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Stellar evolution

Stellar evolution is the process by which a star changes over the course of time. Depending on the mass of the star, its lifetime can range from a few million years for the most massive to trillions of years for the least massive, longer than the age of the universe; the table shows the lifetimes of stars as a function of their masses. All stars are formed from collapsing clouds of gas and dust called nebulae or molecular clouds. Over the course of millions of years, these protostars settle down into a state of equilibrium, becoming what is known as a main-sequence star. Nuclear fusion powers a star for most of its existence; the energy is generated by the fusion of hydrogen atoms at the core of the main-sequence star. As the preponderance of atoms at the core becomes helium, stars like the Sun begin to fuse hydrogen along a spherical shell surrounding the core; this process causes the star to grow in size, passing through the subgiant stage until it reaches the red giant phase. Stars with at least half the mass of the Sun can begin to generate energy through the fusion of helium at their core, whereas more-massive stars can fuse heavier elements along a series of concentric shells.

Once a star like the Sun has exhausted its nuclear fuel, its core collapses into a dense white dwarf and the outer layers are expelled as a planetary nebula. Stars with around ten or more times the mass of the Sun can explode in a supernova as their inert iron cores collapse into an dense neutron star or black hole. Although the universe is not old enough for any of the smallest red dwarfs to have reached the end of their existence, stellar models suggest they will become brighter and hotter before running out of hydrogen fuel and becoming low-mass white dwarfs. Stellar evolution is not studied by observing the life of a single star, as most stellar changes occur too to be detected over many centuries. Instead, astrophysicists come to understand how stars evolve by observing numerous stars at various points in their lifetime, by simulating stellar structure using computer models. Stellar evolution starts with the gravitational collapse of a giant molecular cloud. Typical giant molecular clouds are 100 light-years across and contain up to 6,000,000 solar masses.

As it collapses, a giant molecular cloud breaks into smaller pieces. In each of these fragments, the collapsing gas releases gravitational potential energy as heat; as its temperature and pressure increase, a fragment condenses into a rotating sphere of superhot gas known as a protostar. A protostar continues to grow by accretion of gas and dust from the molecular cloud, becoming a pre-main-sequence star as it reaches its final mass. Further development is determined by its mass. Mass is compared to the mass of the Sun: 1.0 M☉ means 1 solar mass. Protostars are encompassed in dust, are thus more visible at infrared wavelengths. Observations from the Wide-field Infrared Survey Explorer have been important for unveiling numerous Galactic protostars and their parent star clusters. Protostars with masses less than 0.08 M☉ never reach temperatures high enough for nuclear fusion of hydrogen to begin. These are known as brown dwarfs; the International Astronomical Union defines brown dwarfs as stars massive enough to fuse deuterium at some point in their lives.

Objects smaller than 13 MJ are classified as sub-brown dwarfs. Both types, deuterium-burning and not, shine dimly and fade away cooling over hundreds of millions of years. For a more-massive protostar, the core temperature will reach 10 million kelvin, initiating the proton–proton chain reaction and allowing hydrogen to fuse, first to deuterium and to helium. In stars of over 1 M☉, the carbon–nitrogen–oxygen fusion reaction contributes a large portion of the energy generation; the onset of nuclear fusion leads quickly to a hydrostatic equilibrium in which energy released by the core maintains a high gas pressure, balancing the weight of the star's matter and preventing further gravitational collapse. The star thus evolves to a stable state, beginning the main-sequence phase of its evolution. A new star will sit at a specific point on the main sequence of the Hertzsprung–Russell diagram, with the main-sequence spectral type depending upon the mass of the star. Small cold, low-mass red dwarfs fuse hydrogen and will remain on the main sequence for hundreds of billions of years or longer, whereas massive, hot O-type stars will leave the main sequence after just a few million years.

A mid-sized yellow dwarf star, like the Sun, will remain on the main sequence for about 10 billion years. The Sun is thought to be in the middle of its main sequence lifespan; the core exhausts its supply of hydrogen and the star begins to evolve off of the main sequence. Without the outward radiation pressure generated by the fusion of hydrogen to counteract the force of gravity the core contracts until either electron degeneracy pressure becomes sufficient to oppose gravity or the core becomes hot enough for helium fusion to begin. Which of these happens first depends upon the star's mass. What happens after a low-mass star ceases to produce energy through fusion has not been directly observed. Recent astrophysical models suggest that red dwarfs of 0.1 M☉ may stay on the main sequence for s

Transient (computer programming)

In computer programming, transient is a property of any element in the system, temporary. The term applies to transient applications, i.e. software for the end-user, displayed with a transient application posture. Examples of applications of the term are described below. In the Java programming language, transient is a keyword used as a field modifier; when a field is declared transient, it would not be serialized if the class to which it belongs is serialized. In Java, methods and interfaces cannot be declared as transient, because they are never serialized. In Hibernate and other persistence systems, transient describes an object, instantiated, but is not associated with a Hibernate session, i. e. the object resides in memory but is not being persisted. In the X Window System, a window is said to be transient for another window if it belongs to that other window and may not outlast it: a dialog box, such as an alert message, is a common example; this should not be confused with a window containing another window: contained windows lie within their parents, but transients are separate windows which can be moved around the screen.

