Synthesis and nonlinear optical properties of a novel polyurethane containing cyanovinylthiophene with enhanced thermal stability of dipole alignment for electro‐optic applications

Stabilization of electrically induced dipole alignment is one of the important criteria in the development of nonlinear optical (NLO) polymers for electro‐optic device applications. Polyurethanes for NLO applications have attracted attention because of their high thermal stability due to hydrogen bonding. In the work reported here, we designed and synthesized a new type of NLO polyurethane, in which the pendant NLO chromophores are part of the polymer backbone. This mid‐type NLO polymer is expected to have the merits of both main‐chain and side‐chain NLO polymers, namely stable dipole alignment and good solubility. 1‐[3,4‐Di‐(2‐hydroxyethoxy)phenyl]‐2‐(2‐thienyl)ethene was prepared and condensed with 3,3′‐dimethoxy‐4,4′‐biphenylenediisocyanate to yield a polyurethane. This polyurethane was reacted with tetracyanoethylene to give a novel Y‐type polyurethane (7) containing 1‐(3,4‐dioxyphenyl)‐2‐[5‐(1,2,2‐tricyanovinyl)‐2‐thienyl]ethenes as NLO chromophores, which constitute part of the polymer backbone. Polyurethane 7 is soluble in common organic solvents such as N,N‐dimethylformamide and dimethylsulfoxide. It shows a thermal stability up to 280 °C from thermogravimetric analysis with a glass transition temperature obtained from differential scanning calorimetry of ca 162 °C. The second harmonic generation (SHG) coefficient (d₃₃) of a poled polymer film of he polyurethane at 1560 nm fundamental wavelength is ca 1.11 × 10^?18 C. Polymer 7 exhibits an enhanced thermal stability and no significant SHG decay is observed below 150 °C, which is acceptable for NLO device applications. Copyright © 2009 Society of Chemical Industry     

Selection between Weibull and lognormal distributions: A comparative simulation study

How to select the correct distribution for a given set of data is an important issue, especially when the tail probabilities are of interest as in lifetime data analysis. The Weibull and lognormal distributions are assumed most often in analyzing lifetime data, and in many cases, they are competing with each other. In addition, lifetime data are usually censored due to the constraint on the amount of testing time. A literature review reveals that little attention has been paid to the selection problems for the case of censored samples. In this article, relative performances of the two selection procedures, namely, the maximized likelihood and scale invariant procedures are compared for selecting between the Weibull and lognormal distributions for the cases of not only complete but also censored samples. Monte Carlo simulation experiments are conducted for various combinations of the censoring rate and sample size, and the performance of each procedure is evaluated in terms of the probability of correct selection (PCS) and average error rate. Then, previously unknown behaviors and relative performances of the two procedures are summarized. Computational results suggest that the maximized likelihood procedure can be generally recommended for censored as well as complete sample cases.     

Precipitation behavior of Mg17Al12 in monolithic and Al2O3 short fiber reinforced Mg-Al-Zn alloys

The precipitation behavior of Mg₁₇Al₁₂ in monolithic and Al₂O₃ short fiber reinforced Mg-Al-Zn alloys was investigated by optical and transmission electron microscopies and hardness measurements. The maximum hardness was obtained when the long and short axes of the platelet type continuous Mg₁₇Al₁₂ precipitates were about 0.3 μm and 0.04 μm, respectively. The area fraction of the discontinuous Mg₁₇Al₁₂ precipitate nodule reached about 0.23. The coarsening behavior of the discontinuous Mg₁₇Al₁₂ precipitate nodule was found to obey the relationship suggested by the Johnson-Mehl-Avrami model. The slope of the Johnson-Mehl-Avrami plot for the Al₂O₃ short fiber reinforced Mg-Al-Zn alloy was four times larger than that for the monolithic alloy due to the increased number of nucleation sites, i.e. nucleation at the interface between the reinforcing material and the α-Mg matrix as well as at the α-Mg grain boundaries.     

A cognitive reinterpretation of Stanley Milgram's observations on obedience to authority.

Comments on S. Milgram's (1974) observations on obedience to authority. It is suggested that the underlying cause for Milgram's Ss' striking conduct could be conceptual and not the alleged "capacity of man to abandon his humanity…as he merges his unique personality into larger institutional structures." (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Optical BGP Routing Convergence in Lightpath Failure of Optical Internet

Optical Border Gateway Protocol (OBGP) is an extension to BGP for Optical Cross Connects (OXCs) to automatically setup multiple direct optical lightpaths between many different autonomous domains. With OBGP, the routing component of a network may be distributed to the edge of the network while the packet classification and forwarding is done in the core. However, it is necessary to analyze the stable convergence functions of OBGP in case of lightpath failures. In this paper, we first describe the architecture of the OBGP model and analyze the potential problems of OBGP, e.g., virtual BGP router convergence behavior in the presence of lightpath failure. We then propose an OBGP convergence model derived from an inter‐AS (Autonomous System) relationship. The evaluation results show that the proposed model can be used for a stable OBGP routing policy and OBGP routing convergence under lightpath failures of the optical Internet.     

