Pulse Shape Changes Research Articles

An Unusual Pulse Shape Change Event in PSR J1713+0747 Observed with the Green Bank Telescope and CHIME

The millisecond pulsar J1713+0747 underwent a sudden and significant pulse shape change between 2021 April 16 and 17 (MJDs 59320 and 59321). Subsequently, the pulse shape gradually recovered over the course of several months. We report the results of continued multifrequency radio observations of the pulsar made using the Canadian Hydrogen Intensity Mapping Experiment and the 100 m Green Bank Telescope in a 3 yr period encompassing the shape change event, between 2020 February and 2023 February. As of 2023 February, the pulse shape had returned to a state similar to that seen before the event, but with measurable changes remaining. The amplitude of the shape change and the accompanying time-of-arrival residuals display a strong nonmonotonic dependence on radio frequency, demonstrating that the event is neither a glitch (the effects of which should be independent of radio frequency, ν) nor a change in dispersion measure alone (which would produce a delay proportional to ν −2). However, it does bear some resemblance to the two previous “chromatic timing events” observed in J1713+0747, as well as to a similar event observed in PSR J1643−1224 in 2015.

Self-induced transparency in a semiconductor quantum dot medium at ultracold temperatures

We investigate the feasibility of minimum absorption and minimum broadening of pulse propagation in an inhomogeneously broadened semiconductor quantum dot medium. The phonon interaction is inevitable in studying any semiconductor quantum dot system. We have used the polaron transformation technique to deal with quantum dot phonon interaction in solving system dynamics. We demonstrate that a short pulse can propagate inside the medium with minimal absorption and broadening in pulse shape. The stable pulse area becomes slightly higher than the prediction of the pulse area theorem and is also dependent on the environment temperature. The change in the final pulse shape is explained very well by numerically solving the propagation equation supported by the susceptibility of the medium. Our system also exhibits the pulse breakup phenomena for higher input pulse areas. Therefore, the considered scheme can have important applications in quantum communication, quantum information, and mode-locking with the advantage of scalability and controllability.

Mechanical and acoustic properties of deformable alloys

The paper is devoted to correlation dependences of ultrasound velocity with characteristics of strength and plasticity in uniaxial tension of Fe18Cr10Ni austenitic stainless steel with a unique set of physical and mechanical properties. Such a successful set of mechanical properties is provided by dislocation slip and twinning, the formation of stacking faults, and martensitic transformation. It should be noted that the assessment of changes in the mechanical characteristics of metals (especially at low temperatures) is a very laborious task and requires the use of non-destructive control methods. Experimental data was obtained using a bench designed to synchronize with recording of the “stress – strain” diagram for determining the values of ultrasound velocity propagation and the attenuation coefficient of the ultrasonic wave as a function of deformation. Measurement of ultrasound velocity propagation was reduced to determining the time of passage of an ultrasonic Rayleigh pulse between transmitting and receiving transducers. Attenuation was determined from the change in pulse shape. The pulses were excited by a piezoelectric transducer at a frequency of 5 MHz. The authors experimentally studied static loading effect on acoustic characteristics and calculated the destruction parameters. The propagation ultrasound velocity in deformable material is an informative feature for analyzing the nature of the processes that control plasticity. The effect of test temperature in the range 180 K ≤ T ≤ 320 K on acoustic and mechanical characteristics of the steel was studied to ensure control of its structural state and mechanical properties by means of non-destructive testing. The temperature range was chosen taking into account the possibility of direct γ → α′ martensitic transformation.

Determining electron column density fluctuations in a dominant scattering region using pulsar scintillation

ABSTRACT Density fluctuations in the ionized interstellar medium have a profound effect on radio pulsar observations, through angular scattering, intensity scintillations, and small changes in time delays from dispersion. Here we show that it is possible to recover the variations in dispersive delays that originate from a dominant scattering region using measurements of the dynamic spectrum of intensity scintillations, provided that the pulsar velocity and scattering region location are known. We provide a theoretical framework for the technique, which involves estimating the phase gradient from the dynamic spectra and integrating that gradient to obtain phase variations. It can be used to search for “extreme scattering events” (ESEs) in pulsars for which precision dispersion delay measurements are not otherwise possible, or to separate true dispersion variations from apparent variability caused by frequency-dependent pulse shape changes. We demonstrate that it works in practice by recovering an ESE in PSR J1603−7202, which is known from precision dispersion delay measurements from pulsar timing. For this pulsar, we find that the phase gradients also track the long-term variations in electron column density observed by pulsar timing, indicating that the column density variations and the scattering are dominated by the same thin scattering screen. We identify a sudden increase in the scintillation strength and magnitude of phase gradients over ∼days in 2010, indicating a compact structure. A decrease in the electron density in 2012 was associated with persistent phase gradients and preceded a period of decreased scintillation strength and an absence of scintillation arcs.

