52,469 research outputs found
Classical mappings of the symplectic model and their application to the theory of large-amplitude collective motion
We study the algebra Sp(n,R) of the symplectic model, in particular for the
cases n=1,2,3, in a new way. Starting from the Poisson-bracket realization we
derive a set of partial differential equations for the generators as functions
of classical canonical variables. We obtain a solution to these equations that
represents the classical limit of a boson mapping of the algebra. The
relationship to the collective dynamics is formulated as a theorem that
associates the mapping with an exact solution of the time-dependent Hartree
approximation. This solution determines a decoupled classical symplectic
manifold, thus satisfying the criteria that define an exactly solvable model in
the theory of large amplitude collective motion. The models thus obtained also
provide a test of methods for constructing an approximately decoupled manifold
in fully realistic cases. We show that an algorithm developed in one of our
earlier works reproduces the main results of the theorem.Comment: 23 pages, LaTeX using REVTeX 3.
Analytical design and simulation evaluation of an approach flight director system for a jet STOL aircraft
A program was undertaken to develop design criteria and operational procedures for STOL transport aircraft. As part of that program, a series of flight tests shall be performed in an Augmentor Wing Jet STOL Aircraft. In preparation for the flight test programs, an analytical study was conducted to gain an understanding of the characteristics of the vehicle for manual control, to assess the relative merits of the variety of manual control techniques available with attitude and thrust vector controllers, and to determine what improvements can be made over manual control of the bare airframe by providing the pilot with suitable command guidance information and by augmentation of the bare airframe dynamics. The objective of the study is to apply closed-loop pilot/vehicle analysis techniques to the analysis of manual flight control of powered-lift STOL aircraft in the landing approach and to the design and experimental verification of an advanced flight director display
A note on the computation of geometrically defined relative velocities
We discuss some aspects about the computation of kinematic, spectroscopic,
Fermi and astrometric relative velocities that are geometrically defined in
general relativity. Mainly, we state that kinematic and spectroscopic relative
velocities only depend on the 4-velocities of the observer and the test
particle, unlike Fermi and astrometric relative velocities, that also depend on
the acceleration of the observer and the corresponding relative position of the
test particle, but only at the event of observation and not around it, as it
would be deduced, in principle, from the definition of these velocities.
Finally, we propose an open problem in general relativity that consists on
finding intrinsic expressions for Fermi and astrometric relative velocities
avoiding terms that involve the evolution of the relative position of the test
particle. For this purpose, the proofs given in this paper can serve as
inspiration.Comment: 8 pages, 2 figure
Clusters and Fluctuations at Mean-Field Critical Points and Spinodals
We show that the structure of the fluctuations close to spinodals and
mean-field critical points is qualitatively different than the structure close
to non-mean-field critical points. This difference has important implications
for many areas including the formation of glasses in supercooled liquids. In
particular, the divergence of the measured static structure function in
near-mean-field systems close to the glass transition is suppressed relative to
the mean-field prediction in systems for which a spatial symmetry is broken.Comment: 5 pages, 1 figur
Evidence for a distant ( 8700 R sub J) Jovian magnetotail: Voyager 2 observations
A correlative survey of magnetometer (MAG) and Planetary Radio Astronomy (PRA) 1.2 kHz continuum radiation measurements from Voyager 2 provide evidence for at least eight distant Jovian magnetotail sightings occurring about once a month over the first 2/3 of 1981 at distances of approximately 5,000 to 9,000 R sub J. The occurrences of these events are in good agreement with prior Plasma Wave Science and Plasma Science identifications. Observations of these distant magnetotail, or tail filament, encounters appear most prevalent in both MAC and PRA data sets when the spacecraft was closest to the Jupiter-Sun axis at approximately 6,500 R sub J from the planet; the PRA events are also most intense during those times. A specific tail encounter occurring in mid-February 1981 is analyzed and shown to possess a remarkably symmetric magnetic field signature and to have a bipolar field structure in the central region. The bipolarity is characteristic of most of the eight events
Heat pipe dynamic behavior
The vapor flow in a heat pipe was mathematically modeled and the equations governing the transient behavior of the core were solved numerically. The modeled vapor flow is transient, axisymmetric (or two-dimensional) compressible viscous flow in a closed chamber. The two methods of solution are described. The more promising method failed (a mixed Galerkin finite difference method) whereas a more common finite difference method was successful. Preliminary results are presented showing that multi-dimensional flows need to be treated. A model of the liquid phase of a high temperature heat pipe was developed. The model is intended to be coupled to a vapor phase model for the complete solution of the heat pipe problem. The mathematical equations are formulated consistent with physical processes while allowing a computationally efficient solution. The model simulates time dependent characteristics of concern to the liquid phase including input phase change, output heat fluxes, liquid temperatures, container temperatures, liquid velocities, and liquid pressure. Preliminary results were obtained for two heat pipe startup cases. The heat pipe studied used lithium as the working fluid and an annular wick configuration. Recommendations for implementation based on the results obtained are presented. Experimental studies were initiated using a rectangular heat pipe. Both twin beam laser holography and laser Doppler anemometry were investigated. Preliminary experiments were completed and results are reported
25 kHz narrow spectral bandwidth of a wavelength tunable diode laser with a short waveguide-based external cavity
We report on the spectral properties of a diode laser with a tunable external
cavity in integrated optics. Even though the external cavity is short compared
to other small-bandwidth external cavity lasers, the spectral bandwidth of this
tunable laser is as small as 25 kHz (FWHM), at a side-mode suppression ratio
(SMSR) of 50 dB. Our laser is also able to access preset wavelengths in as
little as 200 us and able to tune over the full telecom C-band (1530 nm - 1565
nm).Comment: 8 pages, 7 figure
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