Changes In Pulse Width Research Articles

10-GHz optical soliton transmission experiment in a sliding-frequency recirculating fiber loop

A 10-GHz optical soliton transmission experiment was performed in a recirculating fiber loop in which the carrier frequency was slowly shifted by an acousto-optic modulator with respect to an optical bandpass filter to simulate the sliding-frequency effect. The soliton pulses were transmitted over 4000 km without any significant change in pulse width.

The use of very low and very high frequencies in the development of an acoustical deterrent for bird–aircraft collisions

Bird strikes have become an increasing problem at commercial and military airports. With the demand for reduced aircraft noise and increased speed, birds are presented with reduced auditory cues and less reaction time when confronted with planes. The major drawback to the use of acoustic deterrents is the rapid habituation. Caged sparrowhawks readily detected signals between 5 and 40 Hz with thresholds of detectability ranging from 76 to 64 dB SPL. No flying induced startles were noted, although the birds did try to localize the source. Habituation to low‐frequency stimuli occurred with as little as three presentations. Free‐ranging geese were presented with the same frequencies as substrate vibration along with sound pressure stimulation. In a limited sample (three geese) avoidance was noted. The application of low‐frequency sound as substrate vibration on runways is promising. Alternatively, microwaves produce an auditory stimulus to the ear that can be altered by changes in frequency, pulse width, and overall power. Pulsed microwaves or microwaves modulated by low‐frequency sound are potential sources alerting birds from a flying plane already carrying navigation radar.

Stretched-pulse additive pulse mode-locking in fiber ring lasers: theory and experiment

Stretched-pulse additive pulse mode-locking uses segments of fiber of large positive and large negative group velocity dispersion (GVD) in the cavity. The changes in pulse width per pass due to the varying GVD can be an order of magnitude or more. A theory is developed based on the master equation that covers this case of large pulse changes in one transit. The general predictions of the theory are verified by experimental results. >

Serial Defibrillation Threshold Measures in Man: A Prospective Controlled Study

Serial DFT Measures in Man. The defibrillation threshold (DFT) may change throughout the first year following implantation of a cardioverter defibrillator, but it remains uncertain if changes are a consequence of changes in clinical condition or are related to fundamental alterations at the electrode-tissue interface. The purpose of this study was to evaluate the extent and time course of DFT changes over the first year following implantable cardioverter defibrillator (ICD) surgery when extraneous clinical and device variables potentially affecting the DFT were excluded. We prospectively enrolled 61 patients undergoing epicardial or nonthoracotomy/transvenous ICD therapy into a series of follow-up studies where the DFT was measured at implant and at 1, 6, 12, and 52 weeks following implantation in a uniform manner. Stored energy DFT was measured and recorded for all patients. Patient exclusion criteria were: (1) inability to complete all five measures of the DFT; (2) institution of Class I or Class III antiarrhythmic drugs at any time during the study; (3) lead system changes (relocation or new leads) or programming changes in pulse width or current pathway; or (4) development of a significant change in their clinical status, such as decompensated congestive heart failure or acute ischemia. Only 20 of the 61 patients satisfied the criteria required to complete the study. Two of the excluded patients developed high DFTs, which required reprogramming of the current pathway. Eight patients had an epicardial lead system, and 12 had a nonthoracotomy lead system.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of varying laser parameters on pulsed Ho:YAG ablation of bovine knee joint tissues

We investigated the effect of varying laser parameters on ablation of fresh bovine knee joint tissues (fibrocartilage, hyaline cartilage, and bone) with a free-running Ho:YAG laser. Ablation rate was measured in saline for each tissue type as a function of laser fluence (160-950 J/cm2), pulse width (150-450 microseconds, full width at half maximum), and fiber core diameter (400 and 600 microns). A weight that was attached to the fiber end was used to exert a constant pressure of 40 g/mm2 to the tissue underneath to ensure a constant contact between the fiber tip and the tissue throughout the ablation process. All tissues could be efficiently ablated, and the ablation rate increased linearly with the fluence. Change in laser pulse width and fiber core diameter resulted in minor variations in the ablation rate for fibro- and hyaline cartilage. On the other hand, use of longer pulses and/or the larger fiber significantly accelerated bone ablation. Histology analysis revealed that zones of thermal damage in Ho:YAG irradiated bovine knee joint tissues differed by tissue types and ranged between 100 and 400 microns, but were independent of fluence, pulse width, and fiber size within the range tested.

