977 research outputs found
Echoes in classical dynamical systems
Echoes arise when external manipulations to a system induce a reversal of its
time evolution that leads to a more or less perfect recovery of the initial
state. We discuss the accuracy with which a cloud of trajectories returns to
the initial state in classical dynamical systems that are exposed to additive
noise and small differences in the equations of motion for forward and backward
evolution. The cases of integrable and chaotic motion and small or large noise
are studied in some detail and many different dynamical laws are identified.
Experimental tests in 2-d flows that show chaotic advection are proposed.Comment: to be published in J. Phys.
Ferromagnetic phase transition for the spanning-forest model (q \to 0 limit of the Potts model) in three or more dimensions
We present Monte Carlo simulations of the spanning-forest model (q \to 0
limit of the ferromagnetic Potts model) in spatial dimensions d=3,4,5. We show
that, in contrast to the two-dimensional case, the model has a "ferromagnetic"
second-order phase transition at a finite positive value w_c. We present
numerical estimates of w_c and of the thermal and magnetic critical exponents.
We conjecture that the upper critical dimension is 6.Comment: LaTex2e, 4 pages; includes 6 Postscript figures; Version 2 has
expanded title as published in PR
Exchange Anisotropy in Epitaxial and Polycrystalline NiO/NiFe Bilayers
(001) oriented NiO/NiFe bilayers were grown on single crystal MgO (001)
substrates by ion beam sputtering in order to determine the effect that the
crystalline orientation of the NiO antiferromagnetic layer has on the
magnetization curve of the NiFe ferromagnetic layer. Simple models predict no
exchange anisotropy for the (001)-oriented surface, which in its bulk
termination is magnetically compensated. Nonetheless exchange anisotropy is
present in the epitaxial films, although it is approximately half as large as
in polycrystalline films that were grown simultaneously. Experiments show that
differences in exchange field and coercivity between polycrystalline and
epitaxial NiFe/NiO bilayers couples arise due to variations in induced surface
anisotropy and not from differences in the degree of compensation of the
terminating NiO plane. Implications of these observations for models of induced
exchange anisotropy in NiO/NiFe bilayer couples will be discussed.Comment: 23 pages in RevTex format, submitted to Phys Rev B
Anomalous magnetoresistance behavior of CoFe nano-oxide spin valves at low temperatures
We report magnetoresistance curves of CoFe nano-oxide specular spin valves of
MnIr/CoFe/nano-oxidized CoFe/CoFe/Cu/CoFe/nano-oxidized CoFe/Ta at different
temperatures from 300 to 20 K. We extend the Stoner-Wolfarth model of a common
spin valve to a specular spin valve, introducing the separation of the pinned
layer into two sublayers and their magnetic coupling across the nano-oxide. We
study the effect of different coupling/exchange (between the antiferromagnetic
layer and the bottom sublayer) field ratios on the magnetization and
magnetoresistance, corresponding with the experimentally observed anomalous
bumps in low temperature magnetoresistance curves.Comment: 4 pages; 3 figure
Indication of Superconductivity at 35 K in Graphite-Sulfur Composites
We report magnetization measurements performed on graphite--sulfur composites
which demonstrate a clear superconducting behavior below the critical
temperature T = 35 K. The Meissner-Ochsenfeld effect, screening
supercurrents, and magnetization hysteresis loops characteristic of type-II
superconductors were measured. The results indicate that the superconductivity
occurs in a small sample fraction, possibly related to the sample surface.Comment: published versio
Nonequilibrium stationary states and equilibrium models with long range interactions
It was recently suggested by Blythe and Evans that a properly defined steady
state normalisation factor can be seen as a partition function of a fictitious
statistical ensemble in which the transition rates of the stochastic process
play the role of fugacities. In analogy with the Lee-Yang description of phase
transition of equilibrium systems, they studied the zeroes in the complex plane
of the normalisation factor in order to find phase transitions in
nonequilibrium steady states. We show that like for equilibrium systems, the
``densities'' associated to the rates are non-decreasing functions of the rates
and therefore one can obtain the location and nature of phase transitions
directly from the analytical properties of the ``densities''. We illustrate
this phenomenon for the asymmetric exclusion process. We actually show that its
normalisation factor coincides with an equilibrium partition function of a walk
model in which the ``densities'' have a simple physical interpretation.Comment: LaTeX, 23 pages, 3 EPS figure
Expressive and Instrumental Offending: Reconciling the Paradox of Specialisation and Versatility
Although previous research into specialisation has been dominated by the debate over the existence of specialisation versus versatility, it is suggested that research needs to move beyond the restrictions of this dispute. The current study explores the criminal careers of 200 offenders based on their criminal records, obtained from a police database in the North West of England, aiming to understand the patterns and nature of specialisation by determining the presence of differentiation within their general offending behaviours and examining whether the framework of Expressive and Instrumental offending styles can account for any specialised tendencies that emerge. Fifty-eight offences were subjected to Smallest Space Analysis. Results revealed that a model of criminal differentiation could be identified and that any specialisation is represented in terms of Expressive and Instrumental offending styles
The importance of looking credible: the impact of the behavioural sequelae of post-traumatic stress disorder on the credibility of asylum seekers
Cultural preferences for formal versus intuitive reasoning
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/91932/1/cultural_preferences.pd
Hot Photoluminescence in γ-In2Se3Nanorods
The energy relaxation of electrons in γ-In2Se3nanorods was investigated by the excitation-dependent photoluminescence (PL). From the high-energy tail of PL, we determine the electron temperature (Te) of the hot electrons. TheTevariation can be explained by a model in which the longitudinal optical (LO)-phonon emission is the dominant energy relaxation process. The high-quality γ-In2Se3nanorods may be a promising material for the photovoltaic devices
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