The Zero-n Gap Soliton

Periodic structures consisting of alternating layers of positive index and negative index materials possess a novel band gap at the frequency at which the average refractive index is zero. We show that in the presence of a Kerr nonlinearity, this zero-n gap can switch from low transmission to a perfectly transmitting state, forming a nonlinear resonance or gap soliton in the process. This zero-n gap soliton is omnidirectional in contrast to the usual Bragg gap soliton of positive index periodic structure

Surface polaritons on left-handed cylinders: A complex angular momentum analysis

We consider the scattering of electromagnetic waves by a left-handed cylinder -- i.e., by a cylinder fabricated from a left-handed material -- in the framework of complex angular momentum techniques. We discuss both the TE and TM theories. We emphasize more particularly the resonant aspects of the problem linked to the existence of surface polaritons. We prove that the long-lived resonant modes can be classified into distinct families, each family being generated by one surface polariton propagating close to the cylinder surface and we physically describe all the surface polaritons by providing, for each one, its dispersion relation and its damping. This can be realized by noting that each surface polariton corresponds to a particular Regge pole of the $S$ matrix of the cylinder. Moreover, for both polarizations, we find that there exists a particular surface polariton which corresponds, in the large-radius limit, to the surface polariton which is supported by the plane interface. There exists also an infinite family of surface polaritons of whispering-gallery type which have no analogs in the plane interface case and which are specific to left-handed materials.Comment: published version. v3: reference list correcte

Negative diffraction pattern dynamics in nonlinear cavities with left-handed materials

We study a ring cavity filled with a slab of a right-handed material and a slab of a left-handed material. Both layers are assumed to be nonlinear Kerr media. First, we derive a model for the propagation of light in a left-handed material. By constructing a mean-field model, we show that the sign of diffraction can be made either positive or negative in this resonator, depending on the thicknesses of the layers. Subsequently, we demonstrate that the dynamical behavior of the modulation instability is strongly affected by the sign of the diffraction coefficient. Finally, we study the dissipative structures in this resonator and reveal the predominance of a two-dimensional up-switching process over the formation of spatially periodic structures, leading to the truncation of the homogeneous hysteresis cycle.Comment: 8 pages, 5 figure

Amplification of evanescent waves in a lossy left-handed material slab

We carry out finite-difference time-domain (FDTD) simulations, with a specially-designed boundary condition, on pure evanescent waves interacting with a lossy left-handed material (LHM) slab. Our results provide the first full-wave numerical evidence for the amplification of evanescent waves inside a LHM slab of finite absorption. The amplification is due to the interactions between the evanescent waves and the coupled surface polaritons at the two surfaces of the LHM slab and the physical process can be described by a simple model.Comment: 4 pages, 2 figure

Abnormal phenomena in a one-dimensional periodic structure containing left-handed materials

The explicit dispersion equation for a one-dimensional periodic structure with alternative layers of left-handed material (LHM) and right-handed material (RHM) is given and analyzed. Some abnormal phenomena such as spurious modes with complex frequencies, discrete modes and photon tunnelling modes are observed in the band structure. The existence of spurious modes with complex frequencies is a common problem in the calculation of the band structure for such a photonic crystal. Physical explanation and significance are given for the discrete modes (with real values of wave number) and photon tunnelling propagation modes (with imaginary wave numbers in a limited region).Comment: 10 pages, 4 figure

Carrier capture processes in strain-induced InxGa1-xAs/GaAs quantum dot structures

We investigate carrier capture processes in strain-induced quantum dot structures. The quantum dots consist of a near-surface InGaAs/GaAs quantum well in which a lateral confining potential is generated by the strain from InP stressor islands grown on the sample surface. Using photoluminescence spectroscopy, we show that the rate of carrier capture into the quantum dots increases dramatically when the energetic depth of the confinement potential is reduced by enlarging the quantum well/surface separation D. While carriers in the quantum well region between the quantum dots are found to experience D-dependent nonradiative surface recombination, this process seems to be negligible for carriers in the quantum dots, presumably due to the protecting InP islands.Peer reviewe

