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61.
We investigate the dependence of the intensity of radiation due to high-harmonic generation as a function of the wavelength lambda of the fundamental driver field. Superimposed on a smooth power-law dependence observed previously, we find surprisingly strong and rapid fluctuations on a fine lambda scale. We identify the origin of these fluctuations in terms of quantum path interferences with up to five returning orbits significantly contributing. 相似文献
62.
The Steiner connectivity problem has the same significance for line planning in public transport as the Steiner tree problem for telecommunication network design. It consists in finding a minimum cost set of elementary paths to connect a subset of nodes in an undirected graph and is, therefore, a generalization of the Steiner tree problem. We propose an extended directed cut formulation for the problem which is, in comparison to the canonical undirected cut formulation, provably strong, implying, e.g., a class of facet defining Steiner partition inequalities. Since a direct application of this formulation is computationally intractable for large instances, we develop a partial projection method to produce a strong relaxation in the space of canonical variables that approximates the extended formulation. We also investigate the separation of Steiner partition inequalities and give computational evidence that these inequalities essentially close the gap between undirected and extended directed cut formulation. Using these techniques, large Steiner connectivity problems with up to 900 nodes can be solved within reasonable optimality gaps of typically less than five percent. 相似文献
63.
Feist J Bäcker A Ketzmerick R Rotter S Huckestein B Burgdörfer J 《Physical review letters》2006,97(11):116804
We investigate electronic quantum transport through nanowires with one-sided surface roughness. A magnetic field perpendicular to the scattering region is shown to lead to exponentially diverging localization lengths in the quantum-to-classical crossover regime. This effect can be quantitatively accounted for by tunneling between the regular and the chaotic components of the underlying mixed classical phase space. 相似文献
64.
Deiss C Rohringer N Burgdörfer J Lamour E Prigent C Rozet JP Vernhet D 《Physical review letters》2006,96(1):013203
We investigate the heating of the quasifree electrons in large rare-gas clusters (N exceeding 10(5) atoms) by short laser pulses at moderate intensities (I approximately = 10(15) W cm(-2)). We identify elastic large-angle backscattering of electrons at ionic cores in the presence of a laser field as an efficient heating mechanism. Its efficiency as well as the effect of collective electron motion, electron-impact ionization, and cluster charging are studied employing a mean-field classical transport simulation. Results for the absolute x-ray yields are in surprisingly good quantitative agreement with recent experimental results. 相似文献
65.
Mestayer JJ Wyker B Lancaster JC Dunning FB Reinhold CO Yoshida S Burgdörfer J 《Physical review letters》2008,100(24):243004
We demonstrate a protocol to create localized wave packets in very-high-n Rydberg states which travel in nearly circular orbits around the nucleus. Although these wave packets slowly dephase and eventually lose their localization, their motion can be monitored over several orbital periods. These wave packets represent the closest analog yet achieved to the original Bohr model of the hydrogen atom, i.e., an electron in a circular classical orbit around the nucleus. The possible extension of the approach to create "planetary atoms" in highly correlated stable multiply excited states is discussed. 相似文献
66.
Kotulla M Trnka D Mühlich P Anton G Bacelar JC Bartholomy O Bayadilov D Beloglazov YA Bogendörfer R Castelijns R Crede V Dutz H Ehmanns A Elsner D Ewald R Fabry I Fuchs M Essig K Funke Ch Gothe R Gregor R Gridnev AB Gutz E Höffgen S Hoffmeister P Horn I Hössl J Jaegle I Junkersfeld J Kalinowsky H Klein F Klein F Klempt E Konrad M Kopf B Krusche B Langheinrich J Löhner H Lopatin IV Lotz J Lugert S Menze D Messchendorp JG Mertens T Metag V Mosel U Nanova M Novotny R Ostrick M Pant LM van Pee H 《Physical review letters》2008,100(19):192302
Information on hadron properties in the nuclear medium has been derived from the photoproduction of omega mesons on the nuclei C, Ca, Nb, and Pb using the Crystal Barrel/TAPS detector at the ELSA tagged photon facility in Bonn. The dependence of the omega-meson cross section on the nuclear mass number has been compared with three different types of models: a Glauber analysis, a Boltzmann-Uehling-Uhlenbeck analysis of the Giessen theory group, and a calculation by the Valencia theory group. In all three cases, the inelastic omega width is found to be 130-150 MeV/c(2) at normal nuclear matter density for an average 3-momentum of 1.1 GeV/c. In the rest frame of the omega meson, this inelastic omega width corresponds to a reduction of the omega lifetime by a factor approximately 30. For the first time, the momentum dependent omegaN cross section has been extracted from the experiment and is in the range of 70 mb. 相似文献
67.
