Effect Of Pulse Shape Research Articles

Effect of neural adaptation and degeneration on pulse-train ECAPs: A model study

Electrically evoked compound action potentials (eCAPs) are measurements of the auditory nerve's response to electrical stimulation. ECAP amplitudes during pulse trains can exhibit temporal alternations. The magnitude of this alternation tends to diminish over time during the stimulus. How this pattern relates to the temporal behavior of nerve fibers is not known. We hypothesized that the stochasticity, refractoriness, adaptation of the threshold and spike-times influence pulse-train eCAP responses. Thirty thousand auditory nerve fibers were modeled in a three-dimensional cochlear model incorporating pulse-shape effects, pulse-history effects, and stochasticity in the individual neural responses. ECAPs in response to pulse trains of different rates and amplitudes were modeled for fibers with different stochastic properties (by variation of the relative spread) and different temporal properties (by variation of the refractory periods, adaptation and latency). The model predicts alternation of peak amplitudes similar to available human data. In addition, the peak alternation was affected by changing the refractoriness, adaptation, and relative spread of auditory nerve fibers. As these parameters are related to factors such as the duration of deafness and neural survival, this study suggests that the eCAP pattern in response to pulse trains could be used to assess the underlying temporal and stochastic behavior of the auditory nerve. As these properties affect the nerve's response to pulse trains, they are of uttermost importance to sound perception with cochlear implants.

Effect of acceleration pulse shape on the safety of unbelted motorcoach passengers in frontal collision under uncertainty of their seating posture

Crashworthiness design of motorcoaches is a new research area driven by the constantly upgrading crash safety regulations. One important parameter to be considered during the crashworthiness design is the shape of acceleration profile experienced by the vehicle’s occupants. The paper presents the results of the analysis of the influence of the pulse shape on the safety of motorcoach passengers in a frontal collision. Owing to a large number of uncertainties involved in a real-world crash, a probabilistic approach is undertaken for the parametric study. For each considered acceleration pulse, several random occupant postures are generated and used in the numerical sled test. The influence of the pulse shape on occupants’ injury criteria is then evaluated and compared to the amount of scatter introduced by the random postures. The results indicate the effect of the uncertainty in the seating posture overcomes the effect of the pulse shape changes. The coefficient of variation (CV) in the Head Injury Criterion (HIC) across stochastic postures is found to be from 11% to 34% while the average total change in the HIC values between different acceleration profiles is only 8%. Overall, the research demonstrates the significance of the consideration of the posture variation in the parametric crash test studies.

Effect of ultrafast laser pulse shape on the electron-plane wave interaction in vacuum

In this study, the effects of laser pulse shape on the laser-electron acceleration in vacuum have been considered. It was found that the laser plane wave with a finite duration trapezoidal envelope was more effective in transferring energy to the electron. A million electron volt single electron axially injected to the front of a trapezoidal short laser pulse with a linearly chirping frequency was shown to gain more than 50 GeV energy.

New method of out-of-time energy subtraction for the CMS hadronic calorimeter

The CMS hadronic calorimeter employs plastic scintillator active material in the barrel and endcap (HBHE). In Run 2, the LHC operates at 13 TeV center-of-mass energy with up to 50 simultaneous collisions per bunch crossing (pileup) and a 25 ns bunch spacing. The HBHE scintillator light pulse is only 60% contained in a 25 ns window, resulting in significant pulse overlap for consecutive events (out-of-time pileup). This talk presents a novel algorithm that will be used in 2018 for subtracting out-of-time pileup in HBHE both online in the software trigger and offline. The algorithm includes methods for both the barrel with hybrid photodiode photosensors and QIE8 digitizers, and the endcap with silicon photomultipliers and QIE11 digitizers, including the challenging charge-dependent pulse shaping effects of the QIEs. The on-detector pulse shape measurement method and results are also shown. The new algorithm is five-to-ten times faster than the previous one, and for the first time CMS will use the offline method at the trigger level.

