DCC缩合酯化法合成水杨酸低聚壳聚糖酯及抑菌性研究

在保留C2-NH2抗茵活性基团的基础上,以DCC为脱水剂制备了具有双抑菌活性中心的水杨酸低聚壳聚糖酯(SEC),并对其抑菌活性进行了研究.结果显示,SEC最佳合成反应条件为:n(低聚壳聚糖):n(水杨酸):n(DCC)=1:4:4,冰浴条件下酯化反应48 h,产物酯化度接近73%.该条件下制备的壳聚糖衍生物对各种常见菌...     

A 2–8-GHz adaptive duty-cycle corrector loop with background calibration

A novel adaptive duty-cycle correction (DCC) architecture based on background calibration is developed. The proposed DCC loop is capable of correcting 17–80% duty error up to 4.6% at 8.1 GHz within 172 ns convergent time. During calibration, the whole loop including DCC buffer consumes 6.4 mA from 0.95 V supply but after calibration, digital feedback section does not burn additional dynamic power. The corner results show that the proposed calibration methodology can cope with process, voltage and temperature (PVT) variation adaptively. The architecture is implemented in 45 nm CMOS process and occupies 0.0032 mm².     

Fatigue crack growth in 2024 aluminum alloy with inhomogeneous solidification microstructure

This study reports the investigation of the fatigue crack growth behavior in 2024 aluminum alloy billets manufactured using the direct chill casting (DCC) and electromagnetic casting (EMC). It was expected that the billets produced from these different casting procedures would vary in terms of their microstructure. Therefore, they should exhibit different fatigue crack growth behavior. The results showed that, the structure of the middle center portion of both billets is not homogeneous and relatively coarse, while the structure of the center and edge portions is homogeneous compared with the structure of the middle center portion. As fatigue crack growth extended through many grains having different morphologies, it became unstable through the overall crack path, and the Paris zone almost disappeared. The effects of 5% rolling and commercially rolled DCC billets on the fatigue crack growth rate were also investigated. Striations were enhanced around Al₂Cu particles refined by commercial rolling, and fatigue crack growth was stable until large crack length.     

Functionalization of carbon nanomaterials for advanced polymer nanocomposites: A comparison study between CNT and graphene

The allotropes of carbon nanomaterials (carbon nanotubes, graphene) are the most unique and promising substances of the last decade. Due to their nanoscale diameter and high aspect ratio, a small amount of these nanomaterials can produce a dramatic improvement in the properties of their composite materials. Although carbon nanotubes (CNTs) and graphene exhibit numerous extraordinary properties, their reported commercialization is still limited due to their bundle and layer forming behavior. Functionalization of CNTs and graphene is essential for achieving their outstanding mechanical, electrical and biological functions and enhancing their dispersion in polymer matrices. A considerable portion of the recent publications on CNTs and graphene have focused on enhancing their dispersion and solubilization using covalent and non-covalent functionalization methods. This review article collectively introduces a variety of reactions (e.g. click chemistry, radical polymerization, electrochemical polymerization, dendritic polymers, block copolymers, etc.) for functionalization of CNTs and graphene and fabrication of their polymer nanocomposites. A critical comparison between CNTs and graphene has focused on the significance of different functionalization approaches on their composite properties. In particular, the mechanical, electrical, and thermal behaviors of functionalized nanomaterials as well as their importance in the preparation of advanced hybrid materials for structures, solar cells, fuel cells, supercapacitors, drug delivery, etc. have been discussed thoroughly.     

The Technology and Economic Analysis of the DCC and MIP Processes at Anqing Petrochemical Company

1 Introduction With the increasing emphasis on the environmental protec- tion the olefins and sulfur contents in the gasoline must be limited. Therefore the State Bureau of Environmental Protec- tion promulgated on June 1, 1999 the “Standard for Control over Toxic Substances in Automotive Gasoline”, stipulating the olefin content in automotive gasoline to be less than 35 v%, the aromatic content— less than 40 v%, the benzene content — less than 2.5 v% and the sulfur content to be less …     

