- 标题
- 摘要
- 关键词
- 实验方案
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Effects of repetitive polarization switching on the coercive voltage of Pt/Pb(Zr0.52Ti0.48)O3/Pt thin films analyzed using impedance spectroscopy
摘要： We investigated the effect of repetitive switching of polarization on the ferroelectric Pt/Pb(Zr0.52Ti0.48)O3/Pt thin film capacitor by using impedance spectroscopy. From the Cole-Cole plot, the equivalent circuit is described as a combination of the bulk part (a capacitor), the interface part (the constant phase element (CPE), and a parallelly-connected resistor). The circuit parameters were analyzed at various stages of switching. An early increase and a subsequent decrease of the bulk capacitance may represent the wake-up and fatigue phenomena, respectively. The change in the interface part was characterized by an increase in resistance and the growth of n, the exponent of CPE, which may have come from a reduction of defects and the diminished inhomogeneity in the interfacial layer, respectively. The change in the resistance and the coefficient of the CPE in the interface part collectively resulted in an increase in the interfacial impedance. The coercive voltage, which may have intrinsically increased due to the repetitive switching, was even larger as a result of the increased interfacial impedance.
关键词： Impedance spectroscopy,Wake-up,Coercive voltage,PZT,Fatigue
更新于2025-11-14 17:28:48
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The influence of the thermal wake due to pulsating optical discharge on the aerodynamic-drag force
摘要： The influence of a thermal wake due to gas injection and due to a pulsating optical discharge (POD) on the aerodynamic-drag force of a body in a supersonic air flow with Mach number M = 1.45 are experimentally examined. With the help of a single-component aerodynamic balance, the influence of the injected subsonic jet and the thermal wake produced by POD on the aerodynamic drag of a hemisphere-on-cylinder model was studied. It is shown that the observed aerodynamic-force reduction phenomenon can be made more pronounced by increasing the laser power and pulse repetition frequency, or by decreasing the distance between the model and the pulsating optical discharge. The maximum aerodynamic-force reduction (up to 15%) due to the thermal-wake action was observed at a maximum laser-radiation power of W = 2.3 kW and at a pulse rate of f = 90 kHz. The joint effect due to the argon jet and due to the POD caused an aerodynamic-drag force reduction reaching 30%.
关键词： thermal wake,gas injection,CO2-laser,supersonic flow,pulsating optical discharge,aerodynamic-drag force
更新于2025-09-23 15:23:52
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Combined effects of unsteady wake and free-stream turbulence on turbine blade film cooling with laid-back fan-shaped holes using PSP technique
摘要： Detailed film cooling effectiveness distribution for a gas turbine blade under the effects of unsteady wakes and oncoming free-stream turbulence intensities was obtained using pressure sensitive paint (PSP) technique. Tests were performed on a linear cascade at Reynolds number of 3.85 × 10^5 based on the blade chord at cascade exit. Upstream unsteady wakes were simulated using a spoke-wheel type wake generator. The test blade has three rows of compound angled cylindrical film holes at the leading edge, five rows of laid-back fan-shaped holes on the pressure surface and three rows of laid-back fan-shaped holes on the suction surface. The wake Strouhal number was varied from 0 to 0.36 and three mass flux ratios were determined. The oncoming free-stream turbulence intensities are 2.7% and 26.9%, respectively. Results show that the effect of the mass flux ratio on the film cooling effectiveness decreases under the high turbulence intensity and unsteady wake conditions. In most regions of the blade surface, the film cooling effectiveness decreases with the increase of wake Strouhal number, and the free-stream turbulence superimposed on the unsteady wake reduces the film cooling effectiveness further. The effect of the unsteady wake decreases under the high free-stream turbulence conditions.
关键词： Turbulence intensity,Film cooling effectiveness,PSP,Wake,Mass flux ratio,Turbine blade,Strouhal number,Laid-back fan-shaped hole
更新于2025-09-23 15:23:52
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[IEEE 2018 China International SAR Symposium (CISS) - Shanghai (2018.10.10-2018.10.12)] 2018 China International SAR Symposium (CISS) - On the Ship Wake Simulation for Multi-Frequncy and Mutli-Polarization SAR Imaging
摘要： In this paper, computer simulation of SAR (Synthetic Aperture Radar) image of surface-ship wakes is studied. Furthermore, the simulation results of the ship wake are compared at different frequencies and polarizations. The model adopted in the simulation accounts for not only the Kelvin wake produced in the water by the moving ship, but also the influence of the sea surface. The radar back-scatter coefficients of the wake is calculated using the Bragg mechanism. Based on the combination of hydrodynamic and radar scatter calculations, the simulation can provide the backscattering coefficients of the ship wake. Simulation results show that, in general, the back-scattering coefficient of ship wake has little dependence on the radar frequency, however, significantly on the polarization.
关键词： simulation,sea surface model,ship wake,SAR,Radar scattering model,Ship wake model
更新于2025-09-23 15:22:29
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A Wake-Up Receiver With a Multi-Stage Self-Mixer and With Enhanced Sensitivity When Using an Interferer as Local Oscillator
摘要： An ultra-low power wake-up receiver with an energy-detection passive-RF architecture uses a multi-stage self-mixer that has a better conversion gain than the conventional envelope detector. The self-mixer, co-designed with the RF matching network, optimizes the sensitivity and minimizes the power consumption of the receiver. A wake-up receiver prototype in 0.13-μm CMOS operates at 550 MHz, consumes 220 nW from 0.5 V, and achieves a sensitivity of ?56.4 dBm at a 400-kb/s chip rate using an 11-bit wake-up code. When a large interferer is present, the receiver operates in an interferer-enhanced mode, leveraging the interferer as a local oscillator to improve the sensitivity; in the presence of a ?43.5-dBm interferer, a ?63.6-dBm sensitivity is achieved while consuming 1.1 μW.
