Optical dilatometer

An optical dilatometer is a non-contact device able to measure thermal expansions or sintering kinetics of any kind of materials, unlike traditional push rod dilatometer, it can push up to the dilatometric softening of the specimen. It is a device for measuring changes in the dimensions of a specimen, optically, the achieved resolution can result in greater values than those of a conventional pushrod dilatometer. A monochromatic light source, such as a laser, illuminates the specimen. Some of the light is reflected by the specimen and interferes with the incoming light, creating optical interference fringes. As the specimen contracts or expands, there is a proportional movement of the interference fringes, which can be measured using a camera system. The measurement resolution is determined by the wavelength of the light, and is typically 0.5 μm for blue light. Optical dilatometers are used to measure thermal expansion.
The optical dilatometer is in fact complementary to the traditional higher resolution push rod dilatometer when it comes to measure dimensional changes of materials, as a function of temperature, and no contact between specimen and instrument is required.
Structure and types.
The most recent types of optical dilatometer use a direct-beam system so as to avoid contact-related problems by measuring the image that the specimen projects on an image sensor, when irradiated by a light beam. By using a single beam of light with short wavelength and a very high resolution image sensor it is possible to achieve good resolutions, although not comparable to those of the standard dilatometers. For example, using a blue light with a wavelength below 1500 micrometers, it is possible to achieve images with an actual resolution of nearly 1500 micrometers/pixel of the camera (not an interpolated resolution but an actual resolution). By using two light beams, which illuminate two small portions of material at the extremities of the sample, set perpendicularly to the beams direction, it is then possible to achieve an absolute measurement of longitudinal variation while heat-treating the specimen.
There are two major types of optical dilatometers which are currently in use:
History.
The first optical dilatometer was invented by Abbe and Fizeau in the second half of 19th century. This design has a reflected beam of monochromatic light and the measurement of the displacement is carried out by counting the interference fringes between the forward going beam and the reflected beam. After the Abbe invention, many improvements were achieved on the original design and there are now many models available on the market, which use modern optics and designs.
Over the last five decades, interest has grown in the use of thermomechanical technologies for characterising materials in different fields of science and engineering. In particular, the use of optical methods has been playing a role in the field of ceramics and have been used to measure the coefficient of thermal expansion of bodies and glazes in order to ensure an optimal match of their thermomechanical behaviour.
Applications and fields of research.
In order to measure thermal expansion up to high temperatures, the material to be tested has to be set on a sample holder inside an oven which has its own thermal expansion. In order to achieve a good accuracy it is necessary to measure the expansion of the sample holder and to subtract it from the actual expansion of the specimen. The best approach is to split the laser beam into two beams of light, which are reflected by the top-edge of the sample and by the top-edge of the sample holder, or by both longitudinal edges of the specimen. By detecting the longitudinal variations at both the extremities of the specimen the measurement achieved is absolute and there is no need for further corrections. This is the most accurate way of measuring thermal expansion and it may attain nanometric resolution. This is the type of instrument used by the suppliers of certified standard materials. For example, the National Institute for Standards and Technology uses a Fizeau double-beam interferometer to certify the thermal expansion of their certified reference materials. This method has proved to be very accurate, with a resolution of a fraction of the wavelength of the incident light, but it is limited by the reflectivity of the surface of the specimen. If the specimen is not reflective, or it becomes non reflective during the test, it is then necessary to use a mirror, which is set in contact with the specimen by using a refractory push rod. By doing so such method loses the advantage of being non contact and becomes substantially similar to the electronic dilatometer.
Optical dilatometers are used along traditional dilatometers in ceramics for non-destructive testing of a sample's behavior during a thermal treatment. Optical dilatometers are used for thermal analysis of various types of materials, such as incoherent materials (expansion and contraction of an incoherent granular frit, as applied, for example, on raw tiles) and polymers (behaviour above the glass transition temperature, where the surface tension starts pulling the edges and making the sample shrink), as well as for analysis of various processes in materials manufacturing, for example, sintering kinetics, thermal expansion and sintering behaviour of thin glaze layer or polymer thin films.


305 Gordonia

Gordonia (minor planet designation: 305 Gordonia) is a fairly typical, although sizeable Main belt asteroid.
It was discovered by Auguste Charlois on 16 February 1891 in Nice and named after James Gordon Bennett Jr., his patron.
The light curve of 305 Gordonia shows a periodicity of , during which time the brightness of the object varies by in magnitude.


3352 McAuliffe

3352 McAuliffe (), provisional designation , is a rare-type asteroid and suspected binary system, classified as near-Earth object of the Amor group, approximately 2 kilometers in diameter. It was discovered on 6 February 1981, by American astronomer Norman Thomas at Lowell's Anderson Mesa Station near Flagstaff, Arizona, United States.
Originally, this asteroid was the target of the 1998 Deep Space 1 mission, but that mission was eventually rerouted to 9969 Braille. It was named in memory of Challenger crew member Christa McAuliffe.
Orbit.
"McAuliffe" orbits the Sun at a distance of 1.2–2.6 AU once every 2 years and 7 months (941 days). Its orbit has an eccentricity of 0.37 and an inclination of 5° with respect to the ecliptic.
It has an "Earth minimum orbital intersection distance" of , which translates into 79.5 lunar distances. Due to its eccentric orbit, "McAuliffe" is also a Mars-crosser. As no precoveries were taken, and no prior identifications were made, the body's observation arc begins with its official discovery observation at Anderson Mesa in 1981.
Physical characteristics.
Spectral type.
In the SMASS taxonomy, "McAuliffe" is a rare A-type asteroid, meaning that it is rich in olivine. In addition, the large-scale survey conducted by PanSTARRS also classified as a SQ-type, a transitional type between the common stony and Q-type asteroids, indicating the presence of pyroxene minerals.
Diameter and albedo.
The "Collaborative Asteroid Lightcurve Link" assumes an albedo of 0.18 and derives a diameter of 1.99 kilometers, based on an absolute magnitude of 16.068, a figure previously obtained by the Wide-field Infrared Survey Explorer with its subsequent NEOWISE mission, and later revised by Czech astronomer Petr Pravec.
Rotation period.
Between 1998 and 2016, several rotational lightcurves of "McAuliffe" were obtained from photometric observations taken by astronomers Petr Pravec at Ondřejov Observatory, Czech Republic, by Andreas Howell at Willowcroft Observatory, Florida, as well as by Brian Warner at his Palmer Divide Observatory, Colorado, and at the Center for Solar System Studies, California. The best-rated lightcurve gave a rotation period of 2.206 to 2.212 hours with a brightness variation between 0.08 and 0.12 magnitude ().
Suspected moon.
During the photometric observations in March 2012, Brian Warner found evidence of the existence of a minor-planet moon orbiting "McAuliffe" every 20.86 hours. However, it is only a "possible" synchronous binary system, as no mutual eclipsing/occultation events were observed. Follow-up observations in September and October 2016, did not confirm the binary nature of "McAuliffe".
DS 1 mission.
"McAuliffe" together with comet 76P/West–Kohoutek–Ikemura had been the original fly-by targets for the Deep Space 1 (DS1) mission.
Launched was scheduled for 1 July 1998. A delay in the delivery of the spacecraft's power electronics system as well as insufficient time to test the flight software, caused the launch to be postponed to 24 October 1998. Due to this delay, new targets had to be selected.
In July 1999, DS1 passed the alternative target 9969 Braille a distance of 15 kilometers, in January 2001, comet 107P/Wilson–Harrington was encountered, and in September 2001, short-period comet 19P/Borrelly was passed at distance of only 2,200 kilometers.
Naming.
This minor planet was named in memory of Christa McAuliffe (1948–1986), teacher, civilian astronaut and one of the seven crew members who died in the Space Shuttle Challenger disaster on 28 January 1986. The minor planets , , , , , and were named for the other crew members of the ill-fated STS-51-L mission. The approved naming citation was published by the Minor Planet Center on 26 March 1986 ().


2507 Bobone


Fourth Dimension Records

Fourth Dimension Records is a British record label, specialising in international underground music. It was founded by Gary Levermore as an offshoot of his Third Mind label before being taken over by Richard Johnson (aka Richo) in 1984. The label became quite successful in the 1990s, releasing music by Simon Wickham-Smith & Richard Youngs, KK Null, The Gerogerigegege, Circle, Splintered (band), Thurston Moore, Hijokaidan (band), and Merzbow, side projects by members of Amp and Skullflower and myriad 7" and 10" singles by experimental artists from the UK, US, New Zealand, the Netherlands and Japan. Alongside the label, Johnson also ran a mail order service, stocking rare underground releases from around the world.
Shortly before taking over the label, Johnson began editing a fanzine called Grim Humour, initially covering non-mainstream artists such as Big Black, Swans, Killing Joke, Lydia Lunch, Whitehouse and Sonic Youth. These often came with cassette or vinyl compilations (usually given FD catalogue numbers) with participants including the aforementioned Sonic Youth, Cindytalk, Ausgang, Con Demek and Portion Control. The fanzine ceased in the mid 1990s but Johnson has since launched a new title, Adverse Effect, which has been praised by Record Collector and Ptolemaic Terrascope, lasted four editions and now can be found as a blogspot and via the Fourth Dimension website.
Although Fourth Dimension was dormant for a short while in the late 1990s, it has since relaunched with further releases from Merzbow and Circle, as well as albums by Johnson's own project Theme, The Fields of Hay and British sound artist Andrew Liles. He has also begun a second label, Lumberton Trading Company, a joint venture initially started with Hassni Malik The Vitamin B12. It has issued a number of albums by artists including Experimental Audio Research, Theme, Thighpaulsandra, Human Greed and Michael Gira. More releases are also planned.
Besides the fact Fourth Dimension and Lumberton Trading Company continue to this day, Richard Johnson is still writing about music, is involved in Theme (band), plans to oversee a reissue campaign by his last group, Splintered (band) and is working on a book devoted to his Grim Humour fanzine. Another book dedicated to Adverse Effect will then follow.


