Longer Pulse Duration Research Articles

Plasma boundary shape control and real-time equilibrium reconstruction on NSTX-U

The upgrade to the National Spherical Torus eXperiment (NSTX-U) included two main improvements: a larger center-stack, enabling higher toroidal field and longer pulse duration, and the addition of three new tangentially aimed neutral beam sources, which increase available heating and current drive, and allow for flexibility in shaping power, torque, current, and particle deposition profiles. To best use these new capabilities and meet the high-performance operational goals of NSTX-U, major upgrades to the NSTX-U control system (NCS) hardware and software have been made. Several control algorithms, including those used for real-time equilibrium reconstruction and shape control, have been upgraded to improve and extend plasma control capabilities. As part of the commissioning phase of first plasma operations, the shape control system was tuned to control the boundary in both inner-wall limited and diverted discharges. It has been used to accurately track the requested evolution of the boundary (including the size of the inner gap between the plasma and central solenoid, which is a challenge for the ST configuration), X-point locations, and strike point locations, enabling repeatable discharge evolutions for scenario development and diagnostic commissioning.

Development of a Single-Degree-of-Freedom Mechanical Model for Predicting Strain-Based Brain Injury Responses.

Linking head kinematics to injury risk has been the focus of numerous brain injury criteria. Although many early forms were developed using mechanics principles, recent criteria have been developed using empirical methods based on subsets of head impact data. In this study, a single-degree-of-freedom (sDOF) mechanical analog was developed to parametrically investigate the link between rotational head kinematics and brain deformation. Model efficacy was assessed by comparing the maximum magnitude of displacement to strain-based brain injury predictors from finite element (FE) human head models. A series of idealized rotational pulses covering a broad range of acceleration and velocity magnitudes (0.1-15krad/s2 and 1-100 rad/s) with durations between 1 and 3000 ms were applied to the mechanical models about each axis of the head. Results show that brain deformation magnitude is governed by three categories of rotational head motion each distinguished by the duration of the pulse relative to the brain's natural period: for short-duration pulses, maximum brain deformation depended primarily on angular velocity magnitude; for long-duration pulses, brain deformation depended primarily on angular acceleration magnitude; and for pulses relatively close to the natural period, brain deformation depended on both velocity and acceleration magnitudes. These results suggest that brain deformation mechanics can be adequately explained by simple mechanical systems, since FE model responses and experimental brain injury tolerances exhibited similar patterns to the sDOF model. Finally, the sDOF model was the best correlate to strain-based responses and highlighted fundamental limitations with existing rotational-based brain injury metrics.

New data on the kinetics and governing factors of the spall fracture of metals

This paper presents two examples of significant departures from usual trends of varying the resistance to spall fracture (spall strength) with changing loading history, load duration and peak shock stress. In experiments with vanadium single crystals we observed an important decrease of spall strength when increasing the shock stress. This was interpreted in terms of disruption of the matter homogeneity as a result of its twinning at shock compression. In experiments with 12Kh18N10T austenitic stainless steel we observed a sharp increase of recorded spall strength value when short load pulses of a triangular profile were replaced by shock pulses of long duration having a trapezoidal shape. This anomaly is associated with formation of the deformation-induced martensitic phase.

Effects of nonlinear modelling of the base-isolation system on the seismic analysis of r.c. buildings

Long-duration and high-amplitude horizontal velocity pulses are expected at sites located near an active fault; these are able to generate notable displacement at the level of the isolation system and pounding effects between closely spaced structural parts (e.g. in the case of an insufficient seismic gap between the elevator and building). A base-isolated commercial building, recently built in the Sicilian town of Augusta, designed in line with the former Italian seismic code, is considered as test structure. In particular, an r.c. framed structure with rectangular plan, composed of a basement and three storeys above ground level, is seismically isolated with a hybrid system including sixteen high-damping-rubber bearings (HDRBs) and twenty steel-PTFE low friction flat sliding bearings (LFSBs). An elevator shaft with steel framed structure crossing the isolation level is also placed in non symmetrical way along the longitudinal axis. A computer code for the nonlinear seismic analysis of base-isolated r.c. framed structures is improved by adding advanced nonlinear models of HDRBs and LFSBs. Finally, nonlinear dynamic analysis of the Augusta building is carried out with reference to near-fault earthquakes selected from the Pacific Earthquake Engineering Research center database and scaled in line with the design hypotheses adopted.