Alexander Schindler Reinhard K nig Thomas Herrmannsd rfer 《Physica B: Condensed Matter》2000,280(1-4):247-248
Superconductivity of compressed, high-purity platinum powder (average grain size 2–3 μm) was found by measurements of resistivity, AC susceptibility and magnetization. The transition temperature into the superconducting state Tc and the critical magnetic field Bc strongly depend on the packing fraction f of the samples: we found 0.62Tc(0)1.38 mK and 6.6Bc(0)67 μT for 0.8f0.5, respectively. The temperature dependence of the critical magnetic fields can be described by Bc(T)=Bc(0)(1−(T/Tc)2). The discussion of these results includes possible explanations for the origin of superconductivity in this new superconducting material. 相似文献
68.
This paper is about set packing relaxations of combinatorial optimization problems associated with acyclic digraphs and linear orderings, cuts and multicuts, and set
packings themselves. Families of inequalities that are valid for such a relaxation as well as the associated separation routines
carry over to the problems under investigation.
Received: September 1997 / Accepted: November 1999?Published online June 8, 2000 相似文献
69.
Helmut Werner Ulrich Schmidt Birgit Weberndrfer Carsten D. Brandt 《无机化学与普通化学杂志》2002,628(11):2383-2394
Mono‐ and Dinuclear Rhodium Complexes with Arsino(phosphino)methanes in Different Coordination Modes The cyclooctadiene complex [Rh(η4‐C8H12)(κ2‐tBu2AsCH2PiPr2)](PF6) ( 1a ) reacts with CO and CNtBu to give the substitution products [Rh(L)2(κ2‐tBu2AsCH2PiPr2)](PF6) ( 2 , 3 ). From 1a and Na(acac) in the presence of CO the neutral compound [Rh(κ2‐acac)(CO)(κ‐P‐tBu2AsCH2PiPr2)] ( 4 ) is formed. The reactions of 1a , the corresponding B(ArF)4‐salt 1b and [Rh(η4‐C8H12)(κ2‐iPr2AsCH2PiPr2)](PF6) ( 5 ) with acetonitrile under a H2 atmosphere affords the complexes [Rh(CH3CN)2(κ2‐R2AsCH2PiPr2)]X ( 6a , 6b , 7 ), of which 6a (R = tBu; X = PF6) gives upon treatment with Na(acac‐f6) the bis(chelate) compound [Rh(κ2‐acac‐f6)(κ2‐tBu2AsCH2PiPr2)] ( 8 ). From 8 and CH3I a mixture of two stereoisomers of composition [Rh(CH3)I(κ2‐acac‐f6)(κ2‐tBu2AsCH2PiPr2)] ( 9/10 ) is generated by oxidative addition, and the molecular structure of the racemate 9 has been determined. The reactions of 1a and 5 with CO in the presence of NaCl leads to the formation of the “A‐frame” complexes [Rh2(CO)2(μ‐Cl)(μ‐R2AsCH2PiPr2)2](PF6) ( 11 , 12 ), which have been characterized crystallographically. From 11 and 12 the dinuclear substitution products [Rh2(CO)2(μ‐X)(μ‐R2AsCH2PiPr2)2](PF6) ( 13 ‐ 16 ) are obtained by replacing the bridging chloride for bromide, hydride or hydroxide, respectively. While 12 (R = iPr) reacts with NaI to give the related “A‐frame” complex 18 , treatment of 11 (R = tBu) with NaI yields the mononuclear chelate compound [RhI(CO)(κ2‐tBu2AsCH2PiPr2)] ( 20 ). The reaction of 20 with CH3I affords the acetyl complex [RhI2{C(O)CH3}(κ2‐tBu2AsCH2PiPr2)] ( 21 ) with five‐coordinate rhodium atom. 相似文献
70.