bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Proprioceptive Neuromuscular Facilitation on Force-Time Curve and Electromyogram Parameters in Competitive Aerobics Athletes
Authors: Yao Li Qin
Published: May 2010

Objective: to investigate the effect of proprioceptive neuromuscular facilitation stretching on force-time curve and EMG Parameters in competitive aerobics athletes. Methods: we take 36 competitive aerobics athletes as participants, and they were tested after bicycle exercise and bicycle exercise/PNF stretching protocol,then the data were compared and analyzed.Conclusion: PNF stretching for lower extremity will not cause the maximum muscular strength and force - time curve parameters (MVC,F100,IRF,and TMVC) significantly decreased in competitive aerobics athletes, however,EMG voltage of rectus femoris has undergone a significant decline,which is showed that PNF stretch will cause change in excited mode,but force - time curve parameters will not be affected significantly.EMG showed that neural inhibition did not affect the maximum isometric muscle strength and characteristics of time - the power curve parameters, indicating PNF stretching can improve capability of muscle coordination.To take full advantage of PNF stretching exercises, changes of muscular strength and force - time curve parameters caused by PNF stretching should be studied in a more comprehensive, in-depth detail.
Observation Test on the Physical Properties of Accumulated Snow in Constructing Embankment
Authors: Liang Shou Yun , Ma Xiang Xian , Wang Xiang Yang
Published: May 2010

Drifting snow is one of the main disasters in blocking railways and road traffics in cold areas. It has been becoming a key issue to reduce hazards from drifting snow in the engineering constructions in cold areas. The physical properties of snowfall and drifting snow, together with the transformation over terrain by engineering construction, give significant influence on the formation and growth of drifting snow. The accumulated snow distributing on high embankment transects built in the Jinghe-Yining Railway (JYR) has been chosen as the main object of this research, and a field observation of weather conditions over this area with in-situ experiments of the physical properties of snow and has been reported. All results indicated: the snow density and hardness were generally changed with the similar trending of air temperature variation, and both snow density and hardness increased with the duration of snow accumulated. However, the change of snow density and hardness appeared much more complicated variations than that of the air temperature. The snow depth and pressure, as well as the density and hardness were complicatedly distributed on both sides of the embankment transect, either roughly symmetrical or significantly different. We concluded that a great influence on the physical properties of snow had been exerted by many factors such as the topographic features, the redistribution of snowfall brought by engineering constructions, the weather conditions during snow accumulating etc.
Research on Fault Diagnosis of PCCP Based on Support Vector Machine
Authors: Yang Chun Ting , Liu Yang
Published: May 2010

Recent years, many utilities have experienced catastrophic rupture of critical Prestressing Concrete Cylinder Pipe (PCCP) lines throughout the world. Much attention has been focused on reliably assessing the condition of PCCP mains. However, assessment of embedded prestressing wire is difficult. Continuous acoustic monitoring can provide a means of locating problematic pipe sections. In this paper the application of support vector machine (SVM) in acoustic signal detection is proposed. And the effect of this method is investigated. Some key parameters of SVM and kernel functions are surveyed. SVM methods are more effective, especially for the case of lack of training samples. The experiment shows that the SVM method has good classification ability and robust performances. The techniques can provide the opportunity to identify problematic pipe sections and repair the pipe prior to failure. Therefore it can help to prolong the life of a suspect pipeline while minimizing the potential for catastrophic failure.
Traffic Evacuation Analysis for Explosion and Burning Radius of CNG Station
Authors: Luo Yong , Guo Xiu Chun
Published: May 2010

With the shortage of the gasoline resource day by day, the adjustment of county’s energy strategy, environment protect requirement and the continuous progress of the automobile technology, more and more automobiles were designed on the CNG as their fuel and corresponding CNG stations were increasing at the same time. But the consequential accident such as the leakage of the gas and the fire disaster made the security of the CNG station became a serious problem a problem which people pay more and more attention on it. if the gas was not fired immediately it may construct the gas cloud cluster and will explode when it comes out a fire, and people in a certain distance may wounded by the shockwave also the architectures in the dangerous range will be destroyed. This paper will contribute to formulate the evacuate conditions for pedestrian after the explode accident happening and also will provide the basis for evaluating the new constructed CNG stations.
Modelling and Simulation of High Fidelity CDU for Flight Simulator Based on Object-Oriented and Hardware-in-Loop Technique
Authors: Zhu Si Bin , Ye Zheng Mao , Li Gui Xian
Published: May 2010

A high fidelity, reliable and extensible real-time CDU simulation system is built on the basis of self-made membrane keyboard and object-oriented simulation method in this paper to improve the visual feelings and simulation fidelity of CDU in flight management system research. Based on embedded PC104 CPU and 8255 programmable peripheral equipment interface card, the membrane keyboard hardware circuit and the keyboard code scanning program are designed. Accordingly, the confused logical problem of keystokes is solved and meanwhile, the emulation CDU keyboard is realized. And then, an extensible and reliable CDU pages system is constructed utilizing object-oriented simulation technique, inheritance and polymorphism mechanisms. Thus, the tiresome generation and management problem of pages system is tackled. Simulation experiments illustrate that routing data and performance parameters can be input and displayed realistically on the CDU system developed in this paper.
The Anti-Skidding Control for Hybrid Braking System Based on Model Following Control Method
Authors: Xiong Lu , Zhang Zhao Liang , Yu Zhuo Ping
Published: May 2010

