Scour effects on the response of laterally loaded piles considering stress history of sand     

Cheng Lin  Caroline Bennett  Jie Han  Robert L. Parsons 《Computers and Geotechnics》2010,37(7-8):1008-1014

Scour is the removal of soils around pile foundations of bridges or offshore platforms, resulting in reduced capacity of the foundations in either lateral or vertical direction. A common way to analyze the scour-affected pile foundations is to remove the scoured soil layers while keeping the properties of the remaining soil unchanged. However, this approach ignores the fact that the remaining soil experiences different stress histories before and after scour, which can be expected to change the properties of the remaining soil. As a result, the resistance of the remaining soil provided to the pile foundation may be different. The present study focused on the response of laterally loaded pile foundations in sand under scour considering the stress history of the remaining sand. Relative density and coefficient of lateral earth pressure of the sand were evaluated when it changed from a normally consolidated (NC) soil to an over-consolidated (OC) soil due to scour. The relative density was then used to estimate other properties of sand, e.g., unit weight, friction angle, and modulus of subgrade reaction of the sand based on their correlation. The lateral load–deflection (p–y) curve for a pile in sand was modified and input into the computer software, LPILE Plus V 5.0, to account for the effect of the stress history induced by scour. A field test was referenced as an example to compare the calculated results from the modified p–y curves with those from the initially developed p–y curves for the tested sand. The results showed that the change in the over-consolidation ratio (OCR) resulted in the most significant effect on the lateral soil resistance among all the effects due to the changes in the properties of the remaining sand. The sand changing from an NC to OC state increased the lateral soil resistance to the pile foundation. Ignoring the stress history would result in a conservative design of laterally loaded piles under scour.  相似文献   

Integrated System for Robust 6-DOF Positioning Utilizing New Closed-Form Visual Motion Estimation Methods in Planar Terrains     

Shahriar Negahdaripour Caroline Barufaldi Ali Khamene 《Oceanic Engineering, IEEE Journal of》2006,31(3):533-550

Estimating the relative positions and (or) trajectory of a camera from video images is a fundamental problem in motion vision. Of special relevance is the closed-form solution for planar scenes, for processing fly-over imagery from airborne and underwater robotics platforms, automated airplane landing utilizing runway landmarks, photomosaicing, etc. However, the method's robustness can break down in certain scenarios, e.g., due to inherent translation-rotation ambiguity of visual motion with short baselines and narrow field of view. The robustness can be improved by devising methods that compute a smaller set of motion parameters, utilizing other sensors to measure the remaining components. This paper addressed key issues in six degrees of freedom positioning from fly-over imagery by integrating vision with rotational angle sensors. First, we propose and utilize robust closed-form solutions for estimating the motion and orientation of a planar surface from the image flow variations up to first order, given measurements of pitch and roll motions. We also describe a calibration technique to enable the integration of angle sensor and visual measurements. Next, an error analysis enables us to evaluate the impact of inaccurate pitch and roll measurements on the estimates from the new closed-form solutions. Finally, the performance of our new methods and the integrated positioning system are evaluated in various experiments with synthetic and real data  相似文献   

Numerical simulations of type I planetary migration in non-turbulent magnetized discs     

Sébastien Fromang  Caroline Terquem  Richard P. Nelson 《Monthly notices of the Royal Astronomical Society》2005,363(3):943-953

Using 2D magnetohydrodynamic (MHD) numerical simulations performed with two different finite-difference Eulerian codes, we analyse the effect that a toroidal magnetic field has on low-mass planet migration in non-turbulent protoplanetary discs. The presence of the magnetic field modifies the waves that can propagate in the disc. In agreement with a recent linear analysis, we find that two magnetic resonances develop on both sides of the planet orbit, which contribute to a significant global torque. In order to measure the torque exerted by the disc on the planet, we perform simulations in which the latter is either fixed on a circular orbit or allowed to migrate. For a     planet, when the ratio β between the square of the sound speed and that of the Alfven speed at the location of the planet is equal to 2, we find inward migration when the magnetic field   B _φ  is uniform in the disc, reduced migration when   B _φ  decreases as   r ⁻¹  and outward migration when   B _φ  decreases as   r ⁻²  . These results are in agreement with predictions from the linear analysis. Taken as a whole, our results confirm that even a subthermal stable field can stop inward migration of an earth-like planet.  相似文献   

MicroRaman spectroscopy of diamond and graphite in Almahata Sitta and comparison with other ureilites     