Transient windows may be treated specially by the window manager, unlike top-level windows, must never require any user interaction on appearing. Transient refers to a module that, once loaded into main memory, is expected to remain in memory for a short time. Today, the term is used, may be obsolete; the term Overlay is used instead, refer to a program module, brought to memory when it is needed by the running program and replaced with another when it is no longer needed, so a program had lower memory requirements. Program modules were written to allow different modules to share the same memory region and the main program itself was responsible of exchanging modules between disk and memory as necessary. In the mid-to-late 1960s, mainframe computers, such as the IBM System/360, had memory sizes from 8 KB to 512 KB. In order to conserve memory, transients were small modules that supported a specific task, were swapped in and out of memory; the operating system for the 360 had two areas reserved for transients that supported input/output operations.

These were referred to as the “logical transient area,” and the “physical transient area.” If an application program, for example, needed to use the printer, transients that supported printing were brought into the transient areas. If an application needed to use tape drives, transients that supported tape drive access were brought into the transient areas. At the level of message passing, transient communication means the way by which the messages are not saved into a buffer to wait for its delivery at the message receiver; the messages will be delivered. If the receiver is not running at the send time, the message will be discarded, because it has not been stored into intermediate buffers. Temporary

Atergatis subdentatus

Atergatis subdentatus known as the red reef crab, dark-finger coral crab or eyed coral crab, is a species of crab in the family Xanthidae. Atergatis subdentatus has a compact shape, may appear either uniform crimson in colour, or may have an irregularly mottled yellow on a crimson background, it has a broadly subquadrilateral carapace which grows to about 90 millimetres wide, has finely punctulated by the anterior and antero-lateral borders. It has an orange spot in the centre of the carapace with two small, white'eyes' within; the arms have a flattish inner surface with inward-pointing teeth. Beside the teeth are brush-like hairs grouped together in five bundles; the type locality for this species is Japan, it can be found around many of the Japanese islands. It occurs in the waters of Taiwan, in the Lakshadweep Islands and Gulf of Mannar; this species lives on rocky beaches at a range of 3 -- 30 m in depth. Paul F. Clark, Peter K. L. Ng & P.-H. Ho. "Atergatis subdentatus, Atergatopsis germaini A. Milne Edwards, 1865 and Platypodia eydouxi – first stage zoeal descriptions with implications for the subfamily".

Raffles Bulletin of Zoology. 52: 563–592. Media related to Atergatis subdentatus at Wikimedia Commons

Daniel Price (priest)

Daniel Price was Dean of St Asaph from 1696 until his death on 7 November 1706. Price was educated at Trinity College, Cambridge, he was ordained on 26 May 1678. He held livings at Westmill and Llansantffraed. John Aubrey noted in his collection of short autobiographies Brief Lives that he was a "mighty Pontificall proud man", in 1656 that...one time when they went in procession about the cathedral church, he would not do it in the usual way in his surplice, etc on foot, but rode on a mare, thus habited, with the Common Prayer book in his hand, reading. A stallion happened to break loose, smelled the mare, ran and leapt her, held the reverend dean all the time so hard in his embraces, that he could not get off till the horse had done his business, but he would never ride in procession afterwards

Windsor Heights, West Virginia

Windsor Heights is a village in Brooke County, West Virginia, United States. It is part of West Virginia Metropolitan Statistical Area; the population was 423 at the 2010 census. Grace Davis was the mayor as of June, 2017. Windsor Heights is located at 40°11′30″N 80°39′56″W. According to the United States Census Bureau, the village has a total area of 0.14 square miles, all of it land. As of the census of 2010, there were 423 people, 170 households, 121 families living in the village; the population density was 3,021.4 inhabitants per square mile. There were 185 housing units at an average density of 1,321.4 per square mile. The racial makeup of the village was 99.5 % 0.5 % African American. There were 170 households of which 32.9% had children under the age of 18 living with them, 54.7% were married couples living together, 10.6% had a female householder with no husband present, 5.9% had a male householder with no wife present, 28.8% were non-families. 25.3% of all households were made up of individuals and 14.7% had someone living alone, 65 years of age or older.

The average household size was 2.48 and the average family size was 2.94. The median age in the village was 40.6 years. 22.2% of residents were under the age of 18. The gender makeup of the village was 49.6 % female. As of the census of 2000, there were 431 people, 180 households, 124 families living in the village; the population density was 3,053.2 people per square mile. There were 197 housing units at an average density of 1,395.6 per square mile. The racial makeup of the village was 99.07% White, 0.46% Native American, 0.46% from two or more races. There were 180 households out of which 26.1% had children under the age of 18 living with them, 55.0% were married couples living together, 9.4% had a female householder with no husband present, 31.1% were non-families. 26.7% of all households were made up of individuals and 17.2% had someone living alone, 65 years of age or older. The average household size was 2.39 and the average family size was 2.91. The age distribution is 20.9% under the age of 18, 7.9% from 18 to 24, 26.7% from 25 to 44, 25.5% from 45 to 64, 19.0% who were 65 years of age or older.

