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https://en.wikipedia.org/wiki/Square%20matrix | In mathematics, a square matrix is a matrix with the same number of rows and columns. An n-by-n matrix is known as a square matrix of order Any two square matrices of the same order can be added and multiplied.
Square matrices are often used to represent simple linear transformations, such as shearing or rotation. For example, if is a square matrix representing a rotation (rotation matrix) and is a column vector describing the position of a point in space, the product yields another column vector describing the position of that point after that rotation. If is a row vector, the same transformation can be obtained using where is the transpose of
Main diagonal
The entries () form the main diagonal of a square matrix. They lie on the imaginary line which runs from the top left corner to the bottom right corner of the matrix. For instance, the main diagonal of the 4×4 matrix above contains the elements , , , .
The diagonal of a square matrix from the top right to the bottom left corner is called antidiagonal or counterdiagonal.
Special kinds
Diagonal or triangular matrix
If all entries outside the main diagonal are zero, is called a diagonal matrix. If only all entries above (or below) the main diagonal are zero, is called an upper (or lower) triangular matrix.
Identity matrix
The identity matrix of size is the matrix in which all the elements on the main diagonal are equal to 1 and all other elements are equal to 0, e.g.
It is a square matrix of order and also a special kind of diagonal matrix. It is called identity matrix because multiplication with it leaves a matrix unchanged:
for any matrix
Invertible matrix and its inverse
A square matrix is called invertible or non-singular if there exists a matrix such that
If exists, it is unique and is called the inverse matrix of denoted
Symmetric or skew-symmetric matrix
A square matrix that is equal to its transpose, i.e., is a symmetric matrix. If instead then is called a skew-symmet |
https://en.wikipedia.org/wiki/Software%20development%20kit | A software development kit (SDK) is a collection of software development tools in one installable package. They facilitate the creation of applications by having a compiler, debugger and sometimes a software framework. They are normally specific to a hardware platform and operating system combination. To create applications with advanced functionalities such as advertisements, push notifications, etc; most application software developers use specific software development kits.
Some SDKs are required for developing a platform-specific app. For example, the development of an Android app on the Java platform requires a Java Development Kit. For iOS applications (apps) the iOS SDK is required. For Universal Windows Platform the .NET Framework SDK might be used. There are also SDKs that add additional features and can be installed in apps to provide analytics, data about application activity, and monetization options. Some prominent creators of these types of SDKs include Google, Smaato, InMobi, and Facebook.
Details
An SDK can take the form of application programming interfaces (APIs) in the form of on-device libraries of reusable functions used to interface to a particular programming language, or it may be as complex as hardware-specific tools that can communicate with a particular embedded system. Common tools include debugging facilities and other utilities, often presented in an integrated development environment (IDE). SDKs may include sample software and/or technical notes along with documentation, and tutorials to help clarify points made by the primary reference material.
SDKs often include licenses that make them unsuitable for building software intended to be developed under an incompatible license. For example, a proprietary SDK is generally incompatible with free software development, while a GPL-licensed SDK could be incompatible with proprietary software development, for legal reasons. However, SDKs built under the GNU Lesser General Public License (L |
https://en.wikipedia.org/wiki/Paper%20size | Paper size standards govern the size of sheets of paper used as writing paper, stationery, cards, and for some printed documents.
The ISO 216 standard, which includes the commonly used A4 size, is the international standard for paper size. It is used across the world except in North America and parts of Central and South America, where North American paper sizes such as "Letter" and "Legal" are used. The international standard for envelopes is the C series of ISO 269.
International standard paper sizes
The international paper size standard is ISO 216. It is based on the German DIN 476 standard for paper sizes. Each ISO paper size is one half of the area of the next larger size in the same series. ISO paper sizes are all based on a single aspect ratio of the square root of 2, or approximately 1:1.41421. There are different series, as well as several extensions.
The following international paper sizes are included in Cascading Style Sheets (CSS): A3, A4, A5, B4, B5.
A series
There are 11 sizes in the A series, designated A0–A10, all of which have an aspect ratio of , where a is the long side and b is the short side.
Since A series sizes share the same aspect ratio they can be scaled to other A series sizes without being distorted, and two sheets can be reduced to fit on exactly one sheet without any cutoff or margins.
The A0 base size is defined as having an area of 1 m; given an aspect ratio of , the dimensions of A0 are:
by .
or, rounded to the nearest millimetre, .
A series sizes are related in that the smaller dimension of a given size is the larger dimension of the next smaller size, and folding an A series sheet in half in its larger dimension—that is, folding it in half parallel to its short edge—results in two halves that are each the size of the next smaller A series size. As such, a folded brochure of a given A-series size can be made by folding sheets of the next larger size in half, e.g. A4 sheets can be folded to make an A5 brochure. The |
https://en.wikipedia.org/wiki/Indirection | In computer programming, indirection (also called dereferencing) is the ability to reference something using a name, reference, or container instead of the value itself. The most common form of indirection is the act of manipulating a value through its memory address. For example, accessing a variable through the use of a pointer. A stored pointer that exists to provide a reference to an object by double indirection is called an indirection node. In some older computer architectures, indirect words supported a variety of more-or-less complicated addressing modes.
Another important example is the domain name system which enables names such as en.wikipedia.org to be used in place
of network addresses such as 208.80.154.224. The indirection from human-readable names to network addresses means that the references to a web page become more memorable, and links do not need to change when a web site is relocated to a different server.
Overview
A famous aphorism of Butler Lampson goes: "All problems in computer science can be solved by another level of indirection" (the "fundamental theorem of software engineering").
This is often deliberately mis-quoted with "abstraction layer" substituted for "level of indirection". An often cited corollary to this is, "...except for the problem of too many layers of indirection."
A humorous Internet memorandum, , insists that:
Object-oriented programming makes use of indirection extensively, a simple example being dynamic dispatch. Higher-level examples of indirection are the design patterns of the proxy and the proxy server. Delegation is another classic example of an indirection pattern. In strongly typed interpreted languages with dynamic datatypes, most variable references require a level of indirection: first the type of the variable is checked for safety, and then the pointer to the actual value is dereferenced and acted on.
Recursive data types are usually implemented using indirection, because otherwise if a value of a data |
https://en.wikipedia.org/wiki/Sides%20of%20an%20equation | In mathematics, LHS is informal shorthand for the left-hand side of an equation. Similarly, RHS is the right-hand side. The two sides have the same value, expressed differently, since equality is symmetric.
More generally, these terms may apply to an inequation or inequality; the right-hand side is everything on the right side of a test operator in an expression, with LHS defined similarly.
Example
The expression on the right side of the "=" sign is the right side of the equation and the expression on the left of the "=" is the left side of the equation.
For example, in
is the left-hand side (LHS) and is the right-hand side (RHS).
Homogeneous and inhomogeneous equations
In solving mathematical equations, particularly linear simultaneous equations, differential equations and integral equations, the terminology homogeneous is often used for equations with some linear operator L on the LHS and 0 on the RHS. In contrast, an equation with a non-zero RHS is called inhomogeneous or non-homogeneous, as exemplified by
Lf = g,
with g a fixed function, which equation is to be solved for f. Then any solution of the inhomogeneous equation may have a solution of the homogeneous equation added to it, and still remain a solution.
For example in mathematical physics, the homogeneous equation may correspond to a physical theory formulated in empty space, while the inhomogeneous equation asks for more 'realistic' solutions with some matter, or charged particles.
Syntax
More abstractly, when using infix notation
T * U
the term T stands as the left-hand side and U as the right-hand side of the operator *. This usage is less common, though.
See also
Equals sign
References
Mathematical terminology |
https://en.wikipedia.org/wiki/Pseudovector | In physics and mathematics, a pseudovector (or axial vector) is a quantity that behaves like a vector in many situations, but its direction does not conform when the object is rigidly transformed by rotation, translation, reflection, etc. This can also happen when the orientation of the space is changed. For example, the angular momentum is a pseudovector because it is often described as a vector, but by just changing the position of reference (and changing the position vector), angular momentum can reverse direction, which is not supposed to happen with true (polar) vectors.
In three dimensions, the curl of a polar vector field at a point and the cross product of two polar vectors are pseudovectors.
One example of a pseudovector is the normal to an oriented plane. An oriented plane can be defined by two non-parallel vectors, a and b, that span the plane. The vector is a normal to the plane (there are two normals, one on each side – the right-hand rule will determine which), and is a pseudovector. This has consequences in computer graphics, where it has to be considered when transforming surface normals.
A number of quantities in physics behave as pseudovectors rather than polar vectors, including magnetic field and angular velocity. In mathematics, in three dimensions, pseudovectors are equivalent to bivectors, from which the transformation rules of pseudovectors can be derived. More generally, in n-dimensional geometric algebra, pseudovectors are the elements of the algebra with dimension , written ⋀n−1Rn. The label "pseudo-" can be further generalized to pseudoscalars and pseudotensors, both of which gain an extra sign-flip under improper rotations compared to a true scalar or tensor.
Physical examples
Physical examples of pseudovectors include torque, angular velocity, angular momentum, magnetic field, and magnetic dipole moment.
Consider the pseudovector angular momentum . Driving in a car, and looking forward, each of the wheels has an angular momentum |
https://en.wikipedia.org/wiki/Ultra-wideband | Ultra-wideband (UWB, ultra wideband, ultra-wide band and ultraband) is a radio technology that can use a very low energy level for short-range, high-bandwidth communications over a large portion of the radio spectrum. UWB has traditional applications in non-cooperative radar imaging. Most recent applications target sensor data collection, precise locating, and tracking. UWB support started to appear in high-end smartphones in 2019.
Characteristics
Ultra-wideband is a technology for transmitting information across a wide bandwidth (>500 MHz). This allows for the transmission of a large amount of signal energy without interfering with conventional narrowband and carrier wave transmission in the same frequency band. Regulatory limits in many countries allow for this efficient use of radio bandwidth, and enable high-data-rate personal area network (PAN) wireless connectivity, longer-range low-data-rate applications, and the transparent co-existence of radar and imaging systems with existing communications systems.
Ultra-wideband was formerly known as pulse radio, but the FCC and the International Telecommunication Union Radiocommunication Sector (ITU-R) currently define UWB as an antenna transmission for which emitted signal bandwidth exceeds the lesser of 500 MHz or 20% of the arithmetic center frequency. Thus, pulse-based systems—where each transmitted pulse occupies the UWB bandwidth (or an aggregate of at least 500 MHz of a narrow-band carrier; for example, orthogonal frequency-division multiplexing (OFDM))—can access the UWB spectrum under the rules.
Theory
A significant difference between conventional radio transmissions and UWB is that conventional systems transmit information by varying the power level, frequency, or phase (or a combination of these) of a sinusoidal wave. UWB transmissions transmit information by generating radio energy at specific time intervals and occupying a large bandwidth, thus enabling pulse-position or time modulation. The informatio |
https://en.wikipedia.org/wiki/Lyapunov%20exponent | In mathematics, the Lyapunov exponent or Lyapunov characteristic exponent of a dynamical system is a quantity that characterizes the rate of separation of infinitesimally close trajectories. Quantitatively, two trajectories in phase space with initial separation vector diverge (provided that the divergence can be treated within the linearized approximation) at a rate given by
where is the Lyapunov exponent.
The rate of separation can be different for different orientations of initial separation vector. Thus, there is a spectrum of Lyapunov exponents—equal in number to the dimensionality of the phase space. It is common to refer to the largest one as the maximal Lyapunov exponent (MLE), because it determines a notion of predictability for a dynamical system. A positive MLE is usually taken as an indication that the system is chaotic (provided some other conditions are met, e.g., phase space compactness). Note that an arbitrary initial separation vector will typically contain some component in the direction associated with the MLE, and because of the exponential growth rate, the effect of the other exponents will be obliterated over time.
The exponent is named after Aleksandr Lyapunov.
Definition of the maximal Lyapunov exponent
The maximal Lyapunov exponent can be defined as follows:
The limit ensures the validity of the linear approximation
at any time.
For discrete time system (maps or fixed point iterations) ,
for an orbit starting with this translates into:
Definition of the Lyapunov spectrum
For a dynamical system with evolution equation in an n–dimensional phase space, the spectrum of Lyapunov exponents
in general, depends on the starting point . However, we will usually be interested in the attractor (or attractors) of a dynamical system, and there will normally be one set of exponents associated with each attractor. The choice of starting point may determine which attractor the system ends up on, if there is more than one. (For Hamiltonian s |
https://en.wikipedia.org/wiki/Dirac%20%28video%20compression%20format%29 | Dirac is an open and royalty-free video compression format, specification and system developed by BBC Research & Development. Schrödinger and dirac-research (formerly just called "Dirac") are open and royalty-free software implementations (video codecs) of Dirac. Dirac format aims to provide high-quality video compression for Ultra HDTV and beyond, and as such competes with existing formats such as H.264 and VC-1.
The specification was finalised in January 2008, and further developments are only bug fixes and constraints. In September of that year, version 1.0.0 of an I-frame only subset known as Dirac Pro was released and has since been standardised by the SMPTE as VC-2. Version 2.2.3 of the full Dirac specification, including motion compensation and inter-frame coding, was issued a few days later. Dirac Pro was used internally by the BBC to transmit HDTV pictures at the Beijing Olympics in 2008.
The format implementations are named in honour of the theoretical physicists Paul Dirac and Erwin Schrödinger, who shared the 1933 Nobel Prize in physics.
Technology
Dirac supports resolutions of HDTV (1920×1080) and greater, and is claimed to provide significant savings in data rate and improvements in quality over video compression formats such as MPEG-2 Part 2, MPEG-4 Part 2 and its competitors, e.g. Theora, and WMV. Dirac's implementers make the preliminary claim of "a two-fold reduction in bit rate over MPEG-2 for high definition video", which makes it comparable to standards such as H.264/MPEG-4 AVC and VC-1.
Dirac supports both constant bit rate and variable bit rate operation. When the low delay syntax is used, the bit rate will be constant for each area (Dirac slice) in a picture to ensure constant latency. Dirac supports lossy and lossless compression modes.
Dirac employs wavelet compression, like the JPEG 2000 and PGF image formats and the Cineform professional video codec, instead of the discrete cosine transforms used in MPEG compression formats. Two of t |
https://en.wikipedia.org/wiki/Proof%20%28play%29 | Proof is a 2000 play by the American playwright David Auburn. Proof was developed at George Street Playhouse in New Brunswick, New Jersey, during the 1999 Next Stage Series of new plays. The play premiered Off-Broadway in May 2000 and transferred to Broadway in October 2000. The play won the 2001 Pulitzer Prize for Drama and the Tony Award for Best Play.
Plot
The play focuses on Catherine, the daughter of Robert, a recently deceased mathematical genius in his fifties and professor at the University of Chicago, and her struggle with mathematical genius and mental illness. Catherine had cared for her father through a lengthy mental illness. Upon Robert's death, his ex-graduate student Hal discovers a paradigm-shifting proof about prime numbers in Robert's office. The title refers both to that proof and to the play's central question: Can Catherine prove the proof's authorship? Along with demonstrating the proof's authenticity, Catherine also finds herself in a relationship with Hal. Throughout, the play explores Catherine's fear of following in her father's footsteps, both mathematically and mentally and her desperate attempts to stay in control.
Act I
The play opens with Catherine sitting in the backyard of her large, old house. Robert, her father, reveals a bottle of champagne to help celebrate her 25th birthday. Catherine complains that she hasn't done any worthwhile work in the field of mathematics, at least not to the same level as her father, a well-known math genius. He reassures her that she can still do good work as long as she stops sleeping until noon and wasting time reading magazines. Catherine confesses she is worried about inheriting Robert's inclination towards mental instability. He begins to comfort her but then alludes to a "bad sign" when he points out that he did, in fact, die a week ago. Robert disappears as Catherine dozes off. She awakens when Hal, one of Robert's students, exits the house. He has been studying the hundreds of notebooks Robe |
https://en.wikipedia.org/wiki/On%20Numbers%20and%20Games | On Numbers and Games is a mathematics book by John Horton Conway first published in 1976. The book is written by a pre-eminent mathematician, and is directed at other mathematicians. The material is, however, developed in a playful and unpretentious manner and many chapters are accessible to non-mathematicians. Martin Gardner discussed the book at length, particularly Conway's construction of surreal numbers, in his Mathematical Games column in Scientific American in September 1976.
The book is roughly divided into two sections: the first half (or Zeroth Part), on numbers, the second half (or First Part), on games. In the Zeroth Part, Conway provides axioms for arithmetic: addition, subtraction, multiplication, division and inequality. This allows an axiomatic construction of numbers and ordinal arithmetic, namely, the integers, reals, the countable infinity, and entire towers of infinite ordinals. The object to which these axioms apply takes the form {L|R}, which can be interpreted as a specialized kind of set; a kind of two-sided set. By insisting that L<R, this two-sided set resembles the Dedekind cut. The resulting construction yields a field, now called the surreal numbers. The ordinals are embedded in this field. The construction is rooted in axiomatic set theory, and is closely related to the Zermelo–Fraenkel axioms. In the original book, Conway simply refers to this field as "the numbers". The term "surreal numbers" is adopted later, at the suggestion of Donald Knuth.
In the First Part, Conway notes that, by dropping the constraint that L<R, the axioms still apply and the construction goes through, but the resulting objects can no longer be interpreted as numbers. They can be interpreted as the class of all two-player games. The axioms for greater than and less than are seen to be a natural ordering on games, corresponding to which of the two players may win. The remainder of the book is devoted to exploring a number of different (non-traditional, mathem |
https://en.wikipedia.org/wiki/Greek%20numerals | Greek numerals, also known as Ionic, Ionian, Milesian, or Alexandrian numerals, are a system of writing numbers using the letters of the Greek alphabet. In modern Greece, they are still used for ordinal numbers and in contexts similar to those in which Roman numerals are still used in the Western world. For ordinary cardinal numbers, however, modern Greece uses Arabic numerals.
History
The Minoan and Mycenaean civilizations' Linear A and Linear B alphabets used a different system, called Aegean numerals, which included number-only symbols for powers of ten: = 1, = 10, = 100, = 1000, and = 10000.
Attic numerals composed another system that came into use perhaps in the 7th century BCE. They were acrophonic, derived (after the initial one) from the first letters of the names of the numbers represented. They ran = 1, = 5, = 10, = 100, = 1,000, and = 10,000. The numbers 50, 500, 5,000, and 50,000 were represented by the letter with minuscule powers of ten written in the top right corner: , , , and . One-half was represented by (left half of a full circle) and one-quarter by ɔ (right side of a full circle). The same system was used outside of Attica, but the symbols varied with the local alphabets, for example, 1,000 was in Boeotia.
The present system probably developed around Miletus in Ionia. 19th century classicists placed its development in the 3rd century BCE, the occasion of its first widespread use. More thorough modern archaeology has caused the date to be pushed back at least to the 5th century BCE, a little before Athens abandoned its pre-Eucleidean alphabet in favour of Miletus's in 402 BCE, and it may predate that by a century or two. The present system uses the 24 letters adopted under Eucleides, as well as three Phoenician and Ionic ones that had not been dropped from the Athenian alphabet (although kept for numbers): digamma, koppa, and sampi. The position of those characters within the numbering system imply that the first two were still |
https://en.wikipedia.org/wiki/Equivalent%20rectangular%20bandwidth | The equivalent rectangular bandwidth or ERB is a measure used in psychoacoustics, which gives an approximation to the bandwidths of the filters in human hearing, using the unrealistic but convenient simplification of modeling the filters as rectangular band-pass filters, or band-stop filters, like in tailor-made notched music training (TMNMT).
Approximations
For moderate sound levels and young listeners, the bandwidth of human auditory filters can be approximated by the polynomial equation:
where f is the center frequency of the filter in kHz and ERB(f) is the bandwidth of the filter in Hz. The approximation is based on the results of a number of published simultaneous masking experiments and is valid from 0.1 to 6.5 kHz.
