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Li, Yaqiong, Emily Biermann, Sigurd Naess, Simone Aiola, Rui An, Nicholas Battaglia, Tanay Bhandarkar et al. "The Atacama Cosmology Telescope: Systematic Transient Search of 3 Day Maps". Astrophysical Journal 956, n.º 1 (1 de octubre de 2023): 36. http://dx.doi.org/10.3847/1538-4357/ace599.
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Abstract 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.
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Ngeow, Chow-Choong, Nick Konidaris, Robert Quimby, Andreas Ritter, Alexander R. Rudy, Edward Lin y Sagi Ben-Ami. "The SED Machine: A Spectrograph to Efficiently Classify Transient Events Discovered by PTF". Proceedings of the International Astronomical Union 8, S290 (agosto de 2012): 281–82. http://dx.doi.org/10.1017/s1743921312020017.
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AbstractThe Palomar Transient Factory (PTF) is a project aimed to discover transients in the Universe, including Type Ia supernovae, core-collapse supernovae, and other exotic and rare transient events. PTF utilizes the Palomar 48-inch Telescope (P48) for discovering the transients, and follow-up mainly by the Palomar 60-inch Telescope (P60, for photometric light and color curves), as well as other telescopes. The discovery rate of PTF is about 7000 candidate transients per year, but currently only about 10% of the candidates are being followed-up and classified. To overcome this shortcoming, a dedicated spectrograph, called the SED Machine, is being designed and built at the California Institute of Technology for the P60 Telescope, aiming to maximize the classification efficiency of transients discovered by PTF. The SED Machine is a low resolution (R ~ 100) IFU spectrograph. It consists of a rainbow camera for spectrophotometric calibration, and a lenslet array plus 3-prism optics system for integrated field spectra. An overview of the science and design of the SED Machine is presented here.
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Sinha, Pampa, Sudipta Debath y Swapan Kumar Goswami. "Classification of Power Quality Events Using Wavelet Analysis and Probabilistic Neural Network". IAES International Journal of Artificial Intelligence (IJ-AI) 5, n.º 1 (20 de agosto de 2016): 1. http://dx.doi.org/10.11591/ijai.v5.i1.pp1-12.
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<p>Power quality studies have become an important issue due to widespread use of sensitive electronic equipment in power system. The sources of power quality degradation must be investigated in order to improve the power quality. Switching transients in power systems is a concern in studies of equipment insulation coordination. In this paper a wavelet based neural network has been implemented to classify the transients due to capacitor switching, motor switching, faults, converter and transformer switching. The detail reactive powers for these five transients are determined and a model which uses the detail reactive power as the input to the Probabilistic neural network (PNN) is set up to classify the above mentioned transients. The simulation has been executed for an 11kv distribution system. With the help of neural network classifier, the transient signals are effectively classified.</p>
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Qin, Yu-Jing, Ann Zabludoff, Marina Kisley, Yuantian Liu, Iair Arcavi, Kobus Barnard, Peter Behroozi, K. Decker French, Curtis McCully y Nirav Merchant. "Linking Extragalactic Transients and Their Host Galaxy Properties: Transient Sample, Multiwavelength Host Identification, and Database Construction". Astrophysical Journal Supplement Series 259, n.º 1 (24 de febrero de 2022): 13. http://dx.doi.org/10.3847/1538-4365/ac2fa1.
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Abstract Understanding the preferences of transient types for host galaxies with certain characteristics is key to studies of transient physics and galaxy evolution, as well as to transient identification and classification in the LSST era. Here we describe a value-added database of extragalactic transients—supernovae, tidal disruption events, gamma-ray bursts, and other rare events—and their host galaxy properties. Based on reported coordinates, redshifts, and host galaxies (if known) of events, we cross-identify their host galaxies or most likely host candidates in various value-added or survey catalogs, and compile the existing photometric, spectroscopic, and derived physical properties of the host galaxies in these catalogs. This new database covers photometric measurements from the far-ultraviolet to mid-infrared. Spectroscopic measurements and derived physical properties are also available for a smaller subset of hosts. For our 36,333 unique events, we have cross-identified 13,753 host galaxies using host names, plus 4480 using host coordinates. Besides those with known hosts, there are 18,100 transients with newly identified host candidates. This large database will allow explorations of the connections of transients to their hosts, including a path toward transient alert filtering and probabilistic classification based on host properties.
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Duza, Tasmia y Ingrid H. Sarelius. "Localized transient increases in endothelial cell Ca2+ in arterioles in situ: implications for coordination of vascular function". American Journal of Physiology-Heart and Circulatory Physiology 286, n.º 6 (junio de 2004): H2322—H2331. http://dx.doi.org/10.1152/ajpheart.00006.2004.
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Intracellular Ca2+ transients were identified in endothelial cells (ECs) in intact blood-perfused arterioles. ECs in cremaster muscle arterioles (diameter ∼45 μm) in anesthetized mice were loaded with the Ca2+ indicator fluo 4-AM by intraluminal perfusion, after which blood flow was reestablished. Confocal microscopy was used to visualize Ca2+ as a function of fluo-4 intensity in real time. Separate sets of experiments were performed under the following conditions: control, ischemia, during inhibition of P2x or P1 purinoreceptors, and with the application of exogenous adenosine. In controls, spontaneous EC Ca2+ transients displayed a wide range of activity frequency (1–32 events/min) and about one-third of these transient events were synchronized between adjacent ECs. The increase in Ca2+ remained localized and did not spread to encompass the entire cell body. Ca2+ transient activity decreased significantly with ischemia (from 9.9 ± 0.6 to 3.1 ± 0.3 events/min, n = 135) but was unaffected by P2x or P1 receptor inhibition. Exogenous adenosine significantly increased the frequency of Ca2+ transients (to 12.8 ± 0.9 events/min) and increased synchronization so that 50% of all Ca2+ events were synchronized between ECs. This response to adenosine was not due to an increase in shear stress. These data indicate that localized Ca2+ transients are sensitive to flow conditions and, separately, to metabolically active pathways (exogenous adenosine), although the basal activity occurs independently of P2x or P1 receptors. These transients may represent a mechanism by which individual EC responses are integrated to result in coordinated arteriolar responses in situ.
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Whitfield, Paul H. y Kathleen Dohan. "Identification and characterization of water quality transients using wavelet analysis. II. Application to electronic water quality data". Water Science and Technology 36, n.º 5 (1 de septiembre de 1997): 337–48. http://dx.doi.org/10.2166/wst.1997.0232.
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Two wavelet transform techniques for identifying water quality transients are applied to example data sets from two small streams. Temperature and conductance represent the range of properties from periodic processes to transient events. Both methods were successful in identifying the location, duration and magnitude of the transient events in these data sets. The methods may be refined to automate the detection and classification of transient events.
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Klimov, Pavel, Gali Garipov, Boris Khrenov, Violetta Morozenko, Vera Barinova, Vitaly Bogomolov, Margarita Kaznacheeva, Mikhail Panasyuk, Kirill Saleev y Sergey Svertilov. "Vernov Satellite Data of Transient Atmospheric Events". Journal of Applied Meteorology and Climatology 56, n.º 8 (agosto de 2017): 2189–201. http://dx.doi.org/10.1175/jamc-d-16-0309.1.
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AbstractData on transient atmospheric events (TAEs) were obtained from the Vernov satellite and are presented in this paper. The data are considered in conjunction with previous data obtained by the Universitetsky-Tatiana-1 and Universitetsky-Tatiana-2 satellites. The larger volume of stored scientific data in the Vernov mission and its advanced ultraviolet (UV) and red–infrared (R–IR) radiation detector (DUV) measurements allowed improved TAE-distribution data to be obtained over a wide range of photon numbers. The difference between features of luminous transients and “dim” transients, measured by the Universitetsky-Tatiana-2 satellite, is confirmed by Vernov’s data. There are also interesting dim UV events with no R–IR radiation. Such events are expected to be deep in the atmosphere at the level of thunderstorm clouds. They might be radiated by electric discharges of less power than lightning; in fact, at the preliminary stage of lightning. The observation of repeating dim TAEs in various time intervals, starting from tens of milliseconds and up to minutes, indicates that thunderstorm electric activity is much more variable than pure lightning strikes.
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Anderson, G. E., B. W. Stappers, I. Andreoni, M. Caleb, D. Coppejans, S. Corbel, R. P. Fender et al. "Radio Transients in the Era of Multi-Messenger Astrophysics". Proceedings of the International Astronomical Union 14, S339 (noviembre de 2017): 207–14. http://dx.doi.org/10.1017/s1743921318002624.
