碳纳米管中封装富勒烯的机理

利用经典分子动力学模型,发现C60进入单壁碳纳米管(SWNTs)形成(C60)n@SWNTs的吸入和俘获机理.揭示了吸入和俘获势垒只局域于SWNTs的管口区,而在SWNTs的管内区,C60沿管轴方向的运动几乎不受力.最后,系统地计算了吸入和俘获势垒随SWNTs管径的变化,发现只有当SWNTs的管径大于阈值1238nm时才能吸入C 关键词： 富勒烯相关材料 碳纳米管 类虹吸作用     

Some further remarks on good sets

We show that in n-fold cartesian product, n ≥ 4, a related component need not be a full component. We also prove that when n ≥ 4, uniform boundedness of lengths of geodesics is not a necessary condition for boundedness of solutions of (1) for bounded function f.     

The hypoelliptic Laplacian on the cotangent bundle

In this paper, we construct a new version of Hodge theory, where the corresponding Laplacian acts on the total space of the cotangent bundle. This Laplacian is a hypoelliptic operator, which is in general non-self-adjoint. When properly interpreted, it provides an interpolation between classical Hodge theory and the generator of the geodesic flow. The construction is also done in families in the superconnection formalism of Quillen and extends earlier work by Lott and the author.

     

Filling carbon nanotubes with metals by the arc-discharge method: the key role of sulfur

Various filled carbon nanotubes have recently been successfully produced by the arc-discharge method by doping a 99.4% graphite anode with a transition metal like Cr, Ni, a rare earth like Yb, Dy, or a covalent element like S, Ge. In this work, the structural characteristics of these encapsulated nanowires were studied by High Resolution Transmission Electron Microscopy and their chemical composition was investigated using Electron Energy-Loss Spectroscopy with high spatial resolution: this analysis mode provides elemental concentration profiles across or along the filled nanotubes. Except in the case of Ge for which only pure Ge fillings were identified, surprising amounts of sulfur, which was present as an impurity ( 0.25%) in the graphite rods, were found within numerous filling materials. When using high purity carbon rods, no filled nanotube was obtained. We chose the case of Cr to clearly evidence that the addition of sulfur in catalytic quantity is responsible for the formation of filled nanotubes, including sulfur free encapsulated nanowires. A growth mechanism based on a catalytic process involving three elements, i.e. carbon, a metal and sulfur, and taking into account the experimental results is proposed. Received: 20 January 1998 / Received in final form and accepted: 9 April 1998     

Synthesis of Ipratropium Bromide–Related Compounds

Synthesis of ipratropium bromide metabolites is described.     

Quantitative 1H NMR spectroscopy (qNMR) in the early process development of a new quorum sensing inhibitor

2-methyl-5,6,7,8-tetrahydro-2H-chromen-4(3H)-one (called 6-oxo) is presented as a new AI-1 quorum sensing inhibitor for Vibrio harveyi. The development of a chemical process to afford traceable materials for new biological assays demands the development of analytical methods to ensure their purity and quality. This work describes the use of quantitative ¹H nuclear magnetic resonance (NMR) spectroscopy (qNMR) to assess the purity of a sample of 6-oxo (99.88%) and a sample of its major process impurity (E)-1-(2-hydroxycyclohex-2-en-1-yl)but-2-en-1-one (called HCB; 98.28%). To explore the scope of the use of qNMR to quantify the amount of low-content components in samples related to the chemical process for 6-oxo synthesis, this work also determined the amount of 6-oxo in two HCB samples: (a) the high-purity HCB sample described above and (b) a crude HCB sample collected during the chemical process. Despite the complexity of the crude sample, the amount of 6-oxo was readily assessed and could help to estimate the extent to which 6-oxo was already formed during the HCB synthesis. This information can help the understanding of how the process parameters can be modified to improve the performance of the whole process, by controlling the reaction mechanisms working at each step of this chemical process. In this context, our results reinforce qNMR as a complementary analytical tool for the quantification of the main component found in a sample, contributing to the standardization of reference materials and thus allowing the development of analytical methods for process control and traceability of the samples used for biological assays.     

