High-speed Propagation Research Articles

Shock-wave processes evolution in fused quartz under intense energy action

The paper considers gas-dynamical processes evolving as a result of laser action in fused quartz. A conventional approach is used to construct a model for equation of state which provides an adequate description of the silica state at high densities of energy typical for local optical silica damage. Shock-wave processes generated in the medium due to the local laser energy deposition are calculated using fully conservative numerical technique. The obtained results provide relatively accurate description of the process in a wide range of parameters and allow further research to get clear interpretation of high-speed propagation of the laser absorbing front through the silica optical fiber.

Precipitation response of monsoon low‐pressure systems to an idealized uniform temperature increase

AbstractThe monsoon low‐pressure systems (LPSs) are one of the most rain‐bearing synoptic‐scale systems developing during the Indian monsoon. We have performed high‐resolution, convection‐permitting experiments of 10 LPS cases with the Weather Research and Forecasting regional model, to investigate the effect of an idealized uniform temperature increase on the LPS intensification and precipitation. Perturbed runs follow a surrogate climate change approach, in which a uniform temperature perturbation is specified, but the large‐scale flow and relative humidity are unchanged. The differences between control and perturbed simulations are therefore mainly due to the imposed warming and moisture changes and their feedbacks to the synoptic‐scale flow. Results show that the LPS precipitation increases by 13%/K, twice the imposed moisture increase, which is on the same order as the Clausius‐Clapeyron relation. This large precipitation increase is attributed to the feedbacks in vertical velocity and atmospheric stability, which together account for the high sensitivity. In the perturbed simulations the LPSs have higher propagation speeds and are more intense. The storms intensification to the uniform temperature perturbation can be interpreted in terms of the conditional instability of second kind mechanism where the condensational heating increases along with low‐level convergence and vertical velocity in response to temperature and moisture increases. As a result, the surface low deepens.

Visual Stimuli Evoked Action Potentials Trigger Rapidly Propagating Dendritic Calcium Transients in the Frog Optic Tectum Layer 6 Neurons.

The superior colliculus in mammals or the optic tectum in amphibians is a major visual information processing center responsible for generation of orientating responses such as saccades in monkeys or prey catching avoidance behavior in frogs. The conserved structure function of the superior colliculus the optic tectum across distant species such as frogs, birds monkeys permits to draw rather general conclusions after studying a single species. We chose the frog optic tectum because we are able to perform whole-cell voltage-clamp recordings fluorescence imaging of tectal neurons while they respond to a visual stimulus. In the optic tectum of amphibians most visual information is processed by pear-shaped neurons possessing long dendritic branches, which receive the majority of synapses originating from the retinal ganglion cells. Since the first step of the retinal input integration is performed on these dendrites, it is important to know whether this integration is enhanced by active dendritic properties. We demonstrate that rapid calcium transients coinciding with the visual stimulus evoked action potentials in the somatic recordings can be readily detected up to the fine branches of these dendrites. These transients were blocked by calcium channel blockers nifedipine CdCl2 indicating that calcium entered dendrites via voltage-activated L-type calcium channels. The high speed of calcium transient propagation, >300 μm in <10 ms, is consistent with the notion that action potentials, actively propagating along dendrites, open voltage-gated L-type calcium channels causing rapid calcium concentration transients in the dendrites. We conclude that such activation by somatic action potentials of the dendritic voltage gated calcium channels in the close vicinity to the synapses formed by axons of the retinal ganglion cells may facilitate visual information processing in the principal neurons of the frog optic tectum.

Natural light harvesting systems: unraveling the quantum puzzles

In natural light harvesting systems, the sequential quantum events of photon absorption by specialized biological antenna complexes, charge separation, exciton formation and energy transfer to localized reaction centers culminates in the conversion of solar to chemical energy. A notable feature in these processes is the exceptionally high efficiencies ( $$>$$ 95 %) at which excitation is transferred from the illuminated protein complex site to the reaction centers. The high speed of excitation propagation within a system of interwoven biomolecular network structures, is yet to be replicated in artificial light harvesting complexes. A clue to unraveling the quantum puzzles of nature may lie in the observations of long lived coherences lasting several picoseconds in the electronic spectra of photosynthetic complexes, which occurs even in noisy environmental baths. However the exact nature of the association between the high energy propagation rates and strength of quantum coherences remains largely unsolved. A number of experimental and theoretical studies have been devoted to unlocking the links between quantum processes and information protocols, in the hope of finding the answers to nature’s puzzling mode of energy propagation. This review presents recent developments in quantum theories, and links information-theoretic aspects with photosynthetic light-harvesting processes in biomolecular systems. There is examination of various attempts to pinpoint the processes that underpin coherence features arising from the light harvesting activities of biomolecular systems, with particular emphasis on the effects that factors such non-Markovianity, zeno mechanisms, teleportation, quantum predictability and the role of multipartite states have on the quantum dynamics of biomolecular systems. A discussion of how quantum thermodynamical principles and agent-based modeling and simulation approaches can improve our understanding of natural photosynthetic systems is included.

