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Short Pulses (short + pulse)
Selected AbstractsMicrodimensional Polyaniline: Fabrication and Characterization of Dynamics of Charge Propagation at Microdisk ElectrodesELECTROANALYSIS, Issue 17 2004Karolina Caban Abstract We describe fabrication of microdimensional polyanilne films in a controlled manner by voltammetric potential cycling or controlled potential electrolysis on platinum microdisk electrodes. The film grows in a form of hemispherical microdeposits, and its size largely exceeds the size of a Pt microdisk. Consequently, the film covers both the Pt substrate as well as the surrounding glass seal. Since the adhering polyaniline layer is conducting, the latter situation may lead to an increase in the effective electrode surface area. The lateral growth of polyaniline films outside the microdisk has also been demonstrated by performing diagnostic voltammetric experiments with use of a double microdisk set-up in which independent polarization of each disk is feasible. Microelectrode-based chronocoulometry, that involves an uncomplicated well-defined reduction potential step starting from the emeraldine (conducting) form and ending at leucoemeraldine (nonconducting) form, yields (upon application of a sufficiently short pulse) a well-defined linear response of charge versus square root of time that is consistent with the linear effective diffusion as the predominant charge propagation mechanism. When describing the system kinetics in terms of the effective (apparent) diffusion coefficient, we expect this parameter to be on the level of 10,8,cm2 s,1 or lower. The relative changes in dynamics of charge transport are discussed with respect to the polyaniline film loading, the size of microdisk electrode, expansion of the active electrode area, and the choice of electrolyte (strong acid) anion. The results are consistent with the view that when Pt microelectrode is modified with PANI deposit exceeding the size of the microdisk substrate, it behaves in a way as if its surface area is effectively much larger than the geometric area of Pt microdisk. [source] Nonlinear resonant change in refractive index of a doped saturable medium at short-pulse excitationLASER PHYSICS LETTERS, Issue 10 2005A.V. Kir'yanov Abstract A novel method is reported for calculating the nonlinear resonant change in refractive index of a doped saturable medium at the short-pulse excitation. The derived system of equations for energy density and phase of a short pulse propagating in the doped medium allows one to address a rather general case of the resonant index non-linearity caused by the dope's population perturbation (bleaching) effect. As an example, the energy-dependent changes in the refractive index and transmission coefficient of a Cr4+:YAG crystal under the ns-range (wavelength 1.06 µm) excitation are modeled. (© 2005 by Astro, Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] Pulsed electrical stimulation for control of vasculature: Temporary vasoconstriction and permanent thrombosisBIOELECTROMAGNETICS, Issue 2 2008Daniel Palanker Abstract A variety of medical procedures is aimed to selectively compromise or destroy vascular function. Such procedures include cancer therapies, treatments of cutaneous vascular disorders, and temporary hemostasis during surgery. Currently, technologies such as lasers, cryosurgery and radio frequency coagulation, produce significant collateral damage due to the thermal nature of these interactions and corresponding heat exchange with surrounding tissues. We describe a non-thermal method of inducing temporary vasoconstriction and permanent thrombosis using short pulse (microseconds) electrical stimulation. The current density required for vasoconstriction increases with decreasing pulse duration approximately as t,0.25. The threshold of electroporation has a steeper dependence on pulse duration,exceeding t,0.5. At pulse durations shorter than 5,µs, damage threshold exceeds the vasoconstriction threshold, thus allowing for temporary hemostasis without direct damage to surrounding tissue. With a pulse repetition rate of 0.1,Hz, vasoconstriction is achieved approximately 1 min after the beginning of treatment in both arteries and veins. Thrombosis occurs at higher electric fields, and its threshold increases with vessel diameter. Histology demonstrated a lack of tissue damage during vasoconstriction, but vascular endothelium was damaged during thrombosis. The temperature increase does not exceed 0.1,°C during these treatments. Bioelectromagnetics 29:100,107, 2008. © 2007 Wiley-Liss, Inc. [source] Female Mate Choice, Calling Song and Genetic Variance in the Cricket, Gryllodes sigillatusETHOLOGY, Issue 3 2008Jocelyn Champagnon Female preferences for song patterns of males of Gryllodes sigillatus and genetic variance of morphological traits correlated with them were analyzed. Females preferred short pulses associated with large males. The males' thorax width, wing length and femur III length showed stronger relationship with the song pulse duration, whereas the relationship between pulse duration and wing width was not significant. Interestingly, this last trait was the only one that showed significant levels of genetic variance. Perhaps these results could be explained by the evolutionary response to sexual selection. Sexual selection could deplete the genetic variance in the male traits related to male-mating success. [source] Irreversible electroporation of the pancreas in swine: a pilot studyHPB, Issue 5 2010Kevin P. Charpentier Abstract Background:, Irreversible electroporation (IRE) is a novel, non-thermal method of tissue ablation using short pulses of high-voltage DC current to ablate tissue. Methods:, Irreversible electroporation of the pancreas was performed in four domestic female swine using two monopolar probes spaced 9,15 mm apart. Ninety pulses of 1500 V/cm were delivered for each ablation. Results:, All animals survived for their designated times of 2 h (n= 1), 2 days (n= 1) and 14 days (n= 2), respectively. No procedure-related complications occurred. Three animals in which probes had been spaced at intervals of 10 ± 1 mm showed evidence of irreversible ablation, with