List of hyperbolic comets

This is a list of parabolic and hyperbolic comets in the Solar System. Many of these comets may come from the Oort cloud, or perhaps even have interstellar origin. The Oort Cloud is not gravitationally attracted enough to the Sun to form into a fairly thin disk, like the inner Solar System. Thus, comets originating from the Oort Cloud can come from roughly any orientation (inclination to the ecliptic), and many even have a retrograde orbit. By definition, a hyperbolic orbit means that the comet will only travel through the Solar System once, with the Sun acting as a gravitational slingshot, sending the comet hurtling out of the Solar System entirely unless its eccentricity is otherwise changed. Comets orbiting in this way still originate from the Solar System, however. Typically comets in the Oort Cloud are thought to have roughly circular orbits around the Sun, but their orbital velocity is so slow that they may easily be perturbed by passing stars and the galactic tide. Astronomers have been discovering weakly hyperbolic comets that were perturbed out of the Oort Cloud since the mid-1800s.
Prior to finding a well-determined orbit for comets, the JPL Small-Body Database and the Minor Planet Center list comet orbits as having an assumed eccentricity of 1.0. (This is the eccentricity of a parabolic trajectory; hyperbolics will be those with eccentricity greater than 1.0.) In the list below, a number of comets discovered by the SOHO space telescope have assumed eccentricities of exactly 1.0, because most orbits are based on only an insufficient observation arc of several hours or minutes. The SOHO satellite observes the corona of the Sun and the area around it, and as a result often observes sungrazing comets, including the Kreutz sungrazers.
The Kreutz sungrazers originate from the progenitor of the Great Comet of 1106. Although officially given an assumed eccentricity of 1.0, they have an orbital period of roughly 750 years (which would give an actual eccentricity of ~0.99988), and an inclination of 144 degrees. Many of the Kreutz sungrazers do not survive perihelion, as they are quite literally "sungrazers" – their average perihelion distance is 0.0050 AU, and the radius of the Sun is 0.0046 AU; i.e. they pass 50,000 km above the surface of the Sun.
Three other sungrazing groups, the Meyer, Marsden, and Kracht groups, have respectively a perihelion distance of 0.035, 0.044, and 0.049 AU, an inclination of 72, 13, and 26 degrees, and a period of at least a decade, 5.6, and 3–4 years.
Some comets in this list are designated with an X-designation. This is used for comets whose orbits have not been calculated for various reasons: often they were observed so long ago that nobody recorded their location accurately enough for an orbit to be determined, or they were observed in modern times over such a short period that their long-term orbit was too uncertain to calculate.
Interstellar objects generally have strongly hyperbolic orbits, for example the first known object of this class 1I/2017 U1 ʻOumuamua has an eccentricity of 1.192.


Cycleonium

The cycleonium is a computer based music instrument. Every day objects like a bicycle and a bottle, and also a propeller are put in a new context and form the base of the sound design. They lose their conventional function consequently and have to be considered as indispensable parameters of this instrument." It was developed by Daniel Dominguez Teruel from 2007–2009 and built with the support of Chiron-Werke GmbH & Co. KG.
The physical and mechanical work that is required to make this sound-machine sound basically doesn’t differ from traditional musical instruments. For instance, a guitar: it sounds, respectively do we perceive it acoustically, if the strings are excited or the corpus is oscillated somehow or other. So the player expends energy and translates it into the instrument. The user and viewer of the cycleonium is to be made aware of that, in principle, musical instruments are nothing else than objects that only operate with a certain energy expenditure. The energy flow that is emerged thereby plays here a primary role. Therefore we use the word fluxus, but more in a semantically significance (lat. flux, fluidum = flow) than artistic aesthetics. Any kind of sounds require energy to sound. They have self-energy indeed, but it first has to be excited. Otherwise every sound is only a sounding abstraction (they aren’t a perpetual motion machine) that we don't hear. The player of the cycleonium produces, amongst others, kinetic energy that excites a propeller that simultaneously blows air on the aperture of a bottle: a pitched sound is audible.
Description.
"The cycleonium consists basically of four pieces: a bicycle (...), a bottle and a propeller that form the hardware and a computer for software-based sound processing (live-electronics).
The bicycle is rebuilt in such a way that it resembles a stationary bicycle. In this way the propeller can be powered whereby the emerging air flow hits the angle of the aperture of the bottle. Likewise in a flute, a periodical oscillating air column that is perceivable as a tone pitch is produced in the corpus of the bottle [...]. The intensity of the sound depends on the speed of the propeller and consequently on the expended force of the player...The breath of the player and the sound of the chain and arbor of the bicycle are as equally important as the sound of the bottle itself. The produced sounds are amplified and real-time processed.
The live-electronics take place in Max/Msp [...] on a Laptop. The sounds can be pitched, transposed, filtered, recorded and played and processed with delay or reverb. Each Parameter can be controlled with a MIDI-controller. The following microphones are used:
For instance, over the keynote of the bottle can be formed an overtone scale with 15 partials or more that are controllable individually. The spatialization is realized with delays, which can be filtered, pitched and assigned to the respective audio-outputs discretely in real-time [...]. To bring the bottle in the best possible position to the airflow one can adjust it in height, distance and angle to the propeller."
Purpose.
"The player perches on it like on a stationary bicycle and starts to pedal. The midi-controller and the Laptop can be put on a tray that is at the height of the handlebar. By using a dynamic microphone that is at the height of the mouth he can experiment with his [sic] voice respectively breath and modify it per MIDI in real-time. The sound of the arbor at the propeller and the chain is recorded with a condenser microphone (cardioid). Through reverse turns of the pedals the sound of chain and arbor becomes more concisely and is at the same time a variation of sound. By alternating forward and reverse turns a percussive rhythmical complement is built to the laminary sound of the bottle that mainly can be modified in the pitch. Dense and complex structures of sound can be achieved by adding overtones, glissandi and delays."
From the work with the cycleonium Daniel Dominguez Teruel developed the piece "5 Klangaktionen" that was nominated for the competition for electroacoustic music IMEB Bourges 2009. Also in 2009 the cycleonium was presented at the "6th Sound and Music Computing Conference" in Porto and the "ton:art" in Karlsruhe.


Sri Lankan units of measurement

A number of different units of measurement were used in Sri Lanka to measure quantities like length, mass and capacity from very ancient times. Under the British Empire, imperial units became the official units of measurement and remained so until Sri Lanka adopted the metric system in the 1970s.
Traditional units.
Various units were used in Sri Lanka at different times and some only in certain regions. Some of these remained in use well into the colonial period. The following is only a partial list.
Length.
One covid was equal to 0.464 m (18.5 in). The Bam̆ba (Fathom), still in use as of 2016, is the distance between a man's outstretched arms. It is roughly 6 feet in length. "Bam̆ba" is usually used to measure depth in wells and pits. Units used in measuring long distances included the "Gavuva", "Yoduna", and "Usaba" (plurals Gavu and Yodun - a Yoduna was 4 Gavu) and the "hoo kiyana dura", which was the audible distance of a shout of 'hoo' by a person. Base of these system of measuring length was the human body.
King Nisshankamalla have established milestones called "Gaavutha Kanu" from a Gavu to another. Two of such have been found in Katugahagalge and Valigaththa in Southern Province.
The smallest unit was known as "Paramaanuwa", which was equal to (). A typical span was taken roughly equal to 22.86 cm (9 in). These small units of measurement were used in making of statues and buildings. Following are the relationships between the units used in ancient times.
Area.
Measurements of area used in ancient Sri Lanka was a system derived from paddy agriculture. Area was often measured in terms of the land that could be sown with a specific amount of seed or rice, including the Pǣla, Amuna, Kiriya (4 amunas), and the Riyana. In one region, a Kiriya was about 8 acres. Following are relationships between some typical measures of area.
In an stone inscription written by King Bhathikabhaya Abhaya at Dunumadalakanda in Anuradhapura District, it is stated that he offered a land of 1 Kareesa to a temple in the area. In another stone inscription written by King Kutakannabhaya Thissa at Horiwila in Anuradhapura District, it is stated that he offered a land of 8 Kareesa to a temple named 'Thissa' in the area.
James Prinsep, writing in 1840, stated that "at ... Ceylon ... English measures only are used, or at least a cubit based on the English measure of 18 inches."
Weight.
One candy, or one bahar, was equal to 226.8 kg, or 500 lbs, or according to "The Indian Trader's Guide" 480 Dutch pounds or 520 pounds Avoirdupois. Small weights could be measured in seeds, such as the Thala (Sesame), Amu, Vee (Rice) (3 Amu), Madati (8 Vee), Majadi, Maditi, Kalanda, and Manjadi. In ancient times, there have been an accurate system to measure weights. Following are some such weight measuring units used. Units like Madati ( "Adenanthera pavonina" ), Vee (Rice) are based on weights of those seeds.
It is stated that frauds in weighing was a punishable offence and only weights approved by the government should be used in weighing, in Sorabora Wewa Pillar Inscription (Badulla Pillar Inscription) which was written by King Udaya IV.
Capacity.
Different units were used for liquid and dry capacity.
Liquid.
One seer was equal to 1.2 quarts and one parrah was equal to 6.75 gallons. Another source suggests that a seer was equal to 1.86 imperial pints or 1.06 litres. These were mostly introduced in the period which coastal areas were governed by Portuguese and Dutch.
Dry.
Units to measure dry capacities were mainly used in agriculture. Some of them are as following:
One ammonam was equal to 203.4 l. One parrah = ammonam, oneseer = ammonam and the chundoo was equal to nearly half a pint.
Maccauly stated in 1818 that to the north of Colombo an "Ammonam" contained 16 "Parahs", and "Ammonams" equalled one "Acre", but that to the south there were 8 "Parahs" to the "Ammonam". He describes the "Parah" as a measure 16.7 inches wide and 5.6 inches deep.
Montgomery, writing in 1835, described the interior measurement of a "Parrah" as a perfect cube of 11.571 inches, and the seer as a cylinder of depth 4.35 inches and diameter 4.35 inches.


