696 research outputs found
Nonequilibrium multicritical behavior in anisotropic Heisenberg ferromagnet driven by oscillating magnetic field
The Heisenberg ferromagnet (uniaxially anisotropic along z-direction), in the
presence of time dependent (but uniform over space) magnetic field, is studied
by Monte Carlo simulation. The time dependent magnetic field was taken as
elliptically polarised in such a way that the resulting field vector rotates in
the XZ plane. In the limit of low anisotropy, the dynamical responses of the
system are studied as functions of temperature and the amplitudes of the
magnetic field. As the temperature decreases, it aws found that the system
undergoes multiple dynamical phase transitions. In this limit, the multiple
transitions were studied in details and the phase diagram for this observed
multicritical behaviour was drawn in the field amplitude and temperature
palne.The natures (continuous/discontinuous) of the transitions are determined
by the temperature variations of fourth order Binder cumulant ratio and the
distributions of the order parameter near the transition points. The
transitions are supported by finite size study. The temperature variations of
the variances of dynamic order parameter components (for different system
sizes) indicate the existence of diverging length scale near the dynamic
transition points. The frequency dependences of the transition temperatures of
the multiple dynamic transition are also studied briefly.Comment: 14 Pages Latex, 17 Postscript figures. To appear in Int. J. Mod.
Phys. C (2006) Ma
Dynamic Response of Ising System to a Pulsed Field
The dynamical response to a pulsed magnetic field has been studied here both
using Monte Carlo simulation and by solving numerically the meanfield dynamical
equation of motion for the Ising model. The ratio R_p of the response
magnetisation half-width to the width of the external field pulse has been
observed to diverge and pulse susceptibility \chi_p (ratio of the response
magnetisation peak height and the pulse height) gives a peak near the
order-disorder transition temperature T_c (for the unperturbed system). The
Monte Carlo results for Ising system on square lattice show that R_p diverges
at T_c, with the exponent , while \chi_p shows a peak at
, which is a function of the field pulse width . A finite size
(in time) scaling analysis shows that , with
. The meanfield results show that both the divergence of R
and the peak in \chi_p occur at the meanfield transition temperature, while the
peak height in , for small values of
. These results also compare well with an approximate analytical
solution of the meanfield equation of motion.Comment: Revtex, Eight encapsulated postscript figures, submitted to Phys.
Rev.
Parallel imports, innovations and national welfare: The role of the sizes of the income classes and national markets for health care.
This paper shows that regardless of any intra-country income differences, parallel imports result in a lower level of health-care innovation but, contrary to popular as well as conventional theoretical wisdom, a lower price in the Third World compared to market-based discrimination. Despite such a lower price, however, parallel imports unambiguously make all buyers in the Third World worse off when intra-country income disparity exists. On the other hand, even discarding the MNC's profit, there will be cases in which the richer country prefers price discrimination as well. That is, in those cases, no countries will have any incentive under the welfare criterion to undo price discrimination, contrary to Richardso
Effects of boundary conditions on the critical spanning probability
The fractions of samples spanning a lattice at its percolation threshold are
found by computer simulation of random site-percolation in two- and
three-dimensional hypercubic lattices using different boundary conditions. As a
byproduct we find in the cubic lattice.Comment: 8 pages Latex, To appear in Int. J. Mod. Phys.
Dynamic Phase Transition in a Time-Dependent Ginzburg-Landau Model in an Oscillating Field
The Ginzburg-Landau model below its critical temperature in a temporally
oscillating external field is studied both theoretically and numerically. As
the frequency or the amplitude of the external force is changed, a
nonequilibrium phase transition is observed. This transition separates
spatially uniform, symmetry-restoring oscillations from symmetry-breaking
oscillations. Near the transition a perturbation theory is developed, and a
switching phenomenon is found in the symmetry-broken phase. Our results confirm
the equivalence of the present transition to that found in Monte Carlo
simulations of kinetic Ising systems in oscillating fields, demonstrating that
the nonequilibrium phase transition in both cases belongs to the universality
class of the equilibrium Ising model in zero field. This conclusion is in
agreement with symmetry arguments [G. Grinstein, C. Jayaprakash, and Y. He,
Phys. Rev. Lett. 55, 2527 (1985)] and recent numerical results [G. Korniss,
C.J. White, P. A. Rikvold, and M. A. Novotny, Phys. Rev. E (submitted)].
Furthermore, a theoretical result for the structure function of the local
magnetization with thermal noise, based on the Ornstein-Zernike approximation,
agrees well with numerical results in one dimension.Comment: 16 pp. RevTex, 9 embedded ps figure
Fast 3D Integrated Circuit Placement Methodology using Merging Technique
In the recent years the advancement in the field of microelectronics integrated circuit (IC) design technologies proved to be a boon for design and development of various advanced systems in-terms of its reduction in form factor, low power, high speed and with increased capacity to incorporate more designs. These systems provide phenomenal advantage for armoured fighting vehicle (AFV) design to develop miniaturised low power, high performance sub-systems. One such emerging high-end technology to be used to develop systems with high capabilities for AFVs is discussed in this paper. Three dimensional IC design is one of the emerging field used to develop high density heterogeneous systems in a reduced form factor. A novel grouping based partitioning and merge based placement (GPMP) methodology for 3D ICs to reduce through silicon vias (TSVs) count and placement time is proposed. Unlike state-of-the-art techniques, the proposed methodology does not suffer from initial overlap of cells during intra-layer placement which reduces the placement time. Connectivity based grouping and partitioning ensures less number of TSVs and merge based placement further reduces intra layer wire-length. The proposed GPMP methodology has been extensively against the IBMPLACE database and performance has been compared with the latest techniques resulting in 12 per cent improvement in wire-length, 13 per cent reduction in TSV and 1.1x improvement in placement time
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