Comment on "Existence of Internal Modes of Sine-Gordon Kinks"

In Ref.[1] [Phys. Rev. B. {\bf 42}, 2290 (1990)] we used a rigorous projection operator collective variable formalism for nonlinear Klein-Gordon equations to prove the continuum Sine-Gordon (SG) equation has a long lived quasimode whose frequency $\omega_s$= 1.004 $\Gamma_0$ is in the continuum just above the lower phonon band edge with a lifetime ($1/\tau_s$) = 0.0017 $\Gamma_0$. We confirmed the analytic calculations by simulations which agreed very closely with the analytic results. In Ref.[3] [Phys. Rev. E. {\bf 62}, R60 (2000)] the authors performed two numerical investigations which they asserted ``show that neither intrinsic internal modes nor quasimodes exist in contrast to previous results.'' In this paper we prove their first numerical investigation could not possibly observe the quasimode in principle and their second numerical investigation actually demonstrates the existence of the SG quasimode. Our analytic calculations and verifying simulations were performed for a stationary Sine-Gordon soliton fixed at the origin. Yet the authors in Ref.[3] state the explanation of our analytic simulations and confirming simulations are due to the Doppler shift of the phonons emitted by our stationary Sine-Gordon soliton which thus has a zero Doppler shift.Comment: 5 pages, submitted to Phys. Rev.

Localized Excitations in two-dimensional Hamiltonian Lattices

We analyze the origin and features of localized excitations in a discrete two-dimensional Hamiltonian lattice. The lattice obeys discrete translational symmetry, and the localized excitations exist because of the presence of nonlinearities. We connect the presence of these excitations with the existence of local integrability of the original N degree of freedom system. On the basis of this explanation we make several predictions about the existence and stability of these excitations. This work is an extension of previously published results on vibrational localization in one-dimensional nonlinear Hamiltonian lattices (Phys.Rev.E.49(1994)836). Thus we confirm earlier suggestions about the generic property of Hamiltonian lattices to exhibit localized excitations independent on the dimensionality of the lattice.Comment: LaTeX,20 pages, 11 figures available upon request, Phys.Rev.E accepted for publicatio

Experimental study of noise reduction for an unstiffened cylindrical model of an airplane fuselage

Noise reduction measurements were made for a simplified model of an airplane fuselage consisting of an unstiffened aluminum cylinder 0.5 m in diameter by 1.2 m long with a 1.6-mm-thick wall. Noise reduction was first measured with a reverberant field pink-noise load on the cylinder exterior. Next, noise reduction was measured by using a propeller to provide a more realistic noise load on the cylinder. Structural resonance frequencies and acoustic reverberation times for the cylinder interior volume were also measured. Comparison of data from the relatively simple test using reverberant-field noise with data from the more complex propeller-noise tests indicates some similarity in both the overall noise reduction and the spectral distribution. However, all of the test parameters investigated (propeller speed, blade pitch, and tip clearance) had some effect on the noise-reduction spectra. Thus, the amount of noise reduction achieved appears to be somewhat dependent upon the spectral and spatial characteristics of the flight conditions. Information is also presented on cyclinder resonance frequencies, damping, and characteristics of propeller-noise loads

Geometric efficiency of an electroformed nickel solar concentrator

Geometric efficiency of electroformed paraboloidal nickel solar energy concentrator calculated from optical ray trace dat

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EMC/FDTD/MD simulation of carrier transport and electrodynamics in two-dimensional electron systems

We present the implementation and application of a multiphysics simulation technique to carrier dynamics under electromagnetic excitation in supported two-dimensional electronic systems. The technique combines ensemble Monte Carlo (EMC) for carrier transport with finite-difference time-domain (FDTD) for electrodynamics and molecular dynamics (MD) for short-range Coulomb interactions among particles. We demonstrate the use of this EMC/FDTD/MD technique by calculating the room-temperature dc and ac conductivity of graphene supported on SiO2.Comment: Part of JCEL special issue on Multiscale and Multiphysics Modelin

Dynamics of Labor Demand: Evidence from Plant-level Observations and Aggregate Implications

This paper studies the dynamics of labor demand at the plant and aggregate levels. The correlation of hours and employment growth is negative at the plant level and positive in aggregate time series. Further, hours and employment growth are about equally volatile at the plant level while hours growth is much less volatile than employment growth in the aggregate data. Given these differences, we specify and estimate the parameters of a plant-level dynamic optimization problem using simulated method of moments to match plant-level observations. Our findings indicate that non-convex adjustment costs are critical for explaining plant-level moments on hours and employment. Aggregation generates time series implications which are broadly consistent with observation. Further, we find that a model with quadratic adjustment costs alone can also broadly match the aggregate facts.