A fast‐corrected all‐digital DCC with synchronous input clock

This paper presents a fast‐corrected all‐digital duty‐cycle corrector (DCC) with synchronous input clock. The proposed DCC has many features, including fast locking in 4 cycles, wide range correction, and synchronous 50% duty‐cycle clock with an input clock. The circuit can operate from 500 to 900 MHz and corrects a wide range of input duty cycle ranging from 25 to 75%. The duty‐cycle error of the output clock is between ?2.4 and 2.7%. The largest static phase error between the input and output clock is ?44 ps at 900 MHz. The RMS and peak‐to‐peak jitters are 1.9 and 14.7 ps at 900 MHz, respectively. The proposed DCC is implemented in a 0.18‐µm complementary metal oxide semiconductor process. The proposed DCC occupies an area of 0.05 mm² and dissipates 23 mW with 1.8‐V supply voltage at 900 MHz. Copyright © 2014 John Wiley & Sons, Ltd.     

基于IEEE 802.11协议的EDCC 算法研究

该文对IEEE802．11协议的DCF功能进行了研究,在分析原有的DCC算法的基础上,对其进行了改进,提出了一种增强型的DCC算法——EDCC算法．原有的DCC算法虽然能够有效地减少高负荷网络中各节点接入共享信道的碰撞次数,但其没有有效地利用高负荷网络中连续两次发送时隙利用率的相关性对时隙利用率进行平滑处理,导致对时隙利用率的估值与现实中的结果存在偏差．改进后的EDCC算法采用一维自回归滑动平均模型ARMA(a)平滑处理的方法,改进了原有DCC算法对时隙利用率估计方差较大的缺点,提高了DCC算法的性能．     

Direct coagulation casting of silicon nitride suspension via a dispersant reaction method

A direct coagulation casting method for silicon nitride suspension via dispersant reaction was reported. Tetramethylammonium hydroxide (TMAOH) was used as dispersant to prepare silicon nitride suspension with high solid loading and low viscosity. Influences of TMAOH and pH value on the dispersion of silicon nitride powder were investigated. Glycerol diacetate (GDA) was used to coagulate the silicon nitride suspension. Influences of the concentration of glycerol diacetate on the viscosity and pH value of the suspension were investigated. It was indicated that high viscosity sufficient to coagulate the suspension was achieved by adding 1.0–2.0 vol% glycerol diacetate at 40–70 °C. The coagulation mechanism was proposed that the silicon nitride suspension was destabilized by dispersant reacting with acetic acid which was hydrolyzed from glycerol diacetate at elevated temperature. Coagulated samples could be demolded without deformation by treating 50 vol% silicon nitride suspensions with 0.2 wt% tetramethylammonium hydroxide and 1.0–2.0 vol% glycerol diacetate at different temperatures. Dense silicon nitride ceramics with relative density above 98.8% had been prepared by this method using glycerol diacetate as coagulating agent sintered by different methods.     

直驱永磁同步风电机组不对称故障穿越的研究

在分析不对称电网电压条件下直驱永磁风力发电机组并网逆变器数学模型的基础上,提出了正负序双电流闭环控制策略,完成风力发电机组在电网发生不对称故障下的不脱网运行.在PSCAD/EMTDC环境下建立基于IGBT背靠背变频器的1.5 MW永磁直驱风力发电系统仿真模型,仿真结果证明该控制策略的可行性.     

深度催化裂解石脑油加氢工艺技术的工业应用

介绍了加氢精制和芳烃抽提的组合工艺在陕西延长石油(集团)有限责任公司榆林炼油厂200 kt/a深度催化裂解(DCC)装置的工业应用情况。该工艺可脱除DCC裂解石脑油中的硫和烯烃,降低苯含量,经加氢处理后的脱戊烷油硫和氮的质量分数均小于0.5μg/g,完全满足苯抽提进料性质要求,辛烷值RON在100以上。经苯抽提抽苯后,RON仍在98以上,可用于生产高辛烷值国Ⅴ车用汽油调合组分。该工艺不仅大幅提高了DCC裂解石脑油的经济价值,生产可替代甲基叔丁基醚的汽油调合组分,实现了资源优化配置,为DCC裂解石脑油拓展了产品去向,并大大促进DCC工艺的推广应用。