Search

This paper proposes a double-heterostructure (DH) GaN/AlGaN epitaxial layer that contains an AlGaN interlayer. The electrical properties are characterized and compared with conventional single-heterostructure (SH) GaN/AlGaN epitaxial layers. The Hall effect measurement shows that the DH GaN/AlGaN epitaxial layer has a carrier mobility of 1815 cm2 V−1 s−1, which is approximately 20.37% higher than the SH GaN/AlGaN epitaxial layer. The weak-beam dark-field images taken by transmission electron microscopy show that the AlGaN interlayer in the DH GaN/AlGaN epitaxial layer can block dislocations. The full widths at half maximum results show that there is no significant difference in the screw dislocation density between the SH and DH GaN/AlGaN epitaxial layers. However, the edge dislocation density and the overall internal stress in the DH GaN/AlGaN epitaxial layer are less than those in the SH GaN/AlGaN epitaxial layer. Finally, the physical mechanism of how edge dislocations impact the electrical properties of a DH GaN/AlGaN epitaxial layer is discussed.

A double-channel (DC) GaN/AlGaN high-electron-mobility transistor (HEMT) as a terahertz (THz) detector at 315 GHz frequency is proposed and fabricated in this paper. The structure of the epitaxial layer material in the detector is optimized, and the performance of the GaN HEMT THz detector is improved. The maximum responsivity of 10 kV/W and minimum noise equivalent power (NEP) of 15.5 pW/Hz0.5 are obtained at the radiation frequency of 315 GHz. The results are comparable to and even more promising than the reported single-channel (SC) GaN HEMT detectors. The enhancement of THz response and the reduction of NEP of the DC GaN HEMT detector mainly results from the interaction of 2DEG in the upper and lower channels, which improves the self-mixing effect of the detector. The promising experimental results mean that the proposed DC GaN/AlGaN HEMT THz detector is capable of the practical applications of THz detection.

Metal-sandwiched zinc oxide (ZnO)/titanium (Ti)/copper (Cu)/Ti/ZnO thin film systems were fabricated using magnetron sputtering technology and then annealed using a rapid thermal annealing system at temperatures from 100 to 400°C. The influence of the Ti film thicknesses and annealing temperatures on the surface morphologies, sheet resistance and optical properties were studied. The surface morphologies change a little with the annealing temperature rises. The sheet resistances reduce with the Ti film thickness or annealing temperature increasing. Both the max transmittance and figure of merit reduce with the increase of Ti film thickness. The max transmittance increases with the temperature increasing from 100 to 300°C and then reduces. However, the figure of merit increases with the temperature increasing which indicates that the metal-sandwiched ZnO/Ti/Cu/Ti/ZnO thin film system annealed at 400°C has the optimal performance.

We propose a nonresonant terahertz (THz) detector based on double-channel (DC) GaN/AlGaN high-electron-mobility transistor (HEMT) utilizing a technology computer-aided design platform. The hydrodynamic model is simplified as the drift-diffusion model for nonresonant THz detection simulation. Dependence of THz photoresponse on various structure parameters of the detector is analyzed by simulation. The two typical metrics, responsivity and noise equivalent power (NEP), are theoretically calculated for the optimization of the structure parameters. The optimized responsivity and NEP reach 5.8 kV/W and 50 pW/Hz0.5 at the same gate voltage, respectively, and a minimum NEP of 20 pW/Hz0.5 is obtained. The comparison between our simulation results and the experiment data of single-channel HEMT detector proves that the DC HEMT detector shows an excellent THz detection performance.

Microcontact affects the fabrication and assembly of MEMS/NEMS system, the contact between thin film microcavity and microcantilever beam, and the motion of microstructure. In this work, in the microcontact of three-dimensional elastic-plastic Weierstrass-Mandelbrot (W-M) fractal surfaces, influence of fractal dimension was studied based on a comprehensive contact model. With increasing fractal dimension, maximum microcontact force in the plastic deformation zone shows parabolic change; comparably, the intermediate force in elastic zone parabolically varies. For both the forces, the minimum values are obtained when the fractal dimension is 2.5. Besides, in the plastic deformation zone, the real contact areas increase with the fractal dimension. Experiments were completed to compare with the numerical analysis. The results show that the simulated contact force curve is in line with the experimental load curve when Young’s modulus E and hardness H are equal to the actual measured values. Nevertheless, it will greatly deviate from the experimental load curve when E and H differ from the measured values.

