Pulse Configuration Research Articles

Time-resolved broadband Raman spectroscopies: A unified six-wave-mixing representation

Excited-state vibrational dynamics in molecules can be studied by an electronically off-resonant Raman process induced by a probe pulse with variable delay with respect to an actinic pulse. We establish the connection between several variants of the technique that involve either spontaneous or stimulated Raman detection and different pulse configurations. By using loop diagrams in the frequency domain, we show that all signals can be described as six wave mixing which depend on the same four point molecular correlation functions involving two transition dipoles and two polarizabilities and accompanied by a different gating. Simulations for the stochastic two-state-jump model illustrate the origin of the absorptive and dispersive features observed experimentally.

P 231. A physiological characterization of biphasic transcranial magnetic stimulation

In transcranial magnetic stimulation (TMS), two pulse waveforms are mainly used to study cortical function. While monophasic stimuli are optimal to measure cortical excitability, the biphasic pulse waveform is increasingly used to induce cortical plasticity and to treat neurological as well as psychiatric illnesses. We used a novel stimulation device (flexTMS) to study variable pulse configurations in young healthy volunteers. Primary outcome measure was cortical resting motor threshold (RMT). We determined the strength-duration relationship for single-pulse biphasic TMS using pulse durations between 120 and 400 μ s. To further characterize the biphasic stimulus, we systematically varied amplitude and current direction of the first and second part of the stimulus waveform. The strength-duration relation has a parabolic shape for biphasic stimulation with a minimum at a pulse length of approximately 240 μ s. Varying the amplitude of the part inducing a posterior-anterior oriented current considerably raised RMT, while changes of the part which induces an anterior-posterior current had little effect. Our results clarify the role of pulse duration in biphasic TMS. The part inducing a posterior-anterior current in the brain contributes most to the effect of biphasic stimulation. These findings have important methodological implications and contribute to the understanding of the physiology of TMS.

Time resolved study of the emission enhancement mechanisms in orthogonal double-pulse laser-induced breakdown spectroscopy

The evolution of laser induced ablation plume on aluminum targets has been investigated in orthogonal pre-ablation double pulse scheme at atmospheric pressure from the earliest stages of plasma evolution. Time-resolved emission spectra from neutrals, singly- and doubly-ionized species obtained with the double pulse experiment have been compared with those from the single pulse configuration. Signal-to-noise enhancement reaches values of up to 15 depending on the analyzed species; and the lower the charge state the later its maximum signal-to-noise ratio is reached. Ablation plume dynamics was monitored from 10ns after the plasma onset via shadowgraphy and fast-photography with narrow interference filters to follow the evolution of individual species. Results show that ionic species from the target are located at the plasma core while nitrogen from the background air is found at the plume peripheral. Initially both configurations exhibit similar ablation plume sizes and their expansions were successfully fitted with the strong explosion model for the first 500ns. At later times a good agreement was obtained by using the drag model, which predicts that the plume expansion eventually stops due to interaction with the background gas particles. The emission enhancement measured in the double pulse scheme is discussed in terms of the models describing the plume dynamics.

Two-Dimensional Stimulated Ultraviolet Resonance Raman Spectra of Tyrosine and Tryptophan; A Simulation Study.

We report an ab-initio simulation study of the ultrafast broad bandwidth ultraviolet (UV) stimulated resonance Raman spectra (SRRS) of L-tyrosine, L-tryptophan and trans-L-tryptophan-L-tyrosine (WY) dipeptide. Two-pulse one-dimensional (1D) SRRS and three-pulse 2D SRRS that reveal inter- and intra-residue vibrational coorelations are simulated using electronically resonant or preresonant pulse configurations that select the Raman signal and discriminate against excited state pathways. Multimode effects are incorporated via the cumulant expansion. The 2D SRRS technique is more sensitive to residue couplings than spontaneous Raman.

