# Heterogeneity: Wikis

Note: Many of our articles have direct quotes from sources you can cite, within the Wikipedia article! This article doesn't yet, but we're working on it! See more info or our list of citable articles.

# Encyclopedia

Heterogeneous is an adjective used to describe an object or system consisting of multiple items having a large number of structural variations. It is the opposite of homogeneous, which means that an object or system consists of multiple identical items. The term is often used in a scientific (such as a kind of catalyst), mathematical, sociological or statistical context.

## Physics and chemistry

A heterogeneous mixture is a mixture of two or more compounds. Examples are: mixtures of sand and water or sand and iron filings, a conglomerate rock, water and oil, a salad, trail mix, and concrete (not cement). During the sampling of heterogeneous mixtures of particles, the variance of the sampling error is generally non-zero. Gy's sampling theory [1] quantitatively defines the heterogeneity of a particle as:

$h_i = \frac{(c_i - c_\text{batch})m_i}{c_\text{batch} m_\text{aver}} .$

where hi, ci, cbatch, mi, and maver are respectively: the heterogeneity of the ith particle of the population, the mass concentration of the property of interest in the ith particle of the population, the mass concentration of the property of interest in the population, the mass of the ith particle in the population, and the average mass of a particle in the population.

In chemical kinetics, a heterogeneous reaction is one that takes place at the interface of two or more phases, i.e. between a solid and a gas, a liquid and a gas, or a solid and a liquid. In heterogeneous catalysis the catalyst is in a different phase from the substrate.

## Systems

In the world of enterprise computing, heterogeneous data is a mix of data from two or more sources, often of two or more formats, e.g., SQL and XML.

Distributed systems are called heterogeneous if they contain many different types of hardware and software. heterogeneity of the system means the ability of that system to work with different systems

## Taxonomy

In taxonomy, a heterogeneous taxon is a taxon that contains a great variety of individuals or sub-taxa; usually this implies that the taxon is an artificial grouping.

## Genetics

In genetics, heterogeneity refers to multiple origins causing the same disorder in different individuals. If a number of different mutations occurring within the same gene produce disorders, it is said to manifest allelic heterogeneity. This term has been used when a number of different alleles cause a similar phenotype or different phenotypes.

Example diseases:

## Ecology

In ecology, heterogeneity is the measure of how different parts of a landscape are from one another.

## Computing

Heterogeneous computing systems refer to electronic systems that utilize a variety of different types of computational units. A computational unit could be a general-purpose processor (GPP), a special-purpose processor (i.e. DSP or GPU), a co-processor, or custom acceleration logic (ASIC or FPGA). In general a heterogeneous computing platform consists of processors with different instruction set architectures (ISAs). The demand for increased heterogeneity in computing systems is partially due to the need for high-performance, highly-reactive systems that interact with other environments (audio/video systems, control systems, networked applications, etc.). In the past, huge advances in technology and frequency scaling allowed the majority of computer applications to increase in performance without requiring structural changes or custom hardware acceleration. While these advances continue, their effect on modern applications is not as dramatic as other obstacles such as the memory-wall and powerwall come into play. Now, with these additional constraints, the primary method of gaining extra performance out of computing systems is to introduce additional specialized resources, thus making a computing system heterogeneous. The addition of extra, independent computing resources necessarily allows most heterogeneous systems to be considered parallel computing systems.

## References

1. ^ Gy, P (1979) Sampling of Particulate Materials: Theory and Practice, Elsevier: Amsterdam, 431 pp.