specific surface activity (SPA)
302
specific surface activity (SPA) the relative surface activity for sorption reactions.
SPA is defined by the adsorption of ethylene glycol, and for ocean sediments
is proportional to the empirical base-exchange capacity.
spectral wave analysis in wind waves an almost random pattern of crests and
troughs occurs. In spectral wave analysis this pattern is assumed to be composed of a series of sinusoidal waves of varying frequency and amplitude. In
a wave spectrum obtained by processing of a wave record, the square of the
amplitude (which is proportional to the wave energy) of the composing waves
is given as a function of their frequency or period. The spectrum for a fully
developed wave field in deep water depends on the wind. Different mathematical functions are used as approximations of this spectrum (PiersonMoskowitz spectrum, Joint North Sea Wave Program spectrum). For
stronger winds the maximum of the spectrum shifts to lower frequencies,
and the total energy density (area underneath the spectrum) increases.
spectrum a physical phenomenon such as electromagnetic radiation, where several different frequencies occur can be described by a spectral function or
spectrum which represents the distribution of the energy of the phenomenon over different frequency bands. In analogy with the electromagnetic
spectrum, spectral representations of any other variable (physical) parameter such as current speed or wave height can be constructed. These spectra
give the distribution of the variance of the parameter over different frequency bands or over derived quantities such as period or wave number
bands. Since the energy of a physical process is often proportional to the
mean square, or variance, of the relevant parameter, such a variance spectrum is also called energy spectrum or power spectrum. In oceanography
the spectrum is a well-known way to describe the energy distribution. The
best-known examples are the wave spectrum and the turbulence spectrum.
Generally such spectra have a continuous character, but for some phenomena like the tides, fixed frequencies occur and the spectrum, in extreme
cases, can have the character of a line spectrum.
spermaceti liquid wax from the massive square head of the sperm whale, used
in, e.g., cosmetics, candle products. Once believed to be the semen of the
whale, hence "spermaceti". Probably plays a role in regulating the animal's
buoyancy during deep dives.
spheroplast is a spherical, osmotically sensitive cell derived from a bacterium by
loss of some but not all of the rigid wall layer. If all the rigid wall layer has
been lost, the structure is called a protoplast.
spicula/spicule (pI. spiculae/spicules) small, needle-like part of internal skeleton
in, e.g., Porifera (sponges).
302
specific surface activity (SPA) the relative surface activity for sorption reactions.
SPA is defined by the adsorption of ethylene glycol, and for ocean sediments
is proportional to the empirical base-exchange capacity.
spectral wave analysis in wind waves an almost random pattern of crests and
troughs occurs. In spectral wave analysis this pattern is assumed to be composed of a series of sinusoidal waves of varying frequency and amplitude. In
a wave spectrum obtained by processing of a wave record, the square of the
amplitude (which is proportional to the wave energy) of the composing waves
is given as a function of their frequency or period. The spectrum for a fully
developed wave field in deep water depends on the wind. Different mathematical functions are used as approximations of this spectrum (PiersonMoskowitz spectrum, Joint North Sea Wave Program spectrum). For
stronger winds the maximum of the spectrum shifts to lower frequencies,
and the total energy density (area underneath the spectrum) increases.
spectrum a physical phenomenon such as electromagnetic radiation, where several different frequencies occur can be described by a spectral function or
spectrum which represents the distribution of the energy of the phenomenon over different frequency bands. In analogy with the electromagnetic
spectrum, spectral representations of any other variable (physical) parameter such as current speed or wave height can be constructed. These spectra
give the distribution of the variance of the parameter over different frequency bands or over derived quantities such as period or wave number
bands. Since the energy of a physical process is often proportional to the
mean square, or variance, of the relevant parameter, such a variance spectrum is also called energy spectrum or power spectrum. In oceanography
the spectrum is a well-known way to describe the energy distribution. The
best-known examples are the wave spectrum and the turbulence spectrum.
Generally such spectra have a continuous character, but for some phenomena like the tides, fixed frequencies occur and the spectrum, in extreme
cases, can have the character of a line spectrum.
spermaceti liquid wax from the massive square head of the sperm whale, used
in, e.g., cosmetics, candle products. Once believed to be the semen of the
whale, hence "spermaceti". Probably plays a role in regulating the animal's
buoyancy during deep dives.
spheroplast is a spherical, osmotically sensitive cell derived from a bacterium by
loss of some but not all of the rigid wall layer. If all the rigid wall layer has
been lost, the structure is called a protoplast.
spicula/spicule (pI. spiculae/spicules) small, needle-like part of internal skeleton
in, e.g., Porifera (sponges).