p53 is activated in response to events compromising the genetic integrity of a cell. Recent data show that p53 activity does not increase steadily with genetic damage but rather fluctuates in an oscillatory fashion. Theoretical studies suggest that oscillations can arise from a combination of positive and negative feedbacks or from a long negative feedback loop alone. Both negative and positive...

Sustained oscillations of catalyst temperature have been observed in NH, oxidation on Pt wires and foils in a l-atm flow reactor. Simple and complex oscillations with periods from ~1 set to several minutes were obtained for gas compositions between 20 and 40% NH3 in air. These depend sensitively on gas composition, flow velocity, and geometry. Oscillatory behavior is quite stable over short tim...

Intracellular Ca2+ oscillations are often a response to external signals such as hormones. Changes in the external signal can alter the frequency, amplitude, or form of the oscillations suggesting that information is encoded in the pattern of Ca2+ oscillations. How might a cell decode this signal? We show that an excitable system whose kinetic parameters are modulated by the Ca2+ concentration ...

We study the dynamics of a layer of viscoelastic fluid, in the Stokesian regime, that is driven from below by a 4 4 checkerboard pattern of rotating and counter-rotating disks. At low disk rotation rate (low Weissenberg number) the fluid flow response is slaved to the geometry of this forcing and divides into many steadily rotating cells, each contained within invariant manifolds issuing from h...

A minimal model is constructed for two-dimensional fracture propagation. The heterogeneous process zone is presumed to suppress stress relaxation rate, leading to non-quasistatic behavior. Using the Yoffe solution , I construct and solve a dynamical equation for the tip stress. I discuss a generic tip velocity response to local stress and find that noise-free propagation is either at steady sta...

Because boundary-layer separation is important in determining force between flowing air and solid bodies and separation can be sensitive to unsteadiness, the quasi-steady approximation needs to be examined for the flow-induced oscillations of speech (e.g., phonation and trills). A review of the literature shows that vibratory phenomena, such as phonation and tongue-tip trills, may need to be mo...

We examine the effect of prescribed wall-driven oscillations of a flexible tube of arbitrary cross-section, through which a flow is driven by prescribing either a steady flux at the downstream end or a steady pressure difference between the ends. A large-Womersley-number large-Strouhal-number regime is considered, in which the oscillations of the wall are small in amplitude, but sufficiently ra...