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PubMed2001

Induction of T cell responses against autologous ovarian tumors with whole tumor cell lysate-pulsed dendritic cells.

The loading of dendritic cells (DCs) with whole tumor cell lysates may circumvent the facts that few tumor-specific antigens have been identified in human solid tumors. The present study was designed to investigate whether ovarian cancer cells lysate-pulsed DCs activate T cell responses against autologous ovarian tumors. Incubation of T cells with autologous tumor cell lysate-pulsed DCs stimulated proliferation of autologous T cells. T cells primed by autologous tumor cell lysate-pulsed DCs showed significant killing activity against autologous tumor cells, which could be blocked by anti-MHC-class-I and anti-CD8 mAb. By contrast, T cells primed by autologous unpulsed DCs alone or tumor lysates alone failed to exhibit significant killing activity. In addition, T cells primed by DCs pulsed with allogeneic tumor cell lysates or with autologous normal cell lysate or by these cell lysates alone did not induce the increase in the autologous tumor killing activity. As additional controls, T cells stimulated with autologous tumor lysate-pulsed DCs express no increase in the lysis of autologous monocytes, allogeneic ovarian tumor cells and other cell lines including K562, Daudi and Molt-4. Furthermore, T cells stimulated with autologous tumor lysate-pulsed DCs could produce the considerable amounts of cytokines such as GM-CSF, TNF-alpha and IFN-gamma. The data in the present study suggest that whole tumor cell lysates-pulsed DCs could activate T cell responses against autologous ovarian tumor cells, and that these pulsed DCs may be used as a new approach for the specific immunotherapy of ovarian cancer patients.

Adenocarcinoma↗
PubMed1996

Dendritic cells pulsed with RNA are potent antigen-presenting cells in vitro and in vivo.

Immunization with defined tumor antigens is currently limited to a small number of cancers where candidates for tumor rejection antigens have been identified. In this study we investigated whether pulsing dendritic cells (DC) with tumor-derived RNA is an effective way to induce CTL and tumor immunity. DC pulsed with in vitro synthesized chicken ovalbumin (OVA) RNA were more effective than OVA peptide-pulsed DC in stimulating primary, OVA-specific CTL responses in vitro. DC pulsed with unfractionated RNA (total or polyA+) from OVA-expressing tumor cells were as effective as DC pulsed with OVA peptide at stimulating CTL responses. Induction of OVA-specific CTL was abrogated when polyA+ RNA from OVA-expressing cells was treated with an OVA-specific antisense oligodeoxynucleotide and RNase H, showing that sensitization of DC was indeed mediated by OVA RNA. Mice vaccinated with DC pulsed with RNA from OVA-expressing tumor cells were protected against a challenge with OVA-expressing tumor cells. In the poorly immunogenic, highly metastatic, B16/F10.9 tumor model a dramatic reduction in lung metastases was observed in mice vaccinated with DC pulsed with tumor-derived RNA (total or polyA+, but not polyA- RNA). The finding that RNA transcribed in vitro from cDNA cloned in a bacterial plasmid was highly effective in sensitizing DC shows that amplification of the antigenic content from a small number of tumor cells is feasible, thus expanding the potential use of RNA-pulsed DC-based vaccines for patients bearing very small, possibly microscopic, tumors.

Animals↗
PubMed2006

Charge collection efficiency in ionization chambers exposed to electron beams with high dose per pulse.

