Index

An index is an indirect shortcut derived from and pointing into a greater volume of values, data, information or knowledge. Index may refer to:

Business

Publishing

Database index

A database index is a data structure that improves the speed of data retrieval operations on a database table at the cost of additional writes and storage space to maintain the index data structure. Indexes are used to quickly locate data without having to search every row in a database table every time a database table is accessed. Indexes can be created using one or more columns of a database table, providing the basis for both rapid random lookups and efficient access of ordered records.

An index is a copy of select columns of data from a table that can be searched very efficiently that also includes a low-level disk block address or direct link to the complete row of data it was copied from. Some databases extend the power of indexing by letting developers create indices on functions or expressions. For example, an index could be created on upper(last_name), which would only store the upper case versions of the last_name field in the index. Another option sometimes supported is the use of partial indices, where index entries are created only for those records that satisfy some conditional expression. A further aspect of flexibility is to permit indexing on user-defined functions, as well as expressions formed from an assortment of built-in functions.

Index (statistics)

In statistics and research design, an index is a composite statistic – a measure of changes in a representative group of individual data points, or in other words, a compound measure that aggregates multiple indicators. Indexes summarize and rank specific observations.

Much data in the field of social sciences is represented in various indices such as Gender Gap Index, Human Development Index or the Dow Jones Industrial Average.

Item in indexes are usually weighted equally, unless there are some reasons against it (for example, if two items reflect essentially the same aspect of a variable, they could have a weight of 0.5 each).

Constructing the items involves four steps. First, items should be selected based on their face validity, unidimensionality, the degree of specificity in which a dimension is to be measured, and their amount of variance. Items should be empirically related to one another, which leads to the second step of examining their multivariate relationships. Third, indexes scores are designed, which involves determining their score ranges and weights for the items. Finally, indexes should be validateds, which involves testing whether they can predict indicators related to the measured variable not used in their construction.

Momentum

In classical mechanics, linear momentum or translational momentum (pl. momenta; SI unit kg m/s, or equivalently, Newton second) is the product of the mass and velocity of an object. For example, a heavy truck moving rapidly has a large momentum—it takes a large or prolonged force to get the truck up to this speed, and it takes a large or prolonged force to bring it to a stop afterwards. If the truck were lighter, or moving more slowly, then it would have less momentum.

Like velocity, linear momentum is a vector quantity, possessing a direction as well as a magnitude:

where p is the three-dimensional vector stating the object's momentum in the three directions of three-dimensional space, v is the three-dimensional velocity vector giving the object's rate of movement in each direction, and m is the object's mass.

Linear momentum is also a conserved quantity, meaning that if a closed system is not affected by external forces, its total linear momentum cannot change.

In classical mechanics, conservation of linear momentum is implied by Newton's laws. It also holds in special relativity (with a modified formula) and, with appropriate definitions, a (generalized) linear momentum conservation law holds in electrodynamics, quantum mechanics, quantum field theory, and general relativity. It is ultimately an expression of one of the fundamental symmetries of space and time, that of translational symmetry.

Momentum (electromagnetic simulator)

Momentum is 3-D planar EM simulation software for electronics and antenna analysis, a partial differential equation solver of Maxwell's equations based on the method of moments. It is a 3-D planar electromagnetic (EM) simulator used for passive circuit analysis.

It combines full-wave and quasi-static EM solvers to provide insight into EM behavior of MMIC, RFIC, RF Board, Signal Integrity, and antenna designs. The Momentum simulation engine is integrated into Keysight ADS and Keysight Genesys.

It was originally developed by a Belgian company, Alphabit, a spinoff from IMEC. Early contributors to the technology include Niels Faché, Jan Van Hese, Frank Libbrecht, Jeannick Sercu, Luc Vandormael, Mieke Herreman, Peter Kok, Tom Dhaene and Krist Blomme.

The company was acquired by Hewlett-Packard, later it became part of Agilent Technologies and since November 2014 it is part of Keysight Technologies EEsof division, the current owners.

References

Momentum (organisation)

Momentum is a British left-wing political organisation. Founded in 2015 by Jon Lansman four weeks after Jeremy Corbyn's successful campaign for the Labour Party leadership, it has been described as a grassroots movement supportive of Corbyn and the Labour Party.As of October 2015 Momentum had about 60,000 supporters, charges no membership fee, organises mostly through social media and has around 50 local groups across the UK.

Background

Momentum describes itself as "a network of people and organisations that will continue the energy and enthusiasm of Jeremy's campaign", and campaigns on local issues and on topics within the Labour Party. The organisation states that it aims to organise local groups across the country to "encourage mass mobilisation for a more democratic, equal and decent society" and "assist members in making their voice heard in Labour Party debates". The organisation's founders say it has been registered as a limited company on an interim basis and has a devolved democratic structure, run on a voluntary basis with no plans to charge membership fees.