Vertical stress distribution due to an arbitrarily shaped foundation using triangulation and an analytical expression for a triangular loaded region     

V. Murti  Y. C. Wang 《国际地质力学数值与分析法杂志》1991,15(1):51-60

Using the basic Boussinesq's equation, the expression for the vertical stress distribution (σ_z) underneath any point on the ground surface due to a general triangular loaded region in a preferred orientation with a linearly varied loading has been successfully derived. When the triangle is not in a preferred orientation, a simple axis transformation is required and the expression will be equally applicable. Based on this expression, σ_z due to an arbitrarily shaped loaded foundation can simply be determined by first triangulating the loaded area and summing up the contributions from each generated triangular region. The procedures for triangulating and calculating the stress distribution can be simply automated through computer programs.  相似文献   

Real-time difference imaging analysis of MOA Galactic bulge observations during 2000     

I.A. Bond  F. Abe  R.J. Dodd  J.B. Hearnshaw  M. Honda  J. Jugaku  P.M. Kilmartin  A. Marles  K. Masuda  Y. Matsubara  Y. Muraki  T. Nakamura  G. Nankivell  S. Noda  C. Noguchi  K. Ohnishi  N.J. Rattenbury  M. Reid  To. Saito  H. Sato  M. Sekiguchi  J. Skuljan  D.J. Sullivan  T. Sumi  M. Takeuti  Y. Watase  S. Wilkinson  R. Yamada  T. Yanagisawa  P.C.M. Yock 《Monthly notices of the Royal Astronomical Society》2001,327(3):868-880

We describe observations carried out by the MOA group of the Galactic bulge during 2000 that were designed to detect efficiently gravitational microlensing of faint stars in which the magnification is high and/or of short duration. These events are particularly useful for studies of extrasolar planets and faint stars. Approximately 17 deg² were monitored at a sampling rate of up to six times per night. The images were analysed in real time using a difference imaging technique. 20 microlensing candidates were detected, of which eight were alerted to the microlensing community whilst in progress. Approximately half of the candidates had high magnifications (≳10), at least one had very high magnification (≳50), and one exhibited a clear parallax effect. The details of these events are reported here, together with details of the on-line difference imaging technique. Some nova-like events were also observed and these are described, together with one asteroid.  相似文献   

Fundamental parameters and new variables of the galactic open cluster NGC 7128     

Z. Balog  †  A. J. Delgado  ‡  A. Moitinho  G. F&#;rész  †  G. Kaszás  †  J. Vinkó  E. J. Alfaro 《Monthly notices of the Royal Astronomical Society》2001,323(4):872-886

CCD photometry in Johnson UBV and Strömgren uvby systems and medium-resolution spectroscopy of the galactic open cluster NGC 7128 are presented. Spectral types of the brightest 12 stars in the cluster field were determined based on equivalent widths of the H α and the He  i 6678-Å line. The spectroscopic observations also revealed two obvious and one probable Be-type stars showing H α emission. The analysis of the photometric diagrams gave a colour excess of E ( B − V )=1.03±0.06 mag, a distance modulus DM =13.0±0.2 mag and an age above 10 Myr. Time-resolved photometric observations obtained on one night resulted in the detection of short time-scale light variations of seven new and three already known variable stars in the cluster field.  相似文献   

Comparison of results from several AOGCMs for global and regional sea-level change 1900–2100     

J. M. Gregory  J. A. Church  G. J. Boer  K. W. Dixon  G. M. Flato  D. R. Jackett  J. A. Lowe  S. P. O'Farrell  E. Roeckner  G. L. Russell  R. J. Stouffer  M. Winton 《Climate Dynamics》2001,18(3-4):225-240

 Sea-level rise is an important aspect of climate change because of its impact on society and ecosystems. Here we present an intercomparison of results from ten coupled atmosphere-ocean general circulation models (AOGCMs) for sea-level changes simulated for the twentieth century and projected to occur during the twenty first century in experiments following scenario IS92a for greenhouse gases and sulphate aerosols. The model results suggest that the rate of sea-level rise due to thermal expansion of sea water has increased during the twentieth century, but the small set of tide gauges with long records might not be adequate to detect this acceleration. The rate of sea-level rise due to thermal expansion continues to increase throughout the twenty first century, and the projected total is consequently larger than in the twentieth century; for 1990–2090 it amounts to 0.20–0.37 m. This wide range results from systematic uncertainty in modelling of climate change and of heat uptake by the ocean. The AOGCMs agree that sea-level rise is expected to be geographically non-uniform, with some regions experiencing as much as twice the global average, and others practically zero, but they do not agree about the geographical pattern. The lack of agreement indicates that we cannot currently have confidence in projections of local sea-level changes, and reveals a need for detailed analysis and intercomparison in order to understand and reduce the disagreements. Received: 1 September 2000 / Accepted: 20 April 2001  相似文献   

A new pattern for the north–south asymmetry of sunspots     

E.S. Vernova  K. Mursula  M.I. Tyasto  D.G. Baranov 《Solar physics》2002,205(2):371-382

We study the solar cycle evolution during the last 8 solar cycles using a vectorial sunspot area called the LA (longitudinal asymmetry) parameter. This is a useful measure of solar activity in which the stochastic, longitudinally evenly distributed sunspot activity is reduced and which therefore emphasizes the more systematic, longitudinally asymmetric sunspot activity. Interesting differences are found between the LA parameter and the more conventional sunspot activity indices like the (scalar) sunspot area and the sunspot number. E.g., cycle 19 is not the highest cycle according to LA. We have calculated the separate LA parameters for the northern and southern hemisphere and found a systematic dipolar-type oscillation in the dominating hemisphere during high solar activity times which is reproduced from cycle to cycle. We have analyzed this oscillation during cycles 16–22 by a superposed epoch method using the date of magnetic reversal in the southern hemisphere as the zero epoch time. According to our analysis, the oscillation starts by an excess of the northern LA value in the ascending phase of the solar cycle which lasts for about 2.3 years. Soon after the maximum northern dominance, the southern hemisphere starts dominating, reaching its minimum some 1.2–1.7 years later. The period of southern dominance lasts for about 1.6 years and ends, on an average, slightly before the end of magnetic reversal.  相似文献   

