A0 Exp Research Articles

Linear characteristics of dust acoustic waves in two dimensional inhomogeneous complex plasmas

This paper explores dust acoustic waves (DAWs)’ instability in two dimensional nonuniform complex plasmas. For this purpose, the dispersion relation is obtained using the method of separation of variables. In the process of linearizing the hydrodynamic equations describing the characteristics of two dimensional nonuniform complex plasma equations, the temporal and spatial dependence of all perturbations is assumed to be proportional to A1(x, y)exp[−iωt]. It is shown that the inhomogeneities in indifferent directions have different influences on the linear dispersion characteristics of DAWs. The numerical results show that the present research results are very important in the phenomenon of space astrophysical and experimental plasmas.

Efficacy Analysis of Corneal Photo-vitrification (CPV) for Improved Vision of Age-related Macular Degeneration (AMD) Eyes

Purpose: To analyze the safety and efficacy of corneal photovitrification (CPV) for improved visions of age-related macular degeneration (AMD) eyes.
 Study Design: Using CPV for improved visions of AMD eyes.
 Place and Duration of Study: New Taipei City, Taiwan, and Austin, TX, USA; between
 April, 2022 and June, 2022.
 Methodology: The CPV efficacy is calculated based on the rate equation given by dM/dt=-k(t) M(t), where M(t) is the PCV-treated corneal stroma; and k(t) is the rate coefficient given by an Arrhenius formula, k(t) = A0 exp[−Ea/(RT(t,z)], where t and z are the laser irradiation time and depth of the cornea stroma; Ea is the activation energy and R is the gas constant. The temperature spatial and temporal profiles are given by the numerical solutions of a heat diffusion equation with a volume heating source. Various effective depths including the tissue damage depth, temperature penetration depth and conversion depth, governed by the tissue absorption coefficient, light intensity and dose (or irradiation time), and the related threshold values, are introduced in replacing the conventional penetration depth based on a Beer's law.
 Results: The suggested protocol for CPV treatments include: a diode laser at about 2 µm wavelength (with absorption coefficient about 100 cm-1). The laser dose is about 25 J/cm2/spot and irradiation time of 150 ms.
 Conclusion: The efficacy of CPV may be predicted/calculated by our modeling based on rate equation and the corneal stroma temperature rise due to laser heating. The preferred retinal locus (PRL) movement observed post-CPV is caused mainly by neuroadaptation.

Deactivation of Porous Photocatalytic Particles During a Wastewater Treatment Process

Deactivation of porous photocatalytic materials was studied using three types of microstructured particles: macroporous titania particles, titania microspheres, and porous silica microspheres containing CNTs and TiO2 nanoparticles. All particles were synthesized by emulsion-assisted self-assembly using micron-sized droplets as micro-reactors. During repeated cycles of the photocatalytic decomposition reaction, the non-dimensionalized initial rate constants (a) were estimated as a function of UV irradiation time (t) from experimental kinetics data, and the results were plotted for a regression according to the exponentially decaying equation, a = a0 exp(-kdt). The retardation constant (kd) was then compared for macroporous titania microparticles with different pore diameters to examine the effect of pore size on photocatalytic deactivation. Nonporous or larger macropores resulted in smaller values of the deactivation constant, indicating that the adsorption of organic materials during the photocatalytic decomposition reaction hinders the generation of active radicals from the titania surface. A similar approach was adopted to evaluate the activation constant of porous silica particles containing CNT and TiO2 nanoparticles to compare the deactivation during recycling of the photocatalyst. As the amount of CNTs increased, the deactivation constant decreased, indicating that the conductive CNTs enhanced the generation of active radicals in the aqueous medium during photocatalytic oxidation.

