Pulse Width Variation Research Articles

Soliton switching in a Kerr coupler with coupling constant dispersion: a variational analysis

Soliton switching in a nonlinear directional coupler (NLDC) with Kerr nonlinearity and coupling constant dispersion (caused by intermodal dispersion between the symmetric and the anti-symmetric modes of the coupler) is studied using the well-known variational method. Switching characteristics are calculated and discussed. It is shown that the switching characteristics of the Kerr coupler for all the pulses, with pulse width ranging from 10 to 100 fs, are identical for a given value of the coupling coefficient. The effect of the coupling coefficient on the critical energy for switching is studied and discussed. The amplitude and pulse width variations inside the coupler are presented, discussed and compared with the result of our numerical calculation of soliton evolution inside the coupler.

Size and geometry of microearthquake seismic ruptures fromPandSpulse width data

SUMMARY We propose a method to estimate the radius, dip and strike of a circular seismic rupture through the inversion of first P- and S-wave pulse widths measured on microearthquake records. The method is based on quite general, numerically calibrated relationships relating source and Q parameters under the assumption that the waves are radiated by a circular crack propagating at a constant rupture velocity. To study the influence of both the source and receiver configuration and the properties of seismic rupture, a detailed resolution study on synthetic data has been carried out. For a microearthquake rupture, the pulse width variations with azimuths depend critically on the fault plane orientation and the resolution on fault angle parameters can be qualitatively assessed by the parameter η, defined as the relative variation of the take-off angles with respect to their average value. A statistical approach based on mapping random deviations on data in the (δ, φ) parameter space has been adopted to quantify the uncertainty affecting the fault plane estimates. The method is applied to estimate the source parameters of an ML = 3.1 event recorded during the 1997 Umbria-Marche earthquake sequence. For the considered event, the fault plane solution is in good agreement with the δ‐φ estimates obtained by the method of the joint inversion of P polarities and S polarizations.

All-optical logic gates with bacteriorhodopsin

Abstract All-optical logic gates with bacteriorhodopsin (bR) protein molecules have been demonstrated based on all-optical switching of a cw probe laser beam by multiple pulsed pump laser beams due to nonlinear intensity-induced excited-state absorption. A cw probe laser beam at 640 nm corresponding to the peak absorption of O-state in the bR photocycle is switched by a pulsed pump laser beam at 570 nm corresponding to the maximum initial B state absorption, at relatively low powers. The switching characteristics have been used to design all-optical NOT and the universal NOR and NAND logic gates and the effect of various parameters such as variation in pump pulse width, pump intensity, lifetime of O state and absorption cross-section of the B state at probe wavelength on the switching characteristics has been analyzed.

Fuzzy systems to process ECG and EEG signals for quantification of the mental workload

In this paper, we analyze the ECG and EEG signals by using a set of fuzzy systems developed for signal processing and try to see if one can quantify the mental workload based on the trend of EEG signal changes and the variation of pulse width from ECG signal. The signal data were taken from nuclear power plant operators while they perform the turbine operations. First, we apply a fuzzy system to extract the heart beat intervals from the ECG and a smoothing algorithm for the variation of the resulting heart beat intervals to obtain a trend variable. Next, we apply the same smoothing algorithm to the α-band frequencies and to the θ -band frequencies to get their trend curves. Finally, the three trend variables; the variation of the heart beat intervals, the α -band power, and the θ -band power are combined by a pair of fuzzy systems to estimate the mental workload during nuclear power plant operations. The results of applying our algorithm to three different data sets are included, along with a comparison between these results and the results obtained by applying a linear combination of the three variables. Compared results show that the `mental workload' computed by fuzzy systems with nonlinear rules reflects the changes more clearly than the ones computed by linear functions .

Optical time-domain reflectometry for distributed sensing of the structural strain and deformation

A unique structure of microbend optical fiber sensor (MOFS) for measuring tensile and compressive strain is described in this paper. The average measuring sensitivity for tensile strain is 35 με using 3 MOFS arrays. The repeatability and stability of MFOS are better than 18 με. The loss sensitivity of single-mode (SM) fiber and multi-mode (MM) fiber used in MOFS, as well as the relationship between the pulse width of diode laser and loss sensitivity are also studied in this paper. From these studies, some conclusions have been obtained. They are (1) the loss sensitivity and repeatability of SM fiber are better when compared to MM fiber in MOFS, and (2) the variation of pulse width of laser would only influent the signal-to-noise ratio and dynamic range, but has no contribution to loss sensitivity. Experimental results also show that loss of SM fiber highly depends on the wavelength of laser, but MM fiber has no such property. The loss of SM fiber between the wavelength of 1550 and 1310 nm is about the ratio of 6.5. Therefore, the experiments reported in this paper used a wavelength of 1310 nm to measure tensile strain and 1550 nm to measure compressive strain based on the above property of SM fiber, without changing the configuration of MOFS.

