Pulse Components Research Articles

Influence of velocity pulse directivity on seismic response of cross-fault bridges

Pulse-type ground motions have special destructive effects on structures, and directivity is one of the fundamental characteristics of velocity pulses. In this paper, the impact of the velocity pulse directivity of seismic motions on both sides of the fault on the seismic response of fault-crossing bridges was quantified using the original records from the Chi-Chi earthquake in Taiwan. First, an automatic baseline correction method was applied to restore the permanent ground displacement, and the direction corresponding to the strongest pulse energy on both sides of the fault was identified based on continuous wavelet transformation. On this basis, the variability of the peak intensity of ground motions on the hanging wall and footwall in different directions, as well as the differences in pulse characteristics between the strongest pulse component and the two initial horizontal components, were analysed. Finally, a typical 5 × 30 m continuous girder bridge was considered as the research object to reveal the influence of the velocity pulse directivity on the seismic response of key parts on both sides of the fault. The results showed that the variability in the peak ground-motion intensity on the hanging wall of the fault was higher than that on the footwall. The displacement variability was up to 863 %, velocity was 262 %, and acceleration was 124 %. The pulse characteristics of the strongest pulse component were stronger than those of the parallel and vertical fault components, and its acceleration, velocity, and displacement response spectra were larger. The amplification effects of the velocity pulse directivity on the transverse bending moment, longitudinal bending moment, and torque of the pier bottom reached 1.3, 1.1, and 1.6, respectively. However, the amplification effect of the velocity pulse directivity on the relative displacement of the pier top, displacement of the main beam, and displacement of the bearing was more than 1.6 times, which was more significant than the internal force of the pier bottom.

Pulse component extraction and its application in simulation of pulse-like ground motions

A procedure for simulating new pulse-like ground motion based on natural pulse-like ground motion record is proposed. Firstly, an extraction method of pulse waveform based on Modified Ensemble Empirical Mode Decomposition is proposed, which reveals the relationship between half-wavelength width and pulse time-frequency information. Secondly, according to the response spectrum of the extracted non-pulse time-history, a triangular series is used to generate a stationary time-history, and then the extracted pulse component is added to the time-history, and the intensity envelope is adjusted to obtain the simulated pulse-like ground motion. Finally, the seismic response results of the Bouc-Wen-Baber-Noori model and the three-dimensional finite element model of the high-rise building are validated. It shows that the nonlinear effect of the simulated pulse-like ground motion by this method is close to that of the original natural pulse-like ground motion. The simulated pulse-like ground motion by this method can be used to analyze the inelastic response of various structures.

Analytical and numerical models to predict the shape of incident pulse in split-Hopkinson bar experiments

In typical split-Hopkinson pressure bar experiments (SHPB), the striker bar impacts the incident bar via discs made from soft materials such as copper. These discs, also called pulse shapers, are used (i) to eliminate the high frequency components of the incident pulse, (ii) to obtain a finite rise time of the incident pulse and (iii) to obtain a constant strain rate. Although these pulse shapers have been used for over decades in SHPB experiments, no analytical solutions or simple models are available that can predict the incident pulse as a function of the striker velocity, pulse shaper geometry and material parameters. Assuming that the pulse shaper is a rigid-linearly hardening material, we derive the analytical solution for the incident pulse when the rise time of the incident pulse is less than twice the time taken for a longitudinal wave to travel along the length of the striker. For larger rise times, we additionally assume that the striker is rigid to obtain a simple numerical model to predict the incident pulse in the presence of a pulse shaper. Both these models are validated against numerical simulations and experiments to demonstrate their accuracy.

Harnessing complexity: Nonlinear optical phenomena in L-shapes, nanocrescents, and split-ring resonators.