This paper puts forward one new anti-skidding method based on the model following control method. With the new feedback function and control parameter, the braking performace, especially the phase-delay of the electric motor's torque is, according to the result of the simulation, improved. Combined with the advantage of the origin MFC, we think the improved MFC can be widely applied in anti-skidding method.
Research on the Dynamic Performance and Parameter Design of Parallel Hybrid Electric Vehicle
Authors: Zheng Wei , Zhang Qian Fan , Cui Shu Mei
Published: May 2010

According to the Parallel Hybrid Electric Vehicle (PHEV) demands on powertrain systems, the dynamic models of PHEV are built in this paper. Base on the analysis of dynamical characteristics of both internal combustion engine (ICE) and electric machine (EM), the dynamic ability and fuel economy performance of PHEV is presented. The paper focuses on the parametric design of powertrain on vehicle performance, which provided the theoretical foundation for PHEV design. The paper also puts forward the control strategy of PHEV during the operating modes switching, which aims to solve the problem of the power distribution between the ICE and electric motor, which can effectively resolve process control problems of the complex PHEV system. By employing the dynamic model and performing MATLAB simulation, the results of simulation are given, which demonstrate that the PHEV improve performance well.
A Software Enterprise Unit Testing Method
Authors: Wang Yu Ling , Gui Ying
Published: May 2010

Unit testing is an important quality assurance activities in the process of software development, unit testing quality will have a great effect on the final quality of software products. In this article,we expatiate upon some critical factors of unit well testing in three aspects from the organizational structure, testing process and technology,that can serve as a software enterprises to carry out unit testing activities for reference.
Visualization of Streamline Fluid Flow with Bézier Surface
Authors: Lu Xiao Lin
Published: May 2010

Streamline visualization is very important for the fluid dynamics and manufacture design. The visualization method constructed by the stream function and fluid flow model can not interactively change the visualization shapes upon the request to amend the surface. This paper presents a new visualization method with Bézier control mesh to achieve the streamline fluid flow visualization. The stream function is in accordance with the principles of fluid motion by using Bézier surfaces to find the constraint condition. The constructed surfaces can be interactively modified accurately to reflect the local details of the flow field to meet the engineering requirements. The streamline visualization can be modified and controlled interactively by a set of control parameters like the Bézier surface. It has an important practical value for fluid flow design and manufacturing.
The Research of Two-Dimension Micromachined Level Posture Sensor
Authors: Piao Lin Hua , Li Yan Jie , Li Bai Hua , Ji Ming Ming , Zhang Xue Yan
Published: May 2010

Two-dimension level posture sensor which can be sensitive to two vertical-directional tilt angle at one time is described. Adopt micro-machined technique two deep groove are corroded on the silicon plate, and two cantilever beams of metal heated hot wire is set up at each deep groove. Semicircle airtight space forms sense elements. Through two Wheatstone bridge, we get the tilt output voltage of x axis and y axis. To overcome environmental factors, a series of signal processing methods are proposed ,such as: zero temperature compensation, sensitive temperature compensation and linear compensation. The test about the sensor showed the sensor’s performance is as follow: resolution<0.05°,nonlinear<0.1%,the working temperature is enlarged.
The Research of Micromachined Airflow Tilt Sensor
Authors: Piao Lin Hua , Li Yan Jie , Li Bai Hua , Ji Ming Ming , Zhang Xue Yan
Published: May 2010

Micromachine airflow tilt sensor which can be sensitive to tilt angle is described. Adopt micro-machined technique two deep groove are corroded on the silicon plate, and two cantilever beams of metal film heated hot wire is set up at each deep groove. Semicircle airtight space forms sense elements. Through Wheatstone bridge, we get the tilt output voltage. Single-chip computer and temperature sensor constitute compensation circuit to achieve temperature compensation and linear compensation. The test showed the sensor’s performance is as follow: measuring range is ±30,resolution<0.1°, working temperature is better than 50ms ,nonlinear<0.1%.The sensor is not only in small size but also in simply crafting. It is good in sensitive organ’s output consistency, and suitable for mass production.
A New 3D Medical Data Field Segmentation Algorithm Based on Improved K_Means Clustering
Authors: Li Xin Wu
Published: May 2010

Direct 3D volume segmentation is one of the difficult and hot research fields in 3D medical data field processing. Using K-means clustering techniques, a new clustering segmentation algorithm is presented. Firstly, According to the physical means of the medical data, the data field is preprocessed to speed up succeed processing. Secondly, the paper deduces and analyzes the clustering and segmentation algorithm and presents some methods to increase the process speed, including improving cluster seed selection, improving calculation flow, and amending pixel processing and operational principle of algorithm. Finally, the experimental results show that the algorithm has high accuracy when used to segment 3D medical tissue and can improve process speed greatly.
Application of ANN Trained with GA in Energy Characteristics of Hydraulic Turbine
Authors: Wang Li Ying , Zhao Wei Guo , Zhang Chuan Hong
Published: May 2010

