Small Pulse Research Articles

Ударное воздействие сверхкороткого импульса света на прецессию намагниченности в магнитоупругой системе

The task about interaction of super-short light pulse on magnetoelastic system which has precession motion of magnetization is investigated. As a main mechanism it is investigated the decreasing of magnetization with power light action on spin system. It is investigated the development of magnetization precession by the action of light pulse. It is found that during the pulse action the amplitude vibrations is decreased and its frequency is increased. It is investigated the precession development in different meanings of light power. It is established the multi-regime character of magnetization vibrations by small pulse duration which is the same order as signal excitation period. It is established three regimes: regime №1 – stabile vibrations, regime №2 – the destroy of stabilization, regime №3 – shock excitation. It is established that the main distinguishing of regime №3 from first two regimes is the sharp jump increasing of amplitude as magnetic so the elastic vibrations which take pulse as a result of pulse action. It is found that as a result of high power long duration pulse it is arising the regime of in-flatness magnetic component stabilization. It is found that the main role in formation of this regime plays the magnetoelastic interaction.

Dynamics of pulsating solitons with chaotic behaviors from a 1.7 μm ultrafast fiber laser

We demonstrate observation and dynamics of unique soliton pulsation regime in an ultrafast fiber laser at 1.7 μm. It is found that with either single-soliton pulse or multiple-soliton pulses in cavity the laser emission could exhibit periodic intensity and shot-to-shot spectra variations as measured based on the dispersive Fourier transformation (DFT) technique. Further, detailed studies turned out that the soliton pulsation can comprise numerous small pulses with random intensities, exhibiting chaotic characteristics. Besides, all the pulses within the multiple solitons possess identical pulsation period. In addition, despite of the fact that the temporal intervals between the multiple solitons are on the order of tens of nanoseconds among them, their pulsations demonstrate excellent synchronicity. The experimental observations are further revealed by numerical simulations. These results can provide insights into ways to optimize designs of laser sources and open up new potential for generation of pulsating solitons in ultrafast fiber lasers at different wavelengths.

Establishing a limited‐area model based on a global model: A consistency study

AbstractA limited‐area model (LAM) is established based on a global model (Global–Regional Integrated Forecast System; GRIST). GRIST–LAM inherits all the technical features of its global counterpart, enabling independent regional weather and climate modeling. The key advancement involves extending the original dynamical core to integrate it under the lateral boundary conditions (LBCs). As an initial development and evaluation study, this paper focuses on the consistency issue between the LAM and the global model. Three perfect‐model tests, using global solutions as LBCs and background truths, were performed to evaluate the LAM behaviors. In the pure dynamical core test, the LBC errors do not compromise the solutions within the interior domain. However, certain configurations can lead to more discontinuous solutions at the domain boundary. The solution error for a specified region decreases as the domain size increases when all other factors are equal. A small error pulse is generated during the initial stage of integration due to the presence of artificial transient waves induced by the LBCs. The model generates fine‐scale details and smaller errors based on coarser‐resolution LBCs. The consistency between LAM and LBC also influences the errors. The climate simulations demonstrate that both hydrostatic and non‐hydrostatic LAMs can reach statistical equilibrium. Regional model climates in the interior domain have higher quality but are sensitive to domain size and LBC configuration. Using a variable LBC coefficient is helpful to alleviate the artificial precipitation at the boundary. In the kilometer‐scale test, the global variable‐resolution model and its LAM counterpart show comparable results. Their performance is competitive with that of a uniform‐resolution global storm‐resolving simulation. Global variable‐resolution and LAM generate higher magnitudes in the tail part of the kinetic energy spectra due to higher local resolution and produce a consistent time evolution of precipitation. The broad implication of this study is also discussed.

