Elasto-plastic earthquake response of arch dams including fluid–structure interaction by the Lagrangian approach

Elasto-plastic earthquake response of arch dams including fluid–structure interaction by the Lagrangian approach is mainly investigated in this study. To this aim, three-dimensional eight-noded version of Lagrangian fluid finite element including the effects of compressible wave propagation and surface sloshing motion, and three-dimensional version of Drucker–Prager model based on associated flow rule assumption were programmed in FORTRAN language by authors and incorporated into the program NONSAP. Two new components added into the NONSAP were tested on a simple fluid tank and a simple fluid–structure system and obtained very reasonable results.     

Optimizing venture capital investments in a jump diffusion model

We study two practical optimization problems in relation to venture capital investments and/or Research and Development (R&D) investments. In the first problem, given the amount of the initial investment and the cash flow structure at the initial public offering (IPO), the venture capitalist wants to maximize overall discounted cash flows after subtracting subsequent investments, which keep the invested company solvent. We describe this problem as a mixture of singular stochastic control and optimal stopping problems. The second problem is concerned with optimal dividend policy. Rather than selling the company at an IPO, the investor may want to harvest technological achievements in the form of dividend when it is appropriate. The optimal control policy in this problem is a mixture of singular and impulse controls. E. Bayraktar was supported in part by the National Science Foundation, under grant DMS-0604491.     

Estimation of stochastic nonlinear dynamic response of rock-fill dams with uncertain material parameters for non-stationary random seismic excitation

This research investigates the effect of uncertain material parameters on the stochastic, dynamic response of a rock-fill dam-foundation system subjected to non-stationary random excitation. The uncertain material parameter of particular interest is the shear modulus, developed from a lognormal distribution model. The stochastic seismic response model of the dam-foundation system, with uncertain material parameters and subjected to random loads is the result of a Monte Carlo simulation method. The nonlinear behavior model arises from an equivalent linear method, which considers the nonlinear variation of soil shear modulus and soil damping as a function of shear strain. Specification of the non-stationary stochastic process arises from a simulation method, which generates artificial earthquake accelerograms obtained from the product of a deterministic function of time and a stationary process. The artificial earthquake ground acceleration records reflect the characteristics of soft, medium and firm soil types. Comparison of the numerical results from these approaches provides stochasticity in earthquake seismic excitation and randomness in material parameter (shear modulus) cases. Further, the results indicate that both these cases generally influence the nonlinear dynamic response of rock-fill dams to a non-stationary seismic excitation.     

Hyperbranched Polymers by Type II Photoinitiated Self‐Condensing Vinyl Polymerization

Type II photoinitiated self‐condensing vinyl polymerization for the preparation of hyperbranched polymers is explored using 2‐hydroxyethyl methacrylate (HEMA) or 2‐(dimethylamino)ethyl methacrylate (DMAEMA), and methyl methacrylate as hydrogen donating inimers and comonomer, respectively, in the presence of benzophenone and camphorquinone under UV and visible light. Upon irradiation at the corresponding wavelength, the excited photoinitiator abstracts hydrogen from HEMA or DMAEMA leading to the formation of initiating radicals. Depending on the concentration of inimers, type of the photoinitiator, and irradiation time, hyperbranched polymers with different branching densities and cross‐linked polymers are formed.

     

Synthesis of a monolithic, micro-immobilised enzyme reactor via click-chemistry

An immobilised enzyme reactor (IMER) in the form of capillary monolith was developed for a micro-liquid chromatography system. The plain monolith was obtained by in situ thermal copolymerisation of glycidyl methacrylate and ethylene dimethacrylate in a fused silica capillary (200 × 0.53 mm ID) by using n-propanol/1,4-butanediol as porogen. The enzyme, α-chymotrypsin (CT), was covalently attached onto the monolith via triazole ring formation by click-chemistry. For this purpose, the monolithic support was treated with sodium azide and reacted with the alkyne carrying enzyme derivative. CT was covalently linked to the monolith by triazole-ring formation. The activity behaviour of monolithic IMER was investigated in a micro-liquid chromatography system by using benzoyl-L-tyrosine ethyl ester (BTEE) as synthetic substrate. The effects of mobile-phase flow rate and substrate feed concentration on the final BTEE conversion were investigated under steady-state conditions. In the case of monolithic IMER, the final substrate conversion increased with increasing feed flow rate and increasing substrate feed concentration. Unusual behaviour was explained by the presence of convective diffusion in the macropores of monolith. The results indicated that the monolithic-capillary IMER proposed for micro-liquid chromatography had significant advantages with respect to particle-based conventional high-performance liquid chromatography-IMERs.     

