Power of a test

The power of a binary hypothesis test is denoted by "(1−β)" and is the probability of a "true positive". It is the probability that the test correctly rejects the null hypothesis (formula_1) when a specific alternative hypothesis (formula_2) is true. It is the probability of avoiding a "false negative", otherwise known as a type II error. The statistical power ranges from 0 to 1, and as statistical power increases, the size of "β" - the probability of making a type II error by wrongly failing to reject the null hypothesis - decreases.
Notation.
This article uses the following notation
Description.
For a type II error probability of , the corresponding statistical power is 1 − . For example, if experiment E has a statistical power of 0.7, and experiment F has a statistical power of 0.95, then there is a stronger probability that experiment E had a type II error than experiment F. This reduces experiment E's sensitivity to detect significant effects. However, experiment E is consequently more reliable than experiment F due to its lower probability of a type I error. It can be equivalently thought of as the probability of accepting the alternative hypothesis (formula_2) when it is true — that is, the ability of a test to detect a specific effect, if that specific effect actually exists. Thus,
If formula_2 is not an equality but rather simply the negation of formula_1 (so for example with formula_7 for some unobserved population parameter formula_8 we have simply formula_9) then power cannot be calculated unless probabilities are known for all possible values of the parameter that violate the null hypothesis. Thus one generally refers to a test's power "against a specific alternative hypothesis".
As the power increases, there is a decreasing probability of a type II error, also called the "false negative rate" () since the power is equal to 1 − . A similar concept is the type I error probability, also referred to as the "false positive rate" or the level of a test under the null hypothesis.
In the context of binary classification, the power of a test is called its "statistical sensitivity", its "true positive rate", or its "probability of detection".
Power analysis.
A related concept is "power analysis". Power analysis can be used to calculate the minimum sample size required so that one can be reasonably likely to detect an effect of a given size. For example: "How many times do I need to toss a coin to conclude it is rigged by a certain amount?" Power analysis can also be used to calculate the minimum effect size that is likely to be detected in a study using a given sample size. In addition, the concept of power is used to make comparisons between different statistical testing procedures: for example, between a parametric test and a nonparametric test of the same hypothesis.
Background.
Statistical tests use data from samples to assess, or make inferences about, a statistical population. In the concrete setting of a two-sample comparison, the goal is to assess whether the mean values of some attribute obtained for individuals in two sub-populations differ. For example, to test the null hypothesis that the mean scores of men and women on a test do not differ, samples of men and women are drawn, the test is administered to them, and the mean score of one group is compared to that of the other group using a statistical test such as the two-sample "z"-test. The power of the test is the probability that the test will find a statistically significant difference between men and women, as a function of the size of the true difference between those two populations.
Factors influencing power.
Statistical power may depend on a number of factors. Some factors may be particular to a specific testing situation, but at a minimum, power nearly always depends on the following three factors:
A significance criterion is a statement of how unlikely a positive result must be, if the null hypothesis of no effect is true, for the null hypothesis to be rejected. The most commonly used criteria are probabilities of 0.05 (5%, 1 in 20), 0.01 (1%, 1 in 100), and 0.001 (0.1%, 1 in 1000). If the criterion is 0.05, the probability of the data implying an effect at least as large as the observed effect when the null hypothesis is true must be less than 0.05, for the null hypothesis of no effect to be rejected. One easy way to increase the power of a test is to carry out a less conservative test by using a larger significance criterion, for example 0.10 instead of 0.05 . This increases the chance of rejecting the null hypothesis (obtaining a statistically significant result) when the null hypothesis is false; that is, it reduces the risk of a type II error (false negative regarding whether an effect exists). But it also increases the risk of obtaining a statistically significant result (rejecting the null hypothesis) when the null hypothesis is not false; that is, it increases the risk of a type I error (false positive).
The magnitude of the effect of interest in the population can be quantified in terms of an effect size, where there is greater power to detect larger effects. An effect size can be a direct value of the quantity of interest, or it can be a standardized measure that also accounts for the variability in the population. For example, in an analysis comparing outcomes in a treated and control population, the difference of outcome means formula_10 would be a direct estimate of the effect size, whereas formula_11 would be an estimated standardized effect size, where formula_12 is the common standard deviation of the outcomes in the treated and control groups. If constructed appropriately, a standardized effect size, along with the sample size, will completely determine the power. An unstandardized (direct) effect size is rarely sufficient to determine the power, as it does not contain information about the variability in the measurements.
The sample size determines the amount of sampling error inherent in a test result. Other things being equal, effects are harder to detect in smaller samples. Increasing sample size is often the easiest way to boost the statistical power of a test. How increased sample size translates to higher power is a measure of the efficiency of the test — for example, the sample size required for a given power.
The precision with which the data are measured also influences statistical power. Consequently, power can often be improved by reducing the measurement error in the data. A related concept is to improve the "reliability" of the measure being assessed (as in psychometric reliability).
The design of an experiment or observational study often influences the power. For example, in a two-sample testing situation with a given total sample size , it is optimal to have equal numbers of observations from the two populations being compared (as long as the variances in the two populations are the same). In regression analysis and analysis of variance, there are extensive theories and practical strategies for improving the power based on optimally setting the values of the independent variables in the model.
Interpretation.
Although there are no formal standards for power (sometimes referred to as ), most researchers assess the power of their tests using  = 0.80 as a standard for adequacy. This convention implies a four-to-one trade off between -risk and -risk. ( is the probability of a type II error, and α is the probability of a type I error; 0.2 and 0.05 are conventional values for and ). However, there will be times when this 4-to-1 weighting is inappropriate. In medicine, for example, tests are often designed in such a way that no false negatives (type II errors) will be produced. But this inevitably raises the risk of obtaining a false positive (a type I error). The rationale is that it is better to tell a healthy patient "we may have found something—let's test further," than to tell a diseased patient "all is well."
Power analysis is appropriate when the concern is with the correct rejection of a false null hypothesis. In many contexts, the issue is less about determining if there is or is not a difference but rather with getting a more refined estimate of the population effect size. For example, if we were expecting a population correlation between intelligence and job performance of around 0.50, a sample size of 20 will give us approximately 80% power ( = 0.05, two-tail) to reject the null hypothesis of zero correlation. However, in doing this study we are probably more interested in knowing whether the correlation is 0.30 or 0.60 or 0.50 . In this context we would need a much larger sample size in order to reduce the confidence interval of our estimate to a range that is acceptable for our purposes. Techniques similar to those employed in a traditional power analysis can be used to determine the sample size required for the width of a confidence interval to be less than a given value.
Many statistical analyses involve the estimation of several unknown quantities. In simple cases, all but one of these quantities are nuisance parameters. In this setting, the only relevant power pertains to the single quantity that will undergo formal statistical inference. In some settings, particularly if the goals are more "exploratory", there may be a number of quantities of interest in the analysis. For example, in a multiple regression analysis we may include several covariates of potential interest. In situations such as this where several hypotheses are under consideration, it is common that the powers associated with the different hypotheses differ. For instance, in multiple regression analysis, the power for detecting an effect of a given size is related to the variance of the covariate. Since different covariates will have different variances, their powers will differ as well.
Any statistical analysis involving multiple hypotheses is subject to inflation of the type I error rate if appropriate measures are not taken. Such measures typically involve applying a higher threshold of stringency to reject a hypothesis in order to compensate for the multiple comparisons being made ("e.g." as in the Bonferroni method). In this situation, the power analysis should reflect the multiple testing approach to be used. Thus, for example, a given study may be well powered to detect a certain effect size when only one test is to be made, but the same effect size may have much lower power if several tests are to be performed.
It is also important to consider the statistical power of a hypothesis test when interpreting its results. A test's power is the probability of correctly rejecting the null hypothesis when it is false; a test's power is influenced by the choice of significance level for the test, the size of the effect being measured, and the amount of data available. A hypothesis test may fail to reject the null, for example, if a true difference exists between two populations being compared by a t-test but the effect is small and the sample size is too small to distinguish the effect from random chance. Many clinical trials, for instance, have low statistical power to detect differences in adverse effects of treatments, since such effects may be rare and the number of affected patients small.
"A priori" vs. "post hoc" analysis.
Power analysis can either be done before ("a priori" or prospective power analysis) or after ("post hoc" or retrospective power analysis) data are collected. "A priori" power analysis is conducted prior to the research study, and is typically used in estimating sufficient sample sizes to achieve adequate power. "Post-hoc" analysis of "observed power" is conducted after a study has been completed, and uses the obtained sample size and effect size to determine what the power was in the study, assuming the effect size in the sample is equal to the effect size in the population. Whereas the utility of prospective power analysis in experimental design is universally accepted, post hoc power analysis is fundamentally flawed. Falling for the temptation to use the statistical analysis of the collected data to estimate the power will result in uninformative and misleading values. In particular, it has been shown that "post-hoc" "observed power" is a one-to-one function of the "p"-value attained. This has been extended to show that all "post-hoc" power analyses suffer from what is called the "power approach paradox" (PAP), in which a study with a null result is thought to show "more" evidence that the null hypothesis is actually true when the "p"-value is smaller, since the apparent power to detect an actual effect would be higher. In fact, a smaller "p"-value is properly understood to make the null hypothesis "relatively" less likely to be true.
Application.
Funding agencies, ethics boards and research review panels frequently request that a researcher perform a power analysis, for example to determine the minimum number of animal test subjects needed for an experiment to be informative. In frequentist statistics, an underpowered study is unlikely to allow one to choose between hypotheses at the desired significance level. In Bayesian statistics, hypothesis testing of the type used in classical power analysis is not done. In the Bayesian framework, one updates his or her prior beliefs using the data obtained in a given study. In principle, a study that would be deemed underpowered from the perspective of hypothesis testing could still be used in such an updating process. However, power remains a useful measure of how much a given experiment size can be expected to refine one's beliefs. A study with low power is unlikely to lead to a large change in beliefs.
Example.
The following is an example that shows how to compute power for a randomized experiment: Suppose the goal of an experiment is to study the effect of a treatment on some quantity, and compare research subjects by measuring the quantity before and after the treatment, analyzing the data using a paired t-test. Let formula_13 and formula_14 denote the pre-treatment and post-treatment measures on subject formula_15, respectively. The possible effect of the treatment should be visible in the differences formula_16 which are assumed to be independently distributed, all with the same expected mean value and variance.
The effect of the treatment can be analyzed using a one-sided t-test. The null hypothesis of no effect will be that the mean difference will be zero, i.e. formula_17 In this case, the alternative hypothesis states a positive effect, corresponding to formula_18 The test statistic is:
where
 is the sample size and formula_21 is the standard error. The test statistic under the null hypothesis follows a Student t-distribution with the additional assumption that the data is identically distributed formula_22. Furthermore, assume that the null hypothesis will be rejected at the significance level of formula_23 Since is large, one can approximate the t-distribution by a normal distribution and calculate the critical value using the quantile function formula_24, the inverse of the cumulative distribution function of the normal distribution. It turns out that the null hypothesis will be rejected if
Now suppose that the alternative hypothesis is true and formula_26. Then, the power is
For large , formula_28 approximately follows a standard normal distribution when the alternative hypothesis is true, the approximate power can be calculated as
According to this formula, the power increases with the values of the parameter formula_30 For a specific value of formula_31 a higher power may be obtained by increasing the sample size .
It is not possible to guarantee a sufficient large power for all values of formula_32 as formula_31 may be very close to 0. The minimum (infimum) value of the power is equal to the confidence level of the test, formula_34 in this example 0.05 . However, it is of no importance to distinguish between formula_35 and small positive values. If it is desirable to have enough power, say at least 0.90, to detect values of formula_36 the required sample size can be calculated approximately:
from which it follows that
Hence, using the quantile function
where formula_40 is a standard normal quantile; refer to the Probit article for an explanation of the relationship between formula_41 and z-values.
Extension.
Bayesian power.
In the frequentist setting, parameters are assumed to have a specific value which is unlikely to be true. This issue can be addressed by assuming the parameter has a distribution. The resulting power is sometimes referred to as Bayesian power which is commonly used in clinical trial design.
Predictive probability of success.
Both frequentist power and Bayesian power use statistical significance as the success criterion. However, statistical significance is often not enough to define success. To address this issue, the power concept can be extended to the concept of predictive probability of success (PPOS). The success criterion for PPOS is not restricted to statistical significance and is commonly used in clinical trial designs.
Software for power and sample size calculations.
Numerous free and/or open source programs are available for performing power and sample size calculations. These include


