11,844 research outputs found
Thermalization of gluons in ultrarelativistic heavy ion collisions by including three-body interactions in a parton cascade
We develop a new 3+1 dimensional Monte Carlo cascade solving the kinetic
on-shell Boltzmann equations for partons including the inelastic gg ggg
pQCD processes. The back reaction channel is treated -- for the first time --
fully consistently within this scheme. An extended stochastic method is used to
solve the collision integral. The frame dependence and convergency are studied
for a fixed tube with thermal initial conditions. The detailed numerical
analysis shows that the stochastic method is fully covariant and that
convergency is achieved more efficiently than within a standard geometrical
formulation of the collision term, especially for high gluon interaction rates.
The cascade is then applied to simulate parton evolution and to investigate
thermalization of gluons for a central Au+Au collision at RHIC energy. For this
study the initial conditions are assumed to be generated by independent
minijets with p_T > p_0=2 GeV. With that choice it is demonstrated that overall
kinetic equilibration is driven mainly by the inelastic processes and is
achieved on a scale of 1 fm/c. The further evolution of the expanding gluonic
matter in the central region then shows almost an ideal hydrodynamical
behavior. In addition, full chemical equilibration of the gluons follows on a
longer timescale of about 3 fm/c.Comment: 121 pages with 55 figures, revised version. Two eps-figures and
comments are added. Formula (54) which has typo in journal version is given
correctl
Depletion isolation effect in Vertical MOSFETS during transition from partial to fully depleted operation
A simulation study is made of floating-body effects (FBEs) in vertical MOSFETs due to depletion isolation as the pillar thickness is reduced from 200 to 10 nm. For pillar thicknesses between 200â60 nm, the output characteristics with and without impact ionization are identical at a low drain bias and then diverge at a high drain bias. The critical drain bias Vdc for which the increased drainâcurrent is observed is found to decrease with a reduction in pillar thickness. This is explained by the onset of FBEs at progressively lower values of the drain bias due to the merging of the drain depletion regions at the bottom of the pillar (depletion isolation). For pillar thicknesses between 60â10 nm, the output characteristics show the opposite behavior, namely, the critical drain bias increases with a reduction in pillar thickness. This is explained by a reduction in the severity of the FBEs due to the drain debiasing effect caused by the elevated body potential. Both depletion isolation and gateâgate coupling contribute to the drainâcurrent for pillar thicknesses between 100â40 nm
Energy and entropy of relativistic diffusing particles
We discuss energy-momentum tensor and the second law of thermodynamics for a
system of relativistic diffusing particles. We calculate the energy and entropy
flow in this system. We obtain an exact time dependence of energy, entropy and
free energy of a beam of photons in a reservoir of a fixed temperature.Comment: 14 pages,some formulas correcte
The relation between cardiac 123I-mIBG scintigraphy and functional response 1 year after CRT implantation
Cardiac resynchronization therapy (CRT) is a disease-modifying therapy in patients with chronic heart failure (CHF). Current guidelines ascribe CRT eligibility on three parameters only: left ventricular ejection fraction (LVEF), QRS duration, and New York Heart Association (NYHA) functional class. However, one-third of CHF patients does not benefit from CRT. This study evaluated whether 123I-meta-iodobenzylguanidine (123I-mIBG) assessed cardiac sympathetic activity could optimize CRT patient selection
Orientation and symmetry control of inverse sphere magnetic nanoarrays by guided self-assembly
Inverse sphere shaped Ni arrays were fabricated by electrodeposition on Si through the guided self-assembly of polystyrene latex spheres in Si/SiO2 patterns. It is shown that the size commensurability of the etched tracks is critical for the long range ordering of the spheres. Moreover, noncommensurate guiding results in the reproducible periodic triangular distortion of the close packed self-assembly. Magnetoresistance measurements on the Ni arrays were performed showing room temperature anisotropic magnetoresistance of 0.85%. These results are promising for self-assembled patterned storage media and magnetoresistance devices
Moment evolution across the ferromagnetic phase transition of giant magnetocaloric (Mn,Fe)2(P,Si,B) compounds
