Search Results (4)

Numerical simulations, based on the theories of computational fluid dynamics and combustion, are currently a powerful tool in the field of fire engineering. Field models allow us to analyze key aspects such as the integrity of buildings and safety. However, it is fundamental to define strategies that allow engineers to obtain a balance between the precision of the results and the computational cost. One of the most relevant sub-models is the turbulence model. This paper presents the research carried out in the field of two-dimensional computational simulations of turbulent dilatable flows to evaluate the behavior of diffusion flames, hot gases, and smoke produced in accidental fires. Several computational simulations have been performed using direct numerical simulations and large eddy simulation turbulence models in the two-dimensional field, analyzing the ability of the models to correctly characterize the transport of hot gases and the behavior of the thermal plumes if the grid resolution is adequate to the physics of the problem. Additionally, several three-dimensional models have been developed to contrast and validate the results obtained in the two-dimensional simulations. In order to validate the capacity to develop a qualitative analysis of two-dimensional models in fire engineering, an evaluation criterion is presented based on the frequency spectral analysis to study the capacity of each type of turbulence model to accurately capture the vorticity of these dilatable flows. Full article

Flame holders are widely used in ramjet combustors. We propose using surface nanosecond-pulsed surface-dielectric-barrier-discharge (NS-DBD) to manipulate the flame-holder flow field experimentally. The electrical characteristics, induced flow performance, and temperature distribution of NS-DBD were investigated via the electrical and optical measurement system. In the filamentary discharge mode, the discharge energy rose with decrease of the ambient pressure. The discharge pattern of NS-DBD changed from filamentous to uniform around 5 kPa. Starting-vortex intensity and jet-flow angle relative to the wall increased at low pressure. The recirculation zone was asymmetrical at pressures above 60 kPa. The recirculation zone’s area and length were smaller at lower pressures, but when the actuator was operating, the recirculation zone was nearly 11.8% longer. The vorticity increased with pressure. When the pulse width was 300 ns, the actuator had the greatest effect, and the low velocity region (LVR) area and the fuel–air-mixture residence time (FMRT) could be increased by 31.8% and 20.5%, respectively. The actuator had a smaller widening effect on the LVR area at lower pressure. Rising-edge time should increase with pressure to optimize LVR increase; it should be above 300 ns to optimize FMRT increase. We conclude that NS-DBD is a viable method of controlling flame-holder airflow at low pressure. Full article

Two-dimensional superconductors with disorder at the nanoscale can host a variety of intriguing phenomena. The superconducting transition is marked by a broad percolative transition with a long tail of the resistivity as function of the temperature. The fragile filamentary superconducting clusters, forming at low temperature, can be strengthened further by proximity effect with the surrounding metallic background, leading to an enhancement of the superfluid stiffness well below the percolative transition. Finite-frequency dissipation effects, e.g., related to the appearance of thermally excited vortices, can also significantly contribute to the resulting physics. Here, we propose a random impedance model to investigate the role of dissipation effects in the formation and strengthening of fragile superconducting clusters, discussing the solution within the effective medium theory. Full article

Hodgkin and Huxley showed that even if the filaments are dissolved, a neuron’s membrane alone can generate and transmit the nerve spike. Regulating the time gap between spikes is the brain’s cognitive key. However, the time modula-tion mechanism is still a mystery. By inserting a coaxial probe deep inside a neuron, we have re-peatedly shown that the filaments transmit electromagnetic signals ~200 μs before an ionic nerve spike sets in. To understand its origin, here, we mapped the electromagnetic vortex produced by a filamentary bundle deep inside a neuron, regulating the nerve spike’s electrical-ionic vortex. We used monochromatic polarized light to measure the transmitted signals beating from the internal components of a cultured neuron. A nerve spike is a 3D ring of the electric field encompassing the perimeter of a neural branch. Several such vortices flow sequentially to keep precise timing for the brain’s cognition. The filaments hold millisecond order time gaps between membrane spikes with microsecond order signaling of electromagnetic vortices. Dielectric resonance images revealed that ordered filaments inside neural branches instruct the ordered grid-like network of actin–beta-spectrin just below the membrane. That layer builds a pair of electric field vortices, which coherently activates all ion-channels in a circular area of the membrane lipid bilayer when a nerve spike propagates. When biomaterials vibrate resonantly with microwave and radio-wave, simultaneous quantum optics capture ultra-fast events in a non-demolition mode, revealing multiple correlated time-domain operations beyond the Hodgkin–Huxley paradigm. Neuron holograms pave the way to understanding the filamentary circuits of a neural network in addition to membrane circuits. Full article