Assessing the ability of chemical similarity measures to discriminate between active and inactive compounds

Summary A method for assessing the biological discriminating power of chemical similarity measures is presented. The main concern of this work was to develop an objective way of evaluating different similarity measures in terms of how well they distinguished between active and inactive compounds. In addition, we have explored the level of similarity required for optimal separation and commented on its implications for work in the field of chemical diversity studies. The results for one simple similarity measure showed that statistically significant separation could be achieved, and indicated a reasonable similarity value for future work.     

Linear response and relaxation in quantum lattice systems

For spin-lattice systems, the Kubo formula, expressing the relaxation function in terms of the linear response function, is found to be exact in the thermodynamic limit. In addition, analyticity properties are obtained.     

Modeling, measuring, and minimizing the instrument response function of a tunable diode laser spectrometer

The instrument response function (IRF) of a spectrometer limits the accuracy of measured spectroscopic parameters by broadening recorded spectral lines/features. We describe methods to model the effects of the IRF on spectral data, to minimize the IRF widths, and to measure the resulting width of the spectrometer IRF. We have modeled the IRF of our Tunable Diode Laser Spectrometer as a Voigt function. A real-time method of eliminating the effects of low-frequency spectrometer drift has been implemented and has resulted in a substantial reduction in the width of the IRF, its residual Gaussian component reduced from about to about . An accurate measurement of the IRF Gaussian width utilizes a computationally simple method making use of the spectral dependence of the RMS noise of each signal-averaged data point. Various noise sources affecting the spectrometer (preamp/detector noise, laser AM noise, and laser FM noise) are identified and separately quantified by use of the same method. The IRF Gaussian-width measurement can be automatically applied to each measured spectrum of an experimental data set. A related method is discussed which allows accurate determination of the spectral dependence of statistical noise appropriate for use in quantitative Chi-square fitting of absorption spectra. We explore simple, efficient numerical processes which can dramatically enhance the quality and usefulness of acquired spectral data, improving the ability to apply TDL spectroscopy to high-precision, quantitative measurements and the determination of detailed spectroscopic lineshape parameters. This paper provides a guide for interested readers to implement these developments in their own spectrometers.     

Modulation Characteristics of Tunable Quantum-Well Heterolasers at the Radiation Frequency Tuning

The influence of the tuning of the radiation frequency of quantum-well heterolasers within the limits of their amplification band on the output laser radiation parameters at different frequencies of pump-current modulation has been numerically simulated using two optical models of an active medium under the assumption that the excess of the invariable component of the pump current over its threshold value at any point of the amplification band is constant. It has been established that the amplitude-detuning characteristics of the lasers studied are linear at high current-modulation frequencies and nonlinear at medium ones. The behavior of the nonlinear spectral response of a laser diode is explained by its multiresonance structure and is mainly determined by the ratio between the pump-current modulation frequency and the maximum resonance frequency of the laser. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 4, pp. 473–478, July–August, 2005.     

Chromatographic impulse response technique with curve fitting to measure binary diffusion coefficients and retention factors using polymer-coated capillary columns

The theoretical basis of a Gaussian-like approximate solution was applied to a chromatographic impulse response technique with curve fitting for measuring binary diffusion coefficients and retention factors using a polymer-coated capillary column. The formulae were derived for evaluating both the accuracy of the approximate solution and the sensitivity of the parameters. The validity of the solution also was confirmed experimentally for pulse injection of phenol in acetone into supercritical carbon dioxide flowing at 313.15 K and 11.6-28.6 MPa. Potential sources for experimental errors of the method are discussed.     

Permanence for a delayed discrete ratio-dependent predator-prey system with Holling type functional response

Sufficient conditions are established for the permanence in a delayed discrete predator-prey model with Holling type III functional response:

     

Asymptotic Normality of Cross-correlogram Estimates of the Response Function

The problem of estimation of an unknown response function of a time-invariant continuous linear system is considered. Discrete-time sample input–output cross-correlograms are taken as estimates of the response function. The inputs are supposed to be zero-mean stationary Gaussian processes close, in some sense, to a white noise. Both asymptotic normality of finite-dimensional distributions of the estimates and their asymptotic normality in spaces of continuous functions are studied. Our basic tool is a new integral representation for cumulants of the estimate as a finite sum of integrals involving cyclic products of kernels. Some inequalities for these integrals are obtained and their asymptotic behaviour is studied.     

Transient rheology of discotic mesophases

This paper presents an analysis of the role of orientation on the rheology of discotic mesophases subjected to slow shear start-up flows, using a projection of the Landau-de Gennes equations of nematodynamics. Analysis of the shear stress surface as a function of tilt and twist orientation with respect to the shear plane shows that the stress surface is dense in well-oriented and periodically located sets of maxima and minima. Thus overshoots and undershoot stress responses to shear-start up are predicted to be the rule rather than the exception. In-plane (within the shear plane) shear start-up stress responses can exhibit multiple, single, or no overshoots, depending on the number of maxima traversed on the way to steady state. Responses originating from orientations close to the vorticity axis lead to stress undershoots. Complex stress responses, such as a weak overshoot-strong undershoot sequence, are found for intermediate tilt-twist initial states. In-plane modes lead to amplitude and strain scaling. Out-of-plane modes do not display amplitude or strain scaling. These results provide will be useful to interpret and use transient shear rheological data of carbonaceous mesophases and highly filled suspensions of disc-like particles.     

济阳坳陷陡坡带砂砾岩体储层测井识别及描述技术

陆相断陷湖盆陡坡带发育各种成围的砂砾岩扇体,其储集性能具有极强的非均质性,已成为高成熟勘探区重要的勘探目标,钻前对有利沉积相带的预测以及钻后对储集性能的分析,已成为提高勘探开发效益的关键．针对胜利油田济阳坳陷陡坡带发育的各种成围的砂砾岩扇体,综合应用测井相、多种测井咱应交会法、储层参数的测井定量解释、含油渗透层的测井判识等多种技术和方法,有效地对砂砾岩扇体的成围类型和储层岩性进行了判识,建立了孔隙度、渗透卑等储层参数解释的理论模型并进行了定量解释,划分了有效渗透层,取得了明显的勘探开发效果．这些新技术的综合运用为其他类似地区砂砾岩扇体的勘探与开发提供了技术支持．     

Unconventional Hamilton-type variational principle in phase space and symplectic algorithm

By a novel approach proposed by Luo, the unconventional Hamilton-type variational principle in phase space for elastodynamics of multidegree-of-freedom system is established in this paper. It not only can fully characterize the initial-value problem of this dynamic, but also has a natural symplectic structure. Based on this variational principle, a symplectic algorithm which is called a symplectic time-subdomain method is proposed. A non-difference scheme is constructed by applying Lagrange interpolation polynomial to the time subdomain. Furthermore, it is also proved that the presented symplectic algorithm is an unconditionally stable one. From the results of the two numerical examples of different types, it can be seen that the accuracy and the computational efficiency of the new method excel obviously those of widely used Wilson-θ and Newmark-β methods. Therefore, this new algorithm is a highly efficient one with better computational performance.