Leo Arons

Martin Leo Arons (15 February 1860 – 10 October 1919) was a German physicist and social democratic politician. He was the namesake of the "Lex Arons", a law which disallowed members of the Social Democratic Party of Germany (, SPD) to teach at Prussian universities.
Life and work.
Leo Arons came from a wealthy Jewish banking family in Berlin. His parents were Albert Arons (1826–1897), a partner in the prestigious private banking house "Gebrüder Arons", and Clara Goldschmidt (1837–1867). In 1887 Leo Arons married Johanna Bleichröder (1861–1938), a daughter of the banker Julius Bleichröder (1828-1907). Arons' brother, the banker Paul Arons (1861–1932), married Johanna's sister Gertrude (1865–1917) a few years later.
After taking his "Abitur", Leo Arons studied chemistry and physics, earning a doctorate degree in Strasbourg in 1888. As a scientist he worked in the area of experimental physics. He developed the mercury vapor lamp (also called "Arons' tube"), which was later marketed by AEG as "Dr. Arons' mercury vapor lamp". In 1890 he became a "Privatdozent" at the "Friedrich-Wilhelms-Universität Berlin" (now Humboldt University of Berlin). A year later he became the First Assistant in the Physics department, but resigned from this position in 1893. After that, he again worked as a "Privatdozent".
Via the land reform movement Arons came into contact with the SPD, which he joined in the early 1890s after some hesitation. As a member of the bourgeoisie he had particular reservations about the class struggle advocated by the party. The party's commitment to achieve its goals through legal means facilitated his entry. He subsequently wrote several articles for the party press. Within the party, he was on the reformists' side. He demanded the SPD's participation in the Prussian state elections and became an expert on the Prussian three-class franchise system. Since the 1890s he also attempted to unite middle-class social reformers and social democrats by organizing regular informal meetings, the "Schmalzstullenclub" ("Lard Bread Club"). He was a leading participant in the organization of the SPD's campaign for the general election of 1903. The press sometimes referred to him as the "Chief of Staff of the party for the election campaign." From 1904 to 1914 Arons was a member of the Berlin City Council. His candidacy for the post of alderman failed, however. Besides the party Arons also supported free trade unions and the building association "Ideal", founded in 1907.
Arons financed the first union hall in Berlin from his own assets, and small apartments for workers in conjunction with Ideal. From 1908, he increasingly withdrew from political life due to health reasons.
He was a representative in the Berlin district of Neukölln, where the "Aronsstraße" was named after him in 1973 (called "Leo-Arons-Straße" from 1926 and 1934, and "Sackführerdamm" from 1934 to 1973).
"Lex Arons".
Soon after Arons became a member of the Social Democratic Party, Prussian authorities sought to remove him from his teaching post. The university department responsible for carrying out this procedure objected to this request several times. A majority of the conservative members defended the autonomy of the university against state regulations. Their argument was that university teachers were free in their political beliefs and also that a "Privatdozent" was not subject to state discipline. As Arons spoke at the Social Democratic Party's congress in 1897, Kaiser Wilhelm II said, "I will not tolerate Socialists as ... the teachers of our youth at the Royal universities."
This royal declaration pressured the Prussian government and the reluctant official responsible for higher education, Friedrich Althoff, to bring about a solution. Since the government had no right to directly intervene in the appointment of lecturers, a law was passed in 1898 that made a lecturer subject to state disciplinary authority. Since this law was tailored especially for Arons' case, it is called the "Lex Arons". This law was one of the attempts in the 1890s to prevent the further advancement of the Social Democrats with exceptional laws. The "Lex Arons" was only one of these laws that passed the parliamentary hurdle of the Prussian House of Representatives; the Revolution Bill (1894) and the Jail Bill (1899) failed to find majorities in the Reichstag. Arons was suspended on the basis of the "Lex Arons". Due to fear of clashes with the concerned departments, Arons' was the only case in which the law was used.
In public, and especially in the scientific community, the law sparked debates about the freedom of science. Immediately after the November Revolution, Arons was rehabilitated by the new government shortly before his death.


Compact quantum group

In mathematics, a compact quantum group is an abstract structure on a unital separable C*-algebra axiomatized from those that exist on the commutative C*-algebra of "continuous complex-valued functions" on a compact quantum group.
The basic motivation for this theory comes from the following analogy. The space of complex-valued functions on a compact Hausdorff topological space forms a "commutative" C*-algebra. On the other hand, by the Gelfand Theorem, a commutative C*-algebra is isomorphic to the C*-algebra of continuous complex-valued functions on a compact Hausdorff topological space, and the topological space is uniquely determined by the C*-algebra up to homeomorphism.
S. L. Woronowicz introduced the important concept of compact matrix quantum groups, which he initially called compact pseudogroups. Compact matrix quantum groups are abstract structures on which the "continuous functions" on the structure are given by elements of a C*-algebra. The geometry of a compact matrix quantum group is a special case of a noncommutative geometry.
Formulation.
For a compact topological group, , there exists a C*-algebra homomorphism
where is the minimal C*-algebra tensor product — the completion of the algebraic tensor product of and ) — such that
for all formula_3, and for all formula_4, where
for all formula_6 and all formula_7. There also exists a linear multiplicative mapping
such that
for all formula_3 and all formula_11. Strictly speaking, this does not make into a Hopf algebra, unless is finite.
On the other hand, a finite-dimensional representation of can be used to generate a *-subalgebra of which is also a Hopf *-algebra. Specifically, if
is an -dimensional representation of , then
for all , and
for all . It follows that the *-algebra generated by formula_15 for all and formula_16 for all is a Hopf *-algebra: the counit is determined by
for all formula_18 (where formula_19 is the Kronecker delta), the antipode is , and the unit is given by
Compact Matrix Quantum Groups.
As a generalization, a compact matrix quantum group is defined as a pair , where is a C*-algebra and
is a matrix with entries in such that
As a consequence of continuity, the comultiplication on is coassociative.
In general, is a bialgebra, and is a Hopf *-algebra.
Informally, can be regarded as the *-algebra of continuous complex-valued functions over the compact matrix quantum group, and can be regarded as a finite-dimensional representation of the compact matrix quantum group.
Compact Quantum Groups.
For C*-algebras and acting on the Hilbert spaces and respectively, their minimal tensor product is defined to be the norm completion of the algebraic tensor product in ; the norm completion is also denoted by .
A compact quantum group is defined as a pair , where is a unital separable C*-algebra and
Representations.
A representation of the compact matrix quantum group is given by a corepresentation of the Hopf *-algebra Furthermore, a representation, "v", is called unitary if the matrix for "v" is unitary, or equivalently, if
Example.
An example of a compact matrix quantum group is , where the parameter is a positive real number.
First Definition.
, where is the C*-algebra generated by and , subject to
and
so that the comultiplication is determined by formula_30, and the coinverse is determined by formula_31. Note that is a representation, but not a unitary representation. is equivalent to the unitary representation
Second Definition.
, where is the C*-algebra generated by and , subject to
and
so that the comultiplication is determined by formula_35, and the coinverse is determined by formula_36, formula_37. Note that is a unitary representation. The realizations can be identified by equating formula_38.
Limit Case.
If , then is equal to the concrete compact group .


STAR detector

The STAR detector (for Solenoidal Tracker at RHIC) is one of the four experiments at the Relativistic Heavy Ion Collider (RHIC) in Brookhaven National Laboratory, United States.
The primary scientific objective of STAR is to study the formation and characteristics of the quark-gluon plasma (QGP), a state of matter believed to exist at sufficiently high energy densities. Detecting and understanding the QGP allows physicists to understand better the Universe in the seconds after the Big Bang, when the presently-observed symmetries (and asymmetries) of the Universe were established.
Unlike other physics experiments where a theoretical prediction can be tested directly by a single measurement, STAR must make use of a variety of simultaneous studies in order to draw strong conclusions about the QGP. This is due both to the complexity of the system formed in the high-energy nuclear collision and the unexplored landscape of the physics studied. STAR therefore consists of several types of detectors, each specializing in detecting certain types of particles or characterizing their motion. These detectors work together in an advanced data acquisition and subsequent physics analysis that allows definitive statements to be made about the collision.
The physics of STAR.
In the immediate aftermath of the Big Bang, the expanding matter was so hot and dense that protons and neutrons could not exist. Instead, the early universe comprised a plasma of quarks and gluons, which in today's cool universe are confined and exist only within composite particles (bound states) – the hadrons, such as protons and neutrons. Collisions of heavy nuclei at sufficiently high energies allow physicists to study whether quarks and gluons become deconfined at high densities, and if so, what the properties of this matter (i.e. quark–gluon plasma) are.
In particular, STAR studies the collective expansion of the hot quark-gluon matter, such as the elliptic flow. This allows to extract the transport coefficients that characterize the quark-gluon matter, including the shear and bulk viscosity, and to investigate macroscopic quantum phenomena, such as the chiral magnetic effect.
Collaboration governance.
The governance of STAR is via two branches: the institutional Council which is run by a Chairperson elected from the Council ranks, and elected Spokesperson(s) and their management team. The Spokesperson(s) represent the Collaboration in scientific, technical, and managerial concerns. The Council deals with general issues that concern the collaboration. Examples include the organization and governance of the Collaboration, adoption of bylaws and amendments thereto, the policy on admission of new members institutions to the Collaboration, and Policies for the Publication and Presentation of STAR Results.
The term of the office of the Council Chair is nominally two years. he Council elects, a Spokesperson or a team of two Spokespersons who then serve at the discretion of the Council. The normal term of office for the Spokesperson(s) is 3 years, and an individual is eligible to serve at most two consecutive terms as Spokesperson(s).
The elected Spokesperson(s) and their team of Deputies, and the Council Chairs of STAR are listed below. The Institute listed indicates the institute the person was at when they held the position.


