Benzylation of arenes and heteroarenes catalyzed by HfCl_4/HfO_2

A highly efficient benzylation of arenes and heteroarenes catalyzed by HfCl_4/HfO_2 has been developed.Broad scope of benzylation reagents have been used in this process with high yields under mild condition.Additionally,the HfO_2 can be re-used after the reaction.     

皮秒X射线分幅相机性能实验研究

介绍了扫描型皮秒X射线分幅相机的分幅原理,主要技术指标的测试方法和结果。相机的动态空间分辨优于61p/mm,最短曝光时间75ps(FWHM),触发晃动(80％发次)小于±30ps,几何畸变小于±5％,达到现场实验诊断的要求。     

Acoustic communication in two freshwater gobies: ambient noise and short-range propagation in shallow streams

Noise is an important theoretical constraint on the evolution of signal form and sensory performance. In order to determine environmental constraints on the communication of two freshwater gobies Padogobius martensii and Gobius nigricans, numerous noise spectra were measured from quiet areas and ones adjacent to waterfalls and rapids in two shallow stony streams. Propagation of goby sounds and waterfall noise was also measured. A quiet window around 100 Hz is present in many noise spectra from noisy locations. The window lies between two noise sources, a low-frequency one attributed to turbulence, and a high-frequency one (200-500 Hz) attributed to bubble noise from water breaking the surface. Ambient noise from a waterfall (frequencies below 1 kHz) attenuates as much as 30 dB between 1 and 2 m, after which values are variable without further attenuation (i.e., buried in the noise floor). Similarly, courtship sounds of P. martensii attenuate as much as 30 dB between 5 and 50 cm. Since gobies are known to court in noisy as well as quiet locations in these streams, their acoustic communication system (sounds and auditory system) must be able to cope with short-range propagation dictated by shallow depths and ambient noise in noisy locations.     

Asymptotic Theory for the Gamma Frailty Model with Dependent Censoring

In many clinical studies, there are two dependent event times with one of the events being terminal, such as death, and the other being nonfatal, such as myocardial infarction or cancer relapse. Morbidity can be dependently censored by mortality, but not vice versa. Asymptotic theory is developed for simultaneous estimation of the marginal distribution functions in this semi-competing risks setting. We specify the joint distribution of the event times in the upper wedge, where the nonfatal event happens before the terminal event, with the popular gamma frailty model. The estimators are based on an adaptation of the self-consistency principle. To study their properties, we employ a modification of the functional delta-method applied to Z-estimators. This approach to weak convergence leads naturally to asymptotic validity of both the nonparametric and multiplier bootstraps, facilitating inference in spite of the complexity of the limiting distribution.     

The effects of solvent screening in quantum mechanical calculations in protein systems

We report on an implementation of quantum mechanical density functional calculations carried out in a dielectric medium. The dielectric medium is introduced by integrating the solution of the Poisson-Boltzmann equations into the density functional calculation. The calculations are carried out for a simple amide in vacuum, in the field of an ion, and in the ion field in several dielectric environments. The environment was constructed to include a low dielectric interior embedded in a high dielectric continuum of dielectric 80 (corresponding to aqueous solution). The energies and electron densities of formamide in the ion field were calculated at various configurations in this system, including at the low dielectric–high dielectric interface. The systems were designed to simulate situations which are similar to those that occur in proteins (i.e., the protein constitutes the low dielectric medium surrounded by aqueous solution). The system mimics situations in which charges in such proteins located in various regions interact with other parts of the protein and with ligands which mainly bind to the surface. © 1994 by John Wiley & Sons, Inc.     

Principle of operation of the thermal energy analyzer for the trace analysis of volatile and non-volatile N-nitroso compounds.

The theoretical basis for the thermal energy analyzer is discussed. Using the principles outlined, the feasibility of selectivity detecting mug/kg levels of volatile and non-volatile N-nitroso compounds is established.     

Temperature dependence of the superconducting gap in high-Tc cuprates

It is proposed that the temperature dependence of the superconducting gap Delta(T) in high-T(c) cuprates can be predicted just from the knowledge of Delta(0) and the critical temperature T(c), and, in particular, Delta(0)/T(c)>4 implies that Delta(T(c)) not equal 0, while Delta(0)/T(c)相似文献