5,484 research outputs found
Quantization of a generally covariant gauge system with two super Hamiltonian constraints
The Becci-Rouet-Stora-Tyutin (BRST) operator quantization of a
finite-dimensional gauge system featuring two quadratic super Hamiltonian and m
linear supermomentum constraints is studied as a model for quantizing generally
covariant gauge theories. The proposed model ``completely'' mimics the
constraint algebra of General Relativity. The Dirac constraint operators are
identified by realizing the BRST generator of the system as a Hermitian
nilpotent operator, and a physical inner product is introduced to complete a
consistent quantization procedure.Comment: 17 pages. Latex file. Minor changes, two references adde
Environmental induced renormalization effects in quantum Hall edge states
We propose a general mechanism for renormalization of the tunneling exponents
in edge states of the fractional quantum Hall effect. Mutual effects of the
coupling with out-of-equilibrium 1/f noise and dissipation are considered both
for the Laughlin sequence and for composite co- and counter-propagating edge
states with Abelian or non-Abelian statistics. For states with
counter-propagating modes we demonstrate the robustness of the proposed
mechanism in the so called disorder-dominated phase. Prototypes of these
states, such as \nu=2/3 and \nu=5/2, are discussed in detail and the rich
phenomenology induced by the presence of a noisy environment is presented. The
proposed mechanism justifies the strong renormalizations reported in many
experimental observations carried out at low temperatures. We show how
environmental effects could affect the relevance of the tunneling excitations,
leading to important implications in particular for the \nu=5/2 case.Comment: 14 pages, 4 figure
Blue Straggler masses from pulsation properties. I. The case of NGC6541
We used high-spatial resolution images acquired with the WFC3 on board HST to
probe the population of variable blue straggler stars in the central region of
the poorly studied Galactic globular cluster NGC 6541. The time sampling of the
acquired multi wavelength (F390W, F555W and F814W) data allowed us to discover
three WUma stars and nine SX Phoenicis. Periods, mean magnitudes and pulsation
modes have been derived for the nine SX Phoenicis and their masses have been
estimated by using pulsation equations obtained from linear non adiabatic
models. We found masses in the range 1.0-1.1Mo, with an average value of
1.06+-0.09 Mo (sigma = 0.04), significantly in excess of the cluster Main
Sequence Turn Off mass (~ 0.75Mo). A mild trend between mass and luminosity
seems also to be present. The computed pulsation masses turn out to be in very
good agreement with the predictions of evolutionary tracks for single stars,
indicating values in the range ~ 1.0-1.2 Mo for most of the BSS population, in
agreement with what discussed in a number of previous studies.Comment: 8 pages, 9 figures, ApJ, accepte
Born-Infeld electrostatics in the complex plane
The complex method to obtain 2-dimensional Born-Infeld electrostatic
solutions is presented in a renewed form. The solutions are generated by a
holomorphic seed that makes contact with the Coulombian complex potential. The
procedure is exemplified by solving the Born-Infeld multipolar configurations.
Besides, it is shown that the attractive force between two equal but opposite
charges is lower than its Coulombian partner; it decreases up to vanish when
the charges approach each other below a distance ruled by the Born-Infeld
constant.Comment: 15 pages, 4 figure
Explicit finite element implementation of a shape memory alloy constitutive model and associated analyses
Shape memory alloys (SMA) represent an important class of smart metallic materials employed in various innovative applications thanks to their unique thermomechanical behavior. Since the 1980s, several SMA constitutive models have been proposed and implemented into both commercial and academic ïŹnite element analysis software tools. Such models have demonstrated their reliability and robustness in the design and optimization of a wide variety of SMA-based components. However, most models are implemented using implicit integration schemes, thus limiting their applicability in highly nonlinear analyses. The objective of this work is to present a novel explicit integration scheme for the numerical implementation of the three-dimensional Souza-Auricchio model, a phenomenological model able to reproduce the primary SMA responses (i.e., pseudoelasticity and shape memory eïŹect). The model constitutive equations are formulated by adopting the continuum thermodynamic theory with internal variables, following a plasticity-like approach. An elastic predictor-inelastic corrector scheme is here used to solve the time-discrete non-linear constitutive equations in the explicit framework. The proposed algorithm is investigated through several benchmark boundary-value problems of increasing complexity, considering both pseudoelastic and shape memory response in quasi-static conditions; a comparison with an implicit integration scheme is also performed. Such numerical tests demonstrate the ability of the algorithm to reproduce key material behaviors with eïŹectiveness and robustness. Particularly, the analysis of SMA cables demonstrates the eïŹectiveness of the explicit algorithm to solve complex problems involving widespread nonlinear contact, which prevent the convergence of the implicit scheme. Details such as mass-scaling options are also discussed
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
Horizontal-Branch Models and the Second-Parameter Effect. IV. The Case of M3 and Palomar 3
We present a detailed analysis of the "second-parameter pair" of globular
clusters M3 (NGC 5272) and Palomar 3. Our main results can be summarized as
follows: i) The horizontal-branch (HB) morphology of M3 is significantly bluer
in its inner regions (observed with the Hubble Space Telescope) than in the
cluster outskirts (observed from the ground), i.e., M3 has an internal second
parameter. Most plausibly the mass loss on the red giant branch (RGB) has been
more efficient in the inner than in the outer regions of the cluster. ii) The
dispersion in mass of the Pal 3 HB is found to be very small -- consistent with
zero -- and we argue that this is unlikely to be due to a statistical
fluctuation. It is this small mass dispersion that leads to the most apparent
difference in the HB morphologies of M3 and Pal 3. iii) The relative HB types
of M3 and Pal 3, as measured by mean colors or parameters involving the number
of blue, variable, and red HB stars, can easily be accounted for by a fairly
small difference in age between these clusters, of order 0.5-1 Gyr -- which is
in good agreement with the relative age measurement, based on the clusters'
turnoffs, by VandenBerg (2000).Comment: 20 pages, 12 figures, emulateapj5 style. The Astrophysical Journal,
in press. Figs. 1, 6, 9, 10 are in png format. The preprint (postscript
format) with full resolution (embedded) figures is available from
http://www.astro.virginia.edu/~mc6v
Reliable source of conditional non-Gaussian states from single-mode thermal fields
We address both theoretically and experimentally the generation of pulsed
non-Gaussian states from classical Gaussian ones by means of conditional
measurements. The setup relies on a beam splitter and a pair of linear
photodetectors able to resolve up to tens of photons in the two outputs. We
show the reliability of the setup and the good agreement with the theory for a
single-mode thermal field entering the beam splitter and present a thorough
characterization of the photon statistics of the conditional states.Comment: 18 pages, 12 figure
The binary fraction in the globular cluster M10 (NGC 6254): comparing core and outer regions
We study the binary fraction of the globular cluster M10 (NGC 6254) as a
function of radius from the cluster core to the outskirts, by means of a quan-
titative analysis of the color distribution of stars relative to the fiducial
main sequence. By taking advantage of two data-sets, acquired with the Advanced
Camera for Survey and the Wide Field Planetary Camera 2 on board the Hubble
Space Telescope, we have studied both the core and the external regions of the
cluster. The binary fraction is found to decrease from 14% within the core, to
1.5% in a region between 1 and 2 half-mass radii from the cluster centre. Such
a trend and the derived values are in agreement with previous results ob-
tained in clusters of comparable total magnitude. The estimated binary fraction
is sufficient to account for the suppression of mass segregation observed in
M10, without any need to invoke the presence of an intermediate-mass black hole
in its centre.Comment: Accepted for publication in ApJ (22 pages, 7 figures, 3 tables
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