检索结果-南通市图书馆

Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2009年第1期10卷 1-6页

作者： Michael K.H.LEUNG Kit-ying CHAN Department of Mechanical Engineering the University of Hong Kong

Soil in a cold region is subject to frequent freezing and thawing *** frozen for a prolonged period may cause adverse freeze damage to the plants due to cell dehydration or root cell *** is important to understand the detailed heat transfer behaviors of the freezing and thawing processes to prevent freeze damage,and to devise proper mitigation measures for effective pot planting in cold regions.A theoretical model was developed to analyze the transient moving phase-change interface heat transfer in the freezing and thawing of porous potting *** theoretical derivation is based on the assumption that the soil freezes completely at a single *** poromechanic effects on heat transfer behavior were *** spatial domain of the problem was simplified to a 1D spherical coordinate system with variation in the radial ***'s function was applied to solve for the time-dependent body *** were conducted for validation of the theoretical *** agreement between the theoretical predictions and experimental measurements was *** theoretical model developed can be easily used to determine the sensitivity of various parameters in the freezing/thawing processes,e.g.,thermal properties of soil,ambient temperature,and planting pot size.

关键词： Porous soil Freezing thawing Moving phase-change interface Theoretical model

Changes in freezing and thawing indices over the source region of the Yellow River from 1980 to 2014

在线全文

学校读者我要写书评

暂无评论

Journal of Forestry Research 2019年第1期30卷 257-268页

作者： Rui Wang Qingke Zhu Hao Ma School of Geography and Tourism Shaanxi Normal University School of Soil and Water Conservation Beijing Forestry University Northwest Institute of Forest Inventory and Planning and Design State Forestry Administration

Freezing and thawing indices are not only of great significance for permafrost research but also are important indicators of the effects of climate ***,to date,research on ground-surface freezing and thawing indices and their relationship with air indices is *** on daily air and ground-surface temperatures collected from 11 meteorological stations in the source region of the Yellow River,the freezing and thawing indices were calculated,and their spatial distribution and trends were *** air-freezing index(AFI),air-thawing index(ATI),ground surface-freezing index(GFI),ground surface-thawing index(GTI),air thawing-freezing index ratio(Na)and surface ground thawing-freezing index ratio(Ng)were 1554.64,1153.93,1.55,2484.85,850.57℃-days and 3.44,*** affected the spatial distribution of the freezing and thawing *** the altitude increased,the freezing indices gradually increased,and the thawing indices and thawing-freezing index ratio *** 1980 to 2014,the AFI and GFI decreased at rates of 8.61 and 11.06℃-days a^(-1),the ATI and GTI increased at 9.65 and 14.53℃-days a^(-1),and Na and Ng significantly increased at 0.21 and 0.79 decade^(-1).Changes in the freezing and thawing indices were associated with increases in the air and ground-surface *** rates of change of the ground surface freezing and thawing indices were faster than the air ones because the rate of increase of the groundsurface temperature was faster than that of the air and the difference between the ground surface and air *** change point of the time series of freezing and thawing indices occurred in 2000–*** 2000–2001,the AFI and GFI were lower than before the change point,and the changing trend was *** ATI,GTI,Na and Ng during 2001–2014 were higher,with faster rates than *** addition,the annual thawing indices composed a greater proportion of the mean annual air temperature and mean annual ground surfac

关键词： Climate change Freezing and thawing indices Permafrost The source region of the Yellow River

Numerical study on freezing-thawing phase change heat transfer in biological tissue embedded with two cryoprobes

在线全文

学校读者我要写书评

暂无评论

Journal of Central South University 2009年第2期16卷 326-331页

作者：赵芳陈振乾施明恒 School of Energy and Environment Southeast University

A two-dimensional model for freezing and thawing phase change heat transfer in biological tissue embedded with two cryoprobes was *** this model,the blood vessels were considered as tree-like branched fractal network,and the effective flow rate and effective thermal conductivity of blood were obtained by fractal *** temperature distribution and ice crystal growth process in biological tissue embedded with two cryoprobes during freezing-thawing process were numerically *** results show that the growth velocity of ice crystal in freezing process from 200 to 400 s is more rapid than that from 400 to 600 s. thawing process of frozen tissue occurs in the regions around cryoprobes tips and tissue boundary simultaneously,and the phase interfaces are close to each other until ice crystal melts *** distance of two cryoprobes has a more profound effect on the temperature distribution in freezing process at 400 s than at 800 s.