The correction for charge recombination was determined for different plane-parallel ionization chambers exposed to clinical electron beams with low and high dose per pulse, respectively. The electron energy was nearly the same (about 7 and 9 MeV) for any of the beams used. Boag's two-voltage analysis (TVA) was used to determine the correction for ion losses, k(s), relevant to each chamber considered. The presence of free electrons in the air of the chamber cavity was accounted for in determining k(s) by TVA. The determination of k(s) was made on the basis of the models for ion recombination proposed in past years by Boag, Hochhäuser and Balk to account for the presence of free electrons. The absorbed dose measurements in both low-dose-per-pulse (less than 0.3 mGy per pulse) and high-dose-per-pulse (20-120 mGy per pulse range) electron beams were compared with ferrous sulphate chemical dosimetry, a method independent of the dose per pulse. The results of the comparison support the conclusion that one of the models is more adequate to correct for ion recombination, even in high-dose-per-pulse conditions, provided that the fraction of free electrons is properly assessed. In this respect the drift velocity and the time constant for attachment of electrons in the air of the chamber cavity are rather critical parameters because of their dependence on chamber dimensions and operational conditions. Finally, a determination of the factor k(s) was also made by zero extrapolation of the 1/Q versus 1/V saturation curves, leading to the conclusion that this method does not provide consistent results in high-dose-per-pulse beams.

Calibration↗
PubMed2001

A fuzzy system for detecting distorted plethysmogram pulses in neonates and paediatric patients.

Pulse oximetry is a useful, quick, non-invasive and widely used technology for monitoring oxygen saturation (SaO2) for neonates and paediatric patients. However, pulse oximetry is fraught with artefacts, causing false alarms resulting from patient or probe movement. The shape of the plethysmogram is a useful visual indicator for determining the reliability of SaO2 numerical readings. If certain features could be defined that tag valid plethysmogram pulses, then automatic recognition of valid SaO2 values can be attained. We observed that the systolic upstroke time (t1), the diastolic time (t2) and heart rate (HR) extracted from the plethysmogram pulse constitute features which can be used for detecting normal and distorted plethysmogram pulses. Therefore, we developed a knowledge-based system using fuzzy logic for classifying plethysmogram pulses into two categories: valid and artefact. A total of 22,497 pulse waveforms were used to define the system parameters. These were obtained from 13 patients with heart rates ranging between 62 and 209 beats min-1. A further 1420 waveforms obtained from another four patients were used for testing the system, and visually classified into 833 (59%) valid and 587 (41%) distorted segments. The system was able to classify 679 (82%) valid segments and 543 (93%) distorted segments correctly. The calculations of the system's performance showed 82% sensitivity, 86% accuracy and 93% specificity. We, therefore, conclude that the algorithm used in this system can be implemented in its present from for real-time SaO2 monitoring in intensive care for detecting valid and distorted plethysmogram pulses.

Adolescent↗
PubMed2003

Experimental study of the efficiency of lithotripsy with duplicate pulses.

BACKGROUND AND PURPOSE: Theoretical study had shown that compared with a single pulse, a duplicate pulse could improve the efficiency of lithotripsy. We conducted a series of studies to validate this idea. MATERIALS AND METHODS: The experimental study in vitro and in vivo used a lithotripsy machine with duplicate, single, and electromagnetic pulses. RESULTS: Use of a duplicate pulse improved the wastage of the model stones about 44.15% and the efficiency of lithotripsy about 44.76%. In pigs, the efficiency of lithotripsy was greater with a duplicate pulse than with single and electromagnetic pulses. CONCLUSION: Compared with single and electromagnetic pulses, duplicate pulses could improve the efficiency of lithotripsy by more than 40%.

Animals↗
PubMed2004

The comparison of effects between pulsed and CW lasers on wound healing.

OBJECTIVE: In order to evaluate the effects of pulsed continuous wave (CW) laser and detect the role of wound healing in rats using both pulsed and CW 635-nm low-level laser therapy (LLLT), a pilot study was undertaken. BACKGROUND DATA: Some acceleration effects of wound healing on animals were found after treatment using various lasers with CW. There are other reports, however, using pulsed CW laser to evaluate the effects of wound healing in rats. MATERIALS AND METHODS: An elliptic wound was created aseptically with a scalpel on the shaved back of the rats after anesthesia. The rats treated were restrained in a Plexiglas cage without anesthesia during the laser irradiation period. An Erchonia pulse laser (635 nm) was used in the experiment. The laser beam was delivered through an expander. The percentage of relative wound healing was calculated. RESULTS: The percentage of relative wound healing was 4.32 in 100 Hz, 3.21 in 200 Hz, 3.83 in 300 Hz, 2.22 in 400 Hz, 1.73 in 500 Hz and 4.81 in CW. CONCLUSION: LLLT using pulsed, CW laser at the appropriate dosimetry and frequency can provide acceleration in wound healing in rats. The 100-Hz frequency had a better effect than other pulse frequencies used in the study. The effects of treatment using CW laser was higher than pulse frequency. The frequency of pulsed CW laser was not found to increase wound healing in rats compared with normal CW laser, as reported in our previous studies.