ablation height ranging from <10 mm to 21 mm and ablation width ranging from <10 mm to 16 mm by gross appearance and triphenyltetrazolium chloride (TTC) staining. The only animal in which probes had been spaced at intervals of 15 mm did not show evidence of irreversible ablation at 2 weeks. This may be secondary to the wider probe spacing and relatively low voltage, which results in a mostly reversible form of electroporation without cell death. Conclusions:, Irreversible electroporation appears to be a safe method for pancreas tissue ablation. Staining with TTC can predict the zone of IRE ablation within 2 h of treatment. [source] NOx storage and reduction with propylene on Pt/BaO/aluminaAICHE JOURNAL, Issue 10 2004Rachel L. Muncrief Abstract An experimental study was carried out of periodically operated NOx (NO + NO2) storage and reduction on a model Pt/BaO/Al2O3 catalyst powder. The effect of the reductant (propylene) injection policy on time-averaged NOx conversion was evaluated in terms of feed composition and temperature, reductant pulse duration, and overall cycle time. Conditions giving time-averaged NOx conversions exceeding 90% were identified. The reductant-to-oxidant ratio during the injection and the total cycle time are both found to be critical factors to achieve high conversion. The time-averaged conversion is bounded above and below by the steady-state conversions obtained with feeds having the same compositions as that during the rich and lean part of the cycle, respectively. For a fixed supply of propylene, short pulses of high concentration are much more effective than longer pulses of reduced concentration. The NOx conversion achieves a maximum value at an intermediate overall cycle time when the propylene pulse of fixed duty fraction is net reducing. High conversions are sustained over a wide temperature window (200,400°C). A simple storage,reduction cycle is proposed that elucidates the main findings in the study. The key factor for high NOx conversion is the temporal production of oxygen-deficient conditions coupled with high catalyst temperatures, both resulting from the intermittent catalytic oxidation of propylene. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2526,2540, 2004 [source] Quaternary phase coding and decoding of short pulses at 40 Gb/s using superstructured fiber BRAGG gratingsMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 3 2006Xiaogang Chen Abstract A three-chip, 240-Gchip/s quaternary phase-shift code is assigned to short pulses after reflection from a encoder. The code is then recognized by a decoder. The encoder and decoder consist of superstructured fiber Bragg gratings (SSFBGs). The quaternary phase encoding and decoding of short pulses at 40 Gb/s is experimentally demonstrated, and it is required in optical-code division multiplexing (OCDM) systems and packet-switched networks. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 575,577 2006; Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/mop.21411 [source] Electrically wavelength-tunable optical short-pulse generation in a self-seeding scheme with intensity controllable feedbackMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 2 2003D. N. Wang Abstract A simple and robust system is presented to generate electrically wavelength-tunable optical short pulses from a gain-switched Fabry,Perot laser diode. The laser external cavity consists of a tunable filter and an erbium-doped fiber amplifier, which provides wavelength selectivity and intensity controllable feedback. As a result, a side mode suppression ratio SMSR of better than 30 dB over the wavelength tuning range of 17.5 nm can be obtained. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 38: 98,99, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10982 [source] Efficacy and efficiency of gastric electrical stimulation with short pulses in the treatment of vasopressin-induced emetic responses in dogsNEUROGASTROENTEROLOGY & MOTILITY, Issue 5 2006G. Song Abstract, The aim of this study was to determine the most effective and efficient anti-emetic parameters of short-pulse gastric electrical stimulation (GES) in dogs. Seven female beagle dogs implanted with four pairs of gastric electrodes were studied in eight randomized sessions (saline, vasopressin, and six GES sessions with different parameters). Each session consisted of four 20-min recordings of gastric slow waves and symptoms. In sessions 1 and 2, saline and vasopressin, respectively, were infused during the second 20-min period. The protocol of the other six sessions was the same as session 2 except that GES was continuously applied. It was found that: (1) vasopressin induced gastric dysrhythmia and emetic response (P < 0.01, anova); (2) short-pulse GES with a frequency of 14 or 40 Hz and pulse width of 0.1 or 0.3 ms, but not 0.6 ms was able to reduce symptoms induced by vasopressin; (3) short-pulse GES with a pulse width of 0.3 ms was the most effective in preventing vasopressin-induced symptoms; (4) none of the tested GES methods improved vasopressin-induced gastric dysrhythmia. We conclude that vasopressin induces gastric dysrhythmia and symptoms. Short-pulse GES with a pulse width of 0.3 ms and frequency of 14 Hz is most effective and efficient in preventing vasopressin-induced emetic responses in dogs. [source] Electrochemical Microstructuring with Short Voltage PulsesCHEMPHYSCHEM, Issue 1 2007Rolf Schuster Prof. Dr. Abstract The application of short (nanosecond) voltage pulses between a tool electrode and a workpiece immersed in an electrolyte solution allows the three-dimensional machining of electrochemically active materials with submicrometer resolution. The method is based on the finite charging time constant of the double-layer capacitance, which varies approximately linearly with the local separation between the electrode surfaces. Hence, the polarization of the electrodes during short pulses and subsequent electrochemical reactions are confined to regions where the electrodes are in sufficiently close proximity. This Minireview describes the principles behind electrochemical microstructuring with short voltage pulses, and its current achievements and limitations. [source] | ||||||||||||||||