bluuebunny/crossref_metadata_2025 huggingface dataset:
A Simulation-Based Analysis of Electricity Access in Uganda
Authors: Namujju Donna Lillian , Yücel Gönenç , Pruyt Erik , Okou Richard
Published: April 2015

Access to power is tied to a country's development. It facilitates improved social welfare, education, health and income generating opportunities. Uganda's economy is stifled by its low electrification rates - 16% nationally. This study builds a working theory on the internal setup of Uganda's power sector utilizing this theory to surface influential behavior modes as they pertain to power generation and supply and how these ultimately affect electricity access. Based on this working theory a System Dynamics simulation model is built. The model simulations show how Uganda's power sector is expected to evolve over 80 years in terms of power supply and demand given existing market structure and prevailing conditions. The study finds major problems in the nature of power accessed specifically an insufficient and unreliable power supply. The root cause is found in the nature of the existing capacity planning process in terms of how future capacity requirements are determined and the agreements made with generators as to how and when they fulfill their investment obligations.
Designing and Evaluating Digital Game-Based Learning with the ARCS Motivation Model, Humor, and Animation
Authors: Lee Lai-Chung , Hao Kuang-Chung
Published: April 2015

Multimedia teaching applications have been widely utilized in various subjects. The presentation of teaching materials with animations and games helps to stimulate the visual sense and enhance the learning motivation of learners. Successful learning, however, requires the stimulation of learning motivation that can inspire learners to achieve the desired learning objectives. This study combines the ARCS (Attention, Relevance, Confidence, Satisfaction) motivation model, and humor to design a set of multimedia applications that include teaching animations and games for sixth graders' natural science and technology course, called the Cat's Cradle Multimedia Learning System (CCMLS). The scenario stories of anthropomorphic characters introduce four units of natural science: levers, axles, pulleys and gears. Additionally, games are designed to impress learners even more. After the applications were prepared, tests for learning effectiveness, learning motivation and perceived fun associated with teaching materials were conducted with 106 students at the Qishan Elementary School in Kaohsiung. The experimental group used CCMLS, while the control group used videos of the textbook as the applications. A pre-test and post-test, ARCS Learning Motivation Questionnaire, Smileyometer and interviews were conducted with both groups. According to the statistical analysis, significance was detected in regard to learning effectiveness between the experimental group and the control group. Significance was also found in ARCS learning motivation and perceived fun of teaching materials. Moreover, there is a significant positive correlation between the perceived fun related to the teaching materials and learning motivation. The contribution of this study lies in the proposal of the digital game-based learning (DGBL) from the design perspective: to enhance students' learning motivation and use willingness regarding the teaching materials of the drama and the cartoon characters in humorous dialogues. The proper sound and light effects and examples that are close to daily life will also be taken into consideration in the design of the multimedia applications.
Interfacial Wettability and Thermal Conductivity of Diamond/Al Based Composites with Ti and B Additions
Authors: Li Shu Xian , Guo Hong , Fan Ye Ming , Han Yuan Yuan , Zhang Xi Min , Wang Peng Peng
Published: April 2015

Al-based and Al-alloy-based diamond composites were made by pressure infiltration process in order to obtain composites with high thermal conductivity and light weight for thermal management applications. Interfacial bonding strength and thermal physical properties of the Al-alloy-based composites were improved with additions elements of Ti and B. Influence of Ti and B on interfaces at 950 °C between diamond and Al matrix were found to play an effective bridge role of wettability, a large improvement of selectivity was observed between {100} and {111} diamond surfaces. SEM and EDS analysis suggested that the segregation of B element was confirmed to have primary effect on the interfacial bonding. The as-fabricated diamond/Al (Ti, B) composite exhibited thermal conductivity value as high as 449 W/m·K, thermal expansion coefficient as low as 6.2 × 10-6 K-1, and the bending strength as high as 312 MPa.
Influence of the Metal Particle Size and Sintering Process on the Electrical Resistivity of m-ZrO2/30%Mo Cermet
Authors: Guo Yan Ling , Zhao Hai , Tang Lei , Wang Yao Jie , Zhang Jie Yu
Published: April 2015

Monolithic zirconia-molybdenum (m-ZrO2/Mo) cermets have been prepared by traditional powder metallurgy process with molybdenum volume concentration of 30% and different molybdenum powders with average particle sizes of 80nm, 3μm, 8μm and 13μm. The influence of metal particle size on the morphology and electrical conductivity of the cermet has been investigated. The electrical resistivity of the cermet was measured via 4-probe DC technique from 500 °C to 1600 °C. All the samples showed the positive temperature coefficient of electrical resistivity, but the sample prepared with 80 nm molybdenum powder showed very high resistivity over 0.5 Ω·cm. Hot-press sintering was proved to be helpful to the elongated conductive phase formation, thus the electrical conductivity of cermet increased compared to the pressureless sintering process.
Effect of Sr and La on the In Situ A356-TiB2 Composite Fabricated via Remelting and Diluting Approach
Authors: Zheng Yuan Ping , Li Ming Yu , Zhao Yu Fe , Chen Zong Ning , Wang Tong Min , Kang Hui Jun
Published: April 2015

In this paper, a remelting and diluting (RD) approach was used to fabricate in situ A356-3wt.%TiB2 composites and the effect of Sr and La on the modification of the composites is investigated in comparison with the conventional flux assisted synthesis (FAS) approach. The microstructure was examined and tensile properties were tested to evaluate the modification efficiency on the composites. The results demonstrated that composites fabricated via RD approach achieve preferable modification by Sr and La due to the higher level of melt cleanliness so as to minimize the Sr-B interaction, in which the eutectic Si which displays a microstructure with globular-fibrous eutectic Si particles. Superior mechanical properties are obtained in the RD composites (especially the elongation) after modified by Sr and La.
Preparation, Microstructure and Properties of ZrO2 Gradient Porous Ceramics by Freeze-Casting Process
Authors: Ai Tao Tao
Published: April 2015

