155 research outputs found
Second Order Phase Transitions : From Infinite to Finite Systems
We investigate the Equation of State (EOS) of classical systems having 300
and 512 particles confined in a box with periodic boundary conditions. We show
that such a system, independently on the number of particles investigated, has
a critical density of about 1/3 the ground state density and a critical
temperature of about . The mass distribution at the critical point
exhibits a power law with . Making use of the grand partition
function of Fisher's droplet model, we obtain an analytical EOS around the
critical point in good agreement with the one extracted from the numerical
simulations.Comment: RevTex file, 17 pages + 9 figures available upon request from
[email protected]
Quantum Coherence Oscillations in Antiferromagnetic Chains
Macroscopic quantum coherence oscillations in mesoscopic antiferromagnets may
appear when the anisotropy potential creates a barrier between the
antiferromagnetic states with opposite orientations of the Neel vector. This
phenomenon is studied for the physical situation of the nuclear spin system of
eight Xe atoms arranged on a magnetic surface along a chain. The oscillation
period is calculated as a function of the chain constant. The environmental
decoherence effects at finite temperature are accounted assuming a dipole
coupling between the spin chain and the fluctuating magnetic field of the
surface. The numerical calculations indicate that the oscillations are damped
by a rate , where is the number of spins and is
the relaxation time of a single spin.Comment: 10 pages, Latex, two postscript figures; submitted to Phys. Rev.
Author Correction: High-resolution cryo-EM structure of urease from the pathogen Yersinia enterocolitica
A Correction to this paper has been published: https://doi.org/10.1038/s41467-020-19845-z
Time Scales in Spectator Fragmentation
Proton-proton correlations and correlations of p-alpha, d-alpha, and t-alpha
from spectator decays following Au + Au collisions at 1000 AMeV have been
measured with an highly efficient detector hodoscope. The constructed
correlation functions indicate a moderate expansion and low breakup densities
similar to assumptions made in statistical multifragmentation models. In
agreement with a volume breakup rather short time scales were deduced employing
directional cuts in proton-proton correlations.
PACS numbers: 25.70.Pq, 21.65.+f, 25.70.MnComment: 8 pages, with 5 included figures; To appear in the proceedings of the
CRIS 2000 conference; Also available from
http://www-kp3.gsi.de/www/kp3/aladin_publications.htm
The liquid to vapor phase transition in excited nuclei
For many years it has been speculated that excited nuclei would undergo a
liquid to vapor phase transition. For even longer, it has been known that
clusterization in a vapor carries direct information on the liquid- vapor
equilibrium according to Fisher's droplet model. Now the thermal component of
the 8 GeV/c pion + 197Au multifragmentation data of the ISiS Collaboration is
shown to follow the scaling predicted by Fisher's model, thus providing the
strongest evidence yet of the liquid to vapor phase transition.Comment: four pages, four figures, first two in color (corrected typo in Ref.
[26], corrected error in Fig. 4
Searching for the Nuclear Liquid-Gas Phase Transition in Au + Au Collisions at 35 MeV/nucleon
Within the framework of Classical Molecular Dynamics, we study the collision
Au + Au at an incident energy of 35 MeV/nucleon. It is found that the system
shows a critical behaviour at peripheral impact parameters, revealed through
the analysis of conditional moments of charge distributions, Campi Scatter
Plot, and the occurrence of large fluctuations in the region of the Campi plot
where this critical behaviour is expected. When applying the experimental
filters of the MULTICS-MINIBALL apparatus, it is found that criticality signals
can be hidden due to the inefficiency of the experimental apparatus. The
signals are then recovered by identifying semi-peripheral and peripheral
collisions looking to the velocity distribution of the largest fragment, then
by selecting the most complete events.Comment: RevTex file, 21 pages + 19 figures available upon request from
[email protected]
Thermal and Chemical Freeze-out in Spectator Fragmentation
Isotope temperatures from double ratios of hydrogen, helium, lithium,
beryllium, and carbon isotopic yields, and excited-state temperatures from
yield ratios of particle-unstable resonances in 4He, 5Li, and 8Be, were
determined for spectator fragmentation, following collisions of 197Au with
targets ranging from C to Au at incident energies of 600 and 1000 MeV per
nucleon. A deviation of the isotopic from the excited-state temperatures is
observed which coincides with the transition from residue formation to
multi-fragment production, suggesting a chemical freeze-out prior to thermal
freeze-out in bulk disintegrations.Comment: 14 pages, 10 figures, submitted to Phys. Rev. C, small changes as
suggested by the editors and referee
Temperatures of Exploding Nuclei
Breakup temperatures in central collisions of 197Au + 197Au at bombarding
energies E/A = 50 to 200 MeV were determined with two methods. Isotope
temperatures, deduced from double ratios of hydrogen, helium, and lithium
isotopic yields, increase monotonically with bombarding energy from 5 MeV to 12
MeV, in qualitative agreement with a scenario of chemical freeze-out after
adiabatic expansion. Excited-state temperatures, derived from yield ratios of
states in 4He, 5Li, 6Li, and 8Be, are about 5 MeV, independent of the
projectile energy, and seem to reflect the internal temperature of fragments at
their final separation from the system.
PACS numbers: 25.70.Mn, 25.70.Pq, 25.75.-qComment: 10 pages, RevTeX with 4 included figures; Also available from
http://www-kp3.gsi.de/www/kp3/aladin_publications.htm
Circumstantial Evidence for a Critical Behavior in Peripheral Au + Au Collisions at 35 MeV/nucleon
The fragmentation resulting from peripheral Au + Au collisions at an incident
energy of E = 35 MeV/nucleon is investigated. A power-law charge distribution,
with , and an intermittency signal are observed
for events selected in the region of the Campi scatter plot where "critical"
behavior is expected.Comment: 11 pages, RevTex file, 4 postscript figures available upon request
from [email protected]
Breakup Temperature of Target Spectators in Au + Au Collisions at E/A = 1000 MeV
Breakup temperatures were deduced from double ratios of isotope yields for
target spectators produced in the reaction Au + Au at 1000 MeV per nucleon.
Pairs of He and Li isotopes and pairs of He and H
isotopes (p, d and d, t) yield consistent temperatures after feeding
corrections, based on the quantum statistical model, are applied. The
temperatures rise with decreasing impact parameter from 4 MeV for peripheral to
about 10 MeV for the most central collisions.
The good agreement with the breakup temperatures measured previously for
projectile spectators at an incident energy of 600 MeV per nucleon confirms the
observed universality of the spectator decay at relativistic bombarding
energies. The measured temperatures also agree with the breakup temperatures
predicted by the statistical multifragmentation model. For these calculations a
relation between the initial excitation energy and mass was derived which gives
good simultaneous agreement for the fragment charge correlations.
The energy spectra of light charged particles, measured at =
150, exhibit Maxwellian shapes with inverse slope parameters much
higher than the breakup temperatures. The statistical multifragmentation model,
because Coulomb repulsion and sequential decay processes are included, yields
light-particle spectra with inverse slope parameters higher than the breakup
temperatures but considerably below the measured values. The systematic
behavior of the differences suggests that they are caused by
light-charged-particle emission prior to the final breakup stage.
PACS numbers: 25.70.Mn, 25.70.Pq, 25.75.-qComment: 29 pages, TeX with 11 included figures; Revised version accepted for
publication in Z. Phys. A Two additional figure
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