Systematic errors in searches for nanohertz gravitational waves

ABSTRACT A number of pulsar timing arrays have recently reported preliminary evidence for the existence of a nanohertz frequency gravitational wave background. These analyses rely on noise analyses, which are inherently complex due to the many astrophysical and instrumental factors. We investigate whether realistic systematic errors, stemming from misspecified noise models that fail to capture salient features of the pulsar timing noise, could bias the evidence for gravitational waves. We consider two plausible forms of misspecification: small instrumental pulse arrival time offsets and radio-frequency-dependent time-correlated noise. Using simulated data, we calculate the distribution of the commonly used optimal statistic with no signal present and using plausibly misspecified noise models. By comparing the optimal statistic distribution with the distribution created using “quasi-resampling” techniques (such as sky scrambles and phase shifts), we endeavour to determine the extent to which plausible misspecification might lead to a false positive. The results are reassuring: we find that quasi-resampling techniques tend to underestimate the significance of pure-noise data sets. We conclude that recent reported evidence for a nanohertz gravitational wave background is likely robust to the most obvious sources of systematic errors; if anything, the significance of the signal is potentially underestimated.

Recent advances in relativistic excitation of atomic hydrogen

Within the framework of the relativistic regime ( E k > 2700 eV) and the first Born approximation, we investigate the inelastic excitation of atomic hydrogen by electron impact from 1 s to 2 p state. The incoming and outgoing electrons are described by free Dirac spinors, while the hydrogen atom target is described by the exact solutions of Dirac equation with a central potential. A detailed study has been devoted to the non-relativistic regime as well as the relativistic regime of the process, and the results obtained show the differences between the two regimes. These differences have revealed that the differential cross section (DCS) is influenced by the parameters of the 1 s and 2 p states, along with significant effects on diffusion during small pulse transfers. The relativistic effects are responsible for the significant changes in the DCS as a function of diffusion angles which depend on the chosen geometry.

A Fully Self‐Healing Patch of Integrated Bio‐Signal Monitoring Sensors with Self‐Healing Microporous Foam and Au Nanosheet Electrodes

AbstractA fully self‐healing sensor patch consisting of an in‐plane integrated dual‐mode sensor and a pressure sensor with a vertically integrated electrocardiogram (ECG) electrode is reported. For a full‐device self‐healing, interlayer self‐bonding by using self‐healing oxime‐carbamate bond‐based polyurethane and room temperature self‐healing TUEG3 capped Au nanosheet (T‐Au NS) electrodes are devised. Via the use of a self‐healing sensor foam prepared by a coating of a self‐healing composite of polyurethane and polyaniline onto a microporous graphene foam, a self‐healing dual‐mode sensor is fabricated to detect the pressure and temperature simultaneously without interference. Furthermore, the interdigitated self‐healing electrode of T‐Au NS is applied to the pressure sensor to enhance the sensitivity up to 208.62 kPa−1 (<1 kPa), enabling the detection of small pulse signals even after multiple self‐healing events. By using the common self‐healing T‐Au NS electrode vertically integrated onto the sensor patch, ECG signals are also detected. With this sensor patch, skin temperature, wrist pulse, and ECG signals are successfully detected after a simultaneous full‐device self‐healing from complete bisection. This study demonstrates the facile fabrication of a high‐performance, fully self‐healing patch of multi‐sensors via the deliberate selection of sensor design and the associated functional materials, confirming its high potential applicability to highly durable health monitoring systems.

High Efficiency Operation of a 4K-Gifford-McMahon Cryocooler without Rotary Valve with a Metal Bellows Compressor

Traditional Gifford-McMahon cryocoolers are operated with an integrated rotary valve which regulates the compressed Helium supply and return into and from the cold head. Theory predicts that about 50% of the input energy is lost in this rotary valve [1]. In this work we removed the rotary valve from a Sumitomo RDK-101G cold head and drove the Gifford-McMahon cryocooler in Stirling-mode directly with a slow-moving metal bellows compressor at around 1.2Hz. We could demonstrate that the energy efficiency of the cryocooler system improves by almost 50%. As a result, we were able to operate this cold head with 650W of total electrical input power with a cooling power of 140mW at 4.2K on the second stage and no-load temperatures of below 40K on the first stage. This corresponds to a COP of 215mW/1000W which one of the highest COPs reached for small and medium size 4K GM and pulse tube cryocoolers.

