Pulse Separation Research Articles

Nearby SN-associated GRB 190829A: Environment, Jet Structure, and VHE Gamma-Ray Afterglows

Abstract We present a self-consistent paradigm to interpret the striking features of nearby low-luminosity GRB 190829A. Its prompt gamma-ray lightcurve has two separated pulses. We propose that the interaction of the hard prompt gamma-ray photons ( E p = 624 − 303 + 2432 keV) of its initial pulse with the dusty medium (A V = 2.33) not only results in the second soft gamma-ray pulse (E p ∼ 12 keV) but also makes a pre-accelerated e ± -rich medium shell via the γγ annihilation. In this paradigm, we show that the observed radio, optical, and X-ray afterglow lightcurves are well-fitted with the forward shock model. Its jet is almost isotropic (θ j > 1.0 rad) with a Lorentz factor of ∼35, and the electron density of the e ± -rich medium shell is ∼15 cm−3, which is about seven times higher than the electron density of its normal surrounding medium. The GRB ejecta catches up with and propagates into the e ± -rich medium shell at a region of R = (4.07–6.46) × 1016 cm. This results in a bright afterglow bump at ∼103 seconds after the GRB trigger. The predicted very high energy (VHE) gamma-ray emission from the synchrotron self-Compton process agrees with the H.E.S.S. observation. The derived broadband spectral energy distribution shows that GRB 190829A like nearby GRBs would be promising targets of the VHE gamma-ray telescopes, such as H.E.S.S., MAGIC, and CTA (Cerenkov Telescope Arrays).

An innovative approach to partial discharge measurement and analysis in DC insulation systems during voltage transient and in steady state

Measuring partial discharges in DC insulation systems is an issue due to the lack of a reference relating the voltage waveform to the physics of discharge phenomena. Also, DC is not always steady state, due to voltage and load transients that generate electric field profile variations inside an insulation system, which can affect partial discharge inception likelihood and characteristics. Partial discharge measurement technology must be able to separate discharge pulses from noise and identify the type of sources generating partial discharge, which is related to condition assessment and maintenance. Eventually, measurement and analysis should be automatic and unsupervised, in order to get rid, partially or totally, of expert support. This study addresses a new approach to partial discharge measurements in DC insulation systems, presenting algorithms for separation, recognition and identification, which are effective both in DC steady state and during voltage (and load) transients. These algorithms are automatic and do not require expert support. Various cases of algorithm application on test objects consisting of multilayer polymeric specimens with an internal cavity and defective cable models are presented and discussed. Their effectiveness is proved, at least at a laboratory level, with effective noise separation and identification of discharge typology.

ResNet and CycleGAN for pulse shape discrimination of He-4 detector pulses: Recovering pulses conventional algorithms fail to label unanimously

Pulse shape discrimination (PSD) capable detectors, such as He-4, that respond to neutron and gamma-ray interactions have a threshold deposited energy value below which n/γ discrimination vanishes when using conventional PSD algorithms. Recent attempts in applying supervised learning based artificial neural networks for PSD use the pulses in the separated regions to train the networks so they can be used to classify another set of separated pulses. In doing so, pulses previously indistinguishable are not recovered for classification, which would have increased the number of neutron and gamma-ray pulses that could be used for further analysis. Assuming the reason why conventional PSD algorithms have unseparated regions is because the parameter space of the algorithms fail to capture the intrinsic (but subtle) distinguishing behavior of some of the neutron and gamma-ray pulses, a cycle-consistent generative adversarial network (CycleGAN) was trained to amplify those differences and extract well separated neutron and gamma-ray clusters. Results show that, once the network is trained with pulses from separated and unseparated regions, it was able to transform the pulses in the unseparated region to improve the PSD. Subsequent n/γ classification was performed using deep residual network (ResNet) that takes pulses with 512 data points as an input. Two different ResNets were explored – simple ResNet and modified ResNet which takes segmented pulse inputs in the first layer and the corresponding time axis values in the last hidden layer. The later approach enables the network to extract time correlated pulse features to enhance its ability to capture the pulse behaviors relevant for PSD. Although it achieves slightly lower accuracy, 99.41% versus 99.89%, based on simply counting the number of correct n/γ labels assigned, compared to the simple ResNet, the modified ResNets architecture was able to decreases the cross-entropy loss function by half, which implies that the correct n/γ labels assigned are less likely to be accidental. PSD parameter distributions based on n/γ classification by ResNet before and after transforming unseparated pulses using CycleGAN show that by enhancing the separation between neutrons and gamma-rays, the transformation helps improve the performance of classifier networks that are trained using labeled dataset. The enhancement of neutron and gamma-ray separation by the CycleGAN increased the PSD figure of merit (FOM) by up to 70% in some regions. The results show that, if a given detector achieves clear separation between neutron and gamma-ray pulses in any energy region, such neural network approaches can help lower the energy threshold for the separation and increasing the number of neutron and gamma-ray pulses that can be used for further analysis.

