138 research outputs found
Low frequency structural dynamics of warm dense matter
Measurements of the microscopic response of warm dense matter have been demonstrated by multi-keV inelastic x-ray scattering using laser-based sources. These techniques have been used to study the high frequency electron correlations (plasmons) in low to mid-Z plasmas. The advent of fourth generation light sources will provide high fluxes of narrowband and coherent x rays that will allow to look at the low frequency correlations (the ion-acoustic waves). In this paper we present an analysis of such low frequency modes by calculating the frequency dependent ion-ion structure factor. Our model includes all the relevant multibody contributions arising from strong coupling and nonideal plasma effects. In particular, the ion-ion structure factor is obtained within the memory function formalism by satisfying a finite number of sum rules. This work could be used as a basis to a direct experimental test of dense plasma model as soon as keV free electron laser sources will become available
The Thomson scattering cross section in a magnetized, high density plasma
We calculate the Thomson scattering cross section in a non-relativistic,
magnetized, high density plasma -- in a regime where collective excitations can
be described by magnetohydrodynamics. We show that, in addition to cyclotron
resonances and an elastic peak, the cross section exhibits two pairs of peaks
associated with slow and fast magnetosonic waves; by contrast, the cross
section arising in pure hydrodynamics possesses just a single pair of Brillouin
peaks. Both the position and the width of these magnetosonic-wave peaks depend
on the ambient magnetic field and temperature, as well as transport and
thermodynamic coefficients, and so can therefore serve as a diagnostic tool for
plasma properties that are otherwise challenging to measure.Comment: Main paper: pp 1-8. Appendix: pp 8-10. 2 figure
Scaling of Magneto-Quantum-Radiative Hydrodynamic Equations: From Laser-produced Plasmas to Astrophysics
We introduce here the equations of magneto-quantum-radiative hydrodynamics.
By rewriting them in a dimensionless form, we obtain a set of parameters that
describe scale-dependent ratios of all the characteristic hydrodynamic
quantities. We discuss how these dimensionless parameters relate to the scaling
between astrophysical observations and laboratory experiments.Comment: 12 page
Axion driven cosmic magneto-genesis during the QCD crossover
We propose a mechanism for the generation of a magnetic field in the early
universe during the QCD crossover assuming that dark matter is made of axions.
Thermoelectric fields arise at pressure gradients in the primordial plasma due
to the difference in charge, energy density and equation of state between the
quark and lepton components. The axion field is coupled to the EM field, so
when its spatial gradient is misaligned with the thermoelectric field, an
electric current is driven. Due to the finite resistivity of the plasma an
electric field appears that is generally rotational. For a QCD axion mass
consistent with observational constraints and a conventional efficiency for
turbulent dynamo amplification --- driven by the same pressure gradients
responsible for the thermoelectric fields --- a magnetic field is generated on
subhorizon scales. After significant Alfv\'enic unwinding it reaches a present
day strength of G on a characteristic scale 20
pc. The resulting combination of is significantly stronger than in
any astrophysical scenario, providing a clear test for the cosmological origin
of the field through -ray observations of distant blazars. The
amplitude of the pressure gradients may be inferred from the detection of
concomitant gravitational waves, while several experiments are underway to
confirm or rule out the existence of axions.Comment: Published in PR
Quantum Effects on Dynamic Structure Factors in Dense Magnetized Plasmas
We extend the classical magnetohydrodynamics formalism to include nonlocal
quantum behavior via the phenomenological Bohm potential. We then solve the
quantum magnetohydrodynamics equations to obtain a new analytical form of the
dynamic structure factor (DSF), a fundamental quantity linking theory and
experiments. Our results show that the three-peak structure -- one central
Rayleigh peak and two Brillouin peaks -- of the DSF arising from quantum
hydrodynamic fluctuations becomes (in general) a five-peak structure -- one
central Rayleigh peak and two pairs of peaks associated with fast and slow
magnetosonic waves. The Bohm contribution influences the positions and
characteristics (height, width, and intensity) of the peaks by introducing
three significant modifications: (a) an increase in effective thermal pressure,
(b) a reduction in the adiabatic index, and (c) an enhancement of effective
thermal diffusivity. The multiple DSF peaks enable concurrent measurements of
diverse plasma properties, transport coefficients, and thermodynamic parameters
in magnetized dense plasmas. The potential for experimental validation of our
theory looms large, particularly through future experiments conducted at
state-of-the-art laser facilities.Comment: 13 pages including 5 figures and 1 table; Comments are welcom
Fault Awareness in the MPI 4.0 Session Model
The latest version of MPI introduces new functionalities like the Session
model, but it still lacks fault management mechanisms. Past efforts produced
tools and MPI standard extensions to manage fault presence, including ULFM.
These measures are effective against faults but do not fully support the new
additions to the standard. In this paper, we combine the fault management
possibilities of ULFM with the new Session model functionality introduced in
version 4.0 of the standard. We focus on the communicator creation procedure,
highlighting criticalities and proposing a method to circumvent them. The
experimental campaign shows that the proposed solution does not significantly
affect applications' execution time and scalability while better managing the
insurgence of faults
«Principi optimo»: un aspetto della propaganda imperiale da Augusto a Traiano nelle fonti letterarie ed epigrafiche
Detection of high-frequency gravitational waves using high-energy pulsed lasers
We propose a new method for detecting high-frequency gravitational waves
(GWs) using high-energy pulsed lasers. Through the inverse Gertsenshtein
effect, the interaction between a GW and the laser beam results in the creation
of an electromagnetic signal. The latter can be detected using single-photon
counting techniques. We compute the minimal strain of a detectable GW which
only depends on the laser parameters. We find that a resonance occurs in this
process when the frequency of the GW is twice the frequency of the laser. With
this method, the frequency range Hz is explored
non-continuously for strains for current laser systems and
can be extended to with future generation facilities.Comment: 15 pages, 2 figures, v2 matches the published versio
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