The learning algorithm of artificial neural network (ANN) trained with genetic algorithm (GA) are introduced, based on the operation data of hydropower station, the network model of energy characteristics is established based on GA-ANN, the relationship curve between head H and output N is gained under some efficiency. The results show that the algorithm is better than BP neural network and avoid the limitations of BP neural network, the results can be used in the optimal operation of hydropower, and it has a practical significance. The results show the new model has a great importance in hydraulic unit study. It could be generalized into other all efficiency prediction, and it offers a new way in water conservancy and at the meantime a new method for the study of ANN and GA.
An Effective Scheme of Wavelet Coefficients for Multiresolution Image Fusion
Authors: Huang Shu Ying , Yang Yong
Published: May 2010

Image fusion has become an important and powerful technique for image analysis and computer vision. This paper presents a novel multiresolution image fusion method, which is based on wavelet transform combing with an effective fusion scheme. The main contribution of this research is that by considering the physical meaning of the wavelet coefficients, a selection scheme that treats the coefficients in different ways is proposed. This scheme selects the coefficients in the high frequency bands by a wavelet entropy based strategy, while selects the coefficients in the low frequency band by a variance based strategy. The performance of the proposed fusion method is compared with several existing fusion techniques. Comparison results show that the proposed method can effectively fuse the images with less error.
Dynamic Accuracy Loss Prediction Model Based on BPNN
Authors: Jiang Min Lan , Wang Xiao Dong , He Xiu Hui
Published: May 2010

In this paper, study the dynamic accuracy loss prediction model of measurement system, using measurement standard deviation as the systemic accuracy, the change of measurement standard deviation in different time as the systemic accuracy loss. Using BPNN build the dynamic accuracy loss prediction model about the practical measurement, model precision reach , realized real-time prediction of systemic accuracy loss , the establishment of predictive models to the system Real-time error correction and compensation to provide a theoretical basis, and that can cost-effectively improve the system of measurement accuracy.
Field Measurement of Wind Characteristics and Numerical Simulation at the Site Nearby Western Gap of Valley Areas
Authors: Bai Hua , Li Jia Wu , Wang Lei
Published: May 2010

Few site measurements were carried out in inner-China area, partly due to researcher conceiving that the wind in inner-China area is not as strong as that in coastal area. Recent serious damages caused by local gales in middle reaches of Yellow River, far away from sea, were observed. In order to guarantee the safety of the structure, the wind load acting on the structure must be studied. But in the existing anti-wind specification the parameters of wind characteristics on complicated mountain, gorge and mountain pass terrain have no explicit stipulation. So it is obviously significant to study the wind characteristics on complicated terrain. It’s the first time to put the wind field observation of special topography on the upper and middle yellow river into practice. Field measurement tower was conducted at the site. Five 2-d anemometers and a 3-d ultrasonic anemometer were installed on the 65-meter-high tower from the 10 meters to 60meters high above ground, and two 30-meter-high towers erected on the bank of the river. Based on the method of data statistical analysis, a data processing system of wind speed observation V1.0 based on Borland C++ Builder is developed, which can rapidly and automatically process massive data. The specific wind space distribution and regular pattern around the western gap of valley areas are firstly gained. Wind field of terrain liking bell where the river flows from canyon to the open field have been simulated by CFD. The result of analysis testifies the correctness and efficiency of the numerical method. It would be provided with great theoretical significance and practical engineering value passes through the foregoing study.
Temperature Detecting System of Beer Fermentation Based on DS18B20
Authors: Zhou Fen Ping , Ma Hong Tao , Sui Bing Dong , Sun Jia Mo
Published: May 2010

This Paper introduces a temperature detection system in beer fermentation. A temperature monitoring system with characteristics of bus topology structure is composed of industrial computer, temperature detector, bus converter, transmission bus and especially 1-wire digital temperature sensor DS18B20. Four-core cable is used to form a tree-like or star-like network, in which 54 digital temperature sensors existing on 18 fermentation tanks can be connected. The quantity of junction wires between temperature sensor and computer will be reduced greatly. Temperature detector provides power supply for bus converter and DS18B20 through Four-core cable. Because bus converter has used hardware fault detecting technology, the fault temperature sensor can automatically detach from the main bus and will not affect normal working of other sensor in network. So to solve the problem of a certain sensor or branch's damage causing the paralysis of entire bus. The length of detecting temperature bus can reach more than 500 meters. These all make system maintenance and expansion easy. The experiments show that this system is characterized by high intelligence, high-precision, capability of making temperature test on multi-points and compensating function. The method has a good applicable value to the temperature test.
Character-Oriented Education to Success Information Technology Self-Study Center
Authors: Tian Xian Zhi
Published: May 2010

In the present day, many universities have put their efforts on teaching reform. As for linguistic teaching reform, many teachers have probed into reform measures concerning character-oriented education to success and information technology. Therefore, the author has put her focus on linguistic teaching reform of independent college . Thus, zero-approach teaching mode and self-study center become her study focuses in the paper. The author tries her best to study relationships among them and tries to improve linguistic teaching reform in independent college.
Shear Test on CFRP Full-Field Measurement and Finite Element Analysis
Authors: Mistou Sébastien , Fazzini Marina , Karama Moussa
Published: May 2010

