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991.
Volodin A Ahlskog M Seynaeve E Van Haesendonck C Fonseca A Nagy JB 《Physical review letters》2000,84(15):3342-3345
Coiled carbon nanotubes were produced catalytically by thermal decomposition of hydrocarbon gas. After deposition on a silicon substrate, the three-dimensional structure of the helix-shaped multiwalled nanotubes can be visualized with atomic force microscopy. Helical structures of both chiralities are present in the nanotube deposits. For larger coil diameters ( >170 nm), force modulation microscopy allows one to probe the local elasticity along the length of the coil. Our results agree with the classical theory of elasticity. Similar to the case of straight nanotubes, the Young modulus of coiled multiwalled nanotubes remains comparable to the very high Young modulus of hexagonal graphene sheets. 相似文献
992.
993.
Sijbersa J Van Audekerke J Verhoye M Van der Linden A Van Dyck D 《Magnetic resonance imaging》2000,18(7):881-886
Nowadays, electroencephalography signals can be acquired from a patient lying in a magnetic resonance imaging system. It is even possible to acquire EEG signals during an MR imaging sequence. However, such EEG signals are severely distorted by artifacts originating from various effects (e.g., MR gradients, ECG). In this paper, a simple method is presented to reduce such artifacts. Thereby, special attention is focused on artifacts related to the patient's electrocardiogram. The method is shown to be effective, adaptive, and automatic. 相似文献
994.
Van Audekerkea J Peeters R Verhoye M Sijbers J Van der Linden A 《Magnetic resonance imaging》2000,18(7):887-891
The construction of a high quality MR RF-antenna with incorporated EEG electrodes for simultaneous MRI and EEG acquisition is presented. The antenna comprises an active decoupled surface coil for receiving the MR signal and a whole body coil for transmitting the excitation RF pulses. The surface coil offers a high signal-to-noise ratio required for fMRI application and the whole body coil has a good B(1) excitation profile, which enables the application of homogeneous RF pulses. Non-invasive carbon electrodes are used in order to minimise the magnetic susceptibility artefacts that occur upon application of conductive materials. This dedicated set-up is compared to a standard set-up being a linear birdcage coil and commercially available Ag/AgCl electrodes. As the acquired EEG signals are heavily disturbed by the gradient switching, intelligent filtering is applied to obtain a clean EEG signal. 相似文献
995.
van Der Voort M Rella CW van Der Meer LF Akimov AV Dijkhuis JI 《Physical review letters》2000,84(6):1236-1239
We present results of the first vibrational photon-echo, transient-grating, and temperature dependent transient-bleaching experiments on a-Si:H. Using these techniques, and the infrared light of a free electron laser, the vibrational population decay and phase relaxation of the Si-H stretching mode were investigated. Careful analysis of the data indicates that the vibrational energy relaxes directly into Si-H bending modes and Si phonons, with a distribution of rates determined by the amorphous host. Conversely, the pure dephasing appears to be single exponential, and can be modeled by dephasing via two-phonon interactions. 相似文献
996.
A. E. L. Dieperink P. Van Isacker 《The European Physical Journal A - Hadrons and Nuclei》2007,32(1):11-18
We discuss to what extent information on ground-state properties of finite nuclei (energies and radii) can be used to obtain
constraints on the symmetry energy in nuclear matter and its dependence on the density. The starting point is a generalized
Weizs?cker formula for ground-state energies. In particular, effects from the Wigner energy and shell structure on the symmetry
energy are investigated. Strong correlations in the parameter space prevent a clear isolation of the surface contribution.
Use of neutron skin information improves the situation. The result of the analysis appears consistent with a rather soft density
dependence of the symmetry energy in nuclear matter. 相似文献
997.
E. I. Moses R. E. Bonanno C. A. Haynam R. L. Kauffman B. J. MacGowan R. W. Patterson Jr R. H. Sawicki B. M. Van Wonterghem 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,44(2):215-218
The National Ignition Facility (NIF) is a 192-beam laser
facility presently under construction at LLNL. When completed, NIF will be a
1.8-MJ, 500-TW ultraviolet laser system. Its missions are to obtain fusion
ignition and to perform high energy density experiments in support of the
US nuclear weapons stockpile. Four of the NIF beams have been commissioned
to demonstrate laser performance and to commission the target area including
target and beam alignment and laser timing. During this time, NIF
demonstrated on a single-beam basis that it will meet its performance goals
and demonstrated its precision and flexibility for pulse shaping, pointing,
timing and beam conditioning. It also performed four important experiments
for Inertial Confinement Fusion and High Energy Density Science. Presently,
the project is installing production hardware to complete the project in
2009 with the goal to begin ignition experiments in 2010. An integrated plan
has been developed including the NIF operations, user equipment such as
diagnostics and cryogenic target capability, and experiments and
calculations to meet this goal. This talk will provide NIF status, the plan
to complete NIF, and the path to ignition. 相似文献
998.
G. Epurescu G. Dinescu A. Moldovan R. Birjega F. Dipietrantonio E. Verona P. Verardi L.C. Nistor C. Ghica G. Van Tendeloo M. Dinescu 《Superlattices and Microstructures》2007,42(1-6):79
The high exciton binding energy and band gap energy of ZnO thin films open the prospect of fabricating semiconductor lasers in the ultraviolet spectral range. A prerequisite for laser diode fabrication is highly p-doped ZnO which was not reproducibly obtained up to now. Without intentional doping ZnO exhibits n-type conduction. ZnO thin films have been obtained by radio-frequency assisted pulsed laser deposition. A metallic Zn target was used for ablation in an oxygen and nitrogen RF discharge. The electrical and morphological properties of the films grown on Si were studied by Atomic Force Microscopy (AFM), X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), optical absorption and Hall Effect measurements for different ratios between the nitrogen and oxygen content. The AFM images of the as-grown ZnO films reveal high quality surfaces with low values for the surface roughness and a sharp distribution of grains sizes as an effect of the RF discharge. The XRD patterns for all samples exhibit only (002) and (004) peaks indicating that the c-axis is always oriented normal to the substrate surface. The films present p-type conductivity with different carrier concentration and mobility depending on the nitrogen/oxygen ratio. 相似文献
999.
Eric Messens Alfons Lenaerts Marc Van Montagu André De Bruyn Arnold W.H. Jans Georges Van Binst 《Journal of carbohydrate chemistry》2013,32(4):683-699
The 1H NMR data of agrocinopine in D2O solution as extracted from standard 2D NMR experiments, along with 1D 31P and 13C NMR experiments allow to support the trisaccharide structure originally proposed on basis of comparative 13C NMR measurements. 相似文献
1000.
The application of micro-Raman spectroscopy is discussed for the analysis of structural features of human tooth tissues affected by high doses of external ionizing radiation (0.5–1.7 Gy) after the nuclear plant catastrophe in Chernobyl in 1986. The results have shown significant changes in the mineral matrix of dental enamel that lead to the decrease of tooth enamel hardness. Destruction of the collagen chain of the organic matrix has been observed for dentin and cementum. 相似文献