3,123 research outputs found
Letter from Geraldine Ferraro to an Aspiring Journalist in Italy
Letter from Geraldine Ferraro to an aspiring journalist in Italy.https://ir.lawnet.fordham.edu/vice_presidential_campaign_correspondence_1984_international/1338/thumbnail.jp
The optical companion to the binary millisecond pulsar J1824-2452H in the globular cluster M28
We report on the optical identification of the companion star to the
eclipsing millisecond pulsar PSR J1824-2452H in the galactic globular cluster
M28 (NGC 6626). This star is at only 0.2" from the nominal position of the
pulsar and it shows optical variability (~ 0.25 mag) that nicely correlates
with the pulsar orbital period. It is located on the blue side of the cluster
main sequence, ~1.5 mag fainter than the turn-off point. The observed light
curve shows two distinct and asymmetric minima, suggesting that the companion
star is suffering tidal distortion from the pulsar. This discovery increases
the number of non-degenerate MSP companions optically identified so far in
globular clusters (4 out of 7), suggesting that these systems could be a common
outcome of the pulsar recycling process, at least in dense environments where
they can be originated by exchange interactions.Comment: accepted for publication on ApJ, 17 pages, 5 figure
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
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
Magnetic flux pumping in 3D nonlinear magnetohydrodynamic simulations
A self-regulating magnetic flux pumping mechanism in tokamaks that maintains
the core safety factor at , thus preventing sawteeth, is analyzed
in nonlinear 3D magnetohydrodynamic simulations using the M3D-C code. In
these simulations, the most important mechanism responsible for the flux
pumping is that a saturated quasi-interchange instability generates
an effective negative loop voltage in the plasma center via a dynamo effect. It
is shown that sawtoothing is prevented in the simulations if is
sufficiently high to provide the necessary drive for the
instability that generates the dynamo loop voltage. The necessary amount of
dynamo loop voltage is determined by the tendency of the current density
profile to centrally peak which, in our simulations, is controlled by the
peakedness of the applied heat source profile.Comment: submitted to Physics of Plasmas (23 pages, 15 Figures
Elementary analysis of the special relativistic combination of velocities, Wigner rotation, and Thomas precession
The purpose of this paper is to provide an elementary introduction to the
qualitative and quantitative results of velocity combination in special
relativity, including the Wigner rotation and Thomas precession. We utilize
only the most familiar tools of special relativity, in arguments presented at
three differing levels: (1) utterly elementary, which will suit a first course
in relativity; (2) intermediate, to suit a second course; and (3) advanced, to
suit higher level students. We then give a summary of useful results, and
suggest further reading in this often obscure field.Comment: V1: 25 pages, 6 figures; V2: 22 pages, 5 figures. The revised version
is shortened and the arguments streamlined. Minor changes in notation and
figures. This version matches the published versio
Optimal unambiguous comparison of two unknown squeezed vacua
We propose a scheme for unambiguous state comparison (USC) of two unknown
squeezed vacuum states of an electromagnetic field. Our setup is based on
linear optical elements and photon-number detectors, and achieves optimal USC
in an ideal case of unit quantum efficiency. In realistic conditions, i.e., for
non-unit quantum efficiency of photodetectors, we evaluate the probability of
getting an ambiguous result as well as the reliability of the scheme, thus
showing its robustness in comparison to previous proposals.Comment: 7 pages, 4 figures (revised version
Radio Timing and Optical Photometry of the Black Widow System PSR J1953+1846A in the Globular Cluster M71
We report on the determination of the astrometric, spin and orbital
parameters for PSR J1953+1846A, a "black widow" binary millisecond pulsar in
the globular cluster M71. By using the accurate position and orbital parameters
obtained from radio timing, we identified the optical companion in ACS/Hubble
Space Telescope images. It turns out to be a faint (m_F606W>=24, m_F814W>=23)
and variable star located at only ~0.06" from the pulsar timing position. The
light curve shows a maximum at the pulsar inferior conjunction and a minimum at
the pulsar superior conjunction, thus confirming the association with the
system. The shape of the optical modulation suggests that the companion star is
heated, likely by the pulsar wind. The comparison with the X-ray light curve
possibly suggests the presence of an intra-binary shock due to the interaction
between the pulsar wind and the material released by the companion. This is the
second identification (after COM-M5C) of an optical companion to a black widow
pulsar in a globular cluster. Interestingly, the two companions show a similar
light curve and share the same position in the color magnitude diagram.Comment: Accepted for publication by ApJ; 33 Pages, 10 Figures, 3 Table
Local temperature in quantum thermal states
We consider blocks of quantum spins in a chain at thermal equilibrium,
focusing on their properties from a thermodynamical perspective. Whereas in
classical systems the temperature behaves as an intensive magnitude, a
deviation from this behavior is expected in quantum systems. In particular, we
see that under some conditions the description of the blocks as thermal states
with the same global temperature as the whole chain fails. We analyze this
issue by employing the quantum fidelity as a figure of merit, singling out in
detail the departure from the classical behavior. The influence in this sense
of zero-temperature quantum phase transitions can be clearly observed within
this approach. Then we show that the blocks can be considered indeed as thermal
states with a high fidelity, provided an effective local temperature is
properly identified. Such a result originates from typical properties of
reduced sub-systems of energy-constrained Hilbert spaces. Finally, the relation
between local and global temperature is analyzed as a function of the size of
the blocks and the system parameters.Comment: 10 pages, 10 figures. New fidelity measure with similar result
A new explanation of the sawtooth phenomena in tokamaks
The ubiquitous sawtooth phenomena in tokamaks are so named because the central temperature rises slowly and falls rapidly, similar to the blades of a saw. First discovered in 1974, it has so far eluded a theoretical explanation that is widely accepted and consistent with experimental observations. We propose here a new theory for the sawtooth phenomena in auxiliary heated tokamaks, which is motivated by our recent understanding of "magnetic flux pumping." In this theory, the role of the (m, n) = (1, 1) mode is to generate a dynamo voltage, which keeps the central safety factor, q(0), just above 1.0 with low central magnetic shear. When central heating is present, the temperature on axis will increase until at some point, and the configuration abruptly becomes unstable to ideal MHD interchange modes with equal poloidal and toroidal mode numbers, m = n > 1. It is these higher order modes and the localized magnetic stochasticity they produce that cause the sudden crash of the temperature profile, not magnetic reconnection. Long time 3D MHD simulations demonstrate these phenomena, which appear to be consistent with many experimental observations.</p
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