Vibration diagnostics of transportation structures on railroads

The article presents the results of the natural frequencies of vibrations of the span structure during the express-diagnostics, to excite the process of vibrations of the structure the pulse impact of the concentrated load of small mass is applied in the middle of the span structure (the method of small pulse impacts – “human jump”). The analysis of the obtained data, allowed to establish the parameters of free vibrations of unloaded span structures, the predominant frequencies on the graph of spectral density of dispersion are identical, regardless of the number of jumps, that is, the frequency of impact, if the time between jumps corresponds to the complete damping of vibrations. Of practical interest in the assessment of the technical condition is a quantitative assessment of the change in the natural frequency of vibration of girder metal and reinforced concrete spans depending on the presence of defects accumulated during the operation of the bridge. The obtained characteristics can serve as initial data, increasing the accuracy of calculations for calculations of artificial structures for seismic resistance, as well as in dynamic stability calculations for prospective loads and in the development of a model of the structure, the formation of algorithms of tasks to identify defects.

Investigation of pulsed direct-current plasma jets in a turbulent boundary layer

Characteristics of the plasma jet produced by a pulsed direct-current (pulsed-DC) dielectric barrier discharge (DBD) and its interaction with a turbulent boundary layer (TBL) are investigated in detail using stereo particle imaging velocimetry. Quiescent-flow characterization results show that a positive starting vortex and a negative near-wall jet structure are induced by the pulsed-DC DBD plasma actuator. With increasing pulse width and discharge frequency, the jet velocity magnitude increases monotonously, as a direct result of the extension of fluid particle acceleration time. During the interaction with a cross-flow TBL, two streamwise vortices with opposite signs are observed at the two sides of the electrode junction, which essentially originate from the starting vortex and negative jet in quiescent air. The skin-friction drag variations are dominated by the cross-stream momentum transportation of streamwise vortices, with drag reduction in the vortex upwash zone and drag increase in the downwash zone. Compared with the conventional alternating-current DBD plasma actuators, the turbulent fluctuations produced by pulsed-DC DBD are much higher, which also affects the skin-friction drag. Further proper orthogonal decomposition (POD) analysis reveals that two distinctly different flow patterns are produced by pulsed-DC DBD working at small and large pulse widths. The dominant POD modes causing the most velocity fluctuation are the spanwise translation and deformation of plasma-induced streamwise vortices. These results provide insights into the basic phenomenon of pulsed-DC plasma jets in cross flow, which recently has demonstrated its promising applications in turbulent skin-friction reduction.

Deep learning and data augmentation for partial discharge detection in electrical machines

Fault testing in the production line of automotive traction machines is essential to ensure the desired lifetime. Since repetitive partial discharges (PDs) caused by anomalies in the insulation system lead to premature breakdowns of electrical machines, a reliable PD detection is of great importance. This paper proposes deep learning (DL) methods to improve the discrimination of PD from background noise in comparison with the state-of-the-art amplitude based PD detection in the production line. First, a systematic data extraction and labeling procedure is introduced to obtain correctly labeled datasets from arbitrary PD measurements. In addition, datasets are enhanced with low signal-to-noise ratio PD pulses by applying a special data augmentation approach. 13 different convolutional, recurrent and fully connected neural networks are compared for various time-frequency representations of the input signals. Hyperparameters for input transform, network topology and solver are optimized for all 13 combinations to ensure a fair case study. As a result, the two-dimensional convolutional neural network with continuous wavelet transform achieves the best accuracy of around 99.76% on a test dataset of PD signals originating from previously not utilized test objects. All DL models considered in this comparison outperform the state-of-the-art threshold-based PD classification. Even for PD events with an amplitude close to the noise level, the detection rate is still around 95% for the best network. Furthermore, without applying the proposed data augmentation procedure, the DL models investigated are not able to distinguish small PD pulses from noise.