Vibing Up the Senile Man (Part One)

Vibing Up the Senile Man (Part One) is the second studio album by English rock band Alternative TV, released in March 1979 by record label Deptford Fun City. On this album, the band followed an even more experimental and avant-garde approach than on "The Image Has Cracked" (1978).
Recording.
The album's tracks were all reportedly recorded in a single take.
Musical style.
Regarding its musical style, Alternative TV frontman Mark Perry recalled: "There are free jazz influences; I'd got into the Art Ensemble of Chicago, Sun Ra [...] I'd moved into this house with an amazing music room – pianos, clarinets, you name it – and we'd always be picking up stuff from junk shops."
Reception.
According to Simon Reynolds in "", the album received a "uniformly hostile" response from reviewers upon its release. "Trouser Press" described the record as being "up the pseudo-avant creek without a paddle".
in his retrospective review of the album, Dean McFarlane of AllMusic noted: "On the second album of Alternative TV, Mark Perry and friends did to punk exactly what the movement had intended for the establishment. About-facing punk and turning it on its ear would be a difficult task in 1980, and while Alternative TV's peers headed down new wave paths or into commercialism [...] who would have expected a follow-up as avant-garde abstraction that challenges P.I.L's "Second Edition" for absolute left-field swing? With Genesis P-Orridge in the ranks, "Vibing Up the Senile Man" became closer to free improvisation and avant-garde jazz without a punk anthem in sight, and a dub edge to some of the tracks of the double LP suggest that Alternative TV had similar modernist aspirations to John Lydon's post-Sex Pistols project. Captain Beefheart and Frank Zappa spring to mind as much as Pere Ubu and the Red Krayola, who were similarly exploring the avant-garde liberties of post-punk and disappointing the punks and record industry alike. What "Vibing Up the Senile Man" represents two decades later is a door opening on multi-faceted post-rock music – which draws on avant-garde, noise and jazz and arguably makes more sense in the context of year 2000 as a musical treasure much more than in 1980, when it seemed simply a spit in the eye to the industry that codified punk."
Legacy.
Paul Hegarty, in "Noise Music: A History", described the album as "forming the bridge into industrial music".
The record was placed at number 19 on "Mojo"'s list of readers' choice of 50 "Weirdest Albums".


Multiple granularity locking

In computer science, multiple granularity locking (MGL) is a locking method used in database management systems (DBMS) and relational databases.
In multiple granularity locking, locks are set on objects that contain other objects. MGL exploits the hierarchical nature of the "contains" relationship. For example, a database may have files, which contain pages, which contain records. This can be thought of as a tree of objects, where each node contains its children. A lock on this structure (such as a shared or exclusive lock) locks the targeted node as well as all of its descendants.
Multiple granularity locking is usually used with non-strict two-phase locking to guarantee serializability.
Lock modes.
In addition to shared (S) locks and exclusive (X) locks from other locking schemes, like strict two-phase locking, MGL also uses intentional "locks", which do not directly lock a node, but instead denote the existence, or intent to add, a lock of the specified type lower in the node hierarchy. Intentional locks include "intention shared" (IS), "intention exclusive" (IX), and the combined "shared and intention exclusive" (SIX) locks. IS locks conflict with X locks, while IX locks conflict with S and X locks. The null lock (NL) is compatible with everything.
To lock a node in S (or X), MGL has the transaction lock on all of its ancestors with IS (or IX), so if a transaction locks a node in S (or X), no other transaction can access its ancestors in X (or S and X). This protocol is shown in the following table:
Determining what level of granularity to use for locking is done by locking the finest level possible (i.e., at the lowest leaf), and then escalating these locks to higher levels in the file hierarchy to cover more records or file elements as needed in a process known as "lock escalation". MGL locking modes are compatible with each other as defined in the following matrix.
Following the locking protocol and the compatibility matrix, if one transaction holds a node in S mode, no other transactions can have locked any ancestor in X mode.


Tucker (dog)

Tucker is a scat detection dog famous for his ability to find orca scat from the prow of a boat. A black Labrador retriever mix, he was born in August 2004, and adopted by Conservation Canines in May 2006 from SnoLine Kennels in Arlington, WA. Aside from studying resident killer whales in Washington state, he has twice been to the Alberta oil sands to survey for caribou, grey wolf, and moose, and he has located iguanas in the Caribbean.


Limma

The word limma or leimma (from Greek: λείμμα, "leimma"; meaning "remnant") can refer to several different musical intervals, whose only common property is their small size.


Hemispherical electron energy analyzer

A hemispherical electron energy analyzer or hemispherical deflection analyzer is a type of electron energy spectrometer generally used for applications where high energy resolution is needed—different varieties of electron spectroscopy such as angle-resolved photoemission spectroscopy (ARPES), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) or in imaging applications such as photoemission electron microscopy (PEEM) and low-energy electron microscopy (LEEM).
It consists of two concentric conductive hemispheres that serve as electrodes that bend the trajectories of the electrons entering a narrow slit at one end so that their final radii depend on their kinetic energy. The analyzer, therefore, provides a mapping from kinetic energies to positions on a detector.
Function.
An ideal hemispherical analyzer consists of two concentric hemispherical electrodes (inner and outer hemispheres) of radii formula_1 and formula_2 held at proper voltages. In such a system, the electrons are linearly dispersed, depending on their kinetic energy, along the direction connecting the entrance and the exit slit, while the electrons with the same energy are first-order focused.
When two voltages, formula_3 and formula_4, are applied to the inner and outer hemispheres, respectively, the electric potential in the region between the two electrodes follows from the Laplace equation:
The electric field, pointing radially from the center of the hemispheres out, has the familiar planetary motion formula_6 form
The voltages are set in such a way that the electrons with kinetic energy formula_8 equal to the so-called "pass energy" formula_9 follow a circular trajectory of radius formula_10. The centripetal force along the path is imposed by the electric field formula_11. With this in mind,
The potential difference between the two hemispheres needs to be
A single pointlike detector at radius formula_14 on the other side of the hemispheres will register only the electrons of a single kinetic energy. The detection can, however, be parallelized because of nearly linear dependence of the final radii on the kinetic energy. In the past, several discrete electron detectors (channeltrons) were used, but now microchannel plates with phosphorescent screens and camera detection prevail.
In general, these trajectories are described in polar coordinates formula_15 for the plane of the great circle for electrons impinging at an angle formula_16 with respect to the normal to the entrance, and for the initial radii formula_17 to account for the finite aperture and slit widths (typically 0.1 to 5 mm):
As can be seen in the pictures of calculated electron trajectories, the finite slit width maps directly into energy detection channels (thus confusing the real energy spread with the beam width). The angular spread, while also worsening the energy resolution, shows some focusing as the equal negative and positive deviations map to the same final spot.
When these deviations from the central trajectory are expressed in terms of the small parameters formula_20 defined as formula_21, formula_22, and having in mind that formula_16 itself is small (of the order of 1°), the final radius of the electron's trajectory, formula_24, can be expressed as
If electrons of one fixed energy formula_8 were entering the analyzer through a slit that is formula_27 wide, they would be imaged on the other end of the analyzer as a spot formula_27 wide. If their maximal angular spread at the entrance is formula_16, an additional width of formula_30 is acquired, and a single energy channel is smeared over formula_31 at the detector side. But there, this additional width is interpreted as energy dispersion, which is, to the first order, formula_32. It follows that the instrumental energy resolution, given as a function of the width of the slit, formula_27, and the maximal incidence angle, formula_16, of the incoming photoelectrons, which is itself dependent on the width of the aperture and slit, is
The analyzer resolution improves with increasing formula_14. However, technical problems related to the size of the analyzer put a limit on its actual value, and most analyzers have it in the range of 100–200 mm. Lower pass energies formula_9 also improve the resolution, but then the electron transmission probability is reduced, and the signal-to-noise ratio deteriorates accordingly.
The electrostatic lenses in front of the analyzer have two main purposes: they collect and focus the incoming photoelectrons into the entrance slit of the analyzer, and they decelerate the electrons to the range of kinetic energies around formula_9, in order to increase the resolution.
When acquiring spectra in "swept" (or "scanning") mode, the voltages of the two hemispheres – and hence the pass energy – are held fixed; at the same time, the voltages applied to the electrostatic lenses are swept in such a way that each channel counts electrons with the selected kinetic energy for the selected amount of time. In order to reduce the acquisition time per spectrum, the so-called "snapshot" (or "fixed") mode can be used. This mode exploits the relation between the kinetic energy of a photoelectron and its position inside the detector. If the detector energy range is wide enough, and if the photoemission signal collected from all the channels is sufficiently strong, the photoemission spectrum can be obtained in one single shot from the image of the detector.


National Testing Agency

National Testing Agency (NTA) is an Indian government agency that has been approved by the Union Council of Ministers and established in November 2017 to conduct entrance examinations for higher educational institutions. The government appointed Vineet Joshi as the first Director-General of the agency. NTA is responsible for conducting the Joint Entrance Examination – Main (JEE Main), National Eligibility cum Entrance Test-Undergraduate (NEET UG), National Eligibility Test (NET), Common Management Admission Test (CMAT) and Graduate Pharmacy Aptitude Test (GPAT).
History.
The roots of the agency can be traced to the Programme of Action 1992, related to National Policy of Education 1986, which mentioned conducting national level common entrance tests to professional and non-professional programmes of study. Its actual start was in 2010 with a report submitted to the Ministry of Human Resources Development (MHRD) by a committee consisting of some of the directors of the Indian Institutes of Technology (IITs), which recommended that the national testing agency be "created by an Act of Parliament". The report mentioned that a statutory agency can ensure independence and transparency in testing of the magnitude that is being envisaged. In 2013 the MHRD constituted a seven member task force to "prepare a blue print for creating a special purpose vehicle to take the concept of National Testing Agency (NTA) forward". This was following a decision made in April 2013 to set up the agency. In 2017 an announcement about NTA was made by the Finance Minister in the budget speech of 2017, and this was followed by cabinet approval.
On 7 July 2018, Union HRD Minister Prakash Javadekar stated during a press conference that the NTA will be holding the Joint Entrance Examination – Main (JEE Main) and the National Eligibility cum Entrance Test-Undergraduate (NEET UG) twice a year, and will also be holding National Eligibility Test (NET), Common Management Admission Test (CMAT) and Graduate Pharmacy Aptitude Test (GPAT).
Finance.
Union cabinet has granted an initial amount of to NTA to start its operations in the first year.
Members and their nature.
The administration of the NTA has been entrusted to the Governing Body.
Examinations conducted by NTA.
NTA conducts the following examinations.
Controversies and credibility of NTA.
2020 JEE Main Assam topper scam.
In 2020 Neel Nakshatra Das, a candidate for JEE Mains used a substitute to give the exam. He subsequently scored 99.8 per cent and topped in his state, Assam. Seven persons have been arrested including Bhargav Deka, owner of a city-based coaching institute Global Edu Light, Tata Consultancy Services employees, the candidate (Neel Nakshatra Das), Neel's father - Dr. Jyotirmoy Das, and an invigilator.
NEET (UG) related.
In NEET (UG) 2020 exam, NTA incorrectly declared that Vidhi Suryavanshi of Madhya Pradesh’s Chhindwara district had only scored 6 marks which were later found out to be false after Vidhi committed suicide. Vidhi's response sheet proved that she had actually scored 590 marks.
In NEET (UG) 2020 exam, NTA had allegedly declared Mridul Rawat as failed. Rawat claimed that he challenged the NTA and after rechecking his OMR sheet and Answer Key, it was found that he is an All India Topper (ST Category). Rawat also claimed that even after the rechecking, in the revised scorecard, his score was 650 but only three hundred twenty-nine were written in words. NTA refuted the claims of Mridul Rawat. Director-General Vineet Joshi of NTA said “An aspirant has claimed that he has 650 marks whereas he has obtained 329 marks in NEET 2020 results. The emails purported to have been written by NTA are also fake. This news has been broadcast by some local news channels in some cities. This news is totally fake, fabricated, and one-sided and news channels should have confirmed from NTA prior to broadcasting it. In the instant case, a complaint is being filed by NTA with the cybersecurity cell under the IT Act at Noida, UP.”


