Longer Pulse Duration Research Articles

Novel Injector of Intense Long Pulse Electron Beam for Linear Plasma Devices

A novel high-power (10 MW) sub-millisecond electron beam is developed for injection into the open (linear) plasma devices. The beam is produced by extraction of electrons from a plasma of pulsed arc discharge in hydrogen. The beam is extracted and accelerated with multiaperture diode-type electron optical system with 241 small round apertures, which are arranged in a hexagon-al pattern. The injector prototype was installed into the end plasma tank of GOL-3 multiple mirror trap and tested to produce an electron beam with up to 100 keV electron energy, about 100 A total beam current and 0.7 ms or longer pulse duration. In a series of preliminary experiments the electron beam was injected into the GOL-3 plasma chamber filled with deuterium gas with a density of 1014-1015cm-3 and transported in a corrugated magnetic field (<B> up to 1.4 T) along the trap at a distance of 12 m.

Effect of different parameters used for in vitro gene electrotransfer on gene expression efficiency, cell viability and visualization of plasmid DNA at the membrane level

Gene electrotransfer is a nonviral method used for DNA delivery into cells. Several steps are involved. One of them is the interaction of DNA with the cell membrane, which is crucial before DNA can enter the cell. We analysed the level of DNA-membrane interaction in relation to electrotransfer efficiency and the importance of the electrophoretic accumulation of DNA at the cell membrane. Systematic comparison of long-duration, short-duration and combinations of electropermeabilizing short (high-voltage; HV) and electrophoretic long (low-voltage; LV) pulses were performed. The effect of Mg(2+) ion concentrations on electrotransfer and their effect on DNase activity were explored. To visualize the DNA-membrane interaction, TOTO-1 labeled DNA was used. Transfection efficiency was assessed with plasmid DNA coding for green fluorescent protein. Higher relative electrotransfer efficiency was obtained by using longer pulses, whereas shorter pulses preserved cell viability. Short-duration pulses enabled higher (24%) overall transfection yield compared to long-duration pulses (12%), although a higher DNA-membrane interaction was observed. No significant difference in transfection was obtained between different HV-LV pulsing protocols, although the highest DNA-membrane interaction was observed with HV + LV pulses. The formation of the DNA-membrane complex depended on the Mg(2+) concentration, whereas DNase inhibitor did not affect gene expression. Gene electrotransfer is a complex phenomenon, where many factors mutually affect the process and the DNA-membrane interaction only comprises the first step. We showed that longer electric pulses are optimal for higher transfection efficiency but reduce viability, whereas shorter pulses enable moderate transfection efficiency and preserve viability. Thus, each application needs a careful choice of pulsing protocol.

Saturation of vibrational coherent anti-Stokes Raman scattering mediated by saturation of the rotational Raman transition

Saturation of vibrational Raman coherence and coherent anti-Stokes Raman scattering (CARS) using femtosecond (fs) excitation pulses is investigated theoretically. The pump in a typical fs-CARS configuration has a bandwidth of a few hundred cm${}^{\ensuremath{-}1}$ that can couple tens of rotational states of room-air nitrogen molecules simultaneously, unlike in CARS with longer pulse durations. It is demonstrated that the vibrational coherence and also the vibrational CARS with fs excitation display saturationlike behavior once the rotational coherence is saturated. The Raman saturation threshold for the fs pump is numerically estimated to be at a peak intensity of $\ensuremath{\sim}$${10}^{22}$ W/m${}^{2}$, which is six to seven orders of magnitude higher than that in the nanosecond regime. The results are compared with the known saturation thresholds in different pulse-duration regimes and placed in perspective with other nonlinear thresholds reported in fs excitation regimes.