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AbstractRadio emission from astrophysical transients allows us to derive calorimetry of kinetic feedback and detailed imaging in ways that are not possible at other wavelengths, and as such it forms an important part of the multi-messenger follow-ups of these events. The field is burgeoning, with a renaissance of interest in accretion, stellar explosions and jetted supernovæ, alongside newer classes of phenomena such as fast radio bursts and tidal disruption events. The purpose of this workshop was to discuss the infrastructure and techniques for detecting, identifying and probing radio transients, with a particular focus on how best to exploit transient alerts from multi-messenger facilities. We examined the type of transient alerts those facilities will broadcast, and methods for following them up, such as rapid-response triggering and shadowing. In break-out groups, participants chose a science question related to a particular radio transient type or class and discussed whether the planned transient strategies and observing techniques on the Square Kilometre Array will be adequate to address the particular question. The classes they chose included fast radio bursts, supernovæ, cataclysmic variable and unknown transients. Any proposed adaptation or suggestion was relayed to a panel of experts for further discussion. The second part of the workshop concentrated on the application of long baseline interferometry for detecting and measuring radio transients.
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Yillia, P. T., N. Kreuzinger y K. K. Mwetu. "Temporal variability of two contrasting transient pollution events in a pastoral stream". Water Science and Technology 61, n.º 4 (1 de febrero de 2010): 1053–63. http://dx.doi.org/10.2166/wst.2010.566.
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Two transient pollution events were monitored in a pastoral stream in southwestern Kenya to evaluate their relative contribution to diffuse pollution. Peak loads of pollutants during storm-induced transients were within 3–4 orders of magnitude higher than the short-lived (30–60 minutes) diurnal episodes provoked by in-stream activities of people and livestock. Transient yields were striking during storm-induced events; 778,000, 8,400, 550 and 100 kg day−1 for suspended solids, BOD5, total P and total N, respectively, compared to wet weather base flow (150, 30, 0.8 and 1.4 kg day−1, for the same parameters, respectively). Two forms of concentration-discharge relationships were observed: increases in concentration for turbidity, suspended solids, BOD5, total P and the faecal indicator bacteria at the peak of the stream hydrograph, and concurrent decreases in concentration for conductivity and total N. Following each storm-induced transient event, a marked improvement in water quality was observed within 48–72 hrs of the receding limb of the stream hydrograph before the next base low was established. It was concluded that storm-induced transients are exceedingly important for the mobilization of pollutants from diffuse sources but both transient events affect stream-channel processes, especially water quality, with the possibility of attendant consequences on the health of riparian inhabitants.
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Tucker, M. A., B. J. Shappee, M. E. Huber, A. V. Payne, A. Do, J. T. Hinkle, T. de Jaeger et al. "The Spectroscopic Classification of Astronomical Transients (SCAT) Survey: Overview, Pipeline Description, Initial Results, and Future Plans". Publications of the Astronomical Society of the Pacific 134, n.º 1042 (1 de diciembre de 2022): 124502. http://dx.doi.org/10.1088/1538-3873/aca719.
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Abstract We present the Spectroscopic Classification of Astronomical Transients (SCAT) survey, which is dedicated to spectrophotometric observations of transient objects such as supernovae and tidal disruption events. SCAT uses the SuperNova Integral-Field Spectrograph (SNIFS) on the University of Hawai’i 2.2 m (UH2.2m) telescope. SNIFS was designed specifically for accurate transient spectrophotometry, including absolute flux calibration and host-galaxy removal. We describe the data reduction and calibration pipeline including spectral extraction, telluric correction, atmospheric characterization, nightly photometricity, and spectrophotometric precision. We achieve ≲5% spectrophotometry across the full optical wavelength range (3500–9000 Å) under photometric conditions. The inclusion of photometry from the SNIFS multi-filter mosaic imager allows for decent spectrophotometric calibration (10%–20%) even under unfavorable weather/atmospheric conditions. SCAT obtained ≈640 spectra of transients over the first 3 yr of operations, including supernovae of all types, active galactic nuclei, cataclysmic variables, and rare transients such as superluminous supernovae and tidal disruption events. These observations will provide the community with benchmark spectrophotometry to constrain the next generation of hydrodynamic and radiative transfer models.
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Kuiack, Mark, Ralph A. M. J. Wijers, Aleksandar Shulevski, Antonia Rowlinson, Folkert Huizinga, Gijs Molenaar y Peeyush Prasad. "The AARTFAAC 60 MHz transients survey". Monthly Notices of the Royal Astronomical Society 505, n.º 2 (28 de mayo de 2021): 2966–74. http://dx.doi.org/10.1093/mnras/stab1504.
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ABSTRACT We report the experimental set-up and overall results of the AARTFAAC wide-field radio survey, which consists of observing the sky within 50° of Zenith, with a bandwidth of 3.2 MHz, at a cadence of 1 s, for 545 h. This yielded nearly 4 million snapshots, two per second, of on average 4800 square degrees and a sensitivity of around 60 Jy. We find two populations of transient events, one originating from PSR B0950+08 and one from strong ionospheric lensing events, as well as a single strong candidate for an extragalactic transient, with a peak flux density of 80 ± 30 Jy and a dispersion measure of $73\pm 3\, \mathrm{~pc~cm^{-3}}$. We also set a strong upper limit of 1.1 all-sky per day to the rate of any other populations of fast, bright transients. Lastly, we constrain some previously detected types of transient sources by comparing our detections and limits with other low-frequency radio transient surveys.
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Stein, Robert, Ashish Mahabal, Simeon Reusch, Matthew Graham, Mansi M. Kasliwal, Marek Kowalski, Suvi Gezari et al. "tdescore: An Accurate Photometric Classifier for Tidal Disruption Events". Astrophysical Journal Letters 965, n.º 2 (1 de abril de 2024): L14. http://dx.doi.org/10.3847/2041-8213/ad3337.
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Abstract Optical surveys have become increasingly adept at identifying candidate tidal disruption events (TDEs) in large numbers, but classifying these generally requires extensive spectroscopic resources. Here we present tdescore, a simple binary photometric classifier that is trained using a systematic census of ∼3000 nuclear transients from the Zwicky Transient Facility (ZTF). The sample is highly imbalanced, with TDEs representing ∼2% of the total. tdescore is nonetheless able to reject non-TDEs with 99.6% accuracy, yielding a sample of probable TDEs with recall of 77.5% for a precision of 80.2%. tdescore is thus substantially better than any available TDE photometric classifier scheme in the literature, with performance not far from spectroscopy as a method for classifying ZTF nuclear transients, despite relying solely on ZTF data and multiwavelength catalog cross matching. In a novel extension, we use “Shapley additive explanations” to provide a human-readable justification for each individual tdescore classification, enabling users to understand and form opinions about the underlying classifier reasoning. tdescore can serve as a model for photometric identification of TDEs with time-domain surveys, such as the upcoming Rubin observatory.
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Kostrzewa-Rutkowska, Z., P. G. Jonker, S. T. Hodgkin, D. Eappachen, D. L. Harrison, S. E. Koposov, G. Rixon et al. "Electromagnetic counterparts to gravitational wave events from Gaia". Monthly Notices of the Royal Astronomical Society 493, n.º 3 (13 de febrero de 2020): 3264–73. http://dx.doi.org/10.1093/mnras/staa436.
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ABSTRACT The recent discoveries of gravitational wave events and in one case also its electromagnetic (EM) counterpart allow us to study the Universe in a novel way. The increased sensitivity of the LIGO and Virgo detectors has opened the possibility for regular detections of EM transient events from mergers of stellar remnants. Gravitational wave sources are expected to have sky localization up to a few hundred square degrees, thus Gaia as an all-sky multi-epoch photometric survey has the potential to be a good tool to search for the EM counterparts. In this paper, we study the possibility of detecting EM counterparts to gravitational wave sources using the Gaia Science Alerts system. We develop an extension to current used algorithms to find transients and test its capabilities in discovering candidate transients on a sample of events from the observation periods O1 and O2 of LIGO and Virgo. For the gravitational wave events from the current run O3, we expect that about 16 (25) per cent should fall in sky regions observed by Gaia 7 (10) d after gravitational wave. The new algorithm will provide about 21 candidates per day from the whole sky.
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Drumm, Bernard T., Grant W. Hennig, Matthew J. Battersby, Erin K. Cunningham, Tae Sik Sung, Sean M. Ward, Kenton M. Sanders y Salah A. Baker. "Clustering of Ca2+ transients in interstitial cells of Cajal defines slow wave duration". Journal of General Physiology 149, n.º 7 (7 de junio de 2017): 703–25. http://dx.doi.org/10.1085/jgp.201711771.
