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排序方式: 共有425条查询结果,搜索用时 31 毫秒
31.
Revenue risk management, risk aversion and the use of Livestock Gross Margin for Dairy Cattle insurance 总被引:1,自引:0,他引:1
Mayuri Valvekar Jean P. Chavas Brian W. Gould Victor E. Cabrera 《Agricultural Systems》2011,104(9):671-678
The Livestock Gross Margin Insurance for Dairy Cattle is a federally reinsured insurance program that enables US dairy producers to establish minimum levels of milk income net of feed cost. Given the structure of this program there are an infinite number of possible contract designs based on the choice of deductible level and proportion of production insured. Adding to this complexity, producers vary in their risk preferences, which affect the incentive to insure their margin. It is unclear as to how producers may adopt this program for revenue risk management. This paper investigates the interplay between producer risk preferences, contract design and the subsidization of premium in determining program coverage. We undertook this analysis within an expected utility framework. Optimal contracts under different rates of constant relative rate of risk aversion and subsidies were analyzed using a nonlinear optimization model. We found that total optimal coverage increased significantly with the level of risk of aversion at lower deductibles but as deductible level increased, the level of risk aversion had a lesser impact on total optimal coverages. As expected, at the same deductible and risk aversion levels, inclusion of a premium subsidy increased the total optimal coverage. 相似文献
32.
Imaging crystals, polymers, and processes in water with the atomic force microscope 总被引:45,自引:0,他引:45
B Drake C B Prater A L Weisenhorn S A Gould T R Albrecht C F Quate D S Cannell H G Hansma P K Hansma 《Science (New York, N.Y.)》1989,243(4898):1586-1589
The atomic force microscope (AFM) can be used to image the surface of both conductors and nonconductors even if they are covered with water or aqueous solutions. An AFM was used that combines microfabricated cantilevers with a previously described optical lever system to monitor deflection. Images of mica demonstrate that atomic resolution is possible on rigid materials, thus opening the possibility of atomic-scale corrosion experiments on nonconductors. Images of polyalanine, an amino acid polymer, show the potential of the AFM for revealing the structure of molecules important in biology and medicine. Finally, a series of ten images of the polymerization of fibrin, the basic component of blood clots, illustrate the potential of the AFM for revealing subtle details of biological processes as they occur in real time. 相似文献
33.
The formyl cation, HCO+, has long been believed to be an important intermediate in the chemistry of carbon monoxide (CO) in acidic environments, but its spectroscopic observation in solution has been elusive. This species was generated by the reaction of CO with the liquid superacid hydrofluoric acid-antimony pentafluoride (HF-SbF5) under pressure and was observed by nuclear magnetic resonance and infrared spectroscopy. Equilibria between CO in the gas phase, CO dissolved in HF-SbF5, the SbF5 adduct of formyl fluoride, and HCO+ associated with several equilibrating anions of the type [SbxF5x+1]- are proposed to describe the system. 相似文献
34.
The earliest known response of eggs to sperm in many species is a change in egg membrane potential. However, for no species is it known what components of the sperm cause the opening of the egg plasma membrane channels. Protein isolated from sperm acrosomal granules of the marine worm Urechis caused electrical responses in oocytes with the same form, amplitude, and ion dependence as the fertilization potentials induced by living sperm. Sperm initiated fertilization potentials in oocytes when sperm-oocyte fusion, but not binding, was inhibited by clamping oocyte membrane potentials to positive values. Acrosomal protein also initiated electrical responses in clamped oocytes. These results support the hypothesis that it is the sperm acrosomal protein that opens ion channels in the oocyte membrane. 相似文献
35.