Understanding Physics

Understanding Physics (1966) is a popular science book written by Isaac Asimov (1920-1992). It is considered to be a reader-friendly informational guide regarding the fields of physics, written for lay people. It is one of several science guides by Asimov.
The book is divided into three volumes, each of which have also been published separately as books. They are:


Jonathan How

Jonathan P. How is a Canadian-American astrophysicist and aeronautical engineer currently the Richard Cockburn Maclaurin Professor at Massachusetts Institute of Technology and Editor-in-Chief of the "IEEE Control Systems Magazine", also previously a Davis Faculty Scholar at Stanford University. His current concerns are technology systems engineering and space engineering.
How was born in England in 1965. He moved to Canada and attended the University of Toronto, earning his college degree in engineering. He moved to the Massachusetts Institute of Technology (MIT) for graduate. He also earned his Doctorate of Philosophy (often called a Ph.D.) at MIT too. After getting his doctorate, he became a professor at Stanford, having moved to California. In 2000, he moved to MIT and is now a professor there.
How is director of the Ford-MIT Alliance. In terms of editorships, he is Editor-In-Chief of "IEEE Control Systems Magazine" and one of the associate editors for "Journal of Aerospace Information Systems" of AIAA. He was also on the Scientific Advisory Board (SAB) for the United States Air Force.
Awards.
How has won multiple AIAA Best Paper in Conference Awards, including those of 2011, 2012, and 2013. Additionally in 2011, he earned the IFAC Automatica award for best applications paper. He received the 2002 Institute of Navigation Burka Award. In 2015, How won the AeroLion Technologies Outstanding Paper Award for the Journal Unmanned Systems. In 2016, How was named a Fellow of the American Institute of Aeronautics and Astronautics and two years later was became a Fellow of the Institute of Electrical and Electronics Engineers (IEEE).


Body surface area

In physiology and medicine, the body surface area (BSA) is the measured or calculated surface area of a human body. For many clinical purposes, BSA is a better indicator of metabolic mass than body weight because it is less affected by abnormal adipose mass. Nevertheless, there have been several important critiques of the use of BSA in determining the dosage of medications with a narrow therapeutic index, such as chemotherapy.
Typically there is a 4–10 fold variation in drug clearance between individuals due to differing the activity of drug elimination processes related to genetic and environmental factors. This can lead to significant overdosing and underdosing (and increased risk of disease recurrence). It is also thought to be a distorting factor in Phase I and II trials that may result in potentially helpful medications being prematurely rejected. The trend to personalized medicine is one approach to counter this weakness.
Uses.
Examples of uses of the BSA:
There is some evidence that BSA values are less accurate at extremes of height and weight, where Body Mass Index may be a better estimate (for hemodynamic parameters).
Calculation.
Various calculations have been published to arrive at the BSA without direct measurement. In the following formulae, BSA is expressed in m2, weight (or, more properly, mass) W in kg, and height H in cm.
The most widely used is the Du Bois formula, which has been shown to be equally as effective in estimating body fat in obese and non-obese patients, something the Body mass index fails to do.
The Mosteller formula is also commonly used, and is mathematically simpler:
Other formulas for BSA in m2 include:
For any formula, the units should match. Mosteller pointed out that his formula holds only if the density is treated as a constant for all humans. Lipscombe, following Mosteller's reasoning, observed that the formulas obtained by Fujimoto, Shuter and Aslani, Takahira, and Lipscombe are suggestive of formula_3, which is dimensionally correct for the case of constant density. It equals formula_4.
A weight-based formula was proposed by Costeff and recently validated for the pediatric age group that does not include a square root, making it easier to use. It is [4W (kg) + 7]/[90 + W (kg)].
Average values.
Average BSA for children of various ages, for men, and for women, can be estimated using statistical survey data and a BSA formula:
The estimations in the above tables are based weight and height data from the U.S. NCHS National Health and Nutrition Examination Survey (2011-2014).
There was an average BSA of for 3,000 cancer patients from 1990 to 1998 in a European Organisation for Research and Treatment of Cancer (EORTC) database.
During 2005 there was an average BSA of for 3,613 adult cancer patients in the UK. Among them the average BSA for men was and for women was .


Eun-Ah Kim

Eun-Ah Kim (born 1975) is a Korean-American condensed matter physicist interested in high-temperature superconductivity, topological order, strange metals, and the use of neural network based machine learning to recognize patterns in these systems. She is a professor of physics at Cornell University.
Education and career.
Kim was born in Jeonju in 1975. She graduated from Seoul National University in 1998 with a bachelor's degree in physics, and earned a master's degree there in 2000. She completed her Ph.D. in 2005 at the University of Illinois at Urbana-Champaign. Her dissertation, "Quantum Hall Tunnel Junctions: Luttinger Liquid Physics, Quantum Coherence Effect and Fractional Quantum Numbers", was supervised by Eduardo Fradkin.
After postdoctoral research at Stanford University, Kim joined the Cornell University faculty in 2008, and was promoted to full professor in 2019.
Recognition.
In 2020, Kim was elected as a Fellow of the American Physical Society (APS), after a nomination from the APS Division of Condensed Matter Physics, "for broad contributions to theoretical condensed matter physics, including new conceptual frameworks for interpreting experiments".


Timeline of particle discoveries

This is a timeline of subatomic particle discoveries, including all particles thus far discovered which appear to be elementary (that is, indivisible) given the best available evidence. It also includes the discovery of composite particles and antiparticles that were of particular historical importance.
More specifically, the inclusion criteria are:


Walter H. Barkas

Walter Henry Barkas (2 September 1912 – 28 March 1969) was Professor of Physics at the University of California, Riverside from 1965 on. He specialized in the use of nuclear emulsions, i.e., photographic plates having a thick sensitive layer, for purposes of Particle physics.
Together with his collaborators, he discovered the difference in range between positive and negative mesons of the same initial energy, and he ascribed this effect to the difference in stopping power between positively and negatively charged particles. Hence, this difference is called "Barkas effect" or "Barkas-Andersen effect", see Bethe formula.
Barkas was a visiting scholar at the Institute for Advanced Study in 1938-40.
Biography.
He was born on 2 September 1912 in Portland, Oregon to Leander Henrikson Barkas and Ester Emilia Gustafsson. He became a professor of physics at the University of California, Riverside in 1965. He died on 28 March 1969 in Riverside, California.


Institute of Physics and Engineering in Medicine

The Institute of Physics and Engineering in Medicine (IPEM) is the United Kingdom's professional body and learned society for physicists, engineers and technologists within the field of medicine, founded in 1995, changing its name from the Institution of Physics and Engineering in Medicine and Biology (IPEMB) in 1997. The Institute is governed by an elected Board of Trustees reporting to which are the Science, Research and Innovation Council and the Professional and Standards Council. The councils have operational responsibility for scientific and professional aspects of the Institute's work, respectively. Beneath the councils is a substructure of committees, groups and panels of members, which undertake the work of the Institute.
The Institute is licensed by the Engineering Council to register Chartered Engineers, Incorporated Engineers and Engineering Technologists and by the Science Council to register Chartered Scientists, Registered Scientists and Registered Science Technicians.
The aim of the Institute and its members, set out in its charitable objects and articles of association, is to promote for the public benefit the advancement of physics and engineering applied to medicine and biology, and to advance public education in the field.
History.
The organization can trace its origin to three societies:
The HPA created its scientific arm in 1984, the Institute of Physical Sciences in Medicine (IPSM). The trade union and scientific activities split in 1989: the scientific arm merged with the BES to form IPEMB while the trade union (HPA) joined the Manufacturing, Science and Finance Trades Union (MSF).
The Association of Medical Technologists (AMT), formerly HPTA, merged with IPEM in 2001.
Membership.
There are several categories of membership:
Equality, diversity and inclusion.
The Institute is a signatory of the Engineering Diversity Concordat of the Royal Academy of Engineering and the Science Council Diversity Declaration and has its own Equality Policy.
Annual Conference and Woolmer Lecture.
The Institute holds an annual conference on Medical Physics and Engineering. During this conference the flagship lecture of the Institute, the Woolmer Lecture, is presented. The lecture is dedicated to Professor Ronald Woolmer who was the first Director of the Research Department of Anaesthetics at the Royal College of Surgeons. Woolmer convened a meeting at the Royal College of Surgeons, London, to discuss the evolving field of engineering applied to medicine. It was agreed that the group should hold regular meetings and as a result the Biological Engineering Society (BES) was formed with Ronald Woolmer as the first President. Woolmer died two years after the formation of the BES and it was agreed that a memorial lecture would be sponsored in recognition of his achievements.

The following table includes a list of the lectures since 2002:

Publications.
IPEM owns three international peer-reviewed journals:
PMB and Physiological Measurement are published in association with IOP Publishing while Medical Engineering and Physics is published by Elsevier.

The Institute also publishes:
President of IPEM.
The IPEM president serves for two years and takes office at the Annual Conference. The following table includes a list of all past presidents of IPEMB/IPEM.