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Interstitial cells of Cajal (ICC) in the myenteric plexus region (ICC-MY) of the small intestine are pacemakers that generate rhythmic depolarizations known as slow waves. Slow waves depend on activation of Ca2+-activated Cl− channels (ANO1) in ICC, propagate actively within networks of ICC-MY, and conduct to smooth muscle cells where they generate action potentials and phasic contractions. Thus, mechanisms of Ca2+ regulation in ICC are fundamental to the motor patterns of the bowel. Here, we characterize the nature of Ca2+ transients in ICC-MY within intact muscles, using mice expressing a genetically encoded Ca2+ sensor, GCaMP3, in ICC. Ca2+ transients in ICC-MY display a complex firing pattern caused by localized Ca2+ release events arising from multiple sites in cell somata and processes. Ca2+ transients are clustered within the time course of slow waves but fire asynchronously during these clusters. The durations of Ca2+ transient clusters (CTCs) correspond to slow wave durations (plateau phase). Simultaneous imaging and intracellular electrical recordings revealed that the upstroke depolarization of slow waves precedes clusters of Ca2+ transients. Summation of CTCs results in relatively uniform Ca2+ responses from one slow wave to another. These Ca2+ transients are caused by Ca2+ release from intracellular stores and depend on ryanodine receptors as well as amplification from IP3 receptors. Reduced extracellular Ca2+ concentrations and T-type Ca2+ channel blockers decreased the number of firing sites and firing probability of Ca2+ transients. In summary, the fundamental electrical events of small intestinal muscles generated by ICC-MY depend on asynchronous firing of Ca2+ transients from multiple intracellular release sites. These events are organized into clusters by Ca2+ influx through T-type Ca2+ channels to sustain activation of ANO1 channels and generate the plateau phase of slow waves.
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Caspers, Philip, Blaine M. Harker, Chris Toole, Simon Freeman y Lauren Freeman. "Analysis of spatial-temporal variations in coral reef transients observed off the coast of Hawaii". Journal of the Acoustical Society of America 146, n.º 4_Supplement (1 de octubre de 2019): 2885. http://dx.doi.org/10.1121/1.5137009.
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Short duration acoustic transients are a conspicuous mechanism of sound generation by organisms within a coral reef environment. In this work, we investigate patterns of transients recorded in a coral reef environment during a crepuscular period associated with interactions between species. Video synchronized to hydrophone array element recordings at three different locations were used to identify times and positions of coral reef species interactions, i.e., predator-prey interactions. Normalized, directional audio reconstructions along fixed bearing directions were analyzed with a power law detector at different temporal resolutions to identify the occurrence of transient events. Segmented transients were collated with time and incident direction information and grouped into temporal windows within the audio reconstruction. Dimensional reduction of the transient audio was applied and changes in temporal characteristics of the compressed features associated with particular species were evaluated. Analysis of the order-statistic normalizer and power law detector parameters to detect biological transients is also discussed.
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Mattila, S., M. J. Graham, E. Kankare, E. Kool, T. Moriya, M. Perez-Torres y Ł. Wyrzykowski. "Nuclear Transients". Proceedings of the International Astronomical Union 14, S339 (noviembre de 2017): 263–68. http://dx.doi.org/10.1017/s1743921318002727.
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AbstractWorkshop 11 covered the substantial recent progress in studies of supernovæ (SNe), tidal disruption events (TDEs), and other types of luminous transients occurring within the nuclear regions of galaxies. In the past, such transients have largely been missed owing to the substantial extinction of those regions, and to the problems of contrast against the bright (and often complex) nuclear background – or mistaken for normal active galactic nucleus (AGN) variability.
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Mo, Xuejing, Hongtao Wen, Yanming Yang, Hongtao Zhou y Hailin Ruan. "Statistical characteristics of under-ice noise on the Arctic Chukchi Plateau". Journal of the Acoustical Society of America 154, n.º 4 (1 de octubre de 2023): 2489–98. http://dx.doi.org/10.1121/10.0021871.
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In the context of global warming leading to rapidly changing Arctic sea ice and the environment, it is necessary to understand the statistical characteristics of noise under existing Arctic ocean environmental conditions. The data recorded from August 1, 2018 to November 2, 2019, on the Arctic Chukchi Plateau, have been studied to analyze the relationship between the ice transient events and the non-Gaussian statistics of under-ice noise. The ice-generated transient noise largely contributes to the under-ice noise environment, and the total under-ice noise exhibits non-Gaussian statistics due to the occurrence of these ice transients. The number of ice transients has a strong negative correlation with the characteristic index α, meaning that the higher the occurrence of transient events, the stronger the non-Gaussian statistics of under-ice noise. Stronger non-Gaussian noise with full ice coverage is observed compared to partial ice coverage. The under-ice noise in 0.5–1 kHz exhibits the strongest non-Gaussian statistics, followed by 1–4 kHz, while it is weakest in 20–500 Hz. The statistics of ice transients and under-ice noise have been provided in this paper, which can be used in sonar detection algorithms and have important significance for the performance prediction and optimization of sonar processors.
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Xiao, Xiaoyin, Fu-Ren F. Fan, Jiping Zhou y Allen J. Bard. "Current Transients in Single Nanoparticle Collision Events". Journal of the American Chemical Society 130, n.º 49 (10 de diciembre de 2008): 16669–77. http://dx.doi.org/10.1021/ja8051393.
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Zeidan, Mohamad, Márton Németh, Gopinathan R. Abhijith, Richárd Wéber y Avi Ostfeld. "Transient Flow Dynamics in Tesla Valve Configurations: Insights from Computational Fluid Dynamics Simulations". Water 16, n.º 23 (4 de diciembre de 2024): 3492. https://doi.org/10.3390/w16233492.
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This study investigates the transient flow dynamics and pressure interactions within Tesla valve configurations through comprehensive CFD simulations. Tesla valves offer efficient passive fluid control without the need for external power, making them favorable in various applications. Previous observations indicated that Tesla valves effectively reduce the amplitude of pressure transients, prolonging their duration and distributing energy over an extended timeframe. While suggesting a potential role for Tesla valves as pressure dampers during transient events, the specific mechanisms behind this behavior remain unexplored. This research focuses on elucidating the internal dynamics of Tesla valves during transient events, aiming to unravel the processes responsible for the observed attenuation in pressure transients. This study reveals the emergence of “pressure pockets” within Tesla valves, deviating from conventional uniform pressure fronts. These pockets manifest as discrete chambers with varying lengths and volumes, contributing to the non-uniform propagation of pressure throughout the system. This investigation employs advanced CFD simulations as a crucial tool to unravel the governing dynamics of transient flow within Tesla valve configurations. By elucidating underlying fluid dynamics, this study lays the groundwork for future Tesla valve design optimization, holding potential implications for applications where the control of transient flow events is crucial.
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Lucarelli, Fabrizio y Marco Tavani. "AGILEγ-ray sources coincident with cosmic neutrino events". EPJ Web of Conferences 209 (2019): 01026. http://dx.doi.org/10.1051/epjconf/201920901026.
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Using data obtained by theγ-ray imager on board of the AGILE satellite, we systematically searched for transientγ-ray sources above 100 MeV in temporal and spatial coincidence with high-energy neutrino IceCube events. We found some significantγ-ray transients possibly associated with HESE neutrinos recently detected by the IceCube experiment. In this talk, we review the AGILE results and we will show that the probability of this association to be by chance is very low. One of the sources detected by AGILE is related to the blazar AGN TXS 0506+056. For the other sources, there are no obvious known counterparts.
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Oskinova, Lidia M., Tomasz Bulik y Ada Nebot Gómez-Morán. "Infrared outbursts as potential tracers of common-envelope events in high-mass X-ray binary formation". Astronomy & Astrophysics 613 (mayo de 2018): L10. http://dx.doi.org/10.1051/0004-6361/201832925.
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Context. Classic massive binary evolutionary scenarios predict that a transitional common-envelope (CE) phase could be preceded as well as succeeded by the evolutionary stage when a binary consists of a compact object and a massive star, that is, a high-mass X-ray binary (HMXB). The observational manifestations of common envelope are poorly constrained. We speculate that its ejection might be observed in some cases as a transient event at mid-infrared (IR) wavelengths. Aims. We estimate the expected numbers of CE ejection events and HMXBs per star formation unit rate, and compare these theoretical estimates with observations. Methods. We compiled a list of 85 mid-IR transients of uncertain nature detected by the Spitzer Infrared Intensive Transients Survey and searched for their associations with X-ray, optical, and UV sources. Results. Confirming our theoretical estimates, we find that only one potential HMXB may be plausibly associated with an IR-transient and tentatively propose that X-ray source NGC 4490-X40 could be a precursor to the SPIRITS 16az event. Among other interesting sources, we suggest that the supernova remnant candidate [BWL2012] 063 might be associated with SPIRITS 16ajc. We also find that two SPIRITS events are likely associated with novae, and seven have potential optical counterparts. Conclusions. The massive binary evolutionary scenarios that involve CE events do not contradict currently available observations of IR transients and HMXBs in star-forming galaxies.
