Spectral line

A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to identify atoms and molecules. These "fingerprints" can be compared to the previously collected "fingerprints" of atoms and molecules, and are thus used to identify the atomic and molecular components of stars and planets, which would otherwise be impossible.
Types of line spectra.
Spectral lines are the result of interaction between a quantum system (usually atoms, but sometimes molecules or atomic nuclei) and a single photon. When a photon has about the right amount of energy (which is connected to its frequency) to allow a change in the energy state of the system (in the case of an atom this is usually an electron changing orbitals), the photon is absorbed. Then it will be spontaneously re-emitted, either in the same frequency as the original or in a cascade, where the sum of the energies of the photons emitted will be equal to the energy of the one absorbed (assuming the system returns to its original state).
A spectral line may be observed either as an emission line or an absorption line. Which type of line is observed depends on the type of material and its temperature relative to another emission source. An absorption line is produced when photons from a hot, broad spectrum source pass through a cold material. The intensity of light, over a narrow frequency range, is reduced due to absorption by the material and re-emission in random directions. By contrast, a bright emission line is produced when photons from a hot material are detected in the presence of a broad spectrum from a cold source. The intensity of light, over a narrow frequency range, is increased due to emission by the material.
Spectral lines are highly atom-specific, and can be used to identify the chemical composition of any medium capable of letting light pass through it. Several elements were discovered by spectroscopic means, including helium, thallium, and caesium. Spectral lines also depend on the physical conditions of the gas, so they are widely used to determine the chemical composition of stars and other celestial bodies that cannot be analyzed by other means, as well as their physical conditions.
Mechanisms other than atom-photon interaction can produce spectral lines. Depending on the exact physical interaction (with molecules, single particles, etc.), the frequency of the involved photons will vary widely, and lines can be observed across the electromagnetic spectrum, from radio waves to gamma rays.
Nomenclature.
Strong spectral lines in the visible part of the spectrum often have a unique Fraunhofer line designation, such as K for a line at 393.366 nm emerging from singly-ionized Ca+, though some of the Fraunhofer "lines" are blends of multiple lines from several different species. In other cases the lines are designated according to the level of ionization by adding a Roman numeral to the designation of the chemical element, so that Ca+ also has the designation Ca II or CaII. Neutral atoms are denoted with the Roman numeral I, singly ionized atoms with II, and so on, so that, for example, FeIX (IX, Roman nine) represents eight times ionized iron.
More detailed designations usually include the line wavelength and may include a multiplet number (for atomic lines) or band designation (for molecular lines). Many spectral lines of atomic hydrogen also have designations within their respective series, such as the Lyman series or Balmer series. Originally all spectral lines were classified into series: the "Principle series", "Sharp series", and "Diffuse series". These series exist across atoms of all elements, and the patterns for all atoms are well-predicted by the Rydberg-Ritz formula. For this reason, the NIST spectral line database contains a column for Ritz calculated lines. These series were later associated with suborbitals.
Line broadening and shift.
There are a number of effects which control spectral line shape. A spectral line extends over a range of frequencies, not a single frequency (i.e., it has a nonzero linewidth). In addition, its center may be shifted from its nominal central wavelength. There are several reasons for this broadening and shift. These reasons may be divided into two general categories – broadening due to local conditions and broadening due to extended conditions. Broadening due to local conditions is due to effects which hold in a small region around the emitting element, usually small enough to assure local thermodynamic equilibrium. Broadening due to extended conditions may result from changes to the spectral distribution of the radiation as it traverses its path to the observer. It also may result from the combining of radiation from a number of regions which are far from each other.
Broadening due to local effects.
Natural broadening.
The lifetime of excited states results in natural broadening, also known as lifetime broadening. The uncertainty principle relates the lifetime of an excited state (due to spontaneous radiative decay or the Auger process) with the uncertainty of its energy. A short lifetime will have a large energy uncertainty and a broad emission. This broadening effect results in an unshifted Lorentzian profile. The natural broadening can be experimentally altered only to the extent that decay rates can be artificially suppressed or enhanced.
Thermal Doppler broadening.
The atoms in a gas which are emitting radiation will have a distribution of velocities. Each photon emitted will be "red"- or "blue"-shifted by the Doppler effect depending on the velocity of the atom relative to the observer. The higher the temperature of the gas, the wider the distribution of velocities in the gas. Since the spectral line is a combination of all of the emitted radiation, the higher the temperature of the gas, the broader the spectral line emitted from that gas. This broadening effect is described by a Gaussian profile and there is no associated shift.
Pressure broadening.
The presence of nearby particles will affect the radiation emitted by an individual particle. There are two limiting cases by which this occurs:
Pressure broadening may also be classified by the nature of the perturbing force as follows:
Inhomogeneous broadening.
"Inhomogeneous broadening" is a general term for broadening because some emitting particles are in a different local environment from others, and therefore emit at a different frequency. This term is used especially for solids, where surfaces, grain boundaries, and stoichiometry variations can create a variety of local environments for a given atom to occupy. In liquids, the effects of inhomogeneous broadening is sometimes reduced by a process called "motional narrowing".
Broadening due to non-local effects.
Certain types of broadening are the result of conditions over a large region of space rather than simply upon conditions that are local to the emitting particle.
Opacity broadening.
Electromagnetic radiation emitted at a particular point in space can be reabsorbed as it travels through space. This absorption depends on wavelength. The line is broadened because the photons at the line center have a greater reabsorption probability than the photons at the line wings. Indeed, the reabsorption near the line center may be so great as to cause a self reversal in which the intensity at the center of the line is less than in the wings. This process is also sometimes called self-absorption.
Macroscopic Doppler broadening.
Radiation emitted by a moving source is subject to Doppler shift due to a finite line-of-sight velocity projection. If different parts of the emitting body have different velocities (along the line of sight), the resulting line will be broadened, with the line width proportional to the width of the velocity distribution. For example, radiation emitted from a distant rotating body, such as a star, will be broadened due to the line-of-sight variations in velocity on opposite sides of the star. The greater the rate of rotation, the broader the line. Another example is an imploding plasma shell in a Z-pinch.
Radiative broadening.
Radiative broadening of the spectral absorption profile occurs because the on-resonance absorption in the center of the profile is saturated at much lower intensities than the off-resonant wings. Therefore, as intensity rises, absorption in the wings rises faster than absorption in the center, leading to a broadening of the profile. Radiative broadening occurs even at very low light intensities.
Combined effects.
Each of these mechanisms can act in isolation or in combination with others. Assuming each effect is independent, the observed line profile is a convolution of the line profiles of each mechanism. For example, a combination of the thermal Doppler broadening and the impact pressure broadening yields a Voigt profile.
However, the different line broadening mechanisms are not always independent. For example, the collisional effects and the motional Doppler shifts can act in a coherent manner, resulting under some conditions even in a collisional "narrowing", known as the Dicke effect.
Spectral lines of chemical elements.
Visible light.
For each element, the following table shows the spectral lines which appear in the visible spectrum at about 400-700 nm.
Other wavelengths.
Without qualification, "spectral lines" generally implies that one is talking about lines with wavelengths which fall into the range of the visible spectrum. However, there are also many spectral lines which show up at wavelengths outside this range. At the much shorter wavelengths of x-rays, these are known as characteristic X-rays. Other frequencies have atomic spectral lines as well, such as the Lyman series, which falls in the ultraviolet range.


Trauma symptom inventory

The Trauma Symptom Inventory (TSI) is a Psychological evaluation/assessment instrument that taps symptoms of Posttraumatic stress disorder and other posttraumatic emotional problems. It was originally published in 1995 by its developer, John Briere. It is one of the most widely used measures of posttraumatic symptomatology.
The TSI is relatively unique in comparison to other measures of posttraumatic symptomatology, in that it is a multi-scale instrument, including 10 scales of various forms of clinical psychopathology related to psychological trauma. Also unique, it has three validity scales in order to assess the trauma victim's test-taking attitude, such as overreporting, underreporting and inconsistency. The TSI was not developed to detect the Malingering of posttraumatic stress disorder although clinicians have used it to do so. Research shows that the TSI serves as a general validity screen but should be used cautiously in detecting malingered PTSD.
Original psychometric data on the TSI demonstrated statistically adequate internal consistency (alphas ranging from .84 to .87). Validity with a civilian trauma-exposed sample has been demonstrated, with substantial relationships found between the TSI's clinical scale scores and other established measures of PTSD. Further corroboration of the TSI's psychometric properties, with trauma-exposed military veterans, was recently documented.
In 2011 a second edition of the TSI was published (TSI-2), Initial research demonstrated improved ability to detect simulated PTSD. Research in Sweden found the TSI-2 to be statistically sound and a good broad-spectrum assessment instrument.