SOLITON CHARACTERISTICS OF GAUSSIAN OPTICAL PULSES PROPAGATION IN THE NONLINEAR GAIN MEDIUM

In this paper, propagation of Gaussian optical pulses in the nonlinear gain medium is ana-lyzed theoretically. The mechanism of Gaussian optical pulses compression, broadening and optical soliton formation is also explained. Gaussian optical pulses with different parameters propagating in nonlinear gain medium are simulated with computer. The change of pulse width during the propagation is obtained. The results indicate that it is possible for the ini-tial Gaussian optical pulses with different peak power to form different order solitons in the medium, nevertheless, their propagation distance is limited due to the existence of gain.

ABOVE-THRESHOLD-IONIZATION BY MULTIPHOTON ABSORPTION OF ATOM UNDER SHORT LASER PULSE

The Above-threshold-ionization(ATI) Spectrum of electrons produced by multiphoton absorption of atom has been obtained with spatial Gauss and temporal Sech shape of the incident laser pulse. It is found that our model can explain many phenomena such as peak suppression and switching. In addition, what is more important is that we can explain the red shift of the peaks decreases to zero gradually, as the pulse width changes from short to long pulse regime.

Is the 35 day cycle of her x-1 caused by the free precession of the neutron star?

It has been suggested that the 35 day clock mechanism of Her X-1 is caused by the precession of the neutron star. We made calculations for this model. Comparing our calculated results with observations we find: 1. (1) The theoretical light curve over the the 35 day cycle does not agree with the observed curve by Jones and Forman (1976). 2. (2) The change of pulse width and intensity with the 35 day phase is large in the model, seemingly disagreeing with the observations (e.g., Gruber et al. 1980). 3. (3) Parmer et al. (1985) reported that they did not see the expected 35 day variation in X-ray intensity expected in the model. Pravdo et al. (1977) suggested that the observed X-ray pulses were formed by Thomson scattering of symmetric radiating beams generated near the surface of the neutron star. Our analysis based on the theory of Thomson scattering in strong magnetic fields shows that this model agrees well with the observations.

Effect of stimulated Raman scattering on pulse-compression characteristics

The effect of stimulated Raman scattering on pulse-compression characteristics has been studied experimentally and theoretically. When an optical pulse is compressed by an optical fiber and a grating pair, the generation of stimulated Raman scattering becomes important. When stimulated Raman scattering occurs, the compressed pulse width changes asymmetrically with respect to the magnitude of the anomalous dispersion created by the grating pair. The compressed pulse has much residual energy in its wings, and it does not have a smooth envelope for large anomalous dispersion.

Kinematic analysis of strong motion P and SV waves from the Sterling Event

P and SV velocity waveforms from the Sterling explosion of December 3, 1966, are analyzed from a point of view often taken in earthquake source studies. The detonation occurred in the cavity excavated by the Salmon explosion within the Tatum salt dome, Mississippi. Velocity recordings taken from nearby borehole strong motion instruments show the occurrence of significant SV energy (Perret, 1968a, b). Kinematic source models are constructed by considering constraints afforded by the preshot cavity, condition of the surrounding material, and aspects of the P and SV waveforms such as wave polarity and duration. Waveforms for these models are computed and compared directly with the data. Modeling results suggest that the SV waves were radiated primarily by induced normal faulting occurring beneath the cavity rather than by an asymmetric pressure distribution based on the preshot cavity geometry. Secondary arrivals within the P waveforms and SV amplitudes suggest that these normal faults also had a component of tensional displacement which was probably due to forceable injection of material from the blast. A measurement for Qβ of 35 is obtained for salt from the amplitude decay arid pulse width changes observed for SV waves along a profile taken at shot level. This value for Qβ is for the region away from the cracked area induced by the previous Salmon explosion and qualitatively explains the differing frequency content observed at the closest Sterling sensors between P and SV waves. The anomalous SV radiation has little to do with ‘tectonic’ stress release but is a result of the medium's geometry and anisotropy.

Damaging effect of therapeutic radiation on programmable pacemakers.

Two series of present-day pacemakers were tested in vitro with pulsed x-ray radiation. The first series of 12 pacemakers consisted of 10 different types and models of demand pacemakers (VVI). The second series of 13 pacemakers had 9 different types and models of programmable pacemakers. Unlike the first series which showed only mild changes in frequency and pulse width, all but four of the programmable pacemakers presented sudden complete failure after different radiation doses. We conclude that direct pulse radiation at therapeutic levels of programmable pacemakers should be avoided.

Electrocutaneous Pulse Rate and Pulse Width Psychometric Functions for Sensory Communications

Psychometric functions of pulse rate (PR) and pulse width (PW) from electrocutaneous stimuli were determined using the method of comparative judgments. The study revealed that changes in PR were more easily detected than changes in PW, as measured by the percent of just noticeable difference (jnd). The PR jnd data from test subjects indicated that maximum frequency discrimination occurred near 20 pulses per second. Using the PR and PW psychometric curves, compensatory transfer functions can be determined which will improve the efficacy of sensory communication systems based on electrocutaneous stimulation.