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Johnstone, Doug, Bhavana Lalchand, Steve Mairs, Hsien Shang, Wen Ping Chen, Geoffrey C. Bower, Gregory J. Herczeg et al. "The JCMT Transient Survey: Single-epoch Transients and Variability of Faint Sources". Astrophysical Journal 937, n.º 1 (1 de septiembre de 2022): 6. http://dx.doi.org/10.3847/1538-4357/ac8a48.
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Abstract Short-duration flares at millimeter wavelengths provide unique insights into the strongest magnetic reconnection events in stellar coronae and combine with longer-term variability to introduce complications to next-generation cosmology surveys. We analyze 5.5 yr of JCMT Transient Survey 850 μm submillimeter monitoring observations toward eight Gould Belt star-forming regions to search for evidence of transient events or long-duration variability from faint sources. The eight regions (30′ diameter fields), including ∼1200 infrared-selected YSOs, have been observed on average 47 times with integrations of approximately half an hour, or one day total, spread over 5.5 yr. Within this large data set, only two robust faint source detections are recovered: JW 566 in OMC 2/3 and MGM12 2864 in NGC 2023. JW 566, a Class II T Tauri binary system previously identified as an extraordinary submillimeter flare, remains unique, the only clear single-epoch transient detection in this sample with a flare eight times bright than our ∼4.5σ detection threshold of 55 mJy beam−1. The lack of additional recovered flares intermediate between JW 566 and our detection limit is puzzling if smaller events are more common than larger events. In contrast, the other submillimeter variable identified in our analysis, Source 2864, is highly variable on all observed timescales. Although Source 2864 is occasionally classified as a YSO, the source is most likely a blazar. The degree of variability across the electromagnetic spectrum may be used to aid source classification.
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Soraisam, Monika, Thomas Matheson, Chien-Hsiu Lee, Abhijit Saha, Gautham Narayan, Nicholas Wolf, Adam Scott et al. "Optical Rebrightening of Extragalactic Transients from the Zwicky Transient Facility". Astrophysical Journal Letters 926, n.º 2 (1 de febrero de 2022): L11. http://dx.doi.org/10.3847/2041-8213/ac4e99.
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Abstract Ongoing large-scale optical time-domain surveys, such as the Zwicky Transient Facility (ZTF), are producing alerts at unprecedented rates. Analysis of transient sources has so far followed two distinct paths: archival analysis of data on transient sources at a time when they are no longer observable and real-time analysis at the time when the sources are first detected. The latter is the realm of alert brokers such as the Arizona-NOIRLab Temporal Analysis and Response to Events System (ANTARES). In this paper, we synthesize the two analysis paths and present a first systematic study of archival alert-broker data, focusing on extragalactic transients with multipeaked light curves identified in the ANTARES archive of ZTF alerts. Our analysis yields a sample of 37 such sources, including core-collapse supernovae (with two analogs of iPTF14hls), thermonuclear supernovae interacting with their surrounding circumstellar medium, tidal disruption events, luminous blue variables, and as yet unclassified objects. A large fraction of the identified sources is currently active, warranting allocation of follow-up resources in the immediate future to further constrain their nature and the physical processes at work.
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Zenati, Yossef, Alexey Bobrick y Hagai B. Perets. "Faint rapid red transients from neutron star–CO white dwarf mergers". Monthly Notices of the Royal Astronomical Society 493, n.º 3 (20 de febrero de 2020): 3956–65. http://dx.doi.org/10.1093/mnras/staa507.
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ABSTRACT Mergers of neutron stars (NS) and white dwarfs (WD) may give rise to observable explosive transient events. We use 3D hydrodynamical (smoothed particle hydrodynamics – SPH) simulations and 2D hydrodynamical–thermonuclear simulations (using the flash adaptive mesh refinement code) to model the disruption of CO-WDs by NSs, which produce faint transient events. We post-process the simulations using a large nuclear network and make use of the SuperNu radiation transfer code to predict the observational signatures and detailed properties of these transients. We calculate the light curves and spectra for five models of NS–CO-WD mergers. The small yields of 56Ni (few $\times 10^{-3}\, {\rm M_{\odot }}$) result in faint, rapidly evolving reddened transients (RRTs) with B(R) peak magnitudes of at most ∼−12 (−13) to ∼−13 (−15), much shorter and fainter than both regular and faint/peculiar Type Ia supernovae. These transients are likely to be accompanied by several months long, 1–2 mag dimmer red/infrared afterglows. We show that the spectra of RRTs share some similarities with rapidly evolving transients such as SN 2010X, although RRTs are significantly fainter, especially in the I/R bands, and show far stronger Si lines. We estimate that the upcoming Large Synoptic Survey Telescope could detect RRTs at a rate of up to ∼10–70 yr−1 through observations in the R/I bands. The qualitative agreement between the SPH and flash approaches supports the earlier hydrodynamical studies of these systems.
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ter Veen, S., J. E. Enriquez, H. Falcke, J. P. Rachen, M. van den Akker, P. Schellart, A. Bonardi et al. "The FRATS project: real-time searches for fast radio bursts and other fast transients with LOFAR at 135 MHz". Astronomy & Astrophysics 621 (enero de 2019): A57. http://dx.doi.org/10.1051/0004-6361/201732515.
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Context. In the previous decade, two new classes of fast radio transients were detected: the Galactic, rotating radio transients (RRATs) and the extragalactic fast radio bursts (FRBs). If the detectable emission of these objects extends to lower radio frequencies, the LOw Frequency ARray (LOFAR) is ideally suited to seek and localize these transients at frequencies of 10–250 MHz. This is due to LOFAR’s sensitivity, diverse beamform capabilities, and transient buffers for the individual elements that allow post-event imaging of events, potentially at arcsecond resolution. Aims. Our aim is to identify and localize pulses at frequencies below 250 MHz and, in the case of nondetections, derive upper limits on the sky and volume rates of FRBs. Methods. A real-time search program for fast radio transients is installed on the LOFAR systems which runs commensally with other observations, and uses the wide incoherent LOFAR beam (11.25 deg2 at 150 MHz). Buffered data from hundreds of dipoles are used to reconstruct the direction and polarization information of the event, and to distinguish between celestial, terrestrial, and instrumental origins. Results. Observations were taken covering either the frequency range 119–151 MHz or in four frequency bands, each of 2 MHz in width, centered at 124, 149, 156, and 185 MHz. A first pilot survey covered a range of dispersion measures (DM) below 120 pc cm−3, focusing on Galactic sources, and resulted in an upper limit on the transient rate at LOFAR frequencies of less than 1500 events per sky per day above a fluency of 1.6 kJy ms for an 8-ms pulse. A second pilot survey covered a range of DMs below 500 pc cm−3, focusing on extragalactic sources to about 1 Gpc, and resulted in an upper limit of 1400 events per sky per day above a fluency of 6.0 kJy ms for an 8-ms pulse. Using a model for the distance-DM relationship, this equates to an upper limit of 134 events per Gpc3 per day.
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Dgany, Yael, Iair Arcavi, Lydia Makrygianni, Craig Pellegrino y D. Andrew Howell. "Needle in a Haystack: Finding Supermassive Black Hole-related Flares in the Zwicky Transient Facility Public Survey". Astrophysical Journal 957, n.º 1 (27 de octubre de 2023): 57. http://dx.doi.org/10.3847/1538-4357/ace971.
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Abstract Transient accretion events onto supermassive black holes (SMBHs), such as tidal disruption events (TDEs), Bowen Fluorescence Flares (BFFs), and active galactic nuclei (AGNs), which are accompanied by sudden increases of activity, offer a new window onto the SMBH population, accretion physics, and stellar dynamics in galaxy centers. However, such transients are rare and finding them in wide-field transient surveys is challenging. Here we present the results of a systematic real-time search for SMBH-related transients in Zwicky Transient Facility (ZTF) public alerts, using various search queries. We examined 345 rising events coincident with a galaxy nucleus, with no history of previous activity, of which 223 were spectroscopically classified. Of those, five (2.2%) were TDEs, one (0.5%) was a BFF, and two (0.9%) were AGN flares. Limiting the search to blue events, the fraction of TDEs nearly doubles to 4.1%, and no TDEs are missed. Limiting the search further to candidate post-starburst galaxies increases the relative number of TDEs to 16.7%, but the absolute numbers in such a search are small. The main contamination source is supernovae (95.1% of classified events), of which the majority (82.2% of supernovae) are of Type Ia. In a comparison set of 39 events with limited photometric history, the AGN contamination increases to ∼30%. Host galaxy offset is not a significant discriminant of TDEs in current ZTF data, but might be useful in higher-resolution data. Our results can be used to quantify the efficiency of various SMBH-related transient search strategies in optical surveys such as ZTF and the Legacy Survey of Space and Time.