Effects of laser pulse shape on forward Thomson scattering

The effects of super-cycle (or sub-cycle) and super-Gaussian laser pulse shapes on the forward Thomson scattering by an electron moving in a linearly polarized laser field are investigated. The numerical results show that for forward scattering spectra, there are only harmonics of odd orders. With increasing the super-cycle parameter, the intensity of the scattering spectra increases and more harmonics orders appear. In the case of sub-cycle laser pulse shape, decreasing the sub-cycle parameter leads to a gradual decrease in the interval between the adjacent harmonics and scattering spectra exhibiting quasi-continuity. Furthermore, the intensity of the high-order harmonic increases and the harmonic with peak intensity shifts from fundamental to higher order with increasing super-Gaussian parameter. Besides, the effects of the electron's initial direction and speed as well as the carrier envelope phase on the scattering spectra are also explored. Our results indicate the possibility of future application in X-ray source devices based on Thomson scattering.

Pressure–impulse diagrams for elastoplastic beams subjected to pulse-pressure loading

Pressure–impulse (or p−I) diagrams are developed for fully-clamped elastic-plastic beams subjected to pulse-pressure loading with varying degree of negative phase. Unlike traditional p−I diagrams, the loading parameter space are instead divided into re´gimes, corresponding to the three modes of deformation (I, II and III) observed in blast experiments. The effects of pulse shape, beam aspect ratio and negative phase loading on the isodamage curves that delineate the different re´gimes are investigated. In addition, it is further demonstrated that contour lines of structural performance (maximum deflection, total work done, partitioned energy and saturated) can also be incorporated into the non-dimensionalised pressure-impulse space to provide further information for the design, and assessment, of elastic-plastic beams to blast loading.

Giant Goos-Hänchen shift in two different enantiomers' chiral molecules via quantum coherence.

The Goos and Hänchen (GH) shifts in reflected and transmitted probe light through a cavity mixture of left- and right-handed chiral molecules into two enantiomer states are investigated. Due to the broken mirror symmetry of the left- and right-handed chiral molecules in the presence of cyclic population transfer, such quantum systems can be selectively excited because of the coexistence of one- and two-photon transitions. With the help of coupling Rabi frequency and damping effects due to scattering processes, the generated GH shifts accompanied by simultaneously negative and positive lateral shifts in reflected and transmitted probe lights are greatly enhanced. It is found that the large negative and positive GH shifts are available in the presence of multiphoton resonance and off-resonance conditions for two different enantiomers' chiral molecules. Moreover, the switching between superluminal and subluminal light propagation is extremely dependent on choosing the left- and right-handed chiral molecules. Furthermore, the effects of pulse shape and mode of Laguerre-Gaussian probe light on the GH shifts that lead to a switch between negative and positive shift are also studied. The negative and positive GH shifts in a reflected and transmitted probe beam for an incident Gaussian and different mode of Laguerre-Gaussian shaped beam with various widths by the use of two different enantiomers' chiral molecules are also discussed.

Pulse-shape effects in fifth-order multidimensional optical spectroscopy

We study how the effects of finite pulse durations modify the fifth-order two-quantum two-dimensional (2Q-2D) and three-dimensional (3D) optical spectra. Instead of directly calculating the time domain polarization, the equivalent approach in frequency domain significantly simplifies the calculations and delivers exact expressions for the 2Q-2D and 3D spectra. Our results minimize the number of numerical integrations needed. We also derive simple analytical formulas for practically important situations when the laser pulses are short on the timescale of nuclear motion as well as short (or long) on the timescale of electronic dephasing. These formulas evaluate the measured spectra by multiplying the spectral response function by a factor depending on the spectral pulse envelopes.

Mechanical performance of laser spot-welded joints in Al-Al/Cu solar thermal absorbers

The mechanical performance of laser spot welded joints used in Al-Cu and Al-Al thermal absorber systems has been evaluated under different laser welding and mechanical loading conditions. In the experimental investigation, the effect of laser pulse shape and laser heat input on the spot weld strength has been examined under static and cyclic shear loading. The residual strength of spot welds after initial cyclic loading has also been evaluated. The experimental results are supported by metallographic analysis of welds and fractography of failed spot welds. It is concluded that the static and cyclic shear strength is primarily influenced by the laser heat input, which regulates the size of the generated laser spot weld section and to a lesser extent by the laser pulse shape. The influence of laser heat input parameter on the mechanical performance seems not to be as severe in the case of residual strength. This may be associated with the presence of brittle intermetallic compounds in the bimetallic Al-Cu welds which induce small scale defects during the welding process, thus further affecting mechanical performance leading to a reduction of the load bearing capacity of the spot weld.