740 Cantabia

740 Cantabia is a minor planet orbiting the Sun.
Cantabia is a contraction of Cantabrigia, Latin for Cambridge, named in honor of Cambridge, Massachusetts.


857 Glasenappia

857 Glasenappia is a minor planet orbiting the Sun. It was named after Russian astronomer Sergey Glazenap, who was often referred to as "S. de Glasenapp" in pre-Revolution publications.


Hypolydian mode

The Hypolydian mode, literally meaning "below Lydian", is the common name for the sixth of the eight church modes of medieval music theory. The name is taken from Ptolemy of Alexandria's term for one of his seven "tonoi", or transposition keys. This mode is the plagal counterpart of the authentic fifth mode.
In medieval theory the Hypolydian mode was described either as (1) the diatonic octave species from C to the C an octave higher, divided at the final F (C–D–E–F + F–G–A–B–C) or (2) a mode with F as final and an ambitus from the C below the final to the D above it. The third above the final, A—corresponding to the reciting tone or "tenor" of the sixth psalm tone—was regarded as having an important melodic function in this mode. The sequence of intervals was therefore divided by the final into a lower tetrachord of tone-tone-semitone, and an upper pentachord of tone-tone-tone-semitone. However, from as early as the time of Hucbald the Hypolydian mode—even more than the corresponding authentic mode, the Lydian—was characterized by the predominance of B instead of B as the fourth degree above the final. The melodic centering on F and A, as well as the use of B instead of B, is illustrated in the accompanying example from the Requiem Mass introit, "Requiem aeternam".
Finer distinctions among the scale degree are sometimes made, with the D below the final called the "mediant", the lowest note, C, the "participant" (a tone functioning as an auxiliary to the mediant), the G, B, and B the "conceded modulations" (subsidiary degrees), and the lowest C, the final, F, and (rarely) the D the "absolute initials".


4426 Roerich


235 Carolina

Carolina (minor planet designation: 235 Carolina) is a sizeable Main belt asteroid. It is an S-type asteroid.
It was discovered by Johann Palisa on 28 November 1883 in Vienna.
The asteroid was named after Caroline Island, now part of Kiribati.


Secondary Level English Proficiency test

The Secondary Level English Proficiency Test® was a test created by ETS and administered by American middle and high schools to applicants whose first language is not English.
The SLEP® test was discontinued June 30, 2012 and replaced by the TOEFL® Junior™ test. However, a limited number of private schools continue to use the SLEP test. In addition, a large number of schools that formerly used SLEP began using the iTEP SLATE exam by Boston Educational Services after June 2012.


Shure SM58

The Shure SM58 is a professional cardioid dynamic microphone, commonly used in live vocal applications. Produced since 1966 by Shure Incorporated, it has built a strong reputation among musicians for its durability and sound, and half a century later it is still considered the industry standard for live vocal performance microphones. The SM58 and its sibling, the SM57, are the best-selling microphones in the world. The SM stands for Studio Microphone.
Like all directional microphones, the SM58 is subject to proximity effect, a low frequency boost when used close to the source. The cardioid response reduces pickup from the side and rear, helping to avoid feedback onstage. There are wired (with and without on/off switch) and wireless versions. The wired version provides balanced audio through a male XLR connector. The SM58 uses an internal shock mount to reduce handling noise.
A distinctive feature of the SM58 is its pneumatic suspension system for the microphone capsule. The capsule, a readily replaceable component, is surrounded by a soft rubber balloon, rather than springs or solid rubber. This gives notably good isolation from handling noise; one reason for its being a popular microphone for stage vocalists. Microphones with this feature are intended primarily for hand-held use, rather than on a stand or for instrument miking.
The SM58 is unswitched, while the otherwise identical SM58S has a sliding on-off switch on the body. Other suffixes refer to any accessories supplied with the microphone: when a cable is provided, the model is actually SM58-CN, while the SM58-LC has no provided cable; the SM58-X2u kit consists of the SM58-LC and an inline X2u XLR-to-USB signal adaptor (capable of providing phantom power for condenser microphones, and offering an in-built headphone jack for monitoring).
Specifications.
Type: Dynamic (moving coil)
Counterfeiting.
The SM58 and SM57 have been extensively counterfeited. Most of these counterfeit microphones are at least functional, but have poorer performance and do not have the pneumatic suspension. There are many other subtle details which can reveal most of these fakes.