Shure SM57

The Shure SM57 is a low-impedance cardioid dynamic microphone made by Shure Incorporated and commonly used in live sound reinforcement and studio recording. It is one of the best-selling microphones in the world. It is used extensively in amplified music and has been used for speeches by every U.S. president since its introduction in 1965. In 2004, honoring its four decades of "solid, dependable performance", it was inducted into the first-ever TEC Awards TECnology Hall of Fame.
Background.
The origin of SM57 may be traced to 1937, when Shure engineer Benjamin Bauer developed the first single-element directional microphone, the Unidyne, which had a cardioid pickup pattern. In 1959, another Shure engineer, Ernie Seeler, advanced the art of microphone design significantly with the Unidyne III. Seeler torture-tested the Unidyne III during three years of research and development and thereby, produced the SM series of rugged and reliable Shure microphone capsules. The "SM" stands for Studio Microphone; Seeler was an aficionado of classical music and expected the SM57 to be used for orchestras. Because he "despised" rock music, the TEC Foundation said that it was ironic that the microphone has become "a mainstay of rock music."
Characteristics.
The SM57 uses the same capsule as the popular SM58. Like the SM58, the SM57 is fitted with an XLR connector and features a balanced output, which helps to minimize electrical hum and noise pickup. According to Shure, the frequency response extends from 40 Hertz (Hz) to 15 kHz. The SM57 is manufactured in the United States, Mexico, and China.
The Shure A2WS is an accessory windscreen for the SM57 that attenuates wind noise and plosives ("pop" sounds), and protects the microphone capsule.
Use.
The SM57 is a popular choice of musicians due to its sturdy construction and ability to work well with instruments that produce high sound pressure levels, such as percussion instruments and electric guitars. The School of Audio Engineering (SAE) recommends the SM57 (along with other makes and models) for four roles in a drum kit: kick drum, snare drum, rack toms, and floor tom. The cardioid pickup pattern of the microphone reduces the pickup of unwanted background sound and the generation of acoustic feedback. SM57s have also been a staple when reinforcing the sound from guitar amplifiers.
In a more unconventional fashion, the SM57 has been favoured by some as a vocal mic, both live and in the studio. Notable singers known to have recorded vocals with an SM57 include Anthony Kiedis, Brandon Flowers, Madonna, David Bowie, John Lennon, Jack White, Bjork, Peter Gabriel, Paul Rodgers, Tom Waits, Wayne Coyne, Tom Petty Alice Cooper, Erykah Badu, Caleb Followill and Raphael Saadiq. An early model of the mic, the Unidyne 545 was used on "Pet Sounds" for Brian Wilson's vocal tracks.
Every U.S. president since Lyndon B. Johnson has delivered speeches through an SM57. It became the lectern microphone of the White House Communications Agency in 1965, the year of its introduction, and remains so.
Due to its popularity, the SM57 has been counterfeited frequently by manufacturers in China and Thailand. Shure Distribution UK reports that the SM57, SM58, Beta 57A, and Beta 58A are their microphones that are most commonly counterfeited. In 2006, Shure mounted a campaign against the trading of counterfeit microphones.


2098 Zyskin

2098 Zyskin, provisional designation , is a vestoid asteroid from the inner regions of the asteroid belt, approximately 10 kilometers in diameter. It was discovered by Russian–Ukrainian astronomer Lyudmila Zhuravleva at the Crimean Astrophysical Observatory in Nauchnyj on 18 August 1972. The asteroid was named for surgeon Lev Zyskin (1930–1994).
Orbit and classification.
"Zyskin" is a member of the Vesta family. Asteroids with these spectral and orbital characteristics are thought to have all originated from the "Rheasilvia crater", a large impact crater on the south-polar surface of 4 Vesta, which is the main-belt's second-most-massive asteroid after 1 Ceres. It orbits the Sun in the inner main-belt at a distance of 2.1–2.7 AU once every 3 years and 9 months (1,378 days). Its orbit has an eccentricity of 0.13 and an inclination of 6° with respect to the ecliptic.
First identified as at Johannesburg Observatory, the body's first used observation was taken at Goethe Link Observatory in 1957, when it was identified as , extending the asteroid's observation arc by 15 years prior to its official discovery observation.
Physical characteristics.
In October 2010, a rotational lightcurve of "Zyskin" was obtained from photometric observations made at the Palomar Transient Factory in California. Lightcurve analysis gave a rotation period of 3.920 hours with a brightness variation of 0.08 magnitude ().
Diameter and albedo.
According to the survey carried out by NASA's Wide-field Infrared Survey Explorer with its subsequent NEOWISE mission, "Zyskin" measures between 10.44 and 12.8 kilometers in diameter, and its surface has an albedo between 0.10 and 0.18. The "Collaborative Asteroid Lightcurve Link" assumes a standard albedo for S-type asteroids of 0.20 and calculates a diameter of 8.9 kilometers with an absolute magnitude of 12.61.
Naming.
This minor planet was named in honor of Lev Yur'evich Zyskin, professor at the Crimean Medical Institute, who was head of its Pulmonary Surgery Center. Lyudmila Zhuravleva also discovered 1858 Lobachevsk on the same day she discovered "2098 Zyskin". She is a prolific astronomer with more than 200 minor planets discovered between 1972 and 1992 and (still) ranks in 61st position on the Minor Planet Center's discoverer-list as of 2015. The official naming citation was published by the Minor Planet Center on 1 April 1980 ().


Amulet Records

Amulet Records is a record label based in New Jersey specialising in percussion, avant-garde, and experimental music. The label was established by the percussionist composer and visual artist Billy Martin in 1997, inspired by a percussion session with the Lounge Lizards drummers Grant Calvin Weston and Billy Martin who released their first duet record "Percussion Duets" in 1997.
Celebrating its tenth anniversary, the catalogue has grown to titles ranging from percussion repertoire produced by Martin; the "Mozown series", dedicated to preserving vintage Bob Moses recordings; hip-hop and remix projects; a "Sound Healing" series and other visionary music and art.


SPECvirt

SPECvirt_sc2010 is a computer benchmark that evaluates the performance of a server computer for virtualization. It is available from the Standard Performance Evaluation Corporation (SPEC). It was introduced in July, 2010.
The SPECvirt_sc2010 benchmark measures the maximum number of workloads that a platform can simultaneously run while maintaining specific quality of service metrics. Each workload, called a tile, consists of a specific set of virtual machines.
In addition to generating results that show performance, the benchmark can also be used to generate performance per watt results.
The SPECvirt_sc2010 was not supported by SPEC from February 26, 2014 and its successor is SPECvirt_sc2013.


Diploma Entrance Test Odisha

Diploma Entrance Test, Odisha is a complete state government controlled centralised entrance examination for getting admission to many government & private diploma engineering schools or polytechnics in Odisha. Students can get admission to Diploma Engineering, Diploma Non-Engineering like Hotel Management, Hospitality management & Film Making studies etc. after 10th, ITI & +2 Science.
Examination Procedure.
Candidates can appear in this examination after 10th, ITI or after +2 science. There is two types of admission done in this process. First one is freshers for getting admission to first semester or first year & another one is lateral entry, that is after ITI or +2 Science getting admission to second year or third semester. For freshers students the test is based on general Science & Mathematics, but for lateral students the test prospective is harder than the freshers students. Also the lateral students have only 20% over the whole seats and no reservation quota is available for them.


9 Metis

Metis (minor planet designation: 9 Metis) is one of the larger main-belt asteroids. It is composed of silicates and metallic nickel-iron, and may be the core remnant of a large asteroid that was destroyed by an ancient collision. Metis is estimated to contain just under half a percent of the total mass of the asteroid belt.
Metis passed within 0.034AU, or , of Vesta on 19 August 2004.
Discovery and naming.
Metis was discovered by Andrew Graham on 25 April 1848, at Markree Observatory in Ireland; it was his only asteroid discovery. It also has been the only asteroid to have been discovered as a result of observations from Ireland until 7 October 2008, when, 160 years later, Dave McDonald from observatory J65 discovered (281507) 2008 TM9. Its name comes from the mythological Metis, a Titaness and Oceanid, daughter of Tethys and Oceanus. The name "Thetis" was also considered and rejected (it would later devolve to 17 Thetis).
Characteristics.
Metis' direction of rotation is unknown at present, due to ambiguous data. Lightcurve analysis indicates that the Metidian pole points towards either ecliptic coordinates (β, λ) = (23°, 181°) or (9°, 359°) with a 10° uncertainty. The equivalent equatorial coordinates are (α, δ) = (12.7 h, 21°) or (23.7 h, 8°). This gives an axial tilt of 72° or 76°, respectively.
Hubble Space Telescope images and lightcurve analyses are in agreement that Metis has an irregular elongated shape with one pointed and one broad end. Radar observations suggest the presence of a significant flat area, in agreement with the shape model from lightcurves.
The Metidian surface composition has been estimated as 30–40% metal-bearing olivine and 60–70% Ni-Fe metal.
Light curve data on Metis led to an assumption that it could have a satellite. However, subsequent observations failed to confirm this. Later searches with the Hubble Space Telescope in 1993 found no satellites.
Family relationships.
Metis was once considered to be a member of an asteroid family known as the Metis family, but more recent searches for prominent families did not recognize any such group, nor is a clump evident in the vicinity of Metis by visual inspection of proper orbital element diagrams.
However, a spectroscopic analysis found strong spectral similarities between Metis and 113 Amalthea, and it is suggested that these asteroids may be remnants of a very old (at least ~1 Ga) dynamical family whose smaller members have been pulverised by collisions or perturbed away from the vicinity. The putative parent body is estimated to have been 300 to 600 km in diameter (Vesta-sized) and differentiated. Metis would be the relatively intact core remnant (though smaller than 16 Psyche), and Amalthea a fragment of the mantle, with 90% of the original body unaccounted for. Coincidentally, both Metis and Amalthea have namesakes among Jupiter's inner moons.
Occultations.
In 1984 an occultation of a star produced seven chords that Kristensen used to derive an ellipsoidal profile of 210×170 km. On 6 August 1989, Metis occulted a magnitude 8.7 star producing five chords suggesting a diameter of 173.5 km. Observations of an occultation on 11 February 2006, produced only two chords indicating a minimum diameter 156 km. All three of these occultations fit the ellipsoid 222×182×130 km suggested by Baer.
On 7 March 2014, Metis occulted the star HIP 78193 (magnitude 7.9) over parts of Europe and the Middle East.