A Propagation Model for Subsurface and Through-Wall Imaging Applications under the Frequency Dispersion Perspective

The frequency-dependent behavior in subsurface and through-the-wall media is analyzed in this paper as well as the formation of the Brillouin precursor waveforms inherently related to this feature. The emergence of these forerunners is presented as a plausible form to explain classical impairments observed in imaging technologies. The evolution of mono- and multicycle rectangular and first derivative Gaussian pulses through two dispersive media—concrete blocks and soil—is analyzed using a frequency-domain technique and the Debye dielectric model to characterize the media, at operating frequencies below 3 GHz. The frequency-domain approach facilitated to check the influence of some parameters considered critical for the precursor emergence—operating frequency, input pulse configuration, and internal structure of the underlying medium—results in a versatile tool suitable for any kind of modulated input signal propagated through any dispersive medium. The internal multireflection model has been considered as the most suitable model to describe the transmission process underlying both subsurface and through-wall imaging technologies. Two different moisture contents have been considered for concrete as a parameter to determine the performance of through-wall imaging radar from the precursor formation perspective. The results reveal that precursor is a phenomenon to take into account for application demanding larger signal-to-noise ratios.

Enhancement of intra-body propagation and communication under the Brillouin precursor perspective

The emergence of the Brillouin precursor is presented as a plausible form to understand classical phenomena observed in intra-body propagation and through-tissue imaging technologies that can be associated with the features of these precursors formation, such as the non-exponentially level decay and the broadening of pulse duration. The authors describe the evolution of different pulses through skin, muscle as well as normal and malignant breast tissues by using both a time-domain and a frequency-domain analysis technique and multi-pole Debye models to characterise the dielectric properties of the considered tissues, in a frequency band designated by the Federal Communication Commission (FCC) for ultra wideband medical applications, 0.5–20 GHz. The Cole–Cole model is also tested for the same frequency range and tissues in order to determine the influence of the dielectric model. The authors tested the influence of one of the main parameters considered critical for precursor emergence: the input pulse configuration. The results reveal that the precursor is a phenomenon to take into account for application in areas where larger signal-to-noise ratios can be of interest.

Transcranial magnetic stimulation with a half-sine wave pulse elicits direction-specific effects in human motor cortex

BackgroundTranscranial magnetic stimulation (TMS) commonly uses so-called monophasic pulses where the initial rapidly changing current flow is followed by a critically dampened return current. It has been shown that a monophasic TMS pulse preferentially excites different cortical circuits in the human motor hand area (M1-HAND), if the induced tissue current has a posterior-to-anterior (PA) or anterior-to-posterior (AP) direction. Here we tested whether similar direction-specific effects could be elicited in M1-HAND using TMS pulses with a half-sine wave configuration.ResultsIn 10 young participants, we applied half-sine pulses to the right M1-HAND which elicited PA or AP currents with respect to the orientation of the central sulcus.Measurements of the motor evoked potential (MEP) revealed that PA half-sine stimulation resulted in lower resting motor threshold (RMT) than AP stimulation. When stimulus intensity (SI) was gradually increased as percentage of maximal stimulator output, the stimulus–response curve (SRC) of MEP amplitude showed a leftward shift for PA as opposed to AP half-sine stimulation. Further, MEP latencies were approximately 1 ms shorter for PA relative to AP half-sine stimulation across the entire SI range tested. When adjusting SI to the respective RMT of PA and AP stimulation, the direction-specific differences in MEP latencies persisted, while the gain function of MEP amplitudes was comparable for PA and AP stimulation.ConclusionsUsing half-sine pulse configuration, single-pulse TMS elicits consistent direction-specific effects in M1-HAND that are similar to TMS with monophasic pulses. The longer MEP latency for AP half-sine stimulation suggests that PA and AP half-sine stimulation preferentially activates different sets of cortical neurons that are involved in the generation of different corticospinal descending volleys.

Laser-driven shock propagation into quartz targets driven by various drive pulse configurations: experiments

Both direct-drive and indirect-drive inertial confinement fusion targets use temporally shaped drive pulses to optimize the target performance. The timing of multiple shock waves is crucial to the performance of inertial confinement fusion ignition targets. This paper reports an experimental study on the shock wave characteristics of laser-irradiated targets. The shock wave velocity profiles are measured using the velocity interferometer system for any reflector (VISAR). Presented are measurements of velocities from shock waves in quartz targets driven by single 120 ps pulse, two 120 ps pulses separated by 1.1 ns and a special shaped pulse. These pulses drive two shock waves that coalesce in the target, and the coalescence times and transit times are observed by VISAR.

