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111.
We investigate the electronic and ionic dynamics of Na clusters under the influence of a laser pulse in the range 100 femtoseconds
to picoseconds. The dynamics is described by means of the time-dependent local-density approximation coupled to ionic molecular
dynamics (TDLDA-MD). Variation of pulse length allows us to explore the time scales of ionic motion in a manner similar to
pump and probe experiments. Resonant enhancement of electron emission serves as a measure for the time scale of Coulomb explosion.
Received: 3 July 2001 / Published online: 10 October 2001 相似文献
112.
G. Carotenuto S. DeNicola G.P. Pepe L. Nicolais 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(4):437-441
A simple and high-reproducible method for the synthesis of polymer-protected silver cluster of controlled size is described.
UV-visible spectroscopy has been used for investigating the influence of the aging of the protective poly(vinylpyrrolidone)
layer on the cluster growth rate at different reaction temperatures and poly(vinylpyrrolidone)/ethylene glycol weight ratios.
The obtained results show that the aging time of the polymeric stabilizer solution plays a fundamental role in the reproducibility
of the cluster growth process. A model for the metal cluster formation-grow process is also proposed.
Received 18 July 2001 and Received in final form 3 October 2001 相似文献
113.
B. Fisher J. Genossar K.B. Chashka L. Patlagan G.M. Reisner 《Solid State Communications》2006,137(12):641-644
Electrical conductivities with temperature dependencies of the type σ(T)−σ(0)∝Tp are remarkable when measurements over extended ranges of T show that p=1 or 2 over wide ranges of σ. We report on such behaviors for inter-grain conductivities of polycrystalline Sr2CrMoO6 samples. We show that for certain ranges of parameters the ‘fluctuation induced tunneling’ model fits these dependencies very well. 相似文献
114.
Oxidative (δ>0) nonstoichiometry in the perovskite ‘LaMnO3+δ’ has been known to be manifested not with O interstitials but rather with cation vacancies of equal amounts at the two cation sites, La and Mn, i.e. La1−xMn1−yO3 with x=y. Here, we report the fabrication of samples with record-high cation-vacancy concentrations (x>0.12 or δ>0.4) by means of a variety of high-pressure oxygenation techniques. Linear (negative) dependence of the cell volume on x was observed within the whole x range investigated, down to 56.9 Å3 (per formula unit) for a sample oxygenated at 5 GPa and 1100 °C using Ag2O2 as an excess oxygen source. With increasing degree of cation deficiency in La1−xMn1−xO3, the ferromagnetic transition temperature was found to follow a bell shape with respect to x exhibiting a maximum of ∼250 K about x≈0.1. For moderately oxygenated samples large magnetoresistance effect was evidenced. 相似文献
115.
We study magnetoresistance (MR) and interlayer exchange coupling (IEC) in perovskite manganite junctions. We show that in La2/3Sr1/3MnO3/SrTiO3/La2/3Sr1/3MnO3 tunneling junctions, the MR ratio remains finite up to high temperatures near TC of bulk manganites. In the case of La2/3Ba1/3MnO3/LaNiO3/La2/3Ba1/3MnO3 metallic trilayers, we predict that the oscillation period of the IEC constant is dramatically changed by hole doping into the LaNiO3 spacer, while the MR ratio is relatively unaffected. 相似文献
116.
J. Favand F. Mila 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(3):293-299
In order to study the tunneling of electrons through an interacting, 1D, dimerized molecule connected to leads, we consider
the persistent current in a ring embedding this molecule. We find numerically that, for spinless fermions, a molecule with
a gap mostly due to interactions, i.e. a Mott-Hubbard gap, gives rise to a larger persistent current than a molecule with the same gap, but due only to the dimerization.
In both cases, the tunneling current decreases exponentially with the size of the molecule, but more slowly in the interacting
case. Implications for molecular electronic are briefly discussed.
Received: 17 November 1997 / Revised: 16 January 1998 /
Accepted: 16 January 1998 相似文献
117.
