The relationship between apparent equilibrium temperature and closure temperature with application to oxygen isotope geospeedometry     

Huaiwei Ni 《中国地球化学学报》2014,33(2):125-130

Oxygen isotope fractionation between coexisting minerals in slowly cooled rocks conveys information about their cooling history. By using the fast grain boundary （FGB） model to simulate closed-system diffusive ex- change of oxygen isotopes between coexisting minerals, I show that the apparent equilibrium temperatures （Tae） by the mineral pair with the largest isotopic fractionation （PLIF） always lies between the closure temperatures （To） of those two minerals. Therefore, when the rate of oxygen diffusion and hence Tc for the PLIF chance to be comparable （such as in the case of quartz and magnetite）, Tae will serve as a good approximation of To regardless of variation in mineral proportions. The specialty of the PLIF in constraining Tac within their Tc range can be generalized to other stable isotope systems and element partitioning. By approximating Tc with Tac and inverting Dodson＇s equation, the cooling rate of plutonic or metamorphic rocks can be inferred.  相似文献   

Low‐cost monitoring of snow height and thermal properties with inexpensive temperature sensors     

Dominik E. Reusser  Erwin Zehe 《水文研究》2011,25(12):1841-1852

Small, self‐recording temperature sensors were installed at several heights along a metal rod at five locations in a case study catchment. For each sensor, the presence or absence of snow cover was determined on the basis of its insulating effect and the resulting reduction of the diurnal temperature oscillations. Sensor coverage was then converted into a time series of snow height for each location. Additionally, cold content was calculated. Snow height and cold content provide valuable information for spring flood prediction. Good agreement of estimated snow heights with reference measurements was achieved and increased discharge in the study catchment coincided with low cold content of the snow cover. The results of the proposed distributed assessment of snow cover and snow state show great potential for (i) flood warning, (ii) assimilation of snow state data and (iii) modelling snowmelt process. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

多参数信息扩散估计的精度评定     

于中伟  花向红  陈梦华  张伟 《测绘工程》2009,18(3):13-16

作为一种稳健估计方法,同选权迭代估计一样,信息扩散估计也是通过对粗差观测值降权达到抗差效果,由于不需迭代,信息扩散得到的权就相当于迭代稳定后的权.在此思想基础上,讨论高斯-马尔柯夫模型下多参数信息扩散估计的精度评定方法.  相似文献   

The sweeping rate in diffusion-mediated reactions on dust grain surfaces   总被引：1，自引：0，他引：1  

I. Lohmar  J. Krug 《Monthly notices of the Royal Astronomical Society》2006,370(2):1025-1033

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Peat porewater chloride concentration profiles in the Everglades during wet/dry cycles from January 1996 to June 1998: field measurements and theoretical analysis     

Michael M. Reddy  Micaela B. Reddy  Kenneth L. Kipp  Aaron Burman  Paul Schuster  Peter S. Rawlik Jr. 《水文研究》2008,22(11):1713-1724

Water quality is a key aspect of the Everglades Restoration Project, the largest water reclamation and ecosystem management project proposed in the United States. Movement of nutrients and contaminants to and from Everglades peat porewater could have important consequences for Everglades water quality and ecosystem restoration activities. In a study of Everglades porewater, we observed complex, seasonally variable peat porewater chloride concentration profiles at several locations. Analyses and interpretation of these changing peat porewater chloride concentration profiles identifies processes controlling conservative solute movement at the peat–surface water interface, that is, solutes whose transport is minimally affected by chemical and biological reactions. We examine, with an advection–diffusion model, how alternating wet and dry climatic conditions in the Florida Everglades mediate movement of chloride between peat porewater and marsh surface water. Changing surface water–chloride concentrations alter gradients at the interface between peat and overlying water and hence alter chloride flux across that interface. Surface water chloride concentrations at two frequently monitored sites vary with marsh water depth, and a transfer function was developed to describe daily marsh surface water chloride concentration as a function of marsh water depth. Model results demonstrate that porewater chloride concentrations are driven by changing surface water chloride concentrations, and a sensitivity analysis suggests that inclusion of advective transport in the model improves the agreement between the calculated and the observed chloride concentration profiles. Published in 2007 by John Wiley & Sons, Ltd.  相似文献   

Local And Global Diffusion Along Resonant Lines in Discrete Quasi-integrable Dynamical Systems     

Claude Froeschlé  Massimiliano Guzzo  Elena Lega 《Celestial Mechanics and Dynamical Astronomy》2005,92(1-3):243-255

We detect and measure diffusion along resonances in a quasi-integrable symplectic map for different values of the perturbation parameter. As in a previously studied Hamiltonian case (Lega et al., 2003) results agree with the prediction of the Nekhoroshev theorem. Moreover, for values of the perturbation parameter slightly below the critical value of the transition between Nekhoroshev and Chirikov regime we have also found a diffusion of some orbits along macroscopic portions of the phase space. Such a diffusion follows in a spectacular way the peculiar structure of resonant lines.  相似文献   

