The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Shouguo Wang - One of the best experts on this subject based on the ideXlab platform.
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borides of preferred orientation formed in the transient liquid phase joint of γ strengthened co base single crystal superalloy
Materials Letters, 2019Co-Authors: Shouguo Wang, Y P Sun, Xiaorui Hou, C Y Cui, X F Sun, Y Z ZhouAbstract:Abstract γ′-Strengthened Co-base single crystal superalloy was jointed with B-Ni76CrWB alloy powder by transient liquid phase bonding. The growth mechanism of the borides of preferred orientation formed in the diffusion affect zone of the joint was investigated. Results indicated that the prepared borides were (Co,W,Ta)3B2 and were long plate-shaped in three dimensions. The preferred growth orientation of the borides in the diffusion affect zone of transient liquid phase joint was 〈0 0 1〉 matrix, enjoying a significant orientation relationship with the substrate.
P Brown - One of the best experts on this subject based on the ideXlab platform.
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using large meteoroids as global infrasound reference events
2015 AGU Fall Meeting, 2019Co-Authors: Christoph Pilger, Lars Ceranna, Alexis Le Pichon, P BrownAbstract:The explosive fragmentation of large meteoroids entering the Earth’s atmosphere is one of the strongest sources of infrasound and can be detected at distances of thousands of kilometers by arrays all over the world. Influence parameters on the detection capability are quantified for a single infrasound station and for the complete infrasound network of the International Monitoring System (IMS) operated by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO). They are applied to a number of strong Bolides of the past 15 years including the 2013 Chelyabinsk, 2010 Sulawesi, and 2009 North Pacific events. Long-range infrasound propagation modeling and realistic atmospheric background conditions are used to identify propagation paths that connect the sources and globally distributed receivers, highlighting usual as well as unusual propagation pattern, to stations detecting and stations not detecting a meteorite event. Potential influences on infrasound detection capability are due to the directivity of the acoustic source energy emission, the long-range ducting via stratosphere and thermosphere and the diurnal change of meteorological parameters and noise conditions at the stations during the signal arrivals. Since infrasound of large Bolides has probably the most similar characteristics to an atmospheric nuclear explosion, it can be utilized as reference event for studies on the global performance of the CTBTO infrasound network. Detections and non-detections of bolide infrasound at the more than 40 operational IMS infrasound stations are studied for the estimation of station and network performance and thus verification of nuclear test ban.
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infrasound production by Bolides a global statistical study
Journal of Atmospheric and Solar-Terrestrial Physics, 2012Co-Authors: T Ens, P Brown, Wayne N Edwards, E A SilberAbstract:Abstract We have examined a dataset consisting of 71 Bolides detected by satellite sensors, which provide energy and location estimates, with simultaneous measurements of the same events on 143 distinct waveforms. These Bolides have total source energies ranging from 0.02 kt TNT equivalent yield to ≈ 20 kt and probable diameters of order a few meters on average. We find that it is possible to detect large events with energies of ≈ 20 kt or more globally. Infrasonic detections of these events for stratospheric arrivals have ranges between 350–17,000 km and show clear wind-related amplitude modifications. We find that our period–yield relations are virtually identical to that found from AFTAC nuclear test data with the most robust period–yield correlation found for those events having multiple station averaged periods. We have also found empirical expressions relating maximum expected detection range for infrasound as a function of energy and low and high frequency cut-off as a function of energy. Our multi-variate fits suggest that 1 2 yield-scaling is most appropriate for long range bolide infrasound measurements with a distance scaling exponent of ≈ 1.1 best representing the data. Our best-fit wind correction exponent is a factor of ≈ 3 smaller than found by previous studies which we suggest may indicate a decrease in the value of k with range. We find that the integral acoustic efficiency for Bolides is ≥ 0.01 % with a best lower limit estimate nearer 0.1%. Finally, we conclude that a range independent atmosphere implementation of the normal-mode approach to simulate bolide amplitudes is ineffective at large ranges due to the large change in atmospheric conditions along source-receiver paths.
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an estimate of the terrestrial influx of large meteoroids from infrasonic measurements
Journal of Geophysical Research, 2009Co-Authors: Elizabeth A Silber, P Brown, Douglas O Revelle, Wayne N EdwardsAbstract:[1] The influx rate of meteoroids hitting the Earth is most uncertain at sizes of � 10 m. Here we make use of historical data of large Bolides recorded infrasonically over a period of 13 years by the U.S. Air Force Technical Applications Center (AFTAC) to refine the terrestrial influx rate at these sizes. Several independent techniques were applied to these airwave data to calculate bolide kinetic energies. At low energies our flux results are within a factor of two in agreement with previous estimates. For 5–20-m diameter objects, however, our measurements of the cumulative number of Earth-impacting meteoroids are as much as an order of magnitude higher than estimates from telescopic surveys of near-Earth objects and satellite-detected Bolides impacting the Earth. The precise cause of this disagreement is unclear, though we propose several possible explanations. From our infrasound study, our best estimate for the cumulative annual flux of impactors with energy equal to or greater than E (in kilotons of TNT equivalent) is N = 4.5 E � 0.6 .
