CPT correlations for thermal properties of soils

Acta Geotechnica - Obtaining in situ thermal properties of soils is often difficult and time-consuming. Here, cone penetration test (CPT) correlations are proposed and validated for thermal...     

Shock Wave Effects from the Impacts of Cosmic Objects with Diameters from 20 m to 3 km

Izvestiya, Physics of the Solid Earth - Abstract—Destruction on the Earth’s surface caused by a shock wave is one of the most important and dangerous effects from asteroid and comet...     

Hook whistlers observed at low latitude ground station Varanasi

Employing the Haselgrove ray tracing equations and a diffusive equilibrium model of the ionosphere, the propagation characteristics of hook whistlers recorded at low-latitude ground station Varanasi (geomag. lat., 16°6′.N) are discussed. It is shown that the two traces of the hook whistlers are caused by the VLF waves radiated from the return stroke of a lightning discharge which after penetrating the ionosphere at two different entry points, propagated to the opposite hemisphere in the whistler mode and were received at 16 geomagnetic latitude. Further the crossing of ray paths for the same frequency leads to the explanation of the hook whistler. The lower and higher cut-off frequencies are explained in terms of their deviating away from the bunch of the recorded whistler waves and crossing of ray paths for the same frequency.     

Ground-based electromagnetic studies combined with remote sensing based on Demeter mission: A way to monitor active faults and volcanoes

The identification of magnetic, electric and electromagnetic (EM) precursory signals related to volcanic activities and earthquakes is still a matter of debate. Some examples are now well established, but they are often based on a few parameters recorded on sparse equipments and with no multi-disciplinary approach. Demeter program takes into account a more complete approach of EM phenomena related to volcanic eruptions and earthquakes, by combining both ground-based and satellite EM monitoring, from direct current to several kilohertz, i.e. from ULF, ELF to VLF frequency domains.The research program stands in two parts: one is the identification of EM signals at the satellite altitude and the other consists in detailed studies in a few pilot sites on the ground. Two main test sites have been considered: La Fournaise volcano in Réunion Island and the seismogenic Corinth rift in Greece. Both sites allow for performing EM studies in a multi-disciplinary environment.La Fournaise volcano erupts on average two times a year. The self-recording Demeter EM station is composed of three modules measuring the components of the magnetic and electric fields in three different frequency domains: DC to 0.5 Hz, 0.0033-160 Hz and 8-10 kHz. Preliminary observations made during the May 2003 eruption show that electric and magnetic signals appeared before the eruption. Some signals present sharp step-like variations, with amplitudes up to several hundreds mV per km and a few hour duration, followed by periods with a higher spectral frequency content. The frequency of these signals can be of several tens of Hz.The Corinth rift is a highly seismic area, frequently affected by seismic swarms. In 2004 the region has experienced tens of earthquakes of magnitude less than 4.6. A Demeter station has been set up on the Trizonia Island along the northern mainland coast, where a 30 km long seismic gap has been identified. The station is composed of two modules recording the three components of the magnetic field and the two horizontal components of the electric field in the ULF and ELF-VLF frequency bands. The audiomagnetotelluric soundings show that the station is close to a regional conductive fault connected to the sea. The first 4 months of observation clearly show that 29 earthquakes, even of low magnitude (M?2.8), occurring at less than 140 km of distance of the station, have generated electric signals when the seismic waves have passed the EM station. For a given magnitude of the earthquake, the energy of the electric signal is independent of the distance between the focal source and the EM station, which points out local electric source mechanisms. The greater the magnitude of the earthquake, the greater is the energy of the electric signal is. The co-seismic electric signals have the same morphology as that of the passing seismic wave, and there is no noticeable time delay between the electric and the seismic signals. This simultaneity between the seismic and the electric signal is best explained by the generation of an electrokinetic effect due to the passage of the seismic wave through the seawater-saturated ground.     

Current gradient-driven linear and nonlinear electromagnetic waves in a magnetized electron-positron plasma

A set of coupled nonlinear differential equations which govern the dynamics of finite amplitude electromagnetic waves in the presence of an external current gradient in a magnetized electron-positron plasma has been derived. It is shown that the current gradient can make shear Alfvén-like waves unstable. A quasi-stationary solution of the mode-coupling equations is the well-localized dipole vortex. Application of our results to plasma transport in the pulsar magnetosphere is briefly discussed.     

An analytical representation of non-gyrotropic distributions and related space applications

Clear signature of non-gyrotropic energetic electron distributions was found by ISEE 1 and ISEE 2 spacecrafts just upstream of the Earth's bow shock and recently detected by in situ observations of the WIND plasma experiment. On the other hand, the appearance of non-gyrotropic ion velocity distributions is well established in the magnetotail providing evidence of magnetic reconnection processes. Motivated by these findings we introduce an analytical representation of non-Maxwellian/non-gyrotropic distribution functions, accurately fitting the characteristics of observations, where Maxwellians are recovered as special case of these highly general velocity space distributions. In particular, the analytical distribution function model can serve as basis of detailed wave-particle interaction analysis and of studies of the physical background of the evolution of both, non-gyrotropic electron and ion distributions, which is discussed for various space plasma environments.     

Climatic and environmental characteristics of Moscow megalopolis according to the data of the Moscow State University Meteorological Observatory over 60 years

Analyzed are the results of meteorological and environmental measurements performed over the 60-year period (1954–2013) at the Meteorological Observatory of Lomonosov Moscow State University. The significant positive temperature trend (0.04°C/year for 1954–2013) was obtained; it increased up to 0.07°C/year in 1976–2012. Considered are the features of seasonal variations of different atmospheric characteristics. Discussed are the type and causes of low-frequency changes in meteorological parameters, radiation balance components, radiation in different spectral ranges, and chemical composition of precipitation. Demonstrated are possible mechanisms of the more significant increase observed in air temperature in Moscow as compared with that in Central Federal District and their connection with the greenhouse effect in the urban atmosphere.     

Changes in the Period of Negative Superhumps of Type SU UMa Dwarf Novae. II. NY Her (2017 and 2020)

Astrophysics - Photometric studies of the type SU UMa dwarf nova NY Her were made during 2017 and 2020 at the Crimean Astrophysical Observatory and at the Sanglokh Observatory over a total of 77...     

Detailed mineralogical-geochemical study of a large spinel Lherzolite xenolith in alkali basalt of Shavaryn Tsaram paleovolcano,Mongolia

Mineralogical-geochemical data obtained on a large xenolith of spinel lherzolite from basanites of Shavaryn Tsaram volcano (Middle Pleistocene) provide evidence that the xenolith was affected by heat and fluid that came from the basalt melt and induced geochemical heterogeneity of the xenolith. Olivine crystals from the central portion of the xenolith contain much more CaO than this mineral from the peripheral zones of the xenolith as well as in xenocrystals of the host basalts. The large xenolith was unevenly annealed by the host basalt melt, and this predetermined the heterogeneous diffusion-controlled “purification” of olivine crystals from their CaO admixture. The xenolith is heterogeneously enriched in LREE and some trace elements (Zr, Hf, Nb, Th, and U), and their distribution demonstrates unclearly pronounced concentric zoning: these elements enriched the outer portions of the xenolith. The enrichment of the xenolith in LREE and other mobile trace elements is explained by their occurrence not only as structurally bound (isomorphic) components in minerals but also in the form of nonstructural admixtures (contaminant), as minute grains of compounds hosted in the interstitial space and tiny cracks cutting mineral grains. The enrichment of the xenolith in these admixtures proceeded via their infiltration-controlled introduction with fluid from the basalt along minute cracks.