The efficiency of gravitational diffusion for the separation of elements in the prestellar gas

The gravitational separation of iron atoms with respect to hydrogen is evaluated by simple models of globular clusters and spherical galaxies before star formation, as well as in a column of gas perpendicular to the galactic plane in the solar neighborhood. The changes of the iron abundance are small, but qualitatively consistent with the observed facts: (1) there is a positive correlation between the mass number of the element and the steepness of its abundance gradient; (2) there is a connection between the mass and the density concentration of the globular clusters and their chemical composition; (3) the changes of the chemical content in the galactic plane are very small during the life of the galactic disk, but are increasingly significant in the upper layers.     

Static spherical configurations of cold matter in the Einstein-Cartan theory of gravitation

We investigate static, spherical configurations of cold catalized matter in the Einstein-Cartan theory of gravitation. Assuming that density of spin is proportional to the number density of baryonsn and using an equation of state of a degenerate, relativistic Fermi gas, we numerically integrated the relativistic equation of equilibrium. We have also studied the stability of those configurations. Configurations with central number densityn _c such that where is the effective pressure, are very similar to general relativistic configurations with the same central density. In the Einstein-Cartan theory there exists another disjoint family of equilibrium configurations for which but . Those configurations have very small masses 10^–6 g and raddi 10^–34 cm and are unstable.Supported in part by Research Grant MR-I-7.     

Comparison of Two Wavelet Transform Coherence and Cross-Covariance Functions Applied on Polar Motion and Atmospheric Excitation

The wavelet transform techniques were applied to compute time-frequency spectra, coherence and cross-covariance functions between complex-valued polar motion and atmospheric excitation functions. These wavelet transform approaches are based on the classical wavelet transform with Morlet wavelet and the harmonic wavelet transform. The computed coherence and cross-covariance functions enable comparison of polar motion and atmospheric excitation functions data in the chosen frequency band. In the study we concentrate on short period oscillations with periods ranging from several to about 250 days. The time lag functions show frequency dependent time lags corresponding to maxima of the modules of cross-covariance functions between the polar motion and atmospheric excitation functions.     

Assessment of long‐term Holocene soil erosion rates in Polish loess areas using sedimentary archives from closed depressions

Soil erosion is a particularly important problem in the loess areas of Central Europe. Numerous studies of past and present soil erosion based on colluvial sediments have so far been conducted. The main problem is the fact that colluvia usually do not represent the complete sedimentation record. Closed depressions (CDs) collect all colluvial sediments from their catchment, therefore, constitute sediment stores enabling the calculation of soil erosion rates. Colluvial sediments and fossil soils, infilling four CDs in the Polish loess belt, were OSL and C‐14 dated. Human settlements near the studied CDs were analyzed. Phases of soil erosion and colluviation from the Neolithic (5400–2900 bc ), from the Middle Bronze Age to the Early Iron Age (1600–0 bc ), and from the Early Middle Ages to Modern Times (500 AD until today) were documented within the CDs studied. Phases of low soil erosion rate and pedogenesis occurred from the Late Vistulian to the Early Neolithic and from the Iron Age to Early Middle Ages. This study reveals that these phases are not synchronous with the soil erosion phases in Central Europe, as the latter mainly occurred in the Bronze Age, Roman Period and Middle Ages. The obtained soil erosion rates were compared with erosion rates in different areas of Central Europe. This study indicates that in loess regions with long‐term agricultural land use, mean erosion rates (i.e. 3.7–5.9 t ha^‐1 yr^‐1) from the Middle Ages to Modern Times were ten times higher than during the entire prehistoric period (0.39–0.67 t ha^‐1 yr^‐1). The mean soil erosion rates for forested CDs was 0.24–0.74 t ha^‐1 yr^‐1. Soil erosion phases are most probably caused by human activities (i.e. land use change) but the early Holocene erosion phase (7.96 +/‐ 0.67 kyr) could have been induced by a climatic fluctuation (e.g. a 8.2 kyr Bond event). Copyright © 2018 John Wiley & Sons, Ltd.     

Effect of Catchment Land Use on Trophic State Variables of Small Water Bodies (Northern Poland)

We examined the land use impact on the water quality of small water bodies located in northern Poland. Twenty nine ponds, located in the urban area or a typical agricultural land were analyzed based on physical-chemical parameters: water temperature, conductivity, oxygen concentration, content of particulate suspended matter and chlorophyll “a”, and nutrients concentration. Additionally, to describe and compare the trophic condition of investigated small water bodies, we used the Carlson type trophic state. Performed measurements showed that nutrient concentrations significantly differentiated the agricultural ponds from urban water bodies. Mean total phosphorus and nitrogen concentration in midfield ponds were about 5 and 3 times higher, respectively, than in urban ponds. Moreover the phytoplankton chlorophyll “a” mean values were on average fivefold higher in agricultural ponds. Furthermore, urban ponds were characterized by lower values of TSI, thus lower trophy level: generally on the border of meso- and eutrophy. The agricultural ponds trophy changed from meso- to hypertrophy.     

