共查询到20条相似文献,搜索用时 46 毫秒
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用巨正则蒙特卡罗分子模拟方法研究了单壁纳米碳管中的微孔即单壁纳米碳管基本孔-内管腔和管间孔对单壁纳米碳管储氢性能的影响.与低温下氮气吸附实验结果的比较发现单壁纳米碳管的内管腔是吸附的主要位置.分析单壁纳米碳管内管腔中吸附势的叠加和利用效率,发现管径为2nm左右时单壁纳米碳管内管腔的储氢容量最高.当单壁纳米碳管阵列的管间距增加时,单壁纳米碳管的管间孔也会成为有效的氢吸附位.
关键词:
Monte Carlo方法
单壁纳米碳管
储氢
微孔 相似文献
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采用巨正则蒙特卡罗方法 ,模拟常温、1 0MPa下氢在扶手椅型多壁壁碳纳米管中的物理吸附过程 .氢分子之间、氢分子与碳原子之间的相互作用采用Lennard Jones势能模型 .研究了双壁碳纳米管外 (内 )径固定而内 (外 )径改变时的物理吸附储氢情况 ,发现氢分子主要储存在双壁碳纳米管的管壁附近 ,当双壁碳纳米管的内外管壁间距由 0 .34nm增大到 0 .6 1或 0 .88nm时可有效增加物理吸附储氢量 ,并给出了相应的理论解释 .在此基础上 ,计算了管壁间距为 0 .34、0 .6 1和 0 .88nm时的三壁碳纳米管的物理吸附储氢量 ,并与相同条件下单壁和双壁碳纳米管的物理吸附储氢量作了比较 ,发现多壁碳纳米管的物理吸附储氢量随碳管层数的增加而减小 . 相似文献
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采用燃烧法制备了Fe/Mo/MgO催化剂,用化学气相沉积法在1000℃下催化裂解甲烷制得了单壁纳米碳管.实验结果表明,550℃下焙烧的催化剂效果最好,适宜的酸碱性应该是催化剂具有较高活性的原因.用扫描电镜、透射电镜、高分辨透射电镜、热重分析和拉曼光谱等方法对制备的纳米碳管粗产品进行了表征.结果表明,该产物确为高质量单壁纳米碳管,其形态基本都以束状存在,且单壁纳米碳管直径分布较窄(0.85~1.22nm);对反应气氛的考察表明,CH4/N2=50/300为最佳,该气氛下所制得粗产物中单壁碳管的含量接近40%,经稀盐酸室温处理后,碳管含量可达到75%以上. 相似文献
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介绍了一种新的制备纳米石墨粉的方法——炸药爆轰法.通过对爆轰合成的黑色粉末进行x射线衍射分析,确认其为六方结构的纳米石墨,平均晶粒度为1.86—2.61nm.用BET气体吸附仪测试纳米石墨粉的比表面积约为500—650m2/g,由比表面积计算得到的纳米石墨粒度为4.41—6.85nm.在室温(≈290K)和12MPa压力条件下对纳米石墨粉进行储放氢气性能测试,结果表明纳米石墨粉样品的储放氢量为0.33wt%—0.37wt%.在相同实验条件下,纳米石墨粉原始样品的储放氢能力较原始纳米炭纤维(0.15wt%—0.35wt%)和多壁碳纳米管(0.15wt%—0.20wt%)的储放氢能力略强,但低于超级活性炭(0.92wt%—0.98wt%).纳米碳材料的比表面积在其储放氢实验中起关键作用.
关键词:
爆轰
纳米石墨粉
比表面积
储放氢量 相似文献
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运用第一性原理的密度泛函理论,结合非平衡格林函数,研究了氮原子取代掺杂手性单壁(6,3)碳纳米管的电子结构和输运特性.计算结果表明:不同构形和不同数目的氮原子取代掺杂对手性碳管的输运性质有很复杂的影响.研究发现,氮原子掺杂明显改变了碳管的电子结构,使金属型手性碳管的输运性能降低,电流-电压曲线呈非线性变化,而且输运性能随着杂质原子间间距的变化而发生显著改变.在一定条件下,金属型碳管向半导体型转变.
关键词:
手性单壁碳纳米管
氮掺杂
电子结构
输运性能 相似文献
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采用共沉淀方法制备了名义组分为Zn1-xMnxO(x=0.001,0.005,0.007,0.01)的Mn掺杂的ZnO基稀磁半导体材料,并研究了在大气气氛下经过不同温度退火后样品的结构和磁性的变化.结果表明:样品在600℃的大气条件下退火后, 仍为单一的六方纤锌矿结构的ZnO颗粒材料;当样品经过800℃退火后,Mn掺杂量为0.007,0.01的样品中除了ZnO纤锌矿结构外还观察到ZnMnO3第二相的存在.磁性测量表明,大气条件下600℃退火后的样品,呈现出室温铁磁性;而800℃退火后的样品,其室温铁磁性显著减弱,并表现为明显的顺磁性.结合对样品的光致发光谱的分析,认为合成样品的室温铁磁性是由于Mn离子对ZnO中的Zn离子的替代形成的.