As a result of the influence of man-made or other factors, the recorded fault data in the process of keeping maintenance of ship electromechanical system are often inaccurate with incomplete record information, low-quality data and small size sample. For the incomplete failure data, this paper will analyze the failure data of the certain type of ship electromechanical system thoroughly and comprehensively through Bayesian method. Sorting the data firstly and then analyzing graphical statutory representation to determine the failure trend, I will adopt the homogeneous Poisson process and the non-homogeneous Poisson process (power law process (PLP) and Duane) on quantitative analysis to establish failure data analysis model with Bayesian method and obtain the analysis result through PyMC3 probability programming. Finally, the Bayesian estimation of the average failure frequency of ship electromechanical system will be concluded in this paper.

The technical manual of complex equipment has vast text, which makes it slow for relevant staff to obtain knowledge, and then restricts efficiency. IETM is made of unstructured text or pictures, and this kind of form does not improve efficiency of obtaining knowledge radically or make use of computer to get further support. To deal with this problem, this paper researches domain ontology of technical manual. After analyzing technical manual systematically, the domain ontology which is able to provide structured text is built. The domain ontology present will promote progress of IETM.

Technical manual is vital source of fault diagnosis and maintenance knowledge. To deal with the mass of manual text, which influence the speed of knowledge acquisition, and then effect the diagnostic efficiency, this paper proposes a method for extracting information of Chinese technical manual text based on rule-matching. With the help of domain ontology and syntactic analysis, extracting rules could be established to extract manual text information, and reasoning algorithm based on hierarchical directed graph is built to assist the fault diagnosis. The information extraction method presented in this paper can supply knowledge to maintenance staff and help to diagnose the fault automatically.

To explore the application of double pedicle blood supply pectoralis major myocutaneous flap in reconstruction of laryngeal and hypo pharyngeal defect after carcinoma resection.All the patients received initial treatment. Pectoralis major myocutaneous flap was Applied in one-stage reconstruction in 22 cases of laryngocarcinoma and hypopharyngeal carcinoma with post-operation defect. During operation, pectoral branches of thoracoacromial vessels and branch of lateral thoracic vessels were reserved and prepared to be double pedicle vessel fascia bundle without muscle at the beginning part, rearched to defect area through subclavian tunnel. After operation, it is necessary to closely observe the subcutaneous swelling, quantity and color of the drain and others of neck surgery area to exclude the occurrence of surgical hematoma. When there is suspicion, do timely exploration.Pectoralis major myocutaneous flaps of 22 patients were all survived. Pharyngeal fistula occurred in 2 cases and was cured by change of dressing. Twenty-one cases received radiotherapy after operation without secondary flap necrosis. After follow-up of 6 months to 24 months, one case of roll repairment of circumferential defect in cervical esophagus,found to have anastomotic stenosis 8 months after radiotherapy and then underwent gastrostomy treatment,the other 21 cases showed good recovery of swallowing function. Among 13 cases with laryngeal function reserved, only 1 case wearing tube and the extubation rate was 92.3% without communication barriers, no patient died in the short follow-up period.For double pedicle blood supply pectoralis major nyocutaneous flap, blood supply are fully guaranteed and does not require complicated equipment to observe and monitor the flap blood supply after operation, it is important to exclude factors that may lead to muscular flap necrosis to ensure the survival of pectoralis major myocutaneous flap.

This paper discusses the key problems for case based and ruled-based intelligent design system in order to shorten the product cycle; make full use of the available designing resources and implement the intelligent and rapid response design for hydraulic actuators. The framework and the working process of the CAD system are introduced. The knowledge involved in the design process is divided into three types: rules, cases, and 3-D case model. In CBR, each available design result is considered as a case, so we must represent each case in a way computer can understand. In this paper, not only a series of data is structured for each case, but also the complicated assembly is represented in a hierarchical data structure and 3-D models are created with Pro/E parametric modeling function to facilitate the design process.