High-speed Propagation Research Articles

Experimental and numerical study on focused wave generation using different energy modes

This paper reports an experimental and numerical study on the generation of freak waves related to the spatiotemporal focusing mechanism, where multiple water waves converge at a specific point in space and time to produce a large transient wave. A new energy distribution mode of constant-difference wave number (CDK) within the wave group is proposed and applied to both a physical and a numerical flume to generate focused waves, with primary attention given to the water surface elevation, underlying kinematics, and internal spectrum structure during the focused wave generation process. The classical experiment by Baldock et al. [“A laboratory study of nonlinear surface waves on water,” Philos. Trans. R. Soc., Ser. A 354, 649–676 (1996)], which used a constant-difference wave period within the wave group, is chosen for comparison. Spectral analysis shows that the CDK energy distribution mode can easily stimulate multiwave resonance in the focused wave group, where significant energy transfer from the main frequencies to higher harmonics is observed. Compared with the data from Baldock et al. [“A laboratory study of nonlinear surface waves on water,” Philos. Trans. R. Soc., Ser. A 354, 649–676 (1996)], the CDK wave group produces larger focused wave crests with higher propagation speeds and larger velocity gradients near the water surface due to strong multiwave resonance. The effects of the input spectrum, incident amplitude and initial water depth under different energy modes on focused-wave generation are analyzed. All the results indicate that the CDK energy distribution mode can produce larger focused waves compared to other energy distribution modes, which offers a novel approach for generating freak waves in the laboratory.

Sub-millimeter propagation of antiferromagnetic magnons via magnon-photon coupling

For the realization of magnon-based current-free technologies, referred to as magnonics, all-optical control of magnons is an important technique for both fundamental research and practical applications. Magnon-polariton is a coupled state of magnon and photon in a magnetic medium, expected to exhibit magnon-like controllability and photon-like high-speed propagation. While recent studies have observed magnon-polaritons as modulation of incident terahertz waves, the influence of magnon-photon coupling on magnon propagation properties remains unexplored. This study aimed to observe the spatiotemporal dynamics of coherent magnon-polaritons through time-resolved imaging measurements. BiFeO3 was selected as the sample due to its anticipated strong coupling between magnons and photons. The observed dynamics suggest that antiferromagnetic magnons can propagate over long distances, up to hundreds of micrometers, through strong coupling with photons. These results enhance our understanding of the optical control of magnonic systems, thereby paving the way for terahertz opto-magnonics.

Investigation of gas exchange parameters of small two stroke engine correlated with hydrogen fuel supplement

Due to the lack of complete dedicated suction and exhaust strokes and obviate the need of valvetrain assembly in two stroke engines, the bottom surface of the piston and the crankcase is used as a scavenging pump leads to that about one fifth of the fresh charge is short-circuited to the exhaust results in very high hydrocarbon emissions and poor fuel consumption. It is suggested that a combination of gasoline and hydrogen could be a superior solution combining the advantages of both engine itself and hydrogen doping. An accurate amount of hydrogen that has high flame propagation speed blended with gasoline could provide faster combustion of fuel mixture over the few crank angle degrees in the short gas exchange process reducing short-circuited charge with little modifications to the engine system. In this paper hydrogen-gasoline blend as an alternative fuel in a 63.3 cc, air cooled single cylinder, crankcase scavenged two stroke engine is tested. The unseen decommissioning of small two stroke engine in near future, the attractiveness of studying alternative fuel specially hydrogen and absence of investigation of the effect of hydrogen fuel supplement on gas exchange parameters molded this paper.