Pulse microwave-assisted synthesis of Pt nanoparticles onto carbon nanotubes as electrocatalysts for proton exchange membrane fuel cells

This study represents a comprehensive pulse microwave-assisted polyol synthesis method to deposit Pt catalysts onto multi-walled carbon nanotubes (CNTs). Three electrocatalysts have been prepared using different microwave pulse (MP=ton/toff) configurations, namely, CAT 3-1 (MP=3), CAT 2-1 (MP=2), and CAT 3-2 (MP=1.5). The experimental results reveal that the CAT 3-2 catalyst possesses the smallest mean particle size of 2.1nm and the most uniform distribution among these catalysts. The CAT 3-2 catalyst also exhibits the highest electrochemical surface area with excellent stability and the best peak power density of 11.4kWgPt−1 (as anode catalyst) and 5.45kWg−1 (as cathode catalyst) at 80°C. On the basis of the experimental results, the well-dispersed Pt particles over the CNT support by the microwave-assisted deposition deliver an improved catalytic activity and excellent stability not only for hydrogen oxidation reaction but also oxygen reduction reaction kinetics.

Investigations on tailoring the deposition conditions in HIPIMS by varying the pulse durations and the argon partial pressure

In most cases HIPIMS is used to get the highest possible ionisation of the deposition particles, which is realised by pulse durations with short on- and very long off-times. These conditions are combined with a more or less pronounced decrease in deposition rate. In this work the pulse configuration has been varied. A three dimensional matrix of parameters was spanned, made of 3 on- and 3 off-times at 4 argon partial pressures. The average power was kept constant and the data achieved were additionally compared to DC-magnetron sputtering. The experiments were carried out using 50 mm diameter targets made of Ti, powered by a MELEC SPIK1000A pulser unit. The deposition rate was measured by quartz microbalance mounted in front of the target. Peak current density and target voltage were recorded and time averaged optical emission spectroscopy (t.a.OES) measurements provided information about the ionisation conditions in the plasma. The results of the data analysis provide a coherent overview of the impact of the HIPIMS parameters as well as of their complex interrelations.

Modelling of target effects in reactive HIPIMS

In reactive High Power Impulse Magnetron Sputtering (HIPIMS) of oxides, target effects such as reduced surface oxidation during pulse off time, increased implantation of reactive gas due to the higher discharge voltage as compared to normal DC sputtering, and enhanced target cleaning during on time are considered to be responsible for the differences compared to reactive DC sputtering. These effects are assumed to cause changes in the target oxide coverage and hence lead to the hysteresis shifts observed in experimental studies. In this contribution, the target processes are simulated using the binary collision approximation code TRIDYN. Using an Al target sputtered in Ar+O2 mixture as a model system, a range of pulse configurations is simulated for different oxygen partial pressures. The results indicate that the target effects alone are not sufficient to explain the observed shift of hysteresis and its frequency dependence.

Investigation of materials of different crystal structure under various time delays using double pulse laser induced breakdown spectroscopy

The performance of a commercial, compact and portable laser induced breakdown spectroscopy (LIBS) system and a constructed laboratory LIBS system with different experimental approaches were investigated in order to make improvements in the qualitative results. One of the experimental studies pertained to the investigation of the different crystal surfaces of silicon. The second experimental study involved the polarization effects by which the polarization dependency was demonstrated. The third and final experimental study was an unconventional orthogonal double pulse configuration with a 45° angle of incidence for both lasers in opposite directions. By means of these experimental approaches reliable, reproducible results were obtained, relative intensities of the emission lines were enhanced and better signal to noise ratios were observed. Furthermore, the qualitative analysis performance of the commercial system software was compared with the code developed. The code yielded more accurate and precise analysis capability.

