Transient Detection Research Articles

Control of excitation selectivity in pulse EPR on spin-correlated radical pairs with shaped pulses.

Spin-correlated radical pairs generated by photoinduced electron transfer are characterised by a distinctive spin polarisation and a unique behaviour in pulse electron paramagnetic resonance (EPR) spectroscopy. Under non-selective excitation, an out-of-phase echo signal modulated by the dipolar and exchange coupling interactions characterising the radical pair is observed and allows extraction of geometric information in the two-pulse out-of-phase electron spin echo envelope modulation (ESEEM) experiment. The investigation of the role of spin-correlated radical pairs in a variety of biological processes and in the fundamental mechanisms underlying device function in optoelectronics, as well as their potential use in quantum information science, relies on the ability to precisely address and manipulate the spins using microwave pulses. Here, we explore the use of shaped pulses for controlled narrowband selective and broadband non-selective excitation of spin-correlated radical pairs in two model donor-bridge-acceptor triads, characterised by different spectral widths, at X- and Q-band frequencies. We demonstrate selective excitation with close to rectangular excitation profiles using BURP (band-selective, uniform response, pure-phase) pulses and complete non-selective excitation of both spins of the radical pair using frequency-swept chirp pulses. The use of frequency-swept pulses in out-of-phase ESEEM experiments enables increased modulation depths and, combined with echo transient detection and Fourier transformation, correlation of the dipolar frequencies with the EPR spectrum and therefore the potential to extract additional information on the donor-acceptor pair geometry.

Modulating the Product Distribution of the Electrochemical Reduction of CO2 on Copper at Relevant Current Densities

The electrochemical reduction of CO2 (CO2RR) has the potential to be an economically-viable method to produce platform chemicals synergistically with renewable energy sources. Copper is one of the most used electro-catalysts for this purpose, as it allows carbon-carbon bond formation, crucial for broader product distribution. Despite great achievements, controlling selectivity is yet a stepping stone between R&D and an actual industrial application. Among others, a kinetic resolution could be applied to enhance the selectivity toward targeted products, for which exploiting available and inexpensive additives or co-electrolytes such as ionic liquids is a promising direction. Herein, we present an initial systematic analysis of the effect of various tetra alkyl ammonium salts on the CO2RR products distribution with the aim on ethylene, important industrial feedstock or building block. A selected ammonium salts of different alkyl chain length and number of charges provided very concise but sufficient chemical space to overview a structure-activity relationships, including changes in the reactions’ onset potentials and limiting currents. The overall experimentation progress was intensified by the employing a developed in our lab a gas diffusion electrode (GDE) cell, coupled to a mass spectrometer. This enabled to scan the selected library of salts during CO2RR under dynamic operations with detection of transients in real-time at relatively high current densities, between 10 to 400 mA/cm2, within further quantitative validation over standard long-term steady-state experiments. These results have broad implications for effectively stirring the CO2RR selectivity towards products containing either one or two carbon atoms.Key words: CO2, Electroreduction, Copper, Electrocatalysis, Modifiers, Real-time, GDE

Estimation of Lightning Flash Rate in Precipitation Features by Applying Shallow AI Neural Network Models to the GMI Passive Microwave Brightness Temperatures

