Segui questo link per vedere altri tipi di pubblicazioni sul tema: Accelerated Flames.
Articoli di riviste sul tema "Accelerated Flames"
Cita una fonte nei formati APA, MLA, Chicago, Harvard e in molti altri stili
Vedi i top-50 articoli di riviste per l'attività di ricerca sul tema "Accelerated Flames".
Accanto a ogni fonte nell'elenco di riferimenti c'è un pulsante "Aggiungi alla bibliografia". Premilo e genereremo automaticamente la citazione bibliografica dell'opera scelta nello stile citazionale di cui hai bisogno: APA, MLA, Harvard, Chicago, Vancouver ecc.
Puoi anche scaricare il testo completo della pubblicazione scientifica nel formato .pdf e leggere online l'abstract (il sommario) dell'opera se è presente nei metadati.
Vedi gli articoli di riviste di molte aree scientifiche e compila una bibliografia corretta.
1
Lou, Bo, Yonghai Qiu e Jianhong Xu. "Characteristics of diffusion flames with accelerated motion". Thermal Science 20, n. 6 (2016): 2113–24. http://dx.doi.org/10.2298/tsci150413180l.
Testo completoAbstract (sommario):
The aim of this work is to present an experiment to study the characteristics of a laminar diffusion flame under acceleration. A Bunsen burner (nozzle diameter 8 mm), using liquefied petroleum gas as its fuel, was ignited under acceleration. The temperature field and the diffusion flame angle of inclination were visualised with the assistance of the visual display technology incorporated in MATLAB?. Results show that the 2-d temperature field under different accelerations matched the variation in average temperatures: they both experience three variations at different time and velocity stages. The greater acceleration has a faster change in average temperature with time, due to the accumulation of combustion heat: the smaller acceleration has a higher average temperature at the same speed. No matter what acceleration was used, in time, the flame angle of inclination increased, but the growth rate decreased until an angle of 90?: this could be explained by analysis of the force distribution within the flame. It is also found that, initially, the growth rate of angle with velocity under the greater acceleration was always smaller than that at lower accelerations; it was also different in flames with uniform velocity fire conditions.
2
Zhu, Yuejin, Lei Yu, Gang Dong, Jianfeng Pan e Zhenhua Pan. "Flow Topology of Three-Dimensional Spherical Flame in Shock Accelerated Flows". Advances in Materials Science and Engineering 2016 (2016): 1–12. http://dx.doi.org/10.1155/2016/3158091.
Testo completoAbstract (sommario):
The flow topologies of compressible large-scale distorted flames are studied by means of the analysis of the invariants of the velocity gradient tensor (VGT). The results indicate that compressibility plays a minor role in the distorted flame zone. And the joint probability density function (p.d.f.) of the Q-R diagram appears as a teardrop shape, which is a universal feature of turbulence. Therefore, the distorted flame exhibits the characteristic of large-scale turbulence combustion, especially behind the reflected shock wave, while the p.d.f. of the QS⁎-QW diagram implies that the dissipation is enhanced in the compression and expansion regions, where it is higher than that when P=0. Furthermore, we identify that the flame evolution is dominated by rotation by means of a quantitative statistical study, and the SFS topology is the predominant flow pattern. Not surprisingly, negative dilatation could suppress the unstable topologies, whereas positive dilatation could suppress the stable topologies.
3
Dunn-Rankin, D., e M. A. McCann. "Overpressures from nondetonating, baffle-accelerated turbulent flames in tubes". Combustion and Flame 120, n. 4 (marzo 2000): 504–14. http://dx.doi.org/10.1016/s0010-2180(99)00109-1.
Testo completo
4
Boettcher, Philipp A., Shyam K. Menon, Brian L. Ventura, Guillaume Blanquart e Joseph E. Shepherd. "Cyclic flame propagation in premixed combustion". Journal of Fluid Mechanics 735 (23 ottobre 2013): 176–202. http://dx.doi.org/10.1017/jfm.2013.495.
Testo completoAbstract (sommario):
AbstractIn experiments of hot surface ignition and subsequent flame propagation, a puffing flame instability is observed in mixtures that are stagnant and premixed prior to ignition. By varying the size of the hot surface, power input, and combustion vessel volume, it was determined that the instability is a function of the interaction of the flame, with the fluid flow induced by the combustion products rather than the initial plume established by the hot surface. Pressure ranges from 25 to 100 kPa and mixtures of n-hexane/air with equivalence ratios between $\phi = 0. 58$ and 3.0 at room temperature were investigated. Equivalence ratios between $\phi = 2. 15$ and 2.5 exhibited multiple flame and equivalence ratios above $\phi = 2. 5$ resulted in puffing flames at atmospheric pressure. The phenomenon is accurately reproduced in numerical simulations and a detailed flow field analysis revealed competition between the inflow velocity at the base of the flame and the flame propagation speed. The increasing inflow velocity, which exceeds the flame propagation speed, is ultimately responsible for creating a puff. The puff is then accelerated upward, allowing for the creation of the subsequent instabilities. The frequency of the puff is proportional to the gravitational acceleration and inversely proportional to the flame speed. A scaling relationship describes the dependence of the frequency on gravitational acceleration, hot surface diameter, and flame speed. This relation shows good agreement for rich n-hexane/air and lean hydrogen/air flames, as well as lean hexane/hydrogen/air mixtures.
5
Kiverin, Alexey, Alexey Tyurnin e Ivan Yakovenko. "On the Critical Condition for Flame Acceleration in Hydrogen-Based Mixtures". Materials 16, n. 7 (31 marzo 2023): 2813. http://dx.doi.org/10.3390/ma16072813.
Testo completoAbstract (sommario):
The paper presents a novel numerical approach to the quantitative estimation of the concentration limits for flame acceleration in hydrogen-based mixtures. A series of calculations are carried out for hydrogen–air and hydrogen–oxygen flames in channels. The analysis of the obtained numerical results provided the value of 11 ± 0.25 % hydrogen content in the mixture as a lean concentration limit of flame acceleration that agrees well with the available experimental data. Moreover, the basic physical mechanism responsible for the transition from the steady mode of flame propagation to the accelerated one is distinguished. The mechanism is related to flame stretching in the region of interaction with the boundary layer and the competition between the joint increase in burning rate and heat losses. The novel technique for the estimation of concentration limits of flame acceleration presented here can be applied to assess combustion conditions inside combustors of energy and propulsion systems fed with hydrogen. The results are also useful in estimating explosion and fire risks in hydrogen storage, transport, and utilization facilities as parts of hydrogen energy and propulsion systems.
6
Xu, Cong, Junguang Lin, Zhihua Wang, Kaidi Wan, Shien Sun e Zhijun Zhou. "Three-Dimensional Direct Numerical Simulation of Near-Field Ozone-Enhanced Lean Premixed Syngas Turbulent Jet Flame". Energies 15, n. 11 (26 maggio 2022): 3945. http://dx.doi.org/10.3390/en15113945.
Testo completoAbstract (sommario):
Due to its enhancement in the flame speed, ozone added in lean premixed syngas turbulent jet flame was investigated by the three-dimensional direct numerical simulation method in the near field of the flame. In the present study, numerical simulations were conducted in the lean premixed syngas turbulent jet flame configuration to explore the effects of ozone addition on freely-propagating turbulent flames. It was seen that turbulence began to significantly affect the flame surface to produce wrinkles in lean premixed gas flame with ozone added after 4D; ozone started to affect the composition field and temperature field after 8D; it accelerated the generation of intermediate products, OH and O radicals; and it will promote the production of CO2 in the near field range. Ozone will increase the flame surface area of the lean premixed syngas flame during the ignition period and can promote the ignition process and make the combustion occur earlier. The flame surface of the case with ozone added is more easily stretched by turbulence, and ozone can improve the stability of combustion. Ozone does not affect the effective radius of the flame curvature but will broaden the distribution of the curvature term because of the enhancement effect on the displacement speed of the flame surface.
7
Di Sarli, V., A. Di Benedetto, G. Russo, S. Jarvis, E. J. Long e G. K. Hargrave. "Large Eddy Simulation and PIV Measurements of Unsteady Premixed Flames Accelerated by Obstacles". Flow, Turbulence and Combustion 83, n. 2 (11 febbraio 2009): 227–50. http://dx.doi.org/10.1007/s10494-008-9198-3.