1008 SACRAL NEUROSTIMULATION (SNS) IN A RODENT MODEL: EFFECTS OF NERVE LOCATION AND PULSE PARAMETERS ON SYNAPTIC ELEMENTS OF A SEXUAL RESPONSE SPINAL CIRCUIT

You have accessJournal of UrologySexual Function/Dysfunction/Andrology: Basic Research II1 Apr 20121008 SACRAL NEUROSTIMULATION (SNS) IN A RODENT MODEL: EFFECTS OF NERVE LOCATION AND PULSE PARAMETERS ON SYNAPTIC ELEMENTS OF A SEXUAL RESPONSE SPINAL CIRCUIT Richard Johnson, Sunny Ferrero, and Victoria Dugan Richard JohnsonRichard Johnson Gainesville, FL More articles by this author , Sunny FerreroSunny Ferrero Gainesville, FL More articles by this author , and Victoria DuganVictoria Dugan Gainesville, FL More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2012.02.1110AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Electrical neurostimulation of human sacral spinal nerves (SNS) is used to treat overactive bladder. SNS also activates axons involved in sexual function and recent clinical studies document a potential benefit on sexual outcomes. A rat model was developed to investigate neurostimulation (NS) nerve sites and pulse parameters. We evaluated the NS effects on a spinal reflex circuit involved in sexual response. The pudendal motoneuron reflex discharge (PMRD) has been previously described in males as a sensitive measure of the spinal circuit integrity for ejaculation (e.g. chronic spinal cord injury, premature ejaculation) and in females to assess treatments for bladder control. The PMRD is triggered by the dorsal nerve of the penis (DNP). Elimination of any of the penile sensory, spinal cord, or pudendal motor limbs of this reflex prevents the occurrence of ejaculation and sensations of orgasm. METHODS In anesthetized male rats, the magnitude of the DNP-elicited PMRD test response on the right side of the animal was quantitated by recording reflex-evoked action potentials in pudendal motor axons elicited by penile afferent activation. The central spinal effects of NS applied to multiple nerves on the left side was evaluated by quantifying the contralateral synaptic modulation of the right-sided PMRD in this bilateral circuit. NS periods of 20 sec to 5 min were induced over a wide range of frequencies (1- 50 Hz) and pulse configurations. RESULTS Results were (i) a frequency-dependent (maximum at 20-25 Hz) but mostly transient (initial 20 sec) depression of PMRD magnitude occurred during NS of the DNP, compound pudendal nerve, and L6 spinal nerve but not during NS of the superficial perineal nerve or the S1 spinal nerve, and (ii) the reflex depression was significantly less when only large diameter afferents were stimulated (biphasic NS pulse widths of 0.01-0.02 ms) compared to when large and small diameter afferents are stimulated (pulse widths of 0.5 ms) particularly when the current intensity was set near 1.0 times reflex threshold. CONCLUSIONS We conclude that the NS at certain targets and parameters, can induce transient depression of the PMRD. The PMRD depression is elicited only when nerves containing DNP afferents are stimulated. The depression is frequency dependent and minimized when only large diameter myelinated afferents are stimulated using short duration pulses and low current intensity. The nerve site and parameter differences may explain the high variability in NS-induced sexual response effects in patients. © 2012 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 187Issue 4SApril 2012Page: e410 Advertisement Copyright & Permissions© 2012 by American Urological Association Education and Research, Inc.MetricsAuthor Information Richard Johnson Gainesville, FL More articles by this author Sunny Ferrero Gainesville, FL More articles by this author Victoria Dugan Gainesville, FL More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Direct micro-joining of flexible printed circuit and metal electrode by pulsed Nd:YAG laser

Laser micro-welding has proven to be a very successful tool for micro-joining in the electrical and electronic industries, where the miniaturization, the high strength and the high heat resistance are constantly requested. Recently, a flexible printed circuit (FPC) is expected as a new connection technology between electrical conductors according to the improvements of reliability and controllability with the diversification of the design concept. In this technology, it is required to weld a several tens μm thickness of FPC and a several hundreds μm thickness of metal electrode. This material combination accompanies the difficulty to control the welding phenomenon due to the differences of thermal property and heat capacity. As a good alternative, laser micro-welding has advantages of non-contact tool, low heat distortion and consistent weld integrity. In this study, the overlap welding of thin copper circuit on a polyimide film and a thick brass electrode was experimentally and numerically investigated by using a pulsed Nd:YAG laser. In addition, the shearing stress of overlap welding was evaluated with and without the control of pulse waveform, which can provide a well-directed controlling of the heat input with high energy density. The results showed that a porosity was observed as the major weld defect in the welding process without a pulse control. However, the appropriate controlled laser pulse configuration of micro-welding could remove the weld defects in the molten zone, improve the weld penetration stability and increase the weld strength. The potential benefits of controlled pulse waveform were discussed for the direct laser micro-welding process. It is clarified that the direct laser micro-welding of a thin copper circuit on a polyimide film and a thick brass electrode could be successfully achieved by appropriate controlled pulse waveform and heat input.

