Remote Assessment of 4-D Phytoplankton Distributions off the Washington Coast

Satellite-based optical measurements were coupled with physical and optical measurements from Seaglider – a long-range autonomous glider – to study interactions between biological and physical processes off the coast of Washington, USA, and to evaluate space-time variability of regional phytoplankton and particle distributions. Using satellite ocean color data variability in near-surface chlorophyll a was characterized across a range of spatial and temporal scales ranging from 1 – 500 km and from days – years to assess region-wide responses by phytoplankton to changes in environmental conditions. Results from 1998 – 2002 revealed both strong negative and positive anomalies associated with lingering effects of the 1997-98 El Niño and an invasion of Subartic water into the California Current System in 2002, respectively. Ocean color satellite data were also used to derive ‘spectral signatures’ for waters associated with the Juan de Fuca Eddy to monitor these waters as they moved southwards towards Washington beaches. Episodic southward transport of these waters may play a role in bloom initiation of the potentially toxigenic pennate diatom Pseudo-nitzschia and the ability to track these waters by remote sensing could help determine when to initiate more intensive sampling for domoic acid along the Washington coast. From April 2002 – December 2005 Seaglider conducted highly resolved (~5 km horizontal spacing, ~1 m vertical resolution, ~15 d temporal resolution) surveys across the northern California Current System. A new matchup procedure minimized discrepancies between Seaglider fluorescence and satellite-derived estimates of chlorophyll a at the surface (r = 0.834) allowing observations from these disparate remote sensing platforms to be fused together to create a quasi-4-dimensional representation of the phytoplankton distribution within a persistent offshore eddy in September and October 2004. Unfortunately daytime fluorescence is quenched at all times of the year in these waters with maximum quenching exceeding 80% during summer making it difficult to compare near-surface fluorescence measurements with satellite-derived estimates of surface phytoplankton biomass. A detailed statistical characterization of mid-day fluorescence quenching in April 2002 and from August 2003 – December 2005 was conducted to constrain the magnitude and variability in mid-day quenching to better use fluorescence as an independent validation for phytoplankton biomass at the surface

On Shape Transformations and Shape Fluctuations of Cellular Compartments and Vesicles

We discuss the shape formation and shape transitions of simple bilayer vesicles in context with their role in biology. In the first part several classes of shape changes of vesicles of one lipid component are described and it is shown that these can be explained in terms of the bending energy concept in particular augmented by the bilayer coupling hypothesis. In the second part shape changes and vesicle fission of vesicles composed of membranes of lipid mixtures are reported. These are explained in terms of coupling between local curvature and phase separation

Satellite-derived ecosystem indicators: a retrospective analysis of high resolution ocean color and sea surface temperature products in the Salish Sea

A complete set of MERIS CoastColour data products (2002 to 2012) were developed for the greater Salish Sea, including Puget Sound, Strait of Georgia, and the continental shelf/slope off Washington and Vancouver Island, BC. These data were processed by Integral Consulting Inc. for the Salish Sea Marine Survival Project and is being made available to the regional research community for any number of applications. The dataset includes both nearshore and offshore processed satellite data products at 300 m resolution for over 10 years (3 day revisit). Data products highlight seasonal water quality trends in the Salish Sea and show how events, such as algal blooms, have wide reaching effects across multiple ecosystems. It also provides a decade’s worth of baseline conditions that can be compared with future remote sensing data and incorporated into modelling projects. Data products include (1) temporal composites (monthly, seasonally, and yearly) of processed ocean color data products (e.g., chlorophyll a concentration, turbidity, and colored dissolved organic matter concentration, remote sensing reflectance, etc.); (2) extracted time series of select ocean color data products; (3) time series derived from available in situ data sets that can be used to corroborate satellite-derive ecosystem indicators

Diffusion of active tracers in fluctuating fields

The problem of a particle diffusion in a fluctuating scalar field is studied. In contrast to most studies of advection diffusion in random fields we analyze the case where the particle position is also coupled to the dynamics of the field. Physical realizations of this problem are numerous and range from the diffusion of proteins in fluctuating membranes and the diffusion of localized magnetic fields in spin systems. We present exact results for the diffusion constant of particles diffusing in dynamical Gaussian fields in the adiabatic limit where the field evolution is much faster than the particle diffusion. In addition we compute the diffusion constant perturbatively, in the weak coupling limit where the interaction of the particle with the field is small, using a Kubo-type relation. Finally we construct a simple toy model which can be solved exactly.Comment: 13 pages, 1 figur