Denys Wilkinson Building

The Denys Wilkinson Building is a prominent 1960s building in Oxford, England, designed by Philip Dowson at Arup in 1967.
The building houses the astrophysics and particle physics sub-departments of the Department of Physics at Oxford University, plus the undergraduate teaching laboratories. It was originally built for the then Department of Nuclear Physics and named the Nuclear Physics Laboratory. In 2001, the building was renamed as the Denys Wilkinson Building, in honour of the British nuclear physicist Sir Denys Wilkinson (1922-2016), who was involved in its original creation.
The building is located on the corner of Banbury Road to the west and Keble Road to the south. To the north is the tall Thom Building of Oxford University's Department of Engineering Science, also built in the 1960s. It forms part of the Keble Road Triangle. Attached is a large and distinctive fan-shaped superstructure that was built to house a Van de Graaff generator. Pevsner commented that this marked "the arrival of the 'New Brutalism' in Oxford".
Particle Accelerators.
The building was originally built to host 2 small (by today's standards) particle accelerators.
Tandem Accelerator.
The first was a vertical folded tandem electrostatic accelerator (see Tandem accelerators, the top being at floor level in the fan-shaped superstructure, the bottom in the basements. Negatively charged ions were introduced at the bottom, and would be accelerated towards the large charge (10 million volts) built up by the Van de Graaff generator by electrostatic attraction. At the top the ions would pass through a thin foil to strip off electrons, and then their trajectory would be bent 180° by a large magnetic field. The now positively charged nuclei would then be electrostatically repelled by the same charge, accelerating them back down another vacuum tube. At the bottom the beam pipe exited, the beam was bent 90° by another magnet before entering a linear accelerator.
This particular accelerator consisted of a pressure vessel, about 40 feet tall, containing an annular lift/elevator platform to enable work to be carried out at different levels inside. Stacked in the centre was the accelerator column, comprising the Van de Graaff generator (a thick, rubber/canvas belt approximately 2 feet wide), the up/down vacuum tubes, and the electron stripper and magnet systems on top. The magnet was powered by a generator driven the by Van de Graaff belt. The column was surrounded by electrostatic discharge protection rings, in case of sparks. The whole column was resting on glass bricks at the bottom, with no lateral supports whatsoever.
The pressure vessel was filled with sulphur hexafluoride gas. The storage tank for this was located outside on eastern side of the building. The gas served as an insulator, allowing higher voltages on the Van de Graaff generator to be run resulting in greater particle energies being attained than had air been used. It also served as a fire suppressant, in the event of a spark discharge (which, when they did occur, was described as being "very loud indeed"). The sulphur hexafluoride was sourced from a company in Italy, and occasionally shipments of "bombola di gas" addressed to the "Nuclear Physics Department" Oxford would get stuck on the Italian/French border.
Linear RF Accelerator.
This was an RF resonant cavity accelerator, and would add additional energy to the nucelei. It was located down in a basement. On exiting the accelerator the nuclei would drift to a target station for experiments. The particle engergy at the target station was about 22MeV.
In the late 1980s this accelerator was sold to Beijing University. To extract it holes had to be cut through the floor of the covered loading dock located at the north side of the building all the way down to the lowest basement.
Nuclear Structure Physics.
The accelerators were intended to support research into nuclear structure, a field that was popular at the time of the building's construction. However, it was discovered that the field was extremely complex and progress was slow. The field was overtaken by other fields in nuclear physics, and the accelerators in the Denys Wilkinson Building fell into disuse.
Building Design.
The building was designed around conducting particle physics. The bulk of the accelerator infrastructure and experimental target station is in basement levels. The walls of the building at the lower levels are very thick concrete and is laden with boron. This was to keep the natural background radiation count inside the building as low as possible, and not (as was the popular and local civic belief) to keep radiation in. Some of the more exposed parts of the building suffered from rebar corrosion.
The building was originally going to be further extended on the eastern side, but the funding never became available.
Other uses.
In the 1970s and 1980s the building's basements was also designated as the emergency shelter for Oxford City Council. There was occasionally tension with the local council, which periodically tried to shut down the "Nuclear Physics Department" of the university. Generally such tensions were resolved with arranged visits, and explanations as to the role it would also serve for the councillors in the event of a nuclear attack on the United Kingdom.


Gabrielle Allen

Gabrielle D. Allen is a British and American computational astrophysicist known for her work in astrophysical simulations and multi-messenger astronomy, and as one of the original developers of the Cactus Framework for parallel scientific computation. She is a professor of mathematics and statistics at the University of Wyoming.
Education and career.
Allen is originally from Barking, London. She earned a bachelor's degree in mathematics from the University of Nottingham in 1988, and took Part III of the Mathematical Tripos at the University of Cambridge in applied mathematics and mathematical physics in the following year. She completed her Ph.D. in physics at Cardiff University in 1993, and also has a Masters of Advanced Study in mathematics from the University of Cambridge, earned in 2011.
She became a researcher at the Max Planck Institute for Gravitational Physics before moving in 2003 to a position as an assistant professor at Louisiana State University. She became a program director for cyberinfrastructure at the National Science Foundation in 2010, became a professor at the Skolkovo Institute of Science and Technology in Russia in 2012, and moved to the University of Illinois at Urbana–Champaign in 2014. At the University of Illinois, she became a professor of astronomy and a senior research scientist in the National Center for Supercomputing Applications, where she was co-leader of the Gravity Group. She was also named Associate Dean for Research in the university's College of Education in 2016.
She moved to the University of Wyoming, as a professor of mathematics and statistics, in 2020, in connection with her partner Ed Seidel's accession as president of the university.
Recognition.
Allen was one of the 2001 winners of the Gordon Bell Prize for supercomputing, in the special category, "for supporting efficient execution in the heterogeneous distributed computing environments with Cactus and Globus".
She was named a Fellow of the American Physical Society (APS) in 2017, after a nomination from the APS Division of Computational Physics, "for international leadership in development of widely used simulation frameworks for numerical relativity, relativistic astrophysics, and other areas, laying a foundation for many groups to address complex problems in multi-messenger astronomy".


List of things named after Niels Bohr

Niels Bohr (1885–1962), Danish physicist who made foundational contributions to understanding atomic structure and quantum theory, is the eponym of the topics listed below.


Ottavio Forte

Ottavio Forte, is a physics professor at Boston College. From the City College of New York, he got a B.S. in electrical engineering; from Northeastern, he got an M.S. in electrical engineering, and in Boston University he got his MBA. He has worked for over 22 years at MIT's laboratories, including Draper Laboratory and Lincoln Laboratory. He is most well known for his guidance and landing systems for the Apollo, Poseidon and Trident missions.


Georges Sagnac

Georges Sagnac (14 October 1869 – 26 February 1928) was a French physicist who lent his name to the Sagnac effect, a phenomenon which is at the basis of interferometers and ring laser gyroscopes developed since the 1970s.
Life and work.
Sagnac was born at Périgueux and entered the École Normale Supérieure in 1889. While a lab assistant at the Sorbonne, he was one of the first in France to study X-rays, following Wilhelm Conrad Röntgen. He belonged to a group of friends and scientists that notably included Pierre and Marie Curie, Paul Langevin, Jean Perrin, and the mathematician Émile Borel. Marie Curie says that she and her husband had traded ideas with Sagnac around the time of the discovery of radioactivity. Sagnac died at Meudon-Bellevue.
Sagnac effect.
In 1913, Georges Sagnac showed that if a beam of light is split and sent in two opposite directions around a closed path on a revolving platform with mirrors on its perimeter, and then the beams are recombined, they will exhibit interference effects. From this result Sagnac concluded that light propagates at a speed independent of the speed of the source. The motion of the earth through space had no apparent effect on the speed of the light beam, no matter how the platform was turned. The effect had been observed earlier (by Harress in 1911), but Sagnac was the first to correctly identify the cause.
This Sagnac effect (in vacuum) had been theoretically predicted by Max von Laue in 1911. He showed that such an effect is consistent with stationary ether theories (such as the Lorentz ether theory) as well as with Einstein's theory of relativity. It is generally taken to be inconsistent with a complete ether drag; and also inconsistent with emission theories of light, according to which the speed of light depends on the speed of the source.
Sagnac was a staunch opponent of the theory of relativity, despite the Sagnac effect being consistent with it.


Postulates of special relativity

In physics, Albert Einstein's 1905 theory of special relativity is derived from first principles now called the postulates of special relativity. Einstein's formulation only uses two postulates, though his derivation implies a few more assumptions.
Postulates of special relativity.
1. First postulate (principle of relativity)
2. Second postulate (invariance of "c")
The two-postulate basis for special relativity is the one historically used by Einstein, and it remains the starting point today. As Einstein himself later acknowledged, the derivation of the Lorentz transformation tacitly makes use of some additional assumptions, including spatial homogeneity, isotropy, and memorylessness. Also Hermann Minkowski implicitly used both postulates when he introduced the Minkowski space formulation, even though he showed that "c" can be seen as a space-time constant, and the identification with the speed of light is derived from optics.
Alternative derivations of special relativity.
Historically, Hendrik Lorentz and Henri Poincaré (1892–1905) derived the Lorentz transformation from Maxwell's equations, which served to explain the negative result of all aether drift measurements. By that the luminiferous aether becomes undetectable in agreement with what Poincaré called the principle of relativity (see History of Lorentz transformations and Lorentz ether theory). A more modern example of deriving the Lorentz transformation from electrodynamics (without using the historical aether concept at all), was given by Richard Feynman.
Following Einstein's original derivation and the group theoretical presentation by Minkowski, many alternative derivations have been proposed, based on various sets of assumptions. It has often been argued (such as by Vladimir Ignatowski in 1910,
or Philipp Frank and Hermann Rothe in 1911,
and many others in subsequent years)
that a formula equivalent to the Lorentz transformation, up to a nonnegative free parameter, follows from just the relativity postulate itself, without first postulating the universal light speed. These formulations rely on the aforementioned various assumptions such as isotropy. The numerical value of the parameter in these transformations can then be determined by experiment, just as the numerical values of the parameter pair "c" and the Vacuum permittivity are left to be determined by experiment even when using Einstein's original postulates. Experiment rules out the validity of the Galilean transformations. When the numerical values in both Einstein's and other approaches have been found then these different approaches result in the same theory.
Mathematical formulation of the postulates.
In the rigorous mathematical formulation of special relativity, we suppose that the universe exists on a four-dimensional spacetime "M". Individual points in spacetime are known as events; physical objects in spacetime are described by worldlines (if the object is a point particle) or worldsheets (if the object is larger than a point). The worldline or worldsheet only describes the motion of the object; the object may also have several other physical characteristics such as energy-momentum, mass, charge, etc.
In addition to events and physical objects, there are a class of inertial frames of reference. Each inertial frame of reference provides a coordinate system formula_1 for events in the spacetime "M". Furthermore, this frame of reference also gives coordinates to all other physical characteristics of objects in the spacetime; for instance, it will provide coordinates formula_2 for the momentum and energy of an object, coordinates formula_3 for an electromagnetic field, and so forth.
We assume that given any two inertial frames of reference, there exists a coordinate transformation that converts the coordinates from one frame of reference to the coordinates in another frame of reference. This transformation not only provides a conversion for spacetime coordinates formula_1, but will also provide a conversion for all other physical coordinates, such as a conversion law for momentum and energy formula_2, etc. (In practice, these conversion laws can be efficiently handled using the mathematics of tensors.)
We also assume that the universe obeys a number of physical laws. Mathematically, each physical law can be expressed with respect to the coordinates given by an inertial frame of reference by a mathematical equation (for instance, a differential equation) which relates the various coordinates of the various objects in the spacetime. A typical example is Maxwell's equations. Another is Newton's first law.
1. First Postulate (Principle of relativity)
2. Second Postulate (Invariance of "c")
Informally, the Second Postulate asserts that objects travelling at speed "c" in one reference frame will necessarily travel at speed "c" in all reference frames. This postulate is a subset of the postulates that underlie Maxwell's equations in the interpretation given to them in the context of special relativity. However, Maxwell's equations rely on several other postulates, some of which are now known to be false (e.g., Maxwell's equations cannot account for the quantum attributes of electromagnetic radiation).
The second postulate can be used to imply a stronger version of itself, namely that the spacetime interval is invariant under changes of inertial reference frame. In the above notation, this means that
for any two events "A", "B". This can in turn be used to deduce the transformation laws between reference frames; see Lorentz transformation.
The postulates of special relativity can be expressed very succinctly using the mathematical language of pseudo-Riemannian manifolds. The second postulate is then an assertion that the four-dimensional spacetime "M" is a pseudo-Riemannian manifold equipped with a metric "g" of signature (1,3), which is given by the Minkowski metric when measured in each inertial reference frame. This metric is viewed as one of the physical quantities of the theory; thus it transforms in a certain manner when the frame of reference is changed, and it can be legitimately used in describing the laws of physics. The first postulate is an assertion that the laws of physics are invariant when represented in any frame of reference for which "g" is given by the Minkowski metric. One advantage of this formulation is that it is now easy to compare special relativity with general relativity, in which the same two postulates hold but the assumption that the metric is required to be Minkowski is dropped.
The theory of Galilean relativity is the limiting case of special relativity in the limit formula_17 (which is sometimes referred to as the non-relativistic limit). In this theory, the first postulate remains unchanged, but the second postulate is modified to:
The physical theory given by classical mechanics, and Newtonian gravity is consistent with Galilean relativity, but not special relativity. Conversely, Maxwell's equations are not consistent with Galilean relativity unless one postulates the existence of a physical aether. In a surprising number of cases, the laws of physics in special relativity (such as the famous equation formula_28) can be deduced by combining the postulates of special relativity with the hypothesis that the laws of special relativity approach the laws of classical mechanics in the non-relativistic limit.