Gradient induced artifacts in simultaneous EEG-fMRI: Effect of synchronization on spiral and EPI k-space trajectories

The nature of the gradient induced electroencephalography (EEG) artifact is analyzed and compared for two functional magnetic resonance imaging (fMRI) pulse sequences with different k-space trajectories: echo planar imaging (EPI) and spiral. Furthermore, the performance of the average artifact subtraction algorithm (AAS) to remove the gradient artifact for both sequences is evaluated. The results show that the EEG gradient artifact for spiral sequences is one order of magnitude higher than for EPI sequences due to the chirping spectrum of the spiral sequence and the dB/dt of its crusher gradients. However, in the presence of accurate synchronization, the use of AAS yields the same artifact suppression efficiency for both pulse sequences below 80 Hz. The quality of EEG signal after AAS is demonstrated for phantom and human data. EEG spectrogram and visual evoked potential (VEP) are compared outside the scanner and use both EPI and spiral pulse sequences. MR related artifact residues affect the spectra over 40 Hz (less than 0.2 μV up to 120 Hz) and modify the amplitude of P1, N2 and P300 in the VEP. These modifications in the EEG signal have to be taken into account when interpreting EEG data acquired in simultaneous EEG-fMRI experiments.     

Shiva diagrams for composite-boson many-body effects: how they work

The purpose of this paper is to show how the diagrammatic expansion in fermion exchanges of scalar products of N-composite-boson (“coboson”) states can be obtained in a practical way. The hard algebra on which this expansion is based, will be given in an independent publication. Due to the composite nature of the particles, the scalar products of N-coboson states do not reduce to a set of Kronecker symbols, as for elementary bosons, but contain subtle exchange terms between two or more cobosons. These terms originate from Pauli exclusion between the fermionic components of the particles. While our many-body theory for composite bosons leads to write these scalar products as complicated sums of products of “Pauli scatterings” between two cobosons, they in fact correspond to fermion exchanges between any number P of quantum particles, with 2 ≤P≤N. These P-body exchanges are nicely represented by the so-called “Shiva diagrams”, which are topologically different from Feynman diagrams, due to the intrinsic many-body nature of the Pauli exclusion from which they originate. These Shiva diagrams in fact constitute the novel part of our composite-exciton many-body theory which was up to now missing to get its full diagrammatic representation. Using them, we can now “see” through diagrams the physics of any quantity in which enters N interacting excitons — or more generally N composite bosons —, with fermion exchanges included in an exact — and transparent — way.     

COmplex-Model-Based Estimation of thermal noise for fMRI data in the presence of artifacts

Due to the presence of artifacts induced by fast-imaging acquisition in functional magnetic resonance imaging (fMRI) studies, it is very difficult to estimate the variance of thermal noise by traditional methods in magnitude images. Moreover, the existence of incidental phase fluctuations impairs the validity of currently available solutions based on complex datasets. In this article, a time-domain model is proposed to generalize the analysis of complex datasets for nonbrain regions by incorporating artifacts and phase fluctuations. Based on this model, a novel estimation schema has been developed to find an appropriate set of voxels in nonbrain regions according to their levels of artifact and phase fluctuation. In addition, noise intensity from these voxels is estimated. The whole schema is named COmplex-Model-Based Estimation (COMBE). Theoretical and experimental results demonstrate that the proposed COMBE method provides a better estimation of thermal noise in fMRI studies compared with previously proposed methods and suggest that the new method can adapt to a broader range of applications, such as functional connectivity studies, evaluation of sequence designs and reconstruction schemas.     

薹草属广义菱形果薹草组（莎草科）的叶表皮微形态特征及其分类学意义

利用光学显微镜,对薹草属广义菱形果薹草组Carexsect.Rhomboidales s.l.(莎草科)54种、2亚种、8变种,共76个样品进行了叶片表皮形态特征的观察研究.结果表明:表皮细胞形状和垂周壁式样在大多数种中表现出稳定性,上、下表皮细胞大多为长方形,少数为近方形、近圆形或长条形,其垂周壁式样多为深波状,少数为波状;气孔器在下表皮脉间呈列或随机分布,气孔的大小、气孔指数及密度在种内有差异;有些种具硅质乳突,而表皮附属物分为刺突和刺毛2种,刺突常出现在sect.Rhomboidales s.str.的成员中.根据表皮的各项性状尚无法区分sect.Rhomboidales s.str.和sect.Careyanae,叶表皮性状近缘种之间存在显著区别,可以作为区分种或种下类群的依据.