We conduct systematic studies of the optical characteristics of plasmonic nanoparticles that exhibit C2v symmetry. In particular, we analyze three distinct geometric configurations: an L-type shape, a crescent, and a split-ring resonator shaped like the Greek letter π. Optical properties are examined using the finite-difference time-domain method. It is demonstrated that all three shapes exhibit two prominent plasmon modes associated with the two axes of symmetry. This is in addition to a wide range of resonances observed at high frequencies corresponding to quadrupole modes and peaks due to sharp corners. Next, to facilitate nonlinear analysis, we employ a semiclassical hydrodynamic model, where the electron pressure term is explicitly accounted for. This model goes beyond the standard Drude description and enables capturing nonlocal and nonlinear effects. Employing this model enables us to rigorously examine the second-order angular resolved nonlinear optical response of these nanoparticles in each of the three configurations. Two pumping regimes are considered, namely, continuous wave (CW) and pulsed excitations. For CW pumping, we explore the properties of the second harmonic generation (SHG). Polarization and angle-resolved SHG spectra are obtained, revealing strong dependence on the nanoparticle geometry and incident wave polarization. The C2v symmetry is shown to play a key role in determining the polarization states and selection rules of the SHG signal. For pulsed excitations, we discuss the phenomenon of broadband terahertz (THz) generation induced by the difference-frequency generation . It is shown that the THz emission spectra exhibit unique features attributed to the plasmonic resonances and symmetry of the nanoparticles. The polarization of the generated THz waves is also examined, revealing interesting patterns tied to the nanoparticle geometry. To gain deeper insight, we propose an analytical theory that agrees very well with the numerical experiments. The theory shows that the physical origin of the THz radiation is the mixing of various frequency components of the fundamental pulse by the second-order nonlinear susceptibility. An expression for the far-field THz intensity is derived in terms of the incident pulse parameters and the nonlinear response tensor of the nanoparticle. The results presented in this work offer new insights into the linear and nonlinear optical properties of nanoparticles with C2v symmetry. The demonstrated strong SHG response and efficient broadband THz generation hold great promise for applications in nonlinear spectroscopy, nanophotonics, and optoelectronics. The proposed theoretical framework also provides a valuable tool for understanding and predicting the nonlinear behavior of other related nanostructures.

PSR B0943+10: Mode Switch, Polar Cap Geometry, and Orthogonally Polarized Radiation

As one of the paradigm examples to probe into pulsar magnetospheric dynamics, PSR B0943+10 (J0946+0951) manifests representatively, showing a mode switch, orthogonal polarization, and subpulse drifting, frequently studied below 600 MHz. Here, both integrated and single pulses are studied at a high frequency (1.25 GHz) with FAST. The mode switch is studied using a profile decomposition method. A phase space evolution for the pulsar’s mode switch shows a strange-attractor-like pattern. The radiative geometry is proposed by fitting polarization position angles with the rotating vector model. The pulsar pulse profile is then mapped to the sparking locations on the pulsar surface, and the differences between the main pulse’s and the precursor component’s radiative processes may explain the X-ray’s synchronization with radio mode switch. Detailed single pulse studies on B0943+10's orthogonally polarized radiation are presented, which may support certain models of radiative transfer of polarized emission. In particular, the difference in orthogonal polarization modes’ circular polarization might reflect the cyclotron absorption in pulsar magnetospheres. B0943+10's B and Q modes evolve differently with frequency and have different proportions of orthogonal modes, which indicates possible magnetospheric changes during mode switch. For Q mode pulse profile, the precursor and the main pulse components are orthogonally polarized, and are probably originated from different depths in the magnetosphere. The findings could impact significantly on the pulsar electrodynamics and the radiative mechanism related.

Indirect temperature protection of an asynchronous generator by stator winding resistance measurement with superimposition of high-frequency pulse signals

The article deals with the indirect methods for calculating the temperature of asynchronous generators with the introduction of a pulse component in the power supply circuit of the stator windings of asynchronous generators with squirrel-cage rotor. The relevance of this issue is determined by the need to improve asynchronous energy converters to increase their reliability and safety. The object of the study is an asynchronous generator with squirrel-cage rotor, which consume 40 % of the total electricity generated, and are the most affordable. One of the dangerous modes of asynchronous generators is their overheating as a result of increased currents and temperatures. The thermal protection of the stator winding of asynchronous generators relies primarily on measuring or determining the winding temperature. An indirect method for determining temperature based on measuring the resistance of the stator of an asynchronous generator with squirrel-cage rotor is proposed. The method is based on superimposing pulse signals of small amplitude and high frequency of 600 Hz on an alternating sinusoidal voltage with a frequency of 50 Hz. A simulation model for a 3 kW asynchronous generator has been developed. There were given the simulation results. The estimated values of the active resistances of the stator can be used to indirectly determine the temperature of the windings in thermal protection devices of asynchronous generators, as well as for control, monitoring and diagnostics of the technical condition. The research results confirm the possibility of indirect temperature determination and the creation of a thermal protection system for asynchronous energy converters based on the use of estimation methods.

