only restores critical habitat for animals and plants, but also stores a surprising amount of carbon…
The “old growth” engineering technique succeeded in creating diverse habitats. But the kicker, Keeton says, is that it has also allowed the forest to store a significant amount of carbon, much more than several other conventional tree selection harvesting techniques. That’s key to fighting climate change.
Now, forests that are left alone — with no trees harvested — store the most carbon. But Keeton’s study is finding that it is possible to manage the forest to maximize carbon capture, and still keep it a working forest.
“This greater amount of carbon storage as compared to the conventional treatments was actually a combination of having left more trees behind in the first place, and growth rates that were actually 10 percent higher in this treatment as compared to the conventional harvest,” Keeton says. “And that was really surprising.”
Keeton says after 10 years, the old growth forest management plot stored nearly as much carbon as the unlogged control forest. It came within 16 percent of carbon storage in the unharvested plots. | <urn:uuid:6cb0b46d-ff1c-4af4-9607-c487c72fb18f> | 3.265625 | 1,042 | Content Listing | Science & Tech. | 32.043703 | 95,542,866 |
Quantum computing researchers in China have broken their own record for quantum entanglement, reaching 18 quantum bits or 'qubits' - and have now set their sights on pushing that number up to 50.
Their old record of 10 was only set in 2016.
The results of the study were published in the US journal Physical Review Letters. The team of physicists were led by China's leading quantum scientist, Pan Jianwei. Their work takes the possibility of large-scale quantum computing one step closer.
Qubits are the basic building blocks of quantum computing, in the same way that bits are to traditional computing. However, what's challenging about them is that they rely on sub-atomic particles and their ability to exist in more than one state at the same time.
While regular bits can exist in two states - 1 or 0 - qubits can be based on this binary system but also, thanks to entanglement, they can exist in a superposition of states, rather than one or the other. The successful manipulation of qubits in quantum computing would, therefore, allow for computing that is incredibly more powerful than that of today.
"The speed of quantum computing grows exponentially as the number of qubits in an entangled state increases […] the achievement of an 18-qubit entanglement this time has set the world record for largest entanglement state in all physical systems," Wang Xilin, a member of Pan's team told the Global Times.
But that's not all. After their success at 18 qubits, the Chinese scientists have already set themselves a goal of hitting 50 qubits of entanglement in an attempt to demonstrate the abilities of quantum computing devices to solve problems that classical computers cannot. This experiment is called "the quantum supremacy experiment" in international academia, said Wang.
"With that goal, the team's next step will be to realise a 50-qubit entanglement and manipulation," he added.
"The potential applications of quantum computing are huge, [and] so are the challenges faced."
As physicists around the world aim to break such records, quantum computing has quickly become one of the most competitive fields in the world in science.
For example, the US House Science Committee recently introduced a bill creating a 10-year National Quantum Initiative (PDF) aimed at developing quantum information science and technology.
Microsoft receives a 30 per cent cut of all purchases on the Xbox digital store
Credit card thieves used Apple ID accounts to buy and sell virtual currency for Clash of Clans and Clash Royale and Marvel Contest of Champions
$5.1bn fine further evidence that the EU is anti-US, claims Trump
New cable will connect Virginia to France | <urn:uuid:6d2d08c4-4810-49cf-8506-ea301951c3d1> | 3.015625 | 547 | News Article | Science & Tech. | 39.728012 | 95,542,880 |
|By:||Rolf Langsdorf (LanX) from Darmstadt.pm|
|Date:||Not scheduled yet.|
Domain-Specific Languages (DSL) are a popular but controversial topic.
DSLs are small languages, focused on a particular aspect of a software system.
Invented in the LISP world they were later considered a killer feature of Ruby driving its reputation of being intuitive,
In this talk we'll concentrate on "internal DSLs" (contrary to "external DSLs" which just parse and interpret an external sub language like for instance Template::Toolkit with it's own sub language to build HTML)
Internal DSL bend and twist a host language to make it feel like a different one. Being fully embedded they allow to mix in features of the host language without syntax incompatibilities.
For instance does C# provide a build-in query language called LINQ.
Perl as host language provide a big variety of tools to design syntactic sugar, which needs to be mastered.
We will concentrate on the following questions:
- What exactly are internal DSLs
- What are their advantages over other approaches
- How can they be best designed
- What are the down sides and how can they be mitigated
- What are appropriate techniques for their implementation
- Which Perl specifics can be used here
As a practical examples we will design an own internal DSL for:
- An Assembler
- An IDE configuration
- A SQL abstraction | <urn:uuid:ca928f1c-b1c5-41c3-9d4b-001ce88de2d6> | 3.109375 | 313 | Product Page | Software Dev. | 33.621696 | 95,542,892 |
posted by waslat
1) a bullet of mass 0.02 kg is fired into a block of wood of mass 1.5 kg resting on a horizontal table. The block moves offwith an initial speed of 8 m/s. Estimate the speed with the bullet strikes the block.
