Comparison of excavation-induced wall deflection using top-down and bottom-up construction methods in Taipei silty clay   总被引：2，自引：0，他引：2  

Gordon Tung-Chin Kung 《Computers and Geotechnics》2009

This paper compares the excavation-induced wall deflection caused by the top-down method (TDM) and the bottom-up method (BUM). First, a total of 26 quality excavation case histories in Taipei silty clay were collected and analyzed. The field observations show that the maximum lateral wall deflection (δ_hm) induced by the TDM were 1.28 times as large as that induced by the BUM. Factors affecting wall deflection are investigated and four of them are selected for further numerical experimentation to investigate the discrepancy of δ_hm caused by the two methods. Analysis results showed that the average ratio of δ_hm induced by the TDM over that induced by the BUM is approximately equal to 1.1, excluding the effect of thermal shrinkage of concrete floor slabs. Both observed data and analysis results revealed that greater δ_hm is generally induced by the TDM despite its use of floor slabs with higher support stiffness.  相似文献   

Effect of the cyanide-producing bacterium Chromobacterium violaceum on ultraflat gold surfaces     

Lintern Fairbrother  Joseph G. Shapter  Joël Brugger  Gordon Southam  Allan Pring  Frank Reith 《Journal of Geochemical Exploration》2009

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DMSP and DMS dynamics and microzooplankton grazing in the Labrador Sea: application of the dilution technique     

Gordon V. Wolfe  Maurice Levasseur  Guy Cantin  Sonia Michaud 《Deep Sea Research Part I: Oceanographic Research Papers》2000,47(12):687

We adapted the dilution technique to study microzooplankton grazing of algal dimethylsulfoniopropionate (DMSP) vs. Chl a, and to estimate the impact of microzooplankton grazing on dimethyl sulfide (DMS) production in the Labrador Sea. Phytoplankton numbers were dominated by autotrophic nanoflagellates in the Labrador basin, but diatoms and colonial Phaeocystis pouchetii contributed significantly to phytomass at several high chlorophyll stations and on the Newfoundland and Greenland shelfs. Throughout the region, growth of algal Chl a and DMSP was generally high (0.2–1 d⁻¹), but grazing rates were lower and more variable, characteristic of the early spring bloom period. Production and consumption of Chl a vs. DMSP followed no clear pattern, and sometimes diverged greatly, likely because of their differing distributions among algal prey taxa and size class. In several experiments where Phaeocystis was abundant, we observed DMS production proportional to grazing rate, and we found clear evidence of DMS production by this haptophyte following physical stress such as sparging or filtration. It is possible that grazing-activated DMSP cleavage by Phaeocystis contributes to grazer deterrence: protozoa and copepods apparently avoided healthy colonies (as judged by relative growth and grazing rates of Chl a and DMSP), and grazing of Phaeocystis was significant only at one station where cells were in poor condition. Although we hoped to examine selective grazing on or against DMSP-containing algal prey, the dilution technique cannot differentiate selective ingestion and varying digestion rates of Chl a and DMSP. We also found that the dilution method alone was poorly suited for assessing the impact of grazing on dissolved sulfur pools, because of rapid microbial consumption and the artifactual release of DMSP and DMS during filtration. Measuring and understanding the many processes affecting organosulfur cycling by the microbial food web in natural populations remain a technical challenge that will likely require a combination of techniques to address.  相似文献   

Thermokarst lakes and ponds on Mars in the very recent (late Amazonian) past   总被引：1，自引：0，他引：1  

Richard J. Soare  Gordon R. Osinski  Charlotte L. Roehm 《Earth and Planetary Science Letters》2008,272(1-2):382-393