Generation and observation of noise-like pulses in an ultrafast fiber laser at 1.7 μm

In this manuscript, we demonstrate the generation and real-time dynamics of noise-like pulses (NLPs) in a 1.7 μm ultrafast thulium-doped fiber laser with all-fiber structure. NLPs with a central wavelength of ∼ 1742.5 nm and a 3-dB spectral width of ∼ 10.95 nm could be observed with pulse energy up to 4.19 nJ. The dynamic characteristics of NLPs were explored by using time-stretch dispersive Fourier transformation technology, which shows that the NLPs actually consist of many chaotic small pulse envelopes with random and changeable energies. These experimental results indicate that NLPs are the intrinsic features of fiber lasers and hold significant importance for further academic research, which can contribute to the development and application of 1.7 μm fiber laser in fields such as biomedicine and short-range remote sensing.

Study on Correction Method of Counting Loss below the Threshold for Low Energy Radionuclides Based on Monte Carlo Simulation.

In the absolute measurement method of nuclide radioactivity by the internal gas proportional counter, the reasonable correction of the small pulse counting loss is the key to obtaining the measurement results accurately. Considering the decay type and energy of radioactive gas nuclides, the influence of the low-energy beta particles and the wall effect counting loss on the activity measurement results is different also. To this end, two typical radioactive gas nuclides ( 37 Ar and 3 H) are used to study the cause of counting loss based on the Monte Carlo simulation. The results show that the counting loss of small pulse in the activity measurement of 37 Ar comes mainly from the wall effect generated by x rays. Within the given gas pressure of 60-300 kPa, the simulated wall effect correction factors are 1.063-1.021. The decay energy of β particles generated by 3 H is very low, and there is no obvious wall effect. The small pulse counting loss mainly comes from the low-energy beta particles' contribution with the energy below the counting threshold, which can be corrected by extrapolating the beta energy spectrum at a lower counting threshold (below 1 keV).

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Effective Light‐Induced Fluorescent H‐Aggregation of Fluorinated Pyridyl‐Azo Dye via Photoisomerization

AbstractHere we present the synthesis of a new fluorinated pyridyl‐azo dye and demonstrate an effective way to convert monomer fluorinated pyridyl‐azo dye to H‐aggregated form through UV‐light induced trans‐cis‐trans photoisomerization. And upto a 12 : 88 ratio between monomer : aggregation was achieved through a small pulse of UV irradiation. The H‐aggregation shows a unique high extinction co‐efficient in UV‐visible absorbance and unexpected fluorescence emission with a remarkably large Stokes shift. The solvent DMF and fluorine substituent were found to have a critical role in aggregation. 1H, 19F NMR, and 19F‐DOSY NMR experiments were used to confirm the aggregation and also confirm the absence of π‐π stacking.

Simulation of radon detection efficiency with small pulse ionization chamber based on Geant4

Radon measurement is crucial in assessing the damage to the human body caused by natural radiation. Pulsed ionization chambers are effective for real-time radon measurement and have widespread applications in other radiation techniques. However, due to practical constraints such as limited space and portability concerns, it becomes imperative to consider not only the detection efficiency but also their ease of transportation. This work utilizes the Geant4 Monte Carlo simulation toolkit to characterize the detection models of small cylindrical and flat plate-type pulsed ionization chambers, and carry out a simulation study to analyze the three crucial factors that influence detection efficiency, including the geometry of the chamber, electrode size, and operating temperature. The results indicate that the cylindrical pulse ionization chamber, with a length of 8 cm and radius of 2 cm, has the best detection efficiency and portability in terms of geometric dimensions, achieving a detection efficiency of (58 ± 4)%. Meanwhile, the flat plate pulse ionization chamber, with dimensions of 7 cm in length and 3 cm in width, achieves the best detection efficiency and portability, with a detection efficiency of (54 ± 3)%. In terms of electrode wire size, the cylindrical ionization chamber electrode wire with a length of 7 cm and a radius of 2.5 mm was optimal with a detection efficiency of (59 ± 4)%. In terms of operating temperature, the detection efficiency of the flat-plate pulsed ionization chamber was the highest at 30 °C, which was (58 ± 4)%, and that of the cylindrical pulsed ionization chamber was the highest at 20 °C, which was (63 ± 4)%. By analyzing the influencing factors of the detection efficiency of the pulsed ionization chamber, it has a certain reference value and guiding significance for the research and design of small pulsed ionization chamber detectors for radon measuring instruments.

