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The flame spread behavior over a filter paper in opposed flow was investigated on the ISS/Kibo, and the results were compared with the flammability map predicted in advance by scale analysis for a two-dimensional flame. The on-orbit experiments were conducted in the solid combustion experimental module (SCEM) as the first combustion test of the FLARE project by JAXA. A filter paper with a length of 130 mm, a width of 40 mm or 20 mm, and a thickness of 0.12 mm was used as the specimen. The opposed flow velocity and the oxygen concentration were varied from 0 cm/s to 25 cm/s, and from 13.5% to 34%, respectively. The ambient pressure is 101.3 kPa. The predicted limiting curve reasonably agreed with the minimum limiting oxygen concentration observed. On the other hand, in extremely slow flows, very robust flames were observed beyond the limiting curve. When the condition reached the limit of two-dimensional flame, the flame front changed from a linear shape to a spherical shape (flamelet) to shorten the preheat zone length, reducing the radiative heat loss to survive. In these cases, the flamelet was sustained for a long time (> 100 s), and a large amount of decomposed gas was released at the periphery of the pyrolysis zone generating a combustible vapor cloud around the spherical flame font. The presence of a long-life robust flamelet and the accumulation of such combustible mist can be fire hazards in microgravity. [ABSTRACT FROM AUTHOR]

In the study, experiments of airburst blast extinguishment of a methane-air jet diffusion flame have been conducted with 20 mg silver azide pellets, and the extinguishing processes have been observed using a high-speed camera and schlieren method. From the experimental results, we have examined the extinguishing mechanisms. When the blast wave interacts with the diffusion flame, vortex pair is generated in the flame due to the baroclinic effect which is caused by the misalignment between the pressure gradient of the blast wave and the density gradient in the combustion region. The vortical motion leads to the local extinction, and finally, the whole flame is blown off. In airburst, a reflected shock wave occurs on the ground surface. Depending on the height of burst and the distance between the explosion location and the extinguishing target, the reflected blast wave merges with the incident blast wave and the Mach stem is formed before the blast wave interferes with the diffusion flame. As a result, it is found that the extinguishing effectiveness is increased by the presence of the Mach Stem. Moreover, the optimal height of burst in the airburst blast extinguishment is clarified. • Airburst blast extinguishment of a diffusion flame with micro explosive was done. • Observation of the extinguishing process with schlieren method. • The extinguishing mechanism of airburst blast extinguishment is clarified. • The extinguishing effectiveness increases due to the presence of the Mach Stem. • The optimal height of burst in the airburst blast extinguishment is revealed. [ABSTRACT FROM AUTHOR]

In this study, an extinguishing method using a rubber balloon filled with inert gas is proposed against fires in confined space such as spacecraft and space station. The proposed method has a possibility to increase extinguishing effectiveness of inert gas and decrease its volume amount needed for firefighting. In order to clarify the extinguishing characteristics, the blowoff experiments have been performed under normal gravity condition. CO2, N2, Ar and Ar + N2 mixture gases were used as an extinguishing gas and ethanol, 1-butanol and n-heptane were used to form a pool fire. The fuel pan diameters were varied from 47 mm to 94 mm. From the experimental results, it is found that there exists the extinguishment limit, which indicates the minimum inert gas volume needed for achieving flame extinguishment with the rubber balloon. By using the magnitude of the extinguishment limit value, the extinguishing ability of inert gas in the rubber balloon extinguishment can be evaluated. As a result, the effectiveness ranking of the inert gas in rubber balloon extinguishment agrees well with that of cup-burner tests. Moreover, it is found that when the size of the pool fire (fuel pan diameter) is same, the value of the lower heating value of fuel divided by the inert gas heat capacity at the extinguishment limit shows a certain constant value independent of inert gas and fuel species. As a result, the extinguishment limit of the rubber balloon extinguishing method is considered to be determined due to the balance between the heat release rate of the pool fire and the heat absorption rate of inert gas released from the bursting balloon. Thus, a rubber balloon can be used as an extinguishing capsule, by which a high concentration inert gas is easily delivered to the flame. In addition, it is much easier to grasp heat capacity effect of inert gas on flame extinguishment than the conventional methods, such as the cup-burner test. [ABSTRACT FROM AUTHOR]

