Optimization of Transport Capacity for Fodder-Straw in Syria

Rosana G. Moreira, Editor-in-Chief; Texas A&M UniversityThis is a Technical article from International Commission of Agricultural Engineering (CIGR, Commission Internationale du Genie Rural) E-Journal Volume 3 (2001): M. Gebreselassie, O. Kaufman, and J. Hahn. Optimization of Transport Capacity for Fodder-Straw in Syria. Vol. III, December 2001

Magnetic properties of σ\sigma-FeCr alloy as calculated with the charge and spin self-consistent KKR(CPA) method

Magnetic properties of a $\sigma-$Fe$_{16}$Cr$_{14}$ alloy calculated with the charge and spin self- consistent Korringa-Kohn-Rostoker (KKR) and combined with coherent potential approximation (KKR-CPA) methods are reported. Non-magnetic state as well as various magnetic orderings were considered, i.e. ferromagnetic (FM) and more complex anti-parallel (called APM) arrangements for selected sublattices, as follows from the symmetry analysis. It has been shown that the Stoner criterion applied to non-magnetic density of states at the Fermi energy, $E_F$ is satisfied for Fe atoms situated on all five lattice sites, while it is not fulfilled for all Cr atoms. In FM and APM states, the values of magnetic moments on Fe atoms occupying various sites are dispersed between 0 and 2.5 $\mu_B$, and they are proportional to the number of Fe atoms in the nearest-neighbor shell. Magnetic moments of Cr atoms havin much smaller values were found to be coupled antiparallel to those of Fe atoms. The average value of the magnetic moment per atom was found to be $=0.55 \mu_B$ that is by a factor of 4 larger than the experimental value found for a $\sigma-$Fe$_{0.538}$Cr$_{0.462}$ sample. Conversely, admitting an anti- parallel ordering (APM model) on atoms situated on C and D sites, according to the group theory and symmetry analysis results, yielded a substantial reduction of to 0.20 $\mu_B$. Further diminution of to 0.15 $\mu_B$, which is very close to the experimental value of 0.14 $\mu_B$, has been achieved with the KKR-CPA calculations by considering a chemical disorder on sites B, C and D

Integración de Ecuaciones Diferenciales rígidas de valor de contorno en problemas de combustión con cinética de reacción detallada

Modelos detallados de la llama de difusión plana, laminar de jets opuestos requieren la solución de las ecuaciones de conservación de cantidad de movimiento, energía y especies químicas en conjunto con una cinética de reacción química stiff. El problema tiene soluciones autosimilares y se puede resolver mediante integración numérica de un conjunto de ecuaciones diferenciales ordinarias stiff de segundo orden, con condiciones de contorno, cada una de las cuales tiene un punto de torno de primer orden debido a la ecuación de conservación de cantidad de movimiento. El uso de discretización en diferencias finitas standard (en el dominio espacial) y la expansión en serie de Taylor alrededor de la iteración anterior (en el espacio temporal) del término cinético de las reacciones químicas lleva a una ecuación de matrices en la cual la matriz de coeficientes es del tipo tridiagonal en bloques y muy grande de tamaño. También representa una matriz de banda y se puede obtener una solución al problema mediante una descomposición LU. Inestabilidades numéricas debidas a la malla finita de espaciamiento irregular y a la difusión de errores numéricos hacia los bordes forzaron el uso de una malla regular con un gran número de puntos. Esto restringió el estudio a la solución de problemas con esquemas cinéticos relativamente simples, debido a la alta necesidad de memoria de computador. Este dilema fue resuelto por el desarrollo de un esquema de diferenciación modificado, que asume que la solución puntual del problema está dada por una suma de exponenciales. A Usando esta nueva técnica fue posible hallar la solución de una llama con 150 reacciones envolviendo las ecuaciones de ccnservación de 70 especies químicas. En este artículo formulamos el problema y describimos resultados de los varios esquemas numéricos mediante los que se intentó resolver el mismo. El foco principal, sin embargo, está u dirigido hacia la modificación del esquema de diferencias finitas, acoplado con la expansión en serie de Taylor de los términos de reacción química.Detailed models of the flat, laminar, opposed jet diffusion flame involve the solution of the momentu, energy and species conservation equations coupled with stiff chemical kinetics. The problem has self similar solutions and can be solved through numerical integration of a set of second order, stiff, boundary valued, ordinary differential equations, each with a regular first order turning point arising from convection. Use of standard finite difference discretization (in the spatial domain) and expansion of the reaction rate source terms in a Taylor series abaut the backward iteration (in the temporal domain), lead to a matrix equation in which the coefficient matrix is a very large block tridiagonal matrix. It is also a band matrix and solution is obtained through LU descomposition. Instabiiities originating from the unevenly spaced grid and from diffusion of numerical errors towards the boundaries forced the use of a large number of equally spaced grid points which contrained the program to solution of relatively small kinetic problems (due to core storage limitations). This dilemma was resolved by developing a modified central difference discretization which assumes that the solution at a mesh point is given by the sum of exponentials. Using the new technique it was possible to obtain the solution of the opposed jet problem with 150 reactions and 70 species on the available CYBER 175 computer.Peer Reviewe

