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91.
The exciton-exciton interaction is investigated for spatially indirect excitons in coupled quantum wells. The Hartree-Fock and Heitler-London approaches are improved by a full two-exciton calculation including the van der Waals effect. Using these potentials for the singlet and triplet channel, the two-body scattering matrix is calculated and employed to derive a modified relation between exciton density and blue shift. Such a relation is of central importance for gauging exciton densities on the way toward Bose condensation. 相似文献
92.
Amitesh Paul Thomas KristAnke Teichert Roland Steitz 《Physica B: Condensed Matter》2011,406(8):1598-1606
We report on the enhanced capabilities of neutron reflectometer V6 at the research reactor BER II at Helmholtz-Zentrum Berlin für Materialien und Energie (HZB) in investigating magnetic thin films and multilayers. It is now fully equipped for simultaneous measurements of specular and off-specular scattering with polarization and polarization analysis. The magnetization configuration of a [CoO/Co/Au]×16 polycrystalline multilayer at room temperature is reported in demonstrating the efficiency of the instrument. The data is simulated within the supermatrix formalism under the distorted wave Born approximation for a quantitative analysis. 相似文献
93.
Nikolaev S Nilsson P Nishimura S Nomokonov P Nystrand J Obenshain FE Oskarsson A Otterlund I Pachr M Pavliouk S Peitzmann T Petracek V Pinganaud W Plasil F Poblotzki U Purschke ML Rak J Raniwala R Raniwala S Ramamurthy VS Rao NK Retiere F Reygers K Roland G Rosselet L Roufanov I 《Physical review letters》2000,85(17):3595-3599
A measurement of direct photon production in 208Pb+208Pb collisions at 158A GeV has been carried out in the CERN WA98 experiment. The invariant yield of direct photons in central collisions is extracted as a function of transverse momentum in the interval 0.5
1.5 GeV/c. The result constitutes the first observation of direct photons in ultrarelativistic heavy-ion collisions. It could be significant for diagnosis of quark-gluon-plasma formation. 相似文献
94.
Roland Kaschek 《Discrete Mathematics》2010,310(8):1275-1281
This paper proves a necessary and sufficient condition for the endomorphism monoid of a lexicographic product G[H] of graphs G,H to be the wreath product of the monoids and . The paper also gives respective necessary and sufficient conditions for specialized cases such as for unretractive or triangle-free graphs G. 相似文献
95.
96.
It is shown that if the edges of a 2-connected graph G are partitioned into two classes so that every vertex is incident with edges from both classes, then G has an alternating cycle. The connectivity assumption can be dropped if both subgraphs resulting from the partition are regular, or have only vertices of odd degree. 相似文献
97.
Dr. Kevin Pappert Dr. Kateryna Loza Dr. Meital Shviro Dr. Ulrich Hagemann Dr. Marc Heggen Prof. Dr. Rafal E. Dunin-Borkowski Dr. Roland Schierholz Dr. Takuya Maeda Prof. Dr. Kenji Kaneko Prof. Dr. Matthias Epple 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(47):11048-11057
Porous particle superstructures of about 15 nm diameter, consisting of ultrasmall nanoparticles of iridium and iridium dioxide, are prepared through the reduction of sodium hexachloridoiridate(+IV) with sodium citrate/sodium borohydride in water. The water-dispersible porous particles contain about 20 wt % poly(N-vinylpyrrolidone) (PVP), which was added for colloidal stabilization. High-resolution transmission electron microscopy confirms the presence of both iridium and iridium dioxide primary particles (1–2 nm) in each porous superstructure. The internal porosity (≈58 vol%) is demonstrated by electron tomography. In situ transmission electron microscopy up to 1000 °C under oxygen, nitrogen, argon/hydrogen (all at 1 bar), and vacuum shows that the porous particles undergo sintering and subsequent compaction upon heating, a process that starts at around 250 °C and is completed at around 800 °C. Finally, well-crystalline iridium dioxide is obtained under all four environments. The catalytic activity of the as-prepared porous superstructures in electrochemical water splitting (oxygen evolution reaction; OER) is reduced considerably upon heating owing to sintering of the pores and loss of internal surface area. 相似文献
98.
Anna Boisits Roland Königsgruber 《Central European Journal of Operations Research》2016,24(1):177-205
In this paper we analyze a model which addresses two stylized facts which have received little attention in disclosure theory. (a) Information that is acquired for internal decision-making can subsequently be disclosed to outside investors who can use it to update their assessment of the firm’s prospects. Thus, the decision to gather information in the first place does not only depend on the decision value of information. (b) Information disclosed by firms is only one element of the information environment upon which investors can draw. This setting creates an interaction between firms’ information gathering and disclosure decisions as well as alternative sources of information. We identify an equilibrium structure which we call a Countersignaling equilibrium in which only average firms acquire information whereas good and bad firms do not. We show that while several equilibria can coexist, a Countersignaling equilibrium is often the economically most efficient one. 相似文献
99.
Letf(n) be the smallest integer such that every tournament of orderf(n) contains every oriented tree of ordern. Sumner has just conjectures thatf(n)=2n–2, and F. K. Chung has shown thatf(n)(1+o(1))nlog2
n. Here we show thatf(n)12n andf(n)(4+o(1))n. 相似文献
100.
Alkali‐free Cu(In,Ga)Se2(CIGS) absorbers grown on Mo‐coated alumina (Al2O3) substrates were doped with potassium (K) after CIGS growth by a potassium fluoride (KF) post‐deposition treatment (PDT). The addition of K to the absorber leads to a strong increase in cell efficiency from 10.0% for the K‐free cell to 14.2% for the K‐doped cell, mainly driven by an increase in the open‐circuit voltage Voc and the fill factor FF, and to an increase in the net charge carrier density. Hence K doping by KF‐PDT is comparable to doping with Na.