The effect of carbon coating thickness on the capacity of LiFePO4/C composite cathodes

Two types of carbon source and precursor mixing pellets were employed simultaneously to prepare the LiFePO₄/C composite materials: Type I using the LiFePO₄ precursor with 20 wt.% polystyrene (PS) as a primary carbon source, and Type II using the LiFePO₄ precursor with 50 wt.% malonic acid as a secondary carbon vapor source. During final sintering, a Type I pellet was placed down-stream and Type II precursor pellet(s) was(were) placed upstream next to a Type I precursor pellet in a quartz-tube furnace. The carbon-coated product of the sintered Type I precursor pellet was obtained by using both PS and malonic acid as carbon sources. When two Type II pellets were used as a carbon vapor source (defined as Product-2), a more uniform film between 4 and 8 nm was formed, as shown in the TEM images. In the absence of a secondary carbon source (defined as Product-0), the discharge capacity of Product-0 was 137 mAh g⁻¹ with 100 cycles at a 0.2C-rate, but Product-2 demonstrated a high capacity of 151 mAh g⁻¹ with 400 cycles. Our results indicate that electrochemical properties of LiFePO₄ are correlated to the amount of carbon and its coating thickness and uniformity.     

Reflow soldering and isothermal solid-state aging of Sn-Ag eutectic solder on Au/Ni surface finish

The reaction between the eutectic Sn-3.5Ag solder and the Au/Ni surface finish during reflow as well as during isothermal aging was studied. The Au layer was electroplated and had a thickness of the one μm. The peak reflow temperature was fixed at 250 C while the reflow time was varied between 10 sec and one h. Samples that went through 90 sec reflow time were then subjected to 160 C isothermal aging for up to 875 h. It was found that during reflow the Au layer reacted very quickly with the solder to form AuSn₄. One μm of Au layer was consumed in less than 10 sec. As the aging time increased, AuSn₄ grains began to separate themselves from the Ni layer at the roots of the grains and started to fall into the solder. When, the reflow time reached 30 sec, all the Au intermetallic head left the interface, and Ni₃Sn₄ started, to form at the interface. The Ni₃Sn₄ growth rate followed linear kinetics initially (<240 sec), but the growth rate slowed down afterward. During the isothermal aging, only a small amount of (Au_xNi_1-x)Sn₄ resettled back to the interface, and a continuous (Au_0.45Ni_0.55)Sn₄ layer did not form at the interface, unlike the case for the Sn-37Pb solder. This is an important advantage for Sn-3.5 Ag over Sn-37Pb because a continuous (Au_0.45Ni_0.55)Sn₄ layer inevitably will weaken a solder joint. Our observation indicated that many (Au_xNi_1-x)Sn₄ particles were trapped by the Ag₃Sn particles, and were hindered from resettling back to the interface.     

The first MAJC microprocessor: a dual CPU system-on-a-chip

The first implementation of MAJC architecture achieves high performance by using very long instruction word (VLIW), single instruction multiple data (SIMD), and chip multiprocessing. The chip integrates two processors, a memory controller, two high-speed parallel I/O interfaces, and a PCI controller. The chip, fabricated in a 0.22-μm CMOS process with six layers of copper interconnect, contains 13 million transistors and operates at 500 MHz. It is packaged in a 624-pin ceramic column grid array using flip-chip assembly technology     

甘油对中试魔芋葡甘聚糖流延膜性能的影响

目的解决可食性魔芋葡甘聚糖膜在连续化生产过程中出现的皱缩、易破损的问题。方法向魔芋葡甘聚糖料液中添加一定量的甘油,改善其平整度、柔韧性、拉伸性。结果当甘油添加量达到魔芋葡甘聚糖质量的25%时,制备出了皱缩率最低达0和断裂伸长率最高达65%的薄膜,该膜具有平整、透明度高以及拉伸性能好的特性。结论随着甘油添加量的增加,膜的皱缩率和拉伸强度降低;膜厚度、透明性、断裂伸长率和透湿系数增大。     

水泥厂热工检测数据处理系统的开发

针对水泥厂热工检测后数据处理的繁杂计算过程,研究开发数据处理的软件,提高计算效率,同时验证了该软件系统的正确性、实用性和通用性,为热工检测数据处理提供了有效的手段。     

