3,878 research outputs found
Classical to quantum correspondence in dissipative directed transport
We compare the quantum and classical properties of the (Quantum) Isoperiodic
Stable Structures -- (Q)ISSs -- which organize the parameter space of a
paradigmatic dissipative ratchet model, i.e. the dissipative modified kicked
rotator. We study the spectral behavior of the corresponding classical
Perron-Frobenius operators with thermal noise and the quantum superoperators
without it for small values. We find a remarkable similarity
between the classical and quantum spectra. This finding significantly extends
previous results -- obtained for the mean currents and asymptotic distributions
only -- and on the other hand unveils a classical to quantum correspondence
mechanism where the classical noise is qualitatively different from the quantum
one. This is crucial not only for simple attractors but also for chaotic ones,
where just analyzing the asymptotic distribution reveals insufficient.
Moreover, we provide with a detailed characterization of relevant eigenvectors
by means of the corresponding Weyl-Wigner distributions, in order to better
identify similarities and differences. Finally, this model being generic, it
allows us to conjecture that this classical to quantum correspondence mechanism
is a universal feature of dissipative systems.Comment: 7 pages, 6 figure
Blessing of Roesch Library Renovation: President\u27s Remarks
President Eric F. Spina\u27s remarks in celebration of the completion of Roesch Refresh, the 2018-19 renovation of the first and second floors of Roesch Library
Turbulence measurements in hypersonic boundary layers using constant-temperature anemometry and Reynolds stress measurements in hypersonic boundary layers
The primary objective in the two research investigations performed under NASA Langley sponsorship (Turbulence measurements in hypersonic boundary layers using constant temperature anemometry and Reynolds stress measurements in hypersonic boundary layers) has been to increase the understanding of the physics of hypersonic turbulent boundary layers. The study began with an extension of constant-temperature thermal anemometry techniques to a Mach 11 helium flow, including careful examinations of hot-wire construction techniques, system response, and system calibration. This was followed by the application of these techniques to the exploration of a Mach 11 helium turbulent boundary layer (To approximately 290 K). The data that was acquired over the course of more than two years consists of instantaneous streamwise mass flux measurements at a frequency response of about 500 kHz. The data are of exceptional quality in both the time and frequency domain and possess a high degree of repeatability. The data analysis that has been performed to date has added significantly to the body of knowledge on hypersonic turbulence, and the data reduction is continuing. An attempt was then made to extend these thermal anemometry techniques to higher enthalpy flows, starting with a Mach 6 air flow with a stagnation temperature just above that needed to prevent liquefaction (To approximately 475 F). Conventional hot-wire anemometry proved to be inadequate for the selected high-temperature, high dynamic pressure flow, with frequent wire breakage and poor system frequency response. The use of hot-film anemometry has since been investigated for these higher-enthalpy, severe environment flows. The difficulty with using hot-film probes for dynamic (turbulence) measurements is associated with construction limitations and conduction of heat into the film substrate. Work continues under a NASA GSRP grant on the development of a hot film probe that overcomes these shortcomings for hypersonic flows. Each of the research tasks performed during the NASA Langley research grants is discussed separately below
IDF relationships for short duration rainfall
The intensity-duration-frequency (IDF) relationships bound rainfall intensity to duration and return period. These relationships are commonly used as an input in design of many hydraulic structures and drainage systems. Empirical IDF are estimated on the basis of recorded maximum annual precipitation of given durations, often ranging from 1 h to 24 h. For shorter durations, extrapolations are applied. In this paper, maximum annual precipitation for durations shorter than 1 h (namely, 30 min and 10 min) are evaluated using a rainfall disaggregation model and then used for the evaluation of the IDF relationship. A comparison of values obtained with the extrapolated values is then performed, and the results are discussed. Keywords: intensity-duration-frequency curves, rainfall disaggregation, entropy. © 2013 AIP Publishing LLC
The noise reduction potential of dual-stream coaxial rectangular improperly expanded jet flows
The research performed began during Spring 1991 as a project to assess the noise reduction potential of rectangular coaxial nozzle configurations for improperly expanded jets. The research plan consisted of: (1) design of coaxial rectangular nozzle configuration by Syracuse graduate research assistant; (2) construction of nozzles by NASA Langley machinists; and (3) acquisition of preliminary acoustic and optical data for a variety of inner and outer jet pressure ratios
An HST Imaging Survey of Low-Mass Stars in the Chamaeleon I Star Forming region
We present new HST/WFPC2 observations of 20 fields centered around T Tauri
stars in the Chamaeleon I star forming region. Images have been obtained in the
F631N ([OI]6300A), F656N (Ha) and F673N ([SII]6716A+6731A) narrow-band filters,
plus the Johnson V-band equivalent F547M filter. We detect 31 T Tauri stars
falling within our fields. We discuss the optical morphology of 10 sources
showing evidence of either binarity, circumstellar material, or mass loss. We
supplement our photometry with a compilation of optical, infrared and
sub-millimeter data from the literature, together with new sub-mm data for
three objects, to build the Spectral Energy Distributions (SED) of 19 single
sources. Using an SED model fitting tool, we self-consistently estimate a
number of stellar and disk parameters, while mass accretion rates are directly
derived from our Ha photometry. We find that bolometric luminosities derived
from dereddened optical data tend to be underestimated in systems with high
alpha(2-24} IR spectral index, suggesting that disks seen nearly edge-on may
occasionally be interpreted as low luminosity (and therefore more evolved)
sources. On the other hand, the same alpha(2-24) spectral index, a tracer of
the amount of dust in the warmer layers of the circumstellar disks, and the
mass accretion rate appear to decay with the isocronal stellar age, suggesting
that the observed age spread (~0.5-5 Myr) within the cluster is real. Our
sample contains a few outliers that may have dissipated their circumstellar
disks on shorter time-scale.Comment: to appear on Astronomical Journal, accepted April 16, 2012 (AJ-10740
Quantum Spectra of Triangular Billiards on the Sphere
We study the quantal energy spectrum of triangular billiards on a spherical
surface. Group theory yields analytical results for tiling billiards while the
generic case is treated numerically. We find that the statistical properties of
the spectra do not follow the standard random matrix results and their peculiar
behaviour can be related to the corresponding classical phase space structure.Comment: 18 pages, 5 eps figure
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