The history of water is fundamental to understanding the geological evolution of Mars and to questions concerning the possible development of life on the Red Planet. Today, Mars is cold and dry; its regolith is permanently frozen and except under highly localised and transient conditions, liquid water is unstable at the surface. Intriguingly, we have identified geological features that could be markers of very late-Amazonian “wet” or ice-rich periglacial processes in Utopia and western Elysium Planitiae: 1. rimless, flat-floored and lobate, sometimes scalloped, depressions that are suggestive of terrestrial alases (evaporated/drained thermokarst lakes); 2. small-sized polygonal patterned-ground (perhaps formed by thermal-contraction cracking and possibly underlain by ice wedges); and, 3. circular/near-circular raised-rim depressions (consistent in morphology and scale with pingo-scars) that are nested in rimless depressions. In terrestrial cold-climate, non-glacial environments, landscape assemblages of this type occur only in the presence of ice-rich permafrost.Commenting upon the origin of the putative periglacial features on Mars, most workers have suggested that sublimation and not evaporation has been the dominant process. By contrast, we propose that two key characteristics of the rimless depressions – inner terraces and orthogonally-oriented polygons – are markers of stable, ponded water and its slow loss by evaporation or drainage. If the raised-rim landforms are pingo scars, then this also points to boundary conditions that are supportive of stable liquid water.With regard to the relative age of the features described above, previous work identified some lobate depressions superposed on crater-rim gullies in the region (Soare et al., 2007). Gullies could be amongst the youngest geological features on Mars; superposed depressions point to an origin that is more youthful than the gullies. In turn, as some raised-rim landforms are superposed on rimless depressions, this is indicative of an origin that is even more recent than that of the depressions. Together with the geological evidence showing that the rimless depressions could have been formed by ponded water, the stratigraphy of the putative periglacial-landscape in this region suggests that the very late Amazonian period could have been warmer and wetter than had been thought hitherto.  相似文献   

Seismic anisotropy in granite at the Underground Research Laboratory, Manitoba   总被引：2，自引：0，他引：2  

Gordon M. Holmes  Stuart Crampin  & R. Paul Young 《Geophysical Prospecting》2000,48(3):415-435

The Shear-Wave Experiment at Atomic Energy of Canada Limited's Underground Research Laboratory was probably the first controlled-source shear-wave survey in a mine environment. Taking place in conjunction with the excavation of the Mine-by test tunnel at 420 m depth, the shear-wave experiment was designed to measure the in situ anisotropy of the rockmass and to use shear waves to observe excavation effects using the greatest variety of raypath directions of any in situ shear-wave survey to date. Inversion of the shear-wave polarizations shows that the anisotropy of the in situ rockmass is consistent with hexagonal symmetry with an approximate fabric orientation of strike 023° and dip 35°. The in situ anisotropy is probably due to microcracks with orientations governed by the in situ stress field and to mineral alignment within the weak gneissic layering. However, there is no unique interpretation as to the cause of the in situ anisotropy as the fabric orientation agrees approximately with both the orientation expected from extensive-dilatancy anisotropy and that of the gneissic layering. Eight raypaths with shear waves propagating wholly or almost wholly through granodiorite, rather than granite, do not show the expected shear-wave splitting and indicate a lower in situ anisotropy, which may be due to the finer grain size and/or the absence of gneissic layering within the granodiorite. These results suggest that shear waves may be used to determine crack and mineral orientations and for remote monitoring of a rockmass. This has potential applications in mining and waste monitoring.  相似文献   

A guide to TAURUS-2 Fabry–Perot data reduction     

Scott Gordon  Bärbel Koribalski  Sally Houghton  Keith Jones 《Monthly notices of the Royal Astronomical Society》2000,315(2):248-262

The data reduction process for optical emission-line observations of galaxies using the TAURUS-2 Fabry–Perot interferometer mounted on the 3.9-m Anglo-Australian Telescope is described in detail. The initial steps (bias subtraction, flat-fielding, etc.) are the same as for calibration of CCD images, and the wavelength calibration is similar to that in optical spectroscopy. The final steps are specific to Fabry–Perot instruments, and include the fitting of several instrumental parameters and a phase correction to convert the raw ( x ,  y ,  z ) data cube into a useful position–velocity ( α ,  δ ,  v ) cube. Software has been written to assist with the latter steps of the data reduction. H α observations of NGC 1808, NGC 2442 and Circinus are used to demonstrate the reduction process.  相似文献   

The Dakhleh Glass: Product of an impact airburst or cratering event in the Western Desert of Egypt?     

