Approximate solution for two stage open networks with Markov-modulated queues minimizing the state space explosion problem

Analytical solutions for two-dimensional Markov processes suffer from the state space explosion problem. Two stage tandem networks are effectively used for analytical modelling of various communication and computer systems which have tandem system behaviour. Performance evaluation of tandem systems with feedbacks can be handled with these models. However, because of the numerical difficulties caused by large state spaces, considering server failures and repairs at the second stage employing multiple servers has not been possible. The solution proposed in this paper is approximate with a high degree of accuracy. Using this approach, two stage open networks with multiple servers, break downs, and repairs at the second stage as well as feedback can be modelled as three-dimensional Markov processes and solved for performability measures. Results show that, unlike other approaches such as spectral expansion, the steady state solution is possible regardless of the number of servers employed.     

Synthesis of Symmetrical Multichromophoric Bodipy Dyes and Their Facile Transformation into Energy Transfer Cassettes

Multichromophoric boron‐dipyrromethene (Bodipy) dyes synthesized on phenylene‐ethynylene platforms have been be converted to energy transfer cassettes in a one‐step chemical transformation. Excitation energy transfer processes in these highly symmetrical derivatives were studied in detail, including time‐resolved fluorescence spectroscopy techniques. Excitation spectra and the emission lifetimes suggest efficient energy transfer between the donor and acceptor chromophore. These novel energy transfer cassettes, while highlighting a short‐cut approach to similar energy transfer systems, could be useful as large pseudo‐Stokes shift multichromophoric dyes with potential applications in diverse applications.     

Numerical simulation of minimum B‐jumps at abrupt drops

A numerical simulation of minimum B‐jumps in horizontal rectangular channels having an abrupt drop is given. Gradually varied, steady, supercritical flow is assumed as the initial condition. An unsteady flow is created by increasing the downstream depth. One‐dimensional, unsteady Saint‐Venant equations are solved by using the MacCormack and the dissipative two–four explicit finite difference schemes. The steady flow solution is obtained by treating the time variable as an iteration parameter and letting the solution converge to the steady state. The abrupt drop is treated as an interior boundary and solved by the method of characteristics. The results are compared with experimental and analytical studies. Copyright © 2007 John Wiley & Sons, Ltd.     

Coherence of acoustic modes propagating through shallow water internal waves

The 1995 Shallow Water Acoustics in a Random Medium (SWARM) experiment [Apel et al., IEEE J. Ocean. Eng. 22, 445-464 (1997)] was conducted off the New Jersey coast. The experiment featured two well-populated vertical receiving arrays, which permitted the measured acoustic field to be decomposed into its normal modes. The decomposition was repeated for successive transmissions allowing the amplitude of each mode to be tracked. The modal amplitudes were observed to decorrelate with time scales on the order of 100 s [Headrick et al., J. Acoust. Soc. Am. 107(1), 201-220 (2000)]. In the present work, a theoretical model is proposed to explain the observed decorrelation. Packets of intense internal waves are modeled as coherent structures moving along the acoustic propagation path without changing shape. The packets cause mode coupling and their motion results in a changing acoustic interference pattern. The model is consistent with the rapid decorrelation observed in SWARM. The model also predicts the observed partial recorrelation of the field at longer time scales. The model is first tested in simple continuous-wave simulations using canonical representations for the internal waves. More detailed time-domain simulations are presented mimicking the situation in SWARM. Modeling results are compared to experimental data.     

Synthesis,characterization, antioxidant properties and DFT calculation of some new pyrimidine derivatives

Abstract

In this study, 5-benzoyl-4-(4-(methylthio)phenyl)-6-phenyl-1,2,3,4-tetrahydro-2-thioxo (1), oxo (2) and imino (3) pyrimidine derivatives were prepared via Multicomponent Cyclocondensation Reactions (MCRs). The compounds thiazolo[3,2-a]pyrimidin-3(5H)-one (4) and thiazin-4(6H)-one (5) were obtained via the reaction of compound 1 with bromoacetic acid and 3-bromopropionic acid, respectively. Structures were determined by using FT-IR, ¹H/¹³C NMR and elemental analyses. Also the compounds 4 and 5 were analyzed by X-ray single crystal analysis. All compounds were investigated as corrosion inhibitors using density functional theory (DFT) at the level of B3LYP/6-31G (d, p). According to the calculations, the compound 3 appears to be a good inhibitor for corrosion. On the other hand, total antioxidant properties were measured in vitro by DPPH^?, ABTS^?+ test, hemolysis of phenylhydrazine erythrocytes and metal chelating effect. The results were compared with standard antioxidants such as trolox and α-tocopherol. These data revealed that compounds 1, 2 and 5 are more active with respect to 3 and 4 in scavenging the radicals.     