Rydberg ionization spectroscopy

Rydberg ionization spectroscopy is a spectroscopy technique in which multiple photons are absorbed by an atom causing the removal of an electron to form an ion.
Resonance ionization spectroscopy.
The ionization threshold energy of atoms and small molecules are typically larger than the photon energies that are most easily available experimentally. However, it can be possible to span this ionization threshold energy if the photon energy is resonant with an intermediate electronically excited state. While it is often possible to observe the lower Rydberg levels in conventional spectroscopy of atoms and small molecules, Rydberg states are even more important in laser ionization experiments. Laser spectroscopic experiments often involve ionization through a photon energy resonance at an intermediate level, with an unbound final electron state and an ionic core. On resonance for phototransitions permitted by selection rules, the intensity of the laser in combination with the excited state lifetime makes ionization an expected outcome. This RIS approach and variations permit sensitive detection of specific species.
Low Rydberg levels and resonance enhanced multiphoton ionization.
High photon intensity experiments can involve multiphoton processes with the absorption of integer multiples of the photon energy. In experiments that involve a multiphoton resonance, the intermediate is often a Rydberg state, and the final state is often an ion. The initial state of the system, photon energy, angular momentum and other selection rules can help in determining the nature of the intermediate state. This approach is exploited in resonance enhanced multiphoton ionization spectroscopy (REMPI). An advantage of this spectroscopic technique is that the ions can be detected with almost complete efficiency and even resolved for their mass. It is also possible to gain additional information by performing experiments to look at the energy of the liberated photoelectron in these experiments. (Compton and Johnson pioneered the development of REMPI)
Near-threshold Rydberg levels.
The same approach that produces an ionization event can be used to access the dense manifold of near-threshold Rydberg states with laser experiments. These experiments often involve a laser operating at one wavelength to access the intermediate Rydberg state and a second wavelength laser to access the near-threshold Rydberg state region. Because of the photoabsorption selection rules, these Rydberg electrons are expected to be in highly elliptical angular momentum states. It is the Rydberg electrons excited to nearly circular angular momentum states that are expected to have the longest lifetimes. The conversion between a highly elliptical and a nearly circular near-threshold Rydberg state might happen in several ways, including encountering small stray electric fields.
Zero electron kinetic energy spectroscopy.
Zero electron kinetic energy (ZEKE) spectroscopy was developed with the idea of collecting only the resonance ionization photoelectrons that have extremely low kinetic energy. The technique involves waiting for a period of time after a resonance ionization experiment and then pulsing an electric field to collect the lowest energy photoelectrons in a detector. Typically, ZEKE experiments utilize two different tunable lasers. One laser photon energy is tuned to be resonant with the energy of an intermediate state. (This may be resonant with an excited state at a multiphoton transition.) Another photon energy is tuned to be close to the ionization threshold energy. The technique worked extremely well and demonstrated energy resolution that was significantly better than the laser bandwidth. It turns out that it was not the photoelectrons that were detected in ZEKE. The delay between the laser and the electric field pulse selected the longest lived and most circular Rydberg states closest to the energy of the ion core. The population distribution of surviving long-lived near threshold Rydberg states is close to the laser energy bandwidth. The electric field pulse stark shifts the near-threshold Rydberg states and vibrational autoionization occurs. ZEKE has provided a significant advance in the study of the vibrational spectroscopy of molecular ions. Schlag, Peatman and Müller-Dethlefs originated ZEKE spectroscopy.
Mass analyzed threshold ionization.
Mass analyzed threshold ionization (MATI) was developed with idea of collecting the mass of the ions in a ZEKE experiment.
MATI offered a mass resolution advantage to ZEKE. Because MATI also exploits vibrational autoionization of near-threshold Rydberg states, it also can offer a comparable resolution with the laser bandwidth. This information can be indispensable in understanding a variety of systems.
Photo-induced Rydberg ionization.
Photo-induced Rydberg ionization (PIRI) was developed following REMPI experiments on electronic autoionization of low-lying Rydberg states of carbon dioxide. In REMPI photoelectron experiments, it was determined that a two-photon ionic core photoabsorption process (followed by prompt electronic autoionization) could dominate the direct single photon absorption in the ionization of some Rydberg states of carbon dioxide. These sorts of two excited electron systems had already been under study in the atomic physics, but there the experiments involved high order Rydberg states. PIRI works because electronic autoionization can dominate direct photoionization (photoionization). The circularized near-threshold Rydberg state is more likely to undergo a core photoabsorption than to absorb a photon and directly ionize the Rydberg state. PIRI extends the near-threshold spectroscopic techniques to allow access to the electronic states (including dissociative molecular states and other hard to study systems) as well as the vibrational states of molecular ions.


663 Gerlinde

663 Gerlinde is a minor planet orbiting the Sun.


Proton-enhanced nuclear induction spectroscopy

Proton-enhanced nuclear induction spectroscopy (PENIS), also called cross-polarisation (CP), is a nuclear magnetic resonance technique invented by Michael Gibby and Alexander Pines (who named it specifically for the inappropriate acronym) while they were graduate students in the lab of Professor John S. Waugh at the Massachusetts Institute of Technology. Due to the suggestive nature of its acronym, the latter name is used more often. This technique is an integral part of most solid-state NMR experiments involving spin-1/2 nuclei.
PENIS was one of the first of Pines' experiments transferring spin orientation from one atomic nucleus to another, which has been one of the running themes throughout his career as a leading pioneer in the applications of NMR to the study of non-liquid samples. The PENIS technique was patented in 1972.
Technique.
In this technique the natural polarization of an abundant spin (1H, the "proton" which begins the name of the technique) is exploited to increase the polarization of a rare spin (such as 13C) by irradiating the sample with radio waves at the frequency which corresponds to the difference between the rotation frequencies of the two different spins.
Besides its utility for boosting signals from dilute spins, transferring spin-polarization can also be used by surface-scientists to selectively enhance the spin-polarization of molecules on a sample's surface over the spins in the bulk by transferring spin-polarization from a gas to the surface.