Green's function for metamaterial superlens: Evanescent wave in the image

We develop a new method to calculate the evanescent wave, the subdivided evanescent waves (SEWs), and the radiative wave, which can be obtained by separating the global field of the image of metamaterial superlens. The method is based on Green's function, and it can be applied in other linear systems. This study could help us to investigate the effect of evanescent wave on metamaterial superlens directly, and give us a new way to design new devices.Comment: 15 pages, 3 figure

Self-induced and induced transparencies of two-dimensional and three- dimensional superlattices

The phenomenon of transparency in two-dimensional and three-dimensional superlattices is analyzed on the basis of the Boltzmann equation with a collision term encompassing three distinct scattering mechanisms (elastic, inelastic and electron-electron) in terms of three corresponding distinct relaxation times. On this basis, we show that electron heating in the plane perpendicular to the current direction drastically changes the conditions for the occurrence of self-induced transparency in the superlattice. In particular, it leads to an additional modulation of the current amplitudes excited by an applied biharmonic electric field with harmonic components polarized in orthogonal directions. Furthermore, we show that self-induced transparency and dynamic localization are different phenomena with different physical origins, displaced in time from each other, and, in general, they arise at different electric fields.Comment: to appear in Physical Review

Effectiveness of an evidence-based chiropractic continuing education workshop on participant knowledge of evidence-based health care

BACKGROUND: Chiropractors must continue to learn, develop themselves professionally throughout their careers, and become self-directed and lifelong learners. Using an evidence-based approach increases the probability of optimal patient outcomes. But most chiropractors lack knowledge and interest in evidence-based approaches. The purpose of this study was to develop and measure the effectiveness of evidence-based training for chiropractic practitioners in a continuing education setting. METHODS: We developed and evaluated a continuing education workshop on evidence-based principles and methods for chiropractic practitioners. Forty-seven chiropractors participated in the training and testing. The course consisted of 12.5 hours of training in which practitioners learned to develop focused questions, search electronic data bases, critically review articles and apply information from the literature to specific clinical questions. Following the workshop, we assessed the program performance through the use of knowledge testing and anonymous presentation quality surveys. RESULTS: Eighty-five percent of the participants completed all of the test, survey and data collection items. Pretest knowledge scores (15-item test) were low (47%). Post intervention scores (15-item test) improved with an effect size of 2.0. A 59-item knowledge posttest yielded very good results (mean score 88%). The quality of presentation was rated very good, and most participants (90%) would "definitely recommend" or "recommend" the workshop to a colleague. CONCLUSION: The results of the study suggest that the continuing education course was effective in enhancing knowledge in the evidence-based approach and that the presentation was well accepted

Do multiple outcome measures require p-value adjustment?

BACKGROUND: Readers may question the interpretation of findings in clinical trials when multiple outcome measures are used without adjustment of the p-value. This question arises because of the increased risk of Type I errors (findings of false "significance") when multiple simultaneous hypotheses are tested at set p-values. The primary aim of this study was to estimate the need to make appropriate p-value adjustments in clinical trials to compensate for a possible increased risk in committing Type I errors when multiple outcome measures are used. DISCUSSION: The classicists believe that the chance of finding at least one test statistically significant due to chance and incorrectly declaring a difference increases as the number of comparisons increases. The rationalists have the following objections to that theory: 1) P-value adjustments are calculated based on how many tests are to be considered, and that number has been defined arbitrarily and variably; 2) P-value adjustments reduce the chance of making type I errors, but they increase the chance of making type II errors or needing to increase the sample size. SUMMARY: Readers should balance a study's statistical significance with the magnitude of effect, the quality of the study and with findings from other studies. Researchers facing multiple outcome measures might want to either select a primary outcome measure or use a global assessment measure, rather than adjusting the p-value