Fine estimation of timing offset for OFDM

基于时域的帧同步估计算法在通过高斯信道和多径衰落信道时,其时间测度由于循环前缀的影响有峰值平台,难于准确的判定帧到达的时刻。文中提出了一种低复杂度的符号定时估计算法,利用简化的时间测度函数检测峰值来实现同步。分析了该算法的性能,并在各种信道中进行了性能分析,给出了了仿真结果。结果表明,该算法具有较高的精度和较低的计算复杂度。Symbol synchronization estimation based on time domain correlation is a problem of timing metric plateau in an AWGN channel and estimation error in multipath fading channel due to cyclic prefix.This paper proposes a novel low complex timing metric using a simple timing metric to achieve symbol synchronization.Performance of the algorithm is analyzed.The results show that the algorithm has high precision and low computation complexity.国家自然科学基金资助项目(60572106

Plant-mediated synthesis of silver nanoparticles and application in antibacterial fabric

纳米银是以纳米技术为基础研制而成的新型抗菌产品,由于量子效应和尺寸效应具有普通银系抗菌剂无法比拟的抗菌效果。本研究以黄芩、丁香、洋浦桃、芳樟4种植物质提取液制备银纳米颗粒,并借助于uV-VIS、TEM以及Xrd对产物进行表征,结果表明增加植物质提取液浓度或增大nA OH加入量,均有利于制得粒径较小的银纳米颗粒。SEM图片表明采用浸渍法可将所得纳米银颗粒负载于纯棉织物上,通过考察浸渍时间、温度、浴比对织物上载银量的影响,确定较优的浸渍条件为时间30 H,温度55℃,浴比为1:25。分别考察了银纳米颗粒粒径和植物质种类对所得载银织物抗菌性能的影响,发现负载到织物上的纳米银粒径越小,织物抑菌效果越好;利用本身具有抑菌效果的黄芩、丁香来制备银纳米颗粒,有利于增强所得载银织物的整体抗菌性能;4种植物质中以黄芩制得的载银织物抗菌效果最优,对金黄色葡萄球菌、大肠杆菌等实验菌株均有强烈的抑制作用。Nano silver, based on the nanoscience and nanotechnology, exhibits excellent antibacterial ability due to the quantum effect and size effect.In this work, the plant-mediated synthesis of silver nanoparticles(Ag NPs) was reported from four plants, including Scutellaria baicalensis, Syzygium aromaticum, Syzygium samarangense and Cinnamomum camphora.The as-synthesized Ag NPs were characterized by UV-Vis, TEM and XRD techniques.The results indicated that the Ag NPs tended to be smaller with the increase of biomass concentration or Na OH adding amounts.SEM images verified that the Ag NPs can be loaded onto cotton fabric through impregnation, and the optimal conditions were time of 30 h, temperature of 55℃ and liquor ratio of 1:25.Furthermore, the effects of Ag NPs size and plant species on the antibacterial ability of the resulting Ag-coated fabrics were investigated, respectively.Ag NPs loaded on the fabrics with smaller size displaied superior antibacterial activity against Escherichia coli.Moreover, Ag-coated fabrics prepared from Scutellaria baicalensis and Syzygium aromaticum extracts, which possessed own antibacterial ability, showed the cooperative antibacterial effect between biomass and nano-silver.The as-prepared fabric by the extract of Scutellaria baicalensis exhibited the best antibacterial ability with high inhibition ratio against various bacteria such as Staphylococcus aureus and Escherichia coli.国家自然科学基金项目(21206140); 厦门市科技计划项目(3502Z20133006)~

