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An experimental researcher whose joint study tracked the Brownian motion of ellipsoidal particles. Their nonspherical shape makes motion along the long axis differ from motion across it. Following both position and orientation with video microscopy reveals how particle geometry changes random motion even in an otherwise uniform liquid.^[ref]

An experimental researcher whose joint work studied the spatial distribution of ultracold atoms obeying Fermi-Dirac statistics. The team’s 2001 measurement of degeneracy pressure compared trapped atomic clouds as they cooled, using the difference between bosonic and fermionic behavior to expose the effect of quantum statistics. The measurement connects a macroscopic cloud shape with the allowed occupation of single-particle states.^[ref]

An experimental researcher whose team observed degeneracy pressure in a trapped gas of atoms obeying Fermi-Dirac statistics. Cooling a fermionic cloud alongside a bosonic one lets their sizes be compared under common experimental conditions. The fermionic distribution resists the concentration expected for a classical gas because the Pauli exclusion principle prevents identical fermions from all occupying the same low-energy state. The cloud’s spatial profile therefore makes a consequence of quantum statistics directly measurable.^[ref]

Institutional author and issuer of Online Dictionary of Crystallography by International Union of Crystallography.

Institutional issuer and web host of photonics technical education material and product catalogues. No individual author is established for the cited photodiode documents.

Inspected laboratory document: www.thorlabs.com/images/TabImages/Photodetector_Lab.pdf

Institutional physics teaching laboratory at Universität Leipzig.

Official website: home.uni-leipzig.de/prakphys/

Institutional physics teaching-resource host.

Official website: physics.umd.edu

Corporate issuer of semiconductor detector technical notes.

Official website: www.hamamatsu.com

Instrument manufacturer and institutional issuer of its operating manuals.

Official website: www.thinksrs.com

Institutional source issuer.

Institutional source issuer.

Friedrich Hund organized complicated atomic spectral lines through relationships between the angular momenta and energy levels of many-electron configurations. In modern notation, a term symbol ${}^{2S+1}{L}_J$ records total electron spin $S$, total orbital angular momentum $L$ and coupled total angular momentum $J$. For example, $S=1$ permits three spin projections, whereas $S=0$ permits one. The classification reduces a large pattern of lines to relationships between fewer quantum states. This modern spin notation should be distinguished from the historical language of his original spectral analysis.^[ref]

Edward W. Morley and Albert A. Michelson tested whether the orientation of an interferometer revealed motion through the proposed luminiferous aether. Perpendicular optical paths were recombined to form interference fringes; rotating the instrument tested for the predicted change in their relative travel times. The measured shift was much smaller than the prediction based on a stationary luminiferous aether and the Earth's orbital motion. The experiment constrained that model through a differential optical measurement, rather than directly timing a single light pulse.^[ref]

An experimental nuclear physicist who, with Hans Geiger, related the range of emitted alpha particles to a radioactive substance's transformation period. The Geiger-Nuttall law connects the particle's escape energy with the enormous variation in alpha decay lifetimes. It began as an empirical correlation, before quantum tunnelling supplied a mechanism for nuclear escape.^[ref]

Photoelectron spectroscopy measures the kinetic energies of photoelectrons produced by illuminating matter with photons of known energy. The photoelectric effect supplies the emission mechanism; spectroscopy turns the distribution of emitted electron energies into information about occupied energy levels and chemical bonds. A broad survey helps identify chemical elements, while small shifts within one element's lines can distinguish different chemical surroundings. These are different questions: finding carbon does not establish which chemical bonds its chemical atoms form.

The useful inversion is an energy balance. A known incoming photon energy pays for removal of an electron and for its outgoing kinetic energy. To apply that balance to a solid, specify the zero of energy and the work function of the instrument. Photoelectron binding energy reference derives the conversion for a conducting sample in electrical contact with its analyzer. A free molecule instead has an ionization energy referenced to an electron at rest in vacuum; it need not share a Fermi level with the analyzer.

Absorption takes a chemical substance into a material's bulk, as when carbon dioxide dissolves in water. Adsorption instead concerns accumulation at a boundary. Bulk uptake and interfacial accumulation can coexist; total uptake alone does not separate their contributions. This use of absorption concerns material uptake, whereas absorbance describes attenuation of electromagnetic radiation.

Chemical thermodynamics studies energy, entropy, and equilibrium in chemical systems. At fixed temperature and pressure, the direction of spontaneous change is constrained by Gibbs free energy, and equilibrium corresponds to an appropriate minimum subject to the system's conserved quantities.

For a reaction, ${\Delta }_{r}G={\Delta }_r{G}^{\circ }+RT\ln Q$, where $Q$ is the reaction quotient. Setting ${\Delta }_{r}G=0$ gives $K=\exp (-{\Delta }_r{G}^{\circ }/RT)$ for the dimensionless equilibrium constant. This connects measurable composition with free energy. It does not determine the reaction rate, which also depends on the accessible pathway and its activation barriers.

Electrophoresis is motion of charged dispersed species relative to a surrounding medium under an applied electric field. The drift depends on electrical driving and friction, including the surrounding ionic atmosphere. Gel electrophoresis adds a porous matrix that makes migration sensitive to molecular size and conformation.

A nuclear emulsion is a photographic emulsion prepared for recording charged particles. The sensitive material serves as both target and record: a particle may slow, stop, decay or cause a nuclear reaction inside it. Reading that record requires track reconstruction, not recognizing a miniature picture of a particle. Unlike a cloud chamber photograph, the exposed nuclear emulsion itself retains the record until it is developed and examined.

A developed grain is a visible deposit of silver produced during photographic processing. The chain of developed grains in a nuclear emulsion records interactions along a charged particle's path. Its width is a property of the recording and viewing process, not a measurement of the particle's diameter.