6,567 research outputs found
A transferable machine-learning framework linking interstice distribution and plastic heterogeneity in metallic glasses
When metallic glasses (MGs) are subjected to mechanical loads, the plastic
response of atoms is non-uniform. However, the extent and manner in which
atomic environment signatures present in the undeformed structure determine
this plastic heterogeneity remain elusive. Here, we demonstrate that novel site
environment features that characterize interstice distributions around atoms
combined with machine learning (ML) can reliably identify plastic sites in
several Cu-Zr compositions. Using only quenched structural information as
input, the ML-based plastic probability estimates ("quench-in softness" metric)
can identify plastic sites that could activate at high strains, losing
predictive power only upon the formation of shear bands. Moreover, we reveal
that a quench-in softness model trained on a single composition and quenching
rate substantially improves upon previous models in generalizing to different
compositions and completely different MG systems (Ni62Nb38, Al90Sm10 and
Fe80P20). Our work presents a general, data-centric framework that could
potentially be used to address the structural origin of any site-specific
property in MGs
The Maximum Lifetime of the Quark-Gluon Plasma
The width of the deconfinement transition region is shown to
influence strongly the flow structure in the (Landau-) hydrodynamical expansion
of a quark-gluon plasma. For a sharp first order transition () the
mixed phase is rather long-lived, with a lifetime that has a maximum when the
initial energy density is at the phase boundary between mixed and pure
quark-gluon matter. For increasing , however, the lifetime decreases
rapidly. Hadronic matter, however, remains long-lived as a consequence of the
rapid change in the degrees of freedom in the transition region and the
corresponding ``softening'' of the equation of state.Comment: 22 pages, latex, 12 uuencoded figure
Collective flow and QCD phase transition
In the first part I discuss the sensitivity of collective matter expansion in
ultrarelativistic heavy-ion collisions to the transition between quark and
hadronic matter (physics of the softest point of the Equation of State). A kink
in the centrality dependence of elliptic flow has been suggested as a signature
for the phase transition in hot QCD matter. Indeed, preliminary data of NA49
presented at this conference show first indications for the predicted kink. In
the second part I have a look at the present theories of heavy-ion reactions.
These remarks may also be seen as a critical comment to B. Mueller's summary
talk (nucl-th/9906029) presented at this conference.Comment: Write-up of QM '99 talk. Typo's correcte
Unraveling the temperature dependence of the yield strength in single-crystal tungsten using atomistically-informed crystal plasticity calculations
We use a physically-based crystal plasticity model to predict the yield
strength of body-centered cubic (bcc) tungsten single crystals subjected to
uniaxial loading. Our model captures the thermally-activated character of screw
dislocation motion and full non-Schmid effects, both of which are known to play
a critical role in bcc plasticity. The model uses atomistic calculations as the
sole source of constitutive information, with no parameter fitting of any kind
to experimental data. Our results are in excellent agreement with experimental
measurements of the yield stress as a function of temperature for a number of
loading orientations. The validated methodology is then employed to calculate
the temperature and strain-rate dependence of the yield strength for 231
crystallographic orientations within the standard stereographic triangle. We
extract the strain-rate sensitivity of W crystals at different temperatures,
and finish with the calculation of yield surfaces under biaxial loading
conditions that can be used to define effective yield criteria for engineering
design models
Energy and Virtuality Scale Dependence in Quark and Gluon Jets
We discuss some important issues concerning multiplicities in quark and gluon
jets in e+e- annihilation. In QCD the properties of a jet in general depend on
two scales, the energy and virtuality of the jet. Frequently theoretical
predictions apply to a situation where these scales coincide, while for
experimental data they are often different. Thus an analysis to extract e.g.
the asymptotic multiplicity ratio CF/CA between quark and gluon jets, needs a
carefully specified jet definition, together with a calculation of nonleading
corrections to the multiplicity evolution.
We propose methods to systematically study the separate dependence upon the
two scales in experimental data and compare the results with theory. We present
jet finding algorithms which corresponds well to the theoretically considered
jets. We also show that recoil effects add corrections to the modified leading
log approximation which are quantitatively important, though formally
suppressed at high energies.Comment: 31 pages, 15 figures. Submitted to JHEP. Replaced with extensively
rewritten versio
SPS energy scan results and physics prospects at FAIR
Experimental studies of nucleus-nucleus collisions in the whole SPS energy
range are reviewed. Selected topics such as statistical properties of the
hadronic phase, strangeness production, fluctuations and correlations are
discussed with regard to information on the onset of deconfinement and the
critical point of strongly interacting matter. In spite of the very interesting
results obtained in particular at the low SPS energies, additional data
including rare probes such as charmed particles and di-leptons are required for
a precise understanding of the underlying physics. An outlook about prospects
and capabilities of upcoming experiments in this interesting energy region at
RHIC, SPS, and in particular with CBM at FAIR, is given.Comment: 8 pages, 8 figures - To appear in the conference proceedings for
Quark Matter 2009, March 30 - April 4, Knoxville, Tennesse
Neutron star properties in density-dependent relativistic Hartree-Fock theory
With the equations of state provided by the newly developed density dependent
relativistic Hartree-Fock (DDRHF) theory for hadronic matter, the properties of
the static and -equilibrium neutron stars without hyperons are studied
for the first time, and compared to the predictions of the relativistic mean
field (RMF) models and recent observational data. The influences of Fock terms
on properties of asymmetric nuclear matter at high densities are discussed in
details. Because of the significant contributions from the - and
-exchange terms to the symmetry energy, large proton fractions in
neutron stars are predicted by the DDRHF calculations, which strongly affect
the cooling process of the star. The critical mass about 1.45 , close
to the limit 1.5 determined by the modern soft X-ray data analysis,
is obtained by DDRHF with the effective interactions PKO2 and PKO3 for the
occurrence of direct Urca process in neutron stars. The maximum masses of
neutron stars given by the DDRHF calculations lie between 2.45 M and
2.49 M, which are in reasonable agreement with high pulsar mass from PSR B1516+02B. It is also found that the mass-radius
relations of neutron stars determined by DDRHF are consistent with the
observational data from thermal radiation measurement in the isolated neutron
star RX J1856, QPOs frequency limits in LMXBs 4U 0614+09 and 4U 1636-536, and
redshift determined in LMXBs EXO 0748-676.Comment: 28 pages, 11 figure
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