(LIBS) A PROMISING TECHNIQUE, ITS LIMITATIONS AND A PROPOSED METHOD

Laser Induced Breakdown spectroscopy (LIBS) is an extremely potential spectroscopic analytical tool. A highly focused laser bean stiochiometerically ablates the surface of the material in the form of a plasma plume. Excited species in the plasma plume emit their characteristic wavelengths upon de-excitation which are collected, dispersed and analyzed for qualitative and quantitative analyses. Basic LIBS setup includes a laser, target sample, optical fiber and a spectrometer. However it has been used in different configurations like single–pulse and double pulse configurations. LIBS has several advantages over other currently practiced analytical techniques in terms of higher resolution, better limit of detection (LOD), negligible sample preparation etc. Despite of all these advantages it is suffering from poor accuracy and reproducibility of results due to uncontrolled atmosphere around the targeted sample and variations in other experimental parameters. In order to improve reliability of LIBS in terms of accuracy and reproducibility we have designed a methodology for experimentation under controlled environmental conditions inside an especially designed ablation chamber. We will make use of multiple simultaneous laser pulses, which are supposed to play a significant role in improving the analytical accuracy of LIBS particularly for non homogeneous samples. In this article we will briefly review the basics of LIBS, its types, common instrumentations, advantages, limitations applications and at the end our proposed methodology.

Nanostructure transition in Cr–C–N coatings deposited by pulsed closed field unbalanced magnetron sputtering

Cr–C–N coatings with different compositions, i.e. (C+N)/Cr atomic ratios (x) of 0.81–2.77, were deposited using pulsed closed field unbalanced magnetron sputtering by varying the chromium and graphite target powers, the pulse configuration and the ratio of the nitrogen flow rate to the total gas flow rate. Three kinds of nanostructures were identified in the Cr–C–N coatings dependent on the x values: a nano-columnar structure of hexagonal closed-packed (hcp) Cr2(C,N) and face-centered cubic (fcc) Cr(C,N) at x=0.81 and 1.03 respectively, a nanocomposite structure consisting of nanocrystalline Cr(C,N) embedded in an amorphous C(N) matrix at x=1.26 and 1.78, and a Cr-containing amorphous C(N) structure at x=2.77. A maximum hardness of 31.0GPa and a high H/E ratio of 1.0 have been achieved in the nc-Cr(C,N)/a-C(N) nanocomposite structure at x=1.26, whereas the coating with a Cr-containing amorphous C(N) structure had a minimum hardness of 10.9GPa and a low H/E ratio of 0.08 at x=2.77. The incorporation of carbon into the Cr–N coatings led to a phase transition from hcp-Cr2(C,N) to fcc-Cr(C,N) by the dissolution into the nanocrystallites, and promoted the amorphization of Cr–C–N coatings with the precipitation of amorphous C(N). It was found that a high x value over 1.0 in the Cr–C–N coatings is the composition threshold to the nanostructure transition.

Low Friction CrNMPP/TiNDCMS Multilayer Coatings.

