2,819 research outputs found
The mathematical description of the electrosynthesis of composites of oxy-hydroxycompounds cobalt with polypyrrole overooxidazed
The electrosynthesis of the composite with of the overoxidized polypyrrole with cobalt oxy-hydroxide in strongly acidic media has been described mathematically, using linear stability theory and bifurcation analysis. The steadystates stability conditions and oscillatory and monotonic instability requirements have been described too. The system´s behavior was compared with behavior of other systems with overoxidation, electropolymerization of heterocyclic compounds and electrosynthesis of the cobalt oxy-hydroxides
Integral Equations for Heat Kernel in Compound Media
By making use of the potentials of the heat conduction equation the integral
equations are derived which determine the heat kernel for the Laplace operator
in the case of compound media. In each of the media the parameter
acquires a certain constant value. At the interface of the media the
conditions are imposed which demand the continuity of the `temperature' and the
`heat flows'. The integration in the equations is spread out only over the
interface of the media. As a result the dimension of the initial problem is
reduced by 1. The perturbation series for the integral equations derived are
nothing else as the multiple scattering expansions for the relevant heat
kernels. Thus a rigorous derivation of these expansions is given. In the one
dimensional case the integral equations at hand are solved explicitly (Abel
equations) and the exact expressions for the regarding heat kernels are
obtained for diverse matching conditions. Derivation of the asymptotic
expansion of the integrated heat kernel for a compound media is considered by
making use of the perturbation series for the integral equations obtained. The
method proposed is also applicable to the configurations when the same medium
is divided, by a smooth compact surface, into internal and external regions, or
when only the region inside (or outside) this surface is considered with
appropriate boundary conditions.Comment: 26 pages, no figures, no tables, REVTeX4; two items are added into
the Reference List; a new section is added, a version that will be published
in J. Math. Phy
A Study of the \eta \pi^{0} Spectrum and Search for a J^{PC} = 1^{-+} Exotic Meson
A partial wave analysis (PWA) of the of the system (where ) produced in the charge exchange reaction at an incident momentum of 18 GeV is presented as a function of
invariant mass, , and momentum transfer squared,
, from the incident to the outgoing system. , and waves were included in the PWA. The
and states are clearly observed in the overall
effective mass distribution as well as in the amplitudes associated with
wave and waves respectively after partial wave decomposition. The observed
distributions in moments (averages of spherical harmonics) were compared to the
results from the PWA and the two are consistent. The distribution in
for individual waves associated with natural and
unnatural parity exchange in the -channel are consistent with Regge
phenomenology. Of particular interest in this study is the wave since this
leads to an exotic for the system. A wave is
present in the data, however attempts to describe the mass dependence of the
amplitude and phase motion with respect to the wave as a Breit-Wigner
resonance are problematic. This has implications regarding the existence of a
reported exotic meson decaying into with a mass
near 1.4 GeV.Comment: 19 pages, 29 figures, to appear in Phys. Rev.
Single-magnet rotary flowmeter for liquid metals
We present a theory of single-magnet flowmeter for liquid metals and compare
it with experimental results. The flowmeter consists of a freely rotating
permanent magnet, which is magnetized perpendicularly to the axle it is mounted
on. When such a magnet is placed close to a tube carrying liquid metal flow, it
rotates so that the driving torque due to the eddy currents induced by the flow
is balanced by the braking torque induced by the rotation itself. The
equilibrium rotation rate, which varies directly with the flow velocity and
inversely with the distance between the magnet and the layer, is affected
neither by the electrical conductivity of the metal nor by the magnet strength.