Gaudi BS Bennett DP Udalski A Gould A Christie GW Maoz D Dong S McCormick J Szymanski MK Tristram PJ Nikolaev S Paczynski B Kubiak M Pietrzynski G Soszynski I Szewczyk O Ulaczyk K Wyrzykowski L;OGLE Collaboration Depoy DL Han C Kaspi S Lee CU Mallia F Natusch T Pogge RW Park BG;MuFUN Collaboration Abe F Bond IA Botzler CS Fukui A Hearnshaw JB Itow Y Kamiya K Korpela AV Kilmartin PM Lin W Masuda K Matsubara Y Motomura M Muraki Y Nakamura S Okumura T Ohnishi K Rattenbury NJ Sako T Saito T Sato S 《Science (New York, N.Y.)》2008,319(5865):927-930
Searches for extrasolar planets have uncovered an astonishing diversity of planetary systems, yet the frequency of solar system analogs remains unknown. The gravitational microlensing planet search method is potentially sensitive to multiple-planet systems containing analogs of all the solar system planets except Mercury. We report the detection of a multiple-planet system with microlensing. We identify two planets with masses of approximately 0.71 and approximately 0.27 times the mass of Jupiter and orbital separations of approximately 2.3 and approximately 4.6 astronomical units orbiting a primary star of mass approximately 0.50 solar mass at a distance of approximately 1.5 kiloparsecs. This system resembles a scaled version of our solar system in that the mass ratio, separation ratio, and equilibrium temperatures of the planets are similar to those of Jupiter and Saturn. These planets could not have been detected with other techniques; their discovery from only six confirmed microlensing planet detections suggests that solar system analogs may be common. 相似文献
36.
Rats trained in a one-way avoidance situlation were made tolerant to the depressant effects of Delta(9)-tetrahydrocannabinol. Ethyl alcohol (3.2 grams per kilogram, intraperitoneally) did not greatly affect rats that were tolerant to delta(9)tetrahydrocannabinol but depressed the behavior of nontolerant rats. Rats made tolerant to ethyl alcohol were less affected by Delta(9)-tetrahydrocannabinol. 相似文献
37.
38.
PC Sereno DB Dutheil M Iarochene HCE Larsson GH Lyon PM Magwene CA Sidor DJ Varricchio JA Wilson 《Science (New York, N.Y.)》1996,272(5264):986-991
Late Cretaceous (Cenomanian) fossils discovered in the Kem Kem region of Morocco include large predatory dinosaurs that inhabited Africa as it drifted into geographic isolation. One, represented by a skull approximately 1.6 meters in length, is an advanced allosauroid referable to the African genus Carcharodontosaurus. Another, represented by a partial skeleton with slender proportions, is a new basal coelurosaur closely resembling the Egyptian genus Bahariasaurus. Comparisons with Cretaceous theropods from other continents reveal a previously unrecognized global radiation of carcharodontosaurid predators. Substantial geographic differentiation of dinosaurian faunas in response to continental drift appears to have arisen abruptly at the beginning of the Late Cretaceous. 相似文献
39.
40.
Gould D Pettitt L McLaughlin B Holmes N Forman O Thomas A Ahonen S Lohi H O'Leary C Sargan D Mellersh C 《Veterinary ophthalmology》2011,14(6):378-384
Primary lens luxation (PLL) is a well-recognized, painful and potentially blinding inherited ocular condition in dogs. We screened PLL-affected dogs of 30 different breeds, to identify those which carried a previously described c.1473+1 G>A mutation in ADAMTS17 that is associated with PLL in Miniature Bull terriers, Lancashire Heelers, and Jack Russell terriers. This ADAMTS17 mutation was identified in PLL-affected dogs from 14 additional breeds. PLL-affected dogs from some breeds (most notably the Shar pei and the Brittany spaniel) did not carry the G1473+1A ADAMTS17 mutation, indicating they must suffer from a genetically distinct form of the condition. We also estimated the frequency of this ADAMTS17 mutation in some of the breeds. Our findings indicate the mutation segregates in a large number of different breeds of dog, many of which are terriers or breeds with terrier co-ancestry, but some of which have more diverse origins. Our results also indicate that the mutation is present at high frequency within most of the breeds in which it segregates. In the miniature bull terrier breed estimates of mutation frequency ranged from 0.27 to 0.39, corresponding to 7.3-15.2% PLL-affected dogs in this breed. We also identified an increased risk of PLL associated with heterozygosity at ADAMTS17, suggesting that carriers carry a low risk of developing PLL. 相似文献