The purpose of this work is to study the Iosipescu shear test and more precisely its ability to characterize the shear modulus of a carbone/epoxy composite material. The parameters influencing this identification are the fibre orientation, the geometry of the notch and the boundary conditions. Initially these parameters were studied through the finite element analysis of the shear test. Then, the measurement of the shear strains was carried out by traditional methods of measurement (strain gauges) but also by optical methods. These optical methods: the digital image correlation and the electronic speckle pattern interferometry (ESPI); allow for various levels of loading, to reach a full-field measurement of the shear strain. This enabled us to study the strain distribution on the section between the two notches. The finite element model enabled us to study the parameters influencing the calculation of the shear modulus in comparison with strain gauges, image correlation and ESPI. This work makes it possible to conclude on optimal parameters for the Iosipescu test.
Identification of the Sn96.5Ag3.5 Law Behavior with the Scatter of the Parameters - Study of Aeronautical Application in Power Module
Authors: Micol Alexandre , Zéanh Adrien , Dalverny Olivier , Karama Moussa
Published: May 2010

This work studies the reliability of power electronic component in aeronautical environment to the ageing eect of the thermal cycling. The structure fatigue is sensitive to the process assembly conditions especially of the soldering process. To correclty evaluate the reliability of the power module, the identication of the solder behavior is one of the rst steps. Anand Model is here identied. Experimental test have to be established to evaluate the parameters of the law. A srt study is made to evaluate the indetiability of the law according to the dierent experimantal test. Then, the scatter of the parameters is evaluated in a context of time series. In the end, the scatter of the parameters is included in a nite element model to understand the inuence of this scatter on the evaluation of the number of cycle before failure.
Study of Optical Properties of Carbon Nanotube and Fabrication of Nano Fiber Optic for Optical Communication
Authors: Karthik R. , Umasankar G. , Thirumurugan K.
Published: May 2010

The success of the developed nano-engineering technology will lead to a redefinition of optical device manufacturing and integration and the functional and economic displacement of traditional bulk-optics devices. The discovery of nonlinear optical properties of the Carbon Nanotube (CNT) has paved the way for the research and development of high optical non linearity in CNT based nano optical fiber. In this paper, a novel structure of our proposed high optical non linearity CNT based nano optical fiber has been studied. In addition, a mathematical analysis on a high third-order optical non linearity of CNT based nano optical fiber has been done.
Theoretical Modeling of Front Propagation of CdS Nanoparticles in a Gel
Authors: Al-Ghoul Mazen , Ghaddar Tarek
Published: May 2010

We report a theoretical model to describe the spatiotemporal dynamics of a new
system consisting of sulde ions di¤using into an organic gel containing mercaptoethanol-capped
cadmium ions. The product, cadmium sulde, exhibits a faint yellow transparent propagating
front starting at the gel-outer electrolyte interface. When subjected to UV light, this system
reveals uorescing CdS nuclei localized spatially in a narrow region (constant width), called
pulse, that leads the front and propagates down the tube. The reported model is based on
reaction-di¤usion equations coupled to dynamical competitive particle growth. The resulting
evolution equations were solved numerically and the results are shown.
Effects of Microwave Irradiation Type on the Morphological and Dimensional Properties of Silver Nanoparticles
Authors: Shokuhfar Ali , Kazemzadeh S.M. , Vaezi Mohammad Reza , Hassanjani-Roshan Amir
Published: May 2010

Microwave irradiation is a novel method to accelerate the preparation of inorganic nanoparticles as well as various nanostructures such as nanotubes, nanorods, and nanowires. In this research, silver (Ag) nanostructures with various morphologies were prepared via a rapid microwave-assisted technique. The spherical and polygonal Ag nanoparticles were synthesized in the presence of Polyvinilpyroliden (PVP) as stabilizing agent. Ethylene glycol (EG) serves as a solvent. The silver nanoparticles were produced by Continuous and Discontinuous Wave irradiation. The obtained materials were characterized by UV-visible and transmission electron microscopy (TEM). The results present that the size of nanoparticles increase in continuous irradiation. In this process, the morphology of product is polygonal. In the discontinuous process the colloidal particle size is smaller than that obtained from the continuous process. Furthermore, the Ag nanoparticles have spherical shapes. The final data show that microwave processing has unique advantages over conventional heating processes.
A Powerful Method to Describe Transport Properties of Nano and Bio Materials
Authors: Di Sia Paolo , Dallacasa Valerio , Dallacasa Filippo
Published: May 2010

A key factor for the efficiency in nanostructured devices is charge transport. Despite considerable attention to this subject, the precise nature of transport processes in these systems has remained unresolved. To understand the microscopic aspects of carrier dynamics, we suggest a method for the calculation of correlation functions. They can be expressed as the Fourier transform of a kernel containing the frequency-dependent conductivity (). We present results for the velocity correlation functions , the mean square deviation of position R2 = <[R(t)-R(o)]2> and the diffusion coefficient D = (R2/t) in materials, like TiO2, ZnO, Si, for which a Drude-Lorentz description or its generalizations applies with a good agreement with experiments. We find that D = 0, indicating absence of diffusion at long times, except in the Drude case (o = 0). For small times t/ < 1, however, diffusion can occur even when o 0, within a limited region of size increasing with the value of o. The quantum mechanical extension of this method allows applications for the nanodiffusion in nanostructured, porous and cellular materials, as for biological, medical and nanopiezotronic devices.
Preparation of Porous Biphasic Calcium Phosphate-Gelatin Nanocomposite for Bone Tissue Engineering
Authors: Bakhtiari L. , Rezaie Hamid Reza , Hosseinalipour S.M. , Shokrgozar Mohammad A.
Published: May 2010