Graph literacy

Graph literacy is the ability to understand information that presented graphically, which are including general knowledge about how to extract information and make inferences from different graphical formats. Although related, graph literacy is distinct from other forms of literacy (e.g., general health literacy or numeracy) in the sense that it relates more specifically to one's ability to obtain meaning from information presented graphically. It can include the storage of mental representations in long-term memory, knowledge about the properties of different types of formats, and procedures to interpret them. However, similar to other types of literacy, higher graph literacy is associated with higher education levels and suggests that developing the skills required to interpret graphical information requires knowledge that is acquired through formal education and experience.
Graph literacy is very important in everyday life: graphs appear throughout the published media, in newspapers and magazines, on TV and on the internet, and are used to provide information for many important decisions including medical, nutritional, financial and political choices. Yet many people can have difficulty understanding even the simplest graphs. Up to one third of the general population lacks the skills needed to understand basic numerical formats (e.g., percentages or ratios) and basic graphic displays (such as bar or pie charts, line graphs, or icon arrays). While graphical displays can improve understanding and comprehension of quantitative information, such as the risks and benefits of medical treatments, they may not be helpful for everyone. Visual displays may be of greater help to people with low numeracy whereas numbers may be better for people who have poor graph literacy. Determining what type of information displays lead to better comprehension of information, and for whom, is an ongoing topic of research, particularly within the area of risk communication.
Graph comprehension.
Graphical displays can contain a vast amount of information such as information contained within the title, labels and axes, but also within features of the display (e.g., size, spacing, patterns in the data) that can vary in their complexity (e.g., multiple variables). Both perceptual and cognitive processes are required to interpret the information contained within a graphic display. Different processes are required to extract information depending on the task or goal, such as extracting a specific value or making inferences based on the data (e.g., predicting future trends).
Graph comprehension depends not only on people's knowledge, familiarity or experience with reading graphic displays but also on the way in which the graphic is designed. For example, some features of graphs make use of spatial-to-conceptual mappings that are grounded in our everyday experience, such as the tendency for higher bars to relate to greater or larger quantities. However, other aspects need to be learned, such as arbitrary graph conventions (e.g., axis labels and scales). Graph literacy can affect how people attend to and encode some of these features.
Graph literacy scale.
The Graph Literacy Scale consists of 13 items and measures three abilities related to graph comprehension (see ) (1) the ability to read the data, that is, to find specific information in the graph; (2) the ability to read between the data, that is, to find relationships in the data as shown on the graph; and (3) the ability to read beyond the data, or make inferences and predictions from the data. The scale was validated in a survey conducted on probabilistic national samples in Germany and the USA.
Previous measures of graph comprehension have tended to focus on the comprehension of specific features or types of graphs (e.g., line or bar graphs), incorporate relatively complex items, or have been developed in the context of examining the effects of teaching methods on the acquisition of graph skills (e.g.,). Some numeracy scales include a few items related to the comprehension of graphical information but these are limited in their ability to measure a range of graphs, features, or tasks.


BB Phoenicis

BB Phoenicis is a variable star in the constellation of Phoenix. It has an average visual apparent magnitude of 6.17, being visible to the naked eye with excellent viewing conditions. From parallax measurements by the Gaia spacecraft, it is located at a distance of from Earth. Its absolute magnitude is calculated at 0.6.
BB Phoenicis is a Delta Scuti variable, and shows stellar pulsations that cause brightness variations with an amplitude of 0.04 magnitudes. Its variability was discovered by accident in 1981, when the star was used as a comparison star for the eclipsing binary AG Phoenicis. Photometric and spectroscopic data have allowed the detection of at least 13 modes of radial and non-radial pulsations, the strongest one having a period of 0.174 days and an amplitude of 11.1 milli-magnitudes. Observations in different epochs show evidence that the pulsations modes vary in amplitude, which is common among Delta Scuti variables. Pulsation models indicate that the stellar rotation axis is inclined by 50–70° in relation to the line of sight.
This star is classified as an F-type giant with a spectral type of F0/2III. It appears to be expanding after depleting all the nuclear hydrogen and leaving the main sequence. BB Phoenicis has an estimated mass of 2.25 times the solar mass and a radius of 4.7 times the solar radius. It is radiating 55 times the Sun's luminosity from its photosphere at an effective temperature of 7,200 K.


Portrait of Lotte

Portrait of Lotte is a time-lapse viral video involving a girl growing from a newborn in 1999 into a teenager. It was first posted by filmmaker Frans Hofmeester from Utrecht, Netherlands on 17 April 2012.
It has reached widespread and the video was used on a Sprint commercial.
Vince.
After 12 years of recording Lotte, Hoffmeester started recording videos of his son, Vince.
He described Lotte's video as being more "sweet" and Vince's as more "playful".
Background.
Hoffmeester recorded 15 second videos every week of his daughter, Lotte, from a newborn to a teenager and compiled them together to make a time-lapse video. He calls it "the ultimate coming of age time-lapse". He has done several videos of her being recorded to different ages, such as 12, 14, 16, 18 and 20 years old.
Hofmeester explains, "She was changing at such a rapid pace, that I felt the need to document the way she looked, to keep my memories intact".
Commenting on the occasions he found it difficult to get the footage required, he said, "Sometimes they did not feel like it. Then I said, 'Just one minute. Tell me about your ball game, did you win?' That way I stalled them so I could complete the shot".


List of longest bridges

This is a list of the world's longest bridges that are more than in length sorted by their full length above land and water. The main span is the longest span without any ground support
" Note: There is no standard way to measure the total length of a bridge. Some bridges are measured from the beginning of the entrance ramp to the end of the exit ramp. Some are measured from shoreline to shoreline. Yet others use the length of the total construction involved in building the bridge. Since there is no standard, no ranking of a bridge should be assumed because of its position in the list. Additionally, numbers are merely estimates and measures in U.S. customary units (feet) may be imprecise due to conversion rounding."


Table of the Elements

Table of the Elements is an American record label. It concentrates on re-released and specially recorded experimental music, including many avant-garde musicians of the 20th and 21st centuries, such as John Cale, Tony Conrad and La Monte Young, as well as lesser-known artists such as Loren Mazzacane Connors, Derek Bailey, Rhys Chatham, Fushitsusha/Keiji Haino, and Mats Gustafsson.
The label numbers its releases to correspond to symbols from the periodic table in increasing order of atomic weight, rather than using the traditional numerical system. The label hosted multiple-day experimental music festivals. It also releases recordings under two other imprints, Radium and Xeric.