Au(Ⅲ)离子在黑曲霉菌上的吸附热力学和动力学特性

以黑曲霉菌作为生物吸附剂,研究其对Au(Ⅲ)离子的吸附特性,考察了pH值、吸附时间、温度和初始Au(Ⅲ)离子浓度等因素对吸附过程的影响。结果表明,Au(Ⅲ)离子在黑曲霉菌上的吸附过程对溶液pH值具有一定的依赖性,最佳pH值为2.0～3.0。升温能明显加快吸附进程,20℃下吸附过程分为2个阶段进行,分别对应于Au(Ⅲ)离子还原前和还原后的吸附,24h后吸附趋于平衡,而30℃、40℃、60℃下吸附过程均无明显分段现象,并分别于12h、6h和1h后趋于吸附平衡。Au(Ⅲ)离子初始浓度367.94mg·L–1时,升温明显促进了吸附的进行。Au(Ⅲ)离子在黑曲霉菌上的吸附等温线可用Langmuir方程很好地模拟,20℃、30℃、40℃和50℃时其饱和吸附量分别为185.19mg·g–1、202.02mg·g–1、235.85mg·g–1和277.78mg·g–1。热力学参数吉布斯自由能变(0ΔG)、吸附焓变(0ΔH)和吸附熵变(0ΔS)的计算结果表明,Au(Ⅲ)离子在黑曲霉菌上的吸附过程是一个自发的吸热和熵增过程。其吸附动力学可用准二级速率方程描述,吸附活化能为55.71kJ·mol–1。傅立叶变换红外光谱分析的结果进一步揭示了菌体表面的酰氨基、羧基和羟基是参与吸附的主要功能基团

LiCoO_2正极材料电子和离子传输特性的电化学阻抗谱研究

运用电化学阻抗谱(EIS)研究了LiCoO2正极的电子和离子传输特性,及其在电解液中贮存和充放电过程中的变化规律.发现当LiCoO2正极在电解液中贮存达到9h时,在EIS的中频区域出现一个新的半圆,随着贮存时间进一步延长,该半圆不断增大.在充放电过程中,这一中频区域半圆随电极电位的变化发生可逆的增大和减小,其变化规律与LixCoO2电子电导率随电极电位的变化规律相一致.因此,这一新的EIS特征应归属于LiCoO2正极在贮存或锂离子嵌脱过程中LixCoO2电子电导率的变化.研究结果还发现,LiCoO2正极表面SEI膜阻抗在充放电过程中可逆地增大和减小,也可归因于充放电过程中LiCoO2正极活性材料电子电导率的变化.国家重点基础研究发展计划(批准号:2002CB211804)资助项

LiCoO_2电极/电解液界面特性的电化学阻抗谱研究

运用电化学阻抗谱研究了LiCoO2电极在电解液中的贮存和首次脱锂过程.发现LiCoO2电极在电解液中,随浸泡时间延长其表面SEI膜不断增厚,归结为LiCoO2电极与电解液之间的自发反应导致生成一些高介电常数的有机碳酸锂化合物.研究结果指出LiCoO2电极首次脱锂过程中,SEI膜在3.8~3.95V电位区间发生可逆坍塌,对应其可逆溶解;由于过充反应,当电位大于4.2VSEI膜迅速增厚.研究结果同时表明,Li/LiCoO2电池体系的感抗来源于充放电过程中LiCoO2电极中存在LiCoO2/Li1?xCoO2局域浓差电池.发现锂离子在LiCoO2电极中的嵌脱过程可较好地用Langmuir嵌入等温式和Frumkin嵌入等温式描述,测得LiCoO2电极中锂离子嵌脱过程中电荷传递反应的对称因子α=0.5.国家重点基础研究发展计划资助项目(批准号:2002CB211804

黑曲霉负载银纳米颗粒的制备及其抗菌性能

采用非酶还原法,以黑曲霉菌原位还原银氨离子制备一种新型银纳米颗粒(AgNPs)/菌体复合抗菌材料,着重考察了反应温度与pH值对还原过程和所得复合材料的抗菌性能及稳定性的影响。结果表明,在温度为30℃、60℃和pH 9.5、11.5条件下,能够合成出粒径为6.9～8.2nm的近球形AgNPs。该AgNPs均匀地分布在菌体表面上,对E.coli显示出高的抗菌性能:最小抑菌浓度(MIC)为217～434mg·L-1(以菌粉总质量表示)或8～20mg Ag·L-1(以银含量表示)。提高反应温度有利于提高菌体银负载量,但AgNPs粒径增大,抗菌性能有所下降;提高反应pH值有利于提高还原速率,而对抗菌性能影响不显著。复合材料中AgNPs与菌体结合牢固,单位质量复合材料释出的Ag+含量为1.7～6.8mg.g-1,提高反应温度和pH值后Ag+的释出均减少

Electrochemical Impedance Spectroscopic Study of the First Delithiation of Spinel Lithium Manganese Oxide