The ZrO2 gradient porous ceramics were prepared by a novel freeze-casting process. The porous structure of the ZrO2 ceramics was investigated by scanning electron microscopy (SEM). And the porosity and compressive strength were also measured. Experimental results indicated that the porous structure of the specimens was remarkably affected by the sintering temperature. The dendritic pores were obtained after sintered at 1300 °C. The porosity and compressive strength of the specimen were 56.79% and 4.37 MPa, respectively. As the sintering temperature reached to 1500 °C, a lamellar structure was obtained on the cross-section of the specimen. Meanwhile, the porosity decreased to 26.77% and the compressive strength increased to 8.26 MPa. The ceramics can be divided subsequently into three distinctive zones along the solidification direction, i.e. lamellar zone, transition zone and cellular zone.
Interaction between Nb-Silicide Based Alloys and Y2O3 Crucible
Authors: Ma Li Min , Zhang Jia Zhen , Yue Guang Quan , Zhang Hua Rui , Zhang Hu
Published: April 2015

Y2O3 crucibles have been prepared for as-cast Nb-22Ti-16Si-2Al-2Cr-2Hf and Nb-22Ti-16Si-2Al-2Cr alloys at 1950 °C. The microstructures, metal-crucible interfaces and contaminations were evaluated. Experimental results demonstrated that a mild interface reaction occurred between the Y2O3 crucibles and Hf, resulting in some inclusions dispersed in the metallic matrix. However, without Hf addition, no apparent reaction layers or inclusions were found. Both alloys were slightly contaminated with oxygen as the result of slow thermal dissociation of Y2O3, and its extent depended on Hf contents and holding times.
Aging Precipitation Evolving Process and its Effects on Mechanical Properties of 0Cr21Ni6Mn9N Austenitic Stainless Steel
Authors: Jiang Na Yun , Liu Fu Shun
Published: April 2015

The solution treatment (ST) and the the second phase morphology changing duing the aging precipitation process of 0Cr21Ni6Mn9N austenitic stainless steel were investigated using optical microscope (OM), X-ray diffraction (XRD), scanning electron microscope (SEM) with EDS and transmission electron microscope (TEM). The results showed that the precipitation phase was Cr2N which initially nucleated along austenitic grain boundaries and then grew towards into the inner grains in strip morphology. Also, with the longer aging time the proportion of Cr2N increased. The mechanical properties of alloys with and without the presence of the precipitation Cr2N were also studied. It was observed that due to the exiting of the precipitation Cr2N, the strength of 2169N stainless steel reduced during a certain range of aging time, and then improved when the aging time reached to 48h, while the elongation decreased thoroughly.
Surface Pretreatment and Fabrication Technology of Woven Carbon Fiber Cloth Aluminium Alloy Matrix Composite
Authors: Zhang Jun Jia , Liu Shi Chao , Chen Hang , Lu Yi Ping , Chen Qiu Shi , Dong Yong , Wang Tong Min , Li Ting Ju
Published: April 2015

Carbon fiber is mainly distributed in the shape of short fibers and unidirectional fibers as the reinforcing phase in metal matrix composites, and it is seldom studied as woven-cloth shaped to reinforce the matrix. In this paper, the pretreatment and the surface metallization of the woven carbon fiber were studied. Besides, the casting experiment without external pressure was carried out under the application of magnetic field. The result shows that when burning about 45mins at 500°C in the atmospheric environment, the pretreatment can achieve the best result according to differential thermal analysis and weight-time variation curve. Meanwhile the surface wettability between the carbon fiber and the matrix is greatly improved after the surface treatment and at the same time the reaction between the carbon fiber and molten aluminium alloy matrix is necessarily avoided, and it can consequently achieve an excellent bonding between the woven carbon fiber and aluminium alloy matrix. The application of magnetic field also provides magnetic force to promote the penetration of the molten matrix into the carbon fiber bundles.
Optimization of Ta Content of a Third Generation Ni3Al Base Single Crystal Superalloy
Authors: Han Song Ming , Li Wei , Ma Yue , Zhao Xin Bao , Li Shu Suo , Gong Sheng Kai
Published: April 2015

In order to optimize the Ta content of a newly developed 3rd generation Ni3Al-based single crystal superalloy, a series of alloys with the varying of Ta content of 3.0, 4.2, 4.5, 6.0wt. % were prepared. The experimental results showed that with the addition of Ta, the size and volume fraction of bulky γ' phase significantly increased while the primary dendrite arm spacing decreased. Meanwhile, the difficulty of solution treatment significantly increased with increasing Ta content. And the thermodynamic calculation results showed that the volume fractions of γ' phase in this series of alloys were significantly higher than those of typical Ni based single crystal superalloys, indicating that the 3rd generation Ni3Al based single crystal superalloys can serve in the temperature of 1150oC to 1200oC.
Influence of Rotating Speed on Mechanical Alloying Behavior of the Elemental Powder Blends of Nb-Ti-Si Based Alloy during Ball Milling Process
Authors: Zhang Li Jing , Guo Xi Ping
Published: April 2015

