ESC: an efficient error-based stopping criterion for kriging-based reliability analysis methods

The ever-increasing complexity of numerical models and associated computational demands have challenged classical reliability analysis methods. Surrogate model-based reliability analysis techniques, and in particular those using kriging meta-model, have gained considerable attention recently for their ability to achieve high accuracy and computational efficiency. However, existing stopping criteria, which are used to terminate the training of surrogate models, do not directly relate to the error in estimated failure probabilities. This limitation can lead to high computational demands because of unnecessary calls to costly performance functions (e.g., involving finite element models) or potentially inaccurate estimates of failure probability due to premature termination of the training process. Here, we propose the error-based stopping criterion (ESC) to address these limitations. First, it is shown that the total number of wrong sign estimation of the performance function for candidate design samples by kriging, S, follows a Poisson binomial distribution. This finding is subsequently used to estimate the lower and upper bounds of S for a given confidence level for sets of candidate design samples classified by kriging as safe and unsafe. An upper bound of error of the estimated failure probability is subsequently derived according to the probabilistic properties of Poisson binomial distribution. The proposed upper bound is implemented in the kriging-based reliability analysis method as the stopping criterion. The efficiency and robustness of ESC are investigated here using five benchmark reliability analysis problems. Results indicate that the proposed method achieves the set accuracy target and substantially reduces the computational demand, in some cases by over 50%.

     

A new fast settling low power CMOS gain stage architecture

This paper presents a new gain stage for high accuracy and fast settling applications. In the proposed structure a novel combination of closed loop and open loop amplifiers is employed to achieve high accuracy and enhanced settling behavior while adding only negligible power to the main circuit power constraint. To evaluate the functionality of the proposed idea, a zero cross based circuit and a switch capacitor amplifier are designed to implement the open loop and the closed loop stages, respectively. Though, other topologies for implementation of open loop and closed loop amplifiers are applicable in the presented gain stage. The proposed structure is implemented in 0.18 μm CMOS technology. HSPICE simulation results, using level 49 models, demonstrate that the new configuration improves the power efficiency and the settling behavior as well as the system accuracy. The proposed scheme shows very fast settling times of 0.8, 1.01, 1.41 ns for the gain accuracies of 6, 8 and 10 bits, respectively, while loaded with 1 pF capacitance and the output swing is 1.6 V. In comparison with a conventional switched capacitor closed loop amplifier, the proposed architecture improves the settling performance by a factor of 3 for 6 bit resolution, while it adds only 0.63 mW power to the total power consumption that is 8.68 mW.     

Extra-framework charge and impurities effect,Grand Canonical Monte Carlo and volumetric measurements of CO2/CH4/N2 uptake on NaX molecular sieve

In this work, Monte Carlo simulation of CO₂, N₂, and CH₄ adsorption on zeolite 13X is carried out in grand canonical ensemble. FAU framework was used to reproduce the structure of zeolite 13X. Universal force field was used to calculate the interactions between adsorbates and 13X. Metropolis method was used for calculating adsorption isotherm. Volumetric measurements were carried out to confirm the simulation results. The simulation results using Universal force field showed good agreement with experimental results. Highest CO₂ uptake for this zeolite was found as 5.67 mol/kg from GCMC. Isosteric heat of adsorption was investigated to find the heat released during adsorption of each gas. The simulation result of isosteric heat of adsorption for CO₂, N₂, and CH₄ was utmost 17.00, 4.37, and 6.14 kcal/mole, respectively. Radial distribution graphs were used to find affinity of constituents of zeolite for CO₂. Henry’s constant evaluation was also performed at low pressure to find the selectivity of the structure. Henry’s constant of CO₂ in an equimolar mixture of N₂ and CH₄ was calculated 3.49 and 1.49 mol/kg.kPa, respectively. Finally, simulation results were fitted to Toth and dual-site Langmuir isotherms to find the best fit that belongs to dual-site Langmuir.     

