排序方式: 共有105条查询结果,搜索用时 132 毫秒
31.
Lisowski M Loukakos PA Melnikov A Radu I Ungureanu L Wolf M Bovensiepen U 《Physical review letters》2005,95(13):137402
Femtosecond electron and spin dynamics of the Gd(0001) surface are investigated by time-resolved photoemission and second harmonic generation. Upon optical excitation the spin polarization of the surface state is reduced by half while its exchange splitting remains nearly unchanged. Electron-magnon interaction is proposed to facilitate electron-spin-flip scattering among spin-mixed surface and bulk states, which provides a mechanism for ultrafast demagnetization. 相似文献
32.
Lindinger A Lupulescu C Plewicki M Vetter F Merli A Weber SM Wöste L 《Physical review letters》2004,93(3):033001
We report on selective optimization of different isotopes in an ionization process by means of spectrally broad shaped fs-laser pulses. This is demonstrated for (39,39)K2 and (39,41)K2 by applying evolution strategies in a feedback loop, whereby a surprisingly high enhancement of one isotope versus the other and vice versa is achieved (total factor approximately 140). Information about the dynamics on the involved vibrational states is extracted from the optimal pulse shapes, which provides a new spectroscopical approach of yielding distinct frequency pattern on fs-time scales. The method should, in principle, be feasible for all molecules. 相似文献
33.
Buica George-Octavian Soare Maria-Laura Inel Georgiana Anca Razus Alexandru C. Birzan Liviu Oprisanu Alexandra Ungureanu Eleonora-Mihaela 《Journal of Solid State Electrochemistry》2016,20(11):3151-3164
Journal of Solid State Electrochemistry - The electrochemical behavior of substituted 1-phenylselanyl azulenes has been established by cyclic, differential pulse, and rotating disk electrode... 相似文献
34.
Daniel Cosmin Porumbel 《Journal of Mathematical Modelling and Algorithms》2011,10(2):119-143
This paper deals with algorithms for detecting graph isomorphism (GI) properties. The GI literature consists of numerous research
directions, from highly theoretical studies (e.g. defining the GI complexity class) to very practical applications (pattern
recognition, image processing). We first present the context of our work and provide a brief overview of various algorithms
developed in such disparate contexts. Compared to well-known NP-complete problems, GI is only rarely tackled with general-purpose
combinatorial optimization techniques; however, classical search algorithms are commonly applied to graph matching (GM). We
show that, by specifically focusing on exploiting isomorphism properties, classical GM heuristics can become very useful for
GI. We introduce a polynomial graph extension procedure that provides a graph coloring (labeling) capable of rapidly guiding
a simple-but-effective heuristic toward the solution. The resulting algorithm (GI-Ext) is quite simple, very fast and practical:
it solves GI within a time in the region of O(|V|3) for numerous graph classes, including difficult (dense and regular) graphs with up to 20.000 vertices and 200.000.000 edges.
GI-Ext can compete with recent state-of-the-art GI algorithms based on well-established GI techniques (e.g. canonical labeling)
refined over the last three decades. In addition, GI-Ext also solves certain GM problems, e.g. it detects important isomorphic
structures induced in non-isomorphic graphs. 相似文献
35.
36.
Vincent Monchiet Cosmin Gruescu Eric Charkaluk Djimedo Kondo 《Comptes Rendus Mecanique》2006,334(7):431-439
Following the study of Gologanu et al. (1997) which has extended the well-known approach of Gurson (1975), we propose approximate yield criteria for anisotropic plastic voided metals containing non spherical cavities. The plastic anisotropy of the matrix is described by means of Hill's quadratic criterion. The procedure to establish the closed form expression of approximate macroscopic criteria, in which void shape and plastic anisotropic effects are included, is detailed. The new criteria allow us to recover existing results in the cases of spherical and cylindrical voids in an Hill type plastic matrix. Moreover, they agree with previous criteria for non spherical voids in an isotropic plastic matrix. Finally, for validation purposes, we provide, in the general case of non spherical cavities in the anisotropic matrix, a comparison with the numerical exact two field criteria. To cite this article: V. Monchiet et al., C. R. Mecanique 334 (2006). 相似文献
37.
