69,325 research outputs found
Memory Effects and Scaling Properties of Traffic Flows
Traffic flows are studied in terms of their noise of sound, which is an
easily accessible experimental quantity. The sound noise data is studied making
use of scaling properties of wavelet transforms and Hurst exponents are
extracted. The scaling behavior is used to characterize the traffic flows in
terms of scaling properties of the memory function in Mori-Lee stochastic
differential equations. The results obtained provides for a new theoretical as
well as experimental framework to characterize the large-time behavior of
traffic flows. The present paper outlines the procedure by making use of
one-lane computer simulations as well as sound-data measurements from a real
two-lane traffic flow. We find the presence of conventional diffusion as well
as 1/f-noise in real traffic flows at large time scales.Comment: 3 figure
Massive sterile neutrinos as warm Dark Matter
We show that massive sterile neutrinos mixed with the ordinary ones may be
produced in the early universe in the right amount to be natural warm dark
matter particles. Their mass should be below 40 keV and the corresponding
mixing angles sin^2 2\theta > 10^{-11} for mixing with \nu_\mu or \nu_\tau,
while mixing with \nu_e is slightly stronger bounded with mass less than 30
keV.Comment: 13 pages, 1 figure, references and acknowledgement added; discussion
on SN bound updated, matches version in Astropart.phy
Hydrophobic interactions with coarse-grained model for water
Integral equation theory is applied to a coarse-grained model of water to
study potential of mean force between hydrophobic solutes. Theory is shown to
be in good agreement with the available simulation data for methane-methane and
fullerene-fullerene potential of mean force in water; the potential of mean
force is also decomposed into its entropic and enthalpic contributions. Mode
coupling theory is employed to compute self-diffusion coefficient of water, as
well as diffusion coefficient of a dilute hydrophobic solute; good agreement
with molecular dynamics simulation results is found
Self-consistent Ornstein-Zernike approximation for molecules with soft cores
The Self-Consistent Ornstein-Zernike Approximation (SCOZA) is an accurate
liquid state theory. So far it has been tied to interactions composed of hard
core repulsion and long-range attraction, whereas real molecules have soft core
repulsion at short distances. In the present work, this is taken into account
through the introduction of an effective hard core with a diameter that depends
upon temperature only. It is found that the contribution to the configurational
internal energy due to the repulsive reference fluid is of prime importance and
must be included in the thermodynamic self-consistency requirement on which
SCOZA is based. An approximate but accurate evaluation of this contribution
relies on the virial theorem to gauge the amplitude of the pair distribution
function close to the molecular surface. Finally, the SCOZA equation is
transformed by which the problem is reformulated in terms of the usual SCOZA
with fixed hard core reference system and temperature-dependent interaction
Spectral distortion of cosmic background radiation by scattering on hot electrons. Exact calculations
The spectral distortion of the cosmic background radiation produced by the
inverse Compton scattering on hot electrons in clusters of galaxies (thermal
Sunyaev-Zeldovich effect) is calculated for arbitrary optical depth and
electron temperature. The distortion is found by a numerical solution of the
exact Boltzmann equation for the photon distribution function. In the limit of
small optical depth and low electron temperature our results confirm the
previous analyses. In the opposite limits, our method is the only one that
permits to make accurate calculations.Comment: 18 pages, 7 figures, to be published in Ap
Grain boundary melting in ice
We describe an optical scattering study of grain boundary premelting in water
ice. Ubiquitous long ranged attractive polarization forces act to suppress
grain boundary melting whereas repulsive forces originating in screened Coulomb
interactions and classical colligative effects enhance it. The liquid enhancing
effects can be manipulated by adding dopant ions to the system. For all
measured grain boundaries this leads to increasing premelted film thickness
with increasing electrolyte concentration. Although we understand that the
interfacial surface charge densities and solute concentrations can
potentially dominate the film thickness, we can not directly measure them
within a given grain boundary. Therefore, as a framework for interpreting the
data we consider two appropriate dependent limits; one is dominated by
the colligative effect and one is dominated by electrostatic interactions.Comment: 6 pages, 5 figure
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