AbstractThe satellite‐constellation passive‐microwave Brightness Temperature (TB) observations, with global coverage, and more additions from upcoming CubeSats, have been mainly used in surface precipitation retrievals. However, these observations can also be used to indicate the intensity of convective systems. This study attempts to relate Global Precipitation Mission (GPM) Microwave Imager (GMI) TBs to Geostationary Lightning Mapper (GLM) lightning flashes by using 4 years (02/2018–04/2022) of GPM Precipitation Feature (PF) database. GMI TBs are collocated to the GLM lightning counts, and to the ERA5 reanalysis 2‐m air temperature in PFs. Three Artificial Intelligent Neural Network Models (AI‐NN) are trained to classify PFs producing lightning in a 20‐min window respectively for land, ocean, or coast. The flash rate of the determined Lightning producing PFs (LPFs) is then quantified by three other AI‐NNs, each trained for one of the three regions. Though the models clearly capture the global geographical distribution of LPFs with a Probability Of Detection over 90%, high False Alarm Rates are found, ranging from 49.9% over land to 91.5% over the ocean. The importance of TB at each passive microwave channel varies regionally, corresponding to the different microphysical properties in various types of precipitation systems. The global lightning distribution is derived by applying the AI models to global PFs and is well compared to the lightning climatology from Lightning Imaging Sensor and Optical Transient Detector. This suggests that the use of passive microwave TBs can help to fill the gaps in lightning monitoring thanks to their global coverage.

The Large Array Survey Telescope—Pipeline. I. Basic Image Reduction and Visit Coaddition

The Large Array Survey Telescope (LAST) is a wide-field telescope designed to explore the variable and transient sky with a high cadence and to be a test-bed for cost-effective telescope design. A LAST node is composed of 48 (32 already deployed), 28 cm f/2.2 telescopes. A single telescope has a 7.4 deg2 field of view and reaches a 5σ limiting magnitude of 19.6 (21.0) in 20 (20 × 20) s (filter-less), while the entire system provides a 355 deg2 field of view. The basic strategy of LAST is to obtain multiple 20 s consecutive exposures of each field (a visit). Each telescope carries a 61 Mpix camera, and the system produces, on average, about 2.2 Gbit s−1. This high data rate is analyzed in near real-time at the observatory site, using limited computing resources (about 700 cores). Given this high data rate, we have developed a new, efficient data reduction and analysis pipeline. The LAST data pipeline includes two major parts: (i) Processing and calibration of single images, followed by a coaddition of the visit’s exposures. (ii) Building the reference images and performing image subtraction and transient detection. Here we describe in detail the first part of the pipeline. Among the products of this pipeline are photometrically and astrometrically calibrated single and coadded images, 32 bit mask images marking a wide variety of problems and states of each pixel, source catalogs built from individual and coadded images, Point-Spread Function photometry, merged source catalogs, proper motion and variability indicators, minor planets detection, calibrated light curves, and matching with external catalogs. The entire pipeline code is made public. Finally, we demonstrate the pipeline performance on real data taken by LAST.

Design of High Transmission Frequency Circuit for Multiturn Small Loop Transient Electromagnetic Detection

Limited by urban road width and other factors, urban TEM detection can only use multiturn small loop as the transmitting coil. The traditional TEM transmitting circuit cannot transmit high frequency repetitive pulse for such large inductance coil. In order to solve this problem, a high transmission frequency circuit is proposed and built in this paper, which can clamp both the rising and falling edges of the emission current, and effectively improve the frequency. The repeated transmission frequency of 250 Hz for 0.73 mH coil at current of 30 A is realized. The circuit effectively improves the strong magnetic field excitation ability, which is of positive significance for the application of multiturn small loop TEM in urban environment.

Utilizing MATLAB machine learning models to categorize transient events in a nuclear power plant using generic pressurized water reactor simulator

