381 research outputs found
Universal fluctuations in heavy-ion collisions in the Fermi energy domain
We discuss the scaling laws of both the charged fragments multiplicity
fluctuations and the charge of the largest fragment fluctuations for Xe+Sn
collisions in the range of bombarding energies between 25 MeV/A and 50 MeV/A.
We show close to E_{lab}=32 MeV/A the transition in the fluctuation regime of
the charge of the largest fragment which is compatible with the transition from
the ordered to disordered phase of excited nuclear matter. The size (charge) of
the largest fragment is closely related to the order parameter characterizing
this process.Comment: 4 pages, 3 figure
Els Drs. Botet, una nissaga de metges per a Igualada
Al número 60 de la Rambla Sant Ferran d’Igualada hi podem trobar una bonica casa modernista que ha acollit, des de fa més de 100 anys, un metge de la mateixa família donant servei als ciutadans d’Igualada. En aquest treball hom resum la vida dels dos més emblemàtics, el Dr. Francesc Botet i Pallarès i el Dr. Francesc Botet i Casadesús.En el número 60 de la Rambla San Fernando de Igualada podemos encontraruna bonita casa modernista que ha acogido, desde hace más de 100 años, un médico de la misma familia dando servicio a los ciudadanos de Igualada. En este trabajo se resumen la vida de los dos más emblemáticos, el Dr. Francisco Botet y Pallarès y el Dr. Francisco Botet y Casadesús (1933-1955)
Universal features of the order-parameter fluctuations : reversible and irreversible aggregation
We discuss the universal scaling laws of order parameter fluctuations in any
system in which the second-order critical behaviour can be identified. These
scaling laws can be derived rigorously for equilibrium systems when combined
with the finite-size scaling analysis. The relation between order parameter,
criticality and scaling law of fluctuations has been established and the
connexion between the scaling function and the critical exponents has been
found. We give examples in out-of-equilibrium aggregation models such as the
Smoluchowski kinetic equations, or of at-equilibrium Ising and percolation
models.Comment: 19 pages, 10 figure
The phase diagram of the anisotropic Spin-1 Heisenberg Chain
We applied the Density Matrix Renormalization Group to the XXZ spin-1 quantum
chain. In studing this model we aim to clarify controversials about the point
where the massive Haldane phase appears.Comment: 2 pages (standart LaTex), 1 figure (PostScript) uuencode
Looking for bimodal distributions in multi-fragmentation reactions
The presence of a phase transition in a finite system can be deduced,
together with its order, from the shape of the distribution of the order
parameter. This issue has been extensively studied in multifragmentation
experiments, with results that do not appear fully consistent. In this paper we
discuss the effect of the statistical ensemble or sorting conditions on the
shape of fragment distributions, and propose a new method, which can be easily
implemented experimentally, to discriminate between different fragmentation
scenarii. This method, based on a reweighting of the measured distribution to
account for the experimental constraints linked to the energy deposit, is
tested on different simple models, and appears to provide a powerful
discrimination.Comment: 11 pages, 7 figure
Metamagnetism of antiferromagnetic XXZ quantum spin chains
The magnetization process of the one-dimensional antiferromagnetic Heisenberg
model with the Ising-like anisotropic exchange interaction is studied by the
exact diagonalization technique. It results in the evidence of the first-order
spin flop transition with a finite magnetization jump in the N\'eel ordered
phase for . It implies that the S=1/2 chain is an exceptional case
where the metamagnetic transition becomes second-order due to large quantum
fluctuations.Comment: 4 pages, Revtex, with 6 eps figure
Nuclear Multifragmentation in the Non-extensive Statistics - Canonical Formulation
We apply the canonical quantum statistical model of nuclear
multifragmentation generalized in the framework of recently proposed Tsallis
non-extensive thermostatistics for the description of nuclear
multifragmentation process. The test calculation in the system with A=197
nucleons show strong modification of the 'critical' behaviour associated with
the nuclear liquid-gas phase transition for small deviations from the
conventional Boltzmann-Gibbs statistical mechanics.Comment: 4 pages, 4 figure
Field-Induced Transition in the S=1 Antiferromagnetic Chain with Single-Ion Anisotropy in a Transverse Magnetic Field
The field-induced transition in one-dimensional S=1 Heisenberg
antiferromagnet with single-ion anisotropy in the presence of a transverse
magnetic field is obtained on the basis of the Schwinger boson mean-field
theory. The behaviors of the specific heat and susceptibility as functions of
temperature as well as the applied transverse field are explored, which are
found to be different from the results obtained under a longitudinal field. The
anomalies of the specific heat at low temperatures, which might be an
indicative of a field-induced transition from a Luttinger liquid phase to an
ordered phase, are explicitly uncovered under the transverse field. A schematic
phase diagram is proposed. The theoretical results are compared with
experimental observations.Comment: Revtex, 7 figure
Hiding in Plain View: Colloidal Self-Assembly from Polydisperse Populations
We report small-angle x-ray scattering experiments on aqueous dispersions of colloidal silica with a broad monomodal size distribution (polydispersity, 14%; size, 8 nm). Over a range of volume fractions, the silica particles segregate to build first one, then two distinct sets of colloidal crystals. These dispersions thus demonstrate fractional crystallization and multiple-phase (bcc, Laves AB2, liquid) coexistence. Their remarkable ability to build complex crystal structures from a polydisperse population originates from the intermediate-range nature of interparticle forces, and it suggests routes for designing self-assembling colloidal crystals from the bottom up
Quantum numbers for relative ground states of antiferromagnetic Heisenberg spin rings
We suggest a general rule for the shift quantum numbers k of the relative
ground states of antiferromagnetic Heisenberg spin rings. This rule generalizes
well-known results of Marshall, Peierls, Lieb, Schultz, and Mattis for even
rings. Our rule is confirmed by numerical investigations and rigorous proofs
for special cases, including systems with a Haldane gap. Implications for the
total spin quantum number S of relative ground states are discussed as well as
generalizations to the XXZ model.Comment: 8 pages, 2 figures, submitted to Phys. Rev. B. More information at
http://www.physik.uni-osnabrueck.de/makrosysteme
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