A new porous structure as a bone tissue engineering scaffold was developed by a freeze-drying method. The porous nanocomposite was prepared from Biphasic Calcium Phosphate (BCP) which was a mixture of 70% hydroxy apatite and 30%ß-TCP (ß-Tricalcium Phosphate). Porogen was naphthalene and gelatin from bovine skin type B was used as polymer. Gelatin was stabilized with EDC (N-(3-dimethyl aminopropyl)-N´-ethyl carbodiimide hydrochloride) by a cross-linking method. The scaffold was characterized by scanning electronic microscope (SEM), Fourier-Transformed Infrared spectroscopy (FTIR). The biocompatibility of this nanocomposite carried out through MTT (3-(4, 5-Dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide, a tetrazole) cell viability assay. Also other properties of scaffold such as morphology, grain size, bending strength were investigated. Highly porous structure with interconnected porosities, good mechanical behavior and high biocompatibility with bone tissue, were benefits of this porous nanocomposite for bone tissue engineering.
Study of Symmetries on some Chemical Nanostructure
Authors: Moghani Ali
Published: May 2010

In this paper, we apply a new simple method to specify how a given finite group is matured or unmatured introduced by Shinsaku Fujita. Then, the all integer-valued characters of the fullerene C80 and Tert-Butyl Alcohol are verified.
Microwave Sintering and Melting of Titanium Powder for Low-Cost Processing
Authors: Bruce Ralph W. , Fliflet Arne W. , Huey Hugo E. , Stephenson Chad , Imam M. Ashraf
Published: May 2010

The emerging reduction technologies for titanium from ore produce powder instead of sponge. Conventional methods for sintering and melting of titanium powder are costly, as they are energy intensive and require high vacuum, 10-6 Torr or better, since titanium acts as a getter for oxygen at high temperature, adversely affecting mechanical properties. Other melting processes such as plasma arcs have the additional problem of electrode consumption, and direct induction heating of the titanium powder is problematic. Microwave sintering or melting in an atmospheric pressure argon gas environment is potentially cost effective and energy efficient due to the possibility of direct microwave heating of the titanium powder augmented by hybrid heating in a ceramic casket. We are investigating this approach at the Naval Research Laboratory using an S–Band microwave system. The experimental setup and the results of melting and sintering experiments will be described including a rough estimate of energy usage.
Microwave Sintering of Titanium
Authors: Luo Shu Dong , Bettles Colleen J. , Yan Ming , Schaffer Graham B. , Qian Ma
Published: May 2010

Effective sintering of titanium requires the use of a high sintering temperature (≥1200 °C), preferably in high vacuum (< 10-2 Pa). This confines the heating and cooling rates to ~ 4 °C/min because of the limited thermal shock resistance of ceramic tube furnaces. Consequently, it leads to lengthy sintering cycles (10-12 hr). This work presents an assessment of microwave (MW) sintering of titanium. Titanium powders in the size ranges of <20 µm, 45-63 µm, and 100-150 µm were used to make green samples with compaction pressures ranging from 200-800 MPa. Sintering was carried out at 1200 °C for 2 hr in a 3 kW MW furnace with a 2.45 GHz multimode cavity under a vacuum of 2-6×10-3 Pa. The characteristics of MW heating of green titanium samples in vacuum are described in terms of the heating rate, vacuum fluctuations, and sparking discharge. The actual MW heating rate achieved from 350 °C to 1200 °C was 34 °C/min. The attendant densities are comparable to those attained by conventional vacuum sintering. Cross-sectional examinations revealed a fairly uniform pore distribution in MW-sintered samples made from either the coarse or fine titanium powder.
Structure Formation during Preparation of Variable Porosity Titanium Foams by Solid State Replication
Authors: Orlova Yuliya , Maekawa K. , Rack Henry J.
Published: May 2010

Fabrication of variable porosity titanium foams through incorporation of sacrificial sodium chloride powder has been investigated. A three-dimensional solid foam pore skeleton containing macro- (200-400m), micro- (5-10m) and sub-micropores (< 1.5m) was formed during high temperature sintering of commercial purity titanium powder containing sacrificial sodium chloride particles, faceting of the interior pore powder surface being noted throughout. The largest macro-pores had a cubical topography representative of the sodium chloride powder that had been vaporized during heating to the sintering temperature. Formation of the smaller micro-pores appeared to have occurred during the compaction process these being retained in the specimen body due to incomplete sintering of the host powder. Finally formation of the smallest sub-micropores was associated with high temperature gas evolution and entrapment during sodium chloride vaporization.
Laser Welding ATI 425® Alloy
Authors: Edwards Paul , Morton Todd , Ramsey Gregory L.
Published: May 2010

