Surrogate constraint normalization for the set covering problem

The set covering problem (SCP) is central in a wide variety of practical applications for which finding good feasible solutions quickly (often in real-time) is crucial. Surrogate constraint normalization is a classical technique used to derive appropriate weights for surrogate constraint relaxations in mathematical programming. This framework remains the core of the most effective constructive heuristics for the solution of the SCP chiefly represented by the widely-used Chvátal method. This paper introduces a number of normalization rules and demonstrates their superiority to the classical Chvátal rule, especially when solving large scale and real-world instances. Directions for new advances on the creation of more elaborate normalization rules for surrogate heuristics are also provided.     

TRANSFORM-ANN for online optimization of complex industrial processes: Casting process as case study

Artificial Neural Networks (ANNs) are well known for their credible ability to capture non-linear trends in scientific data. However, the heuristic nature of estimation of parameters associated with ANNs has prevented their evolution into efficient surrogate models. Further, the dearth of optimal training size estimation algorithms for the data greedy ANNs resulted in their overfitting. Therefore, through this work, we aim to contribute a novel ANN building algorithm called TRANSFORM aimed at simultaneous and optimal estimation of ANN architecture, training size and transfer function. TRANSFORM is integrated with three standalone Sobol sampling based training size determination algorithms which incorporate the concepts of hypercube sampling and optimal space filling. TRANSFORM was used to construct ANN surrogates for a highly non-linear industrially validated continuous casting model from steel plant. Multiobjective optimization of casting model to ensure maximum productivity, maximum energy saving and minimum operational cost was performed by ANN assisted Non-dominated Sorting Genetic Algorithms (NSGA-II). The surrogate assisted optimization was found to be 13 times faster than conventional optimization, leading to its online implementation. Simple operator's rules were deciphered from the optimal solutions using Pareto front characterization and K-means clustering for optimal functioning of casting plant. Comprehensive studies on (a) computational time comparisons between proposed training size estimation algorithms and (b) predictability comparisons between constructed ANNs and state of art statistical models, Kriging Interpolators adds to the other highlights of this work. TRANSFORM takes physics based model as the only input and provides parsimonious ANNs as outputs, making it generic across all scientific domains.     

L-convergence rate to diffusion waves for p-system with relaxation

In this paper, we consider the asymptotic behavior of solution for the Cauchy problem for p-system with relaxation

(E)     

A simple formula for the temperature dependence of the relaxation frequency in glassy systems

A simple,five-parameter empirical formula for the temperature dependence of the relaxation frequency is presented. It is shown that this formula reduces to the Arrhenius equation at higher temperatures and to the Vogel-Fulcher-Tamman equation at lower temperatures. Apart from parameters which may be obtained independently from either equation the proposed formula contains an additional parameter describing the sharpness of the transition between the regions of validity of Arrhenius or Vogel-Fulcher-Tamman equation. The applicability of the formula is tested on dielectric relaxation data of acrylic polymers and on other dielectric data available in the literature. The physical meaning of individual parameters is discussed.     

A o(n logn) algorithm for LP knapsacks with GUB constraints

A specialization of the dual simplex method is developed for solving the linear programming (LP) knapsack problem subject to generalized upper bound (GUB) constraints. The LP/GUB knapsack problem is of interest both for solving more general LP problems by the dual simplex method, and for applying surrogate constraint strategies to the solution of 0–1 Multiple Choice integer programming problems. We provide computational bounds for our method of o(n logn), wheren is the total number of problem variables. These bounds reduce the previous best estimate of the order of complexity of the LP/GUB knapsack problem (due to Witzgall) and provide connections to computational bounds for the ordinary knapsack problem.We further provide a variant of our method which has only slightly inferior worst case bounds, yet which is ideally suited to solving integer multiple choice problems due to its ability to post-optimize while retaining variables otherwise weeded out by convex dominance criteria.     