Effect of the temporal laser pulse asymmetry on pair production processes during intense laser-electron scattering

We investigate the effects of laser pulse shape on strong-field quantum electrodynamics (QED) processes during the collision between a relativistic electron beam and an intense laser pulse. The interplay between high-energy photon emission and two pair production processes, i.e. nonlinear Breit–Wheeler (BW) and Trident, was investigated using particle-in-cell simulations. We found that the temporal evolution of these two processes could be controlled by using laser pulses with different degrees of asymmetry. The temporal envelope of the laser pulse can significantly affect the number of pairs coming from the Trident process, while the nonlinear BW process is less sensitive to it. This study shows that the two QED processes can be examined with state-of-the-art petawatt lasers and the discrimination of the two pair creation processes is feasible by adjusting the temporal asymmetry of the colliding laser pulse.

Effect of Pulse Shape on Spall Strength

This paper analyzes the effect of the time-dependent shape of a load pulse on the spall strength of materials. Within the framework of a classical one-dimensional scheme, triangular pulses with signal rise and decay portions and with no signal rise portions considered. Calculation results for the threshold characteristics of fracture for rail steel are given. The possibility of optimization of fracture by selecting a loading time with the use of an introduced characteristic of dynamic strength (pulse fracture capacity) is demonstrated. The study is carried out using a structure–time fracture criterion.

The effects of focusing power on TEA CO2 laser-induced gas breakdown and the consequent pulse shaping effects

Transversely Excited Atmospheric (TEA) CO2 laser pulses were used in order to generate an optical breakdown in a variety of mono- and polyatomic molecules using different focusing powers. The dependence of the spark kernel geometry and the transmitted pulse shapes on the focusing power as well as the pressure, molecular weight, and ionization energy of the gases was investigated in detail. Partial removal of the transmitted pulse tail in the 0.05–2.6 μs range together with shortened spikes in the 10–60 ns range has been observed by applying a 2.5 cm focal length lens for all the gases. At higher focal lengths, this effect is only incompletely observed for He gas. Spatial-temporal analyses of the laser beams and the relevant plasma plumes indicate that this behavior is due to the drop in the plasma density below the critical level, before the laser pulse tail is completed.

Laser-pulse shape effects on magnetic field generation in underdense plasmas

Laser pulse shape effect has been considered to estimate the self-generated magnetic field in laser-plasma interaction. A ponderomotive force based physical mechanism has been proposed to investigate the self-generated magnetic field for different spatial profiles of the laser pulse in inhomogeneous plasmas. The spatially inhomogeneous electric field of a laser pulse imparts a stronger ponderomotive force on plasma electrons. Thus, the stronger ponderomotive force associated with the asymmetric laser pulse generates a stronger magnetic field in comparison to the case of a symmetric laser pulse. Scaling laws for magnetic field strength with the laser and plasma parameters for different shape of the pulse have been suggested. Present study might be helpful to understand the plasma dynamics relevant to the particle trapping and injection in laser-plasma accelerators.

Impact of initial pulse characteristics on the mitigation of self-phase modulation by sinusoidally time varying phase

A simple and efficient approach to suppress undesirable self-phase modulation (SPM) of optical pulses propagating in fiber-optic systems is based on imposing a sinusoidal temporal phase modulation on the pulses to offset the chirp generated by SPM (Audo et al. Opt Lett 42(15):2902–2905, 2017). Here, we present a detailed analysis of this method. We derive an exact formula for the reduction of the SPM-induced rms spectrum broadening of an initially Gaussian pulse enabled by the sinusoidal compensation, and we assess the effects of the initial pulse shape and duration on the effectiveness of the technique by means of numerical simulation. The differences between pre- and post-propagation compensation schemes are also discussed.

