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81.
B L Hart 《Veterinary Clinics of North America: Food Animal Practice》1987,3(2):383-391
The behavior of the sick animal is not necessarily a result of physical debilitation; it can be viewed as part of a highly organized adaptive strategy that is at times critical to survival if the animal were living in the wild state. Domestic ruminants appear to have retained this behavioral mode when they are sick. This article brings together several lines of current research about depression, appetite control, and the role of fever in facilitating an animal's ability to combat viral and bacterial infections. 相似文献
82.
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84.
The Earth as a seismic absorption band 总被引:1,自引:0,他引:1
Attenuation of seismic waves indicates that the earth is not perfectly elastic. Dispersion accompanying absorption gives frequency-dependent "elastic" moduli, a fact that must be taken into account when inverting seismic data. Normal mode data are reinverted after correcting for absorption. The correction removes the discrepancy between body wave and free oscillation interpretations of earth structure. 相似文献
85.
A computer program that uses artificial intelligence techniques has successfully identified the location of a porphyry molybdenum deposit. Given geological maps of readily available predrilling exploration data for Mount Tolman in Washington State and using rules obtained from a porphyry molybdenum exploration specialist, the program (called PROSPECTOR) identified the location of previously unknown ore-grade mineralization. This appears to be the first reported determination of the location of mineralization by such a computer-based approach. 相似文献
86.
Fleischer RL Haines EL Hanneman RE Hart HR Kasper JS Lifshin E Woods RT Price PB 《Science (New York, N.Y.)》1970,167(3918):568-571
Particle tracks in Apollo 11 samples are dominantly of cosmic ray and solar origin: primary galactic and solar flare particles, likely spallation recoil tracks, and possible solar-wind heavy particles. The energy spectrum of irongroup nuclei is inferred from track density gradients in surface layers, and a limit of < 10(-7) centimeter per year is deduced for the surface erosion rate. From cosmic ray tracks in rock and core samples it is clear that the lunar soil is stirred often during each few million years. X-rays reveal augite, anorthite, olivine, ilmenite, troilite, nonmeteoritic iron, and assorted glasses, but no major structural damage. Hydrogen, helium, and other gases in the fines are compatible with expected solar wind ratios. 相似文献
87.
The Apollo helmets are being used to record the dose of heavy particles to which astronauts are exposed on space missions. An improved method for examining and identifying the etched tracks of heavy charged particles consists of replicating tracks and measuring the etching rate as a function of position along the track. Tracks have been observed in Apollo helmets that correspond to ionized atoms heavier than iron. 相似文献
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T L Doering J Raper L U Buxbaum S P Adams J I Gordon G W Hart P T Englund 《Science (New York, N.Y.)》1991,252(5014):1851-1854
Trypanosoma brucei, the protozoan parasite responsible for African sleeping sickness, evades the host immune response through the process of antigenic variation. The variant antigen, known as the variant surface glycoprotein (VSG), is anchored to the cell surface by a glycosyl phosphatidylinositol (GPI) structure that contains myristate (n-tetradecanoate) as its only fatty acid component. The utilization of heteroatom-containing analogs of myristate was studied both in a cell-free system and in vivo. Results indicated that the specificity of fatty acid incorporation depends on chain length rather than on hydrophobicity. One analog, 10-(propoxy)decanoic acid, was highly toxic to trypanosomes in culture although it is nontoxic to mammalian cells. 相似文献
90.
Tim G. B. Hart 《Agriculture and Human Values》2011,28(3):321-333
Technologies and services provided to resource-poor farmers need to be relevant and compatible with the context in which they
operate. This paper examines the contribution of extension services to the food security of resource-poor farmers in a rural
village in South Africa. It considers these in terms of the local context and the production of African vegetables in household
food plots. A mixture of participatory, qualitative and quantitative research tools, including a household survey, is used
to argue that local production practices contribute more to food security requirements than the extension services. This is
because of the ability of African vegetables to grow relatively well in semi-arid areas where other exotic plants do not,
their ability to provide at least two foodstuffs during their life cycle, and the ability of either the fruit or the leaves,
or both, to be dried and stored for consumption in the winter months. These crops can make a significant contribution in terms
of household food security, but a number of social and agroecological factors are constraining their production and placing
their availability under threat. Despite this, the extension services remain focused on certain activities within vegetable
garden projects, even when these are not meeting their proposed purpose—food security by means of cash-crop production. The
paper concludes that social and agroecological constraints could be improved if the extension services were changed. This
could include the use of context specific and low-cost technologies to ensure that these crops are able to increase their
contribution to household food security for resource-poor farmers in semi-arid areas. 相似文献