Due to its extreme hardness, chemical and mechanical stability, large band gap, low dielectric constant and highest thermal conductivity, diamond film is expected to be an excellent electronic packaging material for high frequency and high power devices. Under an alcohol concentration of 0.8% and a substrate temperature of 850 °C, high quality diamond films deposited on alumina are obtained by hot filament chemical vapor deposition (HFCVD) method using the optimum parameters determined by an infrared spectroscopic ellipsometer. Prior to the deposition of diamond film, carbon ions are implanted into alumina wafers to release the residual stress between interfaces. The measurement results indicate that dielectric properties and the thermal conductivity of diamond film/alumina composites are improved further with the increase of diamond coating. When the thickness of diamond coating is up to 100 μm, dielectric constant and dielectric loss of diamond film/alumina composite are 6.5 and 1.1 × 10− 3, respectively. However, a thermal conductivity of 3.98 W/cm·K is obtained. 相似文献
A novel color image encryption algorithm based on coarse-grained fractional chaotic system signals is proposed in this paper. First, color images are divided into three channels, which are encrypted based on the corresponding three states of the chaotic system. Second, the chaotic systems are defined as fractional chaotic, in which the fractional order enlarges the parameter space. Third, the fractional chaotic signals are handled with unfixed coarse-grained methods instead of being utilized directly. In addition, the original image and the chaotic signals are divided into bit signals from the pixel values, and the high and low bits are encrypted, respectively. To demonstrate the effectiveness and robustness of the proposed color image encryption algorithm, its properties, including the key space, information entropy, correlation analysis, key sensitivity, and resistance to differential attacks, are provided using a numerical simulation.
New generation wireless communication systems require characterisations of dielectric permittivity and loss tangent at microwave and terahertz bands. La2Ti2O7 is a candidate material for microwave application. However, all the reported microwave dielectric data are average value from different directions of a single crystal, which could not reflect its anisotropic nature due to the layered crystal structure. Its dielectric properties at the microwave and terahertz bands in a single crystallographic direction have rarely been reported. In this work, a single crystal ferroelectric La2Ti2O7 was prepared by floating zone method and its dielectric properties were characterized from 1 kHz to 1 THz along one single direction. The decrease in dielectric permittivity with increasing frequency is related to dielectric relaxation from radio frequency to microwave then to terahertz band. The capability of characterizing anisotropic dielectric properties of a single crystal in this work opens the feasibility for its microwave and terahertz applications. 相似文献
Response time (RT) of Networked Automation Systems (NAS) is affected by timing imperfections induced due to the network, computing and hardware components. Guaranteeing RT in the presence of such timing imperfections is essential for building dependable NAS, and to avoid costly upgrades after deployment in industries.This investigation proposes a methodology and work-flow that combines modelling, simulation, verification, experiments, and software tools to verify the RT of the NAS during the design, rather than after deployment. The RT evaluation work-flow has three phases: model building, modelling and verification. During the model building phase component reaction times are specified and their timing performance is measured by combining experiments with simulation. During the modelling phase, component based mathematical models that capture the network architecture and inter-connection are proposed. Composition of the component models gives the NAS model required for studying the RT performance on system level. Finally, in the verification step, the NAS formal models are abstracted as UPPAAL timed automata with their timing interfaces. To model timing interfaces, the action patterns, and their timing wrapper are proposed. The formal model of high level of abstraction is used to verify the total response time of the NAS where the reactions to be verified are specified using a subset of timed computation tree logic (TCTL) in UPPAAL model checker. The proposed approach is illustrated on an industrial steam boiler deployment. 相似文献
Control of autonomous systems subject to stochastic uncertainty is a challenging task. In guided airdrop applications, random wind disturbances play a crucial role in determining landing accuracy and terrain avoidance. This paper describes a stochastic parafoil guidance system which couples uncertainty propagation with optimal control to protect against wind and parameter uncertainty in the presence of impact area obstacles. The algorithm uses real-time Monte Carlo simulation performed on a graphics processing unit (GPU) to evaluate robustness of candidate trajectories in terms of delivery accuracy, obstacle avoidance, and other considerations. Building upon prior theoretical developments, this paper explores performance of the stochastic guidance law compared to standard deterministic guidance schemes, particularly with respect to obstacle avoidance. Flight test results are presented comparing the proposed stochastic guidance algorithm with a standard deterministic one. Through a comprehensive set of simulation results, key implementation aspects of the stochastic algorithm are explored including tradeoffs between the number of candidate trajectories considered, algorithm runtime, and overall guidance performance. Overall, simulation and flight test results demonstrate that the stochastic guidance scheme provides a more robust approach to obstacle avoidance while largely maintaining delivery accuracy. 相似文献