750 Oskar

750 Oskar is a minor planet orbiting the Sun that was discovered by Johann Palisa on 28 April 1913 in Vienna. Photometric observations made in 2012 at the Organ Mesa Observatory in Las Cruces, New Mexico, produced a light curve with a period of 6.2584 ± 0.0002 hours and a brightness variation of 0.21 ± 0.02 in magnitude. This is a member of the Nysa family of asteroids that share similar orbital elements.


John J. Hopfield (spectroscopist)

John Joseph Hopfield (8 August 1891 – 8 January 1953) was a Polish-American spectroscopist, discoverer of the Hopfield bands of oxygen and co-discoverer of the Lyman-Birge-Hopfield bands of nitrogen. Hopfield's major research pursuits included vacuum ultraviolet spectroscopy and solar ultraviolet spectroscopy. He was well known in these disciplines. Hopfield published frequently and produced several patents.
Life and education.
Hopfield was born in Poland in 1891. In 1917 he received an A.B. from Syracuse University. From 1918 to 1920 he continued at Syracuse as a Physics Instructor.
For the term 1920–1921 Hopfield was awarded a Whiting Research Fellowship. From 1921 to 1923 he was Associate in Physics, then from 1923 to 1925 was Instructor in Physics, and in 1925 appointed to Assistant Professor of Physics at the University of California, Berkeley.
Hopfield earned his Ph.D. in Physics, Chemistry in 1923 from the University of California, Berkeley. His advisor was Raymond T. Birge and his thesis subject was: "Spectra of hydrogen, nitrogen, and oxygen in the extreme ultra-violet".
At Berkeley, a graduate student working under Hopfield was Gerhard Heinrich Dieke.
In 1928 John Joseph Hopfield received a Guggenheim Fellowship appointment: "for experimental study of the Zeeman effect on the infra-red spectra of oxygen and nitrogen with reference to the classification of the extreme ultra-violet spectra of these elements, chiefly with Professor F. Paschen, of Berlin."
By the time he left Berlin in 1929, the stock market crash and depression had ended most new faculty hiring. Purdue University appointed him as a National Research Council Fellow for two years. He next was employed in creating the physics exhibit for the 1933 ‘Century of Progress’ World’s Fair in Chicago, followed by a position with the Libby-Owens-Ford glass company in Toledo Ohio. With the onset of WWII, physicists were again in great demand, and he moved to Washington DC to participate in war-related research. The end of his career was spent at the Johns Hopkins Applied Physics Laboratory and at the Naval Research Laboratory in the Optics Division in Washington, D.C.. On 8 January 1953, Hopfield died after a brief illness.
Known for and credits.
John J. Hopfield is known and credited for:


GACE

The Georgia Assessments for the Certification of Educators, also known as GACE (abbreviated) is a standardized test all teachers in the US state of Georgia must pass in order to teach at public schools and gain a credential.
The basic skills section is divided into three parts, three multiple choice (selected-response) sections of Reading, Writing, and Mathematics and one essay (constructed-response) portion which is part of the Writing section. Timing is for the entire exam, so examinees may take as much time in any testing area as needed, however the total exam time is four hours.


August Herman Pfund

August Herman Pfund (December 28, 1879 – January 4, 1949) was an American physicist, spectroscopist, and inventor.
Early life.
Pfund was born in Madison, Wisconsin and attended Wisconsin public schools until his entry into the University of Wisconsin–Madison, where he earned a B.S. degree in physics and studied under Robert W. Wood.
Career.
Both Wood and Pfund left Wisconsin for Johns Hopkins University in 1903. From 1903 to 1905 Pfund was a Carnegie research assistant and continued to work under Wood. In 1906 Pfund earned his Ph.D. in physics and was a Johnston scholar from 1907 to 1909. He remained at Hopkins for the remainder of his career, eventually becoming a full professor and later chair of the physics department. From 1943 to 1944 Pfund served as the president of the Optical Society of America.
Within the hydrogen spectral series Pfund discovered the fifth series, where an electron jumps up from or drops down to the fifth fundamental level. This Series is known as the "Pfund series". He also invented the Pfund telescope, which is a method for achieving a fixed telescope focal point regardless of where the telescope line of sight is positioned, and the Pfund sky compass, which arose from Pfund's studies of the polarization of scattered light from the sky in 1944, and which greatly helped transpolar flights by allowing the determination of the Sun's direction in twilight. Pfund is also noted for his work into the area of infrared gas analysis.


German submarine U-480

U-480 was an experimental "Kriegsmarine" Type VIIC U-boat of World War II. Considered by many to be the first stealth submarine, it was equipped with a special rubber coating (codenamed "Alberich", after the German mythological character who had the ability to become invisible), that made it difficult to detect with British ASDIC (sonar).
The U-boat was laid down in the Deutsche Werke in Kiel as yard number 311 on 8 August 1942, launched on 14 August 1943 and commissioned on 6 October 1943 under "Oberleutnant zur See" Hans-Joachim Förster. "U-480" carried out three war patrols, all under Förster's command. Because of its coating, the boat was sent to the heavily defended English Channel. The "Alberich" worked; "U-480" was never detected by sonar.
Design.
German Type VIIC submarines were preceded by the shorter Type VIIB submarines. "U-480" had a displacement of when at the surface and while submerged. She had a total length of , a pressure hull length of , a beam of , a height of , and a draught of . The submarine was powered by two Germaniawerft F46 four-stroke, six-cylinder supercharged diesel engines producing a total of for use while surfaced, two Siemens-Schuckert GU 343/38–8 double-acting electric motors producing a total of for use while submerged. She had two shafts and two propellers. The boat was capable of operating at depths of up to .
The submarine had a maximum surface speed of and a maximum submerged speed of . When submerged, the boat could operate for at ; when surfaced, she could travel at . "U-480" was fitted with five torpedo tubes (four fitted at the bow and one at the stern), fourteen torpedoes, one SK C/35 naval gun, (220 rounds), one Flak M42 and two twin C/30 anti-aircraft guns. The boat had a complement of between forty-four and sixty.
Service history.
On its first patrol, the boat was attacked by a Canadian PBY Catalina flying boat of 162 Squadron RCAF, piloted by Laurance Sherman. The aircraft was shot down.
On the second patrol, Förster departed from Brest in occupied France on 3 August 1944, and sank two warships and two merchantmen:
For his success, Förster was awarded the Knight's Cross on 18 October 1944.
Fate.
"U-480" left Trondheim, Norway, on 6 January 1945 for its third and last patrol. It did not return. In 1997, the wreck of a Type VIIC U-boat was discovered by accident by divers at , southwest of the Isle of Wight. The following year, it was correctly identified as the Alberich-coated "U-480" by nautical archaeologist Innes McCartney. Subsequent research by the Naval Historical Branch established that it had fallen victim to the secret minefield 'Brazier D2' some time between 29 January and 20 February. A mine had damaged the stern of "U-480", sending it to the bottom down. The entire crew of 48 was lost. Helmsman Horst Rösner only survived because he had been left behind in Norway for training.
The coating.
The Germans developed a 4-millimetre (0.16 in) thick sheet of synthetic rubber anechoic tile. The coating reduced echoes by 15% in the 10 to 18 kHz range. This frequency range matched the operating range of the early ASDIC active sonar used by the Allies. The ASDIC types 123, 123A, 144 and 145 all operated in the 14 to 22 kHz range. However, this degradation in echo reflection was not uniform at all diving depths due to the voids being compressed by the water pressure. An additional benefit of the coating was it acted as a sound dampener, containing the U-boat’s own engine noises.
The rubber contained a series of holes, which helped break up sound waves. There were problems with this technology: the material performed differently at different depths, due to the holes being compressed by water pressure, and securing the tiles to the submarine's hull required a special adhesive and careful application. The first tests were conducted in 1940, but it was not used operationally until 1944, with "U-480". According to the "Naked Science" television episode "Stealth Submarine", "U-480" had a perforated inner rubber layer covered by a smooth outer one. This formed air pockets with the right separation and size to muffle sonar waves.


4796 Lewis


Second solar spectrum

The second solar spectrum is an electromagnetic spectrum of the Sun that shows the degree of linear polarization. The term was coined by V. V. Ivanov in 1991. The polarization is at a maximum close to the limb (edge) of the Sun, thus the best place to observe such a spectrum is from just inside the limb. It is also possible to get polarized light from outside the limb, but since this is much dimmer compared to the disk of the Sun, it is very easily polluted by scattered light.
The second solar spectrum differs significantly from the solar spectrum determined by the intensity of light.
Large effects come around the Ca II K and H line. These have broad effects 200 Å wide and show a sign reversal at their centers. Molecular lines with stronger polarization than the background due to MgH and C2 are common. Rare-earth elements stand out far more than expected from the intensity spectrum.
Other odd lines include Li I at 6708 Å which has 0.005% more polarization at its peak, but is almost unobservable in the intensity spectrum. The Ba II 4554 Å appears as a triplet in the second solar spectrum. This is due to differing isotopes and hyperfine structure.
Two lines at 5896 Å 4934 Å being the D1 lines of sodium and barium were predicted not to be polarized, but nevertheless are present in this spectrum.
Continuum.
The continuum in the spectrum is the light with wavelengths between the lines. Polarization in the continuum is due to Rayleigh scattering by neutral hydrogen atoms (H I) and Thomson scattering by free electrons. Most of the opacity in the sun is due to the hydride ion, H− which however does not alter polarization. In 1950 Subrahmanyan Chandrasekhar came up with a solution for the degree of polarization due to scattering, and predicted 11.7% polarization at the limb of the Sun. But nowhere near this level is observed. What happens at the limb is that there is a forest of spicules poking out from the edge, so it is not possible to get parallel to such a rough surface.
For most of the solar disk the degree of linear polarization of the continuum is under 0.1%, but it rises to 1% at the limb. The polarization also depends strongly on the wavelength, and for near ultraviolet 3000 Å the light near the limb is 100 times more polarized than red light at 7000 Å. At the limit of the Balmer series a change happens where at shorter wavelengths more bound-bound Balmer series transitions cause more opacity. This extra opacity drops the polarization degree by a factor of two near 3746 Å.