Transition curvature analysis

On-track recording losses associated with transition curvature in a merged magnetoresistive-read/inductive-write recording system were investigated. Variations in write head design resulted in a wide variation of reproduced pulse width. Magnetic force microscope (MFM) observation of written tracks revealed that transition curvature was related to the pulse width variation. The effect of transition curvature is modeled as a separable loss function by convolving a reader cross-track sensitivity function with a cross-track phase delay profile. Curvature loss has a different spectral content than transition broadening, allowing us to separate the two effects by comparing discrete Fourier transforms of isolated pulses. Results of such an analysis agree satisfactorily with MFM measurements. Planarization of mid-shields had minimal impact on the pulse width, but a notched write head design mitigated the effect. Transition curvature must be taken into account during write head design and in decisions regarding relative read and write widths.

Time-resolved studies of short pulse laser-produced plasmas in silicon dioxide near breakdown threshold

Using the technique of frequency-domain interferometry, we demonstrate a new way of studying laser-induced breakdown at the surface of dielectric materials. A theoretical model based on electron production by multiphoton ionisation, inverse bremsstrahlung heating, and collisional ionisation is in quantitative agreement with both the detailed time variation of the dielectric constant and the pulse width variation of the fluence threshold. From the complex reflection coefficient measured with the two probe pulse polarisations in quadrature, we deduce the time variation of the dielectric constant of silica during breakdown.

Electrically induced vasomotor responses and their propagation in rat renal vessels in vivo.

1. Vasomotor responses (VMR) induced by local electrical stimulation were studied in the vasculature of the split hydronephrotic rat kidney by in vivo microscopy. 2. Unipolar pulses, which were applied by a micropipette positioned close to the vessel wall, elicited local and propagated VMR. Depolarizing and hyperpolarizing currents caused vasoconstriction and vasodilatation, respectively. 3. The magnitude of VMR could be controlled within seconds by variation of pulse frequency, pulse width and voltage. VMR were abolished by slight retraction of the stimulating micropipette. Repetitive electrical stimulation resulted in reproducibly uniform VMR. 4. Propagated VMR decayed with increasing distance from the stimulation site. They decayed more rapidly in the upstream than in the downstream flow direction in interlobular arteries. The longitudinal decay was well approximated by an exponential function with significantly different length constants of 150 +/- 40 microns (upstream, n = 5) and 420 +/- 90 microns (downstream, n = 8). 5. Our results show that vasomotor responses, which are initiated by changes in membrane potential, are propagated over distances of potential physiological importance in interlobular arteries.

Active harmonic modelocking of an erbium fiber laser with intracavity Fabry-Perot filters

We present both experimental and theoretical investigations of the operation of a harmonically modelocked erbium fiber ring laser stabilized by an intracavity bit-rate etalon. Our model analyzes the effects of cavity components and operating parameters on laser stability and output pulse characteristics. The model predicts the output pulsewidth variation with laser cavity parameters such as cavity length, dispersion, and finesse of intracavity Fabry-Perot etalons. If the laser cavity length is not optimized, a maximum 50% increase in pulsewidth can occur at 5 Gb/s pulse rate. A repetition rate etalon with a finesse of 50 is sufficient to provide a side-mode suppression ratio of over 50 dB in the laser output. We also discuss how detuning from the optimal modulation frequency increases the excess noise that affects the laser stability. The theory predicts a maximum detuning range of /spl plusmn/100 kHz, which agrees with the experimental observations. These theoretical results can guide the design of similar lasers over a wide range of operating parameters.

Observations of the millisecond pulsar J0437-4715 at 76 MHz

We report observations of the millisecond pulsar J0437-4715 at 76 and 90 MHz. These observations give a five-fold increase in the frequency range of measurements of this pulsar and provide the first record of the pulsed emission from any millisecond pulsar below 100 MHz. We find that the radio spectrum of the mean pulsed emission of J0437-4715 is similar to that of many other pulsars with a spectral turnover between 90 and 400 MHz. J0437-4715 differs from most other pulsars with respect to the variation of pulse width with radiation frequency and the relative spectra of pulse components.

