1,492 research outputs found
Experimental Study on a Laboratory Test Bench for Sea Wave Generation Systems
Abstract The paper presents a laboratory test bench specifically designed for sea wave generation systems. In particular a DC Micro Grid is realized to experimentally validate the energy performance of a PM Brushless ball screw actuator, during motor-regenerative operative conditions, which is representative of an oscillating body wave generation system. The proposed architecture is based on a DC bus, which features the integration of renewable energy sources and buffered storage systems, with the aim of smoothing the natural power fluctuations of wave energy generation systems. The wave generation is simulated in laboratory by controlling an electric motor, which is directly coupled with the PM brushless generator. The experimental validation phase is mainly devoted to verify the design criteria of the architecture scheme and the control strategies of the power fluxes related to power converters
The giant, horizontal and asymptotic branches of galactic globular clusters. I. The catalog, photometric observables and features
A catalog including a set of the most recent Color Magnitude Diagrams (CMDs)
is presented for a sample of 61 Galactic Globular Clusters (GGCs). We used this
data-base to perform an homogeneous systematic analysis of the evolved
sequences (namely, Red Giant Branch (RGB), Horizontal Branch (HB) and
Asymptotic Giant Branch (AGB)). Based on this analysis, we present: (1) a new
procedure to measure the level of the ZAHB (V_ZAHB) and an homogeneous set of
distance moduli obtained adopting the HB as standard candle; (2) an independent
estimate for RGB metallicity indicators and new calibrations of these
parameters in terms of both spectroscopic ([Fe/H]_CG97) and global metallicity
([M/H], including also the alpha-elements enhancement). The set of equations
presented can be used to simultaneously derive a photometric estimate of the
metal abundance and the reddening from the morphology and the location of the
RGB in the (V,B-V)-CMD. (3) the location of the RGB-Bump (in 47 GGCs) and the
AGB-Bump (in 9 GGCs). The dependence of these features on the metallicity is
discussed. We find that by using the latest theoretical models and the new
metallicity scales the earlier discrepancy between theory and observations
(~0.4 mag) completely disappears.Comment: 51 pages, 23 figures, AAS Latex, macro rtrpp4.sty included, accepted
by A
BRST operator quantization of generally covariant gauge systems
The BRST generator is realized as a Hermitian nilpotent operator for a
finite-dimensional gauge system featuring a quadratic super-Hamiltonian and
linear supermomentum constraints. As a result, the emerging ordering for the
Hamiltonian constraint is not trivial, because the potential must enter the
kinetic term in order to obtain a quantization invariant under scaling. Namely,
BRST quantization does not lead to the curvature term used in the literature as
a means to get that invariance. The inclusion of the potential in the kinetic
term, far from being unnatural, is beautifully justified in light of the
Jacobi's principle.Comment: 16 pages (LaTeX manuscript). Revised version (minor changes) to
appear in Physical Review
Calorimetry of photon gases in nonlinear multimode optical fibers
Because of their massless nature, photons do not interact in linear optical
media. However, light beam propagation in nonlinear media permits to break this
paradigm, and makes it possible to observe photon-photon interactions. Based on
this principle, a beam of light propagating in a nonlinear multimode optical
system can be described as a gas of interacting particles. As a consequence,
the spatio-temporal evolution of this photon gas is expressed in terms of
macroscopic thermodynamic variables, e.g., temperature and chemical potential.
Moreover, the gas evolution is subject to experiencing typical thermodynamic
phenomena, such as thermalization. The meaning of thermodynamic variables
associated with the photon gas must not be confused with their classical
counterparts, e.g., the gas temperature cannot be measured by means of standard
thermometers. Although the thermodynamic parameters of a multimode photon gas
result from a rigorous mathematical derivation, their physical meaning is still
unclear. In this work, we report on optical calorimetric measurements, which
exploit nonlinear beam propagation in multimode optical fibers. Our results
show that, indeed, heat only flows from a hot to a cold photon gas subsystem.
This provides an unequivocal demonstration that nonlinear multimode wave
propagation phenomena are governed by the second law of thermodynamics. In
addition to be fundamental, our findings provide a new approach to
light-by-light activated management of laser beams
Blue Straggler Stars in Globular Clusters: a powerful tool to probe the internal dynamical evolution of stellar systems
This chapter presents an overview of the main observational results obtained
to date about Blue Straggler Stars (BSSs) in Galactic Globular Clusters (GCs).