Laser Beam Welding of ATI 425® Alloy was performed on 2.5 mm thick butt joints. This new alloy could be used in place of standard Ti-6Al-4V for a variety of lower-cost structural solutions.
Demonstration of its fusion weldability with laser welding is of particular interest because it is a near-net- shape process, capable of high welding speeds, which will further enable lower cost manufacturing options. It was found that ATI 425® Alloy could be successfully welded using a fiber laser at speeds over 3 m/min. Microstructural, microhardness and tensile property evaluations were performed on the resulting welds. It was found that there was a 15% hardness increase in the weld and the strength of the joints was within 2% of base metal properties.
SiC Heterojunction Bipolar Transistors with AlN/GaN Short-Period Superlattice Widegap Emitter
Authors: Miyake Hiroki , Kimoto Tsunenobu , Suda Jun
Published: May 2010

In this study, new SiC-based heterojunction bipolar transistors (HBT) are proposed. An n-type AlN/GaN short-period superlattice (quasi-AlGaN) layer is grown on a SiC pn junction as a widegap emitter. By using quasi-AlGaN emitter, we have demonstrated successful control of band offset of AlGaN/SiC. Quasi-AlGaN/SiC HBT with an Al content over 0.5, which has no potential barrier to electron injection from an n-AlGaN emitter to a p-SiC base, exhibited a common-emitter current gain of β ~ 2.7, whereas the HBT with an Al content below 0.5 showed β ~ 0.1.
Experimental Study of Degradation in 4H-SiC BJTs by Means of Electrical Characterization and Electroluminescence
Authors: Farese Luca , Malm B. Gunnar , Domeij Martin , Östling Mikael
Published: May 2010

SiC power bipolar junction transistors (BJTs), for high voltage applications, have been studied under elevated temperature and electrical stress conditions. Electroluminescence has been used to capture effects of defect motion and growth, in complete transistor structures, leading to a quantifiable degradation in the electrical performance. The observed degradation of current gain (β) and on-resistance (RON) was relatively modest and saturated after a limited stress time, resulting in stable device performance. The characteristic wavelength (450 nm) of the electroluminescence, or light emission, in the visual and near infrared (NIR) range, coupled to the shape of the defects indicates that basal plane dislocations and stacking faults are involved.
Chloride-Based CVD at High Growth Rates on 3” Vicinal Off-Angles SiC Wafers
Authors: Leone Stefano , Henry Anne , Kordina Olof , Janzén Erik
Published: May 2010

Chloride-based growth on on-axis SiC substrates has been studied at higher temperature than typical CVD conditions. The use of chlorinated precursors allows to grow homo-polytypic layers and to achieve high growth rates for thick layers deposition.
In this study a vertical reactor with the gas flow inlet at the bottom has been used to grow layers up to 1.5 mm thick. Thanks to the addition of hydrogen chloride (HCl) to the standard precursors mixture, growth rates up to 300 μm/h have been achieved at a process temperature lower than 1900 °C. Very pure layers, micropipe free, and with a low background doping have been grown on 4H and 6H-SiC carbon and silicon-face, respectively, on-axis 3” diameter substrates. The results obtained indicates that this process has the potential to become a novel bulk growth technique at lower temperature than usual, which could give several advantages.
Silicon Carbide APD with Improved Detection Sensitivity and Stability
Authors: Bakowski Mietek , Schöner Adolf , Petermann Ingemar , Savage Susan
Published: May 2010

This paper describes a novel design to achieve sensitive and stable performance of an avalanche photodiode based on silicon carbide material. The design includes a field-stopping layer with limited extension, and junction termination, in order to achieve avalanche multiplication only in the central region of the device. Also, sensitivity is increased by the achievement of a rectangular field distribution, and full depletion of the absorption region by the onset of avalanche multiplication. Evaluation of devices produced with this design show that a low leakage current and a sharp and stable avalanche breakdown point around 120V is achieved. Optical responsivity to radiation of wavelength 200 to 400 nm is shown to increase with increasing applied reverse bias, until a factor of 8 increase is achieved at the breakdown voltage.
Application of SiC Normally-On JFETs in Photovoltaic Power Converters: Suitable Circuits and Potentials
Authors: Araújo Samuel V. , Sahan Benjamin , Zacharias Peter , Rupp Roland , Zhang Xi
Published: May 2010

Photovoltaic systems have been considered as one of most promising fields of application for SiC semiconductors mainly due to the requirements for very high efficiency values. Several other system aspects like volume and cost may also profit from the interesting characteristics of such innovative devices. One promising example is the vertical JFET, mainly due to its relative structural simplicity. Nevertheless, its inherent normally-on characteristic calls for especially tailored topologies, as some suitable applications for photovoltaic systems will be presented.
Performance and Reliability of SiC MOSFETs for High-Current Power Modules
Authors: Matocha Kevin , Losee Peter A. , Gowda Arun , Delgado Eladio , Dunne Greg , Beaupre Richard , Stevanovic Ljubisa
Published: May 2010

We address the two critical challenges that currently limit the applicability of SiC MOSFETs in commercial power conversion systems: high-temperature gate oxide reliability and high total current rating. We demonstrate SiC MOSFETs with predicted gate oxide reliability of >106 hours (100 years) operating at a gate oxide electric field of 4 MV/cm at 250°C. To scale to high total currents, we develop the Power Overlay planar packaging technique to demonstrate SiC MOSFET power modules with total on-resistance as low as 7.5 m. We scale single die SiC MOSFETs to high currents, demonstrating a large area SiC MOSFET (4.5mm x 4.5 mm) with a total on-resistance of 30 m, specific on-resistance of 5 m-cm2 and blocking voltage of 1400V.
Characterization of 6H-SiC JFET Integrated Circuits over a Broad Temperature Range from -150 °C to +500 °C
Authors: Neudeck Philip G. , Krasowski Michael J. , Chen Liang Yu , Prokop Norman F.
Published: May 2010

