Resonance Spikes Research Articles

Multiple-Objective Control Scheme for Input-Series–Output-Series LCL-Filtered Grid-Connected Inverter System

An input-series–output-series inverter system is suitable for the large-capacity high-voltage ac power applications. If such a combined system comprising a number of small-capacity inverters is utilized in the high-power grid-connected power generation to replace a single high-capacity inverter, the voltage stress of the module would be greatly reduced. Additionally, the reliability of the whole grid-connected system could be effectively heightened owning to its flexible assembled-connection architecture. The principal issues for this grid-connected combined system touch upon multiple control objectives, including power balance, high power factor of the grid current, suppression of LCL resonance spike, and redundant operation of the system. Above all, the control variables are attentively screened to obtain a concise scheme to achieve the first three fundamental demands. Furthermore, the control units are dispersed into each module and a hot-swap technique is proposed to actualize the last objective, acquiring the superior reliability of the system. Finally, a three-module prototype is fabricated and the experimental results verify the effectiveness of the proposed strategy.

Monte Carlo studies on neutron interactions in radiobiological experiments.

Monte Carlo method was used to study the characteristics of neutron interactions with cells underneath a water medium layer with varying thickness. The following results were obtained. (1) The fractions of neutron interaction with 1H, 12C, 14N and 16O nuclei in the cell layer were studied. The fraction with 1H increased with increasing medium thickness, while decreased for 12C, 14N and 16O nuclei. The bulges in the interaction fractions with 12C, 14N and 16O nuclei were explained by the resonance spikes in the interaction cross-section data. The interaction fraction decreased in the order: 1H > 16O > 12C > 14N. (2) In general, as the medium thickness increased, the number of “interacting neutrons” which exited the medium and then further interacted with the cell layer increased. (3) The area under the angular distributions for “interacting neutrons” decreased with increasing incident neutron energy. Such results would be useful for deciphering the reasons behind discrepancies among existing results in the literature.

Tunneling spectroscopy and Josephson current of superconductor-ferromagnet hybrids on the surface of a 3D TI

We investigate the charge transport property of superconductor (S)/normal metal (N)/ ferromagnet insulator (FI)/(normal metal) N’ and S/N/FI/N’/S Josephson junctions on a three-dimensional topological insulator surface. We find the asymmetric local density of states (LDOSs) in a S/N/FI/N’ junction and show that the N interlayer gives rise to subgap resonant spikes in the differential conductance and LDOSs. In a S/N/FI/N’/S junction, the Josephson current shows a non-sinusoidal current-phase relation and the N (or N’) interlayer decreases the magnitude of the critical current monotonically.

HARBOUR RESONANCE UNDER IMPACT OF POWERFUL TSUNAMI

The powerful tsunami events caused by Feb. 27th, 2010 Chilean earthquake and Mar. 11th, 2011 Tohoku earthquake lead to the revelation of influence of tide level change in harbour oscillation. During a long time span of harbour excitement, the ocean surface will shift up and down, which, through dispersion relationship, makes the primary resonant mode to appear in various resonant spikes in the spectral density distribution. For the time domain analysis, the present paper uses the numerical model of the improved formula of Peregrine’s Boussinesq-type equations to study the oscillation properties of three harbours in California with five representative tide levels. By white-noise analysis, the result of present paper in time domain is cross checked with earlier studies in frequency domain, and the effect of fluctuating tide level and the corresponding change of harbour layout is ascertained.

Detecting Rotating Stall Precursors in Axial Compressors via Perturbations Part 1: Theory

The nonlinear dynamics of fluid instabilities such as rotating stall and surge in axial compressors are typically modeled as subcritical Hopf bifurcations with hysteresis. In this paper, nonlinear dynamical systems with subcritical Hopf bifurcations under periodic forcing are analyzed, and the theoretic results are applied to prediction of rotating stall precursors. Depending on the forcing amplitude and frequency, there are possibly two types of features for the periodic solutions as the bifurcation parameter approaches the critical values. For the first type, the sensitivity of the amplitude of the periodic orbits to the bifurcation parameter becomes infinitely large while the amplitude itself remains finite, which corresponds to the double-cycle bifurcation of the periodic orbits, whereas, in the second case, though the sensitivity is not as steep, there are secondary resonant peaks in the power spectrum in addition to those of the multiples of periodic orbits. These secondary resonant spikes correspond to the Neimark–Sacker bifurcation of periodic orbits, which typically leads to quasi-periodic orbits. These two types of prominent features can serve as precursors to subcritical Hopf bifurcations. The theoretic results are applied to the Moore–Greizter model for rotating stall in axial compressors. In the second part of the paper, experiments are carried out on a single-stage low-pressure axial compressor with inlet circumferential distortions, and it is demonstrated that the theory can yield identification of rotating stall precursors much earlier than the case without distortions.

