Bismuth oxide based ceramics with improved electrical and mechanical properties: Part I. Preparation and characterisation

A study of the preparative variables in the synthesis of ceramics based on Bi₂O₃-Er₂O₃ solid solutions has shown that the best results are obtained with a coprecipitation method. Critical parameters in the synthesis are found to be i) wet milling of the precalcined powder with an appropriate liquid and ii) calcining and sintering temperatures. With the proposed method it is possible to produce monophasic, contamination free, dense and machineable ceramics suitable for practical applications.     

An approach to geometric modeling of solids bounded by sculptured surfaces

In this paper we present the design and implementation of a geometric modeling system for modeling solids bounded by sculptured surfaces. The three most important solid representation schemes—constructive solid geometry, boundary representation, and octree representation—are combined together in our system in such a way that the resulting scheme enjoys many of the advantages of its individual schemes. We also developed algorithms for conversion of objects from their boundary representation to octree representation, and for the boundary evaluation of octree encoded objects. The system was implemented on a DEC 1090 computer in PASCAL, and we have presented a simple illustrative example to show the use of the system to create solid objects bounded by sculptured surfaces.     

Universal noiseless and noisy data compression techniques — the state of the art

The technique of data compression demonstrates desirable properties that assure performance improvements of advanced network architectures such as ISDN, serial communication channels, data storage and data archiving. A global trend in telecommunications networks is the conversion from analogue to digital transmission. The design goal of these new networks is that voice, data, and images will be transmitted in fundamentally the same way, requiring neither prior knowledge as to the type of data being transmitted nor operator intervention. However, the bandwidth requirements for digital transmission are generally high. Spectrum bandwidth utilization is a design parameter for these systems that will benefit from the transmission of compressed data. The proposed Integrated Services Digital Network (ISDN) combines digital voice, data, and images on the same network. Since this network has limited bandwidth for transmission of information, the available bandwidth must be used as efficiently as possible.     

增压中冷车用柴油机EGR率阶跃工况响应

利用实时EGR率测量系统及瞬态工况测控平台对增压中冷柴油机废气再循环(EGR)阶跃工况下的EGR率、进气量、发动机转矩、燃烧过程特征参数、排气烟度及气态有害排放物的响应历程进行了试验研究.试验结果表明:在1 600 r/min5、0%负荷工况,EGR率从0分别阶跃到3%、5%、13%和28%时,EGR率、进气流量及发动机有效转矩响应速度较快且相近,均为0.5 s左右;排气烟度和以最高燃烧压力表征的缸内燃烧过程趋于稳定状态历时较长且时间相近,不同EGR率阶跃时均为2.5 s左右;以气态有害物排放表征的柴油机排放响应历时最长为6 s左右.这说明在EGR阶跃工况下,当EGR率达到稳定时,由于燃烧边界条件存在迟滞效应,从而会导致燃烧过程、有害物排放存在较长的延迟.     

Nanostructured titanium nitride for highly sensitive localized surface plasmon resonance biosensing

Titanium nitride (TiN) as an alternative plasmonic ceramic material with superb properties including high hardness, outstanding corrosion resistance and excellent biocompatibility, has exhibited great potential for optical biochemical sensing applications. By sputtering about 35 nm–50 nm TiN on glass (f-TiN), the surface was found to provide sensing capability toward NaCl solution through the phenomenon of surface plasmon resonance. When the TiN film of about 27 nm–50 nm in thickness was sputtered onto a roughened glass surface (R–TiN), the sensing capability was improved. This was further improved when holes at nanoscale were created in the TiN film of about 19 nm–27 nm in thickness (NH–TiN). The roughened surface and nanohole patterns provided confinement of surface plasmons and significantly improved the sensitivity toward the local refractive index changes. In detail, the calculated refractive index resolution (RIR) of the optimal NH–TiN sensors for NaCl was found to be 9.5 × 10⁻⁸ refractive index unit (RIU), which had outperformed the f-TiN and R–TiN sensors. For biosensing, the optimized NH–TiN sensor was found to be capable to detect both small and large biomolecules, i.e. biotin (molecular weight of 244.3 g/mol) and human IgG (160,000 g/mol), in a label-free manner. Especially, the NH–TiN sensor significantly improved sensitivity in detecting small molecules due to the localized plasmonic confinement of electromagnetic field. Combining with the excellent mechanical and durability properties of TiN, the proposed NH–TiN can be a strong candidate for plasmonic biosensing applications.     