Aidan J. ROSS  Andrew STEELE  Marc D. FRIES  Lukas KATER  Hilary DOWNES  Adrian P. JONES  Caroline L. SMITH  Peter M. JENNISKENS  Michael E. ZOLENSKY  Muawia H. SHADDAD 《Meteoritics & planetary science》2011,46(3):364-378

This work is the first detailed study of carbon phases in the ureilite Almahata Sitta (sample #7). We present microRaman data for diamond and graphite in Almahata Sitta, seven unbrecciated ureilites, and two brecciated ureilites. Diamond in Almahata Sitta was found to be distinct from that in unbrecciated and brecciated ureilites, although diamond in unbrecciated and brecciated ureilites is indistinguishable. Almahata Sitta diamond shows a peak center range of 1318.5–1330.2 cm^?1 and a full width at half maximum (FWHM) range of 6.6–17.4 cm^?1, representing a shock pressure of at least 60 kbar. The actual peak shock pressure may be higher than this due to postshock annealing, if shock synthesis is the source of ureilite diamonds. Diamond in unbrecciated and brecciated ureilites have peak center wave numbers closer to terrestrial kimberlite diamond, but show a wider range of FWHM than Almahata Sitta. The larger peak shift observed in Almahata Sitta may indicate the presence of lonsdaleite. Alternatively, the lower values in brecciated ureilites may be evidence of an annealing step either following the initial diamond‐generating shock or as a consequence of heating during reconsolidation of the breccia. Graphite in Almahata Sitta shows a G‐band peak center range of 1569.1–1577.1 cm^?1 and a G‐band FWHM range of 24.3–41.6 cm^?1 representing a formation temperature of 990 ± 120 °C. Amorphous carbon was also found. We examine the different theories for diamond formation in ureilites, such as chemical vapor deposition and shock origin from graphite, and explore explanations for the differences between Almahata Sitta and other ureilites.  相似文献   

On the dynamics of the Hadley circulation and subtropical drying     

Kristopher B. Karnauskas  Caroline C. Ummenhofer 《Climate Dynamics》2014,42(9-10):2259-2269

Changes in subtropical precipitation and the Hadley circulation (HC) are inextricably linked. The original Halley–Hadley model cannot explain certain aspects of the Earth’s meridional circulation in the tropics and is of limited use in understanding regional changes in precipitation. Here, we expand on previous work on the regional and seasonal aspects of the HC, in particular how land–sea temperature contrasts contribute to the strength and width of the HC. We show that the Earth’s HC is well described by three regionally distinct cells along the eastern edges of the major ocean basins with opposite circulations elsewhere. Moreover, comparable summertime hemisphere cells emerge in each region. While it has been recognized that continents modify the meridional pressure gradient, we demonstrate that a substantial part of the Earth’s HC is driven by zonal pressure gradients (ZPGs) that only exist due to continental heating and air–sea interaction. Projected changes in land–sea temperature contrasts in a warming climate due to the relatively low thermal capacity of land will also affect ZPGs and thus HC strength and width, with implications for extremes in hydroclimate and freshwater resources across the increasingly vulnerable subtropics.  相似文献   

Urban Contestation in a Feminist Register     

Fran Klodawsky  Janet Siltanen  Caroline Andrew 《Urban geography》2013,34(4):541-559

Abstract

Approaches to urban contestation that challenge the dichotomy between institutionalization and opposition, and understand contestation as including engagement, are explored. The emphasis is on how recent forms of feminist analysis and critical scholarship open up a conceptual terrain for such thinking, and the discussion is grounded using further details of City for All Women Initiative/Initiative: une ville pour toutes les femmes (CAWI-IVTF), which is seen to be a concrete, successful case. Its tactics and strategies are noteworthy because of the manner in which ideas drawn from feminist and progressive organizing in other (including non-urban and non-Western) contexts have been incorporated. CAWI-IVTF's successes are most striking in relation to women who previously felt alienated from local politics. The organization's rationale, strategies, and tactics provide insights into how women active in this network create new spatialities, and how their interactions in space are producing new political subjects.  相似文献   

Rethinking Geographies of Assimilation     

Caroline R. Nagel 《The Professional geographer》2013,65(3):400-407

This commentary argues for a reconsideration of the concept of assimilation in geographical research. Whereas critics of assimilation theory have often misrepresented assimilation research, those working within the assimilation framework have seldom explored societal understandings of “sameness.” This commentary advocates that geographers look at assimilation not only in terms of spatial patterns but also in terms of the discursive and material practices through which dominant and subordinate groups negotiate the terms of social membership. The need to arrive at a richer understanding of assimilation becomes more pressing as the assimilability of migrants becomes an increasingly salient topic of debate.  相似文献   