In this study, we have investigated an extinguishing method of a diffusion flame with water vapor produced from a water droplet impacting onto a headed plate, which is called as indirect fire attack. In order to clarify the extinguishing characteristics, the extinguishing experiments of a methane-air diffusion flame have been performed by using a pure water droplet with the diameter of 3.2 mm. The droplet dropped from the height of 400 mm. The wall superheat and the burner height were varied from 0 K to 330 K and from 32 mm to 102 mm, respectively. As a result, under certain wall-heat conditions, the water-vapor vortex ring is formed and visualized by the white water fog. At wall superheat of 150 K, the formation probability of the vortex ring is unity and the extinguishing probability always shows the peak values regardless of the burner height. As a result, it can be said in our study that the wall superheat of 150 K is the most effective value for the indirect extinguishing method. [ABSTRACT FROM AUTHOR]

Liquid nitrogen which is a cryogenic fluid can be used as a fire extinguishing agent. This is because liquid nitrogen vaporizes rapidly under atmospheric condition, which results in cooling of burning materials and its surroundings in firefighting, and also the volume of the vaporized nitrogen becomes approximately 700 times larger than that of its liquid state, which results in reduction of oxygen concentration in air or fuel concentration in combustion zone. Moreover, liquid nitrogen has no water damage and can extinguish fires more cleanly than dry chemical extinguishing agents. However, it is difficult to delivery liquid nitrogen over long distance from the extinguishing equipment to fires through the surrounding air because of its rapid vaporization. If liquid nitrogen is filled into a capsule and the capsule wall suppresses heat transfer from the surroundings to the liquid nitrogen, it will be easy to transport liquid nitrogen to the targeted fire area without rapid vaporization. Moreover, by using the capsule, it may be possible to increase the extinguishing effectiveness of liquid nitrogen. In the present study, in order to clarify the fundamental characteristics of flame extinguishment by using the capsule filled with liquid nitrogen, extinguishing experiments of a methane-air jet diffusion flame have been performed. The spherical hollow ball made of ice was used as the extinguishing capsule and the ice capsule was formed by rotating casting machine. The wall thickness and the outer diameter were 2 mm and 20 mm, respectively. The filling volume of liquid nitrogen was 20 cm. The ice capsule was dropped freely from the height of 800 mm and impacted on the aluminum plate, in which the round burner to form a jet diffusion flame was embedded. The extinguishing probability was measured by varying the distance from the impact point of the ice capsule and the flame. The extinguishing processes were recorded with high-speed camera. Moreover, for comparison, the same extinguishing experiments have been performed using the ice capsule filled with water. As a result, liquid nitrogen shows the higher extinguishing effectiveness than water because liquid nitrogen droplets released from the ice capsule to the collided horizontal plate can travel over the longer distance due to the Leidenfrost effect and liquid nitrogen can be vaporized rapidly under room temperature condition. The extinguishable range of the ice capsule filled with liquid nitrogen is less than 200 mm. [ABSTRACT FROM AUTHOR]

Spike-timing-dependent plasticity (STDP) is a form of synaptic modification that depends on the relative timings of presynaptic and postsynaptic spikes. In this letter, we proposed a calcium-based simple STDP model, described by an ordinary differential equation having only three state variables: one represents the density of intracellular calcium, one represents a fraction of open state NMDARs, and one represents the synaptic weight. We shown that in spite of its simplicity, the model can reproduce the properties of the plasticity that have been experimentally measured in various brain areas (e.g., layer 2/3 and 5 visual cortical slices, hippocampal cultures, and layer 2/3 somatosensory cortical slices) with respect to various patterns of presynaptic and postsynaptic spikes. In addition, comparisons with other STDP models are made, and the significance and advantages of the proposed model are discussed. [ABSTRACT FROM AUTHOR]

A novel rotate-and-fire digital spiking neuron is presented. The digital neuron is a wired system of shift registers and thus it is suited to on-chip learning unlike many other analog spiking neuron models. By adjusting the wiring pattern among the registers, the digital neuron can generate spike trains with various spike patterns and can exhibit related bifurcations. A discrete–continuous hybrid map, which describes the neuron dynamics without any approximation, is derived analytically. Using the hybrid map, it is shown that the digital spiking neuron can mimic typical bifurcation phenomena and various nonlinear responses of biological neurons. [ABSTRACT FROM AUTHOR]

