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2 definitions found
 for first-order
From The Collaborative International Dictionary of English v.0.48 :

  First-order \First`-or"der\, a.
     decaying at an exponential rate; -- a mathematical concept
     applied to various types of decay, such as radioactivity and
     chemical reactions.
     Note: In first order decay, the amount of material decaying
           in a given period of time is directly proportional to
           the amount of material remaining. This may be expressed
           by the differential equation: dA/dt = -kt where dA/dt
           is the rate per unit time at which the quantity (or
           concentration) of material (expressed as A) is
           increasing, t is the time, and k is a constant. The
           minus sign in front of the "kt" assures that the amount
           of material remaining will be decreasing as time
           progresses. A solution of the differential equation to
           give the quantity A shows that: A = e^{-kt where e is
           the base for natural logarithms. Thus this type of
           decay is called exponential decay. In certain chemical
           reactions that are in fact second-order, involving two
           reactants, the conditions may be chosen in some cases
           so that one reactant is vastly in excess of the other,
           and its concentration changes very little in the course
           of the reaction, so that the reaction rate will be
           approximately first order in the more dilute reactant;
           such reactions are called pseudo first order.

From The Free On-line Dictionary of Computing (30 December 2018) :

     Not higher-order.

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