Shockley–Queisser Limit

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 \(\lambda\), MTBF is its reciprocal: \(MTBF = 1/\lambda\). This simple relationship is fundamental in reliability engineering for predicting system uptime and planning maintenance schedules, assuming failures follow an exponential distribution.

For a system of components in series, where any single failure causes system failure, the overall failure rate is the sum of individual rates. The system's MTBF is the reciprocal of this sum: \(MTBF_{system} = (\sum_{i=1}^{n} \lambda_i)^{-1} = (1/MTBF_1 + 1/MTBF_2 + ... + 1/MTBF_n)^{-1}\). This implies the system's MTBF is always less than the lowest individual component's MTBF.

This method uses high-energy photons emitted from a radioisotope source, typically Cobalt-60, to sterilize products. The gamma rays pass through materials, creating free radicals and causing irreparable damage to microbial DNA, leading to cell death. It is a 'cold' process suitable for heat-sensitive items and can be performed on products already in their final sealed packaging.

Developed by French engineer Pierre Bézier for Renault in the 1960s, UNISURF was one of the first true 3D CAD/CAM systems. Its core innovation was the use of what are now known as Bézier curves and surfaces. These are parametric curves defined by a set of control points, allowing for the intuitive and mathematical creation of complex freeform shapes for car bodies.

Physics of Failure (PoF) is a reliability engineering approach that uses knowledge of materials science and physics to understand and model the root-cause mechanisms of failure. Instead of relying purely on statistical data from past failures, it focuses on predicting failure by analyzing the physical processes (e.g., fatigue, corrosion, creep) that lead to degradation and breakdown.

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.

For repairable systems, Mean Time Between Failures (MTBF) is the sum of Mean Time To Failure (MTTF) and Mean Time To Repair (MTTR). The formula is \(MTBF = MTTF + MTTR\). MTTF represents the average operational time before a failure, while MTTR is the average time taken to repair the system. This distinction is critical for understanding system availability.

Cleanrooms utilize two primary airflow principles to control contamination. Turbulent (or non-unidirectional) flow involves mixed air streams, suitable for less stringent classes (ISO 6-9). Laminar (or unidirectional) flow uses parallel, constant-velocity air streams to sweep particles out of the environment, essential for high-purity applications like ISO 1-5, preventing cross-contamination and ensuring rapid particle removal.

CMOS (Complementary Metal-Oxide-Semiconductor) is the dominant technology for constructing integrated circuits. It uses complementary pairs of p-type and n-type MOSFETs to build logic gates. Its primary advantage is very low static power consumption, as one transistor in the pair is always off during steady state, resulting in minimal current flow except during switching transitions.

Top-down synthesis involves creating nanomaterials by starting with a larger, bulk material and breaking it down or patterning it to the nanoscale. Key techniques include mechanical methods like ball milling and lithographic methods like photolithography, electron-beam lithography, and nanoimprint lithography. These methods are often used for creating structured surfaces and integrated circuits, but can suffer from surface imperfections.

Molecular electronics explores using individual molecules or nanoscale molecular collections as fundamental electronic components. This approach aims to build circuits at the ultimate limit of miniaturization, far beyond traditional silicon-based technology. Key components include molecular wires, switches, and rectifiers, leveraging quantum mechanical properties like electron tunneling through molecular orbitals for their function.

Lithium-ion batteries function via an intercalation mechanism, a reversible insertion of ions into a layered host material. During discharge, lithium ions (\(Li^+\)) de-intercalate from a negative electrode (anode), typically graphite, and move through a non-aqueous electrolyte to intercalate into a positive electrode (cathode), typically a metal oxide. Electrons travel through the external circuit, creating current.