Abstract: A novel chaotic spiking neuron is presented and its nonlinear dynamics and encoding functions are analyzed. A set of paralleled neurons accepts a common analog input and outputs a set of chaotic spike-trains. Three theorems which guarantee that the neurons can encode the analog input into a summation of the chaotic spike-trains are derived: (1) a spike histogram of the summed spike-train can mimic waveforms of various inputs, (2) the spike-trains do not synchronize to each other and thus the summed spike-train can have times higher encoding resolution than each single spike-train, and (3) firing rates of the neurons can be adjusted by internal parameters. The theorems are proven by using nonlinear iterative maps and are confirmed by numerical simulations as well. Electronic circuit implementation methods of the paralleled neurons are also presented and typical paralleled encoding functions are confirmed by both experimental measurements and SPICE simulations. [Copyright &y& Elsevier]

Abstract: A digital spiking neuron is a wired system of shift registers and can generate various spike-trains by adjusting the wiring pattern. In this paper we analyze the basic relations between the wiring pattern and characteristics of the spike-train. Based on the relations, we present a learning algorithm which utilizes successive changes of the wiring pattern. It is shown that the neuron can reproduce spike-trains of another neuron which has an unknown wiring pattern. It is also shown that the neuron can approximate various spike-trains of a chaotic analog spiking neuron. [Copyright &y& Elsevier]

This paper studies stabilization of low-period unstable periodic orbits (UPOs) in a simplified model of a current mode H-bridge inverter. The switching of the inverter is controlled by pulse-width modulation signal depending on the sampled inductor current. The inverter can exhibit rich nonlinear phenomena including period doubling bifurcation and chaos. Our control method is realized by instantaneous opening of inductor at a zero-crossing moment of an objective UPO and can stabilize the UPO instantaneously as far as the UPO crosses zero in principle. Typical system operations can be confirmed by numerical experiments. [ABSTRACT FROM AUTHOR]

Abstract: A digital spiking neuron (DSN), a quantized analog spiking neuron (QSN) and a discrete spike position map are introduced, and their relations are discussed. Spike position modulations for various spike-trains of DSN and QSN are considered. In addition, some applications are discussed. [Copyright &y& Elsevier]

We investigated and quantified the extinction phenomena of laminar and turbulent counterflow CH4/N2–O2/N2 nonpremixed flames. Experimental conditions such as the stoichiometric mixture fraction, the molar stoichiometry, and the turbulent flow characteristics are widely modulated. For a given set of experiments, the molar ratio of CH4–O2–N2 is held fixed, hence fixing the adiabatic flame temperature. The bulk velocity gradient at extinction, i.e., the critical strain rate, increases monotonically with increasing stoichiometric mixture fraction regardless of the initial turbulent flow property. For all the experimental conditions, extinction is more sensitive to variation in the mass fraction of oxygen in the oxidizer stream than that of methane in the fuel stream. If the extinction limit is quantified by the bulk velocity gradient, turbulence levels affect the extinction limit significantly when higher turbulence encounters the reaction zone directly. Estimations of the scalar dissipation rate at extinction are obtained from the experimentally observed quantities founded on the theoretical consideration of the flame characteristics. For the laminar counterflow nonpremixed flames, the critical value of the scalar dissipation rate at extinction, χq, scaled with that of the CH4–air laminar counterflow nonpremixed flames by the ratio of the bulk velocity gradient at extinction. This scaling is a suitable approximation for the present study. As to the turbulent flames, the scalar dissipation rates at extinction of the same stoichiometric mixture fraction are estimated including the contributions of both turbulent effect and mean flow effect. These show good agreement regardless of the initial turbulent flow condition. [Copyright &y& Elsevier]

We consider quantized chaotic dynamics for a spiking oscillator with two periodic inputs. As the first input is applied, the oscillator generates various periodic and chaotic pulse-trains governed by a pulse position map. As the second input is added, the oscillator produces pulse positions restricted on a lattice, and the pulse position map is quantized. Then the oscillator generates a set of super-stable periodic pulse-trains (SSPTs). The oscillator has various coexisting SSPTs and generates one of them depending on the initial state condition. In order to characterize the set of SSPTs, we elucidate the number and the minimum pulse interval of the SSPTs theoretically. By presenting a simple test circuit, we then verify some typical phenomena in the laboratory environment. [ABSTRACT FROM AUTHOR]

Presents a study which considered a spiking oscillator to which two periodic and synchronized inputs can be applied. Method; Results; Conclusions.

