阿拉斯加输油管的设计和施工方式方案变更过程及其背后的原因和哲学思想   总被引：3，自引：1，他引：3  

金会军  胡万志  张欣佳  陈剑锋 《冰川冻土》2006,28(6):809-817

阿拉斯加输油管道公司曾经研发和使用了3种主要施工方案和技术:传统地埋式、特殊埋设和地上敷设方式.在传统地埋式施工方案中,管顶埋深变化于0.9~2.7 m.这主要是考虑了地形变化,而不是沿途的岩性和土壤类型.在特殊埋设方案中,在原油管道必须埋设的地段,如大规模动物迁徙常用地段则使用通道冷液循环降(保)温系统和(或)热管(桩)降(保)温,来保护多年冻土.地上敷设方案包括桩基架设和地上洁净砾石管堤(垫护层).后者只在管道进入和离开多年冻土时采用.架设桩基横梁方案中使用有或没有热管保温的垂直支架梁(单元)(VSM).在初步规划和设计阶段,管道的业主公司(即横穿阿拉斯加管道系统,或TAPS)和随后的阿拉斯加管道服务公司(APSC)不容商量的坚决要求100%的埋设方案.但是,随着勘察工作的进展和设计方案的细化,施工设计方案在不断变化.1977年管道施工结束时,只有57%的管道采用了埋设方式.管道运行30 a后的今天(考虑运行期间维护中所产生的问题),很多经验丰富的工程师认为53%的埋设可能更合理.设计和施工方案变更的原因主要有:1)为了获得通过联邦政府所属的土地所需的许可证,政府有特殊的规定和要求;2)管道公司的设计、施工和管理人员进行了现场野外调查、研究,并积极参与了详细设计和研发;3)美国环境政策法案(NEPA)的最新要求(启用了核准制).阿拉斯加管道服务公司是7家主要石油公司的服务机构.由于这个项目的巨大规模和所涉及的高昂费用,致使各大石油公司的工程师非同寻常程度的参与.在文章中,笔者论述了与阿拉斯加管道施工有关的阿拉斯加管道服务公司、美国联邦和阿拉斯加州政府相关组织机构的形成历史,管道设计演变过程及其背后的哲学思想,以及阿拉斯加管道工程项目的经验和教训.  相似文献   

The recent history of erosion and sedimentation on the Southern Tablelands of southeastern Australia: sediment flux dominated by channel incision   总被引：2，自引：0，他引：2  

R.J Wasson  R.K Mazari  B Starr  G Clifton 《Geomorphology》1998,24(4):291-308

As in other regions colonised from Europe within the last few centuries, Australia's vegetation and soils have been dramatically changed by clearing, cropping and grazing. In southeastern Australia, particularly on the Southern Tablelands, the impacts of European settlement are clearly manifested by channel incision. By using stratigraphic and documentary evidence, in conjunction with aerial photographs, sediment budgets for the post-settlement period have been constructed to define the fluxes and stores of sediment for each of the major geomorphic components of the 136 km² catchment of Jerrabomberra Creek near Canberra. Using these budgets, and some plausible assumptions, it has been possible to approximate the history of both the sediment delivery ratio and sediment yield for this catchment. While the quantities estimated in this analysis are approximations, the trends through time are credible. Sediment yield increased rapidly to a peak after European settlement, and has returned to a level between the peak and the pre-European value. The delivery ratio has followed a similar trend. The most general conclusion to emerge is that in this landscape both the total sediment flux and the sediment yield of the catchment have been dominated by channel erosion. This result is contrary to the findings in many parts of the world where sheet and rill erosion dominates the fluxes. The soil conservation implication of these results is clear: to control off-site effects of erosion, the focus must be on the channels.  相似文献   

Amino-acid racemizarion in Quaternary shell deposits at Willapa Bay,Washington     

Keith A. Kvenvolden  David J. Blunt  H.Edward Clifton 《Geochimica et cosmochimica acta》1979,43(9):1505-1520

Extents of racemization ($\text{d}\text{l}$ ratios) of amino acids in fossil Saxidomus giganteus (Deshayes) and Ostrea lurida Carpenter were measured on shell deposits exposed at 21 sites on the east side of Willapa Bay, Washington. Amino acids from Saxidomus show less variability in $\text{d}\text{Spl}$ ratios and, therefore, are of greater use in correlation and age estimation than are amino acids from Ostrea. Shells of two different ages, about 120,000 ± 40,000 yr old and about 190,000 ± 40,000 yr old, are present. These ages correspond to Stages 5 and 7 of the marine isotope record defined by Shackleton and Opdyke in 1973 and hence the shell deposits likely formed during two different high stands of sea level. The stratigraphic record at Willapa Bay is consistent with this interpretation.  相似文献   

