Electronegativity, symbol < span class =" nounderlines "> χ </ span >, is a chemical property that describes the tendency of an atom or a functional group to attract electrons ( or electron density ) towards itself.

Mutual information is closely related to the log-likelihood ratio test in the context of contingency tables and the multinomial distribution and to Pearson's χ < sup > 2 </ sup > test: mutual information can be considered a statistic for assessing independence between a pair of variables, and has a well-specified asymptotic distribution.

The labarum () was a vexillum ( military standard ) that displayed the " Chi-Rho " symbol < big >☧</ big >, formed from the first two Greek letters of the word " Christ " (, or Χριστός ) — Chi ( χ ) and Rho ( ρ ).

Here, the coefficients χ < sup >( n )</ sup > are the n-th order susceptibilities of the medium and the presence of such a term is generally referred to as an n-th order nonlinearity.

In general χ < sup > n </ sup > is an n + 1 order tensor representing both the polarization dependent nature of the parametric interaction as well as the symmetries ( or lack thereof ) of the nonlinear material.

If the pump waves and the signal wave are superimposed in a medium with a non-zero χ < sup >( 3 )</ sup >, this produces a nonlinear polarization field:

where δ ( E < sub > ψ </ sub >– E < sub > χ </ sub >) restricts tunneling to occur only between electron levels with the same energy.

is the degrees of freedom for the estimator and χ < sup > 2 </ sup > is the degrees of freedom for a certain probability.

The electric susceptibility χ < sub > e </ sub > of a dielectric material is a measure of how easily it polarizes in response to an electric field.

: χ ( frequently written χ < sub > e </ sub >) is the electric susceptibility of the material.

The upper limit of this integral can be extended to infinity as well if one defines χ ( Δt ) = 0 for Δt < 0.

Moreover, the fact that the polarization can only depend on the electric field at previous times ( i. e. χ ( Δt ) = 0 for Δt < 0 ), a consequence of causality, imposes Kramers – Kronig constraints on the susceptibility χ ( 0 ).

From thermodynamic arguments it can be shown that χ < sub > ij </ sub > = χ < sub > ji </ sub >, i. e. the χ tensor is symmetric.

In accordance with the spectral theorem, it is thus possible to diagonalise the tensor by choosing the appropriate set of coordinate axes, zeroing all components of the tensor except χ < sub > xx </ sub >, χ < sub > yy </ sub > and χ < sub > zz </ sub >.

Therefore by 5 ) and 4 ), χ ( a < sup > φ ( k )</ sup >)

1, and by 3 ), χ ( a < sup > φ ( k )</ sup >)

There are two other measures of susceptibility, the mass magnetic susceptibility ( χ < sub > mass </ sub > or χ < sub > g </ sub >, sometimes χ < sub > m </ sub >), measured in m < sup > 3 </ sup >· kg < sup >− 1 </ sup > in SI or in cm < sup > 3 </ sup >· g < sup >− 1 </ sup > in CGS and the molar magnetic susceptibility ( χ < sub > mol </ sub >) measured in m < sup > 3 </ sup >· mol < sup >− 1 </ sup > ( SI ) or cm < sup > 3 </ sup >· mol < sup >− 1 </ sup > ( CGS ) that are defined below, where ρ is the density in kg · m < sup >− 3 </ sup > ( SI ) or g · cm < sup >− 3 </ sup > ( CGS ) and M is molar mass in kg · mol < sup >− 1 </ sup > ( SI ) or g · mol < sup >− 1 </ sup > ( CGS ).

If the graph G is connected, then the rank of the free group is equal to 1 − χ ( G ): one minus the Euler characteristic of G.

The value 1 + χ is called the relative permittivity of the medium, and is related to the refractive index n, for non-magnetic media, by

# If gcd ( n, k ) > 1 then χ ( n )

1 then χ ( n ) ≠ 0.

By property 3 ), χ ( 1 )=

χ ( 1 × 1 )= χ ( 1 ) χ ( 1 ).

4 >< li > χ ( 1 ) = 1 .</ ol >

Property 1 ) says that a character is periodic with period k ; we say that χ is a character to the modulus k. This is equivalent to saying that

The sign of the character χ depends on its value at − 1.

Specifically, χ is said to be odd if χ (− 1 ) = − 1 and even if χ (− 1 ) = 1.

The wave experiences a susceptibility χ < sub > xx </ sub > and a permittivity ε < sub > xx </ sub >.

Chi < sup > 1 </ sup > Orionis ( χ < sup > 1 </ sup > Ori, χ < sup > 1 </ sup > Orionis ) is a star about 28 light years away.

χ < sup > 1 </ sup > Ori is a G0V main-sequence star.

Chi Orionis ( Chi Ori, χ Orionis, χ Ori ) is the name of two stars:

A character χ is a linear functional on A which is at the same time multiplicative, χ ( ab )

The best known example in the Milky Way is the Double Cluster of NGC 869 and NGC 884 ( sometimes mistakenly called h and χ Persei ; h refers to a neighboring star and χ to both clusters ), but at least 10 more double clusters are known to exist.

Note the factors of two before ψ and χ corresponding respectively to the facts that any polarization ellipse is indistinguishable from one rotated by 180 °, or one with the semi-axis lengths swapped accompanied by a 90 ° rotation.

In SI units, permittivity ε is measured in farads per meter ( F / m ); electric susceptibility χ is dimensionless.

That is, the polarization is a convolution of the electric field at previous times with time-dependent susceptibility given by χ ( Δt ).

Alternatively, it can be defined in terms of the Euler characteristic χ, via the relationship χ = 2 − 2g for closed surfaces, where g is the genus.

Alternatively, it can be defined for a closed surface in terms of the Euler characteristic χ, via the relationship χ = 2 − k, where k is the non-orientable genus.

Chi Cygni ( χ Cyg, χ Cygni ) is a variable star of the Mira type in the constellation Cygnus.

The Bayer designation Chi Sagittarii ( Chi Sgr, χ Sagittarii, χ Sgr ) is shared by three star systems in the constellation Sagittarius.

* These three χ star, together with φ Sgr, σ Sgr, ζ Sgr and τ Sgr were Al Naʽām al Ṣādirah ( النعم السادرة ), the Returning Ostriches.

Chi Scorpii ( χ Sco, χ Scorpii ) is a star in the constellation Scorpius.

Chi Serpentis ( χ Ser, χ Serpentis ) is a star in the constellation Serpens.

Chi Tauri ( χ Tau, χ Tauri ) is a binary star in the constellation Taurus.

Chi Ursae Majoris ( Chi UMa, χ Ursae Majoris, χ UMa ) is a star in the constellation Ursa Major.

Chi Virginis ( χ Vir, χ Virginis ) is a double star in the constellation Virgo.