Testo completo
8
Zhang, Xiaoliang, Shibing Kuang, Yanli Zhao, Jun Zhang e Shengfeng Luo. "Experimental Investigation and Theoretical Analysis of Flame Spread Dynamics over Discrete Thermally Thin Fuels with Various Inclination Angles and Gap Sizes". Fire 7, n. 6 (23 maggio 2024): 177. http://dx.doi.org/10.3390/fire7060177.
Testo completoAbstract (sommario):
Flame spread over discrete fuels is a typical phenomenon in fire scenes. Experimental and theoretical research on flame spread over discrete thermally thin fuels separated by air gaps with different inclination angles was conducted in the present study. Experiments with six inclination angles ranging from 0° to 85° and various fuel coverage rates from 0.421 to 1 were designed. The flame spread behavior, the characteristic flame size, and the flame spread rate were analyzed. The results show that the flow pattern, stability, and flame size exhibit different characteristics with different inclination angles and gap sizes. As the inclination angle increases, particularly with smaller gaps, turbulent and oscillating flames are observed, while larger gap sizes promote flame stability. The mechanism of flame propagation across the gap depends on the interplay between the flame jump effect and heat transfer, which evolves with gap size. Average flame height, average flame width, and flame spread rate initially increase and then decline with the increase in fuel coverage, peaking at fuel coverage rates between 0.93 and 0.571 for different inclination angles. A theoretical model is proposed to predict the flame spread rate and the variation in the flame spread rate with inclination angle and fuel coverage. Furthermore, the map determined by inclination angle and fuel coverage is partitioned into distinct regions, comprising the accelerated flame spread region, the flame spread weakening region, and the failed flame spread region. These findings provide valuable insights into flame spread dynamics over discrete thermally thin fuels under diverse conditions.
9
Schneider, F. R. N., O. H. Ramírez-Agudelo, F. Tramper, J. M. Bestenlehner, N. Castro, H. Sana, C. J. Evans et al. "The VLT-FLAMES Tarantula Survey". Astronomy & Astrophysics 618 (ottobre 2018): A73. http://dx.doi.org/10.1051/0004-6361/201833433.
Testo completoAbstract (sommario):
The 30 Doradus (30 Dor) nebula in the Large Magellanic Cloud (LMC) is the brightest HII region in the Local Group and a prototype starburst similar to those found in high redshift galaxies. It is thus a stepping stone to understand the complex formation processes of stars in starburst regions across the Universe. Here, we have studied the formation history of massive stars in 30 Dor using masses and ages derived for 452 mainly OB stars from the spectroscopic VLT-FLAMES Tarantula Survey (VFTS). We find that stars of all ages and masses are scattered throughout 30 Dor. This is remarkable because it implies that massive stars either moved large distances or formed independently over the whole field of view in relative isolation. We find that both channels contribute to the 30 Dor massive star population. Massive star formation rapidly accelerated about 8 Myr ago, first forming stars in the field before giving birth to the stellar populations in NGC 2060 and NGC 2070. The R136 star cluster in NGC 2070 formed last and, since then, about 1 Myr ago, star formation seems to be diminished with some continuing in the surroundings of R136. Massive stars within a projected distance of 8 pc of R136 are not coeval but show an age range of up to 6 Myr. Our mass distributions are well populated up to 200 M⊙. The inferred IMF is shallower than a Salpeter-like IMF and appears to be the same across 30 Dor. By comparing our sample of stars to stellar models in the Hertzsprung–Russell diagram, we find evidence for missing physics in the models above log L/L⊙ = 6 that is likely connected to enhanced wind mass loss for stars approaching the Eddington limit. Our work highlights the key information about the formation, evolution and final fates of massive stars encapsulated in the stellar content of 30 Dor, and sets a new benchmark for theories of massive star formation in giant molecular clouds.
10
Hamed, AM, AE Hussin, MM Kamal e AR Elbaz. "Combustion of a hydrogen jet normal to multiple pairs of opposing methane–air mixtures". Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 231, n. 2 (6 gennaio 2017): 145–58. http://dx.doi.org/10.1177/0957650916685944.
Testo completoAbstract (sommario):
The combustion performance of a cylindrical burner accommodating up to six multiple pairs of opposing methane–air mixtures with a cross-flow of hydrogen was addressed. The cross-flow initially duplicated the stagnation impact and enriched the vortical structures. Aided by the resulting flow strain, the transport of heat and active species from the hydrogen oxidation zone to the methane reaction zones accelerated the combustion across the opposing premixed flames and reduced the peak temperature across the outer diffusion flame. Increasing the cross-flow/opposing jets’ velocity ratio to 0.89 merged the two stagnation centers and maximized the shearing stress. By the slight increase in the velocity ratio to 1.07, the H and OH pools provided for methane combustion became closer to the ports such that a hydrogen/methane mass percent of 10.3% extended the stoichiometric blowout velocity from 28.3 to 35.7 m/s. Since the turbulent kinetic energy thus increased to 8.4 m2/s2, the firing intensity reached values as high as 48.2 MW/m3. Not only was there a reduction in the residence time for NOx formation, but also the blowout velocity relative gain overrode the relative increase in the NOx formation rates such that the NOx emission index decreased to 17 g/MWhr. By the excessive increase in velocity ratio, the vortical structures shrank such that the NOx exponential increase became dominant above 21 ppm. With fuel-lean mixtures, the hydrogen was partially combusted by the excess air from the opposing flames but the blowout velocity decreased to 13.1 m/s at Φ = 0.50. The hydrogen flame NOx emissions decreased by providing the excess air at larger jets’ diameter/separation ratios, thus reducing the residence times for thermal NOx formation and simultaneously interrupting the prompt NOx formation. At the lean operational limit, tripling the number of opposing jets decreased the hydrogen flame length by 54% such that the NOx emissions decreased by 38.4%.
11
Otta, Eliana. "Manifesto: Fertilizing mourning – Global South’s offering to a world in flames". Journal of Greek Media & Culture 8, n. 2 (1 ottobre 2022): 247–57. http://dx.doi.org/10.1386/jgmc_00060_1.
Testo completoAbstract (sommario):
This manifesto takes the coincidence of Peru’s and Greece’s bicentennials of independence, and their overlap with the COVID-19 pandemic, as a departure point, in order to propose a different understanding of mourning from the Global South. The article is an open invitation to reinforce mourning’s capacity to be a reproductive life force, responding to contemporary experiences of loss in the face of the COVID-19 pandemic and the accelerated processes of extinction, especially in resource extraction zones, like the Amazon. Taking inspiration from ancient Indigenous techniques for soil regeneration, fertilizing mourning is a call to merge traditional knowledge, collective practices and non-anthropocentric world-views that resist individualism and capitalism both in the Global South and in places that defend communal life in the north of the planet. This manifesto proposes that to transform prevalent colonial, modern structures, it is necessary to develop a different relationship with nature, by reconsidering the entanglements between life, death and regeneration.
12
Pang, Kar Mun, Mehdi Jangi, Xue-Song Bai, Jesper Schramm e Jens Honore Walther. "Modelling of diesel spray flames under engine-like conditions using an accelerated Eulerian Stochastic Field method". Combustion and Flame 193 (luglio 2018): 363–83. http://dx.doi.org/10.1016/j.combustflame.2018.03.030.
Testo completo
13
Taniguchi, Masayuki, Hirofumi Okazaki, Hironobu Kobayashi, Shigeru Azuhata, Hiroshi Miyadera, Hidetaka Muto e Toshikazu Tsumura. "Pyrolysis and Ignition Characteristics of Pulverized Coal Particles". Journal of Energy Resources Technology 123, n. 1 (30 ottobre 2000): 32–38. http://dx.doi.org/10.1115/1.1347989.
Testo completoAbstract (sommario):
Pyrolysis and ignition characteristics of pulverized coals were examined under similar burning conditions to those of industrial burners. In the early stage, fine particles (less than 37 μm) were mainly pyrolyzed by convective heat transfer from surrounding gas. The coals ignited when pyrolyzed volatile matter mixed with surrounding air and formed a combustible mixture. Pyrolysis of large particles was delayed, but accelerated after ignition by radiant heat transfer from coal flames. The effects of radiant heat transfer were strong for intermediate-size particles (37–74 μm). Ignition temperature was examined analytically by using a modified distributed activation energy model for pyrolysis. The calculated results agreed with experimental ones obtained from both laboratory-scale and semi-industrial-scale burners.