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global detection of infrasonic signals from three large Bolides
Earth Moon and Planets, 2008Co-Authors: Stephen J Arrowsmith, Douglas O Revelle, Wayne N Edwards, P BrownAbstract:We present the infrasonic observations of three large Bolides that were observed at numerous International Monitoring System (IMS) infrasound arrays on a global scale. First, a simple procedure for the global association of infrasound detections from large infrasound events is outlined. Infrasound signals are associated with large events based on arrival time, backazimuth and uniqueness at a given IMS array. Next, we apply the algorithm to three Bolides and investigate some of the factors affecting the detectability of infrasound from large events. Our findings suggest that site-noise effects significantly degrade the capability of the IMS infrasound network, suggesting that more effort is required to reduce ambient site noise. These results have implications for the use of infrasound measurements (in particular those from IMS stations) as a tool for evaluating the global flux of near-Earth objects.
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multi station infrasonic observations of two large Bolides signal interpretation and implications for monitoring of atmospheric explosions
Geophysical Research Letters, 2002Co-Authors: P Brown, Douglas O Revelle, Rodney W Whitaker, E TagliaferriAbstract:[1] Observations of two large Bolides occurring over the Western Pacific on August 25, 2000 and April 23, 2001 are presented. These large Bolides produced infrasonic signals at numerous stations in the Americas and Europe as well as being observed by US Department of Defence satellite sensors. The energy, location and physical characteristics of these Bolides is inferred from available infrasound records and compared to satellite data. The infrasonic energy of the events from the observed signal frequencies is estimated to be 3 kT and 1 kT respectively, while the satellite energies are approximately 3 kT and 11 kT. The disagreement in energies for the April 23, 2001 (the third largest satellite observed bolide on record) event is significant and indicates acoustic/optical processes not typical of most Bolides. The integrated infrasonic acoustic energy of the signals indicates that the percentage of acoustic energy deposited into the atmosphere is a minimum of ∼0.1–1% of the total source energy for each event.
I V Nemtchinov - One of the best experts on this subject based on the ideXlab platform.
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Bolides produced by impacts of large meteoroids into the earth s atmosphere comparison of theory with observations i benesov bolide dynamics and fragmentation
Astronomy and Astrophysics, 1998Co-Authors: Jiři Borovicka, P Spurný, O P Popova, I V Nemtchinov, Zdenek CeplechaAbstract:Detailed analysis of one of the largest and well doc- umented Bolides - the Benebolide (EN 070591) - has been performed. The bolide had an initial velocity of 21 km s 1 , reached a maximal absolute magnitude of 19:5 at the altitude of 24 km and radiated down to 17 km. Detailed photographic data for the light curve, geometry and dynamics of the main body and several fragments are available. This enabled us to test the theoretical radiative-hydrodynamic model used previously for the analysis of satellite-detected Bolides. The conventional analysis produces a huge discrepancy between the dynamic (80-300 kg) and photometric (5000- 13,000 kg) mass. The discrepancy might be removed assuming a low density of 0.5 g cm 3 but this is unrealistic. The radiative- hydrodynamic modeling yielded a mass of 2000 kg and density of 1-2 g cm 3 . However, the dynamics was not sufficiently well reproduced. There is direct observational evidence of meteoroid frag- mentation at altitudes of 38-31 km and of catastrophic disrup- tion at 24 km. These, however, do not explain the problem with the mass. The crucial point is that the bolide was significantly decelerated already at the altitudes between 50-40 km, while enormous luminosity was produced below 40 km. We suggest that the meteoroid must have been fragmented into 10-30 pieces of a mass of 100-300 kg already at an altitude of 60-50 km. By creating a progressive fragmentation model with two types of fragmentation at three different altitude levels, we were able to reproduce the dynamics and luminosity sufficiently well. The best estimate of the initial mass is 3000-4000 kg for a density of 2gc m 3 . The comparison with the bolide PN 39434 suggests that the behavior of Beneis typical for large stony meteoroids. Early fragmentation under dynamic pressures of the order of 1 Mdyn cm 2 is very important. The analysis of the light curve with the radiative-hydrodynamic model can give good order-of- magnitude estimates of mass, if no dynamic data are available.
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Bolides produced by impacts of large meteoroids into the earth s atmosphere comparison of theory with observations ii benesov bolide spectra
Astronomy and Astrophysics, 1998Co-Authors: Jiři Borovicka, O P Popova, A P Golub, I B Kosarev, I V NemtchinovAbstract:The unique observational spectrum of the very bright Benesov bolide EN 070591 is compared to theoretical bolide spectra. The −19.5 mag bolide was induced by a meteoroid of an estimated initial mass of 4000 kg, a density of 2 g cm−3 and a kinetic energy of1012 J (0.2 kT TNT). The ablating piston model predicts spectra of large Bolides by radiative hydrodynamics calculations. We present examples of the calculated H-chondrite vapor spectral opacities and of the resulting spectra for various parameters. Both theoretical and observed spectra show that bolide radiation is composed of atomic line emissions, molecular bands and continuum radiation. The role of the continuum increases with increasing meteoroid size and with decreasing altitude. The atomic lines are produced under the effective excitation temperature of 4000–6000 K. The lines of Fe i are too faint and the lines of Ca i are too bright in the model in comparison with the observations. Also the computed continuum level is too high. These differences can be explained by the fact that the vapors occupy a larger volume and have lower density than predicted. This is probably a consequence of a mutual interaction of fragments after the meteoroid fragmentation and of a not well understood ablation process. Other differences between the theory and the observation are described and possible model improvements are discussed.
