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71.
L. Proville S. Aubry 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(1):41-58
The spatially localized bound states of two electrons in the adiabatic two-dimensional Holstein-Hubbard model on a square
lattice are investigated both numerically and analytically. The interplay between the electron-phonon coupling g, which tends to form bipolarons and the repulsive Hubbard interaction , which tends to break them, generates many different ground-states. There are four domains in the phase diagram delimited by first order transition lines. Except for the domain at weak electron-phonon coupling (small g) where the electrons remain free, the electrons form bipolarons which can 1) be mostly located on a single site (small , large g); 2) be an anisotropic pair of polarons lying on two neighboring sites in the magnetic singlet state (large , large g); or 3) be a “quadrisinglet state” which is the superposition of 4 electronic singlets with a common central site. This quadrisinglet
bipolaron is the most stable in a small central domain in between the three other phases. The pinning modes and the Peierls-Nabarro
barrier of each of these bipolarons are calculated and the barrier is found to be strongly depressed in the region of stability
of the quadrisinglet bipolaron.
Received 10 December 1998 相似文献
72.
Recent achievements and trends of research for geophysical prospection of archaeological sites 总被引:1,自引:0,他引:1
L. Aubry C. Benech E. Marmet A. Hesse 《Journal of Radioanalytical and Nuclear Chemistry》2001,247(3):621-628
Our times are characterized by an increasing need for prospection particularly within the context of rescue archaeology. Geophysics has an important part to play due to its ability to identify some well defined targets as well as to investigate large areas. Several recent surveys, using carefully selected methods chosen in accordance with the type of expected remain or a combination of methods in order to refine or confirm the interpretation, have demonstrated the expertise of several organisations in a wide variety of archaeological contexts. However, important improvements are still to be expected from the laboratories. Our team, working within the framework of three dissertations, is investigating several original subjects, for which the initial results are presented and discussed here: (1) The use of magnetic susceptibility measurements on wide mesh grids in order to survey extensive areas immediately prior to their occupation or destruction by large modern equipment; (2) Experiments to test a new survey device (Slingram - CS150) able to measure the magnetic susceptibility of the ground; (3) Interpretation of a series of geophysical measurements integrated with other types of data into a G.I.S. 相似文献
73.
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76.
Wahlen J De Vos D De Hertogh S Nardello V Aubry JM Alsters P Jacobs P 《Chemical communications (Cambridge, England)》2005,(7):927-929
Lanthanum(III)-exchanged zeolites Beta and USY are active and selective catalysts for the generation of singlet oxygen from H2O2 showing superior activity and oxidant efficiency compared to unsupported La-catalysts, e.g. La(OH)3. 相似文献
77.
N-Boc-protected-5-substituted delta-lactams were readily prepared from the corresponding beta 3-amino acids. Alkylation reactions of their Na enolates with various electrophiles proceeded in high yields with high facial selectivity. The structure of the alkylation products was confirmed by single-crystal X-ray analysis. This method provides a fast access to optically active alpha, delta-disubstituted delta-amino acids. 相似文献
78.
Two water soluble1O2 traps: dipotassium 1,3 - diphenylisobenzofuran - 5,6 - dicar?ylate and tetrapotassium 9,10 - diphenylanthracene - 2,3,6,7 - tetracar?ylate have been prepared in good yields and a new access to the anthracene skeleton is described. The key-step of this synthesis consists of a cycloaddition between 1,3 - diphenylisobenzofurans and dimethyl 7 - oxabicyclo[2.2.1] - 5 - heptene - 2,3 - dicar?ylate; the adducts thus obtained undergo dehydration to afford the corresponding anthracenes. 相似文献
79.
80.
M. Johansson A.M. Morgante S. Aubry G. Kopidakis 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(2):279-283
Modulational instability of travelling plane waves is often considered as the first step in the formation of intrinsically
localized modes (discrete breathers) in anharmonic lattices. Here, we consider an alternative mechanism for breather formation,
originating in oscillatory instabilities of spatially periodic or quasiperiodic nonlinear standing waves (SWs). These SWs
are constructed for Klein-Gordon or Discrete Nonlinear Schr?dinger lattices as exact time periodic and time reversible multibreather
solutions from the limit of uncoupled oscillators, and merge into harmonic SWs in the small-amplitude limit. Approaching the
linear limit, all SWs with nontrivial wave vectors (0 < Q < π) become unstable through oscillatory instabilities, persisting for arbitrarily small amplitudes in infinite lattices.
The dynamics resulting from these instabilities is found to be qualitatively different for wave vectors smaller than or larger
than π/2, respectively. In one regime persisting breathers are found, while in the other regime the system thermalizes.
Received 6 October 2001 / Received in final form 1st March 2002 Published online 2 October 2002
RID="a"
ID="a"e-mail: mjn@ifm.liu.se 相似文献