ALBERT

Description: Magnetic disturbances caused by the Earth's ring current, particularly during storm time activity, have a dominant effect on the geomagnetic field. Strong currents and large kinetic and magnetic energies can change considerably local field geometry, and depress the ground geomagnetic field. The multi-spacecraft magnetic measurements of Cluster allow extensive in situ coverage of the ring current, We select 48 storm time Cluster crossing events to investigate the variation of the local current density distribution and magnetic configuration of the ring current. We find direct evidence for the existence of an inner, eastward flowing current in addition to the dominant westward current, in the ring plane. The radius of curvature of the magnetic field lines (MFLs) is found to be increasingly reduced at all local times during increasing storm activity, changing the resulting ring current magnetic geometry considerably, where the MFL configuration and the azimuthal current density distribution, are asymmetric with the local time. During similar storm activity the radius of curvature of the local MFLs, R C , is smallest on the nightside to duskside, medium on the dawnside, and largest on the dayside. This change in geometry may have significant influence on the spatial distribution of the particles with various energies in the plasmasphere, ring current and radiation belts.

Description: Unambiguous knowledge of magnetic field structure and the electric current distribution is critical for understanding the origin, evolution and related dynamic properties of magnetic flux ropes (MFRs). In this paper, a survey of 13 MFRs in the Earth's magnetotail are conducted by Cluster multi-point analysis, so that their force-free feature, i.e., the kind of magnetic field structure satisfying J  ×  B  =  0 , can be probed directly. It is showed that the selected flux ropes with the bipolar signature of the South–north magnetic field component generally lie near the equatorial plane, as expected, and that the magnetic field gradient is rather weak near the axis center, where the curvature radius is large. The current density (up to several tens of nA/m 2 ) reach their maximum values as the center is approached. It is found that the stronger the current density, the smaller the angles between the magnetic field and current in MFRs. The direct observations show that only quasi force-free structure is observed and it tends to appear in the low plasma beta regime (in agreement with the theoretic results). The quasi force-free region is generally found to be embedded in the central portion of the MFRs, where the current is approximately field-aligned and proportional to the strength of core field. It is shown that, ~60% of surveyed MFRs can be globally approximated as force-free. The force-free factor α is found to be non-constantly varied through the quasi force-free MFR, suggesting that the force-free structure is non-linear.

Description: A sedimentological and geochemical study was performed on the travertines in the southern part of the Uşak geothermal field, western Turkey, to assess the applicability of a fluvial tufa facies model in interpreting late Quaternary travertine deposits developed along the stream valleys that follow fault and fracture systems. Modern thermal (31 to 38ºC) springs are found on the floor of the valley between 480 m and 520 m above sea-level. The distribution and nature of travertine facies were determined from natural outcrops. Samples of the travertines and spring water were characterized using a range of geochemical and petrographic methods. Waterfall, slope and pool facies associations consist of various combinations of travertine facies and subordinate detrital facies. Waterfall and slope facies associations of the older deposits occur where the springs emerged onto a hillslope or topographic break. In contrast, the pool facies association developed in depressions or flat areas that were fed by thermal springs. The youngest generation (1.85 ka) precipitated at lower elevations than the older ones (147 to 153 ka). Stable carbon and oxygen isotope values of the Aksaz travertines range between +4.3‰ and +6.3‰ (Vienna Pee Dee Belemnite) and -12.6‰ and -7.2‰ (Vienna Pee Dee Belemnite), respectively. The high δ 13 C values suggest that the thermal waters were charged with isotopically heavy CO 2 of deep origin. Based on palaeotemperature calculations, the temperatures of the palaeosprings are slightly higher (up to 44ºC) than the present equivalents, but sometimes the temperature is lower, probably due to mixing with the stream water. Although the thermal waters occasionally are impeded by fluvial activity, travertine precipitation occurs in the protected parts of the Aksaz Stream valley. This contribution highlights the applicability of the fluvial facies model for tufa for the interpretation of travertine deposits worldwide. This article is protected by copyright. All rights reserved.

Description: Particle filters (PFs) constitute a sequential data assimilation method based on the Monte Carlo approximation of Bayesian estimation theory. Standard PFs use scalar weights derived from the likelihood of the approximate posterior probability density functions (PDFs) of observations and use resampling schemes to generate posterior particles. However, the scalar weights approach interferes with the localization algorithm and often results in filter degeneracy. Recently, a localized particle filter (LPF) was developed by extending the scalar weights of PF to vector weights, which produces various (local) posterior PDFs for different model grids and variables. With a sampling and merging approach in the resampling, an LPF can effectively solve the filter degeneracy problem and offer a practical, efficient algorithm for localization. However, this algorithm assumes the variations in the weights of a state variable of neighbouring grids to be continuous and uses a spatially linear interpolation of PF weights to determine the local weights. In this paper, we first analyse the possible concerns associated with the linear continuity of PF weights. This assumption is found to challenge the theoretical properties of nonlinear and non-Gaussian variations in weights and alleviate the intrinsic spatial variations of PF weights. On this basis, we propose a new algorithm to produce vector weights for PFs for neighbouring grids. Numerical experiments using the Lorenz ’96 model show that our new localized particle filter performs better than the existing LPF algorithm, indicating the advantages and potential applications of this new algorithm of vector weights in the field of data assimilation.