Double delay alternating with nutation for tailored excitation facilitates banding-free isotropic high-resolution intracranial vessel wall imaging.

The purpose of this study was to evaluate the use of a double delay alternating with nutation for tailored excitation (D‐DANTE)‐prepared sequence for banding‐free isotropic high‐resolution intracranial vessel wall imaging (IC‐VWI) and to compare its performance with regular DANTE in terms of signal‐to‐noise ratio (SNR) as well as cerebrospinal fluid (CSF) and blood suppression efficiency. To this end, a D‐DANTE–prepared 3D turbo spin echo sequence was implemented by interleaving two separate DANTE pulse trains with different RF phase‐cycling schemes, but keeping all other DANTE parameters unchanged, including the total number of pulses and total preparation time. This achieved a reduction of the banding distance compared with regular DANTE enabling banding‐free imaging up to higher resolutions. Bloch simulations assuming static vessel wall and flowing CSF spins were performed to compare DANTE and D‐DANTE in terms of SNR and vessel wall/CSF contrast. Similar image quality measures were assessed from measurements on 13 healthy middle‐aged volunteers. Both simulation and in vivo results showed that D‐DANTE had only slightly lower vessel wall/CSF and vessel wall/blood contrast‐to‐noise ratio values compared with regular DANTE, which originated from a 10%–15% reduction in vessel wall SNR but not from reduced CSF or blood suppression efficiency. As anticipated, IC‐VWI acquisitions showed that D‐DANTE can successfully remove banding artifacts compared with regular DANTE with equal scan time or DANTE preparation length. Moreover, application was demonstrated in a patient with an intracranial aneurysm, indicating improved robustness to slow flow artifacts compared with clinically available 3D turbo spin echo scans. In conclusion, D‐DANTE provides banding artifact‐free IC‐VWI up to higher isotropic resolutions compared with regular DANTE. This allows for a more flexible choice of DANTE preparation parameters in high‐resolution IC‐VWI protocols.

Generation of coherent multicolor noise-like pulse complex in Yb-doped fiber laser mode-locked by GIMF-SA

We have demonstrated the generation of multicolor noise-like pulse complex in a passively Yb-doped mode-locked fiber laser based on a single mode-graded index multimode-single mode fiber (SMF-GIMF-SMF) device as the saturable absorber (SA). The stimulated Raman scattering (SRS) effect leads to the cascaded generation of the main noise-like pulse (NLP) at 1028.8 nm together with the noise like Raman pulse (RP) at 1076.1 nm. The generated dual wavelength pulses demonstrate the unique properties of mutually synchronization and coherence. The autocorrelation traces show that each of the synchronously mode-locked pulses exhibits a double-scale structure with a narrow peak which consists of a train of quasi-periodic beat pulses with a 35.7 fs pulse width and a pulse separation of about 77.2 fs. The total output power reaches 102.5 mW with 34% of it belonging to the RP. And furthermore, by separating the two pulses with spectral filters, the modulation fringes cannot be observed anymore. These results indicate that the Raman component participates in the mode-locking operation as a 'signal' instead of 'noise'. Such a coherent Raman pulse source provides a novel platform for numerous applications, such as frequency comb spectroscopy and so on.