14
Hincapié, Fredy F., e Manuel J. García. "A Surrogate Model of Heat Transfer Mechanism in a Domestic Gas Oven: A Numerical Simulation Approach for Premixed Flames". Applied Mechanics 5, n. 2 (14 giugno 2024): 391–404. http://dx.doi.org/10.3390/applmech5020023.
Testo completoAbstract (sommario):
This paper introduces an innovative analytical model to compute flame velocities and temperatures within a premix burner in a domestic gas oven. This model significantly streamlines the heat transfer simulation process by simplifying the modeling of the thermo-chemical energy release during combustion, effectively reducing complexity and computation time. Accelerated solutions are essential at the initial design stages when comparing the effect of the oven parameter variation on the overall performance. The validation of the proposed analytical model involved experimental assessments of the temperature of the false bottom plate in a natural gas oven. The resulting data were then compared against CFD simulations performed utilizing the proposed model. The results revealed a marginal discrepancy of 4% between the experimental measurements and the outcomes generated by the model. Simulations were executed under differing conditions, encompassing scenarios with and without radiation effects. This exploration identified natural convection as the predominant heat transfer mechanism, with heat radiation contributing only modestly to the heating of the false bottom plate. Among its advantages, the proposed model offers a notable reduction in the numerical complexity of the modeling of the combustion process. Furthermore, its straightforward integration into numerical simulations involving premixed flames underscores its practical utility and versatility in evaluating design performance at the early stages of the design. Highly accurate models can be left for the final oven configuration validation.
15
De Giorgi, M. G., G. Cinieri, G. Marseglia, Z. Ali Shah e Ghazanfar Mehdi. "Combustion Efficiency of Carbon-neutral Fuel using Micro-Combustor Designed for Aerospace Applications". Journal of Physics: Conference Series 2716, n. 1 (1 marzo 2024): 012091. http://dx.doi.org/10.1088/1742-6596/2716/1/012091.
Testo completoAbstract (sommario):
Abstract Recent advancements in the field of micro combustor research are growing for achieving high-performance systems in micro power generation and microelectromechanical devices. To mitigate the hazardous emissions from carbon fuels, as an alternative, zero-carbon-free fuels ammonia, and hydrogen are being explored in micro combustion processes. The distinctive feature of a micro combustor lies in its significantly higher area to volume ratio in comparison with traditional combustion systems, leading to accelerated combustion reaction rates. However, the small size of micro combustors poses a challenge in achieving efficient mixing of highly reactive fuels like hydrogen and ammonia with oxidizers. The unique properties of micro combustors can lead to differences in the combustion behavior of hydrogen and ammonia compared to larger-scale combustion systems. Hence, examining the performance of carbon-free fuels in micro combustors is crucial for the advancement of clean energy combustion systems. A numerical investigation on a Y-shaped micro-combustor was carried out to identify the aspects of non-premixed combustion of ammonia/air and hydrogen/air. The findings reveal that in the case of hydrogen combustion, stable flames were reached, even at low equivalence ratios. Therefore, the distinct combustion properties of hydrogen and ammonia result in varying NOx emissions, with hydrogen generally leading to higher NOx levels due to its higher flame temperature and increased thermal NOx production.
16
Lin, R. P. "Particle Acceleration in Solar Flares and Coronal Mass Ejections". Symposium - International Astronomical Union 195 (2000): 15–25. http://dx.doi.org/10.1017/s0074180900162746.
Testo completoAbstract (sommario):
The Sun accelerates ions up to tens of GeV and electrons up to 100s of MeV in solar flares and coronal mass ejections. The energy in the accelerated tens-of-keV electrons and possibly ~1 MeV ions constitutes a significant fraction of the total energy released in a flare, implying that the particle acceleration and flare energy release mechanisms are intimately related. The total rate of energy release in transients from flares down to microflares/nanoflares may be significant for heating the active solar corona.Shock waves driven by fast CMEs appear to accelerate the high-energy particles in large solar energetic particle events detected at 1 AU. Smaller SEP events are dominated by ~1 to tens-of-keV electrons, with low fluxes of up to a few MeV/nucleon ions, typically enriched in 3He. The acceleration in gamma-ray flares appears to resemble that in these small electron-3He SEP events.
17
Thomas, James Chris, Cythia Kunz, Max Fondren, Olivier Mathieu e Eric Petersen. "A Novel Framework for Consequence Prediction of Battery Thermal Runaway Failure Hazards". ECS Meeting Abstracts MA2023-01, n. 2 (28 agosto 2023): 563. http://dx.doi.org/10.1149/ma2023-012563mtgabs.
Testo completoAbstract (sommario):
Lithium-ion batteries (LIBs) are widely utilized for energy storage in a broad range of applications, such as handheld electronics, emobility, spaceflight vehicles, etc. Thermal runaway (TR) and subsequent combustion of LIBs represent several significant hazards to consumers, including substantial energy release, jet flames, toxic gases, airborne particulates, and secondary explosions. Numerous experimental investigations in the literature have measured the energy release and chemical composition of off-gasses during LIB TR, but little theoretical work has been completed to this end. The current study focuses on prediction of product chemical composition, flame temperature, and energy release for LIBs undergoing TR failure through implementation of chemical equilibrium analyses (CEA). Theoretical calculations for various LIB electrolyte decomposition and combustion scenarios were compared to data available in the literature. Excellent agreement was observed between predicted and experimental measured heats of combustion for plain LIB electrolytes, indicating the global thermodynamic properties are well captured by the modeling approach. Theoretical product gas production (i.e., moles of gas per mole of electrolyte) and composition were compared to experimentally measured values from accelerated rate calorimetry experiments. The results indicate that general trends are well captured by the CEA modeling approach developed here and that the standard experimental protocols documented within the literature can be improved. Similar theoretical predictions for battery failure experiments (product gas composition and energy release) are also presented. The novel modeling framework presented here can be used in future work to evaluate LIB failure hazards for existing systems and to evaluate the safety of future designs. In addition, this modeling approach provides unique insight into how adjusting global battery chemistry (cathode, electrolyte, etc.) changes the potential hazards produced battery thermal runaway and failure. Figure 1
18
KOVAL, Yu N., A. S. ANDREEV e N. Z. AGAFONOVA. "Analysis of the Application of Fire Protective Composition for Wooden Structures". Stroitel'nye Materialy 819, n. 11 (novembre 2023): 10–13. http://dx.doi.org/10.31659/0585-430x-2023-819-11-10-13.
Testo completoAbstract (sommario):
In construction, coniferous wood is usually used as load-bearing and enclosing structures. Wood is characterized by the ability to ignite and spread combustion when heated in air. Wooden building structures pose a fire hazard, since with an initial impulse of external thermal energy, ignition is possible. In addition, when a fire occurs in buildings and structures where wood is located, a number of dangerous fire factors arise: flames, sparks, heat flow, toxic combustion products, extremely low oxygen concentrations, decreased visibility due to smoke. In this regard, it becomes relevant to treat wood with special compounds that increase resistance to fire. The authors examined the fire hazardous properties of building structures made of wood, analyzed the fire retardant treatment of wooden structures with a special composition; examined the fire hazardous properties of building structures made of wood, the mechanism of pyrolysis, and the effect of fire retardant treatment on the behavior of wood when exposed to fire. The use of fire retardant significantly affected the pyrolysis processes of the samples. The information obtained during the study made it possible to assess the degree of differences in the values of the average weight loss of samples treated with different fire retardants. Samples using a fire retardant composition have a shallower charring depth. Damage associated with thermal exposure is fundamentally different from untreated samples. Treated and impregnated samples exhibit rapid weight loss. This is due to the fact that in treated and impregnated samples, when exposed to high temperatures in the oven, the reactions of dehydration and cross-linking of cellulose molecules are accelerated.
19
Gopalswamy, Nat. "The Sun and Space Weather". Atmosphere 13, n. 11 (28 ottobre 2022): 1781. http://dx.doi.org/10.3390/atmos13111781.