A z-gradient array for simultaneous multi-slice excitation with a single-band RF pulse.

Multi-slice radiofrequency (RF) pulses have higher specific absorption rates, more peak RF power, and longer pulse durations than single-slice RF pulses. Gradient field design techniques using a z-gradient array are investigated for exciting multiple slices with a single-band RF pulse. Two different field design methods are formulated to solve for the required current values of the gradient array elements for the given slice locations. The method requirements are specified, optimization problems are formulated for the minimum current norm and an analytical solution is provided. A 9-channel z-gradient coil array driven by independent, custom-designed gradient amplifiers is used to validate the theory. Performance measures such as normalized slice thickness error, gradient strength per unit norm current, power dissipation, and maximum amplitude of the magnetic field are provided for various slice locations and numbers of slices. Two and 3 slices are excited by a single-band RF pulse in simulations and phantom experiments. The possibility of multi-slice excitation with a single-band RF pulse using a z-gradient array is validated in simulations and phantom experiments. Magn Reson Med 80:400-412, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Effect of pulse duration and pulse repetition frequency of cavitation histotripsy on erosion at the surface of soft material

Cavitation histotripsy with the short pulse duration (PD) but high pulse repetition frequency (PRF) disintegrates the tissue at a fluid interface. However, longer PD and lower PRF are used in the other focused ultrasound applications, where the acoustic radiation force, streaming, and cavitation are different, and their effects on erosion are unknown. In this study, the erosion at the surface of phantom/ex vivo tissue and the characteristics of induced bubble cloud captured by high-speed photography, passive cavitation detection, and light transmission during histotripsy exposure at varied PDs and PRFs but the same duty cycle were compared. The peak negative pressure of 6.6 MPa at the PD of 20 ms and PRF of 1 Hz began to erode the phantom, which becomes more significant with the increase of peak negative pressure, PD, and interval time between bursts. The increase of the PRF from 1 Hz to 1000 Hz, while the decrease of the PD from 20 ms to 20 μs (duty cycle of 2%) at the same energy was delivered to the gel phantom immersed in the degassed water led to the decrease of erosion volume but a slight increase of the erosion area and smoother surface. Low PRF and long PD produce the significant tissue deformation, acoustic wave refocusing, confinement of bubbles in a conical region, and more bubble dissolution after the collapse for the high acoustic scattering and light transmission signals. In comparison, high PRF and low PD produce a wide distribution of bubbles with only little wave refocusing at the beginning of cavitation histotripsy and high inertial cavitation. Acoustic emission dose has a good correlation with the erosion volume. The erosion on the porcine kidney at the varied PRFs and PDs with the same energy output showed similar trends as those in the phantom but at a slow rate. In summary, the PRF and PD are important parameters for the cavitation histotripsy-induced erosion at the interface of fluid and soft material, and they should be optimized for the best outcome.

Magnetization of superconducting rings by long-duration pulses

After pulsed magnetization of the rings of high-temperature superconductors with a rectangular cross section, the magnitude of the trapped field has been measured depending on the decay time of the magnetization field. It has been shown that, by making use of the break of shielding current, one can magnetize the ring with a single pulse the rings to the maximum value corresponding to the field cooling process.

