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Observing that a sequence of negative logarithms of 1‐year survival probabilities displays a linear relationship with the sequence of corresponding terms with a time lag of a certain number of years, we propose a simple linear regression to model and forecast mortality rates. Our model assuming the linearity between two mortality sequences with a time lag each other does not need to formulate the time trends of mortality rates across ages for mortality prediction. Moreover, the parameters of our model for a given age depend on the mortality rates for that age only. Therefore, whether the span of the study ages with the age included is widened or shortened will not affect the results of mortality fitting and forecasting for that age. In the empirical testing, the regression results using the mortality data for the UK, USA and Japan show a satisfactory goodness of fit, which convinces us of the appropriateness of the linear assumption. Empirical illustrations further show that our model's performances of fitting and forecasting mortality rates are quite satisfactory compared with the existing well‐known mortality models. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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High-quality electron beams from a laser wakefield accelerator using plasma-channel guiding 总被引:2,自引:0,他引:2
Geddes CG Toth CS Van Tilborg J Esarey E Schroeder CB Bruhwiler D Nieter C Cary J Leemans WP 《Nature》2004,431(7008):538-541
Laser-driven accelerators, in which particles are accelerated by the electric field of a plasma wave (the wakefield) driven by an intense laser, have demonstrated accelerating electric fields of hundreds of GV m(-1) (refs 1-3). These fields are thousands of times greater than those achievable in conventional radio-frequency accelerators, spurring interest in laser accelerators as compact next-generation sources of energetic electrons and radiation. To date, however, acceleration distances have been severely limited by the lack of a controllable method for extending the propagation distance of the focused laser pulse. The ensuing short acceleration distance results in low-energy beams with 100 per cent electron energy spread, which limits potential applications. Here we demonstrate a laser accelerator that produces electron beams with an energy spread of a few per cent, low emittance and increased energy (more than 10(9) electrons above 80 MeV). Our technique involves the use of a preformed plasma density channel to guide a relativistically intense laser, resulting in a longer propagation distance. The results open the way for compact and tunable high-brightness sources of electrons and radiation. 相似文献
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Beddington J Cooper CL Field J Goswami U Huppert FA Jenkins R Jones HS Kirkwood TB Sahakian BJ Thomas SM 《Nature》2008,455(7216):1057-1060
Countries must learn how to capitalize on their citizens' cognitive resources if they are to prosper, both economically and socially. Early interventions will be key. 相似文献
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Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 st1\:*{behavior:url(#ieooui) } /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} Coyote ( Canis latrans ) scats from two southern Utah deer herd units were collected and analyzed to establish diet selection. The category showing the most consistent frequency of occurrence was mule deer Odocoileus hemionus ; lagomorphs were next. Formal statistical analysis revealed that the only significant difference in coyote food habits between herd units was in the frequency of rabbits eaten. These data suggest that coyotes in this region of southern Utah show a comparatively higher preference for mule deer but, at the same time, do not eat deer in proportion to the frequency of their occurrence. 相似文献
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王月姣 《中南民族大学学报(自然科学版)》2003,22(4):56-57
讨论了Microsoft C语言中调用MASM 5.0汇编语言程序的方法,并针对一些易出现的问题,如程序接口部分的要求,C语言与汇编程序间参数的传递,寄存器的使用等,提出了解决办法. 相似文献
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We analyzed population trend data during 1991–2004 for the Bruneau hot springsnail ( Pyrgulopsis bruneauensis ) from rangewide hot spring surveys completed along 4 km of Bruneau River. The objectives of this study were to analyze population trends and assess other measured parameters, such as water temperature, specific conductance, and groundwater decline, for changes that may influence population trends. We used simple linear regression to determine significant relationships between measured parameters. Total numbers of hot springs surveyed in the 4-km reach are declining at a rate of ~5 hot springs per year, and numbers of hot springs containing P. bruneauensis in the same reach are declining at a rate of 3.75 per year. We found that the decline of hot springs with and without P. bruneauensis was significantly related to the decline of the thermal aquifer which underlies this area. 相似文献
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Chemical speciation drives hydrothermal vent ecology 总被引:27,自引:0,他引:27
Luther GW Rozan TF Taillefert M Nuzzio DB Di Meo C Shank TM Lutz RA Cary SC 《Nature》2001,410(6830):813-816
The physiology and biochemistry of many taxa inhabiting deep-sea hydrothermal vents have been elucidated; however, the physicochemical factors controlling the distribution of these organisms at a given vent site remain an enigma after 20 years of research. The chemical speciation of particular elements has been suggested as key to controlling biological community structure in these extreme aquatic environments. Implementation of electrochemical technology has allowed us to make in situ measurements of chemical speciation at vents located at the East Pacific Rise (9 degrees 50' N) and on a scale relevant to the biology. Here we report that significant differences in oxygen, iron and sulphur speciation strongly correlate with the distribution of specific taxa in different microhabitats. In higher temperature (> 30 degrees C) microhabitats, the appreciable formation of soluble iron-sulphide molecular clusters markedly reduces the availability of free H2S/HS- to vent (micro)organisms, thus controlling the available habitat. 相似文献
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