Kinetics and Mechanism of Oxidation of S2O32− by a Co‐Bound μ‐Amido‐μ‐Superoxo Complex

ABSTRACTIn acetate buffer media (pH 4.5–5.4) thiosulfate ion (S2O32−) reduces the bridged superoxo complex, [(NH3)4CoIII(μ‐NH2,μ‐O2)CoIII(NH3)4]4+ (1) to its corresponding μ‐peroxo product, [(NH3)4CoIII(μ‐NH2,μ‐O2)CoIII(NH3)4]3+ (2) and along a parallel reaction path, simultaneously S2O32− reacts with 1 to produce the substituted μ‐thiosulfato‐μ‐superoxo complex, [(NH3)4CoIII(μ‐S2O3,μ‐O2)CoIII(NH3)4]3+ (3). The formation of μ‐thiosulfato‐μ‐superoxo complex (3) appears as a precipitate which on being subjected to FTIR shows absorption peaks that support the presence of Co(III)‐bound S‐coordinated S2O32− group. In reaction media, 3 readily dissolves to further react with S2O32− to produce μ‐thiosulfato‐μ‐peroxo product, [(NH3)4CoIII(μ‐S2O3,μ‐O2)CoIII(NH3)4]2+ (4). The observed rate (k0) increases with an increase in [TThio] ([TThio] is the analytical concentration of S2O32−) and temperature (T), but it decreases with an increase in [H+] and the ionic strength (I). Analysis of the log At versus time data (A is the absorbance of 1 at time t) reveals that overall the reaction follows a biphasic consecutive reaction path with rate constants k1 and k2 and the change of absorbance is equal to {a1 exp(–k1t) + a2 exp(–k2t)}, where k1 > k2.

A new species of Alteutha Baird (Harpacticoida: Peltidiidae) from north-western Mexico

As an effort towards improving our knowledge of the Mexican harpacticoid fauna, new species and new records of different families have been published during the last 14 years. The material presented herein belongs to a group of species of Alteutha characterized by the lack of inner armature in P2-P4 EXP1. The new species herein presented seems to be related to Alteutha rara Jakobi and A. oblonga (Goodsir). It resembles A. oblonga from Norway and Argentina given the armature of the A2 EXP and armature of P1 EXP2, but differs from the Norwegian form in the position of the lateral seta of the first endite of the maxilla and in the P1 EXP:ENP length ratio. The Mexican species matches the written description of the Argentinean specimens, but no conclusive comparisons could be made regarding the P1 EXP:ENP length ratio, the relative position of the setae/spines of bucal appendages and swimming legs.http://www.zoobank.org/urn:lsid:zoobank.org:pub:EA23F9A5-60E3-412B-89C4-6957A7D3850B

The impact of AsH3 overflow time and indium composition on the formation of self-assembled InxGa1 − xAs quantum dots studied by atomic force microscopy

We have performed atomic force microscopy to investigate the effect of various indium compositions and various AsH3 flow times during cooling on the formation of self-assembled In x Ga1 − xAs quantum dots (QDs). The In x Ga1 − xAs QDs were grown by metal-organic chemical vapour deposition using the Stranski-Krastanow (S-K) growth mode. The migration of group III species in the growth of In x Ga1 − xAs QDs is influenced by the AsH3 flow during the cooling period due to the increasing surface population of the active arsenic species. It influences the size and density of the dots on the surface. For various indium compositions, an increase in In x Ga1 − xAs QD density with increasing indium composition is observed. It indicates that the dot density depends on lattice parameters. The dot density is inversely proportional to surface diffusion (ρ ∝ R/D), with D = (2kT/h)/a2 exp(−ED/kT). In the growth of In x Ga1 − xAs QDs using the S-K growth mode, the dots were formed on the surface as the effect of elastic strain relaxation due to the lattice mismatch. Increasing indium composition affects the lattice mismatch of the In x Ga1 − xAs/GaAs QD system, which influences the dot formation on the surface. However, due to the stochastic nature of the nucleation of self-assembled growth, control of the spatial ordering of the QDs has proved to be extremely challenging.

A new soft X-ray spectral model for polars with an application to AM Herculis

We present a simple heuristic model for the time-averaged soft X-ray temperature distribution in the accretion spot on the white dwarf in polars. The model is based on the analysis of the Chandra LETG spectrum of the prototype polar AM Her and involves an exponential distribution of the emitting area vs. blackbody temperature a(T) = a0 exp(-T/T0). With one free parameter besides the normalization, it is mathematically as simple as the single blackbody, but is physically more plausible and fits the soft X-ray and far-ultraviolet spectral fluxes much better. The model yields more reliable values of the wavelength-integrated flux of the soft X-ray component and the implied accretion rate than reported previously.

