Stability of a circular tunnel in cohesive-frictional soil subjected to surcharge loading     

Kentaro Yamamoto  Andrei V. Lyamin  Daniel W. Wilson  Scott W. Sloan  Andrew J. Abbo 《Computers and Geotechnics》2011

The stability of circular tunnels in cohesive-frictional soils subjected to surcharge loading has been investigated theoretically and numerically assuming plane strain conditions. Despite the importance of this problem, previous research on the subject is very limited. At present, no generally accepted design or analysis method is available to evaluate the stability of tunnels/openings in cohesive-frictional soils. In this study, continuous loading is applied to the ground surface, and both smooth and rough interface conditions are modelled. For a series of tunnel diameter-to-depth ratios and material properties, rigorous lower- and upper-bound solutions for the ultimate surcharge loading are obtained by applying finite element limit analysis techniques. For practical use, the results are presented in the form of dimensionless stability charts with the actual tunnel stability numbers being closely bracketed from above and below. As an additional check on the solutions, upper-bound rigid-block mechanisms have been developed and the predicted collapse loads from these are compared with those from finite element limit analysis. Finally, an expression that approximates the ultimate surcharge load has been devised which is convenient for use by practising engineers.  相似文献   

Nonthermal particles and photons in starburst regions and superbubbles     

Andrei?M.?BykovEmail author 《Astronomy and Astrophysics Review》2014,22(1):77

Starforming factories in galaxies produce compact clusters and loose associations of young massive stars. Fast radiation-driven winds and supernovae input their huge kinetic power into the interstellar medium in the form of highly supersonic and superalfvenic outflows. Apart from gas heating, collisionless relaxation of fast plasma outflows results in fluctuating magnetic fields and energetic particles. The energetic particles comprise a long-lived component which may contain a sizeable fraction of the kinetic energy released by the winds and supernova ejecta and thus modify the magnetohydrodynamic flows in the systems. We present a concise review of observational data and models of nonthermal emission from starburst galaxies, superbubbles, and compact clusters of massive stars. Efficient mechanisms of particle acceleration and amplification of fluctuating magnetic fields with a wide dynamical range in starburst regions are discussed. Sources of cosmic rays, neutrinos and multi-wavelength nonthermal emission associated with starburst regions including potential galactic “PeVatrons” are reviewed in the global galactic ecology context.  相似文献   

ISOPHOT S Observations of 3 M Dwarfs     

Rainer Wehrse  Philipp Rosenau  Andrei Survernev  James Liebert  Christoph Leinert 《Astrophysics and Space Science》1997,255(1-2):127-133

The M dwarfs GL 832 (spectral type M2), GL 887 (M1), and GL 1 (M2) have been observed with the ISOPHOT spectrophotometers in the range 2.5-12μm at high signal-to-noise ratios. Since optical and ground based near-infrared data are also available, more than 95 % of the total flux is now covered for these objects. It is seen that between 2.5 μm and about 9 μm the fluxes fall off faster than a Rayleigh-Jeans tail of a black body distribution and that for longer wavelengths the decline is smaller. This indicates that the ISO data are probing the region around the temperature minimum and that our stars have some kind of chromosphere although Hα emission is not observed. Comparison with a model indicates that the features are considerably weaker than predicted. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Fluvial and permafrost history of the lower Lena River,north-eastern Siberia,over late Quaternary time     

Georg Schwamborn  Lutz Schirrmeister  Ali Mohammadi  Hanno Meyer  Andrei Kartoziia  Flavio Maggioni  Jens Strauss 《Sedimentology》2023,70(1):235-258