2) The bullet in question 1 is fired from a rifle of mass 2.5 kg. Assuming that the bullet leaves the barrel of the rifle with the speed calculated above, find the recoil speed of the rifle if it is free to move. In reality the rifle is held and for a certain person the rifle recoils a distance of 0.12 m. Determine the average force that the person exerts on the rifle? | <urn:uuid:802e2e1b-e719-4feb-8f90-3fdf153278d4> | 3.625 | 147 | Q&A Forum | Science & Tech. | 84.748869 | 95,542,902 |
Self-Adjoint Operators. SchrÖdinger Operators
In Section 2.1 we define symmetric and self-adjoint operators and give criteria for a symmetric operator to be self-adjoint. In Section 2.2 we study simple spectral properties of self-adjoint operators. A particular class of self-adjoint operators, the socalled multiplication operators, are introduced in Section 2.3, and the results are applied to proving the essential self-adjointness of the Laplacian. In Section 2.4 we give a criterion for the invariance of self-adjointness under perturbations and apply it to Schrödinger operators with non-singular potentials. Finally, in Section 2.5, we give a characterization of the domain of Schrödinger operators with strongly singular potentials. The importance of self-adjointness will be discussed in Section 4.1.
KeywordsMultiplication Operator Symmetric Operator Linear Manifold Singular Potential Resolvent Equation
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July 27, 2013
High CO2 Reduces Tree Water Loss
Many climate scientists expect a hotter world will be drier in many regions. Tough on plant growth. However, higher atmospheric carbon dioxide reduces the need for trees to open pores to absorb carbon dioxide. This reduces water loss from leaves.
DURHAM, NH, July 10, 2013 - A study by scientists with the U.S. Forest Service, Harvard University and partners suggests that trees are responding to higher atmospheric carbon dioxide levels by becoming more efficient at using water.
Whether this will be a benefit to you personally probably depends on where you live. Trees that release less water into the atmosphere will reduce precipitation downwind.
How efficient trees are in using water has implications for ecosystem function, services and feedbacks to the climate system. These include enhanced timber yields and improved water availability, which could partially offset the effects of future droughts. However, reduced evapotranspiration, or the combination of evaporation and plant transpiration from the land to the atmosphere, resulting from higher water-use efficiency could lead to higher air temperatures, decreased humidity, and decreased recycling of continental precipitation. This could cause increased continental freshwater runoff, along with drought in parts of the world that rely on water transpired in other regions.
Some types of plants can grow more rapidly in high CO2, especially since the high CO2 reduces water loss. But if global warming causes massive droughts then at least in the drought areas the high CO2 won't help any. However, it has been argued that forests are expanding into the Israeli Negev desert as a result of higher CO2. So in some areas higher CO2 will increase biomass density.
If the world really heats up (and I have no crystal ball on climate) then keep in mind that some regions will be winners while others will be losers. Some areas will become too hot to live in during summer. Others will become too dry.
If the costs of energy fall then drought could largely be mitigated in industrialized countries. What we could do: build massive desalinization plants on the coasts and pump the water inland. Imagine thorium nuclear reactors on the Washington state and Oregon coasts pumping desal water inland over the Rockies to Montana and the Dakotas. Hotter and drier plains states could grow crops using desal water flowing into Montana. Part of the water would evaporate but come down as rain.
Since I do not expect humanity to do much intentionally to cut CO2 emissions we are going to find out what higher CO2 emissions will do to global climate
Randall Parker, 2013 July 27 08:57 PM
Increased growth from CO2 is only possible until the system comes up against the next limiting nutrient, such as phosphorus or potash or nitrogen.
We really don't need any more CO2 in order to get more warming and more plant growth.
Investigators employed standard, robust multi-proxy techniques based upon examining sediments recovered from Lake El’gygytgyn in northeast Arctic Russia (100 km north of the Arctic circle in Chukotka, Russia) to determine local temperatures between 3.6 to 3.4 million years ago. Their findings revealed that during this middle Pliocene era period,
…summer temperatures were ~8 degrees C warmer than today, when the partial pressure [i.e., atmospheric concentration of] CO2 was ~ 400 parts per million [ppm]
But if plants do decide to grow more, the limiting factor will be water, rather than phosphorus or potassium.
I've been eyeing that low area in southern Australia, along with Death Valley. A canal to the edge, then a power station to make use of the water flow into the depression for electricity, and water evaporating for precip down wind.
Phillep, a canal or pipeline to make lake Kati-thanda Eyre permanent would certainly make things interesting, but the sea level drop is barely enough to make water flow into it and wouldn't be enough to generate power. Evapouration of seawater would leave about 5 centimeters of salt deposit each year which could block the channel. Occasional water flows out to sea in wet years might slow the salt deposition, but water flowing out to sea in Australia is weird. Usually it's more just a standoff between fresh and salt water. Two years ago Australia's largest river actually started flowing into the ocean and we all went down and had a look since it was such a unusual event. It wasn't very impressive.
I'm sure the people of the Sahel and the Sahara are just cursing the rise of CO2 making the desert greener and allowing them to grow more food. Oh, wait, poor people don't care why they aren't starving as much as before... and neither do the plant eating animals. /snark/
Could a large amount of water be moved far enough inland to evaporate and then rain down before heading out to sea again? It is my impression that Australia is a very dry place.
Is desalination used in Australia? Is insufficient water the biggest obstacle to bigger crops?
The amount of water required to green up the dry center of Australia is staggering. Even if humans only had to move that water a few miles inland to evaporation ponds, it would still be an enormous project.
Similar to the United States, desalination in Australia is a boondogle designed so farmers do not have to pay market prices for water. The cost of desalinating a liter of water is perhaps 20-30 times what farmers currently pay for a liter of water for irrigation. While most farmers would be glad to sell their irrigation water for market prices they currently have no ability to do this. At best they can sell their water allotment at far below the cost of desalinated water. There would need to be massive and sustained increases in food prices to make using desalinated water for irrigation possible. Due to the high capital cost of current desalination technology this would still apply even if the energy used for desalination was somehow magically free.