Pulse deinterleaving based on fusing PDWs and PRI extraction process for radar-assisted edge devices considering computational costs

Deinterleaving or radar pulse separation is a very important goal in terms of radar sources for identifying and implementing electronic warfare systems. In order to separate radar pulses, parameters measured by electronic warfare receivers such as electronic warfare support measures (ESM) and electronic signals intelligence (ELINT) are used in pulse separation. This paper presents a multi-parameter improved method for separating the pulse sequence of radar signals based on time of arrival (TOA) processing with sorting the other pulse descriptor words (PDW) parameters. In the proposed method, after extracting all the pulse repetition intervals (PRIs) based on TOA, the parameters of the angle of arrival, pulse width and carrier frequency (RF) are being used in pulse sorting to separate the received interleaved pulse sequences. The sequential difference histogram (SDIF) algorithm or cumulative difference histogram (CDIF) algorithm is used to extract all pulse repetition intervals. Also, in order to separate the sequence of the received pulses from all surroundings emitters, in addition to matching the potential PRI among the TOAs of the pulses and the similarity measurement in the other parameters of the pulse sequence (pulse sorting) have been used. This proposed algorithm is implemented in the integrated and complete design for deinterleaving of the radar pulses. The proposed method by considering low-cost computing sources considers a fast and low-complexity solution that can be used for edge-enabled distributed processors in aerial radar platforms as edge devices for military/combat unmanned aerial vehicles or networked missiles. The simulation results show that our method is completely effective.

EPMA geochemistry and LA-ICPMS dating of allanite, epidote, monazite, florencite and titanite from the Jaduguda uranium deposit, Singhbhum Shear Zone, eastern India: Implications for REE mineralization vis-à-vis tectonothermal events in the Proterozoic Mobile Belt

The Singhbhum shear zone (SSZ), eastern India, located close to the boundary between the Proterozoic North Singhbhum Mobile Belt and the Archaean Singhbhum craton, is the best known uranium province and one of the most important copper districts in India. The uranium ores and associated rocks are enriched in rare earth elements (REEs). This study integrates texture, composition and in situ LA-ICPMS dating of allanite, epidote, monazite, florencite and titanite from the Jaduguda uranium deposit in the SSZ. The earliest LREE-rich allanite (Allanite-Ce) formed at 1883 ± 14 Ma and was subsequently replaced and overgrown respectively by LREE-depleted allanite and epidote at 1637 ± 11 Ma and 1107 ± 18 Ma. The earliest monazite (Monazite-Ce) formed at ca. 1809 ± 9 Ma, while a new generation of monazite and florencite are dated at 952.2 ± 7.9 Ma and 959 ± 83 Ma respectively. Titanite, discordant to the pervasive foliation, records ancient Pb-loss and probably new titanite growth at 978 ± 17 Ma.The SSZ witnessed protracted evolutionary history with accompanying multi-stages REE mineralization and mobilization, spanning over ca. 900 Ma. The Paleoproterozoic LREE-mineralization occurred in two different pulses at ca. 1.88 Ga and ca. 1.80 Ga predating the known ages of metamorphism. It is envisaged that extension-related faults developed at the present location of the SSZ acted as fluid conduits and localized the earliest ca. 1.88 Ga hydrothermal REE mineralization. It is unclear whether the ca 1.80 event is the continuation of the ca 1.88 Ga event or represents a separate and discrete pulse of mineralization in the same locale under different geotectonic environment. The ca. 1.64 Ga event associated with LREE-removal is related to either reactivation of the existing faults or partial closure of the mobile belt with concomitant shear deformation and metamorphism in the shear zone when the rocks in the northern mobile belt were thrust southwards along existing mineralized faults. The status of the ca. 1.11 Ga event is ambiguous. The 950 ± 50 Ma event, which primarily redistributed REEs from existing mineralization is related to the final closure of the mobile belt and reactivation of the SSZ associated with the formation of the greater Indian land mass in Peninsular India.