Description: ABSTRACT Maintenance of hematopoietic stem cells (HSC) takes place in a highly specialized microenvironment within the bone marrow. Technological improvements, especially in the field of in vivo imaging, have helped unravel the complexity of the niche microenvironment and have completely changed the classical concept from what was previously believed to be a static supportive platform, to a dynamic microenvironment tightly regulating HSC homeostasis through the complex interplay between diverse cell types, secreted factors, extracellular matrix molecules and the expression of different transmembrane receptors. To add to the complexity, non-protein based metabolites have also been recognized as a component of the bone marrow niche. The objective of this review is to discuss the current understanding on how the different extracellular matrix components of the niche regulate HSC fate, both during embryonic development and in adulthood. Special attention will be provided to the description of non-protein metabolites, such as lipids and metal ions, which contribute to the regulation of HSC behavior. This article is protected by copyright. All rights reserved

Description: In arid and semi-arid regions there is usually a shortage of irrigation water; thus, wastewater water, as well as other low-quality water resources, may become an important source of water and nutrients. However, (pre)treated wastewater may contain elements and compounds that can damage the environment. It also has the potential to affect water quality adversely in an aquifer that may be the source of drinking water in the area. In order to assess the impacts of wastewater on the enviromnent, groundwater samples were taken and analysed in typical croplands in the North China Plain, where urban wastewater or groundwater have been used for irrigation for several decades. Concentrations of nitrate (NO3-) in groundwater in the study area varied from 50 to 130 mg 1-1 in the croplands irrigated by wastewater, but in the croplands irrigated by pumping wells, away from the Dongming Canal, NO3- concentrations are less than 35 mg 1-1. It was found that values of δ15N ranged from +5 to +13‰, and dominantly from +7 to +11‰, and the NO3- concentration in most wells with depths of less than 40 m was higher than the drinking water standard set by the WHO. Cluster analysis was used to classify the spatial distribution of nitrates resulting from the wastewater. Identification of chemical patterns is found to be effective for the comprehensive assessment of the spatial distribution of groundwater quality. It is also emphasized that the wastewater in this area controls the NO3- distribution in the groundwater, and should be used carefully to protect both soil and groundwater from NO3- pollution. © 2004 John Wiley and Sons, Ltd.

Description: The lower reaches of the Yellow River are basically a discharge zone with a high salt content, and the study area of Yucheng in Shandong Province became arable only after the water diversion project from the Yellow River was implemented in 1972. The sustainability of agriculture in this area is examined through the redistribution of soil moisture and solutes in the vertical profile based on the measurement of soil moisture, potential and solute content in a maize field at the Yucheng Experimental Station. Diurnal moisture fluctuations appear in the surface layers at 30 and 50 cm depths, and the daily water content at 90 cm depth decreases about a month after planting, due mainly to the effect of root water extraction, even reaching a level lower than that at 70 cm depth. Soil moisture obviously increases for the three layers at 30, 50, 90 cm depth, and the relevant peak-time shifts from the surface 30 cm depth to the deep layer at 120 cm depth with a varied time lag in response to rainfall events, but there is little or no signal for the other layers due to the effects of soil properties, roots, and soil storage. The existence of a convergent zero flux plane may explain to some extent the accumulation of moisture and solutes in the layer at 120 cm. depth. Though the chemical facies along the profile from the unsaturated surface to the deep saturated zone generally evolves in a direction of decreasing SO42- and Cl-, a strong driving force upward and the accumulation of solute at 120 cm may change the redistribution pattern and three groups of this pattern were classified according to the evolution and concentration distribution profiles. The main factors affecting the moisture, solute and their distributions for the three groups are varied: rainfall, irrigation and evapotranspiration for the surface layer till 70 cm depth, root extraction for the accumulation layer of 70-120 cm depth, and the fluctuation of the groundwater table for the deep layer at 120-200 cm depth. The agriculture appears sustainable as long as diverted water from the Yellow River is available, but the high content of solute accumulation in the layer at about 120 cm depth is a potential risk. Copyright 2004 John Wiley and Sons, Ltd.