Testo completoAbstract (sommario):
The explosion of space weather research since the early 1990s has been partly fueled by the unprecedented, uniform, and extended observations of solar disturbances from space- and ground-based instruments. Coronal mass ejections (CMEs) from closed magnetic field regions and high-speed streams (HSS) from open-field regions on the Sun account for most of the disturbances relevant to space weather. The main consequences of CMEs and HSS are their ability to cause geomagnetic storms and accelerate particles. Particles accelerated by CME-driven shocks can pose danger to humans and their technological structures in space. Geomagnetic storms produced by CMEs and HSS-related stream interaction regions also result in particle energization inside the magnetosphere that can have severe impact on satellites operating in the magnetosphere. Solar flares are another aspect of solar magnetic energy release, mostly characterized by the sudden enhancement in electromagnetic emission at various wavelengths—from radio waves to gamma-rays. Flares are responsible for the sudden ionospheric disturbances and prompt perturbation of Earth’s magnetic field known as magnetic crochet. Nonthermal electrons accelerated during flares can emit intense microwave radiation that can drown spacecraft and radar signals. This review article summarizes major milestones in understanding the connection between solar variability and space weather.
20
Gong, Zhen, e Hao Tang. "Numerical Study of High-g Combustion Characteristics in a Channel with Backward-Facing Steps". Aerospace 11, n. 9 (19 settembre 2024): 767. http://dx.doi.org/10.3390/aerospace11090767.
Testo completoAbstract (sommario):
High gravity (high-g) combustion can significantly increase flame propagation speed, thereby potentially shortening the axial length of aero-engines and increasing their thrust-to-weight ratio. In this study, we utilized the large eddy simulation model to investigate the combustion characteristics and flame morphology evolution of premixed propane–air flames in a channel with a backward-facing step. The study reveals that both the increase in centrifugal force and flow velocity can enhance pressure fluctuations during combustion and increase the turbulence intensity. The presence of centrifugal force promotes the occurrence of Rayleigh–Taylor instability (RTI) between hot and cold fluids. The combined effects of RTI and Kelvin–Helmholtz instability (KHI) enhance the disturbance between hot and cold fluids, shorten the fuel combustion time, and intensify the dissipation of large-scale vortices. The increase in fluid flow velocity can raise the flame front’s hydrodynamic stretch rate, thereby enhancing the turbulence level during combustion to a certain extent and increasing the fuel consumption rate. When a strong centrifugal force is applied, the global flame propagation speed can be more than doubled. Within a certain range, the increase in high-g field strength can enhance the intensity of RTI and accelerate the transition of RTI to the nonlinear stage.
21
Liu, Duo, Shaochen Sun e Lin Wang. "Numerical Simulation of the Propagation of Premixed Gas in a Pipe Flame Arrestor". Journal of Physics: Conference Series 2488, n. 1 (1 maggio 2023): 012005. http://dx.doi.org/10.1088/1742-6596/2488/1/012005.
Testo completoAbstract (sommario):
Abstract In this paper, a numerical model of the propagation process of premixed gas in a pipeline flame arrestor is established and solved. The numerical simulation results show that the flame propagation velocity and pressure variation curves of the propane-air premixed gas are the same as those of the ethylene-air premixed gas. The flame front and pressure oscillate periodically throughout the process, and the flame speed oscillates down when the flame front reaches approximately the middle and rear of the pipe. In contrast, the flame velocity versus pressure curve for the explosion of hydrogen-air premixed gases is quite different, with the flame propagating at an almost constant velocity in the initial stages, accelerating suddenly when the flame front reaches near the middle of the pipe, reaching a peak, followed by an accelerated decrease in flame velocity; at the middle and rear of the pipe, the flame once again propagates at a nearly constant velocity, and as the flame is quenched, the flame propagation velocity once again accelerates and decreases. The explosion pressures of the propane-air and ethylene-air premixed gases at each measurement point in the pipeline increase linearly with the initial pressure, and the explosion pressure appreciation is very close. The explosion pressure of hydrogen-air premixes increases significantly with increasing initial pressure, but the increase decreases slightly. The increase in initial pressure increases the flame propagation rate of the premixed gas, and the acceleration effect is significant.
22
Wang, Yue, Xin Zhang, Xinmiao Fan e Yanfei Li. "Simulation and Research of Methane Premixed Combustion Characteristics Based on Constant Volume Combustion Chamber with Different Ignition Modes". Energies 16, n. 20 (10 ottobre 2023): 7016. http://dx.doi.org/10.3390/en16207016.
Testo completoAbstract (sommario):
Dual spark plug ignition can accelerate the burning velocity of nature gas and improve the engine performance. However, the mechanism between the two flames and the disturbance characteristics of flame to flow field during the combustion process under different ignition strategies are still unclear. In order to reduce the interference of other external factors, this paper is based on the CFD software CONVERGE 3.0, using G equations combined with SAGE detailed chemical reaction mechanism, the combustion model is constructed based on the closed constant volume combustion chamber. The accuracy of the model was verified using experimental data. The methane–air premixed combustion process under different ignition strategies (single spark ignition, dual spark synchronous ignition and dual spark asynchronous ignition) was simulated using this model. The results show that the flame propagation speeds under the dual spark ignition plan are all smaller than that of single spark ignition due to the inhibition of the opposite side flame. However, it still has obvious fast combustion characteristics, shortens the combustion duration and improves the heat release rate. The flame stability is optimum under synchronous ignition with the pressure offsetting effect, and with the increase in the ignition interval, the flame stability decreases, and the disturbance of the flow field gradually increases. There is little effect of ignition position on combustion pressure and heat release rate. Compared with single spark ignition and dual spark asynchronous ignition, dual spark synchronous ignition has better combustion characteristics. It can improve thermal efficiency while ensuring flame stability. This is a key technology for improving the natural gas engine performance.
23
MIROSHNICHENKO, L. I., e J. A. PEREZ-PERAZA. "ASTROPHYSICAL ASPECTS IN THE STUDIES OF SOLAR COSMIC RAYS". International Journal of Modern Physics A 23, n. 01 (10 gennaio 2008): 1–141. http://dx.doi.org/10.1142/s0217751x08037312.
Testo completoAbstract (sommario):
This review paper comprises main concepts, available observational data and recent theoretical results related to astrophysical aspects of particle acceleration at/near the Sun and extreme capacities of the solar accelerator(s). We summarize underground and ground-based observations of solar cosmic rays (SCR) accumulated since 1942, direct spacecraft measurements of solar energetic particles (SEP) near the Earth's orbit, indirect information on the SCR variations in the past, and other relevant astrophysical, solar and geophysical data. The list of the problems under discussion includes: upper limit spectrum (ULS) for solar cosmic rays; maximum energy (rigidity), Em(Rm), of particles accelerated at/near the Sun; production of the flare neutrinos; energetics of SCR and solar flares; production of flare neutrons and gamma rays; charge states and elemental abundances of accelerated solar ions; coronal mass ejections (CME's) and extended coronal structures in acceleration models; magnetic reconnection in acceleration scenarios; size (frequency) distributions of solar proton events (SPE) and stellar flares; occurrence probability of giant flares; archaeology of solar cosmic rays. The discussion allows us to outline a series of interesting conceptual and physical associations of SCR generation with the high-energy processes at other stars. The most reliable estimates of various parameters are given in each of research fields mentioned above; a set of promising lines of future studies is highlighted. A great importance of SCR data for resolving some general astrophysical problems is emphasized.
24
Han, Haoyang, Jundong Zhang e Ruizheng Jiang. "Feature Design Assessment of the Ship Fire Alarm System". Scientific Programming 2021 (23 luglio 2021): 1–12. http://dx.doi.org/10.1155/2021/3934428.