Fluid–structure coupled simulation of ignition transient in a dual pulse motor using overset grid method

In this paper, the second pulse ignition transient in a dual pulse solid rocket motor with elastomeric barrier pulse separation device has been conducted numerically. An in-house code has been developed to solve governing equations for unsteady compressible flow, heat conduction and structural dynamic. The solid propellant ignition and burning numerical models have been added. The fluid structure interaction is implemented by using the conventional serial staggered algorithm. The large deformation and expansion of the elastomeric barrier are addressed by the dynamic overset grid technology. The accuracy of the numerical method is validated by the experimental cases. Then, the detailed flow field development, pressure evolution, flame propagation characteristics in the combustion chamber, and the structural response of elastomeric barrier are analyzed carefully. The rupture-time and rupture-pressure of the elastomeric barrier are also obtained. The numerical results show that the elastomeric barrier deformation presents a small displacement at the front part and a large displacement at the rear section. The interaction of the compression waves and expansion waves from the convergent portion of the nozzle and from the motor head-end, as well as the supersonic annular jet flow in the combustion chamber, can induce obvious pressure rises with fluctuations and spikes. The first pulse free volume has a significant effect on the time to reach a steady state.

Gold Nanocluster‐Modified Titanium Nitride for Ultrafast Photonics Applications

AbstractTransition metal nitride materials exhibit unique optical characteristics and have attracted much interest for various applications, including waveguiding, photovoltaics, and nonlinear optical devices. Herein, titanium nitride (TiN), as a typical representative of biocompatible transition metal nitrides, is prepared and modified with gold nanoclusters (Au NCs) for promoting the carrier mobility, and the corresponding physical characteristics are systematically characterized. The TiN‐based saturable absorber (SA) on microfiber is fabricated and its nonlinear optical absorption property is also studied experimentally. Furthermore, the TiN‐decorated SA is applied in an ultrafast fiber laser at the communication bands. The fiber laser can generate the stable ultrashort pulses with a pulse width of 1.66 ps, a fundamental repetition rate of 7.49 MHz, and a spectral bandwidth of 2.61 nm. More importantly, the chaotic multiple pulses can be obtained, which is reported for the first time in the fiber laser based on the TiN SA on microfiber as far as it is known. The chaotic multiple pulses show many interesting characteristics, including high average pulse energy, varying pulse separations, and pulse intensities. These results have proved that the TiN shows great potential in many fields, such as advanced optical‐intensity modulator, ultrafast pulse dynamics, and optical fiber communications.

High-Speed PIV of shock boundary layer interactions in the transonic buffet flow of a compressor cascade

The dynamics of a transonic buffet flow on the suction side of a highly loaded 2-D compressor blade model is investigated at a chord-based Reynolds number of 1.4 times 10^6 and an inlet Mach number of 1.05. Near stall the detached bow shock exhibits pronounced modal shock oscillations at buffet frequencies of {omega ^*}=2pi f c / U_1=2.27 which are not related to any structural aeroelastic modes. High-speed PIV at several stations along the chord provides chordwise velocity spectra and wave propagation velocities of shock-induced perturbations. For this purpose, a double-pulse laser system with a high-repetition rate was set up consisting of two combined DPSS lasers. This enables time-resolved PIV using frame straddling at up to 100 kfps and pulse separations down to 800 ns. Synchronized high-speed shadowgraph imaging simultaneously locates the position of the bow shock. Based on cross-correlations between velocity time records at two points and between velocity and shock position, the propagation velocity of the modal perturbations is determined upstream and downstream from the shock. The measured data indicate that feedback occurs between a region immediately downstream of the shock foot and a plane upstream of the shock, up to which transverse velocity disturbances are convected. This observation is contrary to Lee’s model Lee (AIAA J 28(5):942–944, 1990) which describes self-sustained shock-buffet as a consequence of shock–trailing edge interactions.Graphic

