Simulation microscopic chemical processes. IV. Temperature dependence of deactivation and dissociation of bromide in argon

Previous molecular dynamics simulations of the deactivation or dissociation of a bromine molecule at an energy just above the minimum required for dissociation and surrounded by an argon medium in canonical equilibrium has been extended from 1500 K to 160 and 295 K. The aim is to observe the extent to which temperature determines the qualitative as well as quantitative features of the process. Despite an observed sensitivity to the initial state of the medium which required introduction of a Monte Carlo selection procedure the final results indicate that the deactivation—dissociation mechanism is insensitive to temperature changes in the range presently explored. We conclude that a properly constructed independent binary collision theory would have a wide range of applicability.     

Comments on “the scattering of light and phase transition in solutions of tertiary butyl alcohol in water”

In two independent experiments, we have measured the Rayleigh factor of tert-butanol-water mixtures as a function of concentration. Our results are in strong disagreement with those of Vuks and Shurapova in that we find only a single maximum in the Rayleigh factor at mole fraction 0.125 in alcohol. We find that the Rayleigh factors of solutions in the immediate vicinity of 0.03 mole fraction of alcohol depend strongly upon the purity of the components and treatment of the solutions prior to measurement. A possible explanation for this behavior is given.     

Determination of the rate coefficients for the collisional excitation and de-excitation of the upper laser levels of Ar

The absolute concentrations of the argon-ion states of the configurations 3d, 4s, 4p, 4p′, 4d and 5s have been measured for a pulsed laser discharge whose plasma parameters have been previously determined. For the resonant levels, the measurements were made by a self-absorption technique and for other levels by absolute spectroscopic observations. Variations of the populations of these levels as functions of discharge current and filling pressure (i.e. electron temperature and density) permitted calculations of the total excitation and de-excitation rate coefficients due to electrons as functions of temperature for each laser level. For excitation, collisions with the fundamental and long-lived states were taken into account while, for de-excitation, superelastic, excitation and ionization collisions were considered.     

Crystallization of n-doped amorphous silicon PECVD films: comparison between SPC and RTA methods

Amorphous silicon films are deposited by radio-frequency plasma-enhanced chemical-vapor deposition (RF-PECVD) with different n-doping rates. The amorphous films are subsequently crystallized using either solid phase crystallization (SPC) or rapid thermal annealing (RTA). We compare the effect of the n-doping rate on some properties of the microcrystalline silicon films obtained with both techniques. In the SPC process, the time required for the beginning of the crystallization decreases with increasing phosphorus doping. Moreover, doped films present slightly higher crystal size than intrinsic films but the doping rate does not significantly influence the grain size. For RTA, the doping rate decreases the crystallization temperature and increases significantly the crystal size. Whatever the doping rate, the average grain sizes obtained by RTA are larger than those obtained by SPC. The electrical resistance of the crystallized films also depends on the crystallization process: RTA films present a lower dark conductivity than SPC films. These results are discussed taking into account the different kinetics of both crystallization techniques and the role played by the silicon dangling bonds and their charge states on the crystal growth.     

Synthesis of PVDF/BiFeO3 nanocomposite and observation of enhanced electrical conductivity and low‐loss dielectric permittivity at percolation threshold

A novel two‐phase polymer nanocomposite film comprising of polyvinylidene fluoride (PVDF) and nanocrystalline (～90 nm) semiconducting multiferroic BiFeO₃ (BFO) have been fabricated by hot‐molding technique. Such flexible thick nanocomposite films, semicrystalline in nature, exhibited extraordinarily high effective dielectric permittivity ε_eff ～ 10³ (compared with that of pure PVDF) near the low percolation threshold (f_c = 0.12) at room temperature (RT) and the films also possessed low dielectric loss (～0.18). The polarization‐electric field (P‐E) hysteresis loops are displayed at RT, which indicate ferroelectric like behavior of PVDF still persists in the percolative nanocomposite. There is also large increase of remanent polarization of BFO in the composite indicating improvement of the multiferroic behavior of BFO embedded in the PVDF polymer. The sample also indicates good fatigue endurance. Formation of microcapacitors and percolative behavior are correlated to explain the obtained results based on the special geometry of the BFO nanofillers. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Dissipation Length Scale Estimates for Turbulent Flows: A Wiener Algebra Approach

In this paper, a lower bound estimate on the uniform radius of spatial analyticity is established for solutions to the incompressible, forced Navier–Stokes system on an \(n\) -torus. This estimate matches previously known estimates provided that a certain bound on the initial data is satisfied. In particular, it is argued that for two-dimensional (2D) turbulent flows, the initial data is guaranteed to satisfy this hypothesized bound on a significant portion of the 2D global attractor, in which case, the estimate on the radius matches the best known one found in Kukavica (1998). A key feature in the approach taken here is the choice of the Wiener algebra as the phase space, i.e., the Banach algebra of functions with absolutely convergent Fourier series, whose structure is suitable for the use of the so-called Gevrey norms. We note that the method can also be applied with other phase spaces such as that of the functions with square-summable Fourier series, in which case the estimate on the radius matches that of Doering and Titi (1995). It can then similarly be shown that for three-dimensional (3D) turbulent flows, this estimate holds on a significant portion of the 3D weak attractor.     

Compact fiber laser at L-band region using Erbium-doped Zirconia fiber

A compact Erbium-doped fiber laser (EDFL) operating in L-band region is demonstrated using a fabricated Erbium-doped Zirconia fiber (EDZF) for the first time. The fiber is fabricated by combining Zr and Al to achieve the maximum Erbium ion concentration of 4320 wt ppm. By using a fiber Bragg grating (FBG) in a ring configuration, the laser operates at 1579.6 nm with a slope efficiency of 13.6% and the threshold pump power of 25.1 mW. The lasing wavelength is obtained at Bragg wavelength with an output power of 13 dBm and a 3 dB spectral width of 0.02 nm using a piece of 2 m long EDZF in conjunction with 120 mW of 1480 nm pump power.