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Chen, Che Hao, Jong Rong Wang, Hao Tzu Lin y Chun Kuan Shih. "Various MTC Studies of TRACE with RCS Pressure Predictions under ATWS for Maanshan". Applied Mechanics and Materials 284-287 (enero de 2013): 1151–55. http://dx.doi.org/10.4028/www.scientific.net/amm.284-287.1151.
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The objective of this study is to utilize TRACE (TRAC/RELAP Advanced Computational Engine) code to analyze the reactor coolant system (RCS) pressure transients under ATWS (Anticipated Transient Without Scram) for Maanshan PWR (Pressurized Water Reactor) in various MTC (Moderator Temperature Coefficient) conditions. TRACE is an advanced thermal hydraulic code for nuclear power plant safety analysis, which is currently under development by the United States Nuclear Regulatory Commission (USNRC). A graphic user interface program named SNAP (Symbolic Nuclear Analysis Package), which processes inputs and outputs for TRACE is also under development. Maanshan nuclear power plant (NPP) is the only Westinghouse PWR in Taiwan. The rated core thermal power of Maanshan with MUR (Measurement Uncertainty Recapture) is 2822 MWt. In document SECY-83-293, all initializing events were classified as either turbine trip or non-turbine trip events and their ATWS risks were also evaluated according to these two events. Loss of condenser vacuum (LOCV) and Loss of normal feedwater (LONF) ATWS were identified as limiting transients of turbine trip and non-turbine trip events in this study. According to ASME Code Level C service limit criteria, the RCS pressure for Maanshan NPP must be under 22.06 MPa. Furthermore, we select the LOCV transient to analyze various MTC effects on RCS pressure variations.
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Sulis, William. "Transients as the Basis for Information Flow in Complex Adaptive Systems". Entropy 21, n.º 1 (20 de enero de 2019): 94. http://dx.doi.org/10.3390/e21010094.
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Information is the fundamental currency of naturally occurring complex adaptive systems, whether they are individual organisms or collective social insect colonies. Information appears to be more important than energy in determining the behavior of these systems. However, it is not the quantity of information but rather its salience or meaning which is significant. Salience is not, in general, associated with instantaneous events but rather with spatio-temporal transients of events. This requires a shift in theoretical focus from instantaneous states towards spatio-temporal transients as the proper object for studying information flow in naturally occurring complex adaptive systems. A primitive form of salience appears in simple complex systems models in the form of transient induced global response synchronization (TIGoRS). Sparse random samplings of spatio-temporal transients may induce stable collective responses from the system, establishing a stimulus–response relationship between the system and its environment, with the system parsing its environment into salient and non-salient stimuli. In the presence of TIGoRS, an embedded complex dynamical system becomes a primitive automaton, modeled as a Sulis machine.
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Zhelenkova, Olga P. y Elena K. Majorova. "The search of radio transients in the RATAN-600 radio telescope surveys". Proceedings of the International Astronomical Union 12, S325 (octubre de 2016): 270–73. http://dx.doi.org/10.1017/s1743921316012801.
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AbstractWe present the results of the search of variable sources and transient events in the archive data of the sky surveys conducted on 3.9 GHz on the RATAN-600 radio telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS) in 1980-1994. 17% of the total studied sources can be attributed to the variables in radio range. About half of them has significant variations in optical brightness according to the data of the catalogs. At the level of 3-5 r.m.s. we found three transient events. Two weak events probably associated with AGN activities or with cataclysmic events such as GRB and a supernova flash. The nature of the third event has not been established. According to our estimation the surface density of radio transients is 0.03 on one square angular degree with the detection level 8–11 mJy on 3.94 GHz.
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Janiak, Robert, Sean M. Wilson, Stephen Montague y Joseph R. Hume. "Heterogeneity of calcium stores and elementary release events in canine pulmonary arterial smooth muscle cells". American Journal of Physiology-Cell Physiology 280, n.º 1 (1 de enero de 2001): C22—C33. http://dx.doi.org/10.1152/ajpcell.2001.280.1.c22.
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To examine the nature of inositol 1,4,5-trisphosphate (IP3)-sensitive and ryanodine (Ryn)-sensitive Ca2+ stores in isolated canine pulmonary arterial smooth cells (PASMC), agonist-induced changes in global intracellular Ca2+ concentration ([Ca2+]i) were measured using fura 2-AM fluorescence. Properties of elementary local Ca2+release events were characterized using fluo 3-AM or fluo 4-AM, in combination with confocal laser scanning microscopy. In PASMC, depletion of sarcoplasmic reticulum Ca2+ stores with Ryn (300 μM) and caffeine (Caf; 10 mM) eliminated subsequent Caf-induced intracellular Ca2+ transients but had little or no effect on the initial IP3-mediated intracellular Ca2+transient induced by ANG II (1 μM). Cyclopiazonic acid (CPA; 10 μM) abolished IP3-induced intracellular Ca2+ transients but failed to attenuate the initial Caf-induced intracellular Ca2+ transient. These results suggest that in canine PASMC, IP3-, and Ryn-sensitive Ca2+ stores are organized into spatially distinct compartments while similar experiments in canine renal arterial smooth muscle cells (RASMC) reveal that these Ca2+ stores are spatially conjoined. In PASMC, spontaneous local intracellular Ca2+ transients sensitive to modulation by Caf and Ryn were detected, exhibiting spatial-temporal characteristics similar to those previously described for “Ca2+ sparks” in cardiac and other types of smooth muscle cells. After depletion of Ryn-sensitive Ca2+ stores, ANG II (8 nM) induced slow, sustained [Ca2+]i increases originating at sites near the cell surface, which were abolished by depleting IP3stores. Discrete quantal-like events expected due to the coordinated opening of IP3 receptor clusters (“Ca2+puffs”) were not observed. These data provide new information regarding the functional properties and organization of intracellular Ca2+ stores and elementary Ca2+ release events in isolated PASMC.
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Kisley, Marina, Yu-Jing Qin, Ann Zabludoff, Kobus Barnard y Chia-Lin Ko. "Classifying Astronomical Transients Using Only Host Galaxy Photometry". Astrophysical Journal 942, n.º 1 (1 de enero de 2023): 29. http://dx.doi.org/10.3847/1538-4357/aca532.
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Abstract The Legacy Survey of Space and Time (LSST) at the Vera C. Rubin Observatory will discover tens of thousands of extragalactic transients each night. The high volume of alerts demands immediate classification of transient types in order to prioritize observational follow-ups before events fade away. We use host galaxy features to classify transients, thereby providing classification upon discovery. In contrast to past work that focused on distinguishing Type Ia and core-collapse supernovae (SNe) using host galaxy features that are not always accessible (e.g., morphology), we determine the relative likelihood across 12 transient classes based on only 19 host apparent magnitudes and colors from 10 optical and IR photometric bands. We develop both binary and multiclass classifiers, using kernel density estimation to estimate the underlying distribution of host galaxy properties for each transient class. Even in this pilot study, and ignoring relative differences in transient class frequencies, we distinguish eight transient classes at purities significantly above the 8.3% baseline (based on a classifier that assigns labels uniformly and at random): tidal disruption events (TDEs; 48% ± 27%, where ± indicates the 95% confidence limit), SNe Ia-91bg (32% ± 18%), SNe Ia-91T (23% ± 11%), SNe Ib (23% ± 13%), SNe II (17% ± 2%), SNe IIn (17% ± 6%), SNe II P (16% ± 4%), and SNe Ia (10% ± 1%). We demonstrate that our model is applicable to LSST and estimate that our approach can accurately classify 59% of LSST alerts expected each year for SNe Ia, Ia-91bg, II, Ibc, SLSN-I, and TDEs. Our code and data set are publicly available.
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Popkov, Alexander V. y Sergei B. Popov. "The rate of planet–star coalescences due to tides and stellar evolution". Monthly Notices of the Royal Astronomical Society 490, n.º 2 (4 de octubre de 2019): 2390–404. http://dx.doi.org/10.1093/mnras/stz2783.
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ABSTRACT Orbits of close-in planets can shrink significantly due to dissipation of tidal energy in a host star. This process can result in star–planet coalescence within the Galactic lifetime. In some cases, such events can be accompanied by an optical or/and UV/X-ray transient. Potentially, these outbursts can be observed in near future with new facilities such as LSST from distances about few Mpc. We use a population synthesis model to study this process and derive the rate of star–planet mergers of different types. Mostly, planets are absorbed by red giants. However, these events, happening with the rate about 3 per year, mostly do not produce detectable transients. The rate of mergers with main sequence stars depends on the effectiveness of tidal dissipation; for reasonable values of stellar tidal quality factor, such events happen in a Milky Way-like galaxy approximately once in 70 yr or more rarely. This rate is dominated by planets with low masses. Such events do not produce bright transients having maximum luminosities ≲ 1036.5 erg s−1. Brighter events, related to massive planets, with maximum luminosity ∼1037.5–1038 erg s−1, have the rate nearly five times smaller.