The above approximation was given in 1983 by Moore and Glasberg, who in 1990 published another (linear) approximation:
where f is in kHz and ERB(f) is in Hz. The approximation is applicable at moderate sound levels and for values of f between 0.1 and 10 kHz.
ERB-rate scale
The ERB-rate scale, or ERB-number scale, can be defined as a function ERBS(f) which returns the number of equivalent rectangular bandwidths below the given frequency f. The units of the ERB-number scale are known ERBs, or as Cams, following a suggestion by Hartmann. The scale can be constructed by solving the following differential system of equations:
The solution for ERBS(f) is the integral of the reciprocal of ERB(f) with the constant of integration set in such a way that ERBS(0) = 0.
Using the second order polynomial approximation () for ERB(f) yields:
where f is in kHz. The VOICEBOX speech processing toolbox for MATLAB implements the conversion and its inverse as:
where f is in Hz.
Using the linear approximation () for ERB(f) yields:
where f is in Hz.
See also
Critical bands
Bark scale
References
External links
Auditory Scales by Giampiero Salvi: shows comparison between Bark, Mel, and ERB scales
Acoustics
Hearing
Signal processing |
https://en.wikipedia.org/wiki/Fokker%E2%80%93Planck%20equation | In statistical mechanics and information theory, the Fokker–Planck equation is a partial differential equation that describes the time evolution of the probability density function of the velocity of a particle under the influence of drag forces and random forces, as in Brownian motion. The equation can be generalized to other observables as well. The Fokker-Planck equation has multiple applications in information theory, graph theory, data science, finance, economics etc.
It is named after Adriaan Fokker and Max Planck, who described it in 1914 and 1917. It is also known as the Kolmogorov forward equation, after Andrey Kolmogorov, who independently discovered it in 1931. When applied to particle position distributions, it is better known as the Smoluchowski equation (after Marian Smoluchowski), and in this context it is equivalent to the convection–diffusion equation. When applied to particle position and momentum distributions, it is known as the Klein–Kramers equation. The case with zero diffusion is the continuity equation. The Fokker–Planck equation is obtained from the master equation through Kramers–Moyal expansion.
The first consistent microscopic derivation of the Fokker–Planck equation in the single scheme of classical and quantum mechanics was performed by Nikolay Bogoliubov and Nikolay Krylov.
One dimension
In one spatial dimension x, for an Itô process driven by the standard Wiener process and described by the stochastic differential equation (SDE)
with drift and diffusion coefficient , the Fokker–Planck equation for the probability density of the random variable is
In the following, use .
Define the infinitesimal generator (the following can be found in Ref.):
The transition probability , the probability of going from to , is introduced here; the expectation can be written as
Now we replace in the definition of , multiply by and integrate over . The limit is taken on
Note now that
which is the Chapman–Kolmogorov theorem. Changing the |
https://en.wikipedia.org/wiki/River%20delta | A river delta is a landform shaped like a triangle, created by the deposition of sediment that is carried by a river and enters slower-moving or stagnant water. This occurs when a river enters an ocean, sea, estuary, lake, reservoir, or (more rarely) another river that cannot carry away the supplied sediment. It is so named because its triangle shape resembles the Greek letter Delta. The size and shape of a delta are controlled by the balance between watershed processes that supply sediment, and receiving basin processes that redistribute, sequester, and export that sediment. The size, geometry, and location of the receiving basin also plays an important role in delta evolution.
River deltas are important in human civilization, as they are major agricultural production centers and population centers. They can provide coastline defense and can impact drinking water supply. They are also ecologically important, with different species' assemblages depending on their landscape position. On geologic timescales, they are also important carbon sinks.
Etymology
A river delta is so named because the shape of the Nile Delta approximates the triangular uppercase Greek letter delta. The triangular shape of the Nile Delta was known to audiences of classical Athenian drama; the tragedy Prometheus Bound by Aeschylus refers to it as the "triangular Nilotic land", though not as a "delta". Herodotus's description of Egypt in his Histories mentions the Delta fourteen times, as "the Delta, as it is called by the Ionians", including describing the outflow of silt into the sea and the convexly curved seaward side of the triangle. Despite making comparisons to other river-systems' deltas, Herodotus did not describe them as "deltas". The Greek historian Polybius likened the land between the Rhône and Isère rivers to the Nile Delta, referring to both as islands, but did not apply the word delta. According to the Greek geographer Strabo, the Cynic philosopher Onesicritus of Astypalaea, |
https://en.wikipedia.org/wiki/Incidence%20algebra | In order theory, a field of mathematics, an incidence algebra is an associative algebra, defined for every locally finite partially ordered set
and commutative ring with unity. Subalgebras called reduced incidence algebras give a natural construction of various types of generating functions used in combinatorics and number theory.
Definition
A locally finite poset is one in which every closed interval
[a, b] = {x : a ≤ x ≤ b}
is finite.
The members of the incidence algebra are the functions f assigning to each nonempty interval [a, b] a scalar f(a, b), which is taken from the ring of scalars, a commutative ring with unity. On this underlying set one defines addition and scalar multiplication pointwise, and "multiplication" in the incidence algebra is a convolution defined by
An incidence algebra is finite-dimensional if and only if the underlying poset is finite.
Related concepts
An incidence algebra is analogous to a group algebra; indeed, both the group algebra and the incidence algebra are special cases of a category algebra, defined analogously; groups and posets being special kinds of categories.
Upper-Triangular Matrices
Consider the case of a partial order ≤ over any -element set . We enumerate as , and in such a way that the enumeration is compatible with the order ≤ on , that is, implies , which is always possible.
Then, functions as above, from intervals to scalars, can be thought of as matrices , where whenever , and otherwise. Since we arranged in a way consistent with the usual order on the indices of the matrices, they will appear as upper-triangular matrices with a prescribed zero-pattern determined by the incomparable elements in under ≤.
The incidence algebra of ≤ is then isomorphic to the algebra of upper-triangular matrices with this prescribed zero-pattern and arbitrary (including possibly zero) scalar entries everywhere else, with the operations being ordinary matrix addition, scaling and multiplication.
Special elements
The mul |
https://en.wikipedia.org/wiki/Concrete%20category | In mathematics, a concrete category is a category that is equipped with a faithful functor to the category of sets (or sometimes to another category, see Relative concreteness below). This functor makes it possible to think of the objects of the category as sets with additional structure, and of its morphisms as structure-preserving functions. Many important categories have obvious interpretations as concrete categories, for example the category of topological spaces and the category of groups, and trivially also the category of sets itself. On the other hand, the homotopy category of topological spaces is not concretizable, i.e. it does not admit a faithful functor to the category of sets.
A concrete category, when defined without reference to the notion of a category, consists of a class of objects, each equipped with an underlying set; and for any two objects A and B a set of functions, called morphisms, from the underlying set of A to the underlying set of B. Furthermore, for every object A, the identity function on the underlying set of A must be a morphism from A to A, and the composition of a morphism from A to B followed by a morphism from B to C must be a morphism from A to C.
Definition
A concrete category is a pair (C,U) such that
C is a category, and
U : C → Set (the category of sets and functions) is a faithful functor.
The functor U is to be thought of as a forgetful functor, which assigns to every object of C its "underlying set", and to every morphism in C its "underlying function".
A category C is concretizable if there exists a concrete category (C,U);
i.e., if there exists a faithful functor U: C → Set. All small categories are concretizable: define U so that its object part maps each object b of C to the set of all morphisms of C whose codomain is b (i.e. all morphisms of the form f: a → b for any object a of C), and its morphism part maps each morphism g: b → c of C to the function U(g): U(b) → U(c) which maps each member f: a → b of U( |
https://en.wikipedia.org/wiki/ISO%20639 | ISO 639 is a multi-part standard by the International Organization for Standardization (ISO) concerned with representation of names for languages and language groups.
It currently consists of five parts (1-5); a part 6 was published but withdrawn.
It was first approved in 1967 as a single-part ISO Recommendation, ISO/R 639, superseded in 2002 by part 1 of the new series, ISO 639-1
Use of ISO 639 codes
The language codes defined in the several sections of ISO 639 are used for bibliographic purposes and, in computing and internet environments, as a key element of locale data. The codes also find use in various applications, such as Wikipedia URLs for its different language editions.
Current and historical parts of the standard
Each part of the standard is maintained by a maintenance agency, which adds codes and changes the status of codes when needed. ISO 639-6 was withdrawn in 2014.
Characteristics of individual codes
Scopes:
Individual languages
Macrolanguages (Part 3)
Collections of languages (Parts 1, 2, 5). Part 1 contains only one collection (bh), some collections were already in Part 2, and others were added only in Part 5:
Remainder groups: 36 collections in both Part 2 and 5 are of this kind (including one that was also coded in Part 1) — for compatibility with Part 2 when Part 5 was still not published, the remainder groups do not contain any language and collection that was already coded in Part 2 (however new applications compatible with Part 5 may treat these groups inclusively, as long they respect the containment hierarchy published in Part 5 and they use the most specific collection when grouping languages);
Regular groups: 29 collections in both Parts 2 and 5 are of this kind — for compatibility with Part 2, they can not contain other groups;
Families: 50 new collections coded only in Part 5 (including one containing a regular group already coded in Part 2) — for compatibility with Part 2, they may contain other collections except remainder |
https://en.wikipedia.org/wiki/Unit%20vector | In mathematics, a unit vector in a normed vector space is a vector (often a spatial vector) of length 1. A unit vector is often denoted by a lowercase letter with a circumflex, or "hat", as in (pronounced "v-hat").
The term direction vector, commonly denoted as d, is used to describe a unit vector being used to represent spatial direction and relative direction. 2D spatial directions are numerically equivalent to points on the unit circle
and spatial directions in 3D are equivalent to a point on the unit sphere.
The normalized vector û of a non-zero vector u is the unit vector in the direction of u, i.e.,
where ‖u‖ is the norm (or length) of u. The term normalized vector is sometimes used as a synonym for unit vector.
Unit vectors are often chosen to form the basis of a vector space, and every vector in the space may be written as a linear combination of unit vectors.
Orthogonal coordinates
Cartesian coordinates
Unit vectors may be used to represent the axes of a Cartesian coordinate system. For instance, the standard unit vectors in the direction of the x, y, and z axes of a three dimensional Cartesian coordinate system are
They form a set of mutually orthogonal unit vectors, typically referred to as a standard basis in linear algebra.
They are often denoted using common vector notation (e.g., i or ) rather than standard unit vector notation (e.g., ). In most contexts it can be assumed that i, j, and k, (or and ) are versors of a 3-D Cartesian coordinate system. The notations , , , or , with or without hat, are also used, particularly in contexts where i, j, k might lead to confusion with another quantity (for instance with index symbols such as i, j, k, which are used to identify an element of a set or array or sequence of variables).
When a unit vector in space is expressed in Cartesian notation as a linear combination of i, j, k, its three scalar components can be referred to as direction cosines. The value of each component is equal to the cosine |
https://en.wikipedia.org/wiki/Cyrix%205x86 | The Cyrix 5x86 was a line of x86 microprocessors designed by Cyrix and released on June 5 of 1995. Cyrix, being a fabless company, had the chips manufactured by IBM. The line came out about 5 months before the more famous Cyrix 6x86. The Cyrix 5x86 was one of the fastest CPUs ever produced for Socket 3 computer systems. With better performance in most applications than an Intel Pentium processor at 75 MHz, the Cyrix Cx5x86 filled a gap by providing a medium-performance processor option for 486 Socket 3 motherboards (which are incapable of handling Intel's Pentium CPUs, apart from the Pentium Overdrive).
The IBM 5x86C is an IBM branded and produced version of the Cyrix-designed Cyrix Cx5x86 CPU. Previous IBM x86 processors, IBM 386SLC and IBM 486SLC, were based on modified Intel designs.
Design
The Cyrix 5x86 processor, codename "M1sc", was based on a scaled-down version of the "M1" core used in the Cyrix 6x86, which provided 80% of the performance for a 50% decrease in transistors over the 6x86 design. It had the 32-bit memory bus of an ordinary 486 processor, but internally had much more in common with fifth-generation processors such as the Cyrix 6x86, the AMD K5, and the Intel Pentium, and even the sixth-generation Intel Pentium Pro. The chip featured near-complete support for i486 instructions, but very limited support for Pentium instructions. Some performance-enhancing features of the CPU were intentionally disabled due to potentially stability-threatening bugs which were not fixed before release time (these features can be enabled with freely downloadable software utilities; see below).
The similarly named SGS-Thomson (STMicroelectronics) ST5x86 and IBM 5x86C were licensed rebrandings of the Cyrix design (IBM and ST physically produced Cyrix's CPUs for them), marketed separately but identical for practical purposes, apart from the availability of a 75 MHz edition which Cyrix did not bring to market, and slight differences in voltage requirements. The Cyri |
https://en.wikipedia.org/wiki/Adult | An adult is a human or other animal that has reached full growth. The biological definition of the word means an animal reaching sexual maturity and thus capable of reproduction. In the human context, the term adult has meanings associated with social and legal concepts. In contrast to a non-adult or "minor", a legal adult is a person who has attained the age of majority and is therefore regarded as independent, self-sufficient, and responsible. They may also be regarded as a "major". The typical age of attaining legal adulthood is 18 to 21, although definition may vary by legal rights, country, and psychological development.
Human adulthood encompasses psychological adult development. Definitions of adulthood are often inconsistent and contradictory; a person may be biologically an adult, and have adult behavior, but still be treated as a child if they are under the legal age of majority. Conversely, one may legally be an adult but possess none of the maturity and responsibility that may define an adult character.
In different cultures there are events that relate passing from being a child to becoming an adult or coming of age. This often encompasses the passing a series of tests to demonstrate that a person is prepared for adulthood, or reaching a specified age, sometimes in conjunction with demonstrating preparation. Most modern societies determine legal adulthood based on reaching a legally specified age without requiring a demonstration of physical maturity or preparation for adulthood.
Biological adulthood
Historically and cross-culturally, adulthood has been determined primarily by the start of puberty (the appearance of secondary sex characteristics such as menstruation and the development of breasts in women, ejaculation, the development of facial hair, and a deeper voice in men, and pubic hair in both sexes). In the past, a person usually moved from the status of child directly to the status of adult, often with this shift being marked by some type of |
https://en.wikipedia.org/wiki/Nicolas%20Bourbaki | Nicolas Bourbaki () is the collective pseudonym of a group of mathematicians, predominantly French alumni of the École normale supérieure (ENS). Founded in 1934–1935, the Bourbaki group originally intended to prepare a new textbook in analysis. Over time the project became much more ambitious, growing into a large series of textbooks published under the Bourbaki name, meant to treat modern pure mathematics. The series is known collectively as the Éléments de mathématique (Elements of Mathematics), the group's central work. Topics treated in the series include set theory, abstract algebra, topology, analysis, Lie groups and Lie algebras.
Bourbaki was founded in response to the effects of the First World War which caused the death of a generation of French mathematicians; as a result, young university instructors were forced to use dated texts. While teaching at the University of Strasbourg, Henri Cartan complained to his colleague André Weil of the inadequacy of available course material, which prompted Weil to propose a meeting with others in Paris to collectively write a modern analysis textbook. The group's core founders were Cartan, Claude Chevalley, Jean Delsarte, Jean Dieudonné and Weil; others participated briefly during the group's early years, and membership has changed gradually over time. Although former members openly discuss their past involvement with the group, Bourbaki has a custom of keeping its current membership secret.
The group's name derives from the 19th century French general Charles-Denis Bourbaki, who had a career of successful military campaigns before suffering a dramatic loss in the Franco-Prussian War. The name was therefore familiar to early 20th-century French students. Weil remembered an ENS student prank in which an upperclassman posed as a professor and presented a "theorem of Bourbaki"; the name was later adopted.
The Bourbaki group holds regular private conferences for the purpose of drafting and expanding the Éléments. Topics |
https://en.wikipedia.org/wiki/Am5x86 | The Am5x86 processor is an x86-compatible CPU announced in November of 1995 by AMD for use in 486-class computer systems. It began shipping in December of 1995, with a base price of $93 per unit in bulk quantities. Before being released, it was in development under the codename "X5".
Specifications
The Am5x86 (also known as the 5x86-133, Am5x86, X5-133, and sold under various 3rd-party labels such as the Kingston Technology "Turbochip") is an Enhanced Am486 processor with an internally set multiplier of 4, allowing it to run at 133 MHz on systems without official support for clock-multiplied DX2 or DX4 486 processors. Like all Enhanced Am486, the Am5x86 featured write-back L1 cache, and unlike all but a few, a generous 16 kilobytes rather than the more common 8 KB. A rare 150 MHz-rated OEM part was also released by AMD.
Since having a clock multiplier of four is not part of the original Socket 3 design (and that the 486 only have a single CLKMUL pin anyway), AMD made the 5x86 accept a 2x setting from the motherboard and instead operate at a rate of 4x. When using an Am5x86, the motherboard must be set to the 2x setting. The chip will actually physically fit into an older 486 socket such as a socket 1 or 2 or the original 168-pin 80486 socket, but doing this requires a replacement voltage regulator, since the AMD chip runs at 3.45 volts.
The combination of clock speed and the relatively large 16 KB write-back L1 cache allows the 5x86 to equal or slightly exceed an Intel Pentium 75 MHz processor in integer arithmetic in benchmarks. Real world performance varies, however, with later Windows operating systems and many FPU-sensitive games favoring the Pentium 75 MHz. Because it is based on a pure 486 design, it is compatible with older systems, something its slightly faster rival, the Cyrix Cx5x86, has trouble with. The CPU is commonly overclocked to 160 MHz, thereby giving performance similar to that of a Pentium 90 MHz system. There are four main versions of the so |
https://en.wikipedia.org/wiki/Echo%20sounding | Echo sounding or depth sounding is the use of sonar for ranging, normally to determine the depth of water (bathymetry). It involves transmitting acoustic waves into water and recording the time interval between emission and return of a pulse; the resulting time of flight, along with knowledge of the speed of sound in water, allows determining the distance between sonar and target. This information is then typically used for navigation purposes or in order to obtain depths for charting purposes.
Echo sounding can also be used for ranging to other targets, such as fish schools. Hydroacoustic assessments have traditionally employed mobile surveys from boats to evaluate fish biomass and spatial distributions. Conversely, fixed-location techniques use stationary transducers to monitor passing fish.
The word sounding is used for all types of depth measurements, including those that don't use sound, and is unrelated in origin to the word sound in the sense of noise or tones. Echo sounding is a more rapid method of measuring depth than the previous technique of lowering a sounding line until it touched bottom.
History
German inventor Alexander Behm was granted German patent No. 282009 for the invention of echo sounding (device for measuring depths of the sea and distances and headings of ships or obstacles by means of reflected sound waves) on 22 July 1913.
One of the first commercial echo sounding units was the Fessenden Fathometer, which used the Fessenden oscillator to generate sound waves. This was first installed by the Submarine Signal Company in 1924 on the M&M liner S.S. Berkshire.
Technique
Distance is measured by multiplying half the time from the signal's outgoing pulse to its return by the speed of sound in the water, which is approximately 1.5 kilometres per second [T÷2×(4700 feet per second or 1.5 km per second )] For precise applications of echosounding, such as hydrography, the speed of sound must also be measured typically by deploying a sound vel |
https://en.wikipedia.org/wiki/Protein%20production | Protein production is the biotechnological process of generating a specific protein. It is typically achieved by the manipulation of gene expression in an organism such that it expresses large amounts of a recombinant gene. This includes the transcription of the recombinant DNA to messenger RNA (mRNA), the translation of mRNA into polypeptide chains, which are ultimately folded into functional proteins and may be targeted to specific subcellular or extracellular locations.
Protein production systems (also known as expression systems) are used in the life sciences, biotechnology, and medicine. Molecular biology research uses numerous proteins and enzymes, many of which are from expression systems; particularly DNA polymerase for PCR, reverse transcriptase for RNA analysis, restriction endonucleases for cloning, and to make proteins that are screened in drug discovery as biological targets or as potential drugs themselves. There are also significant applications for expression systems in industrial fermentation, notably the production of biopharmaceuticals such as human insulin to treat diabetes, and to manufacture enzymes.