A study of the counter rotating vortex rings interacting with the primary vortex ring in shock tube generated flows

The formation and evolution of counter rotating vortex rings (CRVRs) appearing in shock tube-generated flows at high shock Mach numbers (M) have been studied numerically by solving ax symmetric Navier–Stokes equations and compared with experiments. The AUSM + scheme is used for convective terms, and for time stepping a four-stage Runge–Kutta scheme is used. High-speed smoke flow visualizations and optical shadowgraph techniques are employed for verifying the numerical results. It is observed that the strong shear layer formed near the Mach disc in the axial region of the vortex ring plays a dominant role in CRVR formation. A series of CRVRs is formed for longer driver section and higher M as the shear layer persists for longer duration. The interaction of these CRVRs with the primary vortex and trailing jet vortices is studied for (i) different pressure-pulse durations at the open end keeping the amplitude constant, and (ii) varying pulse amplitude when the duration is fixed. Results are also presented comparing a high-amplitude case against a lower-amplitude one with a longer pulse duration. The maximum vorticity inside the first CRVR is found to be higher than the primary vortex ring during its formation.

Simulation of the Melting Volume in Thin Molybdenum Films as a Function of the Laser Pulse Duration

Abstract The interaction of a laser pulse with molybdenum is studied over a wide range of pulse durations from 5 fs to 100 ps using the two-temperature-model (TTM) at constant energy density. The TTM is used to calculate the electron and lattice temperature dynamics and the resulting melting volume. The results show, the maximum melting volume is reached at a pulse duration of 10 ps. The electron heat transfer is dominant for the ultra-short pulse regime below 10 ps, while the lattice heat transfer is influenced by longer pulse durations.

Effect of Cryotherapy on Neuromuscular Electrical Stimulation: A Review of the Literature

Neuromuscular electrical stimulation (NMES) has been shown to be an eff ective technique to strengthen muscle following musculoskeletal injury or surgery. A limitation of NMES is the discomfort caused by the strong electrical contractions required for eff ective strength gains. This article explores whether the application of cryotherapy over muscle aff ects the ability of the muscle to contract in response to NMES and whether the reduction in discomfort of the stimulus enables greater force production. Eleven studies that met the inclusion criteria were reviewed. This review found that short-duration application of cryotherapy can improve tolerance to strong contractions elicited by NMES for muscle strengthening; however, longerduration applications may aff ect muscle force production. More studies are needed to determine the eff ect of cryotherapy on force production of muscle during NMES and whether greater increases in strength can be achieved. Neuromuscular electrical stimulation (NMES) is a widely used intervention for rehabilitation of weak or damaged muscle. Studies support the use of this technique for strengthening muscle following ligament repairs of the knee and total knee joint arthroplasties.1-4 The typical clinical approach is to place electrodes on the skin overlying the motor points of the muscle, which are usually defi ned as the location over the muscle where the motor nerve to the muscle is most accessible. The intensity of the stimulation depends on the amplitude, duration, and frequency of the electrical pulses, or bursts. A high-amplitude, longpulse duration stimulus is required to achieve a contraction that is at least 50% of maximal voluntary contraction (MVC). This stimulus may not be tolerated by the patient. Farquhar and Snyder-Mackler5 identifi ed patient discomfort as the limiting factor in using NMES in clinical settings, especially “when high contractile forces are sought for strength training regimens.” Most clinical uses of NMES are for strengthening of weak or injured muscle. The use of NMES for uninjured individuals is uncommon because strength gains can be achieved by exercise programs without the use of NMES. Patient tolerance to NMES for muscle strengthening depends primarily on the type of electrical current chosen for the treatment and the patient’s pain coping style.5 Some patients can tolerate burst mode alternating current (Russian stimulation) NMES, whereas other patients prefer biphasic pulsed NMES. Pain coping style varies from those patients who focus on the discomfort of NMES and those who focus on the benefi ts of the treatment and are willing to tolerate discomfort. Patients who focus on the discomfort of NMES require a blunting strategy to decrease their perception of pain. Strategies for blunting the perception of pain can include distraction by listening to music or interventions that interrupt nociception to the central nervous system. Modalities such as cryotherapy applied during or prior to NMES may be an effective blunting strategy; however, decreasing the temperature of tissues overlying a muscle or of the muscle itself may affect the ability of NMES to achieve a muscle contraction. The effect of Dr Nolan and Dr Galantino are from the Physical Therapy Program, School of Health Sciences, The Richard Stockton College of New Jersey, Galloway; and Dr Buccafurni is from Fox Rehabilitation, Northfi eld, New Jersey. Received: January 4, 2011 Accepted: June 12, 2012 Posted Online: January 2, 2013 The authors have no fi nancial or proprietary interest in the materials presented

Abstract 301: Does Refibrillation Occur in High-Impedance Patients Who Have Received Shocks Using Biphasic Waveforms with Longer Pulse Durations?

