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Junction fires involve the merging of two linear fire fronts intersecting at a small anglewhich gives rise to an interaction process with fire-induced convective flows that modifythe behavior of both fires and produce very large v...
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Junction fires involve the merging of two linear fire fronts intersecting at a small anglewhich gives rise to an interaction process with fire-induced convective flows that modifythe behavior of both fires and produce very large values of the rate of spread (ROS) of theinner part of the two fires.In this context, a study on the junction fires on sloped terrain was carried out numerically using the FIRESTAR3D model that predicts the fire behavior. FireStar3D belongs to amultiphase class of models that is based on a very detailed modelling of the physicochemical phenomena involved in a fire, from the thermal degradation of the vegetation to thedevelopment of the turbulent flame inside and above the vegetation layer. This approachsolves two sets of problems, one for the vegetation and one for the surrounding gas whichare coupled together through additional terms. The objective of this study was to analysethe effect of the junction angle variation on the fire behavior, especially on the junction pointvelocity. In a first step, the effect of terrain slope on the fire rate of spread was simulatednumerically under no wind conditions, in order to determine the slope threshold valuebeyond which fire behavior changes noticeably due to flame attachment. Then numericalsimulations of junction fires were conducted using two different values of terrain slope(above and below the threshold value) in order to establish the relationship between thefire rate of spread and the junction angle variation. Finally, numerical simulations wereconducted to study the case where the junction axis is not aligned with the main slopedirection, in order to investigate the effect of this rotation on the junction point speedand trajectory.
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Background: In Pedróg?o Grande on 17 June 2017, two fire fronts merged and the propagation of the fire was influenced by the interaction of these non-symmetric fire fronts. Aims: This wildfire motivated us to study a junction fir...
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Background: In Pedróg?o Grande on 17 June 2017, two fire fronts merged and the propagation of the fire was influenced by the interaction of these non-symmetric fire fronts. Aims: This wildfire motivated us to study a junction fire with two non-symmetrical fire fronts. The analysis of the movement of the intersection point and the angle (γ) between the bisector of the fire lines and the maximum rate of spread (ROS) direction is of particular relevance. Methods: The study was carried out at Forest Fire Laboratory of the University of Coimbra in Lous? (Portugal) with laboratory experiments. Key results: We found that, for small rotation angles (δ), the non-dimensional ROS of the intersection point depends on the slope angle (α) and the initial angle between fire fronts. Conclusions: For high α, the non-dimensional ROS was highly influenced by the convection process and γ where the maximum ROS occurred, increased when δ increased. However, the radiation process was more relevant for lower α and influenced the non-dimensional ROS. For these cases, the maximum spread direction was close to that of the fire line bisector. Implications: The present work aimed to explain fire behaviour during the Pedróg?o Grande wildfire.
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Junction fires, a type of dynamic fire behaviour, involve the merging of two active fire fronts. They have been known to result in extreme increases in rates of fire spread and intensity over short periods of time. When these phen...
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Junction fires, a type of dynamic fire behaviour, involve the merging of two active fire fronts. They have been known to result in extreme increases in rates of fire spread and intensity over short periods of time. When these phenomena occur during wildfires, they pose significant risks to emergency management and communities. Few studies have investigated rates of spread and fireline intensity of junction fires using field scale experiments. This study captured data from 16 junction fires in mallee-heathlands utilising a drone-mounted thermal camera. Mean rates of spread and fireline intensity were found to increase toward the 75 % stage of merging before decreasing, similar to those found in other studies. Although, normalised temperature areas increased continuously for the whole duration of merging. Additionally, a custom-built radiative heat flux device was used to measure temperature and radiant heat at the fireline within the junction fires. Peak radiative heat flux was also found to be highest at the 75 % stage of merging, following a gradual decrease as propagation progressed. Heat flux measurements were found to be similar to those of previous studies conducted in similar vegetation. Due to the many complex interactions between weather, fuel and fire behaviour, further studies need to be conducted to appropriately determine the effects of merging on rates of spread and fire intensity.
