Elmarit is a designation used by the German optics manufacturer Leica for a series of camera lenses, particularly those used with Leica cameras. The designation is often associated with high-quality photographic lenses that provide sharp images and good optical performance. The term "Elmarit" is typically followed by a focal length measurement (e.g., "28mm Elmarit" or "50mm Elmarit"), indicating the specific type or model of the lens.

In fluid dynamics, an "eddy" refers to a localized, swirling flow of fluid that occurs in various types of fluids, be they gases or liquids. Edies develop when the flow of the fluid is disturbed by obstacles, changes in flow velocity, or other discontinuities, leading to a rotational motion of fluid particles.

A post-tropical cyclone is a storm system that has lost its tropical characteristics, typically due to cooler sea surface temperatures or interaction with land. While it may still retain some features of a tropical system, such as a well-defined circulation, it no longer meets the criteria to be classified as a tropical storm or hurricane. Post-tropical cyclones can take on a variety of forms, including extratropical cyclones, which are characterized by fronts and a temperature gradient.

A smoke ring is a vortex of smoke that forms in a circular shape. It is created when a puff of smoke is expelled from a source, such as the mouth, a smoke ring machine, or a cigar, and the motion of the smoke creates a toroidal (doughnut-shaped) formation. The smoke ring is characterized by its circular motion, which is a result of differences in pressure and velocity within the smoke itself.

The angular velocity tensor is a mathematical representation of the angular velocity of a rigid body or a system of particles in three-dimensional space. Unlike the scalar angular velocity, which describes the rate of rotation around a single axis, the angular velocity tensor conveys how an object rotates about multiple axes simultaneously. ### Definitions and Components 1.

The Exterior Angle Theorem is a fundamental principle in triangle geometry that relates the measures of an exterior angle of a triangle to the measures of its remote interior angles. The theorem states that: In any triangle, the measure of an exterior angle is equal to the sum of the measures of the two opposite (or remote) interior angles. To illustrate, consider triangle ABC where angle C is an exterior angle formed by extending side AC.

Hyperbolic orthogonality is a concept that arises in the context of hyperbolic geometry, a non-Euclidean geometry characterized by its unique properties in relation to distances and angles. In Euclidean geometry, orthogonality refers to the notion of two lines being perpendicular to each other, typically in two or three-dimensional spaces. In hyperbolic geometry, the definitions and implications of angles and orthogonality differ from those in Euclidean geometry.

Magnetic declination, also known as magnetic variation, is the angle between magnetic north (the direction a compass points) and true north (the geographic north pole) at a given location on the Earth's surface. This angle is measured in degrees east or west from true north. Because the Earth's magnetic field is not uniform, magnetic declination varies depending on where you are located. It can change over time due to shifts in the Earth’s magnetic field.

The term "subtended angle" refers to the angle formed by two lines or segments that extend from a specific point to the endpoints of a line segment or arc. More commonly, it is used in geometry to describe the angle at a particular point (the vertex) which "sees" a given arc or segment.

Bisection is a mathematical method used to find roots of a continuous function. It is a type of bracketing method, which means it narrows down the search for a root within a certain interval. The key idea behind the bisection method is to divide an interval in half and, based on the signs of the function at the endpoints, determine which half contains the root.

In geometry, a **cross section** refers to the intersection of a solid object with a plane. When a three-dimensional object is cut by a plane, the shape formed by this intersection is known as the cross section. The specific shape of the cross section depends on the orientation and position of the cutting plane relative to the object.

In group theory, the term "component" can refer to various concepts depending on the context. However, one common usage pertains to the component of a group element in a topological or algebraic sense. 1. **Connected Components in Topological Groups**: In the context of topological groups, the component of a group element \( g \) refers to the connected component of the identity element that contains \( g \).

In geometry, a line is a fundamental concept that represents a straight one-dimensional figure that extends infinitely in both directions. It has no thickness, width, or curvature, and is typically defined by at least two points. Lines can be described using a variety of properties: 1. **Definition**: A line is determined by any two distinct points on it.

In geometry, the term "parallel" refers to two or more lines or planes that are the same distance apart at all points and do not meet or intersect, no matter how far they are extended. This property is fundamental in understanding the behavior of lines within Euclidean geometry. ### Key Properties of Parallel Lines: 1. **Equidistant**: Parallel lines maintain a constant distance from each other, meaning the distance between them remains consistent along their entire length.

A spherical shell is a three-dimensional hollow structure that is shaped like a sphere. It is typically defined as the space between two concentric spherical surfaces — an outer surface and an inner surface. The shell has a certain thickness, which is the difference between the radii of the outer and inner surfaces. Key characteristics of a spherical shell include: 1. **Outer Radius (R_outer)**: The radius of the outer surface of the shell.

Bredon cohomology is a type of cohomology theory that is particularly useful in the context of spaces with group actions. It was introduced by Glen Bredon in the 1960s and is designed to study topological spaces with an additional structure of a group action, often leading to insights in equivariant topology.

Witt vector cohomology is a tool in algebraic geometry and number theory that utilizes Witt vectors to study the cohomological properties of schemes in the context of p-adic cohomology theories. Witt vectors are a generalization of the notion of numbers in a ring, particularly for fields of characteristic \( p \), and they allow the construction of an effective cohomology theory that preserves useful algebraic properties. ### Key Concepts 1.

In the context of cohomology, a pullback is a construction that allows you to take a cohomology class on a target space and "pull it back" to a cohomology class on a domain space via a continuous map. This is particularly common in algebraic topology and differential geometry. ### Formal Definition Let \( f: X \to Y \) be a continuous map between two topological spaces \( X \) and \( Y \).

Étale cohomology is a cohomological theory in algebraic geometry that provides a means to study the properties of algebraic varieties over fields, particularly in the context of fields that are not algebraically closed. It was developed in the mid-20th century, notably by Alexander Grothendieck, and is part of the broader framework of schemes in modern algebraic geometry.

In category theory, a preordered set (or preordered set) is a set equipped with a reflexive and transitive binary relation. More formally, a preordered set \( (P, \leq) \) consists of a set \( P \) and a relation \( \leq \) such that: 1. **Reflexivity**: For all \( x \in P \), \( x \leq x \).