A distance adaptive dual-hop routing algorithm for underwater optical wireless networks

Three main kinds of underwater wireless communication, which employ acoustic waves, radio frequency and optical waves, have attracted intensive research interests in recently years. Among them, the underwater optical wireless communication (UOWC) is characterized by high propagation speed and large transmission bandwidth. But, the optical waves in underwater environment are significantly affected by absorption and scattering effects, which limit their transmission range. In order to enhance the performance of UOWC, designing a transmission and energy efficiency routing algorithm has become a non-ignorable issue in UOWC. In this paper, a transmission distance adaptive dual-hop (TDAD) routing algorithm is proposed for underwater optical wireless networks (UOWNs) to improve their efficiency in packet-delivery and energy-consumption. Unlike the existing routing algorithms designed for UOWNs, which pre-set the transmission range of network nodes, the proposed TDAD algorithm adaptively selects the transmission range for each node according to the diversity of heterogeneous service requests and employs location and energy information in its dual-hop based routing procedure. Simulation results indicate that the proposed TDAD algorithm remarkably improves packet delivery rate with more balanced energy consumption when compared to the deviation angle-based single-hop (DAS) algorithm and the distributed sector-based (DS) routing algorithm.

BLPCA-ledger: A lightweight plenum consensus protocols for consortium blockchain based on the hyperledger indy

An examination of different distributed real-time applications operating on the blockchain platform is conducted. These applications can be broadly classified into three types: permissionless public, permissioned private, and consortium chains. In order for a decentralized network to function independently, consensus mechanisms are needed to facilitate the delivery of transactions and keep track of them in a ledger. But the fundamental idea behind Blockchain technology is the use of several consensus protocols, like Proof of Stake, Proof of Elapsed Time, etc., which requires greater processing power. In order to arrange transactions, it increases the demand for buying more computing units. Furthermore, present consortia blockchain consensus mechanisms lack a policy to collect socio-economic financial levies, including monies for charitable donations, education, and social activities. To collect socio-economic taxes, this study suggests a lightweight Plenum consensus algorithm called "BLPCA" for consortium blockchains built on Hyperledger Indy. The Byzantine Fault Tolerance concept combined with optimization is used in the suggested BLPCA systems to manage large-scale decentralized traffic of socioeconomic hierarchy. Because there are no transaction costs, BLPCA encourages government analysts to review funds using fewer resources. By including a multithreading heterogeneous technique, the BLPCA can effectively handle multi-transaction needs and execute this protocol in an industrial setting that operates in real-time. It is observed from the simulations that even in the worst-case network scenario—such as a fork—the suggested consortium blockchain does not crash a single transaction. In order to guarantee node scalability, a high propagation speed is determined. Furthermore, the BLPCA shows an excellent average time while constructing socioeconomic transaction blocks.

The synergistic effect mechanism of H2 generation during coal/ammonia co-pyrolysis

Coal/ammonia (NH3) co-combustion faces the problem of unstable ignition and combustion due to the high ignition temperature and low flame propagation speed of NH3. The pre-pyrolysis of coal and NH3 generates combustible gases such as hydrogen (H2) that aid in enhancing the stability of the subsequent ignition and combustion process. In this paper, the synergistic effect mechanism of H2 generation during coal/NH3 co-pyrolysis are investigated by constant temperature thermogravimetric experiments and reactive molecular dynamics (ReaxFF MD) simulations. The experimental results show that NH3 promotes coal pyrolysis, leading to an increase in the release of coal pyrolysis volatiles during coal/NH3 co-pyrolysis. Furthermore, both experimental and ReaxFF MD simulations results affirm a synergistic effect on H2 generation during coal/NH3 co-pyrolysis. The atomic labeling method is employed to reveal the mechanism of the synergistic effect on H2 generation during coal/NH3 co-pyrolysis. It is found that H2 generated solely from either coal or NH3 during co-pyrolysis is lower than that from the individual pyrolysis of coal or NH3, respectively. The synergistic effect on H2 generation during coal/NH3 co-pyrolysis is mainly attributed by the interactions between coal and NH3, resulting in the generation of coupling H2. The main reaction pathways for H2 generation during coal/NH3 co-pyrolysis are determined by analyzing the frequencies of H2 generation reactions. The mechanisms of the coupling H2 generation are revealed by tracing to the source of the important reactants in the main reactions for H2 generation. The coupling H2 are mainly formed through the directly pyrolysis of the coupling NHi, and the dehydrogenation reactions of the coupling hydrocarbons.