EXACT BRIGHT SELF-SIMILAR SOLITARY WAVES IN AN EXPULSIVE PARABOLIC POTENTIAL

Exact bright self-similar solitary waves are analytically derived in a cigar-shaped condensate with time-dependent atomic scattering length as(t) in an expulsive parabolic potential. The straightforward relation between the Gross–Pitaevskii equation and the standard nonlinear Schrödinger equation is presented for as(t)=a0exp (γt) at the growing or decaying coefficient γ=±|ωz|/ωtwith ωz(ω⊥) the axial (transverse) frequency. In the expulsive parabolic potential, in particular, it is found that the bright self-similar solitary wave is accelerated and set into motion due to the expulsive force. The results tally with the experimental observations by Khaykovich et al. [Science296 (2002) 1290].

Fusion Curves and Enthalpy and Internal Energy Changes of Benzene, Nitrobenzene, Bromobenzene, and Chlorobenzene at Pressures up to 3500 MPa

The fusion temperature as a function of pressure for benzene, nitrobenzene, bromobenzene, and chlorobenzene at pressures up to 3500 MPa has been determined. The new experimental data are an extension to higher pressures and temperatures of previous data and fitted by the equation Tfus = T0(1 + Δp/a1)a2 exp(−a3Δp). Changes of the molar enthalpy and the molar internal energy on fusion were calculated using the parameters of the fitted equation. Comparisons with data from references show that the experimental data, parameters of fitted equations, molar enthalpy changes, and molar internal energy changes are reliable.

Bound states and critical behavior of the Yukawa potential

We investigate the bound states of the Yukawa potential V (r)=−λexp(−αr)/r, using different algorithms: solving the Schrodinger equation numerically and our Monte Carlo Hamiltonian approach. There is a critical α = αC, above which no bound state exists. We study the relation between αC and λ for various angular momentum quantum number l, and find in atomic units, αC(l) = λ[A 1 exp(−l/B 1) + A 2 exp(−l/B 2)], with A 1 = 1.020(18), B 1 = 0.443(14), A 2 = 0.170(17), and B 2 = 2.490(180).

Identifiability of Models for Fluorescence Quenching in Aqueous Micellar Systems

The first deterministic identifiability analysis is presented for four commonly used kinetic models of fluorescence quenching of an excited probe in aqueous micelles: A) model with immobile quenchers, B) model with mobile quenchers, C) an extension of model B in which exchange of quenchers both via the aqueous phase and during micelle collisions is taken into account, and D) model with probe migration. It is shown that these specific models for fluorescence decay of an excited probe solubilized in a micelle and quenched by molecules or ions that are Poisson-distributed over the micelles, resulting in the generalized four-parameter equation f(t)=A(1) exp{-A(2)t-A(3)[1-A(4)t]}, are uniquely identifiable in terms of four descriptive A parameters. Moreover, each model also can be uniquely identified in terms of the underlying rate constants and micellar concentration or mean micellar aggregation number. This means that these parameters can be extracted in a unique way from time-resolved fluorescence quenching experiments on a probe in micelles. For each model the recommended analysis approach is given.

Influence of Concentration and Temperature on Viscosity of Nitrate Solutions of Some Trivalent Lanthanides

Viscosities of aqueous solutions of La(NO3)3, Ce(NO3)3, and Pr(NO3)3 in the concentration range of (0.2 to 1.0) mol·L-1 were measured from (293 to 333) K. Relative viscosity data were interpreted in terms of the Jones−Dole equation, and values of ion−ion and ion−solvent interactions coefficients were evaluated. An empirical equation η = a0 exp(b0C + c0C2) was also applied to the viscosity data and values of coefficients a0, b0, and c0 were calculated for all the three systems.

Nonexponential Decay of Reactive Intermediates: New Challenges for Spectroscopic Observation, Kinetic Modeling and Mechanistic Interpretation

AbstractFor Abstract see ChemInform Abstract in Full Text.

