Seasonal and inter-annual patterns of sediment-water nutrient and oxygen fluxes in Mobile Bay, Alabama (USA): Regulating factors and ecological significance.

Sediment oxygen and nutrient fluxes were measured monthly for 2 yr in Mobile Bay, Alabama, USA. Rates of sediment oxygen consumption (0.1 to 1.25 gO2 m-2 d-1), ammonium flux (-22 to 181 µmol m-2 h-1), nitrate flux (-14 to 67 µmol m-2 h-1), phosphate flux (-2 to 20.4 µmol m-2 h-1), and dissolved silicate flux (-15 to 342 µmol m-2 h-1) were moderate to high compared to values for other estuaries. A step-wise regression analysis revealed that dissolved oxygen concentration and temperature in bottom-waters explained much of the variance in fluxes. This is presumably because of their influence on rates of microbial and physico-chemical processes. Organic matter availability was not found to be an important factor in regulating temporal (month to month) variability of fluxes, possibly because frequent resuspension of the sediments in this shallow system rendered indices of sediment organic matter nearly constant with time. However, warm season-averaged sediment nutrient releases were correlated with sediment chlorophyll a. This relationship in Mobile Bay is in strong agreement with similar relationships found in other estuarine systems, and suggests that the availability of labile organic matter ultimately regulates the maximum rate of nutrient release by the sediments. Annually averaged sediment fluxes supplied 36% of the nitrogen (N) and 25% of the phosphorus (P) required by phytoplankton in Mobile Bay. While this is not particularly high compared to other estuaries, monthly estimates show that the sediments can supply from 0 to 94% of the N, and 0 to 83% of the P required by phytoplankton. In addition, flux ratios show that N and P are released from sediments at N:P ratios that rapidly switch from above (maximum 98) to below (minimum 1.2) that required for phytoplankton growth. This pattern is different from cooler temperate systems, where such switching is seasonally base

A stochastic model for the evolution of the web allowing link deletion

Recently several authors have proposed stochastic evolutionary models for the growth of the web graph and other networks that give rise to power-law distributions. These models are based on the notion of preferential attachment leading to the ``rich get richer'' phenomenon. We present a generalisation of the basic model by allowing deletion of individual links and show that it also gives rise to a power-law distribution. We derive the mean-field equations for this stochastic model and show that by examining a snapshot of the distribution at the steady state of the model, we are able to tell whether any link deletion has taken place and estimate the link deletion probability. Our model enables us to gain some insight into the distribution of inlinks in the web graph, in particular it suggests a power-law exponent of approximately 2.15 rather than the widely published exponent of 2.1

Review: Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution

Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. 2000. Committee on the Causes and Management of Coastal Eutrophication, National Research Council. National Academy Press, Washington, D.C. 405 pages. ISBN 0-309-06948-3. US $54.9

Review: Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution

Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. 2000. Committee on the Causes and Management of Coastal Eutrophication, National Research Council. National Academy Press, Washington, D.C. 405 pages. ISBN 0-309-06948-3. US $54.9

The Relevance of Grain Dissection for Grain Size Reduction in Polar Ice: Insights from Numerical Models and Ice Core Microstructure Analysis

The flow of ice depends on the properties of the aggregate of individual ice crystals, such as grain size or lattice orientation distributions. Therefore, an understanding of the processes controlling ice micro-dynamics is needed to ultimately develop a physically based macroscopic ice flow law. We investigated the relevance of the process of grain dissection as a grain-size-modifying process in natural ice. For that purpose, we performed numerical multi-process microstructure modelling and analysed microstructure and crystallographic orientation maps from natural deep ice-core samples from the North Greenland Eemian Ice Drilling (NEEM) project. Full crystallographic orientations measured by electron backscatter diffraction (EBSD) have been used together with c-axis orientations using an optical technique (Fabric Analyser). Grain dissection is a feature of strain-induced grain boundary migration. During grain dissection, grain boundaries bulge into a neighbouring grain in an area of high dislocation energy and merge with the opposite grain boundary. This splits the high dislocation-energy grain into two parts, effectively decreasing the local grain size. Currently, grain size reduction in ice is thought to be achieved by either the progressive transformation from dislocation walls into new high-angle grain boundaries, called subgrain rotation or polygonisation, or bulging nucleation that is assisted by subgrain rotation. Both our time-resolved numerical modelling and NEEM ice core samples show that grain dissection is a common mechanism during ice deformation and can provide an efficient process to reduce grain sizes and counter-act dynamic grain-growth in addition to polygonisation or bulging nucleation. Thus, our results show that solely strain-induced boundary migration, in absence of subgrain rotation, can reduce grain sizes in polar ice, in particular if strain energy gradients are high. We describe the microstructural characteristics that can be used to identify grain dissection in natural microstructures

Перебіг анемії вагітних у хворих на туберкульоз легень

В статье представлены данные течения анемии беременных и нарушения фетоплацентарного комплекса у 86 женщин, больных туберкулезом легких. Выявлено, что анемия на фоне туберкулезного процесса приводит к существенным функциональным и морфологическим нарушениям в плаценте. показано диагностическое значение оценки плацентарной дисфункции для профилактики и лечения анемии у данного контингента женщин.The article presents the data of course of pregnancy anemia and failures of fetoplacental complex in 86 women with pulmonary tuberculosis. It is found that anemia under tuberculous process leads to significant functional and morphological disturbances in placenta. Diagnostic significance of assessment of placental dysfunction for the prevention and treatment of anemia in this contingent of women is shown