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A conceptual model based on the dynamic interaction between fire, the fuel bed and the surrounding flow to explain the non-monotonic or intermittent behaviour of fires is proposed. According to the model, even in nominally permane...
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A conceptual model based on the dynamic interaction between fire, the fuel bed and the surrounding flow to explain the non-monotonic or intermittent behaviour of fires is proposed. According to the model, even in nominally permanent and uniform boundary conditions, the fire-induced flow modifies the geometry of the flame and its rate of spread. After an initial acceleration, there is a reduction in the rate of spread followed by one or more cycles of growth. Carefully controlled experiments of fires in slopes and canyons show that the evolution of fire properties, namely flame angle and rate of spread, have high-frequency oscillations superimposed on the low-frequency fire growth cycle described above.
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Electrically coupled neurons communicate through channel assemblies called gap junctions, which mediate the transfer of current from one cell to another. Electrical synapses ensure spike synchronization and reliable transmission, ...
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Electrically coupled neurons communicate through channel assemblies called gap junctions, which mediate the transfer of current from one cell to another. Electrical synapses ensure spike synchronization and reliable transmission, which influences bursting patterns and firing frequency. The present study concerns an electrically coupled two-neuron network in the gastropod mollusc, Lymnaea stagnalis. The neurons, designated Visceral Dorsal 1 (VD1) and Right Parietal Dorsal 2 (RPD2), are peptidergic, innervate aspects of the cardio-respiratory system, and show strong coupling, such that they fire synchronously. Using dual sharp-electrode current-clamp recording and morphological staining in isolated brain preparations, the hypothesis that the electrical synapse is necessary for accurate network output was tested. We found that both cells make extensive projections within and out of the brain, including across the visceral-parietal connective, which links VD1 and RPD2. Cutting this connective uncoupled the neurons and disrupted the firing rate and pattern of RPD2 more than VD1, consistent with VD1 being the master and RPD2 the follower. The electrical synapse was inhibited by select gap junction blockers, with niflumic acid and 5-nitro-2-(3-phenylpropylamino) benzoic acid decreasing the VD1 -> RPD2 and RPD2 -> VD1 coupling coefficients, whereas carbenoxolone, alpha-glycyrrhetinic acid, meclofenamic acid, and quinine were ineffective. There was little-to-no impact on VD1 <-> RPD2 firing synchrony or frequency when coupling was reduced pharmacologically. However, in the presence of gap junction blockers, suppressing the activity of VD1 by prolonged hyperpolarization revealed a distinct, low-frequency firing pattern in RPD2. This suggests that strong electrical coupling is key to maintaining a synchronous output and proper firing rate. (C) 2015 Elsevier B.V. All rights reserved.
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Background Two fire ignitions in Pedrogao Grande on 7 June 2017 had very fast due to unusual physical processes associated with the interaction between an overhead thunderstorm and the fire and the subsequent merging of the fires ...
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Background Two fire ignitions in Pedrogao Grande on 7 June 2017 had very fast due to unusual physical processes associated with the interaction between an overhead thunderstorm and the fire and the subsequent merging of the fires as a junction fire, killing 66 persons in 2 h.Aims Using a laboratory simulation of the merging process, we explain the fire spread conditions and verify that the junction of the two fires was responsible for the very intense fire development.Methods The real fire spread was reconstructed from an extensive field survey and physical modelling tests were performed in the Fire Research Laboratory combustion tunnel using various fuels and scale modelling laws.Key results The spread and merging of the two fires in the tests agree very well with field observations, namely the periods of rate of spread (ROS) increase and decrease, peak values of ROS and area growth process using scaling laws.Conclusions Analysis of the Pedrogao Grande fire evolution and its physical simulation at laboratory scale showed the importance of the mechanisms of two fires merging in producing very important convective processes.Implications Our study showed the validity of performing the experimental analysis of complex fire spread situations provided that the similarity conditions are fulfilled.
