The Locations of Wal-Mart and Kmart Supercenters: Contrasting Corporate Strategies     

Thomas O. Graff 《The Professional geographer》1998,50(1):46-57

Wal-Mart and Kmart, the two largest American discount retailers, have begun to utilize a supercenter retailing format that combines a full-service grocery store with a discount department store. Supercenters are expected to be the major format for future expansion of each of these firms. The purpose of this paper is to analyze the spatial expansion strategies of each firm for the locations of its supercenters. Wal-Mart is quickly expanding its number of supercenters in modest-sized communities clustered around its grocery distribution centers, especially in Southern states. Conversely, most Super Kmart Centers are located inthe suburbs of widely scattered major metropolitan markets, and Kmart has yet to develop a grocery distribution network. Kmart currently has major financial problems that severely restrict the expansion of the Super Kmart Center format.  相似文献   

辽东湾东海岸地区热内边界层特性研究     

杨洪斌  刘万军 《气象》1998,24(8):42-43

利用辽东湾东海岸三个低空探测点的实测资料计算了各低空探测点的热内边界层平均高度,并将观测值与用经验公式得到的估算值进行了比较,给出了可用于这一地区的计算公式。  相似文献   

Three‐parameter discontinuous distributions for hydrological samples with zero values     

Stanislaw Weglarczyk  Witold G. Strupczewski  Vijay P. Singh 《水文研究》2005,19(15):2899-2914

A consistent approach to the frequency analysis of hydrologic data in arid and semiarid regions, i.e. the data series containing several zero values (e.g. monthly precipitation in dry seasons, annual peak flow discharges, etc.), requires using discontinuous probability distribution functions. Such an approach has received relatively limited attention. Along the lines of physically based models, the extensions of the Muskingum‐based models to three parameter forms are considered. Using 44 peak flow series from the USGS data bank, the fitting ability of four three‐parameter models was investigated: (1) the Dirac delta combined with Gamma distribution; (2) the Dirac delta combined with two‐parameter generalized Pareto distribution; (3) the Dirac delta combined with two‐parameter Weibull (DWe) distribution; (4) the kinematic diffusion with one additional parameter that controls the probability of the zero event (KD3). The goodness of fit of the models was assessed and compared both by evaluation of discrepancies between the results of both estimation methods (i.e. the method of moments (MOM) and the maximum likelihood method (MLM)) and using the log of likelihood function as a criterion. In most cases, the DWe distribution with MLM‐estimated parameters showed the best fit of all the three‐parameter models. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Migmatite formation at subsolidus conditions–an alternative to anatexis     

ANDERS LINDH  CARL-HENRIC WAHLGREN 《Journal of Metamorphic Geology》1985,3(1):1-12

Abstract This contribution discusses the formation of stromatic high-grade migmatites. Volume considerations require that most of the leucosome material is not added from outside the system. A segregation mechanism is necessary except in those cases where the protolith of the migmatite already had a banded structure. Although partial melting is most often advocated to provide the segregation mechanism, several arguments can be raised against high degrees of melting: mineral compositions and even zoning patterns are similar in both mesosomes and leucosomes; sufficient degrees of melting at reasonable temperatures require more than the available amounts of water; the leucosomes do not always approximate to a minimum melt composition; high degrees of melting cannot occur without an appreciable volume increase; etc. Diffusion works as a segregation mechanism at low temperatures. As diffusion rates increase exponentially with temperature diffusion must become still more important as a segregation mechanism at high temperatures. A model is suggested based on the diffusion of components in response to the gradient δσ/δx, where σ= 1/3∑³_i=1 σ_i is the mean pressure. In homogeneously strained rocks, σ₃ is larger in rock parts rich in incompetent phases than in rock parts depleted in incompetent phases. Accordingly, mechanically competent but chemically incompetent high-volume phases like quartz and feldspars stressed in micadominated parts of a rock (high σσ) migrate to parts of the rock that are depleted in mica (low σ¯). It is suggested that hornblende occurring in many leucosomes may be premigmatitic or early syn-migmatitic and due to its mechanical competency it initiates the segregation. Diffusion occurs along grain boundaries and is enhanced by small amounts of ‘intergranular fluid’;. At the best, semiquantitative estimates of diffusion rates and distances indicate that the process should work over geological times.  相似文献   