Synthesis of gold, platinum, and gold-platinum alloy nanoparticle colloids with high-power megahertz-repetition-rate lasers: the importance of the beam guidance method

Nanoparticles of noble metals and their alloys are of particular interest for biomedicine and catalysis applications. The method of laser ablation of bulk metals in liquids gives facile access to such particles as high-purity colloids and is already used in industrial research. However, the method still lacks sufficient productivity for industrial implementation into series production. The use of innovative laser technology may help to further disseminate this colloid synthesis method in the near future. Ultrashort-pulsed lasers with high powers and megahertz-repetition-rates became available recently, but place high demands on the accurate optical laser pulse delivery on the target. Full lateral pulse separation is necessary to avoid a reduction of nanoparticle productivity due to pulse shielding. In this study, we compare flexible but rather slow galvanometer scanning with much faster but more expensive polygon-wheel scanning in their performance in the production of colloidal nanoparticles by laser ablation in liquid. Both beam guidance technologies are applied in the laser ablation of gold, platinum, and a gold-rich platinum alloy in micromolar saline water. We found that the dimensions of the scan pattern are crucial. A threshold pattern length exists, at which one scan technology becomes more productive than the other one. In addition, a much lower productivity was found for the ablation of gold compared to that of platinum. Alloying gold with only 10 at.% of platinum improved the productivity nearly to the level of platinum, reaching 8.3 g/h.

Simultaneous visualization of left atrial fibrosis and epicardial adipose tissue using 3D Dixon late gadolinium enhancement cardiovascular magnetic resonance

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Swedish Medical Research Council (Grant Number: 2018-02779) Swedish Heart and Lung Foundation (Grant Number: 20170440) Background Cardiovascular magnetic resonance (CMR) is a powerful tool to identify structural changes of the left atrium (LA). LA fibrosis can be quantified using late gadolinium enhancement (LGE) and is a major risk factor for progression of atrial fibrillation (AF). Epicardial adipose tissue (EAT) around the LA can also be assessed using CMR and is associated with incidence and severity of AF. The theory that EAT may induce LA wall inflammation and thus promoting LA fibrosis highlights the need for assessment of the interrelation of the spatial distribution of these two AF risk factors. However, previous CMR studies have used separate pulse sequences to visualize LA fibrosis and EAT. Purpose To develop and evaluate a novel 3D Dixon water-fat separated LGE (Dixon-LGE) pulse sequence for visualization and quantification of LA fibrosis and EAT. Methods 19 subjects were prospectively included and scanned on a 1.5T scanner (mean age 54 ± 20 years; 9 female): 10 patients with a history of AF, and 9 patients without any known cardiovascular disease (NCD). The 3D Dixon-LGE scan was performed 20 minutes after Gd contrast injection. Dixon reconstructed water images were used for LGE quantification while the fat images were used to quantify EAT. Segmentations of the LA myocardium and EAT were performed manually. The image intensity ratio (IIR) method was used for fibrosis quantification, by normalizing the intensity of the LA wall by the mean value of the blood pool intensity and classifying fibrosis as pixels with normalized intensity more than 1.2. For comparison with the automated IIR method, fibrosis was manually segmented in the LGE images as ground truth (GT). Results Example images from an AF and NCD patient are shown in the figure. Heart rate was higher (84 ± 14 vs. 65 ± 14 bpm, P = 0.007), and BMI was higher (28 ± 3 vs. 24 ± 3 kg/m², P = 0.014) in the AF group compared to NCD. AF had also larger LA end-systolic volume index (83 ± 16 vs. 38 ± 9 mL/m², P < 0.001) and larger LA EAT volume index (7.1 ± 4.1 vs. 3.2 ± 2.2 mL/m², P = 0.022) compared to NCD. Further, fibrosis as percentage of LA surface area was larger 14.9 ± 18.4 vs. 3.2 ± 2.5 %, P = 0.028 in AF compared to NCD. The interclass correlation coefficient (ICC) for inter-observer and intra-observer measurements of LA volume were 0.99 (95% CI, 0.97%–0.99%) and 0.99 (95% CI, 0.99%–0.99%), respectively, of LA EAT volume were 0.95 (95% CI, 0.87%–0.98%) and 0.97 (95% CI, 0.89%–0.99%), respectively, and of LA fibrosis, IIR method, were 0.98 (95% CI, 0.94%–0.99%) and 0.99 (95% CI, 0.98%–0.99%), respectively. The IIR method had a very high level of agreement with the GT segmentation, ICC = 0.96 (95% CI, 0.78%-0.99%). Conclusions LA fibrosis and EAT can be visualized simultaneously by using a single 3D LGE-Dixon pulse sequence. This new method has a high level of intra- and inter observer repeatability, can reduce the scan time and allows the analysis of spatial correlation of these AF risk factors. Abstract Figure. Dixon-LGE acquisition and quantification

