Pulse Phase Research Articles

X-ray Pulsar-Based Navigation Using Pulse Phase Delay between Spacecraft and Verification with Real Data

Pulsars are neutron stars with high rotation speeds and have extraordinary long-term rotational stability. X-ray pulsar-based navigation (XNAV) is a navigation method that estimates the position and velocity of a spacecraft using the X-ray radiation from pulsars. Flight experiments on Insight-Hard X-ray Modulation Telescope (Insight-HXMT) and Neutron Star Interior Composition Explorer (NICER) have successfully verified the feasibility of using XNAV for a single spacecraft. For spacecraft in formation, a pulsar-based navigation method that uses the pulse phase delay between spacecraft is derived. Moreover, a direct estimation method for pulse phase delay, which is independent from the pulsar template, is proposed. The proposed method is verified with simulation data of the Crab pulsar and real data of the same pulsar obtained from Insight-HXMT and NICER.

Pump-control approach to enantiospecific state transfer.

Enantiospecific state transfer of chiral molecules is extremely important because enantiomers coexist in many biologically active compounds and play significantly different physiological, pharmacological, and biological roles. The inherently strong electric-dipole optical approaches based on the cyclic three-level model of chiral molecules have been extensively discussed. But, for the cases of large chiral molecules and/or chiral molecules of low asymmetry, the four-level model with two sub-loops is more realistic to describe the molecules. Based on the four-level model, we propose a pump-control approach to realize the highly efficient enantiospecific state transfer. In our approach, two pump pulses are applied to generate molecular coherence between the ground state and the first excited state of our working model. According to the coherence of the molecules, we adjust the phase and pulse area of the control pulse, then we obtain the highly efficient enantiospecific state transfer in the first excited working state. In addition, we further optimize the fraction of enantiopure samples by adjusting the area of the two pump pulses.

Посткоммутационное импульсное закорачивание фаз как фактор повышения безопасности эксплуатации шахтной участковой электрической сети напряжения 3,3 кВ

The efficiency of ground short-circuiting the damaged phase of the network to the ground is analyzed in the context of finding ways to increase the electrical safety of mine site 3.3 kV power network operation. In the context of ensuring human protection from electric shock, the expediency is justified and a technical solution for post-commutation pulse phase short-circuiting in the reverse EMF circuit is provided for the asynchronous motors of the power consumers within a technological mine site.

Phase-Sensitive Plasma Nonlinearity Controlled by Ultrashort Pulses

The generation of spectral components sensitive to the carrier-envelope phase of a laser pulse in a thin zinc selenide film has been experimentally demonstrated and confirmed by a numerical simulation. A pump–probe scheme has been implemented so that a pump pulse with a duration of about 1.5 field cycles, a central wavelength of 1.7 μm, and a stabilized carrier-envelope phase induces photoionization in a thin zinc selenide film. The probe pulse is scattered by the plasma, generating new phase-sensitive spectral components at the edges of its spectrum. The theoretical analysis has confirmed plasma nonlinearity as a mechanism for generating these components. The observed effect can be used to characterize the carrier-envelope phase of ultrashort pulses during the generation of high-order harmonics and sequences of attosecond pulses.

Waiting Time Distribution of Giant Pulses from the Crab Pulsar Modeled with a Non-stationary Poisson Process

We study the waiting time distribution of giant pulses from the Crab pulsar observed with the Nanshan 26-m radio telescope at a center frequency of 1556 MHz with 512 MHz bandwidth. The observations were performed over a duration of 12.6 hours with 32 μs sampling interval. Our analysis has led to the detection of 2097 giant pulses above a threshold of 10 σ, with flux density > 100 Jy. The occurrence rate of giant pulses is characterized by a highly intermittent giant pulse productivity in short clusters with high rates, separated by relatively long quiescent intervals with low occurrence rates, especially for the giant pulses associated with the interpulse emission. The distribution of waiting times between two subsequent giant pulses displays a power-law tail that can be modeled with a non-stationary Poisson process, which indicates that giant pulses are independent and random events. Distinct waiting time distributions between giant pulses in the main pulse and interpulse phases are presented, which implies that the giant pulse emission mechanisms maybe different in the opposite magnetic poles. The ramification for our understanding of the radio emission mechanisms is discussed.