X.L. Zhang Y.G. ZhaoY.H. Sun S.N. GaoP.L. Lang X.P. ZhangM.H. Zhu 《Journal of magnetism and magnetic materials》2006
The electroresistance (ER) of La0.67Ca0.33MnO3 (LCMO) epitaxial thin films with different thicknesses was studied. For the 110 nm thick LCMO film, its ER shows a maximum at Tp, where the resistance shows a peak, and decreases to zero at lower temperatures. While for the 30 nm thick LCMO film, its ER is remarkable in a wide temperature range. Another interesting observation in this work is that the electric current can tune the magnetoresistance of the ultrathin LCMO thin film. The results were discussed by considering the coexistence of ferromagnetic metallic phase with the charge ordered phase, and the variation of the phase separation with film thickness and electric current. This work also demonstrates that electric current can tune the magnetoresistance of the manganites, which is helpful for their applications. 相似文献
118.
X.H. Zhang Z.Q. Li W. Song P. Wu H.L. Bai E.Y. Jiang 《Solid State Communications》2005,135(6):356-360
The structural and magnetic properties of Pr0.75Na0.25MnO3 have been investigated experimentally. At room temperature, the compound shows paramagnetic characteristic. Along with decreasing temperature, a peak appears in the magnetization versus temperature curve around 220 K. To clarify whether this peak is associated with the ordering arrangement of Mn3+ and Mn4+ ions, electron diffraction experiments were carried out below and above 220 K respectively. Only basic Brag diffraction spots can be observed at high temperatures, however, superlattice diffraction appears below 220 K. This provides direct evidence for the existence of charge ordering in Pr0.75Na0.25MnO3. We find the Mn3+ and Mn4+ cations form zigzag chains in a-c plane by analyzing the diffraction patterns. Combining with the magnetization measurements and the results of electron spin resonance, we confirm the antiferromagnetic phase and ferromagnetic component coexist in Pr0.75Na0.25MnO3 below 120 K. 相似文献
119.
B. Tatischeff J. Yonnet M. Boivin M.P. Comets P. Courtat R. Gacougnolle Y. Le Bornec E. Loireleux M. MacCormick F. Reide N. Willis 《The European Physical Journal A - Hadrons and Nuclei》2003,17(2):245-267
The reaction pp → pπ+
X was studied at different incident energies around T
p = 2 GeV. Narrow baryonic structures were observed in the missing mass M
X and in the invariant mass M
pπ{+}. The masses of these structures are 1004, 1044, 1094, 1136, 1173, 1249, 1277, and 1384 MeV (and possibly 1339 MeV). Some
of them were also observed at the same masses in the missing-mass spectra of the dp → ppX reaction although with a weaker
signature. Many checks were performed to make sure that these structures were not produced by experimental artifacts. Several
narrow small-amplitude peaks, were also extracted using already published photonucleon cross-sections. The small widths of
all these results, and the stability of the observed structures, regardless of the experiment, were used to conclude that
they are genuine baryons and not merely the consequence of dynamical rescatterings. These baryons cannot be associated with
classical q3 quark configurations. We associate them with two colored-quark cluster configurations.
Received: 3 July 2002 / Accepted: 30 January 2003 / Published online: 5 June 2003 相似文献
120.
Feng Zhai Yong Guo Bing-Lin Gu 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(1):147-152
We adopt the group velocity approach to the issue of tunneling time in two configurations of magnetic barrier structures,
which are arranged with identical or unidentical building blocks. The effects of an external electric field are also taken
into account. The tunneling time in magnetic barrier structures is found to be strongly dependent on the magnetic configuration,
the applied bias, the incident energy as well as the longitudinal wave vector. The results indicate that for electrons with
equal energy but different incident angles, the tunneling processes are significantly separated in time within the same magnetic
barrier structure. In the configuration arranged with unidentical building blocks, there exists obvious asymmetry of tunneling
time in two opposite tunneling directions. Such a discrepancy of the tunneling time varies distinctly with the longitudinal
wave vector and the applied bias.
Received 4 March 2002 / Received in final form 22 May 2002 Published online 17 September 2002 相似文献