Protein production systems
Commonly used protein production systems include those derived from bacteria, yeast, baculovirus/insect, mammalian cells, and more recently filamentous fungi such as Myceliophthora thermophila. When biopharmaceuticals are produced with one of these systems, process-related impurities termed host cell proteins also arrive in the final product in trace amounts.
Cell-based systems
The oldest and most widely used expression systems are cell-based and may be defined as the "combination of an expression vector, its cloned DNA, and the host for the vector that provide a context to allow foreign gene function in a host cell, that is, produce proteins at a high level". Overexpression is an abnormally and excessively high level of gene expression which produces a pronounced gene-related phenotype.
There are many ways to intro |
https://en.wikipedia.org/wiki/Transcription%20%28biology%29 | Transcription is the process of copying a segment of DNA into RNA. The segments of DNA transcribed into RNA molecules that can encode proteins are said to produce messenger RNA (mRNA). Other segments of DNA are copied into RNA molecules called non-coding RNAs (ncRNAs). mRNA comprises only 1–3% of total RNA samples. Less than 2% of the human genome can be transcribed into mRNA (Human genome#Coding vs. noncoding DNA), while at least 80% of mammalian genomic DNA can be actively transcribed (in one or more types of cells), with the majority of this 80% considered to be ncRNA.
Both DNA and RNA are nucleic acids, which use base pairs of nucleotides as a complementary language. During transcription, a DNA sequence is read by an RNA polymerase, which produces a complementary, antiparallel RNA strand called a primary transcript.
Transcription proceeds in the following general steps:
RNA polymerase, together with one or more general transcription factors, binds to promoter DNA.
RNA polymerase generates a transcription bubble, which separates the two strands of the DNA helix. This is done by breaking the hydrogen bonds between complementary DNA nucleotides.
RNA polymerase adds RNA nucleotides (which are complementary to the nucleotides of one DNA strand).
RNA sugar-phosphate backbone forms with assistance from RNA polymerase to form an RNA strand.
Hydrogen bonds of the RNA–DNA helix break, freeing the newly synthesized RNA strand.
If the cell has a nucleus, the RNA may be further processed. This may include polyadenylation, capping, and splicing.
The RNA may remain in the nucleus or exit the cytoplasm through the nuclear pore complex.
If the stretch of DNA is transcribed into an RNA molecule that encodes a protein, the RNA is termed messenger RNA (mRNA); the mRNA, in turn, serves as a template for the protein's synthesis through translation. Other stretches of DNA may be transcribed into small non-coding RNAs such as microRNA, transfer RNA (tRNA), small nucleolar |
https://en.wikipedia.org/wiki/Mailing%20list | A mailing list is a collection of names and addresses used by an individual or an organization to send material to multiple recipients. The term is often extended to include the people subscribed to such a list, so the group of subscribers is referred to as "the mailing list", or simply "the list".
Transmission may be paper-based or electronic. Each has its strengths, although a 2022 article claimed that "direct mail still brings in the lion's share of revenue for most organizations."
Types
At least two types of mailing lists can be defined:
an announcement list is closer to the original sense, where a "mailing list" of people was used as a recipient for newsletters, periodicals or advertising. Traditionally this was done through the postal system, but with the rise of email, the electronic mailing list became popular. This type of list is used primarily as a one-way conduit of information and may only be "posted to" by selected people. This may also be referred to by the term newsletter. Newsletter and promotional emailing lists are employed in various sectors as parts of direct marketing campaigns.
a "discussion list" allows subscribing members (sometimes even people outside the list) to post their own items which are broadcast to all of the other mailing list members. Recipients may answer in a similar fashion, thus, actual discussion and information exchanges can occur. Mailing lists of this type are usually topic-oriented (for example, politics, scientific discussion, health problems, joke contests), and the topic may range from extremely narrow to "whatever you think could interest us." In this they are similar to Usenet newsgroups, another form of discussion group that may have an aversion to off-topic messages.
Historically mailing lists preceded email/web forums; both can provide analogous functionalities. When used in that fashion, mailing lists are sometimes known as discussion lists or discussion forums. Discussion lists provide some advantages ove |
https://en.wikipedia.org/wiki/Cell%20type | A cell type is a classification used to identify cells that share morphological or phenotypical features. A multicellular organism may contain cells of a number of widely differing and specialized cell types, such as muscle cells and skin cells, that differ both in appearance and function yet have identical genomic sequences. Cells may have the same genotype, but belong to different cell types due to the differential regulation of the genes they contain. Classification of a specific cell type is often done through the use of microscopy (such as those from the cluster of differentiation family that are commonly used for this purpose in immunology). Recent developments in single cell RNA sequencing facilitated classification of cell types based on shared gene expression patterns. This has led to the discovery of many new cell types in e.g. mouse cortex, hippocampus, dorsal root ganglion and spinal cord.
Animals have evolved a greater diversity of cell types in a multicellular body (100–150 different cell types), compared
with 10–20 in plants, fungi, and protists. The exact number of cell types is, however, undefined, and the Cell Ontology, as of 2021, lists over 2,300 different cell types.
Multicellular organisms
All higher multicellular organisms contain cells specialised for different functions. Most distinct cell types arise from a single totipotent cell that differentiates into hundreds of different cell types during the course of development. Differentiation of cells is driven by different environmental cues (such as cell–cell interaction) and intrinsic differences (such as those caused by the uneven distribution of molecules during division). Multicellular organisms are composed of cells that fall into two fundamental types: germ cells and somatic cells. During development, somatic cells will become more specialized and form the three primary germ layers: ectoderm, mesoderm, and endoderm. After formation of the three germ layers, cells will continue to special |
https://en.wikipedia.org/wiki/Liber%20Abaci | (also spelled as Liber Abbaci; "The Book of Calculation") is a historic 1202 Latin manuscript on arithmetic by Leonardo of Pisa, posthumously known as Fibonacci.
Premise
was among the first Western books to describe the Hindu–Arabic numeral system and to use symbols resembling modern "Arabic numerals". By addressing the applications of both commercial tradesmen and mathematicians, it promoted the superiority of the system, and the use of these glyphs.
Although the book's title is sometimes translated as "The Book of the Abacus", notes that it is an error to read this as referring to calculating devices called "abacus". Rather, the word "abacus" was used at the time to refer to calculation in any form; the spelling "abbacus" with two "b"s (which is how Leonardo spelled it in the original Latin manuscript) was, and still is in Italy, used to refer to calculation using Hindu-Arabic numerals, which can avoid confusion. The book describes methods of doing calculations without aid of an abacus, and as confirms, for centuries after its publication the algorismists (followers of the style of calculation demonstrated in ) remained in conflict with the abacists (traditionalists who continued to use the abacus in conjunction with Roman numerals). The historian of mathematics Carl Boyer emphasizes in his History of Mathematics that although "Liber abaci...is not on the abacus" per se, nevertheless "...it is a very thorough treatise on algebraic methods and problems in which the use of the Hindu-Arabic numerals is strongly advocated."
Summary of sections
The first section introduces the Hindu–Arabic numeral system, including methods for converting between different representation systems. This section also includes the first known description of trial division for testing whether a number is composite and, if so, factoring it.
The second section presents examples from commerce, such as conversions of currency and measurements, and calculations of profit and interest.
T |
https://en.wikipedia.org/wiki/Hydrographic%20survey | Hydrographic survey is the science of measurement and description of features which affect maritime navigation, marine construction, dredging, offshore oil exploration and drilling and related activities. Strong emphasis is placed on soundings, shorelines, tides, currents, seabed and submerged obstructions that relate to the previously mentioned activities. The term hydrography is used synonymously to describe maritime cartography, which in the final stages of the hydrographic process uses the raw data collected through hydrographic survey into information usable by the end user.
Hydrography is collected under rules which vary depending on the acceptance authority. Traditionally conducted by ships with a sounding line or echo sounding, surveys are increasingly conducted with the aid of aircraft and sophisticated electronic sensor systems in shallow waters.
Offshore survey is a specific discipline of hydrographic survey primarily concerned with the description of the condition of the seabed and the condition of the subsea oilfield infrastructure that interacts with it.
Organizations
National and international offices
Hydrographic offices evolved from naval heritage and are usually found within national naval structures, for example Spain's Instituto Hidrográfico de la Marina. Coordination of those organizations and product standardization is voluntarily joined with the goal of improving hydrography and safe navigation is conducted by the International Hydrographic Organization (IHO). The IHO publishes Standards and Specifications followed by its Member States as well as Memoranda of Understanding and Co-operative Agreements with hydrographic survey interests.
The product of such hydrography is most often seen on nautical charts published by the national agencies and required by the International Maritime Organization (IMO), the Safety of Life at Sea (SOLAS) and national regulations to be carried on vessels for safety purposes. Increasingly those charts are pr |
https://en.wikipedia.org/wiki/Descent%20%28video%20game%29 | Descent is a first-person shooter (FPS) game developed by Parallax Software and released by Interplay Productions in 1995 for MS-DOS, and later for Macintosh, PlayStation, and RISC OS. It popularized a subgenre of FPS games employing six degrees of freedom and was the first FPS to feature entirely true-3D graphics. The player is cast as a mercenary hired to eliminate the threat of a mysterious extraterrestrial computer virus infecting off-world mining robots. In a series of mines throughout the Solar System, the protagonist pilots a spaceship and must locate and destroy the mine's power reactor and escape before being caught in the mine's self-destruction, defeating opposing robots along the way. Players can play online and compete in either deathmatches or cooperate to take on the robots.
Descent was a commercial success. Together with its sequel, it sold over 1.1 million units as of 1998 and was critically acclaimed. Commentators and reviewers compared it to Doom and praised its unrestrained range of motion and full 3D graphics. The combination of traditional first-person shooter mechanics with that of a space flight simulator was also well received. Complaints tended to focus on the frequency for the player to become disoriented and the potential to induce motion sickness. The game's success spawned expansion packs and the sequels Descent II (1996) and Descent 3 (1999).
Gameplay
Single-player
Descent is a first-person shooter and shoot 'em up game wherein the player pilots a spaceship through labyrinthine mines while fighting virus-infected robots, using the ship's armaments. They must find and destroy each mine's reactor core, triggering a meltdown that will destroy the mine as the player escapes. For two levels, the reactor core is replaced with a boss. To obtain access to the reactor, the player must collect one or a combination of the three colored access keys for each level. As a secondary objective, the player can also choose to rescue PTMC (Post Terran |
https://en.wikipedia.org/wiki/Bartholin%27s%20gland | The Bartholin's glands (named after Caspar Bartholin the Younger; also called Bartholin glands or greater vestibular glands) are two pea sized compound alveolar glands located slightly posterior and to the left and right of the opening of the vagina. They secrete mucus to lubricate the vagina.
They are homologous to bulbourethral glands in males. However, while Bartholin's glands are located in the superficial perineal pouch in females, bulbourethral glands are located in the deep perineal pouch in males. Their duct length is 1.5 to 2.0 cm and they open into navicular fossa. The ducts are paired and they open on the surface of the vulva.
Anatomy
The embryological origin of the Bartholin's glands is derived from the urogenital sinus; therefore, the nerve innervation and blood supply are via the pudendal nerve and external pudendal artery, respectively. The superficial inguinal lymph nodes and pelvic nodes provide lymphatic drainage.
These glands are pea-sized (0.5–1.0 cm) and are lined with columnar epithelium. The duct length is 1.5–2 cm and is lined with squamous epithelium. These are located just beneath the fascia and their ducts drain into the vestibular mucosa. These mucoid alkaline secreting glands are arranged as lobules consisting of alveoli lined by cuboidal or columnar epithelium. Their efferent ducts are composed of transitional epithelium, which merges into squamous epithelium as it enters the distal vagina. The more proximal portions of the ductal system are lined by transitional epithelium and may be lined by columnar epithelium before arborization into glandular secretory elements.
These glands lie on the perineal membrane and beneath the bulbospongiosus muscle at the tail end of the vestibular bulb deep to the posterior labia majora. The intimate relation between the enormously vascular tissue of the vestibular bulb and the Bartholin's glands is responsible for the risk of hemorrhage associated with the removal of this latter structure.
The Bart |
https://en.wikipedia.org/wiki/RISC%20OS | RISC OS is a computer operating system originally designed by Acorn Computers Ltd in Cambridge, England. First released in 1987, it was designed to run on the ARM chipset, which Acorn had designed concurrently for use in its new line of Archimedes personal computers. RISC OS takes its name from the reduced instruction set computer (RISC) architecture it supports.
Between 1987 and 1998, RISC OS was included in every ARM-based Acorn computer model, including the Acorn Archimedes line, Acorn's R line (with RISC iX as a dual-boot option), RiscPC, A7000, and prototype models such as the Acorn NewsPad and Phoebe computer. A version of the OS, named NCOS, was used in Oracle Corporation's Network Computer and compatible systems.
After the break-up of Acorn in 1998, development of the OS was forked and continued separately by several companies, including , Pace Micro Technology, and Castle Technology. Since then, it has been bundled with several ARM-based desktop computers such as the Iyonix PC and A9home. , the OS remains forked and is independently developed by and the community.
Most recent stable versions run on the ARMv3/ARMv4 RiscPC, the ARMv5 Iyonix, ARMv7 Cortex-A8 processors (such as that used in the BeagleBoard and Touch Book) and Cortex-A9 processors (such as that used in the PandaBoard) and the low-cost educational Raspberry Pi computer. SD card images have been released for downloading free of charge to Raspberry Pi 1, 2, 3, & 4 users with a full graphical user interface (GUI) version and a command-line interface only version (RISC OS Pico, at 3.8 MB).
History
The first version of RISC OS was originally released in 1987 as Arthur 1.20. The next version, , became and was released in April 1989. RISC OS 3.00 was released with the A5000 in 1991, and contained many new features. By 1996, RISC OS had been shipped on over 500,000 systems.
Acorn officially halted work on the OS in January 1999, renaming themselves Element 14. In March 1999 a new company, RIS |
https://en.wikipedia.org/wiki/Artturi%20Ilmari%20Virtanen | Artturi Ilmari Virtanen (; 15 January 1895 – 11 November 1973) was a Finnish chemist and recipient of the 1945 Nobel Prize in Chemistry "for his research and inventions in agricultural and nutrition chemistry, especially for his fodder preservation method".
He invented AIV silage which improved milk production and a method of preserving butter, the AIV salt, which led to increased Finnish butter exports.
Personal life
Artturi Ilmari Virtanen was born on 15 January, 1895, in Helsinki, Finland . He is the son of Kaarlo Virtanen, a railway engine driver and Serafina Isotalo.
He completed his school education at the Classical Lyceum in Viipuri, Finland. He married the botanist Lilja Moisio (1894-1972) in 1920 and had two sons with her.
In 1933, he bought a farm near Helsinki where he tested some of his scientific results in practice. He saw in the overproduction of food only a temporary phenomenon. He lived a simple life, he never had a car of his own, never smoked and never consumed alcohol. He died of pneumonia in November 1973, following a broken femur from a fall few weeks prior. He was buried at the Hietaniemi Cemetery.
Academics
Virtanen began his studies at the University of Helsinki in chemistry 1913 earning his Master and in 1918 his PhD in organic chemistry. In 1919 he started to work in the laboratories of Valio, a large producer of dairy products and became director of the laboratory in 1920. Feeling not fully qualified and following his interest in botany and zoology led him to further scientific education and so he left Valio and studied at the ETH, the University of Münster and the University of Stockholm he studied physical chemistry, soil chemistry and microbiology. In 1923 in Sweden he worked with Hans von Euler-Chelpin, who was awarded with the Nobel Prize in Chemistry in 1929. Back in Finland he became lecturer at the University of Helsinki in 1924, known for his lectures on chemistry of life. He worked in the laboratory of the Butter Export As |
https://en.wikipedia.org/wiki/Anatomical%20terms%20of%20location | Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position provides a definition of what is at the front ("anterior"), behind ("posterior") and so on. As part of defining and describing terms, the body is described through the use of anatomical planes and anatomical axes.
The meaning of terms that are used can change depending on whether an organism is bipedal or quadrupedal. Additionally, for some animals such as invertebrates, some terms may not have any meaning at all; for example, an animal that is radially symmetrical will have no anterior surface, but can still have a description that a part is close to the middle ("proximal") or further from the middle ("distal").
International organisations have determined vocabularies that are often used as standards for subdisciplines of anatomy. For example, Terminologia Anatomica for humans and Nomina Anatomica Veterinaria for animals. These allow parties that use anatomical terms, such as anatomists, veterinarians, and medical doctors, to have a standard set of terms to communicate clearly the position of a structure.
Introduction
Standard anatomical and zoological terms of location have been developed, usually based on Latin and Greek words, to enable all biological and medical scientists, veterinarians, doctors and anatomists to precisely delineate and communicate information about animal bodies and their organs, even though the meaning of some of the terms often is context-sensitive. Much of this information has been standardised in internationally agreed vocabularies for humans (Terminologia Anatomica) and animals (Nomina Anatomica Veterinaria).
Different terms are used for groups of creatures with different body layouts, such as bipeds (creatures that stand on two feet, such as humans) and quadrupeds. The reasoning is that the neur |
https://en.wikipedia.org/wiki/Arithmetic%20progression | An arithmetic progression or arithmetic sequence () is a sequence of numbers such that the difference from any succeeding term to its preceding term remains constant throughout the sequence. The constant difference is called common difference of that arithmetic progression. For instance, the sequence 5, 7, 9, 11, 13, 15, . . . is an arithmetic progression with a common difference of 2.
If the initial term of an arithmetic progression is and the common difference of successive members is , then the -th term of the sequence () is given by:
A finite portion of an arithmetic progression is called a finite arithmetic progression and sometimes just called an arithmetic progression. The sum of a finite arithmetic progression is called an arithmetic series.
History
According to an anecdote of uncertain reliability, young Carl Friedrich Gauss, who was in primary school, reinvented this method to compute the sum of the integers from 1 through 100, by multiplying pairs of numbers in the sum by the values of each pair . However, regardless of the truth of this story, Gauss was not the first to discover this formula, and some find it likely that its origin goes back to the Pythagoreans in the 5th century BC. Similar rules were known in antiquity to Archimedes, Hypsicles and Diophantus; in China to Zhang Qiujian; in India to Aryabhata, Brahmagupta and Bhaskara II; and in medieval Europe to Alcuin, Dicuil, Fibonacci, Sacrobosco
and to anonymous commentators of Talmud known as Tosafists.
Sum
Computation of the sum 2 + 5 + 8 + 11 + 14. When the sequence is reversed and added to itself term by term, the resulting sequence has a single repeated value in it, equal to the sum of the first and last numbers (2 + 14 = 16). Thus 16 × 5 = 80 is twice the sum.
The sum of the members of a finite arithmetic progression is called an arithmetic series. For example, consider the sum:
This sum can be found quickly by taking the number n of terms being added (here 5), multiplying by the sum |
https://en.wikipedia.org/wiki/HomePNA | The HomePNA Alliance (formerly the Home Phoneline Networking Alliance, also known as HPNA) is an incorporated non-profit industry association of companies that develops and standardizes technology for home networking over the existing coaxial cables and telephone wiring within homes, so new wires do not need to be installed.
HomePNA was developed for entertainment applications such as IPTV which require good quality of service (QoS).
History
HomePNA 1.0 technology was developed by Tut Systems in the 1990s. The original protocols used balanced pair telephone wire.
HomePNA 2.0 was developed by Epigram and was approved by the ITU as Recommendations G.9951, G.9952 and G.9953.
HomePNA 3.0 was developed by Broadcom (which had purchased Epigram) and Coppergate Communications and was approved by the ITU as Recommendation G.9954 in February 2005.
