High-temperature conductivity in chemical bath deposited copper selenide thin films

This paper reports high-temperature (305–523 K) electrical studies of chemical bath deposited copper (I) selenide (Cu_2−xSe) and copper (II) selenide (Cu₃Se₂) thin films. Cu_2−xSe and Cu₃Se₂ have been prepared on glass substrates from the same chemical bath at room temperature by controlling the pH. From X-ray diffraction (XRD) profiles, it has been found that Cu_2−xSe and Cu₃Se₂ have cubic and tetragonal structures, respectively. The composition of the chemical constituent in the films has been confirmed from XRD data and energy-dispersive X-ray analysis (EDAX). It has been found that both phases of copper selenide thin films have thermally activated conduction in the high-temperature range. In this paper we also report the variation of electrical parameters with film thickness and the applied voltage.     

On a reduced load equivalence for fluid queues under subexponentiality

We propose a general framework for obtaining asymptotic distributional bounds on the stationary backlog in a buffer fed by a combined fluid process A ₁ + A ₂ and drained at a constant rate c. The fluid process A ₁ is an (independent) on–off source with average and peak rates ρ₁ and r₁ , respectively, and with distribution G for the activity periods. The fluid process A ₂ of average rate ρ₂ is arbitrary but independent of A ₁. These bounds are used to identify subexponential distributions G and fairly general fluid processes A ₂ such that the asymptotic equivalence P[W ^A1+A2,c >ϰ]∼P[W ^A1,c—ρ2>ϰ] (ϰ → ∞) holds under the stability condition ρ₁ + ρ₂ < c and the non-triviality condition c – ρ₂ < r ₁. In these asymptotics the stationary backlog results from feeding source A ₁ into a buffer drained at reduced rate c – ρ₂. This reduced load asymptotic equivalence extends to a larger class of distributions G a result obtained by Jelenkovic and Lazar [19] in the case when G belongs to the class of regular intermediate varying distributions. This revised version was published online in June 2006 with corrections to the Cover Date.     

Design of Fiber-Laser Arrays with Genetic Algorithms

The optimization of the far-field pattern of fiber-laser arrays is investigated based on genetic algorithms. A derived objective function of the far-field pattern performs the task of evaluating each of the fiber-laser designs generated by the genetic algorithm. The constrained parameters of the design included are radius of the fiber a, the important V value, the fiber-to-fiber separation S, and the operational wavelength . As results, sidelobe level is optimized to be -38.83 dB for a circular arrays with the given constrained parameters.     

Microphase separation in polyelectrolytic diblock copolymer melt: weak segregation limit

The authors present a generalized theory of microphase separation for charged-neutral diblock copolymer melt. The stability limit of the disordered phase for salt-free melt has been calculated using random phase approximation (RPA) and self-consistent-field theory (SCFT). Explicit analytical free energy expressions for different classical ordered microstructures (lamellar, cylinder, and sphere) are presented. The authors demonstrate that the chemical mismatch required for the onset of microphase separation (chi*N) in charged-neutral diblock melt is higher and the period of ordered microstructures is lower than those for the corresponding neutral-neutral diblock system. Theoretical predictions on the period of ordered structures in terms of Coulomb electrostatic interaction strength, chain length, block length, and chemical mismatch between blocks are presented. SCFT has been used to go beyond the stability limit, where electrostatic potential and charge distribution are calculated self-consistently. Stability limits calculated using RPA are in perfect agreement with the corresponding SCFT calculations. Limiting laws for the stability limit and the period of ordered structures are presented and comparisons are made with an earlier theory. Also, transition boundaries between different morphologies have been investigated.     