Testo completoAbstract (sommario):
Damages and misfortunes caused by fire on ships have recently accelerated the creation of new approaches, development, and building the security and unchanging quality of the fire detection framework. Simultaneously, with the growing interest in better early fire detection and prevention, numerous frameworks are being created for the detection of progress, with control calculations having the task of carefully preparing and identifying true/false signals from fire or flames or the true alarm from false alarms. By utilizing the assistance provided by innovation, transport owners are more likely to service groups and fleets of ships and reduce potential fire accident costs. This article provides an overview of recent methodologies and technology for early detection of ship fires, as well as an enhanced approach for evaluating the Human-Machine-Interface (HMI) function of an alarming ship using a machine operating simulator called DMS-2017B. The DMS-2017B machinery operation simulator can unify the noise environment to avoid the influence of environmental differences on cabin experimental results. Compared to conventional Binomial Testing, a ship simulator coupled with the theory of affordance that provides a more realistic and operable way to assess the feature design of ship fire alarm and the threshold of some influence factors can also be used. According to the quantitative analysis of experimental results based on the ordered logit model, the function of the ship fire alarm would be improved significantly by adding recorded broadcasting and replacing static symbols with flashing symbols. Increasing sound pressure is also an effective way of doing this, but an auditory threshold is present. Above 75 dB, this effect will fade down, along with noise pollution. However, the effect difference between continuous alarm and square wave pulse alarm is negligible. The conclusion can provide some guidance for the design of a ship fire alarm. An appropriate design is expected to facilitate the efficiency of handling accidents and guiding evacuation.
25
Brooks, David H., e Stephanie L. Yardley. "The source of the major solar energetic particle events from super active region 11944". Science Advances 7, n. 10 (marzo 2021): eabf0068. http://dx.doi.org/10.1126/sciadv.abf0068.
Testo completoAbstract (sommario):
Shock waves associated with fast coronal mass ejections (CMEs) accelerate solar energetic particles (SEPs) in the long duration, gradual events that pose hazards to crewed spaceflight and near-Earth technological assets, but the source of the CME shock-accelerated plasma is still debated. Here, we use multi-messenger observations from the Heliophysics System Observatory to identify plasma confined at the footpoints of the hot, core loops of active region 11944 as the source of major gradual SEP events in January 2014. We show that the elemental composition signature detected spectroscopically at the footpoints explains the measurements made by particle counting techniques near Earth. Our results localize the elemental fractionation process to the top of the chromosphere. The plasma confined closest to that region, where the coronal magnetic field strength is high (a few hundred Gauss), develops the SEP composition signature. This source material is continually released from magnetic confinement and accelerated as SEPs following M-, C-, and X-class flares.
26
Costa, Mariana C. F., Valeria S. Marangoni, Pei Rou Ng, Hang T. L. Nguyen, Alexandra Carvalho e A. H. Castro Neto. "Accelerated Synthesis of Graphene Oxide from Graphene". Nanomaterials 11, n. 2 (22 febbraio 2021): 551. http://dx.doi.org/10.3390/nano11020551.
Testo completoAbstract (sommario):
Graphene oxide (GO) is an oxygenated functionalized form of graphene that has received considerable attention because of its unique physical and chemical properties that are suitable for a large number of industrial applications. Herein, GO is rapidly obtained directly from the oxidation of graphene using an environmentally friendly modified Hummers method. As the starting material consists of graphene flakes, intercalant agents are not needed and the oxidation reaction is enhanced, leading to orders of magnitude reduction in the reaction time compared to the conventional methods of graphite oxidation. With a superior surface area, the graphene flakes are quickly and more homogeneously oxidized since the flakes are exposed at the same extension to the chemical agents, excluding the necessity of sonication to separate the stacked layers of graphite. This strategy shows an alternative approach to quickly producing GO with different degrees of oxidation that can be potentially used in distinct areas ranging from biomedical to energy storage applications.
27
Pang, Lei, Qianran Hu, Mengjie Jin e Kai Yang. "Effect of Congestion on Flow Field of Vented Natural Gas Explosion in a Kitchen". Advances in Civil Engineering 2021 (12 gennaio 2021): 1–22. http://dx.doi.org/10.1155/2021/6671875.
Testo completoAbstract (sommario):
The process of gas explosion venting in a typical Chinese civil kitchen was investigated using computational fluid dynamics technology, focusing on the impact of the scale and cross-sectional characteristics of congestion, such as common furniture and electrical appliances, on the explosion flow-field parameters. An asymmetrical distribution of congestion will cause the uneven combustion of explosion flames in the kitchen. The flame will initially spread on one side of the room and then accelerate toward the surrounding areas, thereby increasing the risk of indoor gas explosion. The typical indoor overpressure change process can be divided into five stages, among which Stage V is found to be related to pseudoclosed combustion. Large-scale congestion has an obstructive effect on the explosion flow field, but it changes under certain conditions, while small-scale congestion only acts as a promoter. The flat congestion cross section helps maintain the stability of the flame structure, whereas the continuous and abrupt change of the congestion cross section can induce strong turbulent combustion. The research results provide a theoretical basis for the prevention and control of natural gas explosion hazards in civil kitchens from the perspective of congestion scale and cross-sectional mutation.
28
Jeffrey, Natasha L. S., Säm Krucker, Morgan Stores, Eduard P. Kontar, Pascal Saint-Hilaire, Andrea F. Battaglia, Laura Hayes et al. "A Modeling Investigation for Solar Flare X-Ray Stereoscopy with Solar Orbiter/STIX and Earth-orbiting Missions". Astrophysical Journal 964, n. 2 (27 marzo 2024): 145. http://dx.doi.org/10.3847/1538-4357/ad236f.
Testo completoAbstract (sommario):
Abstract The Spectrometer/Telescope for Imaging X-rays (STIX) on board Solar Orbiter (SolO) provides a unique opportunity to systematically perform stereoscopic X-ray observations of solar flares with current and upcoming X-ray missions at Earth. These observations will produce the first reliable measurements of hard X-ray (HXR) directivity in decades, providing a new diagnostic of the flare-accelerated electron angular distribution and helping to constrain the processes that accelerate electrons in flares. However, such observations must be compared to modeling, taking into account electron and X-ray transport effects and realistic plasma conditions, all of which can change the properties of the measured HXR directivity. Here, we show how HXR directivity, defined as the ratio of X-ray spectra at different spacecraft viewing angles, varies with different electron and flare properties (e.g., electron angular distribution, highest-energy electrons, and magnetic configuration), and how modeling can be used to extract these typically unknown properties from the data. Finally, we present a preliminary HXR directivity analysis of two flares, observed by the Fermi Gamma-ray Burst Monitor and SolO/STIX, demonstrating the feasibility and challenges associated with such observations, and how HXR directivity can be extracted by comparison with the modeling presented here.
29
Scepi, Nicolas, Jason Dexter e Mitchell C. Begelman. "Sgr A* X-ray flares from non-thermal particle acceleration in a magnetically arrested disc". Monthly Notices of the Royal Astronomical Society 511, n. 3 (9 febbraio 2022): 3536–47. http://dx.doi.org/10.1093/mnras/stac337.
Testo completoAbstract (sommario):
ABSTRACT Sgr A* exhibits flares in the near-infrared and X-ray bands, with the luminosity in these bands increasing by factors of 10–100 for ≈60 min. One of the models proposed to explain these flares is synchrotron emission of non-thermal particles accelerated by magnetic reconnection events in the accretion flow. We use the results from particle-in-cell simulations of magnetic reconnection to post-process 3D two-temperature GRMHD simulations of a magnetically arrested disc (MAD). We identify current sheets, retrieve their properties, estimate their potential to accelerate non-thermal particles, and compute the expected non-thermal synchrotron emission. We find that the flux eruptions of MADs can provide suitable conditions for accelerating non-thermal particles to energies γe ≲ 106 and producing simultaneous X-ray and near-infrared flares. For a suitable choice of current-sheet parameters and a simplified synchrotron cooling prescription, the model can simultaneously reproduce the quiescent and flaring X-ray luminosities as well as the X-ray spectral shape. While the near-infrared flares are mainly due to an increase in the temperature near the black hole during the MAD flux eruptions, the X-ray emission comes from narrow current sheets bordering highly magnetized, low-density regions near the black hole, and equatorial current sheets where the flux on the black hole reconnects. As a result, not all infrared flares are accompanied by X-ray ones. The non-thermal flaring emission can extend to very hard (≲ 100 keV) X-ray energies.
30
Fan, Duoming, Donald E. Willcox, Christopher DeGrendele, Michael Zingale e Andrew Nonaka. "Neural Networks for Nuclear Reactions in MAESTROeX". Astrophysical Journal 940, n. 2 (29 novembre 2022): 134. http://dx.doi.org/10.3847/1538-4357/ac9a4b.