Influence of stress confinement, particle shielding and re-deposition on the ultrashort pulse laser ablation of metals revealed by ultrafast time-resolved experiments

The ablation rate in double-pulse material processing is strongly influenced by the pulse separation. For pulse separations exceeding 3 ps a significant decrease in ablation volume has been observed. This was attributed to three mechanisms: rarefaction wave interaction, shielding by ablation plume and material re-deposition. Here we present carefully designed double-pulse ablation experiments on three industrially relevant metals: stainless steel, aluminum and copper and interpret them based on ablation dynamics derived from ultrafast time-resolved pump-probe microscopy and ellipsometry. Adjustment of the fluence distribution within the double-pulse allows us to separate effects arising from rarefaction wave suppression and shielding/re-deposition. We found that the rarefaction wave contribution to the double-pulse ablation volume is about 25% for aluminum and stainless steel and about 40% for copper. A pronounced re-deposition was observed for stainless steel and aluminum, while for copper shielding by the ablation plume plays a dominant role. It was revealed that the ablation volume stays maximal, if the pulse energy is deposited within the mechanical relaxation time of (2–5)ps. According to our findings the ablation process exerts maximum efficiency and precision, when energy is coupled into the material before mechanical relaxation or after material surface equilibration.

Using Temporally Synthesized Laser Pulses to Enhance the Conversion Efficiency of Sn Plasmas for EUV Lithography

We have studied the laser pulse shape dependence of the conversion efficiency of λ = 1.03 μm laser pulse energy into 13.5 nm extreme ultraviolet (EUV) emission from a Sn laser-produced plasma. Laser pulses of arbitrary temporal shape ranging from hundreds of picoseconds to several nanoseconds were generated using a programmable pulse synthesizer based on a diode-pumped chirped pulse amplification Yb: YAG laser. Measurements show that the conversion efficiency favors the use of nearly square pulses of duration longer than 2 ns, in agreement with hydrodynamic/atomic physics simulations. A 35% increase in conversion efficiency was obtained when Q-switched pulses were substituted by square pulses of a similar duration. Experiments conducted irradiating a Sn target with a sequence of two time-delayed 250 ps pulses showed a 30 percent increase in the EUV yield respect to a single pulse of the same total energy when the pulse separation was optimum at 2.1 ns. This suggests that re-heating of the plasma with delayed laser pulses could be used to improve the EUV yield. The spectroscopic characterization of EUV emission and in-band EUV images that characterize the source size are also presented.