The median age was 40 years. For every 100 females, there were 93.3 males. For every 100 females age 18 and over, there were 98.3 males. The median income for a household in the village was $28,523, the median income for a family was $37,794. Males had a median income of $30,833 versus $20,000 for females; the per capita income for the village was $17,315. About 5.6% of families and 8.4% of the population were below the poverty line, including 10.5% of those under age 18 and 3.3% of those age 65 or over. List of cities and towns along the Ohio River

MUSHRA

MUSHRA stands for MUltiple Stimuli with Hidden Reference and Anchor and is a methodology for conducting a codec listening test to evaluate the perceived quality of the output from lossy audio compression algorithms. It is defined by ITU-R recommendation BS.1534-3. The MUSHRA methodology is recommended for assessing "intermediate audio quality". For small audio impairments, Recommendation ITU-R BS.1116-3 is recommended instead. The main advantage over the mean opinion score methodology is that MUSHRA requires fewer participants to obtain statistically significant results; this is because all codecs are presented at the same time, on the same samples, so that a paired t-test or a repeated measures analysis of variance can be used for statistical analysis. The 0–100 scale used by MUSHRA makes it possible to rate small differences. In MUSHRA, the listener is presented with the reference, a certain number of test samples, a hidden version of the reference and one or more anchors; the recommendation specifies that a low-range and a mid-range anchor should be included in the test signals.

These are a 7 kHz and a 3.5 kHz low-pass version of the reference. The purpose of the anchors is to calibrate the scale so that minor artifacts are not unduly penalized; this is important when comparing or pooling results from different labs. Both, MUSHRA and ITU BS.1116 tests call for trained expert listeners who know what typical artifacts sound like and where they are to occur. Expert listeners have a better internalization of the rating scale which leads to more repeatable results than with untrained listeners. Thus, with trained listeners, fewer listeners are needed to achieve statistically significant results, it is assumed that preferences are similar for expert listeners and naive listeners and thus results of expert listeners are predictive for consumers. In agreement with this assumption Schinkel-Bielefeld et al. found no differences in the rank order between expert listeners and untrained listeners when using test signals containing only timbre and no spatial artifacts. However, Rumsey et al. showed that for signals containing spatial artifacts, expert listeners weigh spatial artifacts stronger than untrained listeners, who focus on timbre artifacts.

In addition to this, it has been shown that expert listeners make more use of the option to listen to smaller sections of the signals under test and perform more comparisons between the signals under test and the reference. In contrast to the naive listener who produce a preference rating, expert listeners therefore produce an audio quality rating, rating the differences between the signal under test and the uncompressed original, the actual goal of a MUSHRA-test; the MUSHRA guideline mentions several possibilities to assess the reliability of a listener. The easiest and most common is to disqualify listeners who rate the hidden reference below 90 MUSHRA points for more than 15 percent of all test items; the hidden reference should be rated with 100 MUSHRA points so this is a mistake. While it can happen that the hidden reference and a high-quality signal are confused, a rating of lower than 90 should only be given when the listener is certain that the rated signal is different than the original reference.

The other possibility to assess a listener's performance is eGauge, a framework based on the analysis of variance. It computes agreement and discriminability, though only the latter two are recommended for pre or post screening. Agreement analyses. Repeatability looks at the variance when rating the same test signal again in comparison to the variance of the other test signals and discriminability analyses if listeners can distinguish between test signals of different conditions; as eGauge requires listening to every test signal twice, it is more effort to apply this than to post screen listeners based on the ratings of the hidden reference. However, if a listener has proven a reliable listener using eGauge, he or she can be considered a reliable listener for future listening tests, provided the character of the test does not change, it is important to choose critical test items. At the same time, the test items should be ecological valid. A method to choose critical material is presented by Ekeroot et al. who propose a ranking by elimination procedure.

While this is a good way to choose the most critical test items, it does not ensure inclusion a variety of test items prone to different artifacts. Ideally the character of a MUSHRA test item should not change too much for the whole duration of that item. Otherwise it can be difficult for the listener to decide on a rating if different parts of the items display different or stronger artifacts than others. Shorter items lead to less variability than longer ones, as they are more stationary; however when trying to choose stationary items, ecologically valid stimuli will often have sections that are more critical than the rest of the signal. Thus, listeners who focus on different sections of the signal may evaluate it differently. In this case more critical listeners seem to be better in identifying the most critical regions of a stimulus than less critical listeners. While in ITU-T P.800 tests which are used to evaluate telephone quality codecs the tested speech items should always be in the