4,208 research outputs found
Direct Characterization of Comets and Asteroids via Cosmic Dust Analysis from the Deep Space Gateway
The Deep Space Gateway (DSG) may provide a platform for direct sampling of a large number of comets and asteroids, through employment of an instrument for characterizing dust from these bodies. Every year, the Earth traverses through debris streams of dust and small particles from comets and asteroids in Earth-crossing orbits, generating short-lived outbursts of meteor activity commonly known as "meteor showers" (Figure 1). The material in each debris stream originates from a distinct parent body, many of which have been identified. By sampling this material, it is possible to quantitatively analyze the composition of a dozen or more comets and asteroids (See Figure 2, following page) without leaving cislunar space
RHIC Physics with the Parton Cascade Model
We present an analysis of the net-baryon number rapidity distribution and of
direct photon emission in the framework of the Parton Cascade Model.Comment: 4 pages 4 figures included, proceedings of QM 200
Direct Photons at RHIC
The PHENIX experiment has measured direct photons in
GeV Au+Au collisions and p+p collisions. The fraction of photons due to direct
production in Au+Au collisions is shown as a function of and centrality.
This measurement is compared with expectation from pQCD calculations. Other
possible sources of direct photons are discussed.Comment: 7 pages, 5 figures, presented at Hot Quarks 2004, Taos, N
High Energy Nuclear Collisions: Theory Overview
We review some basic concepts of Relativistic Heavy Ion Physics and discuss
our understanding of some key results from the experimental program at the
Relativistic Heavy Ion Collider (RHIC). We focus in particular on the early
time dynamics of nuclear collisions, some result from lattice QCD, hard probes
and photons.Comment: 11 pages, 3 figures; delivered at ISNP 2009, published in Praman
Recombination Models
We review the current status of recombination and coalescence models that
have been successfully applied to describe hadronization in heavy ion
collisions at RHIC energies. Basic concepts as well as actual implementations
of the idea are discussed. We try to evaluate where we stand in our
understanding at the moment and what remains to be done in the future.Comment: Plenary Talk at Quark Matter 2004, submitted to J. Phys. G, 8 pages,
3 figure
The XFEM with an Explicit-Implicit Crack Description for Hydraulic Fracture Problems
The Extended Finite Element Method (XFEM) approach is applied to the coupled problem of fluid flow, solid deformation, and fracture propagation. The XFEM model description of hydraulic fracture propagation is part of a joint project in which the developed numerical model will be verified against large-scale laboratory experiments. XFEM forms an important basis towards future combination with heat and mass transport simulators and extension to more complex fracture systems. The crack is described implicitly using three level-sets to evaluate enrichment functions. Additionally, an explicit crack representation is used to update the crack during propagation. The level-set functions are computed exactly from the explicit representation. This explicit/implicit representation is applied to a fluid-filled crack in an impermeable, elastic solid and compared to the early-time solution of a plane-strain hydraulic fracture problem with a fluid lag
Evolution of mechanism of parton energy loss with transverse momentum at RHIC and LHC in relativistic collision of heavy nuclei
We analyze the suppression of particle production at large transverse momenta
in ( most) central collisions of gold nuclei at
200 GeV and lead nuclei at 2.76 TeV. Full
next-to-leading order radiative corrections at , and
nuclear effects like shadowing and parton energy loss are included. The parton
energy loss is implemented in a simple multiple scattering model, where the
partons lose an energy per collision, where
is their mean free path. We take for a treatment
which is suggestive of the Bethe Heitler (BH) mechanism of incoherent
scatterings, for LPM mechanism, and
constant for a mechanism which suggests that the rate of energy loss ()
of the partons is proportional to total path length () of the parton in the
plasma, as the formation time of the radiated gluon becomes much larger than
.
We find that while the BH mechanism describes the nuclear modification factor
for 5 GeV/ (especially at RHIC energy), the LPM
and more so the constant mechanism provides a good description at
larger . This confirms the earlier expectation that the energy loss
mechanism for partons changes from BH to LPM for ,
where 1 fm and 1 GeV is the average
transverse kick-squared received by the parton per collision. The energy loss
per collision at the =2.76 TeV is found to be about
twice of that at 0.2 TeV.Comment: Discussion expanded, additional references added, 14 pages, 6
figures, To appear in Journal of Physics
Magnetic properties of (FeCo)B alloys and the effect of doping by 5 elements
We have explored, computationally and experimentally, the magnetic properties
of \fecob{} alloys. Calculations provide a good agreement with experiment in
terms of the saturation magnetization and the magnetocrystalline anisotropy
energy with some difficulty in describing CoB, for which it is found that
both full potential effects and electron correlations treated within dynamical
mean field theory are of importance for a correct description. The material
exhibits a uniaxial magnetic anisotropy for a range of cobalt concentrations
between and . A simple model for the temperature dependence of
magnetic anisotropy suggests that the complicated non-monotonous temperature
behaviour is mainly due to variations in the band structure as the exchange
splitting is reduced by temperature. Using density functional theory based
calculations we have explored the effect of substitutional doping the
transition metal sublattice by the whole range of 5 transition metals and
found that doping by Re or W elements should significantly enhance the
magnetocrystalline anisotropy energy. Experimentally, W doping did not succeed
in enhancing the magnetic anisotropy due to formation of other phases. On the
other hand, doping by Ir and Re was successful and resulted in magnetic
anisotropies that are in agreement with theoretical predictions. In particular,
doping by 2.5~at.\% of Re on the Fe/Co site shows a magnetocrystalline
anisotropy energy which is increased by 50\% compared to its parent
(FeCo)B compound, making this system interesting, for
example, in the context of permanent magnet replacement materials or in other
areas where a large magnetic anisotropy is of importance.Comment: 15 pages 17 figure
Hadronization in heavy ion collisions: recombination or fragmentation?
We show that hadron production in relativistic heavy ion collisions at
transverse momenta larger than 2 GeV/c can be explained by the competition of
two different hadronization mechanisms. Above 5 GeV/c hadron production can be
described by fragmentation of partons that are created perturbatively. Below 5
GeV/c recombination of partons from the dense and hot fireball dominates. This
can explain some of the surprising features of RHIC data like the constant
baryon-to-meson ratio of about one and the small nuclear suppression for
baryons between 2 to 4 GeV/c.Comment: Contribution to the 7th Conference on Strange Quark Matter (SQM
2003), submitted to J.Phys.G; 6 pages LaTeX, 4 eps figures, uses iopart.cl
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