Search

A highly efficient, high-voltage power switching technology, the Optical Transconductance Varistor (OTV) is being developed based on the photoconductive property of 6H-SiC. The behavior of the dislocations in 6H-SiC under the application of voltage and laser in such devices is of particular interest. In this study, both ex-situ and in-situ synchrotron X-ray topography were applied to characterize dislocations and investigate their behaviors when the sample was electrically and photonically stressed. Threading dislocations (TDs) and basal plane dislocations (BPDs) were revealed in transmission topographs and grazing topographs. When the samples were connected to external voltage ranging from 1kV to 4kV, there were no observable signs of dislocation movement. This indicates that the energy released from the transitioning of Vanadium states is lower than the activation energy for dislocation gliding. more...

In 4H-silicon carbide crystals, basal plane slip is the predominant deformation mechanism. However, prismatic slip is often observed in single crystals grown by the physical vapor transport method as the diameter expands to 6 inches or larger. Thermal modeling has shown that occurrence of prismatic slip is attributed to increased radial thermal gradients. While X-ray topography can be used to characterize the presence and extent of prismatic slip, the feasibility of using the chemical etching method to assess the extent of prismatic slip in an industrial setting is investigated. The distribution of scallop shaped etch pits oriented along the directions that correspond to prismatic dislocations, correlate well with the results of the thermal model that predicts the occurrence of prismatic slip dislocations. This capability of the etch pit method to characterize prismatic slip can be used to manage radial thermal gradients during PVT growth. more...

Synchrotron monochromatic beam X-ray topography has been widely applied to characterize structural defects in SiC crystals. Using ray tracing simulations, the dislocation contrast in X-ray topography under strong diffraction conditions (diffraction takes place at or near Bragg angle) has been intensively investigated. However, the contrast and the configurations of the dislocation images recorded under weak diffraction conditions have not been fully investigated. Recently, we demonstrated that the contrast of dislocations in synchrotron grazing incidence topography under weak diffraction conditions can also be analyzed and interpreted by applying ray tracing principles. In this study, we have extended the application of the ray tracing method to analyze the dislocation contrast in weak beam synchrotron back reflection and rocking curve topography. The ray tracing method is shown to successfully simulate and correlate the contrast of threading screw dislocations at various positions on the rocking curve and thus allow to determine the signs of Burgers vectors. more...

Synchrotron X-ray topography techniques are used to characterize the microstructures in gallium nitride materials being developed for selective area doping for power electronic applications. Bulk substrates grown by different methods, epitaxial layers that are subject to ion implantation, annealing, etching and regrowth are characterized by X-ray topography in grazing incidence geometry and X-ray rocking curve topography. Strain and tilt maps of ion implanted epitaxial layers and etched and regrown wafers are generated. From the X-ray topographs, it is concluded that ammonothermal grown substrates show the highest quality among other types and most suitable for high-end electronic applications. It is also revealed that epitaxial growth, ion implantation and the annealing process do not change the dislocation distribution, but ion implantation introduces damage, strain and lattice bending effect, which are removed after annealing. Inductively coupled plasma (ICP) etching gives rise to strain variations in the wafer, while using tertiary butyl chloride (TBCl) to etch the wafer does not affect the strain distribution and can remove some damage from a preceding ICP etching process. more...

Understanding the depth from which contrast from dislocations is still discernible (the effective penetration depth of the X-rays) in grazing-incidence synchrotron monochromatic beam X-ray topography is of great interest as it enables three-dimensional dislocation configuration analysis and accurate density calculations. To this end, systematic analysis has been performed of topographic and ray-tracing simulated contrast of basal plane dislocations with different Burgers vector and line direction combinations, and a universal method to determine the effective penetration depth based on ray tracing has been developed. This study reveals that the observable dislocation contrast depends on the effective misorientation associated with the dislocation modulated by the photoelectric absorption effect. The dislocations with larger effective misorientation tend to have longer projected length and correspondingly deeper effective penetration depths. more...

4H-SiC wafers with 12 um epilayer were implanted at the Tandem Van de Graaff facility at Brookhaven National Laboratory with tunable energy from 13 MeV up to 66 MeV. Lattice strains introduced by the implantation process were characterized in detail by synchrotron rocking curve X-ray topography (SXRCT) and reciprocal space maps (RSMs). It is observed that the strain levels correlate with the atomic mass and energy of acceleration of the dopant atoms. more...