Pulse selection algorithm for NM64 neutron detector

We propose an algorithm to sepearate pile-up pulses in neutron detectors by utilizing a standard pulse. For this method to be effective, the data must consist mostly of isolated pulses. First, we define a reference pulse by averaging a sample of clearly isolated pulses. Then, for an arbitrary signal, we calculate a shape deviation by summing up the squared residuals between it and the reference pulse. The pulse with the greatest shape deviation is removed from the process. We then recalculate the reference pulse and repeat until the remaining pulses have shape deviation within a threshold. These remaining pulses exhibit a very good linear trend between area and height, allowing us to screen those suspected as pile-ups. A pulse much higher than the final reference pulse, despite being in the area-height-trend and having low shape deviation, is considered a pile-up of two identical pulses. The final reference pulse is fitted to a function defined by two pieces of Gaussian-multiplied polynomial, normalized, and called the standard pulse. We attempted to fit the pile-up pulse with one standard pulse to separate pile-up pulses. If the sum of squared normalized residuals is higher than some threshold, we add one more pulse, try fitting again, and repeat up to three pulses. We apply this algorithm to the pulses collected from one counter at the Princess Sirindhorn Neutron Monitor station at the summit of Doi Inthanon Mountain, Chiang Mai, Thailand, measured by an oscilloscope. The algorithm correctly separates obvious pile-up cases, allowing to record individual pulse timing with improved accuracy. However, we found small pulses, usually belong to gamma rays, that blend with neutron pulse and pass 100 mV output filtration. After removing those under 100 mV, the pulse area distribution of the separated pile-up is consistent with that of single pulses except at very small pulse sizes.

Effect research of fuel injection and pressurization pulse width on injection characteristics of ultra high pressure common rail system

Ultra high pressure common rail system can realize adjustable injection rate by controlling the relationship between fuel injection and pressurization timing, and then affect the fuel injection characteristics of diesel engine. In order to ascertain the effect law and its formation mechanism of the fuel injection and pressurization pulse width on the fuel injection characteristics of ultra high pressure common rail system, on the basis of introducing the mathematical model of the system, the simulation model of ultra high pressure common rail system was established, and the accuracy of the model was verified by performance experiment, the effect of fuel injection and pressurization pulse width on the fuel injection characteristics of the system under different common rail pressure were analyzed. The results show that with the increase of fuel injection pulse width, the shape of fuel injection rate curve is similar to saddle shape and the proportion of large fuel injection rate range in the whole injection process increases gradually. At the same time, the fuel injection opening delay remains unchanged, but the fuel injection closing delay increases significantly when the fuel injection pulse width is small (0.6~1 ms), while it remains basically unchanged when the fuel injection pulse width is large (1~1.4 ms). With the increase of pressurization pulse width, the shape of fuel injection rate curve is similar to saddle shape and remains unchanged under the condition of small injection pulse width, while the fuel injection rate curve shape may appear similar to the "inverted saddle-shaped" under the condition of large injection pulse width, this is due to the rapid decrease of pressurization pressure caused by the closing of the solenoid valve control signal in the pressure-amplifier device before the end of fuel injection.

Effect of Si contents on microstructure and mechanical characteristics of TiAlSiN thin film deposited by HiPIMS using different Ti[sbnd]Si target compositions