HomePNA 3.1 was developed by Coppergate Communications and was approved by the ITU as Recommendation G.9954 in January 2007. HomePNA 3.1 added Ethernet over coax. HomePNA 3.1 uses frequencies above those used for digital subscriber line and analog voice calls over phone wires and below those used for broadcast and direct-broadcast satellite TV over coax, so it can coexist with those services on the same wires.
In March 2009, HomePNA announced a liaison agreement with the HomeGrid Forum to promote the ITU-T G.hn wired home networking standard. In May 2013 the HomePNA alliance merged with the HomeGrid Forum.
Technical characteristics
HomePNA uses frequency-division multiplexing (FDM), which uses different frequencies for voice and data on the same wires without interfering with each other. A standard phone line has enough room to support voice, high-speed DSL and a landline phone.
Two custom chips designed using the HPNA specifications were developed by Broadcom: the 4100 chip can send and receive signals over 1,000 ft (305 m) on a typical phone line. The larger 4210 controller chip strips away noise and passes data on |
https://en.wikipedia.org/wiki/Film%20speed | Film speed is the measure of a photographic film's sensitivity to light, determined by sensitometry and measured on various numerical scales, the most recent being the ISO system introduced in the mid-1970s. A closely related ISO system is used to describe the relationship between exposure and output image lightness in digital cameras. Prior to ISO gaining traction the best known systems were ASA in the U.S. and DIN in Europe.
The term speed comes from the early days of photography. Photographic emulsions that were more sensitive to light needed less time to generate an acceptable image and thus a complete exposure could be finished faster, with the subjects having to hold their pose and not make any body movements for a shorter length of time. Emulsions that were less sensitive were called slower because the time to complete an exposure was much longer and often usable only for still lifes. Exposure times for early photographic emulsions went from hours to minutes and then seconds and fractions of a second in the 1800's.
In both film and digital photography, the use of higher sensitivities generally leads to reduced image quality (via coarser film grain or higher image noise of other types). In short, the higher the sensitivity, the grainier the image will be. Ultimately sensitivity is limited by the quantum efficiency of the film or sensor.
To determine the exposure time needed for a given film the light meter was usually used.
Film speed measurement systems
Historical systems
Warnerke
The first known practical sensitometer, which allowed measurements of the speed of photographic materials, was invented by the Polish engineer Leon Warnerke – pseudonym of (1837–1900) – in 1880, among the achievements for which he was awarded the Progress Medal of the Photographic Society of Great Britain in 1882. It was commercialized since 1881.
The Warnerke Standard Sensitometer consisted of a frame holding an opaque screen with an array of typically 25 numbered, gradua |
https://en.wikipedia.org/wiki/Siemens | Siemens AG ( ) is a German multinational technology conglomerate. Its operations encompass automation and digitalization in the process and manufacturing industries, intelligent infrastructure for buildings and distributed energy systems, rail transport solutions, as well as health technology and digital healthcare services. Siemens is the largest industrial manufacturing company in Europe, and holds the position of global market leader in industrial automation and industrial software.
The origins of the conglomerate can be traced back to 1847 to the Telegraphen Bau-Anstalt von Siemens & Halske established in Berlin by Werner von Siemens and Johann Georg Halske. In 1966, the present-day corporation emerged from the merger of three companies: Siemens & Halske, Siemens-Schuckert, and Siemens-Reiniger-Werke. Today headquartered in Munich and Berlin, Siemens and its subsidiaries employ approximately 311,000 people worldwide and reported a global revenue of around €72 billion in 2022. The company is a component of the DAX and Euro Stoxx 50 stock market indices.
As of 2023, the principal divisions of Siemens are Digital Industries, Smart Infrastructure, Mobility, Healthineers, and Financial Services, with Siemens Healthineers and Siemens Mobility operating as independent entities. Major business divisions that were once part of Siemens before being spun off include semiconductor manufacturer Infineon Technologies (1999), Siemens Mobile (2005), Gigaset Communications (2008), the photonics business Osram (2013), and Siemens Energy (2020).
History
1847 to 1901
Siemens & Halske was founded by Werner von Siemens and Johann Georg Halske on 1 October 1847. Based on the telegraph, their invention used a needle to point to the sequence of letters, instead of using Morse code. The company, then called Telegraphen-Bauanstalt von Siemens & Halske, opened its first workshop on 12 October.
In 1848, the company built the first long-distance telegraph line in Europe: 500 km fro |
https://en.wikipedia.org/wiki/Open%20Database%20Connectivity | In computing, Open Database Connectivity (ODBC) is a standard application programming interface (API) for accessing database management systems (DBMS). The designers of ODBC aimed to make it independent of database systems and operating systems. An application written using ODBC can be ported to other platforms, both on the client and server side, with few changes to the data access code.
ODBC accomplishes DBMS independence by using an ODBC driver as a translation layer between the application and the DBMS. The application uses ODBC functions through an ODBC driver manager with which it is linked, and the driver passes the query to the DBMS. An ODBC driver can be thought of as analogous to a printer driver or other driver, providing a standard set of functions for the application to use, and implementing DBMS-specific functionality. An application that can use ODBC is referred to as "ODBC-compliant". Any ODBC-compliant application can access any DBMS for which a driver is installed. Drivers exist for all major DBMSs, many other data sources like address book systems and Microsoft Excel, and even for text or comma-separated values (CSV) files.
ODBC was originally developed by Microsoft and Simba Technologies during the early 1990s, and became the basis for the Call Level Interface (CLI) standardized by SQL Access Group in the Unix and mainframe field. ODBC retained several features that were removed as part of the CLI effort. Full ODBC was later ported back to those platforms, and became a de facto standard considerably better known than CLI. The CLI remains similar to ODBC, and applications can be ported from one platform to the other with few changes.
History
Before ODBC
The introduction of the mainframe-based relational database during the 1970s led to a proliferation of data access methods. Generally these systems operated together with a simple command processor that allowed users to type in English-like commands, and receive output. The best-known examples |
https://en.wikipedia.org/wiki/Data%20haven | A data haven, like a corporate haven or tax haven, is a refuge for uninterrupted or unregulated data. Data havens are locations with legal environments that are friendly to the concept of a computer network freely holding data and even protecting its content and associated information. They tend to fit into three categories: a physical locality with weak information-system enforcement and extradition laws, a physical locality with intentionally strong protections of data, and virtual domains designed to secure data via technical means (such as encryption) regardless of any legal environment.
Tor's onion space, I2P (both hidden services), HavenCo (centralized), and Freenet (decentralized) are four models of modern-day virtual data havens.
Purposes of data havens
Reasons for establishing data havens include access to free political speech for users in countries where censorship of the Internet is practiced.
Other reasons can include:
Whistleblowing
Distributing software, data or speech that violates laws such as the DMCA
Copyright infringement
Circumventing data protection laws
Online gambling
Pornography
Cybercrime
History of the term
The 1978 report of the British government's Data Protection Committee expressed concern that different privacy standards in different countries would lead to the transfer of personal data to countries with weaker protections; it feared that Britain might become a "data haven". Also in 1978, Adrian Norman published a mock consulting study on the feasibility of setting up a company providing a wide range of data haven services, called "Project Goldfish".
Science fiction novelist William Gibson used the term in his novels Count Zero and Mona Lisa Overdrive, as did Bruce Sterling in Islands in the Net. The 1990s segments of Neal Stephenson's 1999 novel Cryptonomicon concern a small group of entrepreneurs attempting to create a data haven.
See also
Anonymity
Anonymous P2P
Pseudonymity
Corporate haven
Crypto-anarchism
Sea |
https://en.wikipedia.org/wiki/Well-ordering%20principle | In mathematics, the well-ordering principle states that every non-empty set of positive integers contains a least element. In other words, the set of positive integers is well-ordered by its "natural" or "magnitude" order in which precedes if and only if is either or the sum of and some positive integer (other orderings include the ordering ; and ).
The phrase "well-ordering principle" is sometimes taken to be synonymous with the "well-ordering theorem". On other occasions it is understood to be the proposition that the set of integers contains a well-ordered subset, called the natural numbers, in which every nonempty subset contains a least element.
Properties
Depending on the framework in which the natural numbers are introduced, this (second-order) property of the set of natural numbers is either an axiom or a provable theorem. For example:
In Peano arithmetic, second-order arithmetic and related systems, and indeed in most (not necessarily formal) mathematical treatments of the well-ordering principle, the principle is derived from the principle of mathematical induction, which is itself taken as basic.
Considering the natural numbers as a subset of the real numbers, and assuming that we know already that the real numbers are complete (again, either as an axiom or a theorem about the real number system), i.e., every bounded (from below) set has an infimum, then also every set of natural numbers has an infimum, say . We can now find an integer such that lies in the half-open interval , and can then show that we must have , and in .
In axiomatic set theory, the natural numbers are defined as the smallest inductive set (i.e., set containing 0 and closed under the successor operation). One can (even without invoking the regularity axiom) show that the set of all natural numbers such that " is well-ordered" is inductive, and must therefore contain all natural numbers; from this property one can conclude that the set of all natural numbers is also wel |
https://en.wikipedia.org/wiki/Corollary | In mathematics and logic, a corollary ( , ) is a theorem of less importance which can be readily deduced from a previous, more notable statement. A corollary could, for instance, be a proposition which is incidentally proved while proving another proposition; it might also be used more casually to refer to something which naturally or incidentally accompanies something else (e.g., violence as a corollary of revolutionary social changes).
Overview
In mathematics, a corollary is a theorem connected by a short proof to an existing theorem. The use of the term corollary, rather than proposition or theorem, is intrinsically subjective. More formally, proposition B is a corollary of proposition A, if B can be readily deduced from A or is self-evident from its proof.
In many cases, a corollary corresponds to a special case of a larger theorem, which makes the theorem easier to use and apply, even though its importance is generally considered to be secondary to that of the theorem. In particular, B is unlikely to be termed a corollary if its mathematical consequences are as significant as those of A. A corollary might have a proof that explains its derivation, even though such a derivation might be considered rather self-evident in some occasions (e.g., the Pythagorean theorem as a corollary of law of cosines).
Peirce's theory of deductive reasoning
Charles Sanders Peirce held that the most important division of kinds of deductive reasoning is that between corollarial and theorematic. He argued that while all deduction ultimately depends in one way or another on mental experimentation on schemata or diagrams, in corollarial deduction:
"it is only necessary to imagine any case in which the premises are true in order to perceive immediately that the conclusion holds in that case"
while in theorematic deduction:
"It is necessary to experiment in the imagination upon the image of the premise in order from the result of such experiment to make corollarial deductions to t |
https://en.wikipedia.org/wiki/Mathematical%20folklore | In common mathematical parlance, a mathematical result is called folklore if it is an unpublished result with no clear originator, but which is well-circulated and believed to be true among the specialists. More specifically, folk mathematics, or mathematical folklore, is the body of theorems, definitions, proofs, facts or techniques that circulate among mathematicians by word of mouth, but have not yet appeared in print, either in books or in scholarly journals.
Quite important at times for researchers are folk theorems, which are results known, at least to experts in a field, and are considered to have established status, though not published in complete form. Sometimes, these are only alluded to in the public literature.
An example is a book of exercises, described on the back cover:
Another distinct category is well-knowable mathematics, a term introduced by John Conway. These mathematical matters are known and factual, but not in active circulation in relation with current research (i.e., untrendy). Both of these concepts are attempts to describe the actual context in which research work is done.
Some people, in particular non-mathematicians, use the term folk mathematics to refer to the informal mathematics studied in many ethno-cultural studies of mathematics. Although the term "mathematical folklore" can also be used within the mathematics circle to describe the various aspects of their esoteric culture and practices (e.g., slang, proverb, limerick, joke).
Stories, sayings and jokes
Mathematical folklore can also refer to the unusual (and possibly apocryphal) stories or jokes involving mathematicians or mathematics that are told verbally in mathematics departments. Compilations include tales collected in G. H. Hardy's A Mathematician's Apology and ; examples include:
Srinivasa Ramanujan's taxicab numbers
Galileo dropping weights from the Leaning Tower of Pisa.
An apple falling on Isaac Newton's head to inspire his theory of gravitation.
The drinking, |
https://en.wikipedia.org/wiki/Somatic%20cell%20nuclear%20transfer | In genetics and developmental biology, somatic cell nuclear transfer (SCNT) is a laboratory strategy for creating a viable embryo from a body cell and an egg cell. The technique consists of taking an denucleated oocyte (egg cell) and implanting a donor nucleus from a somatic (body) cell. It is used in both therapeutic and reproductive cloning. In 1996, Dolly the sheep became famous for being the first successful case of the reproductive cloning of a mammal. In January 2018, a team of scientists in Shanghai announced the successful cloning of two female crab-eating macaques (named Zhong Zhong and Hua Hua) from foetal nuclei.
"Therapeutic cloning" refers to the potential use of SCNT in regenerative medicine; this approach has been championed as an answer to the many issues concerning embryonic stem cells (ESCs) and the destruction of viable embryos for medical use, though questions remain on how homologous the two cell types truly are.
Introduction
Somatic cell nuclear transfer is a technique for cloning in which the nucleus of a somatic cell is transferred to the cytoplasm of an enucleated egg. After the somatic cell transfers, the cytoplasmic factors affect the nucleus to become a zygote. The blastocyst stage is developed by the egg to help create embryonic stem cells from the inner cell mass of the blastocyst. The first animal to be developed by this technique was Dolly, the sheep, in 1996.
Process
The process of somatic cell nuclear transfer involves two different cells. The first being a female gamete, known as the ovum (egg/oocyte). In human SCNT experiments, these eggs are obtained through consenting donors, utilizing ovarian stimulation. The second being a somatic cell, referring to the cells of the human body. Skin cells, fat cells, and liver cells are only a few examples. The genetic material of the donor egg cell is removed and discarded, leaving it 'deprogrammed.' What is left is a somatic cell and an enucleated egg cell. These are then fused by inserti |
https://en.wikipedia.org/wiki/Immunosuppression | Immunosuppression is a reduction of the activation or efficacy of the immune system. Some portions of the immune system itself have immunosuppressive effects on other parts of the immune system, and immunosuppression may occur as an adverse reaction to treatment of other conditions.
In general, deliberately induced immunosuppression is performed to prevent the body from rejecting an organ transplant. Additionally, it is used for treating graft-versus-host disease after a bone marrow transplant, or for the treatment of auto-immune diseases such as systemic lupus erythematosus, rheumatoid arthritis, Sjögren's syndrome, or Crohn's disease. This is typically done using medications, but may involve surgery (splenectomy), plasmapheresis, or radiation. A person who is undergoing immunosuppression, or whose immune system is weak for some other reasons (such as chemotherapy or HIV), is said to be immunocompromised.
Deliberately induced
Administration of immunosuppressive medications or immunosuppressants is the main method for deliberately inducing immunosuppression; in optimal circumstances, immunosuppressive drugs primarily target hyperactive components of the immune system. People in remission from cancer who require immunosuppression are not more likely to experience a recurrence. Throughout its history, radiation therapy has been used to decrease the strength of the immune system. Dr. Joseph Murray of Brigham and Women's Hospital was given the Nobel Prize in Physiology or Medicine in 1990 for work on immunosuppression.
Immunosuppressive drugs have the potential to cause immunodeficiency, which can increase susceptibility to opportunistic infection and decrease cancer immunosurveillance. Immunosuppressants may be prescribed when a normal immune response is undesirable, such as in autoimmune diseases.
Steroids were the first class of immunosuppressant drugs identified, though side-effects of early compounds limited their use. The more specific azathioprine was ident |
https://en.wikipedia.org/wiki/LilyPond | LilyPond is a computer program and file format for music engraving. One of LilyPond's major goals is to produce scores that are engraved with traditional layout rules, reflecting the era when scores were engraved by hand.
LilyPond is cross-platform, and is available for several common operating systems; released under the terms of the GNU General Public License, LilyPond is free software and part of the GNU Project.
History
The LilyPond project was started in 1996 by Han-Wen Nienhuys and Jan Nieuwenhuizen, after they decided to abandon work on MPP (MusiXTeX PreProcessor), a project they began collaborating on in 1995. Its name was inspired both by the Rosegarden project and an acquaintance of Nienhuys and Nieuwenhuizen named Suzanne, a name that means lily in Hebrew ().
Version 1.0
LilyPond 1.0 was released on July 31, 1998, highlighting the development of a custom music font, Feta, and the complete separation of LilyPond from MusiXTeX.
Version 2.0
LilyPond 2.0 was released on September 24, 2003, announcing a simplified syntax model and a much more complete set of facilities for notating various styles of music.
Design
LilyPond is mostly written in C++ and uses Scheme (interpreted by GNU Guile) as its extension language, allowing for user customization. It has a relatively large codebase; as of March 10, 2017, the source includes over 600,000 lines of C++, 140,000 lines of Scheme, and 120,000 lines of Python code.
It uses a simple text notation for music input, which LilyPond interprets and processes in a series of stages. In the final stage, music notation is output to PDF (via PostScript) or other graphical formats, such as SVG or PNG. LilyPond can also generate MIDI files that correspond to the music notation output.
LilyPond is a text-based application, so it does not contain its own graphical user interface to assist with score creation. (However, a text-editor based "LilyPad" GUI for Windows and MacOS is included by default on these systems.) It does |
https://en.wikipedia.org/wiki/Clearance%20rate | In criminal justice, clearance rate is calculated by dividing the number of crimes that are "cleared" (a charge being laid) by the total number of crimes recorded. Clearance rates are used by various groups as a measure of crimes solved by the police.
Clearance rates can be problematic for measuring the performance of police services and for comparing various police services. This is because a police force may employ a different way of measuring clearance rates. For example, each police force may have a different method of recording when a "crime" has occurred and different criteria for determining when a crime has been "cleared." A given police force may appear to have a much better clearance rate because of its calculation methodology.
Some U.S. police forces have been criticized for overuse of "exceptional clearance", which is intended to classify as "cleared" cases where probable cause to arrest a suspect exists, but police are unable to do so for reasons outside their control (such as death or incarceration in a foreign country).
In system conflict theory, it is argued that clearance rates cause the police to focus on appearing to solve crimes (generating high clearance rate scores) rather than actually solving crimes. Further focus on clearance rates may result in effort being expended to attribute crimes (correctly or incorrectly) to a criminal, which may not result in retribution, compensation, rehabilitation or deterrence.
References
Further reading
Schmalleger, Frank. Criminal Justice Today, An Introductory Text For The 21st Century.
External links
- "The Post has mapped more than 52,000 homicides in major American cities over the past decade and found that across the country, there are areas where murder is common but arrests are rare."
See also
Criminal investigation
List of unsolved deaths
Criminology
Law enforcement
Crime statistics
Ratios
Social statistics indicators |
https://en.wikipedia.org/wiki/Shape | A shape is a graphical representation of an object or its external boundary, outline, or external surface, as opposed to other properties such as color, texture, or material type.
A figure is a representation including both shape and size (as in, e.g., figure of the Earth).
A plane shape or plane figure is constrained to lie on a plane, in contrast to solid 3D shapes.
A two-dimensional shape or two-dimensional figure (also: 2D shape or 2D figure) may lie on a more general curved surface (a non-Euclidean two-dimensional space).
Classification of simple shapes
Some simple shapes can be put into broad categories. For instance, polygons are classified according to their number of edges as triangles, quadrilaterals, pentagons, etc. Each of these is divided into smaller categories; triangles can be equilateral, isosceles, obtuse, acute, scalene, etc. while quadrilaterals can be rectangles, rhombi, trapezoids, squares, etc.
Other common shapes are points, lines, planes, and conic sections such as ellipses, circles, and parabolas.
Among the most common 3-dimensional shapes are polyhedra, which are shapes with flat faces; ellipsoids, which are egg-shaped or sphere-shaped objects; cylinders; and cones.
If an object falls into one of these categories exactly or even approximately, we can use it to describe the shape of the object. Thus, we say that the shape of a manhole cover is a disk, because it is approximately the same geometric object as an actual geometric disk.