High-resolution computed microtomography for the characterization of a diffusion tensor imaging phantom

This paper addresses the issue of the quantitative characterization of the structure of the calibration model (phantom) for b-matrix spatial distribution diffusion tensor imaging (BSD-DTI) scanners. The aim of this study was to verify manufacturing assumptions of the structure of materials, since phantoms are used for BSD-DTI calibration directly after manufacturing. Visualization of the phantoms’ structure was achieved through optical microscopy and high-resolution computed microtomography (µCT). Using µCT images, a numerical model of the materials structure was developed for further quantitative analysis. 3D image characterization was performed to determine crucial structural parameters of the phantom: porosity, uniformity and distribution of equivalent diameter of capillary bundles. Additionally calculations of hypothetical flow streamlines were also performed based on the numerical model that was developed. The results obtained in this study can be used in the calibration of DTI-BST measurements. However, it was found that the structure of the phantom exhibits flaws and discrepancies from the assumed geometry which might affect BSD-DTI calibration.     

Anisotropy of magnetic susceptibility as an indicator for palaeocurrent analysis in folded turbidites (Outer Western Carpathians,Poland)

The anisotropy of magnetic susceptibility is a well-known geological proxy in revealing the directional tectonic and sedimentological features of rocks, although it can be ambiguous in situations where these two factors co-occur. This paper demonstrates the usefulness of the anisotropy of magnetic susceptibility in determining palaeotransport directions in turbiditic rocks that underwent subsequent thrusting and folding. This study demonstrates that the magnetic lineation is largely unsuitable as a palaeocurrent direction proxy, and suggests that the imbrication of magnetic foliation is better in such cases. Moreover, the anisotropy of magnetic susceptibility results were analyzed in reference to a joint and fold study within the framework of the regional structural geology. Magnetic fabric investigations were conducted in the eastern part of the Outer Western Carpathians (south-east Poland). During the study, a total of 191 oriented palaeomagnetic samples were collected from three outcrops (Nasiczne, Dwernik and Hoczew) in the Krosno Beds, Silesian Unit. For the purpose of sedimentological analysis, 121 m of turbidite successions were documented and 126 directional sedimentary structures were measured. The magnetic anisotropy of sandstones revealed typical sedimentary fabrics, often overprinted by variably intense tectonic deformation. Oblate susceptibility ellipsoids from Nasiczne showed tilt coherent with the palaeoflow direction, whereas the rocks from Dwernik and Hoczew contained triaxial magnetic fabric developed during compressional palaeostress. This paper suggests that medium-grained and coarse-grained sandstones, preferably with high mica content, are the most suitable for palaeotransport reconstructions among the studied lithologies.     

Modern sediments and sediment accumulation rates on the narrow shelf off central Vietnam,South China Sea

The narrow shelf along the coast of central Vietnam is seasonally supplied by large amounts of sediment from the adjacent mountainous hinterland following monsoonal precipitation. This study examines the fate of these sediments, and their accumulation rates along two transects across the shelf, based on analyses of radionuclides (²¹⁰Pb, ¹³⁷Cs), sediment texture and structure, as well as carbonate content. The inner shelf is covered by sands, and probably serves as bypass zone for fine sediments transported offshore. Sediment characteristics suggest that the transport to the mid and outer shelf is related to flood events. Averaged over the last century, the ²¹⁰Pb-based mud mass accumulation rates on the mid and outer shelf vary between 0.25 g cm ⁻² and 0.56 g cm ⁻² year ⁻¹ (corresponding to linear sediment accumulation rates of 0.20–0.47 cm year ⁻¹). Along with high excess ²¹⁰Pb inventories, these high accumulation rates suggest a significant sediment depocentre on the mid shelf. The ²¹⁰Pb-derived sediment accumulation rates were found to be several times higher than ¹⁴C-derived rates previously reported for the Holocene, at the same location on the outer shelf. This is probably due to the incompleteness of the Holocene record, and an overestimation of the modern rate. Another explanation would be increased erosion within the rivers’ drainage basins, due to 20th century deforestation. This hypothesis is supported by the difference between recent (less sand, more lithic grains in the sand fraction) and older sediments. In terms of modern sedimentation processes and rates, the central Vietnam shelf, although being a part of a narrow passive continental margin, is similar to active flood-dominated continental margins.     

Impact of the surface temperature and vertical shear of zonal wind on the dynamics of a simple two-layer model of the atmosphere

The paper presents and analyzes, from the point of view of smooth dynamic systems theory, a two-layer baroclinic model of the troposphere in geostrophic approximation. The model describes airflow in β-channel within the tropospheric part of the main Hadley circulation cell. It enables to obtain, after application of the Galerkin method, a fairly simple low-parametric dynamic system describing the phenomena of non-linear interactions, bifurcations and blocking in the atmosphere. This enables to take into consideration such basic factors influencing the atmospheric dynamics like the heat exchange within the surface, orography, vertical variability of zonal wind and hydrostatic stability. Impact of zonal thermal variability of the surface and vertical shear of zonal wind in the troposphere on the orographic bifurcation was investigated and the oscillation character in the dynamic system after Hopf bifurcation of the second kind was analyzed. Additionally, the model dynamics was investigated in conditions including momentum forcing in the upper and lower parts of the troposphere and excluding orographic interaction, as well as in the conditions of thermal interaction between the troposphere and the surface for the vertical shear of zonal wind in both tropospheric layers. Impact of the mean zonal wind in the troposphere on the properties of model dynamics was assessed. It was proved that zonally varied surface temperature and layered mean zonal wind in the atmosphere are the parameters that have basic influence on the model dynamics. They cause numerous bifurcations and strongly influence the periods of oscillations of the model variables. They are often Hopf bifurcations of the second kind during which tropospheric states fairly distant from the ones before the bifurcations are generated. This significantly influences the model predictability.