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Topic Review
Riemannian Metric and Lie Bracket in Computational Anatomy
Computational anatomy (CA) is the study of shape and form in medical imaging. The study of deformable shapes in computational anatomy rely on high-dimensional diffeomorphism groups [math]\displaystyle{ \varphi \in \operatorname{Diff}_V }[/math] which generate orbits of the form [math]\displaystyle{ \mathcal{M} \doteq \{ \varphi \cdot m \mid \varphi \in \operatorname{Diff}_V \} }[/math]. In CA, this orbit is in general considered a smooth Riemannian manifold since at every point of the manifold [math]\displaystyle{ m \in \mathcal{M} }[/math] there is an inner product inducing the norm [math]\displaystyle{ \| \cdot \|_m }[/math] on the tangent space that varies smoothly from point to point in the manifold of shapes [math]\displaystyle{ m \in \mathcal{M} }[/math]. This is generated by viewing the group of diffeomorphisms [math]\displaystyle{ \varphi \in \operatorname{Diff}_V }[/math] as a Riemannian manifold with [math]\displaystyle{ \| \cdot \|_\varphi }[/math], associated to the tangent space at [math]\displaystyle{ \varphi \in\operatorname{Diff}_V }[/math] . This induces the norm and metric on the orbit [math]\displaystyle{ m \in \mathcal{M} }[/math] under the action from the group of diffeomorphisms.
  • 487
  • 25 Oct 2022
Biography
Wilhelm Hanle
Wilhelm Hanle (13 January 1901 – 29 April 1993, Gießen) was a German experimental physicist. He is known for the Hanle effect. During World War II, he made contributions to the German nuclear energy project, also known as the Uranium Club. From 1941 until emeritus status in 1969, he was an ordinarius professor of experimental physics and held the chair of physics at the University of Giessen.
  • 487
  • 18 Nov 2022
Topic Review
Quantum Reality
Quantum Reality is a 1985 popular science book by physicist Nick Herbert, a member the Fundamental Fysiks Group which was formed to explore the philosophical implications of quantum theory. The book attempts to address the ontology of quantum objects, their attributes, and their interactions, without reliance on advanced mathematical concepts. Herbert discusses the most common interpretations of quantum mechanics and their consequences in turn, highlighting the conceptual advantages and drawbacks of each.
  • 486
  • 30 Nov 2022
Topic Review
Liquid Mirror Telescope
Liquid mirror telescopes are telescopes with mirrors made with a reflective liquid. The most common liquid used is mercury, but other liquids will work as well (for example, low melting alloys of gallium). The liquid and its container are rotated at a constant speed around a vertical axis, which causes the surface of the liquid to assume a paraboloidal shape, suitable for use as the primary mirror of a reflecting telescope. The rotating liquid assumes the paraboloidal shape regardless of the container's shape. To reduce the amount of liquid metal needed, and thus weight, a rotating mercury mirror uses a container that is as close to the necessary parabolic shape as possible. Liquid mirrors can be a low cost alternative to conventional large telescopes. Compared to a solid glass mirror that must be cast, ground, and polished, a rotating liquid metal mirror is much less expensive to manufacture. Isaac Newton noted that the free surface of a rotating liquid forms a circular paraboloid and can therefore be used as a telescope, but he could not actually build one because he had no way to stabilize the speed of rotation. The concept was further developed by Ernesto Capocci of the Naples Observatory (1850), but it was not until 1872 that Henry Skey of Dunedin, New Zealand constructed the first working laboratory liquid mirror telescope. Another difficulty is that a liquid metal mirror can only be used in zenith telescopes, i.e., that look straight up, so it is not suitable for investigations where the telescope must remain pointing at the same location of inertial space (a possible exception to this rule may exist for a mercury mirror space telescope, where the effect of Earth's gravity is replaced by artificial gravity, perhaps by rotating the telescope on a very long tether, or propelling it gently forward with rockets). Only a telescope located at the North Pole or South Pole would offer a relatively static view of the sky, although the freezing point of mercury and the remoteness of the location would need to be considered. A very large telescope already exists at the South Pole, but the North Pole is located in the Arctic Ocean. The mercury mirror of the Large Zenith Telescope in Canada was the largest liquid metal mirror ever built. It had a diameter of six meters, and rotated at a rate of about 8.5 revolutions per minute. It is now decommissioned. This mirror was a test, built for $1 million but it was not suitable for astronomy because of the test site's weather. They are now planning to build a larger 8 meter liquid mirror telescope ALPACA for astronomical use and a larger project called LAMA with 66 individual 6.15 meter telescopes with a total collecting power equal to a 55 meter telescope, resolving power of a 70 meter scope.