Unruh effect

The Unruh effect (also known as the Fulling–Davies–Unruh effect) is the hypothetical prediction that an accelerating observer will observe a thermal bath, like blackbody radiation, whereas an inertial observer would observe none. In other words, the background appears to be warm from an accelerating reference frame; in layman's terms, an accelerating thermometer (like one being waved around) in empty space, removing any other contribution to its temperature, will record a non-zero temperature, just from its acceleration. Heuristically, for a uniformly accelerating observer, the ground state of an inertial observer is seen as a mixed state in thermodynamic equilibrium with a non-zero temperature bath.
The Unruh effect was first described by Stephen Fulling in 1973, Paul Davies in 1975 and W. G. Unruh in 1976. It is currently not clear whether the Unruh effect has actually been observed, since the claimed observations are disputed. There is also some doubt about whether the Unruh effect implies the existence of Unruh radiation.
Temperature equation.
The Unruh temperature, sometimes called the Davies–Unruh temperature, was derived separately by Paul Davies and William Unruh and is the effective temperature experienced by a uniformly accelerating detector in a vacuum field. It is given by
where is the reduced Planck constant, is the local acceleration, is the speed of light, and is the Boltzmann constant. Thus, for example, a proper acceleration of corresponds approximately to a temperature of . Conversely, an acceleration of corresponds to a temperature of .
The Unruh temperature has the same form as the Hawking temperature with denoting the surface gravity of a black hole, which was derived by Stephen Hawking in 1974. In the light of the equivalence principle, it is, therefore, sometimes called the Hawking–Unruh temperature.
Explanation.
Unruh demonstrated theoretically that the notion of vacuum depends on the path of the observer through spacetime. From the viewpoint of the accelerating observer, the vacuum of the inertial observer will look like a state containing many particles in thermal equilibrium—a warm gas.
The Unruh effect would only appear to an accelerating observer. And although the Unruh effect would initially be perceived as counter-intuitive, it makes sense if the word "vacuum" is interpreted in the following specific way. In quantum field theory, the concept of "vacuum" is not the same as "empty space": Space is filled with the quantized fields that make up the universe. Vacuum is simply the lowest "possible" energy state of these fields.
The energy states of any quantized field are defined by the Hamiltonian, based on local conditions, including the time coordinate. According to special relativity, two observers moving relative to each other must use different time coordinates. If those observers are accelerating, there may be no shared coordinate system. Hence, the observers will see different quantum states and thus different vacua.
In some cases, the vacuum of one observer is not even in the space of quantum states of the other. In technical terms, this comes about because the two vacua lead to unitarily inequivalent representations of the quantum field canonical commutation relations. This is because two mutually accelerating observers may not be able to find a globally defined coordinate transformation relating their coordinate choices.
An accelerating observer will perceive an apparent event horizon forming (see Rindler spacetime). The existence of Unruh radiation could be linked to this apparent event horizon, putting it in the same conceptual framework as Hawking radiation. On the other hand, the theory of the Unruh effect explains that the definition of what constitutes a "particle" depends on the state of motion of the observer.
The free field needs to be decomposed into positive and negative frequency components before defining the creation and annihilation operators. This can only be done in spacetimes with a timelike Killing vector field. This decomposition happens to be different in Cartesian and Rindler coordinates (although the two are related by a Bogoliubov transformation). This explains why the "particle numbers", which are defined in terms of the creation and annihilation operators, are different in both coordinates.
The Rindler spacetime has a horizon, and locally any non-extremal black hole horizon is Rindler. So the Rindler spacetime gives the local properties of black holes and cosmological horizons. The Unruh effect would then be the near-horizon form of Hawking radiation.
The Unruh effect is also expected to be present in de Sitter space.
It is worth stressing that the Unruh effect only says that, according to uniformly-accelerated observers, the vacuum state is a thermal state specified by its temperature, and one should resist reading too much into the thermal state or bath. Different thermal states or baths at the same temperature need not be equal, for they depend on the Hamiltonian describing the system. In particular, the thermal bath seen by accelerated observers in the vacuum state of a quantum field is not the same as a thermal state of the same field at the same temperature according to inertial observers. Furthermore, uniformly accelerated observers, static with respect to each other, can have different proper accelerations (depending on their separation), which is a direct consequence of relativistic red-shift effects. This makes the Unruh temperature spatially inhomogeneous across the uniformly accelerated frame.
Calculations.
In special relativity, an observer moving with uniform proper acceleration through Minkowski spacetime is conveniently described with Rindler coordinates, which are related to the standard (Cartesian) Minkowski coordinates by
The line element in Rindler coordinates, i.e. Rindler space is
where , and where is related to the observer's proper time by (here ).
An observer moving with fixed traces out a hyperbola in Minkowski space, therefore this type of motion is called hyperbolic motion.
An observer moving along a path of constant is uniformly accelerating, and is coupled to field modes which have a definite steady frequency as a function of . These modes are constantly Doppler shifted relative to ordinary Minkowski time as the detector accelerates, and they change in frequency by enormous factors, even after only a short proper time.
Translation in is a symmetry of Minkowski space: it can be shown that it corresponds to a boost in "x", "t" coordinate around the origin. Any time translation in quantum mechanics is generated by the Hamiltonian operator. For a detector coupled to modes with a definite frequency in , we can treat as "time" and the boost operator is then the corresponding Hamiltonian. In Euclidean field theory, where the minus sign in front of the time in the Rindler metric is changed to a plus sign by multiplying formula_4 to the Rindler time, i.e. a Wick rotation or imaginary time, the Rindler metric is turned into a polar-coordinate-like metric. Therefore any rotations must close themselves after 2 in a Euclidean metric to avoid being singular. So
A path integral with real time coordinate is dual to a thermal partition function, related by a Wick rotation. The periodicity formula_6 of imaginary time corresponds to a temperature of formula_7 in thermal quantum field theory. Note that the path integral for this Hamiltonian is closed with period 2. This means that the modes are thermally occupied with temperature . This is not an actual temperature, because is dimensionless. It is conjugate to the timelike polar angle , which is also dimensionless. To restore the length dimension, note that a mode of fixed frequency in at position has a frequency which is determined by the square root of the (absolute value of the) metric at , the redshift factor. This can be seen by transforming the time coordinate of a Rindler observer at fixed to an inertial, co-moving observer observing a proper time. From the Rindler-line-element given above, this is just . The actual inverse temperature at this point is therefore
It can be shown that the acceleration of a trajectory at constant in Rindler coordinates is equal to , so the actual inverse temperature observed is
Restoring units yields
The temperature of the vacuum, seen by an isolated observer accelerating at the Earth's gravitational acceleration of = , is only . For an experimental test of the Unruh effect it is planned to use accelerations up to , which would give a temperature of about .
The Rindler derivation of the Unruh effect is unsatisfactory to some, since the detector's path is super-deterministic. Unruh later developed the Unruh–DeWitt particle detector model to circumvent this objection.
Other implications.
The Unruh effect would also cause the decay rate of accelerating particles to differ from inertial particles. Stable particles like the electron could have nonzero transition rates to higher mass states when accelerating at a high enough rate.
Unruh radiation.
Although Unruh's prediction that an accelerating detector would see a thermal bath is not controversial, the interpretation of the transitions in the detector in the non-accelerating frame is. It is widely, although not universally, believed that each transition in the detector is accompanied by the emission of a particle, and that this particle will propagate to infinity and be seen as Unruh radiation.
The existence of Unruh radiation is not universally accepted. Smolyaninov claims that it has already been observed, while O'Connell and Ford claim that it is not emitted at all. While these skeptics accept that an accelerating object thermalizes at the Unruh temperature, they do not believe that this leads to the emission of photons, arguing that the emission and absorption rates of the accelerating particle are balanced.
Experimental observation.
Researchers claim experiments that successfully detected the Sokolov–Ternov effect may also detect the Unruh effect under certain conditions.
Theoretical work in 2011 suggests that accelerating detectors could be used for the direct detection of the Unruh effect with current technology.


