气体分子在石墨表面的吸附与扩散特性

采用分子动力学方法模拟研究气体分子在石墨表面上的吸附和扩散特性,结果表明气体分子在石墨表面上的吸附强度跟石墨中碳原子和气体分子之间的微观作用力密切相关,不同分子在石墨表面上的吸附强度不同。气体分子在石墨表面上的吸附特性符合Langmuir等温吸附模型,压力越高吸附层内分子的密度越高。通过分子的表面扩散系数随着压力的增加而降低的现象以及特定时间内分子运动距离的正常概率分布,发现石墨表面上分子的扩散主要由分子之间的碰撞控制,趋近于体相扩散。分子在石墨表面吸附层内的密度对表面扩散系数的影响非常显著,导致吸附性强的CO_2和H_2S分子扩散系数要明显低于吸附性弱的CH_4和N_2分子.     

印尼褐煤经溶剂提质后理化特性的变化规律

分析印尼褐煤经乙醇和正己烷两种有机溶剂加压提质后理化特性的变化规律。在反应温度为300℃,压力为17MPa时,褐煤经乙醇提质后的固体产率为65.1%;在反应温度为300℃,压力为12 MPa时,褐煤经正己烷提质后的固体产率为74.4%。提质后褐煤的O/C和H/C降低,热值大幅度提高,煤阶升高。提质后褐煤表面产生较多微孔和大孔,且随着反应温度的增加,小孔数量减少,大孔数量增加。提质后褐煤中羧基、羰基、羟基等含氧官能团大幅度减少,芳香环缩合程度增加。在反应温度为300℃下,褐煤中的羰基所含比例由原煤19.42%分别下降到5.72%(乙醇提质)和2.04%(正己烷提质),而羧基已经全部分解。     

异性官能团修饰石墨烯吸附GIS 特征气体能力的DFT研究

为研制高灵敏度气体绝缘组合开关(GIS)特征气体检测传感器,利用密度泛函理论方法,采用分子模拟软件对GIS特征气体(SO_2,SOF_2,SO_2F_2,CF_4)在异性官能团(羟基、羧基与氨基)修饰石墨烯表面的吸附过程进行模拟计算,从微观角度研究了GIS特征气体在异性官能团修饰石墨烯表面的吸附机理.首先计算了各吸附体系的吸附能、净电荷转移量以及态密度,比较了羟基与羧基修饰石墨烯对GIS特征气体的吸附能力;再通过分子前线轨道与能隙对吸附能力强弱的机理进行了研究,得出强吸附修饰官能团的规律性特征,并通过氨基石墨烯进行验证.结果表明:羧基与羟基修饰石墨烯能够有效提高对SO_2,SOF_2,SO_2F_2的吸附能力,但羧基石墨烯对GIS特征气体的整体吸附能力更强;异性官能团修饰石墨烯后的能隙及其与气体分子前线轨道能量差越小,对GIS特征气体吸附能力就越强,异性官能团修饰石墨烯的能隙与前线轨道能量差可以作为选择特征气体敏感材料的依据.     

异性官能团修饰石墨烯吸附GIS特征气体能力的DFT研究

为研制高灵敏度气体绝缘组合开关(GIS)特征气体检测传感器，利用密度泛函理论方法，采用分子模拟软件对GIS特征气体(SO_2,SOF_2,SO_2F_2,CF_4)在异性官能团(羟基、羧基与氨基)修饰石墨烯表面的吸附过程进行模拟计算，从微观角度研究了GIS特征气体在异性官能团修饰石墨烯表面的吸附机理.首先计算了各吸附体系的吸附能、净电荷转移量以及态密度，比较了羟基与羧基修饰石墨烯对GIS特征气体的吸附能力;再通过分子前线轨道与能隙对吸附能力强弱的机理进行了研究，得出强吸附修饰官能团的规律性特征，并通过氨基石墨烯进行验证.结果表明:羧基与羟基修饰石墨烯能够有效提高对SO_2,SOF_2,SO_2F_2的吸附能力，但羧基石墨烯对GIS特征气体的整体吸附能力更强;异性官能团修饰石墨烯后的能隙及其与气体分子前线轨道能量差越小，对GIS特征气体吸附能力就越强，异性官能团修饰石墨烯的能隙与前线轨道能量差可以作为选择特征气体敏感材料的依据.     

锂离子进入碳纳米管端口速度的分子动力学模拟

锂离子进入碳纳米管端口的速度V Li是影响锂离子电池充电性能的重要因素.采用分子动力学模拟方法,研究了直径、温度、电场强度和端口改性官能团四种因子对其影响.运用正交实验方法,分析得出了各因子及其不同水平的影响规律.结果表明,四种因子的影响力度由大到小依次为:电场强度、官能团类型、碳纳米管直径和温度.在本文的模拟条件下,随着电场强度和碳纳米管直径的增大,V Li逐渐增加,且在电场强度下的增幅会更显著;碳纳米管端口官能团分别改性为氢原子(—H),羟基(—OH),氨基(—NH2)以及羧基(—COOH)时,V Li会逐步降低;随着温度的增大,V Li先增加后减小,但整体波动偏幅不大.     

