332 research outputs found
Structure of Titan's mid-range magnetic tail: Cassini magnetometer observations during the T9 flyby
We analyze the magnetic structure of Titan's mid-range magnetic tail (5-6 Titan radii downstream from the moon) during Cassini's T9 flyby. Cassini magnetometer (MAG) measurements reveal a well-defined, induced magnetic tail consisting of two lobes and a distinct central current sheet. MAG observations also indicate that Saturn's background magnetic field is close to the moon's orbital plane and that the magnetospheric flow has a significant component in the Saturn-Titan direction. The analysis of MAG data in a coordinate system based on the orientation of the background magnetic field and an estimation of the incoming flow direction suggests that Titan's magnetic tail is extremely asymmetric. An important source of these asymmetries is the connection of the inbound tail lobe and the outbound tail lobe to the dayside and nightside hemispheres of Titan, respectively. Another source could be the perturbations generated by changes in the upstream conditions
Soft matrix models and Chern-Simons partition functions
We study the properties of matrix models with soft confining potentials.
Their precise mathematical characterization is that their weight function is
not determined by its moments. We mainly rely on simple considerations based on
orthogonal polynomials and the moment problem. In addition, some of these
models are equivalent, by a simple mapping, to matrix models that appear in
Chern-Simons theory. The models can be solved with q deformed orthogonal
polynomials (Stieltjes-Wigert polynomials), and the deformation parameter turns
out to be the usual parameter in Chern-Simons theory. In this way, we give
a matrix model computation of the Chern-Simons partition function on
and show that there are infinitely many matrix models with this partition
function.Comment: 13 pages, 3 figure
Charged particle environment of Titan during the T9 flyby
The ion measurements of the Cassini Plasma Spectrometer are presented which were acquired on 26 December 2005, during the T9 flyby at Titan. The plasma flow and magnetic field directions in the distant plasma environment of the moon were distinctly different from the other flybys. The near-Titan environment, dominated by ions of Titan origin, had a split signature, each with different ion composition; the first region was dominated by dense, slow, and cold ions in the 16-19 and 28-40 amu mass range, the second region contained only ions with mass 1 and 2, much less dense and less slow. Magnetospheric ions penetrate marginally into region 1, whereas the region-2 ion population is mixed. A detailed analysis has led us to conclude that the first event was due to the crossing of the mantle of Titan, whereas the second one very likely was a wake crossing. The split indicates the non-convexity of the ion-dominated volume around Titan. Both ion distributions are analysed in detail
Jacobi Crossover Ensembles of Random Matrices and Statistics of Transmission Eigenvalues
We study the transition in conductance properties of chaotic mesoscopic
cavities as time-reversal symmetry is broken. We consider the Brownian motion
model for transmission eigenvalues for both types of transitions, viz.,
orthogonal-unitary and symplectic-unitary crossovers depending on the presence
or absence of spin-rotation symmetry of the electron. In both cases the
crossover is governed by a Brownian motion parameter {\tau}, which measures the
extent of time-reversal symmetry breaking. It is shown that the results
obtained correspond to the Jacobi crossover ensembles of random matrices. We
derive the level density and the correlation functions of higher orders for the
transmission eigenvalues. We also obtain the exact expressions for the average
conductance, average shot-noise power and variance of conductance, as functions
of {\tau}, for arbitrary number of modes (channels) in the two leads connected
to the cavity. Moreover, we give the asymptotic result for the variance of
shot-noise power for both the crossovers, the exact results being too long. In
the {\tau} \rightarrow 0 and {\tau} \rightarrow \infty limits the known results
for the orthogonal (or symplectic) and unitary ensembles are reproduced. In the
weak time-reversal symmetry breaking regime our results are shown to be in
agreement with the semiclassical predictions.Comment: 24 pages, 5 figure
Time evolution in the Morse potential using supersymmetry: dissociation of the NO molecule
We present an algebraic method for treating molecular vibrations in the Morse
potential perturbed by an external laser field. By the help of a complete and
normalizable basis we transform the Schr\"{o}dinger equation into a system of
coupled ordinary differential equations. We apply our method to calculate the
dissociation probability of the NO molecule excited by chirped laser pulses.
