Spin and energy correlations in the one dimensional spin 1/2 Heisenberg model

In this paper, we study the spin and energy dynamic correlations of the one dimensional spin 1/2 Heisenberg model, using mostly exact diagonalization numerical techniques. In particular, observing that the uniform spin and energy currents decay to finite values at long times, we argue for the absence of spin and energy diffusion in the easy plane anisotropic Heisenberg model.Comment: 10 pages, 3 figures, gzipped postscrip

The Smallest Molecular Switch

Ab-initio total energy calculations reveal benzene-dithiolate (BDT) molecules on a gold surface, contacted by a monoatomic gold STM tip to have two classes of low energy conformations with differing symmetries. Lateral motion of the tip or excitation of the molecule cause it to change from one conformation class to the other and to switch between a strongly and a weakly conducting state. Thus, surprisingly, despite their apparent simplicity these Au/BDT/Au nanowires are shown to be electrically bi-stable switches, the smallest two-terminal molecular switches to date. Experiments with a conventional or novel self-assembled STM are proposed to test these predictions.Comment: 8 pages, 3 figure

Dynamical Structure Factors for Dimerized Spin Systems

We discuss the transition strength between the disordered ground state and the basic low-lying triplet excitation for interacting dimer materials by presenting theoretical calculations and series expansions as well as inelastic neutron scattering results for the material KCuCl_3. We describe in detail the features resulting from the presence of two differently oriented dimers per unit cell and show how energies and spectral weights of the resulting two modes are related to each other. We present results from the perturbation expansion in the interdimer interaction strength and thus demonstrate that the wave vector dependence of the simple dimer approximation is modified in higher orders. Explicit results are given in 10th order for dimers coupled in 1D, and in 2nd order for dimers coupled in 3D with application to KCuCl_3 and TlCuCl_3.Comment: 17 pages, 6 figures, part 2 is based on cond-mat/021133

Multicritical crossovers near the dilute Bose gas quantum critical point

Many zero temperature transitions, involving the deviation in the value of a $U(1)$ conserved charge from a quantized value, are described by the dilute Bose gas quantum critical point. On such transitions, we study the consequences of perturbations which break the symmetry down to $Z_N$ in $d$ spatial dimensions. For the case $d=1$, $N=2$, we obtain exact, finite temperature, multicritical crossover functions by a mapping to an integrable lattice model.Comment: 10 pages, REVTEX 3.0, 2 EPS figure

Universal properties of thermal and electrical conductivity of gauge theory plasmas from holography

We propose that for conformal field theories admitting gravity duals, the thermal conductivity is fixed by the central charges in a universal manner. Though we do not have a proof as yet, we have checked our proposal against several examples. This proposal, if correct, allows us to express electrical conductivity in terms of thermodynamical quantities even in the presence of chemical potential.Comment: 13 pages, appendix added, close to journal versio

Teen Distracted Reality an Interactive Virtual Education (D.R.I.V.E.): Experience and Impact on Teenage Drivers

Introduction: In 2013, 2,163 teens in the United States ages 16–19 were killed and 243,243 were treated in emergency departments for injuries from motor vehicle crashes. distracted driving (i.e. texting, loud music, or phone conversations) and impaired driving (driving under the influence) play a role in these motor vehicle crashes. Prevention efforts aimed at high-risk teenager driving behavior may encourage safe driving habits. Methods: The Teen D.R.I.V.E. program is a mobile driving simulator that provides teenagers with distracted and impaired driving scenarios. We administered anonymous surveys from April 2015-April 2016 to obtain demographic data and evaluate the program’s impact on their driving behavior. We retrospectively analyzed survey responses using univariate and multivariate statistical analysis. Results: A total of 1374 participants in the survey, however, 50 did not respond to the driving experience portion of the survey. Most participants (70%) were between 16-17 years of age years old and 51% were males. A majority (76%) of respondents had driving experience (26% permit, and 46% license) or had attended a driver’s education course (67%). After experiencing the simulation respondents felt that the consequences of driving distracted (53%) and driving impaired (61%) were worse than previously expected. In addition, participants said that they would never drive distracted (70%) or drive impaired (90%). A majority of participants (72%) feel that simulation is the most effective way to teach driving related topics. Conclusion: Teen D.R.I.V.E. offers a valuable experience to teenagers, teaching them about the dangers of driving distracted and impaired. Participants are likely to never drive impaired compared or distracted. Most teenagers feel simulation teaches these driving lessons most effectively