2857 NOT


Parity plot

A parity plot is a scatterplot that compares experimental data against tabulated data. Each point has coordinates ("x", "y"), where "x" is the tabulated value, and "y" is the corresponding experimental value.
A line of the equation "y" = "x" is sometimes added as a reference. When an experimental value equals a tabulated value, the point will lie on the line.
Parity plots are found in scientific papers and reports, when the author wishes to compare their data to accepted values in an easily understandable way.


Spatially offset Raman spectroscopy

Spatially offset Raman spectroscopy (SORS) is a variant of Raman spectroscopy that allows highly accurate chemical analysis of objects beneath obscuring surfaces, such as tissue, coatings and bottles. Examples of uses include analysis of: bone beneath skin, tablets inside plastic bottles, explosives inside containers and counterfeit tablets inside blister packs. There have also been advancements in the development of deep non-invasive medical diagnosis using SORS with the hopes of being able to detect breast tumors.
Raman spectroscopy relies on inelastic scattering events of monochromatic light to produce a spectrum characteristic of a sample. The technique usually uses the red-shifted photons produced by monochromatic light losing energy to a vibrational motion within a molecule. The shift in colour and the probability of inelastic scatter is characteristic of the molecule that scatters the photon. A molecule may produce over 10 to 20 major lines, though this is restricted only by the number of bonds and symmetry constraints. Importantly, the spectrum produced by a mixture forms a linear combination of the component spectra, enabling relative chemical content to be determined in a simple spectroscopic measurement using chemometric analysis.
Methods.
Conventional Raman spectroscopy is limited to the near-surface of diffusely scattering objects. For example, with tissue it is limited to the first few hundred micrometres depth of surface material. Raman spectroscopy is used for this purpose in many applications where its high chemical specificity enables chemical mapping of surfaces, e.g., tablet mapping. Measurement beyond the surface of diffusely scattering samples is limited because the signal intensity is high in the region of laser excitation and that dominates the collected signal.
The basic SORS technique was invented and developed by Pavel Matousek, Anthony Parker and collaborators at the Rutherford Appleton Laboratory in the UK. The method relies upon the fact that most materials are neither completely transparent to light nor completely block it, but that they tend to scatter the light. An example is when a red laser pointer illuminates the end of a finger - the light scatters throughout all of the tissue in the finger. Wherever the light goes there will be some inelastic scattering due to the Raman effect, so, at some point, most parts of an object will generate a detectable Raman signal, even if it is not at the surface. The trick with SORS is to make a measurement that avoids the dominating excitation region.
A SORS measurement will make at least two Raman measurements; one at the source and one at an offset position of typically a few millimetres away. The two spectra can be subtracted using a scaled subtraction to produce two spectra representing the subsurface and surface spectra. For a simple two-layer system, such as powder in a plastic bottle, the powder spectrum can be measured without knowing the bottle material or its relative signal contribution. To do this without using an offset measurement would be severely restricted by photon shot noise generated by Raman and fluorescence signals originating from the surface layer.
Scaled subtraction works well for two-layer systems but more complicated examples, such as where the overlying material contains components included in the sub-layer (living tissue, for example), may require multi-variate analysis. When multi-variate techniques, such as principal component analysis are used, it is necessary to take several spectra at varied offset distances. As the spatial offset increases the ratio of the spectral contribution sub-surface/surface increases. However, the total signal also decreases with increasing offset, so the ratio cannot increase forever in a practical measurement.
Inverse SORS is a useful sub-variant of SORS that improves certain measurements such as analysis of tissue "in vivo". Rather than use a spot collection geometry and a circular spot for illumination the constant offset can be maintained by illuminating the sample with a ring of light centred on the collection region. This has several advantages, including lowering the total power density and allowing simple manipulation of offset distance.
Micro-spatially offset Raman spectroscopy (micro-SORS) combines SORS with microscopy. The main difference between SORS and micro-SORS is the spatial resolution: while SORS is suited to the analysis of millimetric layers, micro-SORS is able to resolve thin, micrometric-scale layers.


2379 Heiskanen


Benchtop nuclear magnetic resonance spectrometer

A Benchtop nuclear magnetic resonance spectrometer (Benchtop NMR spectrometer) refers to a Fourier transform nuclear magnetic resonance (FT-NMR) spectrometer that is significantly more compact and portable than the conventional equivalents, such that it is portable and can reside on a laboratory benchtop. This convenience comes from using permanent magnets, which have a lower magnetic field and decreased sensitivity compared to the much larger and more expensive cryogen cooled superconducting NMR magnets. Instead of requiring dedicated infrastructure, rooms and extensive installations these benchtop instruments can be placed directly on the bench in a lab and moved as necessary ("e.g.," to the fumehood). These spectrometers offer improved workflow, even for novice users, as they are simpler and easy to use. They differ from relaxometers in that they can be used to measure high resolution NMR spectra and are not limited to the determination of relaxation or diffusion parameters ("e.g.," T1, T2 and D).
Magnet development.
This first generation of NMR spectrometers used large Electromagnets weighing hundreds of kilograms or more. Slightly smaller permanent magnet systems were developed in the 1960s-70s at proton resonance frequencies at 60 and 90 MHz and were widely used for chemical analysis using continuous wave methods but these permanent magnets still weighed hundreds of kilograms and could not be placed on a benchtop. Superconducting magnets were developed to achieve stronger magnetic fields for higher resolution and increased sensitivity. However, these superconducting magnets are expensive, large, and require specialized building facilities. In addition, the cryogens needed for the superconductors are hazardous, and represent an ongoing maintenance cost. As a result, these instruments are usually installed in dedicated NMR rooms or facilities for use by multiple research groups.
Since the early 2000s there has been a renaissance in permanent-magnet technology and design, with advances sufficient to allow development of much smaller NMR instruments with useful resolution and sensitivity for education, research and industrial applications. Samarium–cobalt and neodymium magnets in particular are strong enough for instruments up to 90 MHz. These smaller designs, which operate with magnet temperatures from room temperature to 60°C, allow instruments to be made small enough to fit on a lab bench, and safe to operate in a typical lab environment. They require only single phase local power and with UPS systems can be made portable and can perform NMR analyses at different points in the manufacturing area.
Disadvantage of Small-Size Magnets and Method to Overcome It.
One of the biggest disadvantages of low-field (0.3-1.5T) NMR spectrometers is the temperature dependence of the permanent magnets used to produce the main magnetic field. For small magnets there was a concern that the intensity of external magnetic fields may adversely affect the main field, however the use of magnetic shielding materials inside the spectrometer eliminates this problem. The currently available spectrometers are easily moved from one location to another, including some that are mounted on portable trolleys with continuous power supplies. Another related difficulty is that currently available spectrometers do not support elevated sample temperatures which may be required for some in-situ measurements in chemical reactions.
A recent paper suggests that a special experimental setup, with two or more coils and synchronous oscillators, may help overcome this problem and allow it to work with unstable magnetic fields and with affordable oscillators.
Applications.
NMR spectroscopy can be used for chemical analysis, reaction monitoring, and quality assurance/quality control experiments. Higher-field instruments enable unparalleled resolution for structure determination, particularly for complex molecules. Cheaper, more robust, and more versatile medium and low field instruments have sufficient sensitivity and resolution for reaction monitoring and QA/QC analyses. As such permanent magnet technology offers the potential to extend the accessibility and availability of NMR to institutions that do not have access to super-conducting spectrometers ("e.g.," beginning undergraduates or small-businesses).
Many automated applications utilizing multivariate statistical analyses (chemometrics) approaches to derive structure-property and chemical and physical property correlations between 60 MHz 1H NMR spectra and primary analysis data particularly for petroleum and petrochemical process control applications have been developed over the past decade.
Available Benchtop NMR Spectrometers.
Development of this new class of spectrometers began in the mid-2000s leaving this one of the last molecular spectroscopy techniques to be made available for the benchtop.
Spinsolve.
New Zealand- and Germany-based Magritek's Spinsolve instrument, operating at 80 MHz, 60 MHz and 42.5 MHz, offers very good sensitivity and resolution less than 0.5 Hz and weighs under 73 kg, 60 kg and 55 kg respectively. The ULTRA model has an even higher resolution of 0.2 Hz with a lineshape of 0.2 Hz/ 6 Hz/ 12 Hz comparable to high field NMR specifications. 1D Proton, 19F Fluorine, 13C Carbon and 31P Phosphorus as well as T1, T2 and 2D HETCOR, HMBC, HMQC, COSY and JRES spectra can be measured. The magnet is stabilised with an external lock, which means it does not require the use of deuterated solvents. Samples are measured using standard 5 mm NMR tubes and the spectrometer is controlled through an external computer where standard NMR data collection and processing takes place.
picoSpin.
In 2009, picoSpin LLC, based in Boulder, Colorado, launched the first benchtop NMR spectrometer with the picoSpin 45. A small (7 x 5.75 x 11.5”) 45 MHz spectrometer with good resolution (< 1.8 Hz) and mid-to-low-range sensitivity that weighs 4.76 kg (10.5 lbs) and can acquire a 1D 1H or 19F spectra. PicoSpin was acquired by Thermo Fisher Scientific in December 2012, and subsequently renamed the product Thermo Scientific picoSpin 45. Instead of the traditional static 5 mm NMR tubes, the picoSpin 45 spectrometer uses a flow-through system that requires sample injection into a 1/16” PTFE and quartz capillary. Deuterated solvents are optional due to the presence of a software lock. It needs only a web browser on any external computer or mobile device for control as the spectrometer has a built-in web server board; no installed software on a dedicated PC is required. In August 2013 a second version was introduced, the Thermo Scientific picoSpin 80, that operates at 82 MHz with a resolution of 1.2 Hz and ten times the sensitivity of the original picoSpin 45.
NMReady.
Calgary, AB, Canada based Nanalysis Corp offers two NMReady 60 MHz benchtop NMR instruments that weigh 25 kg. The spectrometers are all-in-one units, controlled by a touchscreen computer that is contained within the same enclosure as the magnet. The NMReady 60e model performs 1D 1H and 19F experiments as well as T1, T2, JRES and COSY. In addition, the NMReady 60Pro is a dual nuclei instrument that can also be tuned to 13C, 31P, 11B, and 7Li and perform DEPT, HSQC, HMBC, with options for additional experiments like signal suppression. The magnet is stabilized with an internal 2H lock so the use of deuterated solvents is recommended but not required. These spectrometers offer resolution < 1.2 Hz, use standard 5 mm NMR tubes, and are compatible with most third-party software suites.
In late 2020, Nanalysis made the 100e and the 100PRO models available. They offer 1D and 1D+2D modes, at 100 MHz, and 2.35 T. The machine weights about 25 kg
X-Pulse / Pulsar.
In 2019, Oxford Instruments launched a new 60 MHz spectrometer called X-Pulse. This instrument is a significant improvement on the previous Pulsar system, launched in 2013. X-Pulse has the highest, as standard, resolution (<0.35 Hz / 10Hz) of the currently available benchtop, cryogen-free NMR analysers. It incorporates a 60 MHz rare-earth permanent magnet. X-Pulse is the only benchtop NMR system to offer a full broadband X channel for the allowing the measurement of 1H,19F, 13C, 31P, 7Li, 29Si, 11B and 23Na on a single probe. A large range of 1D and 2D measurements can be performed on all nuclei, 1D spectra, T1, T2, HETCOR, COSY, HSQC, HMBC, JRES, and many others including solvent suppression and selective excitation. X-Pulse also has options for flow NMR and a variable temperature probe allowing the measurement of samples in NMR tubes at temperatures from 20°C to 60°C. The magnet and spectrometer are in two separate boxes with the magnet weighing 149 kg and the electronics weighing 22 kg. X-Pulse requires a standard mains electrical supply and uses standard 5mm NMR tubes. Instrument control comes from the SpinFlow workflow package, while the processing and manipulation of data is achieved using third-party NMR software suites. Pulsar instruments were discontinued in 2019 following the launch of X-Pulse.
Bruker.
In 2019, Bruker, a long time manufacturer and market leader of high performance NMR machines, introduced a Benchtop NMR, Fourier 80 FT-NMR. The machine uses permanent magnets, and operates using Bruker standard software (a full futured TopSpin 4 software for Windows and Linux; as well Python based API from Windows and Linux; and a simplified app called GoScan). Machine can be configured for 1H and 13C spectra (possibly more by a custom order) in 1D and 2D modes, and operates at 80 MHz (1.88 T). The machine weighs about 93 kg and consumes less than 300W when operating.