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Daylight saving time

Daylight saving time (DST), also known as daylight savings time or daylight time (the United States and Canada), and summer time (United Kingdom, European Union, and some others), is the practice of advancing clocks (typically by one hour) during warmer months so that darkness falls at a later clock time. The typical implementation of DST is to set clocks forward by one hour in the spring ("spring forward") and set clocks back by one hour in autumn ("fall back") to return to standard time. As a result, there is one 23-hour day in late winter or early spring and one 25-hour day in the autumn.
The idea to manipulate clocks was first proposed in 1784 by Benjamin Franklin. In a letter to the editor of "The Journal of Paris," the American inventor and politician jokingly suggested it as a way to economize candle usage. However, George Hudson was serious when he proposed moving the clocks two hours every spring (daylight saving) in 1895. The New Zealand entomologist and astronomer’s proposal was driven by his desire to have extra time to devote to collecting and examining insects. Though the idea did receive some serious consideration in 1907 when British resident William Willett presented it as a way to save energy, it was never implemented. The German Empire and Austria-Hungary organized the first nationwide implementation starting on April 30, 1916. Many countries have used it at various times since then, particularly since the 1970s energy crisis. DST is generally not observed near the equator, where sunrise and sunset times do not vary enough to justify it. Some countries observe it only in some regions; for example, parts of Australia observe it, while other parts do not, and the United States observes it, except Arizona (excepting Navajo Tribal lands, who conform to the national practice), and Hawaii, which do not. Only a minority of the world's population uses DST; Asia and Africa generally do not observe it.
DST clock shifts sometimes complicate timekeeping and can disrupt travel, billing, record keeping, medical devices, and sleep patterns. Computer software generally adjusts clocks automatically.
Rationale.
Industrialized societies usually follow a clock-based schedule for daily activities that do not change throughout the course of the year. The time of day that individuals begin and end work or school, and the coordination of mass transit, for example, usually remain constant year-round. In contrast, an agrarian society's daily routines for work and personal conduct are more likely governed by the length of daylight hours and by solar time, which change seasonally because of the Earth's axial tilt. North and south of the tropics daylight lasts longer in summer and shorter in winter, with the effect becoming greater the further one moves away from the tropics.
By synchronously resetting all clocks in a region to one hour ahead of standard time, individuals who follow such a year-round schedule will wake an hour earlier than they would have otherwise; they will begin and complete daily work routines an hour earlier, and they will have available to them an extra hour of daylight after their workday activities. However, they will have one less hour of daylight at the start of each day, making the policy less practical during winter.
While the times of sunrise and sunset change at roughly equal rates as the seasons change, proponents of daylight saving time argue that most people prefer a greater increase in daylight hours after the typical "nine to five" workday. Supporters have also argued that DST decreases energy consumption by reducing the need for lighting and heating, but the actual effect on overall energy use is heavily disputed.
The shift in apparent time is also motivated by practicality. In American temperate latitudes, for example, the sun rises around 04:30 on the summer solstice and sets around 19:30. Since most people are sound asleep at 04:30, it makes more sense to pretend that 04:30 is actually 05:30, attendantly enabling people to be active in the evening light until what we decide to call 20:30 or later. Of course, these times apply only in the center of the time bands at multiples of fifteen degrees longitude. Farther east within a time zone, the sun rises and sets earlier than 12:00 (rechristened 13:00); farther west, later.
The manipulation of time at higher latitudes (for example Iceland, Nunavut, Scandinavia or Alaska) has little impact on daily life, because the length of day and night changes more extremely throughout the seasons (in comparison to other latitudes), and thus sunrise and sunset times are significantly out of phase with standard working hours regardless of manipulations of the clock. DST is also of little use for locations near the equator, because these regions see only a small variation in daylight in the course of the year. The effect also varies according to how far east or west the location is within its time zone, with locations farther east inside the time zone benefiting more from DST than locations farther west in the same time zone. Neither is daylight savings of much practicality in such places as China, whichdespite its width of thousands of milesis all located within a single time zone per government mandate.
History.
Ancient civilizations adjusted daily schedules to the sun more flexibly than DST does, often dividing daylight into 12 hours regardless of daytime, so that each daylight hour became progressively longer during spring and shorter during autumn. For example, the Romans kept time with water clocks that had different scales for different months of the year; at Rome's latitude, the third hour from sunrise ("hora tertia") started at 09:02 solar time and lasted 44 minutes at the winter solstice, but at the summer solstice it started at 06:58 and lasted 75 minutes. From the 14th century onwards, equal-length civil hours supplanted unequal ones, so civil time no longer varied by season. Unequal hours are still used in a few traditional settings, such as some monasteries of Mount Athos and all Jewish ceremonies.
Benjamin Franklin published the proverb "early to bed and early to rise makes a man healthy, wealthy, and wise", and published a letter in the "Journal de Paris" during his time as an American envoy to France (1776–1785) suggesting that Parisians economize on candles by rising earlier to use morning sunlight. This 1784 satire proposed taxing window shutters, rationing candles, and waking the public by ringing church bells and firing cannons at sunrise. Despite common misconception, Franklin did not actually propose DST; 18th-century Europe did not even keep precise schedules. However, this changed as rail transport and communication networks required a standardization of time unknown in Franklin's day.
In 1810, the Spanish National Assembly Cortes of Cádiz issued a regulation that moved certain meeting times forward by one hour from May 1 to September 30 in recognition of seasonal changes, but it did not actually change the clocks. It also acknowledged that private businesses were in the practice of changing their opening hours to suit daylight conditions, but they did so of their own volition.
New Zealand entomologist George Hudson first proposed modern DST. His shift-work job gave him leisure time to collect insects and led him to value after-hours daylight. In 1895, he presented a paper to the Wellington Philosophical Society proposing a two-hour daylight-saving shift, and considerable interest was expressed in Christchurch; he followed up with an 1898 paper. Many publications credit the DST proposal to prominent English builder and outdoorsman William Willett, who independently conceived DST in 1905 during a pre-breakfast ride when he observed how many Londoners slept through a large part of a summer day. Willett also was an avid golfer who disliked cutting short his round at dusk. His solution was to advance the clock during the summer months, and he published the proposal two years later. Liberal Party member of parliament Robert Pearce took up the proposal, introducing the first Daylight Saving Bill to the House of Commons on February 12, 1908. A select committee was set up to examine the issue, but Pearce's bill did not become law and several other bills failed in the following years. Willett lobbied for the proposal in the UK until his death in 1915.
Port Arthur, Ontario, Canada was the first city in the world to enact DST, on July 1, 1908. This was followed by Orillia, Ontario, introduced by William Sword Frost while mayor from 1911 to 1912. The first states to adopt DST () nationally were those of the German Empire and its World War I ally Austria-Hungary commencing April 30, 1916, as a way to conserve coal during wartime. Britain, most of its allies, and many European neutrals soon followed. Russia and a few other countries waited until the next year, and the United States adopted daylight saving in 1918. Most jurisdictions abandoned DST in the years after the war ended in 1918, with exceptions including Canada, the UK, France, Ireland, and the United States. It became common during World War II, and was widely adopted in America and Europe from the 1970s as a result of the 1970s energy crisis. Since then, the world has seen many enactments, adjustments, and repeals.
Procedure.
The relevant authorities usually schedule clock changes to occur at (or soon after) midnight, and on a weekend, in order to lessen disruption to weekday schedules. A one-hour change is customary, but twenty-minute and two-hour changes have been used in the past. In all countries that observe daylight saving time seasonally (i.e. during summer and not winter), the clock is advanced from standard time to daylight saving time in the spring, and they are turned back from daylight saving time to standard time in the autumn. The practice, therefore, reduces the number of civil hours in the day of the springtime change, and it increases the number of civil hours in the day of the autumnal change. For a midnight change in spring, a digital display of local time would appear to jump from 23:59:59.9 to 01:00:00.0. For the same clock in autumn, the local time would appear to repeat the hour preceding midnight, i.e. it would jump from 23:59:59.9 to 23:00:00.0.
In most countries that observe seasonal daylight saving time, the clock observed in winter is legally named "standard time" in accordance with the standardization of time zones to agree with the local mean time near the center of each region. An exception exists in Ireland, where its winter clock has the same offset () and legal name as that in Britain (Greenwich Mean Time)—but while its summer clock also has the same offset as Britain's (), its legal name is Irish Standard Time as opposed to British Summer Time.
While most countries that change clocks for daylight saving time observe standard time in winter and DST in summer, Morocco observes (since 2019) daylight saving time every month but Ramadan. During the holy month (the date of which is determined by the lunar calendar and thus moves annually with regard to the Gregorian calendar), the country's civil clocks observe Western European Time (UTC+00:00, which geographically overlaps most of the nation). At the close of this month, its clocks are turned forward to Western European Summer Time (UTC+01:00), where they remain until the return of the holy month the following year.
The time at which to change clocks differs across jurisdictions. Members of the European Union conduct a coordinated change, changing all zones at the same instant, at 01:00 Coordinated Universal Time (UTC), which means that it changes at 02:00 Central European Time (CET), equivalent to 03:00 Eastern European Time (EET). As a result, the time differences across European time zones remain constant. North America coordination of the clock change differs, in that each jurisdiction change at 02:00 local time, which temporarily creates unusual differences in offsets. For example, Mountain Time is, for one hour in the autumn, zero hours ahead of Pacific Time instead of the usual one hour ahead, and, for one hour in the spring, it is two hours ahead of Pacific Time instead of one. Also, during the autumn shift from daylight saving to standard time, the hour between 01:00 and 01:59:59 occurs twice in any given time zone, whereasduring the late winter or spring shift from standard to daylight saving timethe hour between 02:00 and 02:59:59 disappears.
The dates on which clocks change vary with location and year; consequently, the time differences between regions also vary throughout the year. For example, Central European Time is usually six hours ahead of North American Eastern Time, except for a few weeks in March and October/November, while the United Kingdom and mainland Chile could be five hours apart during the northern summer, three hours during the southern summer, and four hours for a few weeks per year. Since 1996, European Summer Time has been observed from the last Sunday in March to the last Sunday in October; previously the rules were not uniform across the European Union. Starting in 2007, most of the United States and Canada observed DST from the second Sunday in March to the first Sunday in November, almost two-thirds of the year. Moreover, the beginning and ending dates are roughly reversed between the northern and southern hemispheres because spring and autumn are displaced six months. For example, mainland Chile observes DST from the second Saturday in October to the second Saturday in March, with transitions at local time. In some countries time is governed by regional jurisdictions within the country such that some jurisdictions change and others do not; this is currently the case in Australia, Canada, Mexico, and the United States (formerly in Brazil, etc.).
From year to year, the dates on which to change clock may also move for political or social reasons. The Uniform Time Act of 1966 formalized the United States' period of daylight saving time observation as lasting six months (it was previously declared locally); this period was extended to seven months in 1986, and then to eight months in 2005. The 2005 extension was motivated in part by lobbyists from the candy industry, seeking to increase profits by including Halloween (October 31) within the daylight saving time period. In recent history, Australian state jurisdictions not only changed at different local times but sometimes on different dates. For example, in 2008 most states there that observed daylight saving time changed clocks forward on October 5, but Western Australia changed on October 26.
Politics, religion and sport.
The concept of daylight saving has caused controversy since its early proposals. Winston Churchill argued that it enlarges "the opportunities for the pursuit of health and happiness among the millions of people who live in this country" and pundits have dubbed it "Daylight Slaving Time". Retailing, sports, and tourism interests have historically favored daylight saving, while agricultural and evening-entertainment interests have opposed it; energy crises and war prompted its initial adoption.
The fate of Willett's 1907 proposal illustrates several political issues. It attracted many supporters, including Arthur Balfour, Churchill, David Lloyd George, Ramsay MacDonald, King Edward VII (who used half-hour DST or "Sandringham time" at Sandringham, the managing director of Harrods, and the manager of the National Bank. However, the opposition proved stronger, including Prime Minister H. H. Asquith, William Christie (the Astronomer Royal), George Darwin, Napier Shaw (director of the Meteorological Office), many agricultural organizations, and theatre-owners. After many hearings, a parliamentary committee vote narrowly rejected the proposal in 1909. Willett's allies introduced similar bills every year from 1911 through 1914, to no avail. People in the U.S. demonstrated even more skepticim; Andrew Peters introduced a DST bill to the House of Representatives in May 1909, but it soon died in committee.
Germany together with its allies led the way in introducing DST () during World War I on April 30, 1916, aiming to alleviate hardships due to wartime coal-shortages and from air-raid blackouts. The political equation changed in other countries; the United Kingdom used DST first on May 21, 1916. U.S. retailing and manufacturing interests - led by Pittsburgh industrialist Robert Garland - soon began lobbying for DST, but railroads opposed the idea. The U.S.'s 1917 entry into the war overcame objections, and DST started in 1918.
