Predicting size effect on diffusion-limited current density of oxygen reduction by copper wire     

芦永红  徐海波  王佳  钟莲 《中国海洋湖沼学报》2011,29(1)

The size effect of copper wire radius (0.04–0.82 mm) on the diffusion-limited current density of an oxygen reduction reaction in stagnant simulated seawater (naturally aerated 0.5 mol/L NaCl) is investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) and compared with the results obtained in 0.5 mol/L H2SO4. In the oxygen diffusion-limited range, size effect is found to occur independent of electrolytes, which is attributed to non-linear diffusion. Additionally, to sati...  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   

室内模拟试验确定横向扩散系数的研究--以吉林市第二松花江某江段为例     

梁秀娟  刘耀莹  张文静  盛洪勋  肖长来  王德成  杜艳荣  兰盈盈  杨天行 《吉林大学学报(地球科学版)》2004,34(4):560-565

确定河流横向扩散系数的主要方法有经验公式法和河流示踪试验法.以室内模拟试验求横向扩散系数的方法是一种新的尝试,采用几何相似原理,通过不同流量、流速条件下的室内模拟试验,计算出与河流相应条件下的横向扩散系数,所得结果(0.086 m2/s)与同条件下现场分析计算的结果(0.079～0.088 m2/s)基本一致.模拟试验不仅克服了野外条件下示踪剂投放和测试条件的不便,还能够更好地研究不同水动力条件下污染物的扩散运移规律.  相似文献   

一维热扩散湖模式在太湖的应用研究   总被引：2，自引：1，他引：1  

古红萍  沈学顺  金继明  肖薇  王咏薇 《气象学报》2013,71(4):719-730

利用在太湖获得的2010年8月11-28日的观测资料研究了一维热扩散湖模式在太湖的适用性,通过对比模拟进一步研究了影响太湖湖表温度模拟的主要因子。该湖模式对太湖最初的模拟结果并不理想,模拟的湖表面温度与观测有较大的系统性偏差,温度的日变化幅度与观测相比也偏小。通过分析该模式对太湖的模拟效果不理想的可能原因,针对太湖的生态环境和污染情况,设计了18个测试参数的敏感性试验,从敏感性试验的结果分析得到,适用于太湖的、依赖于湖泊类型的3个参数应做如下修改:消光系数（η₀）应放大3倍,湖泊表层吸收的太阳辐射系数（β）应取0.8,粗糙长度（z₀）采用公式计算得到。用新得到的适用于太湖的3个参数,模拟得到的结果与最初的模拟结果和观测资料对比,发现采用新的参数后,模拟结果比最初的模拟结果有了很大的改进,模拟的湖表温度基本接近观测,模拟的湖水垂直剖面时间序列图也跟观测吻合得较好,随之的感热、潜热通量的模拟也都与观测接近。最后,对输入湖模式的主要大气参量（太阳辐射、2 m气温及风场）±10%的误差引起的模式模拟的湖表面温度误差进行分析,结果表明该湖模式对大气强迫场的误差敏感度不高;相比之下,模拟结果对风场敏感性最小,对辐射和气温的敏感度相当。  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   

Calibration and use of continuous heat-type automated seepage meters for submarine groundwater discharge measurements     

B.M. Mwashote  W.C. Burnett  J. Chanton  I.R. Santos  N. Dimova  P.W. Swarzenski 《Estuarine, Coastal and Shelf Science》2010

Submarine groundwater discharge (SGD) assessments were conducted both in the laboratory and at a field site in the northeastern Gulf of Mexico, using a continuous heat-type automated seepage meter (seepmeter). The functioning of the seepmeter is based on measurements of a temperature gradient in the water between downstream and upstream positions in its flow pipe. The device has the potential of providing long-term, high-resolution measurements of SGD. Using a simple inexpensive laboratory set-up, we have shown that connecting an extension cable to the seepmeter has a negligible effect on its measuring capability. Similarly, the observed influence of very low temperature (≤3 °C) on seepmeter measurements can be accounted for by conducting calibrations at such temperatures prior to field deployments. Compared to manual volumetric measurements, calibration experiments showed that at higher water flow rates (>28 cm day⁻¹ or cm³ cm⁻² day⁻¹) an analog flowmeter overestimated flow rates by ≥7%. This was apparently due to flow resistance, turbulence and formation of air bubbles in the seepmeter water flow tubes. Salinity had no significant effect on the performance of the seepmeter. Calibration results from fresh water and sea water showed close agreement at a 95% confidence level significance between the data sets from the two media (R² = 0.98). Comparatively, the seepmeter SGD measurements provided data that are comparable to manually-operated seepage meters, the radon geochemical tracer approach, and an electromagnetic (EM) seepage meter.  相似文献   

On the magnetic field diffusion in mhd modeling of the inner coma of comet halley     

M. D. Kartalev  V. I. Nikolova 《地球物理与天体物理流体动力学》2013,107(1-2):145-168

Abstract

Some approaches of one-dimensional time-dependent magneto-hydrodynamic modeling of the structure of the inner coma of comet Halley are considered. The influence of the magnetic field diffusion on this structure is studied. The solution of Cravens (1989) approach containing classic magnetic diffusion is compared with an approach containing a specific diffusion, caused by non-instantaneous mass-loading of new ions. A case with no magnetic field is also considered. Common features of all the solutions are obtained. Special attention is paid to the sharp velocity jump, synchronized with a local density pick. Some differences between two types of magnetic field diffusion are discussed. A possible connection is supposed between this consideration and the large-scale shock fitting modeling of the solar plasma-comet interaction.  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   

基于构造导向的叠后处理技术——以渤海湾盆地A油田为例     

田涛  陈文雄  任百聪  唐何兵 《物探化探计算技术》2019,(3):314-318

对地震资料进行叠后解释性处理时,往往只是单纯的数学运算很少受到地质条件的约束。当地下岩层为水平地层时,这种方法会获得较好的效果。但地下岩层具有一定的倾角,这时就可能会发生分辨率降低、信噪比下降或资料失真等现象。针对这个问题,引入构造导向体来约束叠后资料的处理过程。首先根据原始地震资料生成包含倾角和方位角信息的构造导向体;其次在构造导向体的控制下以相似性为判断条件对原始地震资料进行构造导向的中值滤波或扩散滤波;最后通过原始地震资料和相干体等对处理前、后的资料品质进行了综合的分析对比。方向信息的引入使运算沿着构造的走向进行,消除了地层倾斜的影响,最大程度保证资料真实性的同时使资料的品质得到极大地提高,有效指导了A油田井位的设计和实施。  相似文献   

农业科技园技术扩散的机制与模式研究——以杨凌示范区为例   总被引：2，自引：0，他引：2  

李同升  王武科 《世界地理研究》2008,17(1):53-59

农业科技园是我国农业技术创新的重要源头和崭新模式,园区不仅要解决自身发展问题．而且肩负着技术扩散和推广的使命。通过技术创新一中介平台一技术受体之间关系的分析,构建了农业科技园技术扩散系统,分析了园区技术扩散的动力机制和主要类型,并以杨凌示范区为例．归纳和总结出市场经济条件下农业科技园技术扩散的成功模式,以图为我国农业科技园的技术扩散和持续发展提供借鉴。  相似文献