  • 485
  • 08 Oct 2022
Biography
John Boardman
Jack Melton Boardman, commonly known as John Boardman, (born September 8, 1932) is an American physicist. He is a former professor of physics at Brooklyn College; a noted science fiction fan, author and fanzine publisher; and a gaming authority. Boardman earned his B.A. at the University of Chicago in 1952 and his M.S. from Iowa State University in 1956. He then attended Florida State Univers
  • 485
  • 26 Dec 2022
Topic Review
Waveguide-Enhanced Raman Spectroscopy
Photonic chip-based methods for spectroscopy are of considerable interest due to their applicability to compact, low-power devices for the detection of small molecules. Waveguide-enhanced Raman spectroscopy (WERS) has emerged over the past decade as a particularly interesting approach. WERS utilizes the evanescent field of a waveguide to generate Raman scattering from nearby analyte molecules, and then collects the scattered photons back into the waveguide. The large interacting area and strong electromagnetic field provided by the waveguide allow for significant enhancements in Raman signal over conventional approaches.
  • 484
  • 29 Dec 2022
Topic Review
Beyond Special Relativity
There are two different ways in which one can go beyond the kinematics of Special Relativity (SR). One can consider adding to the Standard Model (SM) Lagrangian new terms that violate Lorentz Invariance (LIV). In case one wants to preserve the relativistic invariance, one should modify the transformations between inertial frames and accordingly modify the special relativistic kinematics; this is what is called Doubly/Deformed Special Relativity (DSR). 
  • 484
  • 13 Jul 2022
Topic Review
Public Utility Holding Company Act of 1935
The Public Utility Holding Company Act of 1935 (PUHCA), also known as the Wheeler-Rayburn Act, was a US federal law giving the Securities and Exchange Commission authority to regulate, license, and break up electric utility holding companies. It limited holding company operations to a single state, thus subjecting them to effective state regulation. It also broke up any holding companies with more than two tiers, forcing divestitures so that each became a single integrated system serving a limited geographic area. Another purpose of the PUHCA was to keep utility holding companies engaged in regulated businesses from also engaging in unregulated businesses. The act was based on the conclusions and recommendations of the 1928-35 Federal Trade Commission investigation of the electric industry. On March 12, 1935, President Franklin D. Roosevelt released a report he commissioned by the National Power Policy Committee. This report became the template for the PUHCA. The political battle over its passage was one of the bitterest of the New Deal, and was followed by eleven years of legal appeals by holding companies led by the Electric Bond and Share Company, which finally completed its breakup in 1961. On August 26, 1935, President Franklin D. Roosevelt signed the bill into law. The Energy Policy Act of 2005 repealed the PUHCA.
  • 484
  • 18 Nov 2022
Biography
Christopher Slowe
Christopher Brian Slowe (born November 8, 1978, Boston, MA) is an American businessman. He gained his PhD in Physics from Harvard, went on to co-found reddit, with Aaron Swartz, Alexis Ohanian and Steve Huffman. He later departed reddit and began work for Hipmunk, where he has been Chief Scientist since 2010. Slowe was awarded his Ph.D. in Physics from Harvard for his thesis "Experiments and
  • 484
  • 13 Dec 2022
Topic Review
Spectrochemistry
Spectrochemistry is the application of spectroscopy in several fields of chemistry. It includes analysis of spectra in chemical terms, and use of spectra to derive the structure of chemical compounds, and also to qualitatively and quantitively analyze their presence in the sample. It is a method of chemical analysis that relies on the measurement of wavelengths and intensity of electromagnetic radiation.
  • 482
  • 30 Oct 2022
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