The war's end swung the pendulum back. Farmers continued to dislike DST, and many countries repealed it after the warlike Germany itself, which dropped DST from 1919 to 1939 and from 1950 to 1979. Britain proved an exception; it retained DST nationwide but adjusted transition dates over the years for several reasons, including special rules during the 1920s and 1930s to avoid clock shifts on Easter mornings. summer time began annually on the last Sunday in March under a European Community directive, which may be Easter Sunday (as in 2016). The U.S. dithered more; Congress repealed DST after 1919. President Woodrow Wilsonan avid golfer like Willettvetoed the repeal twice, but his second veto was overridden. Only a few U.S. cities retained DST locally, including New York (so that its financial exchanges could maintain an hour of arbitrage trading with London), and Chicago and Cleveland (to keep pace with New York). Wilson's successor as President, Warren G. Harding, opposed DST as a "deception", reasoning that people should instead get up and go to work earlier in the summer. He ordered District of Columbia federal employees to start work at 8 am rather than 9 am during the summer of 1922. Some businesses followed suit, though many others did not; the experiment was not repeated.
Since Germany's adoption of DST in 1916, the world has seen many enactments, adjustments, and repeals of DST, with similar politics involved. The history of time in the United States features DST during both world wars, but no standardization of peacetime DST until 1966. St. Paul and Minneapolis, Minnesota, kept different times for two weeks in May 1965: the capital city decided to switch to daylight saving time, while Minneapolis opted to follow the later date set by state law. In the mid-1980s, Clorox and 7-Eleven provided the primary funding for the Daylight Saving Time Coalition behind the 1987 extension to U.S. DST. Both senators from Idaho, Larry Craig and Mike Crapo, voted for it based on the premise that fast-food restaurants sell more French fries (made from Idaho potatoes) during DST.
A referendum on the introduction of daylight saving took place in Queensland, Australia, in 1992, after a three-year trial of daylight saving. It was defeated with a 54.5% "no" vote, with regional and rural areas strongly opposed, and those in the metropolitan southeast in favor.
In 2005 the Sporting Goods Manufacturers Association and the National Association of Convenience Stores successfully lobbied for the 2007 extension to U.S. DST.
In December 2008 the Daylight Saving for South East Queensland (DS4SEQ) political party was officially registered in Queensland, advocating the implementation of a dual-time-zone arrangement for daylight saving in South East Queensland, while the rest of the state maintained standard time. DS4SEQ contested the March 2009 Queensland state election with 32 candidates and received one percent of the statewide primary vote, equating to around 2.5% across the 32 electorates contested. After a three-year trial, more than 55% of Western Australians voted against DST in 2009, with rural areas strongly opposed. Queensland Independent member Peter Wellington introduced the Daylight Saving for South East Queensland Referendum Bill 2010 into the Queensland parliament on April 14, 2010, after being approached by the DS4SEQ political party, calling for a referendum at the next state election on the introduction of daylight saving into South East Queensland under a dual-time-zone arrangement. The Queensland parliament rejected Wellington's bill on June 15, 2011.
In the UK, the Royal Society for the Prevention of Accidents supports a proposal to observe SDST's additional hour year-round, but that is opposed by some industries, by some postal workers and farmers, and particularly by those living in the northern regions of the UK. In some Muslim countries, DST is temporarily abandoned during Ramadan (the month when no food should be eaten between sunrise and sunset), since the DST would delay the evening dinner. Iran maintains DST during Ramadan, but most Muslim countries do not use DST, partially for this reason.
Russia declared in 2011 that it would stay in DST all year long; Belarus followed with a similar declaration. (The Soviet Union had operated under permanent "summer time" from 1930 to at least 1982.) Russia's plan generated widespread complaints due to the dark of winter-time mornings, and thus was abandoned in 2014. The country changed its clocks to standard time on October 26, 2014, intending to stay there permanently.
Impacts.
 or is good for business.
A 2017 meta-analysis of 44 studies found that DST leads to electricity savings of 0.3% during the days when DST applies. Several studies have suggested that DST increases motor fuel consumption, but a 2008 United States Department of Energy report found no significant increase in motor gasoline consumption due to the 2007 United States extension of DST. An early goal of DST was to reduce evening usage of incandescent lighting, once a primary use of electricity. Although energy conservation remains an important goal, energy usage patterns have greatly changed since then. Electricity use is greatly affected by geography, climate, and economics, so the results of a study conducted in one place may not be relevant to another country or climate.
Later sunset times from DST are thought to affect behavior; for example, increasing participation in after-school sports programs or outdoor afternoon sports such as golf, and attendance at professional sporting events. Advocates of daylight saving time argue that having more hours of daylight between the end of a typical workday and evening induces people to consume other goods and services.
Many farmers oppose DST, particularly dairy farmers as the milking patterns of their cows do not change with the time. and others whose hours are set by the sun. Young children often have difficulty getting enough sleep at night when the evenings are bright. DST also hurts prime-time television broadcast ratings, drive-ins and other theaters.
It has been argued that clock shifts correlate with decreased economic efficiency, and that in 2000 the daylight-saving effect implied an estimated one-day loss of $31 billion on U.S. stock exchanges, Others have asserted that the observed results depend on methodology and disputed the findings, though the original authors have refuted points raised by disputers.
A correlation between clock shifts and traffic accidents has been observed in North America and the UK but not in Finland or Sweden. Four reports have found that this effect is smaller than the overall reduction in traffic fatalities. DST likely reduces some kinds of crime, such as robbery and sexual assault, as fewer potential victims are outdoors after dusk. Artificial outdoor lighting has a marginal and sometimes even contradictory influence on crime and fear of crime. A 2017 study in the "American Economic Journal: Applied Economics" estimated that "the transition into DST caused over 30 deaths at a social cost of $275 million annually", primarily by increasing sleep deprivation.
Opponents argue that DST disrupts human circadian rhythms (negatively impacting human health in the process), that it increases fatal traffic collisions, that the actual energy savings are inconclusive, and that DST increases health risks such as heart attack. Year-round standard time (not year-round DST) is proposed to be the preferred option for public health and safety. Clock shifts were found to increase the risk of heart attack by 10 percent, and to disrupt sleep and reduce its efficiency. Effects on seasonal adaptation of the circadian rhythm can be severe and last for weeks.
DST's clock shifts have the obvious disadvantage of complexity. People must remember to change their clocks; this can be time-consuming, particularly for mechanical clocks that cannot be moved backward safely. People who work across time zone boundaries need to keep track of multiple DST rules, as not all locations observe DST or observe it the same way. The length of the calendar day becomes variable; it is no longer always 24 hours. Disruption to meetings, travel, broadcasts, billing systems, and records management is common, and can be expensive. During an autumn transition from 02:00 to 01:00, a clock reads times from 01:00:00 through 01:59:59 twice, possibly leading to confusion.
Some clock-shift problems could be avoided by adjusting clocks continuously or at least more gradually—for example, Willett at first suggested weekly 20-minute transitions—but this would add complexity and has never been implemented. DST inherits and can magnify the disadvantages of standard time. For example, when reading a sundial, one must compensate for it along with time zone and natural discrepancies. Also, sun-exposure guidelines such as avoiding the sun within two hours of noon become less accurate when DST is in effect.
Terminology.
As explained by Richard Meade in the English Journal of the (American) National Council of Teachers of English, the form "daylight savings time" (with an "s") was already in 1978 much more common than the older form "daylight saving time" in American English ("the change has been virtually accomplished"). Nevertheless, even dictionaries such as Merriam-Webster's, American Heritage, and Oxford, which describe actual usage instead of prescribing outdated usage (and therefore also list the newer form), still list the older form first. This is because the older form is still very common in print and preferred by many editors. ("Although "daylight saving time" is considered correct, "daylight savings time" (with an "s") is commonly used.") The first two words are sometimes hyphenated ("daylight-saving(s) time"). Merriam-Webster's also lists the forms daylight saving (without "time"), daylight savings (without "time"), and daylight time. The Oxford Dictionary of American Usage and Style explains the development and current situation as follows: "Although the singular form "daylight saving time" is the original one, dating from the early 20th century—and is preferred by some usage critics—the plural form is now extremely common in AmE. [...] The rise of "daylight savings time" appears to have resulted from the avoidance of a miscue: when "saving" is used, readers might puzzle momentarily over whether "saving" is a gerund (the saving of daylight) or a participle (the time for saving). [...] Using "savings" as the adjective—as in "savings account" or "savings bond"—makes perfect sense. More than that, it ought to be accepted as the better form."
In Britain, Willett's 1907 proposal used the term "daylight saving", but by 1911 the term "summer time" replaced "daylight saving time" in draft legislation. The same or similar expressions are used in many other languages: "Sommerzeit" in German, "zomertijd" in Dutch, "kesäaika" in Finnish, "horario de verano" or "hora de verano" in Spanish, and "heure d'été" in French.
The name of local time typically changes when DST is observed. American English replaces "standard" with "daylight": for example, "Pacific Standard Time" ("PST") becomes "Pacific Daylight Time" ("PDT"). In the United Kingdom, the standard term for UK time when advanced by one hour is "British Summer Time" (BST), and British English typically inserts "summer" into other time zone names, e.g. "Central European Time" ("CET") becomes "Central European Summer Time" ("CEST").
The North American English mnemonic "spring forward, fall back" (also "spring ahead ...", "spring up ...", and "... fall behind") helps people remember in which direction to shift the clocks.
Computing.
Changes to DST rules cause problems in existing computer installations. For example, the 2007 change to DST rules in North America required that many computer systems be upgraded, with the greatest impact on e-mail and calendar programs. The upgrades required a significant effort by corporate information technologists.
Some applications standardize on UTC to avoid problems with clock shifts and time zone differences. Likewise, most modern operating systems internally handle and store all times as UTC and only convert to local time for display.
However, even if UTC is used internally, the systems still require external leap second updates and time zone information to correctly calculate local time as needed. Many systems in use today base their date/time calculations from data derived from the tz database also known as zoneinfo.
IANA time zone database.
The tz database maps a name to the named location's historical and predicted clock shifts. This database is used by many computer software systems, including most Unix-like operating systems, Java, and the Oracle RDBMS; HP's "tztab" database is similar but incompatible. When temporal authorities change DST rules, zoneinfo updates are installed as part of ordinary system maintenance. In Unix-like systems the TZ environment variable specifies the location name, as in codice_1. In many of those systems there is also a system-wide setting that is applied if the TZ environment variable is not set: this setting is controlled by the contents of the file, which is usually a symbolic link or hard link to one of the zoneinfo files. Internal time is stored in time-zone-independent Unix time; the TZ is used by each of potentially many simultaneous users and processes to independently localize time display.
Older or stripped-down systems may support only the TZ values required by POSIX, which specify at most one start and end rule explicitly in the value. For example, codice_2 specifies time for the eastern United States starting in 2007. Such a TZ value must be changed whenever DST rules change, and the new value applies to all years, mishandling some older timestamps.
Permanent daylight saving time.
A move to permanent daylight saving time (staying on summer hours all year with no time shifts) is sometimes advocated and is currently implemented in some jurisdictions such as Argentina, Belarus,Chile, Iceland, Kyrgyzstan, Morocco, Namibia, Saskatchewan, Singapore, Turkey, Turkmenistan, Uzbekistan and Yukon. Advocates cite the same advantages as normal DST without the problems associated with the twice yearly time shifts. However, many remain unconvinced of the benefits, citing the same problems and the relatively late sunrises, particularly in winter, that year-round DST entails.
Russia switched to permanent DST from 2011 to 2014, but the move proved unpopular because of the late sunrises in winter, so in 2014, Russia switched permanently back to standard time partially. The United Kingdom and Ireland also experimented with year-round summer time between 1968 and 1971, and put clocks forward by an extra hour during World War II.
In the United States, the Florida, Washington, California, and Oregon legislatures have all passed bills to enact permanent DST, but the bills require Congressional approval in order to take effect. Maine, Massachusetts, New Hampshire, and Rhode Island have also introduced proposals or commissions to that effect. Although 26 states have considered making DST permanent, unless Congress changes federal law, states cannot implement permanent DST—states can only opt out of DST, not standard time.
In September 2018, the European Commission proposed to end seasonal clock changes as of 2019. Member states would have the option of observing either daylight saving time all year round or standard time all year round. In March 2019, the European Parliament approved the commission's proposal, while deferring implementation from 2019 until 2021. , the decision has not been confirmed by the Council of the European Union. The council has asked the commission to produce a detailed impact assessment, but the Commission considers that the onus is on the Member States to find a common position in Council. As a result, progress on the issue is effectively blocked.
Experts in circadian rhythms and sleep caution against permanent daylight saving time, recommending year-round standard time as the preferred option for public health and safety.
Perceived problems with permanent DST.
Since daylight saving time creates the illusion of the sun rising and setting one hour later on the clock, but does not add any additional daylight, the already later sunrise times under standard time are pushed an hour later on the clock with daylight saving time. Late sunrise times can become unpopular in the winter months which essentially forces workers and schoolchildren to begin the day in darkness. In 1974 following the enactment of the Emergency Daylight Saving Time Act in the United States, there were complaints of children going to school in the dark and working people commuting and starting their work day in pitch darkness during the winter months. The complaints led to the repeal of the act in October 1974 when standard time was restored until February 23, 1975. In 1976, the United States returned to the schedule set under the Uniform Time Act of 1966. In 1971, year-round daylight time in the United Kingdom was abandoned after a 3-year experiment because of complaints about winter sunrise times. The same complaints also led to Russia abandoning DST and instituting standard time year round in 2014.


