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A side ohmic contact mode for the double channel GaN/AlGaN epitaxial layer is proposed in this paper. Rectangle transmission line model (TLM) electrodes are prepared, and the specific contact resistance is tested at the annealing temperatures from 700 °C to 850 °C. The results show that the minimum specific contact resistance is 2.58 × 10−7 Ω·cm2 at the annealing temperature of 750 °C, which is three to four times lower than the surface contact mode. Scanning electron microscope (SEM), energy dispersive spectrometer (EDS), and atomic force microscope (AFM) were carried out for the analysis of the morphology, element composition, and the height fluctuation at the contact edge. With the increase in the annealing temperature, the specific contact resistance decreases due to the alloying of electrodes and the raised number of N vacancies. However, when the annealing temperature exceeds 800 °C, the state of the stress in the electrode films transforms from compressive stress to tensile stress. Besides, the volume expansion of metal electrode film and the increase in the roughness at the contact edge leads to the degradation of the side ohmic contact characteristics.

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.

Magnetometers based on nitrogen-vacancy (NV) centers in diamonds have promising applications in fields of living systems biology, condensed matter physics, and industry. This paper proposes a portable and flexible all-fiber NV center vector magnetometer by using fibers to substitute all conventional spatial optical elements, realizing laser excitation and fluorescence collection of micro-diamond with multi-mode fibers simultaneously and efficiently. An optical model is established to investigate multi-mode fiber interrogation of micro-diamond to estimate the optical performance of NV center system. A new analysis method is proposed to extract the magnitude and direction of the magnetic field, combining the morphology of the micro-diamond, thus realizing μm-scale vector magnetic field detection at the tip of the fiber probe. Experimental testing shows our fabricated magnetometer has a sensitivity of 0.73 nT/Hz1/2, demonstrating its feasibility and performance in comparison with conventional confocal NV center magnetometers. This research presents a robust and compact magnetic endoscopy and remote-magnetic measurement approach, which will substantially promote the practical application of magnetometers based on NV centers.

GaN high-electron-mobility transistor (HEMT) terahertz (THz) detectors have been widely studied and applied in the past few decades. However, there are few reports about the influence of GaN/AlGaN heterostructure material properties on the detection model at present. In this paper, a response voltage model for a GaN HEMT THz detector that considers the carrier scattering in a GaN/AlGaN heterostructure is proposed. The phonon scattering, dislocation scattering, and interface roughness scattering mechanisms are taken into account in the classic THz response voltage model; furthermore, the influence of various material parameters on the response voltage is studied. In a low-temperature region, acoustic scattering plays an important role, and the response voltage drops with an increase in temperature. In a high temperature range, optical phonon scattering is the main scattering mechanism, and the detector operates in a non-resonant detection mode. With an increase in carrier surface density, the response voltage decreases and then increases due to piezoelectric scattering and optical phonon scattering. For dislocation and interface roughness scattering, the response voltage is inversely proportional to the dislocation density and root mean square roughness (RMS) but is positively related to lateral correlation length. Finally, a comparison between our model and the reported models shows that our proposed model is more accurate.

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.

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.

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.

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.

In this paper we discuss the features and knowledge representation issues involved in knowledge-based generative CAPP because CAPP is not only related to CAD and but also knowledge about manufacturing. As many forms of knowledge are needed in knowledge-based generative CAPP, with the features we defined based on the cutting tools for the feature machining, we discuss the knowledge representation about the part description, and manufacturing resources knowledge which are manufacturing operations, cutting tools, machine tools. All this knowledge is connected by the features defined to help knowledge-based generative process planning and also this knowledge can have a link to the feature-based part modeling. With the features defined, all knowledge is no longer stand alone knowledge so that it can support knowledge-based generative CAPP well.