Enhancing safety and dependability within nuclear power facilities holds paramount importance in safeguarding both individuals and the environment. The adoption of machine learning for diagnosing faults in these plants is steadily gaining interest, driven by its capacity to detect faults, alleviate human errors in high-pressure scenarios, and ensure the secure and consistent operation of these facilities swiftly and accurately.This paper examines the use of machine learning models for fault diagnostics, specifically, the identification of transient events in a nuclear power plant to reduce human errors. The data was collected from WSC’s Generic Pressurized Water Reactor (GPWR) simulator and processed using MATLAB. The simulator encompasses models for both the primary and secondary systems of the nuclear power plant (NPP). Additionally, it incorporates models for the control systems and instrumentation responsible for monitoring and regulating the reactor, serving as integral components for data extraction and transient modeling. A total of 9 different transient events were simulated with 12 different initial conditions to create a dataset with 72,000 observations. Nine types of classification models (33 total preset models) were trained and validated using the classification learners application. Among them, the Neural Network Classifiers (NNC) displayed the highest average accuracy of 90%. The Fine Tree, Ensemble Bagged Trees, and Medium Neural Network models were the best-performing individual models with validation accuracies above 90% and a maximum training time of 8 min. These models were further analyzed using accuracy, confusion matrix, precision, recall, and F1 score. To optimize these models, techniques such as different validation schemes and feature selection were utilized to further reduce their training time and improve their prediction accuracy. The optimized models boasted comparable accuracies with a maximum training time of under 1.5 min. The results of this study exhibited favorable comparisons with other machine-learning endeavors in the field of reactor transient detection and diagnostics. Notably, the study maintained low execution and computation times while preserving high levels of accuracy. This study offers insightful information on how AI and machine learning can be used to improve nuclear power plant diagnostics, enhance safety, and provide support to the operator.

The STATiX pipeline for the detection of X-ray transients in three dimensions

ABSTRACT The recent serendipitous discovery of a new population of short duration X-ray transients, thought to be associated with collisions of compact objects or stellar explosions in distant galaxies, has motivated efforts to build up statistical samples by mining X-ray telescope archives. Most searches to date, however, do not fully exploit recent developments in the signal and imaging processing research domains to optimize searches for short X-ray flashes. This paper addresses this issue by presenting a new source detection pipeline, STATiX (Space and Time Algorithm for Transients in X-rays), which directly operates on three-dimensional X-ray data cubes consisting of two spatial and one temporal dimension. The algorithm leverages wavelet transforms and the principles of sparsity to denoise X-ray observations and then detect source candidates on the denoised data cubes. The light curves of the detected sources are then characterized using the Bayesian blocks algorithm to identify flaring periods. We describe the implementation of STATiX in the case of XMM–Newton data, present extensive validation and performance verification tests based on simulations and also apply the pipeline to a small subset of seven XMM–Newton observations, which are known to contain transients sources. In addition to known flares in the selected fields, we report a previously unknown short duration transient found by our algorithm that is likely associated with a flaring Galactic star. This discovery demonstrates the potential of applying STATiX to the full XMM–Newton archive.

A rhodamine NIR probe for naked eye detection of mercury ions and its application

Fluorescence imaging technology has developed rapidly with its advantages, and near-infrared probes are worthy of attention because of their less background interference, low light damage, and infinite potential. Rhodamine and its derivatives have the unique structure of lactam helices, which is an ideal platform for the construction of on-off fluorescent sensors. In this paper, a novel near-infrared fluorescent probe (RBLS) based on rhodamine derivatives was synthesized for the transient detection of mercury ions. The closed-on structure can realize reversible sensor recovery by adding S2-. The superior imaging capability in living cells and in vivo in zebrafish holds promise for biological applications. In addition, the naked eye test strips prepared with RBLS probes can be used to detect and screen Hg2+ in the environment and show good gradient change performance.

Model Predictive Control Strategies for Turbine Electrified Energy Management

Abstract The increasing electrification of aircraft propulsion systems is leading to new control architectures being developed to address integration between electric machines and gas-based turbine engines. For hybrid-electric propulsion systems, current conceptual architectures often couple electric machines with the shafts of gas turbine engines and introduce energy storage. Leveraging the electrical power system of hybridized engines, Turbine Electrified Energy Management (TEEM) is a recent control approach that improves transient operability in an effort to enable more efficient and lighter weight turbomachinery. This study seeks to expand TEEM's application beyond traditional proportional-integral (PI) control by presenting linear model predictive control (MPC) schemes to execute the TEEM concept. Through constraint selection and cost function design, transient operability goals for TEEM are considered with no external logic or saturation. Unique to the designs are the use of a washout filter, which simplifies transient detection and motor activation logic. The proposed architectures are implemented with both centralized MPC and distributed MPC approaches, and comparisons are drawn to a benchmark PI controller simulated on a nonlinear turbofan engine model at one ground condition and one cruise condition. Performance is evaluated using compressor maps, stall margin performance, and two novel metrics: transient stack usage and transient excursion integral. Results reveal the linear MPC scheme performs comparably to the baseline controller and can be implemented in at least two distinct configurations with potential for further modifications, thus establishing the groundwork for future investigations.