Pulse-widening measurement

A new time-domain formula is derived for the change in pulse width due to transmission through a two-port network. A simple measurement scheme based on this formula is described. The measurement technique is sensitive enough to allow measurements of pulse widening in short lengths of cable.

Patient survival and instrument performance with permanent cardiac pacing

Among 313 patients who received cardiac pacemakers between 1961 and 1973, there was a 65% survival rate after five years, a progressive decrease in premature pulse generator failures, and a low, stable incidence of electrode malfunction. Decreased survival among more recently paced patients was attributed to an evolution of the selection for pacing that favored older patients with associated diseases. Death due to unexpected pacing failure was extremely rare. Premature pulse generator failures decreased from 0.8 per 100 pacing months among early units to 0.06 per 100 months among units implanted during 1971 to 1973, when a prophylactic replacement policy was in effect. Electrode revisions were required at a frequency of 0.5 to 0.8 per 100 months in both epicardial and endocardial systems. Electrode failures may limit the predictive value of surveillance systems, since these rely on a change of pacing frequency or pulse width to indicate battery depletion.

Patient Survival and Instrument Performance With Permanent Cardiac Pacing

Among 313 patients who received cardiac pacemakers between 1961 and 1973, there was a 65% survival rate after five years, a progressive decrease in premature pulse generator failures, and a low, stable incidence of electrode malfunction. Decreased survival among more recently paced patients was attributed to an evolution of the selection for pacing that favored older patients with associated diseases. Death due to unexpected pacing failure was extremely rare. Premature pulse generator failures decreased from 0.8 per 100 pacing months among early units to 0.06 per 100 months among units implanted during 1971 to 1973, when a prophylactic replacement policy was in effect. Electrode revisions were required at a frequency of 0.5 to 0.8 per 100 months in both epicardial and endocardial systems. Electrode failures may limit the predictive value of surveillance systems, since these rely on a change of pacing frequency or pulse width to indicate battery depletion.

Pulse‐width tracking procedure for determination of auditory threshold of brief tones

Duration as a parameter was used to determine the temporal summation characteristics of normal ears. An apparatus was constructed that permitted a subject to track threshold by modulating pulse width. The apparatus permitted experimenter control of rate of pulse‐width modulation and interpulse interval. The pulse width could be continuously varied by the subject from 10 to 500 msec. The rate of temporal summation was determined in 10 normal ears at octave frequencies between 0.125 and 8.0 kHz. Absolute thresholds were determined using a rate of change in pulse width from 4.5 and 30 msec per second. Subjects tracked threshold at a given intensity level for a time sufficient for the tracing to become stabilized. A constant off‐time of 500 msec was used between pulses. The temporal summation patterns were found to be reliable and indicate potential clinical usefulness in the pathological ear.

Accurate amplitude measurement and time pick-off method for the broad pulse width range of nuclear detectors

Using semiconductor detectors, the optimum shaping time constant varies between 0.1 to 50 μs which leads to a pulse width change of more than two orders of magnitude. In such a wide range, both single- and multichannel analysers can measure amplitudes only at the expense of a loss in the speed of measurement, in energy resolution or accuracy. The device presented here produces square-wave analog pulses by means of sampling technique. Square-wave pulses are ideal both for single- and multichannel amplitude analysers. The choice of the optimum sampling time follows automatically and the time pick-off characteristics are good. There is no additional dead time.

Transmission of a light pulse by a nonlinear medium

Resonance interaction is considered for a pulse of monochromatic radiation in a medium of phthalocyanin type, on the basis of a two-level model. The change in pulse width and height are deduced, as is the degree of bleaching.

Measurement of pacemaker performance

Entirely satisfactory treatment of complete heart block has been prevented by an inability to measure pacemaker function after implantation. Two major problems can be identified in the long-term management of pacemaker patients: first, adequate prediction of when a pacemaker will fail; and second, accurate diagnosis of the type of pacemaker failure if it occurs. Observations on dogs gave precise measurements of interelectrode impedances. A method is described of externally measuring the interelectrode resistance and capacitance of implanted pacemakers. In studies on both dogs and human beings it was found that all changes in interelectrode impedance could be identified by changes in pacemaker rate and pulse width. Serial measurements of these two parameters allowed accurate diagnosis of the different types of “pacemaker failures.” The method also enabled anticipation of failures, other than wire breakage, before they were clinically evident. We think that pacemaker performance can be adequately evaluated by this method, making unnecessary prophylactic replacement of the unit.