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wash out (in atmospheric chemistry) The
removal from the atmosphere of gases and some-
times particles by their solution in or attachment
W to raindrops as they fall.

n
wave equation Let U ⊂ R open and u :
U ×R → R. The (linear) wave equation for u is
wall-coated open-tubular (WCOT) column
(in chromatography) A column in which the liq- u − u = 0.
tt
uid stationary phase is coated on the essentially
unmodified smooth inner wall of the tube. The (nonlinear) wave equation for u is
u − u = f (u).
tt
warehouse problem The manager of a
warehouse buys and sells the stock of a certain
Z, ψ,
wave function (state function), Z, ψ, φ φ φ The
Z, ψ,
commodity, seeking to maximize profit over a
solution of the Schr¨odinger equation, eigen-
period of time, called the horizon. The ware-
function of the Hamiltonian operator.
house has a fixed capacity, and there is a hold-
ing cost that increases with increasing levels of
wave height (electrochemical) The limit-
inventory held in the warehouse (this could vary
ing current of an individual wave, frequently
period to period). The sales price and purchase
expressed in arbitrary units for convenience.
cost of the commodity fluctuate. The warehouse
is initially empty and is required to be empty at
σ σ
the end of the horizon. This is a variation of the wave number, σ- ν - ν - ν The reciprocal of the
production scheduling problem, except demand wavelength λ, or the number of waves per unit
is not fixed. (Level of sales is a decision variable, length along the direction of propagation. Sym-
whichdependsonwhethercostislessthanprice.) bols - ν in a vacuum, σ in a medium.
Let
wavelength, λ λ λ Distance in the direction of
propagation of a periodic wave between two suc-
x(t) = level of production in periodt
cessive points where at a given time the phase is
(before sales)
the same.
y(t) = level of inventory at the end of
period t
z(t) = level of sales in period t wavelength converter Converts radiation
W = warehouse capacity at one wavelength to radiation at another
h(t, u) = holding cost of inventory u detectable wavelength or at a wavelength of
from period t to t + 1 improved responsivity of the detector. The clas-
p(t) = production cost (per unit of produc- sical wavelength converter consists of a screen of
tion) luminescent material that absorbs radiation and
s(t) = sales price (per unit) radiates at a longer wavelength. Such materials
T = horizon are often used to convert ultraviolet to visible
radiation for detection by conventional photo-
Then, the mathematical program is: tubes. In X-ray spectroscopy, a converter that
emits optical radiation is called a scintillator.In

Minimize h(t, y(t)) + px − sz : most cases wavelength conversion is from short
t to long wavelength, but in the case of conver-
sion of long to short wavelength the process is
x, y, z ≥ 0; y(0) = y(T ) = 0;
sometimes called upconversion. Wavelengths of
coherent sources can be converted using non-
y(t) = y(t − 1) + x(t) − z(t) ⇐ W
linear optical techniques. A typical example is
for t = 1, ..., T . frequency doubling.

c

© 2003 by CRC Press LLC
© 2003 by CRC Press LLC