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51.
52.
The freezing transition of a network model for tensionless membranes confined to two dimensions is investigated by Monte Carlo
simulations and scaling arguments. In this model, a freezing transition is induced by reducing the tether length. Translational
and bond-orientational order parameters and elastic constants are determined as a function of the tether length. A finite-size
scaling analysis is used to show that the crystal melts via successive dislocation and disclination unbinding transitions, in qualitative agreement with the predictions of the Kosterlitz-Thouless-Halperin-Nelson-Young
theory. The hexatic phase is found to be stable over only a very small interval of tether lengths.
Received 4 June 1999 and Revised in final form 1 September 1999 相似文献
53.
54.
Exploiting a set of generalized parton distributions (GPDs) derived from analyses of hard exclusive leptoproduction of ρ 0, φ and π + mesons, we investigate the ω spin density matrix elements (SDMEs) recently measured by the HERMES Collaboration. It turns out, from our study, that the pion pole is an important contribution to ω production. It will be treated as a one-particle exchange since its evaluation from the GPD \(\tilde E\) considerably underestimates its contribution. As an intermediate step of our analysis, we extract the πω transition form factor for photon virtualities less than 4 GeV2. From our approach we achieve results for the ω SDMEs in good agreement with the HERMES data. The role of the pion pole in exclusive ρ 0 and φ leptoproduction is discussed too. 相似文献
55.
U. Masood M. Bussmann T. E. Cowan W. Enghardt L. Karsch F. Kroll U. Schramm J. Pawelke 《Applied physics. B, Lasers and optics》2014,117(1):41-52
The recent advancements in the field of laser-driven particle acceleration have made Laser-driven Ion Beam Therapy (L-IBT) an attractive alternative to the conventional particle therapy facilities. To bring this emerging technology to clinical application, we introduce the broad energy assorted depth dose deposition model which makes efficient use of the large energy spread and high dose-per-pulse of Laser Accelerated Protons (LAP) and is capable of delivering homogeneous doses to tumors. Furthermore, as a key component of L-IBT solution, we present a compact iso-centric gantry design with 360° rotation capability and an integrated shot-to-shot energy selection system for efficient transport of LAP with large energy spread to the patient. We show that gantry size could be reduced by a factor of 2–3 compared to conventional gantry systems by utilizing pulsed air-core magnets. 相似文献
56.
Chemical investigation of the cultured cyanobacterium Fischerella sp. (SAG strain number 46.79) led to the isolation of four nitrile-containing indole alkaloids, namely 12-epi-fischerindole I nitrile (1), deschloro 12-epi-fischerindole I nitrile (2), 12-epi-fischerindole W nitrile (3), and deschloro 12-epi-fischerindole W nitrile (4) along with a known metabolite hapalosin. The structures were determined by detailed spectroscopic analyses on the basis of 1D and 2D NMR and HRESIMS data. All isolates were evaluated for cytotoxicity against human cancer cells and for 20S proteasome inhibition. Deschloro 12-epi-fischerindole I nitrile (2) was found to be weakly cytotoxic against HT-29 cells with an ED(50) value of 23 μM. Hapalosin showed weak cytotoxicity against HT-29 and MCF-7 cells with ED(50) values of 22 and 27 μM, respectively, as well as moderate 20S proteasome inhibition with an IC(50) value of 12 μM. Compounds 1-4 all contain a nitrile moiety instead of the isonitrile found in all fischerindoles reported to date. Compounds 3 and 4 also display a new carbon skeleton, in which a six-membered ring replaces the five-membered ring normally found in fischerindole-type alkaloids. 相似文献
57.
Hufenbach W. Gude M. Kroll L. Sokolowski A. Werdermann B. 《Mechanics of Composite Materials》2001,37(1):71-78
During the manufacturing process of multilayered fiber-reinforced composites with variable fiber orientations, residual stresses build up in these composites due to the directional expansion of single unidirectionally reinforced layers. Depending on the laminate lay-up, the inhomogeneous residual stresses, which are caused by thermal effects, moisture absorption, and chemical shrinkage, can lead to large multistable out-of-plane deformations. Instead of avoiding these curvatures, they can be advantageously used for technical applications following the near-net-shape technology. In order to adjust the deformations to the technical requirements, genetic algorithms in combination with a nonlinear calculation method have been developed, which can purposefully adapt the laminate lay-up depending on the loading and process parameters. 相似文献
58.
Hans-Joachim Kroll 《Geometriae Dedicata》1984,16(1):79-83
Ohne ZusammenfassungHerrn Professor Adriano Barlotti zum 60. Geburtstag 相似文献
59.
Hans -Joachim Kroll 《Journal of Geometry》1988,31(1-2):131-133
Ohne ZusammenfassungHerrn Professor Dr. Helmut Karzel zum 60. Geburtstag 相似文献
60.
N. Karamatskos R. Michalak P. Zimmermann S. Kroll M. Kock 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1986,3(4):391-395
Lifetimes of 12VII levels have been measured by using the technique of laser-excited fluorescence from sputtered metal vapour. The uncertainty is between 7–9%. For a determination of the individual transition probabilities the corresponding emission branching ratios have been measured on a high-current hollow-cathode in conjunction with a 1 m Fourier-transform spectrometer. Thef-values of 86 VII lines, which cover a spectral range 260–420 nm, have an uncertainty of about 12%. Comparison is made with literature data. 相似文献