排序方式: 共有157条查询结果,搜索用时 31 毫秒
81.
Doppler profile spectroscopy and Compton-to-peak ratio analysis have been used to study the positronium (Ps) emission from the Kapton surface as a function of the positron implantation energy E.Two different positions for the sample have been performed in the experiment.In the first case the sample and the Ge-detector are perpendicular to the positron beam. With this geometry the emission of para-positronium (p-Ps) is detected as a narrow central peak.In the second case, by rotating the sample 45° with respect to the beam axis, the emission of p-Ps is detected as a blue-shifted fly away peak. The implantation of the positrons is described by the Makhov profile, where we used the modified median implantation for polymers as given by Algers et al. [J. Algers, P. Sperr, W. Egger, G. Kögel, F.H.J. Maurer, Phys. Rev. B 67 (2003) 125404].Thermalised positrons can diffuse to the surface and may pick up an electron to be emitted as Ps. We found a thermal and or epithermal positron diffusion length L+ = 5.43 ± 0.71 nm and L+ = 5.51 ± 0.28 nm correspondingly for both cases, which is much more than the one found by Brusa et al. [R.S. Brusa, A. Dupasquier, E. Galvanetto, A. Zecca, Appl. Phys. A 54 (1992) 233]. The respective efficiency for the emission of Ps by picking up an electron from the surface is found to be fpu = 0.247 ± 0.012 and fpu = 0.156 ± 0.003. 相似文献
82.
A. Politano 《Applied Surface Science》2008,254(21):6854-6859
The adsorption of alkalis (Na, K) on Ni(1 1 1) and their coadsorption with CO and O were studied by high-resolution electron energy loss spectroscopy. Loss measurements of clean alkali adlayers provided the expected behaviour of the alkali-substrate vibration energy as a function of the alkali coverage. This result was achieved by eliminating any trace of CO contamination from the alkali adlayer. As a matter of fact, a significant softening of the alkali-Ni vibration energy was revealed in the alkali + CO coadsorbed phase. Moreover, alkali coadsorption with oxygen caused a weakening of the ONi bond and a strengthening of the alkaliNi bond. 相似文献
83.
High resolution mode-selective excitation in the mixture of C6H6 (992 cm^-1) and C6D6 (945 cm^-1) is experimentally achieved by adaptive femtosecond pulse shaping based on the genetic algorithm (GA), and second harmonic generation frequency-resolved optical gating (SHG-FROG) is adopted to characterize the original and optimal laser pulses, and its mechanism is experimentally validated by tailoring the frequency components of the pump pulses at the Fourier plane. It is indicated that two-pulse coherent mode-selective excitation of the Raman scattering mainly depends on the effective frequency components of the pump pulse related to specific molecular vibrational mode. The experimental results have attractive potential applications in the complicated molecular system. 相似文献
84.
Critical impact velocity (CIV) of oxygen-free high-conductivity (OFHC) copper is experimentally measured with a novel facility in a gas gun system. The results are compared with the theoretical predictions using the typical constitutive relations, and the measured CIV value is much lower than the predictions. The difference of physical mechanisms in experiment and in theoretical calculation is discussed. It is suggested that the reduction of CIV in experiment would be related with the damage evolution in tensile copper that needs to be considered in the computation model. 相似文献
85.
The hydration structure properties of different alkali metal ions with eight water molecules and potassium ions with different numbers of water molecules are studied using the mixed density functional theory, B3LYP, with 6-3110 basis set. The hydration structures are obtained from structure optimization and the optimum numbers of water molecules in the innermost hydration shell for the alkali metal ions are found. Some useful information about the ion channel selectivity is presented. 相似文献
86.
O. Lopez A. Amy-Klein C. Daussy C. Chardonnet F. Narbonneau M. Lours G. Santarelli 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,48(1):35-41
RF frequency transfer over an urban 86 km fibre has
been demonstrated with a resolution of 2×10-18 at one day
measuring time using an optical compensator. This result is obtained with a
reference carrier frequency of 1 GHz, and a rapid scrambling of the
polarisation state of the input light in order to reduce the sensitivity to
the polarisation mode dispersion in the fibre. The limitation due to the
fibre chromatic dispersion associated with the laser frequency fluctuations
is highlighted and analyzed. A preliminary test of an extended compensated
link over 186 km using optical amplifiers gives a resolution below
10-17 at 1 day. 相似文献
87.
The effects of the solvent-surfactant interaction, chain length and stiffness of surfactants on the formation of aggregates
and the aggregation degree of surfactants in the two-dimension solution have been investigated using discontinuous molecular-dynamics
simulations. When the tail-water repulsion increases or the head-water attraction decreases, the aggregation degree increases.
Increasing the chain length and raising the stiffness of surfactants lead to the increment of the aggregation degree.
Received 25 July 2001 and Received in final form 7 May 2002 相似文献
88.
Bellour M Skouri M Munch JP Hébraud P 《The European physical journal. E, Soft matter》2002,8(4):431-436
We have measured the mean-square displacement of colloidal particles embedded in a semi-dilute solution of worm-like micelles,
using diffusing wave spectroscopy. This allowed us to describe their rheological properties over a very wide time range. At
very short times, the particles diffuse freely in the solvent, and then, they experience the characteristic relaxation times
of the living chains. We deduced directly, from the mean-square displacement of the particles, the mechanical properties of
the micellar solution, not only in the high-frequency regime, but also in the low-frequency range, in which we compared our
results with direct mechanical measurements, and found good agreement.
Received 22 March 2002 and Received in final form 5 June 2002 相似文献
89.
Takayuki Iwasaki Tasuku Maki Daisuke Yokoyama Hironori Kumagai Yasuhiro Hashimoto Takuma Asari Hiroshi Kawarada 《固体物理学:研究快报》2008,2(2):53-55
Vertically aligned double‐walled carbon nanotubes (DWCNTs) with the highest selectivity of 90% were synthesized by a controlled heating method and their electric double‐layer capacitor characteristics were evaluated. DWCNT arrays had a specific capacitance of 83 F/g, which is one of the highest values among CNT arrays in a nonaqueous solution and is almost equivalent to that for single‐walled CNT (SWCNT) arrays reported previously. At the same specific capacitance, DWCNTs with superior structural properties are more promising for practical capacitors than SWCNTs. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
90.
One-dimensional Si quantum wires have been grown on silver single crystals upon deposition of ∼0.25 monolayer of Si on Ag(1 1 0) surfaces. Scanning tunneling microscopy (STM) clearly shows parallel 1D Si chains along the [−1 1 0] Ag crystallographic direction. Low Energy Electron Diffraction (LEED) confirms the massively parallel assembly of these selforganized Nanowires (NWs). We have characterized these nano-objects by measuring the dispersion of the NWs valence band at room temperature using Angle-Resolved PhotoEmission Spectroscopy (ARPES). Also, the Fermi Surface (FS) of the Ag(1 1 0) substrate has been mapped before and after the silicon deposition, trying to put in evidence the metallic or semiconductor character of the NWs silicon's states close to the Fermi level. Our results show the existence of well-defined quantum states associated to the silicon super-structure. Both LEED and ARUPS results confirm that the NWs have typical 1D features, however their metallic or semiconductor character could not be confirmed. 相似文献