Erratum to: The Method of Periodic Principal Components for the Dynamic Spectrum of Radio Pulsars and Faraday Rotation of Nine Pulse Components of PSR B0329+54

Erratum to: The Method of Periodic Principal Components for the Dynamic Spectrum of Radio Pulsars and Faraday Rotation of Nine Pulse Components of PSR B0329+54

The Method of Periodic Principal Components for the Dynamic Spectrum of Radio Pulsars and Faraday Rotation of Nine Pulse Components of PSR B0329#

The Method of Periodic Principal Components for the Dynamic Spectrum of Radio Pulsars and Faraday Rotation of Nine Pulse Components of PSR B0329#

Possibility of Monitoring the Dynamic Impact of the Rolling Stock on the Track Superstructure Using Strain Gauges and Vibrometry

One of the priority tasks in development of railway transport is to raise its efficiency by increasing the time between repairs for both the track superstructure and the rolling stock. Solving this problem is impossible without timely, complete, and reliable information about the dynamics of interaction of the rolling stock with the infrastructure. To organise monitoring of dynamic processes, completely different types of primary transducers are used: resistance strain gauges, fibre-optic sensors, dynamometers (force sensor pads), accelerometers, acoustic emission sensors. This implies relevance of the scientific and technical problem of comparative testing of sensors of different types to assess the information content of their signals and justify the criteria for choosing primary transducers when solving specific monitoring problems.The objective of the study is to comparatively test removable resistive strain sensors, optical polarisation strain sensors and accelerometers under a passing train and to evaluate their information content to control rail depression and detect defects on the running surface of wagon wheels.The study using finite element modelling and a physical model of a rail as of a beam on an elastic foundation, substantiates the relationship between longitudinal deformations and vertical accelerations of the rail foot. Comparative tests of removable strain-resistive and optical polarisation strain sensors and accelerometers were held on an experimental section of track under a passing train. A signal processing algorithm has been developed and the equivalence of strain gauges and vibrometers for determining the depression of a rail under a passing train has been proven. Acomparison has been made of the pulse components of the signals of deformation and vibration acceleration during movement of a wheel with a defect on the running surface, and the requirements for the frequency characteristics of the sensors and their mounting on the rail surface have been substantiated.

On-chip spatiotemporal optical vortex generation using an integrated metal–dielectric resonator

We theoretically demonstrate the possibility of generating a spatiotemporal optical vortex (STOV) beam in a dielectric slab waveguide. The STOV is generated upon reflection of a spatiotemporal optical pulse from an integrated metal–dielectric structure consisting of metal strips “buried” in the waveguide. For describing the interaction of the incident pulse with the integrated structure, we derive its “vectorial” spatiotemporal transfer function (TF) describing the transformation of the electromagnetic field components of the incident pulse. We show that if the TF of the structure corresponds to the TF of a spatiotemporal differentiator with a π/2 phase difference between the terms describing temporal and spatial differentiation, then the envelope of the reflected pulse will contain an STOV in all nonzero components of the electromagnetic field. The obtained theoretical results are in good agreement with the results of rigorous numerical simulation of the STOV generation using a three-strip metal–dielectric integrated structure. We believe that the presented results pave the way for the research and application of STOV beams in the on-chip geometry.

Few-cycle optical vortices for strong-field physics

We report on the generation of optical vortices with few-cycle pulse durations, 500μJ per pulse, at a repetition rate of 1 kHz. To do so, a 25 fs laser beam at 800 nm is shaped with a helical phase and coupled into a hollow-core fiber filled with argon gas, in which it undergoes self-phase modulation. Then, 5.5 fs long pulses are measured at the output of the fiber using a dispersion-scan setup. To retrieve the spectrally resolved spatial profile and orbital angular momentum (OAM) content of the pulse, we introduce a method based on spatially resolved Fourier-transform spectroscopy. We find that the input OAM is transferred to all frequency components of the post-compressed pulse. The combination of these two information shows that we obtain few-cycle, high-intensity vortex beams with a well-defined OAM, and sufficient energy to drive strong-field processes.

A time–frequency ridge extraction diagnostic method for composite faults of bearing gears in wind turbine gearboxes

The bearing and gear faults in the gearbox interact with each other, and the weak fault characteristics are often masked by the strong fault characteristics, making it difficult to accurately extract complete fault information. To solve this problem, a time–frequency ridge extraction diagnosis method based on multisynchrosqueezing transform (MSST) is proposed. This method utilizes MSST to enhance the compound fault features, especially the gear fault amplitude modulation components. It also utilizes the time–frequency ridge extraction method to separate the gear fault amplitude modulation components and the bearing fault impact pulse components. Additionally, it uses time shifting to substitute data and verifies the independence of the harmonic zero hypothesis to determine the accuracy of the fault components. This method provides a favorable basis for the extraction and identification of compound faults, especially weak faults, in complex dynamic signals of the gearbox. The effectiveness of this method is validated through simulation examples and practical applications.

