Time-energy Distribution Research Articles

Numerical investigation of lean methane flame response to NRP discharges actuation

This study investigates the response of a laminar methane-air flame to Nanosecond Repetitively Pulsed (NRP) discharges in a canonical wall-stabilized burner using a combined experimental and numerical approach. The flow and flame behaviors were modeled using Direct Numerical Simulation (DNS) with an Analytically Reduced Chemistry for a precise chemical description. A phenomenological model incorporating detailed plasma kinetics and experimental observations was developed to simulate plasma effects. Zero-dimensional plasma reactor simulations were used to build up a reduced-order model describing discharge energy distribution in the specific conditions studied. Experimental measurements of electrical profiles identified two discharge regimes: a low-energy Corona discharge and a higher-energy Glow discharge, characterized by distinct spatial energy distributions. Experimental flame response analysis revealed three major phases: marginal response up to 100 pulses, a downstream shift of the flame tip, and stabilization after 400 pulses. Numerical simulations indicated that the Corona regime is crucial for explaining initial flame responses, while the Glow regime influences later stages. Adjustments in the Vibrational-Translational (VT) energy relaxation time and energy deposition ratios between fresh and burnt gases were necessary to match experimental observations. Additionally, an accurate modeling of the transient and steady-state flame responses requires integrating both the specificity of the Corona and the Glow discharge regimes. Future work should focus on measuring or theoretically calculating N2(v) relaxation times in CH4-H2O-CO2 mixtures and analyzing the spatial energy distribution of discharges interacting with flames to enhance plasma-combustion coupled models.Novelty and significanceIn this work, a phenomenological plasma-assisted combustion model has been developed, to investigate a laminar premixed stagnation plate burner, focusing on VT energy relaxation time and spatio-temporal energy distribution modeling. For the first time, not only O2, N2 and O but also the fuel and combustion intermediates and products have been considered in the VT relaxation model. It revealed their strong influence on the overall flame response in a case where the discharge crosses a flame front, highlighting the strong beneficial effect of energy deposited in vibrational form. The study questions and investigates the energy distribution from fresh to burnt gases, challenging the conventional uniform energy distribution assumption. The experimental identification of two specific plasma regimes was necessary to predict the transient flame response. Additionally, energy deposited downstream of the flame, in fresh gases, was found to more efficient than in hot gases to enhance combustion.

Time–energy distribution of photoelectron from atomic states with different magnetic quantum numbers in elliptically polarized laser fields

Abstract A Wigner-distribution-like (WDL) function based on the strong-field approximation (SFA) theory is used to investigate the ionization time of the photoelectron emitted from the initial states with different magnetic quantum number m in elliptically polarized electric fields. The saddle-point method is adopted for comparisons. For different m states, a discrepancy exists in the WDL distributions of the photoelectrons emitted in a direction close to the major axis of the laser field ellipse. Based on the saddle-point analysis, this discrepancy can be ascribed to the interference between electrons ionized from two tunneling instants. Our results show that the relationships between the tunneling instants and kinetic energy of photoelectrons are the same for different m initial states when the Coulomb potential is not considered. Our work sheds some light on the ionization-time information of electrons from different magnetic quantum states.

Study on coupling characteristics of different welding modes in laser-double TIG hybrid welding