Water Miscible Mono Alcohols’ Effect on the Proteolytic Performance of Bacillus clausii Serine Alkaline Protease

In this study, our investigations showed that the increasing concentrations of all examined mono alcohols caused a decrease in the V _m, k _cat and k _cat/K _m values of Bacillus clausii GMBE 42 serine alkaline protease for casein hydrolysis. However, the K _m value of the enzyme remained almost the same, which was an indicator of non-competitive inhibition. Whereas inhibition by methanol was partial non-competitive, inhibition by the rest of the alcohols tested was simple non-competitive. The inhibition constants (K _I) were in the range of 1.32–3.10 M, and the order of the inhibitory effect was 1-propanol>2-propanol>methanol>ethanol. The ΔG ^≠ and ΔG ^≠ _E???T values of the enzyme increased at increasing concentrations of all alcohols examined, but the ΔG ^≠ _ES value of the enzyme remained almost the same. The constant K _m and ΔG ^≠ _ES values in the presence and absence of mono alcohols indicated the existence of different binding sites for mono alcohols and casein on enzyme the molecule. The k _cat of the enzyme decreased linearly by increasing log P and decreasing dielectric constant (D) values, but the ΔG ^≠ and ΔG ^≠ _E???T values of the enzyme increased by increasing log P and decreasing D values of the reaction medium containing mono alcohols.     

Spectral analysis of the Direct Sum Hamiltonian Operators

In this paper we investigate the deficiency indices theory and the selfad-joint and nonselfadjoint (dissipative, accumulative) extensions of the minimal symmetric direct sum Hamiltonian operators. In particular using the equivalence of the Lax-Phillips scattering matrix and the Sz.-Nagy-Foia¸s characteristic function, we prove that all root (eigen and associated) vectors of the maximal dissipative extensions of the minimal symmetric direct sum Hamiltonian operators are complete in the Hilbert spaces.     

Pd(II) complexes of novel phosphine ligands: Synthesis,characterization, and catalytic activities on Heck reaction

Novel phosphine oxides, (((3-methylpyridin-2-yl)amino)methyl)diphenylphosphine oxide (1) and diphenyl((pyrazin-2-ylamino)methyl)phosphine oxide (2), were synthesized and characterized. Phosphines ligands (3 and 4) were obtained by the reduction of 1 and 2 with AlH₃, monitored by ³¹P NMR spectroscopy. Pd(II) complexes of 3 and 4 were synthesized and characterized (5 and 6). The catalytic activity of 5 and 6 was tested on the reaction of styrene with both activated and deactivated aryl bromides in air. The results of the catalytic experiments were discussed through DFT calculations.     

Combinatorial and high-throughput screening of the effect of siloxane composition on the surface properties of crosslinked siloxane-polyurethane coatings

Libraries of siloxane-polyurethane coatings were designed, formulated, and screened using high-throughput experimentation. Four independent variables that were analyzed were the molecular weight of poly(dimethylsiloxane) (PDMS), presence or absence of poly(epsilon-caprolactone) (PCL) blocks attached to the PDMS backbone, the length of the PCL blocks, and the siloxane polymer level in the coating formulations. In addition to the siloxane libraries (3-aminopropyl-terminated PDMS and poly(epsilon-caprolactone)-poly(dimethylsiloxane)-poly(epsilon-caprolactone) (PCL-PDMS-PCL) triblock copolymers), the coating formulation included a trifunctional isocyanate crosslinker, trifunctional poly(epsilon-caprolactone) polyol, 2,4-pentanedione (pot-life extender), dibutyltin diacetate (catalyst), and a blend of solvents. The resulting coatings were analyzed for their surface energy and pseudobarnacle adhesion both before and after aging the coatings for 30 days in water. The water and methylene iodide contact angle averages increase with increasing molecular weight of PDMS. Coatings prepared from PCL-PDMS-PCL triblock copolymers have lower surface energies than coatings prepared from 3-aminopropyl-terminated PDMS; however, lower pseudobarnacle adhesion results were obtained for the coatings prepared from 3-aminopropyl-terminated PDMS than coatings prepared from PCL-PDMS-PCL triblock copolymers. The siloxane polymer level in the coating formulations does not have a significant effect on the surface energy of the coatings, but it resulted in higher pseudobarnacle adhesion.     

Incremental polynomial time dualization of quadratic functions and a subclass of degree-<Emphasis Type="Italic">k</Emphasis> functions

We consider the problem of dualizing a Boolean function f represented by a DNF. In its most general form, this problem is commonly believed not to be solvable by a quasi-polynomial total time algorithm. We show that if the input DNF is quadratic or is a special degree-k DNF, then dualization turns out to be equivalent to hypergraph dualization in hypergraphs of bounded degree and hence it can be achieved in incremental polynomial time.