The dependence of timing jitter of superconducting nanowire single-photon detectors on the multi-layer sample design and slew rate.

We investigated the timing jitter of superconducting nanowire single-photon detectors (SNSPDs) and found a strong dependence on the detector response. By varying the multi-layer structure, we observed changes in pulse shape which are attributed to capacitive behaviour affecting the pulse heights, rise times and consequently timing jitter. Moreover, we developed a technique to predict the timing jitter of a single device within certain limits by capturing only a single detector pulse, eliminating the need for detailed jitter measurement using a pulsed laser when a rough estimate of the timing jitter is sufficient.

Performance investigation of FSO communication systems with chromatic dispersion, propagation losses and truncated normal modeled time jitter

FSO systems are identified as very reliable, effective and low-cost, wireless technologies for optical communications. However, the information carriers which are the optical pulses are subject to several effects during their propagation path. The atmospheric channels are heavily affected by the current weather conditions, causing signal fluctuations and power losses. Additionally, the very significant physical effect of the group velocity dispersion is responsible for the pulse shape changes along the propagation, especially for very short pulses, i.e. very high data rate transmission and long propagation distances. Furthermore, the time jitter affects strongly the reliability of the links, causing in practice, large irradiance fluctuations that may lead to signal outages or misdetections. All the above mentioned phenomena are studied jointly in this work and, for the first time to the best of our knowledge, the overall link performance is estimated in terms of links’ probability of fade, outage probability and average bit error rate by means of closed form or very accurate approximate mathematical expressions which can be used in any FSO link is needed. The weak-to-moderate time jitter effect, which is assumed in this work, here, is modeled by the truncated normal distribution. The corresponding numerical results for typical and realistic FSO parameters are presented while the obtained outcomes can be easily used for the estimation and designing of any other FSO under consideration.

Design and Development of High Voltage High Pulse Power Supply using FPGA for Dynamic Impedance Matching

High Voltage High Pulse Power Supply (HVHPPS) is designed with the goal to match fixed load, so thatprecise pulse output can be achieved. Generally the loads involve magnetron, klystron, and particle accelerators etc. The HVHPPS output pulse shape changes with load impedance variation due to various reasons. Due to changes in impedance, the performance of Pulse Power Supply degrades and reflects the power at the source end which causes component failure and system shut down. To overcome such problems, a scale down High Voltage High Pulse Power is designed and developed to match the dynamic impedance variations upto 25 % of mismatch. In earlier days, all HVHPPS were designed using microcontrollers where the problem of pulse to pulse monitoring and computational speed was compromised. The availability of variable and self-defined, Field Programmable Gate Array (FPGA) controller, which provided flexibility to design the pulse to pulse shaping and various vital parameter monitoring, made it possible. This paper presents the design and implementation of HVHPPS over an FPGA platform to meet the fast response requirement. This paper provides a solution for impedance mismatch problems associated with such types of power supply, and also presents specifications for major components in a high voltage pulse power system for various types of load ranges. An experimental test hardware was designed and developed for HVHPPS to implement dynamic impedance algorithm and validate the results.

An unusual pulse shape change event in PSR J1713+0747 observed with the Green Bank Telescope and CHIME: Profile data and figure reproduction scripts

An unusual pulse shape change event in PSR J1713+0747 observed with the Green Bank Telescope and CHIME: Profile data and figure reproduction scripts

Impact of electron correlation on the light-induced demagnetization of elemental ferromagnetic metals

The local spin-density approximation (LSDA) is known to describe poorly the electronic structure of 3d transition metals, yet most density-functional-based ab-initio studies of ultra-fast demagnetization rely on it. One way to account for Coulomb correlations among the localized d electrons and go beyond LSDA is to include the effective correlation energy (or Hubbard) U. By doing so, we show here that electronic correlations lead to sizable changes of the laser-induced demagnetization of iron, cobalt, and nickel. We study how the various laser parameters, such as pulse duration or intensity, change the magnetization dynamics. It turns out that the total laser fluence is not suitable to quantify how much a laser pulse demagnetizes a material, as changes in pulse duration and shape influence significantly the outcome. The findings are traced back to the electronic structure of the material, and explained based on phase space for optical transitions.Graphic abstract

Temporally Local Tactile Codes Can Be Stored in Working Memory.

