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Pulse Frequency (pulse + frequency)
Selected Abstracts1-D Self-consistent Fluid Modelling of the Pulsed Magnetron DischargePLASMA PROCESSES AND POLYMERS, Issue S1 2009Philip Thomason Abstract A 1-D fluid code simulation of the region above the racetrack in a magnetron discharge has been developed to yield predictions for the temporal evolution of the axial plasma parameters during pulsed DC operation. To take into account anomalous cross-field diffusion transport rates, an effective magnetic field profile has been calculated based on the real experimental values, to yield ratios in the effective electron gyro and collision frequencies comparable with Bohm diffusion. Pulse frequencies from 100 to 500,kHz are considered, with gas pressures ranging from 0.25 to 0.65,Pa. The model results for the plasma potential, electron and ion densities, during the pulse cycle agree well with experimental measurements made in the Liverpool magnetron using time-resolved Langmuir and emissive probes. In the bulk plasma, the predictions for electron temperature are close to the measured values; however, in the sheath region they are artificially high due to the model assumption that only Maxwellian distributed electrons exist in all regions of the discharge. This inadequacy in the model and the methods to improve has been discussed. Results for DC magnetrons are also shown. [source] Impact of varying pulse frequency and duration on muscle torque production and fatigue,MUSCLE AND NERVE, Issue 4 2007Chris M. Gregory PhD Abstract Neuromuscular electrical stimulation (NMES) involves the use of electrical current to facilitate contraction of skeletal muscle. However, little is known concerning the effects of varying stimulation parameters on muscle function in humans. The purpose of this study was to determine the extent to which varying pulse duration and frequency altered torque production and fatigability of human skeletal muscle in vivo. Ten subjects underwent NMES-elicited contractions of varying pulse frequencies and durations as well as fatigue tests using stimulation trains of equal total charge, yet differing parametric settings at a constant voltage. Total charge was a strong predictor of torque production, and pulse trains with equal total charge elicited identical torque output. Despite similar torque output, higher- frequency trains caused greater fatigue. These data demonstrate the ability to predictably control torque output by simultaneously controlling pulse frequency and duration and suggest the need to minimize stimulation frequency to control fatigue. Muscle Nerve, 2007 [source] The Complexity of External Acoustic Detection of Defects in Björk-Shiley Convexoconcave Heart ValvesARTIFICIAL ORGANS, Issue 1 2001Bas A. De Mol Abstract: Fractures in Björk-Shiley convexoconcave (BScc) heart valves have raised questions about the feasibility of early diagnosis of technical defects by means of acoustic assessment. Three laboratory tests were conducted. To establish acoustic fingerprints, 66 valves with a defect, such as single-leg fracture (SLF) or single-leg separation (SLS), or without a defect were connected with a contact sensor and excited by dropping a small metal ball onto the outlet strut. In the second test, we simulated the valve sound propagation within the thorax. In the third test, intact, SLF, and SLS valves were placed in a mock heart immersed in a large water tank. We observed a resonance frequency corresponding with valve size and presence of defects. The second test showed that both the chest wall and the lungs created numerous reflections. This led to a substantial overlap of the original pulse frequencies and the frequencies measured. The third test confirmed that submersion of the chest in water can significantly reduce chest wall reflections. Reliable noninvasive assessment of BScc valve clicks for the presence of defects of the outlet strut is hampered by complex sound propagation within the thorax and variability of valve excitation. Acoustic fingerprints to diagnose mechanical defects should be integrated in valve design. [source] Cocaine and Amphetamine-Regulated-Transcript Peptide Mediation of Leptin Stimulatory Effect on the Rat Gonadotropin-Releasing Hormone Pulse Generator In VitroJOURNAL OF NEUROENDOCRINOLOGY, Issue 5 2000Lebrethon Pulsatile gonadotropin-releasing hormone (GnRH) secretion was studied in vitro using explants of the retrochiasmatic hypothalamus from prepubertal male and female rats. Leptin caused a dose-dependent reduction of the GnRH interpulse interval in both sexes. We studied the effects of cocaine- and amphetamine-regulated transcript (CART) since this peptide was shown recently to mediate the anorectic effects of leptin in the hypothalamus. CART caused a reduction of the GnRH interpulse interval. This effect was prevented using an anti-CART antiserum which could partially overcome leptin stimulatory effects as well. Using hypothalamic explants