Off-resonance magnetoresistance spike in irradiated ultraclean 2D electron systems

We report on the theoretical studies of a recently discovered strong radiation-induced magnetoresistance spike obtained in ultraclean two-dimensional electron systems at low temperatures. The most striking feature of this spike is that it shows up on the second harmonic of the cyclotron resonance. We apply the radiation-driven electron orbits model in the ultraclean scenario. Accordingly, we calculate the new average advanced distance by the electron in a scattering event which will define the unexpected resonance spike position. Calculated results are in good agreement with experiments.

Microwave‐induced off‐resonance giant magnetoresistance in ultraclean two‐dimensional electron systems

AbstractWe report on theoretical studies of a recently discovered strong radiation‐induced magnetoresistance spike obtained in ultraclean two‐dimensional electron systems at low temperatures. The most striking feature of this strong spike is that it shows up on the second harmonic of the cyclotron resonance. We apply the radiation‐driven electron orbits model in the ultraclean scenario. We calculate the new average advanced distance by the electron in a scattering event which will define the unexpected resonance spike position. Calculated results are in good agreement with experiments. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A Universal Grid-Connected Fuel-Cell Inverter for Residential Application

This paper describes a universal fuel-cell-based grid-connected inverter design with digital-signal-processor-based digital control. The inverter has a direct power conversion mechanism with a high-frequency zero-voltage-switched dc/ac primary-side converter followed by a pair of ac/ac cycloconverters that operates either in parallel or in series to simultaneously address the issues of universal output and high efficiency. The critical design issues focus on the impact and optimization of transformer leakage inductance with regard to effectiveness of zero voltage switching of a primary-side converter, duty-cycle loss, resonance, and voltage spike that has effect on the breakdown voltage rating of the cycloconverter devices. An additional concept of dynamic transformer tapping has been explored to address the impact of varying input voltage on secondary-side voltage spike and inverter efficiency. Finally, detailed grid-parallel and grid-connected results are presented that demonstrate satisfactory inverter performances.

Coherent quantum phenomena in mesoscopic metallic conductors (Review Article)

Quantum coherent phenomena in mesoscopic cylindrical metallic conductors are examined. When pure doubly- and singly-connected normal samples are placed in a longitudinal magnetic field, interference phenomena occur which depend on the magnetic flux through the cross-section of the conductor. The period of the induced oscillations is given by the quantum of flux, hc∕e, of the normal metal. Quantum states are formed in these structures by electron collisions with the dielectric boundary of the sample. The magnetic flux is included in the expression for the quasiparticle spectrum. The proximity effect and its influence on the spectrum of quantum coherent phenomena is investigated. The behavior of cylindrical samples consisting of a superconducting (S) metal with a deposited thin pure normal (N) metal layer is analyzed. In these structures, electrons are localized in a well bounded by a dielectric on one side and by a superconductor on the other. The resulting quantized Andreev levels have the feature that in a varying field H (or temperature T) each of the levels in the well can coincide periodically with the chemical potential of the metal. As a result, the state of the system has a strong degeneracy and the density of states exhibits resonance spikes as a function of the energy of the NS sample. This makes a significant contribution to the magnetic moment. A theory of the reentrant effect for NS structures has been developed for interpreting the anomalous behavior of the magnetic susceptibility of these structures as a function of magnetic field and temperature.

On existence of a paramagnetic contribution to the susceptibility of a mesoscopic cylindrical normal metal–superconductor structure

The density of states N(ε) of a mesoscopic cylindrical structure consisting of a normal pure metal and a superconductor is calculated using the Gorkov–Green functions. It is shown that magnetic fluxes of certain values cause resonance spikes of N(ε), suggesting a large-amplitude paramagnetic contribution which accounts for the reentrant effect detected by P. Visani, A. C. Mota, and A. Pollini, Phys. Rev. Lett. 65, 1514 (1990).

Sharpened Aharanov-Bohm oscillations near resonance in a balanced ring with double quantum dots

In a balanced Aharonov-Bohm ring with an identical quantum dot (QD) in each arm, the transmission amplitude near resonance consists of a zero and pole which can be made to nearly or exactly overlap in the complex-energy plane. This presents a sensitively balanced region of parameter space in which arbitrarily sharp transmission resonance spikes manifest. Analytical results based on a tight-binding solution of the Schrodinger Equation for this system demonstrate the extreme flux sensitivity of the balanced ring in the vicinity of the resonance near the quasi-bound state energy of the QD’s. This effect may have practical applications as a sensitive monitor of magnetic flux.