Preparation and photocatalytic activity of g-C3N4/TiO2 heterojunctions under solar light illumination

The solar light sensitive g-C₃N₄/TiO₂ heterojunction photocatalysts containing 20, 50, 80, and 90 wt% graphitic carbon nitride (g-C₃N₄) were prepared by growing Titania (TiO₂) nanoparticles on the surfaces of g-C₃N₄ particles via one step hydrothermal process. The hydrothermal reactions were allowed to take place at 110 °C at autogenous pressure for 1 h. Raman spectroscopy analyses confirmed that an interface developed between the surfaces of TiO₂ and g-C₃N₄ nanoparticles. The photocatalyst containing 80 wt% g-C₃N₄ was subsequently heat treated 1 h at temperatures between 350 and 500 °C to improve the photocatalytic efficiency. Structural and optical properties of the prepared g-C₃N₄/TiO₂ heterojunction nanocomposites were compared with those of the pristine TiO₂ and pristine g-C₃N₄ powders. Photocatalytic activity of all the nanocomposites and the pristine TiO₂ and g-C₃N₄ powders were assessed by the Methylene Blue (MB) degradation test under solar light illumination. g-C₃N₄/TiO₂ heterojunction photocatalysts exhibited better photocatalytic activity for the degradation of MB than both pristine TiO₂ and g-C₃N₄. The photocatalytic efficiency of the g-C₃N₄/TiO₂ heterojunction photocatalyst heat treated at 400 °C for 1 h is 1.45 times better than that of the pristine TiO₂ powder, 2.20 times better than that of the pristine g-C₃N₄ powder, and 1.24 times better than that of the commercially available TiO₂ powder (Degussa P25). The improvement in photocatalytic efficiency was related to i) the generation of reactive oxidation species induced by photogenerated electrons, ii) the reduced recombination rate for electron-hole pairs, and iii) large specific surface area.     

二硫化钼纳米片用于修饰微生物燃料电池阳极的研究

利用简单的一步水热法制备了MoS2纳米片并用于修饰不锈钢纤维毡阳极(MoS2-SSFF),与未修饰不锈钢纤维毡阳极(SSFF)和多壁碳纳米管修饰阳极(CNT-SSFF)进行了对比研究。装配MFC运行的测试结果表明,MoS2-SSFF/MFC的功率密度为714 m W/m2,略高于CNT-SSFF/MFC的功率密度693 m W/m2,远高于未修饰SSFF/MFC的功率密度197 m W/m2。利用扫描电子显微镜(SEM)观察到MoS2纳米片呈簇状附着于MoS2-SSFF电极表面,显著增加了电极的比表面积。MoS2纳米片修饰改善了SSFF阳极的生物相容性,修饰电极在循环伏安测试(CV)中表现出良好的氧化还原性能。水热法制备的MoS2纳米片用于修饰阳极是一种高效、经济、简单的阳极修饰方法。     

A study of methanol steam reforming on distributed catalyst bed

Heterogeneous catalytic fixed bed usually suffers from severe limitations of mass and heat transfer. These disadvantages limit reformers to a low efficiency of catalyst utilization. Three catalyst activity distributions have been applied to force the reactor temperature profile to be near isothermal operation for maximization of methanol conversion. A plate-type reactor has been developed to investigate the influence of catalyst activity distribution on methanol steam reforming. Cold spot temperature gradients are observed in the temperature profile along the reactor axis. It has been experimentally verified that reducing cold spot temperature gradients contributes to the improvement of the catalytic hydrogen production. The lowest cold spot temperature gradient of 3 K is obtained on gradient catalyst distribution type A. This is attributed to good characteristics of local thermal effect. Low activity at the reactor inlet with gradual rise along with the reactor flow channel forms the optimal activity distribution. Hydrogen production rate of 161.3 L/h is obtained at the methanol conversion of 93.1% for the gradient distribution type A when the inlet temperature is 543 K.     

Wind Effect on Combined Convection and Surface Radiation Heat Losses of a Fully Open Cylindrical Cavity With Insulation

Wind effect, of both the wind incidence angle and the wind speed, on convection and surface radiation heat losses of a fully open cylindrical cavity with constant bottom wall temperature was numerically investigated. The impacts of cavity tilt angle and wall temperature were also considered. Temperature contours, velocity contours, and vectors inside and around the cavity were presented. The variations of average convection and radiation heat loss Nusselt numbers Nu_c and Nu_r and percentages of heat losses with related parameters (wind speed, wind incidence angle, tilt angle, and bottom wall temperature) were also shown. In the end, correlations about Nu_c and Nu_r for practical applications were proposed. Results show that compared with no-wind condition, Nu_c under a wind condition is almost always higher except for head-on wind with velocity of 1.5 m/s, while Nu_r is always lower. Nu_c varies slightly, while Nu_r increases rapidly as the bottom wall temperature increases. With the existence of wind, the effect of tilt angle on heat transfer becomes more complex. A critical wind direction close to 30° is detected, which maximizes Nu_c and percentage of convective heat loss. The results also demonstrate that wind speed, wind incidence angle, and tilt angle should be considered simultaneously when analyzing heat transfer inside the cavity under a wind condition.