Integración de Ecuaciones Diferenciales rígidas de valor de contorno en problemas de combustión con cinética de reacción detallada

Modelos detallados de la llama de difusión plana, laminar de jets opuestos requieren la solución de las ecuaciones de conservación de cantidad de movimiento, energía y especies químicas en conjunto con una cinética de reacción química stiff. El problema tiene soluciones autosimilares y se puede resolver mediante integración numérica de un conjunto de ecuaciones diferenciales ordinarias stiff de segundo orden, con condiciones de contorno, cada una de las cuales tiene un punto de torno de primer orden debido a la ecuación de conservación de cantidad de movimiento. El uso de discretización en diferencias finitas standard (en el dominio espacial) y la expansión en serie de Taylor alrededor de la iteración anterior (en el espacio temporal) del término cinético de las reacciones químicas lleva a una ecuación de matrices en la cual la matriz de coeficientes es del tipo tridiagonal en bloques y muy grande de tamaño. También representa una matriz de banda y se puede obtener una solución al problema mediante una descomposición LU. Inestabilidades numéricas debidas a la malla finita de espaciamiento irregular y a la difusión de errores numéricos hacia los bordes forzaron el uso de una malla regular con un gran número de puntos. Esto restringió el estudio a la solución de problemas con esquemas cinéticos relativamente simples, debido a la alta necesidad de memoria de computador. Este dilema fue resuelto por el desarrollo de un esquema de diferenciación modificado, que asume que la solución puntual del problema está dada por una suma de exponenciales. A Usando esta nueva técnica fue posible hallar la solución de una llama con 150 reacciones envolviendo las ecuaciones de ccnservación de 70 especies químicas. En este artículo formulamos el problema y describimos resultados de los varios esquemas numéricos mediante los que se intentó resolver el mismo. El foco principal, sin embargo, está u dirigido hacia la modificación del esquema de diferencias finitas, acoplado con la expansión en serie de Taylor de los términos de reacción química.Detailed models of the flat, laminar, opposed jet diffusion flame involve the solution of the momentu, energy and species conservation equations coupled with stiff chemical kinetics. The problem has self similar solutions and can be solved through numerical integration of a set of second order, stiff, boundary valued, ordinary differential equations, each with a regular first order turning point arising from convection. Use of standard finite difference discretization (in the spatial domain) and expansion of the reaction rate source terms in a Taylor series abaut the backward iteration (in the temporal domain), lead to a matrix equation in which the coefficient matrix is a very large block tridiagonal matrix. It is also a band matrix and solution is obtained through LU descomposition. Instabiiities originating from the unevenly spaced grid and from diffusion of numerical errors towards the boundaries forced the use of a large number of equally spaced grid points which contrained the program to solution of relatively small kinetic problems (due to core storage limitations). This dilemma was resolved by developing a modified central difference discretization which assumes that the solution at a mesh point is given by the sum of exponentials. Using the new technique it was possible to obtain the solution of the opposed jet problem with 150 reactions and 70 species on the available CYBER 175 computer.Peer Reviewe