Social tie-driven coupling propagation of user awareness and information in Device-to-Device communications

Regarding information dissemination in Device-to-Device (D2D) communications, most existing works only consider user awareness as the influencing factor, which cannot accurately reflect the interaction between users and devices. In fact, user awareness and information interaction are inseparable from the social tie that describes the users’ intimacy. In this paper, we propose a social tie-driven coupling propagation dynamical model, taking into account both user awareness diffusion and information transmission. This model includes interprocess interaction factors that fully describe the user–user and user-device interaction behaviors. Through intensive experiments on the real-world Peer-to-Peer (P2P) and Facebook datasets with a tailored propagation algorithm, we show that the proposed model has a higher propagation speed and covers a larger propagation range than that of an existing single propagation process model. Our work also reveals that a strong social tie between users will promote the transmission of device information, which further accelerates the diffusion of user awareness.

Effect of ammonia addition on combustion characteristics of hydrogen/air using passive turbulent jet ignition

Hydrogen (H2) and ammonia (NH3) are ideal carbon-free fuels, and the application of NH3/H2 in internal combustion engines offers the potential to reduce carbon emissions. And turbulent jet ignition (TJI) is an advanced ignition strategy that can effectively enhance the combustion. This work aims to experimentally investigate the effect of NH3 addition on the combustion characteristics of H2/air mixtures under passive TJI conditions. Combustion images and instantaneous pressure were collected for processing and analysis. The effect of NH3 substitution and equivalence ratio were investigated. The results indicate that the peak combustion pressure decreases with the addition of NH3, accompanied by longer combustion duration and ignition delay, as well as lower jet velocity and flame area growth rate. The hot jet will be quenched by the strong heat transfer, causing the change in the ignition mechanism as the NH3 substitution ratio increases. In addition, compared to lean conditions, the combustion appears to be less sensitive to the equivalence ratio on the rich side and always shows high jet velocity and flame propagation speed. However, a relatively small amount of NH3 addition changes the ignition mechanism on the rich combustion side compared with lean conditions, resulting in a longer ignition delay.

Visible Light‐Sensitive Artificial Photonic Synapse

AbstractComputing based on artificial neuron networks holds great promise in overcoming the von Neumann bottleneck and significantly enhancing computing efficiency. It offers a wide range of possibilities for artificial visual system applications. Photonic synapses, as essential components, can contribute to improved efficiency in visual information processing by leveraging their low latency, high propagation speed, and broad bandwidth capabilities. Herein, a photonic transistor capable of detecting visible light and exhibiting synaptic characteristics under various visible stimuli is presented. This is achieved by integrating a photo‐sensitive polymer as a floating gate charge trapping medium. The synaptic device successfully emulates fundamental synaptic behaviors such as excitatory postsynaptic current (EPSC), pair‐pulse facilitation, the transition of short‐term memory to long‐term memory, and learning and forgetting processes. Furthermore, leveraging the ESPC responses, the informative synaptic outputs modulated by light signals enable a non‐contact writing method, paving the way for advancements in optical wireless communication. It is believed that this work serves as a promising building block to complete the bio‐inspired photonic computing paradigm.

Local propagation of visual stimuli in focus of attention

Fast reactions to changes in the surrounding visual environment require efficient attention mechanisms to reallocate computational resources to the most relevant locations in the visual field. In this paper, we present a biologically-plausible computational model of focus of attention that exhibits spatiotemporal locality and that is very well-suited for parallel and distributed implementations. Attention emerges as a wave propagation process originated by visual stimuli corresponding to details and motion information. The resulting field obeys the principle of “inhibition of return” so as not to get stuck in potential holes. The proposed model is obtained as a hyperbolic regularization of the Poisson equation to which it reduces in the limit of high speed of propagation. According to the MultiMatch algorithm for scanpaths comparison, the proposed model achieves very competitive results when considering dynamical input stimuli.

Unraveling the Ultrafast Coherent Dynamics of Exciton Polariton Propagation at Room Temperature.