Animals↗
PubMed1995

The control of childhood viral infections by pulse vaccination.

Pulse vaccination, the repeated application of vaccine over a defined age range, is gaining prominence as a strategy for the elimination of childhood viral infections such as measles and polio. However, unlike routine or continuous mass infant immunization, epidemiological understanding of this control method is in its infancy. This paper develops initial work by Agur et al. (1993) using simple steady-state and age-structured dynamic models to extend the theory of the mechanism of action of pulse vaccination, and to explore the relationship between the maximum permitted interval between pulses and key epidemiological, demographic and vaccination variables. Initially, a conceptual model is presented to illustrate the principles of pulse vaccination and to make comparison with routine immunization procedures. An ordinary differential equation model, which assumes homogeneous mixing, is then used to derive equilibrium expressions for the pulse interval in relation to (i) different demographic profiles, (ii) population growth characteristics (stationary or exponentially increasing), (iii) combined routine and pulse immunization, and (iv) the age range vaccinated. Finally, simulations using age-structured compartmental deterministic models illustrate complex epidemiological dynamics associated with pulse vaccination, particularly where there is age heterogeneity in contact rates in the population. The resultant uncertainty in defining an optimal pulse interval raises concerns of a practical nature.

Age Factors↗
PubMed1996

Ovulation induction using s.c. pulsatile gonadotrophin-releasing hormone: effectiveness of different pulse frequencies.

To determine the ovarian response to a fixed dose of gonadotrophin-releasing hormone (GnRH) administered s.c. at four different pulse frequencies, 20 patients with hypothalamic amenorrhoea were treated over 41 cycles using a dose of 20 ng/kg/pulse. These patients were randomly assigned to receive GnRH at pulse frequencies of 60, 90, 120 or 180 min. GnRH was administered s.c. using portable infusion pumps. Subjects were paid volunteers with a diagnosis of hypothalamic amenorrhoea. All patients had low to less than detectable serum concentrations of luteinizing hormone and follicle stimulating hormone on 8 h serial sampling, and normal serum concentrations of prolactin and androgen, including androstenedione, testosterone and dihydroepiandrosterone sulphate. Six of the 20 patients were enrolled in the protocol to achieve a pregnancy, while 14 were volunteers using a barrier method of contraception. Highest ovulation rates were achieved using pulse frequencies of 90 and 120 min (60 and 88% of cycles respectively). Ovulation occurred significantly less often with frequencies of 60 and 180 min (12 and 38% respectively; P </= 0.05). Pregnancy was achieved in four of the six patients who desired a pregnancy at pulse frequencies of 90 (three out of three) and 120 (one out of one) min. No pregnancies occurred at pulse frequencies of 60 (none out of one) and 180 (none out of one) min. When ovulatory cycles were considered, oestradiol concentrations were not different among pulse frequencies but varied significantly between ovulatory and anovulatory cycles. Integrated luteal progesterone concentrations for 90 and 120 min frequencies (118.26 +/- 25.89 and 125.15 +/- 32. 10 ng/ml/luteal phase respectively) were significantly higher than for 60 and 180 min (80.1 +/- 48.2 and 42.75 +/- 26.48 ng/ml/luteal phase respectively). Ovulation may be induced by a broad range of pulse frequencies. Pulse frequencies of 90 or 120 min for s.c. GnRH appear to induce more reliably the sequence of follicular development, ovulation and normal luteal function than frequencies of either 60 or 180 min. Significantly higher ovulation rates occurred at 90 and 120 min by s.c. administered GnRH.