Implications of Improved Higgs Mass Calculations for Supersymmetric Models

We discuss the allowed parameter spaces of supersymmetric scenarios in light of improved Higgs mass predictions provided by FeynHiggs 2.10.0. The Higgs mass predictions combine Feynman-diagrammatic results with a resummation of leading and subleading logarithmic corrections from the stop/top sector, which yield a significant improvement in the region of large stop masses. Scans in the pMSSM parameter space show that, for given values of the soft supersymmetry-breaking parameters, the new logarithmic contributions beyond the two-loop order implemented in FeynHiggs tend to give larger values of the light CP-even Higgs mass, M_h, in the region of large stop masses than previous predictions that were based on a fixed-order Feynman-diagrammatic result, though the differences are generally consistent with the previous estimates of theoretical uncertainties. We re-analyze the parameter spaces of the CMSSM, NUHM1 and NUHM2, taking into account also the constraints from CMS and LHCb measurements of B_s to \mu+\mu- and ATLAS searches for MET events using 20/fb of LHC data at 8 TeV. Within the CMSSM, the Higgs mass constraint disfavours tan beta lesssim 10, though not in the NUHM1 or NUHM2.Comment: 22 pages, 17 figure

Measurement of the intrinsic damping constant in individual nanodisks of YIG and YIG{\textbar}Pt

We report on an experimental study on the spin-waves relaxation rate in two series of nanodisks of diameter $\phi=$300, 500 and 700~nm, patterned out of two systems: a 20~nm thick yttrium iron garnet (YIG) film grown by pulsed laser deposition either bare or covered by 13~nm of Pt. Using a magnetic resonance force microscope, we measure precisely the ferromagnetic resonance linewidth of each individual YIG and YIG{\textbar}Pt nanodisks. We find that the linewidth in the nanostructure is sensibly smaller than the one measured in the extended film. Analysis of the frequency dependence of the spectral linewidth indicates that the improvement is principally due to the suppression of the inhomogeneous part of the broadening due to geometrical confinement, suggesting that only the homogeneous broadening contributes to the linewidth of the nanostructure. For the bare YIG nano-disks, the broadening is associated to a damping constant $\alpha = 4 \cdot 10^{-4}$. A 3 fold increase of the linewidth is observed for the series with Pt cap layer, attributed to the spin pumping effect. The measured enhancement allows to extract the spin mixing conductance found to be $G_{\uparrow \downarrow}= 1.55 \cdot 10^{14}~ \Omega^{-1}\text{m}^{-2}$ for our YIG(20nm){\textbar}Pt interface, thus opening large opportunities for the design of YIG based nanostructures with optimized magnetic losses.Comment: 4 pages, 3 figure

On q-Gaussians and Exchangeability

The q-Gaussians are discussed from the point of view of variance mixtures of normals and exchangeability. For each q< 3, there is a q-Gaussian distribution that maximizes the Tsallis entropy under suitable constraints. This paper shows that q-Gaussian random variables can be represented as variance mixtures of normals. These variance mixtures of normals are the attractors in central limit theorems for sequences of exchangeable random variables; thereby, providing a possible model that has been extensively studied in probability theory. The formulation provided has the additional advantage of yielding process versions which are naturally q-Brownian motions. Explicit mixing distributions for q-Gaussians should facilitate applications to areas such as option pricing. The model might provide insight into the study of superstatistics.Comment: 14 page

Electronic control of the spin-wave damping in a magnetic insulator

It is demonstrated that the decay time of spin-wave modes existing in a magnetic insulator can be reduced or enhanced by injecting an in-plane dc current, $I_\text{dc}$, in an adjacent normal metal with strong spin-orbit interaction. The demonstration rests upon the measurement of the ferromagnetic resonance linewidth as a function of $I_\text{dc}$ in a 5~$\mu$m diameter YIG(20nm){\textbar}Pt(7nm) disk using a magnetic resonance force microscope (MRFM). Complete compensation of the damping of the fundamental mode is obtained for a current density of $\sim 3 \cdot 10^{11}\text{A.m}^{-2}$, in agreement with theoretical predictions. At this critical threshold the MRFM detects a small change of static magnetization, a behavior consistent with the onset of an auto-oscillation regime.Comment: 6 pages 4 figure

Inverse Spin Hall Effect in nanometer-thick YIG/Pt system

High quality nanometer-thick (20 nm, 7 nm and 4 nm) epitaxial YIG films have been grown on GGG substrates using pulsed laser deposition. The Gilbert damping coefficient for the 20 nm thick films is 2.3 x 10-4 which is the lowest value reported for sub-micrometric thick films. We demonstrate Inverse spin Hall effect (ISHE) detection of propagating spin waves using Pt. The amplitude and the lineshape of the ISHE voltage correlate well to the increase of the Gilbert damping when decreasing thickness of YIG. Spin Hall effect based loss-compensation experiments have been conducted but no change in the magnetization dynamics could be detected