关键词： self-mixer,wake-up receivers (WuRXs),wake-up radios,low-power wide-area network (LPWAN),Envelope-detectors,low-power wireless
更新于2025-09-23 15:22:29
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Laser-Plasma Accelerated Protons: Energy Increase in Gas-Mixtures Using High Mass Number Atomic Species
摘要： The idea of using a gas-mixture comprising atoms with a high mass number in order to increase proton energies in laser induced plasma acceleration at critical density is investigated by means of 2D PIC (Particle-In-Cell) simulations. Comparing and discussing the case of a pure hydrogen plasma and that of a plasma containing higher mass number species with a small percentage of hydrogen, we demonstrate that the mixture enhances the energies of the accelerated protons. We also show that using a gas-mixture introduces the possibility of using the densities ratio in order to change the relative acceleration of the species.
关键词： laser wake-field acceleration (LWFA),proton acceleration,gas-mixture,high density gas-jet
更新于2025-09-19 17:13:59
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[IEEE 2019 International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD) - Ottawa, ON, Canada (2019.7.8-2019.7.12)] 2019 International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD) - Modeling phase noise in high-power photodetectors
摘要： Enterprises can save a signi?cant energy by letting idle desktops sleep and awake them only when needed. Though existing mechanisms based on centralized or distributed sleep proxy scheme address this issue with good availability, which means that a sleeping machine can always be awoken when needed, they still feature some drawbacks, such as dedicated per-subnet servers, additional per-desktop CPU resource utilization, and extra energy consumption. This seriously impedes their widespread deployment in enterprises. We, thus, propose an improved scheme called wake-up system based on cloud (WaSCO). WaSCO not only provides high availability but also consumes low CPU resource and energy, as it does not need any speci?c server to help achieve high availability. This system of?oads heavy computation from desktops to a stable cloud, which is responsible for managing agents in various subnets by using our proposed algorithm called choosing-and-guaranteeing (CGA) algorithm. When a remote user wakes up a desktop with WaSCO, the cloud sends a message to the selected agents in the subnet, which then send wake-on-LAN packets to wake up the target desktop. In essence, CGA algorithm ensures running agents in each subnet, dynamically adjusts the number of agents, and selects a few desktops, rather than all the desktops, as agents. Experimental results show that WaSCO outperforms centralized and distributed sleep proxy mechanisms in terms of deployment cost, CPU resource cost, and energy consumption, while still maintains high availability.
关键词： Wake-up,energy,cloud,CPU,availability
更新于2025-09-19 17:13:59
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Proof-of-Principle Experiment for Nanoparticle-Assisted Laser Wakefield Electron Acceleration
摘要： Laser electron accelerators have paved the way to build compact electron accelerators, but the quality of the electron beam should be improved to enable efficient use in various specialized applications. We demonstrate a proof-of-principle experiment for nanoparticle-assisted laser wakefield acceleration (NA LWFA) to improve the quality of the electron beam. Nanoparticles are generated through laser ablation of an aluminum target and introduced into a helium plasma to trigger the injection of electrons into the nonlinear plasma wake excited by 70 TW femtosecond laser pulses. We observe a significant enhancement of the electron beam energy, energy spread, and divergence compared with the case of self-injection. For instance, the best quality electron bunches present a maximum energy of up to 340 MeV, with a relative energy spread of 4.7% and a vertical divergence of 5.9 mrad. The initial results on NA LWFA are very promising and motivate further theoretical and experimental research into developing nanoparticle-assisted laser wakefield acceleration.
关键词： femtosecond laser pulses,electron beam quality,plasma wake,nanoparticle-assisted,laser wakefield acceleration
更新于2025-09-19 17:13:59
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Effect of the bubble deformation in the3D nonlinear laser wake-field acceleration
摘要： A new analytical approach for bubble deformation was used for optimization of the electron acceleration in the 3D highly nonlinear laser wake-field regime. Injection of the electron bunch with initial velocity in the bubble was considered in the inhomogeneous plasma with parabolic density ramp. The researchers show that deformation of the bubble shape has an efficient role on the trapping of the electrons in the acceleration region. The influence of the parabolic density ramp on the electron bunch trapping ratio and its mean energy was considered by the numerical method.
关键词： Laser wake-field,Density ramp,Bubble regime,Trapping
更新于2025-09-19 17:13:59
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Optical diagnostics for density measurement in high-quality laser-plasma electron accelerators
摘要： Implementation of laser-plasma-based acceleration stages in user-oriented facilities requires the definition and deployment of appropriate diagnostic methodologies to monitor and control the acceleration process. An overview is given here of optical diagnostics for density measurement in laser-plasma acceleration stages, with emphasis on well-established and easily implemented approaches. Diagnostics for both neutral gas and free-electron number density are considered, highlighting real-time measurement capabilities. Optical interferometry, in its various configurations, from standard two-arm to more advanced common-path designs, is discussed, along with spectroscopic techniques such as Stark broadening and Raman scattering. A critical analysis of the diagnostics presented is given concerning their implementation in laser-plasma acceleration stages for the production of high-quality GeV electron bunches.
关键词： laser-plasma,Raman scattering,Stark broadening,laser wake-field acceleration,gas target,interferometry
更新于2025-09-19 17:13:59