The elemental powder mixtures with the nominal composition of Nb-20Ti-15Si-5Cr-3Hf-3Al (at. %) were ball milled via QM-1SP4-CL planetary ball-milling machine at different rotating speed (300, 400 and 500 rpm). The corresponding mechanical alloying behaviors of the powder blends, including the evolutions of their phase constituent, microstructure, size and morphology, have been analyzed by XRD, SEM and EDS. The results showed that with increasing rotating speed, the particle was remarkably refined and spheroidized, and meanwhile, the grain size decreased, accompanied with an improved microstrain. Herein, a lamellar microstructure of particles formed at the rotating speed of 300 rpm, and became finer with increasing the rotating speed up to 400 rpm. When further increasing the rotating speed up to 500 rpm, the homogenous microstructure composed of a supersaturated Nb solid solution (Nbss) finally formed.
The Effect of Casting Speed on Physical Fields of AZ80 Magnesium Alloy during DC Casting
Authors: Bai Yuan Yuan , Le Qi Chi , Zhang Hai Tao , Zhang Zhi Qiang , Bao Lei
Published: April 2015

A comprehensive two-dimensional (2D) mathematical model based on a combination of the commercial finite element package ANSYS and the commercial finite volume package FLUENT was developed to describe the interaction of the multiple physics fields during DC casting process. ANSYS was for calculation of the stress field and FLUENT was for calculation of the fluid flow, heat transfer of the solidification. The results show that: the model is reliable and accurate to simulate the multiple physics of DC casting. Consequently, the position, which was prone to hot tearing, was confirmed and the max velocity, at which the hot cracking might not occur, was determined. The numerical simulations will be very useful for preventing crack, optimizing casting parameters and obtaining high-quality ingots.
Microstructure, Mechanical and Dielectric Properties of Si3N4-BN Composites with Different Porosities
Authors: Liu Kun , Zhang Chang Rui , Li Bin , Wang Si Qing , Cao Feng
Published: April 2015

Si3N4-BN composites were prepared by die-pressing and precursor infiltration and pyrolysis (PIP) route using borazine as the precursor. The composition, microstructure, mechanical, and dielectric properties of the composites with different porosities were investigated. With the adoption of starch as pore forming substance, drawn the Si3N4 preform from the liquid precursor borazine and decrease the pressure during curing, the porosity of the Si3N4-BN composites were effectively increased. Along with the increase of the porosity of the composites, the mechanical properties were decreased and the dielectric properties were improved. With 20 wt.% starch and drawn Si3N4 preform from borazine before curing, the density, porosity, flexural strength and elastic modulus of the composites were 1.70 g·cm-3, 29.78%, 48.05MPa and 32.45GPa, respectively. The dielectric constants and loss tangents were 4.20~4.44 and 0.48~3.42×10-3 at the frequency 7~ 18GHz. Composites with various dielectric and mechanical properties can be designed and prepared according to the application needs.
Microstructure and Mechanical Properties of Submerged Friction Stir Processing Mg-Y-Nd Alloy
Authors: Cao Geng Hua , Zhang Da Tong
Published: April 2015

Mg-2.5wt%Y-4wt%Nd-0.5wt%Zr casting alloy was subjected to submerged friction stir processing (SFSP) with different rotation rates (ω) and travel speeds (υ). The influence of the ratio of ω/υ on the microstructure and mechanical properties of Mg-Y-Nd alloy was investigated in the present work by optical microscopy, scanning electron microscopy, transmission electron microscopy, tensile test and hardness measurement. The results showed that the average grain sizes of SFSP samples were significantly refined compared with as-cast sample, and the coarse net-shaped Mg12Nd phases which located at grain boundaries in as-cast sample were changed into small particles. The combined effect of grain refinement and uniform particles distribution was responsible for the enhancement of mechanical properties. The relative optimal parameter of 600 rpm/60 mm·min-1 in this research obtained the finest grain size and the best mechanical properties, which were 1.1 μm for average grain size, 305 MPa for ultimate tensile strength and 22% for elongation, respectively.
Solid–Liquid Diffusion and Phase Growth Kinetics in Mg-Ca Binary System
Authors: Li Xin , Jiang Bin , Yang Hong , Xia Xiang Sheng , Dai Jia Hong , Pan Fu Sheng
Published: April 2015

The solid–liquid diffusion between Mg and Mg-10 at.% Ca alloy was studied at a temperature range of 570°C to 630°C for 10, 20, 30min, respectively. Only one compound, Mg2Ca, was observed in the diffusion couples. As the diffusion time increased, the dendritic structure of the diffusion layer became coarser. The thickness of the diffusion layer had an exponential relation to the experimental temperature. The Mg2Ca phase was observed to follow parabolic growth with diffusion time, which suggested that the growth of the Mg2Ca phase was controlled by diffusion mechanism. The activation energy was determined to be 111.28 kJ/mol.
Microstructure Evolution and Mechanical Properties of Mg-3Zn-0.5Er-0.5Al Alloy
Authors: Zheng Xiao Bing , Du Wen Bo , Liu Ke , Wang Zhao Hui , Li Shu Bo
Published: April 2015

The microstructure evolution of the Mg-3Zn-0.5Er-0.5Al (mass fraction, %) alloy under the different condition was investigated. The results showed that as-cast Mg-3Zn-0.5Er-0.5Al alloy mainly consisted of primary large irregular Mg4Zn7 phase and needlelike (Mg, Zn, Er, Al) quaternary phase. Mg4Zn7 phase almost dissolved into the matrix after solid solution treatment at 400 oC for 10 h, while the (Mg, Zn, Er, Al) quaternary phase still existed. The solution treated alloy was extruded at 250 °C. The ultimate tensile strength of the as-extruded alloy was approximately 268 MPa and the YTS was approximately 163 MPa companying with an elongation of 28%. The tensile strength of the as-extruded alloy improved obviously, which was mainly attributed to the grain refinement.
Effective Dispersion of CNTs to Fabricate CNT/Mg Nanocomposite
Authors: Han Guo Qiang , Du Wen Bo , Wang Zhao Hui , Liu Ke , Li Shu Bo , Du Xian
Published: April 2015