关键词： heat transfer fracture phase change freezing thawing

A land surface soil moisture data assimilation framework in consideration of the model subgrid-scale heterogeneity and soil water thawing and freezing

在线全文

学校读者我要写书评

暂无评论

Science China Earth Sciences 2008年第7期51卷 992-1000页

作者： TIAN XiangJun XIE ZhengHui Institute of Atmospheric Physics Chinese Academy of SciencesBeijing 100029China

The Ensemble Kalman Filter (EnKF) is well known and widely used in land data assimilation for its high precision and simple operation. The land surface models used as the forecast operator in a land data assimilation system are usually designed to consider the model subgrid-heterogeneity and soil water thawing and freezing. To neglect their effects could lead to some errors in soil moisture assimilation. The dual EnKF method is employed in soil moisture data assimilation to build a soil moisture data as- similation framework based on the NCAR Community Land Model version 2.0 (CLM 2.0) in considera- tion of the effects of the model subgrid-heterogeneity and soil water thawing and freezing: Liquid volumetric soil moisture content in a given fraction is assimilated through the state filter process, while solid volumetric soil moisture content in the same fraction and solid/liquid volumetric soil moisture in the other fractions are optimized by the parameter filter. Preliminary experiments show that this dual EnKF-based assimilation framework can assimilate soil moisture more effectively and precisely than the usual EnKF-based assimilation framework without considering the model subgrid-scale heteroge- neity and soil water thawing and freezing. With the improvement of soil moisture simulation, the soil temperature-simulated precision can be also improved to some extent.

关键词： dual EnKF NCAR/CLM soil moisture assimilation framework subgrid-heterogeneity soil water thawing and freezing

Freezing and thawing effects of sand-silt mixtures on elastic waves

在线全文

学校读者我要写书评

暂无评论

Research in Cold and Arid Regions 2013年第4期5卷 418-424页

作者： MinGu Kang JongChan Kim Jung-Hee Park Jong-Sub Lee School of Civil Environmental and Architectural Engineering Korea University

Freezing and thawing during the winter season change soil properties such as density. The density change in the particulate media influences soil stiffness. In addition, freezing of partially or fully saturated soils changes the soil matrix from a particulate media to a continuum. The goal of this study is to investigate the cyclic freezing and thawing effects on elastic waves. Sand-silt mixtures with 10% silt fraction in weight and 40% saturation are prepared. The sand-silt mixtures are placed in a nylon cell, onto which a pair of bender elements and a pair of piezoelectric disk elements are installed for the measurement of shear and compressional waves, respectively. The temperature of the mixtures decreases from 20 ℃ to -10 ℃ to freezing. The frozen sample is gradually thawed at room temperature （20 ℃）, These freezing-thawing processes are repeated three times. The test result shows that the shear and compressional wave velocities significantly increase when the specimen is frozen. When the temperature is greater than 0 ℃, the elastic wave velocities are lower during thawing than during freezing due to soil structure change. This study demonstrates that soil strucre change during the winter season may be effectively estimated from elastic waves.

关键词： compressional waves freezing frozen soil shear stiffness shear waves thawing

Environmental Protection Lever Pries the Development of New Snow-thawing Agents

在线全文

学校读者我要写书评

暂无评论

China Chemical Reporter 2010年第14期21卷 31-31页

作者： Zhou Zhonghai and Guo Huiming,the Sciences School of Nanjing University of Technology

*** varietiesChlorides snow-thawing agents mainly includesodium chloride,calcium chloride andmagnesium chloride,as well as their blendswith anti-corrosion and anti-rust *** chloride is a road snow-thawingagent in popular use *** has the featuresof quick snow thawing and low *** heat absorption in dissolution and itscorrosion are however strong and the ap-

关键词： thawing today Agents dissolution Sodium quick Tian

Warming but not thawing of the cold permafrost in northern Alaska during the past 50 years

在线全文

学校读者我要写书评

暂无评论

Research in Cold and Arid Regions 2009年第1期1卷 1-13页

作者： Max C. Brewer State Key Laboratory of Frozen Soils Engineering Cold and Arid Regions Environmental and Engineering Research Institute Chinese Academy of Sciences U. S. Geological Survey 4200 University Drive

