331 research outputs found
Collective modes of asymmetric nuclear matter in Quantum HadroDynamics
We discuss a fully relativistic Landau Fermi liquid theory based on the
Quantum Hadro-Dynamics () effective field picture of Nuclear Matter
({\it NM}).
From the linearized kinetic equations we get the dispersion relations of the
propagating collective modes. We focus our attention on the dynamical effects
of the interplay between scalar and vector channel contributions. A beautiful
``mirror'' structure in the form of the dynamical response in the
isoscalar/isovector degree of freedom is revealed, with a complete parallelism
in the role respectively played by the compressibility and the symmetry energy.
All that strongly supports the introduction of an explicit coupling to the
scalar-isovector channel of the nucleon-nucleon interaction. In particular we
study the influence of this coupling (to a -meson-like effective field)
on the collective response of asymmetric nuclear matter (). Interesting
contributions are found on the propagation of isovector-like modes at normal
density and on an expected smooth transition to isoscalar-like oscillations at
high baryon density. Important ``chemical'' effects on the neutron-proton
structure of the mode are shown. For dilute we have the isospin
distillation mechanism of the unstable isoscalar-like oscillations, while at
high baryon density we predict an almost pure neutron wave structure of the
propagating sounds.Comment: 18 pages (LATEX), 8 Postscript figures, uses "epsfig
Resonant interaction between gravitational waves, electromagnetic waves and plasma flows
In magnetized plasmas gravitational and electromagnetic waves may interact
coherently and exchange energy between themselves and with plasma flows. We
derive the wave interaction equations for these processes in the case of waves
propagating perpendicular or parallel to the plasma background magnetic field.
In the latter case, the electromagnetic waves are taken to be circularly
polarized waves of arbitrary amplitude. We allow for a background drift flow of
the plasma components which increases the number of possible evolution
scenarios. The interaction equations are solved analytically and the
characteristic time scales for conversion between gravitational and
electromagnetic waves are found. In particular, it is shown that in the
presence of a drift flow there are explosive instabilities resulting in the
generation of gravitational and electromagnetic waves. Conversely, we show that
energetic waves can interact to accelerate particles and thereby \emph{produce}
a drift flow. The relevance of these results for astrophysical and cosmological
plasmas is discussed.Comment: 12 pages, 1 figure, typos corrected and numerical example adde
Remediation of Hg-contaminated marine sediments by simultaneous application of enhancing agents and microwave heating (MWH)
The aim of this work was to investigate Hg removal ability of a novel microwave heating (MWH) treatment for marine sediment remediation enhanced by the application of several agents, biodegradable complexing agent (methylglycinediacetic acid, MGDA), surfactant (Tween® 80), and citric acid. Main results revealed that MWH allowed a very rapid heating (∼450 °C in 7 min) of the irradiated medium. However, without the addition of enhancing agents, a maximum Hg removal of ∼72% can be achieved. The application of MGDA led to a higher contaminant removal of ∼87% (residual concentration = 5.4 mg kg−1). For the treatment including the simultaneous addition of both chelating agent and surfactant, their synergetic action and stripping processes resulted in a very high Hg removal of ∼99% for an irradiation time of 7 min, corresponding to a residual concentration of 0.56 mg kg−1, which is lower than the Italian regulatory limit of 1 mg kg−1. The use of citric acid resulted in a shortening of the removal kinetics, which allowed the successful application of a shorter remediation time of 5 min. The observed strong passive ability of sediments to convert a microwave irradiation energy into a rapid and large temperature increase undoubtedly represents a key factor in the whole remediation process, making the studied treatment an excellent choice. Kinetic data are suitable for a preliminarily assessment of the effectiveness of clean-up activities, and as basis for future scaling-up studies on MWH of Hg-contaminated sediment
Asymmetric nuclear matter:the role of the isovector scalar channel
We try to single out some qualitative new effects of the coupling to the
-isovector-scalar meson introduced in a minimal way in a
phenomenological hadronic field theory. Results for the equation of state
() and the phase diagram of asymmetric nuclear matter () are
discussed. We stress the consistency of the -coupling introduction in a
relativistic approach. New contributions to the slope and curvature of the
symmetry energy and the neutron-proton effective mass splitting appear
particularly interesting. A more repulsive for neutron matter at high
baryon densities is expected. Effects on new critical properties of warm ,
mixing of mechanical and chemical instabilities and isospin distillation, are
also presented. The influence is mostly on the {\it isovectorlike}
collective response.