Metal-oxide-semiconductor capacitors with single and multi-layer high-K gate dielectrics on Si (0001) face of n-type 4H-SiC substrates have been investigated. Multi-layered nanolaminated gate-stack comprises alternating ultrathin (6nm) Al2O3 and HfO2. A 5nm thick interfacial silicon oxynitride is deposited prior to laminated films to investigate interface trap properties and tuning of flat band voltage. Total thickness of gate-stack films including interfacial layer is 55nm. The thermal stability of multi-layered nanolaminated film is investigated using XTEM. Localized crystallization of HfO2 is visible after RTA at 900°C while Al2O3 remains fully amorphous. Some of HfO2 grains have extended into Al2O3 layer but was not able to crossover. The measured accumulation capacitance of 55nm thick gate dielectric gives an effective dielectric constant value of 9.6 and an equivalent oxide thickness of 22nm from high-frequency capacitance-voltage measurements. A positive flat band voltage ( of 12.2V and 10.6V are observed from both single layer HfO2 and Al2O3 dielectrics, respectively due to presence of negatively charged oxygen interstitial defects generated during atomic layer deposition process. However, VFB shifted towards negative voltage-7.6V for multi-layered Al2O3/HfO2 stacks probably associated with positive Al and Hf interstitials at interface of Al2O3/HfO2. Ultrathin interfacial oxynitride films is effective to reduce Dit to 3×1011/eVcm2 and tuning of VFB. The breakdown field of stacked gate dielectric on 4H-SiC is 10.0 MV/cm. more...

Chemical hydrogen storage materials such as hydrazine borane (HB) have aroused great interest when the tricky hydrogen storage is still a barrier on the way to sustainable hydrogen energy development. Many efforts have been dedicated to the dehydrogenation of HB, but the catalytic performance is still not sufficient enough. Herein, we develop the synthesis of NiPt–MoOx nanoparticles supported on NH2 functionalized N doped rGO (NiPt–MoOx/NH2–N-rGO) via a green and facile method. Unexpectedly, the supported Ni0.9Pt0.1–MoOx ultrafine nanoparticles (UPs, ∼1.5 nm) show the highest activity by far with 100% selective conversion and a turnover frequency (TOF) of 4412 h−1 at 323 K. more...

The surface adsorption of gas molecules is a key factor limiting the secondary electron yield (SEY) of a material in many areas of applied physics. The influence of O2 adsorption on the SEY of metallic Ag is investigated in this work. To account for the particle distribution, we propose a BET theory based on multilayer O2 physisorption model. Furthermore, based on the phenomenological model of secondary electron (SE) emission and by taking into account the different scattering processes between electrons and particles in the adsorbed layer, we develop a numerical model of SEY in the adsorbed state using Monte Carlo simulations. The relationships among O2 adsorption, adsorption layer thickness, and SEY variation characteristics are then examined through a series of experiments. After 12-h exposure to O2, the clean samples increases 12%–19% of the maximum value of SEY and 2.3 nm in thickness of the adsorbed layer. Experimental results are also compared with the results from the MC model to determine whether the model is accurate. more...

Due to the symmetrical structure, consistent working characteristics in the forward and reverse operations, and good soft-switching characteristics, bidirectional CLLLC resonant converters are widely used in electric vehicles and other fields. To meet the requirements of the on-board charger, this paper uses a bidirectional CLLLC resonant converter as the rear-stage of the on-board charger. The converter uses a constant voltage and constant current control in the forward operation and voltage and current double-closed-loop control in the reverse operation. Aiming at the problem whereby the voltage gain range of the bidirectional CLLLC resonant converter is relatively narrow under frequency-conversion control, the paper proposed a hybrid control method of frequency conversion and phase shift. Frequency-conversion control is used when the voltage gain is high, and phase-shift control is used when the voltage gain is low. The output voltage range of the converter is effectively broadened, and zero voltage switching and zero current switching can be realized in the full load range to improve operating efficiency. A 3.3 kW bidirectional CLLLC resonant converter simulation system is built in the simulation software. The simulation results verify the correctness and feasibility of the designed circuit and control method. more...