Testo completoAbstract (sommario):
Abstract We demonstrate the use of neural networks to accelerate the reaction steps in the MAESTROeX stellar hydrodynamics code. A traditional MAESTROeX simulation uses a stiff ODE integrator for the reactions; here, we employ a ResNet architecture and describe details relating to the architecture, training, and validation of our networks. Our customized approach includes options for the form of the loss functions, a demonstration that the use of parallel neural networks leads to increased accuracy, and a description of a perturbational approach in the training step that robustifies the model. We test our approach on millimeter-scale flames using a single-step, 3-isotope network describing the first stages of carbon fusion occurring in Type Ia supernovae. We train the neural networks using simulation data from a standard MAESTROeX simulation, and show that the resulting model can be effectively applied to different flame configurations. This work lays the groundwork for more complex networks, and iterative time-integration strategies that can leverage the efficiency of the neural networks.
31
Yoshimori, Masato, e Hiroyuki Watanabe. "Numbers of Protons Accelerated in Solar Flares". Journal of the Physical Society of Japan 54, n. 7 (15 luglio 1985): 2406–8. http://dx.doi.org/10.1143/jpsj.54.2406.
Testo completo
32
Chen 陈, Bin 彬., Xiangliang Kong, Sijie Yu, Chengcai Shen, Xiaocan Li, Fan Guo, Yixian Zhang, Lindsay Glesener e Säm Krucker. "Energetic Electrons Accelerated and Trapped in a Magnetic Bottle above a Solar Flare Arcade". Astrophysical Journal 971, n. 1 (1 agosto 2024): 85. http://dx.doi.org/10.3847/1538-4357/ad531a.
Testo completoAbstract (sommario):
Abstract Where and how flares efficiently accelerate charged particles remains an unresolved question. Recent studies revealed that a “magnetic bottle” structure, which forms near the bottom of a large-scale reconnection current sheet above the flare arcade, is an excellent candidate for confining and accelerating charged particles. However, further understanding its role requires linking the various observational signatures to the underlying coupled plasma and particle processes. Here we present the first study combining multiwavelength observations with data-informed macroscopic magnetohydrodynamics and particle modeling in a realistic eruptive flare geometry. The presence of an above-the-loop-top magnetic bottle structure is strongly supported by the observations, which feature not only a local minimum of magnetic field strength but also abruptly slowing plasma downflows. It also coincides with a compact above-the-loop-top hard X-ray source and an extended microwave source that bestrides the flare arcade. Spatially resolved spectral analysis suggests that nonthermal electrons are highly concentrated in this region. Our model returns synthetic emission signatures that are well matched to the observations. The results suggest that the energetic electrons are strongly trapped in the magnetic bottle region due to turbulence, with only a small fraction managing to escape. The electrons are primarily accelerated by plasma compression and facilitated by a fast-mode termination shock via the Fermi mechanism. Our results provide concrete support for the magnetic bottle as the primary electron acceleration site in eruptive solar flares. They also offer new insights into understanding the previously reported small population of flare-accelerated electrons entering interplanetary space.
33
Ramaty, R., e N. Mandzhavidze. "Gamma-rays from Solar Flares". Symposium - International Astronomical Union 195 (2000): 123–32. http://dx.doi.org/10.1017/s0074180900162850.
Testo completoAbstract (sommario):
Gamma-ray emission is the most direct diagnostic of energetic ions and relativistic electrons in solar flares. Analysis of solar flare gamma-ray data has shown: (i) ion acceleration is a major consequence of flare energy release, as the total flare energy in accelerated particles appears to be equipartitioned between ≳ 1 MeV/nucleon ions and ≳ 20 keV electrons, and amounts to an important fraction of the total energy release; (ii) there are flares for which over 50% of the energy is in a particles and heavier ions; (iii) in both impulsive and gradual flares, the particles that interact at the Sun and produce gamma rays are essentially always accelerated by the same mechanism that operates in impulsive flares, probably stochastic acceleration through gyroresonant wave particle interaction; and (iv) gamma-ray spectroscopy can provide new information on solar abundances, for example the site of the FIP-bias onset and the photospheric 3He abundance. We propose a new technique for the investigation of mass motion and mixing in the solar atmosphere: the observations of gamma-ray lines from long-term radioactivity produced by flare accelerated particles.
34
Kimura, Shigeo S., Shinsuke Takasao e Kengo Tomida. "Modeling Hadronic Gamma-Ray Emissions from Solar Flares and Prospects for Detecting Nonthermal Signatures from Protostars". Astrophysical Journal 944, n. 2 (1 febbraio 2023): 192. http://dx.doi.org/10.3847/1538-4357/acb649.
Testo completoAbstract (sommario):
Abstract We investigate gamma-ray emission in the impulsive phase of solar flares and the detectability of nonthermal signatures from protostellar flares. Energetic solar flares emit high-energy gamma rays of GeV energies, but their production mechanism and emission site are still unknown. Young stellar objects, including protostars, also exhibit luminous X-ray flares, but the triggering mechanism of the flaring activity is still unclear owing to the strong obscuration. Nonthermal signatures in millimeter/submillimeter and gamma-ray bands are useful to probe protostellar flares owing to their strong penetration power. We develop a nonthermal emission model of the impulsive phase of solar flares, where cosmic-ray protons accelerated at the termination shock produce high-energy gamma rays via hadronuclear interaction with the evaporation plasma. This model can reproduce gamma-ray data in the impulsive phase of a solar flare. We apply our model to protostellar flares and show that the Cherenkov Telescope Array will be able to detect gamma rays of TeV energies if particle acceleration in protostellar flares is efficient. Nonthermal electrons accelerated together with protons can emit strong millimeter and submillimeter signals via synchrotron radiation, whose power is consistent with the energetic millimeter/submillimeter transients observed from young stars. Future gamma-ray and millimeter/submillimeter observations from protostars, coordinated with a hard X-ray observation, will unravel the nonthermal particle production and triggering mechanism of protostellar flares.
35
Ongar, Bulbul, Iliya K. Iliev, Vlastimir Nikolić e Aleksandar Milašinović. "THE STUDY AND THE MECHANISM OF NITROGEN OXIDES’ FORMATION IN COMBUSTION OF FOSSIL FUELS". Facta Universitatis, Series: Mechanical Engineering 16, n. 2 (1 agosto 2018): 273. http://dx.doi.org/10.22190/fume171114026o.
Testo completoAbstract (sommario):
The burning of all fossil fuels is accompanied by the production of large quantities of nitrogen oxides. Nitrogen oxide from coal combustion is formed from the molecular nitrogen in the air and the nitrogen contained in the fuel. In accordance with the mechanism of formation of nitric oxide from fuel, it is desirable to increase the concentration of coal dust in the flame. The thermal regime of combustion accelerates the release of volatiles, with flames spreading out and the coke residue contributes to the chemical reduction of NOx. In this work we consider the specific issues of the formation mechanism of NOx fuel and ways to reduce their atmospheric emissions. Presented are results from the calculation of the influence of the following on the level of nitric oxides during coal combustion: temperature, oxygen concentration and time of release of fuel nitrogen. It has been established that the influence of nitric oxide fuel on the total nitric oxide emissions is more noticeable at low temperatures of the combustion process.
36
Verma, Virendra Kumar, Nishant Mittal e Ramesh Chandra. "Some kinematics of halo coronal mass ejections". Open Astronomy 29, n. 1 (28 agosto 2020): 81–88. http://dx.doi.org/10.1515/astro-2020-0010.
Testo completoAbstract (sommario):
AbstractWe present an investigation of halo coronal mass ejections (HCMEs) kinematics and other facts about the HCMEs. The study of HCMEs is very important because HCMEs are regarded as the main causes of heliospheric and geomagnetic disturbances. In this study, we have investigated 313 HCMEs observed during 1996-2012 by LASCO, coronal holes, and solar flares. We find that HCMEs are of two types: accelerated HCMEs and decelerated HCMEs. The mean space speed of HCMEs is 1283 km/s while the mean speed of decelerated HCMEs and accelerated HCMEs is 1349 km/s and 1174 km/s, respectively. The investigation shows that 1 (0.3%) HCME was associated with class A SXR, 14 (4.7%) HCMEs were associated with class B SXR-flares, 87 (29.4%) HCMEs were associated with class C SXR-flares, 125 (42.2%) HCMEs were associated with class M SXR-flares and 69 (23.3%) HCMEs were associated with class X SXR-flares. The speed of HCMEs increases with the importance of solar SXR-flares. The various results obtained in the present analysis are discussed in the light of the existing scenario of heliospheric physics.