The results are largely analytical and this makes the physical meaning quite
transparent. Implications for nuclear structure properties of drip-line nuclei
and for reaction dynamics with Radioactive Beams are finally pointed out.Comment: 12 pages, 10 Postscript figure
Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy
We review HB stars in a broad astrophysical context, including both variable
and non-variable stars. A reassessment of the Oosterhoff dichotomy is
presented, which provides unprecedented detail regarding its origin and
systematics. We show that the Oosterhoff dichotomy and the distribution of
globular clusters (GCs) in the HB morphology-metallicity plane both exclude,
with high statistical significance, the possibility that the Galactic halo may
have formed from the accretion of dwarf galaxies resembling present-day Milky
Way satellites such as Fornax, Sagittarius, and the LMC. A rediscussion of the
second-parameter problem is presented. A technique is proposed to estimate the
HB types of extragalactic GCs on the basis of integrated far-UV photometry. The
relationship between the absolute V magnitude of the HB at the RR Lyrae level
and metallicity, as obtained on the basis of trigonometric parallax
measurements for the star RR Lyrae, is also revisited, giving a distance
modulus to the LMC of (m-M)_0 = 18.44+/-0.11. RR Lyrae period change rates are
studied. Finally, the conductive opacities used in evolutionary calculations of
low-mass stars are investigated. [ABRIDGED]Comment: 56 pages, 22 figures. Invited review, to appear in Astrophysics and
Space Scienc
Central-to-peripheral nuclear modification factors in Pb-Pb collisions at sqrt{s_NN} = 17.3 GeV
We present central-to-peripheral nuclear modification factors, R_CP, for the
p_T distributions of K^0_S, Lambda, Anti-Lambda, and negatively charged
particles, measured at central rapidity in Pb-Pb collisions at top SPS energy.
The data cover the 55% most central fraction of the inelastic cross section.
The K^0_S and Lambda R_CP(p_T) are similar in shape to those measured at
sqrt{s_NN} = 200 GeV at RHIC, though they are larger in absolute value. We have
compared our K^0_S R_CP data to a theoretical calculation. The prediction
overestimates the data at p_T \approx 3-4 GeV/c, unless sizeable parton energy
loss is included in the calculation.Comment: 13 pages, 5 figures, submitted to Physics Letters
All-sky search for long-duration gravitational wave transients with initial LIGO
We present the results of a search for long-duration gravitational wave transients in two sets of data collected by the LIGO Hanford and LIGO Livingston detectors between November 5, 2005 and September 30, 2007, and July 7, 2009 and October 20, 2010, with a total observational time of 283.0 days and 132.9 days, respectively. The search targets gravitational wave transients of duration 10-500 s in a frequency band of 40-1000 Hz, with minimal assumptions about the signal waveform, polarization, source direction, or time of occurrence. All candidate triggers were consistent with the expected background; as a result we set 90% confidence upper limits on the rate of long-duration gravitational wave transients for different types of gravitational wave signals. For signals from black hole accretion disk instabilities, we set upper limits on the source rate density between 3.4×10-5 and 9.4×10-4 Mpc-3 yr-1 at 90% confidence. These are the first results from an all-sky search for unmodeled long-duration transient gravitational waves. © 2016 American Physical Society
All-sky search for long-duration gravitational wave transients with initial LIGO
We present the results of a search for long-duration gravitational wave transients in two sets of data collected by the LIGO Hanford and LIGO Livingston detectors between November 5, 2005 and September 30, 2007, and July 7, 2009 and October 20, 2010, with a total observational time of 283.0 days and 132.9 days, respectively. The search targets gravitational wave transients of duration 10-500 s in a frequency band of 40-1000 Hz, with minimal assumptions about the signal waveform, polarization, source direction, or time of occurrence. All candidate triggers were consistent with the expected background; as a result we set 90% confidence upper limits on the rate of long-duration gravitational wave transients for different types of gravitational wave signals. For signals from black hole accretion disk instabilities, we set upper limits on the source rate density between 3.4×10-5 and 9.4×10-4 Mpc-3 yr-1 at 90% confidence. These are the first results from an all-sky search for unmodeled long-duration transient gravitational waves. © 2016 American Physical Society
Search for gravitational waves from Scorpius X-1 in the second Advanced LIGO observing run with an improved hidden Markov model
We present results from a semicoherent search for continuous gravitational waves from the low-mass x-ray binary Scorpius X-1, using a hidden Markov model (HMM) to track spin wandering. This search improves on previous HMM-based searches of LIGO data by using an improved frequency domain matched filter, the J-statistic, and by analyzing data from Advanced LIGO's second observing run. In the frequency range searched, from 60 to 650 Hz, we find no evidence of gravitational radiation. At 194.6 Hz, the most sensitive search frequency, we report an upper limit on gravitational wave strain (at 95% confidence) of h095%=3.47×10-25 when marginalizing over source inclination angle. This is the most sensitive search for Scorpius X-1, to date, that is specifically designed to be robust in the presence of spin wandering. © 2019 American Physical Society
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