Arctic warming and permafrost thaw visibly expose changes in the landscape of the Lena River delta, the largest Arctic delta. Determining the past and modern river regime of thick deltaic deposits shaping the Lena River mouth in north-eastern Siberia is critical for understanding the history of delta formation and carbon sequestration. Using a 65 m long sediment core from the delta apex a set of sedimentological techniques is applied to aid in reconstructing the Lena River history. The analysis includes: (i) grain-size measurements and the determination of the bedload composition; (ii) X-ray fluorescence, X-ray diffractometry, and magnetic susceptibility measurements and heavy mineral analysis for tracking mineral change; (iii) pH, electrical conductivity, ionic concentrations, and the δ¹⁸O and δD stable isotope composition from ground ice for reconstructing permafrost formation. In addition; (iv) total and dissolved organic carbon is assessed. Chronology is based on; (vi) radiocarbon dating of organic material (accelerator mass spectrometry and conventional) and is complemented by two infrared – optically stimulated luminescence dates. The record stretches back approximately to Marine Isotope Stage 7. It holds periods from traction, over saltation, to suspension load sedimentation. Minerogenic signals do not indicate provenance change over time. They rather reflect the change from high energy to a lower energy regime after Last Glacial Maximum time parallel to the fining-up grain-size trend. A prominent minimum in the ground ice stable isotope record at early Holocene highlights that a river arm migration and an associated refreeze of the underlying river talik has altered the isotopic composition at that time. Fluvial re-routing might be explained by internal dynamics in the Lena River lowland or due to a tectonic movement, since the study area is placed in a zone of seismic activity. At the southern Laptev Sea margin, onshore continental compressional patterns are bordering offshore extensional normal faults.  相似文献   

An object-oriented information model for territorial system management     

Andrei A. Kaganovich  Sergei P. Prisyazhnyuk  Andrei S. Prisyazhnyuk 《GeoJournal》2018,83(6):1331-1337

This article examines an object-oriented geospatial information model for territorial system management, its benefits compared to current automated territorial management systems, and special aspects of its development and implementation in multi-level geoinformation systems. The presented study reflects the major functions of geoinformation materials used in spatial planning, particularly in Earth remote sensing. A territorial information management model is developed from the perspective of the object-oriented geoinformation approach. The study identifies the major functions of the proposed management system and demonstrates what kinds of problems can be solved using this system, develops a spatial algorithmic model for managerial decision-making and a methodology for analyzing local territorial system characteristics; and introduces basic information arrays that can be used to solve practical territorial management problems at various levels.  相似文献   

Riders under storms: Contributions of nomadic herders’ observations to analysing climate change in Mongolia     

Andrei Marin 《Global Environmental Change》2010,20(1):162-176

Predictions of climate change and its impacts are highly uncertain at regional and local levels. Downscaled models often operate with a too coarse scale and look at standard parameters that may be irrelevant to resource-dependent people. This article argues that a more robust analysis and prediction of climate change at local levels can be inferred from the integration of local people's observation of change with meteorological records and models.The example proposed here is the analysis of climate change in the desert-steppe region of Mongolia. While regional models and local analyses agree that Mongolia has become warmer, predictions either ignore or are contradictory about the changes in precipitations and sand storms. The Mongolian pastoral nomads on the other hand identify longer and more intense droughts and sand storms as the most important recent climatic changes, relevant to their livelihoods. In addition, they record detailed changes in the precipitations regime. Thus, they are unequivocal that rains have become patchy – ‘silk embroidery rains’ – (forcing pastoralists to move farther and more frequently), more intense (thus less effective due to runoff) and that summer rains are delayed (reducing the growing season).The observations of the pastoralists can only partly be investigated in light of meteorological records due to different parameters observed by the two systems. Nevertheless, additional evidence derived from the analysis of meteorological records resonates with the perceptions of the herders and adds elements for further investigation. This combined evidence suggests that due to a southern shift of the East Asian Monsoon, rains in southern Mongolia rely on re-circulated local moisture, leading to large-scale droughts and in turn more frequent sand storms.The analysis provided herein shows that combining the two knowledge systems (local people's observations and climatology) holds the potential to provide more reliant and relevant investigations of climate change and allow for better planned adaptations.  相似文献   

Holocene Treeline History and Climate Change Across Northern Eurasia   总被引：1，自引：0，他引：1  

Glen M. MacDonald  Andrei A. Velichko  Constantine V. Kremenetski  Olga K. Borisova  Aleksandra A. Goleva  Andrei A. Andreev  Les C. Cwynar  Richard T. Riding  Steven L. Forman  Tom W. D. Edwards  Ramon Aravena  Dan Hammarlund  Julian M. Szeicz  Valery N. Gattaulin 《Quaternary Research》2000,53(3):302

