The distribution of methane mono-oxygenase (MMO) activities between particulate and soluble fractions of cell-free extracts of Methylosinus trichosporium OB3 b was dependent upon growth conditions. Particulate activity was associated with the presence of intracytoplasmic membranes observed only under oxygen-limiting conditions in shake flask cultures. Particulate and soluble activities showed substantially different sensitivities to a range of potential inhibitors. The particulate enzyme was inhibited by metal-chelating agents, thiol reagents and amytal, whereas the soluble MMO was not inhibited by these compounds; both activities were sensitive to KCN, ethyne and 8-hydroxyquinoline. NAD(P)H was the only suitable electron donor. The activities were unstable at 0 OC but the soluble enzyme could be partially stabilized by several compounds. The particulate and soluble MMO activities are compared with previously reported particulate and soluble MMO enzymes from this species and other methane oxidizers.

The quasi-geostrophic model is a simplified geophysical fluid model at asymptotically high rotation rate or at small Rossby number. We consider the quasi-geostrophic equation with dissipation under random forcing in bounded domains. We show that global unique solutions exist for appropriate initial data. Unlike the deterministic quasi-geostrophic equation whose well-posedness is well known, there seems to be no rigorous result on global existence and uniqueness of the randomly forced quasi-geostrophic equation. Our work provides such a rigorous result on global existence and uniqueness, under very mild conditions. ᮊ 1998 Academic Press

In this paper, we formulate a stochastic logistic fish growth model driven by both white noise and non-Gaussian noise. We focus our study on the mean time to extinction, escape probability to measure the noise-induced extinction probability and the Fokker–Planck equation for fish population [Formula: see text]. In the Gaussian case, these quantities satisfy local partial differential equations while in the non-Gaussian case, they satisfy nonlocal partial differential equations. Following a discussion of existence, uniqueness and stability, we calculate numerical approximations of the solutions of those equations. For each noise model we then compare the behaviors of the mean time to extinction and the solution of the Fokker–Planck equation as growth rate [Formula: see text], carrying capacity [Formula: see text], intensity of Gaussian noise [Formula: see text], noise intensity [Formula: see text] and stability index [Formula: see text] vary. The MET from the interval [Formula: see text] at the right boundary is finite if [Formula: see text]. For [Formula: see text], the MET from [Formula: see text] at this boundary is infinite. A larger stability index [Formula: see text] is less likely leading to the extinction of the fish population.

Stochastic dynamical systems arise as models for fluid particle motion in geophysical flows with random velocity fields. Escape probability (from a fluid domain) and mean residence time (in a fluid domain) quantify fluid transport between flow regimes of different characteristic motion.We consider a quasigeostrophic meandering jet model with random perturbations. This jet is parameterized by the parameter β = 2Ω r cos(θ), where Ω is the rotation rate of the earth, r the earth's radius and θ the latitude. Note that Ω and r are fixed, so β is a monotonic decreasing function of the latitude. The unperturbed jet (for 0 < β < 2 3 ) consists of a basic flow with attached eddies. With random perturbations, there is fluid exchange between regimes of different characteristic motion. We quantify the exchange by escape probability and mean residence time.For an eddy, the average escape probability for fluid particles (initially inside the eddy) escape into the exterior retrograde region is smaller than escape into the jet core for 0 < β < 0.3333, while for 0.3333 < β < 2 3 , the opposite holds. For a unit jet core near the jet troughs, the average escape probability for fluid particles (initially inside the jet core) escape into the northern recirculating region is greater than escape into the southern recirculating region for 0 < β < 0.115, while for 0.385 < β < 2 3 , the opposite holds. Moreover, for 0.115 < β < 0.385, fluid particles are about equally likely to escape into either recirculating regions. Furthermore, for a unit jet core near the jet crests, the situation is the opposite as for near the jet troughs.The maximal mean residence time of fluid particles initially in an eddy increases as β increases from 0 to 0.432 (or as latitude decreases accordingly), then decreases as β increases from 0.432 to 2 3 (or as latitude decreases accordingly). However, the maximal mean residence time of fluid particles initially in a unit jet core always increases as β increases (or as latitude decreases).

We investigate fluid transport in random velocity fields with unsteady drift. First, we propose to quantify fluid transport between flow regimes of different characteristic motion, by escape probability and mean residence time. We then develop numerical algorithms to solve for escape probability and mean residence time, which are described by backward Fokker-Planck type partial differential equations. A few computational issues are also discussed. Finally, we apply these ideas and numerical algorithms to a tidal flow model.