Broadband convex impedance ground planes for multi-system GNSS reference station antennas

Common choke ring ground planes are known to contribute to undesirable antenna pattern narrowing in the elevation plane which is associated with difficulties of tracking low elevation satellites. Also known is the comparatively narrow frequency bandwidth of the choke grooves structure. As an alternative, using a convex impedance ground plane has been suggested for full-spectrum GNSS applications. With such ground planes a pin structure is utilized instead of choke grooves to allow a frequency bandwidth increase. A semi-spherical shape of the ground plane is shown to provide increased antenna gain for low elevation angles. Theoretical performance estimates along with experimental test data have been provided.     

On the impact of atmospheric vs oceanic resolutions on the representation of the sea surface temperature in the South Eastern Tropical Atlantic

Climate Dynamics - Despite the efforts of the modelling community to improve the representation of the sea surface temperature (SST) over the South Eastern Tropical Atlantic, warm biases still...     

Postglacial environmental change in the valley of Malye Chily River (the basin of Lake Teletskoye), northeastern Russian Altai

The evolution and current state of landscapes around Lake Teletskoye have not previously been studied in detail. In the valley of the Malye Chily River, which flows into Lake Teletskoye, the timing of dam failure and draining of two moraine-dammed lakes has been identified. Botanical analysis, ash content determination, and radiocarbon dating of two peat profiles provide insight into postglacial evolution of wetlands related to this landscape. We found clear evidence of the disappearance from the peat of higher vascular species that, today, grows mostly in the plains of Siberia. Correlation of the data obtained with the accepted chronology of the Holocene events in the Russian Altai suggests the following stages of postglacial environmental change in the Malye Chily River valley: (1) the continuation of the Late Würm glaciation degradation (before 7000?cal. yr BP); (2) Holocene Climate Optimum (7000–5000?cal. yr BP); (3) Akkem cooling (5000–4200?cal. yr BP); (4) warm period (4200–3700?cal. yr BP); and (5) Historical cooling (3700–1600?cal. yr BP).     

The first case study of 230Th/U and 14C dating of mid-valdai organic deposits

From the viewpoint of precision and reliability of radioisotopic dating, deposits whose quantitative age can be determined through several methods of geochronometry are of special interest. The mutually conforming finite ¹⁴C and ²³⁰Th/U dates of buried Neopleistocene organic deposits, taken from the Tolokonka section by the North Dvina River (100 km downstream from the city of Kotlas), have been obtained for the first time in Russia. The stratigraphical reference of these results to those obtained via the optically induced luminescence for upper and lower bedding layers has been established. The presented geochronometric data have allowed us to consider the age of oxbow lake organic deposits completely reliable and refer the time of their formation to the Tyrbei warming within the MIS-3. The applicability of the new version of the ²³⁰Th/U method for dating of interglacial and interstadial deposits, for the purpose of solving the Middle and Late Neopleistocene chronostratigraphy issues, is confirmed.     

Modulation of the high energy γ-ray flux from PSR B1259-63/SS2883 due to the orbital variation of the maximum energy of accelerated electrons

The inverse Compton (IC) scattering of ultrarelativistic electrons accelerated at the pulsar wind termination shock is generally believed to be responsible for TeV gamma-ray signal recently reported from the binary system PSR B1259-63/SS2883. In such a system the acceleration takes place in the presence of a dense radiation field provided by a companion Be2-type star. Thus it is natural to expect an orbital phase dependence of the acceleration efficiency in the system. The HESS collaboration reported the tendency of reduction of TeV γ-rays around the periastron. In this paper we study a possible explanation of this effect by the “early” (sub-TeV) cutoffs in the energy spectrum of accelerated electrons due to the enhanced rate of Compton losses close to the periastron.     

How global are the Jurassic–Cretaceous unconformities?

The reality of the global‐scale sedimentation breaks remains controversial. A compilation of data on the Jurassic–Cretaceous unconformities in a number of regions with different tectonic settings and character of sedimentation, where new or updated stratigraphic frameworks are established, permits their correlation. Unconformities from three large reference regions, including North America, the Gulf of Mexico, and Western Europe, were also considered. The unconformities, which encompass the Jurassic‐Cretaceous, the Lower–Upper Cretaceous and the Cretaceous–Palaeogene transitions are of global extent. Other remarkable unconformities traced within many regions at the base of the Jurassic and at the Santonian–Campanian transition are not known from reference regions. A correlation of the Jurassic–Cretaceous global‐scale sedimentation breaks and eustatic curves is quite uncertain. Therefore, definition of global sequences will not be possible until eustatic changes are clarified. Activity of mantle plumes is among the likely causes of the documented unconformities.     

New data on the Ladoga transgression,the Neva River formation,and agricultural development of northwestern Russia

Doklady Earth Sciences -     

Modified adaptive local–global upscaling method for discontinuous permeability distribution

The paper is devoted to the upscaling method appropriate for single-phase flow in media with discontinuous permeability distribution. The suggested algorithm is a modification of the iterative adaptive local–global upscaling developed by Chen and coauthors. The key feature of this method is a consistency between local and coarse global calculated characteristics. In this work, we apply a modified procedure to determine the boundary conditions used in the local fine-scale computation. To increase the accuracy of these boundary conditions on each iteration, we involve an additional preliminary step based on the results of coarse scale calculations from the previous iteration. Numerical tests show an essential improvement of the accuracy of upscaled flow rates for most of the realizations of statistical permeability distribution. Although the developed method is universal, its efficiency increases with increasing of permeability contrast.     

A Global Inventory of Burned Areas at 1 Km Resolution for the Year 2000 Derived from Spot Vegetation Data

Biomass burning constitutes a major contribution to global emissions of carbon dioxide, carbon monoxide, methane, greenhouse gases and aerosols. Furthermore, biomass burning has an impact on health, transport, the environment and land use. Vegetation fires are certainly not recent phenomena and the impacts are not always negative. However, evidence suggests that fires are becoming more frequent and there is a large increase in the number of fires being set by humans for a variety of reasons. Knowledge of the interactions and feedbacks between biomass burning, climate and carbon cycling is needed to help the prediction of climate change scenarios. To obtain this knowledge, the scientific community requires, in the first instance, information on the spatial and temporal distribution of biomass burning at the global scale. This paper presents an inventory of burned areas at monthly time periods for the year 2000 at a resolution of 1 kilometer (km) and is available to the scientific community at no cost. The burned area products have been derived from a single source of satellite-derived images, the SPOT VEGETATION S1 1 km product, using algorithms developed and calibrated at regional scales by a network of partners. In this paper, estimates of burned area, number of burn scars and average size of the burn scar are described for each month of the year 2000. The information is reported at the country level. This paper makes a significant contribution to understanding the effect of biomass burning on atmospheric chemistry and the storage and cycling of carbon by constraining one of the main parameters used in the calculation of gas emissions.     

A re-analysis of the marine bird Asiahesperornis from northern Kazakhstan

Fossil bird material is exceptionally rare in the Mesozoic of western Asia. With the notable exception of the Upper Cretaceous foot-propelled diving bird Asiahesperornis bazhanovi from northern Kazakhstan, the only bird fossils described from this region have been bone fragments from the Upper Cretaceous of Uzbekistan. In this paper, all material referred to date to the hesperornithiform Asiahesperornis is reviewed and re-described. New postcranial elements of this taxon from the holotype Kushmurun locality (Maastrichtian Zhuravlovskaya Svita) are presented, and the taxonomic history and likely affinities of this ocean-going bird are discussed.