Solid-State Pulse-Forming Modules by Utilizing the 2-D Electrode Manufacturing Technology

Nowadays, most of solid-state circuits are fabricated through the application of the 2-D electrode manufacturing technology (printed circuit). In this paper, solid-state pulse-forming modules using 2-D electrode manufacturing technology are presented to produce long pulse duration while less space volume is being occupied. First, on a glass-ceramic (dielectric constant 225) substrate with the dimension of 250 mm × 95 mm × 4 mm, as meander line is the usual delay-line circuit in printed circuit boards, the meander pulse-forming line is used to deliver a highvoltage pulse with pulse duration longer than 120 ns by simulation and test validation. Furthermore, we also discuss the double parallel meander-line and the “V” shaped meander-line in this section. Second, with the same substrate, the LC pulse-forming module is used to generate the high-power pulse with good square pulse quality. By changing the inductance L, this module can be adjusted to deliver pulses with different durations. Third, planar concentric ring PFL is proposed with simulation analysis. In simulation, the planar concentric ring PFL is designed using an attractive storage medium-Barium Titanate (BaTiO 3 ) baseceramics (dielectric constant~1000). At last, a compact PFL based on the structure of multilayer ceramic capacitor is introduced, and can generate a quasi-square pulse in simulation. These various types of solid-state pulse-forming modules may be the potential component in the compact pulsed power systems to generate high-voltage, long-duration pulses.

High-speed 2D Raman imaging at elevated pressures.

Two-dimensional (2D) Raman scattering at 10kHz in non-reacting flow mixtures is demonstrated by employing a burst-mode laser with a long-duration pulse of about 70ns and pulse energy of about 750mJ at 532nm. To avoid optical breakdown, the pulse width of the laser was varied in the range of 10-1000ns. The effects of pulse shape, pulse energy, and harmonic conversion on 2D measurements are also studied. The applications of high-speed, single-shot, 2D imaging of CH4 and H2 jets in N2 at elevated pressures are demonstrated. In addition, the scalar dissipation rate of CH4 in N2 at 20bar is determined, and multi-dimensional, multi-species, high-speed imaging of flows at elevated pressures is demonstrated.

The Thrombolytic Effect of Diagnostic Ultrasound-Induced Microbubble Cavitation in Acute Carotid Thromboembolism.

Acute ischemic stroke is often due to thromboembolism forming over ruptured atherosclerotic plaque in the carotid artery (CA). The presence of intraluminal CA thrombus is associated with a high risk of thromboembolic cerebral ischemic events. The cavitation induced by diagnostic ultrasound high mechanical index (MI) impulses applied locally during a commercially available intravenous microbubble infusion has dissolved intravascular thrombi, especially when using longer pulse durations. The beneficial effects of this in acute carotid thromboembolism is not known. An oversized balloon injury was created in the distal extracranial common CA of 38 porcine carotid arteries. After this, a 70% to 80% stenosis was created in the mid common CA proximal to the injury site using partial balloon inflation. Acute thrombotic CA occlusions were created just distal to the balloon catheter by injecting fresh autologous arterial thrombi. After angiographic documentation of occlusion, the common carotid thrombosis was treated with either diagnostic low MI imaging alone (0.2 MI; Philips S5-1) applied through a tissue mimicking phantom (TMP) or intermittent diagnostic high MI stable cavitation (SC)-inducing impulses with a longer pulse duration (0.8 MI; 20 microseconds' pulse duration) or inertial cavitation (IC) impulses (1.2 MI; 20 microseconds' pulse duration). All treatment times were for 30 minutes. Intravenous ultrasound contrast (2% Definity; Lantheus Medical) was infused during the treatment period. Angiographic recanalization in 4 intracranial and extracranial vessels downstream from the CA occlusion (auricular, ascending pharyngeal, buccinator, and maxillary) was assessed with both magnetic resonance 3-dimensional time-of-flight and phase contrast angiography. All magnetic resonance images were interpreted by an independent neuroradiologist using the thrombolysis in cerebral infarction (TICI) scoring system. By phase contrast angiography, at least mild recanalization (TICI 2a or higher) was seen in 64% of downstream vessels treated with SC impulses compared with 33% of IC treated and 29% of low MI alone treated downstream vessels (P = 0.001), whereas moderate or complete recanalization (TICI 2b or higher) was seen in 39% of SC treated vessels compared with 10% IC treated and 21% of low MI alone treated vessels (P = 0.001). High MI 20-microsecond pulse duration impulses during a commercial microbubble infusion can be used to recanalize acutely thrombosed carotid arteries and restore downstream flow without anticoagulants. However, this effect is only seen with SC-inducing impulses and not at higher mechanical indices, when a paradoxical reversal of the thrombolytic effect is observed. Diagnostic ultrasound-induced SC can be a nonsurgical method of dissolving CA thrombi and preventing thromboembolization.