In order to study the low-power pulsed laser-induced double arc coupling discharge effect and improve the energy utilization rate of the hybrid heat source, this paper adopts different heat source arrangement modes (laser-guided, double arc-guided) and conducts welding experiments under different Dla (distance between laser beam and two tungsten electrodes). The high-speed camera and spectral diagnostic system are used to monitor the dynamic behavior of arc plasma information, molten pool, and keyhole in real-time and calculate the characteristics of electron temperature and electron density of the coupled plasma. The physical model is established to analyze and discuss the time characteristics and energy distribution of coupled discharge. The results show that according to the different Dla, the hybrid heat source has three different coupling effects: laser and double arc interfere with each other, laser and double arc good coupling, laser and double arc no significant effect. When the laser and the double arc have a good coupling state, the coupled plasma has a lower electron temperature and a higher electron density. At this time, the Marangoni force and arc pressure on the liquid metal in the laser keyhole is enough to overcome its own gravity. The keyhole has existed for a long time, which is conducive to the extension of the laser-arc coupling discharge effect and improves the energy utilization efficiency of the hybrid heat source. Compared with the laser-guided mode, the double arc-guided mode has a larger coupling discharge period and duty cycle, and the energy density of the conductive region in the center of the keyhole increases by 14.4 %, which is beneficial to improve the energy utilization efficiency of the hybrid heat source and obtain a larger penetration depth.

Evidence for a radiation belt around a brown dwarf.

Ultracool dwarfs (UCDs) are a category of astronomical objects that includes brown dwarfs and very-low-mass stars. Radio observations of UCDs have measured their brightness as a function of time (light curves) and spectral energy distributions, providing insight into their magnetic fields. We present spatially resolved radio observations of the brown dwarf LSRJ1835+3259 using very-long-baseline interferometry showing extended radio emission. The detected morphology is consistent with the presence of a radiation belt. Comparison with models indicates that the radiation belt contains energetic particles confined by magnetic mirroring. We contend that radio-emitting UCDs have dipole-ordered magnetic fields with radiation belt-like morphologies and aurorae that are similar to those of Jupiter.

Graphene oxide modifications by X-rays irradiations in air and vacuum

Graphene oxide (GO) foils have been exposed to X-rays in air and in vacuum. The attenuated total reflectance (ATR) method for Fourier Transmission Infrared (FTIR) spectroscopy has been used to analyze the pristine and the irradiated GO foils. The X-ray exposition in air produces oxidation increment, while in vacuum it induces reduction of the oxygen functional groups and partial removal of water. These processes have been investigated as a function of both the irradiation time and X-ray energy distribution highlighting the variations of some functional groups of oxygen. Some interesting applications of the GO reduction will be suggested in the field of ionization dosimetry, detectors, microelectronic devices, and membranes, as presented hereafter.

Microwave-assisted Synthesis of 3-amino-2-phenylquinazolin-4(3H)-one (QH) and 4-oxo-2-phenylquinazoline-3(4H)-carbothioamide (QTh)

Background: Microwave synthesis has developed as a powerful tool for the cost-effective and greener synthesis of organic molecules, including quinazolines. Irradiation with microwave leads to the excitation of molecules and equitable distribution of thermal energy in a much shorter time than conventional synthesis. This results in shorter reaction time and, more often than not, higher efficiency Objective: The primary objective of the work presented in this article was to prepare hydrazine hydrate or thiourea derivative of quinazolines through microwave synthesis as small-molecule scaffolds for fur-ther need-based functionalisation, isolation, and characterisation. We, herein, report the synthesis of two quinazolinone derivatives of thiourea and hydrazine, 3-amino-2-phenylquinazolin-4(3H)-one (QH) and 4-oxo-2-phenylquinazoline-3(4H)-carbothioamide (QTh), respectively. Method: A multi-step synthetic strategy starting from anthranilic acid was employed to synthesise the small molecule quinazolinones 3-amino-2-phenylquinazolin-4(3H)-one (QH) and 4-oxo-2-phenylquinazoline-3(4H)-carbothioamide (QTh). The compounds were synthesised by reacting hydra-zine and thiourea with 2-benzamidobenzoyl chloride in DMF under microwave irradiation (800 W at 135 °C for 4 min) in the presence of potassium carbonate. The acid chloride was prepared by chlorination of 2-benzamidobenzoic acid, which in turn was synthesised from anthranilic acid by benzoylation. This method is an efficient alternative approach to synthesising quinazolinones from benzoxazin-4-ones. Results: We have successfully synthesised, isolated, and characterised the quinazolinone derivative QH (yield: 81%) and QTh (yield: 85%). The structures of the compounds were established through spectro-scopic techniques. Theoretical optimisation of the structures was also achieved using DFT. The HOMO-LUMO difference for QH and QTh was calculated to be 4.60 and 4.47 eV, respectively. Conclusion: The reported protocol is advantageous over conventional methods of quinazoline synthesis from benzoxazin-4-ones. The time required for the reaction is much less (4 min) as compared to the usual requirements of reflux (> 4 h); the higher energy gap of QH indicates greater stability than that of QTh.