from Zucker rats homozygous for the leptin receptor mutation ( fa/fa), GnRH pulse frequency was not affected by leptin, while a significant acceleration was caused by the CART-peptide. In conclusion, leptin involves the hypothalamic CART-peptide to stimulate the prepubertal GnRH pulse generator in vitro. [source] The influence of polymer concentration, applied voltage, modulation depth and pulse frequency on DNA separation by pulsed field CEJOURNAL OF SEPARATION SCIENCE, JSS, Issue 17-18 2010Zhenqing Li Abstract DNA fragments (0.1,10,kbp (kbp, kilo base pair)) separation by square-wave pulsed field CE in hydroxyethylcellulose (HEC, 1300,K) polymer was performed in this work. The effects of polymer concentration, pulse field strength, pulse frequency and modulation depth were investigated. We found that low HEC (about 0.1%) concentration is suitable for the separation of small DNA fragments (<1,kbp), whereas higher HEC concentration (>0.5%) is appropriated for high-mass DNA molecular (>1,kbp) separation. The mobility of DNA fragments is nearly linearly related to average separation voltage under pulsed field conditions. Higher modulation depth is suited to separate the longer DNA fragments and lower modulation depth favors the resolution of short DNA fragments. Thus, the intermediate modulation depth (100%) and pulse frequency (about 31.3,Hz) are prerequisite for high-resolution DNA separation. [source] Inactivation of orange juice peroxidase by high-intensity pulsed electric fields as influenced by process parametersJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 1 2006Pedro Elez-Martínez Abstract The inactivation of orange juice peroxidase (POD) under high-intensity pulsed electric fields (HIPEF) was studied. The effects of HIPEF parameters (electric field strength, treatment time, pulse polarity, frequency and pulse width) were evaluated and compared with conventional heat pasteurization. Samples were exposed to electric field strengths from 5 to 35 kV cm,1 for up to 1500 µs using square wave pulses in mono- and bipolar mode. Effect of pulse frequency (50,450 Hz), pulse width (1,10 µs) and electric energy on POD inactivation by HIPEF were also studied. Temperature was always below 40 °C. POD was totally inactivated by HIPEF and the treatment was more effective than thermal processing in inactivating orange juice POD. The extent of POD inactivation depended on HIPEF processing parameters. Orange juice POD inhibition was greater when the electric field strength, the treatment time, the pulse frequency and the pulse width increased. Monopolar pulses were more effective than bipolar pulses. Orange juice POD activity decreased with electric energy density input. The Weibull distribution function adequately described orange juice POD inactivation as a function of the majority of HIPEF parameters. Moreover, reduction of POD activity related to the electric field strength could be well described by the Fermi model. Copyright © 2005 Society of Chemical Industry [source] IPL technology: A reviewLASERS IN SURGERY AND MEDICINE, Issue 2 2003Christian Raulin MD Abstract Background and Objectives Intense pulsed light (IPL) systems are high-intensity light sources, which emit polychromatic light. Unlike laser systems, these flashlamps work with noncoherent light in a broad wavelength spectrum of 515,1,200 nm. These properties allow for great variability in selecting individual treatment parameters and adapting to different types of skin types and indications. The purpose of this article was to critically review international medical publications of the many indication in which IPL technology can be used, including our own evaluations and experiences. Study Design/Materials and Methods The range of therapeutic uses for high-intensity flashlamps was reviewed, ranging from benign cavernous hemangiomas, benign venous malformations, essential telangiectasias, leg telangiectasias, poikiloderma of Civatte, and port-wine stains to pigmented lesions, cosmetically undesired hypertrichosis, and facial rhydids. The relative benefits and risks were discussed in detail and compared with other laser systems. Results Because of the wide spectrum of potential combinations of wavelengths, pulse durations, pulse frequency, and fluences, a great deal of experience is required when using IPL technology. Proper patient selection and critical diagnostics serve to keep the adverse effects of the treatment to a minimum. Conclusions The distinctive technical conditions involved combine to make IPL technology an alternative and auxiliary treatment option to existing laser systems and conventional therapies. Lasers Surg. Med. 32:78,87, 2003. © 2003 Wiley-Liss, Inc. [source] Impact of varying pulse frequency and duration on muscle torque production and fatigue,MUSCLE AND NERVE, Issue 4 2007Chris M. Gregory PhD Abstract Neuromuscular electrical stimulation (NMES) involves the use of electrical current to facilitate contraction of skeletal muscle. However, little is known