Imaging of the early acceleration phase of the 2013–2014 Boso slow slip event

AbstractWe analyze GPS and seismic data to examine the spatiotemporal evolution of a slow slip event (SSE) near Boso Peninsula, central Japan, from December 2013 to January 2014. The evolution of this SSE and its associated seismicity is divided into two distinct phases. Slip initially accelerated slowly with low slip rates, low propagation speeds, and no accompanying seismicity during the early phase and then accelerated more rapidly with higher slip rates, a higher propagation speed, and local earthquake swarm activity during the later phase. The seismicity was highly correlated in space and time with slip rate, suggesting that the swarm activity was triggered by stress loading due to the slow slip. The transition from the slow to faster phase shares some similarities with the nucleation of megathrust earthquakes inferred from foreshock activities, suggesting that SSEs may provide insights into the nucleation of large earthquakes.

Achromatic THz wave plate composed of stacked parallel metal plates

We propose a simple achromatic terahertz wave plate composed of stacked parallel metal plates with a hole array. It consists of an ensemble of designed parallel plate waveguides; the high and low propagation speeds of waves in TE and TM waveguide modes with the same group velocity cause a constant phase difference over a wide frequency region. Using that wave plate, we obtained intense single- and multi-cycle THz pulses with circular polarization.

근거리 수중통신을 위한 가시광 LED 적용에 관한 연구

Robust and high speed underwater communication is severely limited when compared to communications in terrestial. In free space, RF communication operates over long distances at high data rates. However, the obstacle in seawater is the severe attenuation due to the conducting nature. Acoustic modems are capable of long range communication up to several tens of kilometers, but it has low data-rate, high power consumption and low propagation speed. An alternative means of underwater communication is based on optics, wherein high data rates are possible. In this paper, the characteristics of underwater channel in the range of visible wavelength is investigated. And the possibility of optical wireless communication in underwater is also described. The LED-based transceiver and CMOS sensor module are integrated in the system, and the performance of image transmission was demonstrated.

Analysis of onset and severity of knock in SI engine based on in-cylinder pressure oscillations

This paper, based on pressure wave equation coupled with KIVA-3V combustion codes with reduced kinetics mechanism, analyzed and discussed the onset and severity of knock identified by different knock metrics in SI engine running at different speeds. The calculated results demonstrated that the knock onset defined by pressure oscillations characteristics here was approximately consistent with that defined by heat release. Meanwhile, the knock onset shifted backwards in high-speed region where relatively high flame propagation speed prevented the occurrence of auto-ignition, and thus knock intensity, characterized by knock metrics, MAPO and KI20, decreased observably. Visualized 3D calculation results were presented to show the flame propagation and pressure oscillation characteristics. Finally, the correlation between engine speed and the onset and severity of knock indicated that knock onset was highly correlated to engine speed, the knock intensity judged by MAPO and KI20 was accurate basically, and KI20 knock metric was better due to more pressure oscillations characteristics information contained. The comparison between experimental and calculated results indicated that the onset and intensity of knock can be characterized and quantified accurately with high-frequency pressure oscillations characteristics calculated with pressure wave equation.

섬유강화 복합재의 동적 취성 파괴현상 규명을 위한 비국부 페리다이나믹스 해석법 개발: 비대칭 하중 연구

In this paper a computational method for a homogenized peridynamics description of unidirectional fiber-reinforced composites is presented. For these materials, dynamic brittle fracture and damage are simulated with the proposed peridynamic model. Compared with observations from dynamic experiments by Coker et al.(2001), the peridynamic computational model can reproduce various characteristics of dynamic fracture and supersonic or intersonic crack growth in asymmetrically loaded unidirectional fiber-reinforced composite plates. Also we analyze the same model in the symmetric loading condition and figure out that the asymmetric loading leads to a much higher propagation speed. Consistent results have been reported in the experiments.