Introduction The electrical impedance between defibrillator pads has a significant effect on the ability of defibrillators to deliver a therapeutic shock. A variety of technologies are used to deliver the chosen therapeutic shocks safely yet effectively across a wide range of patient impedances. Defibrillators will not deliver a shock above pre-set impedance. We assessed the hypothesis that devices which have pulse durations over 20ms may predispose the patient to spontaneous re-fibrillation after a successful shock. Methods Two defibrillators were tested. Device A (A) limited the current delivered and in high impedance patients would extend the pulse duration as needed to deliver the selected energy while staying below the current limit. Device B (B) would truncate the shock to restrict the pulse duration but operated with higher currents. A high impedance porcine model of ventricular fibrillation (VF) was created. Following pilot work we were unable to demonstrate any relationship between pig mass and impedance. Therefore to create high impedance it was necessary to place resistors in series with the pig between the defibrillator under test and the pads. Results From the pilot studies we determined that an impedance of approximately 95ohms resulted in a pulse duration of 20ms when device A delivered a 200J shock. A total of 5 anaesthetised pigs weighing 17-20kg (18.8kg) where used with 168 episodes of VF where impedance was greater than 100 ohms are included in the results. Two energies were tested for A (150 and 200J). B only delivers shocks at a single energy (150J). No re-fibrillation was observed in any patient after any shock. Conclusions This study failed to show any evidence of re-fibrillation even at pulse durations longer than 20ms with either device.

Nonlinear Dynamic Response of RC Buildings with Different Base Isolation Systems Subjected to Horizontal and Vertical Components of Near-Fault Ground Motions

Near-fault ground motions are characterized by long-duration horizontal pulses and high values of the peak vertical acceleration, which can become critical for a base-isolated structure. In order to check if current code provisions can be considered adequate for the design of base-isolated structures located in a near-fault area, base-isolated five-storey r.c. framed buildings with elastomeric bearings acting alone (“Base Isolation” system) or combined in parallel or in series with sliding bearings (“Base Isolation and in-Parallel Sliding”, BIPS, or “Base Isolation and in-Series Sliding”, BISS, systems) are studied. The base-isolated structures are designed assuming the same values for the fundamental vibration period and equivalent viscous damping in the horizontal direction. Different values of the stiffness ratio, defined as the ratio between the vertical and horizontal stiffness of the elastomeric bearings, are considered; moreover, different values of the sliding ratio, defined as the global sliding force corresponding to an examined BIPS or BISS system divided by the maximum sliding force (in the case of a sliding bearing under each column), are also assumed. The nonlinear analysis of the test structures subjected to strong near-fault ground motions is performed using a step-by-step procedure based on a twoparameter implicit integration scheme and an initial-stress-like iterative procedure. At each step of the analysis, plastic conditions are checked at the potential critical sections of the girders (i.e. end sections of the sub-elements in which a girder is discretized) and columns (i.e. end sections), where a bilinear moment-curvature law is adopted. The response of an elastomeric bearing is simulated by a model with variable stiffness properties in the horizontal and vertical directions, depending on the axial force and lateral deformation, and linear viscous damping. Finally, a rigid-plastic (with friction variability) law is assumed to simulate the behaviour of a sliding bearing.

Nonlinear Modeling and Analysis of R.C. Framed Buildings Located in a Near-Fault Area

