232 research outputs found
Do we understand heavy-ion fusion reactions of importance in stellar evolution?
Since the first observation of hindrance in heavy-ion fusion, many extrapolated cross sections for astrophysically interesting fusion reactions, such as 12C + 12C, 12C + 16O, 16O + 16O, 24O etc. need to be reexamined. In this contribution, the effects of fusion hindrance at extreme low energies are discussed
Thermodynamic properties of the two-dimensional S=1/2 Heisenberg antiferromagnet coupled to bond phonons
By applying a quantum Monte Carlo procedure based on the loop algorithm we
investigate thermodynamic properties of the two-dimensional antiferromagnetic
S=1/2 Heisenberg model coupled to Einstein phonons on the bonds. The
temperature dependence of the magnetic susceptibility, mean phonon occupation
numbers and the specific heat are discussed in detail. We study the spin
correlation function both in the regime of weak and strong spin phonon coupling
(coupling constants g=0.1, w=8J and g=2, w=2J, respectively). A finite size
scaling analysis of the correlation length indicates that in both cases long
range Neel order is established in the ground state.Comment: 10 pages, 13 figure
Avalanche Dynamics in Evolution, Growth, and Depinning Models
The dynamics of complex systems in nature often occurs in terms of
punctuations, or avalanches, rather than following a smooth, gradual path. A
comprehensive theory of avalanche dynamics in models of growth, interface
depinning, and evolution is presented. Specifically, we include the Bak-Sneppen
evolution model, the Sneppen interface depinning model, the Zaitsev flux creep
model, invasion percolation, and several other depinning models into a unified
treatment encompassing a large class of far from equilibrium processes. The
formation of fractal structures, the appearance of noise, diffusion with
anomalous Hurst exponents, Levy flights, and punctuated equilibria can all be
related to the same underlying avalanche dynamics. This dynamics can be
represented as a fractal in spatial plus one temporal dimension. We develop
a scaling theory that relates many of the critical exponents in this broad
category of extremal models, representing different universality classes, to
two basic exponents characterizing the fractal attractor. The exact equations
and the derived set of scaling relations are consistent with numerical
simulations of the above mentioned models.Comment: 27 pages in revtex, no figures included. Figures or hard copy of the
manuscript supplied on reques
Identified particles in Au+Au collisions at sqrt{s_NN} = 200 GeV
The yields of identified particles have been measured at RHIC for Au+Au
collisions at sqrt{s_NN} = 200 GeV using the PHOBOS spectrometer. The ratios of
antiparticle to particle yields near mid-rapidity are presented. The first
measurements of the invariant yields of charged pions, kaons and protons at
very low transverse momenta are also shown.Comment: 4 pages, 4 figures, Contribution to Quark Matter 2002, Nantes,
France, July 200
Universal Behavior of Charged Particle Production in Heavy Ion Collisions
The PHOBOS experiment at RHIC has measured the multiplicity of primary
charged particles as a function of centrality and pseudorapidity in Au+Au
collisions at sqrt(s_NN) = 19.6, 130 and 200 GeV. Two kinds of universal
behavior are observed in charged particle production in heavy ion collisions.
The first is that forward particle production, over a range of energies,
follows a universal limiting curve with a non-trivial centrality dependence.
The second arises from comparisons with pp/pbar-p and e+e- data.
N_tot/(N_part/2) in nuclear collisions at high energy scales with sqrt(s) in a
similar way as N_tot in e+e- collisions and has a very weak centrality
dependence. This feature may be related to a reduction in the leading particle
effect due to the multiple collisions suffered per participant in heavy ion
collisions.Comment: 4 Pages, 5 Figures, contributed to the Proceedings of Quark Matter
2002, Nantes, France, 18-24 July 200
Centrality Dependence of Charged Particle Multiplicity at Mid-Rapidity in Au+Au Collisions at sqrt(s_NN) = 130 GeV
We present a measurement of the pseudorapidity density of primary charged
particles near mid-rapidity in Au+Au collisions at sqrt(s_NN) = 130 GeV as a
function of the number of participating nucleons. These results are compared to
models in an attempt to discriminate between competing scenarios of particle
production in heavy ion collisions.Comment: 5 pages, 4 figures, revtex (submitted to Phys. Rev. Letters
Global Observations from PHOBOS
Particle production in Au+Au collisions has been measured in the PHOBOS
experiment at RHIC for a range of collision energies. Three empirical
observations have emerged from this dataset which require theoretical
examination. First, there is clear evidence of limiting fragmentation. Namely,
particle production in central Au+Au collisions, when expressed as
(), becomes energy independent at high energy for a
broad region of around . This energy-independent region grows
with energy, allowing only a limited region (if any) of longitudinal
boost-invariance. Second, there is a striking similarity between particle
production in e+e- and Au+Au collisions (scaled by the number of participating
nucleon pairs). Both the total number of produced particles and the
longitudinal distribution of produced particles are approximately the same in
e+e- and in scaled Au+Au. This observation was not predicted and has not been
explained. Finally, particle production has been found to scale approximately
with the number of participating nucleon pairs for . This scaling
occurs both for the total multiplicity and for high \pT particles (3 <\pT<
4.5 GeV/c).Comment: QM2002 plenary talk, 10 pages, 11 figure
Recent Results from PHOBOS at RHIC
The PHOBOS experiment at RHIC has recorded measurements for Au-Au collisions
spanning nucleon-nucleon center-of-mass energies from 19.6 GeV to 200 GeV.
Global observables such as elliptic flow and charged particle multiplicity
provide important constraints on model predictions that characterize the state
of matter produced in these collisions. The nearly 4 pi acceptance of the
PHOBOS experiment provides excellent coverage for complete flow and
multiplicity measurements. Results including beam energy and centrality
dependencies are presented and compared to elementary systems.Comment: 4 pages, 4 figures, proceedings from PANIC02 in Osaka, Japa
KULIAH KERJA NYATA ALTERNATIF UNIVERSITAS AHMAD DAHLAN PERIODE LXV TAHUN AKADEMIK 2019/2020 DIVISI IV.D.2 RW 08, KELURAHAN TAHUNAN, KECAMATAN UMBULHARJO, KOTA YOGYAKARTA
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