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Two-dimensional frequency domain modeling of lightning EMP-induced perturbations to VLF transmitter signals
No full textThe lightning electromagnetic pulse creates observable modifications to the overlying D region ionosphere, exhibited optically as elves. Recent work, both experimental and theoretical, has shown that elves are accompanied by considerable electron density disturbances of up to a factor of 2 increase in local density. We investigate the possibility that these density disturbances are observed by subionospheric VLF transmitter signals as the so-called early VLF events. We use a finite difference frequency domain model to simulate the VLF transmitter signal propagating subionospherically to a VLF receiver, under ambient conditions and through a disturbed region. We show that modeled electron density disturbances, consistent with optical observations of elves, yield small but detectable perturbations to the VLF transmitter signal and may explain at least some observed early VLF events. We further show that sequences of in-cloud lightning pulses, as in spider lightning, may yield considerably higher density disturbances and similarly more prominent VLF transmitter perturbations. In this way, the model herein supports previously reported correlations between sferic bursts and early VLF events
Low cost flatbed scanner label-free biosensor
No full textIn this paper, we demonstrate utilization of a commercial flatbed document scanner as a label-free biosensor for high-throughput imaging of DNA and protein microarrays. We implemented an interferometric sensing technique through use of a silicon/oxide layered substrate, and easy to implement hardware modifications such as re-aligning moving parts and inserting a custom made sample plate. With a cost as low as 100USD, powered by a USB cable, and scan speed of 30 seconds for a 4mm x 4 mm area with similar to 10 mu m lateral resolution, the presented system offers a super low cost, easy to use alternative to commercially available label-free systems
Semiconductor and dielectric microspheres for optoelectronic applications
No full textMicrospheres possess high quality factor morphology-dependent resonances, i.e., whispering gallery modes. These resonances have narrow linewidths necessary for applications to compact optoelectronic devices for wavelength division multiplexing. The morphology dependent resonances have high quality factors of 104 and 105 with channel spacings of 0.14 nm in glass and 0.05 nm in silicon microspheres
Dynamical analysis of a weakly coupled nonlinear dielectric waveguide: surface-plasmon model as another type of Josephson junction
No full textWe propose that a weakly coupled nonlinear dielectric waveguide surface-plasmon system can be formulated as another type of Josephson junction. Such a system can be realized along a metal-dielectric interface where the dielectric medium hosts a nonlinear waveguide (e.g., fiber) for soliton propagation. We demonstrate that the system is in close analogy to the bosonic Josephson junction of atomic condensates at very low temperatures, yet exhibits different dynamical features. In particular, the inherently dynamic coupling parameter between soliton and surface plasmon generates self-trapped oscillatory states at nonzero fractional populations with zero and p time-averaged phase difference. The salient features of the dynamics are presented in the phase space
Structure and dynamics of ion clusters in linear octupole traps: phase diagrams, chirality, and melting mechanisms
No full textThe stable structures and melting dynamics of clusters of identical ions bound by linear octupole radiofrequency traps are theoretically investigated by global optimization methods and molecular dynamics simulations. By varying the cluster sizes in the range of 10-1000 ions and the extent of trap anisotropy by more than one order of magnitude, we find a broad variety of stable structures based on multiple rings at small sizes evolving into tubular geometries at large sizes. The binding energy of these clusters is well represented by two contributions arising from isotropic linear and octupolar traps. The structures generally exhibit strong size effects, and chiral arrangements spontaneously emerge in many crystals. Sufficiently large clusters form nested, coaxial tubes with different thermal stabilities. As in isotropic octupolar clusters, the inner tubes melt at temperatures that are lower than the overall melting point
Chaotic spin correlations in frustrated Ising hierarchical lattices
No full textSpin-spin correlations are calculated in frustrated hierarchical Ising models that exhibit chaotic renormalization-group behavior. The spin-spin correlations, as a function of distance, behave chaotically. The far correlations, but not the near correlations, are sensitive to small changes in temperature or frustration, with temperature changes having a larger effect. On the other hand, the calculated free energy, internal energy, and entropy are smooth functions of temperature. The recursion-matrix calculation of thermodynamic densities in a chaotic band is demonstrated. The leading Lyapunov exponents are calculated as a function of frustration
Unidirectional reflectionlessness and invisibility in the TE and TM modes of a PT-symmetric slab system
No full textUnidirectional invisibility of a PT-symmetric optical system is of great interest, but challenging as well since it is infeasible to fulfill it through wide optical frequency ranges in all angular directions. Accordingly we study reflectionless and invisible patterns in the TE and TM modes of an optical slab system consisting of an adjacent or separated pair of balanced gain and loss layers with a gap. We provide a comprehensive study of one of the simplest experimentally accessible examples of a unidirectionally reflectionless and invisible PT-symmetric optical slab system. We obtain the physically optimal conditions for the realization of these phenomena. We derive analytic expressions, and show that only certain gain amounts restricted to take values between certain minimum and maximum values give rise to uni- or bidirectionally invisible configurations. The size of gap decides the measure of reflectionlessness and invisibility parameters, especially on gain value and incident angle
Effects of dilute Zn impurities on the uniform magnetic susceptibility of YBa2Cu3O7-δ
No full textThe effects of dilute Zn impurities on the uniform magnetic susceptibility are calculated in the normal metallic state for a model of the spin fluctuations of the layered cuprates. It is shown that scatterings from extended impurity potentials can lead to a coupling of the q∼ (π, π) and the q∼0 components of the magnetic susceptibility χ(q). Within the presence of antiferromagnetic correlations, this coupling can enhance the uniform susceptibility. The implications of this result for the experimental data on Zn substituted YBa2Cu3O7-δ are discussed
Phase separation and charge-ordered phases of the d=3 Falicov-Kimball model at nonzero temperature: temperature-density-chemical potential global phase diagram from renormalization-group theory
No full textThe global phase diagram of the spinless Falicov-Kimball model in d = 3 spatial dimensions is obtained by renormalization-group theory. This global phase diagram exhibits five distinct phases. Four of these phases are charge-ordered (CO) phases, in which the system forms two sublattices with different electron densities. The CO phases occur at and near half filling of the conduction electrons for the entire range of localized electron densities. The phase boundaries are second order, except for the intermediate and large interaction regimes, where a first-order phase boundary occurs in the central region of the phase diagram, resulting in phase coexistence at and near half filling of both localized and conduction electrons. These two-phase or three-phase coexistence regions are between different charge-ordered phases, between charge-ordered and disordered phases, and between dense and dilute disordered phases. The second-order phase boundaries terminate on the first-order phase transitions via critical endpoints and double critical endpoints. The first-order phase boundary is delimited by critical points. The cross-sections of the global phase diagram with respect to the chemical potentials and densities of the localized and conduction electrons, at all representative interactions strengths, hopping strengths, and temperatures, are calculated and exhibit ten distinct topologies
Axi-dilaton gravity in D >= 4 dimensional space-times with torsion
No full textWe study models of axi-dilaton gravity in space-time geometries with torsion. We discuss conformal rescaling rules in both Riemannian and non-Riemannian formulations. We give static, spherically symmetric solutions and examine their singularity behavior