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排序方式: 共有57条查询结果,搜索用时 15 毫秒
1.
M. C. Smith J. H. Massey J. Branson J. W. Epting D. Pennington P. L. Tacker J. Thomas E. D. Vories C. Wilson 《Irrigation Science》2007,25(2):141-147
Rice irrigation-water use was estimated in Mississippi (MS) and Arkansas (AR) in 2003 and 2004. Irrigation inputs were compared
on naturally sloping (i.e. contour-levee system) and mechanically graded fields. In MS, rice production consumed, on average,
895 mm water, but irrigation inputs were greatly affected by production system. Contour-levee systems accounted for 35% of
the production area and consumed 1,034 mm irrigation. Fields mechanically graded to a consistent slope of approximately 0.1%
(i.e. straight-levee systems) consumed 856 mm irrigation and accounted for 60% of the production area. Fields devoid of slope
(i.e. zero-grade system) accounted for 5% of the production area and consumed 382 mm irrigation. In AR, contour-levee rice
production consumed 789 mm compared to 653 mm with a straight-levee system. Using low pressure, thin wall (9–10 mil) disposable
irrigation tubing to deliver water to each paddy independently reduced irrigation inputs by 28% in MS and 11% in AR when compared
to a single-point (levee-gate) distribution system. 相似文献
2.
Riley MB Dumas JA Gbur EE Massey JH Mattice JD Mersie W Mueller TC Potter T Senseman SA Watson E 《Journal of agricultural and food chemistry》2005,53(13):5079-5083
An interlaboratory study was conducted to compare pesticide recovery from Empore C(18) and Speedisks C(18)XF solid phase extraction disks after shipping. Four pesticides were used for the comparison of the two disk extraction materials: atrazine, diazinon, metolachlor, and tebuconazole. These pesticides were chosen to provide a range of physiochemical properties. Water samples were extracted onto the disk types and shipped to a cooperating laboratory for elution and analysis. The mean recoveries from Empore disks were atrazine, 95%; diazinon, 91%; metolachlor, 92%; and tebuconazole, 83%. The recoveries from Speedisks C(18)XF were atrazine, 89%; diazinon, 87%; metolachlor, 86%; and tebuconazole, 79%. Means for each of the pesticides using the different disk types were not statistically different (alpha = 0.05), but results were more variable when using Speedisks C(18)XF as compared to Empore disks. Reasons for the increased variability are discussed, but overall results indicate that Speedisks C(18)XF could be used as an alternative to Empore disks. Speedisks C(18)XF are enclosed in a plastic housing, so they can be used more easily in remote sampling sites without the possibility of glassware breakage, no prefiltration of samples is needed, and there are realignment problems that can be associated with the Empore disks. 相似文献
3.
S Paul D J Volle C M Beach D R Johnson M J Powell R J Massey 《Science (New York, N.Y.)》1989,244(4909):1158-1162
Vasoactive intestinal peptide (VIP) labeled with 125I, [Tyr10-125I]VIP, can be hydrolyzed by immunoglobulin G (IgG) purified from a human subject, as judged by trichloroacetic acid precipitation and reversed-phase high-performance liquid chromatography (HPLC). The hydrolytic activity was precipitated by antibody to human IgG, it was bound by immobilized protein G and showed a molecular mass close to 150 kilodaltons by gel filtration chromatography, properties similar to those of authentic IgG. The Fab fragment, prepared from IgG by papain treatment, retained the VIP hydrolytic activity of the IgG. Peptide fragments produced by treatment of VIP with the antibody fraction were purified by reversed-phase HPLC and identified by fast atom bombardment-mass spectrometry and peptide sequencing. The scissile bond in VIP deduced from these experiments was Gln16-Met17. The antibody concentration (73.4 fmol per milligram of IgG) and the Kd (0.4 nM) were computed from analysis of VIP binding under conditions that did not result in peptide hydrolysis. Analysis of the antibody-mediated VIP hydrolysis at varying concentrations of substrate suggested conformity with Michaelis-Menton kinetics (Km). The values for Km (37.9 X 10(-9) M) and the turnover number kcat (15.6 min-1) suggested relatively tight VIP binding and a moderate catalytic efficiency of the antibody. 相似文献
4.
W E Massey 《Science (New York, N.Y.)》1989,245(4921):915-921
It is argued that the need to improve science education should be a national priority. Ways are suggested by which the federal government and the scientific community, working together, can address this issue. It is recommended that scientists, engineers, and educators make a significant personal and institutional commitment to participate in science education activities, and that the President of the United States provide the personal leadership to generate a national commitment to the improvement of education at all levels. 相似文献
5.