High Power Impulse Magnetron Sputtering (HiPIMS) PVD deposition technology offers smoother coating enhanced mechanical properties and improved substrate-coating adhesion and has become a superior alternative to direct current magnetron sputtering (DCMS). The technology utilizes high peak power with a small pulse duration, leading to a much denser plasma in the order of 1018 m−3. This results in dense, defect-free, and high-quality smoother coatings. In this study, TiAlSiN coatings were deposited on WC-10Co (wt%) cermet using HiPIMS technology with two different TiSi contents. A pair of TiSi targets, either of compositions Ti77Si23 or of Ti66Si34, were used during the depositions along with another pair of Ti40Al60, in successive cathode-stages. The impact of Ti and Si atomic percentages on the microstructure and mechanical properties of the coatings was investigated using various techniques, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), 3D-surface profiling, nano-indentation, Rockwell indentation-adhesion, and scratch test. The coating's thickness and deposition rate were estimated from the cross-section morphology. The results suggested that the TiAlN phase likely existed in an amorphous phase of Si3N4 in TiAlSiN coatings. As the Ti atomic percentage in the layer increased, the hardness improved, reaching up to 42 GPa (max). Additionally, the coating surface roughness decreased from 14.3 nm to 10.9 nm, and the grain size decreased from 10 nm to 9 nm. The adhesion strength observed under the Rockwell-indentation test was rated as HF1 in both cases. Furthermore, the indentation test revealed similar crack patterns, but an increase in Ti content significantly improved the coating-substrate adhesion, as confirmed by the Scratch test. The scratch test demonstrated a maximum load of 173 N during the complete delamination (Lc3) of TiAlSiN from the carbide substrate.

Influence of pulse-tail energy of short-pulse CO2 laser in drilling of various glasses

In a short-pulse CO2 laser based on discharge excitation, there is a pulse tail that depends on the device configuration and operating conditions. The pulse tail is longer than the spike pulse and causes thermal effects such as a crack, heat-affected zones (HAZ), and so on. There are various types of glass having different physical constants related to heat, such as the thermal expansion coefficient and the softening point. Even if the same CO2 laser pulse is radiated onto glass, the processing results may differ depending on the glass material. Four types of glass, namely, crown glass, soda-lime glass, borosilicate glass, and synthetic quartz glass were irradiated with two types of short CO2 laser pulses, one with a large pulse tail and one with a small pulse tail, at a repetition rate of 200 Hz and a fluence per pulse of 22 J/cm2. As the processing characteristics, the ratios of the surface hole diameter and the HAZ diameter to the irradiation diameter, as well as the drilling depth, were investigated. The pulse-tail energy of the short CO2 laser pulses did not affect the surface hole diameter. In the glasses with small softening points of 740 °C or less, the pulse-tail energy of short CO2 laser pulses affected the HAZ with a large number of pulse irradiations with a total irradiation fluence of 2000 J/cm2 or more. The short CO2 laser pulses with a small tail produced a smaller HAZ than the short CO2 laser pulses with a large tail. In drilling with a large number of pulse irradiations, the short CO2 laser pulses with a small tail produced deeper drilling than the short CO2 laser pulses with a large tail. The glass material did not affect the surface hole diameter and the drilling depth. The glass material affected the HAZ.

A low-jitter and low-phase noise switched-loop filter PLL using fast phase-error correction and dual-edge phase comparison technique

This paper presents a low-jitter and low-phase noise type-II charge pump and switched-loop filter-based (SLF) phase-locked loop (PLL) with a fast phase error correction technique (FPEC) and a newly proposed dual-edge phase comparator (DEPC). To improve the phase noise, the bandwidth of the proposed PLL is extended to fREF/5 using the proposed DEPC. It consists of four D flip-flops in true single-phase clock (TSPC) logic, four current-mode logic-based inverters, and two logic OR gates. Unlike conventional DEPCs, the proposed DEPC has a small reset pulse width duration and negligible blind zone, and due to this, it can perform at higher frequencies along with an increased phase detection range. The proposed architecture is implemented for a 2.4 GHz output frequency that embodies DEPC and SLF using the FPEC technique in an 180-nm Semi-Conductor Laboratory (SCL) CMOS process. The proposed DEPC can work up to a maximum of 3.45 GHz frequency with 145 ps of reset delay. The proposed PLL accomplishes the 40 MHz bandwidth with a 200 MHz reference clock. The simulated rms jitter integrated from 10 kHz to 100 MHz and the phase noise of the output signal at an offset of 1 MHz are 860 fs and −122 dBc/Hz respectively. The proposed architecture occupies an area of 0.032 mm2 and consumes 8.2 mW from 1.8 V power supply.