Absence of Chaos in Bohmian Dynamics

The Bohm motion for a particle moving on the line in a quantum state that is a superposition of n+1 energy eigenstates is quasiperiodic with n frequencies.Comment: 1 pag

Quantum fidelity approach to the ground state properties of the 1D ANNNI model in a transverse field

In this work we analyze the ground-state properties of the $s=1/2$ one-dimensional ANNNI model in a transverse field using the quantum fidelity approach. We numerically determined the fidelity susceptibility as a function of the transverse field $B_x$ and the strength of the next-nearest-neighbor interaction $J_2$, for systems of up to 24 spins. We also examine the ground-state vector with respect to the spatial ordering of the spins. The ground-state phase diagram shows ferromagnetic, paramagnetic, floating, $\Braket{2,2}$ phases, and we predict an infinite number of modulated phases in the thermodynamic limit ($L \rightarrow \infty$). The transition lines separating the modulated phases seem to be of second-order, whereas the line between the floating and the $\Braket{2,2}$ phases is possibly of first-order.Comment: 10 pages, 20 figure

Improving Tuberculosis Diagnostics using Deep Learning and Mobile Health Technologies among Resource-poor Communities in Peru

As part of the mini-symposium entitled “Research on Digital Health for Designing Scalable Pervasive Healthcare Monitoring, Rehabilitation, and Home-based Healthcare Systems,” Dr. Alcantara discusses a project to improve the tuberculosis diagnosis in resource poor communities in Peru

Phase transitions in the two-dimensional super-antiferromagnetic Ising model with next-nearest-neighbor interactions

We use Monte Carlo and Transfer Matrix methods in combination with extrapolation schemes to determine the phase diagram of the 2D super-antiferromagnetic (SAF) Ising model with next-nearest-neighbor (nnn) interactions in a magnetic field. The interactions between nearest-neighbor (nn) spins are ferromagnetic along x, and antiferromagnetic along y. We find that for sufficiently low temperatures and fields, there exists a region limited by a critical line of 2nd-order transitions separating a SAF phase from a magnetically induced paramagnetic phase. We did not find any region with either first-order transition or with re-entrant behavior. The nnn couplings produce either an expansion or a contraction of the SAF phase. Expansion occurs when the interactions are antiferromagnetic, and contraction when they are ferromagnetic. There is a critical ratio R_c = 1/2 between nnn- and nn-couplings, beyond which the SAF phase no longer exists.Comment: 12 pages, 10 figure

Breakdown of the perturbative renormalization group for S >= 1 random antiferromagnetic spin chains

We investigate the application of a perturbative renormalization group (RG) method to random antiferromagnetic Heisenberg chains with arbitrary spin size. At zero temperature we observe that initial arbitrary probability distributions develop a singularity at J=0, for all values of spin S. When the RG method is extended to finite temperatures, without any additional assumptions, we find anomalous results for S >= 1. These results lead us to conclude that the perturbative scheme is not adequate to study random chains with S >= 1. Therefore a random singlet phase in its more restrictive definition is only assured for spin-1/2 chains.Comment: 5 pages, 3 figures. To appear in Physical Review

Bacterial colonization of seston particles in brackish waters (Ria de Aveiro, Portugal)

The frequency of attached bacteria, as percentage of total bacteria, in estuarine water of the Ria de Aveiro was determined over a seasonal range of temperature, seston, BOD, salinity and water depth. The frequency was inversely related to temperature only in the marine zone of the lagoon. No other associations could be established with environmental factors The broad spring-summer peak of total bacteria was not apparent in attached bacteria which showed an erratic temporal profile with an average frequency of 9 % (range 1 to 49 %] of total planktonic bacteria The bacterial coverage per unit area of particle surface was densest in small particles The density of coverage decreased sharply to values corresponding to 22,5 and 2 % in particles > 3 to 10, > l0 to 40 and > 40 to 140 pm in diameter respecitvely compared to the density of coverage of the > 1 to 3 pm size-class Colonized seston and sediment particles exhibited similar bacterial numbers per particle of each size-class and did not show tidal spatial 01 seasonal patterns of variation it is suggested that bacteria only seldom attach to particles in the water column of this lagoon and that resuspension of bottom sediments is the main factor governing the frequency of colonized particles in surface water

Dynamics of the Potts model on a fractal lattice

The dynamics of the q-state Potts model on a fractal lattice is studied using Monte Carlo simulations. The Glauber dynamics is used leading to an effective temperature-dependent critical exponent of the form z = AK + B implying the breakdown of conventional dynamic scaling. The value of A is shown to be independent of q, within the error bars

Dynamical properties of an harmonic oscillator impacting a vibrating wall

The dynamics of a spring-mass system under repeated impact with a vibrating wall is investigated using the static wall approximation. The evolution of the harmonic oscillator is described by two coupled difference equations. These equations are solved numerically, and in some cases exact analytical expressions have also been found. For a periodically vibrating wall, Fermi acceleration is only found at resonance. There, the average rebounding velocity increases linearly with the number of collisions. Near resonance, the average rebounding velocity grows initially with the number of collisions and eventually reaches a plateau. In the vicinity of resonance, the motion of the oscillator exhibits scaling properties over a range of frequency ratios. The presence of dissipation at resonance destroys the Fermi-acceleration process and induces scaling behavior similar to that at near resonance. For a moving wall with a random amplitude at collisions, Fermi acceleration is observed independently of the ratio between the wall and oscillator frequencies. In this case the average rebounding velocity grows with the square root of the number of collisions with the wall. Also, in this latter case, dissipation suppresses the Fermi-acceleration mechanism and induces a scaling behavior with the same universality class as that of the dissipative bouncing ball model with random external perturbations