On Interpretation of ESCA Spectra with Application to Thymine and Other Molecules

1s binding energies are calculated for nitrogen atoms in thymine, pyrrole, adenine, and pyridine and for carbon atoms in thymine, adenine, pyrrole, and furan, and compared with experimental values. Calculations are performed in the framework of a perturbational model using CNDO molecular wave functions. Interactions of the 1s electron with its own atom are calculated exactly whereas interactions with neighbor atoms are calculated according to two levels of approximation: (1) Point charge approximation. (2) Rigorous calculations of integrals. Magnitudes of the different interactions and integrals are analysed. The questions of assignments of ESCA shifts and the errors inherent in the calculations are discussed.     

大地电磁测深的拟地震解释法

在水平层状介质条件下,如果把地层划分为电磁波或弹性波在其中的双程旅行时都相等的“微层”,则大地电磁场和弹性波的位移场的反射函数无论是在表现形式上,或是在物理意义上都是十分相似的。这样的话,大地电磁测深法也可以象地震反射法一样画出“时间剖面”进行地质解释。这种方法还可推广到二维大地电磁测深和电测深资料的解释。通过对二层、三层和四层断面的理论模型试算,说明此方法是可行的。但是,无论是在理论上,还是在实践中都有许多值得研究的问题,例如在MT中反射函数的精度受观测精度及计算方法的影响。因此,研究新的观测方法和计算方法就显得很有必要。再如怎样把地震资料处理中一些消除干扰和提高分辨率的措施用于MT法。     

The effects of immediate stimulus repetition on reaction time and event-related potentials in tasks of different complexity.

Examined the effect of immediate stimulus repetition in lexical decision, face recognition, letter search, face/nonface discrimination, and word/number discrimination tasks using reaction time (RT), accuracy, and event-related brain potential (ERP) measures. Repetition facilitated performance in all tasks and for all stimulus types. However, ERPs were strongly affected by repetition only in lexical decision, face recognition, and letter search, when relatively long stimulus analysis and decision making processes were required. The ERP repetition effect consisted of a significant increase in P300 amplitude and a shortening of its latency. Repetition also resulted in the attenuation of a negative component that was tentatively identified as N400. These results suggest that immediate repetition facilitates stimulus identification and eliminates the need for stimulus analysis processes including access to semantic memory while making categorical decisions. While both factors affected RT, ERPs were modulated primarily by the elimination of the need to access to semantic memory and by the consequent speeding of categorical decision processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Path Flow and Trip Matrix Estimation Using Link Flow Density

A macroscopic model is presented that simultaneously estimates route flows and trip matrices for congested road networks using data on link densities instead of link flows. The advantage of this approach is that it avoids errors that may occur in the individual links’ flow-cost relationships when congestion is heavy. Under the proposed methodology, both the flows and the matrices are estimated by the model using an image of the network such as an aerial photograph in which the number of vehicles on each link can be identified. The model itself is formulated as a maximum entropy optimization problem subject to linear constraints given by vehicle densities on the links, and is validated using analytic examples and traffic microsimulations. The results demonstrate the superiority of the link-density approach over the traditional flow-based method.     

An Alternative Approach for Solving the Environmentally-Oriented Discrete Network Design Problem

This paper addresses the discrete network design problem (DNDP) with emphasis on the environmental benefits. These benefits are traditionally quantified by emission models, which in general account for vehicle speeds, traffic flows and emission coefficients. An alternative approach for approximating the environmental impact of traffic is developed. This approach finds the route that keeps the most balanced speed profile throughout the route, which contributes to fuel consumption reduction. The paper formulates an optimization problem that includes the described approach for the DNDP. The solution of the problem consists of projects that contribute the most to the generation of such “balanced speed routes”. The paper illustrates the problem and the solution for a real-size network with a medium-size set of candidate projects.     

Learning parallel portfolios of algorithms

A wide range of combinatorial optimization algorithms have been developed for complex reasoning tasks. Frequently, no single algorithm outperforms all the others. This has raised interest in leveraging the performance of a collection of algorithms to improve performance. We show how to accomplish this using a Parallel Portfolio of Algorithms (PPA). A PPA is a collection of diverse algorithms for solving a single problem, all running concurrently on a single processor until a solution is produced. The performance of the portfolio may be controlled by assigning different shares of processor time to each algorithm. We present an effective method for finding a PPA in which the share of processor time allocated to each algorithm is fixed. Finding the optimal static schedule is shown to be an NP-complete problem for a general class of utility functions. We present bounds on the performance of the PPA over random instances and evaluate the performance empirically on a collection of 23 state-of-the-art SAT algorithms. The results show significant performance gains over the fastest individual algorithm in the collection.      

Quantitative pulsed CEST-MRI at a clinical 3T MRI system

Objectives

The goal of this study was to quantify CEST related parameters such as chemical exchange rate and fractional concentration of exchanging protons at a clinical 3T scanner. For this purpose, two CEST quantification approaches—the AREX metric (for ‘apparent exchange dependent relaxation’), and the AREX-based Ω-plot method were used. In addition, two different pulsed RF irradiation schemes, using Gaussian-shaped and spin-lock pulses, were compared.

Materials and methods

Numerical simulations as well as MRI measurements in phantoms were performed. For simulations, the Bloch–McConnell equations were solved using a two-pool exchange model. MR experiments were performed on a clinical 3T MRI scanner using a cylindrical phantom filled with creatine solution at different pH values and different concentrations.

Results

The validity of the Ω-plot method and the AREX approach using spin-lock preparation for determination of the quantitative CEST parameters was demonstrated. Especially promising results were achieved for the Ω-plot method when the spin-lock preparation was employed.

Conclusion

Pulsed CEST at 3T could be used to quantify parameters such as exchange rate constants and concentrations of protons exchanging with free water. In the future this technique might be used to estimate the exchange rates and concentrations of biochemical substances in human tissues in vivo.