Diversification of Livelihoods in a Society in Transition: A Case Study of Tibetan Communities in Southwest China     

Franz K. Huber  Yongping Yang  Caroline S. Weckerle  Klaus Seeland 《社会与自然资源》2014,27(7):706-723

In recent years, large development and market integration programs have altered the socioeconomic structures and cultural identity of rural communities and ethnic minorities in Southwest China and influenced the management of natural resources. This article analyzes livelihood strategies in the Shuiluo Valley, a remote area of the Sino-Tibetan borderlands. Agricultural activities and the management of natural resources were studied in five villages of Muli Tibetan Autonomous County, Sichuan Province. Characteristic for rural societies in transition, livelihoods were found to be flexible, combining subsistence agriculture, off-farm employment, and the exploitation of both renewable and nonrenewable natural resources. Accessibility of villages did not influence household income and livelihood activities, and poorer households were not found to depend more on natural resources or on income from agriculture than wealthier households. The option of gold prospecting constitutes a major difference compared to more nontimber forest product-based livelihoods in adjacent areas of Southwest China.  相似文献   

Raman spectroscopic properties and Raman identification of CaS‐MgS‐MnS‐FeS‐Cr2FeS4 sulfides in meteorites and reduced sulfur‐rich systems     

Caroline Avril  Valérie Malavergne  Razvan Caracas  Brigitte Zanda  Bruno Reynard  Emeline Charon  Ema Bobocioiu  Fabrice Brunet  Stephan Borensztajn  Sylvain Pont  Martine Tarrida  François Guyot 《Meteoritics & planetary science》2013,48(8):1415-1426

Raman spectra were acquired on a series of natural and synthetic sulfide minerals, commonly found in enstatite meteorites: oldhamite (CaS), niningerite or keilite ((Mg,Fe)S), alabandite (MnS), troilite (FeS), and daubreelite (Cr₂FeS₄). Natural samples come from three enstatite chondrites, three aubrites, and one anomalous ungrouped enstatite meteorite. Synthetic samples range from pure endmembers (CaS, FeS, MgS) to complex solid solutions (Fe, Mg, Ca)S. The main Raman peaks are localized at 225, 285, 360, and 470 cm^?1 for the Mg‐rich sulfides; at 185, 205, and 285 cm^?1 for the Ca‐rich sulfides; at 250, 370, and 580 cm^?1 for the Mn‐rich sulfides; at 255, 290, and 365 cm^?1 for the Cr‐rich sulfides; and at 290 and 335 cm^?1 for troilite with, occasionally, an extra peak at 240 cm^?1. A peak at 160 cm^?1 is present in all Raman spectra and cannot be used to discriminate between the different sulfide compositions. According to group theory, none of the cubic monosulfides oldhamite, niningerite, or alabandite should present first‐order Raman spectra because of their ideal rocksalt structure. The occurrence of broad Raman peaks is tentatively explained by local breaking of symmetry rules. Measurements compare well with the infrared frequencies calculated from first‐principles calculations. Raman spectra arise from activation of certain vibrational modes due to clustering in the solid solutions or to coupling with electronic transitions in semiconductor sulfides.  相似文献   

Comparing uncertain alternatives for a possible airport island location in the North Sea   总被引：3，自引：0，他引：3  

Caroline S. van der Kleij  Suzanne J. M. H. Hulscher  Teunis Louters 《Ocean & Coastal Management》2003,46(11-12):1031-1047

This paper presents a methodology for making decisions based on uncertain information through the use of an analytical feasibility study of an airport island in the North Sea as an alternative to the present inland airport, Amsterdam Schiphol, in The Netherlands. The multidisciplinary project, called Flyland, quantified several conflicting aspects, including uncertainties, for each of five alternative locations for the new airport. The methodology combines the Analytic Hierarchy Process and Monte Carlo approaches and allows comparison of the alternatives on the basis of their morphological and ecological effects. The resulting scores rank the alternatives and quantify the distinctions between them by taking uncertainties into account. We found that with respect to morphology and ecology, it is most favourable to keep the Dutch national airport inland. The methodology can easily be extended to include other factors and reflect a wider range of multidisciplinary aspects (costs, accessibility, environmental aspects) of the airport island location.  相似文献