Metrication in Canada

Metrication in Canada began in 1970 and ceased in 1985. While Canada has converted to the metric system for many purposes, there is still significant use of non-metric units and standards in many sectors of the Canadian economy and everyday life today. This is mainly due to historical ties with the United Kingdom, the traditional use of the imperial system of measurement in Canada, proximity to the United States, and strong public opposition to metrication during the transition period.
Before conversion.
Until the 1970s, Canada traditionally used the imperial measurement system, labelled as "Canadian units of measurement" under Schedule II of the "Weights and Measures Act" (R.S., 1985, c. W-6). These units have the same names and the same values as United States customary units, with the exception of capacity measures such as the gallon. For example, before metrication in Canada, gasoline was sold by the (imperial) gallon (about 4.55 litres). In cross-border transactions with the United States it was often unclear whether values quoted in gallons were referring to United States gallons (3.79 litres) or imperial gallons.
Conversion process.
The Liberal federal government of Pierre Trudeau first began implementing metrication in Canada in 1970 with a government agency dedicated to implementing the project, the Metric Commission, being established in 1971. By the mid-1970s, metric product labelling was introduced. In 1972, the provinces agreed to make all road signs metric by 1977. During the Labour Day weekend in 1977, every speed limit sign in the country was changed from mph to km/h. From the same time every new car sold had to have a speedometer that showed speed in km/h and distance in km. The distances on road signs were changed to kilometres during the next few months. Gasoline pumps changed from imperial gallons to litres in 1979.
There was some resistance to metrication, especially as the sectors of the economy where the federal Weights and Measures Act required metric to be used grew in number. The metrication of gasoline and diesel fuel sales in 1979 prompted 37 Progressive Conservative Members of Parliament to open a "freedom to measure" gas station in Carleton Place, Ontario, selling gas in both imperial gallons and litres. The city of Peterborough, Ontario, was a noted hotbed of opposition to metrication, having been one of the government's three test centres for the metrication process. Bill Domm, a Member of Parliament representing the riding of Peterborough, was one of the country's most outspoken opponents of metrication. During this period, a few government employees lost their jobs for their opposition to metrication. Neil Fraser, an official with Revenue Canada who publicly opposed mandatory metric conversion, was dismissed for "conduct unacceptable for a public servant".
Changeover.
Since 1976, the law requires that all prepackaged food products must declare their mass or their volume in metric units, though Canadian imperial units are still legally permitted on packaging. Milk has been thoroughly metric since 1980. In April 1975, Fahrenheit temperatures were replaced by Celsius. In September 1975, rainfall was first measured in millimetres and snow in centimetres. Since April 1976, wind speed, visibility, and barometric pressure have been in metric units, with the pressure in kilopascals instead of the hectopascals (millibars) used in most of the rest of the world. In September 1977, every speed-limit sign in the country was changed from miles per hour to kilometres per hour.
Metrication stalled.
The election of the Progressive Conservative government of Brian Mulroney in 1984 resulted in the abolition of the Metric Commission on March 31, 1985. This ended the process of affirmative metrication in Canada, and some regulations requiring metric measurements either have been repealed or are no longer enforced.
Training on metric conversion was not universal. Poor metrication training was a contributing factor to Air Canada Flight 143, the so-called Gimli Glider, running out of fuel mid-flight on July 23, 1983.
Notwithstanding the end of officially sanctioned metrication in Canada, most laws, regulations, and official forms exclusively use metric measurements. However, imperial measures still have legal definitions in Canada and can be used alongside metric units. Net quantity declarations on prepackaged products sold to consumers may be stated in metric units.
Common usage today.
Daily usage.
Canadians typically discuss the weather in degrees Celsius, purchase gasoline in litres, observe speed limits set in kilometres per hour (km/h), and read road signs and maps displaying distances in kilometres. Cars have metric speedometers and odometers, although most speedometers include smaller figures in miles per hour (mph). Fuel efficiency for new vehicles is published by Natural Resources Canada in litres per 100 kilometres, ("not" kilometres per litre as a direct equivalent of "miles per gallon") and miles per (imperial) gallon. Window stickers in dealer showrooms often include "miles per gallon" conversions. The railways of Canada such as the Canadian National and Canadian Pacific as well as commuter rail services, continue to measure their trackage in miles and speed limits in miles per hour (although urban railways including subways and light rail have adopted kilometres and kilometres per hour). Canadian railcars show weight figures in both imperial and metric. Canadian railways also maintain exclusive use of imperial measurements to describe train length and height in feet and train masses in short tons.
Canadians typically use a mix of metric and imperial measurements in their daily lives. The use of the metric and imperial systems varies according to generations. Newborns are measured in metric at hospitals, but the birth weight and length is also announced to family and friends in imperial units. Although Canadian driver's licences give height in centimetres, many Canadians also use imperial units to indicate height and weight. Most kitchen appliances in Canada are labelled with both degrees Celsius and Fahrenheit, and metric cooking measures are widely available; but Fahrenheit is often used for cooking, as are imperial cooking measurements, due to the import of kitchen appliances and recipes from the United States. Canadians also occasionally use imperial temperatures outside of the kitchen, such as when measuring the water temperature in a pool. Stationery and photographic prints are also sold in sizes based on inches and the most popular paper sizes, letter and legal, are sized in imperial units, though many agendas and notebooks are sold in ISO 216 sizes. Canadian football games continue to be played on fields measured in yards (with a gridiron layout with a length of 100.6 metres, or 110 yards, from one goal line to the other); golfers also expect courses to be measured in yards.
Experience.
The use of metric or imperial measurements varies by age and region. Canadians who have received only metric instruction in school (from the early 1970s) are more familiar with metric measurements. Quebec has implemented metrication more fully. The use of imperial units is more common in rural areas than in the rest of the country, where opposition to metrication was strongest, rather than in urban areas.
Canadians are exposed to both metric and imperial units, and it is not unusual for there to be references to both metres and feet, square metres and acres, or grams and ounces in the same conversation.
Temperature.
Despite the exclusive use of degrees Celsius in weather reports, some Canadians still use Fahrenheit. Most outdoor thermometers display temperatures in both Fahrenheit and Celsius. Additionally, outdoor signs usually display Celsius with occasional references to Fahrenheit. Inside newer buildings, digital and analog thermostats display temperature settings in degrees Celsius or Fahrenheit. Environment Canada still offers an imperial unit option beside metric units.
Products and retail.
Many food and retail products are sold according to metric units, though this is not always the case. The price of a piece of meat, for example a steak, is typically advertised per pound, but the price printed on the package is per kilogram; the latter is calculated. The prices of fruits and vegetables are usually advertised in pounds, although the price per kilogram is also displayed, usually in smaller type. More expensive items such as deli, meats, and fish are often advertised per 100 grams. Many, but not all, products are sold in imperial sizes, but labelled in metric units. An example of this is butter, which is sold in a 454 gram package (and labelled as such), even though it represents one pound (and in many cases is also labelled with the imperial unit). This is known as "soft metric" (as opposed to a "hard metric" system, where packages and measures are generally sold in "round numbers"; in a hard metric system, butter might come in a 500 g package). Mandatory nutrition facts labelling (the Nutrition Facts Table) uses metric units for several basic nutrients, although serving sizes can be described in any form of unit (can, cup, quantity, etc.).
In restaurants, wine is usually served by the litre, or bottle, but a wine glass is measured in ounces. A 750-millilitre bottle of hard liquor is referred to as a "twenty-sixer" or "two-six", referring to its volume in imperial fluid ounces, rounded down from 26.4. Similarly, fast food restaurants (e.g. McDonald's "Quarter Pounder") often advertise measurements of food and drink in US customary units, but converted to metric units, because either the containers are made to US standards, or the franchise is US-based and uses a standard size for its products. Thus in Canada a 20 US fluid ounce bottled soft drink is labelled as 591 mL (or occasionally rounded up to 600 mL). Beer in bottles continues to be 12 imperial fluid ounces (labelled as 341 mL), but beer in cans is filled to 12 US fluid ounces (labelled as 355 mL). There is also a larger sized beer bottle which is labelled as containing . Some of these package sizes have been introduced since Canadian metrication began; for example, the traditional Canadian soft drink can was 10 imperial fluid ounces (284 mL), later marketed as 280 mL. Only in the early 1990s did the US-derived 355 mL size displace it. Display sizes for screens on television sets and computer monitors almost always have their diagonals measured in inches. Bicycle frames and car wheel diameters are also usually described in inches; tire inflation is in pounds per square inch (psi). Standard and special fasteners like alloys, nuts, bolts, washers, studs, tapping, self drilling screw and socket screware are often quoted in both imperial and metric; products range from diameter up to .
Commercial usage.
Supermarkets will often advertise foods such as meats and produce "per pound", and small businesses are exempt from having metric scales and legally sell by the pound. While most supermarket scales display both metric and imperial units, products advertised by the pound in a supermarket flyer are invariably sold to the customer (at the point of sale) based on a price "per 100 grams" or "per kilogram".
Construction materials, including construction lumber and drywall, continue to be sold in imperial measurements; retrofitting metric-sized (designed for 400 mm centres) wallboard on old spaced studs is difficult. In English-speaking Canada commercial and residential spaces are mostly (but not exclusively) constructed using imperial units and advertised accordingly, while in French-speaking Quebec commercial and residential spaces are constructed in metres and advertised using both metric and imperial units as equivalents. However, the zoning by-laws and building codes that govern construction are in metric, although most building codes will also contain imperial equivalents. In addition, rural areas in Western Canada (Canadian Prairies) were mapped and segmented using the Dominion Land Survey. This based most rural roads on a mile measurement which when viewed from the air has the appearance of a checkerboard or grid. Because of this historical reason, it is still common to refer to distance in miles. In contrast, in much of southern Ontario the basic survey grid was based on a mile-and-a-quarter (1.25 mi), which corresponds almost exactly to a 2 kilometre grid and which makes miles no more natural than kilometres. 1.25 mi is equal to 100 chains (or 10 furlongs) and it was that sized grid that was used in the original surveys and thus would have been more familiar.
Free trade with the United States has resulted in continued exposure to the US system. Since the United States is Canada's largest trading partner and vice versa, Canadian exporters and importers must be accustomed to dealing in US customary units as well as metric.
Agriculture.
Canada uses an Avery or imperial bushel (36.369 litres) when selling oats, wheat, and other grains. When dealing with the US oat markets though, special attention must be paid to the definition of bushel weight because US uses a Winchester bushel (35.239 litres). In livestock auction markets, cattle are sold in dollars per hundredweight (short), whereas hogs are sold in dollars per hundred kilograms.
Health care.
In the health care system, metric units are often given precedence, although actual metric units may still be different than the United States (for example, for measurements of blood cholesterol, the units are millimole per litre, whereas they are milligram per decilitre in the United States). Most physicians chart patient height and weight in imperial units, and while most growth charts display both systems of measurement, the majority of hospitals officially document such parameters in metric. Dieticians still use kilocalories, and doctors use millimetres of mercury. While these units are metric derivatives, they are not metric units.
Engineering.
Because most fasteners, machine parts, pumps, piping, and all building materials are sold in imperial or US customary units, many mechanical and civil engineers in Canada mainly use imperial units for these items. Overall building dimensions for new construction are usually in SI units. . Many chemical, nuclear and electrical engineers and engineering physicists employ metric units. Unlike in the United States, Canadian engineers are not always educated in both systems but those who are not become keenly aware of the differences between the imperial, metric and US customary systems once they enter the workforce.
Trades.
Trades associated with machine work, such as machinists, automotive, and heavy duty technicians, frequently use both metric and imperial. Machines made in Canada often incorporate parts from other countries and thus the finished product may have both metric and imperial parts. Farm and industrial equipment manufactured in Canada will most often use inch system fasteners and structural steel, but fluid capacities are always listed in metric.
Building trades such as plumbing and carpentry often use imperial units. Rough timber, drywall, plywood, fasteners, pipes, and tubing are all sold in imperial units. Nails in hardware stores are measured in inches but sold in metric weight packages.
Electricians in every country use metric units such as volts and amperes, but motors and engines in Canadan are still often quoted in horsepower. Electric car motors are rated in kilowatts. However, Canada uses, among other things, the US American wire gauge standard instead of the square millimetre (mm2) used in the IEC 60228 standard of the International Electrotechnical Commission. Conduit sizes are in inch diameters, although some manufacturers include the metric size printed on the conduits (for example, , , ).
Firearms.
Imperial units remain in common use in firearms and ammunition on the international market. Cartridges may have either commercial or military descriptions. In the former, the manufacturer will choose a name for proprietary reasons, perhaps to associate the name with a brand or designer, or otherwise distinguish it from comparable cartridges. Typical terms include bullet or bore diameter, cartridge length or capacity, a proper name or company. Designs are registered with Sporting Arms and Ammunition Manufacturers' Institute (SAAMI) or Commission internationale permanente pour l'épreuve des armes à feu portatives (CIP) for standardization. Canadian industry follows both conventions, but there is little appetite in the Canadian firearms industry or hobby to pursue metrification simply for the sake of conformity when the trade is global.
Military designations use technical nomenclature to avoid confusion or misrouting of supplies. There are several examples of similar names and similar design dimensions. For example, the civilian cartridge .303 Savage was introduced by the Savage Arms Company in 1894, but is incompatible with the .303 British used throughout the Commonwealth. The .308 Winchester cartridge derived from the 7.62×51mm NATO cartridge in the 1950s, with slight variations in production but not in external dimensions. All four examples are common small arms cartridges in Canada.
Imperial measures are often encountered in the description of cartridges, even when the cartridge is of a relatively recent product introduction (e.g. .204 Ruger, .17 HMR, where the calibre is expressed in decimal fractions of an inch). Ammunition which is classified in metric already is still kept metric (e.g. 9 mm, 7.62 mm). In the manufacture of ammunition, bullet and powder weights are expressed in terms of grains for both metric and imperial cartridges. The popular .30-30 Winchester is a calibre bullet originally loaded with 30 grains of smokeless gunpowder.
Print.
Canada uses the inch-based paper standard e.g. the US Letter (8.5 inches × 11 inches), rather than the metric-based A4 paper size (210 mm × 297 mm) used throughout most of the world. The government, however, uses a combination of ISO paper sizes, and CAN 2-9.60M "Paper Sizes for Correspondence" specifies P1 through P6 paper sizes, which are the US paper sizes rounded to the nearest 5 mm.
Air transportation.
Luggage restrictions and limits at Canadian airports are in metric values with soft imperial conversion values. Runway lengths are given in feet and speed in knots as in the US. Like a number of metric countries altitude is given in feet.
Fuel is nowadays measured in metric units. The Gimli Glider incident in July 1983 is a famous case of a kilogram–pound mistake, in which the miscalculation of the amount of fuel in an Air Canada airplane with a malfunctioning fuel gauge caused the plane to run out of fuel mid-flight.
Education regarding the imperial system.
In 2005, the Ontario government announced changes to the secondary-school mathematics curriculum that would allow imperial units to be taught along with metric units. This marked a departure from previous governments' efforts to make sure that the curriculum used only the metric system. This was done in light of the refusal or reluctance of much of the private sector to metricate; thus students had been leaving school unprepared for the units used in the workplace. Many other provinces and territories also include the imperial system of measurements as part of their educational curriculum.