Cepheid parallaxes and the Hubble constant   总被引：1，自引：0，他引：1  

Floor van Leeuwen  Michael W. Feast  Patricia A. Whitelock  Clifton D. Laney 《Monthly notices of the Royal Astronomical Society》2007,379(2):723-737

Revised Hipparcos parallaxes for classical Cepheids are analysed together with 10 Hubble Space Telescope ( HST )-based parallaxes. In a reddening-free V , I relation we find that the coefficient of log  P is the same within the uncertainties in our Galaxy as in the Large Magellanic Cloud (LMC), contrary to some previous suggestions. Cepheids in the inner region of NGC 4258 with near solar metallicities confirm this result. We obtain a zero-point for the reddening-free relation and apply it to the Cepheids in galaxies used by Sandage et al. to calibrate the absolute magnitudes of Type Ia supernova (SNIa) and to derive the Hubble constant. We revise their result for H ₀ from 62 to 70 ± 5 km s⁻¹ Mpc⁻¹. The Freedman et al. value is revised from 72 to 76 ± 8 km s⁻¹ Mpc⁻¹. These results are insensitive to Cepheid metallicity corrections. The Cepheids in the inner region of NGC 4258 yield a modulus of 29.22 ± 0.03 (int.) compared with a maser-based modulus of 29.29 ± 0.15. Distance moduli for the LMC, uncorrected for any metallicity effects, are 18.52 ± 0.03 from a reddening-free relation in V , I ; 18.47 ± 0.03 from a period–luminosity relation at K ; 18.45 ± 0.04 from a period–luminosity–colour relation in J , K . Adopting a metallicity correction in V , I from Macri et al. leads to a true LMC modulus of 18.39 ± 0.05.  相似文献   

Applying the HAZUS-MH software tool to assess seismic risk in downtown Ottawa,Canada   总被引：3，自引：3，他引：0  

S. K. Ploeger  G. M. Atkinson  C. Samson 《Natural Hazards》2010,53(1):1-20

The aim of this paper is to present earthquake loss estimations for a portion of downtown Ottawa, Canada, using the HAZUS-MH (Hazards United States Multi-Hazard) software tool. The assessment is performed for a scenario earthquake of moment magnitude 6.5, at an epicentral distance of 15 km, occurring during business hours. A level 2 HAZUS-MH analysis was performed where the building inventory, microzonation studies, and site-specific ground motion hazard maps (2% exceedence probability in 50 years) were all improved based on local information. All collected data were assembled into a set of standard geodatabases that are compatible with the HAZUS-MH software using a GIS-specific procedure. The results indicate that the greatest losses are expected in unreinforced masonry buildings and commercial buildings. Sensitivity studies show that soil classes, the vulnerability of schools, and the spatial scale of loss estimations are also important factors to take into account.  相似文献   

Assessment of uncertainties in the response of the African monsoon precipitation to land use change simulated by a regional model     

Samson Hagos  L. Ruby Leung  Yongkang Xue  Aaron Boone  Fernando de Sales  Naresh Neupane  Maoyi Huang  Jin-Ho Yoon 《Climate Dynamics》2014,43(9-10):2765-2775

Land use and land cover (LULC) over Africa have changed substantially over the last 60 years and this change has been proposed to affect monsoon circulation and precipitation. This study examines the uncertainties of model simulated response in the African monsoon system and Sahel precipitation due to LULC change using a set of regional model simulations with different combinations of land surface and cumulus parameterization schemes. Although the magnitude of the response covers a broad range of values, most of the simulations show a decline in Sahel precipitation due to the expansion of pasture and croplands at the expense of trees and shrubs and an increase in surface air temperature. The relationship between the model responses to LULC change and the climatologists of the control simulations is also examined. Simulations that are climatologically too dry or too wet compared to observations and reanalyses have weak response to land use change because they are in moisture or energy limited regimes respectively. The ones that lie in between have stronger response to the LULC changes, showing a more significant role in land–atmosphere interactions. Much of the change in precipitation is related to changes in circulation, particularly to the response of the intensity and latitudinal position of the African Easterly Jet, which varies with the changes in meridional surface temperature gradients. The study highlights the need for measurements of the surface fluxes across the meridional cross-section of the Sahel to evaluate models and thereby allowing human impacts such as land use change on the monsoon to be projected more realistically.  相似文献   