A strong electronic reconstruction resulting in a quenching of the Fe
magnetic moments has recently been predicted to be at the origin of the giant
magnetocaloric effect displayed by Fe2Pbased materials. To verify this
scenario, X-ray Magnetic Circular Dichroism experiments have been carried out
at the L edges of Mn and Fe for two typical compositions of the
(Mn,Fe)2(P,Si,B) system. The dichroic absorption spectra of Mn and Fe have been
measured element specific in the vicinity of the first-order ferromagnetic
transition. The experimental spectra are compared with first-principle
calculations and charge-transfer multiplet simulations in order to derive the
magnetic moments. Even though signatures of a metamagnetic behaviour are
observed either as a function of the temperature or the magnetic field, the
similarity of the Mn and Fe moment evolution suggests that the quenching of the
Fe moment is weaker than previously predicted
Investigating the interstellar dust through the Fe K-edge
The chemical and physical properties of interstellar dust in the densest
regions of the Galaxy are still not well understood. X-rays provide a powerful
probe since they can penetrate gas and dust over a wide range of column
densities (up to ). The interaction (scattering and
absorption) with the medium imprints spectral signatures that reflect the
individual atoms which constitute the gas, molecule, or solid. In this work we
investigate the ability of high resolution X-ray spectroscopy to probe the
properties of cosmic grains containing iron. Although iron is heavily depleted
into interstellar dust, the nature of the Fe-bearing grains is still largely
uncertain. In our analysis we use iron K-edge synchrotron data of minerals
likely present in the ISM dust taken at the European Synchrotron Radiation
Facility. We explore the prospects of determining the chemical composition and
the size of astrophysical dust in the Galactic centre and in molecular clouds
with future X-ray missions. The energy resolution and the effective area of the
present X-ray telescopes are not sufficient to detect and study the Fe K-edge,
even for bright X-ray sources. From the analysis of the extinction cross
sections of our dust models implemented in the spectral fitting program SPEX,
the Fe K-edge is promising for investigating both the chemistry and the size
distribution of the interstellar dust. We find that the chemical composition
regulates the X-ray absorption fine structures in the post edge region, whereas
the scattering feature in the pre-edge is sensitive to the mean grain size.
Finally, we note that the Fe K-edge is insensitive to other dust properties,
such as the porosity and the geometry of the dust.Comment: 11 pages, 10 figures. Accepted for publication in Astronomy and
Astrophysic
Dust absorption and scattering in the silicon K-edge
The composition and properties of interstellar silicate dust are not well
understood. In X-rays, interstellar dust can be studied in detail by making use
of the fine structure features in the Si K-edge. The features in the Si K-edge
offer a range of possibilities to study silicon-bearing dust, such as
investigating the crystallinity, abundance, and the chemical composition along
a given line of sight. We present newly acquired laboratory measurements of the
silicon K-edge of several silicate-compounds that complement our measurements
from our earlier pilot study. The resulting dust extinction profiles serve as
templates for the interstellar extinction that we observe. The extinction
profiles were used to model the interstellar dust in the dense environments of
the Galaxy. The laboratory measurements, taken at the Soleil synchrotron
facility in Paris, were adapted for astrophysical data analysis and implemented
in the SPEX spectral fitting program. The models were used to fit the spectra
of nine low-mass X-ray binaries located in the Galactic center neighborhood in
order to determine the dust properties along those lines of sight. Most lines
of sight can be fit well by amorphous olivine. We also established upper limits
on the amount of crystalline material that the modeling allows. We obtained
values of the total silicon abundance, silicon dust abundance, and depletion
along each of the sightlines. We find a possible gradient of
dex/kpc for the total silicon abundance versus the Galactocentric distance. We
do not find a relation between the depletion and the extinction along the line
of sight.Comment: 18 pages, 16 figures. Accepted for publication in Astronomy and
Astrophysic
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