Exciton polaritons are widely considered as promising platforms for developing room-temperature polaritonic devices, owing to the high-speed propagation and nonlinear interactions. However, it remains challenging to explore the dynamics of exciton polaritons specifically at room temperature, where the lifetime could be as small as a few picoseconds and the prevailing time-averaged measurement cannot give access to the true nature of it. Herein, by using the time-resolved photoluminescence, we have successfully traced the ultrafast coherent dynamics of a moving exciton polariton condensate in a one-dimensional perovskite microcavity. The propagation speed is directly measured to be ∼12.2 ± 0.8 μm/ps. Moreover, we have developed a time-resolved Michelson interferometry to quantify the time-dependent phase coherence, which reveals that the actual coherence time of exciton polaritons could be much longer (nearly 100%) than what was believed before. Our work sheds new light on the ultrafast coherent propagation of exciton polaritons at room temperature.

A classification and extraction method of attribute hybrid big data based on Naive Bayes algorithm

In the identification of network text information, the existing technology is difficult to accurately extract and classify text information with high propagation speed and high update speed. In order to solve this problem, the research combines the Naive Bayes algorithm with the feature two-dimensional information gain weighting method, uses the feature weighting method to optimize the Naive Bayes algorithm, and calculates the dimension of different documents and data categories through a new feature operation method. The data gain between them can improve its classification performance, and the classification models are compared and analyzed in the actual Chinese and English databases. The research results show that the classification accuracy rates of the IGDC-DWNB model in the Sogou database, 20-newsgroup database, Fudan database and Ruster21578 database are 0.89, 0.89, 0.93, and 0.88, respectively, which are higher than other classification models in the same environment. It can be seen that the model designed in the research has higher classification accuracy, stronger overall performance, and stronger reliability and robustness in practical applications, which can provide a new development idea for big data classification technology.

Research progress of optoelectronic devices based on diamond materials

Diamond has a variety of unique characteristics, including integrates mechanics, electricity, heat, optics and other excellent properties, so that it is widely focus on the field of high and new technology, especially in the optoelectronic technology. Because diamond has the characteristics of high thermal conductivity, high breakdown field (10 mV/cm), high electron and hole mobility, it has a wide application prospect in high temperature, high power and high frequency photoelectric equipment. The wide bandgap (5.47 eV) makes diamond an ideal material in ultraviolet detectors (UV). Its high carrier mobility and breakdown field strength make it an ideal choice for field emission materials, which are expected to be used in high-power electronic devices in the next few years. At the same time, in addition to high hardness, it also has various of excellent physical properties, such as low coefficient of thermal expansion, low coefficient of friction, high acoustic propagation speed and high optical transmittance, so that it has broad application prospects in many fields such as machining, microelectronic devices, optical windows and surface coatings. In addition, diamond also has a high exciton binding energy (80 meV), which plays an important development in deep ultraviolet and high-energy particle detectors. In this article, the latest progress in the application of diamond-based optoelectronic devices is reviewed. A variety of advanced devices and physical phenomena are considered, for example, sensors, transistors, memory, Light-emitting diode (LEDs), ultraviolet detectors and field emission. This review will provide a new idea to promote the development of photoelectric applications based on diamond structure.

Computational optimization of the performance of a heavy-duty natural gas pre-chamber engine

Optimization of the performance of a heavy-duty natural gas active pre-chamber (PC) engine was conducted using computational fluid dynamics (CFD) simulations. Seven different piston geometries were evaluated for their impact on engine performance. Unlike the narrow-throat PC, various piston geometries yielded a significant impact on the PC flow motion and fuel–air mixing process using the large-throat PC. Compared to flat-bottom pistons, ω-bottom pistons promoted the reverse flow from the MC and induced a broader lean-mixture distribution in the PC. For various ω-bottom pistons, enlarging the inner piston radius resulted in slower flame propagation within the PC, delaying the jet issuing and slowing down the turbulent flame propagation within the MC. The flat piston effectively reduced jet flame-piston interaction and promoted turbulent flame propagation within the squish region during the late combustion stage, but it generated higher wall heat transfer loss from the cylinder liner. A composite of ω- and flat-shaped pistons maintained the benefits of relatively high flame propagation speed within the squish region but low wall heat transfer loss, yielding the highest thermal efficiency of seven piston designs. The PC fueling ratio (PCFR) was found to be a critical factor in influencing the jet issuing process. A lower PCFR to establish a near-stoichiometric mixture within the PC promoted flame propagation and led to a faster jet ejection. An increase in compression ratio yielded higher engine efficiency due to the advanced combustion phasing and larger expansion ratio, it also resulted in higher wall heat transfer loss and nitric oxide (NOx) emission. The introduction of exhaust gas recirculation was able to effectively inhibit NOx formation, while also resulting in higher engine efficiency due to the lower wall heat transfer loss.