An effective dispersion process to cast CNT-reinforced in a concentrated magnesium alloy (AZ31) nanocomposite was investigated in this study. The metal magnesium powder was first coated with dispersed CNTs by wet process, followed by the fabricating of CNT/Mg precursor using mechanical briquetting and extrusion. The resultant precursor was then added into AZ31 alloy during the melting process. Finally, CNT/Mg nanocomposites with grain refinement matrix composite were fabricated in as-cast and as-extruded. Compared with the commercial AZ31 alloy, CNT/Mg nanocomposites exhibited higher yield strength of 270 MPa with an increase of 22.7%, which can be largely ascribed to the effective dispersion process of CNTs in the alloy matrix, and the elongation is no significant decrease.
Comparation about Refining Efficiency to Microstructure of AZ31 Magnesium Alloy for Sr Master Alloys
Authors: Cheng Ren Ju , Liu Bo , Jiang Bin , Luo Su Qin , Yang Qing Shan , Liu Wen Jun , Pan Fu Sheng
Published: April 2015

In the present work, the influence of Al-Sr and Mg-Sr master alloys on the as-cast microstructure of the AZ31 magnesium alloy was investigated,and the refinement efficiencies of both master alloys were also analyzed and compared. The research results indicate that both the Al-Sr and Mg-Sr master alloys have obvious refinement effect on the as-cast microstructure of the AZ31 magnesium alloy, and the refinement efficiency of the Mg-Sr master alloys was better than that of the Al-Sr master alloys. The mechanisms for the differences of grain refinement efficiency between Al-Sr and Mg-Sr master alloys on the AZ31 magnesium alloys were also discussed.
Microstructure and Mechanical Responses of Extruded Magnesium Alloy Sheets with Lithium Addition
Authors: Yang Qing Shan , Jiang Bin , He Jun Jie , Gao Zheng Yuan , Dai Jia Hong , Pan Fu Sheng
Published: April 2015

After 5% lithium was added to AZ31 magnesium alloy, the alloy was extruded at 380oC with the extrusion ratio of 101. Mechanical responses and microstructure evolution were investigated. The microstructure and texture evolution were examined by electronic backscattered diffraction (EBSD) and X-ray diffraction (XRD). Tensile tests in the tensile directions of 0o, 45o and 90o were carried out at room temperature. Lithium addition brought about the strong divergence of the grain orientation and triggered the spread of the (0002) basal texture. The room temperature ductility of the extruded Mg alloy sheets was improved due to the tilted weak basal texture.
Thermal Stability and Tensile Properties of GH984G Alloy for A-USC Power Plants
Authors: Tan Mei Lin , Wang Chang Shuai , Guo Yong An , Li Gu Song , Guo Jian Ting , Zhou Lan Zhang
Published: April 2015

GH984G is a new Ni-Fe-based alloy which has been designed for use as superheater, reheater, and header materials for boilers in 700°C advanced ultra-supercritical (A-USC) coal-fired power plants. In this paper, the tensile properties and microstructure evolutions of GH984G were investigated during long-term thermal exposure at 700 and 750°C up to 15000h. The results show that the major precipitates were MC, M23C6 and γ ́, and no detrimental TCP or GCP phase appeared during long-term thermal exposure. The morphology of γ ́ was spherical and had no obvious change, but the size increases. After thermal exposure at 700°C for 15000h, the 700°C yield strength slightly increased, but the yield strength decreased after thermal exposure at 750°C for 15000h. The variation of strength is attributed to the coarsening of γ ́ precipitation. The deformation mechanism is the moving dislocations shear γ ́ precipitates and the stacking faults form in γ ́ precipitates at room temperature and 700°C. At 750°C, the deformation mechanism is characterized by the formation of dislocation loops and tangles.
Influence of Fe Content on Microstructure and Mechanical Properties of GH984 Alloy
Authors: Wang Chang Shuai , Wang Ting Ting , Tan Mei Lin , Guo Yong An , Guo Jian Ting , Zhou Lan Zhang
Published: April 2015

GH984 is an economic alloy due to the elimination of Co and its containing more than 20% Fe. As a major constituent of GH984 alloy, the Fe reduces the cost, but promotes the precipitation of TCP phase. In order to get an optimum alloy with desired balance among structural stability, mechanical properties and cost, the influence of Fe content on microstructure and mechanical properties of GH984 alloy was investigated in this paper. The results showed that the Fe content had no obvious influence on the major precipitates which were spherical γ′, blocky MC and discrete M23C6 at grain boundary after standard heat treatment, except the γ/γ ́ misfit. However, during long-term thermal exposure at 750°C, the decrease of the Fe content retarded the precipitation of η phase and enhanced the structural stability. The Fe content had no obvious influence on the tensile strength and ductility. At condition of 700°C/400MPa, the rupture life had not evident change, but the elongation decreased, the fractural model exhibited mix-fracture model and the characteristics of intergranular fracture became obvious with increasing the Fe content. It can be concluded that the decrease of Fe content can improve the structural stability and ductility.
Microstructure and Element Segregation of Ni-Base Superalloy Casting with Radiation and Liquid-Metal Cooling
Authors: Liu Gang , Liu Lin , Zhang Guo Jun , Zhang Jun
Published: April 2015

