2,706 research outputs found
Enhanced molecular dynamics performance with a programmable graphics processor
Design considerations for molecular dynamics algorithms capable of taking
advantage of the computational power of a graphics processing unit (GPU) are
described. Accommodating the constraints of scalable streaming-multiprocessor
hardware necessitates a reformulation of the underlying algorithm. Performance
measurements demonstrate the considerable benefit and cost-effectiveness of
such an approach, which produces a factor of 2.5 speed improvement over
previous work for the case of the soft-sphere potential.Comment: 20 pages (v2: minor additions and changes; v3: corrected typos
CALCULATION OF THERMAL NEUTRON FLUXES IN PRIMARY SHIELDS
A method is presented for calculating thermal neutron fluxes in the primary shields of reactor systems which eliminates reliance on mock-up experimental data. A multigroup P/sub 1/ approach is ernployed with the spatial dependence of the neutron sttenuation adjusted through use of a point source attenuation kernel for a homogeneous hydrogenous medium. Comparison of calculation with experiment is presentad. (auth
The effect of the annealing temperature on the local distortion of LaCaMnO thin films
Mn -edge fluorescence data are presented for thin film samples (3000~\AA)
of Colossal Magnetoresistive (CMR) LaCaMnO: as-deposited,
and post-annealed at 1000 K and 1200 K. The local distortion is analyzed in
terms of three contributions: static, phonon, and an extra,
temperature-dependent, polaron term. The polaron distortion is very small for
the as-deposited sample and increases with the annealing temperature. In
contrast, the static distortion in the samples decreases with the annealing
temperature. Although the local structure of the as-deposited sample shows very
little temperature dependence, the change in resistivity with temperature is
the largest of these three thin film samples. The as-deposited sample also has
the highest magnetoresistance (MR), which indicates some other mechanism may
also contribute to the transport properties of CMR samples. We also discuss the
relationship between local distortion and the magnetization of the sample.Comment: 11 pages of Preprint format, 8 figures in one tar fil
Phase transitions in two-dimensional anisotropic quantum magnets
We consider quantum Heisenberg ferro- and antiferromagnets on the square
lattice with exchange anisotropy of easy-plane or easy-axis type. The
thermodynamics and the critical behaviour of the models are studied by the
pure-quantum self-consistent harmonic approximation, in order to evaluate the
spin and anisotropy dependence of the critical temperatures. Results for
thermodynamic quantities are reported and comparison with experimental and
numerical simulation data is made. The obtained results allow us to draw a
general picture of the subject and, in particular, to estimate the value of the
critical temperature for any model belonging to the considered class.Comment: To be published on Eur. Phys. J.
Active Vibration Isolation of Multi-Degree-of-Freedom Systems
One of the principal objectives of vibration isolation technology is to isolate sensitive equipment from a vibrating structure or to isolate the structure from an uncertain exogenous disturbance source. In this paper, a dynamic observer-based active isolator is proposed that guarantees closed-loop asymptotic stabil ity and disturbance decoupling between the vibrating structure and isolated structure. The proposed active isolator is applied to a uniaxial vibrational system and compared to an optimal linear-quadratic design.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69073/2/10.1177_107754639900500405.pd
The Evidence for a Pentaquark Signal and Kinematic Reflections
Several recent experiments have reported evidence for a narrow baryon
resonance with positive strangeness () at a mass of 1.54 GeV/.
Baryons with cannot be conventional states and the reports have
thus generated much theoretical speculation about the nature of possible
baryons, including a 5-quark, or pentaquark, interpretation. We show that
narrow enhancements in the effective mass spectrum can be generated as
kinematic reflections resulting from the decay of mesons, such as the
, the and the .Comment: 4 pages, 4 figure
Effective action and density functional theory
The effective action for the charge density and the photon field is proposed
as a generalization of the density functional. A simple definition is given for
the density functional, as the functional Legendre transform of the generator
functional of connected Green functions for the density and the photon field,
offering systematic approximation schemes. The leading order of the
perturbation expansion reproduces the Hartree-Fock equation. A renormalization
group motivated method is introduced to turn on the Coulomb interaction
gradually and to find corrections to the Hartree-Fock and the Kohn-Sham
schemes.Comment: New references and a numerical algorithm added, to appear in Phys.
Rev. B. 30 pages, no figure
Anderson-Yuval approach to the multichannel Kondo problem
We analyze the structure of the perturbation expansion of the general
multichannel Kondo model with channel anisotropic exchange couplings and in the
presence of an external magnetic field, generalizing to this case the
Anderson-Yuval technique. For two channels, we are able to map the Kondo model
onto a generalized resonant level model. Limiting cases in which the equivalent
resonant level model is solvable are identified. The solution correctly
captures the properties of the two channel Kondo model, and also allows an
analytic description of the cross-over from the non Fermi liquid to the Fermi
liquid behavior caused by the channel anisotropy.Comment: 23 pages, ReVTeX, 4 figures av. on reques
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