Spin‐Waves in Dilute Antiferromagnets

The effect of dilution on spin waves in isotropic Heisenberg antiferromagnets is studied. The model includes only nearest‐neighbor interactions for a bcc lattice and spin‐wave interactions are neglected, i.e. the results are correct in the limit s→∞. The dynamical susceptibility X (?,ω) and inelastic neutron cross section are obtained for arrays 8192 sites randomly occupied by a concentration c of magnetic ions. For a given array the calculation is done by inverting the dynamical matrix and thus is essentially exact. Our results are as follows. For large k we find that Ising‐like resonances corresponding to different numbers of occupied neighboring sites become increasingly prominent as c is decreased. The envelope of these resonances agrees with previous results using the coherent potential approximation where fluctuations in environment are suppressed. For small k we find a single spinwave resonance broadened by the random dilution. The application of these results to Mnc Zn 1−cF2 is discussed

Self-Organizing Maps Algorithm for Parton Distribution Functions Extraction

We describe a new method to extract parton distribution functions from hard scattering processes based on Self-Organizing Maps. The extension to a larger, and more complex class of soft matrix elements, including generalized parton distributions is also discussed.Comment: 6 pages, 3 figures, to be published in the proceedings of ACAT 2011, 14th International Workshop on Advanced Computing and Analysis Techniques in Physics Researc

CORRELATIONS AMONG GRAIN CHARACTERISTICS USED TO DETERMINE THE EFFECTS OF ROUGH RICE STORAGE TIME AND TEMPERATURE ON AROMATIC RICE QUALITY

Summary statistics and corresponding Spearman correlation coefficients are illustrated for various subsets of aromatic rough rice storage time and temperature data from (a) the College Station texture sensory panel, (b) the New Orleans aroma and flavor sensory panel, and (c) the Beaumont USDA-ARS Rice Quality Laboratory. These correlations represent the inclinations of seemingly-related measures of several attributes to "move together," acting as an indicator of their associations with or impacts on one another.Crop Production/Industries,

Renormalization-Group Approach to Percolation Problems

The relation between the s-state Ashkin-Teller-Potts (ATP) model and the percolation problem given by Fortuin and Kasteleyn is used to formulate a renormalization-group treatment of the percolation problem. Both an ε expansion near 6 spatial dimensions and cluster approximations for the recursion relations of a triangular lattice are used. Series results for the ATP model are adapted to the percolation problem

CORRELATIONS AMONG GRAIN CHARACTERISTICS USED TO DETERMINE THE EFFECTS OF MILLED RICE STORAGE TIME AND TEMPERATURE ON AROMATIC RICE QUALITY

Summary statistics and corresponding Spearman correlation coefficients are illustrated for various subsets of aromatic milled rice storage time and temperature data from (a) the College Station texture sensory panel, (b) the New Orleans aroma and flavor sensory panel, and (c) the Beaumont USDA-ARS Rice Quality Laboratory. These correlations represent the inclinations of seemingly-related measures of several attributes to "move together," acting as an indicator of their associations with or impacts on one another.Crop Production/Industries,

Parametric excitation of plasma waves by gravitational radiation

We consider the parametric excitation of a Langmuir wave and an electromagnetic wave by gravitational radiation, in a thin plasma on a Minkowski background. We calculate the coupling coefficients starting from a kinetic description, and the growth rate of the instability is found. The Manley-Rowe relations are fulfilled only in the limit of a cold plasma. As a consequence, it is generally difficult to view the process quantum mechanically, i.e. as the decay of a graviton into a photon and a plasmon. Finally we discuss the relevance of our investigation to realistic physical situations.Comment: 5 pages, REVTe

Surface, but Not Age, Impacts Lower Limb Joint Work during Walking and Stair Ascent

Older adults often suffer an accidental fall when navigating challenging surfaces during common locomotor tasks, such as walking and ascending stairs. This study examined the effect of slick and uneven surfaces on lower limb joint work in older and younger adults while walking and ascending stairs. Fifteen young (18–25 years) and 12 older (\u3e65 years) adults had stance phase positive limb and joint work quantified during walking and stair ascent tasks on a normal, slick, and uneven surface, which was then submitted to a two-way mixed model ANOVA for analysis. The stair ascent required greater limb, and hip, knee, and ankle work than walking (all p \u3c 0.001), with participants producing greater hip and knee work during both the walk and stair ascent (both p \u3c 0.001). Surface, but not age, impacted positive limb work. Participants increased limb (p \u3c 0.001), hip (p = 0.010), and knee (p \u3c 0.001) positive work when walking over the challenging surfaces, and increased hip (p = 0.015), knee (p \u3c 0.001), and ankle (p = 0.010) work when ascending stairs with challenging surfaces. Traversing a challenging surface during both walking and stair ascent tasks required greater work production from the large proximal hip and knee musculature, which may increase the likelihood of an accidental fall in older adults

Surface, but Not Age Impact Lower Limb Joint Work During Walk and Stair Ascent

During common locomotor activates, such as walk or stair negotiation, older adults exhibit unfavorable lower limb biomechanical changes, including diminished joint torque and power, and proximal mechanical work redistribution that may increase their fall risk. Twelve young (18 to 25 years) and 12 older (\u3e 65 years) adults performed a walk and stair ascent task on a normal, slick, and uneven surface. For each walk and stair ascent trial, synchronous 3D marker trajectories and GRF data were collected. Stance phase positive limb and joint work, and relative joint work were submitted to statistical analysis. Ascending stairs required more positive work than the walk, particularly from the knee, which may increase fall risk. Yet, both walking and ascending stairs over a challenging surface required more, proximally distributed work

Surface, but Not Age Impacts Lower Limb Joint Work During Stair Ascent

Introduction: Age-related loss in lower limb strength, particularly at the ankle, may impair older adults (over 65 years of age) mobility, and result in biomechanical deficits compared to their younger counterparts. Older adults tend to walk slower with shorter steps and exhibit diminished ankle joint kinetics (i.e., moment, power and work). Although the compromised ankle function leads older adults to produce smaller ankle joint torques and power output, reducing forces to propel the center of mass forward, it is unclear if they redistributed, or increase hip or knee work to safely walk, particularly when challenged with an uneven or slick surface. Objective: To compare positive lower limb work for young and older adults when walking over challenging surfaces, and determine whether redistributed power output. Methods: Twenty-eight (16 young, 18 to 25 years and 12 older, over 65 years) adults had positive work in the lower limb quantified when walking a self-selected speed over three surfaces (normal, uneven, and slick). Total limb, hip, knee and ankle positive work, and relative effort (% of total) at each joint were submitted to RM ANOVA to test main effect and interaction between surface (normal, uneven, and slick) and age (young and older adults). Results: Surface, but not age impact positive lower limb work. Surface impacted total limb (p=0.000), hip (p=0.007) and knee (p=0.001) positive work. The limb and knee produced more positive work on the uneven compared normal (

Energy dissipation in wave propagation in general relativistic plasma

Based on a recent communication by the present authors the question of energy dissipation in magneto hydrodynamical waves in an inflating background in general relativity is examined. It is found that the expanding background introduces a sort of dragging force on the propagating wave such that unlike the Newtonnian case energy gets dissipated as it progresses. This loss in energy having no special relativistic analogue is, however, not mechanical in nature as in elastic wave. It is also found that the energy loss is model dependent and also depends on the number of dimensions.Comment: 12 page