Stability in ecological microcosm

In attempt to clarify the significance of interspecific interactions in evolutionary ecology, the growth characteristics of bacterial populations sampled from ecological microcosms which act as fairly realistic models of natural ecosystems were investigated, with a particular emphasis on the ability of a system to remain reasonably stable in the genetic composition in spite of the occurrences of various mutants from native strains. Newly-emerged mutants in a community are inhibited in their multiplication, or excluded by a network of many elementary interactions between the different species of the populations, thus preserving the traits of the parental strains in a community. The interactions in the form of a network may be viewed as evidence for a maintenance of stability in a community.     

可饱和吸收体Cr:YAG做被动调Q元件时的选模作用

研究了可饱和吸收体Cr:YAG做被动调Q元件时所表现出的选模作用.理论分析和实验表明:Cr:YAG晶体的“动态光阑”效果确保了激光器的基横模输出;而不同纵模形成振荡的难易差别也为脉冲单纵模的实现提供了条件.Cr:YAG晶体的选模作用在实践中应得到充分的利用.     

Statistical inference with partial prior information based on a Gauss-type inequality

Potter and Anderson [1] have developed a Bayesian decision procedure requiring the specification of a class of prior distributions restricted to have a minimal probability content for a given subset of the parameter space. They do not, however, provide a method for the selection of that subset. We show how a generalization of Gauss' inequality can be used to determine the relevant parameter subset.     

一种选优排序方案及模型

本文以多条件多因素的选优排序问题为背景 ,利用层次分析法给出了一种科学的选优方案及模型     

Estimation of the degree of differencing of an ARIMA process

Summary A method of estimating the degree of differencing of an ARIMA process is proposed. This is based on fitting an AR model to the original and to each differenced series and calculating the residual sum of squares. As an application, we suggest an identification method of an ARI (p, d) process combining our method of estimating the degree of differencing with Akaike's Information Criterion.     

Mode Selection for a Terahertz Gyrotron Based on a Pulse Magnet System

The TE_6,11 mode has been selected as a candidate for the second harmonic operation of a terahertz gyrotron at 1007.68 GHz. The predicted efficiency is 8.6 percent for the output power 0.38 kW. Time-dependent, multi-mode calculations have been carried out to investigate stability of a single-mode operation at second harmonic. It has been found that with the beam current 0.111 A and the magnetic field 19.282 T the second harmonic operation in the TE_6,11 mode is possible.     

Calculated T1 images derived from a partial saturation-inversion recovery pulse sequence with adiabatic fast passage

Calculated T1 images of the head and abdomen have been obtained using an alternating partial saturation-inversion recovery pulse sequence. Timing parameters were adjusted to yield optimum T1 contrast-to-noise ratio for this sequence for the range of T1 studied. Adiabatic fast passage (AFP) was implemented for the nonselective inverting pulse, to reduce the sensitivity of the measurement to RF and static field inhomogeneity. A nonlinear frequency sweep was used to improve the efficiency of the AFP pulse. The effect on the T1 calculation of slice selection during the pi/2 pulses was also determined and corrected for in the image reconstruction algorithm. The T1's determined by this method show a standard deviation of less than 10%, and good agreement with the literature.     

Effect of drying on bioremediation bacteria properties

Bioremediation bacteria with drought-resistance characteristics were selected and compared to a collection of 10 strains selected only for their bioremediation properties. Twenty-six strains were selected from dried diesel-polluted soil, and they exhibit a better level of survival during drying, compared to collection bioremediation strains (two orders of magnitude difference). The lyophilization process does not affect the strains’ ability to grow on xenobiotic compound when measured immediately after drying. However, collection bioremediation strains selected only for their bioremediation properties lose up to 80% of their properties when stored at 25°C for 15 d, but the strains selected for their drought resistance lose their properties to a lesser extent during the same period. The maximal growth rate and the rate of xenobiotic degradation of the still-active cells are not affected by the drying process.     

A new nuclear spin selective reaction of molecular oxygen

During high-temperature (623–673 K) oxidation of polyarylenes (polypyromellitimide and polyphenylquinoxaline), the molecular oxygen is enriched in the¹⁸O nonmagnetic isotope and impoverished in the¹⁷O magnetic isotope. The isotope selection increases with the increase in the degree of conversion of oxygen. The spin-selective reaction responsible for the selection of the¹⁷O isotope is the addition of molecular oxygen to triplet exited aromatic fragments of macromolecules to give endoperoxides. This reaction, which is selective in terms of the electron spin, is also nuclear-spin selective resulting in a magnetic isotope effect. The selection of nonmagnetic isotopes,¹⁶O and¹⁸O, is caused by competition between the reversible and irreversible decomposition of endoperoxide and by the classical isotope effect in these reactions.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1402–1405, August, 1994.The authors are grateful to E. M. Galimov and I. V. Nikulina for high-quality isotope analyses and to the Russian Foundation for Basic Research for financial support (grant 93-03-5227).     

环境模拟样品中多环芳烃的超临界流体萃取I．利用正交设计选择最佳萃取条件

采用正交设计实验方法，研究了从环境模拟样品中超临界流体萃取（ＳＦＥ）多环芳烃（ＰＡＨ）的最佳萃取条件。着重考察了超临界流体的压力、温度和用量等对萃取效率的影响。结果表明，压力的影响居第一位，温度影响次之，超临界ＣＯ２的用量的影响居第三位。建立了选择超临界流体萃取条件的简单方法