A new approximation scheme in quantum mechanics

An approximation method which combines the perturbation theory with the variational calculation is constructed for quantum mechanical problems. Using the anharmonic oscillator and the He atom as examples, we show that the present method provides an efficient scheme in estimating both the ground and the excited states. We also discuss the limitations of the present method.Comment: 14pages, to be published in Eur. J. Phy

Electromagnetic Hysteretic Response Calculation for Superconductors in Demagnetizing Geometries

The electromagnetic response of the new high Tc superconductors is similar to that of eddy currents in normal metals, except that in the superconductor induced currents are established nonlinearly at a single value known as the critical current density, J c . These materials are extreme Type II superconductors where, in the presence of an external magnetic field and/or a transport current, magnetic flux exists in the material in the form of flux lines distributed on a lattice [1]. Individual flux lines become pinned at microstructural inhomogeneities such that only under a sufficient force caused by locally high current flows will they become depinned and flow throughout the material. The value of the local current density that causes depinning is the microscopic critical current density and is directly proportional to the pinning force strength. A phenomenological approach known as the critical state model [2,3] describes the pinned flux line distribution within the material quasistatically, assuming the equilibrium distribution is achieved at each value of the externally applied field on a short time scale compared to experimental times. Operationally, whenever an external field is increased, flux lines enter the material from the surface and penetrate to a flux front boundary, whose position is determined by the value of the external field at the sample surface. An important nondestructive evaluation (NDE) task to aid the fabrication of high Tc superconductors is to develop methods for quantitatively determining the local current density. In the critical state the current density is either the critical value appropriate to the local value of the induction J c , or it is zero. The electromagnetic response of the material is then determined by the extent of this critical state region and its measurement can be used to determine the local J c . Therefore, a method that can predict the flux front profile with high spatial resolution, and also account for demagnetization effects, is essential. An integral equation technique dealing with a nonuniform applied magnetic field having azimuthal symmetry was presented at the last QNDE conference by the present authors [4]. The current paper shows results from the further development of this technique in two ways. Firstly, the superconducting sample is extended from a half-space to an infinite plate. This is an example of a nonuniform applied magnetic field having azimuthal symmetry. The second application is a sphere, that is a demagnetizing geometry, in a uniform applied magnetic field. In the following section, the general methodology of this technique is outlined. Then some results of both the plate and the sphere examples are given to illustrate this proposed approach. Since the study of the plate sample is still in progress, more results will be reported in future publications. For the sphere sample, detailed discussion and presentation of formulations are given in [5]

Polyamide Nanocomposites for Selective Laser Sintering

Current polyamide 11 and 12 are lacking in fire retardancy and high strength/high heat resistance characteristics for a plethora of finished parts that are desired and required for performance driven applications. It is anticipated that nanomodification of polyamide 11 and 12 will result in enhanced polymer performance, i.e., fire retardancy, high strength and high heat resistance for polyamide 11 and 12. It is expected that these findings will expand the market opportunities for polyamide 11 and 12 resin manufacturers. The objective of this research is to develop improved polyamide 11 and 12 polymers with enhanced flame retardancy, thermal, and mechanical properties for selective laser sintering (SLS) rapid manufacturing (RM). A nanophase was introduced into the polyamide 11 and 12 via twin screw extrusion to provide improved material properties of the polymer blends. Arkema RILSAN® polyamide 11 molding polymer pellets and Degussa VESTAMID® L1670 polyamide 12 were examined with three types of nanoparticles: chemically modified montmorillonite (MMT) organoclays, surface modified nanosilica, and carbon nanofibers (CNFs) to create polyamide 11 and 12 nanocomposites. Wide angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM) were used to determine the degree of dispersion. Injection molded test specimens were fabricated for physical, thermal, mechanical properties, and flammability tests. Thermal stability of these polyamide 11 and 12 nanocomposites was examined by TGA. Mechanical properties such as tensile, flexural, and elongation at break were measured. Flammability properties were also obtained using the Cone Calorimeter at an external heat flux of 50 kW/m2. TEM micrographs, physical, mechanical, and flammability properties are included in the paper. Polyamide 11 and 12 nanocomposites properties are compared with polyamide 11 and 12 baseline polymers. Based on flammability and mechanical material performance, selective polymers including polyamide 11 nanocomposites and control polyamide 11 were cryogenically ground into fine powders and fabricated into SLS parts.Mechanical Engineerin

