中间相沥青基碳纤维的生产及其性能表征

中间相沥青基碳纤维具备高模量、高导热性等特性,在航天、电子等领域具备广阔的应用前景.山东瑞城实现了中间相沥青基碳纤维的产业化生产,本文对其所生产的中间相沥青基碳纤维的结构和性能进行了表征研究.研究结果表明,1.5K连续纤维的平均直径为11μm;强度为2400 MPa;模量为811 GPa;导热率达到600 W/(m·k...     

High molecular weight poly(butylene terephthalate-co-butylene 2,5-furan dicarboxylate) copolyesters: From synthesis to thermomechanical and barrier properties

Poly(butylene terephthalate-co-butylene 2,5-furandicarboxylate) copolyesters (PBTFs) were synthesized from 1,4-butanediol, dimethyl terephthalate (DMT), and 2,5-furandicarboxylic acid (FDCA) by a two-step polymerization method. Their chemical structures were confirmed by Fourier-transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, and carbon nuclear magnetic resonance before thermal properties were explored with differential scanning calorimeter and thermogravimetric analyzer. Results showed that PBTFs changed from semi-crystalline to completely amorphous when the content of FDCA unit was increased to 45 mol% at first, and then became crystallographic again with the further increment of FDCA unit to 75 mol%. For their mechanical properties, the tensile modulus and strength showed the similar trend, decreasing firstly and then increasing later. Their barrier to carbon dioxide and oxygen became better with the increasing of furan content due to the rigidity and higher polarity of furan ring. The performance of PBTFs copolyesters was investigated clearly, and the relative content of FDCA and DMT can be adjusted to satisfy different performance requirements.     

A third-generation SPARC V9 64-b microprocessor

This quad-issue processor achieves 1-GHz operation through improved dynamic circuit techniques in critical paths and a more extensive on-chip memory system which scales in both bandwidth and latency. Critical logic paths use domino, delayed clocked domino, and logic embedded in dynamic flip-flops for minimum delay. A 64-KB sum-addressed memory data cache combines the address offset add with the cache decode, allowing the average memory latency to scale by more than the clock ratio. Memory bandwidth is improved by using wave pipelined SRAM designs for on-chip caches and a write cache for store traffic. Memory power is controlled without increased latency by use of delayed-reset logic decoders. The chip operates at 1000 MHz and dissipates less than 80 W from a 1.6-V supply. It contains 23 million transistors (12 million in RAM cells) on a 244 mm² die     

Fabrication of 3D chitosan–hydroxyapatite scaffolds using a robotic dispensing system

A new robotic desktop rapid prototyping (RP) system was designed to fabricate scaffolds for tissue engineering applications. The experimental setup consists of a computer-guided desktop robot and a one-component pneumatic dispenser. The dispensing material (chitosan and chitosan–hydroxyapatite (HA) dissolved in acetic acid) was stored in a 30-ml barrel and forced out through a small Teflon-lined nozzle into a dispensing medium (sodium hydroxide–ethanol in ratio of 7:3). Layer-by-layer, the chitosan was fabricated with a preprogramed lay-down pattern. Neutralization of the chitosan forms a gel-like precipitate, and the hydrostatic pressure in the sodium hydroxide (NaOH) solution keeps the cuboid scaffold in shape. Comparison of the freeze-dried scaffold to the wet one showed linear and volumetric shrinkage of about 31% and 62%, respectively. A good attachment between layers allowed the chitosan matrix to form a fully interconnected channel architecture. Results of in vitro cell culture studies revealed the scaffold biocompatibility. The results of this preliminary study using the rapid prototyping robotic dispensing (RPBOD) system demonstrated its potential in fabricating three-dimensional (3D) scaffolds with regular and reproducible macropore architecture.     

A boundary integral solution for the problem of multiple interacting cracks in an elastic material

A boundary integral equation method for the solution of a class of two-dimensional elasticity problems involving multiple interacting cracks in an elastic material is presented. The method is used to obtain a procedure for the numerical evaluation of the crack tip stress intensity factors for this class of problems. The stress intensity factors for some specific problems are computed using this procedure.

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Résumé On présente une méthode par équations intégrales de contour pour solutionner une classe de problèmes d'élasticité bidimensionnelle comportant de multiples fissures interactives dans un matériau élastique. On utilise la méthode pour obtenir une procédure d'évaluation numérique des facteurs d'intensité de contraintes à l'extrémité de la fissure, pour cette classe de problèmes. En utilisant cette procédure, on peut calculer les facteurs d'intensité de contraintes correspondant à divers problèmes spécifiques.