High-sensitivity Beamformed Observations of the Crab Pulsar's Radio Emission

We analyzed four epochs of beamformed European VLBI Network data of the Crab Pulsar at 1658.49 MHz. With the high sensitivity resulting from resolving out the Crab Nebula, we are able to detect even the faint high-frequency components in the folded profile. We also detect a total of 65,951 giant pulses, which we use to investigate the rates, fluence, phase, and arrival time distributions. We find that for the main pulse component, our giant pulses represent about 80% of the total flux. This suggests we have a nearly complete giant pulse energy distribution, although it is not obvious how the observed distribution could be extended to cover the remaining 20% of the flux without invoking large numbers of faint bursts for every rotation. Looking at the difference in arrival time between subsequent bursts in single rotations, we confirm that the likelihood of finding giant pulses close to each other is increased beyond that expected for randomly occurring bursts—some giant pulses consist of causally related microbursts, with typical separations of ∼30 μs—but also find evidence that at separations ≳100 μs the likelihood of finding another giant pulse is suppressed. In addition, our high sensitivity enabled us to detect weak echo features in the brightest pulses (at ∼0.4% of the peak giant pulse flux), which are delayed by up to ∼300 μs.

An ameliorative duration of pulse-like ground motion records for nonlinear structural analysis

The near-field pulse-like ground motion contains obvious long-period and large pulse characteristic, which makes the nonlinear response of the structure exceed the general prediction of seismic response results. In order to reserve the obvious pulse component while selecting the strong ground motion duration part of the near-field pulse-like ground motion record without causing a large loss of spectral characteristics, the paper proposes an ameliorative truncated strong ground motion duration—useful duration. It is proposed based on the elastic acceleration response spectrum. Its principle is to make the acceleration response spectrum corresponding to useful duration and that corresponding to the original ground motion record as close and consistent as possible. The research results show that from the perspective of elastic response spectrum matching, the response spectrum matching error corresponding to useful duration is smaller than that of significant duration. In addition, the five types of periods corresponding to useful duration are closer to the period of original ground motion. Ulteriorly, from the displacement ratio spectrum of the elasto-plastic single-degree-of-freedom system, it is found that the average value of the elasto-plastic displacement ratio spectrum of useful duration and the original ground motion record is 0.98, which is very close to 1.00. It shows that the truncated ground motion can be used to replace the original ground motion to fully predict the nonlinear response of typical structures. Additionally, the effectiveness is further verified in the nonlinear response of three reinforced concrete frame structures, and the nonlinear response results of the structures are calculated using the time-history of useful duration, with less discreteness.

Study of the efficiency of ozone synthesis in a point‐to‐plain discharge in N2–O2 mixtures

AbstractThe experimental results of the ozone synthesis and electrodynamic characteristics of the point‐to‐plane DC voltage corona discharge in N2–O2 mixtures at atmospheric pressure are presented. Four different modes of DC corona discharge were investigated: stationary mode of positive point‐to‐plane discharge, two non‐stationary (streamers) modes of positive point‐to‐plane discharge, and mode of negative point‐to‐plane discharge. It was shown that ozone synthesis highly depends on discharge modes and correlates with discharge conditions appropriated to dissociative attachment processes. In the case of positive point‐to‐plane discharge, ozone synthesis behavior is similar to that of the pulse component of the discharge current. It was shown that the mode with secondary streamers propagation is the most effective for ozone production among the four different modes of the point‐to‐plane DC corona discharge.

Coherent two-dimensional THz magnetic resonance spectroscopies for molecular magnets: Analysis of Dzyaloshinskii-Moriya interaction.

To investigate the novel quantum dynamic behaviors of magnetic materials that arise from complex spin-spin interactions, it is necessary to probe the magnetic response at a speed greater than the spin-relaxation and dephasing processes. Recently developed two-dimensional (2D) terahertz magnetic resonance (THz-MR) spectroscopy techniques use the magnetic components of laser pulses, and this allows investigation of the details of the ultrafast dynamics of spin systems. For such investigations, quantum treatment-not only of the spin system itself but also of the environment surrounding the spin system-is important. In our method, based on the theory of multidimensional optical spectroscopy, we formulate nonlinear THz-MR spectra using an approach based on the numerically rigorous hierarchical equations of motion. We conduct numerical calculations of both linear (1D) and 2D THz-MR spectra for a linear chiral spin chain. The pitch and direction of chirality (clockwise or anticlockwise) are determined by the strength and signof the Dzyaloshinskii-Moriya interaction (DMI). We show that not only the strength but also the signof the DMI can be evaluated through the use of 2D THz-MR spectroscopic measurements, while 1D measurements allow us to determine only the strength.