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Aleo, P. D., A. W. Engel, G. Narayan, C. R. Angus, K. Malanchev, K. Auchettl, V. F. Baldassare et al. "Anomaly Detection and Approximate Similarity Searches of Transients in Real-time Data Streams". Astrophysical Journal 974, n.º 2 (1 de octubre de 2024): 172. http://dx.doi.org/10.3847/1538-4357/ad6869.
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Abstract We present Lightcurve Anomaly Identification and Similarity Search (LAISS), an automated pipeline to detect anomalous astrophysical transients in real-time data streams. We deploy our anomaly detection model on the nightly Zwicky Transient Facility (ZTF) Alert Stream via the ANTARES broker, identifying a manageable ∼1–5 candidates per night for expert vetting and coordinating follow-up observations. Our method leverages statistical light-curve and contextual host galaxy features within a random forest classifier, tagging transients of rare classes (spectroscopic anomalies), of uncommon host galaxy environments (contextual anomalies), and of peculiar or interaction-powered phenomena (behavioral anomalies). Moreover, we demonstrate the power of a low-latency (∼ms) approximate similarity search method to find transient analogs with similar light-curve evolution and host galaxy environments. We use analogs for data-driven discovery, characterization, (re)classification, and imputation in retrospective and real-time searches. To date, we have identified ∼50 previously known and previously missed rare transients from real-time and retrospective searches, including but not limited to superluminous supernovae (SLSNe), tidal disruption events, SNe IIn, SNe IIb, SNe I-CSM, SNe Ia-91bg-like, SNe Ib, SNe Ic, SNe Ic-BL, and M31 novae. Lastly, we report the discovery of 325 total transients, all observed between 2018 and 2021 and absent from public catalogs (∼1% of all ZTF Astronomical Transient reports to the Transient Name Server through 2021). These methods enable a systematic approach to finding the “needle in the haystack” in large-volume data streams. Because of its integration with the ANTARES broker, LAISS is built to detect exciting transients in Rubin data.
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Calcinaghi, Novella, Renaud Jolivet, Matthias T. Wyss, Simon M. Ametamey, Fabrizio Gasparini, Alfred Buck y Bruno Weber. "Metabotropic glutamate receptor mGluR5 is not involved in the early hemodynamic response". Journal of Cerebral Blood Flow & Metabolism 31, n.º 9 (6 de julio de 2011): e1-e10. http://dx.doi.org/10.1038/jcbfm.2011.96.
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Activation of astrocytic metabotropic glutamate receptor 5 (mGluR5) is postulated to elicit calcium transients, triggering a chain of events that ultimately regulates cerebral blood flow by changing the tone of smooth muscle cells of nearby arterioles. Using concurrent in vivo optical imaging and determination of receptor occupancy with 11C-ABP688, we report here that blocking ∼80% of mGluR5 in vivo does not affect transient hemodynamic responses on brief whisker stimulations while transiently reducing neuronal activity as measured by voltage-sensitive dye imaging. Our results show that mechanisms other than activation of mGluR5 are required to trigger the initial hemodynamic response in normal physiological conditions.
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Scherberich, A., M. Campos-Toimil, P. Ronde, K. Takeda y A. Beretz. "Migration of human vascular smooth muscle cells involves serum-dependent repeated cytosolic calcium transients". Journal of Cell Science 113, n.º 4 (15 de febrero de 2000): 653–62. http://dx.doi.org/10.1242/jcs.113.4.653.
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Migration of vascular smooth muscle cells (VSMC) is a key event in the formation of neointima during atherosclerosis. Fura-2 loaded VSMCs were used to investigate calcium homeostasis during cell migration. Multiple spontaneous transient increases in cytosolic free calcium [Ca(2+)](i)were observed in single human VSMCs migrating on type I collagen. Such [Ca(2+)](i)transients were dependent on the presence of serum or PDGF-BB. Removal of serum, or loading cells with BAPTA, abolished the transients and decreased cell migration speed. The transients were not affected by disruption of cell polarization by dihydrocytochalasin B. Adhesion was used to investigate the specific role of cell-substrate interactions in the generation of transients. Transients are seen in VSMCs adhering either on collagen or on poly-L-lysine, suggesting that generation of transients is not strictly dependent on integrins. Buffering [Ca(2+)](i) with BAPTA led to accumulation of (beta)1 integrins at the cellular tail, and to increased release of integrin on the extracellular matrix. These results demonstrate a role for [Ca(2+)](i) transients in the rapid, serum-dependent migration of VSMCs. These [Ca(2+)](i)transients are present in migrating VSMCs only when two simultaneous events occur: (1) substrate independent spreading and (2) stimulation of cells by serum components such as PDGF-BB.
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Chitta, L. P., A. R. C. Sukarmadji, L. Rouppe van der Voort y H. Peter. "Energetics of magnetic transients in a solar active region plage". Astronomy & Astrophysics 623 (marzo de 2019): A176. http://dx.doi.org/10.1051/0004-6361/201834548.
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Context. Densely packed coronal loops are rooted in photospheric plages in the vicinity of active regions on the Sun. The photospheric magnetic features underlying these plage areas are patches of mostly unidirectional magnetic field extending several arcsec on the solar surface. Aims. We aim to explore the transient nature of the magnetic field, its mixed-polarity characteristics, and the associated energetics in the active region plage using high spatial resolution observations and numerical simulations. Methods. We used photospheric Fe I 6173 Å spectropolarimetric observations of a decaying active region obtained from the Swedish 1-m Solar Telescope (SST). These data were inverted to retrieve the photospheric magnetic field underlying the plage as identified in the extreme-ultraviolet emission maps obtained from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). To obtain better insight into the evolution of extended unidirectional magnetic field patches on the Sun, we performed 3D radiation magnetohydrodynamic simulations of magnetoconvection using the MURaM code. Results. The observations show transient magnetic flux emergence and cancellation events within the extended predominantly unipolar patch on timescales of a few 100 s and on spatial scales comparable to granules. These transient events occur at the footpoints of active region plage loops. In one case the coronal response at the footpoints of these loops is clearly associated with the underlying transient. The numerical simulations also reveal similar magnetic flux emergence and cancellation events that extend to even smaller spatial and temporal scales. Individual simulated transient events transfer an energy flux in excess of 1 MW m−2 through the photosphere. Conclusions. We suggest that the magnetic transients could play an important role in the energetics of active region plage. Both in observations and simulations, the opposite-polarity magnetic field brought up by transient flux emergence cancels with the surrounding plage field. Magnetic reconnection associated with such transient events likely conduits magnetic energy to power the overlying chromosphere and coronal loops.
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Kulkarni, S. R. "Cosmic Explosions (Optical)". Proceedings of the International Astronomical Union 7, S285 (septiembre de 2011): 55–61. http://dx.doi.org/10.1017/s174392131200021x.
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One of the principal motivations of wide-field and synoptic surveys is the search for, and study of, transients. By transients I mean those sources that arise from the background, are detectable for some time, and then fade away to oblivion. Transients in distant galaxies need to be sufficiently bright as to be detectable, and in almost all cases those transients are catastrophic events, marking the deaths of stars. Exemplars include supernovæ and gamma-ray bursts. In our own Galaxy, the transients are strongly variable stars, and in almost all cases are at best cataclysmic rather than catastrophic. Exemplars include flares from M dwarfs, novæ of all sorts (dwarf novæ, recurrent novæ, classical novæ, X-ray novæ) and instabilities in the surface layers of stars such as S Dor or η Carina. In the nearby Universe (say out to the Virgo cluster) we have sufficient sensitivity to see novæ. In 1 I review the history of transients (which is intimately related to the advent of wide-field telescopic imaging). In 2 I summarize wide-field imaging projects, and I then review the motivations that led to the design of the Palomar Transient Factory (PTF). Next comes a summary of the astronomical returns from PTF (3), and that is followed by lessons that I have learnt from PTF (4). I conclude that, during this decade, the study of optical transients will continue to flourish (and may even accelerate as surveys at other wavelengths—notably radio, UV and X-ray—come on-line). Furthermore, it is highly likely that there will be a proliferation of highly-specialized searches for transients. Those searches may well remain active even in the era of LSST (5). I end the article by discussing the importance of follow-up telescopes for transient object studies—a topical issue, given the Portfolio Review that is being undertaken in the US.
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Watanabe, Yutaka, Keisuke Sato, Tetsuya Uchimoto y Toshiyuki Takagi. "Estimation Method of SCC Initiation Site Based on Electrochemical Transients". Key Engineering Materials 297-300 (noviembre de 2005): 999–1004. http://dx.doi.org/10.4028/www.scientific.net/kem.297-300.999.