A New Measurement of the Spectral Lag of Gamma-Ray Bursts and its Implications for Spectral Evolution Behaviors

Abstract We carry out a systematical study of the spectral lag properties of 50 single-pulsed gamma-ray bursts (GRBs) detected by the Fermi Gamma-Ray Burst Monitor. By dividing the light curves into multiple consecutive energy channels, we provide a new measurement of the spectral lag that is independent of energy channel selections. We perform a detailed statistical study of our new measurements. We find two similar power-law energy dependencies of both the pulse arrival time and pulse width. Our new results on the power-law indices would favor the relativistic geometric effects for the origin of spectral lag. However, a complete theoretical framework that can fully account for the diverse energy dependencies of both arrival time and pulse width revealed in this work is still lacking. We also study the spectral evolution behaviors of the GRB pulses. We find that a GRB pulse with negligible spectral lag would usually have a shorter pulse duration and would appear to have a “hardness-intensity tracking” behavior, and a GRB pulse with a significant spectral lag would usually have a longer pulse duration and would appear to have a “hard-to-soft” behavior.

Differential hemodynamic and respiratory responses to right and left cervical vagal nerve stimulation in rats.

Neuromodulation through vagal nerve stimulation (VNS) is currently explored for a variety of clinical conditions. However, there are no established VNS parameters for animal models of human diseases, such as hypertension. Therefore, the aim of this study was to assess hemodynamic and respiratory responses to right‐ or left‐sided cervical VNS in a hypertensive rat model. Anesthetized stroke‐prone spontaneously hypertensive rats were instrumented for arterial blood pressure and heart rate monitoring and left‐ or right‐sided VNS. Cervical VNS was applied through bipolar coil electrodes. Stimulation parameters tested were 3 V and 6 V, 2 Hz to 20 Hz stimulation frequency, and 50 μsec to 20 msec pulse duration. Each combination of stimulation parameters was applied twice with altered polarity, that is, anode and cathode in the cranial and caudal position. Respiration rate was derived from systolic blood pressure fluctuations. In general, cervical VNS caused bradycardia, hypotension, and tachypnea. These responses were more pronounced with left‐sided than with right‐sided VNS and depended on the stimulation voltage, stimulation frequency, and pulse duration, but not on the polarity of stimulation. Furthermore, the results suggest that at low stimulation frequencies (<5 Hz) and short pulse durations (<0.5 msec) primarily larger A‐fibers are activated, while at longer pulse durations (>0.5 msec) smaller B‐fibers are also recruited. In conclusion, in rats left‐sided cervical VNS causes greater cardio‐respiratory responses than right‐sided VNS and at lower stimulation frequencies (e.g., 5 Hz), longer pulse durations (>0.5 msec) seem to be required to consistently recruit B‐fibers in addition to A‐fibers.