A Re-containing single-crystal superalloy was processed with conventional radiation high rate solidification (HRS) and liquid-metal cooling (LMC) techniques, respectively. Compared with the HRS castings, LMC castings exhibited the greatly refined dendrite structures and lower segregation. At the withdrawal rate of 50 μm/s, the primary and secondary dendrite arm spacing of LMC casting was 103 and 19 μm, which were reduced by 60 % and 53 % compared to the counterpart of HRS castings. Moreover, higher withdrawal rates significantly shortened the characteristic diffusion distance and reduced the residual segregation of refractory elements after homogenization-solution treatments, which is beneficial for improving the local phase stability of Re-containing superalloys.
Effect of Deformation Conditions on Dynamic Recrystallization of As-Cast GH625 Alloy
Authors: Wang Hao Yu , Dong Jian Xin , Zhang Mai Cang , Zheng Lei , Yao Zhi Hao , Zhang Qing Quan
Published: April 2015

High temperature compression tests at a deformation temperature range of 1273K~1473K with various strain rates of 0.01s-1~0.1s-1 on as-cast GH625 alloy were carried out, aiming at the current research status that the deformation process of cogging and the recrystallization behavior of ingot are still in the study. The results indicated that the recrystallization nuclei of ingot formed not only along the original grain boundaries, but also in the interdendrite. Dynamic recrystallization volume percent increased with the increase of temperature and the decrease of strain rate. When the temperature was high and strain rate was low, the dynamic recrystallization behavior of as-cast GH625 alloy was dominated by discontinuous recrystallization. However, when the temperature was low and strain rate was high, continuous recrystallization also existed. These results can provide some reliable experimental support for the cogging process design.
Quantitative Phase Field Study on the Precipitation Dynamics of γ′ Phase in Ni-Based Superalloys with Different Concentration
Authors: Wu Xing Chao , Li Yong Sheng , Hou Zhi Yuan , Liu Wei , Mei Hao Jie
Published: April 2015

A quantitative phase field simulation was performed on the dynamics evolution of γ′ (L12-Ni3X) phase in Ni-based superalloys, the microstructure, the volume fraction and the particle size distribution (PSD) of γ′ phase for Ni-Al alloys aged at 1173K with the Al concentration c=0.178, 0.180 and 0.182 were investigated, and the results were compared with Lifshitz-Slyozov-Wagner (LSW) theory and Brailsford-Wynblatt (BW) theory. As the Al concentration increases the γ′ phase morphology changed from the separated cuboidal shape to the connected rectangle shape, the nucleation and growth of γ′ phase became faster and the volume fraction of the γ′ phase increased. The average particle radius  of γ′ phase and the aging time t has a exponent relationship  ~ tn at the coarsening stage with the exponents n=0.313, 0.235 and 0.204 for c=0.178, 0.180 and 0.182, respectively. The peaks of the fitted PSDs are less than the predicted value from the LSW theory and the fitted PSDs are wider than that of LSW predicted, while they are similar to that of the BW theory as the Al concentration increases. The peaks appear at a smaller r/ than the predictions of the LSW and BW theories.
Preparation and Electrocatalytic Activity of Nanophase WC-Co Composite Powder and WC Powder with Spherical Shell Structure
Authors: Guo Sheng Da , Yang Jian Gao , Chen Hao , Zhu Er Tao , Lv Jian
Published: April 2015

Using ammonium metatungstate (AMT), soluble cobalt salt and organic carbon source as the raw materials, the W-Co precursor powder with spherical shell structure was first fabricated by spray conversion method. Then the nanophase WC-Co composite powder was fabricated via calcinations and low temperature reduction-carbonization methods. And the WC powder with the same spherical shell structure was prepared at last by dissolving the Co phase into H3PO4 and H2O2. The phase composition, powder morphology, chemical components and its distribution of the samples at different stages were characterized by XRD, SEM and EDS. The results confirmed that the powders showing spherical shell structure after spray conversion, calcinations, reduction, carbonization and dissolution. While the amount of surface porosity changed after these treatments. The grain size of WC was about 50nm measured by FWHM of XRD. The electro catalytic activities of the powders towards methanol electro-oxidation were investigated by cyclic voltammetry with a three-electrode system in acidic solution. Compared with the granular WC powder, the electro-catalytic activity of WC-Co composite powder sample decreased, but the electro-catalytic activity of WC powder with spherical shell structure has been significantly improved. These results indicated that the electro catalytic activity of WC can be improved through the formation of spherical shell structure, while the existence and distribution of Co phase could hinder the electro-catalytic activity of WC.
Phenomenon of Gaseous Adiabatic Compression of Powder in Explosive Compaction
Authors: Zhang Kai , Zhang Lu Qing
Published: April 2015

This paper introducesan explosion experiment, in which the powder can be recollected100%. Based on the observations inside the recollected powder case,it can be confirmed that the very small amount of air in the space within the powderis concentrated in the bottom of the powder case,and consequently results in adiabatic compression. The compression energy of air gives rise tothe extra high powder temperature. A theoretical approach to the adiabatic mechanism was discussed and a rough estimationwas provided onthe degree of the increased temperature.
Simulation of Dilatation Curve Associated with Martensitic Transformation in a Dual-Phase Steel
Authors: Chen Peng , Du Peng Ju , Wu Di , Wang Guo Dong , Yi Hong Liang
Published: April 2015