Effect of Fly Ash on Frost-Resistance and Chloride Ions Diffusion Properties of Marine Concrete     

杨文武  钱觉时  章一颖 《中国海洋工程》2009,23(2):367-377

It is necessary to pay more attention to the durability of concrete undergoing freeze-thaw cycles and seawater attack simultaneously.Investigated are the effects of water-binder ratio,fly ash (FA) contents and air-entraining agent on resistance to frost and chloride diffusion of marine concrete blended with FA in natural seawater.The results show that fly ash does not improve the frost resistance of concrete but can improve its resistance to chloride diffusion by addition of less than 30%.The resistance to frost and chloride diffusion of FA concrete can be improved with the decrease of water-binder ratio,and FA may improve both of them simultaneously only being mixed with air-entraining agent.A ratio (named as R) of the frost-resisting durability factor to chloride diffusion coefficient can be used to evaluate the durability of marine concrete.Scanning electron microscope (SEM) analyses are consistent with the evaluations by the value of R.  相似文献   

Effect of nearby supernova remnants on local cosmic rays     

Satyendra Thoudam 《Monthly notices of the Royal Astronomical Society》2007,378(1):48-54

We study in detail the effect of different particle release times from sources on the cosmic ray (CR) spectrum below 10¹⁵ eV in the Galaxy. We discuss different possible forms of particle injection such as burst-like injection, continuous injection for a finite time, injection from a stationary source and energy-dependent injection. When applied to the nearby known supernova remnants, we find that the observed CR anisotropy data favour the burst-like particle injection model for the CR diffusion coefficient   D ( E ) ∝ E ^a   with   a = 0.3 –0.6  in the local region. In this study we have also found that the contribution of the sources G114.3+0.3 and Monogem dominate if the observed anisotropy is a result of the effect of the nearby sources. Further study shows that we should not neglect the contribution of the undetected old sources to the local CR anisotropy.  相似文献   

Asthenospheric Viscosity and Stress Diffusion: A Mechanism to Explain Correlated Earthquakes and Surface Deformations In Ne Japan   总被引：1，自引：0，他引：1  

P. A. Rydelek  I. S. Sacks 《Geophysical Journal International》1990,100(1):39-58

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Cascade model for fluvial geomorphology   总被引：3，自引：0，他引：3  

W. I. Newman  D. L. Turcotte 《Geophysical Journal International》1990,100(3):433-439

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围海造陆工程泄水口悬浮物扩散规律分析   总被引：1，自引：1，他引：0  

陈杰  蒋昌波  张绍华  胡保安 《海洋科学》2015,39(8):58-62

掌握围海造陆工程泄水口悬浮物扩散规律,对保护海洋水环境质量具有重要意义。选取围海造陆工程泄水口为研究对象,基于泥沙对流扩散方程,推求出泄水口悬浮物扩散平面二维分析解表达式。开展现场观测,确定泄水口源强取值,并对泄水口悬浮物扩散进行理论计算和分析。研究结果显示,围海造陆工程施工后期,泄水口悬浮物流失非常严重。泄水口附近水域出现的最大悬浮物浓度主要由源强的大小来决定,悬浮物扩散范围主要由流速的大小来控制。  相似文献   

黄河沉积物向渤海湾扩散的沉积地球化学示踪   总被引：1，自引：0，他引：1       下载免费PDF全文

张爱滨  刘明  廖永杰  张艳丽  范德江 《海洋科学进展》2015,33(2):246-256

使用ICP-AES和ICP-MS对渤海中部118°54′E左右南北向断面的表层沉积物中53种常、微量及稀土元素进行了测试,研究了其含量变化和分布特征,并进行了物质组成分析。研究表明:该区沉积物以B94站为界,南北差异明显,南部区域沉积物以黏土质粉砂为主,富集Al2O3,CaO,Fe2O3,MgO,MnO,P2O5和TiO等常量元素以及绝大多数的微量元素和稀土元素等与细颗粒黏土矿物相关的元素;北部区域沉积物以粉砂-砂为主,富集SiO2,K2O和Na2O等常量元素以及Zr,Ba,Sr,Sb和Hf等微量元素,稀土元素相对亏损。物源对比表明南部沉积物具有黄河来源沉积物特点,北部沉积物具有滦河来源特点,两者的分界大致在38°42′N附近。河口动力过程、渤海环流是影响该区沉积物扩散的主要因素。  相似文献