魔芋葡甘聚糖基可食膜的成膜机理研究进展

魔芋葡甘聚糖(KGM)是魔芋的主要成分,是目前发现的最优良的可溶性膳食纤维之一,由于其良好的成膜性,在食品包装领域有很好的应用前景。研究发现,KGM可与多糖、蛋白等进行不同方式和不同程度的混合,形成特殊的共混体系,干燥后可得到KGM基可食膜。本文就KGM结构和KGM基可食膜的成膜机理进行综述,以期为后续研究与应用提供一定参考。     

Anchor point indexing in Web document retrieval

Traditional World Wide Web search engines, such as AltaVista.com, index and recommend individual Web pages to assist users in locating relevant documents. As the Web grows, however, the number of matching pages increases at a tremendous rate. Users are often overwhelmed by the large answer set recommended by the search engines. Also, if a matching document is a hypertext, the document structure is destroyed and the individual pages that compose the document are returned instead. The logical starting point of the hyperdocument is thus hidden among the large basket of matching pages. Users need to spend a lot of effort browsing through the pages to locate the starting point, a very time consuming process. This paper studies the anchor point indexing problem. The set of anchor points of a given user query is a small set of key pages from which the larger set of documents that are relevant to the query can be easily reached. The use of anchor points helps solve the problems of huge answer set and low precision suffered by most search engines by considering the hyperlink structures of the relevant documents, and by providing a summary view of the result set.     

Formation and resettlement of (AuxNi1−x)Sn4 in solder joints of ball-grid-array packages with the Au/Ni surface finish

The interfacial reactions between eutectic PbSn solder and the solder ball pads with the Au/Ni surface finish were studied. Solder joints subjected to up to three repeated reflow-and-aging treatments were examined. For the reflow, the peak reflow temperature was 225°C, and the reflow time was 115 s. Each aging process was performed at 160°C for 500 h. After the first reflow, all the Au would disappear from the interface, and formed many (Au_xNi_1−x)Sn₄ particles inside the solder joints. The value of x was between 0.99 and 0.75. In addition, there was a thin layer of Ni₃Sn₄ (1.4 μm) at the interface. After one reflow and one subsequent aging, most of the (Au_xNi_1−x)Sn₄ would relocate from inside the solder joint to the interface, and the value of x for (Au_xNi_1−x)Sn₄ at the interface decreased to 0.45. This (Au_xNi_1−x)Sn₄ resettlement process repeated itself for additional reflow-aging cycles. More reflow-aging treatments, however, made the microstructure of (Au_0.45Ni_0.55)Sn₄ at the interface become more non-planar. It was shown that gravitational effect was not the driving force for the resettlement of (Au_xNi_1−x)Sn₄. It is proposed that the driving force is for (Au_xNi_1−x)Sn₄ to seek Ni at the interface so that it can become more Ni-rich. In other words, the driving force is lowering the Gibbs energy of (Au_xNi_1−x)Sn₄ by dissolving more Ni. A decomposition-diffusion mechanism is proposed to explain what happened. Kinetic rationales for this rapid resettlement of (Au_xNi_1−x)Sn₄ at such a low temperature were also discussed.     

数字矿井及其相关技术分析

结合数字地球和数字中国战略的提出 ,对未来的数字矿井进行了构想 ,给出了数字矿井的基本框架 ,全面、系统地论述了数字矿井的相关技术———矿井空间数据的获取与分析技术、网络数据库与分布式计算技术、数据仓库及数据挖掘技术、多种数据整合及虚拟现实技术 ,最后指出数字矿井的作用和意义     

Outage and coverage considerations for microcellular mobile radiosystems in a shadowed-Rician/shadowed-Nakagami environment

This paper presents outage analysis and the associated reuse distance and service area estimations for microcellular mobile radio systems that operate in a shadowed-Rician/shadowed-Nakagami (1960) fading environment. Outages caused either by the minimum carrier-to-interference ratio (CIR) requirement alone or by the CIR plus the minimum signal strength [or, equivalently, carrier-to-noise ratio (CNR)] requirements are considered. The desired signal is assumed to suffer from Rician fading while the interference signals from cochannel cells experience Nakagami fading. The interferers may have identical or different statistics. In addition, the local mean strength of the desired and interference signals may fluctuate due to shadowing