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Although electrochemical transients can provide very sensitive indication about the onset of localized corrosion, including initiation of stress corrosion cracking (SCC), information on location of the initiation site is not available. In the present study, we proposed an estimation method of location and magnitude of SCC initiation events, where electrochemical transients associated with local anodic events are measured by multiple reference electrodes and location of the initiation sites are estimated based on relative magnitude of the electrochemical transients simultaneously measured at multiple locations.
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Nelson, David. "Long-term environmental noise measurement methods for industrial noise sources". INTER-NOISE and NOISE-CON Congress and Conference Proceedings 266, n.º 2 (25 de mayo de 2023): 972–77. http://dx.doi.org/10.3397/nc_2023_0116.
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Industrial noise sources can impact nearby residential communities, especially in rural areas. In order to assess the situation after commissioning, plant noise must be reliably differentiated from prevailing ambient, transient environmental noises, and weather-related events. Continuously attending such measurements is generally impractical. On the other hand, classifying events by eyeballing a stream of Leq values after the fact isn't sufficiently reliable in most cases either. An effective approach is presented that involves measurement and statistical, observational, and analytical methods to perform much of the work in an automated fashion. Methods include statistically excluding transients from the Leq, filtering to eliminate birds and bugs, spectral characteristics of wind events, and potential spectral identifiers indicative of operation. Classifications are confirmed by listening to periodic and/or event-driven audio segments. This approach works best when both the plant noise and prevailing ambient are quasi-steady; plant-generated transients and weather events may require manual reclassification. Examples from long-term environmental noise studies are provided. The methods are neither dramatic nor novel but their effectiveness in combination may be useful, especially for those new to this type of work.
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Nir, Guy, Eran O. Ofek, Sagi Ben-Ami, Noam Segev, David Polishook y Ilan Manulis. "A high-rate foreground of sub-second flares from geosynchronous satellites". Monthly Notices of the Royal Astronomical Society 505, n.º 2 (21 de mayo de 2021): 2477–84. http://dx.doi.org/10.1093/mnras/stab1437.
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ABSTRACT The Weizmann Fast Astronomical Survey Telescope is a 55 cm optical survey telescope with a high-cadence (25 Hz) monitoring of the sky over a wide field of view (≈7 deg2). The high frame rate allows detection of sub-second transients over multiple images. We present a sample of ∼0.1–0.3 s duration flares detected in an untargeted survey for such transients. We show that most, if not all of them, are glints of sunlight reflected off geosynchronous and graveyard orbit satellites. The flares we detect have a typical magnitude of 9–11, which translates to ∼14–16th magnitude if diluted by a 30 s exposure time. We estimate the rate of events brighter than ∼11 mag to be of the order of 30–40 events per day per deg2, for declinations between −20° and +10°, not including the declination corresponding to the geostationary belt directly above the equator, where the rate can be higher. We show that such glints are common in large area surveys (e.g. Zwicky Transient Facility and Legacy Survey of Space and Time), and that some of them have a point-like appearance, confounding searches for fast transients such as fast radio burst counterparts and gamma-ray bursts (GRBs). By observing in the direction of the Earth’s shadow, we are able to put an upper limit on the rate of fast astrophysical transients of 0.052 deg−2 day−1 (95 per cent confidence limit) for events brighter than 11 mag. We also suggest that the single image, high declination flare observed in coincidence with the GN-z11 galaxy and assumed to be a GRB, is also consistent with such a satellite glint.
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Jaconi, M. E., J. M. Theler, W. Schlegel, R. D. Appel, S. D. Wright y P. D. Lew. "Multiple elevations of cytosolic-free Ca2+ in human neutrophils: initiation by adherence receptors of the integrin family." Journal of Cell Biology 112, n.º 6 (15 de marzo de 1991): 1249–57. http://dx.doi.org/10.1083/jcb.112.6.1249.
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Multiple spontaneous transient elevations of cytosolic-free calcium ([Ca2+]i) are observed in single human neutrophils during adherence. The interrelation between adherence and spontaneous [Ca2+]i transients was analyzed by simultaneous monitoring of [Ca2+]i and cell morphology. Fluorescent images of fura 2-loaded neutrophils attached to albumin-coated glass were recorded with a high sensitivity CCD camera while [Ca2+]i was assessed with a dual excitation microfluorimetry. The majority of the initially round cells studied showed changes in shape which started either before or at the same time as the onset of the [Ca2+]i transients. These data suggested that a rise in [Ca2+]i is not a prerequisite for shape change. This conclusion was confirmed by observation of movement and spreading in cells whose [Ca2+]i transients were abolished by chelation of extracellular Ca2+. Instead, our data suggest that spreading or adhesion itself initiates the [Ca2+]i activity. In keeping with this hypothesis, cytochalasin B, which prevents both cell movement and adhesion, completely inhibited generation of [Ca2+]i transients. To determine if the movement alone or adhesion alone is responsible for [Ca2+]i activity, we treated cells with antibodies against the beta chain (CD18, beta 2) or the alpha subunit (CD11b, alpha m) of the dominant leukocyte integrin (CR3). Antibody-treated cells showed normal extension of pseudopods but impaired ability to adhere. Inhibition of adhesion in this way inhibited [Ca2+]i activity. Taken together these results suggest that following sequence of events after contact of neutrophils with surfaces: (a) cell movement and shape change lead to enhanced contact of integrins with the surface; and (b) integrins-mediated adhesion generates multiple [Ca2+]i transients. The [Ca2+]i transients may then control exocytic events associated with movement and may provide a link between adherence and activation or priming of neutrophils to other stimuli.
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Gupta, Girjesh R. y Sushree S. Nayak. "Spectroscopic and imaging observations of transient hot and cool loops by IRIS and SDO". Monthly Notices of the Royal Astronomical Society 512, n.º 3 (31 de marzo de 2022): 3149–62. http://dx.doi.org/10.1093/mnras/stac657.
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ABSTRACT Coronal loops are the basic building blocks of the solar atmosphere and are observed on various length scales. However, their formation mechanism is still unclear. In this paper, we present spectroscopic and imaging observations of small-scale transients and the subsequent formation of transient loops. For this purpose, we have utilized the multiwavelength observations recorded by the Atmospheric Imaging Assembly (AIA) and the Interface Region Imaging Spectrograph (IRIS) slit-jaw imager (SJI), along with spectroscopic measurements provided by IRIS. For the photospheric magnetic field data, we obtained line-of-sight magnetogram data provided by the Helioseismic and Magnetic Imager (HMI). Small-scale transients are simultaneously observed with several EUV and UV passbands of AIA and IRIS/SJI. The HMI magnetogram provides evidence of negative flux cancellations beneath these transients. Differential emission measure (DEM) analysis shows that one of the transients attains temperatures up to 8 MK whereas another one only reaches 0.4 MK. These transients further lead to the formation of small-scale loops with similar temperature distributions, thus termed hot and cool loops respectively. During the course of events, the IRIS slit was rastering the region and thus provided spectroscopic measurements at both transients and associated loops. This enabled us to perform in-depth investigations of the hot and cool loops. Using a density-sensitive O iv line pair, we obtained average electron densities along the hot and cool loops to be 1011.2 and 1010.8 cm−3 respectively. Energy estimates suggest that flux cancellation could easily power the hot transient, while it is insufficient for the cool transient. Lifetime estimates and magnetic field extrapolation suggest the presence of small-scale and fine structures within these loops. The results provide crucial ingredients for the physics of loop formation and the thermodynamics involved.
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Macquart, Jean-Pierre, M. Bailes, N. D. R. Bhat, G. C. Bower, J. D. Bunton, S. Chatterjee, T. Colegate et al. "The Commensal Real-Time ASKAP Fast-Transients (CRAFT) Survey". Publications of the Astronomical Society of Australia 27, n.º 3 (2010): 272–82. http://dx.doi.org/10.1071/as09082.
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AbstractWe are developing a purely commensal survey experiment for fast (<5 s) transient radio sources. Short-timescale transients are associated with the most energetic and brightest single events in the Universe. Our objective is to cover the enormous volume of transients parameter space made available by ASKAP, with an unprecedented combination of sensitivity and field of view. Fast timescale transients open new vistas on the physics of high brightness temperature emission, extreme states of matter and the physics of strong gravitational fields. In addition, the detection of extragalactic objects affords us an entirely new and extremely sensitive probe on the huge reservoir of baryons present in the IGM. We outline here our approach to the considerable challenge involved in detecting fast transients, particularly the development of hardware fast enough to dedisperse and search the ASKAP data stream at or near real-time rates. Through CRAFT, ASKAP will provide the testbed of many of the key technologies and survey modes proposed for high time resolution science with the SKA.
