Influence of higher order effects on the vortex instability of thermal boundary layer flow in a wedge shaped domain

We reconsider the onset of streamwise vortices in the thermal boundary layer flow induced by an inclined upward-facing heated semi-infinite surface placed within a Newtonian fluid. Particular emphasis is laid upon how the induced flow in the isothermal region outside the boundary layer affects the boundary layer itself at higher order, and how this, in turn, affects the stability criterion for the onset of vortices. We find that the stability criterion for thermal boundary layers in air is less susceptible to changes in external geometry than for boundary layers in water. In general, we conclude that the variation of the stability criterion with wedge angle (between the heated and the outer boundary surface) is too great for the theory to predict reliably where disturbances first begin to grow

A quantitative and spatial analysis of cell cycle regulators during the fission yeast cycle

We have carried out a systems-level analysis of the spatial and temporal dynamics of cell cycle regulators in the fission yeast Schizosaccharomyces pombe. In a comprehensive single-cell analysis, we have precisely quantified the levels of 38 proteins previously identified as regulators of the G2 to mitosis transition and of 7 proteins acting at the G1- to S-phase transition. Only 2 of the 38 mitotic regulators exhibit changes in concentration at the whole-cell level: the mitotic B-type cyclin Cdc13, which accumulates continually throughout the cell cycle, and the regulatory phosphatase Cdc25, which exhibits a complex cell cycle pattern. Both proteins show similar patterns of change within the nucleus as in the whole cell but at higher concentrations. In addition, the concentrations of the major fission yeast cyclin-dependent kinase (CDK) Cdc2, the CDK regulator Suc1, and the inhibitory kinase Wee1 also increase in the nucleus, peaking at mitotic onset, but are constant in the whole cell. The significant increase in concentration with size for Cdc13 supports the view that mitotic B-type cyclin accumulation could act as a cell size sensor. We propose a two-step process for the control of mitosis. First, Cdc13 accumulates in a size-dependent manner, which drives increasing CDK activity. Second, from mid-G2, the increasing nuclear accumulation of Cdc25 and the counteracting Wee1 introduce a bistability switch that results in a rapid rise of CDK activity at the end of G2 and thus, brings about an orderly progression into mitosis

Thermal receptivity of free convective flow from a heated vertical surface: linear waves

Numerical techniques are used to study the receptivity to small-amplitude thermal disturbances of the boundary layer flow of air which is induced by a heated vertical flat plate. The fully elliptic nonlinear, time-dependent Navier–Stokes and energy equations are first solved to determine the steady state boundary-layer flow, while a linearised version of the same code is used to determine the stability characteristics. In particular we investigate (i) the ultimate fate of a localised thermal disturbance placed in the region near the leading edge and (ii) the effect of small-scale surface temperature oscillations as means of understanding the stability characteristics of the boundary layer. We show that there is a favoured frequency of excitation for the time-periodic disturbance which maximises the local response in terms of the local rate of heat transfer. However the magnitude of the favoured frequency depends on precisely how far from the leading edge the local response is measured. We also find that the instability is advective in nature and that the response of the boundary layer consists of a starting transient which eventually leaves the computational domain, leaving behind the large-time time-periodic asymptotic state. Our detailed numerical results are compared with those obtained using parallel flow theory

THE UPTAKE AND FLUX OF DISSOLVED NITROGEN IN MARINE WATERS

The biological uptake and transformation of inorganic nitrogen species is described for contrasting marine environments which include a sea loch, riverine plume, polar marginal ice-zone, continental shelf break, oligotrophic ocean and a mesoscale eddy. Uptake of nitrate and ammonium by phytoplankton has been determined using the stable isotope as a tracer and continuous flow stable isotope-ratio mass spectrometry. The analysis of dissolved and atmospheric nitrous oxide was made using electron capture detector gas chromatography in a novel configuration which also allowed for the simultaneous analysis of methane from a single sample. Significant advances in the study of the marine nitrogen cycle have been made and presented to the scientific community via publication in high quality research journals and by the placement of data into the British Oceanographic Data Centre. These are important from local and global perspectives; information on the trophic status of seawaters is presented with respect to seasonal and hydrographical variability, as is the contribution made to knowledge regarding the role of nitrogen in climate change. Nitrogen availability is limiting in many oceans and attempts to constrain the global atmosphere - ocean fluxes of CO2 are based on basin scale nitrogen balances. The development of novel analytical procedures and their subsequent use during a number of field programs and modeling exercises has increased the available knowledge regarding the role of nitrogen in the removal of carbon to the deep ocean. In particular new insights into new production and ultimately carbon export have been made, these include: (i) The accepted threshold limit for phytoplankton uptake of nitrate in the oligotrophic ocean has been reduced from 0.016 to 0.005 mmol m ^ (ii) a relationship has been described relating the size structure of the phytoplankton productivity to new production which can be used as a direct estimate of carbon export, (iii) a series of algorithms have been produced to allow the basin scale estimation of new production from satellite and ship derived data, and (iv) whilst nitrous oxide plays a significant role in radiative forcing and stratospheric ozone depletion, an area in the Southern Ocean was found to provide a seasonal sink to atmospheric N2O