The dependence of the molecular dipole-moment on the interatomic separation is
determined by a quantum-chemical method, and the corresponding transition
dipole moments are given by approximate analytic expressions. These turn out to
be very small between neighboring stationary states around the vibrational
quantum number , therefore we propose to use additional pulses in order
to skip this trapping state, and to obtain a reasonable dissociation
probability.Comment: 4 pages, 3 figure
Preliminary interpretation of Titan plasma interaction as observed by the Cassini Plasma Spectrometer: Comparisons with Voyager 1
The Cassini Plasma Spectrometer (CAPS) instrument observed the plasma environment at Titan during the Cassini orbiter's TA encounter on October 26, 2004. Titan was in Saturn's magnetosphere during the Voyager 1 flyby and also during the TA encounter. CAPS measurements from this encounter are compared with measurements made by the Voyager 1 Plasma Science Instrument (PLS). The comparisons focus on the composition and nature of ambient and pickup ions. They lead to: A) the major ion components of Saturn's magnetosphere in the vicinity of Titan are H+, H-2(+) and O+/CH4+ ions; B) finite gyroradius effects are apparent in ambient O+ ions as the result of their absorption by Titan's extended atmosphere; C) the principal pickup ions are composed of H+, H-2(+), N+/CH2+, CH4+, and N-2(+); D) the pickup ions are in narrow energy ranges; and E) there is clear evidence of the slowing down of background ions due to pickup ion mass loading
Ionospheric electrons in Titan's tail: Plasma structure during the cassini T9 encounter
We present results from the CAPS electron spectrometer obtained during the downstream flyby of Titan on 26 December 2005, which occurred during a period of enhanced plasma pressure inside the magnetosphere. The electron data show an unusual split signature with two principal intervals of interest outside the nominal corotation wake. Interval 1 shows direct evidence for ionospheric plasma escape at several RT in Titan's tail. Interval 2 shows a complex plasma structure, a mix between plasma of ionospheric and magnetospheric origin. We suggest a mechanism for plasma escape based on ambipolar electric fields set up by suprathermal ionospheric photoelectrons
Systematical Approach to the Exact Solution of the Dirac Equation for A Special Form of the Woods-Saxon Potential
Exact solution of the Dirac equation for a special form of the Woods-Saxon
potential is obtained for the s-states. The energy eigenvalues and
two-component spinor wave functions are derived by using a systematical method
which is called as Nikiforov-Uvarov. It is seen that the energy eigenvalues
strongly depend on the potential parameters. In addition, it is also shown that
the non-relativistic limit can be reached easily and directly.Comment: 10 pages, no figures, submitted for Publicatio
The defect variance of random spherical harmonics
The defect of a function is defined as the
difference between the measure of the positive and negative regions. In this
paper, we begin the analysis of the distribution of defect of random Gaussian
spherical harmonics. By an easy argument, the defect is non-trivial only for
even degree and the expected value always vanishes. Our principal result is
obtaining the asymptotic shape of the defect variance, in the high frequency
limit. As other geometric functionals of random eigenfunctions, the defect may
be used as a tool to probe the statistical properties of spherical random
fields, a topic of great interest for modern Cosmological data analysis.Comment: 19 page
Spatial distribution of low-energy plasma around 2 comet 67P/CG from Rosetta measurements
International audienceWe use measurements from the Rosetta plasma consortium (RPC) Langmuir probe (LAP) and mutual impedance probe (MIP) to study the spatial distribution of low-energy plasma in the near-nucleus coma of comet 67P/Churyumov-Gerasimenko. The spatial distribution is highly structured with the highest density in the summer hemisphere and above the region connecting the two main lobes of the comet, i.e. the neck region. There is a clear correlation with the neutral density and the plasma to neutral density ratio is found to be âŒ1-2·10 â6 , at a cometocentric distance of 10 km and at 3.1 AU from the sun. A clear 6.2 h modulation of the plasma is seen as the neck is exposed twice per rotation. The electron density of the collisonless plasma within 260 km from the nucleus falls of with radial distance as âŒ1/r. The spatial structure indicates that local ionization of neutral gas is the dominant source of low-energy plasma around the comet
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