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Susan L Steinberg Gerard J Kluitenberg Scott B Jones Nihad E Daidzic Lakshmi N Reddi Ming Xiao Markus Tuller Rebecca M Newman Dani Or J Iwan D Alexander 《Journal of the American Society for Horticultural Science》2005,130(5):767-774
Baked ceramic aggregates (fritted clay, arcillite) have been used for plant research both on the ground and in microgravity. Optimal control of water and air within the root zone in any gravity environment depends on physical and hydraulic properties of the aggregate, which were evaluated for 0.25-1-mm and 1-2-mm particle size distributions. The maximum bulk densities obtained by any packing technique were 0.68 and 0.64 g cm-3 for 0.25-1-mm and 1-2-mm particles, respectively. Wettable porosity obtained by infiltration with water was approximately 65%, substantially lower than total porosity of approximately 74%. Aggregate of both particle sizes exhibited a bimodal pore size distribution consisting of inter-aggregate macropores and intra-aggregate micropores, with the transition from macro- to microporosity beginning at volumetric water content of approximately 36% to 39%. For inter-aggregate water contents that support optimal plant growth there is 45% change in water content that occurs over a relatively small matric suction range of 0-20 cm H2O for 0.25-1-mm and 0 to -10 cm H2O for 1-2-mm aggregate. Hysteresis is substantial between draining and wetting aggregate, which results in as much as a approximately 10% to 20% difference in volumetric water content for a given matric potential. Hydraulic conductivity was approximately an order of magnitude higher for 1-2-mm than for 0.25-1-mm aggregate until significant drainage of the inter-aggregate pore space occurred. The large change in water content for a relatively small change in matric potential suggests that significant differences in water retention may be observed in microgravity as compared to earth. 相似文献
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A technique has been evolved and standardized for evaluating the cell-mediated immune (CMI) response in cattle induced by 2,4-dinitrochlorobenzene (DNCB). Six healthy cross-bred Jersey cows were used. The dose and the number of applications for primary sensitization and the challenge dose after the 14th day have been standardized. The gross and histological pictures of the CMI response shown by these cattle are described in detail and their usefulness in assessing the CMI response in various disease conditions including tumour is indicated. 相似文献
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The immunological response of the Ln subiliacus (externus) in cattle bearing ethmoid carcinoma was studied. The lymph node was stimulated in vivo by I/D administration of tumour antigen and Bacillus Calmette-Guerin and the changes in the lymph node were studied at 3-day intervals up to 15 days. The histological changes in the lymph node were assessed and the functional activity of the activated macrophages in the lymph node impression smears was evaluated using Nitroblue tetrazolium salt reduction test. Similar studies were also undertaken in age-matched healthy nontumour bearing cattle. On stimulation with BCG and tumour antigen there was stimulation of the T cell dependent area. However, the response to the tumour antigen was quicker but shorter in duration compared with that to BCG. The response in healthy animals was proportionately much less. The studies indicated that tumour-bearing animals which were mostly in stage II were immunocompetent. 相似文献
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Discontinuous pore fluid distribution under microgravity--KC-135 flight investigations 总被引：1，自引：0，他引：1
Reddi LN Xiao M Steinberg SL 《Soil Science Society of America journal. Soil Science Society of America》2005,69(3):593-598
Designing a reliable plant growth system for crop production in space requires the understanding of pore fluid distribution in porous media under microgravity. The objective of this experimental investigation, which was conducted aboard NASA KC-135 reduced gravity flight, is to study possible particle separation and the distribution of discontinuous wetting fluid in porous media under microgravity. KC-135 aircraft provided gravity conditions of 1, 1.8, and 10(-2) g. Glass beads of a known size distribution were used as porous media; and Hexadecane, a petroleum compound immiscible with and lighter than water, was used as wetting fluid at residual saturation. Nitrogen freezer was used to solidify the discontinuous Hexadecane ganglia in glass beads to preserve the ganglia size changes during different gravity conditions, so that the blob-size distributions (BSDs) could be measured after flight. It was concluded from this study that microgravity has little effect on the size distribution of pore fluid blobs corresponding to residual saturation of wetting fluids in porous media. The blobs showed no noticeable breakup or coalescence during microgravity. However, based on the increase in bulk volume of samples due to particle separation under microgravity, groups of particles, within which pore fluid blobs were encapsulated, appeared to have rearranged themselves under microgravity. 相似文献
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Studies on frequency and depth of irrigation for groundnut (Arachis hypogaea) for two summer seasons at Tirupati campus of Andhra Pradesh Agricultural University, India showed that, keeping the total quantity of applied irrigation water almost the same, high frequency irrigation gave the highest yield. For each irrigation frequency, highest yields were obtained when the depth of water applied was equal to that lost in evapotranspiration. Low irrigation frequency and low depth of irrigation resulted in lower yields. Increase in yield with increase in frequency and depth of water was due to optimum available moisture and nutrients in the root zone throughout the crop period. The results from the trial indicated that on sandy loam soils of poor water retentive capacity, high yields can be obtained with frequent irrigations with the depth of water applied equal to that lost in evapotranspiration. 相似文献
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