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degree The number of edges incident to a
node; here notated as d(v).
Comment: The number of reactions in which
D a compound participates is its degree. Simi-
larly, the number of compounds participating in
a reaction is the degree of the reaction. Since the
best-known biochemical network described has
dalton The unit of molecular weight, in
an enzyme for every reaction, one usually means
g/mol.
nonenzymatic degree, when applying the word
Comment: A mole (abbreviated mol) is an
to reactions. Note this would not be the case for
Avogadro’s number (N) of molecules, approxi- other versions of the biochemical network which
mately equal to 6.02252 × 10 23 molecules/mol.
includespontaneousreactions, ordetailedkinetic
Darboux’s theorem On any symplectic and mechanistic views of reactions in which the
manifold (M, ω) there exist local coordi- enzyme does not necessarily appear in the reac-
n
1
nates (canonical coordinates) (x ,...,x , tion equations as a formal catalyst.
1
n
y ,...,y ) in which the symplectic form ω
degree of polymerization The number of
takes the form
monomeric units in a macromolecule or oligomer
n
molecule,a block,ora chain.
i
i
ω = dx ∧ dy .
i=1 degreesoffreedom AsystemofN particles,
dark current See responsivity. free from constraints, has 3N independent coor-
dinates (positions and momenta) called degrees
dark output See responsivity.
of freedom.
dark resistance See responsivity.
delocalization A quantum mechanical con-
data model A computational method for cept most usually applied in organic chemistry
implementing a domain model. to describe the π-bonding in a conjugated sys-
Comment: This is the database management tem. This bounding is not localized between two
system, object-oriented model, set of MatLab atoms: instead, each link has a “fractional double
functions, etc., which [reify] the ideas in the bond character” or bond order. There is a cor-
domain model. Thus, it is the computational responding “delocalization energy,” identifiable
machinery, not (per se) the intellectual basis of with the stabilization of the system compared
the abstract model of the domain. with a hypothetical alternative in which formal
(localized) single and double bonds are present.
decreasing function A function f(x) such Some degree of delocalization is always present
that f(y) ≤ f(x) whenever x ≤ y. andcanbeestimatedbyquantummechanicalcal-
definite integral Let f be a function defined culations.
on a closed interval [a, b] and P a partition a =
delta function See Dirac delta function.
x <x <x < ··· <x = b of [a, b]. Let |P |
n
2
1
0
denote the length of the longest subinterval in the dense A subset S in a space X is dense (in
¯
partition P and let ¯x ∈ [x ,x ] be arbitrary. If X ) if its closure S = X.
i i−1 i
the limit

denser subgraph A subgraph G of the bio-
n
chemical network such that the degree of each
lim f(¯x )(x − x i−1 )
i
i
|P |→0 reaction node v is greater than or equal to x,
i=1 r,i
and the degree of each compound node v m,j is
exists, f is called (Riemann) integrable and
less than or equal to y; that is, d(v ) ≥ x,
r,i
n
b d(v m,j ) ≤ y.
f(x)dx = lim f(¯x )(x − x i−1 ) Comment: Because any two denser subgraphs
i
i
|P|→0
a
i=1 formed with the same values of x and y are not
is called the definite integral (or Riemann inte- necessarily isomorphic, denser subgraphs are not
gral) of f from a to b. necessarily motives. Familarly known as a blob.
© 2003 by CRC Press LLC