Experimental evaluation of an electron-beam pulse modulated blanker (160 MHz) for next-generation electron-beam raster scan systems

The simplicity of raster scan architecture has several benefits for mask-making production tools, the most important being accuracy. Nevertheless, building patterns on a grid resolution determined by the writing address of the raster scan mask generator places limitations on pattern edge locations, or equivalently, on throughput. A method of getting around this throughput bottleneck is pixel-level dose modulation, i.e., graybeam. In this article, a new driver technology in combination with the MEBES(R) 4500 blanker operating at 160 MHz is experimentally evaluated for real-time dose modulation by pulse width variation. Measurements of the rise and fall time of the blanker driver using various input data vectors (i.e., combinations of various pulse width signals) and a beam current modulation transfer function for the blanker are presented. Contributions from electronic artifacts such as electronic jitter are measured. Finally, these measurement results are used to determine the preliminary performance of a graybeam system.

A fixed frequency LCL-Type series resonant converter

A fixed frequency LCL-type series resonant converter (SRC) which uses an inductive output filter is proposed. Steady-state analysis of the converter is presented using complex ac circuit analysis. Based on the analysis, a simple design procedure is given. Detailed space integrated control experiment (SPICE) simulation results are presented to evaluate the performance of the designed converter under varying load and supply voltage conditions. Also, detailed experimental results obtained from a metal-oxide-semiconductor field-effect transistor (MOSFET) based 500 W converter are presented to verify the analysis and SPICE simulation results. The results obtained from the analysis, SPICE simulation and the experimental converter are compared. The proposed converter requires a narrow variation in pulsewidth while maintaining lagging power factor mode of operation for a very wide variation in the load as well as supply voltage.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Slider-disk clearance measurements in magnetic disk drives using the readback transducer

A new method is described for noninvasively measuring the mechanical clearance between a recording head slider and the magnetic medium in hard-disk drives. The method is based on the detection of the pulse width of the read transducer output. A variation in clearance produces a proportional variation in pulse width. The proportionality factor can be determined by simulating the spacing loss using a digitized isolated impulse, typical for the respective head-disk combination. Instrumentation is presented that provides an output voltage proportional to the ratio (PW/sub x//T) of the pulse width at x% of the peak amplitude PW/sub x/ and the period T of the readback signal. This instrumentation measures the absolute slider-disk clearance by evacuating the air from the disk drive. The bandwidth is such that clearance dynamics can also be measured. This allows clearance measurements as well as the detection of undesirable slider-disk interactions, in situ, in fully operational disk drives.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Deep level defects in proton irradiated Zn and Cd doped InP

InP is a relatively radiation-resistant semiconductor and an attractive material for solar cells exposed to radiation in Earth orbit. To better understand this useful property of InP, proton irradiation induced defects in Zn and Cd doped InP have been studied by deep level transient spectroscopy. After 2 MeV proton irradiation the defects H3, H4, and H5 were observed in lightly Zn doped InP, while the defects H3 and H5 were observed in more heavily Zn and Cd doped InP. The concentrations of the irradiation induced defects were measured and the introduction rates were calculated and compared. The activation energies of the defects were measured and corrected for the effect of electric field on carrier emission. The capture cross sections of the defects were measured directly by the pulse width variation technique. The energy levels and capture cross sections of the defects were not affected by the substitution of Cd for Zn, but the introduction rate of the defect H5 was substantially lower in Cd doped InP, suggesting that this material would make an improved solar cell in a high radiation environment.

Effects of variation of the laser pulse width on the laser-induced photoelectrons

Abstract The effects of variation of the laser pulse length on the laser-induced photoelectrons from the BNL gun are presented, including variation of the beam emittance which is crucial to the operation of a free-electron laser (FEL). The radio-frequency (rf) electron gun with a photocathode on the end wall of an rf cavity is excited by a laser pulse that is synchronized witht the rf frequency and powered by a conventional type SLAC klystron. This gun is designed to produce a lowe emittance beam at 4.65 MeV at the gun exit with the field gradient of 100 MV/m on the cathode.

Characterization of two-gated microchannel plate framing cameras

The overall performance of both a single- and a double-microchannel plate framing camera were measured. In the case of the double-plated device, only the front plate was gated. A short-pulse, 20-ps full width half-maximum (FWHM), uv laser was used to create photoelectrons on a time scale rapid compared to the temporal variation of the high-voltage gate pulse (965 V peak amplitude and 270 ps FWHM). Measurements were made of the variation in the light output pulse amplitude (8%–24%), width (85–115 ps), and peak location (±22 ps), the latter corresponding to a temporal jitter. It was found that when a dc bias was applied to the plate (in addition to the high-voltage pulse) the output signal increased as the dc bias to the 13 and 5.2 powers, below and above a bias of 450 V, respectively, and a factor of 20 difference in signal between the single- and double-plate cameras. It was also determined that the rejection ratio drops from 500 to 1300 at a bias value of 450 V to 125–190 at 650 V.