Improving pulsar timing precision through superior time-of-arrival creation

Context. The measurement of pulsar pulse times-of-arrival (ToAs) is a crucial step in detecting low-frequency gravitational waves. To determine ToAs, we can use template-matching to compare each observed pulse profile with a standard template. However, using different combinations of templates and template-matching methods (TMMs) without careful consideration can lead to inconsistent results. Aims. In pulsar timing array (PTA) experiments, distinct ToAs from the same observations can be obtained due to the use of diverse templates and TMMs. In other words, employing diverse approaches can yield different timing results and would thus have a significant impact on subsequent gravitational wave searches. In this paper we examine several commonly used combinations to analyze their effect on pulse ToAs. Methods. We evaluated the potential impact of template and TMM selection on 13 typical millisecond pulsars within the European PTA. We employed pulsar timing methods, specifically the root mean square and reduced chi-square (χ2r) of the residuals of the best timing solution, to assess the outcomes. Additionally, we evaluated the system-limited noise floor (SLNF) for each pulsar at various telescopes operating around 1.4 GHz using frequency-resolved templates. Results. Our findings suggest that utilizing data-derived and smoothed templates in conjunction with the Fourier-domain with Markov chain Monte Carlo TMM is generally the most effective approach, though there may be exceptions that require further attention. Furthermore, we determine that pulse phase jitter noise does not significantly limit the current precision of the European PTA’s timing, as jitter levels derived from other studies are much lower than the SLNF.

Deep learning reconstruction algorithm for frequency-resolved optical gating.

In general, delay operation is the most time-consuming stage in frequency-resolved optical gating (FROG) technology, which limits the use of FROG for high-speed measurement of ultrashort laser pulses. In this work, we propose and demonstrate the reconstruction of ultrashort optical pulses by employing the sequence-to-sequence (Seq2Seq) model with attention, theoretically. To our knowledge, this is the first deep learning framework capable of accurately reconstructing ultrashort pulses using very partial spectrograms. The root mean squared error (RMSE) of the pulse amplitude reconstruction and phase reconstruction on the overall test dataset are 9.5 × 10-4 and 0.20, respectively. Compared with the classic FROG recovery algorithm based on two-dimensional phase retrieval algorithms, the use of our model can shorten the spectral measurement time to 1/8 of the original time or even less. Meanwhile, the time required for pulse reconstruction using our model is roughly 0.2 s. To our knowledge, the pulse reconstruction speed of our model exceeds all current iteration-based FROG recovery algorithms. We believe that this study can greatly facilitate the use of FROG for high-speed measurements of ultrashort pulses.

Study on the partial discharge characteristics induced by the motion of cellulose particles in transformer oil

AbstractCellulose particles present a significant concern within the oil‐paper insulation of transformers, posing potential risks to insulation performance. Under the influence of the electric field, the movement of cellulose particles can compromise the transformer's insulation, leading to potential failure. An experimental platform was established to synchronously record particle motion images, partial discharge (PD) pulses, and electric voltage waveforms in oil, aiming to observe the PD characteristics resulting from particle motion under alternating current (AC) voltage and investigate the relationship between different particle motion modes, motion positions, and PD signals. The findings reveal that the phase distribution of PD signals is correlated with the particle motion mode. Specifically, the phase distribution of PD pulses during the back‐and‐forth motion mode is between 4°–94° and 182°–275°. In the suspended oscillation motion mode, the PD pulses phase is concentrated between 20°–84° and 203°–268°. The generation of PD pulses is closely linked to the particle's motion position. PD pulses occur when the particle remains on the electrode during the back‐and‐forth motion mode, generally, PD pulses rarely occur during the jumping process between the two electrodes. In the suspended oscillation motion mode, PD pulses occur when the particle moves upward, but generally do not occur during downward movement. Furthermore, the Pulse Sequence Analysis technique was used to employ the PD characteristics caused by particle motion in transformer oil. The simulation calculations of the electric field distribution for two different particle motion modes show that the particle's motion can cause distortion of the electric field distribution, leading to the generation of PD. The study of the PD characteristics at different particle motion modes and positions obtained contributes to a deeper understanding of the PD induced by cellulose particle motion under AC voltage and provides a reference for the insulation evaluation of transformers.