Use of pediatric thymus to humanize mice for HIV-1 mucosal transmission

Humanized mice have been used to study human immunodeficiency virus type 1 (HIV-1) transmission, pathogenesis, and treatment. The ability of pediatric thymus tissue implanted either in the leg (Leg PedThy) or under the renal capsule (Renal PedThy) with allogeneic CD34+ hematopoietic cells (HSCs) in NSG mice was evaluated for reconstitution of human immune cells and for rectal transmission of HIV-1. These mice were compared to traditional BLT mice implanted with fetal liver and thymus under the renal capsule and mice injected only with HSCs. Renal PedThy mice had similar immune reconstitution in the blood, spleen and intestine as BLT mice, while Leg PedThy mice had transient detection of immune cells, particularly CD4+ T cells and macrophages, the target cells for HIV-1 infection. Rectal transmission and replication of HIV-1 was efficient in BLT mice but lower and more variable in Renal PedThy mice. HIV-1 was poorly transmitted in HSC mice and not transmitted in Leg PedThy mice, which correlated with the frequencies of target cells in the spleen and intestine. Humanization of NSG mice with pediatric thymus was successful when implanted under the kidney capsule, but led to less efficient HIV-1 rectal transmission and replication compared to BLT mice.

Real-time Detection System for Portable Transient Electromagnetic Unexploded Ordnance

Portable transient electromagnetic systems are not limited by terrain and can detect unexploded ordnance very flexibly. However, existing data processing methods are slow and cannot achieve real-time positioning of targets. In this paper, based on a laboratory-made portable transient electromagnetic detection system, the magnetic dipole model and tensor positioning algorithm are used to achieve fast and accurate target positioning. Using the magnetic gradient tensor algorithm for positioning reduces the calculation load, allowing it to run on embedded systems, and improving target positioning speed while ensuring the accuracy of measurements. Experimental results show that the vertical and horizontal positioning errors of the UXO are within 10 cm, and single-point positioning can be completed within 10 ms.

Consistent physical frequencies in time-frequency analysis

Wavelet transforms have been studied extensively for a wide variety of applications such as signal compression and signal denoising. Wavelet transforms have also been examined for the detection of transient signals. However, wavelet levels (and corresponding pseudo-frequencies) are inherently dependent on the sampling rate of the analyzed data. The work presented herein examines how wavelet analysis can produce inconsistent data representations for the same analytical signal digitized at different sampling rates. Results are compared to time-octave and other time-frequency representations to identify methodologies which produce consistent characterization of physical frequencies. Similarities and difference between approaches are discussed.

The Atacama Cosmology Telescope: Systematic Transient Search of 3 Day Maps

We conduct a systematic search for transients in 3 yr of data (2017–2019) from the Atacama Cosmology Telescope (ACT). ACT covers 40% of the sky at three bands spanning from 77–277 GHz. Analysis of 3 day mean-subtracted sky maps, which were match filtered for point sources, yielded 29 transient detections. Eight of these transients are due to known asteroids, and three others were previously published. Four of these events occur in areas with poor noise models and thus we cannot be confident they are real transients. We are left with 14 new transient events occurring at 11 unique locations. All of these events are associated with either rotationally variable stars or cool stars. Ten events have flat or falling spectra indicating radiation from synchrotron emission. One event has a rising spectrum indicating a different engine for the flare.