The BSS specific frequency, radial distribution, chemical composition and
rotational properties are presented and discussed in the framework of using
this stellar population as probe of GC internal dynamics. In particular, the
shape of the BSS radial distribution has been found to be a powerful tracer of
the dynamical age of stellar systems, thus allowing the definition of the first
empirical "dynamical clock".Comment: Chapter 5, in Ecology of Blue Straggler Stars, H.M.J. Boffin, G.
Carraro & G. Beccari (Eds), Astrophysics and Space Science Library, Springe
Quantum state storage and processing for polarization qubits in an inhomogeneously broadened \Lambda-type three-level medium
We address the propagation of a single photon pulse with two polarization
components, i.e., a polarization qubit, in an inhomogeneously broadened
"phaseonium" \Lambda-type three-level medium. We combine some of the
non-trivial propagation effects characteristic for this kind of coherently
prepared systems and the controlled reversible inhomogeneous broadening
technique to propose several quantum information processing applications, such
as a protocol for polarization qubit filtering and sieving as well as a tunable
polarization beam splitter. Moreover, we show that, by imposing a spatial
variation of the atomic coherence phase, an effcient quantum memory for the
incident polarization qubit can be also implemented in \Lambda-type three-level
systems.Comment: 9 pages, 4 figure
Global phase time and path integral for the Kantowski--Sachs anisotropic univers
The action functional of the anisotropic Kantowski--Sachs cosmological model
is turned into that of an ordinary gauge system. Then a global phase time is
identified for the model by imposing canonical gauge conditions, and the
quantum transition amplitude is obtained by means of the usual path integral
procedure of Fadeev and Popov.Comment: 11 page
A 2.15 Hour Orbital Period for the Low Mass X-Ray Binary XB 1832-330 in the Globular Cluster NGC 6652
We present a candidate orbital period for the low mass X-ray binary XB
1832-330 in the globular cluster NGC 6652 using a 6.5 hour Gemini South
observation of the optical counterpart of the system. Light curves in g' and r'
for two LMXBs in the cluster, sources A and B in previous literature, were
extracted and analyzed for periodicity using the ISIS image subtraction
package. A clear sinusoidal modulation is evident in both of A's curves, of
amplitude ~0.11 magnitudes in g' and ~0.065 magnitudes in r', while B's curves
exhibit rapid flickering, of amplitude ~1 magnitude in g' and ~0.5 magnitudes
in r'. A Lomb-Scargle test revealed a 2.15 hour periodic variation in the
magnitude of A with a false alarm probability less than 10^-11, and no
significant periodicity in the light curve for B. Though it is possible
saturated stars in the vicinity of our sources partially contaminated our
signal, the identification of A's binary period is nonetheless robust.Comment: 7 pages, 7 figures, ApJ in pres
Blue Stragglers in Galactic Open Clusters and the Integrated Spectral Energy Distributions
Synthetic integrated spectral properties of the old Galactic open clusters
are studies in this work, where twenty-seven Galactic open clusters of ages >=
1Gyr are selected as the working sample. Based on the photometric observations
of these open clusters, synthetic integrated spectrum has been made for the
stellar population of each cluster. The effects of blue straggler stars (BSSs)
on the conventional simple stellar population (SSP) model are analyzed on an
individual cluster base. It is shown that the BSSs, whose holding positions in
the color-magnitude diagrams (CMDs) cannot be predicted by the current
single-star evolution theory, present significant modifications to the
integrated properties of theoretical SSP model. The synthesized integrated
spectral energy distributions (ISEDs) of our sample clusters are dramatically
different from the SSPs based on isochrone only. The BSSs corrected ISEDs of
stellar populations show systematic enhancements towards shorter wavelength in
the spectra. When measured with wide-band colors in unresolvable conditions,
the age of a stellar population can be seriously under-estimated by the
conventional SSP model. Therefore, considering the common existence of BSS
component in real stellar populations, a considerable amount of alternations on
the conventional ISEDs should be expected when applying the technique of
evolutionary population synthesis (EPS) to more complicated stellar systems.Comment: 45 pages, 21 figures Accepted for publication in ApJ (Feburary 1,
2005 issue
Mode decomposition method for investigating the nonlinear dynamics of a multimode beam
We overview our recent experimental studies on the nonlinear spatial reshaping of multimode
beams at the output of multimode optical fibers. We use a holographic mode decomposition
technique, which permits to reveal the variation of the spatial mode composition at the fiber
output, as determined by either conservative (the Kerr effect) or dissipative (Raman scattering)
nonlinear processes. For the first case, we consider the effect of spatial beam self-cleaning, and
we compare experimental mode decompositions with predictions based on the thermodynamic
theory, including the case of beams carrying nozero orbital angular momentum. For the second
case, we analyze the beam mode content at the output of a Raman laser based on a graded
index multimode fiber
- …