Mental rotation of the neuronal population vector 总被引:19,自引:0,他引:19
A P Georgopoulos J T Lurito M Petrides A B Schwartz J T Massey 《Science (New York, N.Y.)》1989,243(4888):234-236
A rhesus monkey was trained to move its arm in a direction that was perpendicular to and counterclockwise from the direction of a target light that changed in position from trial to trial. Solution of this problem was hypothesized to involve the creation and mental rotation of an imagined movement vector from the direction of the light to the direction of the movement. This hypothesis was tested directly by recording the activity of cells in the motor cortex during performance of the task and computing the neuronal population vector in successive time intervals during the reaction time. The population vector rotated gradually counterclockwise from the direction of the light to the direction of the movement at an average rate of 732 degrees per second. These results provide direct, neural evidence for the mental rotation hypothesis and indicate that the neuronal population vector is a useful tool for "reading out" and identifying cognitive operations of neuronal ensembles. 相似文献
6.
J F Levine M J Dykstra W L Nicholson R L Walker G Massey H J Barnes 《Research in veterinary science》1990,48(1):64-69
Borrelia anserina (Sakharoff) was successfully grown in a liquid medium (Barbour-Stoenner-Kelly) for 39 passages. By the 12th serial passage in medium, infectivity of B anserina for chicks was lost. Electron microscopy did not reveal structural differences between non-infective and infective cultured organisms. Changes in the protein profiles were found by electrophoresis as the organisms were passed in culture. 相似文献
7.
8.
Materials performance in structural applications is often restricted by a transition from ductile response to brittle fracture with decreasing temperature. This transition is currently viewed as being controlled either by dislocation mobility or by the nucleation of dislocations. Fracture experiments on tungsten single crystals reported here provide evidence for the importance of dislocation nucleation for the fracture toughness in the semibrittle regime. However, it is shown that the transition itself, in general, is controlled by dislocation mobility rather than by nucleation. 相似文献
9.
Insensitivity of soil biological communities to phosphorus fertilization in intensively managed grassland systems 下载免费PDF全文
Efficient soil P cycling is essential for promoting optimal and sustainable grassland growth. The soil biological community is regarded as an important source of available P to the plant community. However, the effects of P fertilization on the soil biota are unclear. This study aimed to investigate the effects of P fertilization on plant and soil biological communities in two intensively managed grassland sites that had been receiving mineral‐based P fertilization over a 14‐year period. Both pastures had been frequently cut and harvested for plant material and had received only inorganic fertilizers from the establishment of the trial. Both sites were sampled four times from October 2009 to April 2011 and plant and a range of soil biological parameters were determined at each sampling period. The main findings of this study showed that soil chemical measures, such as labile inorganic P and total P concentrations, and plant yield and P contents responded as expected to P fertilization. However, all soil biological parameters either showed no response or inconsistent responses to P fertilization over the experimental period. This study indicates that intensive management regimes, for example intensive plant harvesting and fertilizer regimes, appear to override the relationship between plant and soil biological communities with respect to their response to P fertilization, and thus their productivity is apparently not predicated upon biotic activity. 相似文献
10.
P. A. Massey R. E. Creamer R. P. O. Schulte M. J. Whelan K. Ritz 《Biology and Fertility of Soils》2013,49(8):1189-1201
The application of phosphorus (P)-based fertiliser to agricultural soils can result in a skewed vertical distribution of P down the soil profile, since the element tends to accumulate at the soil surface. Such accumulation can have detrimental effects on the environment, as the erosion of surface soil can facilitate the transfer of large quantities of P out of the field into water bodies. Earthworm and plant communities are intricately linked to vertical nutrient distributions in soil, with both communities either facilitating or negating the incorporation of nutrients into the soil matrix. This study aimed to investigate the effect of earthworm presence, plant community structure and fertiliser type to affect the distribution of nutrients in experimental mesocosms; with particular emphasis on the vertical distribution of P. Mesocosms were designed to simulate a soil which has a high P concentration at the surface compared to further down the soil profile. It was hypothesised that the presence of earthworms would facilitate the incorporation of P into the soil matrix and the presence of a more botanically diversity community would assimilate a greater quantity of soil nutrients. After 1 year, mesocosms were deconstructed into five depth ranges, and the distribution of nutrients were modelled and analysed. Results indicated that the presence of earthworms did redistribute soil nutrients from the surface into the matrix beneath. This redistribution was apparent from a reduction in nutrient concentrations in the 0–1 cm depth range. The presence of a more botanically diverse community not only assimilated greater soil nutrient concentrations, but also promoted a less even vertical distribution of soil nutrients, demonstrating the importance of soil biota and plant diversity in the redistribution of soil nutrients. 相似文献