RTS与帧分段机制在地空数据链中的应用与改进

将IEEE802．11的RTS／CTS握手机制与MSDU帧分段机制引入地空数据链,建立了基于改进Markov链的地空数据链MAC层协议模型。以最大饱和吞吐量为性能参数推导出合理的RTS阈值和分段阈值算法。分析表明该方法能够提高无线通信效率,降低了误帧率,解决了隐藏终端等问题。     

Recent developments and applications of screen-printed electrodes in environmental assays—A review

Screen-printed electrodes (SPEs), which are used as economical electrochemical substrates, have gone through significant improvements over the past few decades with respect to both their format and their printing materials. Because of their advantageous material properties, such as disposability, simplicity, and rapid responses, SPEs have been successfully utilised for the rapid in situ analysis of environmental pollutants. This critical review describes the basic fabrication principles, the configuration designs of SPEs and the hybrid analytical techniques based on SPEs. We mainly overview the electrochemical applications of SPEs in environmental analysis over the past 3 years, including the determination of organic compounds, heavy metals and gas pollutants.     

PREPARATION OF SURFACE ION-IMPRINTED ATTAPULGITE-SUPPORTED POLYMER AND ITS ADSORPTION BEHAVIORS OF Sr（II）

The surface ion-imprinting concept and chitosan incorporated sol-gel process were applied to the preparation of a new attapulgite-supported organic-inorganic hybrid polymer for selective separation of Sr（II） from aqueous solution. The prepared polymer was characterized with SEM, IR and XRD. The results showed that as a sorbent, it had good configuration and binding sites. Its adsorption behaviors for Sr（II） was investigated by FAAS and ICP-AES. The effects on adsorption capacities, including pH, quiescent time, and adsorbent amount were discussed, and the adsorption isothermal curve was obtained. Then the Kd a parameter estimating relative adsorbability, was conducted to study the selectivity towards Sr（II） of the prepared polymer. Under the optimum conditions, the ion-imprinted polymer offered a fast kinetics for the adsorption of Sr（II） and the maximum capacity was 12.9mg/g. The Kd and K parameters estimating relative adsorbability towards target ion, suggested that selective recognition of the ion-imprinted polymer towards Sr（II） was much higher than that of the non-imprinted polymer and attapulgite. Furthermore, the ion-imprinted polymer is of great regeneration capacity. The prepared functional polymer was shown to be promising for selective preseparation and enrichment of trace Sr（II） in environmental samples.     

腕管综合征及其生物力学研究进展

腕管综合征(carpal tunnelsyndrome, CTS)是腕部正中神经受到卡压而引起的一种神经病症. 它所带来的高昂的社会和经济花费使得腕管综合征的研究应运而生, 并且在过去的10年里得到突飞猛进的发展. 常规的手术方式是将腕横韧带(transversecarpal ligament)切开, 以释放正中神经(mediannerve)所受到的压力. 本文不仅对腕管的解剖结构、腕管综合征的症状和发病机理、以及诊断和治疗等方面作了简要概述,还主要从以下几个方面探讨了近年来与腕管综合征相关的生物力学研究工作及其进展: (1)影响腕管内压力的因素,包括腕部姿势, 手指、肌腱或手掌所受外荷载的大小, 以及手工劳作的不同频率等; (2)腕管结构的稳定性研究, 如切开腕横韧带或腕骨间掌横韧带对腕刚度的影响, 以及从动力学角度分析腕管减压手术会导致的腕骨失稳现象; (3)腕管内容物(如肌腱、正中神经)的运动及内容物之间以及腕管内容物与腕横韧带之间的相互作用;(4)腕横韧带的延展实验, 如利用外荷载或移位搭接的方法拉长腕横韧带, 以达到降低腕管内压力的目的. 本文旨在加强人们对腕管综合征尤其是对与腕管综合征相关的生物力学研究进展的了解, 并从生物力学的观点提出利用有限元方法对腕管结构进行三维建模与分析将有可能成为腕管综合征进一步研究的一个重要发展方向.      