Linnik interferometer

A Linnik interferometer is a two-beam interferometer used in microscopy and surface contour measurements or topography. The basic configuration is the same as a Michelson interferometer. What distinguishes the Linnik configuration is the use of measurement optics in the reference arm, which essentially duplicate the objective measurement optics in the measurement arm. The advantage of this design its ability to compensate for chromatic dispersion and other optical aberrations.
In the image of a Linnik interferometer at right, 110 is the light source, 164 the detector. The beamsplitter 120 produces the two arms of the interferometer. The measurement arm 140 contains an objective lens 141 for imaging the surface to be studied 152. The reference arm 130 contains complementary optics to compensate for aberrations produced in the measurement arm.


3563 Canterbury

3563 Canterbury, provisional designation , is a dark Dorian asteroid from the middle regions of the asteroid belt, approximately 16 kilometers in diameter. It was discovered on 23 March 1985, by astronomer couple Alan Gilmore and Pamela Kilmartin at Mount John University Observatory near Lake Tekapo, New Zealand. The asteroid was named after New Zealand's Canterbury Province.
Classification and orbit.
Dora family.
"Canterbury" is a member of the Dora family, a large asteroid family of more than 1,200 carbonaceous asteroids, named after 668 Dora. It is also known as the "Zhongolovich family", named after its presumably largest member 1734 Zhongolovich. The Dora family may also contain a subfamily.
Orbit and observation arc.
"Canterbury" orbits the Sun in the central main-belt at a distance of 2.3–3.3 AU once every 4 years and 8 months (1,703 days). Its orbit has an eccentricity of 0.18 and an inclination of 7° with respect to the ecliptic. The asteroid was first identified as at Palomar Observatory, extending the body's observation arc by 7 years prior to its official discovery observation.
Physical characteristics.
"Canterbury" has been characterized as a dark C-type asteroid by Pan-STARRS photometric survey. It is also classified as a hydrated Ch-subtype in the SMASS taxonomy.
Rotation period.
In October 2010, a rotational lightcurve of "Canterbury" was obtained from photometric observations by astronomers at the Palomar Transient Factory in California. Lightcurve analysis gave a rotation period of 15.553 hours with a brightness variation of 0.61 magnitude ().
Diameter and albedo.
According to the survey carried out by the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer, "Canterbury" measures between 15.26 and 21.08 kilometers in diameter and its surface has an albedo between 0.040 and 0.060. The "Collaborative Asteroid Lightcurve Link" assumes a standard albedo for carbonaceous asteroids of 0.057 and calculates a diameter of 13.72 kilometers based on an absolute magnitude of 13.04.
Naming.
This minor planet was named after New Zealand's Canterbury Province, on the eastern side of the South Island. It is also named for the University of Canterbury in Christchurch, New Zealand. The approved naming citation was published by the Minor Planet Center on 28 May 1991 ().


Rietveld (software)

Rietveld is a web-based collaborative code review tool for Subversion written by Guido van Rossum to run on Google's cloud service. Van Rossum based Rietveld on the experience he had writing Mondrian. Mondrian was a proprietary application used internally by Google to review their code.
"Gerrit" is a fork of Rietveld started because ACL patches would not get integrated into Rietveld.
Rietveld was named by its author Guido van Rossum after Gerrit Rietveld, who was "one of [Rossum's] favorite Dutch architects and the designer of the Zig-Zag chair."


