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Difference between revisions of "Entity"

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|description='''Entity''' - The dimension of the count, C, is the entity ''X''.
|description='''Entity''' ''X'' is the [[dimension]] C of the [[count]] ''N<sub>X</sub>''. A count is a number of defined elementary entities. A defined elementary entity is a single countable object or single event. ''X'' and ''N<sub>X</sub>'' have the unit [x], and for ''X'' by definition x=1. If an object is defined as a group of particles, then the entity is the single group but not the particle. "An elementary entity may be an atom, a molecule, an ion, an electron, any other particle or specified group of particles" ([[Bureau International des Poids et Mesures 2019 The International System of Units (SI) |Bureau International des Poids et Mesures 2019)]].  
|info=[[BEC2020.1 doi10.26124bec2020-0001.v1]]
|info=[[BEC2020.1 doi10.26124bec2020-0001.v1]]
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Communicated by [[Gnaiger Erich]] 2020-05-20
== Biological and chemical entities — and count ==
:::: Countable biological objects are entities. An organism can be defined as an entity and counted, to obtain a count of organisms. This is simple for many but not all types of organisms. Think of counting humans or fish versus corals or multicellular algae. The single cell ce is the entity ''X''=ce of the cell count ''N<sub>X</sub>''=''N''<sub>ce</sub>. A cell count can be obtained for a suspension of cells using a cell counter. If the cell counter detects structurally defined elementary entities as cells, then a homogenate of the same cells does not contain a cell count, but it still contains the equivalent of a previously determined cell count. If the cell count was not determined before homogenization, alternative elementary entities may be defined to obtain a cell count, in which case a particular entity is the marker of a single cell. If the single cell of a particular cell type contains one nucleus, then the single nucleus is a marker of the cell. In principle, the same concept holds for molecules.
:::: If a molecule is stable under a set of conditions, such as O<sub>2</sub> or C<sub>6</sub>H<sub>12</sub>O<sub>6</sub> at room temperature, then the pair of oxygen atoms or the atomic composition of glucose defines the entity 'oxygen molecule' or 'glucose molecule'. Typically we do not use an oxygen or glucose counter to measure the number of molecules, but charge or mass are markers of the number of molecules using electrochemical or gravimetric methods. The markers thus define the format and units of an entity, and the conversion between different formats is achieved by constants, such as the [[Avogadro constant]], [[elementary charge]], and [[Faraday constant]].
== Base quantities and count ==
::::{{Template:Base quantities and count}}
{{Keywords: SI base units}}
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Revision as of 08:51, 21 May 2020


high-resolution terminology - matching measurements at high-resolution


Entity

Description

Entity X is the dimension C of the count NX. A count is a number of defined elementary entities. A defined elementary entity is a single countable object or single event. X and NX have the unit [x], and for X by definition x=1. If an object is defined as a group of particles, then the entity is the single group but not the particle. "An elementary entity may be an atom, a molecule, an ion, an electron, any other particle or specified group of particles" (Bureau International des Poids et Mesures 2019).

Abbreviation: X [x]

Reference: BEC2020.1 doi10.26124bec2020-0001.v1

Communicated by Gnaiger Erich 2020-05-20

Biological and chemical entities — and count

Countable biological objects are entities. An organism can be defined as an entity and counted, to obtain a count of organisms. This is simple for many but not all types of organisms. Think of counting humans or fish versus corals or multicellular algae. The single cell ce is the entity X=ce of the cell count NX=Nce. A cell count can be obtained for a suspension of cells using a cell counter. If the cell counter detects structurally defined elementary entities as cells, then a homogenate of the same cells does not contain a cell count, but it still contains the equivalent of a previously determined cell count. If the cell count was not determined before homogenization, alternative elementary entities may be defined to obtain a cell count, in which case a particular entity is the marker of a single cell. If the single cell of a particular cell type contains one nucleus, then the single nucleus is a marker of the cell. In principle, the same concept holds for molecules.
If a molecule is stable under a set of conditions, such as O2 or C6H12O6 at room temperature, then the pair of oxygen atoms or the atomic composition of glucose defines the entity 'oxygen molecule' or 'glucose molecule'. Typically we do not use an oxygen or glucose counter to measure the number of molecules, but charge or mass are markers of the number of molecules using electrochemical or gravimetric methods. The markers thus define the format and units of an entity, and the conversion between different formats is achieved by constants, such as the Avogadro constant, elementary charge, and Faraday constant.

Base quantities and count

SI-units-elementary quantities.png
Quantity Symbol for quantity Q Symbol for dimension Name of abstract unit uQ Symbol for unit uQ [*]
elementary entity *,$ UX U elementary unit x
count *,$ NX = N·UX X elementary unit x
amount of substance *,§ nX = NX·NA-1 N mole mol
charge *,€ Qel = zX·e·NX I·T coulomb C = A·s
length l L meter m
mass m M kilogram kg
time t T second s
electric current I I ampere A
thermodynamic temperature T Θ kelvin K
luminous intensity Iv J candela cd
[*] SI units, except for the canonical 'elementary unit' [x]. The following footnotes are canonical comments, related to iconic symbols.
* For the elementary quantities NX, nX, and Qel, the entity-type X of the elementary entity UX has to be specified in the text and indicated by a subscript: nO2; Nce; Qel.
$ Count NX equals the number of elementary entities UX. In the SI, the quantity 'count' is explicitly considered as an exception: "Each of the seven base quantities used in the SI is regarded as having its own dimension. .. All other quantities, with the exception of counts, are derived quantities" (Bureau International des Poids et Mesures 2019 The International System of Units (SI)). An elementary entity UX is a material unit, it is not a count (UX is not a number of UX). NX has the dimension X of a count and UX has the dimension U of an elementary entity; both quantities have the same abstract unit, the 'elementary unit' [x].
§ Amount nX is an elementary quantity, converting the elementary unit [x] into the SI base unit mole [mol] using the Avogadro constant NA.
Charge is a derived SI quantity. Charge is an elementary quantity, converting the elementary unit [x] into coulombs [C] using the elementary charge e, or converting moles [mol] into coulombs [C] using the Faraday constant F. zX is the charge number per elementary entity UX, which is a constant for any defined elementary entity UX. Qel = zX·F·nX


SI-units.png


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Entity, count, and number, and SI base quantities / SI base units
SI-units.png
Quantity name Symbol Unit name Symbol Comment
elementary UX elementary unit [x] UX, UB; [x] not in SI
count NX elementary unit [x] NX, NB; [x] not in SI
number N - dimensionless = NX·UX-1
amount of substance nB mole [mol] nX, nB
electric current I ampere [A] A = C·s-1
time t second [s]
length l meter [m] SI: metre
mass m kilogram [kg]
thermodynamic temperature T kelvin [K]
luminous intensity IV candela [cd]
Fundamental relationships
» Avogadro constant NA
» Boltzmann constant k
» elementary charge e
» Faraday constant F
» gas constant R
» electrochemical constant f
SI and related concepts
» International System of Units
» elementary unit x
» SI prefixes
» International Union of Pure and Applied Chemistry, IUPAC
» entity
» quantity
» dimension
» format
» motive unit
» iconic symbols



MitoPedia concepts: Ergodynamics