An Adaptive Pulse Separation Strategy for PD Detection in Frequency-Tuned Resonant Tests

Frequency-tuned resonant (ACRF) test is one of the most widely used technologies for power equipment diagnosis. However, the intense interference generated by the variable-frequency power source hinders its further application in partial discharge (PD) detection. For this reason, an adaptive PD separation method based on improved clustering by fast search and find of density peaks (CFSFDP) is proposed in this article to separate PD signals and disturbances under the ACRF test. First, the characteristics of the PD signals and the interference signals generated from the ACRF test system are analyzed and compared. Then, an improved CFSFDP algorithm is proposed to realize the automatic cluster center selection and signal separation, and the working principle of the PD separation strategy based on the improved CFSFDP algorithm is introduced. Finally, the effectiveness of the proposed method is validated by performing the ACRF test on a defective cable. The experimental results show that this method can realize the separation and detection of PD signals in ACRF tests. The proposed method provides a feasible solution for performing PD detection using the ACRF test system without the restriction of the test system structure.

双波长波片导致的脉冲分离对双色场辐射太赫兹波的影响

双波长波片导致的脉冲分离对双色场辐射太赫兹波的影响

MEDIUM-TERM OSCILLATIONS OF THE SOLAR ACTIVITY

In addition to the well-known 11-year cycle, longer and shorter characteristic periods can be isolated in variations of the parameters of helio-geophysical activity. Periods of about 36 and 60 years were revealed in variations of the geomagnetic activity and an approximately 60-year periodicity, in the evolution of correlation between the pressure in the lower atmosphere and the solar activity. Similar periods are observed in the cyclonic activity. Such periods in the parameters of the solar activity are difficult to identify because of a limited database available; however, they are clearly visible in variations of the asymmetry of the sunspot activity in the northern and southern solar hemispheres. In geomagnetic variations, one can also isolate oscillations with the characteristic periods of 5-6 years (QSO) and 2-3 years (QBO). We have considered 5-6-year periodicities (about half the main cycle) observed in variations of the sunspot numbers and the intensity of the dipole component of the solar magnetic field. A comparison with different magnetic dynamo models allowed us to determine the possible origin of these oscillations. A similar result can be reproduced in a dynamo model with nonlinear parameter variations. In this case, the activity cycle turns out to be anharmonic and contains other periodicities in addition to the main one. As a result of the study, we conclude that the 5-6-year activity variations are related to the processes of nonlinear saturation of the dynamo in the solar interior. Quasi-biennial oscillations are actually separate pulses related little to each other. Therefore, the methods of the spectral analysis do not reveal them over large time intervals. They are a direct product of local fields, are generated in the near-surface layers, and are reliably recorded only in the epochs of high solar activity.

RANGE AND RADIAL VELOCITY MEASUREMENT AMBIGUITY ELIMINATION WITH TRAINS OF MULTICOMPONENT SIGNALS

When designing pulse-Doppler radar, one of the key points is the choice of the pulse repetition period, which determines the boundaries of unambiguous measurement of range and radial velocity and creates contradictions in the measurement of these values. This contradiction is especially acute in the analysis of signals reflected from the propellers and turbines of aircraft. The main approaches to solving the problem of expanding the boundaries of unambiguous measurement of range and radial velocity is the use of variable pulse repetition period and the creation of signal ensembles to separate them by shape. Generation of an ensemble of sounding signals for a pulsed radar must be carried out taking into account both cross-correlation and auto-correlation properties. An approach to the generation of multicomponent signal trains with the possibility of pulse separation inside the train is proposed. Each of the pulses in the train is formed by adding a number of chirp signals, which differ in the values of amplitude and frequency deviation. As the frequency deviation increases, the amplitude of the component decreases. Reducing the cross-correlation coefficient of multicomponent signals from the formed ensemble can be achieved by increasing the number of components of each signal. The size of the signal ensemble, which can be formed on the basis of multicomponent chirp signals, depends on the requirements for the cross-correlation coefficient and auto-correlation function of the signals. It is shown that in order to expand the limits of coordinate measurement at a fixed wavelength, it is necessary to increase the number of pulses in the train. The results of the research demonstrate the potential possibility of using the proposed multicomponent chirp signal to form train of pulses with its subsequent separation.