Size and constraint effects on interfacial fracture behavior of microscale solder interconnects

The fracture behavior of solder joints has long been an important issue in the reliability evaluation of electronic components and packages. In this study, experimental and finite element methods were used to characterize the interfacial fracture behavior of “Cu-wire/solder/Cu-wire” sandwich-structured microscale Sn–3.0Ag–0.5Cu solder joints with different diameters (100–575μm) and thicknesses (35–325μm) under quasi-static micro-tension loading, with systematic comparison to Sn–37Pb solder joints. Dynamic stress intensity factors for the microcracks in Cu, Sn–3.0Ag–0.5Cu, and Sn–37Pb under pulse tensile loading and high speed propagation were calculated. The numerical simulation results showed that the interface stress intensity factors KII and KI for the crack set at the solder/IMC interface increased with increasing the thickness of the joints from 35μm to ∼125μm, and thereafter decreased and then became stable. With increasing the diameter of the joints, basically KI increases while KII decreases. Under the quasi-static micro-tension loading, the crack driving forces in Sn–3.0Ag–0.5Cu solder joints are lower than that in Sn–37Pb joints, and this means that fracture is less likely to occur in Sn–3.0Ag–0.5Cu solder joints than in Sn-joints. The rapid expansion of a high hydrostatic pressure region may enhance the mechanical performance of interconnects when the diameter-to-thickness ratios of the joints are very large. As the diameter of the solder joints increases, the evolution of the energy release distribution results in a change of the fracture position and mechanism in the interconnects. Compared to Sn–37Pb solder, the Sn–3.0Ag–0.5Cu lead-free solder shows a lower resistance to rapid crack propagation under constant tensile loading.

Dispersion relations and modes of wave propagation in inclusion-reinforced composite plates

This paper is intended to examine the effect of inclusion shapes, inclusion contents, inclusion elastic constants, and plate thickness on the dispersion relations and modes of wave propagation in inclusion-reinforced composite plates. The shape of inclusion is modeled as spheroid that enables the composite reinforcement geometrical configurations ranging from sphere to short and continuous fiber. Mori–Tanaka mean-field theory is used to predict the effective elastic moduli of the composite plate explicitly. The effective elastic moduli are able to elucidate the effect of inclusion’s shape, stiffness, and volume fraction on the composite’s anisotropic elastic behavior. The resulting moduli are then used to determine the dispersion relations and the modal patterns of Lamb waves using the dynamic stiffness matrix method. The types (symmetric or antisymmetric) of Lamb waves in an isotropic plate can be classified according to the wave motions are symmetrical or antisymmetric about the midplane of the plate. Classifying the wave type in an anisotropic plate is not as simple as that in an isotropic plate, and has not received proper attention in the literature. The wave types and orders are identified by analyzing the dispersion curves and inspecting the calculated modal patterns, and the results indicate that the Lamb waves in an orthotropic composite plate can also be classified as either symmetric or antisymmetric waves. It is also found that the inclusion contents, aspect ratios and plate thickness affect propagation velocities, higher-order mode cutoff frequencies, and modal patterns. Propagation speed is generally increased with the aspect ratio, e.g., using longer fibers generally results in a higher propagation speed.

THE DISAPPEARING SOLAR FILAMENT OF 2003 JUNE 11: A THREE-BODY PROBLEM

The eruption of a large quiescent filament on 2003 June 11 was preceded by the birth of a nearby active region?a common scenario. In this case, however, the filament lay near a pre-existing active region and the new active region did not destabilize the filament by direct magnetic connection. Instead it appears to have done so indirectly via magnetic coupling with the established region. Restructuring between the perturbed fields of the old region and the filament then weakened the arcade overlying the midpoint of filament, where the eruption originated. The inferred rate (~11??day?1) at which the magnetic disturbance propagates from the mature region to destabilize the filament is larger than the mean speed (~5?-6??day?1) but still within the scatter obtained for Bruzek's empirical relationship between the distance from a newly formed active region to a quiescent filament and the time from active region appearance to filament disappearance. The higher propagation speed in the 2003 June 11 case may be due to the broadside (versus ''end-on) angle of attack of the (effective) new flux to the coronal magnetic fields overlying a central section of the axis of the filament.