37
Gritsyk, P. A., e B. V. Somov. "Electron Acceleration in Collapsing Magnetic Traps during the Solar Flare on July 19, 2012: Observations and Models". Proceedings of the International Astronomical Union 13, S335 (luglio 2017): 90–93. http://dx.doi.org/10.1017/s1743921317008912.
Testo completoAbstract (sommario):
AbstractUsing the appropriate kinetic equation, we considered the problem of propagation of accelerated electrons into the solar corona and chromosphere. Its analytical solution was used for modelling the M7.7 class limb flare occurred on July 19, 2012. Coronal above-the-loop-top hard X-Ray source was interpreted in the thin-target approximation, the foot-point source - in the thick-target approximation with account of the reverse-current electric field. For the foot-point source we found a good accordance with the RHESSI observations. For the coronal source we also got very accurate estimate of the power-law spectral index, but significant differences between the modelled and observed hard X-ray intensities were noticed. The last discrepancy was solved by adding the coronal magnetic trap model to the thin target model. The former one implies that the trap collapses in two dimensions, locks and accelerates particles inside itself. In our report, we confirm an existence and high efficiency of the electron acceleration in collapsing magnetic traps during solar flares. Our new results represent (e.g. for RHESSI observations) the theoretical prediction of the double step particle acceleration in solar flares, when the first step is the acceleration in reconnection area and the second one – the acceleration in coronal trap.
38
Ramaty, R. "Nuclear processes and accelerated particles in solar flares". Solar Physics 113, n. 1-2 (gennaio 1987): 203–15. http://dx.doi.org/10.1007/bf00147699.
Testo completo
39
Striepe, Melissa Cusack, Alexandre Milovanoff, Amir F. N. Abdul-Manan, Jon McKechnie, I. Daniel Posen e Heather L. MacLean. "Are vehicle lifespan caps an effective and efficient method for reducing US light-duty vehicle fleet GHG emissions?" Environmental Research: Infrastructure and Sustainability 4, n. 2 (15 maggio 2024): 025002. http://dx.doi.org/10.1088/2634-4505/ad397e.
Testo completoAbstract (sommario):
Abstract With light duty vehicles (LDVs) responsible for 17% of annual US greenhouse gas (GHG) emissions, integrating emerging GHG-reducing technologies into the fleet is essential. However, the slow rate of vehicle turnover presents a significant barrier to the market penetration of new technologies, with adoption delayed by the low number of vehicles needing replacement each year. A strategy of accelerated vehicle turnover through a vehicle lifespan cap could potentially mitigate this limit. While older studies reach differing conclusions on their effectiveness, two newer studies that incorporate life cycle assessment find that accelerated turnover strategies can be effective if coupled with high levels of electric vehicle deployment. We seek to determine whether a vehicle lifespan cap strategy can be an effective and efficient (cost-effective) method for reducing US LDV fleet GHG emissions. We augment the capabilities of the Fleet Life Cycle Assessment and Material Flow Estimation (FLAME) fleet life cycle assessment model, integrating vehicle lifespan caps and comprehensive calculations of cost along with sensitivity analysis for electric vehicle survival curves and battery degradation. The augmented FLAME model is used to analyse the impact of vehicle lifespan caps of varying lengths on a suite of scenarios, including a business as usual (BAU) scenario and eight scenarios modelling different technology improvement assumptions. This work confirms that vehicle lifespan caps have limited effectiveness in reducing GHG emissions under a BAU scenario but show potential to meaningfully reduce GHG emissions in a scenario with accelerated deployment of electric vehicles. However, abatement costs are high, exceeding 2020 USD 1000/tCO2eq under baseline assumptions, but falling within the range of current estimates of the social cost of carbon under more optimistic assumptions. Overall, vehicle lifespan caps must be carefully considered as they accelerate both the benefits and costs of new vehicle technologies, and are best positioned as part of a larger integrated strategy for tackling transportation GHG emissions.
40
Wu, H., Y. Dai e M. D. Ding. "Highly Energetic Electrons Accelerated in Strong Solar Flares as a Preferred Driver of Sunquakes". Astrophysical Journal Letters 943, n. 1 (1 gennaio 2023): L6. http://dx.doi.org/10.3847/2041-8213/acb0d1.
Testo completoAbstract (sommario):
Abstract Sunquakes are enhanced seismic waves excited in some energetic solar flares. Up to now, their origin has still been controversial. In this Letter, we select and study 20 strong flares in Solar Cycle 24, whose impulse phase is fully captured by the Reuven Ramaty High Energy Solar Spectroscopic Imager. For 11 out of 12 sunquake-active flares in our sample, the hard X-ray emission shows a good temporal and spatial correlation with the white-light enhancement and the sunquake. Spectral analysis also reveals a harder photon spectrum that extends to several hundred keV, implying a considerable population of flare-accelerated nonthermal electrons at high energies. Quantitatively, the total energy of electrons above 300 keV in sunquake-active flares is systematically different from that in sunquake-quiet flares, while the difference is marginal for electrons above 50 keV. All these facts support highly energetic electrons as a preferred driver of the sunquakes. Such an electron-driven scenario can be reasonably accommodated in the framework of a recently proposed selection rule for sunquake generation. For the remaining one event, the sunquake epicenter is cospatial with a magnetic imprint, i.e., a permanent change of magnetic field on the photosphere. Quantitative calculation shows that the flare-induced downward Lorentz force can do enough work to power the sunquake, acting as a viable sunquake driver for this specific event.
41
Benz, A. O. "Solar and Stellar Flares". Highlights of Astronomy 8 (1989): 539–42. http://dx.doi.org/10.1017/s153929960000825x.
Testo completoAbstract (sommario):
AbstractThis review concentrates on some selected topics concerning the release of magnetic energy and associated phenomena in flares. Emphasis is on microflares, recent studies of different phases of flares, and propagation and trapping of flare accelerated electrons. The ongoing analysis of the observations of the previous solar cycle reaches a state where quantitative models become possible. The subject of solar flares can be broken up into several, now well defined physical problems.
42
Anttila, A., L. G. Kocharov, J. Torsti e R. Vainio. "Long-duration high-energy proton events observed by GOES in October 1989". Annales Geophysicae 16, n. 8 (31 agosto 1998): 921–30. http://dx.doi.org/10.1007/s00585-998-0921-0.
Testo completoAbstract (sommario):
Abstract. We consider the prolonged injection of the high-energy (>10 MeV) protons during the three successive events observed by GOES in October 1989. We apply a solar-rotation-stereoscopy approach to study the injection of the accelerated particles from the CME-driven interplanetary shock waves in order to find out how the effectiveness of the particle acceleration and/or escape depends on the angular distance from the shock axis. We use an empirical model for the proton injection at the shock and a standard model of the interplanetary transport. The model can reproduce rather well the observed intensity–time profiles of the October 1989 events. The deduced proton injection rate is highest at the nose of the shock; the injection spectrum is always harder near the Sun. The results seem to be consistent with the scheme that the CME-driven interplanetary shock waves accelerate a seed particle population of coronal origin.Key words. Interplanetary physics · Energetic particles · Solar physics · astrophysics and astronomy · Flares and mass ejections
43
Mochtar, A. A., Jalaluddin, A. Mangkau, A. Sakka, I. Aqsa e M. Khoir. "Biogas Production in a Variety of Sawdust and Cow Dung Mixtures Using the Intermittent Mixing Method". Journal of Physics: Conference Series 2739, n. 1 (1 aprile 2024): 012019. http://dx.doi.org/10.1088/1742-6596/2739/1/012019.