The capability of Distributed Generation in Digital Twin platform

The digital Twin of distributed electricity generation is the concept of a smart grid. A smart grid uses advanced digital technologies, including sensors, communication networks, and analytics software, to optimize the distribution and consumption of energy in real time. The future of distributed generation is promising. As more people adopt renewable energy systems like rooftop solar panels, the demand for traditional centralized power grids will decrease. This creates opportunities for smaller, community-based microgrids that can generate and distribute energy locally. By leveraging digital technologies like Digital Twin, the Internet of Things (IoT), blockchain, and artificial intelligence, these microgrids would improve energy efficiency, reduce costs, and enhance reliability. Overall, the combination of distributed energy generation and digital technologies has the potential to revolutionize the energy industry, making it more sustainable, resilient, and equitable. In this paper, the effective factors in the development of distributed production in the digital hybrid platform were identified and it is investigated with the cause and effect loops of the system dynamics.

Evolution of the distribution of flow units of a metallic glass under cyclic loading

Dynamic mechanical relaxation processes (i.e., β relaxation and α relaxation) are closely connected with the mechanical and physical properties of metallic glasses. In the current work, the β relaxation of La60Ni15Al25 metallic glass was studied in sequential heating and cooling experiments by dynamic mechanical analysis. The values of the loss modulus peak were found to reach a relatively stable state during the progress of the heating-cooling cycles. The evolution of the flow unit distribution during thermal cycling was revealed by stress relaxation tests. The experimental results of stress relaxation were well described by a generalized Maxwell model, allowing the analysis of the underlying relaxation time and activation energy distributions. We also show here a suppressed relaxation behavior observed under repeated loading cycles, which is attributed to the annihilation of flow units and the modification of the relaxation time spectrum obtained in the framework of the generalized Maxwell model.

The dynamic stiffness matrix method for seismograms synthesis for layered transversely isotropic half-space

Natural rocks and soils show significant anisotropic behavior owing to sedimentation and weathering, particularly apparent in the crust. However, seismograms synthesis for the anisotropic medium is scarce, especially bottlenecks for large-scale and broadband seismic wave propagation. In this paper, seismogram synthesis for a multi-layered transversely isotropic half-space due to seismic point sources is addressed by using a dynamic stiffness matrix method. The critical step of the proposed method lies in the construction of the global dynamic stiffness matrix in frequency-wavenumber domain, which avoids the accumulation of errors that appeared in the reflection and transmission matrix method. Exponential divergent terms related to wavenumber and layer thickness in dynamic stiffness matrix are extracted for fast simulating large-scale and high-frequency wavefield. The seismic point sources are equated to the external loads imposed at the introduced auxiliary surfaces, through which the dynamic stiffness matrix can be utilized to obtain the solutions. The accuracy is verified by comparing the proposed method results with three examples in the publications, involving different source types and depth scales. Two numerical examples regarding Thomsen parameters are given to illustrate the mechanism of wave propagation and ground motion in an anisotropic media. Numerical results show that the anisotropic characteristics affect the wave propagation time, waveform and wave-front energy distribution, further leading to shear wave splitting phenomena, which remarkably differ from the isotropic case. A case study using a simplified three-layered crustal structure model in Tibet elucidates that peak ground displacement and its distribution difference within the epicenter of 10 km by comparing with the equivalent isotropic model without considering anisotropic properties. The results show a 10.91% deviation in the location of the peaks, with amplitude differences of up to 120% due to a 45° dip-slip source at different frequencies (from 1 Hz to 15 Hz).

