Driven Intrinsic Localized Modes in a Coupled Pendulum Array

Intrinsic localized modes (ILMs), also called discrete breathers, are directly generated via modulational instability in an array of coupled pendulums. These ILMs can be stabilized over a range of driver frequencies and amplitudes. They are characterized by a pi-phase difference between their center and wings. At higher driver frequencies, these ILMs are observed to disintegrate via a pulsating instability, and the mechanism of this breather instability is investigated.Comment: 5 pages, 6 figure

Stochastic Dominance Analysis of Bioenergy Crops as a Production Alternative on an East Tennessee Beef and Crop Farm

This study evaluated prices and incentives for switchgrass stated in a biorefinery’s contract terms that induce switchgrass production on an east Tennessee representative farm when compared with traditional enterprises. The alternate contract terms imitated current subsidies/incentives offered as well as incentives and cost share terms not in the BCAP.switchgrass, contract, risk aversion, net return, Farm Management, Production Economics, Resource /Energy Economics and Policy, Q12,

Nonlinear localized modes in two-dimensional electrical lattices

We report the observation of spontaneous localization of energy in two spatial dimensions in the context of nonlinear electrical lattices. Both stationary and traveling self-localized modes were generated experimentally and theoretically in a family of two-dimensional square, as well as hon- eycomb lattices composed of 6x6 elements. Specifically, we find regions in driver voltage and frequency where stationary discrete breathers, also known as intrinsic localized modes (ILM), exist and are stable due to the interplay of damping and spatially homogeneous driving. By introduc- ing additional capacitors into the unit cell, these lattices can controllably induce traveling discrete breathers. When more than one such ILMs are experimentally generated in the lattice, the interplay of nonlinearity, discreteness and wave interactions generate a complex dynamics wherein the ILMs attempt to maintain a minimum distance between one another. Numerical simulations show good agreement with experimental results, and confirm that these phenomena qualitatively carry over to larger lattice sizes.Comment: 5 pages, 6 figure

Discrete breathers in a nonlinear electric line: Modeling, Computation and Experiment

We study experimentally and numerically the existence and stability properties of discrete breathers in a periodic nonlinear electric line. The electric line is composed of single cell nodes, containing a varactor diode and an inductor, coupled together in a periodic ring configuration through inductors and driven uniformly by a harmonic external voltage source. A simple model for each cell is proposed by using a nonlinear form for the varactor characteristics through the current and capacitance dependence on the voltage. For an electrical line composed of 32 elements, we find the regions, in driver voltage and frequency, where $n$-peaked breather solutions exist and characterize their stability. The results are compared to experimental measurements with good quantitative agreement. We also examine the spontaneous formation of $n$-peaked breathers through modulational instability of the homogeneous steady state. The competition between different discrete breathers seeded by the modulational instability eventually leads to stationary $n$-peaked solutions whose precise locations is seen to sensitively depend on the initial conditions

The Fragmenting Superbubble Associated with the HII Region W4

New observations at high latitudes above the HII region W4 show that the structure formerly identified as a chimney candidate, an opening to the Galactic halo, is instead a superbubble in the process of fragmenting and possibly evolving into a chimney. Data at high Galactic latitudes (b > 5 degrees) above the W3/W4 star forming region at 1420 and 408 MHz Stokes I (total power) and 1420 MHz Stokes Q and U (linear polarization) reveal an egg-shaped structure with morphological correlations between our data and the H-alpha data of Dennison, Topasna, & Simonetti. Polarized intensity images show depolarization extending from W4 up the walls of the superbubble, providing strong evidence that the radio continuum is generated by thermal emission coincident with the H-alpha emission regions. We conclude that the parts of the HII region hitherto known as W4 and the newly revealed thermal emission are all ionized by the open cluster OCl 352. Assuming a distance of 2.35 kpc, the ovoid structure is 164 pc wide and extends 246 pc above the mid-plane of the Galaxy. The shell's emission decreases in total-intensity and polarized intensity in various locations, appearing to have a break at its top and another on one side. Using a geometric analysis of the depolarization in the shell's walls, we estimate that a magnetic field line-of-sight component of 3 to 5 uG exists in the shell. We explore the connection between W4 and the Galactic halo, considering whether sufficient radiation can escape from the fragmenting superbubble to ionize the kpc-scale H-alpha loop discovered by Reynolds, Sterling & Haffner.Comment: 42 pages, 14 figures; Accepted for publication in Ap

Discrete breathers in a forced-damped array of coupled pendula: Modeling, Computation and Experiment

In this work, we present a mechanical example of an experimental realization of a stability reversal between on-site and inter-site centered localized modes. A corresponding realization of a vanishing of the Peierls-Nabarro barrier allows for an experimentally observed enhanced mobility of the localized modes near the reversal point. These features are supported by detailed numerical computations of the stability and mobility of the discrete breathers in this system of forced and damped coupled pendula. Furthermore, additional exotic features of the relevant model, such as dark breathers are briefly discussed

Hyperfine-interaction- and magnetic-field-induced Bose-Einstein-statistics suppressed two-photon transitions

Two-photon transitions between atomic states of total electronic angular momentum $J_a=0$ and $J_b=1$ are forbidden when the photons are of the same energy. This selection rule is analogous to the Landau-Yang theorem in particle physics that forbids decays of vector particle into two photons. It arises because it is impossible to construct a total angular momentum $J_{2\gamma}=1$ quantum-mechanical state of two photons that is permutation symmetric, as required by Bose-Einstein statistics. In atoms with non-zero nuclear spin, the selection rule can be violated due to hyperfine interactions. Two distinct mechanisms responsible for the hyperfine-induced two-photon transitions are identified, and the hyperfine structure of the induced transitions is evaluated. The selection rule is also relaxed, even for zero-nuclear-spin atoms, by application of an external magnetic field. Once again, there are two similar mechanisms at play: Zeeman splitting of the intermediate-state sublevels, and off-diagonal mixing of states with different total electronic angular momentum in the final state. The present theoretical treatment is relevant to the ongoing experimental search for a possible Bose-Einstein-statistics violation using two-photon transitions in barium, where the hyperfine-induced transitions have been recently observed, and the magnetic-field-induced transitions are being considered both as a possible systematic effect, and as a way to calibrate the measurement