25,767 research outputs found
Empirical orbit determination using Apollo 14 data
An empirical orbit determination method is shown to yield highly accurate navigation results when applied to lunar orbit tracking data. Regressions and predictions of free flight Apollo 14 tracking data exhibit minimal residual growth, and the solution orbital elements behave in a very consistent manner. Solutions from data acquired during propulsive maneuvers result in degraded predictions. The residual patterns from free flight processing are shown to be consistent from pass to pass and are correlated with lunar topographic features
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Knots, links, anyons and statistical mechanics of entangled polymer rings
The field theory approach to the statistical mechanics of a system of N polymer rings linked together is extended to the case of links whose paths in space are characterized by a fixed number 2s of maxima and minima. Such kind of links are called 2s-plats and appear for instance in the DNA of living organisms or in the wordlines of quasiparticles associated with vortices nucleated in a quasi-two-dimensional superfluid. The path integral theory describing the statistical mechanics of polymers subjected to topological constraints is mapped here into a field theory of quasiparticles (anyons). In the particular case of s=2, it is shown that this field theory admits vortex solutions with special self-dual points in which the interactions between the vortices vanish identically. The topological states of the link are distinguished using two topological invariants, namely the Gauss linking number and the so-called bridge number which is related to s. The Gauss linking number is a topological invariant that is relatively weak in distinguishing the different topological configurations of a general link. The addition of topological constraints based on the bridge number allows to get a glimpse into the non-abelian world of quasiparticles, which is relevant for important applications like topological quantum computing and high-TC superconductivity. At the end an useful connection with the cosh-Gordon equation is shown in the case s=2. © 201
Intermixture of extended edge and localized bulk energy levels in macroscopic Hall systems
We study the spectrum of a random Schroedinger operator for an electron
submitted to a magnetic field in a finite but macroscopic two dimensional
system of linear dimensions equal to L. The y direction is periodic and in the
x direction the electron is confined by two smooth increasing boundary
potentials. The eigenvalues of the Hamiltonian are classified according to
their associated quantum mechanical current in the y direction. Here we look at
an interval of energies inside the first Landau band of the random operator for
the infinite plane. In this energy interval, with large probability, there
exist O(L) eigenvalues with positive or negative currents of O(1). Between each
of these there exist O(L^2) eigenvalues with infinitesimal current
O(exp(-cB(log L)^2)). We explain what is the relevance of this analysis to the
integer quantum Hall effect.Comment: 29 pages, no figure
High-order myopic coronagraphic phase diversity (COFFEE) for wave-front control in high-contrast imaging systems
The estimation and compensation of quasi-static aberrations is mandatory to
reach the ultimate performance of high-contrast imaging systems. COFFEE is a
focal plane wave-front sensing method that consists in the extension of phase
diversity to high-contrast imaging systems. Based on a Bayesian approach, it
estimates the quasi-static aberrations from two focal plane images recorded
from the scientific camera itself. In this paper, we present COFFEE's extension
which allows an estimation of low and high order aberrations with nanometric
precision for any coronagraphic device. The performance is evaluated by
realistic simulations, performed in the SPHERE instrument framework. We develop
a myopic estimation that allows us to take into account an imperfect knowledge
on the used diversity phase. Lastly, we evaluate COFFEE's performance in a
compensation process, to optimize the contrast on the detector, and show it
allows one to reach the 10^-6 contrast required by SPHERE at a few resolution
elements from the star. Notably, we present a non-linear energy minimization
method which can be used to reach very high contrast levels (better than 10^-7
in a SPHERE-like context)Comment: Accepted in Optics Expres
Large N and double scaling limits in two dimensions
Recently, the author has constructed a series of four dimensional
non-critical string theories with eight supercharges, dual to theories of light
electric and magnetic charges, for which exact formulas for the central charge
of the space-time supersymmetry algebra as a function of the world-sheet
couplings were obtained. The basic idea was to generalize the old matrix model
approach, replacing the simple matrix integrals by the four dimensional matrix
path integrals of N=2 supersymmetric Yang-Mills theory, and the Kazakov
critical points by the Argyres-Douglas critical points. In the present paper,
we study qualitatively similar toy path integrals corresponding to the two
dimensional N=2 supersymmetric non-linear sigma model with target space CP^n
and twisted mass terms. This theory has some very strong similarities with N=2
super Yang-Mills, including the presence of critical points in the vicinity of
which the large n expansion is IR divergent. The model being exactly solvable
at large n, we can study non-BPS observables and give full proofs that double
scaling limits exist and correspond to universal continuum limits. A complete
characterization of the double scaled theories is given. We find evidence for
dimensional transmutation of the string coupling in some non-critical string
theories. We also identify en passant some non-BPS particles that become
massless at the singularities in addition to the usual BPS states.Comment: 38 pages, including an introductory section that makes the paper
self-contained, two figures and one appendix; v2: typos correcte
Electron Transport and Hot Phonons in Carbon Nanotubes
We demonstrate the key role of phonon occupation in limiting the high-field
ballistic transport in metallic carbon nanotubes. In particular, we provide a
simple analytic formula for the electron transport scattering length, that we
validate by accurate first principles calculations on (6,6) and (11,11)
nanotubes. The comparison of our results with the scattering lengths fitted
from experimental I-V curves indicates the presence of a non-equilibrium
optical phonon heating induced by electron transport. We predict an effective
temperature for optical phonons of thousands Kelvin.Comment: 4 pages, 1 figur
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