Diffusion-Limited Annihilation with Initially Separated Reactants

A diffusion-limited annihilation process, A+B->0, with species initially separated in space is investigated. A heuristic argument suggests the form of the reaction rate in dimensions less or equal to the upper critical dimension $d_c=2$. Using this reaction rate we find that the width of the reaction front grows as $t^{1/4}$ in one dimension and as $t^{1/6}(\ln t)^{1/3}$ in two dimensions.Comment: 9 pages, Plain Te

Evidences of a consolute critical point in the Phase Separation regime of La(5/8-y)Pr(y)Ca(3/8)MnO(3) (y = 0.4) single crystals

We report on DC and pulsed electric field sensitivity of the resistance of mixed valent Mn oxide based La(5/8-y)Pr(y)Ca(3/8)MnO(3) (y = 0.4) single crystals as a function of temperature. The low temperature regime of the resistivity is highly current and voltage dependent. An irreversible transition from high (HR) to a low resistivity (LR) is obtained upon the increase of the electric field up to a temperature dependent critical value (V_c). The current-voltage characteristics in the LR regime as well as the lack of a variation in the magnetization response when V_c is reached indicate the formation of a non-single connected filamentary conducting path. The temperature dependence of V_c indicates the existence of a consolute point where the conducting and insulating phases produce a critical behavior as a consequence of their separation.Comment: 5 pages, 6 figures, corresponding author: C. Acha ([email protected]

Innovative Selective Laser Sintering Rapid Manufacturing using Nanotechnology

The objective of this research is to develop an improved nylon 11 (polyamide 11) polymer with enhanced flame retardancy, thermal, and mechanical properties for selective laser sintering (SLS) rapid manufacturing (RM). A nanophase was introduced into nylon 11 via twin screw extrusion to provide improved material properties of the polymer blends. Atofina (now known as Arkema) RILSAN® nylon 11 injection molding polymer pellets was used with three types of nanoparticles: chemically modified montmorillonite (MMT) organoclays, nanosilica, and carbon nanofibers (CNF) to create nylon 11 nanocomposites. Wide angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM) were used to determine the degree of dispersion. Fifteen nylon 11 nanocomposites and control nylon 11 were fabricated by injection molding. Flammability properties (using a cone calorimeter with a radiant flux of 50 kW/m2 ) and mechanical properties such as tensile strength and modulus, flexural modulus, elongation at break were determined for the nylon 11 nanocomposites and compared with the baseline nylon 11. Based on flammability and mechanical material performance, five polymers including four nylon 11 nanocomposites and a control nylon 11 were cryogenically ground into fine powders for SLS RM. SLS specimens were fabricated for flammability, mechanical, and thermal properties characterization. Nylon 11-CNF nanocomposites exhibited the best overall properties for this study.Mechanical Engineerin

Refined Simulations of the Reaction Front for Diffusion-Limited Two-Species Annihilation in One Dimension

Extensive simulations are performed of the diffusion-limited reaction A$+$B$\to 0$ in one dimension, with initially separated reagents. The reaction rate profile, and the probability distributions of the separation and midpoint of the nearest-neighbour pair of A and B particles, are all shown to exhibit dynamic scaling, independently of the presence of fluctuations in the initial state and of an exclusion principle in the model. The data is consistent with all lengthscales behaving as $t^{1/4}$ as $t\to\infty$. Evidence of multiscaling, found by other authors, is discussed in the light of these findings.Comment: Resubmitted as TeX rather than Postscript file. RevTeX version 3.0, 10 pages with 16 Encapsulated Postscript figures (need epsf). University of Geneva preprint UGVA/DPT 1994/10-85

Effects of atmospherics on emotions and intention with respect to involvement under different shopping environments

The present study deals with the S–O–R framework. The past five decades of research have successful validate the S–O–R model in offline and online contexts. However, there is still room for improvements. In particular, hedonic aspects have been proposed as distinctive aspects to differentiate companies. Previous researchers have (i) been somewhat reluctant to investigate dominance and other emotional responses; and (ii) produced mixed results regarding the impact of atmospherics and emotional responses on behavior. Building on this tradition of research, this study investigates the S-O-R model by incorporating delight as an attitudinal emotional response and tests the moderating effects of consumers’ involvement and shopping environment (three-way interactional effects) in connection with the links among atmospherics, emotions and intentions. The current findings demonstrate that the model fit better for low involvement consumers than for high involvement consumers. This was true for both offline and online environments .The theoretical and practical implications are discussed in the conclusions.info:eu-repo/semantics/acceptedVersio