Multivariate optical computing

Multivariate optical computing, also known as molecular factor computing, is an approach to the development of compressed sensing spectroscopic instruments, particularly for industrial applications such as process analytical support. "Conventional" spectroscopic methods often employ multivariate and chemometric methods, such as multivariate calibration, pattern recognition, and classification, to extract analytical information (including concentration) from data collected at many different wavelengths. Multivariate optical computing uses an optical computer to analyze the data as it is collected. The goal of this approach is to produce instruments which are simple and rugged, yet retain the benefits of multivariate techniques for the accuracy and precision of the result.
An instrument which implements this approach may be described as a multivariate optical computer. Since it describes an approach, rather than any specific wavelength range, multivariate optical computers may be built using a variety of different instruments (including Fourier Transform Infrared (FTIR) and Raman).
The "software" in multivariate optical computing is encoded directly into an optical element spectral calculation engine such as an interference filter based multivariate optical element (MOE), holographic grating, liquid crystal tunable filter, spatial light modulator (SLM), or digital micromirror device (DMD) and is specific to the particular application. The optical pattern for the spectral calculation engine is designed for the specific purpose of measuring the magnitude of that multi-wavelength pattern in the spectrum of a sample, without actually measuring a spectrum.
Multivariate optical computing allows instruments to be made with the mathematics of pattern recognition designed directly into an optical computer, which extracts information from light without recording a spectrum. This makes it possible to achieve the speed, dependability, and ruggedness necessary for real time, in-line process control instruments.
Multivariate optical computing encodes an analog optical regression vector of a transmission function for an optical element. Light which emanates from a sample contains the spectral information of that sample, whether the spectrum is discovered or not. As light passes from a sample through the element, the normalized intensity, which is detected by a broad band detector, is proportional to the dot product of the regression vector with that spectrum, i.e. is proportional to the concentration of the analyte for which the regression vector was designed. The quality of the analysis is then equal to the quality of the regression vector which is encoded. If the resolution of the regression vector is encoded to the resolution of the laboratory instrument from which that regression vector was designed and the resolution of the detector is equivalent, then the measurement made by Multivariate Optical Computing will be equivalent to that laboratory instrument by conventional means. The technique is making headway in a niche market for harsh environment detection. Specifically the technique has been adopted for use in the oil industry for detection of hydrocarbon composition in oil wells and pipeline monitoring. In such situations, laboratory quality measurements are necessary, but in harsh environments.
History.
Although the concept of using a single optical element for analyte regression and detection was suggested in 1986, the first full MOC concept device was published in 1997 from the Myrick group at the University of South Carolina, with a subsequent demonstration in 2001. The technique has received much recognition in the optics industry as a new method to perform optical analysis with advantages for harsh environment sensing. The technique has been applied to Raman spectroscopy, fluorescence spectroscopy, absorbance spectroscopy in the UV-Vis, NIR and MIR, microscopy, reflectance spectroscopy and hyperspectral imaging. In the years since first demonstration, applications have been demonstrated for defence, forensics, monitoring of chemical reactions, environmental monitoring, recycling, food and drug, medical and life sciences, and the petroleum industry. The first published demonstration for use of MOC in the harsh environments, was 2012 with a laboratory study with temperatures from 150F to 350F and pressures from 3000psi to 20,000psi, followed in 2013 with field trials in oil wells.


Speed camera


B share (NYSE)

B shares are a special class of shares on the New York Stock Exchange.
Comparison with A shares.
B shares carry a back-end load, whereas A shares carry a front-end load.


Fourths (angle)


762 Pulcova

762 Pulcova is a main-belt asteroid. It was discovered by Grigoriy N. Neujmin in 1913, and is named after Pulkovo Observatory, near Saint Petersburg. Pulcova is 137 km in diameter, and is a C-type asteroid, which means that it is dark in colouring with a carbonate composition.
Photometric observations of this asteroid from Leura, Australia during 2006 gave a light curve with a period of 5.8403 ± 0.0005 hours and a brightness variation of 0.20 ± 0.02 in magnitude. This result is in agreement with previous studies.
Satellite.
On February 22, 2000, astronomers at the Canada-France-Hawaii Telescope on Mauna Kea, Hawaii, discovered a small, 15-km moon (roughly a 10th the size of the primary) orbiting Pulcova at a distance of 800 km. Its orbital period is 4 days. The satellite is about 4 magnitudes fainter than the primary. It was one of the first asteroid moons to be identified.
Density.
In the year 2000, Merline estimated Pulcova to have a density of 1.8 g/cm³, which would make it more dense than the trinary asteroid 45 Eugenia, and binary 90 Antiope. But estimates by Marchis in 2008 suggest a density of only 0.90 g/cm³, suggesting it may be a loosely packed rubble pile, not a monolithic object.


HD 2039

HD 2039 is a yellow dwarf or yellow subgiant star in the constellation Phoenix. The star is not visible to the naked eye, and lies 280 light years away from the Sun. HD 2039 is a relatively stable star, and an exoplanet at least three times the mass of the planet Jupiter has been discovered in its orbit; this exoplanet, known as HD 2039 b, was the 100th exoplanet to be discovered.
Nomenclature.
The designation "HD 2039" from the Henry Draper Catalogue. The catalogue, which was published between 1918 and 1924, was based on the work of Annie Jump Cannon and her team between 1911 and 1915. HD 2039 does not have a common, colloquial name that is characteristic of stars like Sirius, Procyon, and Aldebaran.
Characteristics.
HD 2039 is a stable G-type star, meaning it shines with white light that can be seen in the Sun. HD 2039 exhibits a radius approximately 40 percent larger than the Sun's. The star is slightly hotter than the Sun; while HD 2039 has a temperature of 5935 K, the Sun's surface temperature lies nearly 200 kelvins lower at 5778 K. HD 2039 is unusually metal-rich, which has attracted the attention of astrophysicists.
Distance and visibility.
The star's magnitude as observed from Earth is 9; this signifies that the body is not visible with the naked eye, but can be seen with a telescope. HD 2039 lies roughly 280 light years from the Sun, which is about as far from the Sun as the second brightest star in the night sky, Canopus.
Planetary system.
In 2002, a planet was found by the Anglo-Australian Planet Search team to be orbiting the star in a very eccentric orbit. It has a minimum mass more than four times that of Jupiter and has an orbital period of over three years. The planet orbits its star at a distance of approximately two AU away; the planet Earth, in comparison, orbits at a distance of one AU away from the Sun. HD 2039 b's discovery was reported quietly; no press release was provided by the observatory that discovered the star's planet, and no formal announcement of the planet's existence was made. The entity was the 100th exoplanet to have been verified by the scientific community.


A-sharp minor

A-sharp minor is a minor scale based on A, consisting of the pitches A, B, C, D, E, F, and G. Its key signature has seven sharps, while the direct enharmonic equivalent, B-flat minor, has five flats.
Its relative major is C-sharp major (or enharmonically D-flat major), and its parallel major is A-sharp major, usually replaced by B-flat major, since A-sharp major's three double-sharps make it impractical to use.
A-sharp minor is likely the least used minor key in music as it is not generally considered a practical key for composition. The enharmonic equivalent B-flat minor, which only contains five flats as opposed to A-sharp minor's seven sharps, is preferable to use.
The A-sharp natural minor scale is:
\override Score.TimeSignature #'stencil = ##f
\relative c" {
 \clef treble \key ais \minor \time 7/4
 ais4^\markup "Natural minor scale" bis cis dis eis fis gis ais gis fis eis dis cis bis ais2
</score>
Changes needed for the melodic and harmonic versions of the scale are written in with accidentals as necessary. The A-sharp harmonic minor and melodic minor scales are:
\override Score.TimeSignature #'stencil = ##f
\relative c" {
 \clef treble \key ais \minor \time 7/4
 ais4^\markup "Harmonic minor scale" bis cis dis eis fis gisis ais gisis fis eis dis cis bis ais2
</score>
\override Score.TimeSignature #'stencil = ##f
\relative c" {
 \clef treble \key ais \minor \time 7/4
 ais4^\markup "Melodic minor scale (ascending and descending)" bis cis dis eis fisis gisis ais gis! fis! eis dis cis bis ais2
</score>
In Rinck's 30 Preludes and Exercises in all major and minor keys, the 16th Prelude and Exercise is in A-sharp minor. In Bach's Prelude and Fugue in C-sharp major, a brief section near the beginning of the piece modulates to A-sharp minor.