Tactile exploration often involves sequential touches interspersed with stimulus-free durations (e.g., the time during which the hand moves from one textured surface to the other). Whereas it is obvious that texture-related perceptual variables, irrespective of the encoding strategy, must be stored in memory for comparison, it is rather unclear which of those variables are held in memory. There are two established variables—“intensity” and “frequency”, which are “temporally global” variables because of the long stimulus integration interval required to average the signal or derive spectral components, respectively; on the other hand, a recently established third contender is the “temporally local” variable that codes for kinematic profiles of very short, suprathreshold events in the vibrotactile signal. Here, we present the first psychophysical evidence that temporally local variables can be stored in memory. To that end, we asked participants to detect changes in pulsatile indentation stimuli at their fingertips with and without a gap of 1 s between stimulus presentations. The stimuli either contained global variables alone (change of pulse rate), or a mix of local and global variables (change of pulse shape). We found, first, that humans are much better at detecting a change in stimuli when local variables are available rather than global ones alone—as evident by the fact that 21 compared to only 6 participants out of 25 yielded a valid psychophysical curve, respectively. Second, this observation persists even when there is a gap between the stimuli, implying local variables must be stored in memory. Third, an extensive array of relevant intensity definitions failed to explain participants’ performance in any consistent manner, which implies that perceptual decisions were less likely to be driven by intensity coding. Taken together, our results suggest that humans perform pulsatile change detection utilizing local pulse shape, and to a lesser degree global pulse rate, and that both parameters can be stored in memory.

The Effects of Pulse Shape on the Selectivity and Production Rate in Non-oxidative Coupling of Methane by a Micro-DBD Reactor

The conversion of methane to ethylene has been investigated in a micro-DBD reactor with electrodes containing charge injector parts and excited with a negatively nano-second pulse voltage superimposed on a positive dc voltage. The effect of changing the characteristics of pulsed voltage such as pulse rise time (5–7 ns), total pulse width (12–14 ns), and pulse fall time (5–7 ns) on generation rate and products selectivity of the methane plasma has been studied. The kinetic model includes twenty species (electron, ions, radicals, and neutrals). The results showed that change in input pulse shape changes the generation rate and selectivity of neutral products. The rate of voltage change during pulse on-time significantly changed the instant C2H4 selectivity. With increasing the pulse rise and fall times the ethylene selectivity decreases, while the hydrogen selectivity increases. Results also showed that the electron reactions are dominant conversion channels during pulse on-time, while they had lower contributions in conversion progress during pulse off-time and the conversion process during this period is mainly governed by the radical reactions.

Simultaneous monitoring of residual chromatic dispersion and OSNR of NRZ-OOK signal based on asynchronous delay-tap sampling and image processing

We demonstrated a simultaneous residual chromatic dispersion (CD) and optical signal-to-noise ratio (OSNR) monitoring method for non-return-to-zero on-off keying signals by employing the delay-tap sampling and image processing techniques. Delay-tap sampling scatter plots reflect the signal pulse shape change and image processing can extract the contour of the scatter plots. Numerical simulation shows that the OSNR monitoring range is from 12 to 32 dB with <0.5 dB error and the CD monitoring range is from 0 to 1360 ps/nm. In the experiment, the OSNR monitoring range is from 14 to 30 dB and the CD monitoring range can go up to 1275 ps/nm.

Analysis of relative changes in pulse shapes of intracranial pressure and cerebral blood flow velocity