Decentralized Trajectory Optimization for Multi-Agent Ergodic Exploration

Autonomous exploration is an application of growing importance in robotics. A promising strategy is ergodic trajectory planning, whereby an agent spends in each area a fraction of time which is proportional to its probability information density function. In this letter, a decentralized ergodic multi-agent trajectory planning algorithm featuring limited communication constraints is proposed. The agents' trajectories are designed by optimizing a weighted cost encompassing ergodicity, control energy and close-distance operation objectives. To solve the underlying optimal control problem, a second-order descent iterative method coupled with a projection operator in the form of an optimal feedback controller is used. Exhaustive numerical analyses show that the multi-agent solution allows a much more efficient exploration in terms of completion task time and control energy distribution by leveraging collaboration among agents.

Temporal characterization of electron dynamics in attosecond XUV and infrared laser fields.

We use a Wigner distribution-like function based on the strong field approximation theory to obtain the time-energy distributions and the ionization time distributions of electrons ionized by an XUV pulse alone and in the presence of an infrared (IR) pulse. In the case of a single XUV pulse, although the overall shape of the ionization time distribution resembles the XUV-envelope, its detail shows dependence on the emission direction of the electron and the carrier-envelope phase of the pulse, which mainly results from the low-energy interference structure. It is further found that the electron from the counter-rotating term plays an important role in the interference. In the case of the two-color pulse, both the time-energy distributions and the ionization time distributions change with varying IR field. Our analysis demonstrates that the IR field not only modifies the final electron kinetic energy but also changes the electron's emission time, which is attributed to the change of the electric field induced by the IR pulse. Moreover, the ionization time distributions of the photoelectrons emitted from atoms with higher ionization energy are also given, which show less impact of the IR field on the electron dynamics.

Time-energy analysis of the photoionization process in a double-XUV pulse combined with a few-cycle IR field

We calculate the time-energy distribution (TED) and ionization time distribution (ITD) of photoelectrons emitted by a double-extreme-ultraviolet (XUV) pulse and a two-color XUV-IR pulse using the Wigner distribution-like function based on the strong field approximation. For a double-XUV pulse, besides two identical broad distributions generated by two XUV pulses, many interference fringes resulting from the interference between electrons generated, respectively, by two pulses appear in the TED. After adding an IR field, the TED intuitively exhibits the effect of the IR field on the electron dynamics. The ITDs during two XUV pulses are no longer the same and show the different changes for the different two-color fields, the origin of which is attributed to the change of the electric field induced by the IR field. Our analysis shows that the emission time of electrons ionized during two XUV pulses mainly depends on the electric field of the combined XUV pulse and IR pulse.

INFLUENCE OF SEASONAL DISTRIBUTION OF WAVE ENERGY AND STRUCTURE OF LOCAL STORM EVENTS ON SEDIMENT TRANSPORT

The structure of storm events means the character of the wave energy distribution in time over the storm period. The storm includes three principal phases: increase, stabilization and waning. The main idea that resulting morphological effect of storm depends on both quantity of wave energy within every phases and distribution of different storm phases over the time. The post-storm relief in the coastal zone depends heavily on the particularity of hydro- and lithodynamic processes during the storm waning phase. The main objectives of the study include estimation of seasonal distribution of wave energy and character of structure of separate storm events for different seasons.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/mgDDF-oQg94

Construction of the Gaseous and Solid-State Targets for the Muon Capture Measuring System in 130Xe, 82Kr, and 24Mg

The description of the muon capture system units with different targets (gas and solid-state) is presented. Using the muon-event selection system and high-purity germanium (HPGe) detectors, precise measurements of the time-energy distributions following ordinary muon capture in the isotopically-enriched $^{130}$Xe, $^{82}$Kr, and $^{24}$Mg nuclei were performed. The optimal parameters of the muon capture measuring system to ensure maximum muon stops in the targets under study and to collect effective statistics during measurements are reported. The system makes it possible to separate muonic X-ray events from gamma radiation with high accuracy, which is critical in such studies, and it is also suitable for future measurements with other targets.