In geometry
A geometric shape consists of the geometric information which remains when location, scale, orientation and reflection are removed from the description of a geometric object. That is, the result of moving a shape around, enlarging it, rotating it, or reflecting it in a mirror is the same shape as the original, and not a distinct shape.
Many two-dimensional geometric shapes can be defined by a set of points or vertices and lines connecting the points in a closed chain, as well as the resulti |
https://en.wikipedia.org/wiki/Intuitionistic%20logic | Intuitionistic logic, sometimes more generally called constructive logic, refers to systems of symbolic logic that differ from the systems used for classical logic by more closely mirroring the notion of constructive proof. In particular, systems of intuitionistic logic do not assume the law of the excluded middle and double negation elimination, which are fundamental inference rules in classical logic.
Formalized intuitionistic logic was originally developed by Arend Heyting to provide a formal basis for L. E. J. Brouwer's programme of intuitionism. From a proof-theoretic perspective, Heyting’s calculus is a restriction of classical logic in which the law of excluded middle and double negation elimination have been removed. Excluded middle and double negation elimination can still be proved for some propositions on a case by case basis, however, but do not hold universally as they do with classical logic. The standard explanation of intuitionistic logic is the BHK interpretation.
Several systems of semantics for intuitionistic logic have been studied. One of these semantics mirrors classical Boolean-valued semantics but uses Heyting algebras in place of Boolean algebras. Another semantics uses Kripke models. These, however, are technical means for studying Heyting’s deductive system rather than formalizations of Brouwer’s original informal semantic intuitions. Semantical systems claiming to capture such intuitions, due to offering meaningful concepts of “constructive truth” (rather than merely validity or provability), are Kurt Gödel’s dialectica interpretation, Stephen Cole Kleene’s realizability, Yurii Medvedev’s logic of finite problems, or Giorgi Japaridze’s computability logic. Yet such semantics persistently induce logics properly stronger than Heyting’s logic. Some authors have argued that this might be an indication of inadequacy of Heyting’s calculus itself, deeming the latter incomplete as a constructive logic.
Mathematical constructivism
In the se |
https://en.wikipedia.org/wiki/Macrophage | Macrophages (abbreviated as Mφ, MΦ or MP) (, from Greek μακρός () = large, φαγεῖν () = to eat) are a type of white blood cell of the innate immune system that engulf and digest pathogens, such as cancer cells, microbes, cellular debris, and foreign substances, which do not have proteins that are specific to healthy body cells on their surface. This process is called phagocytosis, which acts to defend the host against infection and injury.
Macrophages are found in essentially all tissues, where they patrol for potential pathogens by amoeboid movement. They take various forms (with various names) throughout the body (e.g., histiocytes, Kupffer cells, alveolar macrophages, microglia, and others), but all are part of the mononuclear phagocyte system. Besides phagocytosis, they play a critical role in nonspecific defense (innate immunity) and also help initiate specific defense mechanisms (adaptive immunity) by recruiting other immune cells such as lymphocytes. For example, they are important as antigen presenters to T cells. In humans, dysfunctional macrophages cause severe diseases such as chronic granulomatous disease that result in frequent infections.
Beyond increasing inflammation and stimulating the immune system, macrophages also play an important anti-inflammatory role and can decrease immune reactions through the release of cytokines. Macrophages that encourage inflammation are called M1 macrophages, whereas those that decrease inflammation and encourage tissue repair are called M2 macrophages. This difference is reflected in their metabolism; M1 macrophages have the unique ability to metabolize arginine to the "killer" molecule nitric oxide, whereas M2 macrophages have the unique ability to metabolize arginine to the "repair" molecule ornithine. However, this dichotomy has been recently questioned as further complexity has been discovered.
Human macrophages are about in diameter and are produced by the differentiation of monocytes in tissues. They can be i |
https://en.wikipedia.org/wiki/CHSH%20inequality | In physics, the CHSH inequality can be used in the proof of Bell's theorem, which states that certain consequences of entanglement in quantum mechanics cannot be reproduced by local hidden-variable theories. Experimental verification of the inequality being violated is seen as confirmation that nature cannot be described by such theories. CHSH stands for John Clauser, Michael Horne, Abner Shimony, and Richard Holt, who described it in a much-cited paper published in 1969. They derived the CHSH inequality, which, as with John Stewart Bell's original inequality, is a constraint on the statistical occurrence of "coincidences" in a Bell test which is necessarily true if there exist underlying local hidden-variable theory. In practice, the inequality is routinely violated by modern experiments in quantum mechanics.
Statement
The usual form of the CHSH inequality is
where
a and a′ are detector settings on side A, b and b′ on side B, the four combinations being tested in separate subexperiments. The terms E(a, b) etc. are the quantum correlations of the particle pairs, where the quantum correlation is defined to be the expectation value of the product of the "outcomes" of the experiment, i.e. the statistical average of A(a)·B(b), where A and B are the separate outcomes, using the coding +1 for the '+' channel and −1 for the '−' channel. Clauser et al.'s 1969 derivation was oriented towards the use of "two-channel" detectors, and indeed it is for these that it is generally used, but under their method the only possible outcomes were +1 and −1. In order to adapt to real situations, which at the time meant the use of polarised light and single-channel polarisers, they had to interpret '−' as meaning "non-detection in the '+' channel", i.e. either '−' or nothing. They did not in the original article discuss how the two-channel inequality could be applied in real experiments with real imperfect detectors, though it was later proved that the inequality itself was equally va |
https://en.wikipedia.org/wiki/Necessity%20and%20sufficiency | In logic and mathematics, necessity and sufficiency are terms used to describe a conditional or implicational relationship between two statements. For example, in the conditional statement: "If then ", is necessary for , because the truth of is guaranteed by the truth of . (Equivalently, it is impossible to have without , or the falsity of ensures the falsity of .) Similarly, is sufficient for , because being true always implies that is true, but not being true does not always imply that is not true.
In general, a necessary condition is one (possibly one of multiple conditions) that must be present in order for another condition to occur, while a sufficient condition is one that produces the said condition. The assertion that a statement is a "necessary and sufficient" condition of another means that the former statement is true if and only if the latter is true. That is, the two statements must be either simultaneously true, or simultaneously false.
In ordinary English (also natural language) "necessary" and "sufficient" indicate relations between conditions or states of affairs, not statements. For example, being a male is a necessary condition for being a brother, but it is not sufficient—while being a male sibling is a necessary and sufficient condition for being a brother.
Any conditional statement consists of at least one sufficient condition and at least one necessary condition.
In data analytics, necessity and sufficiency can refer to different causal logics, where Necessary Condition Analysis and Qualitative Comparative Analysis can be used as analytical techniques for examining necessity and sufficiency of conditions for a particular outcome of interest.
Definitions
In the conditional statement, "if S, then N", the expression represented by S is called the antecedent, and the expression represented by N is called the consequent. This conditional statement may be written in several equivalent ways, such as "N if S", "S only if N", "S implies |
https://en.wikipedia.org/wiki/Radio-frequency%20identification | Radio-frequency identification (RFID) uses electromagnetic fields to automatically identify and track tags attached to objects. An RFID system consists of a tiny radio transponder, a radio receiver and transmitter. When triggered by an electromagnetic interrogation pulse from a nearby RFID reader device, the tag transmits digital data, usually an identifying inventory number, back to the reader. This number can be used to track inventory goods.
Passive tags are powered by energy from the RFID reader's interrogating radio waves. Active tags are powered by a battery and thus can be read at a greater range from the RFID reader, up to hundreds of meters.
Unlike a barcode, the tag does not need to be within the line of sight of the reader, so it may be embedded in the tracked object. RFID is one method of automatic identification and data capture (AIDC).
RFID tags are used in many industries. For example, an RFID tag attached to an automobile during production can be used to track its progress through the assembly line, RFID-tagged pharmaceuticals can be tracked through warehouses, and implanting RFID microchips in livestock and pets enables positive identification of animals. Tags can also be used in shops to expedite checkout, and to prevent theft by customers and employees.
Since RFID tags can be attached to physical money, clothing, and possessions, or implanted in animals and people, the possibility of reading personally-linked information without consent has raised serious privacy concerns. These concerns resulted in standard specifications development addressing privacy and security issues.
In 2014, the world RFID market was worth US$8.89 billion, up from US$7.77 billion in 2013 and US$6.96 billion in 2012. This figure includes tags, readers, and software/services for RFID cards, labels, fobs, and all other form factors. The market value is expected to rise from US$12.08 billion in 2020 to US$16.23 billion by 2029.
History
In 1945, Léon Theremin invented th |
https://en.wikipedia.org/wiki/Logical%20equivalence | In logic and mathematics, statements and are said to be logically equivalent if they have the same truth value in every model. The logical equivalence of and is sometimes expressed as , , , or , depending on the notation being used.
However, these symbols are also used for material equivalence, so proper interpretation would depend on the context. Logical equivalence is different from material equivalence, although the two concepts are intrinsically related.
Logical equivalences
In logic, many common logical equivalences exist and are often listed as laws or properties. The following tables illustrate some of these.
General logical equivalences
Logical equivalences involving conditional statements
Logical equivalences involving biconditionals
Examples
In logic
The following statements are logically equivalent:
If Lisa is in Denmark, then she is in Europe (a statement of the form ).
If Lisa is not in Europe, then she is not in Denmark (a statement of the form ).
Syntactically, (1) and (2) are derivable from each other via the rules of contraposition and double negation. Semantically, (1) and (2) are true in exactly the same models (interpretations, valuations); namely, those in which either Lisa is in Denmark is false or Lisa is in Europe is true.
(Note that in this example, classical logic is assumed. Some non-classical logics do not deem (1) and (2) to be logically equivalent.)
Relation to material equivalence
Logical equivalence is different from material equivalence. Formulas and are logically equivalent if and only if the statement of their material equivalence () is a tautology.
The material equivalence of and (often written as ) is itself another statement in the same object language as and . This statement expresses the idea "' if and only if '". In particular, the truth value of can change from one model to another.
On the other hand, the claim that two formulas are logically equivalent is a statement in metalanguage, which expresse |
https://en.wikipedia.org/wiki/Foundations%20of%20mathematics | Foundations of mathematics is the study of the philosophical and logical and/or algorithmic basis of mathematics, or, in a broader sense, the mathematical investigation of what underlies the philosophical theories concerning the nature of mathematics. In this latter sense, the distinction between foundations of mathematics and philosophy of mathematics turns out to be vague.
Foundations of mathematics can be conceived as the study of the basic mathematical concepts (set, function, geometrical figure, number, etc.) and how they form hierarchies of more complex structures and concepts, especially the fundamentally important structures that form the language of mathematics (formulas, theories and their models giving a meaning to formulas, definitions, proofs, algorithms, etc.) also called metamathematical concepts, with an eye to the philosophical aspects and the unity of mathematics. The search for foundations of mathematics is a central question of the philosophy of mathematics; the abstract nature of mathematical objects presents special philosophical challenges.
The foundations of mathematics as a whole does not aim to contain the foundations of every mathematical topic.
Generally, the foundations of a field of study refers to a more-or-less systematic analysis of its most basic or fundamental concepts, its conceptual unity and its natural ordering or hierarchy of concepts, which may help to connect it with the rest of human knowledge. The development, emergence, and clarification of the foundations can come late in the history of a field, and might not be viewed by everyone as its most interesting part.
Mathematics plays a special role in scientific thought, serving since ancient times as a model of truth and rigor for rational inquiry, and giving tools or even a foundation for other sciences (especially Physics). Mathematics' many developments towards higher abstractions in the 19th century brought new challenges and paradoxes, urging for a deeper and more syst |
https://en.wikipedia.org/wiki/Fluxbox | Fluxbox is a stacking window manager for the X Window System, which started as a fork of Blackbox 0.61.1 in 2001, with the same aim to be lightweight. Its user interface has only a taskbar, a pop-up menu accessible by right-clicking on the desktop, and minimal support for graphical icons. All basic configurations are controlled by text files, including the construction of menus and the mapping of key-bindings. Fluxbox has high compliance to the Extended Window Manager Hints specification.
Fluxbox is basic in appearance, but it can show a few options for improved attractiveness: colors, gradients, borders, and several other basic appearance attributes can be specified. Recent versions support rounded corners and graphical elements. Effects managers such as xcompmgr, cairo-compmgr and transset-df (deprecated) can add true transparency to desktop elements and windows. Enhancements can also be provided by using iDesk or fbdesk, SpaceFM, PCMan File Manager or the ROX Desktop. Fluxbox also has several features Blackbox lacks, including tabbed windows and a configurable titlebar.
Because of its small memory footprint and quick loading time, Fluxbox is popular in many Live CDs such as GParted. It was the default window manager of Damn Small Linux and antiX, but was replaced with JWM in 2007 and 2009, respectively. It is currently the default window manager of PCFluxboxOS, a remaster of PCLinuxOS, and of Linux Mint Fluxbox CE. Fluxbuntu, an Ubuntu derivative with lightweight applications, was released in October 2007.
On December 12, 2019, MX Linux released MX-fluxbox as a fully integrated overlay of MX Linux 19. Previously it had been available from 2014 onward through the Package Installer. A Fluxbox edition has been added to the MX-21 series with Fluxbox in use by default. Fluxbox is also a featured window manager on antiX.
The early versions of Lumina, a desktop environment created for TrueOS, were based on Fluxbox.
As of December 2021 there are 22 flavors of Linux |
https://en.wikipedia.org/wiki/Novell | Novell, Inc. () was an American software and services company headquartered in Provo, Utah, that existed from 1980 until 2014. Its most significant product was the multi-platform network operating system known as Novell NetWare.
Under the leadership of chief executive Ray Noorda, NetWare became the dominant form of personal computer networking during the second half of the 1980s and first half of the 1990s. At its high point, NetWare had a 63 percent share of the market for network operating systems and by the early 1990s there were over half a million NetWare-based networks installed worldwide encompassing more than 50 million users. Novell technology contributed to the emergence of local area networks, which displaced the dominant mainframe computing model and changed computing worldwide. Novell was the second-largest maker of software for personal computers, trailing only Microsoft Corporation, and became instrumental in making Utah Valley a focus for technology and software development.
During the early to mid-1990s, Noorda attempted to compete directly with Microsoft by acquiring Digital Research, Unix System Laboratories, WordPerfect, and the Quattro Pro division of Borland. These moves did not work out, due to new technologies not fitting well with Novell's existing user base or to being too late to compete with equivalent Microsoft products, and NetWare began losing market share once Microsoft bundled network services with the Windows NT operating system and its successors. Despite new products such as Novell Directory Services and GroupWise, Novell entered a long period of decline. Eventually Novell acquired SUSE Linux and attempted to refocus its technology base. Despite building or acquiring several new kinds of products, Novell failed to find consistent success and never regained its past dominance.
The company was an independent corporate entity until it was acquired as a wholly owned subsidiary by The Attachmate Group in 2011, which in turn was acq |
https://en.wikipedia.org/wiki/Sierpi%C5%84ski%20number | In number theory, a Sierpiński number is an odd natural number k such that is composite for all natural numbers n. In 1960, Wacław Sierpiński proved that there are infinitely many odd integers k which have this property.
In other words, when k is a Sierpiński number, all members of the following set are composite:
If the form is instead , then k is a Riesel number.
Known Sierpiński numbers
The sequence of currently known Sierpiński numbers begins with:
78557, 271129, 271577, 322523, 327739, 482719, 575041, 603713, 903983, 934909, 965431, 1259779, 1290677, 1518781, 1624097, 1639459, 1777613, 2131043, 2131099, 2191531, 2510177, 2541601, 2576089, 2931767, 2931991, ... .
The number 78557 was proved to be a Sierpiński number by John Selfridge in 1962, who showed that all numbers of the form have a factor in the covering set }. For another known Sierpiński number, 271129, the covering set is }. Most currently known Sierpiński numbers possess similar covering sets.
However, in 1995 A. S. Izotov showed that some fourth powers could be proved to be Sierpiński numbers without establishing a covering set for all values of n. His proof depends on the aurifeuillean factorization . This establishes that all give rise to a composite, and so it remains to eliminate only using a covering set.
Sierpiński problem
The Sierpiński problem asks for the value of the smallest Sierpiński number. In private correspondence with Paul Erdős, Selfridge conjectured that 78,557 was the smallest Sierpiński number. No smaller Sierpiński numbers have been discovered, and it is now believed that 78,557 is the smallest number.
To show that 78,557 really is the smallest Sierpiński number, one must show that all the odd numbers smaller than 78,557 are not Sierpiński numbers. That is, for every odd k below 78,557, there needs to exist a positive integer n such that is prime. , there are only five candidates which have not been eliminated as possible Sierpiński numbers:
k = 21181, 22699, 247 |
https://en.wikipedia.org/wiki/List%20of%20continuity-related%20mathematical%20topics | In mathematics, the terms continuity, continuous, and continuum are used in a variety of related ways.
Continuity of functions and measures
Continuous function
Absolutely continuous function
Absolute continuity of a measure with respect to another measure
Continuous probability distribution: Sometimes this term is used to mean a probability distribution whose cumulative distribution function (c.d.f.) is (simply) continuous. Sometimes it has a less inclusive meaning: a distribution whose c.d.f. is absolutely continuous with respect to Lebesgue measure. This less inclusive sense is equivalent to the condition that every set whose Lebesgue measure is 0 has probability 0.
Geometric continuity
Parametric continuity
Continuum
Continuum (set theory), the real line or the corresponding cardinal number
Linear continuum, any ordered set that shares certain properties of the real line
Continuum (topology), a nonempty compact connected metric space (sometimes a Hausdorff space)
Continuum hypothesis, a conjecture of Georg Cantor that there is no cardinal number between that of countably infinite sets and the cardinality of the set of all real numbers. The latter cardinality is equal to the cardinality of the set of all subsets of a countably infinite set.
Cardinality of the continuum, a cardinal number that represents the size of the set of real numbers
See also
Continuous variable
Mathematical analysis
Mathematics-related lists |
https://en.wikipedia.org/wiki/Rod%20of%20Asclepius | In Greek mythology, the Rod of Asclepius (⚕; , , sometimes also spelled Asklepios), also known as the Staff of Aesculapius and as the asklepian, is a serpent-entwined rod wielded by the Greek god Asclepius, a deity associated with healing and medicine. In modern times, it is the predominant symbol for medicine and health care, although it is sometimes confused with the similar caduceus, which has two snakes.
Greek mythology and Greek society
The Rod of Asclepius takes its name from the Greek god Asclepius, a deity associated with healing and medicinal arts in ancient Greek religion and mythology. Asclepius' attributes, the snake and the staff, sometimes depicted separately in antiquity, are combined in this symbol.
The most famous temple of Asclepius was at Epidaurus in north-eastern Peloponnese. Another famous healing temple (or asclepeion) was located on the island of Kos, where Hippocrates, the legendary "father of medicine", may have begun his career. Other asclepieia were situated in Trikala, Gortys (Arcadia), and Pergamum in Asia.
In honor of Asclepius, a particular type of non-venomous snake was often used in healing rituals, and these snakes – the Aesculapian snakes – crawled around freely on the floor in dormitories where the sick and injured slept. These snakes were introduced at the founding of each new temple of Asclepius throughout the classical world. From about 300 BCE onwards, the cult of Asclepius grew very popular and pilgrims flocked to his healing temples (Asclepieia) to be cured of their ills. Ritual purification would be followed by offerings or sacrifices to the god (according to means), and the supplicant would then spend the night in the holiest part of the sanctuary – the abaton (or adyton). Any dreams or visions would be reported to a priest who would prescribe the appropriate therapy by a process of interpretation. Some healing temples also used sacred dogs to lick the wounds of sick petitioners.
The original Hippocratic Oath began |
https://en.wikipedia.org/wiki/List%20of%20two-dimensional%20geometric%20shapes | This is a list of two-dimensional geometric shapes in Euclidean and other geometries. For mathematical objects in more dimensions, see list of mathematical shapes. For a broader scope, see list of shapes.