Black holes in Einstein-aether and Hořava-Lifshitz gravity

We study spherical black-hole solutions in Einstein-aether theory, a Lorentz-violating gravitational theory consisting of General Relativity with a dynamical unit timelike vector (the "aether") that defines a preferred timelike direction. These are also solutions to the infrared limit of Horava-Lifshitz gravity. We explore parameter values of the two theories where all presently known experimental constraints are satisfied, and find that spherical black-hole solutions of the type expected to form by gravitational collapse exist for all those parameters. Outside the metric horizon, the deviations away from the Schwarzschild metric are typically no more than a few percent for most of the explored parameter regions, which makes them difficult to observe with electromagnetic probes, but in principle within reach of future gravitational-wave detectors. Remarkably, we find that the solutions possess a universal horizon, not far inside the metric horizon, that traps waves of any speed relative to the aether. A notion of black hole thus persists in these theories, even in the presence of arbitrarily high propagation speeds.

Diesel and rapeseed methyl ester (RME) pilot fuels for hydrogen and natural gas dual-fuel combustion in compression–ignition engines

This paper presents experimental results of rapeseed methyl ester (RME) and diesel fuel used separately as pilot fuels for dual-fuel compression–ignition (CI) engine operation with hydrogen gas and natural gas (the two gaseous fuels are tested separately). During hydrogen dual-fuel operation with both pilot fuels, thermal efficiencies are generally maintained. Hydrogen dual-fuel CI engine operation with both pilot fuels increases NO x emissions, while smoke, unburnt HC and CO levels remain relatively unchanged compared with normal CI engine operation. During hydrogen dual-fuel operation with both pilot fuels, high flame propagation speeds in addition to slightly increased ignition delay result in higher pressure-rise rates, increased emissions of NO x and peak pressure values compared with normal CI engine operation. During natural gas dual-fuel operation with both pilot fuels, comparatively higher unburnt HC and CO emissions are recorded compared with normal CI engine operation at low and intermediate engine loads which are due to lower combustion efficiencies and correspond to lower thermal efficiencies. This could be due to the pilot fuel failing to ignite the natural gas–air charge on a significant scale. During dual-fuel operation with both gaseous fuels, an increased overall hydrogen–carbon ratio lowers CO 2 emissions compared with normal engine operation. Power output (in terms of brake mean effective pressure, BMEP) as well as maximum engine speed achieved are also limited. This results from a reduced gaseous fuel induction capability in the intake manifold, in addition to engine stability issues (i.e. abnormal combustion). During all engine operating modes, diesel pilot fuel and RME pilot fuel performed closely in terms of exhaust emissions. Overall, CI engines can operate in the dual-fuel mode reasonably successfully with minimal modifications. However, increased NO x emissions (with hydrogen use) and incomplete combustion at low and intermediate loads (with natural gas use) are concerns; while port gaseous fuel induction limits power output at high speeds.

Modelling security message propagation in delay tolerant networks

ABSTRACTDelay tolerant networks (DTNs) are new emerging technologies aiming to solve communication issues in challenged network environments. In such networks, any real‐time interactive key agreement protocol does not work due to the intermittent connectivity and long time delay in message round trips. In the context of specific applications, such as single hop authentication, manual public key exchange is the most direct method because single hop authentication can be achieved by holding a small part of node's public key. To evaluate how many public keys should be maintained by each node to achieve a high propagation speed while single hop authentication scheme is used, in this paper, we proposed a security message propagation model for DTNs formed by vehicles where the extended graph theory and rumor spreading terminology in complex networks were harnessed. We find that holding 8–10 public keys by each node is optimal. And decay rate threshold is 0.16 under which message can be disseminated throughout the whole network. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Strain rate effects on the nonlinear development of hydrodynamically unstable flames

In this study we numerically implement the hydrodynamic model for a premixed flame as a nonlinear free boundary problem where the flame is tracked via a level set equation and the flow is described by a solution of the variable density Navier–Stokes equations. Unlike an earlier similar study, the present model is enriched by fully accounting for hydrodynamic strain in the flame stretch relation which, in turn, affects the local flame speed. The objective is to comprehensively analyze the effect of strain on the onset of the hydrodynamic instability and on the nonlinear development that takes place beyond its inception. The initial evolution is corroborated with the results of a linear stability analysis for which strain rate effects are fully included. We show that while strain provides an additional stabilizing effect on the short wavelength disturbances, thereby delaying the onset of the hydrodynamic instability, it acts to sharpen the cusps near the troughs of the corrugated flame that develops beyond the stability threshold resulting in a larger flame surface area and a higher propagation speed.

