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wavelength dispersion (in x-ray emission formofaboundaryvalueproblemisthroughinte-
spectroscopy) Spatial separation of characteristic gration by parts, using Green’s formulas.
x-rays according to their wavelengths.
wedge projection A stereochemical projec-
wavelength-dispersive x-ray fluorescence tion, roughly in the mean plane of the molecule,
analysis A kind of x-ray fluorescence
in which bonds are represented by open wedges,
analysis involving the measurement of the
tapering off from the nearer atom to the farther
wavelength spectrum of the emitted radiation
atom.
e.g., by using a diffraction grating or crystal.
Weierstrass theorem See Bolzano-Weier-
wavelength error (in spectrochemical analysis)
strass theorem.
The error in absorbance which may occur if there
is a difference between the (mean) wavelength
of the radiation entering the sample cell and the weight, G G G Force of gravity acting on a body,
indicated wavelength on the spectrometer scale. G = mg, where m is its mass and g the acceler-
ation of free fall.
2
n
wavelet An orthonormal basis of L (R ).
They are used as phase space localization meth-
weighted mean If in a series of observations
ods. A typical example of a family of wavelets
a statistical weight (w ) is assigned to each value,
i
ψ (x) in one dimension is given by a weighted mean x w can be calculated by the
j,k
formula
−j/2
−j
ψ (x) = 2 ψ(2 x − k) w x
j,k
x = w i i
w
j
−j x − 2 k i
= 2 2 ψ( j ), j, k ∈ Z,
2 Comment: Unless the weights can be assigned
objectively, the use of the weighted mean is not
where ψ is a smooth function with reasonable
decay (say, |ψ(x)| < C(1 + |x|) −(1+") ), and normally recommended.

such that ψ(x)dx = 0. Wavelets bases provide
unconditional bases for many classical function well-ordered set A partially ordered set
p
spaces, such as L spaces 1 < p < ∞, Sobolev (A, ) such that for all B ⊂ A (B non-empty)
s
s
spaces W , Besov spaces B q p,s , H¨older spaces C , B has a minimum.
1
Hardy space H , and BMO space.
well posed Most people mean that the math-
wavelet transformations Approximations ematical program has an optimal solution. Some
that can have lower complexity than fast Fourier
mean just that it is feasible and not unbounded.
transforms (FFT), namely, O(log N) instead of
O(N log N).
wet bulb temperature In psychrometry, the
temperature of the sensor or the bulb of a ther-
weak collision A collision between two
mometer in which a constantly renewed film of
molecules in which the amount of energy trans-
water is evaporating. The temperature of the
ferred from one to the other is not large compared
water used to renew the film must be at the tem-
to k T (k is the Boltzmann constant and T the
B
B
absolute temperature). See strong collision. perature of the gas.
weak formulation To cast a boundary value wetting tension (or work of immersional wet-
problem for a partial differential operator into ting per unit area) The work done on a
weak form means that it is stated as a variational system when the process of immersional wet-
problem over some Banach space V . The usual ting involving unit area of phase β is carried out
way to get this weak formulation from the strong reversibly:
© 2003 by CRC Press LLC
© 2003 by CRC Press LLC