44,430 research outputs found
Algorithm for Liapunov stability analysis
Development of algorithm provides automatic computation of quadratic estimate of domain of stability for stable equilibrium states of nonlinear systems of ordinary differential equations
Parametric Evolution for a Deformed Cavity
We consider a classically chaotic system that is described by a Hamiltonian
H(Q,P;x), where (Q,P) describes a particle moving inside a cavity, and x
controls a deformation of the boundary. The quantum-eigenstates of the system
are |n(x)>. We describe how the parametric kernel P(n|m) = , also
known as the local density of states, evolves as a function of x-x0. We
illuminate the non-unitary nature of this parametric evolution, the emergence
of non-perturbative features, the final non-universal saturation, and the
limitations of random-wave considerations. The parametric evolution is
demonstrated numerically for two distinct representative deformation processes.Comment: 13 pages, 8 figures, improved introduction, to be published in Phys.
Rev.
Diffractive energy spreading and its semiclassical limit
We consider driven systems where the driving induces jumps in energy space:
(1) particles pulsed by a step potential; (2) particles in a box with a moving
wall; (3) particles in a ring driven by an electro-motive-force. In all these
cases the route towards quantum-classical correspondence is highly non-trivial.
Some insight is gained by observing that the dynamics in energy space, where
is the level index, is essentially the same as that of Bloch electrons in a
tight binding model, where is the site index. The mean level spacing is
like a constant electric field and the driving induces long range hopping
1/(n-m).Comment: 19 pages, 11 figs, published version with some improved figure
Lick Slit Spectra of Thirty-Eight Objective Prism QSO Candidates and Low Metallicity Halo Stars
We present Lick Observatory slit spectra of 38 objects which were claimed to
have pronounced ultraviolet excess and emission lines by Zhan \& Chen. Most of
our spectra have FWHM spectral resolutions of about 4~\AA , and relatively high
S/N of about 10 -- 50, although some have FWHM ~\AA ~or lower S/N.
We find eleven QSOs, four galaxies at , twenty-two stars and one
unidentified object with a low S/N spectrum. Six of the QSOs show absorption
systems, including Q0000+027A with a relatively strong associated C~IV
absorption system, and Q0008+008 (V) with a damped Ly
system with an H~I column density of cm. The stars include a
wide variety of spectral types. There is one new DA4 white dwarf at 170~pc, one
sdB at 14~kpc, and three M stars. The rest are of types F, G and K. We have
measured the equivalent widths of the Ca~II~K line, the G-band and the Balmer
lines in ten stars with the best spectra, and we derive metallicities. Seven of
them are in the range ~[Fe/H]~, while the others are less
metal poor. If the stars are dwarfs, then they are at distances of 1 to 7~kpc,
but if they are giants, typical distances will be about 10~kpc.Comment: (Plain Tex, 21 pages, including tables. Send email to
'travell_oir%[email protected]' for 12 pages of figures) To appear in the
%%Astronomical Journal, August, 199
Doubly heavy hadrons and the domain of validity of doubly heavy diquark--anti-quark symmetry
In the limit of heavy quark masses going to infinity, a symmetry is known to
emerge in QCD relating properties of hadrons with two heavy quarks to analogous
states with one heavy anti-quark. A key question is whether the charm mass is
heavy enough so that this symmetry is manifest in at least an approximate
manner. The issue is crucial in attempting to understand the recent reports by
the SELEX Collaboration of doubly charmed baryons. We argue on very general
grounds that the charm quark mass is substantially too light for the symmetry
to emerge automatically via colour coulombic interactions. However, the
symmetry could emerge approximately depending on the dynamical details.Comment: 9 page
The signature of a double quantum-dot structure in the I-V characteristics of a complex system
We demonstrate that by carefully analyzing the temperature dependent
characteristics of the I-V measurements for a given complex system it is
possible to determine whether it is composed of a single, double or multiple
quantum-dot structure. Our approach is based on the orthodox theory for a
double-dot case and is capable of simulating I-V characteristics of systems
with any resistance and capacitance values and for temperatures corresponding
to thermal energies larger than the dot level spacing. We compare I-V
characteristics of single-dot and double-dot systems and show that for a given
measured I-V curve considering the possibility of a second dot is equivalent to
decreasing the fit temperature. Thus, our method allows one to gain information
about the structure of an experimental system based on an I-V measurement.Comment: 12 pages 7 figure
Spectroscopic measurements of temperature and plasma impurity concentration during magnetic reconnection at the Swarthmore Spheromak Experiment
Electron temperature measurements during counterhelicity spheromak merging studies at the Swarthmore Spheromak Experiment (SSX) [M. R. Brown, Phys. Plasmas 6, 1717 (1999)] are presented. VUV monochromator measurements of impurity emission lines are compared with model spectra produced by the non-LTE excitation kinematics code PRISMSPECT [J. J. MacFarlane et al., in Proceedings of the Third Conference on Inertial Fusion Science and Applications (2004)] to yield the electron temperature in the plasma with 1 µs time resolution. Average T_e is seen to increase from 12 to 19 eV during spheromak merging. Average C III ion temperature, measured with a new ion Doppler spectrometer (IDS) [C. D. Cothran et al., Rev. Sci. Instrum. 77, 063504 (2006)], likewise rises during spheromak merging, peaking at ~22 eV, but a similar increase in T_i is seen during single spheromak discharges with no merging. The VUV emission line measurements are also used to constrain the concentrations of various impurities in the SSX plasma, which are dominated by carbon, but include some oxygen and nitrogen. A burst of soft x-ray emission is seen during reconnection with a new four-channel detector (SXR). There is evidence for spectral changes in the soft x-ray emission as reconnection progresses, although our single-temperature equilibrium spectral models are not able to provide adequate fits to all the SXR data
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