Radiocarbon-dated macrofossils are used to document Holocene treeline history across northern Russia (including Siberia). Boreal forest development in this region commenced by 10,000 yr B.P. Over most of Russia, forest advanced to or near the current arctic coastline between 9000 and 7000 yr B.P. and retreated to its present position by between 4000 and 3000 yr B.P. Forest establishment and retreat was roughly synchronous across most of northern Russia. Treeline advance on the Kola Peninsula, however, appears to have occurred later than in other regions. During the period of maximum forest extension, the mean July temperatures along the northern coastline of Russia may have been 2.5° to 7.0°C warmer than modern. The development of forest and expansion of treeline likely reflects a number of complimentary environmental conditions, including heightened summer insolation, the demise of Eurasian ice sheets, reduced sea-ice cover, greater continentality with eustatically lower sea level, and extreme Arctic penetration of warm North Atlantic waters. The late Holocene retreat of Eurasian treeline coincides with declining summer insolation, cooling arctic waters, and neoglaciation.  相似文献   

Reestablishment of an accretionary prism after the subduction of a spreading ridge—constraints by a geometric model for the Golfo de Penas, Chile   总被引：1，自引：1，他引：0  

Andrei Maksymowicz 《Geo-Marine Letters》2013,33(5):345-355

Seismic studies offshore southern Chile have revealed the presence of a 70–80 km wide accretionary prism seaward of the Golfo de Penas (GPAP), where the Chile Ridge collided with the South American Plate between 3 and 6 Ma ago. Using the paleo-positions of the Chile Ridge relative to South America, the maximum age of this accretionary prism, which continues to be formed in the aftermath of the ridge–continent collision, has been estimated. Building on these earlier findings, this study presents a mass balance analysis based on a 2D model of accretionary wedge and trench geometry. This model can explain the relative importance of sedimentary fluxes and deformation front migration for the wedge restoration. The proposed model can also serve to evaluate the effects of fluctuations in (1) terrigenous sediment flux related to climate change, and (2) subduction channel thickness on the accretionary prism growth. Notably, the data reveal that the key parameters controlling the rebuilding of the GPAP are the terrigenous sediment flux (75 km²/10⁶ years), the relative advance of the deformation front (39.6 km/10⁶ years), and the thickness of the subduction channel (0.1 km). Moreover, the range of possible solutions for the observed size of the accretionary prism is narrowed by fitting the present-day thickness of sediments at the deformation front. Finally, climate-induced variations in sedimentary fluxes on the margin can affect the rate of growth of the accretionary prism during short periods of time (<100,000 years).  相似文献   

A DUAL mission for nuclear astrophysics     

Peter von Ballmoos  Jose Alvarez  Nicolas Barrière  Steve Boggs  Andrei Bykov  Juan Manuel Del Cura Velayos  Filippo Frontera  Lorraine Hanlon  Margarita Hernanz  Emmanuel Hinglais  Jordi Isern  Pierre Jean  Jürgen Kn?dlseder  Lucien Kuiper  Mark Leising  Beno?t Pirard  Jean-Pierre Prost  Rui M. Curado da Silva  Tadayuki Takahashi  John Tomsick  Roland Walter  Andreas Zoglauer 《Experimental Astronomy》2012,34(2):583-622

DUAL will study the origin and evolution of the elements and explores new frontiers of physics: extreme energies that drive powerful stellar explosions and accelerate particles to macroscopic energies; extreme densities that modify the laws of physics around the most compact objects known; and extreme fields that influence matter in a way that is unknown on Earth. The variability of these extreme objects requires continuous all-sky coverage, while detailed study demands an improvement in sensitivity over previous technologies by at least an order of magnitude. The DUAL payload is composed of an All-Sky Compton Imager (ASCI), and two optical modules, the Laue-Lens Optic (LLO) and the Coded-Mask Optic (CMO). The ASCI serves dual roles simultaneously, both as an optimal focal-plane sensor for deep observations with the optical modules and as a sensitive true all-sky telescope in its own right for all-sky surveys and monitoring. While the optical modules are located on the main satellite, the All-Sky Compton Imager is situated on a deployable structure at a distance of 30?m from the satellite. This configuration not only permits to maintain the less massive payload at the focal distance, it also greatly reduces the spacecraft-induced detector background, and, above all it provides ASCI with a continuous all-sky exposure.  相似文献   

Laser-like wave amplification in straits     

Pushkarev  Andrei 《Ocean Dynamics》2021,71(2):195-215

Ocean Dynamics - We present research on the excitation of ocean surface wind waves in non-homogeneous situations, for the case of a deep water strait in the presence of a constant wind, blowing...  相似文献