NEAR‐SOURCE PULSE PROPAGATION: APPLICATION TO Q‐DETERMINATION1

AbstractAmong the approaches generally used to measure attenuation from field data, the study of the first pulse broadening appears to be one of the more promising methods to estimate the quality factor Q for different geological formations including soils. Using a numerical scheme, we studied the evolution of the pulse shape in the neighbourhood of the source in order to establish the limits of the method. It was found that the pulse width variations depend strongly upon source depth. At short distances from the source, the pulse shape is controlled mainly by the near‐field terms and/or the onset of surface waves. The investigations proved that the pulse‐broadening method is reliable for distances greater than about 1.2 wavelengths. From numerical experiments, the maximum error in Q‐determination is found to be 10% in the half‐space case.

The field-stimulated vas deferens of the streptozotocin-diabetic mouse: effects of prazosin, ?,?-methylene ATP, and variation of stimulation parameters

The question of diabetic neuropathy was studied in the field-stimulated isolated vas deferens of the mouse. The animals were treated with either buffer or streptozotocin (170 mg/kg i.v.) 2 or 4 weeks, respectively, beforehand. Stimulus-response relationships were tested by variation of frequency (VF) at constant pulse width and by variation of pulse width (VP) at constant frequency. The adrenergic twitch component was eliminated by prazosin (1 microM) and the purinergic component by alpha, beta-methylene ATP (MeATP, 10 microM). The diabetes did not alter the muscular contractility (tested with KCl) and left the twitch-inhibiting effects of prazosin and MeATP unchanged, thereby revealing no difference in susceptibility between noradrenergic and purinergic mechanisms. However, in diabetic vasa, the maximal effectiveness of stimulation was decreased with VF but not VP, whereas the sensitivity of intramural neurons (50% effective frequency or pulse width, respectively) was unchanged with VF and reduced with VP. This may suggest that the diabetic neuron release less transmitter (VF), which can be compensated for by the activation of less sensitive neurons (VP). Actually, the uptake of 3H-noradrenaline into the (4 weeks-) diabetic vas was normal but the stimulation-induced fractional release of tritium was decreased by 26%. It is concluded that a sympathetic neuropathy occurred in the vas deferens of the streptozotocin-diabetic mouse.

Noradrenergic, purinergic, and cholinergic transmission in the mouse vas deferens: influence of field-stimulation parameters, reserpinization, 6-hydroxydopamine and 4-aminopyridine

In the field-stimulated mouse vas deferens the twitch inhibiting potency of prazosin (1 microM) and alpha,beta-methylene ATP (MeATP, 10 microM) was studied, using two types of stimulation-response curves, (a) variation of frequency from 3 to 100 Hz at a constant pulse width of 0.1 ms and (b) variation of pulse width from 0.04 to 0.8 ms at a constant frequency of 15 Hz. Prazosin and MeATP reduced the twitch response by eliminating the noradrenergic and purinergic component, respectively. After the combined application of both compounds a small third twitch component remained that was most prominent at high frequencies. Reserpinization reduced the effect of prazosin but enhanced that of MeATP and increased the cholinergic component. 6-Hydroxydopamine enhanced the effects of prazosin and MeATP to the same extent, but left the cholinergic component intact. In vasa pre-loaded with [3H]-noradrenaline, field stimulation induced a larger release of tritium at high frequency and short pulse duration (100 Hz, 0.1 ms) than at lower frequency and long pulse duration (15 Hz, 0.3 ms). Prazosin (1 microM) augmented both the spontaneous and the stimulation-induced overflow of tritium, whereas MeATP (10 microM) had only a negligible negative effect on the outflow of label. In conclusion, the twitch contraction of the mouse vas deferens has a small cholinergic component in addition to the noradrenergic and purinergic components. Adrenergic and purinergic transmission seem not to run strictly in parallel: the purinergic component dominates during stimulation at low frequency and long pulse duration, and after reserpinization; 4-aminopyridine enhances the adrenergic mechanism more than the purinergic one.

Proton-irradiated silicon: Complete electrical characterization of the induced dominant deep defects after long-term annealing

Deep defects produced by high energy, low dose proton implantation into n-type silicon have been investigated by deep-level transient spectroscopy. The complete set of characteristic electrical parameters is given for the induced dominant electron and hole traps after long-term annealing, i.e. energy levels, emission rates and capture cross-sections for majority and minority carriers, which have been determined directly by the pulse width variation technique.