Hamaker Theory (physics)

The Planckian locus is the path that the color of an incandescent black-body radiator follows in a chromaticity space as its temperature changes. It is typically plotted on the CIE 1931 xy chromaticity diagram, appearing as an arc from the reddish-orange region to the bluish-white region. It serves as the fundamental reference for defining color temperature.

The ultraviolet spectrum is commonly subdivided into UVA (400–315 nm), UVB (315–280 nm), and UVC (280–100 nm). UVA, or long-wave UV, is the least energetic and penetrates the skin deepest. UVB, or medium-wave UV, causes sunburn and is crucial for vitamin D synthesis. UVC, or short-wave UV, is the most energetic and germicidal but is completely absorbed by Earth's atmosphere.

Discovered in 1933 by Walther Meissner and Robert Ochsenfeld, the Meissner effect is the expulsion of a magnetic field from a superconductor during its transition to the superconducting state. When a material is cooled below its critical temperature (\(T_c\)) in the presence of a weak external magnetic field, it actively cancels all magnetic flux inside it, becoming a perfect diamagnet.

A solar cell's core is a p-n junction, an interface between p-type and n-type semiconductor materials. This junction creates a built-in electric field in a depletion region. When photons with sufficient energy strike the semiconductor, they create electron-hole pairs. The electric field separates these charge carriers, driving electrons to the n-side and holes to the p-side, generating a voltage.

The Weissenberg effect is a phenomenon in viscoelastic fluids where the fluid climbs up a rotating rod inserted into it. This is contrary to the behavior of Newtonian fluids, which are pushed outwards by centrifugal force, forming a vortex. The effect is caused by normal stress differences that develop in the fluid under shear.

Digital circuits are categorized into two main types: combinational and sequential logic. In combinational logic, the output is a pure function of the present input values only (e.g., an adder). In sequential logic, the output depends not only on the current inputs but also on the past sequence of inputs, as these circuits have memory elements (e.g., a flip-flop).

Correlated Color Temperature (CCT) is a metric for light sources that do not radiate as ideal black bodies, such as LEDs or fluorescent lamps. It is the temperature of the Planckian radiator whose color is perceived as most similar to the light source. This 'closeness' is determined by finding the point on the Planckian locus nearest to the source's chromaticity coordinates.

The Perfect Reflecting Diffuser, also known as a perfect white, is a theoretical, idealized surface used as a reference standard in colorimetry and spectrophotometry. It is defined as a surface that reflects 100% of all incident light at every wavelength in the visible spectrum and reflects this light perfectly diffusely (lambertian reflectance), meaning its brightness is uniform from any viewing angle.

A superacid is an acid with an acidity greater than that of 100% pure sulfuric acid. The conventional pH scale is inadequate for these media. Instead, their acidity is measured using the Hammett acidity function, \(H_0\). This function is based on the protonation of weak indicator bases and is defined as \(H_0 = pK_{BH^+} - \log\left(\frac{[BH^+]}{[B]}}\right)\).

The anthraquinone process, developed in the 1930s, is the dominant industrial method for producing hydrogen peroxide. It involves the hydrogenation of an anthraquinone derivative to an anthrahydroquinone, followed by its oxidation with air to regenerate the original anthraquinone and produce hydrogen peroxide. The H₂O₂ is then extracted with water and concentrated, creating a continuous, efficient cycle.

The oxidation state, or oxidation number, is a hypothetical charge that an atom would have if all its bonds to different atoms were 100% ionic. It provides a way to track electron transfer in redox reactions. An increase in oxidation state signifies oxidation, while a decrease signifies reduction. This formalism simplifies the analysis of complex chemical reactions.

Thermate is an incendiary composition that enhances standard thermite. It is typically a mixture of thermite, barium nitrate (\(Ba(NO_3)_2\)), and sulfur. The barium nitrate acts as an oxidizer, increasing the thermal output and making the reaction less dependent on atmospheric oxygen. Sulfur is added primarily to lower the ignition temperature, making the mixture easier and more reliably ignited.

Plasticity is the theory describing the deformation of a solid material undergoing non-reversible changes of shape in response to applied forces. Unlike elasticity, where deformation is recovered upon unloading, plastic deformation is permanent. The theory involves a yield criterion to define the onset of plasticity, a flow rule to describe the evolution of plastic strain, and a hardening rule.

The bathtub curve is a graphical model illustrating three phases of a product's life in terms of failure rate. It starts with a high but decreasing 'infant mortality' rate, followed by a low, constant 'useful life' rate, and concludes with an increasing 'wear-out' rate. MTBF calculations using a constant failure rate (\(\lambda\)) are typically only valid during the central 'useful life' phase.