关键词:
ZnO
掺杂
稀磁半导体
铁磁性 相似文献
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Cyclic competition game models, particularly the “rock–paper–scissors” model, play important roles in exploring the problem of multi-species coexistence in spatially ecological systems. We propose an extended “rock–paper–scissors” game to model cyclic interactions among five species, and find that two of the five can coexistent when biodiversity disappears, which is different from the “rock–paper–scissors” game. As the number of fingers is five, we named the new model the “fingers” game, where the thumb, forefinger, middle finger, ring finger, and little finger cyclically dominate their subsequent species and are dominated by their former species. We investigate the “fingers” model in two ways: direct simulations and nonlinear partial differential equations. An important finding is that the number of species in a cyclic competition game has an influence on the emergence of biodiversity. To be specific, the “rock–paper–scissors” model is in favor of maintaining biodiversity in comparison with the “fingers” model when the variables (population size, reproduction rate, selection rate, and migration rate) are the same. It is also shown that the mobility and reproduction rate can promote or jeopardize biodiversity. 相似文献
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The differences of the pitch and duration of Chinese syllables between Putonghua (PTH) and Taiwan Mandarin (TM) were studied. The speech materials to be used are not only isolated syllables, but also sentences. The results reveal that: For the isolated syllables, T1 and T2 in TM are influenced by Minnan dialect, therefore their pitch are lower than those in PTH. T3 is fall-rise in PTH, while it is fall in TM. Moreover, the syllable duration sequence for different tone is T3〉T2〉T1〉T4 in PTH, while it is T1〉T2〉T3〉T4 in TM. For the syllables in sentences, T2 is mid-rise in PTH, while it is mid-level in TM. And the T3 is longer than T4 but shorter than T1 or T2 in PTH, while it is the shortest in TM. Furthermore the effects of prosodic phrase boundary on duration for different tones are almost the same in PTH, but the lengthening part of T1 or T2 is longer than that of T3 or T4 in TM. 相似文献
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Downstep in pitch contour of Chinese Putonghua is examined using subtly designed sentences by controlling tone combinations. The results show both automatic and nonautomatic downstep phenomena exist in Chinese. In non-automatic downstep, low tones compress downwards the pitch range of the following syllables. and the main influence of downstep is on topline. Low tone not only lower the topline behind it, but also raise the high tones before it, the effects are compatible with each other. In automatic downstep, the topline of pitch contour in intonational phrase is presented as a linear downtrend, but it differs among speakers due to the effect of personal stress practice. In comparison with downstep phenomenon in other tone or non-tone languages, the downstep ratio in Chinese is not constant, and the domain of downstep is not limited within the adjacent tones. 相似文献
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JIA Duojie 《中国物理C(英文版)》2008,32(7)
It is shown that SU(2) QCD admits an dual Abelian-Higgs phase, with a Higgs vacuum of a type-Ⅱ superconductor. This is done by using a connection decomposition for the gluon field and the random-direction approximation. Using a bag picture with soft wall, we presented a calculational procedure for the glueball energy based on the recent proof for wall-vortices [Nucl. Phys. B 741(2006)1]. 相似文献
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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. 相似文献
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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. 相似文献
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Based on the research in Ref. [5][Materials Science and Engineering, 1989; A122: 57 63], an improved model of heat source is set up, the different modes of Lamb wave in an isotropic sample generated by a chopped electron beam at frequency f are obtained with integral transform and normal function expansion method, and the output signal of PZT coupled at the back surface of the sample is found out. The generation mechanism of SEAM (Scanning Electron Acoustic Microscopy) signal is discussed. It shows that the SEAM is a near field imaging technique with high spatial resolution and its best lateral spatial resolution is about 2√2α (α is the radius of the focused electron beam). Some of experimental results of SEAM images are presented in the paper and it shows that the spatial resolution of SEAM is better than 0.5 μm and smaller than the thermal diffusion length of the sample. Therefore the character of near field imaging in SEAM is also proved experimentally. 相似文献
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Transmission spectra of coupled cavity structures (CCSs) in two-dimensional (2D) photonic crystals (PCs) are investigated using a coupled mode theory, and an optical filter based on CCS is proposed. The performance of the filter is investigated using finite-difference time-domain (FDTD) method, and the results show that within a very short coupling distance of about 3λ, where λ is the wavelength of signal in vacuum, the incident signals with different frequencies are separated into different channels with a contrast ratio of 20 dB. The advantages of this kind of filter are small size and easily tunable operation frequencies. 相似文献