Comparative Analysis of Unipolar and Bipolar Control of Modular Battery for Thermal and State-of-Charge Balancing

Thermal and state-of-charge (SOC) imbalance is a well-known issue that causes nonuniform aging in batteries. The modular battery based on cascaded converters is a potential solution to this problem. This paper presents bipolar control (BPC) of a modular battery and compares it with previously proposed unipolar control (UPC) mode in terms of thermal/SOC balancing performance and energy efficiency. The BPC needs four-quadrant operation of a full-bridge (FB) converter using bipolar pulsewidth modulation (PWM) inside each module, whereas UPC only needs a half-bridge (HB) converter with unipolar PWM. The BPC, unlike UPC, enables charging of some cells while discharging others. An averaged state-space electrothermal battery model is derived for a convex formulation of the balancing control problem. The control problem is formulated on a constrained linear quadratic (LQ) form and solved in a model predictive control (MPC) framework using one-step-ahead prediction. The simulation results show that BPC, without even requiring load current variations, gives better balancing performance than UPC but at the cost of reduced efficiency. The UPC requires at least current direction reversal for acceptable balancing performance. In short, the UPC is a more cost- and energy-efficient solution for electric vehicle (EV) and plug-in hybrid EV applications, whereas the BPC can be beneficial in applications involving load cycles with high current pulses of long duration.

Molecular effects of fractional ablative erbium:YAG laser treatment with multiple stacked pulses on standardized human three-dimensional organotypic skin models.

The molecular changes in gene expression following ablative laser treatment of skin lesions, such as atrophic scars and UV-damaged skin, are not completely understood. A standardized in vitro model of human skin, to study the effects of laser treatment on human skin, has been recently developed. Therefore, the aim of the investigation was to examine morphological and molecular changes caused by fractional ablative erbium:YAG laser treatment on an in vitro full-thickness 3D standardized organotypic model of human skin. A fractional ablative erbium:YAG laser was used to irradiate organotypic human 3D models. Laser treatments were performed at four different settings using a variety of stacked pulses with similar cumulative total energy fluence (60J/cm2). Specimens were harvested at specified time points and real-time PCR (qRT-PCR) and microarray studies were performed. Frozen sections were examined histologically. Three days after erbium:YAG laser treatment, a significantly increased mRNA expression of matrix metalloproteinases and their inhibitors (MMP1, MMP2, MMP3, TIMP1, and TIMP2), chemokines (CXCL1, CXCL2, CXCL5, and CXCL6), and cytokines such as IL6, IL8, and IL24 could be detected. qRT-PCR studies confirmed the enhanced mRNA expression of IL6, IL8, IL24, CXCLs, and MMPs. In contrast, the mRNA expression of epidermal differentiation markers, such as keratin-associated protein 4, filaggrin, filaggrin 2, and loricrin, and antimicrobial peptides (S100A7A, S100A9, and S100A12) as well as CASP14, DSG2, IL18, and IL36β was reduced. Four different settings with similar cumulative doses have been tested (N10%, C10%, E10%, and W25%). These laser treatments resulted in different morphological changes and effects on gene regulations. Longer pulse durations (1000μs) especially had the strongest impact on gene expression and resulted in an upregulation of genes, such as collagen-1A2, collagen-5A2, and collagen-6A2, as well as FGF2. Histologically, all treatment settings resulted in a complete regeneration of the epidermis 3days after irradiation. Fractional ablative erbium:YAG laser treatment with a pulse stacking technique resulted in histological alterations and shifts in the expression of various genes related to epidermal differentiation, inflammation, and dermal remodeling depending on the treatment setting applied. A standardized in vitro 3D model of human skin proved to be a useful tool for exploring the effects of various laser settings both on skin morphology and gene expression during wound healing. It provides novel data on the gene expression and microscopic architecture of the exposed skin. This may enhance our understanding of laser treatment at a molecular level.

Subterahertz Nanosecond Switches Driven by Second-Long Laser Pulses

Subterahertz semiconductor waveguide switches designed for nanosecond pulse regimes have been studied at much longer pulse durations up to 1 s. The problems of heat dissipation in such switches are discussed. Substituting the microwave Joule heating dissipation mechanism with similarly distributed laser heating in the semiconductor, we can estimate the maximum commutated microwave power, which the switch can operate safely. Operation of a nanosecond-performance switch driven by a 1-s laser pulse, which produced a 1-s microwave pulse at the output, has been demonstrated experimentally. The new typical relaxation time associated with the size of the heat dissipation area in the semiconductor plate has been measured. The process of semiconductor blowout under 20-W laser emission has been recorded and discussed. The minimum commutation time under the maximum waveguide transmittable power has been obtained.