研究了尖晶石锂锰氧化物电极首次脱锂过程中的电化学阻抗特征.通过选取适当的等效电路拟合实验所得的电化学阻抗谱数据,获得了首次脱锂过程中固体电解质相界面膜(SEI膜)的电阻、电容以及电荷传递电阻、双电层电容等随电极极化电位的变化规律.The first delithiation of the spinel LiMn2O4 electrode was studied using electrochemical impedance spectroscopy (EIS). Appropriate equivalent circuits were proposed to fit the experimental EIS data. Based on the fitting results, the variation of the capacitance and the resistance of SEI(solid electrolyte interphase) film, the resistance of charge transfer, and the capacitance of double layer along with the increase of polarization potential were quantitatively analyzed. The results demonstrated that the resistance and the thickness of the SEI film formed on the spinel LiMn2O4 electrode were both increased with the increase of polarization potential in the first delithiation of the spinel LiMn2O4 electrode; The charge transfer resistance decreases below 4.15 V and increases above 4.15 V, corresponding to the two-step reversible (de)intercalation of lithium between LiMn2O4 and λ-MnO2; The double layer capacitance was influenced by both the state of the spinel LiMn2O4 electrode(different polarization potential) and the two-step reversible (de)intercalation of lithium.国家重点基础研究发展规划项目(2002CB211804)资

Fabrication of Au/Pd alloy nanoparticle/Pichia pastoris composites: a microorganism-mediated approach

Fundamental Research Funds for Central Universities [2010121051]; NSFC projects [21106117, 21036004]Synthesis of metal nanoparticles (NPs) is in the limelight in modern nanotechnology. In this present study, bimetallic Au/Pd NP/Pichia pastoris composites were successfully fabricated through a one-pot microbial reduction of aqueous HAuCl4 and PdCl2 in the presence of H-2 as an electron donor. Interestingly, flower-like alloy Au/Pd NP/Pichia pastoris composites were obtained under the following conditions, NaCl concentration 0.9% (w/v), molar ratio of Au/Pd (1 : 2) and the time for pre-adsorption of Au(III) and Pd(II) ions 15 min, through fresh yeast reduction. The mapping results from scanning transmission electron microscopy (STEM) with a high-angle annular dark field detector confirmed that the Au/Pd NPs on the surface of the yeast were indeed alloy. Furthermore, the energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) measurements showed that the composition of the bimetallic NPs were consistent with the initial molar ratio of the precursors

Biogenic flower-shaped Au-Pd nanoparticles: Synthesis, SERS detection and catalysis towards benzyl alcohol oxidation

～40 nm flower-shaped Au-Pd bimetallic nanoparticles were prepared in a facile and eco-friendly way based on the simultaneous bioreduction of HAuCl 4 and Na2PdCl4 with ascorbic acid and Cacumen Platycladi leaf extract at room temperature. Characterization techniques, such as transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction, were employed to confirm that the as-synthesized nanoparticles were alloys. The obtained flower-shaped Au-Pd alloy nanoparticles exhibited an excellent surface enhanced Raman spectroscopic activity with rhodamine 6G and efficient catalytic ability for the oxidation of benzyl alcohol to benzaldehyde. ? 2014 The Royal Society of Chemistry

Electrochemical impedance spectroscopic study of the first delithiation of spinel lithium manganese oxide

The first delithiation of the spinel LiMn2O4 electrode was studied using electrochemical impedance spectroscopy (EIS). Appropriate equivalent circuits were proposed to fit the experimental EIS data. Based on the fitting results, the variation of the capacitance and the resistance of SEI (solid electrolyte interphase) film, the resistance of charge transfer, and the capacitance of double layer along with the increase of polarization potential were quantitatively analyzed. The results demonstrated that the resistance and the thickness of the SEI film formed on the spinel LiMn2O4 electrode were both increased with the increase of polarization potential in the first delithiation of the spinel LiMn2O4 electrode; The charge transfer resistance decreases below 4.15 V and increases above 4.15 V, corresponding to the two-step reversible (de)intercalation of lithium between LiMn2O4 and lambda-MnO2; The double layer capacitance was influenced by both the state of the spinel LiMn2O4 electrode (different polarization potential) and the two-step reversible (de)intercalation of lithium