Milli mass unit

The milli mass unit or (mmu) is used as a unit of mass by some scientific authors even though this unit is not defined by the IUPAP red book nor by the IUPAC green book. It is a short form of the tongue-breaking but formally more correct "milli unified atomic mass unit" (mu) and equivalent to of the unified atomic mass unit (u). A more modern name is the millidalton (mDa)
since the "unified atomic mass unit" is more and more displaced by the unit dalton. (1 Da = 1 u)
Since 1961 the unified atomic mass unit "u" has been defined as the mass of C. Before that the atomic mass unit "amu" was defined as the mass of O (physics) and as the mass of O (chemistry). Thus the publication date in literature ought to be heeded when reading about the milli mass unit as its name does not reveal whether it refers to the old amu or the newer u.
The mass excess is usually indicated in mu or mmu.
In mass spectrometry the mass accuracy of a mass analyzer is often indicated in mu, even though a more correct unit would be mTh (millithomson) since mass spectrometers measure the mass-to-charge ratio, not the mass. The relative mass accuracy is often indicated in ppm, even though this is no longer supported by the IUPAC green book which suggests using units like μTh/Th instead of ppm.


Fresnel diffraction

In optics, the Fresnel diffraction equation for near-field diffraction is an approximation of the Kirchhoff–Fresnel diffraction that can be applied to the propagation of waves in the near field. It is used to calculate the diffraction pattern created by waves passing through an aperture or around an object, when viewed from relatively close to the object. In contrast the diffraction pattern in the far field region is given by the Fraunhofer diffraction equation.
The near field can be specified by the Fresnel number, , of the optical arrangement. When formula_1 the diffracted wave is considered to be in the near field. However, the validity of the Fresnel diffraction integral is deduced by the approximations derived below. Specifically, the phase terms of third order and higher must be negligible, a condition that may be written as
where formula_3 is the maximal angle described by formula_4, and the same as in the definition of the Fresnel number.
The multiple Fresnel diffraction at closely spaced periodical ridges (ridged mirror) causes the specular reflection; this effect can be used for atomic mirrors.
Early treatments of this phenomenon.
Some of the earliest work on what would become known as Fresnel diffraction was carried out by Francesco Maria Grimaldi in Italy in the 17th century. In his monograph entitled "Light", Richard C. MacLaurin explains Fresnel diffraction by asking what happens when light propagates, and how that process is affected when a barrier with a slit or hole in it is interposed in the beam produced by a distant source of light. He uses the Principle of Huygens to investigate, in classical terms, what transpires. The wave front that proceeds from the slit and on to a detection screen some distance away very closely approximates a wave front originating across the area of the gap without regard to any minute interactions with the actual physical edge.
The result is that if the gap is very narrow only diffraction patterns with bright centers can occur. If the gap is made progressively wider, then diffraction patterns with dark centers will alternate with diffraction patterns with bright centers. As the gap becomes larger, the differentials between dark and light bands decrease until a diffraction effect can no longer be detected.
MacLaurin does not mention the possibility that the center of the series of diffraction rings produced when light is shone through a small hole may be black, but he does point to the inverse situation wherein the shadow produced by a small circular object can paradoxically have a bright center. (p. 219)
In his "Optics", Francis Weston Sears offers a mathematical approximation suggested by Fresnel that predicts the main features of diffraction patterns and uses only simple mathematics. By considering the perpendicular distance from the hole in a barrier screen to a nearby detection screen along with the wavelength of the incident light, it is possible to compute a number of regions called half-period elements or Fresnel zones. The inner zone is a circle and each succeeding zone will be a concentric annular ring. If the diameter of the circular hole in the screen is sufficient to expose the first or central Fresnel zone, the amplitude of light at the center of the detection screen will be double what it would be if the detection screen were not obstructed. If the diameter of the circular hole in the screen is sufficient to expose two Fresnel zones, then the amplitude at the center is almost zero. That means that a Fresnel diffraction pattern can have a dark center. These patterns can be seen and measured, and correspond well to the values calculated for them.
The Fresnel diffraction integral.
The electric field diffraction pattern at a point "(x, y, z)" is given by:
where
Analytical solution of this integral is impossible for all but the simplest diffraction geometries. Therefore, it is usually calculated numerically.
The Fresnel approximation.
The main problem for solving the integral is the expression of "r". First, we can simplify the algebra by introducing the substitution:
Substituting into the expression for "r", we find:
Next, by the binomial expansion,
We can express formula_14 as
If we consider all the terms of binomial series, then there is no approximation. Let us substitute this expression in the argument of the exponential within the integral; the key to the Fresnel approximation is to assume that the third term is very small and can be ignored and henceforth any higher orders. In order to make this possible, it has to contribute to the variation of the exponential for an almost null term. In other words, it has to be much smaller than the period of the complex exponential; i.e., formula_16:
expressing "k" in terms of the wavelength,
we get the following relationship:
Multiplying both sides by formula_20, we have
or, substituting the earlier expression for ρ2,
If this condition holds true for all values of "x", "x' ", "y" and "y' ", then we can ignore the third term in the Taylor expression. Furthermore, if the third term is negligible, then all terms of higher order will be even smaller, so we can ignore them as well.
For applications involving optical wavelengths, the wavelength λ is typically many orders of magnitude smaller than the relevant physical dimensions. In particular:
and
Thus, as a practical matter, the required inequality will always hold true as long as
We can then approximate the expression with only the first two terms:
This equation, then, is the Fresnel approximation, and the inequality stated above is a condition for the approximation's validity.
Fresnel diffraction.
The condition for validity is fairly weak, and it allows all length parameters to take comparable values, provided the aperture is small compared to the path length. For the "r" in the denominator we go one step further, and approximate it with only the first term, formula_27. This is valid in particular if we are interested in the behaviour of the field only in a small area close to the origin, where the values of "x" and "y" are much smaller than "z". In general, Fresnel diffraction is valid if the Fresnel number is approximately 1.
For Fresnel diffraction the electric field at point "(x, y, z)" is then given by :
This is the Fresnel diffraction integral; it means that, if the Fresnel approximation is valid, the propagating field is a spherical wave, originating at the aperture and moving along "z". The integral modulates the amplitude and phase of the spherical wave. Analytical solution of this expression is still only possible in rare cases. For a further simplified case, valid only for much larger distances from the diffraction source, see Fraunhofer diffraction. Unlike Fraunhofer diffraction, Fresnel diffraction accounts for the curvature of the wavefront, in order to correctly calculate the relative phase of interfering waves.
Alternative forms.
Convolution.
The integral can be expressed in other ways in order to calculate it using some mathematical properties. If we define the following function:
then the integral can be expressed in terms of a convolution:
in other words we are representing the propagation using a linear-filter modeling. That is why we might call the function "h(x, y, z)" the impulse response of free space propagation.
Fourier transform.
Another possible way is through the Fourier transform. If in the integral we express "k" in terms of the wavelength:
and expand each component of the transverse displacement:
then we can express the integral in terms of the two-dimensional Fourier transform. Let us use the following definition:
where "p" and "q" are spatial frequencies (wave numbers). The Fresnel integral can be expressed as
That is, first multiply the field to be propagated by a complex exponential, calculate its two-dimensional Fourier transform, replace ("p", "q") with formula_35 and multiply it by another factor. This expression is better than the others when the process leads to a known Fourier transform, and the connection with the Fourier transform is tightened in the linear canonical transformation, discussed below.
Linear canonical transformation.
From the point of view of the linear canonical transformation, Fresnel diffraction can be seen as a shear in the time-frequency domain, corresponding to how the Fourier transform is a rotation in the time-frequency domain.


List of language proficiency tests

The following is a non-exhaustive, but growing, list of standardized tests that assess a person's language proficiency of a foreign/secondary language. Various types of such exams exist per many languages—some are organized at an international level even through national authoritative organizations, while others simply for specific limited business or study orientation.
Bulgarian.
(STBFL) (Стандартизиран тест по
български език като чужд език (СТБЕЧ))
http://www.deo.uni-sofia.bg/bg/certificate/bg
https://www.mon.bg/upload/7447/reglament_BG_online.pdf
http://www.legacy.deo.uni-sofia.bg/alte/index.htm
http://www.deo.uni-sofia.bg/bg/coursis
http://www.deo.uni-sofia.bg/bg/language/bulgarian
German.
DSD II, DSH, and TestDaF are accepted by any university in Germany. They are officially recognised as university entrance qualifications. Other tests may be considered, but no guarantees are given. In other German-speaking countries the situation varies.
Hungarian.
 The certificate examinations are staged on four levels of language proficiency according to the Common European Framework of Reference for Languages:
Italian.
According to the Ministero degli Esteri (Italian Foreign Affairs), there are four officials Italian certifications approved CLIQ (Certificato di Lingua Italiana di Qualità): CILS, CELI, PLIDA and .IT ROMA TRE
Kazakh.
 Levels : Reasonable grade
 Elementary : 31-64 grades
 Pre-Intermediate : 65-104 grades
 Intermediate : 105-119 grades
 Upper-Intermediate : 120-134 grades
 Advanced : 135-145 grades
 Higher advanced : 146-150 grades
Norwegian.
- Bergenstest for voksne innvandrere - Level B2


Paraguayan units of measurement

A number of units of measurement were used in Paraguay to measure quantities including length, mass, area, capacity, etc. Metric system had been optional since 1890, and adopted since 1899 in Paraguay.
System before metric system.
Spanish system was used before metric system.
Length.
A number of units were used to measure length. According to legal equivalents, one vara (old) was 0.83856 m. One cuerda or One cordel was vara or 69.88 m, according to legal equivalents. One vara was 0.866 m, according to legal equivalents. Some other units and their legal equivalents are given below:
1 pulgada (inch) = vara
1 linea (line) = vara
1 piede (foot) = vara
1 pouce = vara
1 ligne = vara
1 cuadra = 100 vara
1 lieue (league) = 5000 vara.
Mass.
Several units were used to measure mass. According to legal equivalents, One libra was 0.459 kg (One libra (old) was 460.08 kg). Some other units and their legal equivalents were given below:
1 onza (once) = libra
1 arroba = 25 libra
1 quintal (hundredweight) = 100 libra
1 tonelada (tonne) = 2000 libra.
Area.
Several units were used to measure area. Some units and their legal equalents are given below:
1 lifio (old) = 4883.2 m2
1 lifio = 100 square vara = 75 m2.
Capacity.
Two main systems, dry and liquid, were used to measure capacity.
Dry.
One fanega was 288 l and one almude was fanega.
Liquid.
Several units were used to measure liquid capacity. One frasco was 3.029 litres. Some other units and their legal equivalents are given below:
1 cuarto = frasco
1 baril = 32 frasco
1 pipe = 192 frasco.


