Theory of modified thermally stimulated current and direct determination of trap level distribution

In order to investigate the trap level distribution in polymer films, a new method is proposed based on modified thermally stimulated current (TSC) theory and numerical calculation of the TSC measurement. In this method, a new function is defined to weight the contribution of every trap level to the external current. The demarcation energy is used to study the trap emptying process. The modified TSC theory shows that only the electrons with trap levels very close to the demarcation energy can significantly contribute to the external circuit at any instant temperature. Based on this method, the trap level distribution of the DuPont original polyimide film 100HN and nanocomposite polyimide film 100CR are investigated as an application example. The effectiveness of the method is confirmed by the experiments. The experimental results show that the trap level density in the 100CR PI films is about six times larger than that in the 100HN PI films through the investigated trap level ranges 06–1.3 eV. The increased traps in 100CR should be introduced by nanofillers, probably come from the interfaces formed between nanofillers and the polymer matrix.     

Investigation on push-pull polymer Mach-Zehnder interferometer electro-optic switches using improved 3-D mode propagation analysis method

By introducing normalized mode excitation coefficient and total mode excitation coefficient, we improve the 3-D mode propagation analysis (MPA) method for convenient design and analysis of multimode interference (MMI) coupler. With the improved 3-D MPA method and point-matching method, we present a novel formulation technique to analyze the low- and high-frequency characteristics for the impedance-matched polymer Mach-Zehnder interferometer electro-optic (EO) switch based on MMI couplers. As an application, under 1550 nm, optimization and simulation performed for the designed device reveal low driving voltage of 1.375 V with short EO region length of 5 mm. The insertion loss and extinction ratio are less than 3.75 dB and more than 42 dB, respectively. The microwave characteristic impedance is about 49.6 Ω, and due to the less mismatch between lightwave velocity and microwave velocity, the estimated cutoff switching frequency is up to 263 GHz with the 10–90% rise time and fall time about 1.90 ps under the operation of step-style square-wave switching signal. This theoretical cutoff switching frequency is almost 1.53 times of that of our previous reported shielded EO switch with similar design technique.     

Memory effect and multifractality of cross-correlations in financial markets

We introduce an instantaneous and an average instantaneous cross-correlation function to detect the temporal cross-correlations between individual stocks based on the daily data of the United States and the Chinese stock markets. The memory effect of the instantaneous cross-correlations is investigated by applying the detrended fluctuation analysis (DFA), where the DFA exponents can be partly explained by the correlation function from the common sense. Long-range memory is observed for the average instantaneous cross-correlations, and persists up to a month magnitude of timescale for the United States stock market and half a month magnitude of timescale for the Chinese stock market. In addition, multifractal nature is investigated by a multifractal detrended fluctuation analysis.     

Multiplicity of positive almost periodic solutions in a delayed Hassell–Varley‐type predator–prey model with harvesting on prey

In this paper, we consider a delayed Hassell–Varley‐type predator–prey model with harvesting on prey. By means of Mawhin's continuation theorem of coincidence degree theory, some new sufficient conditions are obtained for the existence of at least two positive almost periodic solutions for the aforementioned model. To the best of the author's knowledge, so far, the result of this paper is completely new. An example is employed to illustrate the result of this paper. Copyright © 2013 John Wiley & Sons, Ltd.     

ERROR ESTIMATION FOR NUMERICAL METHODS USING THE ULTRA WEAK VARIATIONAL FORMULATION IN MODEL OF NEAR FIELD SCATTERING PROBLEM

In this paper, we investigate the use of ultra weak variational formulation to solve a wave scattering problem in near field optics. In order to capture the sub-scale features of waves, we utilize evanescent wave functions together with plane wave functions to approximate the local properties of the field. We analyze the global convergence and give an error estimation of the method. Numerical examples are also presented to demonstrate the effectiveness of the strategy.     

Good congruences on abundant semigroups with PSQ-adequate transversals

In this paper, we will characterize good congruences on abundant semigroups with \(PSQ\) -adequate transversals by using the so called good congruence triple, which generalizes some results on abundant semigroups with multiplicative adequate transversals.     

Condition-based maintenance optimization considering improving prediction accuracy

Condition-based maintenance (CBM) aims to reduce maintenance cost and improve equipment reliability by effectively utilizing condition monitoring and prediction information. It is observed that the prediction accuracy often improves with the increase of the age of the component. In this research, we develop a method to quantify the remaining life prediction uncertainty considering the prediction accuracy improvement, and an effective CBM optimization approach to optimize the maintenance schedule. Any type of prognostics methods can be used, including data-driven methods, model-based methods and integrated methods, as long as the prediction method can produce the predicted failure time distribution at any given inspection point. Furthermore, we develop a numerical method to accurately and efficiently evaluate the cost of the CBM policy. The proposed approach is demonstrated using vibration monitoring data collected from pump bearings in the field as well as simulated degradation data. The proposed policy is compared with two benchmark maintenance policies and is found to be more effective.     

ChemInform Abstract: High Pressure Superconducting Phase of BI3: An ab initio Study.

The high pressure crystal structure of BI₃ with space group P2₁/c consisting of B₂I₆ dimers is determined using an ab initio evolutionary algorithm for crystal structure prediction in conjunction with density functional theory.     

保费收入服从泊松过程的一类相依更新风险模型研究

本文研究了保费收入过程是泊松过程和聚合理赔过程中理赔间隔时间和个别理赔额之间具有Boudreault et al.(2006)中所描述的相依结构的一类更新风险模型.运用生成函数、离散形式的Dickson-Hipp算子和反Z变换等一系列方法,推导出了该模型的Gerber-Shiu函数的生成函数的精确表达式,以及它所满足的瑕疵更新方程.