Technological risk regulation of the subgrade base stability in permafrost areas

Maintenance and risk estimation of a weak roadbed condition during the construction period are described.Risk-management procedure for unstable,weak soils is proposed through adjusting the technological loads and real-time monitoring of their influence.The efficiency of implementing maximum allowable vibroloads and the drainage system for strengthening weak soils is shown in the example of the Northern Latitudinal Railway area.     

First geophysical and shallow ice core investigation of the Kazbek plateau glacier,Caucasus Mountains

First-ever ice core drilling at Mt. Kazbek (Caucasus Mountains) took place in the summer of 2014. A shallow ice core (18 m) was extracted from a plateau at ~4500 m a.s.l. in the vicinity of the Mt. Kazbek summit (5033 m a.s.l.). A detailed radar survey showed that the maximum ice thickness at this location is ~250 m. Borehole temperature of ?7 °C was measured at 10 m depth. The ice core was analyzed for oxygen and deuterium isotopes and dust concentration. From the observed seasonal cycle, it was determined that the ice core covers the time interval of 2009–2014, with a mean annual snow accumulation rate of 1800 mm w. eq. Multiple melt layers have been detected. δ¹⁸O values vary from ?25 to ?5‰. The dust content was determined using a particle sizing and counting analyzer. The dust layers were investigated using scanning electron microscopy and X-ray diffraction analysis. Dust can be separated into two categories by its origin: local and distant. Samples reflecting predominantly local origin consisted mainly of magmatic rocks, while clay minerals were a characteristic of dust carried over large distances, from the deserts of the Middle East and Sahara. The calculated average dust flux over three years at Kazbek was of 1.3 mg/cm² a^?1. Neither δ¹⁸O nor dust records appear to have been affected by summer melting. Overall, the conditions on Kazbek plateau and the available data suggest that the area offers good prospects of future deep drilling in order to obtain a unique environmental record.     

Underthrusting of Tarim beneath the Tien Shan and deep structure of their junction zone: Main results of seismic experiment along MANAS Profile Kashgar-Song-Köl

The results of reflection CMP seismic profiling of the Central Tien Shan in the meridional tract 75–76° E from Lake Song-Köl in Kyrgyzstan to the town of Kashgar in China are considered. The seismic section demonstrating complex heterogeneous structure of the Earth’s crust and reflecting its near-horizontal delamination with vertical and inclined zones of compositional and structural differentiation was constructed from processing of initial data of reflection CMP seismic profiling, earthquake converted-wave method (ECWM), and seismic tomography. The most important is the large zone of underthrusting of the Tarim Massif beneath the Tien Shan.     

Grad–Shafranov Reconstruction of Magnetic Clouds: Overview and Improvements

The Grad–Shafranov reconstruction is a method of estimating the orientation (invariant axis) and cross section of magnetic flux ropes using the data from a single spacecraft. It can be applied to various magnetic structures such as magnetic clouds (MCs) and flux ropes embedded in the magnetopause and in the solar wind. We develop a number of improvements of this technique and show some examples of the reconstruction procedure of interplanetary coronal mass ejections (ICMEs) observed at 1 AU by the STEREO, Wind, and ACE spacecraft during the minimum following Solar Cycle 23. The analysis is conducted not only for ideal localized ICME events but also for non-trivial cases of magnetic clouds in fast solar wind. The Grad–Shafranov reconstruction gives reasonable results for the sample events, although it possesses certain limitations, which need to be taken into account during the interpretation of the model results.     

Local stability and estimation of uncertainty for solutions to inverse problems

 We present a method for studying local stability of a solution to an inverse problem and evaluate the uncertainty in determining true values of particular observables. The investigation is done under the assumption that only the Gaussian part of fluctuations about the local minimum of the cost (likelihood) function is essential. Our approach is based on the spectral analysis of the Hessian operator associated with the cost function at its extremal point, and we put forward an effective iterative algorithm suitable for numerical implementation in the case of a computationally large problem. Received: 16 May 2001 / Accepted: 22 October 2001     

On the latitude migration of polar faculae in the solar activity cycle period: 1970–1978

Coordinates of polar faculae have been measured and processed using daily photoheliograms of the Kislovodsk Station of the Pulkovo observatory with the final goal of studying their latitude distribution during the solar cycles 20–21. The results obtained are as follows:

1. The first polar faculae emerge immediately after the polarity inversion of the solar magnetic field at the latitudes from 40° to 70° with the average ?-55°.
2. The zone of the emergence of polar faculae migrates poleward during the period between the neighbouring polarity inversions of the solar magnetic field. This migration is about 20° for 8 years, which corresponds to a velocity of 0.5 m s^-1.
3. The maximum number of polar faculae was reached at the activity minimum (1975–1976).
4. The last polar faculae were observed in the second half of 1978 at the latitudes from 70° to 80°.

     

Interhemispheric distinctions in wind-regime parameters in the polar mesosphere-lower thermosphere

The wind circulations in the mesosphere-lower thermosphere at polar latitudes of the Northern and Southern hemispheres are compared on the basis of long-term monthly-mean data on the prevailing zonal and meridional winds and on the parameters of diurnal and semidiurnal migrating tides obtained from the international network of radar stations. Comparison of the seasonal cycles and vertical profiles of the prevailing winds and tide parameters points to the existence of significant distinctions between the hemispheres. These distinctions are most clearly pronounced, first, in the prevailing meridional winds (for example, the annual mean winds in the polar regions have opposite directions in different hemispheres) and, second, the annual cycles of semidiurnal-tide amplitudes, as well as the character of changes in the tide phase with height, are fundamentally different for the Northern and Southern hemispheres. Along with these, significant distinctions are revealed in the prevailing zonal winds and in the diurnal-tide parameters.     

Random errors of star abscissae in the ROEMER space astrometry project

We discuss the propagation of random errors in the so-called great-circle reduction of the Hipparcos mission and for the proposed space astrometry project ROEMER. As a step towards the determination of stellar positions, proper motions and parallaxes, one-dimensional instantaneous relative positions of stars along fixed great circles are estimated from elementary measurements of the locations of stellar images within the instrument's field of view. The measurement errors, being dominated by photon noise, can be regarded as uncorrelated. The precision of the calculated one-dimensional positions (abscissae) depends on the precision and number of elementary measurements, the number of stars and their distribution in magnitude, and finally on the rigidity of the great-circle reduction. The rigidity quantifies how well the random measurement errors are averaged out in the least-squares solution, and is closely related to the condition number of the design matrix. We discuss the rigidity concept for idealised situations involving one, two, or several fields of view (zero, one, or more basic angles). A simple model of the error propagation is derived and used to predict the precision for a hypothetical space astrometry project such as ROEMER. It is found that the rigidity is much improved by the greater number of stars observed with ROEMER.