The Bathtub Curve

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.

A solar cell can be modeled by an equivalent electrical circuit. The simplest model includes a current source representing the photogenerated current (\(I_L\)), in parallel with a diode representing the p-n junction. A more accurate model adds a parallel shunt resistance (\(R_{sh}\)) for leakage currents and a series resistance (\(R_s\)) for contact and bulk material resistance.

Developed in 1950 by Vitaly Ginzburg and Lev Landau, this is a phenomenological theory that describes superconductivity near the phase transition. It introduces a complex order parameter, \(\Psi\), to represent the density of superconducting electrons. The theory successfully describes effects like the Meissner effect and predicts the distinction between Type I and Type II superconductors based on a single parameter, \(\kappa\).

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).

A Pourbaix diagram, also known as a potential/pH diagram, is a thermodynamic chart that maps the stable equilibrium phases of an aqueous electrochemical system. It graphically shows the conditions of potential (\(E_H\)) and pH under which a metal is immune (thermodynamically stable), passivated (forms a stable protective film), or susceptible to corrosion (forms soluble ions).

A thermal lance achieves temperatures of 3,500 °C to 4,500 °C, far exceeding conventional torches. This intense heat does not just melt the target material. The jet of pure oxygen also causes rapid oxidation of the material itself, effectively making it part of the fuel source. This combined melting and burning action allows it to cut through thick steel, concrete, and rock.

PUREX, an acronym for Plutonium and Uranium Recovery by Extraction, is the primary industrial method for reprocessing spent nuclear fuel. It employs liquid-liquid extraction (LLE) to separate uranium and plutonium from highly radioactive fission products. The process uses a 30% solution of tributyl phosphate (TBP) in a hydrocarbon diluent to selectively extract U(VI) and Pu(IV) from a nitric acid feed.

The "tonne of TNT" is a unit of energy used to quantify large energy releases, particularly from explosions. It is conventionally defined by international agreement as 4.184 gigajoules (GJ). This value is based on the calculated energy density of TNT upon detonation, which is approximately 4,184 J/g. It serves as a standard reference for comparing the yields of nuclear weapons and other explosive events.