The theory of the reentrant effect in susceptibility of cylindrical mesoscopic samples

A theory has been developed to explain the anomalous behavior of the magnetic susceptibility of a normal metal–superconductor (NS) structure in weak magnetic fields at millikelvin temperatures. The effect was discovered experimentally [A. C. Mota et al., Phys. Rev. Lett. 65, 1514 (1990)]. In cylindrical superconducting samples covered with a thin normal pure metal layer, the susceptibility exhibited a reentrant effect: it started to increase unexpectedly when the temperature was lowered below 100mK. The effect was observed in mesoscopic NS structures when the N and S metals were in good electric contact. The theory proposed is essentially based on the properties of the Andreev levels in the normal metal. When the magnetic field (or temperature) changes, each of the Andreev levels coincides from time to time with the chemical potential of the metal. As a result, the state of the NS structure experiences strong degeneracy, and the quasiparticle density of states exhibits resonance spikes. This generates a large paramagnetic contribution to the susceptibility, which adds to the diamagnetic contribution, thus leading to the reentrant effect. The explanation proposed was obtained within the model of free electrons. The theory provides a good description of the experimental results.

Herpes simplex encephalitis: Adolescents and adults

Herpes simplex encephalitis (HSE) remains one of the most devastating infections of the central nervous system despite available antiviral therapy. Children and adolescents account for approximately one third of all cases of HSE. Clinical diagnosis is suggested in the encephalopathic, febrile patient with focal neurologic signs. However, these clinical findings are not pathognomonic because numerous other diseases in the central nervous system can mimic HSE. Neurodiagnostic evaluation can provide support for the diagnosis by the demonstration of temporal lobe edema/hemorrhage by magnetic resonance image scan and spike and slow-wave activity on electroencephalogram. In the current era, the diagnostic gold standard is the detection of herpes simplex virus (HSV) DNA in the cerebrospinal fluid by polymerase chain reaction (PCR). Although PCR is an excellent test and preferable to brain biopsy, false negatives can occur early after disease onset. Acyclovir is the treatment of choice and is administered at 10 mg/kg every 8 h for 21 days. Even with early administration of therapy after the disease onset, nearly two thirds of survivors have significant residual neurologic deficits. Current investigative efforts are assessing the prognostic value of quantitative PCR detection of viral DNA at the onset of therapy as well as at the completion of therapy and the contribution of prolonged antiviral therapy to improved neurologic outcome.

Herpes simplex: Encephalitis children and adolescents

Herpes simplex encephalitis (HSE) remains one of the most devastating infections of the central nervous system despite available antiviral therapy. Children and adolescents account for approximately one third of all cases of HSE. Clinical diagnosis is suggested in the encephalopathic, febrile patient with focal neurologic signs. However, these clinical findings are not pathognomonic because numerous other infections in the central nervous system can mimic HSE. Support for the diagnosis from a neurodiagnostic perspective is aided by the demonstration of disease of the temporal lobe by magnetic resonance image scan and spike and slow-wave activity on electroencephalogram. In the current era, the gold standard for establishing diagnosis is the detection of herpes simplex virus DNA in the cerebrospinal fluid by polymerase chain reaction (PCR). Although PCR is an excellent test and far more desirable than brain biopsy, false negatives can occur early after disease onset. Current therapeutic management calls for the administration of acyclovir at 10 mg/kg every 8 hours for 21 days. Even with early administration of therapy after the onset of disease, nearly two thirds of survivors will have significant residual neurologic deficits. Recent investigative efforts are assessing the value of PCR detection of viral DNA at the completion of therapy and the value of prolonged antiviral therapy.

Resonant Spikes of the Nuclear Spin Qubits Relaxation Rate in Quantum-Hall Systems With Magnetic Impurities

The magnetic field dependence of the local phononassisted nuclear spin qubit relaxation rate in 2DES with magnetic impurities is studied theoretically. For weak and strong scattering limits under a strong magnetic field, we show that the magnetic field dependence of T/sub 1//sup -1/ exhibits giant spikes, due to the energy matching of the electron Zeeman splitting with the energy spacing between the vibrational mode energies. The localized mode is created by the lattice distortion around the impurity. This resonance phenomenon could be used as a local probe for studying the localized vibrational modes and their coupling to electrons and for the resonant manipulation of the nuclear spin qubits.

Retrieval of in situ electron density in the topside ionosphere from cosmic radio noise intensity by an artificial neural network

An artificial neural network (ANN) is applied to retrieve electron density at satellite height from cosmic radio noise measurements made near the plasma cutoff frequency in the topside ionosphere. Observations were made using the topside sounder on board the Ionosphere Sounding Satellite launched in 1978. The automatic gain control voltage of the sounder receiver supplied information on the spectrum of cosmic radio noise intensity. Local electron densities, which are the target of the ANN, were scaled from the plasma resonance spikes and the echo traces in the ionogram for several passes. Each pass contained about 100 frames of ionograms; it is not a very easy task to scale the local plasma parameters by an eyeball judgment for all passes. With the aid of a neural network application, we determined the in situ electron density for about 150,000 ionograms. The results were applied to global ionospheric mapping.