冠醚壳聚糖多孔微球选择性富集-石墨炉原子吸收法测定雨水中痕量铅的研究

报道用冠醚壳聚糖多孔微球选择性富集雨水中痕量铅并用石墨炉原子吸收法测定.DB-18-crown-6-CTS多孔微球在pH 5.5时,对Pb2+的富集率达到98%.吸附的Pb2+能用5 mL 2 mol·L-1的HCl定量洗脱,洗脱率98.1%.Pb2+被洗脱后,用石墨炉原子吸收法测定.该方法的富集倍数为100倍,检出限(3σ)为0.085 μg·L-1,相对标准偏差小于2.75%,用于分析实际雨水样,回收率为94.5%～102%.     

The combination of QoS,aggregation and RTS/CTS in Very High Throughput IEEE 802.11ac networks

We consider a single WiFi cell in which multiple mobile stations transmit multiple QoS constrained Application flows to the Access Point. We investigate the efficiency of using RTS/CTS in the face of the QoS constraints, in various Access Categories that are defined in the WiFi standard, in a number of transmitting stations and in various amounts of aggregation. We show that using RTS/CTS is efficient in terms of Throughput, when there are collisions and the time to recover these collisions is within the Delay/Loss constraints of the Application flows. It turns out that RTS/CTS is most efficient in the Video and Voice Access Categories and Delay constrains in the order of several tens of milli-seconds. For smaller Delay constraints it is more efficient without RTS/CTS. Thus, we show the existence of cross-points: In Delay constraints smaller than the cross points it is more efficient without RTS/CTS and beyond the cross-points the opposite is true.     

后端实现时几种减小时钟延迟的有效方法

主要探讨在嵌入式芯片后端设计时怎么实现时钟延时最小时钟网络。时钟网络优化的障碍可能来自很多方面,主要包括以下三个方面:不同转换率的输入输出单元,具有大负载电容端口以及来自不同时钟域的时钟网络。针对提出的问题,讨论一般采取的解决方案,优化时钟延时,通过针对性的方法技巧,可以在时钟树自动综合时有效地减少时钟树延时。     

ADCF:IEEE 802.11 DCF协议的自适应简便算法

本文提出了一种自适应型IEEE802．11 DCF协议：ADCF。该协议根据网络规模的变化，动态调节RTS／CTS机制的门限值，优化系统性能。在分析DCF协议的基础上，本文给出了一种估算网络规模的简便算法。仿真结果表明，该算法计算准确快捷。     

Self-start-up fully integrated DC-DC step-up converter using body biasing technique for energy harvesting applications

An ultra-low power, self-start-up switched-capacitor Two Branch Charge Pump (TBCP) circuit for low power, low voltage, and battery-less implantable applications is proposed. In order to make feasible the low voltage operation, the proposed charge pump along with Non-Overlapped Clock generator (NOC) are designed working in sub-threshold region by using body biasing technique. A four-stage TBCP circuit is implemented with both NMOS and PMOS transistors to provide a direct load flow. This leads to a significant drop in reverse charge sharing and switching loss and accordingly improves pumping efficiency. A post-layout simulation of designed four-stage TBCP has been performed by using an auxiliary body biasing technique. Consequently, a low start-up voltage of 300 mV with a pumping efficiency of 95% for 1 pF load capacitance is achieved. The output voltage can rise up-to 1.88 V within 40 μs with 0.2% output voltage ripple in case of using 400 mV power supply. The designed circuit is implemented by 180-nm standard CMOS technology with an effective chip area of 130.5 μm × 141.8 μm while the whole circuit consumes just 3.2 μW.     

ASIC设计中时钟偏移分析

目前的ASIC设计中,时钟偏移对同步数字电路的影响越来越大,它也越来越受到高速电路设计者的关注,因此如何解决它给电路带来的不利影响成了设计中的重要挑战.分析了时钟偏移的产生机理,提出了怎样使用CTS在时钟树中插入不同驱动能力的缓冲器,以平衡时钟网络,以及如何利用有用的时钟偏移来改善电路的时序.