The specific volume of alloys can be calculated using Thermo-Calc® for the problem of diffusion transformation in equilibrium or a single phase. The martensite transformation in a displacive manner can not be treated directly with Thermo-Calc®. A method to calculate the thermal dilatation curves for a dual-phase steel was established in this research associated with martensitic transformation from ferrite plus austenite after intercritical annealing. The equilibrium phase diagram, martensite starting temperature, as well as transformed martensite fraction have been involved in the calculations. The results showed that the calculated dilatation curves were in accordance with the measured curves by dilatometer, and indicated the reason for the ambiguous volume change in the dual-phase steel owing to its small fraction of austenite associating with martensite transformation.
Hot Deformation and Processing Map of C919 Aluminum Alloy
Authors: Yang Yong Biao , Zhang Zhi Min , Zhang Xing
Published: April 2015

The hot deformation behaviors of Aluminum alloy C919 were studied in the present investigation. The hot compression tests for C919 were carried out in the temperature range of 350°C~470°C and strain rates range of 0.001s-1~1s-1 using GLEEBLE-1500 thermal simulate testing machine. Optical microscopy (OM) was used for the microstructure characterization. The experimental results showed that the flow stress of C919 aluminum alloy decreased with increasing temperature and decreasing strain rates and the flow stress curves tended to increase at a strain rate of 1s-1 with increasing strain, while the flow stresses kept with increasing strain at lower strain rate. The alloys were more prone to dynamic recrystallization with decreasing strain rates during hot deformation. The hot compression behavior of C919 aluminum alloy can be described as hyperbolic sine function corrected Arrhenius relation. The processing maps for the alloy were built at a strain of 0.6. The instability deformation domain occurred at temperatures range from 350°C and 380°C and at a strain rate of 0.1-1s-1. Based on the processing maps and microstructure observations, the optimum hot-working parameters were determined to be at a temperature of 470°C in the strain rate range from 0.1-0.01s−1 for the C919 aluminum alloy.
Effect of BN Interphase Coating and PIP Cycles on the Mechanical Properties of VSI SiC/SiC Composites
Authors: Liu Bao Lin , Liu Rong Jun , Zhang Chang Rui , Cao Ying Bin
Published: April 2015

2.5D SiC/SiC composites with and without BN interphase coating were fabricated by VSI process from SiC/C preforms that were produced after 3, 4 and 5 PIP C cycles, respectively. The effect of the BN interphase coating and PIP C cycles on the mechanical properties and microstructure of the composites was investigated. The results indicated that the composites with or without BN interphase coating exhibited catastrophic fracture behavior. Both the excess residual carbon and BN interphase coating played a positive role in protecting the SiC fibers from silication by vapor silicon, which accounted for the less obvious fibers pull-out phenomenon that occurred in the composites. The PIP cycles had an influence on the residual porosity and the content of the newly developed SiC in the composites, and therefore the mechanical properties of the composites were influenced. The composites fabricated from preforms after 4 PIP C cycles and containing BN interphase coating have a flexural strength of 122.5 MPa and a modulus of 86.5 GPa.
Improvement of Anti-Hydrolytic Property of AlN Powder Modified by the Rare-Earth Salts
Authors: Li Yan , Song Mei Hui , Yu Qian , Zhang Xiao Chen
Published: April 2015

In this article, the high-performance modified AlN powder was prepared, using Y(NO3)3·6H2O as the modifying agent, and characterizing by pH meter, TG , XRD and SEM. The results show that the Y2O3 coating was formed on the AlN surface, the pH value of aluminum nitride of treatment suspension solution maintains 7.75 in water bath for 100 hours. Therefore the conclusion is that surface modification with rare earths can effectively inhibit the hydrolysis of the AlN powder.
Fecal Microbiota Transplant to Treat Recurrent Clostridium difficile Infections
Authors: Boyle Miriam L. , Ruth-Sahd Lisa A. , Zhou Zehao
Published: April 2015

The prevalence of recurrent or refractory Clostridium difficile infection has been steadily increasing since 2000. Consequently, alternative treatments to the standard antibiotic therapies are now being considered. One alternative treatment is fecal microbiota transplant. Although fecal microbiota transplant is relatively new—and not appealing to most people—it has been around for many years and has great promise as an inexpensive, safe, and efficient treatment of refractory and recurrent C difficile infection. With a better understanding of the intricacies of the colonic microbiome and its role in colonic physiology and pathophysiology, critical care nurses will recognize that fecal microbiota transplant has the potential to become the standard of care for treatment of recurrent or refractory C difficile infection. The American College of Gastroenterology and the Infectious Diseases Society of America provide the latest treatment guidelines for care of patients with these clostridial infections.
Continuing to Challenge Practice to Be Evidence Based
Authors: Makic Mary Beth Flynn , Rauen Carol , Jones Kimmith , Fisk Anna C.
Published: April 2015

Practice habits continue in clinical practice despite the availability of research and other forms of evidence that should be used to guide critical care practice interventions. This article is based on a presentation at the 2014 National Teaching Institute of the American Association of Critical-Care Nurses. The article is part of a series of articles that challenge critical care nurses to examine the evidence guiding nursing practice interventions. Four common practice interventions are reviewed: (1) weight-based medication administration, (2) chest tube patency maintenance, (3) daily interruption of sedation, and (4) use of chest physiotherapy in children. For weight-based administration of medication, the patient’s actual weight should be measured, rather than using an estimate. The therapeutic effectiveness and dosages of medications used in obese patients must be critically evaluated. Maintaining patency of chest tubes does not require stripping and milking, which probably do more harm than good. Daily interruption of sedation and judicious use of sedatives are appropriate in most patients receiving mechanical ventilation. Traditional chest physiotherapy does not help children with pneumonia, bronchiolitis, or asthma and does not prevent atelectasis after extubation. Critical care nurses are challenged to evaluate their individual practice and to adopt current evidence-based practice interventions into their daily practice.
Training Forward Surgical Teams for Deployment: The US Army Trauma Training Center
Authors: Valdiri Linda A. , Andrews-Arce Virginia E. , Seery Jason M.
Published: April 2015