A Double-Edge-Triggered Digital LDO with Built-In Adaptive VCO Clock for Fast Transient Response and Low Power Consumption

A double-edge-triggered digital low dropout regulator (DLDO) is proposed with a built-in adaptive voltage-controlled oscillator (VCO) clock (AVC) for a system-on-chip (SoC) application. To achieve a fast transient response, the main comparator generates the comparison result at the rising edge of the AVC, and this result is sampled by the coarse or fine bidirectional shifter register at the falling edge of the AVC. Furthermore, the clock frequency can be boosted from 8 MHz at the steady state to 50 MHz by the AVC when the output current suffers from a sudden change, and it can also be adjusted in real-time according to the output voltage, which avoids the oscillation phenomenon and decreases the power consumption during the recovery process. To further lower the power consumption, the self-clock comparator replaces the conventional static comparator in the transient detector. The post-simulation results show that the proposed DLDO consumes a quiescent current of 95.13 μA in the steady state, and drives a maximum load current of 25 mA at the supply power of 0.6 V with an active area of 0.053-mm2 in a 180 nm CMOS process. When the load current jumps from 0.5 mA to 25 mA at the edge of 100 ps, the undershoot voltage and overshoot voltage are only 335 mV with the recovery time of 2.7 μs and 47.6 mV with the recovery time of 2.1 μs at the total on-chip capacitor of 50 pF, respectively, resulting in two competitive figures of merits (FoMs) than the previous works.

An optimized transient detection pipeline for the ASKAP Variables and Slow Transients (VAST) survey

ABSTRACT In this paper, we present an optimized version of the detection pipeline for the ASKAP Variables and Slow Transients (VAST) survey, offering significant performance improvement. The key to this optimization is the replacement of the original w-projection algorithm integrated in the Common Astronomy Software Applications package with the w-stacking algorithm implemented in the WSClean software. Our experiments demonstrate that this optimization improves the overall processing efficiency of the pipeline by approximately a factor of 3. Moreover, the residual images generated by the optimized pipeline exhibit lower noise levels and fewer artefact sources, suggesting that our optimized pipeline not only enhances detection accuracy but also improves imaging fidelity. This optimized VAST detection pipeline is integrated into the Data Activated Liu Graph Engine (DALiuGE) execution framework, specifically designed for SKA-scale big data processing. Experimental results show that the performance and scalability advantages of the pipeline using DALiuGE over traditional MPI or BASH techniques increase with the data size. In summary, the optimized transient detection pipeline significantly reduces runtime, increases operational efficiency, and decreases implementation costs, offering a practical optimization solution for other ASKAP imaging pipelines as well.

Monthly quasi-periodic eruptions from repeated stellar disruption by a massive black hole

In recent years, searches of archival X-ray data have revealed galaxies exhibiting nuclear quasi-periodic eruptions with periods of several hours. These are reminiscent of the tidal disruption of a star by a supermassive black hole. The repeated, partial stripping of a white dwarf in an eccentric orbit around an ~105 M⊙ black hole provides an attractive model. A separate class of periodic nuclear transients, with much longer timescales, have recently been discovered optically and may arise from the partial stripping of a main-sequence star by an ~107 M⊙ black hole. No clear connection between these classes has been made. We present the discovery of an X-ray nuclear transient that shows quasi-periodic outbursts with a period of weeks. We discuss possible origins for the emission and propose that this system bridges the two existing classes outlined above. This discovery was made possible by the rapid identification, dissemination and follow-up of an X-ray transient found by the new live Swift-XRT transient detector, demonstrating the importance of low-latency, sensitive searches for X-ray transients.