Generally composed of straight line segments
Angle
Balbis
Concave polygon
Constructible polygon
Convex polygon
Cyclic polygon
Equiangular polygon
Equilateral polygon
Penrose tile
Polyform
Regular polygon
Simple polygon
Tangential polygon
Polygons with specific numbers of sides
Henagon – 1 side
Digon – 2 sides
Triangle – 3 sides
Acute triangle
Equilateral triangle
Heptagonal triangle
Isosceles triangle
Golden Triangle
Obtuse triangle
Rational triangle
Right triangle
30-60-90 triangle
Isosceles right triangle
Kepler triangle
Scalene triangle
Quadrilateral – 4 sides
Cyclic quadrilateral
Kite
Parallelogram
Rhombus (equilateral parallelogram)
Lozenge
Rhomboid
Rectangle
Square (regular quadrilateral)
Tangential quadrilateral
Trapezoid
Isosceles trapezoid
Pentagon – 5 sides
Hexagon – 6 sides
Lemoine hexagon
Heptagon – 7 sides
Octagon – 8 sides
Nonagon – 9 sides
Decagon – 10 sides
Hendecagon – 11 sides
Dodecagon – 12 sides
Tridecagon – 13 sides
Tetradecagon – 14 sides
Pentadecagon – 15 sides
Hexadecagon – 16 sides
Heptadecagon – 17 sides
Octadecagon – 18 sides
Enneadecagon – 19 sides
Icosagon – 20 sides
Icosikaihenagon - 21 sides
Icosikaidigon - 22 sides
Icositrigon - 23 sides
Icositetragon - 24 sides
Icosikaipentagon - 25 sides
Icosikaihexagon - 26 sides
Icosikaiheptagon - 27 sides
Icosikaioctagon - 28 sides
Icosikaienneagon - 29 sides
Triacontagon - 30 sides
Tetracontagon - 40 sides
Pentacontagon - 50 sides
Hexacontagon - 60 sides
Heptacontagon - 70 sides
Octacontagon - 80 sides
Enneacontagon - 90 sides
Hectogon - 100 sides
Dihectogon - 200 sides
Trihectogon - 300 sides
Tetrahectogon - 400 sides
Pentahectogon - 500 sides
Hexahectogon - 600 sides
Heptahectogon - 700 sides
Octahectogon - 800 |
https://en.wikipedia.org/wiki/Survivor%20%281987%20video%20game%29 | Survivor is an action game released in 1987 by the Spanish software house Topo Soft and later re-released in the UK by U.S. Gold. It was published for several 8-bit formats including Amstrad CPC, MSX and ZX Spectrum.
Overview
The player takes control of an alien (who bears a striking resemblance to the race of aliens from the Alien series of films) aboard a huge spacecraft filled with many extraterrestrial creatures. The player must perpetuate the alien's race by finding ten pods on the ship and introducing them to the incubators.
The ship itself is split into 142 areas divided into four zones. These zones are joined by doors or air-vents (which the player can crawl through). The zones also consist of different levels connected by lifts.
The pods are found in large rooms which are different from the corridors and vents which make up much of the spacecraft and more closely resemble the sort of room found in 1980s platform games.
Some creatures on the ship are dangerous and the player can spit paralysing acid at them.
The player has a limited amount of energy which can be sapped by hostile creatures on the ship or defence systems. This energy can be replenished by managing to place a pod in an incubator or by eating one of the technicians which can be found wandering around the ship.
External links
Your Sinclair review
1987 video games
Amstrad CPC games
Europe-exclusive video games
MSX games
Single-player video games
Topo Soft games
U.S. Gold games
Video games developed in Spain
ZX Spectrum games |
https://en.wikipedia.org/wiki/Rounding | Rounding means replacing a number with an approximate value that has a shorter, simpler, or more explicit representation. For example, replacing $ with $, the fraction 312/937 with 1/3, or the expression with .
Rounding is often done to obtain a value that is easier to report and communicate than the original. Rounding can also be important to avoid misleadingly precise reporting of a computed number, measurement, or estimate; for example, a quantity that was computed as but is known to be accurate only to within a few hundred units is usually better stated as "about ".
On the other hand, rounding of exact numbers will introduce some round-off error in the reported result. Rounding is almost unavoidable when reporting many computations – especially when dividing two numbers in integer or fixed-point arithmetic; when computing mathematical functions such as square roots, logarithms, and sines; or when using a floating-point representation with a fixed number of significant digits. In a sequence of calculations, these rounding errors generally accumulate, and in certain ill-conditioned cases they may make the result meaningless.
Accurate rounding of transcendental mathematical functions is difficult because the number of extra digits that need to be calculated to resolve whether to round up or down cannot be known in advance. This problem is known as "the table-maker's dilemma".
Rounding has many similarities to the quantization that occurs when physical quantities must be encoded by numbers or digital signals.
A wavy equals sign (≈, approximately equal to) is sometimes used to indicate rounding of exact numbers, e.g. 9.98 ≈ 10. This sign was introduced by Alfred George Greenhill in 1892.
Ideal characteristics of rounding methods include:
Rounding should be done by a function. This way, when the same input is rounded in different instances, the output is unchanged.
Calculations done with rounding should be close to those done without rounding.
As a result |
https://en.wikipedia.org/wiki/Stepper%20motor | A stepper motor, also known as step motor or stepping motor, is an electrical motor that rotates in a series of small angular steps, instead of continuously. Stepper motors are a type of digital actuators. Stepper motors are an eletromagnetic actuator; it converts electromagnetic energy into mechanical energy to perform mechanical work.
A stepper motor is a brushless DC electric motor that divides a full rotation into a number of equal steps. The motor's position can be commanded to move and hold at one of these steps without any position sensor for feedback (an open-loop controller), as long as the motor is correctly sized to the application in respect to torque and speed.
Switched reluctance motors are very large stepping motors with a reduced pole count, and generally are closed-loop commutated.
Mechanism
Brushed DC motors rotate continuously when DC voltage is applied to their terminals. The stepper motor is known for its property of converting a train of input pulses (typically square waves) into a precisely defined increment in the shaft’s rotational position. Each pulse rotates the shaft through a fixed angle.
Stepper motors effectively have multiple "toothed" electromagnets arranged as a stator around a central rotor, a gear-shaped piece of iron. The electromagnets are energized by an external driver circuit or a micro controller. To make the motor shaft turn, first, one electromagnet is given power, which magnetically attracts the gear's teeth. When the gear's teeth are aligned to the first electromagnet, they are slightly offset from the next electromagnet. This means that when the next electromagnet is turned on and the first is turned off, the gear rotates slightly to align with the next one. From there the process is repeated. Each of the partial rotations is called a "step", with an integer number of steps making a full rotation. In that way, the motor can be turned by a precise angle.
The circular arrangement of electromagnets is divided into gr |
https://en.wikipedia.org/wiki/CP/M-86 | CP/M-86 is a discontinued version of the CP/M operating system that Digital Research (DR) made for the Intel 8086 and Intel 8088. The system commands are the same as in CP/M-80. Executable files used the relocatable .CMD file format. Digital Research also produced a multi-user multitasking operating system compatible with CP/M-86, MP/M-86, which later evolved into Concurrent CP/M-86. When an emulator was added to provide PC DOS compatibility, the system was renamed Concurrent DOS, which later became Multiuser DOS, of which REAL/32 is the latest incarnation. The FlexOS, DOS Plus, and DR DOS families of operating systems started as derivations of Concurrent DOS as well.
History
Digital Research's CP/M-86 was originally announced to be released in November 1979, but was delayed repeatedly. When IBM contacted other companies to obtain components for the IBM PC, the as-yet unreleased CP/M-86 was its first choice for an operating system because CP/M had the most applications at the time. Negotiations between Digital Research and IBM quickly deteriorated over IBM's non-disclosure agreement and its insistence on a one-time fee rather than DRI's usual royalty licensing plan.
After discussions with Microsoft, IBM decided to use 86-DOS (QDOS), a CP/M-like operating system that Microsoft bought from Seattle Computer Products renaming it MS-DOS. Microsoft adapted it for PC, and licensed it to IBM. It was sold by IBM under the name of PC DOS. After learning about the deal, Digital Research founder Gary Kildall threatened to sue IBM for infringing DRI's intellectual property, and IBM agreed to offer CP/M-86 as an alternative operating system on the PC to settle the claim. Most of the BIOS drivers for CP/M-86 for the IBM PC were written by Andy Johnson-Laird.
The IBM PC was announced on 12 August 1981, and the first machines began shipping in October the same year, ahead of schedule. CP/M-86 was one of three operating systems available from IBM, with PC DOS and UCSD p-System. Di |
https://en.wikipedia.org/wiki/Normal%20matrix | In mathematics, a complex square matrix is normal if it commutes with its conjugate transpose :
The concept of normal matrices can be extended to normal operators on infinite dimensional normed spaces and to normal elements in C*-algebras. As in the matrix case, normality means commutativity is preserved, to the extent possible, in the noncommutative setting. This makes normal operators, and normal elements of C*-algebras, more amenable to analysis.
The spectral theorem states that a matrix is normal if and only if it is unitarily similar to a diagonal matrix, and therefore any matrix satisfying the equation is diagonalizable. The converse does not hold because diagonalizable matrices may have non-orthogonal eigenspaces.
The left and right singular vectors in the singular value decomposition of a normal matrix differ only in complex phase from each other and from the corresponding eigenvectors, since the phase must be factored out of the eigenvalues to form singular values.
Special cases
Among complex matrices, all unitary, Hermitian, and skew-Hermitian matrices are normal, with all eigenvalues being unit modulus, real, and imaginary, respectively. Likewise, among real matrices, all orthogonal, symmetric, and skew-symmetric matrices are normal, with all eigenvalues being complex conjugate pairs on the unit circle, real, and imaginary, respectively. However, it is not the case that all normal matrices are either unitary or (skew-)Hermitian, as their eigenvalues can be any complex number, in general. For example,
is neither unitary, Hermitian, nor skew-Hermitian, because its eigenvalues are ; yet it is normal because
Consequences
The concept of normality is important because normal matrices are precisely those to which the spectral theorem applies:
The diagonal entries of are the eigenvalues of , and the columns of are the eigenvectors of . The matching eigenvalues in come in the same order as the eigenvectors are ordered as columns of .
Another w |
https://en.wikipedia.org/wiki/ReplayTV | ReplayTV was a former DVR company that from 1999 until 2005, produced a brand of digital video recorders (DVR), a term synonymous with personal video recorder (PVR). It is a consumer video device which allows users to capture television programming to internal hard disk storage for later viewing (and time shifting). ReplayTV was founded in September 1997 by future Roku founder Anthony Wood, who was president and CEO of ReplayTV until August 2001.
The first ReplayTV model was introduced in January 1999 during the Consumer Electronics Show in Las Vegas, at the same time as a competing DVR model from rival company TiVo. After the sale of assets to DirecTV, ReplayTV's only ongoing activity was maintenance of the electronic program guide service by D&M Holdings, which was to be discontinued on July 31, 2011. However, on July 29, 2011, a notice was placed on the ReplayTV website stating that service would be continued without interruption for lifetime subscribers and monthly subscribers may have a short interruption in service. On September 2, 2011, programming contact through the ReplayTV dialup system was terminated without any update message being sent to subscribers or posted on replaytv.com. DNNA filed for bankruptcy on July 20, 2015. EPG data from their servers ran out on July 15, 2015. Even with the end of support from DNNA, third-party solutions are available to provide Electronic Program Guide data to ReplayTV units.
History
ReplayTV was founded in September 1997 by businessman Anthony Wood, who later founded Roku in October 2002. Initial sales to consumers were launched in April 1999, while volume production and sales did not begin until later in 2000. ReplayTV was purchased by SONICblue in 2001.
On March 23, 2003, SONICblue filed for Chapter 11 bankruptcy, and on April 16 sold most of its assets, including ReplayTV, to the Japanese electronics giant D&M Holdings. SONICblue was fighting a copyright infringement suit over the ReplayTV's ability to skip commer |
https://en.wikipedia.org/wiki/T%20cell | T cells are one of the important types of white blood cells of the immune system and play a central role in the adaptive immune response. T cells can be distinguished from other lymphocytes by the presence of a T-cell receptor (TCR) on their cell surface.
T cells are born from hematopoietic stem cells, found in the bone marrow. Developing T cells then migrate to the thymus gland to develop (or mature). T cells derive their name from the thymus. After migration to the thymus, the precursor cells mature into several distinct types of T cells. T cell differentiation also continues after they have left the thymus. Groups of specific, differentiated T cell subtypes have a variety of important functions in controlling and shaping the immune response.
One of these functions is immune-mediated cell death, and it is carried out by two major subtypes: CD8+ "killer" (cytotoxic) and CD4+ "helper" T cells. (These are named for the presence of the cell surface proteins CD8 or CD4.) CD8+ T cells, also known as "killer T cells", are cytotoxic – this means that they are able to directly kill virus-infected cells, as well as cancer cells. CD8+ T cells are also able to use small signalling proteins, known as cytokines, to recruit other types of cells when mounting an immune response. A different population of T cells, the CD4+ T cells, function as "helper cells". Unlike CD8+ killer T cells, the CD4+ helper T (TH) cells function by further activating memory B cells and cytotoxic T cells, which leads to a larger immune response. The specific adaptive immune response regulated by the TH cell depends on its subtype (such as T-helper1, T-helper2, T-helper17, regulatory T-cell), which is distinguished by the types of cytokines they secrete.
Regulatory T cells are yet another distinct population of T cells that provide the critical mechanism of tolerance, whereby immune cells are able to distinguish invading cells from "self". This prevents immune cells from inappropriately reacting again |
https://en.wikipedia.org/wiki/Isotropic%20etching | Isotropic etching is a method commonly used in semiconductors to remove material from a substrate via a chemical process using an etchant substance. The etchant may be in liquid-, gas- or plasma-phase, although liquid etchants such as buffered hydrofluoric acid (BHF) for silicon dioxide etching are more often used. Unlike anisotropic etching, isotropic etching does not etch in a single direction, but rather etches in multiple directions within the substrate. Any horizontal component of the etch direction may therefore result in undercutting of patterned areas, and significant changes to device characteristics. Isotropic etching may occur unavoidably, or it may be desirable for process reasons.
References
Semiconductors |
https://en.wikipedia.org/wiki/Tcpdump | tcpdump is a data-network packet analyzer computer program that runs under a command line interface. It allows the user to display TCP/IP and other packets being transmitted or received over a network to which the computer is attached. Distributed under the BSD license, tcpdump is free software.
Tcpdump works on most Unix-like operating systems: Linux, Solaris, FreeBSD, DragonFly BSD, NetBSD, OpenBSD, OpenWrt, macOS, HP-UX 11i, and AIX. In those systems, tcpdump uses the libpcap library to capture packets. The port of tcpdump for Windows is called WinDump; it uses WinPcap, the Windows version of libpcap.
History
tcpdump was originally written in 1988 by Van Jacobson, Sally Floyd, Vern Paxson and Steven McCanne who were, at the time, working in the Lawrence Berkeley Laboratory Network Research Group. By the late 1990s there were numerous versions of tcpdump distributed as part of various operating systems, and numerous patches that were not well coordinated. Michael Richardson (mcr) and Bill Fenner created www.tcpdump.org in 1999.
Common uses
tcpdump prints the contents of network packets. It can read packets from a network interface card or from a previously created saved packet file. tcpdump can write packets to standard output or a file.
It is also possible to use tcpdump for the specific purpose of intercepting and displaying the communications of another user or computer. A user with the necessary privileges on a system acting as a router or gateway through which unencrypted traffic such as Telnet or HTTP passes can use tcpdump to view login IDs, passwords, the URLs and content of websites being viewed, or any other unencrypted information.
The user may optionally apply a BPF-based filter to limit the number of packets seen by tcpdump; this renders the output more usable on networks with a high volume of traffic.
Example of available capture interfaces on a Linux system:
$ tcpdump -D
1.eth0 [Up, Running, Connected]
2.any (Pseudo-device that captures on |
https://en.wikipedia.org/wiki/Jarkko%20Oikarinen | Jarkko Oikarinen (born 16 August 1967) is a Finnish IT professional and the inventor of the first Internet chat network, called Internet Relay Chat (IRC), where he is known as WiZ.
Biography and career
Oikarinen was born in Kuusamo. While working at the University of Oulu in August 1988, he wrote the first IRC server and client programs, which he produced to replace the MUT (MultiUser Talk) program on the Finnish BBS OuluBox. Using the Bitnet Relay chat system as inspiration, Oikarinen continued to develop IRC over the next four years, receiving assistance from Darren Reed in co-authoring the IRC Protocol. In 1997, his development of IRC earned Oikarinen a Dvorak Award for Personal Achievement—Outstanding Global Interactive Personal Communications System; in 2005, the Millennium Technology Prize Foundation, a Finnish public-private partnership, honored him with one of three Special Recognition Awards.
He started working for medical image processing in 1990 in Oulu University Hospital, developing research software for a neurosurgical workstation in Professor John Koivukangas' research group, and between 1993 and 1996 he worked for Elekta in Stockholm, Sweden and Grenoble, France putting the research into commercial products marketed by Elekta. In 1997 he returned to Oulu University Hospital to finish his PhD as Joint Assistant Professor / Research Engineer, receiving the PhD from the University of Oulu in 1999, in areas of computer graphics and medical imaging. During these years he focused on telemedicine, volume rendering, signal processing and computed axial tomography. Once finishing his PhD, he has held the positions of Chief Software Architect of Add2Phone Oy (Helsinki, Finland), Head of R&D in Capricode (Oulu, Finland) and General Manager in Nokia.
He is also partner and chief software architect at an electronic games developer called Numeric Garden (Espoo, Finland).
Oikarinen and his wife, Kaija-Leena, were married in 1996 and have three children: Kaspe |
https://en.wikipedia.org/wiki/Game%20engine | A game engine is a software framework primarily designed for the development of video games and generally includes relevant libraries and support programs such as a level editor. The "engine" terminology is similar to the term "software engine" used in the software industry.
The game engine can also refer to the development software utilizing this framework, typically offering a suite of tools and features for developing games.
Developers can use game engines to construct games for video game consoles and other types of computers. The core functionality typically provided by a game engine may include a rendering engine ("renderer") for 2D or 3D graphics, a physics engine or collision detection (and collision response), sound, scripting, animation, artificial intelligence, networking, streaming, memory management, threading, localization support, scene graph, and video support for cinematics. Game engine implementers often economize on the process of game development by reusing/adapting, in large part, the same game engine to produce different games or to aid in porting games to multiple platforms.
Purpose
In many cases, game engines provide a suite of visual development tools in addition to reusable software components. These tools are generally provided in an integrated development environment to enable simplified, rapid development of games in a data-driven manner. Game-engine developers often attempt to preempt implementer needs by developing robust software suites which include many elements a game developer may need to build a game. Most game-engine suites provide facilities that ease development, such as graphics, sound, physics and artificial-intelligence (AI) functions. These game engines are sometimes called "middleware" because, as with the business sense of the term, they provide a flexible and reusable software platform which provides all the core functionality needed, right out of the box, to develop a game application while reducing costs, comple |
https://en.wikipedia.org/wiki/Smegma | Smegma (Ancient Greek σμῆγμα : smēgma) is a combination of shed skin cells, skin oils, and moisture. It occurs in both male and female mammalian genitalia. In females, it collects around the clitoris and in the folds of the labia minora; in males, smegma collects under the foreskin.
Females
The accumulation of sebum combined with dead skin cells forms smegma. Smegma clitoridis is defined as the secretion of the apocrine glands of the clitoris, in combination with desquamating epithelial cells. Glands that are located around the clitoris, the labia minora, and the labia majora secrete sebum.
If smegma is not removed frequently it can lead to clitoral adhesion which can make clitoral stimulation (such as masturbation) painful (clitorodynia).
Males
In males, smegma helps keep the glans moist and facilitates sexual intercourse by acting as a lubricant.