My interest in desal: I'd like to know the costs of bringing in fresh water if a mega drought hits the US plains states. Desalination might not be the only option. Imagine bringing in fresh water from, say, Alaska rivers via a massive pipeline.
Think of the cost of pumping the Mississippi's flow uphill, after desalinating it.
Not gonna happen.
Bismarck North Dakota is at 1686 feet in elevation. Sioux City Iowa is at 1135 elevation. Lake Superior is 600 feet in elevation. Though if the climate heats up I would expect the evaporation rate from Lake Superior to increase.
But Colorado Springs is going to pump water 1600 feet uphill. But agriculture needs much lower water costs than residential.
The best way to keep the plains in water would be to prevent it from running down to New Orleans in the first place, no?
The average flow rate of the Mississippi at New Orleans is 600,000 cfps. At ~28 kg per cubic foot, that's about 17,000 tonnes per second. Suppose half of that comes from the east, so you only need to move the other half. Raising 8500 tonnes per second an average of even 1000 feet requires a power of more than 25 GW, not including frictional losses.
Moving water for a single city is small potatoes by comparison.
If we have a long massive drought in the plains states will the Mississippi River even run?
25GW: Sounds like about 15 nukes. Affordable as compared to the costs of depopulating the plains states and giving up on the farm output.
What is not clear: how much of the water that rains on the plains comes down the Mississippi as compared to, say evaporating off of crop plants and coming down away from the Mississippi.
Maybe it'll make sense to cover part of the West in massive glass hot houses that can retain the water.
I'll let you calculate the power required to desalinate 8500 tons/sec of seawater.
I'm aware of one technology which might actually make this feasible: the convection towers proposed in "Defeating the son of Andrew". They not only yield fresh water, but they capture most of it at much more than 1000 feet MSL and could provide the energy for pumping it by gravity (though electric power transmission is probably cheaper than pipelines gauged for several thousand PSI). But it's far easier to just nuclearize the economy and remove CO2 from the atmosphere to return rainfall patterns to the cooler, wetter ones of history.
We won't build nukes in time to prevent global warming. If we were going to do that we would already have done it.
Time to start with some numbers:
Desalination plants on average use about 15,000 kilowatt-hours of power for every million gallons of fresh water that’s produced, the Pacific Institute said today in a report.
So assuming 10 cents per kwh (close enough) I read that as $1500 per million gallons. Next I assume: 269 gallons per ton. But maybe you are using a different kind of ton? Assuming 269 is correct (and that you do not mean tonne of water): 269*8500=2286500 gallons per second. Is that right? 2.3 million gallons. So then 2286500/1000000=2.2865*$1500=$3429.75 per second. So now we have a price per second. Feel free to fix it.
So what about a cost per day? Times 60*60*24=$29.6 million per day. That's low. Have I done something wrong? Times 365 days = $108160586000 per year. That's only about $108 billion per year. Seems like chump change.
I figure at high volume we could achieve much lower costs of power. But that cost above is just for power. Everything else is the other half of But, again, in volume with large fleets of nukes costs would be much lower. Plus, even convert nuke power to electricity? Why not just boil water with the heat?
Here is another cost source for desal water:
The San Diego County Water Authority has agreed to buy at least 48,000 acre-feet of water from the plant each year for about $2,000 an acre-foot. An acre-foot equals about 326,000 gallons, roughly enough for two families of four for a year.
So 1 million divided by 326,000 gallons and then times $2000 = $6134 per million gallons, about 4 times the cost I quote above. I would guess in a much larger scale operation costs would be half what San Diego is going to pay. So say $200 billion. Granted, additional costs for moving the water over the Rockies. Though the thought occurs to me: Why not just irrigate deserts and turn them into massive farm areas?
Another idea: Just run pumps in the ocean near the Western shore of southern Alaska and British Colombia to increase the amount of moisture headed toward the great plains? Alberta and the Dakotas would get more rain.
I get $296 million per day (2.963304×10⁸, if that renders correctly) or $108 billion/year. And that's only the energy cost of operation.
Just run pumps in the ocean near the Western shore of southern Alaska and British Colombia to increase the amount of moisture headed toward the great plains?
Hmmm. A concept I saw years ago was for downdraft evaporation towers in California to cool the hot inland air using seawater. This would also add humidity, which would be carried inland. Rainfall could only increase. However, unless the Midwest's rainfall comes from air which passes over California, that wouldn't help.
$100 billion: Another idea: Pump the water inland from Oregon to the Utah Great Salt Lake and let it evaporate from there. So the lake accumulate more salt. Not seeing that as a problem.
To be clear on the pumps: I mean spray ocean water into the air to cause more to travel inland.
Where the plains and midwest rain comes from: That's why I said BC and Alaska. There's got to be a correct place to do this.
During wet years, Utahns have had to set up evaporation ponds uphill of the Great Salt Lake to keep it from flooding SLC. I don't think you're going to get any support for a scheme to use their real estate to increase rainfall elsewhere.