Aims: The aim of this study was to summarize the currently available evidence on the associations between the IL-10-1082G/A, IL-10-592A/C, and IL-10-819G/A polymorphisms and susceptibility to atopic dermatitis (AD). Materials and Methods: Five electronic databases including PubMed, the Web of Science, Excerpta Medica dataBASE, the Cochrane Library, and the China National Knowledge Infrastructure were searched for potential studies. Studies illustrating the association of the IL-10-1082G/A, IL-10-592A/C, and IL-10-819G/A polymorphisms and AD susceptibility were included in this meta-analysis. For a study to be included, it had to have been published before September 20, 2018. Study quality was assessed using the Newcastle-Ottawa scale. Summary odds ratios and 95% confidence intervals were calculated to evaluate potential associations under five genetic models. Results: A total of 15 case-control studies comprising of 1647 AD patients and 2031 controls were included in this meta-analysis. Their methodological qualities were generally high. We confirmed an association between the IL-10-819G/A polymorphism and AD, but there was an insignificant association identified between the IL-10-1082G/A and the IL-10-592A/C polymorphisms and AD when all ethnic groups were considered together. The subgroup analyses revealed some ethnic-specific effects. For the IL-10-819G/A polymorphism, individuals with the GG-genotype seemed to have an increased risk of AD among Caucasian populations, but less so in the Asian populations. However, for the IL-10-1082G/A polymorphism, the GG-genotype carriers seemed to be more susceptible to AD in the Asian populations than in the Caucasian populations. Conclusions: This meta-analysis suggests that the IL-10-819G/A polymorphism seems to be associated with increased risk of AD among Caucasian populations, and that the IL-10-1082G/A polymorphism seems to be correlated with AD among Asian populations. more...

As more and more patients with metastatic prostate cancer develop resistance to androgen-deprivation therapy (ADT) and consequently castration-resistant prostate cancer (CRPC), reasonable selection of therapies is becoming increasingly important for the prediction of the therapeutic results. Many studies show that androgen receptor splice variant 7 (AR-V7) is involved in the development and progression of CRPC and that the expression of AR-V7, absolutely higher in CRPC than in hormone-nave prostate cancer, plays a significant role in the mechanisms of resistance to abiraterone, enzalutamide and taxane chemotherapies. Further more, some clinical trials have revealed that the AR-V7 level may indicate the prognosis of different therapeutic options: AR-V7 negative in circulating tumor cells suggesting the effectiveness of a new hormonal therapy and taxane chemotherapy while AR-V7 positive indicating the poor result of a new hormonal therapy. These findings show that AR-V7 could be a biomarker for therapeutic options and the prognostic evaluation of CRPC. more...

A new-style four-wheeled driving (4WD) series-parallel hybrid electric vehicle (HEV) plus with a two speed transmission is presented in this paper. The system structure and operation principles are discussed systematically, and then the control strategy is proposed. Control strategy focus on the multi modes switch logic and power distribution. In addition, shifting strategy of the two speed transmission is researched. Simulation results indicate that the presented 4WD HEV can realize nice dynamic property; the presented control strategy is correct and effective. more...

For investigating the feasibility of control strategy used in parallel hybrid electric vehicle, a D2P real-time simulation is introduced. A new multi-mode rule-based control strategy is proposed. The strategy is based on splitting the torque from the motor and engine so that these power sources can be operated at high efficiency. A real-time simulation platform is built based on D2P system. Real driver inputs and controller are applied while controlled objects are simulated using the model of parallel hybrid electric system computed in D2P module. Strategy is validated by D2P real-time simulation, which results show that the presented strategy is feasible and effective. more...

Based on tracked vehicle dynamics analysis, a fuzzy control strategy is proposed in this paper for the dual electric tracked vehicle motion control. The inputs of fuzzy system are driver acceleration, braking and steering signals besides vehicle velocity feedback signal, while outputs are dual motors’ torque commands and mechanical braker’s target force. Control strategy contains two fuzzy logics, one is for steering and straight-line running control, the other is for braking control section. Simulation results show that the fuzzy control strategy presented here is correct and effective for electric tracked vehicle motion control. more...

In order to on-line monitor tool wear, an on-line monitor tool wear system was built. The tool wear can only be meseaured indirectly in work. Hence, the motor current and the tool wear is linear dependence. First, the relation model between motor current and cutting parameter of CNC was built, and then on-line monitor the current based on uC/COS, which can be monitor tool wear indirectly was done. The experiment results showed that the model is accuracy, and sensitivity Analysis of parameter was carried out. more...

In order to prolong the life of steel worm pair used in track tension adjuster, a test method was designed to evaluate the effect of hardness on the fretting wear behavior of steel worm gear on a SRVⅣoscillating friction and wear tester. Through this method the fretting wear behavior of 40CrNiMoA steel-18Cr2Ni4WA steel with different hardness matching was studied under dry sliding condition at room temperature. The results show that in the steel worm gear pair composed of 40CrNiMoA steel and 18Cr2Ni4WA steel, the fretting wear volume loss of 40CrNiMoA steel decreased and that of the 18Cr2Ni4WA steel worm material increased with the hardness of 40CrNiMoA steel increasing. When the hardness of 40CrNiMoA steel is about HRC49, fretting wear volumes of the worm specimen was equal to that of the worm wheel specimen. Based on the experimental results, reasonable hardness matching for prolonging the life of steel worm pair used in track tension adjuster was proposed. more...