Robust RPPG Method Based on Reference Signal Envelope to Improve Wave Morphology

Remote physiological monitoring has become increasingly important in improving quality of life, with remote photoplethysmography (RPPG) being a popular choice. This paper introduces an envelope–based method for RPPG channels to improve wave morphology of the collected signal based on the reference signal from finger PPG. Using a model consistent with physiological and optical principles, the authors divided the signal into linear superpositions, comprising pulse, constant, and disturbance components. The correlation coefficients were used to calculate a linear combination of Red–Green–Blue (RGB) channels to approximate the envelope shape of the reference PPG signal. Experiments with different light intensities and stability were designed to compare the envelope approximation ability and robustness of the proposed method with some common methods. Analysis of variance demonstrated the stable performance of the envelopment–based approach in most cases. Additionally, it improved the morphology of the Green (G) channel, including changing trends and directions, adjusting wave sizes, reducing noise, and reinforcing details of the single waveform. The envelope–based linear model approach has the ability to flexibly improve RPPG signals, which helps RPPG play a full role in many fields such as medicine.

Single-pulse Emission Variation of Two Pulsars Discovered by FAST

We investigate the single-pulse emission variations of two pulsars, PSRs J0211+4235 and J0553+4111, observed with the Five-hundred-meter Aperture Spherical radio Telescope at the 1.25 GHz central frequency. The observation sessions span from 2020 December to 2021 July, with 21 and 22 observations for them respectively. The integrated pulse profile of PSR J0211+4235 shows that there is a weak pulse component following the main component, and PSR J0553+4111 displays a bimodal profile with a bridge component in the middle. PSR J0211+4235 presents significant nulling phenomenon with nulling duration lasting from 2 to 115 pulses and burst duration lasting from 2 to 113 pulses. The NF of each observation is determined to be 45%–55%. No emission greater than three σ is found in the mean integrated profile of all nulling pulses. In most cases, the pulse energy changes abruptly during the transition from null to burst, while in the transition from burst to null there are two trends: abrupt and gradual. We find that the nulling phenomenon of PSR J0211+4235 is periodic by the Fourier transform of the null and burst state. In addition, the single-pulse modulation characteristics of these two pulsars are investigated, and the distributions of modulation index, LRFS and 2DFS are analyzed with PSRSALSA. The left peak of PSR J0553+4111 has intensity modulation. Finally, the polarization properties of these two pulsars are obtained through polarization calibration, and their characteristics are analyzed. The possible physical mechanisms of these phenomena are discussed.

Accelerated Damage in Metallized Film Capacitors Under Pulse Surge Combined With Rated DC Voltage

Metallized film capacitors (MFCs) have good self-healing performance and are widely used in pulsed power supplies, power systems, and aerospace equipment. The self-healing time of MFCs is often in the order of microseconds. When the pulsewidth of overvoltage is close to the self-healing time, MFCs are at risk of insulation failure. In this article, self-healing energy and time under pulse surge combined with rated dc voltage are investigated by analyzing the effect of the number of applied pulses on the capacitance loss, dielectric loss, and equivalent series resistance (ESR) of MFC. The correlation between the number of applied pulses and the capacitance loss of MFC at different repetition frequencies, pulse components, and temperatures is studied, fitting the 5% turning points of capacitance loss. The experimental results show that the multiple types of self-healing occur in an active period of one pulse under microsecond overvoltage. According to the level of injection energy and several typical waveforms from voltage and current, the self-healing process of MFC can be classified into effective self-healing, disruptive self-healing, and fatal self-healing. When effective self-healing occurs in the MFC, the performances remain stable for a certain time. As the number of tolerated pulses increases, disruptive self-healing and fatal self-healing significantly decrease capacitance value but increase dielectric loss and ESR.

High-altitude Magnetospheric Emissions from Two Pulsars

We discover three new weak pulse components in two known pulsars, one in PSR J0304+1932 and two in PSR J1518+4904. These components are emitted about halfway between the main emission beam and the interpulse beam (beam from the opposite pole). They are separated from their main pulse peak by 99° ± 3° for J0304+1932 and 123.°6 ± 0.°7 (leading) and 93° ± 0.°4 (trailing) for J1518+4904. Their peak-intensity ratios to main pulses are ∼ 0.06% for J0304+1932 and ∼0.17% and ∼0.83% for J1518+4904. We also analyzed the flux fluctuations and profile variations of the emissions for the two pulsars. The results show correlations between the weak pulses and their main pulses, indicating that these emissions come from the same pole. We estimated the emission altitude of these weak pulses and derived a height of about half of the pulsar’s light-cylinder radius. These pulse components are a unique sample of high-altitude emissions from pulsars, and challenge the current pulsar emission models.