When the interior of the US dries up, and it seems to be happening now:
I don't think there will be grand schemes to maintain crop production on currently arable land. I instead think that once rainfall in an area drops too low in an area farmland there will be abandonned or at least switched to dryland agriculture something like in the sheep/wheat belt of Australia. There are a couple of reasons why I think this. Firstly, there is a coordination problem. If people can't coordinate enough to prevent global warming drying out parts of the United States how will they coordinate enough to raise taxes and pay for grand schemes to allow agriculture to continue in drought stricken regions? And secondly it should be cheaper to increase food production closer to where the water is rather than to attempt to move water to where food is currently grown. The cost of pumping fresh water into the US's dead heart could instead pay for an awful lot of high intensity agriculture where water is available. I suppose the good news is that agricultural robots might make good use of hilly land that is currently not profitable for large scale mechanised farming. (Not sure how the Amish will feel about this, however.) | <urn:uuid:f1714de8-ed75-4362-8d72-4ccdef909970> | 3.40625 | 2,825 | Comment Section | Science & Tech. | 57.95928 | 95,542,935 |
By Ad Hoc Committee to Assess the Science Proposed for a Deep Underground Science and Engineering Laboratory (DUSEL),National Research Council
According to the large bang concept, our Universe started in a kingdom of unimaginably excessive strength and density, contained in an area of subatomic dimensions. at the moment, not like this day, the basic forces of nature have been most likely unified and the debris current have been interacting at energies now not possible via present-day accelerators. Underground laboratories give you the stipulations to enquire techniques concerning infrequent phenomena in subject and to become aware of the vulnerable results of hugely elusive debris through replicating comparable environments to these as soon as harnessed throughout the earliest states of the Earth. those laboratories now seem to be the gateway to knowing the physics of the grand unification of the forces of nature.
Built to defend tremendous delicate detectors from the noise in their atmosphere and the signs linked to cosmic rays, underground amenities were validated over the last 30 years at a few websites around the world. so far, the us' efforts to advance such amenities were modest and consist essentially of small underground laboratories. despite the fact that, the U.S. underground neighborhood has driven for greater underground amenities at the scale of significant laboratories in different international locations. An overview of the Deep Underground technology and Engineering Laboratory (DUSEL) addresses this subject through comparing the main physics questions and experiments that may be explored with the proposed DUSEL. Measuring the capability impression, this review additionally examines the wider results of the DUSEL with reference to schooling and public outreach, and evaluates the necessity linked to constructing U.S. courses just like technological know-how courses in different areas of the world.
Read Online or Download An Assessment of the Science Proposed for the Deep Underground Science and Engineering Laboratory (DUSEL) PDF
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Evaporation(Redirected from Evaporates)
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Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gaseous phase before reaching its boiling point. The surrounding gas must not be saturated with the evaporating substance. When the molecules of the liquid collide, they transfer energy to each other based on how they collide. When a molecule near the surface absorbs enough energy to overcome the vapor pressure, it will "escape" and enter the surrounding air as a gas. When evaporation occurs, the energy removed from the vaporized liquid will reduce the temperature of the liquid, resulting in evaporative cooling.
On average, only a fraction of the molecules in a liquid have enough heat energy to escape from the liquid. The evaporation will continue until an equilibrium is reached when the evaporation of the liquid is the equal to its condensation. In an enclosed environment, a liquid will evaporate until the surrounding air is saturated.
Evaporation is an essential part of the water cycle. The sun (solar energy) drives evaporation of water from oceans, lakes, moisture in the soil, and other sources of water. In hydrology, evaporation and transpiration (which involves evaporation within plant stomata) are collectively termed evapotranspiration. Evaporation of water occurs when the surface of the liquid is exposed, allowing molecules to escape and form water vapor; this vapor can then rise up and form clouds. With sufficient energy, the liquid will turn into vapor.
For molecules of a liquid to evaporate, they must be located near the surface, they have to be moving in the proper direction, and have sufficient kinetic energy to overcome liquid-phase intermolecular forces. When only a small proportion of the molecules meet these criteria, the rate of evaporation is low. Since the kinetic energy of a molecule is proportional to its temperature, evaporation proceeds more quickly at higher temperatures. As the faster-moving molecules escape, the remaining molecules have lower average kinetic energy, and the temperature of the liquid decreases. This phenomenon is also called evaporative cooling. This is why evaporating sweat cools the human body. Evaporation also tends to proceed more quickly with higher flow rates between the gaseous and liquid phase and in liquids with higher vapor pressure. For example, laundry on a clothes line will dry (by evaporation) more rapidly on a windy day than on a still day. Three key parts to evaporation are heat, atmospheric pressure (determines the percent humidity), and air movement.
On a molecular level, there is no strict boundary between the liquid state and the vapor state. Instead, there is a Knudsen layer, where the phase is undetermined. Because this layer is only a few molecules thick, at a macroscopic scale a clear phase transition interface cannot be seen.
Liquids that do not evaporate visibly at a given temperature in a given gas (e.g., cooking oil at room temperature) have molecules that do not tend to transfer energy to each other in a pattern sufficient to frequently give a molecule the heat energy necessary to turn into vapor. However, these liquids are evaporating. It is just that the process is much slower and thus significantly less visible.
If evaporation takes place in an enclosed area, the escaping molecules accumulate as a vapor above the liquid. Many of the molecules return to the liquid, with returning molecules becoming more frequent as the density and pressure of the vapor increases. When the process of escape and return reaches an equilibrium, the vapor is said to be "saturated", and no further change in either vapor pressure and density or liquid temperature will occur. For a system consisting of vapor and liquid of a pure substance, this equilibrium state is directly related to the vapor pressure of the substance, as given by the Clausius–Clapeyron relation:
where P1, P2 are the vapor pressures at temperatures T1, T2 respectively, ΔHvap is the enthalpy of vaporization, and R is the universal gas constant. The rate of evaporation in an open system is related to the vapor pressure found in a closed system. If a liquid is heated, when the vapor pressure reaches the ambient pressure the liquid will boil.