Structural damage to r.c. buildings located in a near-fault area has been observed during strong ground motions, with long-duration horizontal pulses and high values of the ratio between the peak value of the vertical acceleration and the analogous value of the horizontal acceleration. The design provisions of current seismic codes are generally not very accurate for assessing the structural effects of near-fault ground motions. In the present work, six- and twelve-storey r.c. spatial frames are designed according to the provisions of the Italian seismic code, considering horizontal and vertical seismic loads in a high-risk seismic region and assuming low and high ductility classes. A lumped plasticity model based on the Haar-Kàrmàn principle is used to describe the inelastic behavior of the r.c. frame members. In particular, the lumped plasticity model for a column includes a piecewise linearization of the bounding surface of the axial load-biaxial bending moment elastic domain, at the end sections where inelastic deformations are expected. Moreover, the lumped plasticity model for a girder takes into account the potential plastic hinges along the span, due to the vertical ground motion, so avoiding the computational effort required by the sub-discretization of the frame member. The nonlinear dynamic response of the test structures is studied with reference to the horizontal and vertical components of near-fault records. The occurrence of a directivity effect at arbitrary orientations is checked rotating the horizontal components of the selected motions, rather than considering only fault-normal and fault-parallel orientations.

Ablative Fractionated CO2 Laser Treatment of Photoaging: A Clinical and Histologic Study

Ablative fractional photothermolysis (AFP) has been reported to be effective for changes in skin pigmentation and texture associated with photoaging. A prospective study for the treatment of photoaging using a fractionated ablative carbon dioxide laser in 10 subjects. Assessment of laser efficacy was made using two modalities: histologic examination of skin biopsies and blinded physician clinical photographic assessment. For the histologic portion of the study, patients were randomized to treatment with the device at settings of pulse durations of 500, 1,000, 1,500, and 1,800μs. Depth of injury was assessed based on histologic evaluation of depth of thermal coagulation. For the clinical portion of the study, treatment was administered to the face using a carbon dioxide laser at settings of 30W, 500-μm pitch (density of treatment equivalent to ablation of 25% of the skin), and variable pulse duration of 1,000 to 1,500μs. The mean score for dyschromia had improved 47.5% (95% confidence interval (CI)=44.1-50.9%), for skin texture 56.0% (95% CI=51.9-60.1%), for skin laxity 56.0% (95% CI=51.3-60.7%), for rhytides 52.5% (95% CI=48.3-56.7%) and for overall cosmetic outcome 61.5% (95% CI=56.4%,66.6%) 6months after treatment. Histologic data revealed a proportional increase in depth of thermal coagulation at each pulse duration. The mean ablation depth was 283μm for a pulse duration of 500μs, 375μm for 1,000μs, 767μm for 1,500μs, and 1.05mm for 1,800μs. We present a histologic analysis documenting the correlation between longer pulse duration and ablation depth using an AFP device. We identified that pulse duration settings up to 1,800μs could be used safely with an ablation depth up to 1.1mm, correlating with injury into the deep reticular dermis.

Ultrahigh laser pulse energy and power generation at 10 kHz

This Letter presents results from a new master-oscillator, power-amplifier pulse-burst laser system demonstrating ultrahigh pulse energies greater than 2.0 J/pulse at 1064 nm with interpulse separations of 100 μs (10 kHz) for burst durations of 100 pulses. Each pulse generates peak powers exceeding 130 MW and an average power of approximately 20 kW is generated over a 100-pulse-burst. Pulse energies decrease by less than 10% over a 100 sequential pulses, demonstrating negligible "droop" over long-duration pulse trains. Second-harmonic generation of 532 nm with conversion efficiency greater than 50% is demonstrated for 100-pulse-burst durations.

Thermal Damage Patterns of Diode Hair-Removal Lasers According to Various Skin Types and Hair Densities and Colors: A Simulation Study

It is important to prevent unwanted side effects of diode hair-removal lasers especially in dark skin tones. This study simulates the thermal damage patterns caused by diode hair-removal lasers in different skin types, hair colors, and hair densities. LITCIT software has been used with the tissue modeled as two components, the skin and the hair. The absorption coefficients of various skin types (f(mel)=5%, 10%, 15%, and 20%), laser parameters, and optothermal properties of tissue were inputs. For all skin types there was a significant unwanted thermal damage to the epidermis as a result of fluence increase. Using longer pulse durations is accompanied by effective thermal damage to the hair follicle, while preserving the epidermis in skin types II and III, an effect not achieved in darker skins. Regardless of pulse duration, when the distance between hair follicles is ≤ 0.5 mm, there is a significant increase in thermal damage to interfollicular epidermis with high fluences compared with lower hair densities (interfollicular space ≥ 1 mm). In lighter hairs, while using longer pulse durations, higher fluences are needed in order to obtain the same level of thermal damage in the hair follicle as shorter pulse widths. In lighter skin types, lengthening the pulse duration of diode lasers (up to 400 ms) increases efficacy while preserving epidermis from unwanted thermal damage. However, it is necessary to use lower fluences while using longer pulse duration to avoid irreversible thermal damage to epidermis in darker tones, as is also true for locations with higher hair densities.