Copper(II) complexes of acylhydrazones: synthesis,characterization and DNA interaction

Two new acylhydrazone copper(II) complexes of 4‐hydroxy‐N′‐[(1E)‐1‐(4‐methylphenyl)ethylidene]benzohydrazide (HL¹) and 4 ethyl [4‐({(2E)‐2‐[1‐(4‐methylphenyl)ethylidene]hydrazinyl}carbonyl)phenoxy]acetate (HL²) have been synthesized and characterized. The structures of both acylhydrazone and copper(II) complexes were identified by elemental analysis, infrared spectra, UV–visible electronic absorption spectra, magnetic susceptibility measurements, TGA and powder X‐ray diffraction. DNA binding and DNA cleavage activities of the synthesized copper complexes were examined by using UV‐visible titration and agarose gel electrophoresis, respectively. The effect of complex concentration on the DNA cleavage reactions in the absence and presence of H₂O₂ was also investigated. The results indicate that all the complexes bind slightly to calf thymus DNA and cleavage pBR322 DNA. The mechanistic studies demonstrate that a hydrogen peroxide‐derived species and singlet oxygen (¹O₂) are the active oxidative species for DNA cleavage. Copyright © 2013 John Wiley & Sons, Ltd.     

Autoignition in stratified mixtures for pressure gain combustion

The reliable generation of quasi-homogeneous autoignition inside a combustor fed by a continuous air flow would represent a milestone in realizing pressure gain combustion in gas turbines. In this work, the ignition distribution inside a stratified fuel–air mixture is analyzed. The ability of precise and reproducible injection of a desired fuel profile inside a convecting air flow is verified by applying tunable diode laser absorption spectroscopy in non-reacting measurements. High-speed, static pressure sensors and ionization probes allow for simultaneous detection of the flame and pressure rise at several axial positions in reactive measurements with dimethyl ether as fuel. A second, exchangeable combustion tube enables optical observation of OH* intensity in combination with pressure measurements. Experiments with three arbitrary fuel profiles show a set of ignition distributions that vary in shape, homogeneity, and the number of simultaneous autoignition events. Although the measurements show notable variation, a significant and reproducible influence of the fuel injection on the ignition distribution is observed. Results show that uniform autoignition leads to a coupling of the reaction front with the pressure rise and, therefore, induces a greater aerodynamic constraint than non-uniform ignition distributions, which are dominated by propagating deflagration fronts.     

The effects of implementation delay on decision-making under uncertainty

In this paper, we accomplish two objectives: First, we provide a new mathematical characterization of the value function for impulse control problems with implementation delay and present a direct solution method that differs from its counterparts that use quasi-variational inequalities. Our method is direct, in the sense that we do not have to guess the form of the solution and we do not have to prove that the conjectured solution satisfies conditions of a verification lemma. Second, by employing this direct solution method, we solve two examples that involve decision delays: an exchange rate intervention problem and a problem of labor force optimization.     

Nonlinear finite element reliability analysis of Concrete-Faced Rockfill (CFR) dams under static effects

The response of concrete slab on Concrete-Faced Rockfill (CFR) dams is very important. This study investigates the reliability of the concrete slab on a CFR dam by the improved Rackwitz–Fiessler method under static loads. For this purpose, ANSYS finite element analysis software and FERUM reliability analysis program are combined with direct coupled method and response surface method. Reliability index and probability of failure of the concrete are computed in the all critical points of the concrete slab by dam height. This study is also expanded for the reliability of CFR dams including different concrete slab thickness. In addition to the linear behavior, geometrically and materially non-linear responses of the dam are considered in the finite element analysis which is performed with reliability analysis. The Drucker–Prager method and the multi linear kinematic hardening method are, respectively, used for concrete slab and for rockfill and foundation rock. Finite element model used in the analyses includes dam–reservoir–foundation interaction. Reservoir water is modeled by the Lagrangian approach. Welded and friction contact based on the Coulomb’s friction law are considered in the joints of the dam. One-dimensional two noded contact elements are used to define friction. The self-weight of the dam and the hydrostatic pressure of the reservoir water are considered in the numerical solutions. According to this study, hydrostatic pressure, nonlinear response of the rockfill and the decrease in the concrete slab thickness reduce the reliability of the concrete slab of the CFR dam. Besides, the CFR dam models including friction are safer than the models including welded contact in the joints.