Patrick Experton

Patrick Experton was a test pilot who worked for the French aerospace company Dassault Aviation from 1978 until his retirement in 2002.
Biography.
A graduate of the French Air Force Academy Class of 1962, Patrick Experton was first assigned to the EC Roussillon flying Mirage IIIE aircraft then to the EC Alsace in Dijon, also flying Mirage III. He then was transferred to the CEV (Centre D'essais en Vol) in Istres, and then to the USAF Test Pilot School out of Edwards AFB, California in the mid-1970s, becoming the first French pilot to fly the F-15A Eagle. At the time, the Giscard d'Estaing administration was considering an order for two wings of F-15s; the order however never materialized and instead lead to the development of the Mirage 4000. He then returned to France to Istres AB with the CEV where he conducted spin trials for the newly acquired Mirage F-1C. He then commanded the EC 3/30 Lorraine squadron from 1976 to 1978 operating out of Reims AB, also one of the first unit equipped with the aircraft.
Dassault Aviation hired him as a test pilot in 1978, and he assumed the lead role in the development of the Alpha Jet trainer aircraft, variants of the Mirage F-1 such as the CR reconnaissance version, as well as the Mirage 50 (first flight May 1979).
He was the lead test pilot for the Mirage IIING from 1982 to 1984 (first flight December 1982). The aircraft was an attempt by Dassault to maintain its market share with existing Mirage III customers. The project however never gained sufficient traction to clinch any significant domestic or foreign air force orders.
From the mid-1980s onwards, he became closely involved with the development of the newly acquired Mirage 2000 FBW aircraft. His most significant contribution to the program was his critical lead role in the design of the Mirage 2000-5 variant. The 2000-5 is a significantly improved version of the 2000C/RDI aircraft with superior engine performance, weapon and sensor systems.
In the mid-1990s, he switched to the business aircraft side of Dassault Aviation, leading several test programs such as the Dassault Falcon 900 and Falcon 900EX and working on the development of the Falcon Jets next generation avionics systems. Throughout his career, and into retirement, Patrick Experton has maintained strong ties with the US flight testing community and with the Society of Experimental Test Pilots (SETP) in particular.


Longest nails


Extreme Records

Extreme Records is an Australia-based record label.
The label was founded by Ulex Xane and initially specialised in underground experimental and industrial cassettes. Roger Richards became involved in 1987 and eventually became the label’s director after Xane's departure.


Digital Weight Indicator

Digital Weight Indicator also commonly called Weight Indicator is a system of indication or recording of the selector type or one that advances intermittently in which all values are presented digitally, or in numbers. In a digital indicating or recording element, or in digital representation, there are no graduations. The National Conference on Weights and Measures (NWCM) lists these device types as “Indicating Elements” in its certificate databases.
The National Conference on Weights and Measures have categorized Digital Weight Indicator as a Verified Conformity Assessment Program (VCAP). A program has been proposed by the National Conference on Weights and Measures to ensure compliance of certain device types with environmental requirements.
Over the years, it gets more intelligent and complicated than conventional weighing scales. It can interact with different devices such as a load cell, printer, and computer via cables.
Interactions.
With load cell.
Load cell will produce a small electric current when weight is applied. The electric current is sent to Digital Weight Indicator via a normal cable. The Digital Weight Indicator will amplify the electric current and translate it to digital weight. Example: 15.7 kg
With printer.
When attached to a printer via a printer cable, it can print the weight on paper. Usually Weight Indicator come with a basic printing feature. It can be program in the firmware to print in few basic format. Usually there is a print button on the Digital Weight Indicator for user to press to print.
With computer.
A computer can be connected to it via a serial cable to RS-232 port on the computer. Information like weight, unit weight, status (stable, unstable, error) is send to the computer in a particular format. The format is not standard and differs with each brand. A computer interpret the information received and display them on screen and print it on printer. With user interaction, user can enters other information in relation to the weight received and save them to a database. By storing information in a database, many other process can be automated by software application like invoicing, quality control, batch control, warehousing, distribution, and more.


Phi2 Ceti

 Phi2 Ceti (φ2 Ceti), is a star located in the equatorial constellation of Cetus. φ2 Ceti is also known as 19 Cet, and HD 4813. Based upon parallax measurements, it is located about 51 light years away. It has an apparent visual magnitude of +5.19, making it bright enough to be seen with the naked eye.
This is an F-type main sequence star with a stellar classification of F7V and an effective temperature of 6,352 Kelvin. It has a mass of 1.1 solar masses. It is a suspected irregular variable.


Replay Solutions

Replay Solutions is a private, venture-backed independent software vendor founded in 2004 and based in Redwood City, California, United States.
The company's main product, ReplayDIRECTOR, has been described by the "New York Times" as a “TiVo for Software”. It records application execution, and replays code execution without requiring the original environment and stimuli present during recording. Software problems such as crashes or security issues can be reproduced during replay. It is based on the concept of recording any input coming into an application, and then feeding the same inputs back to the application during replay.
Technology created by Replay Solutions has been the subject of multiple patents issued by the USPTO.
The product supports multiple platforms including iOS, Android, Xbox gaming platform and several versions of the Microsoft Windows operating system, as well as applications written in Java and JavaScript.
Replay Solutions was acquired by CA Technologies in June 2012.
Investors.
The company's investors are UV Partners, Sigma Partners, Hummer Winblad and Partech International. It has raised $17 million in two rounds of funding from these venture investors.
Awards.
In 2009, the company was one of six singled out by the audience as "most likely to succeed" at Launch:Silicon Valley.