The ability for a molecule of a liquid to evaporate is based largely on the amount of kinetic energy an individual particle may possess. Even at lower temperatures, individual molecules of a liquid can evaporate if they have more than the minimum amount of kinetic energy required for vaporization.
Factors influencing the rate of evaporationEdit
Note: Air used here is a common example; however, the vapor phase can be other gases.
- Concentration of the substance evaporating in the air
- If the air already has a high concentration of the substance evaporating, then the given substance will evaporate more slowly.
- Concentration of other substances in the air
- If the air is already saturated with other substances, it can have a lower capacity for the substance evaporating.
- Flow rate of air
- This is in part related to the concentration points above. If "fresh" air (i.e., air which is neither already saturated with the substance nor with other substances) is moving over the substance all the time, then the concentration of the substance in the air is less likely to go up with time, thus encouraging faster evaporation. This is the result of the boundary layer at the evaporation surface decreasing with flow velocity, decreasing the diffusion distance in the stagnant layer.
- The amount of minerals dissolved in the liquid
- Inter-molecular forces
- The stronger the forces keeping the molecules together in the liquid state, the more energy one must get to escape. This is characterized by the enthalpy of vaporization.
- Evaporation happens faster if there is less exertion on the surface keeping the molecules from launching themselves.
- Surface area
- A substance that has a larger surface area will evaporate faster, as there are more surface molecules per unit of volume that are potentially able to escape.
- Temperature of the substance
- the higher the temperature of the substance the greater the kinetic energy of the molecules at its surface and therefore the faster the rate of their evaporation.
In the US, the National Weather Service measures the actual rate of evaporation from a standardized "pan" open water surface outdoors, at various locations nationwide. Others do likewise around the world. The US data is collected and compiled into an annual evaporation map. The measurements range from under 30 to over 120 inches (3,000 mm) per year.
Evaporation is an endothermic process, in that heat is absorbed during evaporation.
- Industrial applications include many printing and coating processes; recovering salts from solutions; and drying a variety of materials such as lumber, paper, cloth and chemicals.
- The use of evaporation to dry or concentrate samples is a common preparatory step for many laboratory analyses such as spectroscopy and chromatography. Systems used for this purpose include rotary evaporators and centrifugal evaporators.
- When clothes are hung on a laundry line, even though the ambient temperature is below the boiling point of water, water evaporates. This is accelerated by factors such as low humidity, heat (from the sun), and wind. In a clothes dryer, hot air is blown through the clothes, allowing water to evaporate very rapidly.
- The Matki/Matka, a traditional Indian porous clay container used for storing and cooling water and other liquids.
- The botijo, a traditional Spanish porous clay container designed to cool the contained water by evaporation.
- Evaporative coolers, which can significantly cool a building by simply blowing dry air over a filter saturated with water.
Fuel droplets vaporize as they receive heat by mixing with the hot gases in the combustion chamber. Heat (energy) can also be received by radiation from any hot refractory wall of the combustion chamber.
Internal combustion engines rely upon the vaporization of the fuel in the cylinders to form a fuel/air mixture in order to burn well. The chemically correct air/fuel mixture for total burning of gasoline has been determined to be 15 parts air to one part gasoline or 15/1 by weight. Changing this to a volume ratio yields 8000 parts air to one part gasoline or 8,000/1 by volume.
Thin films may be deposited by evaporating a substance and condensing it onto a substrate, or by dissolving the substance in a solvent, spreading the resulting solution thinly over a substrate, and evaporating the solvent. The Hertz–Knudsen equation is often used to estimate the rate of evaporation in these instances.
|Wikisource has the text of The New Student's Reference Work article Evaporation.|
- Atmometer (evaporation)
- Boiling point
- Eddy covariance flux (a.k.a. eddy correlation, eddy flux)
- Flash evaporation
- Heat of vaporization
- Hertz–Knudsen equation
- Hydrology (agriculture)
- Latent heat
- Latent heat flux
- Pan evaporation
- Sublimation (phase transition) (phase transfer from solid directly to gas)
- "the definition of evaporate". Dictionary.com. Retrieved 2018-01-23.
- The New Student's Reference Work (1914). 1914. p. 636.
- Lohner, Science Buddies,Svenja. "Chilling Science: Evaporative Cooling with Liquids". Scientific American. Retrieved 2018-01-23.
- Silberberg, Martin A. (2006). Chemistry (4th ed.). New York: McGraw-Hill. pp. 431–434. ISBN 0-07-296439-1. | <urn:uuid:afa17366-4abc-4c68-b0a0-9b144f990a19> | 4.0625 | 2,097 | Knowledge Article | Science & Tech. | 29.68275 | 95,542,956 |
Radioactivity may have a bad rap, but it plays a critical role in medical research. A revolutionary new technique to create radioactive molecules, pioneered in the lab of Princeton chemistry
professor David MacMillan, has the potential to bring new medicines to patients much faster than before.
“Your average drug takes 12 to 14 years to come to market,” said MacMillan, the James S. McDonnell Distinguished University Professor of Chemistry. “So everything that we can do to take that 14- or 12-year time frame and compress it is going to advantage society, because it gets medicines to people — to society — so much faster.”