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Provan, G., T. K. Yeoman y S. E. Milan. "CUTLASS Finland radar observations of the ionospheric signatures of flux transfer events and the resulting plasma flows". Annales Geophysicae 16, n.º 11 (30 de noviembre de 1998): 1411–22. http://dx.doi.org/10.1007/s00585-998-1411-0.
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Abstract. The CUTLASS Finland radar has been run in a two-beam special scan mode, which offered excellent temporal and spatial information on the flows in the high-latitude ionosphere. A detailed study of one day of this data revealed a convection reversal boundary (CRB) in the CUTLASS field of view (f.o.v) on the dayside, the direction of plasma flow either side of the boundary being typical of a dawn-cell convection pattern. Poleward of the CRB a number of pulsed transients are observed, seemingly moving away from the radar. These transients are identified here as the ionospheric signature of flux transfer events (FTEs). Equatorward of the CRB continuous backscatter was observed, believed to be due to the return flow on closed field lines. The two-beam scan offered a new and innovative opportunity to determine the size and velocity of the ionospheric signatures associated with flux transfer events and the related plasma flow pattern. The transient signature was found to have an azimuthal extent of 1900 ± 900 km and an poleward extent of ∼250 km. The motion of the transient features was in a predominantly westward azimuthal direction, at a velocity of 7.5 ± 3 km.Key words. Magnetospheric physics (auroral phenomena; magnetopause · cusp and boundary layers; magnetosphere - ionosphere interaction)
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Ball, Lewis y Michael Vlassis. "Synchrotron Bubbles and Radio Transients". Publications of the Astronomical Society of Australia 10, n.º 4 (1993): 342–45. http://dx.doi.org/10.1017/s132335800002600x.
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AbstractWe discuss a generalisation of the synchrotron bubble model which has been applied to short-lived radio transients which can peak and decay over just a few days. The assumptions of the simple model imply that when the flux is increasing with time, it must also be an increasing function of frequency. Observations of two recent radio transients, Nova Muscae 1991 and the Galactic Centre Transient, include the first data showing such a rising phase, and in both cases the radio flux was a decreasing function of frequency during the observed rising phases. Thus the simple synchrotron bubble model is inadequate, at least for these events. A fundamental feature of the simple model is the assumption that the process accelerating the radiating electrons ceases before the radio emission can escape. We relax this assumption by including an injection of electrons, with a constant energy spectrum, into the synchrotron bubble.
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Kim, Hyunjun y Sanghyun Kim. "Evaluation of chlorine decay models under transient conditions in a water distribution system". Journal of Hydroinformatics 19, n.º 4 (8 de marzo de 2017): 522–37. http://dx.doi.org/10.2166/hydro.2017.082.
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Residual chlorine concentration decreases along distribution networks because of factors such as water quality, physical properties of the pipeline, and hydraulic conditions. Hydraulic conditions are primarily governed by transient events generated by valve modulation or pumping action. We investigate the impact of transient events on the rate of chlorine decay under various flow conditions. To comprehensively compare the performance of existing chlorine models, 14 candidate models for chlorine concentration were used under various transient conditions. Two-dimensional (2D) transient flow analysis was conducted to investigate the unknown processes of chlorine decay under transient conditions. General formulations for modeling chlorine decay were used to comprehensively study the decay under unsteady conditions and to effectively incorporate the impact of transients into generic model structures. The chlorine decay patterns in the constructed water distribution system were analyzed in the context of transient events. Linear relationships between the model parameters and the frequency of transient events were determined under unsteady conditions, and the impact of turbulence intensity was successfully incorporated into model parameter evaluations. The modeling results from 2D transient analysis exhibit similar predictability as those obtained from calibration using the genetic algorithm.
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Kuiack, Mark J., Ralph A. M. J. Wijers, Aleksandar Shulevski y Antonia Rowlinson. "Apparent radio transients mapping the near-Earth plasma environment". Monthly Notices of the Royal Astronomical Society 504, n.º 4 (26 de abril de 2021): 4706–15. http://dx.doi.org/10.1093/mnras/stab1156.
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ABSTRACT We report the discovery of bright, fast, radio flashes lasting tens of seconds with the AARTFAAC high-cadence all-sky survey at 60 MHz. The vast majority of these coincide with known, bright radio sources that brighten by factors of up to 100 during such an event. We attribute them to magnification events induced by plasma near the Earth, most likely in the densest parts of the ionosphere. They can occur both in relative isolation, during otherwise quiescent ionospheric conditions, and in large clusters during more turbulent ionospheric conditions. Using a toy model, we show that the likely origin of the more extreme (up to a factor of 100 or so) magnification events likely originate in the region of peak electron density in the ionosphere, at an altitude of 300–400 km. Distinguishing these events from genuine astrophysical transients is imperative for future surveys searching for low frequency radio transient at time-scales below a minute.
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Hong, Junho, Yong-Hwa Kim, Hong Nhung-Nguyen, Jaerock Kwon y Hyojong Lee. "Deep-Learning Based Fault Events Analysis in Power Systems". Energies 15, n.º 15 (30 de julio de 2022): 5539. http://dx.doi.org/10.3390/en15155539.
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The identification of fault types and their locations is crucial for power system protection/operation when a fault occurs in the lines. In general, this involves a human-in-the-loop analysis to capture the transient voltage and current signals using a common format for transient data exchange for power systems (COMTRADE) file. Then, protection engineers can identify the fault types and the line locations after the incident. This paper proposes intelligent and novel methods of faulty line and location detection based on convolutional neural networks in the power system. The three-phase fault information contained in the COMTRADE file is converted to an image file and extracted adaptively by the proposed CNN, which is trained by a large number of images under various kinds of fault conditions and factors. A 500 kV power system is simulated to generate different types of electromagnetic fault transients. The test results show that the proposed CNN-based analyzer can classify the fault types and locations under various conditions and reduce the fault analysis efforts.
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Hodgkin, Simon T., Łukasz Wyrzykowski, Nadejda Blagorodnova y Sergey Koposov. "Transient astronomy with the Gaia satellite". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 371, n.º 1992 (13 de junio de 2013): 20120239. http://dx.doi.org/10.1098/rsta.2012.0239.
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Gaia is a cornerstone European Space Agency astrometry space mission and a successor to the Hipparcos mission. Gaia will observe the whole sky for 5 years, providing a serendipitous opportunity for the discovery of large numbers of transient and anomalous events, e.g. supernovae, novae and microlensing events, gamma-ray burst afterglows, fallback supernovae, as well as theoretical or unexpected phenomena. In this paper, we discuss our preparations to use Gaia to search for transients at optical wavelengths, and briefly describe the early detection, classification and prompt publication of anomalous sources.
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Bayguinov, Orline, Brian Hagen, Adrian D. Bonev, Mark T. Nelson y Kenton M. Sanders. "Intracellular calcium events activated by ATP in murine colonic myocytes". American Journal of Physiology-Cell Physiology 279, n.º 1 (1 de julio de 2000): C126—C135. http://dx.doi.org/10.1152/ajpcell.2000.279.1.c126.
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ATP is a candidate enteric inhibitory neurotransmitter in visceral smooth muscles. ATP hyperpolarizes visceral muscles via activation of small-conductance, Ca2+-activated K+ (SK) channels. Coupling between ATP stimulation and SK channels may be mediated by localized Ca2+ release. Isolated myocytes of the murine colon produced spontaneous, localized Ca2+ release events. These events corresponded to spontaneous transient outward currents (STOCs) consisting of charybdotoxin (ChTX)-sensitive and -insensitive events. ChTX-insensitive STOCs were inhibited by apamin. Localized Ca2+ transients were not blocked by ryanodine, but these events were reduced in magnitude and frequency by xestospongin C (Xe-C), a blocker of inositol 1,4,5-trisphosphate receptors. Thus we have termed the localized Ca2+ events in colonic myocytes “Ca2+ puffs.” The P2Y receptor agonist 2-methylthio-ATP (2-MeS-ATP) increased the intensity and frequency of Ca2+ puffs. 2-MeS-ATP also increased STOCs in association with the increase in Ca2+ puffs. Pyridoxal-phospate-6-azophenyl-2′,4′-disculfonic acid tetrasodium, a P2 receptor inhibitor, blocked responses to 2-MeS-ATP. Spontaneous Ca2+ transients and the effects of 2-MeS-ATP on Ca2+ puffs and STOCs were blocked by U-73122, an inhibitor of phospholipase C. Xe-C and ryanodine also blocked responses to 2-MeS-ATP, suggesting that, in addition to release from IP3receptor-operated stores, ryanodine receptors may be recruited during agonist stimulation to amplify release of Ca2+. These data suggest that localized Ca2+ release modulates Ca2+-dependent ionic conductances in the plasma membrane. Localized Ca2+ release may contribute to the electrical responses resulting from purinergic stimulation.