     

Mechanism of nitrogen-enhanced negative bias temperature instability in pMOSFET

From the detailed analysis of the dependence of threshold voltage shift and positive fixed charge/interface state generation on the stress time/temperature of negative bias temperature instability (NBTI) for various nitrogen concentrations at the oxide/Si interface, the mechanism of nitrogen-enhanced NBTI effect has been studied experimentally. The experimental results can be understood in terms of the reaction energies of the hydrogen trapping reactions at the interface, which are obtained from first-principles calculations. The calculations show that the nitrogen's lone-pair electrons can trap dissociated hydrogen species more easily than oxygen. From the experimental and theoretical studies, one can conclude that the roles of nitrogen in the NBTI are two folds, i.e., it provides more reaction sites, and it can also enhance the NBTI reaction by reducing the reaction energy.     

Axial impeller selection for anchorage dependent animal cell culture in stirred bioreactors: Methodology based on the impeller comparison at just-suspended speed of rotation

Animal cells, which are nowadays essential for the industrial production of proteinic compounds, are commonly cultivated inside stirred tank bioreactors. In case of anchorage dependent cells, they are usually fixed on microcarriers. The choice of agitation conditions (impeller type, rotational speed…) in this type of process is not an easy task as it has to fulfil three potentially conflicting goals: (1) maintaining microcarriers in complete suspension, (2) homogenizing the culture medium, and (3) limiting mechanical constraints generated by the hydrodynamics on the cells. The aim of this study is to present an original methodology to select the most appropriate axial impeller for this specific application. Seven propellers are preselected on basis of their characteristics available in the literature. Instead of comparing impellers at a given rotational speed or a given power input, they are compared at their respective minimum impeller rotational speed that leads to a complete microcarrier suspension, i.e. at their respective just-suspended speed N_js. They are then compared at higher rotational speeds N, expressed as multiples of N_js. The impeller classification is based on the intensity of mechanical constraints they produced, evaluated from: (1) the macro-shear rate quantified by the spatial derivative of time average velocity fields measured by P.I.V., (2) the micro-shear rate characterized by the ratio between the microcarrier diameter to the average Kolmogorov scale computed from power input measurements, and (3) the impact of microcarrier collisions on cells described via the turbulent collision severity index also computed from power input measurements. Results show that the 125 mm diameter TTP impeller (Mixel) and the 150 mm diameter Elephant Ear impeller (Applikon) produce the smallest mechanical constraints at their just-suspended speed (50 and 20 rpm, respectively). Moreover, the mechanical constraints they produce increase more slowly with the N/N_js ratio than the mechanical constraints produced by other impellers. These propellers are thus even more advantageous if rotational speeds higher than the just-suspended speed have to be used.     

闪蒸对昌黎产区‘马瑟兰’葡萄酒单体酚类物质的影响

以欧亚种酿酒葡萄‘马瑟兰’为试材,研究闪蒸处理对葡萄酒发酵及陈酿过程中单体酚类物质和CIELab色泽参数的影响。结果表明,与传统浸渍发酵（对照组）相比,闪蒸有利于提高发酵过程中多数单体花色苷的质量浓度,但不利于保持陈酿过程中各单体花色苷质量浓度。闪蒸增加了葡萄酒发酵及陈酿过程中槲皮素-3-O-葡萄糖苷、儿茶素、反式白藜芦醇及白藜芦醇葡萄糖苷等非花色苷单体酚类物质的质量浓度,但降低了槲皮素、杨梅酮、酚酸类单体酚、顺式白藜芦醇及白皮杉醇等酚类物质的质量浓度。闪蒸处理可降低葡萄酒亮度L*、黄蓝度b*值和色调角hab,显著增加红绿度a*、色度Cab*值,使葡萄酒颜色更红、更深、更耐陈酿,两组葡萄酒间颜色差异明显。结论：闪蒸有利于增加‘马瑟兰’葡萄酒单体酚总质量浓度及葡萄酒颜色的稳定性。     

橡皮布打孔机凹凸模的研究与设计

着重探讨了模架的静力学仿真分析和凹凸模的结构设计,并在此基础上设计制作了橡皮布打孔机.此设备的应用改变了原有的打孔模式,提高了打孔的质量和精度,大幅提高了打孔效率及装卡成功率.