Every potential new medication has to go through testing to confirm that it affects the part of the body it is intended to affect. “Is it going to the right place? The wrong place? The right place and the wrong place?” MacMillan asked.
Tracing the path of a chemical that dissolves into the bloodstream presented a serious challenge, but one that radiochemists solved years ago by swapping out individual atoms with radioactive substitutes. Once that is done, “the properties of the molecule — of the drug — are exactly the same except that they’re radioactive, and that means that you can trace them really, really well,” MacMillan said.
But that introduced a new problem.
“Getting these radioactive atoms into the drug is not a trivial thing to do,” he said. “People have developed long, sometimes month-long, two-month, three-month long sequences just to get a tiny amount of a substance with a few radioactive atoms.”
But now he and his colleagues have found a better way, drawing on their work using blue LED lights and catalysts that respond to light, known as photocatalysts. Their research was published online in the journal Science on Nov. 9.
“It was a wacky idea! Fortunately, it worked,” MacMillan said. “What we came up with was, if you shine light on them, and you have a photocatalyst, could these photocatalysts actually remove the non-radioactive atom and then install the radioactive atom?”
MacMillan’s technique uses “heavy water,” which replaces the hydrogen (H) in H2O with tritium, a radioactive version of hydrogen that has an extra two neutrons per atom.
“If you just let your drug sit in the radioactive water and shine light on it with a catalyst, the catalyst will remove the atom which is not radioactive — in this case it’s hydrogen — and replace it with tritium,” he said.
Suddenly, attaching one of these atomic labels takes hours instead of months, and the technique works on many kinds of frequently used compounds. The researchers have already tested it on 18 commercially available medicines, as well as candidates in the Merck drug discovery pipeline.
For compounds that don’t need radioactive tags, the same one-step process can swap in deuterium, a version of hydrogen with only one extra neutron. These “stable labels” (with deuterium) and “radio labels” (with tritium) have countless applications, in academia as well as drug discovery.
The simplicity of this new approach has another implication, said Jennifer Lafontaine, the senior director of synthesis and analytical chemistry for Pfizer in La Jolla, California, who was not involved in the research.
Because the previous process was so resource intensive, deuterium- or tritium-labeled molecules were often only created for chemicals that were “quite advanced in the drug discovery process,” she said. “This methodology could therefore open the door to earlier and expanded use of isotopic labeling in drug discovery, significantly enhancing our ability to study drug candidates on a deeper level, and across a range of applications.”
“No one’s patenting any of this, because we want it to be available for everyone to use,” MacMillan said.
Learn more: LEDs light the way for better drug therapies
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In a pool of Medicare recipients in New England, more deaths occurred when summer temperatures significantly increased. More research is still to be done.
It's no secret that most climate experts are expecting surface temperatures to rise in the coming years. It was already confirmed earlier this year that 2014 was the hottest year on record, with warming oceans identified as a main driver in this harmful change. Now experts are saying that if things stay on track, mussels will be one of the first species to be in hot water - literally.
Crops such as blueberries and others may soon be affected, because bumblebees' range is narrowing, researchers say.
A new type of leafhopper has been found in the New Jersey Pine Barrens.
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A type of lizard in Australia's Western Queensland changes sex from male to female in temperatures over 90 degrees, helping them to lay more eggs and colonize areas faster, researchers believe.
Like in the Arctic, Antarctic and even Canada, glaciers in Alaska are melting. Now, new research reveals that like their famous brethren, they may make large contributions to global sea level rise.
For the first time ever, scientists have witnessed polar bears eating white-beaked dolphins in the Arctic, and they claim it's the bizarre result of climate change.
It looks like even for plants, there can be too much of a good thing. Trees and flowers use carbon dioxide (CO2) to make energy, absorbing the gas to help fuel the process of photosynthesis. For this reason, some experts have theorized that rising carbon levels will eventually promote plant growth. Now, new research claims that this assumption is dead wrong.
Climate change: it's a subject that is full of uncertainties. That's especially true in the case of how it will affect plant life around the globe. Past studies have revealed that a warming world and changing atmosphere could help plants spread and grow. However, new research has now found evidence of the complete opposite. Plants, it appears, may actually be running out of time to grow in the face of climate change.
Coral reefs have been the subject of much research given the ongoing threats they are dealing with related to climate change. Ocean acidification, for one, is wreaking havoc on these delicate ecosystems, but a remarkable new study says that coral reefs in Palau may be able to defy the odds.
China's greenhouse gas emissions may peak by the year 2025, according to a new report from the London School of Economics (LSE), easing scientists' fears of its contribution to climate change.
Warmer ocean waters are creating such a challenge for marine species worldwide, that new research shows they will consequently shift entire marine habitats.
The infamous global warming hiatus, which has puzzled scientists and been hailed by climate change skeptics, may have never really happened, according to a new, updated NOAA analysis.