Malaysian University English Test

The Malaysian University English Test (commonly abbreviated as MUET) is a test of English language proficiency, largely used for university admissions in Malaysia. The test is set and run by the Malaysian Examinations Council. MUET is largely recognised in Malaysia and Singapore, with limited recognition in other countries worldwide.
MUET is a prerequisite for admissions into all public universities and colleges in Malaysia. Besides that, public servants also take MUET as an English qualification and for promotion opportunities.
From 2012 onwards, MUET is administered three times a year, in March, July and November. Besides that, an alternative test, MUET on Demand, is also held in nearly every month for candidates who are urgent to get the MUET results. On average, 85,000 candidates sit for the MUET each time.
From 2021, MUET has undergone a major change in format.
Components, Scoring and Grading.
There are four components in MUET:
Starting from MUET 2021, the maximum scores for each component are 90, makes an aggregated score of 360. The scores are graded in nine bands, including half bands, with Band 5+ being the highest while Band 1.0 the lowest.
Prior to MUET 2020, the maximum scores for each component is 45 for Listening and Speaking, 120 for Reading Comprehension and 90 for Writing, with an aggregated score of 300. The scores are then graded in six bands, with Band 6 being the highest while Band 1 the lowest.
Locations and test dates.
The MUET test centres are largely in public secondary schools that offer Form Six, matriculation colleges, certain universities, as well as certain private and semi-private colleges.
Listening, Reading and Writing components are usually tested on the same day, normally the second or the fourth Saturday of the month. The Speaking component is held on separate days, usually before the written tests.


Canadian Academic English Language Assessment

The Canadian Academic English Language, or CAEL (), Assessment is a standardized test designed to measure English language proficiency for admission to college and university, and for membership in professional associations. Test takers read articles, listen to a lecture, answer questions, and write a short essay, as they would be expected to do in a first-year university or college classroom.
The CAEL Assessment is accepted by over 150 academic institutions across Canada and the United States as well as to several international institutions. The test is also accepted at a number of professional organizations, including the Canadian Veterinary Association, the Royal Architectural Institute of Canada, and the Immigration Consultants of Canada Regulatory Council (ICCRC).
The CAEL Assessment is developed in Canada, by Canadians. It incorporates Canadian English and accents as used in Canadian academic contexts and post-secondary institutions. The CAEL Assessment is a fully integrated and topic-based performance test. Test takers use the information from the Reading and Listening components to write their essay.
In June 2015, Paragon Testing Enterprises, a Canadian English language testing company and a subsidiary of the University of British Columbia, acquired the CAEL Assessment from Carleton University.
History.
The CAEL Assessment was first developed by Carleton University in 1987. It was created out of a need to standardize the existing English language test given to students requiring a proficiency test as part of their admission to Carleton. However, in June 2015, Paragon Testing Enterprises, a subsidiary of The University of British Columbia (UBC), acquired the test.
Paragon currently administers three tests: the Canadian English Language Proficiency Index Program (CELPIP), the Canadian Academic English Language (CAEL) Assessment, and the Language Proficiency Index (LPI). The CELPIP Test is one of two tests designated by Immigration, Refugees and Citizenship Canada (IRCC) as proof of English language proficiency for permanent resident status in Canada and Canadian citizenship. With the acquisition of the CAEL Assessment, Paragon Testing Enterprises retired the CELPIP- Academic Test.
CAEL Test Format.
The language tasks and activities in the CAEL Assessment are systematically sampled from those that are commonly undertaken within the university academic community. The content for the tasks are drawn from introductory university courses at times when professors are introducing new topics to their students with the expectation that the students know little or nothing about the content.
Topics for the CAEL Assessment are drawn from introductory university courses such as arts, sociology, anthropology, business, engineering, sports, law, and medicine. Possible topics include criminal behaviour, global warming, urban development, cultural diversity, weather systems, team management, competition, and organizational behaviour.
The total allotted test time is approximately 145 minutes (2 hours and 25 minutes). Some test centres offer the CAEL Assessment over 2 days, with the Written Assessment and the OLT held on separate days.
The CAEL Assessment has two parts: Part 1, the Written Assessment and Part 2, the Oral Language Test (OLT).
Written Assessment.
Reading.
The time allotted for the Reading section is 55 minutes. Test takers are given two readings that are on the same topic as the Listening and Writing components.
The readings are taken from the following sources:
Reading tasks include:
Listening.
The time allotted for the Listening section is 20 minutes. Test takers listen to a pre-recorded lecture and answer relevant questions on the same topic as the Reading and Writing components.
Listening tasks include:
Writing.
The time allotted for the Writing section 45 minutes. Test takers will use the information from the Reading and Listening components to write a short essay. It is encouraged that test takers plan their essays prior to writing.
The essay topic asks the test taker to:
Oral Language Test (OLT).
The time allotted for the Oral Language Test (OLT) is 25 minutes. The OLT is carried out on a computer equipped with a headset and microphone, however test takers will not be required to use the computer mouse or keyboard. The OLT may be taken before or after the Written Assessment.
It consists of five tasks which sample typified and recurring speech acts within college and university settings:
Scoring.
CAEL Assessment Scores are reported for Listening, Reading, Writing, and Speaking test components. The scores range from band level 10 to band level 90.
CAEL Band Descriptors.
Each band score corresponds to a descriptive statement summarizing the level of English language proficiency of a test taker.
Results.
Results of tests taken at Canadian test centres are available within 10 to 15 business days after the scheduled test date. However, the results of tests taken at international test locations are available within 20 business days after the scheduled test date.
Test takers’ test scores can be sent to five institutions, which is included in the registration fee. Institution details are provided by the test takers when registering online, or up to 4 days before the chosen test date. The official score reports will only be mailed to academic and professional institutions.
Test Centre Locations and Test Dates.
Test takers can currently take the CAEL Assessment at test centres across Canada and China.
To see the full list of test centres and their corresponding test dates, please visit the CAEL website: https://www.cael.ca/
Institutions that Accept CAEL.
The CAEL Assessment is accepted by over 150 academic institutions across Canada and internationally as proof of English proficiency. A number of professional associations also recognize the CAEL Assessment as proof of English language proficiency required for membership.
Other English Language Proficiency Tests.
Many post-secondary institutions in Canada and the United States of America require proof of English language proficiency as one of their admission requirements. The most common English language proficiency tests other than the CAEL Assessment include: the International English Language Testing System (IELTS), Test of English as a Foreign Language (TOEFL), the Michigan English Language Assessment Battery (MELAB), Test of English for International Communication (TOEIC), the Pearson Test of English Academic (PTE Academic), and more.


Micropound

The micropound (abbreviation μlb) is a small unit of avoirdupois weight and mass in the US and imperial systems of measurement, equal to one-millionth () pound. It is equal to exactly kg or about 453.6μg.


OICETS

The Optical Inter-orbit Communications Engineering Test Satellite (OICETS), also called Kirari, was an experimental satellite launched by JAXA to demonstrate interorbital communication between satellites through optical (laser) means. OICETS was originally slated for a launch on the second J-I launcher. Due to problems with that launcher, the launch had to be put on hold. Using the H-IIA was out of question: it would have been overkill to use the H-IIA to send a satellite into low Earth orbit, and there was no budget for another H-IIA launch. Finally, in order to be able to perform the tests during the lifetime of the European Artemis satellite (since 2014, sold to Avanti Communications to exploit its Ka, S, and L-band payloads), OICETS was successfully launched on a Dnepr rocket (OiCETS riding on a decommissioned SS-18 ICBM in place of the warheads).
The satellite was decommissioned and its mission terminated on 24 September 2009 at 05:48 UTC.


Rayleigh interferometer

The Rayleigh interferometer employs two beams of light from a single source, and determines the difference in optical path length between the two paths using interference between the two beams when they are recombined following traversal of the paths. An example is shown in the figure. Light from a source (top) is collimated by a lens and split into two beams using slits. The beams are sent through two different paths and pass through compensating plates. They are brought to a focus by a second lens (bottom) where an interference pattern is observed to determine the optical path difference in terms of wavelengths of the light.
Advantages and disadvantages.
The advantage of the Rayleigh interferometer is its simple construction. Its drawbacks are (i) it requires a point or line source of light for good fringe visibility, and (ii) the fringes must be viewed with high magnification.


Tanzanian units of measurement

A number of units of measurement have been used in Tanzania to measure length, mass, capacity, etc. The metric system was adopted in Tanzania from 1967 to 1969.
System before metric system.
A number of units were used.
Zanzibar.
Several units were used in Zanzibar
Length.
One ohra was equal to 0.571 m (22.48 in).
Weight.
One bazla was equal to 15.525 kg (32.226 lb). One mane was equal to 2.0071 lb. One franzella of 36 rotoli was equal to 35.2822 lb.
Capacity.
One djezla was equal to 257.4 l (7.305 bushels).


Jill DeMatteis

Jill Marie Montaquila DeMatteis is an American statistician specializing in survey methodology. She has worked as a statistician in the US Bureau of Labor Statistics, and is a research associate professor at the University of Maryland, College Park and a vice president in the Statistics and Evaluation Sciences Group of Westat.
Education and career.
DeMatteis graduated from Ashland College in 1989, majoring in mathematics and economics; she credits Ashland mathematics professor Alan G. Poorman with her decision to study mathematics there. After earning a master's degree in statistics from Miami University in Ohio, she became a Bureau of Labor Statistics researcher from 1991 to 1995.
She moved to Westat in 1995 and returned to graduate study, completing her Ph.D. at American University in 1998. Her dissertation, "All-Cases Imputation Variance Estimator: A New Approach to Variance Estimation for Imputed Data", was supervised by Robert Jernigan.
Service and recognition.
DeMatteis was president of the Washington Statistical Society for 2006–2007, chaired the Survey Research Methods Section of the American Statistical Association (ASA) in 2013, and chaired the ASA Government Statistics Section in 2014.
She was named a Fellow of the American Statistical Association in 2008. In 2016 the Government Statistics Section gave her their Pat Doyle Award.