Adult↗
PubMed1986

Circadian and photoperiodic effects of brief light pulses in male Djungarian hamsters.

The effects of brief light pulses (1-60 min in duration) on the circadian rhythm of locomotor activity and/or the neuroendocrine-gonadal axis was investigated in male Djungarian hamsters. Exposure of hamsters free-running in constant darkness to a single 1-h pulse of light induced phase-dependent phase shifts in the rhythm of locomotor activity. The general shape of the "phase-response curve" was similar to that observed in other animals; phase-delays and phase-advances were induced by light pulses delivered in the early and late subjective night, respectively, while light pulses during the subjective day induced little or no phase-shift in the activity rhythm. Animals exposed for 7 days to 1-min of light during the night in animals otherwise exposed to 6L:18D resulted in increased levels of serum FSH and testicular weight. Daily exposure to two 1-h or two 10-min pulses of light (but not two 1-min pulses) for 10 days resulted in stable entrainment of the activity rhythm as well as testicular weight gains and serum FSH increases. When two 10-min pulses of light were presented 8 and 16 h apart, some animals showed a short-day entrainment pattern (i.e., locomotor activity confined to the long period of darkness) while other animals showed a long-day entrainment pattern (i.e., locomotor activity confined to the short period of darkness). Importantly, the stimulatory effects of light on neuroendocrine-gonadal activity were clearly dependent on the phase-relationship between the light pulses and the circadian rhythm of locomotor activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2001

How does the plethysmogram derived from the pulse oximeter relate to arterial blood pressure in coronary artery bypass graft patients?

UNLABELLED: Twenty patients scheduled for coronary artery bypass grafting had their ear and finger oximeter and radial artery blood pressure (Bp(meas)) waveforms collected. The ear and finger pulse oximeter waveforms were analyzed to extract beat-to-beat amplitude and area and width measurements. The Bp(meas) waveforms were analyzed to measured systolic blood pressure (BP), mean BP, and pulse pressure. The correlation coefficient was determined between the derived waveforms from the pulse oximeter and Bp(meas) for the first 10 patients. The ear pulse oximeter width (Width(Ear)) had the best correlation (r = 0.8). Linear regression was done between Width(Ear) and Bp(meas) based on slope (b) and intercept (a) values, BP was calculated (Bp(calc)) in the next 10 patients as: [equation: see text] where i = systolic BP, mean BP, and pulse pressure. The initial bias was too large to be clinically useful. To improve clinical applicability a period of calibration was introduced in which the first 50 readings of Width(Ear) and Bp(meas) for each patient were used to calculate the intercept. After calibration the systolic BP, mean BP and pulse pressure bias values were -2.6, -1.88 and -1.28 mm Hg, and the precision values were 15.9 10.09, and 9.94 mm Hg, respectively. The present attempt to develop a clinically useful method of noninvasive BP measuring was partly successful with the requirement of a calibration period. IMPLICATIONS: Statistical comparison was made between measured blood pressure (BP) from arterial line and calculated BP derived from ear pulse oximeter waveform in 10 patients undergoing coronary artery bypass graft surgery. Using 62,077 paired readings, the mean difference for systolic BP, mean BP, and pulse pressure between the 2 methods was -2.6, -1.88, and -1.28 mm Hg, respectively.

Blood Pressure↗
PubMed2003

Pulse oximetry for perioperative monitoring: systematic review of randomized, controlled trials.

