16,378 research outputs found
Amphiphile Adsorption on Rigid Polyelectrolytes
A theory is presented which quantitatively accounts for the cooperative
adsorption of cationic surfactants to anionic polyelectrolytes. For high salt
concentration we find that the critical adsorption concentration (CAC) is a
bilinear function of the polyion monomer and salt concentrations, with the
coefficients dependent only on the type of surfactant used. The results
presented in the paper might be useful for designing more efficient gene
delivery systems
Geometric phases under the presence of a composite environment
We compute the geometric phase for a spin-1/2 particle under the presence of
a composite environment, composed of an external bath (modeled by an infinite
set of harmonic oscillators) and another spin-1/2 particle. We consider both
cases: an initial entanglement between the spin-1/2 particles and an initial
product state in order to see if the initial entanglement has an enhancement
effect on the geometric phase of one of the spins. We follow the nonunitary
evolution of the reduced density matrix and evaluate the geometric phase for a
single two-level system. We also show that the initial entanglement enhances
the sturdiness of the geometric phase under the presence of an external
composite environment.Comment: 10 pages, 12 figures. Version to appear in Phys. Rev.
Histologic and Histomorphometric Analysis of Posterior Region of the Human Temporomandibular Disc
Objective The aim of this study was to analyze histologic and histomorphometric features of the articular disc in groups with and without disc displacement. Study design A sample of 39 temporomandibular joints TMJs (31 case specimens, 8 control specimens) from 28 patients (mean age 31.2 years) were recruited for this study. The patients were considered to be affected and treated surgically with disc repositioning when presenting painful clinical signs of disc displacement after unsuccessful nonsurgical treatment for at least 6 months. Of the control patients, 4 presented condyle fracture which required opening to be reduced for treatment, and 4 displayed active condyle hyperplasia. The posterior region of the disc was removed and sent for histologic and histomorphometric analysis. Histologic (hematoxylin-eosin) and histomorphometric (picro-Sirius red) analyses were performed. Statistically significant differences between the analyzed groups were accessed through the chi-squared test (P ≤ .05). The Mann-Whitney U test was used to observe the differences between mean values when variables did not present normal distribution [Kolmogorov-Smirnov(a) test]. Results There were no significant differences between the groups in relation to the parameters studied by histologic and histomorphometric analysis (using or not using polarization). Conclusions To the limits of this study, there were no significant histologic and histomorphometric differences in the articular disc between groups with and without TMJ dysfunction
Scalar Spectrum from a Dynamical Gravity/Gauge model
We show that a Dynamical AdS/QCD model is able to reproduce the linear Regge
trajectories for the light-flavor sector of mesons with high spin and also for
the scalar and pseudoscalar ones. In addition the model has confinement by the
Wilson loop criteria and a mass gap. We also calculate the decay amplitude of
scalars into two pion in good agreement to the available experimental data.Comment: Presented in the 4th International Workshop on Astronomy and
Relativistic Astrophysic
Dark/Visible Parallel Universes and Big Bang Nucleosynthesis
We develop a model for visible matter-dark matter interaction based on the
exchange of a massive gray boson called herein the Mulato. Our model hinges on
the assumption that all known particles in the visible matter have their
counterparts in the dark matter. We postulate six families of particles five of
which are dark. This leads to the unavoidable postulation of six parallel
worlds, the visible one and five invisible worlds. A close study of big bang
nucleosynthesis (BBN), baryon asymmetries, cosmic microwave background (CMB)
bounds, galaxy dynamics, together with the Standard Model assumptions, help us
to set a limit on the mass and width of the new gauge boson. Modification of
the statistics underlying the kinetic energy distribution of particles during
the BBN is also discussed. The changes in reaction rates during the BBN due to
a departure from the Debye-Hueckel electron screening model is also
investigated.Comment: Invited talk at the Workshops "CompStar: the physics and astrophysics
of compact stars", Tahiti, June 4-8, 2012, "New Directions in Nuclear
Astrophysics", Castiglion Fiorentino, Italy, June 18-22, 2012, and
"Carpathian Summer School of Physics", Sinaia, Romania, June 24 - July 7,
2012. To be published in AIP Proceeding
Dephasing in matter-wave interferometry
We review different attempts to show the decoherence process in
double-slit-like experiments both for charged particles (electrons) and neutral
particles with permanent dipole moments. Interference is studied when electrons
or atomic systems are coupled to classical or quantum electromagnetic fields.
The interaction between the particles and time-dependent fields induces a
time-varying Aharonov phase. Averaging over the phase generates a suppression
of fringe visibility in the interference pattern. We show that, for suitable
experimental conditions, the loss of contrast for dipoles can be almost as
large as the corresponding one for coherent electrons and therefore, be
observed. We analyze different trajectories in order to show the dependence of
the decoherence factor with the velocity of the particles.Comment: 9 pages, 1 eps-figure. To appear in J. Phys. A: Math. Ge
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