Anomalies in the decay rates of antiprotonic helium-atom states

Six resonance transitions of the antiprotonic helium atom in helium gas at densities of $3\ifmmode\times\else\texttimes\fi{}{10}^{20}--3\ifmmode\times\else\texttimes\fi{}{10}^{21} {\mathrm{cm}}^{\ensuremath{-}3}$ were studied at the antiproton decelerator (AD) of CERN. The decay rates of the daughter states of these transitions were determined either from the time distributions of the resonance spikes or from the widths of the resonance lines. Whereas most of the observed decay rates agree with theoretical calculations of Auger rates, two states, $(n,l)=(37,33)$ and (32,31), were found to have decay rates two orders of magnitude larger than predicted by these calculations. The effect of coupling with near-lying electron-excited states is considered to be the reason for the anomaly of the (37, 33) state, as pointed out by Kartavtsev et al. [Phys. Rev. A $61,$ 062507 (2000)].

Coherent quantum phenomena in a normal cylindrical conductor with a superconducting coating

The thermodynamic properties of a mesoscopic-size, simply connected cylindrical normal metal in good metallic contact with superconducting banks are studied theoretically. It is commonly accepted that if the superconductor thickness is quite small (of the order of the coherence length), as is assumed to be the case here, a vector potential field, whose value can be varied, exists inside the normal layer. It is further assumed that the quasiparticles with energy E<Δ (2Δ is the superconducting gap) move ballistically through the normal metal and undergo Andreev scattering caused by the off-diagonal potential of the superconductor. An equation is obtained within the multidimensional quasiclassical method which permits us to determine the spectrum of the Andreev levels and to calculate the density of states of the system in question. It is shown that the Andreev levels shift as the trapped flux Φ changes inside the normal conductor. At a certain flux value they coincide with the Fermi level. A resonance spike in the density of states ν(E) appears in this case, since near E=0 there is strong degeneracy of the quasiparticle states in respect to the quantum number q characterizing their motion along the cylinder axis. As a result, a macroscopic number of q states contribute to the amplitude of the effect. As the flux is increased, the density of states v(E) behaves as a stepwise function of Φ. The distance between the steps is equal to the superconducting flux quantum hc/2e.

Ion channeling phenomena and Tl-upd induced film dynamics in model biomembranes studied with EQCN and QCI techniques

The electrochemical behavior of bilayer lipid films ( l-α-dipalmitoyl phosphatidyl choline, DPPC) on Au electrodes was investigated using the electrochemical quartz crystal nanobalance (EQCN) and quartz crystal immittance (QCI) techniques. The bilayer DPPC film was modified with ion channel forming molecules of gramicidin (GR) permeable to Tl + ions. The QCI measurements have shown that a DPPC BLM/GR film on a Au electrode is in the solid state at room temperature and behaves as a perfectly rigid film. In the potential step chronopiezogravimetric experiments, it has been found that Tl atoms are being deposited at the Au ∣ lipid film interface and form a Tl-upd interlayer. Sharp resonant frequency spikes, associated with Tl-upd formation and dissolution, were discovered. The evaluation of mechanistic models of the processes taking place during the negative potential step, indicates an intermediate phase formation, involving aggregation of lipid molecules in the electrode sub-surface region, followed by a collapse of aggregates and formation of a new bilayer lipid film on the Tl-upd surface. The formation of lipid aggregates was not observed when only 3D-Tl had been formed or dissolved. Model calculations confirm that the formation of cylindrical non-overlapping DPPC BLM aggregates can result in trapping of sufficient amounts of solvent and this process can account for the observed frequency down-shifts. The Tl-upd induced lipid film lifting and intermediate lipid aggregation were observed only in potential step experiments and, thus, represent a dynamic transition phenomenon. In contrast to this, in the potential scan piezogravimetric experiments, where the film reorganization due to the changing substrate (from Au to Tl-upd) progresses at a slower rate, no lipid aggregation was observed.

Nonlinear dynamic effects in a two-wave CO2 laser

Theoretical and experimental investigations were made of nonlinear dynamic regimes of the operation of a two-wave CO2 laser with cw excitation in an electric discharge and loss modulation in one of the channels. Nonlinear amplitude — frequency characteristics of each of the laser channels have two low-frequency resonance spikes, associated with forced linear oscillations of two coupled oscillators, and high-frequency spikes, corresponding to doubling of the period of the output radiation oscillations. At low loss-modulation frequencies the intensity oscillations of the output radiation in the coupled channels are in antiphase, whereas at high modulation frequencies the dynamics is cophasal. Nonlinear dynamic effects, such as doubling of the period and of the repetition frequency of the pulses and chaotic oscillations of the output radiation intensity, are observed for certain system parameters.