Just yesterday, Nature World News reported on Greenland's mysteriously vanishing lakes, which can drain entirely in just a matter of a few hours. But now, a subsequent study is saying that while warming temperatures have created more of these supraglacial lakes, they are not likely to worsen Greenland's contribution to sea level rise. | <urn:uuid:9d882d6a-f6b1-47ab-9d31-27b5ba3edb53> | 3.265625 | 676 | Content Listing | Science & Tech. | 43.823408 | 95,542,991 |
|Name, Symbol, Number||lithium, Li, 3|
|Chemical series||alkali metals|
|Group, Period, Block||1, 2, s|
|Atomic mass||6.941(2) g/mol|
|Electron configuration||1s2 2s1|
|Electrons per shell||2, 1|
|Density (near r.t.)||0.534 g/cm³|
|Liquid density at m.p.||0.512 g/cm³|
|Melting point||453.69 K
(180.54 °C, 356.97 °F)
|Boiling point||1615 K
(1342 °C, 2448 °F)
3223 K, 67 MPa
|Heat of fusion||3.00 kJ/mol|
|Heat of vaporization||147.1 kJ/mol|
|Heat capacity||(25 °C) 24.860 J/(mol·K)|
|Crystal structure||cubic body centered|
(strongly basic oxide)
|Electronegativity||0.98 (Pauling scale)|
|Ionization energies||1st: 520.2 kJ/mol|
|2nd: 7298.1 kJ/mol|
|3rd: 11815.0 kJ/mol|
|Atomic radius||145 pm|
|Atomic radius (calc.)||167 pm|
|Covalent radius||134 pm|
|Van der Waals radius||182 pm|
|Electrical resistivity||(20 °C) 92.8 nΩ·m|
|Thermal conductivity||(300 K) 84.8 W/(m·K)|
|Thermal expansion||(25 °C) 46 µm/(m·K)|
|Speed of sound (thin rod)||(20 °C) 6000 m/s|
|Speed of sound (thin rod)||(r.t.) 4.9 m/s|
|Shear modulus||4.2 GPa|
|Bulk modulus||11 GPa|
|CAS registry number||7439-93-2|
Lithium (chemical symbol Li, atomic number 3) is the lightest solid chemical element and a member of the group of elements known as alkali metals. It is flammable, corrosive to the skin, and readily reacts with water and air. Pure lithium is soft and silvery white in color, but it tarnishes rapidly. It is one of only four elements theorized to have been created in the first three minutes of the origin of the universe, through a process called "Big Bang nucleosynthesis."
Lithium, its alloys, and compounds have a wide range of applications. For instance, lithium is used in specialized rechargeable batteries, alloys for aircraft parts, and appliances like toasters and microwave ovens. Lithium niobate is used in mobile phones, lithium stearate is a high-temperature lubricant, lithium hydroxide is an efficient air purifier, and lithium chloride and bromide are used as desiccants. In addition, lithium salts are used in mood-stabilizing drugs.
Toward the end of the 1700s, Brazilian scientist José Bonifácio de Andrada e Silva discovered the lithium-containing mineral petalite (LiAl(Si2O5)2) on a trip to Sweden. When Johan Arfvedson analyzed a petalite ore in 1817, he discovered lithium. In 1818, Christian Gmelin was the first to observe that lithium salts give a bright red color when held in a flame. Both Arfvedson and Gmelin tried to isolate the element from its salts but failed.
The element was not isolated until William Thomas Brande and Sir Humphry Davy later performed electrolysis on lithium oxide in 1818. Robert Bunsen and Matiessen isolated larger quantities of the metal by electrolysis of lithium chloride in 1855. Commercial production of lithium metal was achieved in 1923 by a German company (Metallgesellschaft), by the electrolysis of molten lithium chloride and potassium chloride.
The name "lithium" (from the Greek λιθoς (lithos), meaning "stone") was chosen apparently because it was discovered from a mineral, while other common alkali metals were first discovered from plant tissue.
The Earth's crust contains about 65 parts per million (ppm) of lithium. The element is widely distributed in nature, but because of its reactivity, it is always found combined with other elements.
Lithium production has greatly increased since the end of World War II. The metal is separated from other elements in igneous rocks, and is also extracted from the water of mineral springs. Lepidolite, spodumene, petalite, and amblygonite are the more important minerals containing it.
In the United States, lithium is recovered from brine pools in Nevada. Today, most commercial lithium is recovered from brine sources in Argentina and Chile. The metal is produced by electrolysis from a mixture of fused (molten) lithium chloride and potassium chloride. Chile is currently the world's leading producer of pure lithium metal.
Lithium leads the family of elements known as "alkali metals" in group 1 of the periodic table. Two well-known elements in this group are sodium and potassium. Lithium is also at the start of period 2, located just before beryllium. The atomic number of lithium is 3, which places it right after helium (atomic number 2). Thus lithium is the lightest metallic element.
Like all other alkali metals, lithium has a single electron in its outermost shell, and it can readily lose this electron to become a positive ion. For this reason, lithium readily reacts with water and does not occur freely in nature. Nevertheless, it is less reactive than the chemically similar sodium.
Lithium is soft enough to be cut with a knife, though this is significantly more difficult to do than cutting sodium. The fresh metal has a silvery color, but it rapidly tarnishes to black in the air. Lithium has only about half the density of water, because of which sticks of this metal have the odd heft of a light wood such as balsa.
In its pure form, lithium is highly flammable and slightly explosive when exposed to water and air. It is the only metal that reacts with nitrogen at room temperature. Lithium fires are difficult to extinguish, requiring special chemicals designed to smother them. For these reasons, storage of lithium in the laboratory involves placing sticks of the metal in jars of nonreactive, liquid hydrocarbons. Given their low density, the sticks tend to float, so they need to be held down mechanically by the lid of the jar and other sticks.
When placed over a flame, lithium gives off a striking crimson color, but when it burns strongly, the flame becomes brilliant white. Lithium has a high specific heat capacity (3582 J/(kg·K)), which means that a large amount of heat is required to raise the temperature of a unit mass (1 kilogram or 1 gram) of the substance by 1 kelvin. In addition, its liquid form has a great temperature range. These properties make lithium a useful chemical.