Monitoring CO2 Hazards of Volcanic Origin: A Case Study at the Island of Vulcano (Italy) during 2021–2022

The La Fossa volcano is near the inhabited zone of the island of Vulcano and is a suitable case for studying gas sources of different geological origins. Since the last eruption, fumarolic-solfataric activity has interested this area with fumarolic emissions, mainly at the top of the volcanic cone and at Vulcano Porto. In recent decades, the anomalous degassing zones on the island have not significantly changed their location. On the contrary, there have been several significant changes in the emission rate due to the addition of volcanic gas. In these zones, CO2 flux from the ground is responsible for a decrease in the indoor air quality. A recent increase in volcanic degassing led to an increase in the gas hazard in the inhabited area of Vulcano Island, and people were temporarily displaced from Vulcano Porto. The results of this study show that a monitoring system can be used for the early detection of transients in soil CO2 flux (φCO2) in the anomalous degassing zone of Vulcano. Synchronous monitoring of φCO2 and outdoor air CO2 concentration has shown variations in volcanic degassing that affect outdoor air CO2 concentration in the populated zone of Faraglione.

Simulation and FPGA Implementation of Transient Power Quality Disturbance Detection

With the access to new energy in the smart grids and the massive use of nonlinear and unbalanced large loads, the problem of power quality becomes more and more serious. At present, the transient power quality disturbance problem has been paid more attention to. The research on transient power quality is relatively late, and various detection methods and technologies are not mature. It is necessary to use more efficient methods to detect and identify transient power quality to improve the safety of electricity use. This paper proposes to detect transient power quality disturbance by wavelet transform. In this paper, the original signal modelling of five kinds of power quality problems such as voltage sag and voltage swell. The 9/7 wavelet lifting coefficient is optimized in this paper and is carried out on the MATLAB software platform to improve the processing speed of the algorithm and realize parallel processing. The simulation results show that the improved lifting wavelet processing can effectively detect the transient power quality disturbance.

Transient electromagnetic detection and numerical simulation analysis of the deformation characteristics of an old goaf in an alpine coal mine area

In this paper, Qinghai alpine mining area is taken as the research object to explore the deformation characteristics of overlying strata in alpine mining area, so as to prevent geological disasters caused by over-exploitation in alpine mining area. The location of old goaf in coal mine is detected by transient electromagnetic method, and the results are used for numerical simulation. The numerical simulation results show that after coal seam mining, the stress gradually increases from the surface to the bottom, and the stress concentration occurs at both ends and the middle of the mining area. The displacement change area is highly coincident with the stress concentration area, and the displacement monitoring map is consistent with the horizontal displacement cloud map analysis, showing a “U” type distribution. The research results have certain reference value for the future study of surface mining subsidence in inclined coal seams.

Enhancing Neutral Hydrogen (HI) Detection in Galaxies through Optimized Matched Filter Analysis

Neutral Hydrogen (HI) is a fundamental component in the composition of galaxies, providing crucial insights into their structure and dynamics. In this research, we propose a novel approach to improve the detection of H1 spectral lines in radio telescope data by employing a matched filter algorithm. The algorithm capitalizes on the convolution of a template function, optimized using the "Busy" function that defines the line profile properties, with a randomly generated H1 peak. This H1 peak is subsequently embedded within noisy data, accounting for the effects of telescope measurements, such as thermal broadening and radio-frequency interference. The incorporation of the Voigt profile in the noise generation ensures a realistic representation of these effects. Through comprehensive analysis, we demonstrate that a matched filter with a multi-layered convolution scheme yields the highest efficiency in recovering H1 peaks. The effectiveness of peak recovery is shown to be influenced by the injected noise profiles, allowing for a direct comparison of the matched filter’s performance concerning the Integrated and Peak Signal to Noise ratios. This research contributes to the advancement of observational techniques in astrophysics and deepens our understanding of the distribution and properties of Neutral Hydrogen in galaxies. It represents the first such exploration of this technique in the context of the Canadian Hydrogen Observatory and Radio Transient Detector (CHORD), which is under construction at the Dominion Radio Astronomy Observatory in Penticton, BC and which will survey the HI sky more broadly and deeply than has been previously possible.