Bruno Bertotti

Bruno Bertotti (24 December 1930 – 20 October 2018) was an Italian physicist, emeritus professor at the University of Pavia. He was one of the last students of physicist Erwin Schrödinger.
Bertotti was well known for his contributions to general relativity – particularly the Bertotti-Robinson electrovacuum, an exact solution of the Einstein field equation. He has also obtained a more accurate measurement of the parameter gamma of the parameterized post-Newtonian formalism, with the Cassini radioscience experiment. The PPN gamma parameter measures the curvature of space in the metric theory of gravitation and it is equal to one in general relativity.
More recent studies revealed that the measured value of the PPN parameter gamma is affected by gravitomagnetic effect caused by the orbital motion of Sun around the barycenter of the solar system. The gravitomagnetic effect in the Cassini radioscience experiment was implicitly postulated by Bertotti as having a pure general relativistic origin but its theoretical value has been never tested in the experiment which effectively makes the experimental uncertainty in the measured value of gamma actually larger (by a factor of 10) than that claimed by Bertotti and co-authors in Nature.
Bertotti was a visiting scholar at the Institute for Advanced Study in Princeton, in 1958-59. In 2007 he was awarded the Italian Gold Medal for Merit in Science and Culture.
Among the last scholars in relativity from the University of Pavia are Alessandro Spallicci and Alberto Vecchio.


Anastigmat

An anastigmat or anastigmatic lens is a photographic lens completely corrected for the three main optical aberrations: spherical aberration, coma, and astigmatism. Early lenses often included the word "Anastigmat" in their name to advertise this new feature ("Doppel-Anastigmat", "Voigtländer Anastigmat Skopar", etc.). The first Anastigmat was designed by Paul Rudolph for the Carl Zeiss AG in 1890.
All modern photographic lenses are close to being anastigmatic, meaning that they can create extremely sharp images for all objects across their field of view; the underlying limitation is that the lens can deliver the anastigmatic performance only up to a maximum maximum aperture (i.e., it has a minimum F-number) and only within a given working distance (focusing range). Note that all optical aberrations (except spherical aberration) become more pronounced for objects lying in the edges of the field of view, which applies even to high-end anastigmatic lenses.
Anastigmatic performance is accomplished by a proper combination of multiple lenses (optical surfaces), usually three of more. Aspheric lenses can minimize the number of surfaces required and, thus, the bulk and weight of the composite lens; however, aspheric surfaces are more costly to manufacture compared to spherical and other conic section (hyperbolic, parabolic) ones. Many high-end catoptric telescopes are three-mirror anastigmat, while the corresponding catadioptric telescopes use two mirrors (reflector) and one lens (refractor) to accomplish the same result.


