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Classification of imbalanced data with a geometric digraph family
No full textWe use a geometric digraph family called class cover catch digraphs (CCCDs) to tackle the class imbalance problem in statistical classification. CCCDs provide graph theoretic solutions to the class cover problem and have been employed in classification. We assess the classification performance of CCCD classifiers by extensive Monte Carlo simulations, comparing them with other classifiers commonly used in the literature. In particular, we show that CCCD classifiers perform relatively well when one class is more frequent than the other in a two-class setting, an example of the cl ass imbalance problem. We also point out the relationship between class imbalance and class overlapping problems, and their influence on the performance of CCCD classifiers and other classification methods as well as some state-of-the-art algorithms which are robust to class imbalance by construction. Experiments on both simulated and real data sets indicate that CCCD classifiers are robust to the class imbalance problem. CCCDs substantially undersample from the majority class while preserving the information on the discarded points during the undersampling process. Many state-of-the-art methods, however, keep this information by means of ensemble classifiers, but CCCDs yield only a single classifier with the same property, making it both appealing and fast
Metallodielectric photonic crystal resonators
No full textA resonator has been manufactured using a photonic crystal at K-u band frequencies. The photonic crystal has a face centered cubic Bravais lattice structure. In the transmission measurements, the photonic crystal displayed a directional bandgap with a lower band edge of 13.0 GHz, an upper band edge of 21.5 GHz, and a center frequency of 17.25 GHz. The corresponding stop bandwidth center frequency ratio is 50%. The maximum rejection at the band center is 35 dB. The unit cell rejection ratio is 7 dB per unit cell. The resonance has a quality factor of 200, and a maximum transmission peak of -5 dB
A MEMS based visible-NIR Fourier transform microspectrometer - art. no. 61860C
No full textDesign, fabrication and characterization of a novel out-of-plane vertical comb-drive actuator based Fourier transform microspectrometer (FTS) is presented. The spectrometer utilizes resonant mode vertical comb actuators as a variable-depth diffraction grating and a single photodetector to monitor the 0th order of the diffraction pattern. The spectrum of the source illuminating the gratings is computed by Fourier transforming the 0th order intensity as a function of the optical path difference. The vertical comb actuators have a travel range of 100 mu m under atmospheric pressure with 28V excitation, which yields a theoretical spectral resolution of 0.5nm in the visible and better than 5nm in the telecom wavelengths
Exact semiclassical evolutions in relativistic and non-relativistic scalar quantum mechanics and quantum cosmology
No full textThe necessary and sufficient conditions for the exactness of the semiclassical approximation for the solution of the Schrodinger and Klein-Gordon equations are obtained, It is shown that the existence of an exact semiclassical solution of the Schrodinger equation determines both the semiclassical wave function and the interaction potential uniquely up to the choice of the boundary conditions. This result also holds for the Klein-Gordon equation. Its implications for the solution of the Wheeler-DeWitt equation for the FRW scalar field minisuperspace models are discussed. In particular, exact semiclassical solutions of the Wheeler-DeWitt equation for the case of massless scalar field and exponential matter potentials are constructed, The existence of exact semiclassical solutions for polynomial matter potentials of the form lambda phi(2p) is also analyzed. It is shown that for p = 1, 2 and 3, right-going semiclassical solutions do not exist, A generalized semiclassical perturbation expansion is also developed which is quite different from the traditional (h) over bar and M-p(-1) expansions. (C) 1998 Published by Elsevier Science B.V
Is weak pseudo-Hermiticity weaker than pseudo-Hermiticity?