Efficient binary to quaternary and vice versa converters: embedding in quaternary arithmetic circuits

The Journal of Supercomputing - Reversible logic is a nowadays promising choice for circuit design technologies since it is having diversified applications in the fields of digital signal...     

Kinetics and thermal properties of epoxy resin cured with Ni(II)‐tris‐(O‐pheneylendiamine) bromide

Diglycidyl ether of bisphenol A (DGEBA) is cured with a nickel complex of O‐phenylendiamine (OPD) as a ligand. The structure of the synthesized curing agent is confirmed through IR and elemental analysis. The curing kinetics of DGEBA/Ni(OPD)₃Br₂ system is studied by the dynamic DSC and isothermal FTIR techniques. In all cases, we have observed at least two exothermic peaks during DSC traces up to 350°C. Dynamic activation energies are calculated by using the two isoconversional, Kissinger and Ozawa, methods applied to peak maximum. A two‐parameter (m, n) autocatalytic model (Sestak–Berggren equation) is found to be the most adequate model to describe the cure kinetics of the observed thermal events. Isothermal kinetic parameters are estimated using the Horie model. The onset decomposition temperature and char yield (at 700°C) of the crosslinked material were 290°C and 27%, respectively. The activation energy of the solid‐state thermal degradation process is evaluated by Ozawa approach, resulting in 95–138 kJ/mol on a range of 2–20% decomposition conversion. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1257–1265, 2006     

High speed ant colony optimization CMOS chip

Ant colony optimization (ACO) is an optimization computation inspired by the study of the ant colonies’ behavior. This paper presents design and CMOS implementation of the ant colony optimization based algorithm for solving the TSP problem. In order to implement ant colony optimization algorithm in CMOS, we will present a new algorithm. This algorithm is based on the original ant colony optimization but it can be implemented in CMOS. Briefly, pheromone matrix is transformed on the chip area and ants move up-down through the pheromone matrix and they make their decisions. Finally ants select a global path. In previous researches only pheromone values is used, but select the next city in this paper is based on heuristics value and pheromone value. In definition of problem, we use heuristics value as a matrix. Previous researches could not be used for wide type of optimization problem but our chip gives heuristics value initially and we can change initial value of heuristics value according to the optimization problem so this capability increases the flexibility of ACO chip. Simple circuit is used in blocks of our chip to increase the speed of convergence of ACO chip. We use Linear Feedback Shift Register (LSFR) circuit for random number generator in ACO chip. ACO chip has capability of solving the big TSP problem. ACO chip is simulated by HSPICE software and simulation results show the good performance of final chip.     

A context-aware adaptive learning system using agents

Evolution of Web technologies has made e-learning a popular common way of education and training. As an outcome, learning content adaptation has been the subject of many research projects lately. This paper suggests a framework for building an adaptive Learning Management System (LMS). The proposed architecture is based upon multi-agent systems and uses both Sharable Content Object Reference Model (SCORM) 2004 and semantic Web ontology for learning content storage, sequencing and adaptation. This system has been implemented upon a well known open-source LMS and its functionalities are demonstrated through the simulation of a scenario mimicing the real life conditions. The result reveals the system effectiveness for which it appears that the proposed approach may be very promising.     

A reliability-based methodology for considering corrosion effects on fatigue deterioration in steel bridges - Part I: Methodology -

It is known that the effects of corrosion on fatigue originate from two major sources: stress concentration due to corrosion discontinuities (CNF factor) and stress amplification due to loosing net section (NAF factor). In order to account for these effects, a performance function is developed which takes CNF and NAF factors into account and considers both random and time-dependent nature of the involved parameters. In order to consider real fatigue and environmental conditions, the available CNF-y and y-t functions are extended employing α and φ factors, respectively. In addition, some recommendations have been made to establish corrosion pattern of different steel sections. The final output of the methodology is development of a reliability-based procedure to establish time-dependent deterioration profile of a structural member, which assists in decision-making with regard to maintenance activities. The proposed methodology has been applied to Neka Bridge, a railway bridge in northern Iran, which is presented in Part II.