Compact Muon Solenoid

The Compact Muon Solenoid (CMS) experiment is one of two large general-purpose particle physics detectors built on the Large Hadron Collider (LHC) at CERN in Switzerland and France. The goal of CMS experiment is to investigate a wide range of physics, including the search for the Higgs boson, extra dimensions, and particles that could make up dark matter.
CMS is 21 metres long, 15 m in diameter, and weighs about 14,000 tonnes. Over 4,000 people, representing 206 scientific institutes and 47 countries, form the CMS collaboration who built and now operate the detector. It is located in a cavern at Cessy in France, just across the border from Geneva. In July 2012, along with ATLAS, CMS tentatively discovered the Higgs boson.
By March 2013 its existence was confirmed.
Background.
Recent collider experiments such as the now-dismantled Large Electron-Positron Collider and the newly renovated Large Hadron Collider (LHC) at CERN, as well as the () recently closed Tevatron at Fermilab have provided remarkable insights into, and precision tests of, the Standard Model of Particle Physics. A principal achievement of these experiments (specifically of the LHC) is the discovery of a particle consistent with the Standard Model Higgs boson, the particle resulting from the Higgs mechanism, which provides an explanation for the masses of elementary particles.
However, there are still many questions that future collider experiments hope to answer. These include uncertainties in the mathematical behaviour of the Standard Model at high energies, tests of proposed theories of dark matter (including supersymmetry), and the reasons for the imbalance of matter and antimatter observed in the Universe.
Physics goals.
The main goals of the experiment are:
The ATLAS experiment, at the other side of the LHC ring is designed with similar goals in mind, and the two experiments are designed to complement each other both to extend reach and to provide corroboration of findings. CMS and ATLAS uses different technical solutions and design of its detector magnet system to achieve the goals.
Detector summary.
CMS is designed as a general-purpose detector, capable of studying many aspects of proton collisions at 0.9–13 TeV, the center-of-mass energy of the LHC particle accelerator.
The CMS detector is built around a huge solenoid magnet. This takes the form of a cylindrical coil of superconducting cable that generates a magnetic field of 4 tesla, about 100 000 times that of the Earth. The magnetic field is confined by a steel 'yoke' that forms the bulk of the detector's weight of 12 500 t. An unusual feature of the CMS detector is that instead of being built in-situ underground, like the other giant detectors of the LHC experiments, it was constructed on the surface, before being lowered underground in 15 sections and reassembled.
It contains subsystems which are designed to measure the energy and momentum of photons, electrons, muons, and other products of the collisions. The innermost layer is a silicon-based tracker. Surrounding it is a scintillating crystal electromagnetic calorimeter, which is itself surrounded with a sampling calorimeter for hadrons. The tracker and the calorimetry are compact enough to fit inside the CMS Solenoid which generates a powerful magnetic field of 3.8 T. Outside the magnet are the large muon detectors, which are inside the return yoke of the magnet.
CMS by layers.
For full technical details about the CMS detector, please see the Technical Design Report.
The interaction point.
This is the point in the centre of the detector at which proton-proton collisions occur between the two counter-rotating beams of the LHC. At each end of the detector magnets focus the beams into the interaction point. At collision each beam has a radius of 17 μm and the crossing angle between the beams is 285 μrad.
At full design luminosity each of the two LHC beams will contain 2,808 bunches of protons. The interval between crossings is 25 ns, although the number of collisions per second is only 31.6 million due to gaps in the beam as injector magnets are activated and deactivated.
At full luminosity each collision will produce an average of 20 proton-proton interactions. The collisions occur at a centre of mass energy of 8 TeV. But, it is worth noting that for studies of physics at the electroweak scale, the scattering events are initiated by a single quark or gluon from each proton, and so the actual energy involved in each collision will be lower as the total centre of mass energy is shared by these quarks and gluons (determined by the parton distribution functions).
The first test which ran in September 2008 was expected to operate at a lower collision energy of 10 TeV but this was prevented by the 19 September 2008 shutdown. When at this target level, the LHC will have a significantly reduced luminosity, due to both fewer proton bunches in each beam and fewer protons per bunch. The reduced bunch frequency does allow the crossing angle to be reduced to zero however, as bunches are far enough spaced to prevent secondary collisions in the experimental beampipe.
Layer 1 – The tracker.
Momentum of particles is crucial in helping us to build up a picture of events at the heart of the collision. One method to calculate the momentum of a particle is to track its path through a magnetic field; the more curved the path, the less momentum the particle had. The CMS tracker records the paths taken by charged particles by finding their positions at a number of key points.
The tracker can reconstruct the paths of high-energy muons, electrons and hadrons (particles made up of quarks) as well as see tracks coming from the decay of very short-lived particles such as beauty or “b quarks” that will be used to study the differences between matter and antimatter.
The tracker needs to record particle paths accurately yet be lightweight so as to disturb the particle as little as possible. It does this by taking position measurements so accurate that tracks can be reliably reconstructed using just a few measurement points. Each measurement is accurate to 10 µm, a fraction of the width of a human hair. It is also the inner most layer of the detector and so receives the highest volume of particles: the construction materials were therefore carefully chosen to resist radiation.
The CMS tracker is made entirely of silicon: the pixels, at the very core of the detector and dealing with the highest intensity of particles, and the silicon microstrip detectors that surround it. As particles travel through the tracker the pixels and microstrips produce tiny electric signals that are amplified and detected. The tracker employs sensors covering an area the size of a tennis court, with 75 million separate electronic read-out channels: in the pixel detector there are some 6,000 connections per square centimetre.
The CMS silicon tracker consists of 14 layers in the central region and 15 layers in the endcaps. The innermost four layers (up to 16 cm radius) consist of 100 × 150 μm pixels, 124 million in total. The pixel detector was upgraded as a part of the CMS phase-1 upgrade in 2017, which added an additional layer to both the barrel and endcap,
and shifted the innermost layer 1.5 cm closer to the beamline.
The next four layers (up to 55 cm radius) consist of silicon strips, followed by the remaining six layers of strips, out to a radius of 1.1 m. There are 9.6 million strip channels in total.
During full luminosity collisions the occupancy of the pixel layers per event is expected to be 0.1%, and 1–2% in the strip layers. The expected HL-LHC upgrade will increase the number of interactions to the point where over-occupancy would significantly reduce trackfinding effectiveness. An upgrade is planned to increase the performance and the radiation tolerance of the tracker.
This part of the detector is the world's largest silicon detector. It has 205 m2 of silicon sensors (approximately the area of a tennis court) in 9.3 million microstrip sensors comprising 76 million channels.
Layer 2 – The Electromagnetic Calorimeter.
The Electromagnetic Calorimeter (ECAL) is designed to measure with high accuracy the energies of electrons and photons.
The ECAL is constructed from crystals of lead tungstate, PbWO4. This is an extremely dense but optically clear material, ideal for stopping high energy particles. Lead tungstate crystal is made primarily of metal and is heavier than stainless steel, but with a touch of oxygen in this crystalline form it is highly transparent and scintillates when electrons and photons pass through it. This means it produces light in proportion to the particle's energy. These high-density crystals produce light in fast, short, well-defined photon bursts that allow for a precise, fast and fairly compact detector. It has a radiation length of χ0 = 0.89 cm, and has a rapid light yield, with 80% of light yield within one crossing time (25 ns). This is balanced however by a relatively low light yield of 30 photons per MeV of incident energy. The crystals used have a front size of 22 mm × 22 mm and a depth of 230 mm. They are set in a matrix of carbon fibre to keep them optically isolated, and backed by silicon avalanche photodiodes for readout.
The ECAL, made up of a barrel section and two "endcaps", forms a layer between the tracker and the HCAL. The cylindrical "barrel" consists of 61,200 crystals formed into 36 "supermodules", each weighing around three tonnes and containing 1,700 crystals. The flat ECAL endcaps seal off the barrel at either end and are made up of almost 15,000 further crystals.
For extra spatial precision, the ECAL also contains preshower detectors that sit in front of the endcaps. These allow CMS to distinguish between single high-energy photons (often signs of exciting physics) and the less interesting close pairs of low-energy photons.
At the endcaps the ECAL inner surface is covered by the preshower subdetector, consisting of two layers of lead interleaved with two layers of silicon strip detectors. Its purpose is to aid in pion-photon discrimination.
Layer 3 – The Hadronic Calorimeter.
The Hadron Calorimeter (HCAL) measures the energy of hadrons, particles made of quarks and gluons (for example protons, neutrons, pions and kaons). Additionally it provides indirect measurement of the presence of non-interacting, uncharged particles such as neutrinos.
The HCAL consists of layers of dense material (brass or steel) interleaved with tiles of plastic scintillators, read out via wavelength-shifting fibres by hybrid photodiodes. This combination was determined to allow the maximum amount of absorbing material inside of the magnet coil.
The high pseudorapidity region formula_1 is instrumented by the Hadronic Forward (HF) detector. Located 11 m either side of the interaction point, this uses a slightly different technology of steel absorbers and quartz fibres for readout, designed to allow better separation of particles in the congested forward region.
The HF is also used to measure the relative online luminosity system in CMS.
About half of the brass used in the endcaps of the HCAL used to be Russian artillery shells.
Layer 4 – The magnet.
The CMS magnet is the central device around which the experiment is built, with a 4 Tesla magnetic field that is 100,000 times stronger than the Earth's. CMS has a large solenoid magnet. This allows the charge/mass ratio of particles to be determined from the curved track that they follow in the magnetic field. It is 13 m long and 6 m in diameter, and its refrigerated superconducting niobium-titanium coils were originally intended to produce a 4 T magnetic field. The operating field was scaled down to 3.8 T instead of the full design strength in order to maximize longevity.
The inductance of the magnet is 14 Η and the nominal current for 4 T is 19,500 A, giving a total stored energy of 2.66 GJ, equivalent to about half-a-tonne of TNT. There are dump circuits to safely dissipate this energy should the magnet quench. The circuit resistance (essentially just the cables from the power converter to the cryostat) has a value of 0.1 mΩ which leads to a circuit time constant of nearly 39 hours. This is the longest time constant of any circuit at CERN. The operating current for 3.8 T is 18,160 A, giving a stored energy of 2.3 GJ.
The job of the big magnet is to bend the paths of particles emerging from high-energy collisions in the LHC. The more momentum a particle has the less its path is curved by the magnetic field, so tracing its path gives a measure of momentum. CMS began with the aim of having the strongest magnet possible because a higher strength field bends paths more and, combined with high-precision position measurements in the tracker and muon detectors, this allows accurate measurement of the momentum of even high-energy particles.
The tracker and calorimeter detectors (ECAL and HCAL) fit snugly inside the magnet coil whilst the muon detectors are interleaved with a 12-sided iron structure that surrounds the magnet coils and contains and guides the field. Made up of three layers this “return yoke” reaches out 14 metres in diameter and also acts as a filter, allowing through only muons and weakly interacting particles such as neutrinos. The enormous magnet also provides most of the experiment's structural support, and must be very strong itself to withstand the forces of its own magnetic field.
Layer 5 – The muon detectors and return yoke.
As the name “Compact Muon Solenoid” suggests, detecting muons is one of CMS's most important tasks. Muons are charged particles that are just like electrons and positrons, but are 200 times more massive. We expect them to be produced in the decay of a number of potential new particles; for instance, one of the clearest "signatures" of the Higgs Boson is its decay into four muons.
Because muons can penetrate several metres of iron without interacting, unlike most particles they are not stopped by any of CMS's calorimeters. Therefore, chambers to detect muons are placed at the very edge of the experiment where they are the only particles likely to register a signal.
To identify muons and measure their momenta, CMS uses three types of detector: drift tubes (DT), cathode strip chambers (CSC) and resistive plate chambers (RPC). The DTs are used for precise trajectory measurements in the central "barrel" region, while the CSCs are used in the "end caps". The RPCs provide a fast signal when a muon passes through the muon detector, and are installed in both the barrel and the end caps.
The drift tube (DT) system measures muon positions in the barrel part of the detector. Each 4-cm-wide tube contains a stretched wire within a gas volume. When a muon or any charged particle passes through the volume it knocks electrons off the atoms of the gas. These follow the electric field ending up at the positively charged wire. By registering where along the wire electrons hit (in the diagram, the wires are going into the page) as well as by calculating the muon's original distance away from the wire (shown here as horizontal distance and calculated by multiplying the speed of an electron in the tube by the time taken) DTs give two coordinates for the muon's position. Each DT chamber, on average 2 m x 2.5 m in size, consists of 12 aluminium layers, arranged in three groups of four, each with up to 60 tubes: the middle group measures the coordinate along the direction parallel to the beam and the two outside groups measure the perpendicular coordinate.
Cathode strip chambers (CSC) are used in the endcap disks where the magnetic field is uneven and particle rates are high. CSCs consist of arrays of positively charged “anode” wires crossed with negatively charged copper “cathode” strips within a gas volume. When muons pass through, they knock electrons off the gas atoms, which flock to the anode wires creating an avalanche of electrons. Positive ions move away from the wire and towards the copper cathode, also inducing a charge pulse in the strips, at right angles to the wire direction. Because the strips and the wires are perpendicular, we get two position coordinates for each passing particle. In addition to providing precise space and time information, the closely spaced wires make the CSCs fast detectors suitable for triggering. Each CSC module contains six layers making it able to accurately identify muons and match their tracks to those in the tracker.
Resistive plate chambers (RPC) are fast gaseous detectors that provide a muon trigger system parallel with those of the DTs and CSCs. RPCs consist of two parallel plates, a positively charged anode and a negatively charged cathode, both made of a very high resistivity plastic material and separated by a gas volume. When a muon passes through the chamber, electrons are knocked out of gas atoms. These electrons in turn hit other atoms causing an avalanche of electrons. The electrodes are transparent to the signal (the electrons), which are instead picked up by external metallic strips after a small but precise time delay. The pattern of hit strips gives a quick measure of the muon momentum, which is then used by the trigger to make immediate decisions about whether the data are worth keeping. RPCs combine a good spatial resolution with a time resolution of just one nanosecond (one billionth of a second).
Collecting and collating the data.
Pattern recognition.
New particles discovered in CMS will be typically unstable and rapidly transform into a cascade of lighter, more stable and better understood particles. Particles travelling through CMS leave behind characteristic patterns, or ‘signatures’, in the different layers, allowing them to be identified. The presence (or not) of any new particles can then be inferred.
Trigger system.
To have a good chance of producing a rare particle, such as a Higgs boson, a very large number of collisions is required. Most collision events in the detector are "soft" and do not produce interesting effects. The amount of raw data from each crossing is approximately 1 megabyte, which at the 40 MHz crossing rate would result in 40 terabytes of data a second, an amount that the experiment cannot hope to store, let alone process properly. The full trigger system reduces the rate of interesting events down to a manageable 1,000 per second.
To accomplish this, a series of "trigger" stages are employed. All the data from each crossing is held in buffers within the detector while a small amount of key information is used to perform a fast, approximate calculation to identify features of interest such as high energy jets, muons or missing energy. This "Level 1" calculation is completed in around 1 µs, and event rate is reduced by a factor of about 1,000 down to 50 kHz. All these calculations are done on fast, custom hardware using reprogrammable field-programmable gate arrays (FPGA).
If an event is passed by the Level 1 trigger all the data still buffered in the detector is sent over fibre-optic links to the "High Level" trigger, which is software (mainly written in C++) running on ordinary computer servers. The lower event rate in the High Level trigger allows time for much more detailed analysis of the event to be done than in the Level 1 trigger. The High Level trigger reduces the event rate by a further factor of 100 down to 1,000 events per second. These are then stored on tape for future analysis.
Data analysis.
Data that has passed the triggering stages and been stored on tape is duplicated using the Grid to additional sites around the world for easier access and redundancy. Physicists are then able to use the Grid to access and run their analyses on the data.
There are a huge range of analyses performed at CMS, including:
Etymology.
The term Compact Muon Solenoid comes from the relatively compact size of the detector, the fact that it detects muons, and the use of solenoids in the detector. "CMS" is also a reference to the center-of-mass system, an important concept in particle physics.