Quantitative acoustic analysis of the vocal repertoire of the golden rocket frog (Anomaloglossus beebei)

This study describes the vocal repertoire of the Guyanan golden rocket frog, Anomaloglossus beebei, a bromeliad specialist with biparental care. Using multivariate analyses of nine call properties, as well as the occurrence of nonlinear phenomena, three signal types were distinguished-advertisement, courtship, and aggressive calls. Although all three call types were composed of a short series of rapidly repeated pulses, advertisement calls were produced at higher amplitudes and had longer pulse durations than both courtship calls and aggressive calls. Courtship calls exhibited lower dominant frequencies than both advertisement and aggressive calls, which had similar dominant frequencies. Aggressive calls had more pulses per call, had longer intervals between calls, and occasionally contained one or two introductory pulses preceding the pulsed call. Several acoustic properties predicted aspects of the signaler's body size and condition. Our study demonstrates the reliability of human observers to differentiate the multiple call types of A. beebei based on hearing calls and observing the social context in which they are produced under field conditions.

Molecular Dynamics Simulations of Lipid Membrane Electroporation

The permeability of cell membranes can be transiently increased following the application of external electric fields. Theoretical approaches such as molecular modeling provide a significant insight into the processes affecting, at the molecular level, the integrity of lipid cell membranes when these are subject to voltage gradients under similar conditions as those used in experiments. This article reports on the progress made so far using such simulations to model membrane-lipid bilayer-electroporation. We first describe the methods devised to perform in silico experiments of membranes subject to nanosecond, megavolt-per-meter pulsed electric fields and of membranes subject to charge imbalance, mimicking therefore the application of low-voltage, long-duration pulses. We show then that, at the molecular level, the two types of pulses produce similar effects: provided the TM voltage these pulses create are higher than a certain threshold, hydrophilic pores stabilized by the membrane lipid headgroups form within the nanosecond time scale across the lipid core. Similarly, when the pulses are switched off, the pores collapse (close) within similar time scales. It is shown that for similar TM voltages applied, both methods induce similar electric field distributions within the membrane core. The cascade of events following the application of the pulses, and taking place at the membrane, is a direct consequence of such an electric field distribution.

Fibre laser microvia drilling and ablation of Si with tuneable pulse shapes

The dramatic increase in hole quality on single crystalline silicon with an 1 µm fibre laser has been reported recently, it redefines the processing options for Si at that wavelength. This study investigated the effects of the MOPA based pulse tuning on the changes of the machined depth and the mass removal mechanism for the generation of microvia holes. Hole depths were measured and surface morphology studied using SEM and optical interferometric profilometry. The pulse peak power was found to strongly influence the material removal mechanism with fixed pulse duration. High peak powers (>1 kW) gave vaporisation dominated ablation, left a limited resolidified molten layer and clean hole formation. The pulse duration was found to strongly influence the machined depth. Longer pulse durations generated deeper holes with constant peak power (>1 kW). In comparison with the DPSS UV laser, the IR fibre laser of longer pulse durations machined deeper holes and generated less resolidifed melt beyond the hole rim at high fluencies. The comparison suggests that some applications (microvia drilling) of the DPSS UV laser can be replaced with the more flexible, low cost IR fibre laser.

Stable passively Q-switched operation of Tm3+ doped silica fiber laser by anti-resonant Fabry-Perot saturable absorber

We demonstrate a diode-pumped passively Q-switched Tm-doped double-cladding silica fiber laser operating at wavelength of 1960 nm using an anti-resonant Fabry-Perot saturable absorber as passive modulation element. To determine a relatively preferable fiber length for stable cw Q-switched operation, three active fiber simples with the length of 1.1, 5.3, and 7.0 m were employed respectively in our experiments. With 1.1 m gain fiber, we generated Q-switched pulses with a pulse width of 245 ns and an average power of up to 2.2 W at a repetition rate of 620 kHz. For the longer two fiber samples, Q-switched operation with longer pulse duration, Q-switched mode-locking and cw mode-locking were observed, respectively.