Smegma was originally thought to be produced by sebaceous glands near the frenulum called Tyson's glands; however, subsequent studies have failed to find these glands. Joyce Wright states that smegma is produced from minute microscopic protrusions of the mucosal surface of the foreskin and that living cells constantly grow towards the surface, undergo fatty degeneration, separate off, and form smegma. Parkash et al. found that smegma contains 26.6% fats and 13.3% proteins, which they judged to be consistent with necrotic epithelial debris.
Newly produced smegma has a smooth, moist texture. It is thought to be rich in squalene and contain prostatic and seminal secretions, desquamated epithelial cells, and the mucin content of the urethral glands of Littré. Smegma contains cathepsin B, lysozymes, chymotrypsin, neutrophil elastase and cytokines, which aid the immune system.
According to Wright, the production of smegma, which is low in childhood, increases from adolescence until sexual maturity when the function of smegma for lubrication assumes its full value. From middle-age, production starts to decline and in o |
https://en.wikipedia.org/wiki/Understory | In forestry and ecology, understory (American English), or understorey (Commonwealth English), also known as underbrush or undergrowth, includes plant life growing beneath the forest canopy without penetrating it to any great extent, but above the forest floor. Only a small percentage of light penetrates the canopy so understory vegetation is generally shade-tolerant. The understory typically consists of trees stunted through lack of light, other small trees with low light requirements, saplings, shrubs, vines and undergrowth. Small trees such as holly and dogwood are understory specialists.
In temperate deciduous forests, many understory plants start into growth earlier in the year than the canopy trees, to make use of the greater availability of light at that particular time of year. A gap in the canopy caused by the death of a tree stimulates the potential emergent trees into competitive growth as they grow upwards to fill the gap. These trees tend to have straight trunks and few lower branches. At the same time, the bushes, undergrowth, and plant life on the forest floor become denser. The understory experiences greater humidity than the canopy, and the shaded ground does not vary in temperature as much as open ground. This causes a proliferation of ferns, mosses, and fungi and encourages nutrient recycling, which provides favorable habitats for many animals and plants.
Understory structure
The understory is the underlying layer of vegetation in a forest or wooded area, especially the trees and shrubs growing between the forest canopy and the forest floor.
Plants in the understory comprise an assortment of seedlings and saplings of canopy trees together with specialist understory shrubs and herbs. Young canopy trees often persist in the understory for decades as suppressed juveniles until an opening in the forest overstory permits their growth into the canopy. In contrast understory shrubs complete their life cycles in the shade of the forest canopy. Some sma |
https://en.wikipedia.org/wiki/Step%20function | In mathematics, a function on the real numbers is called a step function if it can be written as a finite linear combination of indicator functions of intervals. Informally speaking, a step function is a piecewise constant function having only finitely many pieces.
Definition and first consequences
A function is called a step function if it can be written as
, for all real numbers
where , are real numbers, are intervals, and is the indicator function of :
In this definition, the intervals can be assumed to have the following two properties:
The intervals are pairwise disjoint: for
The union of the intervals is the entire real line:
Indeed, if that is not the case to start with, a different set of intervals can be picked for which these assumptions hold. For example, the step function
can be written as
Variations in the definition
Sometimes, the intervals are required to be right-open or allowed to be singleton. The condition that the collection of intervals must be finite is often dropped, especially in school mathematics, though it must still be locally finite, resulting in the definition of piecewise constant functions.
Examples
A constant function is a trivial example of a step function. Then there is only one interval,
The sign function , which is −1 for negative numbers and +1 for positive numbers, and is the simplest non-constant step function.
The Heaviside function , which is 0 for negative numbers and 1 for positive numbers, is equivalent to the sign function, up to a shift and scale of range (). It is the mathematical concept behind some test signals, such as those used to determine the step response of a dynamical system.
The rectangular function, the normalized boxcar function, is used to model a unit pulse.
Non-examples
The integer part function is not a step function according to the definition of this article, since it has an infinite number of intervals. However, some authors also define step functions with an infinite nu |
https://en.wikipedia.org/wiki/BITNET%20Relay | BITNET Relay, also known as the Inter Chat Relay Network, was a chat network setup over BITNET nodes. It predated Internet Relay Chat and other online chat systems. The program that made the network possible was called "Relay" and was developed by Jeff Kell of the University of Tennessee at Chattanooga in 1985 using the REXX programming language.
This system drew its name from "relay race" which shares a comparable behavior, where messages travel hop-by-hop along the network of Relay servers until they reached their destination. Messages sent within the United States would take a few seconds to reach their destinations, but communication times varied in other countries or internationally. If one or more network links were down, BITNET would store and forward the messages when the network links recovered, minutes or even hours later.
Background
Before BITNET Relay was implemented, any form of communication over BITNET required identifying the remote user and host.
Relay ran on a special ID using several BITNET hosts. To use it, a message was sent to a user ID called RELAY. The Relay program running on that user ID would then provide multi-user chat functions, primarily in the form of "channels" (chat rooms). The message could contain either a command for Relay (preceded by the popular "/" slash character command prefix, still in use today), or a message at the remote host (typically a mainframe computer).
Computers connected to BITNET were generally located at universities and government agencies, due to limited access to computer network bandwidth. It was not uncommon for a university's entire network connection to run over a single leased telephone line or even a 4800 baud dial-up connection. Thus using scarce computing and network resources for "frivolous" purposes, such as chat, was often discouraged.
Popularity
One of the reasons Relay gained acceptance was that its system of peer servers decreased the network bandwidth consumed by group chat, due to no |
https://en.wikipedia.org/wiki/Hayes%20AT%20command%20set | The Hayes command set (also known as the AT command set) is a specific command language originally developed by Dale Heatherington and Dennis Hayes for the Hayes Smartmodem 300 baud modem in 1981.
The command set consists of a series of short text strings which can be combined to produce commands for operations such as dialing, hanging up, and changing the parameters of the connection. The vast majority of dial-up modems use the Hayes command set in numerous variations.
The command set covered only those operations supported by the earliest 300 bit/s modems. When new commands were required to control additional functionality in higher speed modems, a variety of one-off standards emerged from each of the major vendors. These continued to share the basic command structure and syntax, but added any number of new commands using some sort of prefix character – & for Hayes and USR, and \ for Microcom, for instance. Many of these were re-standardized on the Hayes extensions after the introduction of the SupraFAXModem 14400 and the market consolidation that followed.
The term "Hayes compatible" was and as of 2018 still is important within the industry.
History
Background
Prior to the introduction of the Bulletin Board System (BBS), modems typically operated on direct-dial telephone lines that always began and ended with a known modem at each end. The modems operated in either "originate" or "answer" modes, manually switching between two sets of frequencies for data transfer. Generally, the user placing the call would switch their modem to "originate" and then dial the number by hand. When the remote modem answered, already set to "answer" mode, the telephone handset was switched off and communications continued until the caller manually disconnected.
When automation was required, it was commonly only needed on the answer side — for instance, a bank might need to take calls from a number of branch offices for end-of-day processing. To fill this role, some modems inclu |
https://en.wikipedia.org/wiki/Zone%20melting | Zone melting (or zone refining, or floating-zone method, or floating-zone technique) is a group of similar methods of purifying crystals, in which a narrow region of a crystal is melted, and this molten zone is moved along the crystal. The molten region melts impure solid at its forward edge and leaves a wake of purer material solidified behind it as it moves through the ingot. The impurities concentrate in the melt, and are moved to one end of the ingot. Zone refining was invented by John Desmond Bernal and further developed by William G. Pfann in Bell Labs as a method to prepare high-purity materials, mainly semiconductors, for manufacturing transistors. Its first commercial use was in germanium, refined to one atom of impurity per ten billion, but the process can be extended to virtually any solute–solvent system having an appreciable concentration difference between solid and liquid phases at equilibrium. This process is also known as the float zone process, particularly in semiconductor materials processing.
Process details
The principle is that the segregation coefficient k (the ratio of an impurity in the solid phase to that in the liquid phase) is usually less than one. Therefore, at the solid/liquid boundary, the impurity atoms will diffuse to the liquid region. Thus, by passing a crystal boule through a thin section of furnace very slowly, such that only a small region of the boule is molten at any time, the impurities will be segregated at the end of the crystal. Because of the lack of impurities in the leftover regions which solidify, the boule can grow as a perfect single crystal if a seed crystal is placed at the base to initiate a chosen direction of crystal growth. When high purity is required, such as in semiconductor industry, the impure end of the boule is cut off, and the refining is repeated.
In zone refining, solutes are segregated at one end of the ingot in order to purify the remainder, or to concentrate the impurities. In zone leveling, th |
https://en.wikipedia.org/wiki/Engineering%20drawing | An engineering drawing is a type of technical drawing that is used to convey information about an object. A common use is to specify the geometry necessary for the construction of a component and is called a detail drawing. Usually, a number of drawings are necessary to completely specify even a simple component. The drawings are linked together by a master drawing or assembly drawing which gives the drawing numbers of the subsequent detailed components, quantities required, construction materials and possibly 3D images that can be used to locate individual items. Although mostly consisting of pictographic representations, abbreviations and symbols are used for brevity and additional textual explanations may also be provided to convey the necessary information.
The process of producing engineering drawings is often referred to as technical drawing or drafting (draughting). Drawings typically contain multiple views of a component, although additional scratch views may be added of details for further explanation. Only the information that is a requirement is typically specified. Key information such as dimensions is usually only specified in one place on a drawing, avoiding redundancy and the possibility of inconsistency. Suitable tolerances are given for critical dimensions to allow the component to be manufactured and function. More detailed production drawings may be produced based on the information given in an engineering drawing. Drawings have an information box or title block containing who drew the drawing, who approved it, units of dimensions, meaning of views, the title of the drawing and the drawing number.
History
Technical drawing has existed since ancient times. Complex technical drawings were made in renaissance times, such as the drawings of Leonardo da Vinci. Modern engineering drawing, with its precise conventions of orthographic projection and scale, arose in France at a time when the Industrial Revolution was in its infancy. L. T. C. Rolt's biog |
https://en.wikipedia.org/wiki/Collision%20detection | Collision detection is the computational problem of detecting the intersection of two or more objects. Collision detection is a classic issue of computational geometry and has applications in various computing fields, primarily in computer graphics, computer games, computer simulations, robotics and computational physics. Collision detection algorithms can be divided into operating on 2D and 3D objects.
Overview
In physical simulation, experiments such as playing billiards are conducted. The physics of bouncing billiard balls are well understood, under the umbrella of rigid body motion and elastic collisions. An initial description of the situation would be given, with a very precise physical description of the billiard table and balls, as well as initial positions of all the balls. Given a force applied to the cue ball (probably resulting from a player hitting the ball with their cue stick), we want to calculate the trajectories, precise motion and eventual resting places of all the balls with a computer program. A program to simulate this game would consist of several portions, one of which would be responsible for calculating the precise impacts between the billiard balls. This particular example also turns out to be ill conditioned: a small error in any calculation will cause drastic changes in the final position of the billiard balls.
Video games have similar requirements, with some crucial differences. While computer simulation needs to simulate real-world physics as precisely as possible, computer games need to simulate real-world physics in an acceptable way, in real time and robustly. Compromises are allowed, so long as the resulting simulation is satisfying to the game players.
Collision detection in computer simulation
Physical simulators differ in the way they react on a collision. Some use the softness of the material to calculate a force, which will resolve the collision in the following time steps like it is in reality. This is very CPU intensiv |
https://en.wikipedia.org/wiki/The%20Extended%20Phenotype | The Extended Phenotype is a 1982 book by the evolutionary biologist Richard Dawkins, in which the author introduced a biological concept of the same name. The book’s main idea is that phenotype should not be limited to biological processes such as protein biosynthesis or tissue growth, but extended to include all effects that a gene has on its environment, inside or outside the body of the individual organism.
Dawkins considers The Extended Phenotype to be a sequel to The Selfish Gene (1976) aimed at professional biologists, and as his principal contribution to evolutionary theory.
Summary
Genes as the unit of selection in evolution
The central thesis of The Extended Phenotype, and of its predecessor by the same author, The Selfish Gene, is that individual organisms are not the true units of natural selection. Instead, the gene — or the ‘active, germ-line replicator’ — is the unit upon which the forces of evolutionary selection and adaptation act. It is genes that succeed or fail in evolution, meaning that they either succeed or fail in replicating themselves across multiple generations.
These replicators are not subject to natural selection directly, but indirectly through their “phenotypical effects.” These effects are all the effects that the gene (or replicator) has on the world at large, not just in the body of the organism in which it is contained. In taking as its starting point the gene as the unit of selection, The Extended Phenotype is a direct extension of Dawkins’ first book, The Selfish Gene.
Genes synthesise only proteins
Dawkins argues that the only thing that genes control directly is the synthesis of proteins. He points to the arbitrariness of restricting the idea of the phenotype to apply only to the phenotypic expression of an organism's genes in its own body. Dawkins develops this idea by pointing to the effect that a gene may have on an organism's environment through that organism's behaviour.
Genes may affect more than the organism's |
https://en.wikipedia.org/wiki/Skid-steer%20loader | A skid loader, skid-steer loader, SSL, or skidsteer is any of a class of compact heavy equipment with lift arms that can attach to a wide variety of buckets and other labor-saving tools or attachments.
The wheels typically have no separate steering mechanism and hold a fixed straight alignment on the body of the machine. Turning is accomplished by differential steering, in which the left and right wheel pairs are operated at different speeds, and the machine turns by skidding or dragging its fixed-orientation wheels across the ground. Skid-steer loaders are capable of zero-radius turning, by driving one set of wheels forward while simultaneously driving the opposite set of wheels in reverse. This "zero-turn" capability (the machine can turn around within its own length) makes them extremely maneuverable and valuable for applications that require a compact, powerful and agile loader or tool carrier in confined-space work areas.
Like other front loaders, they can push material from one location to another, carry material in the bucket, load material into a truck or trailer and perform a variety of digging and grading operations.
History
The first three-wheeled, front-end loader was invented by brothers Cyril and Louis Keller in Rothsay, Minnesota, in 1957. The Kellers built the loader to help a farmer, Eddie Velo, mechanize the process of cleaning turkey manure from his barn. The light and compact machine, with its rear caster wheel, was able to turn around within its own length while performing the same tasks as a conventional front-end loader, hence its name.
The Melroe brothers, of Melroe Manufacturing Company in Gwinner, North Dakota, purchased the rights to the Keller loader in 1958 and hired the Kellers to continue refining their invention. As a result of this partnership, the M-200 Melroe self-propelled loader was introduced at the end of 1958. It featured two independent front-drive wheels and a rear caster wheel, a engine and a lift capacity. Two years |
https://en.wikipedia.org/wiki/Almquist%20shell | Almquist shell (also known as A Shell, ash and sh) is a lightweight Unix shell originally written by Kenneth Almquist in the late 1980s. Initially a clone of the System V.4 variant of the Bourne shell, it replaced the original Bourne shell in the BSD versions of Unix released in the early 1990s.
History
ash was first released via a posting to the Usenet news group, approved and moderated by Rich Salz on 30 May 1989. It was described as "a reimplementation of the System V shell [with] most features of that shell, plus some additions".
Fast, small, and virtually compatible with the POSIX standard's specification of the Unix shell, ash did not provide line editing or command history mechanisms, because Almquist felt that such functionality should be moved into the terminal driver. However, current variants support it.
The following is extracted from the ash package information from Slackware v14:
Myriad forks have been produced from the original ash release. These derivatives of ash are installed as the default shell (/bin/sh) on FreeBSD, NetBSD, DragonFly BSD, MINIX, and in some Linux distributions. MINIX 3.2 used the original ash version, whose test feature differed from POSIX. That version of the shell was replaced in MINIX 3.3. Android used ash until Android 4.0, at which point it switched to mksh.
Dash
In 1997 Herbert Xu ported ash from NetBSD to Debian Linux. In September 2002, with release 0.4.1, this port was renamed to Dash (Debian Almquist shell). Xu's main priorities are POSIX conformance and slim implementation.
Like its predecessor, Dash implements support for neither internationalization and localization nor multi-byte character encoding (both required in POSIX). Line editing and history support based on GNU Readline is optional ().
Adoption in Debian and Ubuntu
Because of its slimness, Ubuntu decided to adopt Dash as the default /bin/sh in 2006. The reason for using Dash is faster shell script execution, especially during startup of the opera |
https://en.wikipedia.org/wiki/Root%20of%20unity | In mathematics, a root of unity, occasionally called a de Moivre number, is any complex number that yields 1 when raised to some positive integer power . Roots of unity are used in many branches of mathematics, and are especially important in number theory, the theory of group characters, and the discrete Fourier transform.
Roots of unity can be defined in any field. If the characteristic of the field is zero, the roots are complex numbers that are also algebraic integers. For fields with a positive characteristic, the roots belong to a finite field, and, conversely, every nonzero element of a finite field is a root of unity. Any algebraically closed field contains exactly th roots of unity, except when is a multiple of the (positive) characteristic of the field.
General definition
An th root of unity, where is a positive integer, is a number satisfying the equation
Unless otherwise specified, the roots of unity may be taken to be complex numbers (including the number 1, and the number −1 if is even, which are complex with a zero imaginary part), and in this case, the th roots of unity are
However, the defining equation of roots of unity is meaningful over any field (and even over any ring) , and this allows considering roots of unity in . Whichever is the field , the roots of unity in are either complex numbers, if the characteristic of is 0, or, otherwise, belong to a finite field. Conversely, every nonzero element in a finite field is a root of unity in that field. See Root of unity modulo n and Finite field for further details.
An th root of unity is said to be if it is not an th root of unity for some smaller , that is if
If n is a prime number, then all th roots of unity, except 1, are primitive.
In the above formula in terms of exponential and trigonometric functions, the primitive th roots of unity are those for which and are coprime integers.
Subsequent sections of this article will comply with complex roots of unity. For the case of roo |
https://en.wikipedia.org/wiki/Cyclotomic%20polynomial | In mathematics, the nth cyclotomic polynomial, for any positive integer n, is the unique irreducible polynomial with integer coefficients that is a divisor of and is not a divisor of for any Its roots are all nth primitive roots of unity
, where k runs over the positive integers not greater than n and coprime to n (and i is the imaginary unit). In other words, the nth cyclotomic polynomial is equal to
It may also be defined as the monic polynomial with integer coefficients that is the minimal polynomial over the field of the rational numbers of any primitive nth-root of unity ( is an example of such a root).
An important relation linking cyclotomic polynomials and primitive roots of unity is
showing that is a root of if and only if it is a dth primitive root of unity for some d that divides n.
Examples
If n is a prime number, then
If n = 2p where p is an odd prime number, then
For n up to 30, the cyclotomic polynomials are:
The case of the 105th cyclotomic polynomial is interesting because 105 is the least positive integer that is the product of three distinct odd prime numbers (3*5*7) and this polynomial is the first one that has a coefficient other than 1, 0, or −1:
Properties
Fundamental tools
The cyclotomic polynomials are monic polynomials with integer coefficients that are irreducible over the field of the rational numbers. Except for n equal to 1 or 2, they are palindromes of even degree.
The degree of , or in other words the number of nth primitive roots of unity, is , where is Euler's totient function.
The fact that is an irreducible polynomial of degree in the ring is a nontrivial result due to Gauss. Depending on the chosen definition, it is either the value of the degree or the irreducibility which is a nontrivial result. The case of prime n is easier to prove than the general case, thanks to Eisenstein's criterion.
A fundamental relation involving cyclotomic polynomials is
which means that each n-th root of unity is a primitiv |
https://en.wikipedia.org/wiki/Classful%20network | A classful network is an obsolete network addressing architecture used in the Internet from 1981 until the introduction of Classless Inter-Domain Routing (CIDR) in 1993. The method divides the IP address space for Internet Protocol version 4 (IPv4) into five address classes based on the leading four address bits. Classes A, B, and C provide unicast addresses for networks of three different network sizes. Class D is for multicast networking and the class E address range is reserved for future or experimental purposes.