Flat slab subduction

Flat slab subduction is characterized by a low subduction angle (<30 degrees to horizontal) beyond the seismogenic layer and a resumption of normal subduction far from the trench. A slab refers to the subducting lower plate. Although, some would characterize flat slab subduction as any shallowly dipping lower plate as in western Mexico. Flat slab subduction is associated with the pinching out of the asthenosphere, an inland migration of arc magmatism (magmatic sweep), and an eventual cessation of arc magmatism. The coupling of the flat slab to the upper plate is thought to change the style of deformation occurring on the upper plate's surface and form basement-cored uplifts like the Rocky Mountains. The flat slab also may hydrate the lower continental lithosphere and be involved in the formation of economically important ore deposits. During the subduction, a flat slab itself may be deformed, or buckling, causing sedimentary hiatus in marine sediments on the slab. The failure of a flat slab is associated with ignimbritic volcanism and the reverse migration of arc volcanism. Multiple working hypotheses about the cause of flat slabs are subduction of thick, buoyant oceanic crust (15–20 km) and trench rollback accompanying a rapidly overriding upper plate and enhanced trench suction. The west coast of South America has two of the largest flat slab subduction zones. Flat slab subduction is occurring at 10% of subduction zones.
History of idea.
The idea has its beginnings in the late 1970s. Seismic studies of the Andean margin seemed to show a zone of subhorizontal lower plate at a depth of 100 km. The Cornell-Carnigie debate between Cornell University geophysicists and workers at the Carnegie Institute of Washington centered on whether local deployments of seismometers would yield better results than looking at global (teleseismic) data. The Carnegie Institution seemed to have won the day with the local deployment imaging the flat slab where teleseismic data argued for a shallowing dipping slab with no near horizontal zone. The idea was taken up to explain the Laramide orogeny, as the flat slab subduction zones on the Andean margin are associated with more inboard surface deformation and magmatic gaps. Flat slab subduction is an active area of research; the causal mechanisms for its occurrence have not been sorted out.
Causal mechanisms and consequences of flat slab subduction.
Causal mechanisms.
There are several working hypotheses for the initiation of flat slab subduction. The buoyant ridge hypothesis seems to be favored at the moment.
Subduction of buoyant oceanic crust.
The subduction of bathymetric highs such as aseismic ridges, oceanic plateaus, and seamounts has been posited as the primary driver of flat slab subduction. The Andean flat slab subduction zones, the Peruvian slab and the Pampean (Chilean) flat slab, are spatially correlated with the subduction of bathymetric highs, the Nazca Ridge and the Juan Fernandéz Ridge, respectively. The thick, buoyant oceanic crust lowers the density of the slab, and the slab fails to sink into the mantle after coming to a shallow depth (~100 km) due to the lessened density contrast. This is supported by the fact that all slabs under ~50 Ma. However, there are cases where aseismic ridges on the same scale as the Nazca Ridge are subducting normally, and cases where flat slabs are not associated with bathymetric highs. There are few flat slabs in the Western Pacific in areas associated with the subduction of bathymetric highs. Geodynamic modeling has called into question whether buoyant oceanic crust alone can generate flat slab subduction.
Trenchward motion of overriding plate with cratonic keel.
Another explanation for slab flattening is the lateral movement of the overriding plate in a direction opposite to that of the downgoing slab. The overriding plate is often equipped with a cratonic keel of thick continental lithosphere which, if close enough to the trench, can impinge upon the flow in the mantle wedge. Trench suction is included in this causal mechanism. Trench suction is induced by the flow of the asthenosphere in the mantle wedge area; trench suction increases with subduction velocity, a decrease of the mantle wedge thickness, or an increase in the mantle wedge viscosity. Trench retreat is motion of the trench in a direction opposite to that of plate convergence thought to be related to the position of the trench along the larger subduction zone with retreat occurring near the edges of subduction zones. Modeling experiments have shown that if the cratonic lithosphere is thick and the trench retreats, the shutdown of the mantle wedge increases trench suction to an extent that the slab flattens.
Consequences.
Delay in the eclogitization.
Eclogite is a dense (3.5 g/cu. cm), garnet-bearing rock that is formed as the oceanic crust subducts to zones of high pressure and temperature. The reaction that forms eclogite dehydrates the slab, and hydrates the mantle wedge above. The now denser slab more effectively sinks. A delay in eclogitization could arise through the subduction of zone thicker oceanic lithosphere without deeply penetrating faults. Oceanic crust is normally faulted at the trench rise by the bending of the plate as it subducts. This may be an effect or a cause of flat slab subduction, but it seems as though it is more likely an effect. A resumption of normally dipping subduction beyond the flat slab portion is associated with the eclogite reaction, and the amount of time needed to accumulate enough eclogite for the slab to start sinking may be what limits temporal scale of flat slab subduction.
Magmatic gaps and adakitic volcanism.
As the subducting plate flattens there is an inboard migration in the magmatic arc that can be tracked. In the Chilean flat slab region (~31–32 degrees S), around 7–5 Ma there was an eastward migration, broadening and gradual shutdown down of the volcanic arc associated with slab flattening. This occurs as the previous magmatic arc position on the upper plate (100–150 km above subducting plate) is no longer aligned with the zone of partial melting above the flattening slab. The magmatic arc migrates to a new location that coincides with the zone of partial melting above the flattening slab. Magmatism before the Laramide orogeny migrated all the way to western South Dakota. Eventually, the magmatic activity above the flat slab may completely cease as the subducting plate and upper plate pinch out the mantle wedge. Upon the failure of the flat slab, the mantle wedge can again start circulating hot asthenosphere (1300 degrees C) in an area that has been heavily hydrated, but that had not produced any melt; this leads to widespread ignimbritic volcanism, which is seen in both the Andean flat slab effected regions and the western United States.
Adakites are dacitic and andesitic magmas that are highly depleted in heavy rare-earth elements and high strontium/yttrium ratios and may be derived of melting of the oceanic crust. Adakites are thought to erupt or be emplaced during the transition from normally dipping subduction to flat subduction as the magmatic arc widens and migrates more inland. Adakitic rocks can be seen in modern Ecuador, a possible incipient flat slab zone, and in central Chile there are 10-5 Ma adakitic rocks. Thus, adakitic rocks could be used as marker of past episodes of flat slab subduction.
Surface deformation.
Flat slabs are thought to result in zones of broad, diffuse deformation in the upper plate located far landward from the trench. Flat slab subduction is associated with basement-cored uplifts also known as "thick-skinned" deformation of the overriding plate like the Sierra Pampeanas in South America possibly associated with the subduction of the Juan Fernandéz Ridge. These areas of basement-cored uplifts are visually correlated with flat slab subduction zones. In contrast, "thin-skinned" deformation is the normal mode of upper plate deformation, and does not involve basement rock. Crustal shortening is observed to extend farther inland than in normally dipping subduction zones; the Sierra Pampeanas are over 650 km east of the trench axis. Flat slabs have been used as an explanation for the Laramide Orogeny and the central Altiplano-Puna region. Another interesting feature that may be associated with the flat slab subduction of the Nazca Ridge is the Fitzcarrald arch located in the Amazonian Basin. The Fitzcarrald arch is a long-wavelength, linear topographic feature extending from eastern Peru to western Brazil beyond the Subandean thrust front into an undeformed area and rising ~600 masl. The Fitzcarrald arch has the effect of splitting the Amazonian Basin into three subbasins: northern Amazonian foreland basin, southern Amazonian foreland basin, and the eastern Amazonian foreland basin.
Seismicity.
The shape of the flat slab is constrained through earthquakes within the subducting slab and the interface between the upper plate and the subducting slab. Flat slab zones along the Andean margin release 3–5 times more energy through upper plate earthquakes than adjacent, more steeply dipping subduction zones. Upper plate earthquake focal mechanisms indicate that stress is aligned parallel with motion of the plate, and that stress is transmitted high into the upper plate from the lower. The reason for this enhanced seismicity is more effective coupling of the upper and lower plates. In normal subduction zones the coupling interface, the area in which the two plates are in close proximity, between the two plates is ~100–200 km long, but in flat slab subduction zones the coupling interface is much longer, 400–500 km. Although the lower lithosphere of the upper deforms plastically, numerical modeling has shown stress can be transmitted to crustal regions which behave in a brittle fashion. Along the subducting plate seismicity is more variable, especially intermediate-depth earthquakes. The variability may be controlled by the thickness of the crust and how efficiently it can release water. Thick crust that is not as deeply fractured by trench rise normal faulting may not dehydrate rapidly enough to induce intermediate-depth earthquakes. The Peruvian flat slab lacks significant intermediate-depth earthquakes and is associated with the subduction of the ~17 km thick Nazca Ridge.
Andean flat slabs.
In the late 1970s early research recognized the unique nature of the two large flat slab subduction zones along the Andean margin of South America. Two large and one smaller current flat slab subduction segments exist along the Andean margin: the Peruvian, Pampean, and the Bucaramanga. Three Cenozoic flat slab segment are also known: Altiplano, Puna, and Payenia.
The Peruvian flat slab is located between the Gulf of Guayaquil (5 degrees S) and Arequipa (14 degrees S), extending ~1500 km along the strike of the subduction zone. The Peruvian flat slab is the largest in the world, and extends ~700 km inboard from the trench axis. The subducting plate starts at a dip of 30 degrees then flattens out at a depth of 100 km under the Eastern Cordillera and Subandean zone. The segment is visually correlated with the subduction of the Nazca Ridge, an aseismic ridge with thickened crust. The second highest zone in the Andes, Cordillera Blanca, is associated with the Peruvian flat slab segment and uplift of basement-cored blocks. Volcanism in the area ceased in the Late Miocene (11-5 Ma). Plate reconstructions time the collision of the Nazca Ridge with the subduction zone at 11.2 Ma at 11 degree S, which implies that the northern extent of the Peruvian flat slab may require some other subducted feature like an oceanic plateau. A putative subducted plateau, the Inca Plateau, has been argued for.
The Pampean or Chilean flat slab segment is located between 27 degrees S and 33 degrees S, extending ~550 km along the strike of the subduction zone. The Pampean flat slab similarly extends ~700 km inboard from the trench axis. The segment is visually correlated with the Juan Fernandez Ridge, and the highest peak in the Andes, the non-volcanic Aconcagua (6961 m). This area has undergone the same "thick-skinned" deformation, leading to the high mountain peaks.
The Bucaramanga segment was recognized in early eighties from limited seismological evidence. The segment is encompassed between 6 and 9 degrees N in Colombia, extending ~350 km along the strike of the subduction zone.
Other flat slabs.
There are several other flat slab segments that warrant a mention:
Economic geology.
Subduction of thick oceanic crust could be linked with the metallogenesis of copper and gold deposits. The 10 largest young (<18 Ma) gold deposits in South America are associated with flat slab segments. Enhanced metallogenesis may be caused by the cessation of magmatism in the arc allowing the conservation of sulfur-rich volatiles. The failure of the putative flat slab under western North America may have been vital in producing Carlin-type gold deposits.
Early Earth subduction.
Early Earth's mantle was hotter and it has been proposed that flat slab subduction was the dominant style. Computer modeling has shown that an increase in oceanic plate buoyancy associated with enhanced oceanic crust production would have been counteracted by decreased mantle viscosity, so flat slab subduction would not have been dominant or non-existent.


National Eligibility Test

The National Eligibility Test (NET), also known as UGC NET or NTA-UGC-NET, is the examination for determining the eligibility for the post of assistant professor and/or Junior Research Fellowship award in Indian universities and colleges. The examination is conducted by National Testing Agency on behalf of University Grants Commission. Till July 2018, the Central Board of Secondary Education (CBSE) conducted the UGC NET exam, which the NTA has been conducting since December 2018. Currently, the exam is being conducted twice a year in the months of June and December in online mode.
Jobs for NET qualified candidates.
University Grants Commission (UGC) announced in 2013 that the candidates who clear the NET successfully would be eligible for lucrative also for private college lectureship jobs in public sector undertakings (PSUs). PSUs can use UGC-NET scores for the recruitment process of the posts of executives in their organizations in disciplines like science (R&D), management, corporate communications, human resources, and finance. This step taken by the UGC would also increase the number of students taking the UGC-NET examination which has witnessed a gradual decline in recent years.
UGC Net Qualifying Criteria And Cut Off Percentages.
UGC NET Procedure and Criteria for the declaration of result steps:
Reservations quota in Junior Research Fellowships.
Candidates clearing JRF exams are also eligible for the National Eligibility Test. UGC follows the Government of India's reservation policy, as per which a minimum of 27%, 10%, 15%, 7.5% and 3% of fellowships are reserved for the OBC (non-creamy layer), EWS, SC, ST and persons with disabilities (PWD).
UGC NET Age Limit and Relaxation.
JRF: Candidate should not be more than 30 years as on 01.06.2020. There are a few relaxations as well.
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