10,960 research outputs found
A continuous population of variable stars up to about 1.5 mag above the horizontal branch?
Increasing samples of pulsating variable stars populating the classical
instability strip from the horizontal branch to a few magnitudes brighter are
being found in several Local Group galaxies, irrespective of the galaxy
morphological type. We will review the observational scenario focusing in
particular on the Anomalous Cepheids and related objects.Comment: 5 pages, 2 figures, invited review in JENAM 2003, "Minisymposium:
Asteroseismology and Stellar Evolution", Communications in Asteroseismology,
in pres
The Step-Harmonic Potential
We analyze the behavior of a quantum system described by a one-dimensional
asymmetric potential consisting of a step plus a harmonic barrier. We solve the
eigenvalue equation by the integral representation method, which allows us to
classify the independent solutions as equivalence classes of homotopic paths in
the complex plane. We then consider the propagation of a wave packet reflected
by the harmonic barrier and obtain an expression for the interaction time as a
function of the peak energy. For high energies we recover the classical
half-period limit.Comment: 19 pages, 7 figure
Kinetics of first-order phase transitions from microcanonical thermostatistics
More than a century has passed since van't Hoff and Arrhenius formulated
their celebrated rate theories, but there are still elusive aspects in the
temperature-dependent phase transition kinetics of molecular systems. Here I
present a theory based on microcanonical thermostatistics that establishes a
simple and direct temperature dependence for all rate constants, including the
forward and the reverse rate constants, the equilibrium constant, and the
nucleation rate. By considering a generic model that mimic the microcanonical
temperature of molecular systems in a region close to a first-order phase
transition, I obtain shape-free relations between kinetics and thermodynamics
physical quantities which are validated through stochastic simulations.
Additionally, the rate theory is applied to results obtained from protein
folding and ice nucleation experiments, demonstrating that the expressions
derived here can be used to describe the experimental data of a wide range of
molecular systems.Comment: 22 pages, 5 figure
Receiver-Based Auralization of Broadband Aircraft Flyover Noise Using the NASA Auralization Framework
The NASA Auralization Framework (NAF) consists of a set of dynamic link libraries (DLLs) to facilitate auralization of aircraft noise. Advanced capabilities for synthesis, propagation, and external interfaces are provided by the NAF Advanced Plugin Libraries (APL); a separate set of DLLs that are made accessible through the NAFs plugin architecture. In the typical time domain use case, the sound is first synthesized at the source location based on a source noise definition, and is then propagated in the time domain to a receiver on or near the ground. Alternatively, it may be desirable to synthesize the sound at the receiver, after it has been propagated in the frequency domain, e.g., when the source definition is inaccessible or when alternative propagation methods are needed. Receiver-based auralization requires three new developments in the NAF APL: a component plugin to interpolate the propagated noise spectra as a function of time for input to sound synthesis, and a path finder and path traversal plugin to calculate the effects of the differential propagation path length between the direct and ground reflected rays. This paper describes those developments and demonstrates their use in the auralization of broadband flyover noise
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