The fractional quantum Hall effect in infinite layer systems

Stacked two dimensional electron systems in transverse magnetic fields exhibit three dimensional fractional quantum Hall phases. We analyze the simplest such phases and find novel bulk properties, e.g., irrational braiding. These phases host ``one and a half'' dimensional surface phases in which motion in one direction is chiral. We offer a general analysis of conduction in the latter by combining sum rule and renormalization group arguments, and find that when interlayer tunneling is marginal or irrelevant they are chiral semi-metals that conduct only at T > 0 or with disorder.Comment: RevTeX 3.0, 4p., 2 figs with epsf; reference to the detailed companion paper cond-mat/0006506 adde

Temperature dependence of single particle excitations in a S=1 chain: exact diagonalization calculations compared to neutron scattering experiments

Exact diagonalization calculations of finite antiferromagnetic spin-1 Heisenberg chains at finite temperatures are presented and compared to a recent inelastic neutron scattering experiment for temperatures T up to 7.5 times the intrachain exchange constant J. The calculations show that the excitations at the antiferromagnetic point q=1 and at q=0.5 remain resonant up to at least T=2J, confirming the recent experimental observation of resonant high-temperature domain wall excitations. The predicted first and second moments are in good agreement with experiment, except at temperatures where three-dimensional spin correlations are most important. The ratio of the structure factors at q=1 and at q=0.5 is well predicted for the paramagnetic infinite-temperature limit. For T=2J, however, we found that the experimentally observed intensity is considerably less than predicted. This suggests that domain wall excitations on different chains interact up to temperatures of the order of the spin band width.Comment: 9 pages revtex, submitted to PR

Finite temperature transport at the superconductor-insulator transition in disordered systems

I argue that the incoherent, zero-frequency limit of the universal crossover function in the temperature-dependent conductivity at the superconductor-insulator transition in disordered systems may be understood as an analytic function of dimensionality of system d, with a simple pole at d=1. Combining the exact result for the crossover function in d=1 with the recursion relations in d=1+\epsilon, the leading term in the Laurent series in the small parameter \epsilon for this quantity is computed for the systems of disordered bosons with short-range and Coulomb interactions. The universal, low-temperature, dc critical conductivity for the dirty boson system with Coulomb interaction in d=2 is estimated to be 0.69 (2e)^2 /h, in relatively good agreement with many experiments on thin films. The next order correction is likely to somewhat increase the result, possibly bringing it closer to the self-dual value.Comment: 9 pages, LaTex, no figure

Microcontroller Based Three Phase Inverter

This paper presents the idea and design of a three-phase inverter that produces a symmetric AC output voltage of desired magnitude and frequency. Although the inverter has traditionally been designed as analog circuitry, now the digital inverters are preferred. Microcontroller used for generating the control signal for the three-phase inverter. The importance of the proper design of control signals with powerful switching is to reduce the harmonics and power losses of the inverter output voltage. The potential of the microcontroller to carry out the mathematical and logical functions allows it to imitate logic and electronics circuit. The PIC18FXX2 of Microchip is used for the implementation of inverter. PWM control is the most powerful technique that offers a simple method for controlling of analog systems with the processor’s digital output. All PWM generating methods aim at generating a sinusoidal inverter output voltage without low-order harmonics. With the availability of low cost high performance microchips characterized by the execution of most instructions in one instruction cycle, complicated control algorithms can be executed with fast speed, making very high sampling rate possible for digitally-controlled inverters. DOI: 10.17762/ijritcc2321-8169.150310