活性炭表面含氧官能团对汞吸附的作用

本文对采用不同方法处理后的活性炭进行BET、官能团分析和汞吸附性能实验,研究其表面含氧官能团对汞吸附的作用。结果表明:活性炭表面的酯基与羰基能提高汞的吸附效率,高于100℃时是影响活性炭汞吸附效率的主要因素。物理吸附,羰基与酯基吸附的汞的程序升温脱附温度峰值分别为100,210和320℃。汞在与活性炭表面接触后优先被吸附能高的化学吸附位点吸附,化学吸附饱和后,才会进行物理吸附。     

红外光谱研究Fenton试剂对多壁碳纳米管表面的影响

碳纳米管经焙烧和稀硝酸纯化处理后,在不同实验条件下采用Fenton试剂对多壁碳纳米管进行化学改性,红外光谱(FTIR)结果表明,Fenton试剂化学处理后能够在碳纳米管表面引入羟基和羰基,且羰基峰的吸收强度随着反应时间的增加而增加;碳纳米管的化学处理条件即过氧化氢与亚铁离子物质的量之比、pH值和反应时间等因素能够影响碳纳米管的改性效果;过氧化氢与亚铁离子物质的量之比控制在10左右,pH保持在3,反应10h即能在碳纳米管表面产生较多的羰基.此外,根据Fenton试剂产生羟基自由基的机理和碳纳米管改性前后的FTIR变化,初步分析了Fenton试剂与碳纳米管作用的可能机理.机理分析表明,羟基和羰基的产生是由亲电性的HO·对碳纳米管上的不饱和键进行加成氧化引起的.     

功能化石墨烯改性聚乙烯热力学特性的分子动力学模拟

聚乙烯绝缘材料在我国高压电缆中有着广泛的应用.为了提高其耐热稳定性和力学性能,利用石墨烯对聚乙烯进行掺杂改性,并基于分子动力学模拟的研究方法分别建立了低密度聚乙烯(LDPE)、石墨烯和3种官能团接枝石墨烯掺杂聚乙烯的复合模型.研究表明,相比石墨烯直接掺杂聚乙烯,羧基(-COOH)、氨基(-NH)和羟基(-OH)接枝石墨烯能够更加有效地提高聚乙烯的玻璃化温度(分别提高了16 K、7 K、5 K),减弱聚乙烯分子链的移动和降低聚乙烯的热膨胀系数、均方位移(MSD),从而使得聚乙烯复合体系的热学性能得到了有效增强.此外发现石墨烯的掺杂能够提高复合模型的力学模量,其中官能团接枝石墨烯改进效果更明显,室温下弹性模量和剪切模量的提升幅度由不接枝的33.98%、36.18%,提升到了44%和42.89%(羧基功能化体系).研究结果可为聚乙烯绝缘材料的热老化抑制和力学性能的改善提供有益的参考.     

光谱法研究酵母菌对铜离子的吸附机理

采用AAS,FTIR,SEM/EDS等方法研究了啤酒酵母对铜离子的吸附作用。 酵母菌经丙酮和NaOH处理后对Cu2+的吸附量明显增加,而将羧基酯化和将氨基甲基化使得酵母菌对Cu2+的吸附能力显著降低。化学修饰与酵母菌对Cu2+吸附的吸附结果表明,细胞壁上的羧基、氨基在酵母菌吸附铜时起着重要的作用。 红外光谱表明,酵母菌表面有结合金属的官能团,如羟基、羧基、氨基等,吸附Cu2+后,3 392 cm-1处的吸收峰紫移至3 404,1 405 cm-1处的峰红移到1 383 cm-1,细胞的主要成分和结构保持完整。 SEM/EDS分析表明,吸附后酵母菌表面变化不大,酵母菌仅结合少量Cu2+。     

燃料电池阴极扩散层扩散特性研究

本文采用粗粒化分子动力学方法研究了燃料电池阴极扩散层的扩散特性。采用全原子方法的计算结果校验了粗粒化方法的准确性,并提出了一种定量校正方案。分析了碳纳米管气体扩散层中气体和水的扩散特性,其中气体和水的扩散存在各向异性,气体和水两者在碳纳米管中轴向的扩散系数均较低,且气体和水的轴向扩散系数也随着该分子比例的降低而进一步降低;对带缺陷气体扩散层的研究表明气体扩散层中缺陷的形态对其扩散性能有显著的影响。     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Research on beamforming method for dual-line array with space mismatch between the two line arrays

The performance of port/starboard discrimination of dual-line array will be seriously degraded when the space between the two line arrays of the dual-line array is mismatched. The directivity function of the delay-sum and delay-subtract beamforming is deduced and the port/starboard discrimination of the delay-sum and delay-subtract beamforming is also studied both under the ideal status and the status under which the space between the two line arrays of the dual-line array is mismatched. Analysis results show the delay-subtract beamforming has better performance of port/starboard discrimination. At last, the sea trial results demonstrate the theoretical results.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.