The significance of subsurface chlorophyll, nitrite and ammonium maxima in relation to nitrogen for phytoplankton growth in stratified waters of the Gulf of Maine

Data on the distributions in summer of phytoplankton and inorganic nutrients in the Gulf of Maine and across Georges Bank are presented. The chlorophyll maximum represents a phytoplankton biomass maximum and occurs at a depth where both light and nitrate availability allow net growth of the population. The dominant species were generally flagellates and included the toxic dinoflagellate, Gonyaulax tamarensis var. excavata, at some stations. The ammonium and nitrite profiles suggest that nitrification is occurring at the base of the pycnocline below the chlorophyll maximum, and this may be an important source of nitrate during the summer months. The highest levels of nitrite and ammonium were found over the slopes of Georges Bank

Simulation Approach for Timing Analysis of Genetic Logic Circuits

Constructing genetic logic circuits is an application of synthetic biology in which parts of the DNA of a living cell are engineered to perform a dedicated Boolean function triggered by an appropriate concentration of certain proteins or by different genetic components. These logic circuits work in a manner similar to electronic logic circuits, but they are much more stochastic and hence much harder to characterize. In this article, we introduce an approach to analyze the threshold value and timing of genetic logic circuits. We show how this approach can be used to analyze the timing behavior of single and cascaded genetic logic circuits. We further analyze the timing sensitivity of circuits by varying the degradation rates and concentrations. Our approach can be used not only to characterize the timing behavior but also to analyze the timing constraints of cascaded genetic logic circuits, a capability that we believe will be important for design automation in synthetic biology

Chalk-Ex—fate of CaCO3 particles in the mixed layer : evolution of patch optical properties

Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 114 (2009): C07020, doi:10.1029/2008JC004902.The fate of particles in the mixed layer is of great relevance to the global carbon cycle as well as to the propagation of light in the sea. We conducted four manipulative field experiments called “Chalk-Ex” in which known quantities of uniform, calcium carbonate particles were injected into the surface mixed layer. Since the production term for these patches was known to high precision, the experimental design allowed us to focus on terms associated with particle loss. The mass of chalk in the patches was evaluated using the well-calibrated light-scattering properties of the chalk plus measurements from a variety of optical measurements and platforms. Patches were surveyed with a temporal resolution of hours over spatial scales of tens of kilometers. Our results demonstrated exponential loss of the chalk particles with time from the patches. There was little evidence for rapid sinking of the chalk. Instead, horizontal eddy diffusion appeared to be the major factor affecting the dispersion of the chalk to concentrations below the limits of detection. There was unequivocal evidence of subduction of the chalk along isopycnals and subsequent formation of thin layers. Shear dispersion is the most likely mechanism to explain these results. Calculations of horizontal eddy diffusivity were consistent with other mixed layer patch experiments. Our results provide insight into the importance of physics in the formation of subsurface particle maxima in the sea, as well as the importance of rapid coccolith production and critical patch size for maintenance of natural coccolithophore blooms in nature.We would like to thank the Office of Naval Research/Optical and Biological Oceanography Program for their support of Chalk-Ex with awards N000140110042 (WMB) and N00014-01-1-0141 (AJP). Additional funding for this work came from ONR (N00014-05-1- 0111) and NASA (NNG04Gl11G, NNX08AC27G, NNG04HZ25C) to W.M.B

A gray-box model for a probabilistic estimate of regional ground magnetic perturbations: Enhancing the NOAA operational Geospace model with machine learning

We present a novel algorithm that predicts the probability that the time derivative of the horizontal component of the ground magnetic field $dB/dt$ exceeds a specified threshold at a given location. This quantity provides important information that is physically relevant to Geomagnetically Induced Currents (GIC), which are electric currents { associated to} sudden changes in the Earth's magnetic field due to Space Weather events. The model follows a 'gray-box' approach by combining the output of a physics-based model with machine learning. Specifically, we combine the University of Michigan's Geospace model that is operational at the NOAA Space Weather Prediction Center, with a boosted ensemble of classification trees. We discuss the problem of re-calibrating the output of the decision tree to obtain reliable probabilities. The performance of the model is assessed by typical metrics for probabilistic forecasts: Probability of Detection and False Detection, True Skill Statistic, Heidke Skill Score, and Receiver Operating Characteristic curve. We show that the ML enhanced algorithm consistently improves all the metrics considered.Comment: under revie

Low-energy elastic electron scattering by acetylene

We report measurements and first-principles calculations of the differential cross sections for elastic scattering of low-energy electrons by acetylene, C_2H_2, at collision energies from 1 to 100 eV, with an emphasis on energies near and below that of the π* shape resonance. The measurements cover angles from 5° to 130°. We compare our results to previous experimental and theoretical values

Hormone replacement therapy after surgery for stage 1 or 2 cutaneous melanoma

A total of 206 women were followed for a minimum of 5 years after primary melanoma surgery to establish if hormone replacement therapy (HRT) adversely affected prognosis. In all, 123 had no HRT and 22 have died of melanoma; 83 had HRT for varying periods and one has died of melanoma. After controlling for known prognostic factors, we conclude that HRT after melanoma does not adversely affect prognosis

The Influence of Particle Concentration and Bulk Characteristics on Polarized Oceanographic Lidar Measurements

Oceanographic lidar measurements of the linear depolarization ratio, δ, contain information on the bulk characteristics of marine particles that could improve our ability to study ocean biogeochemistry. However, a scarcity of information on the polarized light-scattering properties of marine particles and the lack of a framework for separating single and multiple scattering effects on δ have hindered the development of polarization-based retrievals of bulk particle properties. To address these knowledge gaps, we made single scattering measurements of δ for several compositionally and morphologically distinct marine particle assemblages. We then used a bio-optical model to explore the influence of multiple scattering and particle characteristics on lidar measurements of δ made during an expedition to sample a mesoscale coccolithophore bloom. Laboratory measurements of linear depolarization revealed a complex dependency on particle shape, size, and composition that were consistent with scattering simulations for idealized nonspherical particles. Model results suggested that the variability in δ measured during the field expedition was driven predominantly by shifts in particle concentration rather than their bulk characteristics. However, model estimates of δ improved when calcite particles were represented by a distinct particle class, highlighting the influence of bulk particle properties on δ. To advance polarized lidar retrievals of bulk particle properties and to constrain the uncertainty in satellite lidar retrievals of particulate backscattering, these results point to the need for future efforts to characterize the variability of particulate depolarization in the ocean and to quantify the sensitivity of operational ocean lidar systems to multiple scattering