1,083 research outputs found
Long term variation of the solar diurnal anisotropy of galactic cosmic rays observed with the Nagoya multi-directional muon detector
We analyze the three dimensional anisotropy of the galactic cosmic ray (GCR)
intensities observed independently with a muon detector at Nagoya in Japan and
neutron monitors over four solar activity cycles. We clearly see the phase of
the free-space diurnal anisotropy shifting toward earlier hours around solar
activity minima in A>0 epochs, due to the reduced anisotropy component parallel
to the mean magnetic field. The average parallel component is consistent with a
rigidity independent spectrum, while the perpendicular component increases with
GCR rigidity. We suggest that this harder spectrum of the perpendicular
component is due to contribution from the drift streaming. We find that the
bidirectional latitudinal density gradient is positive in A>0 epoch, while it
is negative in A<0 epoch, in accord with the drift model prediction. The radial
density gradient, on the other hand, varies with ~11-year cycle with maxima
(minima) in solar maximum (minimum) periods, but there is no significant
difference seen between average radial gradients in A>0 and A<0 epochs. The
average parallel mean free path is larger in A0. We also find,
however, that parallel mean free path (radial gradient) appears to persistently
increase (decreasing) in the last three cycles of weakening solar activity. We
suggest that simple differences between these parameters in A>0 and A<0 epochs
are seriously biased by these long-term trends.Comment: accepted for the publication in the Astrophysical Journa
An experimental and analytical investigation of the aerodynamics of a hypersonic vehicle at free stream Mach 6
The goal of this research is the assessment of the validity of existing three dimensional numerical programs in the prediction of the flow fields about general three dimensional hypersonic bodies. A detailed experimental research program was performed in which surface and flow field pressures were mapped. The results of the experimental work were compared with existing inviscid programs. Improvements were made on the existing numerical methods to include angle of attack. A summary of this work is presented
Multiplicative noise: A mechanism leading to nonextensive statistical mechanics
A large variety of microscopic or mesoscopic models lead to generic results
that accommodate naturally within Boltzmann-Gibbs statistical mechanics (based
on ). Similarly, other classes of models
point toward nonextensive statistical mechanics (based on , where the value of the entropic index depends on
the specific model). We show here a family of models, with multiplicative
noise, which belongs to the nonextensive class. More specifically, we consider
Langevin equations of the type , where
and are independent zero-mean Gaussian white noises with
respective amplitudes and . This leads to the Fokker-Planck equation
. Whenever the
deterministic drift is proportional to the noise induced one, i.e., , the stationary solution is shown to be (with and ). This distribution is
precisely the one optimizing with the constraint constant. We also
introduce and discuss various characterizations of the width of the
distributions.Comment: 3 PS figure
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Visual Representation in the Wild: How Rhesus Monkeys Parse Objects
Visual object representation was studied in free-ranging rhesus monkeys. To facilitate comparison with humans, and to provide a new tool for neurophysiologists, we used a looking time procedure originally developed for studies of human infants. Monkeys' looking times were measured to displays with one or two distinct objects, separated or together, stationary or moving. Results indicate that rhesus monkeys used featural information to parse the displays into distinct objects, and they found events in which distinct objects moved together more novel or unnatural than events in which distinct objects moved separately. These findings show both common-alities and contrasts with those obtained from human infants. We discuss their implications for the development and neural mechanisms of higher-level vision.Psycholog
SOLAR CYCLE DEPENDENCE OF THE DIURNAL ANISOTROPY OF 0.6 TeV COSMIC-RAY INTENSITY OBSERVED WITH THE MATSUSHIRO UNDERGROUND MUON DETECTOR