Since the late 1980s, the US Army has been deploying forward surgical teams to the most intense areas of conflict to care for personnel injured in combat. The forward surgical team is a 20-person medical team that is highly mobile, extremely agile, and has relatively little need of outside support to perform its surgical mission. In order to perform this mission, however, team training and trauma training are required. The large majority of these teams do not routinely train together to provide patient care, and that training currently takes place at the US Army Trauma Training Center (ATTC). The training staff of the ATTC is a specially selected 10-person team made up of active duty personnel from the Army Medical Department assigned to the University of Miami/Jackson Memorial Hospital Ryder Trauma Center in Miami, Florida. The ATTC team of instructors trains as many as 11 forward surgical teams in 2-week rotations per year so that the teams are ready to perform their mission in a deployed setting. Since the first forward surgical team was trained at the ATTC in January 2002, more than 112 forward surgical teams and other similar-sized Department of Defense forward resuscitative and surgical units have rotated through trauma training at the Ryder Trauma Center in preparation for deployment overseas.
Epitope-Specific CD8+ T Cell Kinetics Rather than Viral Variability Determine the Timing of Immune Escape in Simian Immunodeficiency Virus Infection
Authors: Martyushev Alexey P. , Petravic Janka , Grimm Andrew J. , Alinejad-Rokny Hamid , Gooneratne Shayarana L. , Reece Jeanette C. , Cromer Deborah , Kent Stephen J. , Davenport Miles P.
Published: April 2015

CD8+ T cells are important for the control of chronic HIV infection. However, the virus rapidly acquires “escape mutations” that reduce CD8+ T cell recognition and viral control. The timing of when immune escape occurs at a given epitope varies widely among patients and also among different epitopes within a patient. The strength of the CD8+ T cell response, as well as mutation rates, patterns of particular amino acids undergoing escape, and growth rates of escape mutants, may affect when escape occurs. In this study, we analyze the epitope-specific CD8+ T cells in 25 SIV-infected pigtail macaques responding to three SIV epitopes. Two epitopes showed a variable escape pattern and one had a highly monomorphic escape pattern. Despite very different patterns, immune escape occurs with a similar delay of on average 18 d after the epitope-specific CD8+ T cells reach 0.5% of total CD8+ T cells. We find that the most delayed escape occurs in one of the highly variable epitopes, and that this is associated with a delay in the epitope-specific CD8+ T cells responding to this epitope. When we analyzed the kinetics of immune escape, we found that multiple escape mutants emerge simultaneously during the escape, implying that a diverse population of potential escape mutants is present during immune selection. Our results suggest that the conservation or variability of an epitope does not appear to affect the timing of immune escape in SIV. Instead, timing of escape is largely determined by the kinetics of epitope-specific CD8+ T cells.
Suppressor of Cytokine Signaling 1 Is a Positive Regulator of TGF-β–Induced Prostaglandin Production in Human Follicular Dendritic Cell–like Cells
Authors: Cho Whajung , Kim Youngmi , Kim Jini , Park Seongji , Park Deokbum , Kim Byung-Chul , Jeoung Dooil , Kim Young-Myeong , Choe Jongseon
Published: April 2015

PGs are emerging as important immune modulators. Since our report on the expression of PG synthases in human follicular dendritic cells, we investigated the potential immunoregulatory function of PGs and their production mechanisms. In this study, we explored the intracellular signaling molecules mediating TGF-β–induced cyclooxygenase (COX)-2 augmentation in follicular dendritic cell–like cells. TGF-β triggered phosphorylation of Smad3 and ERK, which were essential for the increase in COX-2 protein. Interestingly, depletion of suppressor of cytokine signaling 1 (SOCS1) resulted in an almost complete inhibition of Smad3 phosphorylation and COX-2 induction. Nuclear translocation of Smad3 was inhibited in SOCS1-depleted cells. SOCS1 knockdown also downregulated TGF-β–stimulated Snail expression and its binding to the Cox-2 promoter. In contrast, overexpression of SOCS1 gave rise to a significant increase in Snail and COX-2 proteins. SOCS1 was reported to be a negative regulator of cytokine signaling by various investigators. However, our current data suggest that SOCS1 promotes TGF-β–induced COX-2 expression and PG production by facilitating Smad3 phosphorylation and Snail binding to the Cox-2 promoter. The complete understanding of the biological function of SOCS1 might be obtained via extensive studies with diverse cell types.
Impaired Dendritic Cell Function in a Spontaneous Autoimmune Polyneuropathy
Authors: Quan Songhua , Kim Hye-Jung , Dukala Danuta , Sheng Jian Rong , Soliven Betty
Published: April 2015