Transition metal nitrides like CrN and TiN are widely used in automotive applications due to their high hardness and wear resistance. Recently, we showed that a multilayer architecture of CrN and TiN, deposited using the hybrid—high power impulse magnetron sputtering (HIPIMS) and direct current magnetron sputtering (DCMS)—HIPIMS/DCMS deposition technique, results in coatings which indicate not only increased mechanical and tribological properties but also friction coefficients in the range of diamond-like-carbon coatings when tested at RT and ambient air conditions. The modulated pulsed power (MPP) deposition technique was used to replace the HIPIMS powered cathode within this study to allow for a higher deposition rate, which is based on the complex MPP pulse configuration. Our results on MPP/DCMS deposited CrN/TiN multilayer coatings indicate excellent mechanical and tribological properties, comparable to those obtained for HIPIMS/DCMS. Hardness values are around 25 GPa with wear rates in the range of 2 × 10−16 Nm/m3 and a coefficient of friction around 0.05 when preparing a superlattice structure. The low friction values can directly be correlated to the relative humidity in the ambient air during dry sliding testing. A minimum relative humidity of 13% is necessary to guarantee such low friction values, as confirmed by repeated tests, which are even obtained after vacuum annealing to 700 °C. Our results demonstrate that the co-sputtering of high metal ion sputtering techniques and conventional DC sputtering opens a new field of applications for CrN/TiN coatings as high wear resistance and low friction coatings.

A comparative study of single and double pulse of laser induced breakdown spectroscopy of silver

We present a comparative study of the collinear and orthogonal pre-ablation dual pulse configurations of laser induced breakdown spectroscopy (LIBS) of silver using Nd:YAG lasers. The effect of the inter-pulse delay and the ratio of the laser pulse energies on the signal intensity enhancement for both the dual pulse configurations have been investigated. Using the first laser at 532 nm and second laser at 1064 nm delayed by 5 μs, we achieved nearly 2 times signal enhancement in the collinear double-pulsed configuration and nearly 12 times in the pre-ablation orthogonal configuration as compared to SP LIBS. It is ascertained that at the optimized value of the inter-pulse delay between the two lasers, the intensity ratio of the neutral silver lines follows the local thermo dynamical equilibrium (LTE) condition and it is also in excellent agreement with that of the relative transitions probabilities ratio listed in the NIST data base.

SU‐E‐I‐83: Filling the Gap: Using Detailed Machine Parameters to Refine Skin Dose Calculations for Fluoroscopic Sentinel Events

Purpose: To examine the role that detailed machine logs, supplementary procedural documentation and vendor‐generated technique and dosimetry information can play in refining calculation of peak skin dose for sentinel event investigations.Methods: Vendor‐specific machine logs, skin‐dose estimations, and procedural observations can supplement the fluoroscopic times and air kerma values that all fluoroscopic machines are required to report since 2006. Information available from vendors varies considerably, and in some cases specific application products must be purchased to access this information. Information embodied may include table position, c‐arm geometry, collimation, individual run and fluoro acquisition dosimetry, technique factors (mA, kVp, pulse configuration), mode of operation and other data. Peak skin dose estimates based on HIS/RIS data and DICOM image headers were compared to calculations supplemented by the detailed machine logs and vendor dosimetry estimates. Skin dose maps were generated from air kerma readings and from the DICOM information associated with each run. Assumptions are necessary in this approach to apportion the fluoroscopic contribution, which can be 80% of the air kerma. Corresponding skin dose maps were generated with inclusion of more detailed machine log data and the resulting peak skin dose location and magnitudes were compared.Results: Significant deviations were observed between peak skin dose calculations based on DICOM information alone with attendant assumptions versus those obtained with more detailed machine log data. Detailed logs provide complementary information that replaces assumptions on fluoroscopic dose contributions with more reliable values. Conclusions: Additional information from vendorˈs logs and dose‐ estimates and from other sources can increase the confidence in skin‐dose calculations, but the specific assumptions made by both the physicist and the vendor in making such estimates must be carefully examined. The comparison enables the stand‐alone assumptions to be validated and also allows evaluation of vendor dosimetry estimates.

Coherent Control Protocol for Separating Energy-Transfer Pathways in Photosynthetic Complexes by Chiral Multidimensional Signals

Adaptive optimizations performed using a genetic algorithm are employed to construct optimal laser pulse configurations that separate spectroscopic features associated with the two main energy-transfer pathways in the third-order nonlinear optical response simulated for the Fenna-Matthews-Olson (FMO) photosynthetic complex from the green sulfur bacterium Chlorobium tepidum. Superpositions of chirality-induced tensor components in both collinear and noncollinear pulse configurations are analyzed. The optimal signals obtained by manipulating the ratios of various 2D spectral peaks reveal detailed information about the excitation dynamics.