Objective. Analysis of relative changes in the shapes of pulse waveforms of intracranial pressure (ICP) and transcranial Doppler cerebral blood flow velocity (CBFV) may provide information on intracranial compliance. We tested this hypothesis, introducing an index named the ratio of pulse slopes (RPS) that is based on inclinations of the ascending parts of the ICP and CBFV pulse waveforms. It has hypothetically a simple interpretation: a value of 1 indicates good compliance and a value less than 1, reduced compliance. Here, we investigated the usefulness of RPS for assessment of intracranial compliance. Approach. ICP and CBFV signals recorded simultaneously in 30 normal-pressure hydrocephalus patients during infusion tests were retrospectively analysed. CBFV was measured in the middle cerebral artery. Changes in RPS during the test were compared with changes in the height ratio of the first and second peak of the ICP pulse (P1/P2) and the shape of the ICP pulse was classified from normal (1) to pathological (4). Values are medians (lower, upper quartiles). Main results. There was a significant correlation between baseline RPS and intracranial elasticity (R = −0.55, p = 0.0018). During the infusion tests, both RPS and P1/P2 decreased with rising ICP [RPS, 0.80 (0.56, 0.92) versus 0.63 (0.44, 0.80), p = 0.00015; P1/P2, 0.58 (0.50, 0.91) versus 0.52 (0.36, 0.71), p = 0.00009] while the ICP pulses became more pathological in shape [class: 3 (2, 3) versus 3 (3, 4), p = 0.04]. The magnitude of the decrease in RPS during infusion was inversely correlated with baseline P1/P2 (R = −0.40, p < 0.03). Significance. During infusion, the slopes of the ascending parts of ICP and CBFV pulses become increasingly divergent with a shift in opposite directions. RPS seems to be a promising methodological tool for monitoring intracranial compliance with no additional volumetric manipulation required.

Improvement of ignition and burning target design for fast ignition scheme

For the fast ignition scheme of laser fusion, a highly compressed fuel core is necessary using a cone-inserted spherical solid target. We design an optimal compression method with a multistep laser pulse shape using a 2D radiation hydrodynamics simulation. In the design, the maximum areal density is ρR max = 0.46 g cm−2 with 8 kJ of implosion laser. Considering the scaling law of hydrodynamic, we obtained 82 kJ and 1.3 MJ for the ignition-scale-target (ρR max = 1.1 g cm−2) and burning-scale-target (ρR max = 2.5 g cm−2), respectively. In a preliminary study of hydrodynamic instability in the optimized cone-inserted implosion, there is no significant growth of the instabilities that affect the implosion performance. A parameter search to investigate the feasibility and robustness of a high areal density design for changes in the laser pulse shape is performed. As a result, a delay of several tens of pico-second of the rising laser pulse is acceptable.

Electron bunch charge enhancement in laser wakefield acceleration using a flattened Gaussian laser pulse

We demonstrate the charge enhancement of the electron bunch using a flattened Gaussian laser pulse in laser wakefield accelerations. In laser wakefield accelerations, the change in laser pulse shape affects the diffraction pattern, resulting in laser intensity variation during plasma interaction. We employ a flattened Gaussian laser pulse to excite wakefields for electron acceleration. The central flattened region of the flattened Gaussian laser pulse, having the same energy as the Gaussian pulse, helps to enhance the pulse intensity via self-focusing. Thus, the evolution of flat Gaussian pulse enhances self-injection, which leads a considerable amount of electrons into the accelerating fields. A linear theoretical model is adopted to understand the wakefield generation mechanism using Gaussian and flattened Gaussian pulses. In order to broaden our understanding, quasi-three-dimensional PIC simulations are also performed. Our results show that a flattened Gaussian laser pulse with N=2 (where N is the order of the super Gaussian shape) yields a good quality electron bunch with retaining a relatively higher charge (about 300 pC) with respect to the case of a Gaussian laser pulse. We also show a twofold increase in bunch peak current when a flattened Gaussian pulse is employed. The electron bunches with high charge and high current may be promising candidates to drive next-generation compact free-electron lasers with unique X-ray properties.

Evidence for Multiple Pulse-shape Changes during the Third Chromatic Timing Event of PSR J1713 + 0747

Abstract Millisecond pulsar J1713 + 0747 recently underwent a drastic change in its pulse shape. The pulsar has undergone two previous “chromatic timing events,” frequency-dependent changes in pulse arrival times, with some evidence for low-amplitude achromatic changes in the pulse shape. Ongoing monitoring efforts of the pulsar show that the latest significant shape change has persisted for several months, longer than the recovery of the behavior in previous events. I examine profiles from the Nançay Radio Telescope presented in Astronomer’s Telegram #14642 and find evidence for multiple profile shapes after the start of the third event, hinting at the possibility of several new mode changes to consider.

