7,599 research outputs found
Maximum Distance Between the Leader and the Laggard for Three Brownian Walkers
We consider three independent Brownian walkers moving on a line. The process
terminates when the left-most walker (the `Leader') meets either of the other
two walkers. For arbitrary values of the diffusion constants D_1 (the Leader),
D_2 and D_3 of the three walkers, we compute the probability distribution
P(m|y_2,y_3) of the maximum distance m between the Leader and the current
right-most particle (the `Laggard') during the process, where y_2 and y_3 are
the initial distances between the leader and the other two walkers. The result
has, for large m, the form P(m|y_2,y_3) \sim A(y_2,y_3) m^{-\delta}, where
\delta = (2\pi-\theta)/(\pi-\theta) and \theta =
cos^{-1}(D_1/\sqrt{(D_1+D_2)(D_1+D_3)}. The amplitude A(y_2,y_3) is also
determined exactly
Maximum of N Independent Brownian Walkers till the First Exit From the Half Space
We consider the one-dimensional target search process that involves an
immobile target located at the origin and searchers performing independent
Brownian motions starting at the initial positions all on the positive half space. The process stops when the target is
first found by one of the searchers. We compute the probability distribution of
the maximum distance visited by the searchers till the stopping time and
show that it has a power law tail: for large . Thus all moments of up to the order
are finite, while the higher moments diverge. The prefactor increases
with faster than exponentially. Our solution gives the exit probability of
a set of particles from a box through the left boundary.
Incidentally, it also provides an exact solution of the Laplace's equation in
an -dimensional hypercube with some prescribed boundary conditions. The
analytical results are in excellent agreement with Monte Carlo simulations.Comment: 18 pages, 9 figure
Brane-world cosmology with black strings
We consider the simplest scenario when black strings / cigars penetrate the
cosmological brane. As a result, the brane has a Swiss-cheese structure, with
Schwarzschild black holes immersed in a
Friedmann-Lema\^{\i}tre-Robertson-Walker brane. There is no dark radiation in
the model, the cosmological regions of the brane are characterized by a
cosmological constant and flat spatial sections. Regardless of the
value of , these brane-world universes forever expand and forever
decelerate. The totality of source terms in the modified Einstein equation sum
up to a dust, establishing a formal equivalence with the general relativistic
Einstein-Straus model. However in this brane-world scenario with black strings
the evolution of the cosmological fluid strongly depends on . For
it has positive energy density and negative pressure
and at late times it behaves as in the Einstein-Straus model. For (not too
high) positive values of the cosmological evolution begins with
positive and negative , but this is followed by an epoch with both
and positive. Eventually, becomes negative, while stays
positive. A similar evolution is present for high positive values of , however in this case the evolution ends in a pressure singularity,
accompanied by a regular behaviour of the cosmic acceleration. This is a novel
type of singularity appearing in brane-worlds.Comment: 6 pages, 4 figures; expanded version, references added, to appear in
Physical Review
Morphological instability of a nonequilibrium icecolloid interface
We assess the morphological stability of a nonequilibrium icecolloidal suspension interface, and apply the theory to bentonite clay. An experimentally convenient scaling is employed which takes advantage of the vanishing segregation coefficient at low freezing velocities, and when anisotropic kinetic effects are included the interface is shown to be unstable to travelling waves. The potential for traveling wave modes reveals a possible mechanism for the polygonal and spiral ice lenses observed in frozen clays. A weakly nonlinear analysis yields a long-wave evolution equation for the interface shape containing a new parameter related to the highly nonlinear liquidus curve in colloidal systems. We discuss the implications of these results for the frost susceptibility of soils and the fabrication of microtailored porous materials
Spatial survival probability for one-dimensional fluctuating interfaces in the steady state
We report numerical and analytic results for the spatial survival probability
for fluctuating one-dimensional interfaces with Edwards-Wilkinson or
Kardar-Parisi-Zhang dynamics in the steady state. Our numerical results are
obtained from analysis of steady-state profiles generated by integrating a
spatially discretized form of the Edwards-Wilkinson equation to long times. We
show that the survival probability exhibits scaling behavior in its dependence
on the system size and the `sampling interval' used in the measurement for both
`steady-state' and `finite' initial conditions. Analytic results for the
scaling functions are obtained from a path-integral treatment of a formulation
of the problem in terms of one-dimensional Brownian motion. A `deterministic
approximation' is used to obtain closed-form expressions for survival
probabilities from the formally exact analytic treatment. The resulting
approximate analytic results provide a fairly good description of the numerical
data.Comment: RevTeX4, 21 pages, 8 .eps figures, changes in sections IIIB and IIIC
and in Figs 7 and 8, version to be published in Physical Review
Anderson-Mott Transition Driven by Spin Disorder: Spin Glass Transition and Magnetotransport in Amorphous GdSi
A zero temperature Anderson-Mott transition driven by spin disorder can be
`tuned' by an applied magnetic field to achieve colossal magnetoconductance.
Usually this is not possible since spin disorder by itself cannot localise a
high density electron system. However, the presence of strong structural
disorder can realise this situation, self consistently generating a disordered
magnetic ground state. We explore such a model, constructed to understand
amorphous GdSi, and highlight the emergence of a spin glass phase,
Anderson-Mott signatures in transport and tunneling spectra, and unusual
magneto-optical conductivity. We solve a disordered strong coupling
fermion-spin-lattice problem essentially exactly on finite systems, and account
for all the qualitative features observed in magnetism, transport, and the
optical spectra in this system.Comment: Final version of cond-mat/0209579, to appear in Phys. Rev. Let
Residual resistivity ratio and its relation to the positive magnetoresistance behavior in natural multilayer LaMn2Ge2; relevance to artificial multilayer physics
Results of low temperature magnetoresistance () and
isothermal magnetization (M) measurements on polycrystalline ferromagnetic (T_C
close to 300 K) natural multilayers, LaMn_{2+x}Ge_{2-y}Si_y, are reported. It
is found that the samples with large residual resistivity ratio,
, exhibit large positive magnetoresistance at high
magnetic fields. The Kohler's rule is not obeyed in these alloys. In addition,
at 4.5 K, there is a tendency towards linear variation of
with magnetic field with increasing ); however, the field
dependence of does not track that of M, thereby suggesting
that the magnetoresistance originates from non-magnetic layers. It is
interesting that these experimental findings on bulk polycrystals are
qualitatively similar to what is seen in artificially grown multilayer systems
recently.Comment: 5 pages, 3 figures, separate figures. This work is a follow-up of our
earlier paper in APL, Ref. : APL Vol 71, pp 2385 (1997
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