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排序方式: 共有311条查询结果,搜索用时 15 毫秒
1.
We investigate the dynamics of the Λ system driven by two resonant laser fields in presence of dissipation for coupling strengths where the rotating‐wave approximation starts to break down. This regime is characterised by Rabi frequencies being approximately equal or smaller than the field frequencies. A systematic procedure to obtain an expansion for the solution of the Bloch evolution equations of the system is presented. The lowest contribution results to be the well‐known rotating‐wave approximation. The method is based on a semi‐classical treatment of the problem, and its predictions are interpreted fully quantum mechanically. The theory is illustrated by a detailed study of the disappearance of coherent population trapping as the intensities of the fields increase. 相似文献
2.
It is shown that the dephasing which suppresses the weak localization correction to the conductivity has the same physical origin than pair-breaking in superconductors and thus-following de Gennes-may be expressed in terms of the correlation function of the operator for time reversal. 相似文献
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4.
Gudrun Thter 《Mathematical Methods in the Applied Sciences》2002,25(10):875-894
The Neumann problem is crucial in mathematical physics. Nevertheless, as far as cylindrical domains are concerned there is still the open question how to construct solutions to data in usual Sobolev spaces since the standard Kondratiev theory does not apply. In this paper that unsatisfactory gap is filled and moreover, data with polynomial asymptotic behaviour are considered. As interesting special case we find solutions with bounded Dirichlet integral. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
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Matthew M. Malwitz Paul D. Butler Lionel Porcar Drew P. Angelette Gudrun Schmidt 《Journal of polymer science. Part A, Polymer chemistry》2004,42(17):3102-3112
The influence of shear on viscoelastic solutions of poly(ethylene oxide) (PEO) and clay [montmorillonite, i.e., Cloisite NA+ (CNA)] was investigated with rheology and small-angle neutron scattering (SANS). The steady-state viscosity and SANS were used to measure the shear-induced orientation and relaxation of the polymer and clay platelets. Anisotropic scattering patterns developed at much lower shear rates than in pure clay solutions. The scattering anisotropy saturated at low shear rates, and the CNA clay platelets aligned with the flow, with the surface normal parallel to the gradient direction. The cessation of shear led to partial and slow randomization of the CNA platelets, whereas extremely fast relaxation was observed for laponite (LRD) platelets. These PEO–CNA networklike solutions were compared with previously reported PEO–LRD networks, and the differences and similarities, with respect to the shear orientation, relaxation, and polymer–clay interactions, were examined. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3102–3112, 2004 相似文献
7.
Doz. Dr. Karl Gewald Gudrun Heinhold 《Monatshefte für Chemie / Chemical Monthly》1976,107(6):1413-1421
The alkylation of arylaminomethylenecyanamides1 or cyano-imidothiocarbamates2 with -halogen carbonyl compounds followed by base catalysed cyclization yields substituted 4-amino-imidazoles4. Imidazo[4,5-d]pyrimidones5, 6 and imidazo[4,5-b]pyridines7 can be obtained from4. 相似文献
8.
Meinhard Wlaschek Gudrun Heinen Arndt Poswig Agatha Schwarz Thomas Krieg Karin Scharffetter-Kochanek 《Photochemistry and photobiology》1994,59(5):550-556
Abstract— Previous work has shown that fibroblast-derived collagenase/matrix-metalloproteinase-1(MMP–1), responsible for the breakdown of dermal interstitial collagen, was dose-dependently induced in vitro and in vivo by UVA irradiation and this induction was at least partly mediated byinterleukin–6(IL–6). We here provide evidence that UVA-inducedIL–1α andIL–1β play a central role in the induction of the synthesis both ofIL–6 and collagenase/MMP–1. In contrast to the late increase ofIL–1α andIL–1β mRNA levels at 6 h postirradiation, bioactivity ofIL–1 is already detectable at 1 h postirradiation. This early peak ofIL–1 bioactivity appears to be responsible for the induction ofIL–6 synthesis and together withIL–6 lead to an increase of the steady-state mRNA level of collagenase/MMP–1 as deduced from studies usingIL–1α andIL–1β antisense oligonucleotides or neutralizing antibodies againstIL–1α andIL–1β Besides the early posttranslationally controlled release of intracellularIL–1, a latter pretranslationally controlled synthesis and release ofIL–1 perpetuates the UV response. From these data we suggest a UV-induced cytokine network consisting ofIL–1α,IL–1β andIL–6, which via interrelated autocrine loops induce collagenase/MMP–1 and thus may contribute to the loss of interstitial collagen in cutaneous photoaging. 相似文献
9.
Dietmar Brandes 《Journal of organometallic chemistry》1977,136(1):25-31
Novel organylthio(alkoxy)silanes (I, II, III and XII) and organylthio(diethylamino)silanes (IV, V) are described. They were prepared by treating lithium or lead thiolates with the corresponding chlorosilanes or by cleavage of dimethylbis(diethylamino)silane with thiols. Phenylthiosilanes (Me3SiSPh, III and XIII) furthermore can be obtained by reaction of chlorosilanes with benzenethiol in the presence of tertiary amines. The SiS bond of Me3SiSPh is cleaved by chlorosilanes like Me2Si(NEt2)Cl or Me2Si(OPr)Cl. This reaction is a convenient route to prepare compounds I and IV. The physical and chemical properties of the novel compounds were investigated. 相似文献
10.
Gudrun Albrecht 《Journal of Geometry》1994,50(1-2):1-10
In 1809 J. IVORY found a distance relation between any two confocal ellipsoids in Euclidean space E3. After that, the theorem of IVORY has been formulated for any two nondegenerate confocal quadrics of the same type. In this paper we succeed in completing these results and in formulating and proving them uniformly for any two quadrics of the same type belonging to a general system of confocal quadrics.
Herrn Prof. Dr. Oswald Giering zum 60. Geburtstag gewidmet 相似文献
Herrn Prof. Dr. Oswald Giering zum 60. Geburtstag gewidmet 相似文献