Dust tail of the active distant Comet C/2003 WT42 (LINEAR) studied with photometric and spectroscopic observations

We present the study of dust environment of dynamically new Comet C/2003 WT42 (LINEAR) based on spectroscopic and photometric observations. The comet was observed before and after the perihelion passage at heliocentric distances from 5.2 to 9.5 AU. Although the comet moved beyond the zone where water ice sublimation could be significant, its bright coma and extended dust tail evidenced the high level of physical activity. Afρ values exceeded 3000 cm likely reaching its maximum before the perihelion passage. At the same time, the spectrum of the comet did not reveal molecular emission features above the reflected continuum. Reddening of the continuum derived from the cometary spectrum is nonlinear along the dispersion with the steeper slop in the blue region. The pair of the blue and red continuum images was analyzed to estimate a color of the comet. The mean normalized reflectivity gradient derived from the innermost part of the cometary coma equals to 8% per 1000 Å that is typical for Oort cloud objects. However, the color map shows that the reddening of the cometary dust varies over the coma increasing to 15% per 1000 Å along the tail axis. The photometric images were fitted with a Monte Carlo model to construct the theoretical brightness distribution of the cometary coma and tail and to investigate the development of the cometary activity along the orbit. As the dust particles of distant comets are expected to be icy, we propose here the model, which describes the tail formation taking into account sublimation of grains along their orbits. The chemical composition and structure of these particles are assumed to correspond with Greenberg’s interstellar dust model of comet dust. All images were fitted with the close values of the model parameters. According to the results of the modeling, the physical activity of the comet is mainly determined by two active areas with outflows into the wide cones. The obliquity of the rotation axis of the nucleus equals to 20° relative to the comet’s orbital plane. The grains occupying the coma and tail are rather large amounting to 1 mm in size, with the exponential size distribution of a^−4.5. The outflow velocities of the dust particles vary from a few centimeters to tens of meters per second depending on their sizes. Our observations and the model findings evidence that the activity of the nucleus decreased sharply to a low-level phase at the end of April–beginning of May 2007. About 190 days later, in the first half of November 2007 the nucleus stopped any activity, however, the remnant tail did not disappear for more than 1.5 years at least.     

238U/206Pb-235U/207Pb-232Th/208Pb zircon geochronology in alpine and non-alpine environment

Based on regular arrays in a U-Pb diagram of data points of zircons from polymetamorphic rocks of the Alps quantitative models are developed that include several episodic lead losses, continuous lead losses during discrete periods and combinations of both.The data from the Alps can be explained by assuming an initial age of the zircons of 2000 and/or 2500–2600 m.y. and three episodic lead losses 520–580 m.y., 300 m.y. and 30 m.y. ago with regionally varying intensities of the events as can be seen from the efficiency parameters which define the shape of the discordia. On the other hand, zircon data from North American basement rocks satisfy a model assuming a discrete interval of continuous lead loss that starts with the time of uplift of the rocks.The Th-U-Pb diagrams are valuable for recognising whether the history of the zircons and their host rock is a complex one or not which is not always noticeable in a U-Pb diagram.     

Opening geometry of the Kurile Basin (Okhotsk Sea) as inferred from structural data

Abstract   The Kurile Basin in the Okhotsk Sea, northwestern Pacific, is a back-arc basin located behind the Kurile Island Arc. It is underlain by oceanic crust and its origin has been attributed to back-arc spreading. Two models for the opening of the Kurile Basin exist, for which the spreading axis is oriented northeast–southwest and northwest–southeast, respectively. New data are presented here on the morphostructure of the slope of the northern Kurile Basin and of the central Kurile Basin which support a strike of the spreading axis in the latter direction. Bathymetric as well as single-channel and multichannel seismic reflection data demonstrate the existence of dominant northwest-striking normal faults on the northern slope of the Kurile Basin. In the central Kurile Basin a basement rise striking north-northwest–south-southeast (here named the Sakura Rise) was mapped. The rise morphology has the distinct imprint of a rift structure with symmetrical volcanic edifices on the rise axis and faulted blocks that tilt in opposite directions on the flanks. These data suggest that the Kurile Basin opened in a northeast–southwest direction. In the generally accepted plate tectonic reconstructions, northwest–southeast spreading associated with dextral strike–slip along the north–south-striking shear zone of Sakhalin and Hokkaido islands has been assumed. In the present model, spreading in the Kurile Basin was presumably connected with dextral displacement along a northeast-striking shear zone on the southern segment of the Okhotsk Sea.     

Undrained cyclic behavior of bentonite–sand mixtures and factors affecting it

In this work, the cyclic behavior of bentonite–sand mixtures and factors affecting it were studied by means of a ring-shear apparatus and a scanning electron microscope. It was found that bentonite content had a significant influence on the liquefaction potential of the studied soils. A small amount of bentonite in the mixtures would cause the formation of “loose” microstructures, resulting in the occurrence of rapid liquefaction under cyclic loading, while a high bentonite content would cause the formation of clay matrixes, thus raising the soil resistance to liquefaction. In addition, the effect of pore water chemistry on the cyclic behavior of a high plasticity bentonite–sand mixture was carefully examined. It was also found that the presence of ions in pore water would change the clay microfabric, making it more open and thus more vulnerable to liquefaction. Finally, the effects of loading frequency on the cyclic behavior of mixtures with different amounts of bentonite were investigated. It was found that as the bentonite content increased, the influence became more pronounced.     