A multiscale approach to mesh-based surface tension flows

We present an approach to simulate flows driven by surface tension based on triangle meshes. Our method consists of two simulation layers: the first layer is an Eulerian method for simulating surface tension forces that is free from typical strict time step constraints. The second simulation layer is a Lagrangian finite element method that simulates sub-grid scale wave details on the fluid surface. The surface wave simulation employs an unconditionally stable, symplectic time integration method that allows for a high propagation speed due to strong surface tension. Our approach can naturally separate the grid- and sub-grid scales based on a volume-preserving mean curvature flow. As our model for the sub-grid dynamics enforces a local conservation of mass, it leads to realistic pinch off and merging effects. In addition to this method for simulating dynamic surface tension effects, we also present an efficient non-oscillatory approximation for capturing damped surface tension behavior. These approaches allow us to efficiently simulate complex phenomena associated with strong surface tension, such as Rayleigh-Plateau instabilities and crown splashes, in a short amount of time.

Experimental investigation of dynamics of premixed acetylene–air flames in a micro-combustor

This paper describes a detailed experimental study performed to investigate the flame propagation behaviour of premixed flames in micro-channels. A novel, modular, stackable micro-combustor was developed for this purpose. For a chosen planar channel geometry, the flow condition and the mixture equivalence ratio of premixed acetylene–air were varied to investigate various modes of operation. Three different modes of operation were observed; they were (i) stable periodic operation – consisting of ignition, flame propagation, flame extinction, and re-ignition, (ii) a-periodic operation, and (iii) anchored flame condition. The present work also aims to provide quantitative information on the dynamics of premixed acetylene–air flames propagating inside micro-channels. A novel measurement approach based on OH * chemiluminescence measurements employing a single photomultiplier unit was developed for this purpose. The data recorded were post processed using an in-house developed MATLAB code to evaluate the mean flame propagation speed measured between three different spatial locations along the length of the micro-channel. The results from the flame propagation speed measurements performed during ‘periodic’ mode of operation indicated that the flame travelled at higher propagation speed in the mid-length region of the channel compared to that at the initial entry point, suggesting flame acceleration. This flame acceleration could be attributed to a situation where the flame experienced different local equivalence ratio conditions at different upstream locations. The results suggest that after completion of a cycle of operation consisting of ignition, flame propagation and flame extinction, the fresh mixture that filled the channel was diluted with the exhaust gas from the previous cycle. This pocket of diluted mixture convected downstream with time, thus enabling the spatial variation in local equivalence ratio along the micro-channel.

Numerical simulations of interactions between a flame bubble with an incident shock wave and its focusing wave

The numerical investigations of interactions between a flame bubble with an incident shock wave (IW) and its focusing wave (FW) in a reactive CH4—O2—N2 mixture are presented. The time-dependent, two-dimensional axisymmetric, reactive Navier—Stokes equations, with detailed chemical mechanisms, are employed to simulate the multiple shock—flame interactions process. The effects of the IW Mach number and chemical reactivity of mixture on flame structure and evolution are examined. The results of simulations show that the initial flame bubble can interact with IW, bow wave (BW), reflected BW, and FW in sequence. For the weak IW case, the repeated shock—flame interactions produce multiple Richtmyer—Meshkov (RM) instabilities that lead to the convolved flame with vortex structures, and the chemical heat release does not play a major role. While for the strong IW case, the multiple RM instabilities lead to the highly distorted flame with the complex vortices structures of large magnitude. With the lower reactive mixture, the instability process is the major mechanism for shock—flame interaction, while the chemistry only plays a minor role. However, with the higher reactive mixture, the distorted flame expands rapidly and finally forms the large-scale combustion through the interaction with FW. Both instability and chemical heat release play the important mechanisms in this case. The combustion acceleration in the highly reactive mixture can produce the stronger overpressure and the higher propagation speed of complex FW because of the chemi-acoustic interaction effect.

High-Frequency Propagation on Printed Circuit Board Using a Material With a Low Dielectric Constant, a Low Dielectric Loss, and a Flat Surface

For the next-generation printed circuit boards with a fine pattern, low power consumption and high-speed propagation with low variation of signal propagation must be satisfied. In order to meet such requirements, we investigated a dielectric material for printed circuit boards which has three superior features: low dielectric constant (permittivity), low dielectric loss, and a flat surface with sufficient adhesion force for plating metal. The propagation loss of a microstrip line on the developed material is about 40% of the conventional material at 10 GHz. Significant reduction of the manufacturing fluctuation of the developed materials is achieved due to the flat surface. We adopted a distributed constant model to the propagation results and revealed that the significant reduction of the propagation loss is caused by the flat surface and low dielectric loss. This technology greatly contributes to the next generation of printed circuit boards.