Monitoring with pulse oximetry might improve patient outcome by enabling an early diagnosis and, consequently, correction of perioperative events that might otherwise cause postoperative complications or even death. The aim of the study was to clarify the effect of perioperative monitoring with pulse oximetry and to identify the adverse outcomes that might be prevented or improved by its use. Trials were identified by computerized searches of the Cochrane Library, MEDLINE, EMBASE, and by checking the reference lists of trials and review articles. All controlled trials that randomized patients to either pulse oximetry or no pulse oximetry during the perioperative period, including in the operating and recovery room, were included in the study. The search identified six reports. Of these 6 reports, 4 studies with data from 21,773 patients were considered eligible for analysis. Two studies specifically addressed the outcomes in question; both found no effect on the rate of postoperative complications using perioperative pulse oximetry. Hypoxemia was reduced in the pulse oximetry group both in the operating room and in the recovery room. During observation in the recovery room, the incidence of hypoxemia in the pulse oximetry group was 1.5-3 times less. There were postoperative complications in 10% of the patients in the oximetry group and in 9.4% in the control group. The duration of hospital stay was a median of 5 days in both groups, and an equal number of in-hospital deaths was registered in both groups. The studies confirmed that pulse oximetry could detect hypoxemia and related events. However, given the relatively small number of patients studied and the rare events being sought, the studies were not able to show an improvement in various outcomes.

Blood Gas Analysis↗
PubMed1991

Measurement of systolic blood pressure using pulse oximetry during helicopter flight.

OBJECTIVE: Monitoring of vital signs in critically ill patients during helicopter flight is difficult because of the noise and vibrations of the aircraft. We evaluated the use of a pulse oximeter to measure systolic BP intraflight. DESIGN: Systolic BP measured by pulse oximetry was compared with systolic BP measured by the direct intra-arterial and the arterial occlusion methods intraflight. Systolic BP by pulse oximetry was measured by observing the return of the plethysmographic waveform of the pulse oximeter as the BP cuff ipsilateral to the pulse oximeter probe was slowly deflated. Arterial occlusion pressure was measured by observing the return of the intraarterial waveform as the BP cuff ipsilateral to the arterial cannula was slowly deflated. SETTING: The study was performed during patient transport, intraflight. PATIENTS: Ten critically ill patients were studied. INTERVENTIONS: None MEASUREMENTS AND MAIN RESULTS: Seventy-three sets of measurements were recorded. The best correlation (r2 = .99) was found between pulse oximetry and the arterial occlusion method. The indirect methods correlated better with each other than with direct intraarterial measurements. The noise and the vibrations of the helicopter did not significantly interfere with the operation of the pulse oximeter. CONCLUSIONS: We conclude that a pulse oximeter that displays a plethysmographic waveform can accurately measure systolic BP intraflight.

Adult↗
PubMed1996

Accuracy of pulse oximetry in hypothermic neonates and infants undergoing cardiac surgery.

OBJECTIVES: To assess the accuracy of pulse oximetry under hypothermic conditions in neonates and infants undergoing cardiac surgery, and to assess the effect of probe site as well as probe site skin temperature on the reliability of pulse oximetry. DESIGN: Prospective Study. SETTING: Cardiac operating room and intensive care unit of children's hospital. PATIENTS: Twenty-five infants <3 months of age undergoing cardiac surgery with cardiopulmonary bypass. INTERVENTIONS: Pulse oximeter readings (Sp O2) from probes placed on the hand and foot were recorded at various skin temperatures and compared with hemoximeter oxygen saturations (Sa O2) obtained on simultaneously drawn arterial blood samples. Core temperature, arterial pressure and vasodilator use were recorded simultaneously. MEASUREMENTS AND MAIN RESULTS: Pulse oximetry bias (Sp O2 - Sa O2) increased to an unacceptable range (>+3% or <-3%) in 45.5% of the readings at foot probe site temperatures of <27 degrees. Pulse oximetry bias was within an acceptable range in 94.7% of the readings at temperatures >29 degrees. There was no significant difference between oximeter readings obtained from two probe sites (hand and foot). Administration of phenoxybenzamine improved the accuracy of pulse oximetry in ten infants at skin temperature of <27 degrees. CONCLUSIONS: Pulse oximetry readings in small infants are likely to be unreliable at skin temperatures of <27 degrees, irrespective of probe site. Intravenous phenoxybenzamine appeared to improve the accuracy of pulse oximetry at low temperatures.