concerning the effects of varying stimulation parameters on muscle function in humans. The purpose of this study was to determine the extent to which varying pulse duration and frequency altered torque production and fatigability of human skeletal muscle in vivo. Ten subjects underwent NMES-elicited contractions of varying pulse frequencies and durations as well as fatigue tests using stimulation trains of equal total charge, yet differing parametric settings at a constant voltage. Total charge was a strong predictor of torque production, and pulse trains with equal total charge elicited identical torque output. Despite similar torque output, higher- frequency trains caused greater fatigue. These data demonstrate the ability to predictably control torque output by simultaneously controlling pulse frequency and duration and suggest the need to minimize stimulation frequency to control fatigue. Muscle Nerve, 2007 [source] Electric Parameters Optimization in Spinal Cord Stimulation.NEUROMODULATION, Issue 4 2010Study in Conventional Nonrechargeable Systems Background:, Spinal cord stimulation devices provide a means of creating an electric field. The parameters used to produce this electric field are: pulse amplitude, pulse width (Pw), and pulse frequency (F). Aims:, The purpose is to document the effects that the various stimulus parameters have on patient perception of paresthesia and the relationship that this perception has on pain relief. Methods:, Stimulus parameters were varied independently keeping the electrode polarity constant while recording stimulation thresholds. The Pw was varied from 195 to 300 µsec while maintaining the frequency at 50 Hz. The F was varied from 10 to 100 Hz while maintaining the Pw at 300 µsec. We also measured the paresthesia coverage percentage and the subjective perception of quality reported by the patients with each one of the parameter changes. Results:, There was a statistically significant correlation between Pw and all the stimulation thresholds. As for the therapeutic range, the differences observed also were statistically significant. Pw variation did not produce significant differences in coverage and subjective quality of the paresthesia. The perception threshold did not vary significantly with F changes. However, F significantly affected both coverage of the painful area and paresthesia perception quality. Conclusions:, In the usual Pw ranges, it seems that its usefulness is limited to obtaining finer adjustments in the stimulation amplitude. Frequency management may be significantly useful to get a wider coverage of the stimulated area. [source] Electrical stimulation of the vestibular system prevents postoperative nausea and vomitingACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 9 2000F. Pusch Background: Electrical stimulation of the vestibular system may prevent nausea and vomiting. We studied the influence of transcutaneous impulse stimulation in prevention of postoperative nausea and vomiting (PONV) following gynaecological surgery. Methods: In this randomised study 70 women undergoing elective gynaecological surgery under general anaesthesia were assigned to receive either the activated (stimulation group) or the inactivated (non-stimulation group) impulse stimulator. The stimulator comprises the stimulator itself, two negative electrodes on a headset applied over both mastoid processes and a nuchal positive electrode. The device yielded a pulse frequency of 5 Hz direct current, individually adjustable between 0.5 and 4 mA. A trapezoid stimulation of 50 ms was applied. Nausea, vomiting, dizziness and the amount of antiemetic drugs used were assessed during the first 4 h postoperatively. Results: Lower postoperative nausea scores with a lower incidence of vomiting and postoperative dizziness were found in the stimulation group. A lower amount of antiemetic drugs was needed in the stimulation group when compared to the non-stimulation group (P<0.01 between groups). Conclusion: This study suggests that electrical stimulation of the vestibular system may be useful in prevention of PONV. [source] Deposition of Cubic Boron Nitride in a Supersonic Plasma Jet Reactor with Secondary DischargePLASMA PROCESSES AND POLYMERS, Issue S1 2007Jami McLaren Abstract We have deposited cubic boron nitride thin films with a supersonic plasma jet chemical vapor deposition system with bipolar pulsed substrate bias. Deposited films were characterized by Fourier transform infrared spectroscopy, micro-X-ray diffraction, and scanning electron microscopy. The cubic boron nitride content is observed to scale well with the degree of ion bombardment of the substrate and growing film, which is affected most drastically by the substrate bias pulse frequency, and positive and negative duty cycle. The magnitude of the negative substrate bias was also critical in depositing cubic boron nitride, with a threshold voltage of approximately 90 V necessary for cubic boron nitride deposition. [source] | |||||||||||||