Rift-related Jurassic basaltic phreatomagmatic volcanism in the central Transantarctic Mountains: precursory stage to flood-basalt effusion     

Richard E. Hanson  David H. Elliot 《Bulletin of Volcanology》1996,58(5):327-347

 The Middle Jurassic Kirkpatrick flood basalts and comagmatic Ferrar intrusions in the Transantarctic Mountains represent a major pulse of tholeiitic magmatism related to early stages in the breakup of Gondwana. A record of the volcano-tectonic events leading to formation of this continental flood-basalt province is provided by strata underlying and only slightly predating the Kirkpatrick lavas. In the central Transantarctic Mountains, the lavas rest on widespread (≥7500 km²) tholeiitic pyroclastic deposits of the Prebble Formation. The Prebble Formation is dominated by lahar deposits and is an unusual example of a regionally developed basaltic lahar field. Related, partly fault-controlled pyroclastic intrusions cut underlying strata, and vents are represented by the preserved flanks of two small tephra cones associated with a volcanic neck. Lahar and air-fall deposits typically contain 50–60% accidental lithic fragments and sand grains derived from underlying Triassic – Lower Jurassic strata in the upper part of the Beacon Supergroup. Juvenile basaltic ash and fine lapilli consist of nonvesicular to scoriaceous tachylite, sideromelane, and palagonite, and have characteristics indicating derivation from hydrovolcanic eruptions. The abundance of accidental debris from underlying Beacon strata points to explosive phreatomagmatic interaction of basaltic magma with wet sediment and groundwater, which appears to have occurred in particular where rising magma intersected upper Beacon sand aquifers. Composite clasts in the lahar deposits exhibit complex peperitic textures formed during fine-scale intermixing of basaltic magma with wet sand and record steps in subsurface fuel-coolant interactions leading to explosive eruption. The widespread, sustained phreatomagmatic activity is inferred to have occurred in a groundwater-rich topographic basin linked to an evolving Jurassic rift zone in the Transantarctic Mountains. Coeval basaltic phreatomagmatic deposits of the Mawson and Exposure Hill Formations, which underlie exposures of the Kirkpatrick Basalt up to 1500 km to the north along strike in Victoria Land, appear to represent other parts of a regional, extension-related Middle Jurassic phreatomagmatic province which developed immediately prior to rapid outpouring of the flood basalts. This is consistent with models which assign an important role to lithospheric stretching in the generation of flood-basalt provinces. Received: 28 August 1995 / Accepted: 18 April 1996  相似文献   

A techno-economic comparison of power systems for autonomousunderwater vehicles     

Schubak  G.E. Scott  D.S. 《Oceanic Engineering, IEEE Journal of》1995,20(1):94-100

This paper compares lead-acid batteries, sodium-sulfur batteries, solid polymer fuel cells and closed-cycle diesel engines for autonomous underwater vehicle (AUV) applications. The service is described in terms of a parametric mission and life cycle. A generic AUV is used as a basis for comparison. Power systems are evaluated by two criteria: (1) submerged endurance capability and (2) life cycle cost. This study determines categories of service for which each power system is preferred. The solid polymer fuel cell can provide greater submerged endurance than other power systems examined. For extremely long duration AUV missions, the fuel cell is the required system, indicating a possible market niche for today's fuel cell technology. Considering cost projections for each power system, the results also show that the SPFC can become cost-competitive with conventional technologies, particularly for services characterized by high levels of utilization  相似文献   

Occurrence of noble metals in aluminum- and chromium- rich objects in ordinary chondrites and of baddeleyite (ZrO2) in a chromite inclusion     

M. Christophe Michel-Lvy  E. Robin  Ph. Blanc 《Meteoritics & planetary science》1995,30(1):15-19

Abstract— Platinum group elements (PGE) enrichments are found in Fe-Ni blebs (<1 μm) in Al- and Cr-rich objects in the ordinary chondrites Ste. Marguerite, Forest Vale, Montferré. In Ste. Marguerite, high ZrO₂ concentrations (baddeleyite) are also present in a chromite inclusion. Iridium enrichment in this material compared to its metal content is confirmed by INAA. The widespread occurrence of PGE in Al- and Cr-rich objects, mostly present in H-group chondrites of nearly equilibrated types, must be taken into account to understand their conditions of formation.  相似文献   

Gut feelings for cholera     

S.Y. Lee 《Marine pollution bulletin》1994,28(12):716

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Vertical-Critical Periodic Orbits in the General Three-Body Problem     

E.A. Perdios  K.E. Papadakis 《Astrophysics and Space Science》1997,253(1):73-85

We present special generating plane orbits, the vertical-critical orbits, of the coplanar general three-body problem. These are determined numerically for various values of m₃, for the entire range of the mass ratio of the two primaries. The vertical-critical orbits are necessary in order to specify the vertically stable segments of the families of plane periodic orbits, and they are also the starting points of the families of the simplest possible three-dimensional periodic orbits, namely the simple and double periodic. The initial conditions of the vertical-critical periodic orbits of the basic families l, m, i, h, b and c and their stability parameters are determined. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献