A METHOD FOR IMPROVING THE QUALITY INDICATORS OF A DISTRIBUTED FORENSIC INFORMATION SYSTEM

Subject of research: the process of monitoring the quality indicators of a computer network of a forensic information system using methods for increasing the frequency resolution of acousto-optic spectrum analyzers. The aim of this work is the possibility of increasing the QoS indicators of a computer network by achieving the potential accuracy of estimating the frequencies of two simultaneously arriving radio pulses using the super-Rayleigh resolution method in acousto-optic spectrum analyzers (AOSA). The following tasks are solved in the article: analysis of various information systems of forensic examination and the tasks that they solve; analysis of the use of acousto-optic spectrum analyzers to determine the parameters of the transmitted signal in a distributed forensic system; derivation of an analytical expression for evaluating the potential accuracy of the frequency detuning value of two pulses. The following methods and models are used: models and methods of systems theory (based on the information approach), models and methods for constructing distributed systems and their components in accordance with various hierarchical levels of their organization and operating conditions; models and methods of theories of propagation and interaction of electromagnetic waves with wave structures of various physical nature. The following results were obtained: The analysis has established that forensic information systems are distributed in nature and impose high requirements on the quality of the functioning of telecommunications equipment of the corresponding computer networks (CN). To meet these requirements, it is necessary to improve the systems for monitoring, protecting and transmitting information in the corresponding CN, which is impossible without solving the problem of monitoring signal parameters. Research has been carried out on the use of AOSA to ensure control over communication channels of computer networks. It was found that most of the AOSA frequency resolution methods have limitations associated with the Rayleigh criterion, which significantly limits the potential for frequency separation of pulses. The use of the method of super-Rayleigh resolution of narrow-band pulses in terms of their arrival time is proposed. An analytical expression is obtained to estimate the potential accuracy of determining the value of the detuning in the frequency of two pulses. Conclusions. The forensic information system is a complex heterogeneous distributed system. To improve the efficiency of its functioning, it is necessary to control the parameters of the signal propagating in the network. The use of the super-Rayleigh resolution method in AOSA will increase the resolution of AOSA by increasing the frequency resolution of two non-simultaneous radio pulses of long duration.

Least-squares fitting algorithm for peak pile-up correction in gamma-ray spectroscopy

In gamma-ray spectroscopy, a pulse pile-up occurs when a gamma-ray hits the detector within a time period shorter than the duration of the pulse induced by a preceding gamma-ray. The resulting pulse is the sum of two overlapping pulses. At a high counting rate, the pulse pile-up can lead to significant loss of data and/or deterioration of the measured gamma-ray energy spectrum. If the temporal separation of consecutive gamma-ray events is small enough, the resulting pile-up pulse exhibits only a single peak. Such events are described as peak pile-ups. It is not trivial to detect and correct peak pile-ups. Consequently, such events are typically wrongly reconstructed as a single pulse or rejected by the pile-up correction algorithms developed to date. We study a least-squares fitting algorithm modified to include detection and correction of peak pile-ups. Performance of the proposed algorithm is studied using data measured with LaBr3:Ce scintillator and a 400 MBq 137Cs source as well as with artificially synthesized pile-up data. The pile-up correction success rate grows rapidly with the temporal separation of piled-up pulses and reaches 50% as soon as the pulses are separated by a time at least of the order of the single pulse rise time. A success rate exceeding 90% is reached for the temporal separation equal to about twice the rise time. The reconstruction efficiency measured as the overall rate of the successful reconstruction of the double-pulse pile-up is about 92%.