An evaluation of the effect of pulse-shape on grey and white matter stimulation in the rat brain

Despite the current success of neuromodulation, standard biphasic, rectangular pulse shapes may not be optimal to achieve symptom alleviation. Here, we compared stimulation efficiency (in terms of charge) between complex and standard pulses in two areas of the rat brain. In motor cortex, Gaussian and interphase gap stimulation (IPG) increased stimulation efficiency in terms of charge per phase compared with a standard pulse. Moreover, IPG stimulation of the deep mesencephalic reticular formation in freely moving rats was more efficient compared to a standard pulse. We therefore conclude that complex pulses are superior to standard stimulation, as less charge is required to achieve the same behavioral effects in a motor paradigm. These results have important implications for the understanding of electrical stimulation of the nervous system and open new perspectives for the design of the next generation of safe and efficient neural implants.

Effect of Pulse Shape on Spall Strength

Effect of Pulse Shape on Spall Strength

Impact of Spectral Filtering on Multipulsing Instability in Mode-Locked Fiber Lasers

We investigate the impact of spectral filtering in mode-locked fiber lasers with an extended geometrical model. Our iterative model, which includes gain, loss, and the pulse shaping effects of chromatic dispersion and self-phase modulation, is used to model the laser cavity dynamics. Simulations show that broadband pulses experience large losses from spectral filtering in the cavity, leading to a number of potential laser instabilities and outcomes such as multipulsing, periodic and chaotic states, or a single pulse which transits to a higher energy state. For narrow band spectral filtering, the laser dynamics is dominated by the gain–loss dynamics in the cavity which causes multipulsing. For broadband spectral filtering, the nonlinearity-induced spectral reshaping of the single pulse can lead to a discontinuous pulse energy transition that circumvents multipulsing. The inclusion of third-order dispersion shows that the multipulsing instability is induced even in the case of broadband spectral filtering.

Pulse shape effects on the dynamic response of a steel beam under combined action of fire and explosion loads

Numerical analysis of the responses of steel beam under the combined action of fire and explosion loads are performed by using the ABAQUS general finite element program. The pulse shape effects on the fire and blast resistance capabilities of steel beam are investigated. The peak amplitude of the pulse load–impulse curve and the critical temperature–impulse curve is proposed to distinguish safe and unsafe areas. Two scenarios that apply fire and explosion loads in different orders are considered. Numerical analysis results show that the blast resistance capability of steel beam sequentially decreases under the action of exponential, triangular, and rectangular pulse loads; the effects of rectangular, triangular, and exponential explosion pulse loads on the fire resistance performance of steel beam consecutively decrease; and the pulse shape effects on the fire resistance capability of steel beam decreases with the increase in dynamic load ratio.

Momentum distribution of particles created in space-time-dependent colliding laser pulses

We study the pair-production process in the presence of two counterpropagating linearly polarized short laser pulses. By means of a nonperturbative technique, we take into account the full coordinate dependence of the external field going beyond the dipole and standing-wave approximations. In particular, we analyze the momentum distribution of particles created. It is demonstrated that the spatial variations of the laser pulses may play a crucial role. The more accurate treatment reveals a number of prominent features: the pair-production probabilities become considerably smaller, the quantitative behavior of the momentum spectra changes dramatically, and the pulse shape effects become much less pronounced. The results of our study are expected to be very important for future theoretical and experimental investigations.

Dynamic structural response of laminated glass panels to blast loading

This paper presents an analytical model of ‘fully-clamped’ laminated glass panel subjected to pulse-pressure loading in an air-blast. The dynamic structural response of the laminated glass panel is decoupled into two distinct phases of motion: phase I is controlled by the elastic deformation of the brittle glass plies whilst phase II is dominated by the large inelastic deformation of the Polyvinyl Butyral (PVB) interlayer. Transition between the two phases follows the large scale fragmentation of the glass plies – this will be captured through a stress-based damage criterion. Following the work of others, the PVB interlayer is idealised as a rigid-perfectly plastic material which allows its large inelastic response to be modelled within the constitutive framework of limit analysis. An interactive yield criterion is adopted to capture the simultaneous influence of bending and membrane stretch that governs plastic flow in the interlayer. Predictions by the analytical model are validated against existing experimental data and they will be shown to be in good agreement. Parametric studies were performed to elucidate the effects of total mass (per unit area) and thickness ratio on the maximum transverse deflection. The efficacy of Youngdahl’s technique on desensitising pulse shape effects is also studied.