Y Z Zhou - One of the best experts on this subject based on the ideXlab platform.
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borides of preferred orientation formed in the transient liquid phase joint of γ strengthened co base single crystal superalloy
Materials Letters, 2019Co-Authors: Shouguo Wang, Y P Sun, Xiaorui Hou, C Y Cui, X F Sun, Y Z ZhouAbstract:Abstract γ′-Strengthened Co-base single crystal superalloy was jointed with B-Ni76CrWB alloy powder by transient liquid phase bonding. The growth mechanism of the borides of preferred orientation formed in the diffusion affect zone of the joint was investigated. Results indicated that the prepared borides were (Co,W,Ta)3B2 and were long plate-shaped in three dimensions. The preferred growth orientation of the borides in the diffusion affect zone of transient liquid phase joint was 〈0 0 1〉 matrix, enjoying a significant orientation relationship with the substrate.
Jiři Borovicka - One of the best experts on this subject based on the ideXlab platform.
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Bolides produced by impacts of large meteoroids into the earth s atmosphere comparison of theory with observations i benesov bolide dynamics and fragmentation
Astronomy and Astrophysics, 1998Co-Authors: Jiři Borovicka, P Spurný, O P Popova, I V Nemtchinov, Zdenek CeplechaAbstract:Detailed analysis of one of the largest and well doc- umented Bolides - the Benebolide (EN 070591) - has been performed. The bolide had an initial velocity of 21 km s 1 , reached a maximal absolute magnitude of 19:5 at the altitude of 24 km and radiated down to 17 km. Detailed photographic data for the light curve, geometry and dynamics of the main body and several fragments are available. This enabled us to test the theoretical radiative-hydrodynamic model used previously for the analysis of satellite-detected Bolides. The conventional analysis produces a huge discrepancy between the dynamic (80-300 kg) and photometric (5000- 13,000 kg) mass. The discrepancy might be removed assuming a low density of 0.5 g cm 3 but this is unrealistic. The radiative- hydrodynamic modeling yielded a mass of 2000 kg and density of 1-2 g cm 3 . However, the dynamics was not sufficiently well reproduced. There is direct observational evidence of meteoroid frag- mentation at altitudes of 38-31 km and of catastrophic disrup- tion at 24 km. These, however, do not explain the problem with the mass. The crucial point is that the bolide was significantly decelerated already at the altitudes between 50-40 km, while enormous luminosity was produced below 40 km. We suggest that the meteoroid must have been fragmented into 10-30 pieces of a mass of 100-300 kg already at an altitude of 60-50 km. By creating a progressive fragmentation model with two types of fragmentation at three different altitude levels, we were able to reproduce the dynamics and luminosity sufficiently well. The best estimate of the initial mass is 3000-4000 kg for a density of 2gc m 3 . The comparison with the bolide PN 39434 suggests that the behavior of Beneis typical for large stony meteoroids. Early fragmentation under dynamic pressures of the order of 1 Mdyn cm 2 is very important. The analysis of the light curve with the radiative-hydrodynamic model can give good order-of- magnitude estimates of mass, if no dynamic data are available.
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Bolides produced by impacts of large meteoroids into the earth s atmosphere comparison of theory with observations ii benesov bolide spectra
Astronomy and Astrophysics, 1998Co-Authors: Jiři Borovicka, O P Popova, A P Golub, I B Kosarev, I V NemtchinovAbstract:The unique observational spectrum of the very bright Benesov bolide EN 070591 is compared to theoretical bolide spectra. The −19.5 mag bolide was induced by a meteoroid of an estimated initial mass of 4000 kg, a density of 2 g cm−3 and a kinetic energy of1012 J (0.2 kT TNT). The ablating piston model predicts spectra of large Bolides by radiative hydrodynamics calculations. We present examples of the calculated H-chondrite vapor spectral opacities and of the resulting spectra for various parameters. Both theoretical and observed spectra show that bolide radiation is composed of atomic line emissions, molecular bands and continuum radiation. The role of the continuum increases with increasing meteoroid size and with decreasing altitude. The atomic lines are produced under the effective excitation temperature of 4000–6000 K. The lines of Fe i are too faint and the lines of Ca i are too bright in the model in comparison with the observations. Also the computed continuum level is too high. These differences can be explained by the fact that the vapors occupy a larger volume and have lower density than predicted. This is probably a consequence of a mutual interaction of fragments after the meteoroid fragmentation and of a not well understood ablation process. Other differences between the theory and the observation are described and possible model improvements are discussed.