Age Factors↗
PubMed1987

Pulse oximetry: applications and limitations.

The pulse oximeter estimates arterial hemoglobin saturation by measuring the light absorbance of pulsating vascular tissue at two wavelengths. The relationship between measured light absorbances and saturation was developed empirically and is built into the oximeter software. Studies in human volunteers have shown good performance of the device in healthy adults for saturations in the range of 70 to 100%. Studies in the operating room and intensive care unit have established its clinical accuracy and usefulness. The pulse oximeter has already found a number of clinical applications outside of the operating room, such as monitoring during patient transport, respiratory monitoring during narcotic administration, and evaluation of home-oxygen therapy. To use this monitor to its full potential, we must be aware of its limitations as well as its advantages. Because of the nature of the HbO2 dissociation curve, saturation measurements will not be sensitive to changes in PaO2 when the PaO2 is greater than 100 torr. This also implies that the pulse oximeter may fail to detect an inadvertent endobronchial intubation in the operating room. It may take minutes to detect an esophageal intubation in a well-preoxygenated patient. When desaturation does occur, the pulse oximeter detects it quickly, accurately, and reliably. Since the pulse oximeter uses two wavelengths of light, it cannot distinguish more than two hemoglobin species. Thus, COHb and MetHb will cause errors in SpO2 if present in large amounts. Intravenously administered dyes can also cause errors because of their absorbance properties, particularly methylene blue and indocyanine green. The pulse oximeter may be unable to detect an adequate signal during abnormal hemodynamic conditions. The pulse oximeter is one of the most important advances in noninvasive monitoring because it provides a means of continuously and quickly assessing arterial blood oxygenation. It is easy to use and interpret, requires little setup time, and poses no additional risks to the patient. Pulse oximetry may soon be a standard of practice for routine monitoring in any clinical setting in which the patient is at risk of hypoxemia.

Blood Gas Monitoring, Transcutaneous↗
PubMed2003

Pulse pressure is associated with age and cardiovascular disease in type 1 diabetes: the Eurodiab Prospective Complications Study.

OBJECTIVE: Type 1 diabetic individuals are thought to have increased arterial stiffness, and are at high risk for cardiovascular disease. However, it is not known whether increased arterial stiffness in type 1 diabetes causes cardiovascular disease. To explore this issue, the present study investigated the association, in type 1 diabetes, of age and pulse pressure, an estimate of arterial stiffness, and the influence of the presence of microvascular complications on this association. In addition, we determined the association of mean arterial pressure and pulse pressure with incident cardiovascular disease. METHODS: We studied a cohort of 3250 type 1 diabetic individuals of the EURODIAB Prospective Complications Study. Mean age and median follow-up were 33 and 7.4 years. One hundred and sixty-three individuals developed a first manifestation of cardiovascular disease during follow-up. Linear regression analysis was used to determine the association of age with pulse pressure. Relative risks of cardiovascular disease were estimated by Cox regression analyses adjusted for age, sex and mean arterial pressure or pulse pressure.RESULTS In cross-sectional analyses, age was associated with pulse pressure (P < 0.001) and this association was stronger in the presence of micro- or macroalbuminuria or retinopathy than in their absence (interaction for albuminuria, P < 0.001; interaction for retinopathy, P < 0.001). In prospective analyses, both mean arterial pressure and pulse pressure were associated with cardiovascular disease [adjusted relative risks and (95% confidence interval) per 10 mmHg increase were 1.08 (0.94-1.24) and 1.09 (0.98-1.21)]. CONCLUSIONS: This study shows an association of age with pulse pressure in young type 1 diabetic individuals, which is stronger in the presence of microvascular complications. In addition, both mean arterial pressure and pulse pressure are associated with incident cardiovascular disease. These findings support the concept of early vascular ageing in type 1 diabetes, especially in the presence of microvascular complications.

