755 research outputs found
Ring diagram analysis of near-surface flows in the Sun
Ring diagram analysis of solar oscillation power spectra obtained from MDI
data is carried out to study the velocity fields in the outer part of the solar
convection zone. The three dimensional power spectra are fitted to a model
which has a Lorentzian profile in frequency and which includes the advection of
the wave front by horizontal flows, to obtain the two components of the
sub-surface flows as a function of the horizontal wave number and radial order
of the oscillation modes. This information is then inverted using OLA and RLS
methods to infer the variation in horizontal flow velocity with depth. The
average rotation velocity at different latitudes obtained by this technique
agrees reasonably with helioseismic estimates made using frequency splitting
data. The shear layer just below the solar surface appears to consist of two
parts with the outer part up to a depth of 4 Mm, where the velocity gradient
does not show any reversal up to a latitude of 60 degrees. In the deeper part
the velocity gradient shows reversal in sign around a latitude of 55 degrees.
The zonal flow velocities inferred in the outermost layers appears to be
similar to those obtained by other measurements. A meridional flow from equator
polewards is found. It has a maximum amplitude of about 30 m/s near the surface
and the amplitude is nearly constant in the outer shear layer.Comment: aastex, 12 figures, to appear in Ap.
Seismic investigation of the solar structure using GONG frequencies
Using the recently obtained GONG frequencies, we investigate the properties
of the solar interior by constructing solar models with various input physics
like opacities, equation of state, nuclear reaction rates etc. The differential
asymptotic inversion technique is then used to infer the relative difference in
sound speed between the Sun and solar models. Here we apply these results to
test equation of state and different formulation for calculating the convective
flux.Comment: Latex, 2 pages, 3 figures, To appear in the IAU Symp. # 181:
"Sounding solar and stellar interiors", eds. F.X. Schmider & J. Provos
Experimental Quantum Cloning of Single Photons
Although perfect copying of unknown quantum systems is forbidden by the laws
of quantum mechanics, approximate cloning is possible. A natural way of
realizing quantum cloning of photons is by stimulated emission. In this context
the fundamental quantum limit to the quality of the clones is imposed by the
unavoidable presence of spontaneous emission. In our experiment a single input
photon stimulates the emission of additional photons from a source based on
parametric down-conversion. This leads to the production of quantum clones with
near optimal fidelity. We also demonstrate universality of the copying
procedure by showing that the same fidelity is achieved for arbitrary input
states.Comment: 4 pages, 2 figure
Comparison of High-degree Solar Acoustic Frequencies and Asymmetry between Velocity and Intensity Data
Using the local helioseismic technique of ring diagram we analyze the
frequencies of high--degree f- and p-modes derived from both velocity and
continuum intensity data observed by MDI. Fitting the spectra with asymmetric
peak profiles, we find that the asymmetry associated with velocity line
profiles is negative for all frequency ranges agreeing with previous
observations while the asymmetry of the intensity profiles shows a complex and
frequency dependent behavior. We also observe systematic frequency differences
between intensity and velocity spectra at the high end of the frequency range,
mostly above 4 mHz. We infer that this difference arises from the fitting of
the intensity rather than the velocity spectra. We also show that the frequency
differences between intensity and velocity do not vary significantly from the
disk center to the limb when the spectra are fitted with the asymmetric profile
and conclude that only a part of the background is correlated with the
intensity oscillations.Comment: Accepted for publication in Astrophysical Journa
On the control of acute rodent malaria infections by innate immunity
Does specific immunity, innate immunity or resource (red blood cell) limitation control the first peak of the blood-stage parasite in acute rodent malaria infections? Since mice deficient in specific immunity exhibit similar initial dynamics as wild-type mice it is generally viewed that the initial control of parasite is due to either limitation of resources (RBC) or innate immune responses. There are conflicting views on the roles of these two mechanisms as there is experimental evidence supporting both these hypotheses. While mathematical models based on RBC limitation are capable of describing the dynamics of primary infections, it was not clear whether a model incorporating the key features of innate immunity would be able to do the same. We examine the conditions under which a model incorporating parasite and innate immunity can describe data from acute <i>Plasmodium chabaudi</i> infections in mice. We find that innate immune response must decay slowly if the parasite density is to fall rather than equilibrate. Further, we show that within this framework the differences in the dynamics of two parasite strains are best ascribed to differences in susceptibility to innate immunity, rather than differences in the strains' growth rates or their propensity to elicit innate immunity. We suggest that further work is required to determine if innate immunity or resource limitation control acute malaria infections in mice
Thermodynamics Property of Magnetic Materials in a Ferromagnetic System using the Ising Model
There is hardly any branch of physics one can approach successfully without resorting to quantum statistical mechanics. It has been proven that the quantum mechanical description of a system gives accurate results. To use quantum statistical mechanics, the system are treated at their microscopic level. Most systems consist of many particles and in order o deal with such large numbers, one has to resort to statistical method related to the partition function of statistical mechanics. In this study, we haves used the partition function which is a statistical parameter to explore the thermodynamic properties such as Helmoltz free energy, Entropy, internal energy and heat capacity of a magnetic materials in a ferromagnetic system using the first and second dimensional Ising model. The results show that in one-dimensional model, phase transition does not occur at finite temperature but susceptibility of a system can be measured from the fluctuations in the magnetization in the second dimensional Ising model
One-dimensional lattice of oscillators coupled through power-law interactions: Continuum limit and dynamics of spatial Fourier modes
We study synchronization in a system of phase-only oscillators residing on
the sites of a one-dimensional periodic lattice. The oscillators interact with
a strength that decays as a power law of the separation along the lattice
length and is normalized by a size-dependent constant. The exponent of
the power law is taken in the range . The oscillator frequency
distribution is symmetric about its mean (taken to be zero), and is
non-increasing on . In the continuum limit, the local density of
oscillators evolves in time following the continuity equation that expresses
the conservation of the number of oscillators of each frequency under the
dynamics. This equation admits as a stationary solution the unsynchronized
state uniform both in phase and over the space of the lattice. We perform a
linear stability analysis of this state to show that when it is unstable,
different spatial Fourier modes of fluctuations have different stability
thresholds beyond which they grow exponentially in time with rates that depend
on the Fourier modes. However, numerical simulations show that at long times,
all the non-zero Fourier modes decay in time, while only the zero Fourier mode
(i.e., the "mean-field" mode) grows in time, thereby dominating the instability
process and driving the system to a synchronized state. Our theoretical
analysis is supported by extensive numerical simulations.Comment: 7 pages, 4 figures. v2: new simulation results added, close to the
published versio
Experimental Violation of a Spin-1 Bell Inequality Using Maximally Entangled Four-Photon States
We demonstrate the experimental violation of a spin-1 Bell inequality. The spin-1 inequality is based on the Clauser, Horne, Shimony, and Holt formalism. For entangled spin-1 particles, the maximum quantum-mechanical prediction is 2.55 as opposed to a maximum of 2, predicted using local hidden variables. We obtained an experimental value of 2.27±0.02 using the four-photon state generated by pulsed, type-II, stimulated parametric down-conversion. This is a violation of the spin-1 Bell inequality by more than 13 standard deviations
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