Myron Mathisson

Myron Mathisson (December 4, 1897 – September 13, 1940) was a theoretical physicist of Polish and Jewish descent. He is known for his work in general relativity, for developing a new method to analyze the properties of fundamental solutions of linear hyperbolic partial differential equations, and proved, in a special case, the Hadamard conjecture on the class of equations that satisfy the Huygens principle.
Life and work.
Education.
Mathisson was born in Warsaw, 4 December 1897. He graduated from a Russian philological gymnasium with a gold medal in 1915. He began his studies at the Faculty of Civil Engineering of the Warsaw University of Technology. Then, from 1917 he studied at the University of Warsaw where he graduated in 1924 under the guidance of Czesław Białobrzeski.
Military service.
Between the years 1918–1919 he served in the military.
Physics research.
In 1930, earned his doctorate at the University of Warsaw on the work of "Sur le movement tournant d'un corps dans un champ de gravitation", and began to live there in 1932. He became a professor at the University of Kazan in 1936. The following year, he returned to Warsaw. He corresponded with Albert Einstein. In the years 1937–1939, he worked at the Jagiellonian University, under .
His works have been recognized by . Niels Bohr invited him to Copenhagen. In 1939 he went to Paris, where he met with Jacques Hadamard, and to Cambridge, where he met with Paul Dirac who was impressed enough to publish his recent work posthumously, and to post his obituary.
In chronological order; M. Mathisson, A. Papapetrou, and W. G. Dixon contributed to the derivation of the equations for a spinning body moving in a gravitational field, now known as the Mathisson–Papapetrou–Dixon equations.
Other work.
Due to financial difficulties, Mathisson had to work as a Hebrew translator, as a draftsman producing technical drawings, and engineering calculations of the statics of reinforced concrete structures.
Mathisson died of tuberculosis in Cambridge, on 13 September 1940.
Publications.
During his short lifetime, he published the following 12 scientific papers:


Thomas Hertog

Thomas Hertog is a Belgian cosmologist at KU Leuven university and a key collaborator of Professor Stephen Hawking.
Early life.
Thomas Hertog was born on 27 May 1975. He graduated Summa cum laude from KU Leuven in 1997 with an MSc degree in physics. He obtained his Master's degree at the University of Cambridge in Part III of the Mathematical Tripos and obtained a Ph.D. degree at Cambridge with a thesis on the origins of cosmic expansion under the supervision of Stephen Hawking.
Career.
Hertog had the opportunity to conduct research with Stephen Hawking in the field of cosmic inflation, a branch of the Big Bang theory.
He then worked as a researcher at the University of California - Santa Barbara in the United States and the Université de Paris VII in France. He became a fellow at CERN in Geneva in 2005. In October 2011, Hertog was appointed professor at the Institute for Theoretical Physics at KU Leuven through the Odysseus program of the Flemish government. He led a research group studying the relationship between the Big Bang and string theory, with the idea that concepts like space and time lose their meaning. He also emphasized Georges Lemaître's insight that the Big Bang is central to Einstein's gravitational waves. Hertog worked in the field of quantum cosmology and string theory with James Hartle and Stephen Hawking. In 2011, after years of research, they came to a new insight by combining the mathematics of quantum cosmology and that of string theory.


Mukunda Prasad Das

Mukunda Prasad Das (born 4 January 1945) is an Indian-born Australian physicist at the Australian National University.
He was elected a Fellow of the American Physical Society after he was nominated by their Forum on International Physics in 2003, for "notable theoretical investigations in condensed matter physics, namely: mesoscopic transport and noise, high temperature superconductivity and density functional theory; and for significant leadership in promoting international meetings and collaborations."


Physical Review B

Physical Review B: Condensed Matter and Materials Physics (also known as PRB) is a peer-reviewed, scientific journal, published by the American Physical Society (APS). The Editor of PRB is Laurens W. Molenkamp. It is part of the "Physical Review" family of journals. The current Editor in Chief is Michael Thoennessen. PRB currently publishes over 4500 papers a year, making it one of the largest physics journals in the world.
Scope.
The focus of this journal is on new results in condensed matter physics, which includes a wide variety of subject areas, such as semiconductors, superconductivity, magnetism, structure, phase transitions, ferroelectrics, nonordered systems, liquids, quantum solids, superfluidity, electronic structure, photonic crystals, mesoscopic systems, surfaces, clusters, fullerenes, graphene, nanoscience, etc.
History.
PRB was created in 1970 when the original "Physical Review" (founded in 1893) was subdivided into "Physical Review A", "B", "C", and "D", based on subject matter. Peter D. Adams was the Editor from inception until 2012 when Laurens W. Molenkamp took over. Anthony M. Begley is currently the Managing Editor.
Features.
PRB has a reputation among professional physicists for publishing useful, comprehensive long papers in physics. It also contains short (four page) papers in its Rapid Communications section, designed for research important enough to deserve special handling and speedy publication. The journal can be searched for free via PROLA. Titles and abstracts can be freely viewed but a journal subscription is needed to read the full text of papers. PRB and the other APS journals are available entirely free at many US public libraries.
PRB is rare among physics journals in that it has a staff of 12 full-time professional editors, and does not employ the more common model of using part-time editors who are active researchers. The journal is available in print format (at University libraries) but the archival version is the online one. Authors can pay extra charges to make their papers open access. Such papers are published under the terms of the Creative Commons Attribution 3.0 License (CC-BY), the most permissive of the CC licenses, which permits authors and others to copy, distribute, transmit, and adapt the work, provided that proper credit is given. A small percentage of the PRB papers published are chosen (highlighted) as an Editors' Suggestions. Artistic images from papers in the journal are published as a feature named Kaleidoscope.
Abstracting and Indexing.
"Physical Review B" is indexed in the following bibliographic databases:


Hot spot effect in subatomic physics

Hot spots in subatomic physics are regions of high energy density or temperature in hadronic or nuclear matter.
Finite size effects.
Hot spots are a manifestation of the finite size of the system: in subatomic physics this refers both to atomic nuclei, which consist of nucleons, as well as to nucleons themselves, which are made of quarks and gluons, Other manifestations of finite sizes of these systems are seen in scattering of electrons on nuclei and nucleons. For nuclei in particular finite size effects manifest themselves also in the isomeric shift and isotopic shift.
Statistical methods in subatomic physics.
The formation of hot spots assumes the establishment of local equilibrium, which in its turn occurs if the thermal conductivity in the medium is sufficiently small.
The notions of equilibrium and heat are statistical. The use of statistical methods assumes a large number of degrees of freedom. In macroscopic physics this number usually refers to the number of atoms or molecules, while in nuclear and particle physics it refers to the energy level density.
Hot spots in nucleons.
Local equilibrium is the precursor of global equilibrium and the hot spot effect can be used to determine how fast, if at all, the transition from local to global equilibrium takes place. That this transition does not always happen follows from the fact that the duration of a strong interaction reaction is quite short (of the order of 10−22–10−23 seconds) and the propagation of "heat", i.e. of the excitation, through the finite sized body of the system takes a finite time, which is determined by the thermal conductivity of the matter the system is made of.
Indications of the transition between local and global equilibrium in strong interaction particle physics started to emerge in the 1960s and early 1970s. In high-energy strong interactions equilibrium is usually not complete. In these reactions, with the increase of laboratory energy one observes that the transverse momenta of produced particles have a tail, which deviates from the single exponential Boltzmann spectrum, characteristic for global equilibrium. The slope or the effective temperature of this transverse momentum tail increases with increasing energy. These large transverse momenta were interpreted as being due to particles, which "leak" out before equilibrium is reached. Similar observations had been made in nuclear reactions and were also attributed to pre-equilibrium effects. This interpretation suggested that the equilibrium is neither instantaneous, nor global, but rather local in space and time. By predicting a specific asymmetry in peripheral high-energy hadron reactions based on the hot spot effect Richard M. Weiner proposed a direct test of this hypothesis as well as of the assumption that the heat conductivity in hadronic matter is relatively small. The theoretical analysis of the hot spot effect in terms of propagation of heat was performed in Ref.
In high-energy hadron reactions one distinguishes peripheral reactions with low multiplicity and central collisions with high multiplicity. Peripheral reactions are also characterized by the existence of a "leading particle" which retains a large proportion of the incoming energy. By taking the notion of peripheral literally Ref.2 suggested that in this kind of reaction the surface of the colliding hadrons is locally excited giving rise to a hot spot, which is de-excited by two processes: 1) emission of particles into the vacuum 2) propagation of “heat” into the body of the target (projectile) wherefrom it is eventually also emitted through particle production. Particles produced in process 1) will have higher energies than those due to process 2), because in the latter process the excitation energy is in part degraded. This gives rise to an asymmetry with respect to the leading particle, which should be detectable in an experimental event by event analysis. This effect was confirmed by Jacques Goldberg in K− p→ K− p π+ π− reactions at 14 GEV/c. This experiment represents the first observation of local equilibrium in hadronic interactions, allowing in principle a quantitative determination of heat conductivity in hadronic matter along the lines of Ref.3 . This observation came as a surprise, because, although the electron proton scattering experiments had shown beyond any doubt that the nucleon had a finite size, it was a-priori not clear whether this size was sufficiently big for the hot spot effect to be observable, i. e. whether heat conductivity in hadronic matters was sufficiently small. Experiment4 suggests that this is the case.
Hot spots in nuclei.
In atomic nuclei, because of their larger dimensions as compared with nucleons, statistical and thermodynamical concepts have been used already in the 1930s. Hans Bethe had suggested that propagation of heat in nuclear matter could be studied in central collisions and Sin-Itiro Tomonaga had calculated the corresponding heat conductivity. The interest in this phenomenon was resurrected in the 1970s by the work of Weiner and Weström who established the link between the hot spot model and the pre-equilibrium approach used in low-energy heavy-ion reactions. Experimentally the hot spot model in nuclear reactions was confirmed in a series of investigations some of which of rather sophisticated nature including polarization measurements of protons and gamma rays. Subsequently on the theoretical side the link between hot spots and limiting fragmentation and transparency in high-energy heavy ion reactions was analyzed and “drifting hot spots” for central collisions were studied.
With the advent of heavy ion accelerators experimental studies of hot spots in nuclear matter became a subject of current interest and a series of special meetings was dedicated to the topic of local equilibrium in strong interactions. The phenomena of hot spots, heat conduction and preequilibrium play also an important part in high-energy heavy ion reactions and in the search for the phase transition to quark matter.
Hot spots and solitons.
Solitary waves (solitons) are a possible physical mechanism for the creation of hot spots in nuclear interactions. Solitons are a solution of the hydrodynamic equations characterized by a stable localized high density region and small spatial volume. They were predicted to appear in low-energy heavy ion collisions at velocities of the projectile slightly exceeding the velocity of sound (E/A ~ 10-20 MeV; here E is the incoming energy and A the atomic number). Possible evidence for this phenomenon is provided by the experimental observation that the linear momentum transfer in 12C induced heavy-ion reactions is limited.