Rescattering time-energy analysis of high-order above-threshold ionization in few-cycle laser fields

A Wigner distributionlike function based on the improved strong-field approximation theory is proposed to calculate the rescattering time-energy distribution (RTED) of high-energy photoelectrons of atomic above-threshold ionization process in few-cycle laser fields with different frequencies. The RTED shows bell-like stripes and the outermost stripe is compared with semiclassical results given by the simple-man model with consideration of different positions of tunnel exit and different initial longitudinal momenta. Analysis indicates the existence of the tunnel exit. However, though it shifts farther away from the core with decreasing frequency, the position of the tunnel exit is significantly less than the prediction by adiabatic theory even for the low-frequency case which is well in the tunneling regime. Our results also imply that the effect of the tunnel exit is more important than that of the initial longitudinal momentum at the tunnel exit for the backward-scattering electrons. Moreover, the inner stripe structures in the RTED are attributed to interference between electrons with the same final energy emitted at different ionization times.

Wihi: WiFi Based Human Identity Identification Using Deep Learning

Human identity identification based on channel state information (CSI) using commercial WiFi devices has drawn increasingly attention, and it can be used in many applications such as smart home, intrusion detection, building monitoring, activity recognition, etc. However, most of the existing identity identification approaches are sensitive to the influence of random noise derived from indoor environments, and thus their identification accuracies are far from satisfactory. In the present paper, a device-free CSI based human identity identification approach using deep learning (Wihi) is proposed. Wihi mainly utilizes three key techniques to identify different people. Firstly, to eliminate the influence of the random noise, discrete wavelet transform (DWT) strategy is introduced to denoise raw CSI data by leveraging signal decomposition. Secondly, in order to characterize human’s gaits profoundly, several representative features are exploited from different statistical profiles, including channel power distribution in time domain (CPD), time-frequency analysis (TFA), and energy distribution in different frequency bands (ED). Thirdly, a recurrent neural network (RNN) model with long short-term memory (LSTM) blocks is employed to learn the representative gait features extracted above and encode temporal information for realizing human identity identification. The proof-of-concept prototype of the proposed Wihi approach is implemented on a set of commercial WiFi devices, and multiple comprehensive experiments have been carried out to evaluate the performance of identity identification. The experimental results confirm that the proposed Wihi can achieve a satisfactory performance compared with some state-of-the-art approaches.

The Research of Pulsed Magnetron Discharge Electronic Component

In magnetron sputtering systems, an arc and arcing may happen at the cathode of a magnetron when operating in a reactive environment. To avoid their occurrence, pulse operating modes are used. For this, rectangular unipolar or bipolar pulses can be used or in the form of a sine wave with frequencies from 10 kHz to 1 MHz. The purpose of this work is to study the electronic component of a magnetron discharge when it is excited by a pulse in the form of a damped sine wave, the so-called impact excitation. A comparison of its characteristics with similar characteristics of a magnetron discharge which is excited by unipolar rectangular pulses of the same duration, also. A physically topological model of a magnetron sputtering system has been created to compare the characteristics of an electron cloud when a discharge is excited by rectangular pulses and pulses in the form of a damped sine wave. A pulse of this shape is obtained by applying a current pulse to the oscillating circuit. A feature of this discharge is the ultrahigh voltage of the first pulses. This is caused by resonant phenomena in the power circuit. The work presents a 2D design of a simulated magnetron sputtering system, a structural diagram of a physical-topological model, and input parameters. The physical models for calculating magnetic and electric fields, the distribution in space and time of electron density and their energy are also given. As a result of the calculations, the distribution of the magnetic and electric fields in the magnetron sputtering system, the distribution of electron density in space and time, the distribution of electron energy in space and time of electrons during rectangular and impact excitation of the discharge were obtained. An analysis of the results confirmed the feature previously indicated by other authors. This is the formation of an increased electron density at the fronts of discharge excitation pulses. This can be explained by the acquisition by the electrons at the front of the momentum of energy which corresponds to the ionization cross section of Ar atoms. The electron energy leaves the optimal energy range for ionization of Ar atoms with a further increase of the voltage. Therefore, the ionization efficiency of the operating gas atoms decreases. It was also found that upon impact excitation of a magnetron discharge: 1) The electron energy above the surface of the target is several times higher than when the discharge was excited by a rectangular pulse. Therefore, the sputtering of the target surface is more intense; 2) The erosion zone of the target increases and therefore the utilization rate of the target material increases 3) Ions bombard and sputter the deposited film in the positive period of the sine wave, if it is under the ground potential.

