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In 1968 Shirley Chisholm became the first Black woman elected to the United States Congress. In 1972 she launched a campaign for the Democratic presidential nomination, breaking another political barrier.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
Polymer physics is the field of physics that studies polymers, their fluctuations, mechanical properties, as well as the kinetics of reactions involving degradation of polymers and polymerisation of monomers. While it focuses on the perspective of condensed matter physics, polymer physics was originally a branch of statistical physics. Polymer physics and polymer chemistry are also related to the field of polymer science, which is considered to be the applicative part of polymers. Polymers are large molecules and thus are very complicated for solving using a deterministic method. Yet, statistical approaches can yield results and are often pertinent, since large polymers (i.e., polymers with many monomers) are describable efficiently in the thermodynamic limit of infinitely many monomers (although the actual size is clearly finite). Thermal fluctuations continuously affect the shape of polymers in liquid solutions, and modeling their effect requires the use of principles from statistical mechanics and dynamics. As a corollary, temperature strongly affects the physical behavior of polymers in solution, causing phase transitions, melts, and so on. The statistical approach to polymer physics is based on an analogy between polymer behavior and either Brownian motion or another type of a random walk, the self-avoiding walk. The simplest possible polymer model is presented by the ideal chain, corresponding to a simple random walk. Experimental approaches for characterizing polymers are also common, using polymer characterization methods, such as size exclusion chromatography, viscometry, dynamic light scattering, and Automatic Continuous Online Monitoring of Polymerization Reactions (ACOMP) for determining the chemical, physical, and material properties of polymers. These experimental methods help the mathematical modeling of polymers and give a better understanding of the properties of polymers. Flory is considered the first scientist establishing the field of polymer physics. French scientists contributed since the 70s (e.g. Pierre-Gilles de Gennes, J. des Cloizeaux). Doi and Edwards wrote a famous book in polymer physics. Soviet/Russian school of physics (I. M. Lifshitz, A. Yu. Grosberg, A.R. Khokhlov, V.N. Pokrovskii) have been very active in the development of polymer physics.
In fluid dynamics, Couette flow is the flow of a viscous fluid in the space between two surfaces, one of which is moving tangentially relative to the other. The relative motion of the surfaces imposes a shear stress on the fluid and induces flow. Depending on the definition of the term, there may also be an applied pressure gradient in the flow direction. The Couette configuration models certain practical problems, like the Earth's mantle and atmosphere, and flow in lightly loaded journal bearings. It is also employed in viscometry and to demonstrate approximations of reversibility. It is named after Maurice Couette, a Professor of Physics at the French University of Angers in the late 19th century. Isaac Newton first defined the problem of Couette flow in Proposition 51 of his Philosophiæ Naturalis Principia Mathematica, and expanded upon the ideas in Corollary 2.
K-value or k value may refer to: Thermal conductivity The force constant of a spring, see Hooke's law Vapor–liquid equilibrium, the ratio of vapor concentration to liquid concentration at equilibrium The relative permittivity, κ a statistical value used in the Elo rating system analysis provides a methodology for studying different factors that affect the size of a biological population. K value (viscosity), is an empirical parameter closely related to intrinsic viscosity, often defined in slightly different ways in different industries to express viscosity based estimate of statistical molecular mass of polymeric material used particularly for PVC. The most commonly used K value in Europe is the Fikentscher K value (referenced in DIN EN ISO 1628-1) obtained by dilute solution viscometry and solving Fikentscher equation. KIc or linear-elastic plane-strain fracture toughness of materials rate of change of curvature, used to assess and design vertical alignment of road and rail crests and dips The K value, also called the bending limit, of a cyclotron is the ratio between achievable energy and the charge-to-mass ratio according to E k A ≡ K ( Z A ) 2 {\displaystyle {\frac {E_{k}}{A}}\equiv K\left({\frac {Z}{A}}\right)^{2}} , where E k {\displaystyle E_{k}} is the kinetic energy of the particle, A {\displaystyle A} the atomic mass number and Z {\displaystyle Z} the charge. Freshness Quality Index for assessing fish quality. It represents the ratio between the sum of inosine and hypoxanthine to the sum of all other products of ATP degradation.
A carbon nanotube (CNT) is a tube made of carbon with a diameter in the nanometre range (nanoscale). They are one of the allotropes of carbon. Two broad classes of carbon nanotubes are recognized: Single-walled carbon nanotubes (SWCNTs) have diameters around 0.5–2.0 nanometres, about a 100,000th the width of a human hair. They can be idealised as cutouts from a two-dimensional graphene sheet rolled up to form a hollow cylinder. Multi-walled carbon nanotubes (MWCNTs) consist of nested single-wall carbon nanotubes in a nested, tube-in-tube structure. Double- and triple-walled carbon nanotubes are special cases of MWCNT. Carbon nanotubes can exhibit remarkable properties, such as exceptional tensile strength and thermal conductivity because of their nanostructure and strength of the bonds between carbon atoms. Some SWCNT structures exhibit high electrical conductivity while others are semiconductors. In addition, carbon nanotubes can be chemically modified. These properties are expected to be valuable in many areas of technology, such as electronics, optics, composite materials (replacing or complementing carbon fibres), nanotechnology (including nanomedicine), and other applications of materials science. The predicted properties for SWCNTs were tantalising, but a path to synthesising them was lacking until 1993, when Iijima and Ichihashi at NEC, and Bethune and colleagues at IBM independently discovered that co-vaporising carbon and transition metals such as iron and cobalt could specifically catalyse SWCNT formation. These discoveries triggered research that succeeded in greatly increasing the efficiency of the catalytic production technique, and led to an explosion of work to characterise and find applications for SWCNTs.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Joe Louis.