Nonexponential decay of reactive intermediates: new challenges for spectroscopic observation, kinetic modeling and mechanistic interpretation

AbstractA thermally generated reactive intermediate is generally presumed to consist of a population with a distribution of lifetimes characterized by a single, well‐defined parameter, τ. The decay of an instantaneously generated population, whose conversion to products occurred by parallel unimolecular steps, would be expected to be defined by a simple, single‐exponential expression: A(t)=A0 exp(−t/τ), where A(t) is the population at time t, and A0 is the population at t=0. In this model, the lifetime is also related to the first‐order rate constants, ki, for the unimolecular product‐forming steps; specifically τ = (Σiki)−1. The ratio of the products is equal to the ratio of the rate constants for their formation. Given an accurate potential energy surface (PES) for the reaction, one would expect to be able to compute the values of the ki under the specified reaction conditions, and hence both the lifetime of the intermediate and the ratio of products. This simple picture, which has formed the basis for most mechanistic investigation of reactive intermediates, and most kinetic modeling of reactions in which they are involved, has been challenged in recent years by molecular dynamics (MD) simulations, which have predicted that a variety of thermally generated intermediates should exhibit bimodal or even multimodal lifetime distributions. In several cases the shortest lifetime populations have been found to lead to products in a ratio quite different from that for the longer‐lived populations, and also quite unlike that expected from RRKM or transition state theory calculations based on the same PES used for the MD simulations. This commentary reviews the origins of this behavior and discusses the challenges of designing experiments to test the predictions. Copyright © 2003 John Wiley & Sons, Ltd.

Exact steady-state solution of the Boltzmann equation: a driven one-dimensional inelastic Maxwell gas.

The exact nonequilibrium steady-state solution of the nonlinear Boltzmann equation for a driven inelastic Maxwell model was obtained by Ben-Naim and Krapivsky [Phys. Rev. E 61, R5 (2000)] in the form of an infinite product for the Fourier transform of distribution function f(c). In this paper we have inverted the Fourier transform to express f(c) in the form of an infinite series of exponentially decaying terms. The dominant high-energy tail is exponential, f(c) approximately A0 exp(-a|c|), where a identical with 2/square root[1-alpha(2)] and amplitude A0 is given in terms of a converging sum. This is explicitly shown in the totally inelastic limit (alpha-->0) and in the quasielastic limit (alpha-->1). In the latter case, the distribution is dominated by a Maxwellian for a very wide range of velocities, but a crossover from a Maxwellian to an exponential high-energy tail exists for velocities |c-c(0)| approximately 1/square root[q] around a crossover velocity c(0) approximately ln q(-1)/square root[q], where q identical with (1-alpha)/2<<1. In this crossover region the distribution function is extremely small, ln f(c(0)) approximately q(-1) ln q.

Direct Surface Force Measurement for Synthetic Smectites Using the Atomic Force Microscope

An atomic force microscope with a colloid probe technique was used to measure forces interacting between smectites, that is, saponite and hectorite. The measured forces fit well to the forces calculated by the Derjaguin−Landau−Verwey−Overbeek (DLVO) theory at separations larger than 4 nm over concentrations of 10-5−10-2 M NaCl and the pH range of 4−10. There is also a good agreement between zeta potential and the electrical double-layer (EDL) potential extracted from the best fit to the DLVO force curve. According to the analysis on the pH dependence of the EDL potential using the Gouy−Chapman−Stern−Graham model, the inner Helmholtz layer capacitance for the good fit of the outer Helmholtz plane potential to the EDL potential required a much lower value for hectorite (∼5 μF/cm2) than that for saponite (∼500 μF/cm2), reflecting the difference in the location of the lattice charge between saponite and hectorite. This provided evidence for the fact that the EDL force for smectites is dominated by the location of the charges as well as the density of the charges. Extra short-range repulsion was observed at separations below ∼3 nm with increasing NaCl concentration and pH and then disappeared with decreasing pH or the NaCl concentration. The short-range repulsion was extracted as a double-exponential function, that is, F/R = A1 exp(−D/D1) + A2 exp(−D/D2), by subtracting the DLVO forces from the measured forces in the same way as the study with a surface force apparatus (Pashley, R. M. J. Colloid Interface Sci. 1981, 83, 531). The values of two decay lengths (D1 and D2) for smectites showed a very similar result to those for muscovite mica rather than silica. It was also found that the sum of the force constants (A1 + A2) was closely related to the density and structure of the lattice charge.