Ignition sensitivity and flame propagation of titanium powder cloud

The ignition sensitivity and flame propagation of titanium dust cloud were investigated to evaluate the risk of combustion and explosion of titanium powder. The minimum ignition temperature(MIT) was determined by Godbert-Greenwald furnace and the minimum ignition energy(MIE) was determined by Hartmann apparatus. The flame propagation behavior in the Hartmann apparatus was recorded by high-speed camera and infrared thermal imager. The results show that the spherical titanium powder with a median diameter of 12.5μm had a minimum ignition temperature of 400°C, a minimum ignition energy of less than 1mJ, and a maximum flame temperature of 1666°C. The dust concentration had a greater influence on the minimum ignition temperature than the dispersion pressure, titanium dust cloud had high ignition sensitivity and fast flame propagation speed. The experimental results can provide a reliable basis for judging the explosive risk of titanium powder.

Novel ammonia-driven chemically recuperated gas turbine cycle based on dual fuel mode

The potential safety hazards of hydrogen are relatively large due to its high flame propagation speed, strong permeability, small quenching distance and wide flammability limits. Decarbonization movement around the world has already driven ammonia (NH3) to become a potential solution for carbon-free economy and power generation with well-established infrastructure. Based on the principle of complementary fuel advantages and integrated cascade energy utilization, this study innovatively develops a novel power cycle based on a partial ammonia decomposition chemical reaction. The new design significantly ameliorates the problems of incomplete combustion of ammonia, as well as the safety hazards of hydrogen. By integrating with a chemically-recuperated unit, the exhaust heat can be fully utilized since the low-temperature waste heat is further used for evaporation of liquid NH3 and NH3 cracking processes. The thermal efficiency in the new design reaches 35.48–36.09% which is at least 21.67% higher than that (29.16–31.79%) in the reference system. The optimal condition is found as the ammonia split ratio reaches the maximum at 1 with a H2 molar ratio of 62.80–64.38%. The power generation efficiency can be improved to 43.55–43.90%, showing obvious advantages over pure ammonia condition. For a future carbon-free economy, this study should provide a new and efficient way for ammonia utilization.

Flame structure and stability for oxygen enhanced non-premixed combustion of highly diluted methane with helium and nitrogen

Laminar flames of highly diluted methane in a non-premixed co-flow configuration have been studied experimentally and numerically for two burners with different diameters. As the fuel is highly diluted methane, the oxidizer stream is oxygen-enhanced to get a stable anchored or lifted flame. Two different diluents, i.e., helium and nitrogen are used in the fuel stream, and the flame structure turns out to be notably different for these two cases. The nitrogen-diluted flames exhibit almost anchored nature. However, a helium-diluted flame can be stable at a lifted position despite having a less than unity Schmidt number (Sc). A higher propagation speed helps the helium-diluted flames to sustain till a lower oxygen percentage compared to nitrogen-diluted flames. The helium flames have a much higher positive buoyancy effect resulting in a higher lift-off height than nitrogen-diluted flames. On the other hand, varying the burner diameter from 4 mm to 9 mm shifted the flames from momentum-controlled regime to buoyancy-controlled regime, which attributed to the higher lift-off height for 4-mm burner flames for both helium and nitrogen cases. Apart from the lift-off height, the nature of the flame length is also explored for flames with both diluents. The structure of the flame – whether anchored or lifted – is also found to affect the variation of flame length with variation in oxygen percentage in the co-flow.