Gordon R. OSINSKI  Johanna KIENIEWICZ  Jennifer R. SMITH  Mark B. E. BOSLOUGH  Mark ECCLESTON  Henry P. SCHWARCZ  Maxine R. KLEINDIENST  Albert F. C. HALDEMANN  Charles S. CHURCHER 《Meteoritics & planetary science》2008,43(12):2089-2107

Abstract— Impact cratering is a ubiquitous geological process on the terrestrial planets. Meteorite impact craters are the most visible product of impact events, but there is a growing recognition that large aerial bursts or airbursts should occur relatively frequently throughout geological time. In this contribution, we report on an unusual impact glass‐the Dakhleh Glass (DG)–which is distributed over an area of ?400 km ²of the Dakhleh Oasis, Egypt. This region preserves a rich history of habitation stretching back to over 400,000 years before the emergence of Homo sapiens. We report on observations made during recent fieldwork and subsequent analytical analyses that strengthen previous suggestions that the DG formed during an impact event. The wide distribution and large size of DG specimens (up to ?50 cm across), the chemistry (e.g., CaO and Al₂O₃ contents up to ?25 and ?18 wt, respectively), the presence of lechatelierite and burnt sediments, and the inclusion of clasts and spherules in the DG is inconsistent with known terrestrial processes of glass formation. The age and other textural characteristics rule out a human origin. Instead, we draw upon recent numerical modeling of airbursts to suggest that the properties of DG, coupled with the absence of a confirmed crater, can best be explained by melting of surficial sediments as a result of a large airburst event. We suggest that glass produced by such events should, therefore, be more common in the rock record than impact craters, assuming that the glass formed in a suitable preserving environment.  相似文献   

Dense planetary rings and the viscous overstability     

Henrik N. Latter  Gordon I. Ogilvie 《Icarus》2008,195(2):725-751

This paper examines the onset of the viscous overstability in dense particulate rings. First, we formulate a dense gas kinetic theory that is applicable to the saturnian system. Our model is essentially that of Araki and Tremaine [Araki, S., Tremaine, S., 1986. Icarus 65, 83-109], which we show can be both simplified and generalised. Second, we put this model to work computing the equilibrium properties of dense planetary rings, which we subsequently compare with the results of N-body simulations, namely those of Salo [Salo, H., 1991. Icarus 90, 254-270]. Finally, we present the linear stability analyses of these equilibrium states, and derive criteria for the onset of viscous overstability in the self-gravitating and non-self-gravitating cases. These are framed in terms of particle size, orbital frequency, optical depth, and the parameters of the collision law. Our results compare favourably with the simulations of Salo et al. [Salo, H., Schmidt, J., Spahn, F., 2001. Icarus 153, 295-315]. The accuracy and practicality of the continuum model we develop encourages its general use in future investigations of nonlinear phenomena.  相似文献   

Mineralogical alteration of artificial meteorites during atmospheric entry. The STONE-5 experiment     

Franz Brandsttter  Andr Brack  Pietro Baglioni  Charles S. Cockell  Ren Demets  Howell G.M. Edwards  Gero Kurat  Gordon R. Osinski  Judith M. Pillinger  Claude-Alain Roten  Suzy Sancisi-Frey 《Planetary and Space Science》2008,56(7):976-984