Fragility Assessment Model of Building Structures Using Characteristics of Artificial Aftershock Motions

Any additional loads applied to a damaged structure can aggravate its instability and thus, the impact of successive earthquakes need to be considered. This study proposed a quantitative assessment model for the fragility of a damaged structure subjected to aftershock. Mean period and the strong motion duration were considered as characteristics of earthquake motions. Simulation models of two reinforced concrete structures and one steel structure were selected to examine the applicability of the model. Based on the suggested fragility and residual deformation coefficients, critical earthquake sequences for each structure were identified. The proposed model was efficient in selecting critical earthquake sequences by using the limited number of aftershocks, and these sequences are expected to be useful indicators in the establishment of a retrofit plan according to the predicted structural response and target performance levels.     

Corrosion performance of high pressure die-cast Al-6Si-3Ni and Al-6Si-3Ni-2Cu alloys in aqueous NaCl solution

The corrosion performance of high pressure die-cast Al-6Si-3Ni (SN63) and Al-6Si-3Ni-2Cu (SNC632) alloys in 3.5% (mass fraction) NaCl solution was investigated. X-ray diffraction (XRD) and microstructural studies revealed the presence of single phase Si and binary Al₃Ni/Al₃Ni₂ phases along the grain boundary. Besides, the single Cu phase was also identified at the grain boundaries of the SNC632 alloy. Electrochemical corrosion results revealed that, the SNC632 alloy exhibited nobler shift in corrosion potential (?_corr), lower corrosion current density (J_corr) and higher corrosion resistance compared to the SN63 alloy. Equivalent circuit curve fitting analysis of electrochemical impedance spectroscopy (EIS) results revealed the existence of two interfaces between the electrolyte and substrate. The surface layer and charge transfer resistance (R_ct) of the SNC632 alloy was higher than that of the SN63 alloy. Immersion corrosion test results also confirmed the lower corrosion rate of the SNC632 alloy and substantiated the electrochemical corrosion results. Cu addition improved the corrosion resistance, which was mainly attributed to the absence of secondary Cu containing intermetallic phases in the SNC632 alloy and Cu presented as single phase.     

Model Updating Technique Based on Modal Participation Factors for Beam Structures

This article proposes a model updating technique based on modal participation factors for a beam structure. In this model updating technique, the error functions of the dynamic characteristic differences between measurement and model are generated as the number of modes under consideration and minimized using the multiobjective optimization techniques. A modal influence factor defined by modal participation factors for each mode is presented for the selection of the best solution from among Pareto solutions. The selection rule represented in this article makes it possible to reflect the contributions of each mode on the behavior of a structure. The model is updated using natural frequencies measured in an impact hammer test of a beam structure and the validity of the updated model is confirmed by the strain responses measured from the test. It is found that the bending stiffness of the beam structure as the parameter for model updating can be identified by the proposed techniques. Furthermore, through comparing the models updated by the simple sum model updating and the technique in this research, it is verified that the proposed technique is more appropriate for the model updating.     

GA‐Based Multi‐Objective Optimization for Retrofit Design on a Multi‐Core PC Cluster

This article presents a distributed nondominated sorting genetic algorithm II (NSGA‐II) for optimal seismic retrofit design using buckling restrained braces (BRBs) on a cluster of multi‐core PCs. In the formulation, two conflicting objective functions of the initial BRB installation cost required for seismic retrofitting and damage cost that can be incurred by earthquakes expected during the life cycle of the structure were minimized. Because time‐consuming nonlinear structural analyses are required for fitness evaluations of individuals in every generation, parallelism at candidate design level or individual level is exploited by assigning fitness evaluations for individuals to slave core processors evenly. The distributed algorithm is applied to seismic retrofit design of 2D steel frame structure and 3D irregular reinforced concrete structure. The performance of the distributed NSGA‐II was assessed based on three criteria: convergence of the distributed algorithm, efficiency of distributed computing, and quality of optimal solutions. Implementation of the distributed algorithm on the multi‐core cluster consisting of up to 64 core processors resulted in relatively high speedups or efficiencies of the distributed optimization without deteriorating the quality of the optimal solutions.