Spontaneous autoimmune polyneuropathy (SAP) in B7-2 knockout NOD mice mimics the progressive form of chronic inflammatory demyelinating polyradiculoneuropathy, and is mediated by myelin protein zero (P0)–reactive Th1 cells. In this study, we focused on the effect of B7-2 deletion on the function of dendritic cells (DCs) within the context of SAP. We found that development of SAP was associated with a preponderance or increase of CD11b+ DCs in peripheral lymph nodes and sciatic nerves. B7-2 deletion led to altered immunophenotypic properties that differ between CD11b+ DCs and CD8α+ DCs. Both DC subsets from B7-2 knockout NOD mice exhibited impaired capacity to capture fluorophore-labeled myelin P0, but diminished Ag-presenting function was observed only in CD11b+ DCs. Clinical assessment, electrophysiologic studies, and splenocyte proliferation studies revealed that absence of B7-2 on DCs was sufficient to cause impaired ability to induce tolerance to P0, which could be overcome by preconditioning with IL-10. Tolerance induction by Ag-pulsed wild-type NOD DCs was dependent on IL-10 and was associated with increased CD4+ regulatory T cells, whereas tolerance induction by IL-10–conditioned B7-2–deficient DCs was associated with increased percentages of both regulatory T cells and B10 cells in the spleen. We conclude that B7-2 deletion has an impact on the distribution of DC subsets in lymphoid organs and alters the expression of costimulatory molecules, but functional consequences are not uniform across DC subsets. Defective tolerance induction in the absence of B7-2 can be restored by preconditioning of DCs with IL-10.
Effect of TLR Agonists on the Differentiation and Function of Human Monocytic Myeloid-Derived Suppressor Cells
Authors: Wang Jing , Shirota Yuko , Bayik Defne , Shirota Hidekazu , Tross Debra , Gulley James L. , Wood Lauren V. , Berzofsky Jay A. , Klinman Dennis M.
Published: April 2015

Tumors persist by occupying immunosuppressive microenvironments that inhibit the activity of tumoricidal T and NK cells. Monocytic myeloid-derived suppressor cells (mMDSC) are an important component of this immunosuppressive milieu. We find that the suppressive activity of mMDSC isolated from cancer patients can be reversed by treatment with TLR7/8 agonists, which induce human mMDSC to differentiate into tumoricidal M1-like macrophages. In contrast, agonists targeting TLR1/2 cause mMDSC to mature into immunosuppressive M2-like macrophages. These two populations of macrophage are phenotypically and functionally discrete and differ in gene expression profile. The ability of TLR7/8 agonists to reverse mMDSC-mediated immune suppression suggests that they might be useful adjuncts for tumor immunotherapy.
IL-18 Triggered by the Nlrp3 Inflammasome Induces Host Innate Resistance in a Pulmonary Model of Fungal Infection
Authors: Ketelut-Carneiro Natália , Silva Grace Kelly , Rocha Fernanda Agostini , Milanezi Cristiane Maria , Cavalcanti-Neto Florêncio Figueiredo , Zamboni Dario Simões , Silva João Santana
Published: April 2015

Pathogens are sensed by innate immune receptors that initiate an efficient adaptive immune response upon activation. The elements of the innate immune recognition process for Paracoccidioides brasiliensis include TLR-2, TLR-4, and dectin-1. However, there are additional receptors necessary for the host immune responses to P. brasiliensis. The nucleotide-binding oligomerization domain–like receptor (NLRs), which activate inflammasomes, are candidate receptors that deserve renewed investigation. After pathogen infection, the NLRs form large signaling platforms called inflammasomes, which lead to caspase-1 activation and maturation of proinflammatory cytokines (IL-18 and IL-1β). In this study, we showed that NLR family pyrin domain–containing 3 (Nlrp3) is required to induce caspase-1 activation and further secretion of IL-1β and IL-18 by P. brasiliensis–infected macrophages. Additionally, potassium efflux and lysosomal acidification induced by the fungus were important steps in the caspase-1 activation mechanism. Notably, Nlrp3 and caspase-1 knockout mice were more susceptible to infection than were the wild-type animals, suggesting that the Nlrp3-dependent inflammasomes contribute to host protection against P. brasiliensis. This protective effect occurred owing to the inflammatory response mediated by IL-18, as shown by an augmented fungus burden in IL-18 knockout mice. Taken together, our results show that the Nlrp3 inflammasome is essential for resistance against P. brasiliensis because it orchestrates robust caspase-1 activation and triggers an IL-18–dependent proinflammatory response.
Defects in Regulatory T Cells Due to CD28 Deficiency Induce a Qualitative Change of Allogeneic Immune Response in Chronic Graft-versus-Host Disease
Authors: Akieda Yuki , Wakamatsu Ei , Nakamura Tomoe , Ishida Yasuo , Ogawa Shuhei , Abe Ryo
Published: April 2015

In patients receiving allogeneic hematopoietic cell transplantation, chronic graft-versus-host disease (cGVHD) remains a frequent complication and resembles autoimmune diseases such as systemic lupus erythematosus and systemic sclerosis. Our previous work demonstrated the critical role of CD28 costimulation of donor T cells for GVHD induction. In this study, we investigate the role of CD28 costimulation of host T cells in cGVHD. CD28-intact mice as hosts showed systemic lupus erythematosus–type cGVHD, whereas CD28-deficient mice developed a distinct phenotype of cGVHD, with fibrotic damage in skin and internal organs, resembling systemic sclerosis. This phenotype was due to a lack of signaling through the C-terminal proline-rich motif within host CD28’s cytoplasmic tail, a motif previously shown to be required for development of regulatory T cells (Tregs) and function of conventional T cells. Adoptive transfer experiments demonstrated that a defect in host CD4+CD25+ Tregs, but not in conventional T cells, was responsible for disease phenotype. Host Treg deficiency altered the cytokine pattern of donor CD4+ T cells and the Ag specificity of autoantibodies, and these might lead to phenotypic change. Thus, host CD28 signaling controlled the pathogenesis of cGVHD through effects on host Tregs, whose status impacts qualitatively on the allogeneic immune responses.