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Turn-on time is the time interval required for decreasing the forward voltage occurring across a cell to 10% of its initial value after a gate current is applied. It contains two parts: (1) delay time ¿ the period needed for th...
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Turn-on time is the time interval required for decreasing the forward voltage occurring across a cell to 10% of its initial value after a gate current is applied. It contains two parts: (1) delay time ¿ the period needed for the voltage to reduce from 100% to 90%, and (2) rise time ¿ the period during which the voltage reduces from 90% to 10%.
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The name silicon-controlled rectifier has been given to a new 3-terminal semiconductor device which has electrical characteristics similar to a thyratron. This device has been developed by the Semiconductor Products Department of ...
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The name silicon-controlled rectifier has been given to a new 3-terminal semiconductor device which has electrical characteristics similar to a thyratron. This device has been developed by the Semiconductor Products Department of the General Electric Company and has been given the developmental designation ZJ-39A. Its characteristics are made possible through the use of a p-n-p-n junction configuration. It is capable of handling load currents up to 16 amperes average at peak voltages up to 300 volts. Its fast switching action, small size, and relatively high-current ratings make this new device adaptable to a great many applications. Its characteristics and ratings, which are of utmost importance to the circuit designer, are the subject of this discussion.
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Abstract The study focuses on the analysis of a 16th-century lime plaster sample sourced from Arab Ki Sarai, part of the Humayun tomb complex in Delhi. The lime plaster samples were initially observed under an analytical microscop...
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Abstract The study focuses on the analysis of a 16th-century lime plaster sample sourced from Arab Ki Sarai, part of the Humayun tomb complex in Delhi. The lime plaster samples were initially observed under an analytical microscope. Petrological analysis involved the examination of thin sections of the plaster samples to provide information about the mineral composition and structure. SEM-EDX allowed for detailed imaging of the plaster’s microstructure and elemental composition. The study focused on the interface between the plaster and the brick substrate. FTIR, XRD, and EDX analyses were used to assess changes in mineralogy and composition at this junction. The presence of brick aggregates in the plaster was found to influence mechanical strength and permeability. The analysis of brick aggregates revealed that they were fired at high fusion temperatures. This firing process altered the crystalline structure of clay minerals in the bricks, affecting their pozzolanic activity, surface area, and the formation of high-temperature mineral phases. The study suggested that coarse brick aggregates, fired at high temperatures, were intentionally selected for underwater construction. The analysis indicated the presence of a minor quantity of proteinaceous adhesive in the plaster during its preparation. However, organic additives like jute fibers were not detected. The study provides a comprehensive analysis of the 16th-century lime plaster, shedding light on its composition, properties, and the role of brick aggregates in its performance.
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Direct electrical coupling between neurons through gap junctions is prominent during development, when synaptic connectivity is scarce, providing the additional intercellular connectivity. However, functional studies of gap juncti...
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Direct electrical coupling between neurons through gap junctions is prominent during development, when synaptic connectivity is scarce, providing the additional intercellular connectivity. However, functional studies of gap junctions are hampered by the unspecificity of pharmacological tools available. Here we have investigated gap junctional coupling between CA3 pyramidal cells in neonatal hippo campus and its contribution to early network activity. Four different gap junction inhibitors, including the general blocker carbenoxolone, decreased the frequency of network activity bursts in CA3 area of hippocampus of P3-6 rats, suggesting the involvement of electrical connections in the generation of spontaneous network activity. In CA3 pyramidal cells, spikelets evoked by local stimulation of stratum oriens, were inhibited by carbenoxolone, but not by inhibitors of glutamatergic and GABAergic synaptic transmission, signifying the presence of electrical connectivity through axo-axonic gap junctions. Carbenoxolone also decreased the success rate of firing antidromic action potentials in response to stimulation, and changed the pattern of spontaneous action potential firing of CA3 pyramidal cells. Altogether, these data suggest that electrical coupling of CA3 pyramidal cells contribute to the generation of the early network events in neonatal hippocampus by modulating their firing pattern and synchronization. (C) 2016 Elsevier Ltd. All rights reserved.
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