Macau’s role as a recreation/tourist center in the Pearl River Delta city-region     

Clifton W. Pannell  Philip H. Loughlin 《Urban geography》2015,36(6):883-904

The return of Macau to Chinese sovereignty in 1999 brought far-reaching change to Macau as a special administrative region (SAR). China’s policy and plans for a revitalized Macau as a key urban node offers an opportunity to conceptualize a leading role for Macau as the pre-eminent recreational and tourist center in the dynamic and globally connected Pearl River Delta city-region. We examine and assess the new policies that have led to Las Vegas-style casinos bringing explosive growth in visitors, gambling revenues, and Macau’s economy. New problems of corruption, crime, and social pathologies have appeared as well owing in part to the secretive VIP gambling centers for high rollers from the mainland. Has Macau met China’s goals and expectations for a great tourist and recreational center? Our findings indicate a mixed record with more challenges emerging in the wake of China’s recent anti-corruption campaign.  相似文献   

Stony meteorite characterization by non‐destructive measurement of magnetic properties     

D. L. Smith  R. E. Ernst  C. Samson  R. Herd 《Meteoritics & planetary science》2006,41(3):355-373

Abstract— Four parameters of low‐field magnetic susceptibility (bulk value, frequency dependence, degree of anisotropy, and ellipsoid shape) have been determined for 321 stony meteorites from the National Collection of Canada. These parameters provide a basis for rapid, non‐destructive, and accurate meteorite classification as each meteorite class tends to have a distinct range of values. Chondrites show a clear trend of increasing bulk susceptibility from LL to L to H to E within the 3.6 to 5.6 logχ (in 10⁻⁹ m³/kg) range, reflecting increasing Fe‐Ni metal and Fe‐Ni sulfide content. Achondrite values range in logχ from 2.4 to 4.7 and primitive achondrites from 4.2 to 5.7. Frequency dependence is observed, using 19,000 Hz and 825 Hz, with variations in strength among meteorite classes and individual specimen dependence ranging from 1–25.6%. Degrees of anisotropy range from 1 to 53% with both oblate and prolate ellipsoids present. The aubrite class is marked by high degrees of anisotropy, low bulk magnetic susceptibility, and prolate fabric. Camel Donga is set apart from other eucrites, marked by higher bulk susceptibility, degree of anisotropy, and magnitude of oblate ellipsoid shape. The Shergotty, Nakhla, and Chassigny (SNC) meteorites show subclass distinction using frequency dependence and Chassigny is set apart with a relatively strong oblate fabric. The presence of both strong oblate and prolate fabrics among and within meteorite classes of chondritic and achondritic material points to a complex, multi‐mechanism origin for anisotropy, more so than previously thought, and likely dominated by impact processes in the later stages of stony parent body formation.  相似文献   

Estimation of the magnetic fields of current channels in magnetovariational data     

Xi-shuo Wang  J. C. Samson  D. I. Gough 《Geophysical Journal International》1989,96(3):381-388

  相似文献   

Polarization characteristics of Pi 2 pulsations and implications for their source mechanisms: Location of source regions with respect to the auroral electrojets     

Gordon Rostoker  John C. Samson 《Planetary and Space Science》1981,29(2):225-247

Substorm onsets and intensifications are accompanied on a one-to-one basis by a Pi 2 magnetic pulsation burst. The source region for these pulsations is generally thought to lie in the region of substorm disturbance in the auroral oval. In this paper we outline the characteristics of Pi 2 pulsations in regions near the substorm enhanced electrojet but removed from the locale of the westward travelling surge. We show that a resonance region for the pulsations lies at the equatorwad edge of the westward electrojet, which in the evening sector marks the locus of the Harang discontinuity. Finally we show examples where the maximum amplitude of the Pi 2 is located at or equatorward of the southern border of the eastward electrojet or at the southern border of the westward electrojet. This is clear evidence for the coupling of wave energy into the L-shells far distant from the source of the energy. Mechanisms for Pi 2 generation are discussed in the context of the results presented in this paper.  相似文献