We analyze the temporal variation of the diurnal anisotropy of sub-TeV cosmic-ray intensity observed with the Matsushiro (Japan) underground muon detector over two full solar activity cycles in 1985-2008. We find an anisotropy component in the solar diurnal anisotropy superimposed on the Compton-Getting anisotropy due to Earth's orbital motion around the Sun. The phase of this additional anisotropy is almost constant at similar to 15:00 local solar time corresponding to the direction perpendicular to the average interplanetary magnetic field at Earth's orbit, while the amplitude varies between a maximum (0.043% +/- 0.002%) and minimum (similar to 0.008% +/- 0.002%) in a clear correlation with the solar activity. We find a significant time lag between the temporal variations of the amplitude and the sunspot number (SSN) and obtain the best correlation coefficient of +0.74 with the SSN delayed for 26 months. We suggest that this anisotropy might be interpreted in terms of the energy change due to the solar-wind-induced electric field expected for galactic cosmic rays (GCRs) crossing the wavy neutral sheet. The average amplitude of the sidereal diurnal variation over the entire period is 0.034% +/- 0.003%, which is roughly one-third of the amplitude reported from air shower and deep-underground muon experiments monitoring multi-TeVGCR intensity suggesting a significant attenuation of the anisotropy due to the solar modulation. We find, on the other hand, only a weak positive correlation between the sidereal diurnal anisotropy and the solar activity cycle in which the amplitude in the "active" solar activity epoch is about twice the amplitude in the "quiet" solar activity epoch. This implies that only one-fourth of the total attenuation varies in correlation with the solar activity cycle and/or the solar magnetic cycle. We finally examine the temporal variation of the "single-band valley depth" (SBVD) quoted by the Milagro experiment and, in contrast with recent Milagro's report, we find no steady increase in the Matsushiro observations in a seven-year period between 2000 and 2007. We suggest, therefore, that the steady increase of the SBVD reported by the Milagro experiment is not caused by the decreasing solar modulation in the declining phase of the 23rd solar activity cycle.ArticleThe Astrophysical Journal. 712(2):1100-1106 (2010)journal articl
Langevin equation for the extended Rayleigh model with an asymmetric bath
In this paper a one-dimensional model of two infinite gases separated by a
movable heavy piston is considered. The non-linear Langevin equation for the
motion of the piston is derived from first principles for the case when the
thermodynamic parameters and/or the molecular masses of gas particles on left
and right sides of the piston are different. Microscopic expressions involving
time correlation functions of the force between bath particles and the piston
are obtained for all parameters appearing in the non-linear Langevin equation.
It is demonstrated that the equation has stationary solutions corresponding to
directional fluctuation-induced drift in the absence of systematic forces. In
the case of ideal gases interacting with the piston via a quadratic repulsive
potential, the model is exactly solvable and explicit expressions for the
kinetic coefficients in the non-linear Langevin equation are derived. The
transient solution of the non-linear Langevin equation is analyzed
perturbatively and it is demonstrated that previously obtained results for
systems with the hard-wall interaction are recovered.Comment: 10 pages. To appear in Phys. Rev.
On the Second Law of thermodynamics and the piston problem
The piston problem is investigated in the case where the length of the
cylinder is infinite (on both sides) and the ratio is a very small
parameter, where is the mass of one particle of the gaz and is the mass
of the piston. Introducing initial conditions such that the stochastic motion
of the piston remains in the average at the origin (no drift), it is shown that
the time evolution of the fluids, analytically derived from Liouville equation,
agrees with the Second Law of thermodynamics.
We thus have a non equilibrium microscopical model whose evolution can be
explicitly shown to obey the two laws of thermodynamics.Comment: 29 pages, 9 figures submitted to Journal of Statistical Physics
(2003
Cosmic ray short burst observed with the Global Muon Detector Network (GMDN) on June 22, 2015
We analyze the short cosmic ray intensity increase ("cosmic ray burst": CRB)
on June 22, 2015 utilizing a global network of muon detectors and derive the
global anisotropy of cosmic ray intensity and the density (i.e. the
omnidirectional intensity) with 10-minute time resolution. We find that the CRB
was caused by a local density maximum and an enhanced anisotropy of cosmic rays
both of which appeared in association with Earth's crossing of the heliospheric
current sheet (HCS). This enhanced anisotropy was normal to the HCS and
consistent with a diamagnetic drift arising from the spatial gradient of cosmic
ray density, which indicates that cosmic rays were drifting along the HCS from
the north of Earth. We also find a significant anisotropy along the HCS,
lasting a few hours after the HCS crossing, indicating that cosmic rays
penetrated into the inner heliosphere along the HCS. Based on the latest
geomagnetic field model, we quantitatively evaluate the reduction of the
geomagnetic cut-off rigidity and the variation of the asymptotic viewing
direction of cosmic rays due to a major geomagnetic storm which occurred during
the CRB and conclude that the CRB is not caused by the geomagnetic storm, but
by a rapid change in the cosmic ray anisotropy and density outside the
magnetosphere.Comment: accepted for the publication in the Astrophysical Journa
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