Testo completoAbstract (sommario):
Abstract Cow dung is livestock waste that is very useful for renewable energy sources. The acceleration of the gas rate in cow dung biogas fermentation can be accelerated by the addition of secondary material, sawdust is one of the organic materials that can accelerate the rate of gas production in the formation of cow dung biogas. This study used a mixture composition: (B1) 675 g cow dung and 0 g sawdust, (B2) 472.5 g cow dung and 202.5 sawdust, (B3) 450 g cow dung and 225 g sawdust, and (B4) 427.5 g cow dung and 247.5 g of sawdust by fermentation for 20 days. In the research process, measurements of pH at the beginning and at the end of the study, gas pressure, gas volume, biodigester temperature, production rate, methane gas content, and flame test were carried out. In this study, the pH values ranged from 7-7.5 and the biodigester temperature was 27.5-31°C. The results of this study indicate that an organic mixture with a mixture of sawdust can accelerate production faster than without organic sawdust. Optimal results are found in the variation of the organic mixture of sawdust with a mixture of 450 g cow dung and 250 g sawdust having the highest production rate of 281.72 ml/day.
44
Somov, B. V., e P. A. Gritsyk. "On bremsstrahlung radiation of accelerated electrons in solar flares". Moscow University Physics Bulletin 67, n. 1 (febbraio 2012): 102–8. http://dx.doi.org/10.3103/s0027134912010195.
Testo completo
45
de Klerk, W. P. C., E. L. M. Krabbendam-LaHaye, B. Berger, H. Brechbuhl e C. Popescu. "Thermal studies to determine the accelerated ageing of flares". Journal of Thermal Analysis and Calorimetry 80, n. 2 (maggio 2005): 529–36. http://dx.doi.org/10.1007/s10973-005-0689-3.
Testo completo
46
Manchanda, R. K., L. E. Waldron e R. K. Sood. "Radio Jets and UHE Gamma-ray Emission in Cyg X-3". Publications of the Astronomical Society of Australia 10, n. 3 (1993): 208–10. http://dx.doi.org/10.1017/s1323358000025686.
Testo completoAbstract (sommario):
AbstractThe low-mass X-ray binary source Cyg X–3 has been extensively observed from radio to ultra-high-energy (UHE) gamma-ray energies (i.e., energies >1015eV). In the radio, Cyg X–3 exhibits intense non-thermal outbursts (flares) and a double-sided relativistic jet morphology. Interestingly, at energies above 1 TeV (1012eV), the gamma-ray emission is highly variable and possibly correlated with the radio outbursts. This emission results primarily from the radiative decay of π°-mesons generated in inelastic collisions between relativistic nuclei (predominantly protons) and the surrounding matter. The observed flux of UHE gamma-rays from Cyg X–3 implies that Cyg X–3 is a localised accelerator of such particles.We propose a model of Cyg X–3 wherein particles expelled by the source are accelerated by Shockwaves in the relativistically expanding jets. Intense flaring episodes then lead to time variations in the ambient particle flux which account for the observed features at UHE energies.
47
Kupriyanova, Elena, Dmitrii Kolotkov, Valery Nakariakov e Anastasiia Kaufman. "QUASI-PERIODIC PULSATIONS IN SOLAR AND STELLAR FLARES. REVIEW". Solar-Terrestrial Physics 6, n. 1 (1 aprile 2020): 3–23. http://dx.doi.org/10.12737/stp-61202001.
Testo completoAbstract (sommario):
This paper provides an overview of the state-of-the-art studies of oscillatory processes in solar and stellar flares, based on modern observational data from ground-based and space-borne instruments with high temporal, spatial, and spectral resolution in different bands of the electromagnetic spectrum. We examine the mecha-nisms that generate flare emission and its quasi-periodic modulation. We discuss similarities and differences be-tween solar and stellar flares, and address associated problems of superflares on the Sun and space weather. Quasi-periodic pulsations (QPPs) of flare emission are shown to be an effective tool for diagnosing both the flare processes themselves and the parameters of flaring plasmas and accelerated particles. We consider types of QPPs, their statistical properties, and methods of analysis, taking into account the non-stationarity of the QPPs’ parameters. We review the proposed mechanisms of QPPs and summarize open questions.
48
Mandzhavidze, Natalie, e Reuven Ramaty. "Gamma Rays from Solar Flares". Highlights of Astronomy 11, n. 2 (1998): 759–62. http://dx.doi.org/10.1017/s1539299600018712.
Testo completoAbstract (sommario):
AbstractWe review recent results obtained from the analysis of the solar flare gamma ray line emission: (a)The gamma ray derived ambient elemental abundances show that the First Ionization Potential (FIP) effect already sets in at relatively low altitudes in the solar atmosphere.(b)The composition of the flare accelerated particles that produce the gamma rays exhibit heavy element and 3He abundance enhancements that are typical for impulsive flares. Unlike the solar energetic particle (SEP) observations in interplanetary space, the gamma ray method allows us to trace the time development of these enhancements.(c)Solar flare gamma ray spectroscopy provides the most direct measure of the abundances of the two very high FIP elements, He and Ne, in subcoronal regions leading to somewhat higher abundances than the generally accepted values.(d)The high intensities of the aa lines observed from a number of flares imply a high (≳ 0.1) ambient He/H and/or accelerated α/p.(e)There are indications for the isotopic fractionation of He from the photosphere to corona that has important implications on the mechanism of solar wind acceleration, the protosolar deuterium abundance and Galactic chemical evolution.
49
Matsumoto, Keitarou, Satoshi Masuda e Takafumi Kaneko. "Characteristics of the Accelerated Electrons Moving along the Loop Derived from Cyclical Microwave Brightenings at the Footpoints". Astrophysical Journal Letters 955, n. 2 (1 ottobre 2023): L39. http://dx.doi.org/10.3847/2041-8213/acf99c.
Testo completoAbstract (sommario):
Abstract Many particles are accelerated during solar flares. To understand the acceleration and propagation processes of electrons, we require the pitch-angle distributions of the particles. The pitch angle of accelerated electrons has been estimated from the propagation velocity of a nonthermal microwave source archived in Nobeyama Radioheliograph data. We analyzed a flare event (an M-class flare on 2014 October 22) showing cyclical microwave brightenings at the two footpoint regions. Assuming that the brightenings were caused by the accelerated electrons, we approximated the velocity parallel to the magnetic field of the accelerated electrons as ∼7.7 × 104 and 9.0 × 104 km s −1. The estimated pitch angle of the accelerated electrons is 69°–80° and the size of the loss cone at the footpoint (estimated from the magnetic field strength in the nonlinear force-free field model) is approximately 43°. Most of the accelerated electrons could be reflected at the footpoint region. This feature can be interpreted as brightenings produced by bouncing motion of the accelerated electrons.
50
Zhang, Haocheng, Xiaocan Li, Dimitrios Giannios, Fan Guo, Hannes Thiersen, Markus Böttcher, Tiffany Lewis e Tonia Venters. "Radiation and Polarization Signatures from Magnetic Reconnection in Relativistic Jets. II. Connection with γ-Rays". Astrophysical Journal 924, n. 2 (1 gennaio 2022): 90. http://dx.doi.org/10.3847/1538-4357/ac3669.
Testo completoAbstract (sommario):
Abstract It is commonly believed that blazar jets are relativistic magnetized plasma outflows from supermassive black holes. One key question is how the jets dissipate magnetic energy to accelerate particles and drive powerful multiwavelength flares. Relativistic magnetic reconnection has been proposed as the primary plasma physical process in the blazar emission region. Recent numerical simulations have shown strong acceleration of nonthermal particles that may lead to multiwavelength flares. Nevertheless, previous works have not directly evaluated γ-ray signatures from first-principles simulations. In this paper, we employ combined particle-in-cell and polarized radiation transfer simulations to study multiwavelength radiation and optical polarization signatures under the leptonic scenario from relativistic magnetic reconnection. We find harder-when-brighter trends in optical and Fermi-LAT γ-ray bands as well as closely correlated optical and γ-ray flares. The swings in optical polarization angle are also accompanied by γ-ray flares with trivial time delays. Intriguingly, we find highly variable synchrotron self-Compton signatures due to inhomogeneous particle distributions during plasmoid mergers. This feature may result in fast γ-ray flares or orphan γ-ray flares under the leptonic scenario, complementary to the frequently considered minijet scenario. It may also imply neutrino emission with low secondary synchrotron flux under the hadronic scenario, if plasmoid mergers can accelerate protons to very high energy.