靖远地区大厚度黄土地基浸水湿陷过程及土中竖向应力特征试验研究     

刘德仁  安政山  徐硕昌  王旭  张转军  金芯  张严 《岩土力学》2023,44(1):268-278

为了研究靖远大厚度黄土在浸水条件下的水分入渗规律和自重湿陷变形特征,在中兰铁路沿线的靖远北站黄土自重湿陷场地进行了不打注水孔的现场浸水试验,监测并分析了地表及地下湿陷变形、试坑周围裂缝、含水率和土中竖向应力变化情况,对水分扩散规律、自重湿陷特性和土中竖向应力变化规律进行了研究,并对地区修正系数β0值和浸润角进行了探讨。结果表明：体积含水率变化分为浸水稳定（2个）、快速增加（1个）和缓慢增加（1个）共4个阶段;浸水过程中,水分在21m处竖向入渗加快、径向扩散减缓,湿润峰最终形态呈现为椭圆状。根据探井和钻孔含水率测试结果,推算出浸润角最大为41°。该场地黄土自重湿陷过程历经剧烈湿陷、缓慢湿陷和固结稳定3个阶段。试验结束时共计发展了13圈环状裂缝,裂缝最远处距试坑边缘26m。根据室内试验和现场测试结果,建议地区修正系数沿土层深度进行修正,0～10m内β0值取1.05,10～27 m内β0值取0.95。在地表至21 m深度范围内,地基土浸水饱和且湿陷充分,土中竖向应力沿深度呈线性增加,土中竖向应力接近饱和自重应力,21m以下的地基土未能充分湿陷,土中竖向应力逐渐减小。该研究成果可应用于中兰铁路...  相似文献   

Spatial and temporal trends in information technology outsourcing     

《Applied geography (Sevenoaks, England)》2015

Over the last two decades information technology (IT) outsourcing has grown dramatically, and has emerged as a strategic choice for firms searching for ways to control their costs and maintain a competitive edge. The mechanisms driving its growth are not fully understood though. In this research, we employ an approach that focuses on geographic, temporal, and industrial proximity in a mechanism that identifies the process underlying the diffusion of IT outsourcing across firms within the U.S from 2000 to 2010. We focus on the role that firm location plays in the diffusion process, and use space-time clustering techniques from the epidemiology literature to understand the diffusion process. We identify 38 space-time clusters based on IT outsourcing announcement data and the locations of firm headquarters among U.S.-based firms. When supplemented with additional information, such as type of services outsourced, the metropolitan area of the headquarters, and related industry information; the results offer insights into various types of diffusion processes that have been identified in the literature but have not been documented to date in the empirical manner that we have been able to do.  相似文献   

Element spots in Ap and Hg‐Mn stars from current‐driven diffusion     

V. Urpin 《Astronomische Nachrichten》2015,336(3):266-270

The stars of the middle main sequence often have spot‐like chemical structures at their surfaces. We consider the diffusion process caused by electric currents that can lead to the formation of such chemical spots. Diffusion is considered using the partial momentum equations derived by the Chapman‐Enskog method. We argue that diffusion caused by electric currents can substantially change the surface chemistry of stars and form spotted chemical structures even in a relatively weak magnetic field. The considered mechanism can be responsible for a formation of element spots in Hg‐Mn and Ap‐stars. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Long‐term annual surface heat and water balances over Canada and the United States South of 60°N: Reconciliation of precipitation,run‐off and temperature fields     

F. Kenneth Hare 《大气与海洋》2013,51(2):127-153

Abstract

The analysis compares the observed field of run‐off (assumed correct) with adjusted precipitation over North America (as amended by den Hartog and LeDrew over Canada) and derives the principal hydroclimatological ratios for each five‐degree latitude‐longitude square. The amended precipitation field yields values of the Budyko dry ness index close to values suggested by the vegetation distribution. The Priestley‐Taylor parameter, α, lies between unity (equilibrium) and potential (1.26) values over much of humid North America, but exceeds these values in the northwest Pacific squares, where advective heating may be the cause. Other regions of strong seasonal advective heating (e.g. the Great Plains) do not appear to influence the distribution strongly. A weighted convective forcing temperature is derived, varying from 298 K in the extreme south to below 285 K in the north. This function (and the Bowen ratio) achieve improbable values in northern Labrador‐ Ungava. The precipitation, run‐off and net radiation régimes appear still to be out of balance in these squares. An adjustment of either precipitation or net radiation by about a tenth corrects the imbalance, but the method is not capable of deciding which field (or both) is in error. Over the rest of the continent the adjusted precipitation field now appears to be in balance with observed run‐off and temperature distributions.  相似文献