二氟锗烯与乙烯环加成反应的DFT计算研究

用密度泛函理论的B3LYP方法,以6-311 G**为基组,研究了F2Ge(1A1)与C2H4环加成反应的机理,并用经典过渡态理论计算了该反应在不同温度下的反应速率常数和平衡常数,讨论了取代基对该反应的影响.     

尤尔-尼尔逊公式的理论误差探悉

默里-戴维斯公式以及尤尔-尼尔逊公式都可以确定网点密度与网点面积率的关系,常在计算网点面积率、分析网点扩大、进行工艺参数识别(制版时的曝光控制、印刷时的压力调节等)与优化等工艺实践中应用广泛。实践中人们更趋于应用后者,认为其结果更接近现实。针对这一认识误区,通过理论分析和仿真实验,揭示了尤尔-尼尔逊公式存在理论误差,在不考虑工艺因素影响下,该公式只在极少数密度点无计算误差,在其余点均存在非线性误差。     

Aln^m（m=0,±1,n=3,4,5）团簇的稳定性和芳香性研究

采用密度泛函理论中的B3LYP方法,对铝团簇Alnm（m=0,±1,n=3,4,5）进行了理论研究。经过优化得到其基态构型,讨论了其稳定性。通过核独立化学位移（NICS）和分子轨道（MO）分析,确定Al3的次稳态、Al3^-、Al4、Al4^-、Al5和Al5^＋团簇具有芳香性,其余团簇不具有芳香性,芳香性均以π芳香性为主。     

Testing Interval Forecasts: A GMM‐Based Approach

This paper proposes a new evaluation framework for interval forecasts. Our model‐free test can be used to evaluate interval forecasts and high‐density regions, potentially discontinuous and/or asymmetric. Using a simple J‐statistic, based on the moments defined by the orthonormal polynomials associated with the binomial distribution, this new approach presents many advantages. First, its implementation is extremely easy. Second, it allows for a separate test for unconditional coverage, independence and conditional coverage hypotheses. Third, Monte Carlo simulations show that for realistic sample sizes our GMM test has good small‐sample properties. These results are corroborated by an empirical application on SP500 and Nikkei stock market indexes. It confirms that using this GMM test leads to major consequences for the ex post evaluation of interval forecasts produced by linear versus nonlinear models. Copyright © 2011 John Wiley & Sons, Ltd.     

Early Warning with Calibrated and Sharper Probabilistic Forecasts

Given a nonlinear model, a probabilistic forecast may be obtained by Monte Carlo simulations. At a given forecast horizon, Monte Carlo simulations yield sets of discrete forecasts, which can be converted to density forecasts. The resulting density forecasts will inevitably be downgraded by model misspecification. In order to enhance the quality of the density forecasts, one can mix them with the unconditional density. This paper examines the value of combining conditional density forecasts with the unconditional density. The findings have positive implications for issuing early warnings in different disciplines including economics and meteorology, but UK inflation forecasts are considered as an example. Copyright © 2012 John Wiley & Sons, Ltd.     

单阶梯调制金属狭缝中的磁场及能量分布

本文利用时域有限差分(FDTD)算法,研究了由亚波长向非亚波长过渡时,单阶梯调制狭缝内的磁场及能量分布的变化情况.理论计算表明,当结构处于亚波长范围内时,结构中只有零阶模式即SPP传播,I区和II区由于反射场的存在,z方向上呈现振荡的场分布,而III区中没有反射场,其振幅沿z方向上是一常量.当结构处于非亚波长范围内时,除了SPP外,还有高阶模式的存在,它们之间的相互作用及与反射场的相互作用使得缝内场和能量分布变得复杂.     

密度泛函计算中基组的收敛现象:强成键体系CO分子

探讨了用密度泛函理论中7个常见交换-相关密度泛函及8种常见Dunning调和相关基组处理CO分子的三种性质(平衡键长、谐振基频和离解能)时表现出的基组收敛现象.用Dunning的单指数插补法,求得了上述性质的全基组极限值.用扩展的调和相关基组,发现键长的系统误差在0.002 9 (LDA)到0.007 3 A(BP86...     

Construction of protograph LDPC codes with circular generator matrices

The application of protograph low density parity check(LDPC) codes involves the encoding complexity problem.Since the generator matrices are dense,and if the positions of "1" s are irregularity,the encoder needs to store every "1" of the generator matrices by using huge chip area.In order to solve this problem,we need to design the protograph LDPC codes with circular generator matrices.A theorem concerning the circulating property of generator matrices of nonsingular protograph LDPC codes is proposed.The circulating property of generator matrix of nonsingular protograph LDPC codes can be obtained from the corresponding quasi-cyclic parity check matrix.This paper gives a scheme of constructing protograph LDPC codes with circulating generator matrices,and it reveals that the fast encoding algorithm of protograph LDPC codes has lower encoding complexity under the condition of the proposed theorem.Simulation results in additive white Gaussian noise(AWGN) channels show that the bit error rate(BER) performance of the designed codes based on the proposed theorem is much better than that of GB20600 LDPC codes and Tanner LDPC codes.     

论石油密度的测量及影响要素

石油密度的检测是石油在生产及运输过程中的重要质量控制手段,只有保证石油产品贸易中的密度计量的准确性,才能更好的维护贸易双方的合法权益。石油密度有着其特殊的测量方法及其特点,本文对此进行了探讨。     

Density and structure of undercooled liquid titanium

For liquid Ti, it is difficult to achieve high undercooling because of its chemical reactivity; as a result, there is little information available on its properties and structure in the undercooled state. In this study, we investigate the density and structure, using molecular dynamics method, for the undercooling and superheating ranges 0-743 K and 0-457 K. The density increases quadratically for undercooling. At the melting temperature, the density is 4.14 g/cm3, and first and second temperature coefficients are obtained. The pair correlation functions and coordination numbers indicate that the short range degree of order becomes increasingly significant with increasing undercooling.