Adolescent↗
PubMed2001

Assessment of outcomes other than systolic and diastolic blood pressure: pulse pressure, arterial stiffness and heart rate.

In recent years, studies have shown that parameters derived from the arterial pressure wave other than systolic and diastolic blood pressure provide important information on cardiovascular status. Among these parameters, pulse pressure, arterial stiffness and heart rate have emerged as independent markers of cardiovascular risk in different populations. Although a number of studies have used casual measurements of these parameters in a clinic setting, others have focused on their assessment under ambulatory conditions. The pulse pressure represents the amplitude of the pressure wave signal (systolic minus diastolic blood pressure), higher pulse pressure values having been reported in patients possessing cardiovascular risk factors. Close associations between a high pulse pressure and several surrogate end-points have been described. Furthermore, epidemiological studies have shown that a high pulse pressure is an independent predictor of hard end-points in several populations. Arterial stiffness represents one of the major haemodynamic factors determining pulse pressure. Pulse wave velocity, measured from the initial upstroke of the pressure wave, constitutes an established index of arterial stiffness. Studies have reported stiffer arteries in patients with cardiovascular pathology even at an early stage of disease. Close correlations between arterial stiffness and several surrogate markers have been reported, and arterial stiffness and its changes have recently been shown to be an independent predictor of hard end-points in patients with a high cardiovascular risk. Methods to evaluate arterial stiffness under ambulatory conditions are emerging. Heart rate represents the frequency of the cyclical strain of the arterial wall, clinical studies having shown that ambulatory heart rate is correlated to several surrogate markers. A few epidemiological studies have analysed the value of ambulatory heart rate as an independent predictor of hard end-points, but their positive findings need to be confirmed. The analysis of the pressure wave thus allows the determination of several haemodynamic indices other than systolic and diastolic blood pressure. Pulse pressure, arterial stiffness and heart rate constitute other outcomes that may be useful as additional factors in risk assessment for future therapeutic decision-making.

Arteries↗
PubMed2001

Diffraction of short pulses with boundary diffraction wave theory.

The diffraction of short pulses is studied on the basis of the Miyamoto-Wolf theory of the boundary diffraction wave, which is a mathematical formulation of Young's idea about the nature of diffraction. It is pointed out that the diffracted field is given by the superposition of the boundary wave pulse (formed by interference of the elementary boundary diffraction waves) and the geometric (direct) pulse (governed by the laws of geometrical optics). The case of a circular aperture is treated in details. The diffracted field on the optical axis is calculated analytically (without any approximation) for an arbitrary temporal pulse shape. Because of the short pulse duration and the path difference the geometric and the boundary wave pulses appear separately, i.e., the boundary waves are manifested in themselves in the illuminated region (in the sense of geometrical optics). The properties of the boundary wave pulse is discussed. Its radial intensity distribution can be approximated by the Bessel function of zero order if the observation points are in the illuminated region and far from the plane of the aperture and close to the optical axis. Although the boundary wave pulse propagates on the optical axis at a speed exceeding c, it does not contradict the theory of relativity.

Journal Article↗
PubMed2001

Stability of multiple pulses in discrete systems.

The stability of multiple-pulse solutions to the discrete nonlinear Schrödinger equation is considered. A bound state of widely separated single pulses is rigorously shown to be unstable, unless the phase shift Delta phi between adjacent pulses satisfies Delta phi=pi. This instability is accounted for by positive real eigenvalues in the linearized system. The analysis leading to the instability result does not, however, determine the linear stability of those multiple pulses for which Delta phi=pi between adjacent pulses. A direct variational approach for a two-pulse predicts that it is linearly stable if Delta phi=pi, and if the separation between the individual pulses satisfies a certain condition. The variational approach can easily be generalized to study the stability of N pulses for any N>or=3. The analysis is supplemented with a detailed numerical stability analysis.

Journal Article↗