No full textFor a weakly pseudo-Hermitian linear operator, we give a spectral condition that ensures its pseudo-Hermiticity. This condition is always satisfied whenever the operator acts in a finite-dimensional Hilbert space. Hence weak pseudo-Hermiticity and pseudo-Hermiticity are equivalent in finite-dimensions. This equivalence extends to a much larger class of operators. Quantum systems whose Hamiltonian is selected from among these operators correspond to pseudo-Hermitian quantum systems possessing certain symmetries
Analysis of magnetospheric ELF/VLF wave amplification from the Siple Transmitter experiment
No full textControlled experiments with dedicated ground-based ELF/VLF (0.3-30 kHz) transmitters are invaluable in investigating nonlinear whistler mode wave-particle interactions in the Earth's magnetosphere. The most productive such experiment operated between 1973 and 1988 near L = 4 at Siple Station, Antarctica. A major effort has been undertaken to digitize and preserve a significant portion of the historical data set from the original magnetic tapes, and we describe here the data set and the processing techniques used to remove artifacts introduced during recording and playback. We analyze a commonly transmitted diagnostic format from 1986 and present statistics on the occurrence and properties of amplified ELF/VLF waves received by a ground-based receiver at the geomagnetic conjugate location to Siple at Lake Mistissini, Quebec. For the interval examined, only 11% of Siple transmissions are successfully received in the conjugate hemisphere with quiet geomagnetic conditions being significantly more conducive to successful reception. The total growth for the events examined is estimated to be 5-40 dB, and nonlinear growth rates are in the range of 20-350 dB/s. The observations show that as the nonlinear growth rate increases, the duration of nonlinear growth decreases. Significant linear correlation is found between the noise floor and the saturation level, with higher noise floors resulting from increases in natural magnetospheric emissions. Finally, we find a lack of correlation between the nonlinear growth rate and the noise, threshold, and saturation levels
Modeling scattering from lightning-induced ionospheric disturbances with the discontinuous Galerkin method
No full textSimulation of the propagation of very low frequency (VLF) waves in the Earth-ionosphere waveguide remains a significant computational challenge as a result of the variable wavelength at these frequencies in the magnetized plasma environment of the lower ionosphere. The discontinuous Galerkin (DG) method is naturally and easily adapted to nonuniform grids and so is ideal for simulation in media where the characteristic length scale varies significantly. We present an automatic procedure based on minimal system realization to incorporate any linear, anisotropic dispersive material in the DG framework, with application to a perfectly matched layer and scattering from strong disturbances in a magnetoplasma. We apply these techniques to modeling of scattering from lightning electromagnetic pulse-induced ionospheric disturbances, calculating the full 3-D scattered VLF wavefields from intense lightning-induced ionospheric perturbations over a large volume. We plot the spatial distribution of the phase and amplitude response as seen by a ground-based receiver over a large area. The results are consistent with previous results from 2-D models, showing maximum received signal strength amplitude perturbations on the order of 0.1 to 0.2 dB for intense vertical discharges under smooth ambient conditions and on the order of 0.5 dB for very intense, repeated horizontal discharges
Neutron production in terrestrial gamma ray flashes
No full textTerrestrial gamma ray flashes (TGFs) are brief bursts of photons with energies up to 20 MeV typically observed in association with lightning. Such energetic photons may undergo photonuclear reactions with nontrivial cross section in the vicinity of the giant dipole resonance. Pulses of neutrons have been observed experimentally in coincidence with lightning, suggesting such reactions are observable. We present simulations of expected photoneutron production based on initial conditions inferred from observations of TGFs. We predict an average of similar to 10(12) neutrons produced per TGF and give energy, time, and space distributions of neutrons produced and neutrons reaching ground and satellite altitude. The simulation results are consistent with some observations and suggest further experiments may be profitable
Quasi-electrostatic whistler mode wave excitation by linear scattering of EM whistler mode waves from magnetic field-aligned density irregularities
No full textRecent observations by Starks et al. (2008) from multiple spacecraft suggest that the actual nighttime intensity of VLF transmitter signals in the radiation belts is approximately 20 dB below the level that is assumed in the model developed by Abel and Thorne (1998) and approximately 10 dB below model values during the day. In the present work, we discuss one experimentally established mechanism which might be responsible for some of this intensity discrepancy, linear mode coupling as electromagnetic whistler mode waves propagate through regions containing small-scale (2-100 m) magnetic field-aligned plasma density irregularities. The scattering process excites quasi-electrostatic whistler mode waves, which represents a power loss for the input waves. Although the distribution and amplitude of the irregularities is not well known at present, we construct plausible models in order to use numerical simulations to determine the characteristics of the mode coupling mechanism and the conditions under which the input VLF waves can lose significant power to the excited quasi-electrostatic whistler mode waves. For short propagation paths of approximately 15 km, the full-wave model predicts power losses ranging from -3 dB (25% probability) to -7 dB (2% probability). For longer propagation paths of approximately 150 km, the full-wave model predicts power losses ranging from -4 dB (25% probability) to over -10 dB (2% probability). We conclude that for the irregularity models investigated, the mode coupling mechanism can result in significant power loss for VLF electromagnetic whistler mode waves
Bioactive ZnO coatings deposited by MAPLE-an appropriate strategy to produce efficient anti-biofilm surfaces
No full textDeposition of bioactive coatings composed of zinc oxide, cyclodextrin and cefepime (ZnO/CD/Cfp) was performed by the Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique. The obtained nanostructures were characterized by X-ray diffraction, IR microscopy and scanning electron microscopy. The efficient release of cefepime was correlated with an increased anti-biofilm activity of ZnO/CD/Cfp composites. In vitro and in vivo tests have revealed a good biocompatibility of ZnO/CD/Cfp coatings, which recommend them as competitive candidates for the development of antimicrobial surfaces with biomedical applications. The release of the fourth generation cephalosporin Cfp in a biologically active form from the ZnO matrix could help preventing the bacterial adhesion and the subsequent colonization and biofilm development on various surfaces, and thus decreasing the risk of biofilm-related infections