The construction scheme of long-span V-shape rigid frame composite arch bridge is discussed. In process of simulation calculation of the construction, the author compiles APDL command flow program by using the unit birth-death technique, establishes simulation calculation model in the construction process. The creep characteristics of concrete are also taken into account. The whole process of beam first-to-arch later stage construction are calculated and studied.By researching on construction control of Xiaolan channel super large bridge, the feasibility of the construction program is evaluated, the alignment and displacement in each construction ideal state are determined and the alignment and displacement in the following construction state are predicted. The stress controling results of the critical sections are researched on to make the construction go along well as designed, make sure the safety during construction, the structural internal force under constant load and structural alignment are complied with the design requirements and the construction quality and safety are ensured. more...

Forming magnesium alloys with rare earth elements (La, Gd, Nd, Y, Ce) is a routine method for modifying their microstructure and properties. In the present work, the effect of Ce addition on the microstructure evolution and the mechanical properties of as-extruded Mg-8Al-0.5Zn (AZ80) alloy was investigated. All of the extruded AZ80-xCe (x = 0, 0.2, 0.8 and 1.4 wt %) alloys exhibited equiaxed grains formed by fully dynamic recrystallization, and the grain size of the extruded AZ80 alloy was remarkably reduced by ~56.7% with the addition of 1.4 wt % Ce. Furthermore, the bulk-shaped Al4Ce phase formed when Ce was first added, with the Ce content rising to 0.8 wt % or higher, and Al4Ce particles in both the nano- and micron sizees were well distributed in the primary α-Mg matrix. The area fraction of the Al4Ce particles expanded with increasing Ce content, providing more nuclei for dynamic recrystallization, which could contribute to the grain refinement. The results of the tensile tests in this study showed that Ce addition effectively improved the room temperature formability of the as-extruded AZ80 alloy, without sacrificing strength. The significantly improved mechanical properties were ascribed to excellent grain refinement, weakened texture strength, an increased Schmid factor, and a reduced area fraction of low-angle grain boundaries, all resulting from Ce addition to the as-extruded AZ80 alloy. The contribution of the nano-Al4Ce precipitates on improving the mechanical properties was also discussed in this paper. more...

The authors reported in this paper the seasonal variations in major atmospheric tides in the mesosphere and lower thermosphere (MLT) region in the meridian at 120°E. The SABER/TIMED temperature measurements covering November 2004 to January 2006 were used to delineate tidal harmonics through applying the Fourier-least squares fit and the FFT analysis. Tidal harmonics composing the final apparent tides were examined separately. Investigation results showed that the migrating diurnal harmonic increases with altitude and attain maxima at 97 km height, then decreases rapidly with altitude. It was also found that the other harmonics increase with altitude in the MLT region and attain significant amplitude at 97 km height. Using these harmonics, the diurnal, semidiurnal and terdiurnal tides in the meridian were reconstructed. Particular focus was placed on investigating the contribution of nonmigrating tides for each kind tides of different frequency. The primary results showed that in the meridian, migrating tides play dominant role in characterizing the general features both in space and time for diurnal and semidiurnal tides. Regarding the diurnal tides, contribution of migrating component is most predominant during spring equinox, which is characterized by the amplitude maxima at the equator and that at the tropics for both hemispheres. Moreover, consistency was seen in the comparison among the temporal variation in the reconstructed diurnal tides and the previous result obtained by using meteor radar wind measurements taken at Wuhan (30°N, 114°E). Regarding the contribution of diurnal nonmigrating harmonics, it was found that in addition to the previously observed prominent (1, 0), (1, 2) and (1, –3) mode, (1, –2) mode is also prominent showing amplitude comparable to that of the (1, 0) mode. These four modes contribute together during summer solstice to form an area covering 10°N to 30°S with maximal amplitude 20K appearing at the Equator. Due to the domination of migrating semidiurnal tides, prominent semidiurnal tides occur at the tropical latitudes in both hemispheres. In the northern hemisphere, the semidiurnal tides appear intense amplitudes during autumn equinox with the maximum of 13K. In the southern hemisphere, they are intense in between spring and summer equinox. The influences of the nonmigrating semidiurnal tides appear to be clear in other seasons, a number of amplitude maxima are seen. As confined in 40°S~40°N, the terdiurnal tides exhibit much weak amplitudes. Moreover, the nonmigrating terdiurnal tides are stronger during many times than the migrating tides in amplitude, although the later exhibit regular occurrence at the Equator. Nevertheless, the current results suggested that the nonmigratingt ides are predominant during most times in 2005. more...