Multiscale electromagnetic SERS enhancement on self‐assembled micropatterned gold nanoparticle films
Cosmin Leordean Monica Potara Sanda Boca‐Farcau Adriana Vulpoi Simion Astilean Cosmin Farcau 《Journal of Raman spectroscopy : JRS》2014,45(8):627-635
In this work, we demonstrate a cascaded, multiplicative electromagnetic enhancement effect in surface‐enhanced Raman scattering (SERS) on periodically micropatterned films made of colloidal gold nanoparticles, prepared by a self‐assembly approach, without implying lithography procedures. The multiplicative enhancement effect is obtained by combining surface plasmon near‐field enhancement due to nanoscale features with far‐field photonic coupling by periodic microscale features. The effect is observed for both internal Raman reporters (molecules attached to the Au colloids before their assembly) and external Raman probes (molecules adsorbed on the samples after film assembly). The ability of the patterned films for far‐field light coupling is supported by reflectivity spectra, which present minima/maxima in the visible spectral range. Finite‐difference time‐domain computer simulations of the electric field distribution also support this interpretation. The fabricated dual‐scale SERS substrates exhibit a good spot‐to‐spot reproducibility and time stability, as proved by the SERS response over a time scale longer than 1 month. The experimental demonstration of this cascaded electromagnetic enhancement effect contributes to a better understanding of SERS and can affect future design of SERS substrates. Moreover, such dual‐scale colloidal films prepared by convective self‐assembly can be of general interest for the broader field of nanoparticle‐based devices. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
38.
Dan Donescu Mihai Cosmin Corobea Violeta Uricanu Constantin Radovici Sever Serban Sorina Alexandra Garea 《Journal of Dispersion Science and Technology》2013,34(5):671-679
The emulsion polymerisation of vinyl acetate (VAc) in presence of sodium dodecylsulphate (SDS) and sodium montmorillonite (NaMMT) is used in order to achieve polymer‐clay hybrids. The influence of the polyvinylacetate (PVAc), SDS, and PVAc‐SDS complex on the NaMMT structure also was investigated. The VAc emulsion polymerization rate exhibits a maximum as the NaMMT concentration increases. The XRD patterns correspond to hybrids with intercalated structure. If a water soluble comonomer, ammonium sulphato ethylmethacrylate (ASEMA) is used for copolymerization with VAc, a exfoliated hybrid structure (from XRD spectra) is obtained. The solid materials were analysed by TGA, FTIR, XRD, SEM, and TEM. 相似文献
39.
Common waste glasses (window, bottle glass or tableware) with fly ash form a glass matrix for chromium waste immobilization. Soluble chromium from residual waters was adsorbed on fly ash; the resulting solid contained 23.7% Cr6+. The three glass wastes, chromium-containing fly ash, and borax were used to make glasses in weight ratios waste glass: borax: fly ash of 1: 1: 1 and 1.5: 0.5: 1. The hydrolytic stability ranged from 18.46 to 28.13 µg g?1 soluble Na2O, qualifying them in the HGB1 class. The chemical stability, characterized by the dissolution rate, was 0.011–0.077 µg cm?2 h?1, depending on the glass composition and the aggressive medium pH. The chromium leachability is influnced by the glass composition and the pH of the leaching solution, ranging between 0–0.015% of the total chromium. Chromium waste vitrification is a viabile solution with multiple economic advantages.
相似文献
40.
Larissa V. Kuznetsova Antonella Pepe Ioana M. Ungureanu Ralph J. Bernacki 《Journal of fluorine chemistry》2008,129(9):817-828
A series of novel 3′-difluoromethyl-taxoids and 3′-trifluoromethyl-taxoids with modifications at the C2 and C10 positions were synthesized and evaluated for their in vitro cytotoxicities against human breast carcinoma (MCF7-S, MCF7-R, LCC6-WT, LCC6-MDR), non-small cell lung carcinoma (H460) and colon adenocarcinoma (HT-29) cell lines. These second-generation fluoro-taxoids exhibited several times to more than 20 times better potency than paclitaxel against drug-sensitive cancer cell lines, MCF7-S, LCC6-WT, H460, and HT-29. These fluoro-taxoids also possess two orders of magnitude higher potency than paclitaxel against drug-resistant cancer cell lines, MCF7-R and LCC6-MDR. Structure-activity relationship study shows the importance of the C10 modification for increasing the activity against multidrug-resistant cancer cell lines. Effects of the C2-benzoate modifications on the potency in the 3′-difluoromethyl-taxoid series are very clear (i.e., F < MeO < Cl < N3), while those in the 3′-trifluoromethyl-taxoid series are less obvious. Also, different trends in the sensitivity to the C2-substitution are observed between drug-sensitive cell lines and drug-resistant cancer cell lines that overexpress efflux pumps. 相似文献