The generic concept of the artificial meteorite experiment STONE is to fix rock samples bearing microorganisms on the heat shield of a recoverable space capsule and to study their modifications during atmospheric re-entry. The STONE-5 experiment was performed mainly to answer astrobiological questions. The rock samples mounted on the heat shield were used (i) as a carrier for microorganisms and (ii) as internal control to verify whether physical conditions during atmospheric re-entry were comparable to those experienced by “real” meteorites. Samples of dolerite (an igneous rock), sandstone (a sedimentary rock), and gneiss impactite from Haughton Crater carrying endolithic cyanobacteria were fixed to the heat shield of the unmanned recoverable capsule FOTON-M2. Holes drilled on the back side of each rock sample were loaded with bacterial and fungal spores and with dried vegetative cryptoendoliths. The front of the gneissic sample was also soaked with cryptoendoliths.

The mineralogical differences between pre- and post-flight samples are detailed. Despite intense ablation resulting in deeply eroded samples, all rocks in part survived atmospheric re-entry. Temperatures attained during re-entry were high enough to melt dolerite, silica, and the gneiss impactite sample. The formation of fusion crusts in STONE-5 was a real novelty and strengthens the link with real meteorites. The exposed part of the dolerite is covered by a fusion crust consisting of silicate glass formed from the rock sample with an admixture of holder material (silica). Compositionally, the fusion crust varies from silica-rich areas (undissolved silica fibres of the holder material) to areas whose composition is “basaltic”. Likewise, the fusion crust on the exposed gneiss surface was formed from gneiss with an admixture of holder material. The corresponding composition of the fusion crust varies from silica-rich areas to areas with “gneiss” composition (main component potassium-rich feldspar). The sandstone sample was retrieved intact and did not develop a fusion crust. Thermal decomposition of the calcite matrix followed by disintegration and liberation of the silicate grains prevented the formation of a melt.

Furthermore, the non-exposed surface of all samples experienced strong thermal alterations. Hot gases released during ablation pervaded the empty space between sample and sample holder leading to intense local heating. The intense heating below the protective sample holder led to surface melting of the dolerite rock and to the formation of calcium-silicate rims on quartz grains in the sandstone sample.  相似文献   

Predicting landscape sensitivity to present and future floods in the Pacific Northwest,USA   总被引：1，自引：0，他引：1       下载免费PDF全文

Mohammad Safeeq  Gordon E. Grant  Sarah L. Lewis  Brian Staab 《水文研究》2015,29(26):5337-5353

Floods are the most frequent natural disaster, causing more loss of life and property than any other in the USA. Floods also strongly influence the structure and function of watersheds, stream channels, and aquatic ecosystems. The Pacific Northwest is particularly vulnerable to climatically driven changes in flood frequency and magnitude, because snowpacks that strongly influence flood generation are near the freezing point and thus sensitive to small changes in temperature. To improve predictions of future flooding potential and inform strategies to adapt to these changes, we mapped the sensitivity of landscapes to changes in peak flows due to climate warming across Oregon and Washington. We first developed principal component‐based models for predicting peak flows across a range of recurrence intervals (2‐, 10‐, 25‐, 50‐, and 100‐years) based on historical instantaneous peak flow data from 1000 gauged watersheds in Oregon and Washington. Key predictors of peak flows included drainage area and principal component scores for climate, land cover, soil, and topographic metrics. We then used these regression models to predict future peak flows by perturbing the climate variables based on future climate projections (2020s, 2040s, and 2080s) for the A1B emission scenario. For each recurrence interval, peak flow sensitivities were computed as the ratio of future to current peak flow magnitudes. Our analysis suggests that temperature‐induced changes in snowpack dynamics will result in large (>30–40%) increases in peak flow magnitude in some areas, principally the Cascades, Olympics, and Blue Mountains and parts of the western edge of the Rocky Mountains. Flood generation processes in lower elevation areas are less likely to be affected, but some of these areas may be impacted by floodwaters from upstream. These results can assist land, water, and infrastructure managers in identifying watersheds and resources that are particularly vulnerable to increased peak flows and developing plans to increase their resilience. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献