Theory of a quasi-phase-matched optical parametric oscillator of a backward wave: threshold and spectrum

We theoretically study the stationary and nonstationary modes of the backward wave generation of an optical parametric oscillator based on quasi phase-matching. We obtain convenient analytical expressions in both modes. We derive, for the stationary lasing mode, the optimal values of the pump intensity and the total length of the structure. We present a numerical estimate of the threshold intensity for PPKTP and LiNbO3 and a comparison with the experiment. It is shown that the group velocity dispersion leads to a narrowing of the backward wave spectrum. But the forward wave pulse phase modulation contributes to the broadening of the central maximum of the backward wave.

Improving defect detection capability of pulse and pulse phase thermography method for CFRP plates by enhancing rear surface heat transfer coefficient

Infrared pulse thermography (PT) is a noncontact and convenient nondestructive inspection method, and its application to various objects has been reported in many papers. However, conventional PT is not suitable for detecting deep- or near-rear-surface defects. This study focuses on PT inspections of CFRP plates and improvements in their defect detection capabilities. To improve the capability of detecting near-rear-surface defects, a method for enhancing the heat transfer coefficient (HTC) of the rear surface during PT inspection was examined in this study; this would increase the temperature difference in the defective areas observed in thermal images. To investigate the effectiveness of the proposed method, experiments were conducted on CFRP specimens with artificial defects. The CFRP specimens were inspected using the PT method, during which water was brought into contact with the rear surfaces of the specimens to enhance the HTC. The experimental results showed that the capability of detecting near-rear-surface defects improved when the rear surfaces were in contact with water with forced convection. In addition, obtaining phase images by applying a Fourier transform to the experimentally obtained temperature data (that is, pulse phase thermography: PPT) was examined. Consequently, the combination of the enhancement of the rear-surface HTC and the use of phase images was significantly effective in improving the defect detection capability.

Adaptive Grid Search Based Pulse Phase and Doppler Frequency Estimation for XNAV

Adaptive Grid Search Based Pulse Phase and Doppler Frequency Estimation for XNAV

An improved passive solar still integrated with pulsating heat pipes and phase change materials

This paper presents a theoretical analysis of a novel solar still system, which was previously explored through experimental studies. The experimental results demonstrate that integrating phase change material (PCM) to store latent heat from vapor condensed on sidewalls during sunlight exposure, along with the use of pulsating heat pipes (PHPs) to recover this stored energy after sunset, and cooling the condenser sidewalls with PCM, significantly boosts the system’s efficiency from 23.7 % to 48.5 %. These innovative features, applied for the first time in a single-stage passive solar still, are thoroughly examined using a groundbreaking mathematical model. This model is the first to uniquely account for heat transfer and condensation on sidewalls and to accurately simulate the function of pulsating heat pipes (PHPs) within a passive solar still setup. By incorporating measured radiation intensity and ambient temperatures, the model applies an exhaustive energy balance, utilizing heat transfer correlations and resistances for precise temperature predictions of each component. This detailed analysis highlights the system’s innovative aspects and identifies areas for further refinement, shedding light on potential improvements and the system’s limitations. The results show a water production of 6.7931 kg/m2 and an efficiency of 52.2 %, with a discrepancy of 7.8 % compared to experimental findings. Notably, 37.6 % of the total freshwater production is derived from sidewall condensation, significantly reducing heat loss by capturing latent heat. Additionally, by reallocating 9.3 % of stored energy, the PHPs maintain the saline water temperature 6.2 degrees higher at night, thereby sustaining elevated production rates.