Climate warming has not resulted in measurable thawing of the cold (–5°C to –10°C) permafrost in northern Alaska during the last half century. The maximum depths of summer thaw at five locations near Barrow, Alaska, in 2005 were within the ranges of the depths obtained at those same locations during the early 1950s. However, there has been a net warming of about 2°C, after a cooling of 0.4°C during 1953–1960, at the upper depths of the permafrost column at two of the locations. thawing of permafrost from above (increase in active layer thickness) is determined by the summer thawing index for the specific year; any warming, or cooling, of the upper permafrost column results from the cumulative effect of changes in the average annual air temperatures over a period of years, assuming no change in surface conditions. Theoretically, thawing from the base of permafrost should be negligible even in areas of thin (about 100–200 m) permafrost in northern Alaska. The reported shoreline erosion along the northern Alaska coast is a secondary result from changes in the adjacent ocean ice coverage during the fall stormy period, and is not directly because of any 'thawing' of the permafrost.

关键词： cold permafrost climate change thawing northern Alaska

The Influence of Different thawing Rates on the Mechanical Properties of the Cryopreserved Rabbit Arteries

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Biomedical Engineering(English Edition) 2003年第3期12卷 103-110页

作者： SHU Zhi-quan 1, HE Li-qun 1, WANG Pei-tao 1, DING Wei-ping 1, GAO Da-yong 1,2

The cryopreservation of rabbit arteries has been discussed by many researchers. But most of them focused on the cryoprotective agents and cooling process. The analysis of thawing process is not adequate. In this paper, we compared 4 convenient thawing methods and measured the mechanical properties of the cryopreserved arteries wall. The fresh arteries were also measured. From the data, we can see that the longitudinal and circumferential moduli and fracture stresses of the cryopreserved arteries were smaller than the data of fresh ones. The influence of warming rates on the moduli was not clear. But the longitudinal and circumferential fracture stresses of the cryopreserved arteries basically increased with the decrease of the thawing rates. The data of the arteries thawed in liquid nitrogen pre-cooled ice were the most similar to these of the fresh ones. So we can conclude that, in mechanics, gradually thawing can improve the cryopreservation of the arteries,and among the 4 thawing methods, the liquid nitrogen pre-cooled ice thawing method maybe is the best selection.

关键词： cryopreservation artery mechanical properties thawing rates

Ohmic thawing of Frozen Surimi

在线全文

学校读者我要写书评

暂无评论

Ohmic Thawing of Frozen Surimi

国际农业工程大会

作者： Akinori Noguchi Japan Inter. Research Center for Agric. Sci. Tsukuba Japan Ph.D.

＜正＞ A new ohmic thawing system was tested in the thawing of frozen surimi, in comparison with the conventional thawing technique. thawing rate, electric power and surimi gel strength were investigated. In the ohmic thawing, the voltage was set at 20 V and the frequency at 60 Hz. Salt solution in a concentration range of 0.1 % to 8.0 % was used as the electrode solution. In the conventional thawing, a 0 ℃chamber was used.

关键词： ohmic heating thawing frozen food surimi temperature distribution gel strength electric power

来源： cnki会议评论

在线全文

cnki会议

学校读者我要写书评

暂无评论

类石材料——灰泥的冻融过程(英文)

冰川冻土 2004年第S1期26卷 64-69页

作者： TakashiOno Yusuke Abe Hokkai-Gakuen University Sapporo Japan Graduate school of Hokkai-Gakuen University Sapporo Japan

Serious failure on the slope of rock ground can be caused by a cyclic action of freezing and thawing in the cold regions. The frost susceptibilityand the effect of freezing and thawing on the rock material, however, have notbeen well investigated. In order to find out the freezing effect on the rock materials, mortar specimens are frozen as a pseudo-rock material under the constant rate of freezing by means of controlling the temperature of both endsof specimen. The freezing process is given one-dimensionally to the cylindrical samples in the laboratory to simulate the in-situ freezing phenomena in the natural ground. Formation of ice lens, frost heave and water intake during freezing process are observed on the mortar specimen under constant freezing rate, which probably causes cracks or large deformation in the real rock ground. The valuesof the velocity of elastic wave propagation are compared before and after freezing process to estimate the degree of weathering due to freezing and thawing.

关键词： mortar cyclic action of freezing and thawing experiment weathering heave