26pi aromatic core-modified hexaphyrins: syntheses, characterization, and structural diversities

Synthesis and characterization of several 26pi core-modified hexaphyrins are reported. The synthetic methodology involved a well-known acid-catalyzed MacDonald-type condensation reaction of the required tripyrrane with electron deficient pentafluorobenzaldehyde. The nature of the product and yield depends on the nature of the acid catalyst and its concentration. Dioxahexaphyrin 9 was isolated only when 0.5 equiv of TFA was used as a catalyst, while dithiahexaphyrin 10 and diselenahexaphyrin 11 were formed with TFA, PTSA, and even in the absence of catalyst. The detailed 1H and 2-D COSY as well as HSQC experiments reveal the solution structure as well as the conformational mobility of hexaphyrins. In the tetracationic state, 10 and 11 exhibit a four heterocyclic ring inverted structure, while only two completely inverted heterocyclic rings were observed for 9. The other four heterocyclic rings are only partially inverted in 9. All the hexaphyrins reported here show aromatic character inferred from large Deltadelta values (difference in chemical shift between the most shielded and the most deshielded protons). Electronic absorption spectral studies also support the conformational changes observed upon protonation.     

Silver ion beam irradiation effects on poly(lactide-co-glycolide) (PLGA)/clay nanocomposites

Swift heavy ions induced modification of thin films of blends of poly(lactide-co-glycolide) (PLGA) (50:50) with organically modified nanoclay (Cloisite^® 30B) has been studied, using optical, structural and surface morphological analysis. Presence of nanoclay is found to enhance the properties of this degradable copolymer by reducing the rate of degradation even at high irradiation fluence. Optical and structural analysis of the polymer nanocomposites suggests that both the cross-linking and chain scission phenomenon are caused by swift heavy ion irradiation. XRD measurements show intercalation of PLGA in the clay galleries. Surface morphology of a nanocomposite indicates significant changes after irradiation at various fluences.     

Mechanical properties and electronic structure of the incompressible rhenium carbides and nitrides: A first-principles study

By means of first-principles calculations, the structural stability, mechanical properties and electronic structure of the newly synthesized incompressible Re₂C, Re₂N, Re₃N and an analogous compound Re₃C have been investigated. Our results agree well with the available experimental and theoretical data. The proposed Re₃C is shown to be energetically, mechanically and dynamically stable and also incompressible. Furthermore, it is suggested that the incompressibility of these compounds is originated from the strong covalent bonding character with the hybridization of 5d orbital of Re and the 2p orbital of C or N, and a zigzag topology of interconnected bonds, e.g., Re-Re, Re-C or Re-N bonding.     

On nuclear stopping in asymmetric colliding nuclei

Using the isospin-dependent quantum molecular dynamics (IQMD) model, nuclear stopping is analyzed in asymmetric colliding channels by keeping the total reacting mass fixed. The calculations have been performed by varying the mass asymmetry of the colliding pairs with different neutron-proton ratios at an incident beam energy of 250 MeV/nucleon. We find sizable effects of mass asymmetry on nuclear stopping and on the equilibrium of the nuclear matter. A reasonable agreement is also observed between the experimental data and our present calculations.     

Reheating in tachyonic inflationary models: Effects on the large scale curvature perturbations

We investigate the problem of perturbative reheating and its effects on the evolution of the curvature perturbations in tachyonic inflationary models. We derive the equations governing the evolution of the scalar perturbations for a system consisting of a tachyon and a perfect fluid. Assuming the perfect fluid to be radiation, we solve the coupled equations for the system numerically and study the evolution of the perturbations from the sub-Hubble to the super-Hubble scales. In particular, we analyze the effects of the transition from tachyon driven inflation to the radiation dominated epoch on the evolution of the large scale curvature and non-adiabatic pressure perturbations. We consider two different potentials to describe the tachyon and study the effects of two possible types of decay of the tachyon into radiation. We plot the spectrum of curvature perturbations at the end of inflation as well as at the early stages of the radiation dominated epoch. We find that reheating does not affect the amplitude of the curvature perturbations in any of these cases. These results corroborate similar conclusions that have been arrived at earlier based on the study of the evolution of the perturbations in the super-Hubble limit. We illustrate that, before the transition to the radiation dominated epoch, the relative non-adiabatic pressure perturbation between the tachyon and radiation decays in a fashion very similar to that of the intrinsic entropy perturbation associated with the tachyon. Moreover, we show that, after the transition, the relative non-adiabatic pressure perturbation dies down extremely rapidly during the early stages of the radiation dominated epoch. It is these behavior which ensure that the amplitude of the curvature perturbations remain unaffected during reheating. We also discuss the corresponding results for the popular chaotic inflation model in the case of the canonical scalar field.