Self-Tuning Fuzzy Control for Seismic Protection of Smart Base-Isolated Buildings Subjected to Pulse-Type Near-Fault Earthquakes

Pulse-type near-fault earthquakes have obvious long-duration pulses, so they can cause large deformation in a base-isolated system in contrast to non-pulse-type near-fault and far-field earthquakes. This paper proposes a novel self-tuning fuzzy logic control strategy for seismic protection of a base-isolated system, which can operate the control force of the piezoelectric friction damper against different types of earthquakes. This control strategy employs a hierarchic control algorithm, in which a higher-level supervisory fuzzy controller is implemented to adjust the input normalization factors and output scaling factor, while a sub-level fuzzy controller effectively determines the command voltage of the piezoelectric friction damper according to current level of earthquakes. The efficiency of the proposed control strategy is also compared with uncontrolled and maximum passive cases. Numerical results reveal that the novel fuzzy logic control strategy can effectively reduce the isolation system deformations without the loss of potential advantages of base-isolated system.

Effect of Gate Width on High Harmonic Generation from Polarization Gating Pulse with Longer Pulse Duration

Effect of Gate Width on High Harmonic Generation from Polarization Gating Pulse with Longer Pulse Duration

What devices to use or not use in skin of color.

Lasers and light sources, as well as other energy devices, including radiofrequency, ultrasound, and cold-based therapies, can be used for treatment of aging, dyschromic, or texturally uneven skin. In patients with ethnic skin (ie, skin of color), energy devices are used more cautiously to avoid adverse events. The most common and concerning adverse event is postinflammatory hyperpigmentation. Lower fluence, longer pulse durations, and careful device selection can mitigate the risk of scarring and pigmentary abnormality. Modified treatment approaches can allow physicians to safely treat patients with skin of color with energy devices.

Treatment of erythematotelangiectatic rosacea with the fractionation of high-fluence, long-pulsed 595-nm pulsed dye laser.

Various lasers have been used for the treatment of erythematotelangiectatic rosacea (ETR) that does not respond to systemic or topical therapy. The pulsed dye lasers (PDLs) are an effective option for ETR, and the purpuragenic fluence proved to be superior until now. Given that purpura and subsequent possible postinflammatory hyperpigmentation (PIH) are occasionally unbearable in some patients, and several studies using the low nonpurpuragenic fluence were reported. To deliver the sufficient high fluence of a PDL without generating purpura, we designed the fractionation of high fluence using five passes and longer pulse duration (6 milliseconds) of a PDL in succession. A total of eight patients with ETR were enrolled in this study; all patients were treated with PDL 10 times at 2-week intervals. Erythema and telangiectasia scores, as well as improvement, were assessed by two physicians using the digital photographs. Moderate-to-marked improvement was achieved in most of the patients, and erythema and telangiectasia scores were significantly decreased. Purpura and PIH were not reported in all patients. The fractionation of high-fluence, long-pulsed 595 nm PDL is a very safe and effective treatment for ETR.

Effects of pulse duration on removal characteristics of silver nanowire transparent conductive film by nanosecond pulsed laser

In laser processing of silver nanowire transparent conductive film covered with an acrylic resin layer, effects of pulse duration on electrical insulation and surface quality were experimentally investigated by using nanosecond pulsed laser. The minimum laser fluence to achieve the stable electrical insulation by removal of silver nanowire became small with decreasing the pulse duration, but shorter pulse duration showed drastic change of removal trace area of silver nanowires at the boundary region of laser fluence to change conductive state to insulation one. In contrast, longer pulse duration around 200ns indicated almost constant small removal trace area of silver nanowires, and wide processing window to perform the stable electrical insulation with small removal trace area of silver nanowires can be expected by using a proper long pulse duration in nanosecond pulsed laser processing.