Detection of ground ice using ground penetrating radar method

The paper presents the results of a ground penetrating radar (GPR) application for the detection of ground ice. We combined a reflection traveltime curves analysis with a frequency spectrogram analysis. We found special anomalies at specific traces in the traveltime curves and ground boundaries analysis, and obtained a ground model for subsurface structure which allows the ground ice layer to be identified and delineated.     

Propagation of vibrations in thawing deep seasonally frozen soils in railway subgrade

In this study, in-situ testing results are given, and the analytical relationship of the vibrations' amplitudes inside an embankment by the thawing of the subgrade surface of seasonably deep frozen soils is provided. The peculiarities of the vibration waves' propagation during the springtime thawing of soils compared to those during the summertime period and the correlation of the vibrations with the under-rail basement modulus of elasticity are defined.     

Industrial specialization and economic performance: A case of Czech microregions

An influential body of literature suggests that economic diversity rather than specialization fuels the economic performance of regions and nations. The authors argue that this hypothesis has no universal applicability and that a more differentiated view is needed. In particular, historical specificity of the local environment and structural characteristics of regional economies should be taken into account. They focus on the effects of industrial specialization on economic performance and the vulnerability of Central European post-communist regions, namely Czech microregions with less than 200,000 inhabitants. They examine whether the economic performance and vulnerability of these regions is fuelled rather by industrial specialization or diversity when controlling for other potential determinants of regional economic performance. Their findings show that the dependence of Czech regions on manufacturing correlates with higher economic performance but also with higher regional vulnerability. In addition, industrial specialization within manufacturing was found to be instrumental for the economic performance of regions with high dependence on manufacturing. With a decreasing share of employment in manufacturing, industrial diversity rather than specialization becomes more valuable for the economic performance of Czech regions.     

Using terrestrial LiDAR to measure water erosion on stony plots under simulated rainfall

Terrestrial LiDAR scanning (TLS) technology is widely used to detect terrain elevation changes. This study examines the potential use of terrestrial LiDAR to measure erosion on small experimental plots at high resolution. Multitemporal TLS scans were conducted at six positions around plots (12 m²) with three slope treatments through 11 simulated rainfall applications. Surface elevation changes were quantified by comparing scans between rainfall simulations, and elevation changes greater than the level of detection were used to obtain volumetric change estimations. Erosion mass was estimated both by using soil bulk density and the density of sediment collected in runoff, and then compared to the erosion estimated from the runoff samples. Results showed: (1) with the aid of fixed reference controls in the form of concrete target surfaces of varying roughness, registration accuracy was better than 1 mm and mean level of change detection was less than 2.2 mm; (2) the average absolute relative errors of TLS-estimated eroded mass ranged from 6.8% to 31.8%, with greater values on 5% slope; (3) the TLS-estimated erosion accuracy was affected by erosion magnitude, the utilized material density and number of scan positions, and a grid size of 10 mm was found to be appropriate for this scale to estimate the volumetric changes; (4) the number of scan positions could be reduced to three while not significantly impacting volumetric change estimations; and (5) elevating the scanner resulted in much better accuracy for eroded mass estimations. This study suggests that using LiDAR to monitor soil erosion at the plot scale is feasible, and provides guidance about the level of accuracy one might expect in doing so. © 2019 John Wiley & Sons, Ltd.     

On the computation of area probabilities based on a spatial stochastic model for precipitation cells and precipitation amounts

A main task of weather services is the issuing of warnings for potentially harmful weather events. Automated warning guidances can be derived, e.g., from statistical post-processing of numerical weather prediction using meteorological observations. These statistical methods commonly estimate the probability of an event (e.g. precipitation) occurring at a fixed location (a point probability). However, there are no operationally applicable techniques for estimating the probability of precipitation occurring anywhere in a geographical region (an area probability). We present an approach to the estimation of area probabilities for the occurrence of precipitation exceeding given thresholds. This approach is based on a spatial stochastic model for precipitation cells and precipitation amounts. The basic modeling component is a non-stationary germ-grain model with circular grains for the representation of precipitation cells. Then, we assign a randomly scaled response function to each precipitation cell and sum these functions up to obtain precipitation amounts. We derive formulas for expectations and variances of point precipitation amounts and use these formulas to compute further model characteristics based on available sequences of point probabilities. Area probabilities for arbitrary areas and thresholds can be estimated by repeated Monte Carlo simulation of the fitted precipitation model. Finally, we verify the proposed model by comparing the generated area probabilities with independent rain gauge adjusted radar data. The novelty of the presented approach is that, for the first time, a widely applicable estimation of area probabilities is possible, which is based solely on predicted point probabilities (i.e., neither precipitation observations nor further input of the forecaster are necessary). Therefore, this method can be applied for operational weather predictions.