Phase ordering and shape deformation of two-phase membranes

Within a coupled-field Ginzburg-Landau model we study analytically phase separation and accompanying shape deformation on a two-phase elastic membrane in simple geometries such as cylinders, spheres and tori. Using an exact periodic domain wall solution we solve for the shape and phase ordering field, and estimate the degree of deformation of the membrane. The results are pertinent to a preferential phase separation in regions of differing curvature on a variety of vesicles.Comment: 4 pages, submitted to PR

Attractive instability of oppositely charged membranes induced by charge density fluctuations

We predict the conditions under which two oppositely charged membranes show a dynamic, attractive instability. Two layers with unequal charges of opposite sign can repel or be stable when in close proximity. However, dynamic charge density fluctuations can induce an attractive instability and thus facilitate fusion. We predict the dominant instability modes and timescales and show how these are controlled by the relative charge and membrane viscosities. These dynamic instabilities may be the precursors of membrane fusion in systems where artificial vesicles are engulfed by biological cells of opposite charge

Thinking strategically about assessment

Drawing upon the literature on strategy formulation in organisations, this paper argues for a focus on strategy as process. It relates this to the need to think strategically about assessment, a need engendered by resource pressures, developments in learning and the demands of external stakeholders. It is argued that in practice assessment strategies are often formed at the level of practice, but that this produces contradiction and confusion at higher levels. Such tensions cannot be managed away, but they can be reflected on and mitigated. The paper suggests a framework for the construction of assessment strategies at different levels of an institution. However, the main conclusion is that the process of constructing such strategies should be an opportunity for learning and reflection, rather than one of compliance

Lateral phase separation in mixtures of lipids and cholesterol

In an effort to understand "rafts" in biological membranes, we propose phenomenological models for saturated and unsaturated lipid mixtures, and lipid-cholesterol mixtures. We consider simple couplings between the local composition and internal membrane structure, and their influence on transitions between liquid and gel membrane phases. Assuming that the gel transition temperature of the saturated lipid is shifted by the presence of the unsaturated lipid, and that cholesterol acts as an external field on the chain melting transition, a variety of phase diagrams are obtained. The phase diagrams for binary mixtures of saturated/unsaturated lipids and lipid/cholesterol are in semi-quantitative agreement with the experiments. Our results also apply to regions in the ternary phase diagram of lipid/lipid/cholesterol systems

The Angular Momentum Evolution of Very Low Mass Stars

We present theoretical models of the angular momentum evolution of very low mass stars (0.1 - 0.5 M_sun) and solar analogues (0.6 - 1.1 M_sun). We investigate the effect of rotation on the effective temperature and luminosity of these stars. We find that the decrease in T_eff and L can be significant at the higher end of our mass range, but becomes negligible below 0.4 M_sun. Formulae for relating T_eff to mass and v_rot are presented. We compare our models to rotational data from young open clusters of different ages to infer the rotational history of low mass stars, and the dependence of initial conditions and rotational evolution on mass. We find that the qualitative conclusions for stars below 0.6 M_sun do not depend on the assumptions about internal angular momentum transport, which makes these low mass stars ideal candidates for the study of the angular momentum loss law and distribution of initial conditions. We find that neither models with solid body nor differential rotation can simultaneously reproduce the observed stellar spin down in the 0.6 to 1.1 M_sun mass range and for stars between 0.1 and 0.6 M_sun. The most likely explanation is that the saturation threshold drops more steeply at low masses than would be predicted with a simple Rossby scaling. In young clusters there is a systematic increase in the mean rotation rate with decreased temperature below 3500 K (0.4 M_sun). This suggests either inefficient angular momentum loss or mass-dependent initial conditions for stars near the fully convective boundary. (abridged)Comment: To appear in the May 10, 2000 Ap