Acceleration control using fuzzy logic is investigated in this paper for a plug-in series hybrid electric vehicle in order to improve the vehicle response to drivers demand. The transient process of acceleration is mainly considered in this research. Fuzzy logic is used for motor transient torque control according to drivers input and vehicle velocity, outputting a regulatory factor to increase motor torque transiently when drivers acceleration pedal is pushed down deeply and to reduce the torque increment when acceleration process is close to over. Performance of fuzzy control is tested by MATLAB simulation. Simulation results indicate that the presented fuzzy algorithm is feasible and effective for improving vehicle acceleration ability without damaging stable velocity control characteristic; in simulation, vehicle acceleration time of 0-100km/h has been reduced by 2.4 seconds. more...

A turning control strategy based on BP neutral network and modified by a PID algorithm is presented in this paper for the dual electric tracked vehicle. Firstly analyzed the tracked vehicle turning dynamics and establish the torque distribution strategy. The BP network is trained by data from the distribution strategy simulation results; the PID algorithm is used to eliminate the dependence of terra coefficient. Simulation results show that the control strategy presented here is effective for the dual electric tracked vehicle steering. more...

To prepare pneumolysin as a new protein carrier of vaccine against otitis media with genetic engineering technology and establish the base of the study on pneumococcal conjugative vaccines.Genomic DNA was isolated from streptococcus pneumoniae. A pair of primers which included two restriction sites was designed based on the published pneumolysin gene sequence. The pneumolysin gene was amplified from pneumococcal DNA with PCR technology. The restriction enzyme digested fragment was linked into the cloning vector PET-28a and the recombinant plasmid DNA containing pneumolysin was then transfected into host cell E. coli JM109 (DE3).DNA fragments were subcloned to construct the complete pneumolysin gene by a conventional coning and PCR. The inserted pneumolysin gene sequence was confirmed by DNA sequencing and the pneumolysin protein was successfully expressed. The relative molecular mass of the expressed product was 52 000. The expressed product amounted to 8% of the total host cell protein.The pneumolysin gene was successfully cloned into host cell using genetic engineering technology. The recombinant pneumolysin was expressed and purified for preparation. This work laid a foundation of the preparation of pneumococcal conjugative vaccines. more...

To provide the experience for early diagnosis and management of facial nerve neuromas, and to discuss the clinic and imaging feature of facial nerve schwannoma and facial nerve fibroma in 22 cases.Twenty cases facial nerve schwannoma and two cases of facial nerve neurofibroma were diagnosed and reviewed retrospectively. Surgical removal were performed through the middle cranial fossa in 2 cases, through intratemporal approach in 8 cases, through intraparotid approach in 2 cases, and combined intra-temporal with out-temporal approaches in 10 cases. Seventeen cases underwent facial nerve graft for repairing a facial nerve defect. Great auricular nerve was used in 3 cases with intratemporal approach and 1 case with intratemporal combined intraparotid approach. Sural nerve graft was used in 5 cases with intratemporal approach and 8 cases with intra-temporal combined intraparotid approach. Two cases were employed two-stage facial muscle flap-plasty.Facial nerve neuromas were totally removed in 21 cases and subtotal neuroma removed in 1 case. In these cases, 20 patients were no recurrence and 1 patient was lost follow-up. One patient with subtotal neuroma removal received Gamma Knife treatment before and after surgery, and this case was no recurrence. The CT imaging of the temporal bone showed that schwannoma was separated "white mass" with smooth margin along the region of facial nerve without intact canal. But neurofibroma locate in enlarge fallopian with intact canal. Magnetic resonance imaging had the advantage of evaluating all segments of the facial nerve and showed continuity of intratemporal and intraparotid mass with the facial nerve. Pathological results indicated that 20 cases were diagnosed as facial nerve schwannoma and 2 cases were neurofibroma.Although tumors originating from the facial nerve are extremely rare, it is possible to make early diagnosis through finding clinical feature and imaging methods. Generally, systematic surgical approach for tumor removal and facial nerve reconstruction should be considered in the cases with facial neurinoma. more...