1,709 research outputs found
Scaling in the Lattice Gas Model
A good quality scaling of the cluster size distributions is obtained for the
Lattice Gas Model using the Fisher's ansatz for the scaling function. This
scaling identifies a pseudo-critical line in the phase diagram of the model
that spans the whole (subcritical to supercritical) density range. The
independent cluster hypothesis of the Fisher approach is shown to describe
correctly the thermodynamics of the lattice only far away from the critical
point.Comment: 4 pages, 3 figure
Representational task formats and problem solving strategies in kinematics and work
Previous studies have reported that students employed different problem solving approaches when presented with the same task structured with different representations. In this study, we explored and compared studentsâ strategies as they attempted tasks from two topical areas, kinematics and work. Our participants were 19 engineering students taking a calculus-based physics course. The tasks were presented in linguistic, graphical, and symbolic forms and requested either a qualitative solution or a value. The analysis was both qualitative and quantitative in nature focusing principally on the characteristics
of the strategies employed as well as the underlying reasoning for their applications. A comparison was also made for the same studentâs approach with the same kind of representation across the two topics.
Additionally, the participantsâ overall strategies across the different tasks, in each topic, were considered. On the whole, we found that the students prefer manipulating equations irrespective of the representational format of the task. They rarely recognized the applicability of a ââqualitativeââ approach to solve the
problem although they were aware of the concepts involved. Even when the students included visual representations in their solutions, they seldom used these representations in conjunction with the
mathematical part of the problem. Additionally, the students were not consistent in their approach for interpreting and solving problems with the same kind of representation across the two topical areas. The representational format, level of prior knowledge, and familiarity with a topic appeared to influence their
strategies, their written responses, and their ability to recognize qualitative ways to attempt a problem. The nature of the solution does not seem to impact the strategies employed to handle the problem
Isotopic composition of fragments in multifragmentation of very large nuclear systems: effects of the chemical equilibrium
Studies on the isospin of fragments resulting from the disassembly of highly
excited large thermal-like nuclear emitting sources, formed in the ^{197}Au +
^{197}Au reaction at 35 MeV/nucleon beam energy, are presented. Two different
decay systems (the quasiprojectile formed in midperipheral reactions and the
unique source coming from the incomplete fusion of projectile and target in the
most central collisions) were considered; these emitting sources have the same
initial N/Z ratio and excitation energy (E^* ~= 5--6 MeV/nucleon), but
different size. Their charge yields and isotopic content of the fragments show
different distributions. It is observed that the neutron content of
intermediate mass fragments increases with the size of the source. These
evidences are consistent with chemical equilibrium reached in the systems. This
fact is confirmed by the analysis with the statistical multifragmentation
model.Comment: 9 pages, 4 ps figure
Statistical evolution of isotope composition of nuclear fragments
Calculations within the statistical multifragmentation model show that the
neutron content of intermediate mass fragments can increase in the region of
liquid-gas phase transition in finite nuclei. The model predicts also
inhomogeneous distributions of fragments and their isospin in the freeze-out
volume caused by an angular momentum and external long-range Coulomb field.
These effects can take place in peripheral nucleus-nucleus collisions at
intermediate energies and lead to neutron-rich isotopes produced in the
midrapidity kinematic region.Comment: 14 pages with 4 figures. GSI preprint, Darmstadt, 200
COVIDâ19 as a Catalyst for U.S. Child Care Policy Reform: Factsheet
The burden of child care in the wake of widespread K-12 school closures has disproportionately harmed women, communities of color, and lower income families -- a clear indicator that now is the time to adopt a federally-subsidized childcare system in local communities that goes beyond public schools. Current proposals must address regulatory and financial challenges to child care centers and home-based providers, allow for local government involvement and discretion, and maintain flexibility for parents with non-traditional work schedules
Advancing Gender Equity through Legislation: Overview of Select Laws Passed from 2014â2020
Advancing Gender Equity through Legislation: A Compilation of Laws Passed from 2014 - 2020 aims to provide New York City residents with information about legislation passed under the de Blasio administration that aims to promote gender equity in the city
Transient backbending behavior in the Ising model with fixed magnetization
The physical origin of the backbendings in the equations of state of finite
but not necessarily small systems is studied in the Ising model with fixed
magnetization (IMFM) by means of the topological properties of the observable
distributions and the analysis of the largest cluster with increasing lattice
size. Looking at the convexity anomalies of the IMFM thermodynamic potential,
it is shown that the order of the transition at the thermodynamic limit can be
recognized in finite systems independently of the lattice size. General
statistical mechanics arguments and analytical calculations suggest that the
backbending in the caloric curve is a transient behaviour which should not
converge to a plateau in the thermodynamic limit, while the first order
transition is signalled by a discontinuity in other observables.Comment: 24 pages, 11 figure
Spinodal decomposition of expanding nuclear matter and multifragmentation
Density fluctuations of expanding nuclear matter are studied within a
mean-field model in which fluctuations are generated by an external stochastic
field. Fluctuations develop about a mean one-body phase-space density
corresponding to a hydrodinamic motion that describes a slow expansion of the
system. A fluctuation-dissipation relation suitable for a uniformly expanding
medium is obtained and used to constrain the strength of the stochastic field.
The distribution of the liquid domains in the spinodal decomposition is
derived. Comparison of the related distribution of the fragment size with
experimental data on the nuclear multifragmentation is quite satisfactory.Comment: 19 RevTex4 pages, 6 eps figures, to appear in Phys. Rev.
Critical Temperature for the Nuclear Liquid-Gas Phase Transition
The charge distribution of the intermediate mass fragments produced in p (8.1
GeV) + Au collisions is analyzed in the framework of the statistical
multifragmentation model with the critical temperature for the nuclear
liquid-gas phase transition as a free parameter. It is found that
MeV (90% CL).Comment: 4 pages, 3 figures, published in Phys. Rev.
Equation of State, Spectra and Composition of Hot and Dense Infinite Hadronic Matter in a Microscopic Transport Model
Equilibrium properties of infinite relativistic hadron matter are
investigated using the Ultrarelativistic Quantum Molecular Dynamics (UrQMD)
model. The simulations are performed in a box with periodic boundary
conditions. Equilibration times depend critically on energy and baryon
densities. Energy spectra of various hadronic species are shown to be isotropic
and consistent with a single temperature in equilibrium. The variation of
energy density versus temperature shows a Hagedorn-like behavior with a
limiting temperature of 13010 MeV. Comparison of abundances of different
particle species to ideal hadron gas model predictions show good agreement only
if detailed balance is implemented for all channels. At low energy densities,
high mass resonances are not relevant; however, their importance raises with
increasing energy density. The relevance of these different conceptual
frameworks for any interpretation of experimental data is questioned.Comment: Latex, 20 pages including 6 eps-figure
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