High-precision spatiotemporal three-dimensional ultrashort pulse synchronization with optical Kerr effect

In studying the interaction of multiple ultrashort pulses with matter, high requirements are put forward for spatiotemporal synchronization accuracy. Limited by the response time and bandwidth of existing devices, the synchronization of multiple ultrashort pulses still faces significant difficulties. By observing the transient phenomena of the optical Kerr effect, high-precision, three-dimensional (x, y, t) synchronization of ultrashort pulses at different angles was achieved. In the optical Kerr effect, the polarization state of the signal pulse changes only when it coincides with the pump pulse, at which point the signal pulse passes through the analyzer. The changes in the intensity and phase of the signal pulse is positively correlated with the degree of spatiotemporal coincidence. In this study, 10-ps pulses were used in the experiments. By observing the intensity and phase distribution of the signal pulses, a time synchronization accuracy between two pulses of less than 1 ps and spatial synchronization accuracy of ±125 µm and ±3 µm in the x and y directions, respectively, were achieved. Moreover, the synchronization of two pulses at an angle of 90 ° was measured, further proving that the method can achieve the spatiotemporal synchronization of pulses with large angles. Therefore, this method has important application prospects in the study of multi-beam interactions with matter and other ultrafast physical phenomena.

Passive Wireless Partial Discharge Sensors with Multiple Resonances.

Partial discharge (PD) is the dominant insulating defect in Gas-Insulated Switchgear (GIS). The existing detection methods are mainly divided into built-in wire-connected disk antennas with destructive drilling and external ultra-high frequency antennas with poor anti-interference ability. This research introduces a passive wireless PD sensor implanted inside GIS on the observation window. The sensor is implemented by a sheeting branch-inductor with multiple resonances which is able to enhance detection sensitivity. A coaxially aligned readout circuit, positioned outside the GIS, interrogates the PD sensor to wirelessly obtain the PD signal. The proposed sensing scheme improves signal-to-noise ratio and ensures minimal disruption to the electric field distribution inside GIS. An experimental setup was established in a controlled laboratory environment to benchmark the multi-resonant sensor against the commercial UHF sensor. A 2.5-times enhancement of signal strength was observed. Since our sensor was implanted inside the GIS, a high signal-to-noise ratio (68.82 dB) was obtained. Moreover, we constructed a wireless calibration test to investigate the accuracy of the proposed sensor. The precision of the signal test was as high as 0.72 pC. The pulse phase distribution information was collected to demonstrate a phase-resolved partial discharge (PRPD) pattern. The experiment results validate the effectiveness of the proposed method and demonstrate excellent performance in PD detection.

Electron acceleration influenced by sinh-Gaussian laser pulses in a prepared ion channel

The acceleration of electron in a produced ion channel is studied theoretically using a sinh-Gaussian (shG) laser pulse with radial polarization. Compared to Gaussian laser pulses, shG laser pulses propagate differently, presenting as a bright ring encircling a dark hollow core that inhibits early focusing and promotes self-defocusing. They can therefore be used to accelerate electrons to extremely high energies. The electron energy gain is influenced by the laser pulse decentred parameter linked to the shG function, however, the ion stream’s electric field prevents the transverse oscillations from pushing electrons out of the interaction zone. With a decentred parameter of ∼2.15 and a laser pulse intensity value of ∼1020 Wcm −2 incident on density of ∼ 1022 m −3, where the incident pulse phase is ψ 0 = 0, the combined effect of ion channelling and radially polarized (RP) shG laser pulses leads to a significant enhancement of electron energy gain within the ion density channel to the GeV level.

A Novel Approach to Raman Distributed Temperature-Sensing System for Short-Range Applications.

A novel approach to the development of Distributed Temperature-Sensing (DTS) systems based on Raman Scattering in Multimode optical fibers operating at around 800 nm is presented, focusing on applications requiring temperature profile measurement in the range of a few hundreds of meters. In contrast to the standard Raman DTS systems, which aim to shorten the pulse space width as much as possible to improve the precision of measurement, the novel approach studied in this work is based on the use of pulses with a space width that is approximately equal to the distance covered by the fiber under test. The proposed technique relies on numerical post-processing to obtain the temperature profile measurement with a precision of about ±3 °C and a spatial resolution of 8 m, due to the transaction phases of the optical pulses. This solution simplifies the electronic circuit development, also minimizing the required laser peak power needed compared to the typical narrow pulse techniques.