IRIG timecode

Inter-range instrumentation group timecodes, commonly known as IRIG timecode, are standard formats for transferring timing information. Atomic frequency standards and GPS receivers designed for precision timing are often equipped with an IRIG output. The standards were created by the Tele Communications Working Group of the U.S. military's Inter-Range Instrumentation Group (IRIG), the standards body of the Range Commanders Council. Work on these standards started in October 1956, and the original standards were accepted in 1960.
The original formats were described in IRIG Document 104-60, later revised and reissued in August 1970 as IRIG Document 104-70, upgraded later that year as the IRIG Document to the status of a Standard, IRIG Standard 200-70. The latest version of the Standard is IRIG Standard 200-16 from August 2016.
Timecodes.
The different timecodes defined in the Standard have alphabetic designations. A, B, D, E, G, and H are the standards currently defined by IRIG Standard 200-04.
C was in the original specification, but was replaced by H.
The main difference between codes is their rate, which varies between one pulse per minute and 10,000 pulses per second.
IRIG Code B Calculation:

Bit rate = 100 Hz = 100 × (1 / second) = 100 / second = 100 / 1000 ms = 1 / 10ms

Bit time = 1 / (Bit rate) = 1 / (1 / 10 ms) = 10 ms

There are 100 Bits per frame.

Frame time = (Bits per frame) × (Bit time) = 100 × 10 ms = 1000 ms = 1 second

Frame rate = 1 / (Frame time) = 1 / 1 second = 1 Hz

The bits are modulated on a carrier. A three-digit suffix specifies the type and frequency of the carrier, and which optional information is included:
Binary-coded decimal (BCD) day of year, hours, minutes, and (for some formats) seconds and fractions are always included. Optional components are:
The recognized signal identification numbers for each format according to the standard 200-04 consist of:
Thus the complete signal identification number consists of one letter and three digits. For example, the signal designated as B122 is deciphered as follows: Format B, Sine wave (amplitude modulated), 1 kHz carrier, and Coded expressions BCDTOY.
The most commonly used of the standards is IRIG B, then IRIG A, then probably IRIG G. Timecode formats directly derived from IRIG H are used by NIST radio stations WWV, WWVH and WWVB.
For example, one of the most common formats, IRIG B122:
Timecode structure.
IRIG timecode is made up of repeating frames, each containing 60 or 100 bits. The bits are numbered from 0 through 59 or 99.
At the start of each bit time, the IRIG timecode enables a signal (sends a carrier, raises the DC signal level, or transmits Manchester 1 bits). The signal is disabled (carrier attenuated at least 3×, DC signal level lowered, or Manchester 0 bits transmitted), at one of three times during the bit interval:
Bit 0 is the frame marker bit Pr. Every 10th bit starting with bit 9, 19, 29, ... 99 is also a marker bit, known as position identifiers P1, P2, ..., P9, P0. Thus, two marker bits in a row (P0 followed by Pr) marks the beginning of a frame. The frame encodes the time of the leading edge of the frame marker bit.
All other bits are data bits, which are transmitted as binary 0 if they have no other assigned purpose.
Generally, groups of 4 bits are used to encode BCD digits. Bits are assigned little-endian within fields.
In IRIG G, bits 50–53 encode hundredths of seconds, and the years are encoded in bits 60–68.
Not all formats include all fields. Obviously those formats with 60-bit frames omit the straight binary seconds fields, and digits representing divisions less than one frame time (everything below hours, in the case of IRIG D) are always transmitted as 0.
No parity or check bits are included. Error detection can be achieved by comparing consecutive frames to see if they encode consecutive timestamps.
Unassigned 9-bit fields between consecutive marker bits are available for user-defined "control functions". For example, the IEEE 1344 standard defines functions for bits 60–75.
IRIG J timecode.
IRIG standard 212-00 defines a different time-code, based on RS-232-style asynchronous serial communication.
The timecode consists of ASCII characters, each transmitted as 10 bits:
The on-time marker is the leading edge of the first start bit.
IRIG J-1 timecode consists of 15 characters (150 bit times), sent once per second at a baud rate of 300 or greater:
 <SOH>DDD:HH:MM:SS<CR><LF>
At the end of the timecode, the serial line is idle until the start of the next code. There is no idle time between other characters.
IRIG J-2 timecode consists of 17 characters (170 bit times), sent 10 times per second at a baud rate of 2400 or greater:
 <SOH>DDD:HH:MM:SS.S<CR><LF>
This is the same, except that tenths of seconds are included.
The full-timecode specification is of the form "IRIG J-"xy"", where "x" denotes the variant, and "y" denotes a baud rate of 75×2"y".
Normally used combinations are J-12 through J-14 (300, 600, and 1200 baud), and J-25 through J-29 (2400 through 38400 baud).


676 Melitta

676 Melitta is a minor planet orbiting the Sun. It is classified as a main belt asteroid. The name, "Melitta", is the Attic Greek form of the name "Melissa"—a reference both to the nymph of ancient Greek mythology, and to the minor planet's discoverer, Melotte.


9969 Braille

9969 Braille, provisional designation , is an eccentric, rare-type and elongated asteroid from the innermost regions of the asteroid belt, classified as Mars-crosser and slow rotator, approximately 1–2 kilometers in diameter. It was discovered in 1992, by astronomers at Palomar observatory and later named after Louis Braille, the inventor of the writing system for the blind. It was photographed in closeup by the spacecraft Deep Space 1 in 1999, but a malfunction resulted in indistinct images.
Discovery and naming.
Discovered on May 27, 1992, by E. F. Helin and K. J. Lawrence working at the Palomar observatory as part of NASA's Planet-Crossing Asteroid Survey, it was given the provisional designation . Later, it was renamed Braille in honour of Louis Braille as suggested by Kennedy Space Center software engineer Kerry Babcock in The Planetary Society's contest titled "Name That Asteroid". The official naming citation was published by the Minor Planet Center on 28 July 1999 ().
Orbit.
Braille has an unusually inclined orbit, and belongs to the somewhat rare class of asteroids known as Mars-crossing asteroids. Simulations of its orbit by scientists of the Deep Space 1 project predict that it will evolve into an Earth-crossing orbit in about 4000 years. Although its closest approach to the Sun is closer than Mars orbit, its highly elliptical orbit takes it almost half-way to Jupiter at its apoapsis, and as such its semi-major axis is too large for it to be classified as an Amor asteroid.
Physical characteristics.
Braille is a Q-type asteroid, composed mostly of olivine and pyroxene. Early ground-based observations had suggested that it could have been a V-type asteroid with similarities of composition between it and the much larger 4 Vesta. The asteroid is irregularly shaped, measuring approximately 2.1 km × 1 km × 1 km.
Exploration.
Detailed information about Braille comes primarily from the Deep Space 1 probe, which passed within 26 km of the asteroid on July 29, 1999, and from extensive ground based observations done in conjunction with the mission. By the time Deep Space 1 reached Braille, its ultraviolet spectrometer had failed, but it did return two CCD images of medium resolution and three infrared spectra during the encounter. However, although the probe came within 26 km of Braille, the images and spectra were taken from an approximate distance of 14 000 km, due to problems with the tracking system.
The main purpose of the Deep Space 1 mission was technology testing, but the encounter with Braille was of strong scientific value. No lone asteroid as small as Braille had previously been observed from such a short distance.


Huib Bakker

Huib Johan Bakker (born 2 March 1965) is a Dutch physicist working in the field of ultrafast spectroscopy. He has been president of research institute AMOLF since 1 February 2016.
Career.
Bakker was born on 2 March 1965 in Haarlem. He studied physical chemistry at the Vrije Universiteit Amsterdam, and obtained his master's degree in 1987. He subsequently became a PhD student under Ad Lagendijk at the AMOLF research institute. Bakker received his doctorate cum laude in 1991 with a thesis titled:"Time-resolved vibrational spectroscopy with picosecond infrared pulses". Between 1991 and 1994 he was a scientific assistant at the Institute of Semiconductor Technologies of RWTH Aachen University in Germany.
In 1995 Bakker returned to the Netherlands to become scientific group leader at AMOLF. Six years later he started as professor of Ultrafast Spectroscopy of Molecules in the Condensed Phase at the University of Amsterdam. At AMOLF Bakker is group leader of research on ultrafast spectroscopy. In 2003 he became head of the department of molecular nanophysics. In his research at AMOLF Bakker has been founder of a technique which uses special non-linear spectroscopics, which helps researchers in determining the molecular mobility and structure of water in complex systems.
Bakker became adjunct director of AMOLF on 1 September 2015. On 1 February 2016 he succeeded Vinod Subramaniam as director, who became rector-magnificus of the Vrije Universiteit Amsterdam.
Awards and honors.
In 2005 Bakker received the gold medal of the Royal Netherlands Chemical Society. Bakker was elected a member of the Royal Netherlands Academy of Arts and Sciences in 2015. The Academy called him "a renowned expert on the molecular properties of water and ice".


Thundering herd problem

In computer science, the thundering herd problem occurs when a large number of processes or threads waiting for an event are awoken when that event occurs, but only one process is able to handle the event. When the processes wake up, they will each try to handle the event, but only one will win. All processes will compete for resources, possibly freezing the computer, until the herd is calmed down again.
Mitigation.
The Linux-kernel will serialize responses for requests to a single file descriptor, so only one thread (process) is woken up. For epoll() in Linux 4.5 kernel version was added EPOLLEXCLUSIVE flag, thus several epoll sets (different threads or different processes) may wait on same resource and only one set will be woken up. For certain workloads this flag can give significant processing time reduction.
Similarly in Microsoft Windows, I/O completion ports can mitigate the thundering herd problem, as they can be configured such that only one of the threads waiting on the completion port is woken up when an event occurs.
In systems which rely on a backoff mechanism (e.g. exponential backoff), the clients will retry failed calls, by waiting a specific amount of time between consecutive retries. In order to avoid the thundering herd problem, jitter can be purposefully introduced, in order to break the synchronization across the clients thereby avoiding collisions. In this approach, randomness is added to the wait intervals between retries, so that clients are no longer synchronized.