In humans, lithium compounds play no natural biological role and are considered slightly toxic. The metal is corrosive to the touch and requires special handling to avoid skin contact. By contrast, lithium (in the ionic form) appears to be an essential trace element for goats and possibly rats. When used as a drug, blood concentrations of Li+ must be carefully monitored.
Naturally occurring lithium is composed of 2 stable isotopes, 6Li and 7Li, of which the latter is the more abundant (92.5% natural abundance). In addition, seven radioisotopes have been characterized. Among them, 8Li has a half-life of 838 milliseconds (ms), 9Li has a half-life of 178.3 ms, and the others have half-lives that are less than 8.6 ms. The shortest-lived isotope of lithium is 4Li, which decays through proton emission and has a half-life of 7.58043x10-23 seconds.
According to the "Big Bang" model of the origin of the universe, the nuclei of 7Li were among the few types of atomic nuclei formed shortly after the Big Bang, during a phase called the "Big Bang nucleosynthesis" ("nucleosynthesis" refers to the synthesis of atomic nuclei). It is thought that the nuclei of hydrogen, helium, and beryllium atoms were also formed at that time.
Given that the specific heat capacity of lithium is higher than that of any other solid, lithium is used in heat-transfer applications, such as in toasters and microwave ovens. It is also an important material in rechargeable lithium ion batteries. Besides being lighter than the standard dry cells, these batteries produce a higher voltage (3 volts versus 1.5 volts). Additional uses of lithium, its alloys, and its compounds are as follows:
Consumption of lithium increased by 4-5 percent per year between 2002 and 2005, driven by the demand in lithium secondary batteries. Batteries accounted for 20 percent of total consumption in 2005, a rise from under 10 percent in 2000.
Continued expansion in the portable electronic products market and commercialization of hybrid electric vehicles using lithium batteries suggest growth of up to 10 percent per year in lithium carbonate consumption in this market through 2010.
Between 2002 and 2005, lithium minerals production rose by 7 percent per year to reach 18,800 tons lithium. Chile and Australia account for over 60 percent of total output. China may emerge as a significant producer of brine-based lithium carbonate by 2010. Potential capacity of up to 45,000 tons per year could come on-stream if projects in Qinghai province and Tibet proceed .
Some jurisdictions limit the sale of lithium batteries, which are the most readily available source of lithium metal for regular consumers. Lithium can be used to reduce pseudoephedrine and ephedrine to methamphetamine by the Birch reduction method, which employs alkali metals dissolved in ammonia. The effectiveness of such restrictions in controlling the illegal production of methamphetamine remains indeterminate and controversial.
Carriage and shipment of some types of lithium batteries may be prohibited aboard aircraft, because most types of lithium batteries can discharge very rapidly when short-circuited, leading to overheating and possible explosion. Most consumer lithium batteries, however, have built-in thermal overload protection to prevent this type of incident, or their design limits short-circuit currents.
All links retrieved August 9, 2014.
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Scientists don't just think of an idea and do a simple experiment that beautifully verifies it - except in extremely rare instances. Normally data is mucky, has noise, that is say that not all the evidence will support the idea, even when it is mostly correct. Some of the data may not be too relevant to the domain in which the idea applies - try proving Newtons 3 laws of motion in everyday life - you can't, this does not mean that the 3 laws are wrong, just that you need to find the appropriate conditions.
When dealing with something as complicated as weather, one needs a good understanding of Statistics, in addition to knowledge about Physics, Chemistry, and Geography. It also helps enormously if you understand the jargon, and the difference between informal discussions and peer reviewed conclusions. Plus it helps to realize scientists are human, and therefore not expected to be diplomatic about climate denialists in private correspondence.
So sometimes scientists have to either omit data, and/or modify it to be useful.
For example if two boys where trying to decide which of their girl friends preferred chocolate the most, by analysing what the girls bought - they would omit any data relating to buying unrelated items like clothes. Similarly if they wanted to to decide the best level of loudness the girl friends liked music, they would adjust the data depending size of room (and several other factors) to 'normalize' the measurements - so that comparing loudness associated with a party of many people in a large room to the volume for 2 people in a small room. Or planet hunters, who deliberately omit the light from a star to pick the light of a planet - they are modifying the data.
So if an email talks about selecting data sets, and the reader does not bear the above in mind, and is naturally disposed to be untrusting - then quite the wrong conclusion could be drawn.
For a good coverage of this, see the articles about the significance of the leaked climate emails and his follow-up by Phil of Bad Astronomy (he started the site to debunk the Apollo Moon Hoax and others of a similar ilk).
Rorting In The Auckland Property Market !
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Primary energy production and gross domestic product for selected countries. Both scales are logarithmic. Source: U.S. Energy Information Agency, 2002
Business-as-usual approach threatens world energy supplies and environment, but affordable, effective solutions appear within reach
Implementing a plan to keep rising carbon dioxide levels from reaching potentially dangerous levels could cost less than 1 percent of gross world product as of 2050, a cost that is well within reach of developed and developing nations alike. However, without simultaneous progress in the way energy is found, transformed, transported and used, the world is in danger of facing a severe energy crisis sometime within the next century.
Those are the conclusions of a report by Klaus S. Lackner and Jeffrey D. Sachs of The Earth Institute that appears in the most recent issue of Brookings Papers on Economic Activity published by the Brookings Institute.
Ken Kostel | EurekAlert!
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