Rayleigh numberIn fluid mechanics, the Rayleigh number (Ra, after Lord Rayleigh) for a fluid is a dimensionless number associated with buoyancy-driven flow, also known as free (or natural) convection. It characterises the fluid's flow regime: a value in a certain lower range denotes laminar flow; a value in a higher range, turbulent flow. Below a certain critical value, there is no fluid motion and heat transfer is by conduction rather than convection. For most engineering purposes, the Rayleigh number is large, somewhere around 106 to 108.
Majdanek concentration campMajdanek (or Lublin) was a Nazi concentration and extermination camp built and operated by the SS on the outskirts of the city of Lublin during the German occupation of Poland in World War II. It had seven gas chambers, two wooden gallows, and some 227 structures in all, placing it among the largest of Nazi concentration camps. Although initially intended for forced labor rather than extermination, the camp was used to murder people on an industrial scale during Operation Reinhard, the German plan to murder all Polish Jews within their own occupied homeland.
PowderA powder is a dry, bulk solid composed of many very fine particles that may flow freely when shaken or tilted. Powders are a special sub-class of granular materials, although the terms powder and granular are sometimes used to distinguish separate classes of material. In particular, powders refer to those granular materials that have the finer grain sizes, and that therefore have a greater tendency to form clumps when flowing. Granulars refer to the coarser granular materials that do not tend to form clumps except when wet.
Separated setsIn topology and related branches of mathematics, separated sets are pairs of subsets of a given topological space that are related to each other in a certain way: roughly speaking, neither overlapping nor touching. The notion of when two sets are separated or not is important both to the notion of connected spaces (and their connected components) as well as to the separation axioms for topological spaces. Separated sets should not be confused with separated spaces (defined below), which are somewhat related but different.
Brown v. Board of EducationBrown v. Board of Education of Topeka, 347 U.S. 483 (1954), was a landmark decision by the U.S. Supreme Court which ruled that U.S. state laws establishing racial segregation in public schools are unconstitutional, even if the segregated schools are otherwise equal in quality. The decision partially overruled the Court's 1896 decision Plessy v. Ferguson, which had held that racial segregation laws did not violate the U.S. Constitution as long as the facilities for each race were equal in quality, a doctrine that had come to be known as "separate but equal".
Area densityThe area density (also known as areal density, surface density, superficial density, areic density, mass thickness, column density, or density thickness) of a two-dimensional object is calculated as the mass per unit area. The SI derived unit is the kilogram per square metre (kg·m−2). A related area number density can be defined by replacing mass in by number of particles or other countable quantity. In the paper and fabric industries, it is called grammage and is expressed in grams per square meter (g/m2); for paper in particular, it may be expressed as pounds per ream of standard sizes ("basis ream").
Hand surgeryHand surgery deals with both surgical and non-surgical treatment of conditions and problems that may take place in the hand or upper extremity (commonly from the tip of the hand to the shoulder) including injury and infection. Hand surgery may be practiced by post graduates of orthopedic surgery and plastic surgery. Plastic surgeons and orthopedic surgeons receive significant training in hand surgery during their residency training. Also, some graduates do an additional one-year hand fellowship.
Normal spaceIn topology and related branches of mathematics, a normal space is a topological space X that satisfies Axiom T4: every two disjoint closed sets of X have disjoint open neighborhoods. A normal Hausdorff space is also called a T4 space. These conditions are examples of separation axioms and their further strengthenings define completely normal Hausdorff spaces, or T5 spaces, and perfectly normal Hausdorff spaces, or T6 spaces. A topological space X is a normal space if, given any disjoint closed sets E and F, there are neighbourhoods U of E and V of F that are also disjoint.