We obtain simple analytical solutions for the force and torque on slowly moving
and rotating magnets due to eddy currents in a layer of infinite horizontal
extent. The predicted equilibrium rotation rates qualitatively agree with the
magnet rotation rate measured on a liquid sodium flow in stainless steel duct.Comment: 15 pages, 6 figures, revised version, to appear in J. Appl. Phy
Phase transitions and correlations in the bosonic pair contact process with diffusion: Exact results
The variance of the local density of the pair contact process with diffusion
(PCPD) is investigated in a bosonic description. At the critical point of the
absorbing phase transition (where the average particle number remains constant)
it is shown that for lattice dimension d>2 the variance exhibits a phase
transition: For high enough diffusion constants, it asymptotically approaches a
finite value, while for low diffusion constants the variance diverges
exponentially in time. This behavior appears also in the density correlation
function, implying that the correlation time is negative. Yet one has dynamical
scaling with a dynamical exponent calculated to be z=2.Comment: 20 pages, 5 figure
Aharonov-Bohm Oscillations in a One-Dimensional Wigner Crystal-Ring
We calculate the magnetic moment (`persistent current') in a strongly
correlated electron system --- a Wigner crystal --- in a one-dimensional
ballistic ring. The flux and temperature dependence of the persistent current
in a perfect ring is shown to be essentially the same as for a system of
non-interacting electrons. In contrast, by incorporating into the ring geometry
a tunnel barrier that pins the Wigner crystal, the current is suppressed and
its temperature dependence is drastically changed. The competition between two
temperature effects --- the reduced barrier height for macroscopic tunneling
and loss of quantum coherence --- may result in a sharp peak in the temperature
dependence. The character of the macroscopic quantum tunneling of a Wigner
crystal ring is dictated by the strength of pinning. At strong pinning the
tunneling of a rigid Wigner crystal chain is highly inhomogeneous, and the
persistent current has a well-defined peak at
independent of the barrier height ( is the sound velocity of the Wigner
crystal, is the length of the ring). In the weak pinning regime, the Wigner
crystal tunnels through the barrier as a whole and if the effect of
the barrier is to suppress the current amplitude and to shift the crossover
temperature from to . ( is the
amplitude of the pinning potential, is the drift velocity of a Wigner crystal ring with lattice spacing
). For very weak pinning, , the influence of the barrier on the
persistent current of a Wigner crystal ring is negligibly small.Comment: 30 pages, RevTeX, 2 figures available on reques
Diffusion in a generalized Rubinstein-Duke model of electrophoresis with kinematic disorder
Using a generalized Rubinstein-Duke model we prove rigorously that kinematic
disorder leaves the prediction of standard reptation theory for the scaling of
the diffusion constant in the limit for long polymer chains
unaffected. Based on an analytical calculation as well as Monte Carlo
simulations we predict kinematic disorder to affect the center of mass
diffusion constant of an entangled polymer in the limit for long chains by the
same factor as single particle diffusion in a random barrier model.Comment: 29 pages, 3 figures, submitted to PR
The Influence of Macroscopic Pedestrian Structures on Train Boarding Efficiency
A deeper understanding of pedestrian dynamics is essential to improve crowd
flows in public spaces such as train stations. It is essential to understand
both the physical and the psychological processes present in this context.
However, current research on train boarding behavior is limited in scope and
mainly focuses on how group level variables such as number of
boarders/deboarders influence train boarding efficiency. Viewing pedestrian
dynamics through a psychological lens is important for a detailed understanding
of the train boarding context and to recognize target areas for improving crowd
flows. At Dutch train stations, boarders follow a social norm of waiting at the
train door until deboarding is complete. Although people generally adhere to
this norm, the way it is executed may not be optimal for deboarding efficiency.
We investigate how waiting boarders form a deboarding channel (a corridor where
deboarders exit the train) which is a macroscopic structure formed by
pedestrians, and how this channel in turn influences the efficiency of
deboarding. Analyzing a dataset with 3278 boarding events at Utrecht Centraal
Station in the Netherlands from 2017 - 2020 (a subset of a trajectory dataset
that captures 100,000 trajectories per day), we found that higher numbers of
boarders and a higher ratio of boarders to deboarders, reduced the width of the
deboarding channel, and a lower width was associated with lower deboarding
efficiency. These results shift the focus from group level variables to
identifying macroscopic structures that are formed when pedestrians interact
within a social system and provide specific target areas where
nudges/behavioral interventions could be implemented
On the universality of the fluctuation-dissipation ratio in non-equilibrium critical dynamics
The two-time nonequilibrium correlation and response functions in 1D kinetic
classical spin systems with non-conserved dynamics and quenched to their
zero-temperature critical point are studied. The exact solution of the kinetic
Ising model with Glauber dynamics for a wide class of initial states allows for
an explicit test of the universality of the non-equilibrium limit
fluctuation-dissipation ratio X_{\infty}. It is shown that the value of
X_{\infty} depends on whether the initial state has finitely many domain walls
or not and thus two distinct dynamic universality classes can be identified in
this model. Generic 1D kinetic spin systems with non-conserved dynamics fall
into the same universality classes as the kinetic Glauber-Ising model provided
the dynamics is invariant under the C-symmetry of simultaneous spin and
magnetic-field reversal. While C-symmetry is satisfied for magnetic systems, it
need not be for lattice gases which may therefore display hitherto unexplored
types of non-universal kinetics
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