Since its discontinuation, remnants of classful network concepts have remained in practice only in limited scope in the default configuration parameters of some network software and hardware components, most notably in the default configuration of subnet masks.
Background
In the original address definition, the most significant eight bits of the 32-bit IPv4 address was the network number field which specified the particular network a host was attached to. The remaining 24 bits specified the local address, also called rest field (the rest of the address), which uniquely identified a host connected to that network. This format was sufficient at a time when only a few large networks existed, such as the ARPANET (network number 10), and before the wide proliferation of local area networks (LANs). As a consequence of this architecture, the address space supported only a low number (254) of independent networks.
Before the introduction of address classes, the only address blocks available were these large blocks which later became known as Class A networks. As a result, some organizations involved in the early development of the Internet received address space allocations far larger than they would ever need (16,777,216 IP addresses each). It became clear early in the growth of the network that this would be a critical scalability limitation.
Introduction of address classes
Expansion of the network had to ensure compatibility with the existing address spa |
https://en.wikipedia.org/wiki/Partially%20ordered%20group | In abstract algebra, a partially ordered group is a group (G, +) equipped with a partial order "≤" that is translation-invariant; in other words, "≤" has the property that, for all a, b, and g in G, if a ≤ b then a + g ≤ b + g and g + a ≤ g + b.
An element x of G is called positive if 0 ≤ x. The set of elements 0 ≤ x is often denoted with G+, and is called the positive cone of G.
By translation invariance, we have a ≤ b if and only if 0 ≤ -a + b.
So we can reduce the partial order to a monadic property: if and only if
For the general group G, the existence of a positive cone specifies an order on G. A group G is a partially orderable group if and only if there exists a subset H (which is G+) of G such that:
0 ∈ H
if a ∈ H and b ∈ H then a + b ∈ H
if a ∈ H then -x + a + x ∈ H for each x of G
if a ∈ H and -a ∈ H then a = 0
A partially ordered group G with positive cone G+ is said to be unperforated if n · g ∈ G+ for some positive integer n implies g ∈ G+. Being unperforated means there is no "gap" in the positive cone G+.
If the order on the group is a linear order, then it is said to be a linearly ordered group.
If the order on the group is a lattice order, i.e. any two elements have a least upper bound, then it is a lattice-ordered group (shortly l-group, though usually typeset with a script l: ℓ-group).
A Riesz group is an unperforated partially ordered group with a property slightly weaker than being a lattice-ordered group. Namely, a Riesz group satisfies the Riesz interpolation property: if x1, x2, y1, y2 are elements of G and xi ≤ yj, then there exists z ∈ G such that xi ≤ z ≤ yj.
If G and H are two partially ordered groups, a map from G to H is a morphism of partially ordered groups if it is both a group homomorphism and a monotonic function. The partially ordered groups, together with this notion of morphism, form a category.
Partially ordered groups are used in the definition of valuations of fields.
Examples
The integers with their usual o |
https://en.wikipedia.org/wiki/Logit | In statistics, the logit ( ) function is the quantile function associated with the standard logistic distribution. It has many uses in data analysis and machine learning, especially in data transformations.
Mathematically, the logit is the inverse of the standard logistic function , so the logit is defined as
Because of this, the logit is also called the log-odds since it is equal to the logarithm of the odds where is a probability. Thus, the logit is a type of function that maps probability values from to real numbers in , akin to the probit function.
Definition
If is a probability, then is the corresponding odds; the of the probability is the logarithm of the odds, i.e.:
The base of the logarithm function used is of little importance in the present article, as long as it is greater than 1, but the natural logarithm with base is the one most often used. The choice of base corresponds to the choice of logarithmic unit for the value: base 2 corresponds to a shannon, base to a “nat”, and base 10 to a hartley; these units are particularly used in information-theoretic interpretations. For each choice of base, the logit function takes values between negative and positive infinity.
The “logistic” function of any number is given by the inverse-:
The difference between the s of two probabilities is the logarithm of the odds ratio (), thus providing a shorthand for writing the correct combination of odds ratios only by adding and subtracting:
History
There have been several efforts to adapt linear regression methods to a domain where the output is a probability value, , instead of any real number . In many cases, such efforts have focused on modeling this problem by mapping the range to and then running the linear regression on these transformed values. In 1934 Chester Ittner Bliss used the cumulative normal distribution function to perform this mapping and called his model probit an abbreviation for "probability unit";. However, this is computationally mo |
https://en.wikipedia.org/wiki/Adaptive%20filter | An adaptive filter is a system with a linear filter that has a transfer function controlled by variable parameters and a means to adjust those parameters according to an optimization algorithm. Because of the complexity of the optimization algorithms, almost all adaptive filters are digital filters. Adaptive filters are required for some applications because some parameters of the desired processing operation (for instance, the locations of reflective surfaces in a reverberant space) are not known in advance or are changing. The closed loop adaptive filter uses feedback in the form of an error signal to refine its transfer function.
Generally speaking, the closed loop adaptive process involves the use of a cost function, which is a criterion for optimum performance of the filter, to feed an algorithm, which determines how to modify filter transfer function to minimize the cost on the next iteration. The most common cost function is the mean square of the error signal.
As the power of digital signal processors has increased, adaptive filters have become much more common and are now routinely used in devices such as mobile phones and other communication devices, camcorders and digital cameras, and medical monitoring equipment.
Example application
The recording of a heart beat (an ECG), may be corrupted by noise from the AC mains. The exact frequency of the power and its harmonics may vary from moment to moment.
One way to remove the noise is to filter the signal with a notch filter at the mains frequency and its vicinity, but this could excessively degrade the quality of the ECG since the heart beat would also likely have frequency components in the rejected range.
To circumvent this potential loss of information, an adaptive filter could be used. The adaptive filter would take input both from the patient and from the mains and would thus be able to track the actual frequency of the noise as it fluctuates and subtract the noise from the recording. Such an ada |
https://en.wikipedia.org/wiki/Machine%20vision | Machine vision (MV) is the technology and methods used to provide imaging-based automatic inspection and analysis for such applications as automatic inspection, process control, and robot guidance, usually in industry. Machine vision refers to many technologies, software and hardware products, integrated systems, actions, methods and expertise. Machine vision as a systems engineering discipline can be considered distinct from computer vision, a form of computer science. It attempts to integrate existing technologies in new ways and apply them to solve real world problems. The term is the prevalent one for these functions in industrial automation environments but is also used for these functions in other environment vehicle guidance.
The overall machine vision process includes planning the details of the requirements and project, and then creating a solution. During run-time, the process starts with imaging, followed by automated analysis of the image and extraction of the required information.
Definition
Definitions of the term "Machine vision" vary, but all include the technology and methods used to extract information from an image on an automated basis, as opposed to image processing, where the output is another image. The information extracted can be a simple good-part/bad-part signal, or more a complex set of data such as the identity, position and orientation of each object in an image. The information can be used for such applications as automatic inspection and robot and process guidance in industry, for security monitoring and vehicle guidance. This field encompasses a large number of technologies, software and hardware products, integrated systems, actions, methods and expertise. Machine vision is practically the only term used for these functions in industrial automation applications; the term is less universal for these functions in other environments such as security and vehicle guidance. Machine vision as a systems engineering discipline ca |
https://en.wikipedia.org/wiki/Application%20layer | An application layer is an abstraction layer that specifies the shared communication protocols and interface methods used by hosts in a communications network. An application layer abstraction is specified in both the Internet Protocol Suite (TCP/IP) and the OSI model. Although both models use the same term for their respective highest-level layer, the detailed definitions and purposes are different.
Internet protocol suite
In the Internet protocol suite, the application layer contains the communications protocols and interface methods used in process-to-process communications across an Internet Protocol (IP) computer network. The application layer only standardizes communication and depends upon the underlying transport layer protocols to establish host-to-host data transfer channels and manage the data exchange in a client–server or peer-to-peer networking model. Though the TCP/IP application layer does not describe specific rules or data formats that applications must consider when communicating, the original specification (in ) does rely on and recommend the robustness principle for application design.
OSI model
In the OSI model, the definition of the application layer is narrower in scope. The OSI model defines the application layer as only the interface responsible for communicating with host-based and user-facing applications. OSI then explicitly distinguishes the functionality of two additional layers, the session layer and presentation layer, as separate levels below the application layer and above the transport layer. OSI specifies a strict modular separation of functionality at these layers and provides protocol implementations for each. In contrast, the Internet Protocol Suite compiles these functions into a single layer.
Sublayers
Originally the OSI model consisted of two kinds of application layer services with their related protocols. These two sublayers are the common application service element (CASE) and specific application service element (S |
https://en.wikipedia.org/wiki/Transrapid | Transrapid is a German-developed high-speed monorail train using magnetic levitation. Planning for the Transrapid system started in 1969 with a test facility for the system in Emsland, Germany completed in 1987. In 1991, technical readiness for application was approved by the Deutsche Bundesbahn in cooperation with renowned universities.
The last version, the Transrapid 09, is designed for a cruising speed of and allows acceleration and deceleration of approximately .
In 2002, the first commercial implementation was completed – the Shanghai Maglev Train, which connects the city of Shanghai's rapid transit network to Shanghai Pudong International Airport. The Transrapid system has not yet been deployed on a long-distance intercity line.
The system is developed and marketed by Transrapid International, a joint venture of Siemens and ThyssenKrupp.
In 2006, a Transrapid train collided with a maintenance vehicle on the German test track, leading to 23 fatalities.
In 2011, the Emsland test track closed down when its operating license expired. In early 2012, demolition and reconversion of the entire Emsland site including the factory was approved.
Technology
Levitation
The super-speed Transrapid maglev system has no wheels, no axles, no gear transmissions, no steel rails, and no overhead electrical pantographs. The maglev vehicles do not roll on wheels; rather, they hover above the track guideway, using the attractive magnetic force between two linear arrays of electromagnetic coils—one side of the coil on the vehicle, the other side in the track guideway, which function together as a magnetic dipole. During levitation and travelling operation, the Transrapid maglev vehicle floats on a frictionless magnetic cushion with no mechanical contact whatsoever with the track guideway. On-board vehicle electronic systems measure the dipole gap distance 100,000 times per second to guarantee the clearance between the coils attached to the underside of the guideway and the ma |
https://en.wikipedia.org/wiki/Hidden%20message | A hidden message is information that is not immediately noticeable, and that must be discovered or uncovered and interpreted before it can be known. Hidden messages include backwards audio messages, hidden visual messages and symbolic or cryptic codes such as a crossword or cipher. Although there are many legitimate examples of hidden messages created with techniques such as backmasking and steganography, many so-called hidden messages are merely fanciful imaginings or apophany.
Description
The information in hidden messages is not immediately noticeable; it must be discovered or uncovered, and interpreted before it can be known. Hidden messages include backwards audio messages, hidden visual messages, and symbolic or cryptic codes such as a crossword or cipher. There are many legitimate examples of hidden messages, though many are imaginings.
Backward audio messages
A backward message in an audio recording is only fully apparent when the recording is played reversed. Some backward messages are produced by deliberate backmasking, while others are simply phonetic reversals resulting from random combinations of words. Backward messages may occur in various mediums, including music, video games, music videos, movies, and television shows.
Backmasking
Backmasking is a recording technique in which a message is recorded backwards onto a track that is meant to be played forwards. It was popularized by The Beatles, who used backward vocals and instrumentation on their 1966 album Revolver. The technique has also been used to censor words or phrases for "clean" releases of songs.
Backmasking has been a controversial topic in the United States since the 1980s, when allegations of its use for Satanic purposes were made against prominent rock musicians, leading to record-burnings and proposed anti-backmasking legislation by state and federal governments. In debate are both the existence of backmasked Satanic messages and their purported ability to subliminally affect lis |
https://en.wikipedia.org/wiki/Drag%20coefficient | In fluid dynamics, the drag coefficient (commonly denoted as: , or ) is a dimensionless quantity that is used to quantify the drag or resistance of an object in a fluid environment, such as air or water. It is used in the drag equation in which a lower drag coefficient indicates the object will have less aerodynamic or hydrodynamic drag. The drag coefficient is always associated with a particular surface area.
The drag coefficient of any object comprises the effects of the two basic contributors to fluid dynamic drag: skin friction and form drag. The drag coefficient of a lifting airfoil or hydrofoil also includes the effects of lift-induced drag. The drag coefficient of a complete structure such as an aircraft also includes the effects of interference drag.
Definition
The drag coefficient is defined as
where:
is the drag force, which is by definition the force component in the direction of the flow velocity;
is the mass density of the fluid;
is the flow speed of the object relative to the fluid;
is the reference area
The reference area depends on what type of drag coefficient is being measured. For automobiles and many other objects, the reference area is the projected frontal area of the vehicle. This may not necessarily be the cross-sectional area of the vehicle, depending on where the cross-section is taken. For example, for a sphere (note this is not the surface area = ).
For airfoils, the reference area is the nominal wing area. Since this tends to be large compared to the frontal area, the resulting drag coefficients tend to be low, much lower than for a car with the same drag, frontal area, and speed.
Airships and some bodies of revolution use the volumetric drag coefficient, in which the reference area is the square of the cube root of the airship volume (volume to the two-thirds power). Submerged streamlined bodies use the wetted surface area.
Two objects having the same reference area moving at the same speed through a fluid will exper |
https://en.wikipedia.org/wiki/Gene%20pool | The gene pool is the set of all genes, or genetic information, in any population, usually of a particular species.
Description
A large gene pool indicates extensive genetic diversity, which is associated with robust populations that can survive bouts of intense selection. Meanwhile, low genetic diversity (see inbreeding and population bottlenecks) can cause reduced biological fitness and an increased chance of extinction, although as explained by genetic drift new genetic variants, that may cause an increase in the fitness of organisms, are more likely to fix in the population if it is rather small.
When all individuals in a population are identical with regard to a particular phenotypic trait, the population is said to be 'monomorphic'. When the individuals show several variants of a particular trait they are said to be polymorphic.
History
The Russian geneticist Alexander Sergeevich Serebrovsky first formulated the concept in the 1920s as genofond (gene fund), a word that was imported to the United States from the Soviet Union by Theodosius Dobzhansky, who translated it into English as "gene pool."
Gene pool concept in crop breeding
Harlan and de Wet (1971) proposed classifying each crop and its related species by gene pools rather than by formal taxonomy.
Primary gene pool (GP-1): Members of this gene pool are probably in the same "species" (in conventional biological usage) and can intermate freely. Harlan and de Wet wrote, "Among forms of this gene pool, crossing is easy; hybrids are generally fertile with good chromosome pairing; gene segregation is approximately normal and gene transfer is generally easy.". They also advised subdividing each crop gene pool in two:
Subspecies A: Cultivated races
Subspecies B: Spontaneous races (wild or weedy)
Secondary gene pool (GP-2): Members of this pool are probably normally classified as different species than the crop species under consideration (the primary gene pool). However, these species are closely related a |
https://en.wikipedia.org/wiki/Dispersion%20%28materials%20science%29 | In materials science, dispersion is the fraction of atoms of a material exposed to the surface. In general, D = NS/N, where D is the dispersion, NS is the number of surface atoms and NT is the total number of atoms of the material. It is an important concept in heterogeneous catalysis, since only atoms exposed to the surface can affect catalytic surface reactions. Dispersion increases with decreasing crystallite size and approaches unity at a crystallite diameter of about 0.1 nm.
See also
Emulsion dispersion
References
Materials science |
https://en.wikipedia.org/wiki/Lichenology | Lichenology is the branch of mycology that studies the lichens, symbiotic organisms made up of an intimate symbiotic association of a microscopic alga (or a cyanobacterium) with a filamentous fungus.
Study of lichens draws knowledge from several disciplines: mycology, phycology, microbiology and botany. Scholars of lichenology are known as lichenologists.
History
The beginnings
Lichens as a group have received less attention in classical treatises on botany than other groups although the relationship between humans and some species has been documented from early times. Several species have appeared in the works of Dioscorides, Pliny the Elder and Theophrastus although the studies are not very deep. During the first centuries of the modern age they were usually put forward as examples of spontaneous generation and their reproductive mechanisms were totally ignored. For centuries naturalists had included lichens in diverse groups until in the early 18th century a French researcher Joseph Pitton de Tournefort in his Institutiones Rei Herbariae grouped them into their own genus. He adopted the Latin term lichen, which had already been used by Pliny who had imported it from Theophrastus but up until then this term had not been widely employed. The original meaning of the Greek word λειχήν (leichen) was moss that in its turn derives from the Greek verb λείχω (liekho) to suck because of the great ability of these organisms to absorb water. In its original use the term signified mosses, liverworts as well as lichens. Some forty years later Dillenius in his Historia Muscorum made the first division of the group created by Tournefort separating the sub-families Usnea, Coralloides and Lichens in response to the morphological characteristics of the lichen thallus.
After the revolution in taxonomy brought in by Linnaeus and his new system of classification lichens are retained in the Plant Kingdom forming a single group Lichen with eight divisions within the group according |
https://en.wikipedia.org/wiki/Lichen | A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship. Lichens are important actors in nutrient cycling and act as producers which many higher trophic feeders feed on, such as reindeer, gastropods, nematodes, mites, and springtails. Lichens have properties different from those of their component organisms. They come in many colors, sizes, and forms and are sometimes plant-like, but are not plants. They may have tiny, leafless branches (fruticose); flat leaf-like structures (foliose); grow crust-like, adhering tightly to a surface (substrate) like a thick coat of paint (crustose); have a powder-like appearance (leprose); or other growth forms.
A macrolichen is a lichen that is either bush-like or leafy; all other lichens are termed microlichens. Here, "macro" and "micro" do not refer to size, but to the growth form. Common names for lichens may contain the word moss (e.g., "reindeer moss", "Iceland moss"), and lichens may superficially look like and grow with mosses, but they are not closely related to mosses or any plant. Lichens do not have roots that absorb water and nutrients as plants do, but like plants, they produce their own nutrition by photosynthesis. When they grow on plants, they do not live as parasites, but instead use the plant's surface as a substrate.
Lichens occur from sea level to high alpine elevations, in many environmental conditions, and can grow on almost any surface. They are abundant growing on bark, leaves, mosses, or other lichens and hanging from branches "living on thin air" (epiphytes) in rainforests and in temperate woodland. They grow on rock, walls, gravestones, roofs, exposed soil surfaces, rubber, bones, and in the soil as part of biological soil crusts. Various lichens have adapted to survive in some of the most extreme environments on Earth: arctic tundra, hot dry deserts, rocky coasts, and toxic slag heaps. They can even li |
https://en.wikipedia.org/wiki/Stunnel | Stunnel is an open-source multi-platform application used to provide a universal TLS/SSL tunneling service.
Stunnel is used to provide secure encrypted connections for clients or servers that do not speak TLS or SSL natively. It runs on a variety of operating systems, including most Unix-like operating systems and Windows. Stunnel relies on the OpenSSL library to implement the underlying TLS or SSL protocol.
Stunnel uses public-key cryptography with X.509 digital certificates to secure the SSL connection, and clients can optionally be authenticated via a certificate.
If linked against libwrap, it can be configured to act as a proxy–firewall service as well.
Stunnel is maintained by Polish programmer Michał Trojnara and released under the terms of the GNU General Public License (GPL) with OpenSSL exception.
Example
A stunnel can be used to provide a secure SSL connection to an existing non-SSL-aware SMTP mail server. Assuming the SMTP server expects TCP connections on port 25, the stunnel would be configured to map the SSL port 465 to non-SSL port 25. A mail client connects via SSL to port 465. Network traffic from the client initially passes over SSL to the stunnel application, which transparently encrypts and decrypts traffic and forwards unsecured traffic to port 25 locally. The mail server sees a non-SSL mail client.
The stunnel process could be running on the same or a different server from the unsecured mail application; however, both machines would typically be behind a firewall on a secure internal network (so that an intruder could not make its own unsecured connection directly to port 25).
See also
Tunneling protocol
References
External links
Cryptographic software
Free security software
Unix network-related software
Transport Layer Security implementation
Tunneling protocols
Network protocols |
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