Provides information on a study which examined a network of N chaotic oscillators connected by intermittently coupled capacitors (ICC). Description of a nonautonomous chaos generator in the ICC network; Analysis of the ICC network; Conclusion.

Considers a class of switched dynamical systems to which two periodic inputs are applicable. System and analysis tool; Application to the Buck-Boost converter; Description of the circuit model.

Presents information on a study which considered the master-slave synchronization of a complex chaotic system using multiplex pulse trains. Design of the system; Analysis of synchronization behavior; Synchronization via multiplex and stabilized pulse trains; Conclusions.

Presents a study which proposes a network of continuous-time chaotic cells and considers its dynamics. Presentation of a cell exhibits chaos; Methods and materials used in the study; Construction of a network by occasional linear connection.

Abstract: The spreading of a flame over a layer of magnesium powder has been examined to clarify the mechanisms of flame spread over metal powder layers and to establish effective ways to extinguish metal fires. Four grades of magnesium powder were used, with average grain diameters of 60, 170, 360 and 500μm. The flame spread rate for larger particle sizes (D>170μm) increased slightly with increasing particle size. However, the flame spread rate for smaller particle sizes (D<63μm) increased sharply. The detailed surface temperature history of the magnesium powder layer was measured using infrared thermography (IR). Based on the temperature distribution in the pre-heat zone, the characteristic length l, characteristic depth δ, and characteristic time τ were calculated. The characteristic scale ratio, L/δ, for the larger particle sizes (D>170μm) is almost unity, which suggests that the dominant heat transfer mechanism is heat conduction through the magnesium powder layer (solid phase). However, the L/δ for the smaller particle sizes (D<63μm) is about 2.7, suggesting that the dominant heat transfer mechanism is convection. The flame spread rate over the magnesium powder layer was calculated by the de Ris model, a one-dimensional flame spread model, and a surface flash model. For larger particle sizes (D>170μm), there is good agreement between the experimental flame spread rate and the flame spread rate estimated by the one-dimensional model. However, the flame spread rate was underestimated by the de Ris model, apparently because the de Ris model only considers heat feedback from the gas phase. For small-particle sizes (D<63μm), there is good agreement between the experimental flame spread rate and the flame spread rate estimated by the surface flash model. This suggests that the flame spread over a small-particle layer can be described by a mechanism rather similar to that of gas phase flame propagation. [Copyright &y& Elsevier]

Abstract: This paper presents a spiking neuron circuit with a triangular base signal. The circuit can output rich pulse-trains and the dynamics can be analyzed using a piecewise linear one-dimensional pulse-position map. Applying cross-switching to two neurons we construct a pulse-coupled system whose dynamics can be integrated into a composite map of the pulse position maps of two neurons. The composite map is piecewise linear and precise analysis is possible. We can clarify various interesting phenomena caused by the pulse-coupling. For example, periodic behavior of each neuron is changed into chaotic behavior and chaotic behavior of each neuron is changed into periodic behavior. These results provide basic information to construct flexible pulse-coupled neural networks. [Copyright &y& Elsevier]

Discusses control of chaos from an artificial neural cell. Description of the cell as piecewise linear and with bipolar hysteresis; Proof of chaos generation using a mapping procedure; Calculation of the initial point of unstable periodic orbits (UPO) embedded in chaos; Stabilization of the desired UPO by using a modified occasional proportional feedback.

This paper overviews nonlinear dynamics of switching power converters which are common objects in dynamical system theory and power electronics. First, complex dynamics of single switching power converters is discussed. Their nonlinear switching can cause rich chaotic and bifurcation phenomena including complicated superstable periodic behavior in discontinuous conduction mode. Second, paralleled converters with winner-take-all switching is discussed. This system can realize multiphase synchronization relating to current sharing with smaller ripple for low-voltage high-current capabilities. Analysis of the dynamics is performed through simple models having piecewise constant vector field and piecewise linear trajectories. Third, simple hardware implementation method is shown and typical phenomena are confirmed experimentally. Finally some future problems are discussed. [ABSTRACT FROM AUTHOR]

Investigates shock-tube operation initiated by rupturing the diaphragm with laser-beam irradiation to determine the usefulness and the eventual drawbacks of this new technique. Description of an ideal shock-tube operation; Application of remote and temporal control of diaphragm rupture; Apparatus and experimental conditions.