33,610 research outputs found
Dynamical scaling in Ising and vector spin glasses
We have studied numerically the dynamics of spin glasses with Ising and XY
symmetry (gauge glass) in space dimensions 2, 3, and 4. The nonequilibrium
spin-glass susceptibility and the nonequilibrium energy per spin of samples of
large size L_b are measured as a function of anneal time t_w after a quench to
temperatures T. The two observables are compared to the equilibrium spin-glass
susceptibility and the equilibrium energy, respectively, measured as functions
of temperature T and system size L for a range of system sizes. For any time
and temperature a nonequilibrium time-dependent length scale L*(t_w,T) can be
defined by comparing equilibrium and nonequilibrium quantities. Our analysis
shows that for all systems studied, an "effective dynamical critical exponent"
parametrization L*(t_w,T) = A(T) t^(1/z(T)) fits the data well at each
temperature within the whole temperature range studied, which extends from well
above the critical temperature to near T = 0 for dimension 2, or to well below
the critical temperature for the other space dimensions studied. In addition,
the data suggest that the dynamical critical exponent z varies smoothly when
crossing the transition temperature.Comment: 14 pages, 13 figures, 9 table
A study of the semiannual density variation in the upper atmosphere from 1958 to 1966, based on satellite drag analysis
Semiannual density variation in upper atmosphere from 1958 to 1966 based on satellite drag analysi
Extended Scaling for the high dimension and square lattice Ising Ferromagnets
In the high dimension (mean field) limit the susceptibility and the second
moment correlation length of the Ising ferromagnet depend on temperature as
chi(T)=tau^{-1} and xi(T)=T^{-1/2}tau^{-1/2} exactly over the entire
temperature range above the critical temperature T_c, with the scaling variable
tau=(T-T_c)/T. For finite dimension ferromagnets temperature dependent
effective exponents can be defined over all T using the same expressions. For
the canonical two dimensional square lattice Ising ferromagnet it is shown that
compact "extended scaling" expressions analogous to the high dimensional limit
forms give accurate approximations to the true temperature dependencies, again
over the entire temperature range from T_c to infinity. Within this approach
there is no cross-over temperature in finite dimensions above which
mean-field-like behavior sets in.Comment: 6 pages, 6 figure
A rapidly expanding Bose-Einstein condensate: an expanding universe in the lab
We study the dynamics of a supersonically expanding ring-shaped Bose-Einstein
condensate both experimentally and theoretically. The expansion redshifts
long-wavelength excitations, as in an expanding universe. After expansion,
energy in the radial mode leads to the production of bulk topological
excitations -- solitons and vortices -- driving the production of a large
number of azimuthal phonons and, at late times, causing stochastic persistent
currents. These complex nonlinear dynamics, fueled by the energy stored
coherently in one mode, are reminiscent of a type of "preheating" that may have
taken place at the end of inflation.Comment: 12 pages, 7 figure
Three-dimensional Binary Superlattices of Oppositely-charged Colloids
We report the equilibrium self-assembly of binary crystals of
oppositely-charged colloidal microspheres at high density. By varying the
magnitude of the charge on near equal-sized spheres we show that the structure
of the binary crystal may be switched between face-centered cubic, cesium
chloride and sodium chloride. We interpret these transformations in terms of a
competition between entropic and Coulombic forces
Giant nonlinear response of superconducting single crystal niobium in a sweeping magnetic field
Giant enhancement of the nonlinear response of a single crystal of Nb placed
in a sweeping magnetic field has been experimentally observed. The rectified
signal from Nb ( K) has been measured by means of an inductive method
as a function of temperature, dc field, dc field sweep rate, and the amplitude
of ac field. The Nb sample was excited by an amplitude modulated ac field.
Under a stationary regime, the rectified signal appears only for magnetic
fields () in the range . However, when the dc field
was swept slowly, the rectified signal appears at . This experiment
shows that the amplitude of the rectified signal is two orders of magnitude
larger than the amplitude of the signal seen under stationary field conditions.
Moreover, the amplitude of the rectified signal is a power function of the
sweep rate, with the power exponent close to 1.Comment: 3 pages, 3 figures, presented to EUCAS 200
Flux creep in type-II superconductors: self-organized criticality approach
We consider the current density distribution function of a flux creep regime
in type-II superconductors by mapping the flux creep process to the dynamics of
a model with a self-organized criticality. We use an extremal Robin Hood type
model which evolves to Been's type critical state to treat magnetic flux
penetration into a superconductor and derive an analog of the current-voltage
characteristics in the flux creep region.Comment: 7 pages, 7 figure
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