Investigation of photoelectrical properties and relaxation dynamics in photoexcited CdSe nanocrystals in thin film form

Electrical and photoelectrical properties of cubic CdSe nanocrystals in thin film form (including the relaxation dynamics of photocarriers) are investigated. Photoelectrical properties of the obtained films are controlled by chemical (varying the reagent concentration in the reaction system) and physical means (controlling the crystal dimensions). In the case of thin films with optimal photoelectrical properties, the calculated band gap energy and ionization energies of impurity levels (on the basis of experimentally obtained temperature dependence of dark electrical resistance) at 0 K are 1.85, 0.74 and 0.43 eV, correspondingly. The calculated optical band gap energy (on the basis of spectral dependence of photoconductivity) at room temperature of 1.75 eV is in excellent agreement with the value of 1.77 eV which is obtained on the basis of electronic absorption spectrum in the framework of parabolic approximation for dispersion relation. Upon thermal treatment of chemically deposited thin films of cubic CdSe quantum dots, as a result of processes of coalescence and crystal growth, the electronic contact between nanocrystals increases and the confinement effects irreversibly disappear. Relaxation of non-equilibrium charge carriers is practically carried out according to the linear mechanism. The calculated relaxation time of photoexcited charge carriers is 0.4 ms.     

Nuclear magnetic resonance relaxation titration

Summary Quantitative determination of the concentration of paramagnetic ions in aqueous solutions is performed by NMR relaxation titration. By measurement of the nuclear spin-lattice relaxation time T ₁ or the nuclear spin-spin relaxation time T₂ redox titrations and complexometric determinations of the concentration of paramagnetic ions are possible. Also the precipitation of ions from the solution can be followed by this method. The use of a magnetic indicator in this analytical method is shown. The sensitivity of the method goes down to concentrations as low as 10^–3 M. The accuracy of NMR relaxation titration is better than 1%. A number of applications of the method are given.

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Kernmagnetische Relaxationstitration

Zusammenfassung Quantitative Bestimmungen von paramagnetischen Ionen in wäßrigen Lösungen können mit Hilfe der kernmagnetischen Relaxationstitration durchgeführt werden. Durch Messung der Kernspin-Gitter-Relaxationszeit T ₁ oder der Kernspin-Kernspin-Relaxationszeit T ₂ als Funktion der Ionenkonzentration sind Redoxtitrationen oder komplexometrische Titrationen möglich. Der quantitative Ablauf von Fällungen kann ebenfalls verfolgt werden. Die Verwendung von magnetischen Indicatoren bei der Relaxationstitration wird beschrieben. Bestimmungen von Ionenkonzentrationen bis herab zu 10^–3 M Lösungen sind z.Z. möglich. Die Methode erlaubt eine Genauigkeit der Konzentrationsbestimmung von 1% und besser. Die Anwendung der Methode wird an einer Reihe von Beispielen gezeigt.

     

AC impedance analysis of CsNO3:Al2O3 composite solid electrolyte systems

Complex impedance spectroscopic studies were carried out on CsNO₃ and CsNO₃-Al₂O₃ dispersed solid electrolyte systems (DSES) in the temperature range of 100-350 °C and the frequency 50 kHz-1 MHz. Dielectric constant, loss tangent, ac conductivity and dc ionic conductivity (obtained from CIS) in these systems are presented. DC ionic conductivity is noticed to increase with temperature in the extrinsic region in pure and dispersed systems. The enhancement of conductivity in DSES was observed to be about two orders of magnitude over its pure form in the extrinsic region. This enhancement of conductivity was attributed to the formation of space charge layer between the host material and the dispersoid. Enhancement in conductivity is found to increase with m/o up to 40 m/o where as it decreased for 80 m/o. Dielectric constant, dielectric loss and ac conductivity are also found to increase with temperature, and with mole percent it maintained the similar behavior as that of dc conductivity. These dielectric properties are interpreted in terms of space charge polarization and increased concentration of defects in the interfacial layer formed between the host and the dispersoid.     

测量电子自旋——晶格弛豫时间T1的技术问题

本文讨论应用连续波方法测量电子自旋——晶格弛豫时间T₁的实验技术问题。分析液氮翻滚使T₁测量结果很不一致的原因,提出用吹冷气冷冻样品方法,可以解决液氮翻滚对测量T₁所产生的影响.用改进的方法测量ZnS:Mn、Cu粉末样品的T₁,获得重复性较好的实验结果。     

水溶液中组氨酸的14N NMR研究

用NMK法测得不同pH值条件下组氨酸的¹⁴N谱,用反转恢复法测得¹⁴N的T1值。根据¹⁴N谱及T₁值快速且准确地证实了组氨酸在不同电离情况下的结构。