Fokker periodicity block

Fokker periodicity blocks are a concept in tuning theory used to mathematically relate musical intervals in just intonation to those in equal tuning. They are named after Adriaan Daniël Fokker. These are included as the primary subset of what Erv Wilson refers to as constant structures, where "each interval occurs always subtended by the same number of steps".
The basic idea of Fokker's periodicity blocks is to represent just ratios as points on a lattice, and to find vectors in the lattice which represent very small intervals, known as commas. Treating pitches separated by a comma as equivalent "folds" the lattice, effectively reducing its dimension by one; mathematically, this corresponds to finding the quotient group of the original lattice by the sublattice generated by the commas.
For an "n"-dimensional lattice, identifying "n" linearly independent commas reduces the dimension of the lattice to zero, meaning that the number of pitches in the lattice is finite; mathematically, its quotient is a finite abelian group. This zero-dimensional set of pitches is a periodicity block. Frequently, it forms a cyclic group, in which case identifying the "m" pitches of the periodicity block with "m"-equal tuning gives equal tuning approximations of the just ratios that defined the original lattice.
Note that octaves are usually ignored in constructing periodicity blocks (as they are in scale theory generally) because it is assumed that for any pitch in the tuning system, all pitches differing from it by some number of octaves are also available in principle. In other words, all pitches and intervals can be considered as residues modulo octave. This simplification is commonly known as octave equivalence.
Definition of periodicity blocks.
Let an "n"-dimensional lattice (i.e. integer grid) embedded in "n"-dimensional space have a numerical value assigned to each of its nodes, such that moving within the lattice in one of the cardinal directions corresponds to a shift in pitch by a particular interval. Typically, "n" ranges from one to three. Simultaneously the two-dimensional case, the lattice is a square lattice. In the 3-D case, the lattice is cubic.
Examples of such lattices are the following ("x", "y", "z" and "w" are integers):
Once the lattice and its labeling is fixed, one chooses "n" nodes of the lattice other than the origin whose values are close to either 1 or 2.
The vectors from the origin to each one of these special nodes are called "unison vectors". These vectors define a sublattice of the original lattice, which has a fundamental domain that in the two-dimensional case is a parallelogram bounded by unison vectors and their shifted copies, and in the three-dimensional case is a parallelepiped. These domains form the tiles in a tessellation of the original lattice.
The tile has an area or volume given by the absolute value of the determinant of the matrix of unison vectors: i.e. in the 2-D case if the unison vectors are u and v, such that formula_1 and formula_2 then the area of a 2-D tile is
Each tile is called a Fokker periodicity block. The area of each block is always a natural number equal to the number of nodes falling within each block.
Examples.
Example 1: Take the 2-dimensional lattice of perfect fifths (ratio 3/2) and just major thirds (ratio 5/4). Choose the commas 128/125 (the diesis, the distance by which three just major thirds fall short of an octave, about 41 cents) and 81/80 (the syntonic comma, the difference between four perfect fifths and a just major third, about 21.5 cents). The result is a block of twelve, showing how twelve-tone equal temperament approximates the ratios of the 5-limit.
Example 2: However, if we were to reject the diesis as a unison vector and instead choose the difference between five major thirds (minus an octave) and a fourth, 3125/3072 (about 30 cents), the result is a block of 19, showing how 19-TET approximates ratios of the 5-limit.
Example 3: In the 3-dimensional lattice of perfect fifths, just major thirds, and "just minor sevenths" (ratio 7/4), the identification of the syntonic comma, the septimal kleisma (225/224, about 8 cents), and the ratio 1029/1024 (the difference between three septimal whole tones and a perfect fifth, about 8.4 cents) results in a block of 31, showing how 31-TET approximates ratios of the 7-limit.
Mathematical characteristics of periodicity blocks.
The periodicity blocks form a secondary, oblique lattice, superimposed on the first one. This lattice may be given by a function φ:
which is really a linear combination:
where point ("x"0, "y"0) can be any point, preferably not a node of the primary lattice, and preferably so that points φ(0,1), φ(1,0) and φ(1,1) are not any nodes either.
Then membership of primary nodes within periodicity blocks may be tested analytically through the inverse φ function:
Let
then let the pitch "B"("x","y") belong to the scale "M""B" iff formula_10 i.e.
For the one-dimensional case:
where "L" is the length of the unison vector,
For the three-dimensional case,
where formula_18 is the determinant of the matrix of unison vectors.


