Obsidian trade at san lorenzo tenochtitlan, Mexico     

Cobean RH  Coe MD  Perry EA  Turekian KK  Kharkar DP 《Science (New York, N.Y.)》1971,174(4010):666-671

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The end of a Chilean institute     

Barbeito L  Chun J  Binder LI  Neto VM  Perry G  Scazzochio C  Violini G 《Science (New York, N.Y.)》2005,308(5723):792-793

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Patients' voices: the powerful sound in the stem cell debate     

Perry D 《Science (New York, N.Y.)》2000,287(5457):1423

Millions of patients may benefit from the applications of stem cell research, although there is disagreement about whether public funds should be used to develop the science. Patients have been key to winning political support. Acting as advocates, they have contended that public investment will speed the research and bring accountability to biomedical technology. A political dispute about the new research, which holds the potential for cures to devastating diseases and to foster healthy aging, shows the need to respect public sensibilities and to court public approval, as well as the importance of involving patients in debates where the methods of biomedical discoveries and ethical beliefs collide.  相似文献   

Humble Oil Company Radiocarbon Dates I     

Brannon HR  Daughtry AC  Perry D  Simons LH  Whitaker WW  Williams M 《Science (New York, N.Y.)》1957,125(3239):147-150

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Dielectric siphons     

Jones TB  Perry MP  Melcher JR 《Science (New York, N.Y.)》1971,174(4015):1232-1233

The normally weak polarization force density, exerted on insulating dielectric liquids by a nonuniform electric field, is enhanced if high pressures are used. The result is a new class of orientation and guiding structures for liquids: electric "walls" contain the liquid. The dielectric siphon is an example of such a system. A simple laminar flow model for the device successfully describes the operation of the siphon.  相似文献   

Homocystinuria: excretion of a new sulfur-containing amino Acid in urine     

Perry TL  Hansen S  Bar HP  Macdougall L 《Science (New York, N.Y.)》1966,152(3723):776-778

An unusual homocysteine-containing compound, 5-amino-4-imidazolecarboxamide-5'-S-homocysteinylriboside, was isolated from the urine of a child with homocystinuria and detected in the urines of six homocystinurics. Its metabolic origin is not clear, and the data suggest the existence in man of now unknown alternate pathways for the metabolism of methionine and of purines.  相似文献   

Paleomagnetic record of a geomagnetic field reversal from late miocene mafic intrusions, southern nevada     

Ratcliff CD  Geissman JW  Perry FV  Crowe BM  Zeitler PK 《Science (New York, N.Y.)》1994,266(5184):412-416

Late Miocene (about 8.65 million years ago) mafic intrusions and lava flows along with remagnetized host rocks from Paiute Ridge, southern Nevada, provide a high-quality paleomagnetic record of a geomagnetic field reversal. These rocks yield thermoremanent magnetizations with declinations of 227 degrees to 310 degrees and inclinations of -7 degrees to 49 degrees , defining a reasonably continuous virtual geomagnetic pole path over west-central Pacific longitudes. Conductive cooling estimates for the intrusions suggest that this field transition, and mafic magmatism, lasted only a few hundred years. Because this record comes principally from intrusive rocks, rather than sediments or lavas, it is important in demonstrating the longitudinal confinement of the geomagnetic field during a reversal.  相似文献   

Irrigation reliability and the productivity of water: A proposed methodology using evapotranspiration mapping   总被引：1，自引：0，他引：1  

Chris Perry 《Irrigation and Drainage Systems》2005,19(3-4):211-221

Irrigation is the dominant user of water worldwide, but provision of potable water and water for industry are higher priorities and give higher social and economic returns. Irrigation will continue to lose water to competing sectors and the productivity of irrigation systems (since food demand continues to grow) remains a central issue in water management. Performance assessment of irrigation has traditionally been difficult when based on field measurements of flows, deliveries and depths over large areas. Furthermore, performance measures have shifted from narrow engineering indicators to broader productivity issues of production achieved per unit of water consumed. Remote sensing, applied to the estimation of evapotranspiration (ET) over large areas, provides analysts of irrigation systems with extraordinary new tools for the objective assessment of consumption and production – constituting a quantum leap in the assessment of irrigation system performance. Awareness and utilisation of these tools is spreading, but important areas remain to be “converted” from traditional approaches that rely on an array of estimated parameters. The next challenge for remote sensing will be to map the frontier between the reliability of the irrigation service and the productivity achieved. Reliability provides the inducement for farmers to invest in higher productivity – to the benefit of themselves and society – and understanding better how the individual maximises profits within an uncertain irrigation environment can provide important guidance to managers and system designers.  相似文献   

On the variability of simulated source-receptor relationships for sulfur deposition     

Perry J. Samson  Mark Fernau  Patricia Allison 《Water, air, and soil pollution》1986,30(3-4):801-813

The use of Lagrangian models to estimate source-receptor relationships for ambient SO₄ ⁼ concentrations and S deposition has become fairly widespread over the past several years. This paper addresses the sensitivity of long-term simulations of a Lagrangian S transport and deposition model to actual variations in SO₂ emissions and meteorological conditions. The variations of predicted source-receptor relationships due to (1) the inclusion of day to day variations in emissions strength as opposed to the use of the annual average daily emission rate and (2) year-to-year variations in meteorological conditions were studied to identify causes of uncertainty in a Lagrangian model. The results suggested that adding information on day to day emission variations for a specific point source resulted in variations in estimated S wet deposition of the order of only 20% within 500 km of the source.Year-to-year variations in meteorological conditions, on the other hand, resulted in variations in predicted S wet deposition of the order of 50% for some receptors. The variation in estimated source-receptor relationships for a given source/receptor combination was found to range as high as 70% over a 5-yr modeling period.  相似文献   

美国控制土壤侵蚀的经验     

John.W.Peterson PE 《中国水土保持》2002,(7)

对美国土壤侵蚀的历史及其后果的研究十分有意义。自美国殖民时期和 1 8世纪建国开始 ,有许多文献表明 ,最早期的殖民者已明了由于人们耕种土地产生的土壤侵蚀所引发的问题 ,也有意做点什么来减少土壤侵蚀。 1 86 1年各州之间发生战争 ,有记录表明 ,河流被来自管理不善的农田的泥沙淤塞。由于认为土地资源取之不尽 ,当时的农民常常是当农地变得无法耕种时 ,就打起行装向西部新的土地转移。然而很快当全国从东海岸到西海岸都居住有人后 ,这种做法就行不通了。2 0世纪 30年代的大平原“沙尘暴”及随之而来的美国经济大萧条 ,为罗斯福政府创造…  相似文献