Dynamic Response of Phase Change Heat Exchange Unit with Layered Porous Media for Pulsed Electronic Equipment

Effective heat dissipation challenges transient high-power electronic devices in hypersonic vehicle cabins. This study introduces a Phase Change Heat Exchange Unit with Layered Porous Media (PCHEU–LPM) employing pulsed heat flow at the top and forced convection at the bottom. The primary aim was a comparative parametric study analyzing the thermal response of the heating surface under pulsed heat flow conditions. The geometric model was generated using electron microscopy images of manufactured objects and the numerical model was established based on the enthalpy–porosity method. Numerical simulations explored amplitude and frequency effects on pulsed thermal excitation, evaluating temperature and phase fields. A comprehensive time-frequency transformation assessed the temperature response. The results indicated an initial decrease and subsequent increase in interface temperature fluctuation with pulse heat flux amplitude growth. Temperature field uniformity correlated with natural convection strength in two-phase and liquid-phase regions. At mid and low frequencies, the phase change process increasingly suppressed interface temperature fluctuations. Optimal pulse thermal excitation selection was crucial for minimizing temperature fluctuations while maintaining the interface temperature within the expected phase transition range. In conclusion, a novel design concept is posited herein, aiming to enhance surface temperature uniformity and broaden the applicability of electronic devices through the manipulation of porosity rates.

Application of texture signatures based on multiparameter-magnetic resonance imaging for predicting microvascular invasion in hepatocellular carcinoma: Retrospective study.

Despite continuous changes in treatment methods, the survival rate for advanced hepatocellular carcinoma (HCC) patients remains low, highlighting the importance of diagnostic methods for HCC. To explore the efficacy of texture analysis based on multi-parametric magnetic resonance (MR) imaging (MRI) in predicting microvascular invasion (MVI) in preoperative HCC. This study included 105 patients with pathologically confirmed HCC, categorized into MVI-positive and MVI-negative groups. We employed Original Data Analysis, Principal Component Analysis, Linear Discriminant Analysis (LDA), and Non-LDA (NDA) for texture analysis using multi-parametric MR images to predict preoperative MVI. The effectiveness of texture analysis was determined using the B11 program of the MaZda4.6 software, with results expressed as the misjudgment rate (MCR). Texture analysis using multi-parametric MRI, particularly the MI + PA + F dimensionality reduction method combined with NDA discrimination, demonstrated the most effective prediction of MVI in HCC. Prediction accuracy in the pulse and equilibrium phases was 83.81%. MCRs for the combination of T2-weighted imaging (T2WI), arterial phase, portal venous phase, and equilibrium phase were 22.86%, 16.19%, 20.95%, and 20.95%, respectively. The area under the curve for predicting MVI positivity was 0.844, with a sensitivity of 77.19% and specificity of 91.67%. Texture analysis of arterial phase images demonstrated superior predictive efficacy for MVI in HCC compared to T2WI, portal venous, and equilibrium phases. This study provides an objective, non-invasive method for preoperative prediction of MVI, offering a theoretical foundation for the selection of clinical therapy.

Investigation on effects of PRF on pulse Doppler sensor accuracy and phase noise role in clutter mitigation

Investigation on effects of PRF on pulse Doppler sensor accuracy and phase noise role in clutter mitigation

Linear to circular conversion in the polarized radio emission of a magnetar

AbstractRadio emission from magnetars provides a unique probe of the relativistic, magnetized plasma within the near-field environment of these ultra-magnetic neutron stars. The transmitted waves can undergo birefringent and dispersive propagation effects that result in frequency-dependent conversions of linear to circularly polarized radiation and vice versa, thus necessitating classification when relating the measured polarization to the intrinsic properties of neutron star and fast radio burst emission sites. We report the detection of such behaviour in 0.7–4 GHz observations of the P = 5.54 s radio magnetar XTE J1810−197 following its 2018 outburst. The phenomenon is restricted to a narrow range of pulse phase centred around the magnetic meridian. Its temporal evolution is closely coupled to large-scale variations in magnetic topology that originate from either plastic motion of an active region on the magnetar surface or free precession of the neutron star crust. Our model of the effect deviates from simple theoretical expectations for radio waves propagating through a magnetized plasma. Birefringent self-coupling between the transmitted wave modes, line-of-sight variations in the magnetic field direction and differences in particle charge or energy distributions above the magnetic pole are explored as possible explanations. We discuss potential links between the immediate magneto-ionic environments of magnetars and those of fast radio burst progenitors.