The NASA Glenn Research Center has previously reported prolonged stable operation of simple prototype 6H-SiC JFET integrated circuits (logic gates and amplifier stages) for thousands of hours at +500 °C. This paper experimentally investigates the ability of these 6H-SiC JFET devices and integrated circuits to also function at cold temperatures expected to arise in some envisioned applications. Prototype logic gate ICs experimentally demonstrated good functionality down to -125 °C without changing circuit input voltages. Cascaded operation of gates at cold temperatures was verified by externally wiring gates together to form a 3-stage ring oscillator. While logic gate output voltages exhibited little change across the broad temperature range from -125 °C to +500 °C, the change in operating frequency and power consumption of these non-optimized logic gates as a function of temperature was much larger and tracked JFET channel conduction properties.
600-V / 2-A Symmetrical Bi-Directional Power Flow Using Vertical-Channel JFETs Connected in Common Source Configuration
Authors: Veliadis Victor , Urciuoli Damian , Hearne Harold , Ha H.C. , Howell R. , Scozzie Charles
Published: May 2010

Bi-directional solid-state-circuit-breakers (SSCBs) are highly desirable in power-electronic fault-protection applications due to their high actuation speed and repeated fault isolation capability. Normally-on SiC vertical-channel JFETs (VJFETs) are excellent candidates for high power/temperature scalable SSCB applications as majority carrier devices with low conduction losses and stable +300°C thermal characteristics. 600-V / 2-A bi-directional power flow was demonstrated using two VJFETs connected back-to-back with their sources in common. The low VJFET pre-breakdown leakage currents and sharp onset of breakdown are critical in enabling bi-directional power flow. 0.1-cm2 low conduction-loss VJFETs were designed for efficient and reliable SSCB applications.
Mixed Mode Modeling and Characterization of a 4H-SiC Power DMOSFET Based DC-DC Power Converter
Authors: Potbhare Siddharth , Goldsman Neil , Akturk Akin , Lelis Aivars J.
Published: May 2010

We present detailed mixed-mode simulations of a DC-DC converter based on 4H-SiC DMOSFETs. The mixed-mode modeling enables the use of complex physics based models for the interface trap occupation and surface mobility that are typical for 4H-SiC devices, and apply them to a practical circuit application such as a DC-DC boost converter. The mixed mode simulations are performed for a reduced DC-DC converter circuit to evaluate the performance of the DMOSFET when it has an inductive load. The current inside the device and its power dissipation during switching are evaluated numerically. Further, the mixed-mode device simulation shows that the majority carriers (electrons) inside the 4H-SiC DMOSFET require a finite time to go from the ON (strongly inverted) to the OFF (depleted) state, thereby causing power dissipation and heating during the turn-off period. The peak power is dissipated in the JFET region of the device which indicates that maximum heat and therefore maximum temperature may be generated there.
Improvement of Surface Roughness for 4H-SiC Epilayers Grown on 4° Off-Axis Substrates
Authors: Aigo Takashi , Tsuge Hiroshi , Yashiro Hirokatsu , Fujimoto Tatsuo , Katsuno Masakazu , Nakabayashi Masashi , Hoshino Taizo , Ohashi Wataru
Published: May 2010

The epitaxial growth process was optimized in order to obtain good surface morphology for epilayers grown on 4˚ off-axis substrates. The optimization was carried out from growth temperatures and gas chemistry including C/Si ratio. Step-bunching was significantly suppressed by the optimized process and a surface roughness Ra of 0.2 nm was achieved. Etch pit density evaluation by KOH etching indicated that the basal plane dislocations were reduced to less than 50 cm-2 by the use of 4˚ off-axis substrates. Photoluminescence evaluation showed that the epilayer grown by the optimized process had a better crystalline quality than that grown by a standard process. Schottky diodes fabricated on the epilayer by the optimized process represented the ideality factor n of 1.01 and the barrier height of 1.67eV. These results demonstrate that high quality epilayers with smooth surfaces comparable to those on 8˚off-axis substrates were obtained on 4˚off-axis substrates.
Growth of Nanocrystalline Translucent h-BN Films Deposited by CVD at High Temperature on SiC Substrates
Authors: Younes Ghassan , Ferro Gabriel , Soueidan Maher , Brioude Arnaud , Cauwet François
Published: May 2010

h-BN layers were deposited on α-SiC substrates by CVD at high temperature (1500-1900°C) using B2H6 and NH3 diluted in Ar. Growth rates were in the 6-10 µm/h range. In all the conditions studied, the BN as deposited layers were found to be translucent to light, some having a light whitish aspect and other a more yellowish one. It was also observed that the deposit was not always adhesive. µ-Raman and TEM characterization showed that the layers were nano-crystalline with crystallite size < 10 nm. The growth rate was found temperature and N/B ratio dependent due to an N limited growth regime which is more pronounced above 1700°C.
Investigation of 3C-SiC(111) Homoepitaxial Growth by CVD at High Temperature
Authors: Jegenyes Nikoletta , Lorenzzi Jean , Soulière Véronique , Dazord Jacques , Cauwet François , Ferro Gabriel
Published: May 2010