Markus Aspelmeyer

Markus Aspelmeyer is an Austrian quantum physicist.
Aspelmeyer was born 1974 in the Bavarian town Schongau. He also attended the local school, where he received his abitur in 1993.
He studied physics and philosophy at the University of Munich, receiving his BS in philosophy and his Ph.D in physics in 2002. He joined the group of Anton Zeilinger at the University of Vienna in 2002 with a Feodor Lynen PostDoctoral Fellowship of the Alexander von Humboldt Foundation. He became Universitätsassistent at the University and then, Junior, later Senior Researcher, at the Institute for Quantum Optics and Quantum Information (IQOQI) of the Austrian Academy of Sciences where he is leading a research team working on quantum effects in micro- and nanomechanical systems. His research interests are quantum entanglement and quantum optics.
He was awarded the Lieben Prize in 2007 and an ERC Starting Independent Researcher Grant in 2009. He was offered chairs at the University of Oxford, the University of Calgary and the University of Vienna and currently holds the chair for Quantum Information on the Nanoscale at the University of Vienna. For his work in quantum optics, quantum information and quantum-opto-mechanics he has received the Fresnel Prize of the European Physical Society, the Ignaz Lieben Prize of the Austrian Academy of Sciences and the Fritz-Kohlrausch Prize of the Austrian Physical Society. Together with Garrett Cole, co-founding partner of Crystalline Mirror Solutions (CMS), he received the second prize of the Berthold Leibinger Innovationspreis in 2016 for the development of substrate-transferred crystalline coatings. In December 2019 CMS was acquired by Thorlabs Inc.


Allen Caldwell

Allen Caldwell is one of currently seven directors of the Max Planck Institute for Physics. He became director in 2002.


Lay Nam Chang

Lay Nam Chang (章礼南, June 1, 1943 – December 8, 2020) was an American theoretical physicist.  Over the course of his career, he published research on topics in particle physics, nuclear physics, general relativity, and quantum cosmology.  In the mid-1970s, he also published pioneering work on the foundations of string theory. In 2003, he served as the founding dean of the College of Science at Virginia Polytechnic Institute and State University (“Virginia Tech”) and held that position until 2016.
Education.
Lay Nam Chang was born in Singapore on June 1, 1943.  He received his AB degree from Columbia University in 1964 and earned his PhD in Physics from the University of California, Berkeley in 1967. Steven Weinberg, who won the Nobel Prize in Physics in 1979, supervised Chang’s dissertation.
Career and research.
After earning his PhD at Berkeley, Lay Nam Chang was a resident associate at MIT from 1967 to 1969.  He next held a postdoctoral fellowship at the Enrico Fermi Institute of the University of Chicago from 1969 to 1971.
Lay Nam Chang served as an assistant professor of physics at the University of Pennsylvania from 1971 to 1978.  During his time at Penn, he was a visiting scientist at the Niels Bohr Institute in Copenhagen, Denmark (1974), Stanford University, and the Brookhaven National Laboratory (1976, 1978).  In 1976, during his time at Penn, Chang wrote pioneering articles on the foundations of string theory, in collaboration with Freydoon Mansouri of Yale University.
He moved to Virginia Tech in 1978 and rose from associate (1978–83) to full professor (post-1983).  During his tenure at Virginia Tech, he was a visiting scientist at Los Alamos National Laboratory (1981), Stony Brook University (1982, 1984), Brookhaven National Laboratory (1980), and the Kavli Institute for Theoretical Physics at the University of California, Santa Barbara (1988).  For several years he served as chair of the Physics Department at Virginia Tech.  From 2002 to 2003, he served as the last dean of Virginia Tech’s College of Arts and Science, which, following a restructuring, split into a College of Liberal Arts and Human Sciences, and a College of Science.
In 2003, Lay Nam Chang became first dean of Virginia Tech’s newly formed College of Science and filled that role until his retirement in 2016.  He held responsibility for eight departments, established a new School of Neuroscience, and initiated interdisciplinary programs including the Virginia Tech Academy of Integrated Science, which fosters research across fields such as computational analytics and data modeling, nanoscience, and systems biology.
Lay Nam Chang continued to publish research articles in theoretical physics during his years as a dean.  In 2005, for example, he published a study called, "Hydrogen-Atom Spectrum under a Minimal-Length Hypothesis," with Sandor Benczik, Djordje Minic, and Tatsu Takeuchi; while in 2013, he wrote an article with Zachary Lewis, Djordje Minic, and Tatsu Takeuchi entitled, “Is Quantum Gravity a Super-Quantum Theory?”
Legacy.
To honor Lay Nam Chang’s service, Virginia Tech established an endowed chair, called the Lay Nam Chang Dean’s Chair.  This position provides its holder with funds to initiate new programs as dean of the College of Science. Upon establishing this position, the head of the Roundtable – Virginia Tech’s advisory board of alumni and friends – called Chang a “visionary” for his work in promoting neuroscience within the university, while Virginia Tech’s official news bureau described a college dean’s chair like this one “the most prestigious position that can be held” within one of the institution’s constituent colleges.
The statistician Sally C. Morton became the first recipient of the Lay Nam Dean’s Chair in the College of Science at Virginia Tech in 2016.
Lay Nam Chang died on December 8, 2020 from complications arising from COVID-19 during the COVID-19 pandemic in Virginia. Students at Virginia Tech remembered him, among other things, for taking science- and non-science majors to visit CERN, the European Organization for Nuclear Research in Geneva, Switzerland, on a study abroad tour, and for introducing new specialized and interdisciplinary undergraduate programs in subjects like nanomedicine, polymer chemistry, and medicinal chemistry.


Ernest Ambler

Ernest Ambler (November 20, 1923 – February 17, 2017) was a British-American physicist who served as the Acting Under Secretary for Technology in the Department of Commerce (1988–89), as director of the United States' National Bureau of Standards (NBS, 1975–89), and as the first director of the United States' National Institute of Standards and Technology 1988–89.
Early life and education.
Ernest Ambler was born in Bradford, England, in 1923. He received his bachelor of arts degree from the University of Oxford and went on to earn a D.Phil degree in 1953 from the same institution.
Career.
In 1953 Ambler began work in the Cryogenic Physics Section of the United States' National Bureau of Standards, becoming section chief in 1961. In his early years at the NBS, Ambler was principal collaborator with Chien-Shiung Wu on what became the Wu experiment. He was awarded a Guggenheim Fellowship in 1962. He elected a Fellow of the American Physical Society in 1958.
In 1973 Ambler was appointed deputy director of the NBS and, in 1975, served with NBS director Richard W. Roberts as the U.S. delegation to the 15th General Conference on Weights and Measures in France. Ambler assumed the position of acting director in 1975, following the departure of Roberts. In 1977 he was nominated to the office of Director of the National Bureau of Standards by President Jimmy Carter and was confirmed to the post by the U.S. Senate the following year.
Ambler presided over the 1988 change of the NBS to the National Institute of Standards and Technology and became the first director of the new agency. Though he had announced his decision to retire effective April 1989, he agreed to a request by United States Secretary of Commerce William Verity to remain as director through the end of the year and to also accept appointment, on an acting basis, to the newly created position of Under Secretary for Technology in the Department of Commerce.
Personal life.
Ambler was naturalized as a United States citizen in 1957. With his wife, Alice Virginia Seiler, he had two sons. He died at Hilton Head, South Carolina after a brief illness.


International Organization for Medical Physics

The International Organization for Medical Physics (IOMP) is a professional organization for medical physics with nearly 22,000 members in 84 countries.
Objectives and History.
IOMP is charged with a mission to advance medical physics practice worldwide by disseminating scientific and technical information, fostering the educational and professional development of medical physics and promoting the highest quality medical services for patients.
IOMP was formed in January 1963 initially with 4 affiliated national member organizations (Canada, Sweden, UK, USA). After 50 years of active existence and global support for the medical physics profession, IOMP has a membership of 80 national member organizations and 6 regional organizations. IOMP is affiliated to IUPESM, IUPAP and ICSU and is officially connected to IFMBE.
IOMP collaborates with professional bodies such as IRPA and ICRP and international organizations such as WHO and IAEA in promoting the development of medical physics and safe use of radiation and radiological equipment technology.
IOMP publishes an electronic Newsletter (Medical Physics World) and an open-source journal (Medical Physics International).
To raise awareness about the role medical physicists play for the benefit of patients, IOMP organizes the annual International Day of Medical Physics (IDMP) on November 7 - the birthday of Marie Sklodowska-Curie.
The World Congress on Medical Physics and Biomedical Engineering (World Congress) is organised by IOMP (together with IFMBE and IUPESM) as well as the International Congress of Medical Physics (ICMP), held between World Congresses.
IOMP Member Countries.
Countries are represented by the respective National Organizations for Medical Physics.


Viktor Panin (physicist)

Viktor Yevgenievich Panin (; 10 November 1930 – 25 September 2020) was a Soviet and Russian physicist, professor, and advisor of the Russian Academy of Sciences. He was an expert in the fields of solid mechanics, plastic deformation and physical materials.
Curriculum vitae.
He was a Foreign Member of the National Academy of Sciences of Belarus since 1999.
Scientific achievements.
Under the guidance of academician Victor Panin who established and developed physical mesomechanics of materials, uniting physical materials with solid mechanics at macrolevel and with physics of plastic deformation at microlevel. Within this framework, he developed new methods of computer design materials and technologies of their production. Deep mesomechanics ideas can be successfully used in the new approach to earthquake prediction where the seismic source mesostructure appears to be an intermediate term precursor.


Lagrange invariant

In optics the Lagrange invariant is a measure of the light propagating through an optical system. It is defined by
where "y" and "u" are the marginal ray height and angle respectively, and "ȳ" and "ū" are the chief ray height and angle. "n" is the ambient refractive index. In order to reduce confusion with other quantities, the symbol Ж may be used in place of H. "Ж"2 is proportional to the throughput of the optical system (related to étendue). For a given optical system, the Lagrange invariant is a constant throughout all space, that is, it is invariant upon refraction and transfer.
The optical invariant is a generalization of the Lagrange invariant which is formed using the ray heights and angles of any two rays. For these rays, the optical invariant is a constant throughout all space.