Analysis of above-threshold ionization by “Wigner-distribution-like function” method

AbstractAbove-threshold ionization (ATI) is one of the most fundamental processess when atoms or molecules are subjected to intense laser fields. Analysis of ATI process in intense laser fields by a Wigner-distribution-like (WDL) function is reviewed in this paper. The WDL function is used to obtain various time-related distributions, such as time-energy distribution, ionization time distribution, and time-emission angle distribution and so on, of atoms in laser field pulses with different laser parameters. For the linearly polarized laser pulses, the time-energy distribution intuitively shows from a quantum point of view the relationship between the ionization moment and the final energy and clearly reveals the origin of interference structures in the photoelectron spectrum. In particular, for linearly polarized few-cycle laser pulses, all calculated distributions show the dependence of electron behavior on the ionization time, emission direction, and carrier-envelope phase (CEP). For elliptically polarized few-cycle pulses, we calculate the angular distribution, ionization time distribution, and time-emission distribution, which are compared with the semiclassical calculations. Analysis shows that the offset angle (difference between positions of the peaks in the angular distributions obtained by two methods) in the angular distributions does not correspond to the offset time (difference between positions of the peaks in the ionization time distributions obtained by two methods) in the ionization time distributions, which implies that the attosecond angular streaking technique based on this correspondence between the offset angle and time is in principle inaccurate. Furthermore, the offset time cannot be interpreted as tunneling time.

Detecting the Void behind the Tunnel Lining by Impact-Echo Methods with Different Signal Analysis Approaches

A void behind the lining in a tunnel is considered to be a critical condition as it can significantly impair the tunnel service life. In this study, we adopted the impact-echo (IE) method to detect the voids. We designed two test conditions (tunnel lining with and without a void) for our experiments performed in a laboratory environment. The influences of void size and impact-void position were analysed using numerical simulations. The vibration response signals were analysed in the time, frequency, and time–frequency domains using various signal analysis approaches. The results were comparatively analysed to determine the best approach for void detection. The study helped establish that a tunnel void can be evaluated through the vibration energy (amplitude and duration) in the time domain, the resonance frequency and dynamic stiffness in the frequency domain, and the energy distribution in time–frequency domain. The wavelet transform analysis is the most appropriate method to observe the energy flow during the state changing and the dynamic stiffness method can determine the void position precisely.

Closed hierarchies and non-equilibrium steady states of driven systems

We present a class of tractable non-equilibrium dynamical quantum systems which includes combinations of injection, detection and extraction of particles interspersed by unitary evolution. We show how such operations generate a hierarchy of equations tying lower correlation functions with higher order ones. The hierarchy closes for particular choices of measurements and leads to a rich class of evolutions whose long time behavior can be simulated efficiently. In particular, we use the method to describe the dynamics of current generation through a generalized quantum exclusion process, and exhibit an explicit formula for the long time energy distribution in the limit of weak driving.