Starting from 3C-SiC(111) layers grown by Vapour-Liquid-Solid mechanism, homoepitaxial growth by Chemical Vapour Deposition was carried out on top of these seeds. The effect of the growth temperature and of the C/Si ratio in the gas phase was investigated on the surface morphology, the roughness and the defect density. It was found that the initial highly step-bunched surface of the VLS seeds could be greatly smoothen using appropriate conditions. These conditions were also found to reduce significantly the defect size and/or density at the surface.
3C-SiC Heteroepitaxial Growth on Inverted Silicon Pyramids (ISP)
Authors: D'Arrigo Giuseppe , Severino Andrea , Milazzo G. , Bongiorno Corrado , Piluso Nicolò , Abbondanza Giuseppe , Mauceri Marco , Condorelli Giuseppe , La Via Francesco
Published: May 2010

3C-SiC devices are hampered by the defect density in heteroepitaxial films. Acting on the substrate, it is possible to achieve a better compliance between Si and 3C-SiC. We present here an approach to favorite defect geometrical reduction in both [ ] and [ ] directions by creating Inverted Silicon Pyramids (ISP). A study of 3C-SiC growth on ISP is reported showing benefits in the film quality and a reduction in the linear density of stacking faults. Growth on ISP leads also to a decrease in the 3C-SiC residual stress as well as in the bow of the Si/SiC system.
Growth Rate Effect on 3C-SiC Film Residual Stress on (100) Si Substrates
Authors: Anzalone Ruggero , Locke Christopher , Carballo J. , Piluso Nicolò , Severino Andrea , D'Arrigo Giuseppe , Volinsky A.A. , La Via Francesco , Saddow Stephen E.
Published: May 2010

SiC is a candidate material for micro- and nano-electromechanical systems (MEMS and NEMS). In order to understand the impact that the growth rate has on the residual stress of CVD-grown 3C-SiC hetero-epitaxial films on Si substrates, growth experiments were performed and the resulting stress was evaluated. Film growth was performed using a two-step growth process with propane and silane as the C and Si precursors in hydrogen carrier gas. The film thickness was held constant at ~2.5 µm independent of the growth rate so as to allow for direct films comparison as a function of the growth rate. Supported by profilometry, Raman and XRD analysis, this study shows that the growth rate is a fundamental parameter for low-defect and low-stress hetero-epitaxial growth process of 3C-SiC on Si substrates. XRD (rocking curve analysis) and Raman spectroscopy show that the crystal quality of the films increases with decreasing growth rate.
From curvature measurements, the average residual stress within the layer using the modified Stoney’s equation was calculated. The results show that the films are under compressive stress and the calculated residual stress also increases with growth rate, from -0.78 GPa to -1.11 GPa for 3C-SiC films grown at 2.45 and 4 µm/h, respectively.
Fundamental Study of the Temperature Ramp-Up Influence for 3C-SiC Hetero-Epitaxy on Silicon (100)
Authors: Hens Philip , Wagner Günter , Hölzing Astrid , Hock Rainer , Wellmann Peter J.
Published: May 2010

Usually a waiting step at around 1000°C to 1100°C during the carbonization step for 3C-SiC on silicon is implemented for establishing a closed carbon layer to prevent the formation of voids. The latter, however, may lead to non-ideal nucleation conditions for high quality layers with a low density of domain boundaries. Our investigations indicate that a continuous ramp-up as fast as possible with no waiting step would be preferable. The worst layer quality, as measured by peak intensity and FWHM of the (200) reflection of 3C SiC, can be found at a temperature of about 1000°C, which indicates that here the nucleation rate would be the highest. So longer periods within this temperature range should be avoided by applying high ramping speeds during the carbonization step.
Tuning Residual Stress in 3C-SiC(100) on Si(100)
Authors: Pezoldt Joerg , Stauden Thomas , Niebelschütz Florentina , Alsioufy Mohamad Adnan , Nader Richard , Masri Pierre M.
Published: May 2010

Germanium modified silicon surfaces in combination with two step epitaxial growth technique consisting in conversion of the Si(100) substrate near surface region into 3C-SiC(100) followed by an epitaxial growth step allows the manipulation of the residual strain. The morphology and the residual strain in dependence on the Ge coverage are only affected by the Ge quantity and not by the growth technique. The positive effect of the Ge coverage is attributed to changes in the morphology during the conversion process, as well as to a reduced lattice and thermal mismatch between SiC and Si in consequence of alloying the near surface region of the Si substrate with Ge.
Bow in 6 Inch High-Quality Off-Axis (111) 3C-SiC Films
Authors: Severino Andrea , Camarda Massimo , Piluso Nicolò , Italia M. , Condorelli Giuseppe , Mauceri Marco , Abbondanza Giuseppe , La Via Francesco
Published: May 2010

Growth of 3C-SiC films on an off-axis (111) Si substrate, with a miscut of 4° towards the <110> direction, is here reported. An extensive material characterization has been conducted by means of Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD) and Raman spectroscopy, indicating a very promising film quality with extremely flat surface and interface. Notwithstanding the excellent film quality, the wafer bow is still limiting its full employment in device realization.