Pulse-length Effect on Laser Wakefield Acceleration of Electrons by Skewed Laser Pulses

Laser pulse-length-related control and optimization of electron acceleration from laser wakefield acceleration (LWFA) by a shaped laser pulse is proposed to investigate in this study. The laser pulse shape changes and becomes skewed due to the variation in refractive index during propagation in plasmas. The optimum laser pulse-length for excitation of plasma wave in linear regime $(a_{0} is $\tau _{L}=\lambda _{p} / \sqrt {2\pi c} $ , but, in nonlinear regime $(a_{0}>1)$ , is not quite certain. Here, laser strength parameter $(a_{0})$ is defined as the ratio $eE_{L}/\text {m}\omega \text {c}$ . In nonlinear case, the variation in pulse skewedness at an optimized laser pulse-length produces different evolution of the wakefield that might affect the electron beam parameters. The present investigation predicts an optimized laser pulse-length (with an optimize ratio of the leading to the trailing pulse edge duration) 35 fs and laser strength parameter $a_{0}=2$ to control the electron bunch charge, emittance, and energy wakefield. Injected bunch charge is enhanced about 20%, and beam emittance is reported to reduce about 40% by employing the skewed Gaussian laser pulse in place of Gaussian pulse for LWFA. Energy-spread of accelerated electron bunch is also reduced from 18% to 6.6% for $s_{\alpha }=0.45$ for 35-fs laser pulse. The electron bunch parameters can also be controlled and optimized using skewed laser pulse and optimized pulse-length.

UWB Sensor Characterization for Radar Sensing and Imaging in Superluminal Propagation Regions

This article investigates the pulse propagation in the near field of a transmitter and reflector from the perspective of radar sensing and imaging. The peaks of the radiated and reflected pulses were found to have traveled at superluminal speeds in the near field of radar. The conceptual explanation and experimental demonstration of the unique properties of the radiated and reflected pulses and their impact on near field radar imaging are presented in this article. To confirm the superluminal propagation, in this study, we considered several ultrawideband (UWB) sensors and scatterers. The physics behind the superluminal propagation and pulse shape change in the radar near field is demonstrated using the Huygens principle, and a method to improve the imaging of radar in the near field while using synthetic aperture techniques is also proposed.

AstroSat observation of the Be/X-ray binary Pulsar 3A 0726-260 (4U 0728-25)

Results on timing and spectral properties of the Be/X-ray binary pulsar 3A 0726–260 (4U 0728–25) are presented. The binary was observed on 2016 May 6–7 with the Large Area X-ray Proportional Counter (LAXPC) and Soft X-ray Telescope (SXT) instruments onboard the AstroSat satellite. During this observation, the source was in non-flaring persistent state at a flux level of ∼ 8.6 ± 0.3 ×10−11 erg cm−2 s−1 in 0.4–20 keV. Strong X-ray pulsations with a period of 103.144±0.001 s are detected in 0.3–7 keV with the SXT and in 3–40 keV with the LAXPC. The pulse profile is energy dependent, and there is an indication that the pulse shape changes from a broad single pulse to a double pulse at higher energy. At energies above 20 keV, we report the first time detection of pulsation period 103.145±0.001 s and the double peaked pulse profile from the source. The energy spectrum of the source is derived from the combined analysis of the SXT and LAXPC spectral data in 0.4–20 keV. The best spectral fit is obtained by a power law model with a photon index (1.7±0.03) with high energy spectral cut-off at 12.9 ± 0.7 keV. A broad iron line at ∼ 6.3 keV is detected in the energy spectrum. We briefly discuss the implications of these results.

Modeling the Precession of the Warped Inner Accretion Disk in the Pulsars LMC X-4 and SMC X-1 with NuSTAR and XMM-Newton

Abstract We present a broadband X-ray study of the effect of superorbital periods on X-ray spectra and pulse profiles in the neutron star X-ray binaries LMC X-4 and SMC X-1. These two sources display periodic or quasiperiodic variations in luminosity of the order of tens of days, which are known to be superorbital, and are attributed to warped, precessing accretion disks. Using joint NuSTAR and XMM-Newton observations that span a complete superorbital cycle, we examine the broadband spectra of these sources and find the shape to be well described by an absorbed power law with a soft blackbody component. Changes in spectral shape and pulse profile shape are periodic with superorbital period, as expected from a precessing disk. We perform X-ray tomography using the changes in pulse profiles to model the geometry and kinematics of the inner accretion disk. Our simple geometric model of a beam and inner disk indicates that the long-term changes in soft pulse shape and phase are consistent with reprocessed emission from a precessing inner disk.