Integrated Photonic Computing beyond the von Neumann Architecture

In the context of a doomed end of the Moore’s law, various new types of computing architectures have been emerging, aiming to meet the demands of intractable computation and artificial intelligence. Photonic computing is a competitive candidate, in light of the inherent properties of photons, including high propagation speed, strong robustness, and multiple degrees of freedom to encode information. Also, the progress of integrated photonics continues to provide novel possibilities, apart from boosting the scalability and stability of photonic computing architectures. Moreover, an introduction of quantum technology might open a new chapter for photonic computing, from the view of single photons. In this Perspective, we highlight the unique features and advances of integrated photonic platforms, whose roles in constructing a non-von Neumann computing architecture are also outlined. We show their potential in solving problems beyond the reach of traditional computers and in machine learning and further discuss the conceivable challenges and opportunities.

The Mapping of Road Pavement Structure around the Seismically Active Regions by Using Ground Penetrating Radar

The Banda Aceh-Sigli Road has become the central infrastructure in connecting the capital city of Aceh province with other districts. In some places, the road construction was in rice fields dominated by high sedimentation areas. The Aceh also has the Great Sumatran Fault, which has caused many earthquakes and damaged public infrastructure, including roads. The density of the soil structure as an infrastructure buffer needs to be observed before road damage can endanger the community. This study aimed to apply Ground Penetrating Radar (GPR) as a non-destructive method that detects subsurface conditions based on permittivity parameters. The method is measured using the IDS Georadar Opera Duo instrument, which operates with a frequency of 250 MHz and 750 MHz for a penetration depth of 4 m, which is measured on eight intersecting tracks, where two profiles have a length of 110 m measured in the direction of the road segment and five tracks with a length of 11 m is measured by a cross. GresWin2 software is used for optimal analysis and modeling of 2D radargram. The radargram model describes a subsurface structure consisting of three layers, where the first layer with a depth of 0 – 0.25 m is asphalt, and the second and d layer with a depth of 0.25 – 0.75 m was identified as the base course layer. In comparison, the third layer is interpreted as a sub base course layer at a depth of 0.75 - 4 m below. The analysis results also show a linearly damaged road structure with high propagation speed and large wave amplitude. Therefore, based on data processing, it can be concluded that the application of GPR is a non-destructive, fast, and economical method for evaluating road structures.

Transmural Wave Speed Gradient May Distinguish Intrinsic Myocardial Stiffening From Preload-Induced Changes in Operational Stiffness in Shear Wave Elastography.

Shear wave elastography (SWE) is a promising technique to non-invasively assess myocardial stiffness based on the propagation speed of mechanical waves. However, a high wave propagation speed can either be attributed to an elevated intrinsic myocardial stiffness or to a preload-induced increase in operational stiffness. Our objective was to find a way to discriminate intrinsic myocardial stiffening from stiffening caused by an increased pressure in SWE. We used the finite element method to study the shear wave propagation patterns when stiffness and/or pressure is elevated, compared to normal stiffness and pressure. Numerical findings were verified in a few human subjects. The transmural wave speed gradient was able to distinguish changes in intrinsic stiffness from those induced by differing hemodynamic load (a speed of ±3.2 m/s in parasternal short-axis (PSAX) view was associated with a wave speed gradient of -0.17 ± 0.15 m/s/mm when pressure was elevated compared to 0.04 ± 0.05 m/s/mm when stiffness was elevated). The gradient however decreased when stiffness increased (decrease with a factor 3 in PSAX when stiffness doubled at 20 mmHg). The human data analysis confirmed the presence of a wave speed gradient in a patient with elevated ventricular pressure. Cardiac SWE modeling is a useful tool to gain additional insights into the complex wave physics and to guide post-processing. The transmural differences in wave speed may help to distinguish loading-induced stiffening from intrinsic stiffness changes. The transmural wave speed gradient has potential as a new diagnostic parameter for future clinical studies.