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61.
P. Sigmund A. Schinner 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,12(3):425-434
The Bohr theory treats charged-particle stopping as a sequence of interactions with classical target electrons bound harmonically
to their equilibrium positions. We demonstrate that equivalent results can be derived on the assumption of free binary collisions
governed by a suitable effective potential. This kind of mapping is rigorous in the limits of distant and close collisions
and therefore provides a tool to evaluate energy losses via binary-scattering theory. This model was developed with the aim of calculating stopping forces for heavy ions at moderately
high velocities, where a classical-orbital calculation is typically superior to the Born approximation. The effective potential
employed holds equally well for dressed as for stripped ions. Unlike the Bohr theory, the present evaluation avoids a formal
division into regimes of close and distant collisions that do not necessarily join smoothly. Moreover, no perturbation expansion
is necessary. For these reasons the overall accuracy as well as the range of validity of the Bohr model are significantly
enhanced. Extensive tests have been performed, including comparisons with rigorous evaluations of the Z
1
3 effect, with excellent agreement even where such was not necessarily expected. Moreover, credible results have been obtained
under conditions where the perturbation expansion shows poor convergence. A comparison with experimental data on O–Al is encouraging,
even though shell corrections and projectile excitation/ionization have not yet been incorporated and input has not yet been
optimized.
Received 21 April 2000 and Received in final form 16 June 2000
An erratum to this article is available at . 相似文献
62.
63.
Photonic crystal waveguides are optimized for modal confinement and loss related to slow light with high group index. A detailed comparison between optimized circular-hole based waveguides and optimized waveguides with free topology is performed. Design robustness with respect to manufacturing imperfections is enforced by considering different design realizations generated from under-, standard- and over-etching processes in the optimization procedure. A constraint ensures a certain modal confinement, and loss related to slow light with high group index is indirectly treated by penalizing field energy located in air regions. It is demonstrated that slow light with a group index up to ng = 278 can be achieved by topology optimized waveguides with promising modal confinement and restricted group-velocity-dispersion. All the topology optimized waveguides achieve a normalized group-index bandwidth of 0.48 or above. The comparisons between circular-hole based designs and topology optimized designs illustrate that the former can be efficient for dispersion engineering but that larger improvements are possible if irregular geometries are allowed. 相似文献
64.
Grgić J Ott JR Wang F Sigmund O Jauho AP Mørk J Mortensen NA 《Physical review letters》2012,108(18):183903
A common strategy to compensate for losses in optical nanostructures is to add gain material in the system. By exploiting slow-light effects it is expected that the gain may be enhanced beyond its bulk value. Here we show that this route cannot be followed uncritically: inclusion of gain inevitably modifies the underlying dispersion law, and thereby may degrade the slow-light properties underlying the device operation and the anticipated gain enhancement itself. This degradation is generic; we demonstrate it for three different systems of current interest (coupled-resonator optical waveguides, Bragg stacks, and photonic crystal waveguides). Nevertheless, a small amount of added gain may be beneficial. 相似文献
65.
Chaudhuri D Li D Sigmund E Wettach H Höger S Lupton JM 《Chemical communications (Cambridge, England)》2012,48(53):6675-6677
Dual singlet-triplet fluorescence-phosphorescence emitting compounds demonstrate that plasmonic surface enhancement is controlled solely by the underlying oscillator strength of a transition: metal-free compounds with weak spin-orbit coupling show no enhancement in phosphorescence efficiency even though fluorescence is amplified. 相似文献
66.
Szabolcs Béni Gerg? Tóth Béla Noszál Sándor Hosztafi 《Monatshefte für Chemie / Chemical Monthly》2012,45(6):1431-1440
Abstract
Sustained analgesia is crucial for patients suffering from long-acting pain. Ester derivatives of morphine could enhance the lipophilicity of morphine; consequently its transdermal delivery as well as its duration of action are also increased. Therefore, twenty-one 3-O-, 6-O-, and 14-O-benzoate esters of morphine and their derivatives were synthesized in order to elaborate different synthetic methods suitable for esterification of these widely used compounds. Schotten–Baumann reaction was applied with sodium hydrogen carbonate, triethylamine, or pyridine in methylene chloride or 1,2-dichloroethane as solvents. The presence of 4-dimethylaminopyridine catalyst was also successfully utilized mainly in the case of tertiary alcohols. A novel synthesis of dihydromorphine via diacetyl morphine free of by-products is also presented. Structures of all synthesized compounds were elucidated by 1H nuclear magnetic resonance (NMR), 13C NMR, high-resolution mass spectrometry (HRMS), and electron ionization mass spectrometry (EI-MS). The log D (pH 7.4) values of the synthesized compounds were determined by a reversed-phase high-performance liquid chromatography (HPLC)–MS-based method, and calculated hydrolysis rate constants are also provided. The synthesized benzoate esters are potential prodrugs of the parent morphine with enhanced lipophilicity, derivatives which can also be used in transdermal drug delivery as prospective long-acting narcotic analgesics. 相似文献67.
68.
69.
Rajind Mendis Cezary Sydlo Jochen Sigmund Michael Feiginov Peter Meissner Hans L. Hartnagel 《International Journal of Infrared and Millimeter Waves》2005,26(2):201-207
We report on a completely coherent, tunable, continuous-wave THz system where, for the first-time, both the transmitter and receiver are log-periodic-antenna coupled LTG-GaAs based finger-photomixers. This compact room-temperature system exhibits signal-to-noise ratios (> 103) comparable to or better than what is reported in the literature, and has potential applications in high-resolution spectroscopy and imaging. For the purpose of demonstration, we also present results of spectroscopy measurements carried out on fused silica, which are in agreement with previously published THz-TDS measurements. 相似文献
70.
C. Kippenberger F. Fischer C. Reinhardt J. Coquillion J. F. Willard G. Neumann H. Drehschmidt Klas Sondén Wilhelm Thörner W. Mac Farlone P. Caldwell R. Namias Binder W. E. Adeney W. Younger Vivian B. Lewes T. Lonatscheffsky-Petruniaka Maurice Meslans M. Arndt G. Pfeiffer Sigmund Neumann A. Lwoff F. Cowes S. B. Redwood S. Waters Murdy J. A. Wanklyn W. J. Cooper L. L. de Koninck und G. Linossier 《Fresenius' Journal of Analytical Chemistry》1896,35(1):184-200
Ohne Zusammenfassung 相似文献