Pulse shaping fiber laser at 15 μm

In this paper we present, for the first time to our knowledge, a new pulse shaping technology (modulation schemes for seed laser) used to mitigate pulse narrowing effect and SBS effect in a high energy Er:Yb codoped fiber master oscillator power amplifier system at 1.5 μm to obtain longer pulse duration and higher energy. An average power of over 1.3 W and a pulse energy of over 0.13 mJ were obtained at 10 kHz repetition rate with a pulse duration of 200 ns and near-diffraction-limited beam quality (M(2)<1.2).

Generation of isolated attosecond pulse from two-color pulse with duration of 60 fs

We theoretically investigate the high-order harmonic and attosecond pulse generation by numerically solving the one-dimensional time-dependent Schrödinger equation from a hydrogen atom in a two-color laser field, which is synthesized by adding a suitable multicycle infrared pulse to a multicycle 800 nm fundamental pulse. Our results clearly show that when there are 12 Ti: sapphire optical cycles in the pulse envelope, by adding a suitable second optical field, the electric field of the synthesized pulse presents three-segments, and only amplitude of the electric field in middle segment makes a major contribution to the plateau and cutoff region of the harmonic spectrum. By analyzing the compression mechanism of two-color electric field, we further enlarge the duration of the synthesized pulse to 60 fs, and obtain a single 160 as short pulse. This has been the longest pulse duration used for obtaining single attosecond pulse so far. Here the effect of synthesized pulses is similar to the effect of single 5 fs ultrashort pulse. This scheme greatly reduces the requirements for the pump laser system used traditionally for generating an isolated attosecond pulse, and it allows us to use a well-established conventional high-power pumping laser.

Measuring T2 and T1, and imaging T2 without spin echoes

During adiabatic excitation, the nuclear magnetization in the transverse plane is subject to T 2 (spin–spin) relaxation, depending on the pulse length τ. Here, this property is exploited in a method of measuring T 2 using the ratio of NMR signals acquired with short and long-duration self-refocusing adiabatic pulses, without spin-echoes. This Dual- τ method is implemented with B 1-insensitive rotation (BIR-4) pulses. It is validated theoretically with Bloch equation simulations independent of flip-angle, and experimentally in phantoms. Dual- τ T 2 measurements are most accurate at short T 2 where results agree with standard spin-echo measures to within 10% for T 2 ⩽ 100 ms. Dual- τ MRI performed with a long 0° BIR-4 pre-pulse provides quantitative T 2 imaging of phantoms and the human foot while preserving desired contrast and functional properties of the rest of the MRI sequence. A single 0° BIR-4 pre-pulse can provide T 2 contrast-weighted MRI and serve as a “ T 2-prep” sequence with a lower B 1 requirement than prior approaches. Finally, a Tri- τ experiment is introduced in which both τ and flip-angle are varied, enabling measurement of T 2, T 1 and signal intensity in just three acquisitions if flip-angles are well-characterized. These new methods can potentially save time and simplify relaxation measurements and/or contrast-weighted NMR and MRI.

Investigation and Mitigation of Analog SET on a Bandgap Reference in Triple-Well CMOS Using Pulsed Laser Techniques

The devices responsible for a 600-μs Analog Single-Event Transient (ASET) observed in an NPN Brokaw-cell type bandgap reference during heavy-ion irradiation are identified using pulsed laser techniques with two completely different experimental setups. The capability of focusing the beam to specific junctions provided by the lasers led to recognize a novel Long Duration Pulse (LDP) upset mechanism which, contrary to the conventional wisdom in the field, is promoted by heavy capacitive filtering applied to the circuit's output. A thorough comprehension of the cause of the LDP allowed for the proposal of design measures of mitigation that were implemented in silicon. Final tests performed with the same laser setup confirmed the successful resolution of such analog SET problem in this popular class of circuits.