Blumlein pair

Blumlein pair is the name for a stereo recording technique invented by Alan Blumlein for the creation of recordings that, upon replaying through headphones or loudspeakers, recreate the spatial characteristics of the recorded signal.
The pair consists of an array of two matched microphones that have a bi-directional (figure-8) pickup pattern. They are positioned 90° from each other. Ideally, the transducers should occupy the same physical space; since this cannot be achieved, the microphone capsules are placed as close to each other as physically possible, generally with one centered directly above the other. The array is oriented so that the line bisecting the angle between the two microphones points towards the sound source to be recorded (see diagram). The pickup patterns of the pair, combined with their positioning, delivers a high degree of stereo separation in the source signal, as well as the room ambiance.
The Blumlein pair produces an exceptionally realistic stereo image, but the quality of recordings is highly dependent on the acoustics of the room and the size of the sound source.
Both ribbon and condenser microphones can be used for Blumlein-pair recording. A few types of stereo ribbon microphones (B & O, Royer, AEA) have even been purpose-built for just this type of recording. Several types of stereo condenser microphone (Neumann, AKG, Schoeps, Nevaton BPT) have also offered a Blumlein arrangement as one of their possible configurations. Individual microphones with variable patterns (such as those from Pearl/Milab) can be used. The Soundfield microphone used to make Ambisonic recordings can be adjusted to mimic two microphones of any pattern at any angle to each other, including a Blumlein pair.
In his early experiments at EMI with what he called "binaural" sound, Blumlein did not use this actual technique because he did not have access to figure-8 microphones. This meant that he had to develop ways of using omnidirectional microphones to record what we now know as stereo sound. In the claims he made in his U.K. patent application in 1931, as well as details of these techniques, he included the theoretical possibility of using directional microphones in what later became known as a Blumlein pair. During the period when Blumlein's patent (British Patent 394325) was being written, Harry F. Olson published a patent for the first practical ribbon microphone, and much of the later experimental work was carried out with this type of microphone
It is unclear when this approach became known as the Blumlein pair, although it does not appear to have been known by that name during his lifetime.


Piezoelectric sensor

A piezoelectric sensor is a device that uses the piezoelectric effect to measure changes in pressure, acceleration, temperature, strain, or force by converting them to an electrical charge. The prefix "piezo-" is Greek for 'press' or 'squeeze'.
Applications.
Piezoelectric sensors are versatile tools for the measurement of various processes. They are used for quality assurance, process control, and for research and development in many industries. Pierre Curie discovered the piezoelectric effect in 1880, but only in the 1950s did manufacturers begin to use the piezoelectric effect in industrial sensing applications. Since then, this measuring principle has been increasingly used, and has become a mature technology with excellent inherent reliability.
They have been successfully used in various applications, such as in medical, aerospace, nuclear instrumentation, and as a tilt sensor in consumer electronics or a pressure sensor in the touch pads of mobile phones. In the automotive industry, piezoelectric elements are used to monitor combustion when developing internal combustion engines. The sensors are either directly mounted into additional holes into the cylinder head or the spark/glow plug is equipped with a built-in miniature piezoelectric sensor.
The rise of piezoelectric technology is directly related to a set of inherent advantages. The high modulus of elasticity of many piezoelectric materials is comparable to that of many metals and goes up to . Even though piezoelectric sensors are electromechanical systems that react to compression, the sensing elements show almost zero deflection. This gives piezoelectric sensors ruggedness, an extremely high natural frequency and an excellent linearity over a wide amplitude range. Additionally, piezoelectric technology is insensitive to electromagnetic fields and radiation, enabling measurements under harsh conditions. Some materials used (especially gallium phosphate or tourmaline) are extremely stable at high temperatures, enabling sensors to have a working range of up to . Tourmaline shows pyroelectricity in addition to the piezoelectric effect; this is the ability to generate an electrical signal when the temperature of the crystal changes. This effect is also common to piezoceramic materials. Gautschi in "Piezoelectric Sensorics" (2002) offers this comparison table of characteristics of piezo sensor materials vs other types:
One disadvantage of piezoelectric sensors is that they cannot be used for truly static measurements. A static force results in a fixed amount of charge on the piezoelectric material. In conventional readout electronics, imperfect insulating materials and reduction in internal sensor resistance causes a constant loss of electrons and yields a decreasing signal. Elevated temperatures cause an additional drop in internal resistance and sensitivity. The main effect on the piezoelectric effect is that with increasing pressure loads and temperature, the sensitivity reduces due to twin formation. While quartz sensors must be cooled during measurements at temperatures above , special types of crystals like GaPO4 gallium phosphate show no twin formation up to the melting point of the material itself.
However, it is not true that piezoelectric sensors can only be used for very fast processes or at ambient conditions. In fact, numerous piezoelectric applications produce quasi-static measurements, and other applications work in temperatures higher than .
Piezoelectric sensors can also be used to determine aromas in the air by simultaneously measuring resonance and capacitance. Computer controlled electronics vastly increase the range of potential applications for piezoelectric sensors.
Piezoelectric sensors are also seen in nature. The collagen in bone is piezoelectric, and is thought by some to act as a biological force sensor.
Principle of operation.
The way a piezoelectric material is cut defines one of its three main operational modes:
Transverse effect.
A force applied along a neutral axis (y) displaces charges along the (x) direction, perpendicular to the line of force. The amount of charge (formula_1) depends on the geometrical dimensions of the respective piezoelectric element. When dimensions formula_2 apply,
Longitudinal effect.
The amount of charge displaced is strictly proportional to the applied force and independent of the piezoelectric element size and shape. Putting several elements mechanically in series and electrically in parallel is the only way to increase the charge output. The resulting charge is
Shear effect.
The charge produced is exactly proportional to the applied force and is generated at a right angle to the force. The charge is independent of the element size and shape. For formula_10 elements mechanically in series and electrically in parallel the charge is
In contrast to the longitudinal and shear effects, the transverse effect make it possible to fine-tune sensitivity on the applied force and element dimension.
Electrical properties.
A piezoelectric transducer has very high DC output impedance and can be modeled as a proportional voltage source and filter network. The voltage "V" at the source is directly proportional to the applied force, pressure, or strain. The output signal is then related to this mechanical force as if it had passed through the equivalent circuit.
A detailed model includes the effects of the sensor's mechanical construction and other non-idealities. The inductance "L"m is due to the seismic mass and inertia of the sensor itself. "C"e is inversely proportional to the mechanical elasticity of the sensor. "C"0 represents the static capacitance of the transducer, resulting from an inertial mass of infinite size. "R"i is the insulation leakage resistance of the transducer element. If the sensor is connected to a load resistance, this also acts in parallel with the insulation resistance, both increasing the high-pass cutoff frequency.
For use as a sensor, the flat region of the frequency response plot is typically used, between the high-pass cutoff and the resonant peak. The load and leakage resistance must be large enough that low frequencies of interest are not lost. A simplified equivalent circuit model can be used in this region, in which "C"s represents the capacitance of the sensor surface itself, determined by the standard formula for capacitance of parallel plates. It can also be modeled as a charge source in parallel with the source capacitance, with the charge directly proportional to the applied force, as above.
Sensor design.
Based on piezoelectric technology various physical quantities can be measured the most common are pressure and acceleration. For pressure sensors, a thin membrane and a massive base is used, ensuring that an applied pressure specifically loads the elements in one direction. For accelerometers, a seismic mass is attached to the crystal elements. When the accelerometer experiences a motion, the invariant seismic mass loads the elements according to Newton's second law of motion formula_13.
The main difference in working principle between these two cases is the way they apply forces to the sensing elements. In a pressure sensor, a thin membrane transfers the force to the elements, while in accelerometers an attached seismic mass applies the forces.
Sensors often tend to be sensitive to more than one physical quantity. Pressure sensors show false signal when they are exposed to vibrations. Sophisticated pressure sensors therefore use acceleration compensation elements in addition to the pressure sensing elements. By carefully matching those elements, the acceleration signal (released from the compensation element) is subtracted from the combined signal of pressure and acceleration to derive the true pressure information.
Vibration sensors can also harvest otherwise wasted energy from mechanical vibrations. This is accomplished by using piezoelectric materials to convert mechanical strain into usable electrical energy.
Sensing materials.
Three main groups of materials are used for piezoelectric sensors: piezoelectric ceramics, single crystal materials and thin film piezoelectric materials.
The ceramic materials (such as PZT ceramic) have a piezoelectric constant/sensitivity that is roughly two orders of magnitude higher than those of the natural single crystal materials and can be produced by inexpensive sintering processes. The piezoeffect in piezoceramics is "trained", so their high sensitivity degrades over time. This degradation is highly correlated with increased temperature.
The less-sensitive, natural, single-crystal materials (gallium phosphate, quartz, tourmaline) have a higher – when carefully handled, almost unlimited – long term stability. There are also new single-crystal materials commercially available such as Lead Magnesium Niobate-Lead Titanate (PMN-PT). These materials offer improved sensitivity over PZT but have a lower maximum operating temperature and are currently more complicated to manufacture due to four compound vs. three compound material PZT.
Thin film piezoelectric materials can be manufactured utilizing sputtering, CVD (Chemical vapour deposition), ALD (atomic layer epitaxy) etc. methods. Thin film piezoelectric materials are used in applications where high frequency (> 100 MHz) is utilised in the measurement method and/or small size is favored in the application.