Potential-pH Diagram (Pourbaix Diagram)

A non-Newtonian fluid is one whose viscosity changes under an applied shear stress. Unlike a Newtonian fluid where viscosity is constant, its flow properties are not described by a linear relationship between shear stress ([latex]\tau[/latex]) and shear rate ([latex]\dot{gamma}[/latex]). This dependency can manifest as shear-thinning (viscosity decreases with stress) or shear-thickening (viscosity increases with stress).

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.

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).

The fundamental building block of modern digital electronics is the transistor, specifically the MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor). It operates as an electronically controlled switch. By applying a voltage to its gate terminal, the flow of current between its source and drain terminals can be turned on (representing a '1') or off (representing a '0'), enabling the implementation of logic gates.

Mean Time Between Failures (MTBF) is a reliability metric representing the predicted elapsed time between inherent failures of a repairable system. For systems with a constant failure rate [latex]\lambda[/latex], MTBF is its reciprocal: [latex]MTBF = 1/\lambda[/latex]. This simple relationship is fundamental in reliability engineering for predicting system uptime and planning maintenance schedules, assuming failures follow an exponential distribution.

A quantum mechanical phenomenon where a wavefunction can propagate through a potential energy barrier. Classically, a particle lacking sufficient energy to surmount a barrier would be reflected. However, due to the wave-like nature of particles, there is a non-zero probability that the particle can appear on the other side of the barrier, effectively 'tunneling' through it.

Electrochemical potential, [latex]\bar{\mu}_i[/latex], quantifies the total energy of a charged species `i` in a system. It combines the chemical potential, [latex]\mu_i[/latex], which accounts for concentration and intrinsic properties, with the electrostatic potential energy, [latex]z_i F \phi[/latex]. The formula is [latex]\bar{\mu}_i = \mu_i + z_i F \phi[/latex], where [latex]z_i[/latex] is the ion's charge, [latex]F[/latex] is the Faraday constant, and [latex]phi[/latex] is the local electric potential.

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.

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 ([latex]\lambda[/latex]) are typically only valid during the central 'useful life' phase.

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

The Deborah number is a dimensionless quantity in rheology, used to characterize the fluidity of materials. It is the ratio of the relaxation time, which is an intrinsic property of the material, to the characteristic time scale of the experiment or observation. The formula is [latex]De = \frac{t_c}{t_p}[/latex], where [latex]t_c[/latex] is the relaxation time and [latex]t_p[/latex] is the observation time.

Repeatability assesses precision under identical conditions, while reproducibility assesses precision when one or more conditions change, such as the operator, instrument, or location. Reproducibility variance is always greater than or equal to repeatability variance. This distinction is crucial for understanding measurement variability, especially in inter-laboratory comparisons where conditions are inherently different.