Electrical properties of amorphous carbon films

Aromatic polyimide films, Upilex S partially carbonized between 700°C and 1000°C. Electrical conductivity is higher at higher temperatures. The electrical conductivity s could be expresses as s = so exp (−E/kT), where k is the Boltzmann constant, t is the absolute measuring temperature. so and E are found to be 4 × 10−1 Ω−1 m−1 and 0.02eB, respectively. The experimental data show that the Hall coefficient R is negative, and this implies that the carriers are negatively charged, i.e. electrons. The specimens are n-type semiconductors. The carrier density η is given by η = 1/(|e|R) and the mobility μ is μ is s/(η|e|), where |e| is the absolute value of the electron charge and s is the electrical conductivity. Fitting the data, η = A1 exp (−E1/κT) and μ = A2 exp (E2/κT). E1 and E2 depend on carbonized temperature. The polyimide films are not completely carbonized but partially carbonized at 700°C. The partially carbonized polyimide is an n type donor. It is concluded that the “impurity level” lies about 0.36eV below the conduction band.

Nonadiabatic Hopping Conduction in Sr1+xLa1−xFeO4 (0≤x≤0.20) below 300 K

We measured bulk conductivities using complex-plane impedance analyses and frequency dependencies of dielectric properties in Sr1+xLa1−xFeO4 (0≤x≤0.20) with the four-probe dc conductivities. The temperature dependence of bulk conductivity in every specimen exhibits the nonadiabatic hopping conduction; i.e., σ=A0 exp[−(WH+WO/2)/kBT]/T3/2, WH and WO being the hopping energy and the energy required to create a free hopping polaron. In every specimen, a dielectric relaxation process shows up with an activation energy nearly equal to that of the bulk conduction. The electron transfer integrals, J, estimated in the dielectric relaxations meet the nonadiabatic requirements; i.e., J< 4WH and J<(4WHkBT)1/4(ℏωOL)1/2, where ωOL is the frequency of the longitudinal optical mode. Speculation on the pre-exponential factor of the conductivity, A0, indicates that the holes in valence bands created by electron excitation predominantly contribute to electrical transport rather than the doped holes introduced by Sr-substitution for La. The experimental results are explained self-consistently by nonadiabatic hopping conduction.

Partial Carbonization of Aromatic Polyimide Films

ABSTRACTAromatic polyimide films are partially carbonized between 700°C and 1000°C. Electrical conductivity and Hall coeficient have been measured. Electrical conductivity is higher at higher measuring temperatures. The electrical conductivity σ can be expressed as σ= σ0exp (–E /kT), where k is the Boltzman constant. T is the absolute temperature. E depends upon the carborized temperature. The experimental data show the Hall coefficient RH is negative, and this implies the carriers are negatively charged, i.e. electrons. The specimens are n-type semiconductors. The carrier density η can be expressed by η= A1 exp (–E1/κT) and carrier mobility μ can be expressed by μ = A1exp ( E2/κT). E, E1andE2 depend upon the carbonized temperature

Time-dependent charge trap distribution function in polyaniline films

Relaxation processes of photoconductivity in emeraldine base (non-conductive form of polyaniline) are investigated under nanosecond laser excitation. Photocurrent relaxation data are approximated well by the stretched exponential function F1(t) = A1 exp[−(t/τstr)β] in the time interval from 0.45 to 40 ms. It was found that the parameters τstr and β of the function F1(t), which also characterize the energy distribution function of the electron traps, increased with time and allow an estimation of the decrease of the averaged trap depth dispersion in time. These parameters also demonstrated irregular behavior in the temperature range 180–300 K, forming a broad maximum at the temperatures of β-transition to the torsional motion of the rings along the polymer backbone in polyaniline from 180 to 260 K. © 1998 John Wiley & Sons, Ltd.