2208 Pushkin


2852 Declercq


Michelson interferometer

The Michelson interferometer is a common configuration for optical interferometry and was invented by Albert Abraham Michelson. Using a beam splitter, a light source is split into two arms. Each of those light beams is reflected back toward the beamsplitter which then combines their amplitudes using the superposition principle. The resulting interference pattern that is not directed back toward the source is typically directed to some type of photoelectric detector or camera. For different applications of the interferometer, the two light paths can be with different lengths or incorporate optical elements or even materials under test.
The Michelson interferometer (among other interferometer configurations) is employed in many scientific experiments and became well known for its use by Albert Michelson and Edward Morley in the famous Michelson–Morley experiment (1887) in a configuration which would have detected the earth's motion through the supposed luminiferous aether that most physicists at the time believed was the medium in which light waves propagated. The null result of that experiment essentially disproved the existence of such an aether, leading eventually to the special theory of relativity and the revolution in physics at the beginning of the twentieth century. In 2015, another application of the Michelson interferometer, LIGO, made the first direct observation of gravitational waves. That observation confirmed an important prediction of general relativity, validating the theory's prediction of space-time distortion in the context of large scale cosmic events (known as strong field tests).
Configuration.
A Michelson interferometer consists minimally of mirrors "M1" & "M2" and a beam splitter "M".
In Fig 2, a source "S" emits light that hits the beam splitter (in this case, a plate beamsplitter) surface "M" at point "C". "M" is partially reflective, so part of the light is transmitted through to point "B" while some is reflected in the direction of "A". Both beams recombine at point "C' "to produce an interference pattern incident on the detector at point "E" (or on the retina of a person's eye). If there is a slight angle between the two returning beams, for instance, then an imaging detector will record a sinusoidal "fringe pattern" as shown in Fig. 3b. If there is perfect spatial alignment between the returning beams, then there will not be any such pattern but rather a constant intensity over the beam dependent on the differential pathlength; this is difficult, requiring very precise control of the beam paths.
Fig. 2 shows use of a coherent (laser) source. Narrowband spectral light from a discharge or even white light can also be used, however to obtain significant interference contrast it is required that the differential pathlength is reduced below the coherence length of the light source. That can be only micrometers for white light, as discussed below.
If a lossless beamsplitter is employed, then one can show that optical energy is conserved. At every point on the interference pattern, the power that is "not" directed to the detector at "E" is rather present in a beam (not shown) returning in the direction of the source.
As shown in Fig. 3a and 3b, the observer has a direct view of mirror "M1" seen through the beam splitter, and sees a reflected image "M'2" of mirror "M2". The fringes can be interpreted as the result of interference between light coming from the two virtual images "S'1" and "S'2" of the original source "S". The characteristics of the interference pattern depend on the nature of the light source and the precise orientation of the mirrors and beam splitter. In Fig. 3a, the optical elements are oriented so that "S'1" and "S'2" are in line with the observer, and the resulting interference pattern consists of circles centered on the normal to "M1" and "M'2" (fringes of equal inclination). If, as in Fig. 3b, "M1" and "M'2" are tilted with respect to each other, the interference fringes will generally take the shape of conic sections (hyperbolas), but if "M1" and "M'2" overlap, the fringes near the axis will be straight, parallel, and equally spaced (fringes of equal thickness). If S is an extended source rather than a point source as illustrated, the fringes of Fig. 3a must be observed with a telescope set at infinity, while the fringes of Fig. 3b will be localized on the mirrors.
Source bandwidth.
White light has a tiny coherence length and is difficult to use in a Michelson (or Mach–Zehnder) interferometer. Even a narrowband (or "quasi-monochromatic") spectral source requires careful attention to issues of chromatic dispersion when used to illuminate an interferometer. The two optical paths must be practically equal for all wavelengths present in the source. This requirement can be met if both light paths cross an equal thickness of glass of the same dispersion. In Fig. 4a, the horizontal beam crosses the beam splitter three times, while the vertical beam crosses the beam splitter once. To equalize the dispersion, a so-called compensating plate identical to the substrate of the beam splitter may be inserted into the path of the vertical beam. In Fig. 4b, we see using a cube beam splitter already equalizes the pathlengths in glass. The requirement for dispersion equalization is eliminated by using extremely narrowband light from a laser.
The extent of the fringes depends on the coherence length of the source. In Fig. 3b, the yellow sodium light used for the fringe illustration consists of a pair of closely spaced lines, D1 and D2, implying that the interference pattern will blur after several hundred fringes. Single longitudinal mode lasers are highly coherent and can produce high contrast interference with differential pathlengths of millions or even billions of wavelengths. On the other hand, using white (broadband) light, the central fringe is sharp, but away from the central fringe the fringes are colored and rapidly become indistinct to the eye.
Early experimentalists attempting to detect the earth's velocity relative to the supposed luminiferous aether, such as Michelson and Morley (1887) and Miller (1933), used quasi-monochromatic light only for initial alignment and coarse path equalization of the interferometer. Thereafter they switched to white (broadband) light, since using white light interferometry they could measure the point of "absolute phase" equalization (rather than phase modulo 2π), thus setting the two arms' pathlengths equal. More importantly, in a white light interferometer, any subsequent "fringe jump" (differential pathlength shift of one wavelength) would always be detected.
Applications.
The Michelson interferometer configuration is used in a number of different applications.
Fourier transform spectrometer.
Fig. 5 illustrates the operation of a Fourier transform spectrometer, which is essentially a Michelson interferometer with one mirror movable. (A practical Fourier transform spectrometer would substitute corner cube reflectors for the flat mirrors of the conventional Michelson interferometer, but for simplicity, the illustration does not show this.) An interferogram is generated by making measurements of the signal at many discrete positions of the moving mirror. A Fourier transform converts the interferogram into an actual spectrum. Fourier transform spectrometers can offer significant advantages over dispersive ("i.e." grating and prism) spectrometers under certain conditions. (1) The Michelson interferometer's detector in effect monitors all wavelengths simultaneously throughout the entire measurement. When using a noisy detector, such as at infrared wavelengths, this offers an increase in signal to noise ratio while using only a single detector element; (2) the interferometer does not require a limited aperture as do grating or prism spectrometers, which require the incoming light to pass through a narrow slit in order to achieve high spectral resolution. This is an advantage when the incoming light is not of a single spatial mode. For more information, see Fellgett's advantage.
Twyman–Green interferometer.
The Twyman–Green interferometer is a variation of the Michelson interferometer used to test small optical components, invented and patented by Twyman and Green in 1916. The basic characteristics distinguishing it from the Michelson configuration are the use of a monochromatic point light source and a collimator. Michelson (1918) criticized the Twyman–Green configuration as being unsuitable for the testing of large optical components, since the available light sources had limited coherence length. Michelson pointed out that constraints on geometry forced by the limited coherence length required the use of a reference mirror of equal size to the test mirror, making the Twyman–Green impractical for many purposes. Decades later, the advent of laser light sources answered Michelson's objections.
The use of a figured reference mirror in one arm allows the Twyman–Green interferometer to be used for testing various forms of optical component, such as lenses or telescope mirrors. Fig. 6 illustrates a Twyman–Green interferometer set up to test a lens. A point source of monochromatic light is expanded by a diverging lens (not shown), then is collimated into a parallel beam. A convex spherical mirror is positioned so that its center of curvature coincides with the focus of the lens being tested. The emergent beam is recorded by an imaging system for analysis.
Laser unequal path interferometer.
The "LUPI" is a Twyman–Green interferometer that uses a coherent laser light source. The high coherence length of a laser allows unequal path lengths in the test and reference arms and permits economical use of the Twyman–Green configuration in testing large optical components. A similar scheme has been used by Tajammal M in his PhD thesis (Manchester University UK, 1995) to balance two arms of an LDA system. This system used fibre optic direction coupler.
Stellar measurements.
The Michelson stellar interferometer is used for measuring the diameter of stars. In 1920, Michelson and Francis G. Pease used it to measure the diameter of Betelgeuse, the first time the diameter of a star other than the sun was measured.
Gravitational wave detection.
Michelson interferometry is the leading method for the direct detection of gravitational waves. This involves detecting tiny strains in space itself, affecting two long arms of the interferometer unequally, due to a strong passing gravitational wave. In 2015 the first detection of gravitational waves was accomplished using the two Michelson interferometers, each with 4 km arms, which comprise the Laser Interferometer Gravitational-Wave Observatory. This was the first experimental validation of gravitational waves, predicted by Albert Einstein's General Theory of Relativity. With the addition of the Virgo interferometer in Europe, it became possible to calculate the direction from which the gravitational waves originate, using the tiny arrival-time differences between the three detectors. In 2020, India was constructing a fourth Michelson interferometer for gravity wave detection.
Miscellaneous applications.
Fig. 7 illustrates use of a Michelson interferometer as a tunable narrow band filter to create dopplergrams of the Sun's surface. When used as a tunable narrow band filter, Michelson interferometers exhibit a number of advantages and disadvantages when compared with competing technologies such as Fabry–Pérot interferometers or Lyot filters. Michelson interferometers have the largest field of view for a specified wavelength, and are relatively simple in operation, since tuning is via mechanical rotation of waveplates rather than via high voltage control of piezoelectric crystals or lithium niobate optical modulators as used in a Fabry–Pérot system. Compared with Lyot filters, which use birefringent elements, Michelson interferometers have a relatively low temperature sensitivity. On the negative side, Michelson interferometers have a relatively restricted wavelength range, and require use of prefilters which restrict transmittance. The reliability of Michelson interferometers has tended to favor their use in space applications, while the broad wavelength range and overall simplicity of Fabry–Pérot interferometers has favored their use in ground-based systems.
Another application of the Michelson interferometer is in optical coherence tomography (OCT), a medical imaging technique using low-coherence interferometry to provide tomographic visualization of internal tissue microstructures. As seen in Fig. 8, the core of a typical OCT system is a Michelson interferometer. One interferometer arm is focused onto the tissue sample and scans the sample in an X-Y longitudinal raster pattern. The other interferometer arm is bounced off a reference mirror. Reflected light from the tissue sample is combined with reflected light from the reference. Because of the low coherence of the light source, interferometric signal is observed only over a limited depth of sample. X-Y scanning therefore records one thin optical slice of the sample at a time. By performing multiple scans, moving the reference mirror between each scan, an entire three-dimensional image of the tissue can be reconstructed. Recent advances have striven to combine the nanometer phase retrieval of coherent interferometry with the ranging capability of low-coherence interferometry.
Others applications include delay line interferometer which convert phase modulation into amplitude modulation in DWDM networks, the characterization of high-frequency circuits., and low-cost THz power generation.
Atmospheric and space applications.
The Michelson Interferometer has played an important role in studies of the upper atmosphere, revealing temperatures and winds, employing both space-borne, and ground-based instruments, by measuring the Doppler widths and shifts in the spectra of airglow and aurora. For example, the Wind Imaging Interferometer, WINDII, on the Upper
Atmosphere Research Satellite, UARS, (launched on September 12, 1991) measured the global wind and temperature patterns from 80 to 300 km by using the visible airglow emission from these altitudes as a target and employing optical Doppler interferometry to measure the small wavelength shifts of the narrow atomic and molecular airglow emission lines induced by the
bulk velocity of the atmosphere carrying the emitting species. The instrument was an all-glass field-widened achromatically and thermally compensated phase-stepping Michelson interferometer, along with a bare CCD detector that imaged the airglow limb through the interferometer. A sequence of phase-stepped images was processed to derive the wind velocity for two orthogonal view directions, yielding the horizontal wind vector.
The principle of using a polarizing Michelson Interferometer as a narrow band filter was first described by Evans who developed a birefringent photometer where the incoming light is split into two orthogonally polarized components by a polarizing beam splitter, sandwiched between two halves of a Michelson cube. This led to the first polarizing wide-field Michelson interferometer described by Title and Ramsey which was used for solar observations; and led to the development of a refined instrument applied to measurements of oscillations in the sun's atmosphere, employing a network of observatories around the Earth known as the Global Oscillations Network Group (GONG).
The Polarizing Atmospheric Michelson Interferometer, PAMI, developed by Bird et al., and discussed in "Spectral Imaging of the Atmosphere", combines the polarization tuning technique of Title and Ramsey with the Shepherd "et al." technique of deriving winds and temperatures from emission rate measurements at sequential path differences, but the scanning system used by PAMI is much simpler than the moving mirror systems in that it has no internal moving parts, instead scanning with a polarizer external to the interferometer. The PAMI was demonstrated in an observation campaign where its performance was compared to a Fabry–Pérot spectrometer, and employed to measure E-region winds.
More recently, the Helioseismic and Magnetic Imager (HMI), on the Solar Dynamics Observatory, employs two Michelson Interferometers with a polarizer and other tunable elements, to study solar variability and to characterize the Sun's interior along with the various components of magnetic activity. HMI takes high-resolution measurements of the longitudinal and vector magnetic field over the entire visible disk thus extending the capabilities of its predecessor, the SOHO's MDI instrument (See Fig. 9). HMI produces data to determine the interior sources and mechanisms of solar variability and how the physical processes inside the Sun are related to surface magnetic field and activity. It also produces data to enable estimates of the coronal magnetic field for studies of variability in the extended solar atmosphere. HMI observations will help establish the relationships between the internal dynamics and magnetic activity in order to understand solar variability and its effects.
In one example of the use of the MDI, Stanford scientists reported the detection of several sunspot regions in the deep interior of the Sun, 1–2 days before they appeared on the solar disc. The detection of sunspots in the solar interior may thus provide valuable warnings about upcoming surface magnetic activity which could be used to improve and extend the predictions of space weather forecasts.
Technical topics.
Step-phase interferometer.
This is a Michelson interferometer in which the mirror in one arm is replaced with a Gires–Tournois etalon. The highly dispersed wave reflected by the Gires–Tournois etalon interferes with the original wave as reflected by the other mirror. Because the phase change from the Gires–Tournois etalon is an almost step-like function of wavelength, the resulting interferometer has special characteristics. It has an application in fiber-optic communications as an optical interleaver.
Both mirrors in a Michelson interferometer can be replaced with Gires–Tournois etalons. The step-like relation of phase to wavelength is thereby more pronounced, and this can be used to construct an asymmetric optical interleaver.
Phase-conjugating interferometry.
The reflection from phase-conjugating mirror of two light beams inverses their phase difference
formula_1 to the opposite one formula_2. For this reason the interference pattern in twin-beam interferometer changes drastically. Compared to conventional Michelson interference curve with period of half-wavelength formula_3:
formula_4,
where formula_5 is second-order correlation function, the interference curve in phase-conjugating interferometer
has much longer period defined by frequency shift
formula_6 of reflected beams:
formula_7,
where visibility curve is nonzero when optical path difference
formula_8 exceeds coherence length of light beams.
The nontrivial features of phase fluctuations in optical phase-conjugating mirror had been studied via Michelson interferometer with two independent PC-mirrors
. The phase-conjugating Michelson interferometry is a promising technology for coherent summation of laser amplifiers
Constructive interference in an array containing formula_9 beamsplitters of formula_10 laser beams synchronized by
phase conjugation
may increase the brightness of amplified beams as formula_11.