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排序方式: 共有275条查询结果,搜索用时 15 毫秒
51.
52.
Optical Review - We consider probing inhomogeneous waves in the near fields of metallic nanostructures with the aid of a dielectric V-shaped wedge connected to a waveguide. A geometrical model... 相似文献
53.
Sinkkonen J Karonen M Liimatainen J Pihlaja K 《Magnetic resonance in chemistry : MRC》2006,44(6):633-636
Three lignans were isolated from a bioactive fraction of the 70% aqueous acetone extract of the pine (Pinus sylvestris L.) bark. Their structures were identified by high-resolution positive ion EI mass spectrometry and NMR spectroscopy. The complete assignment of proton and carbon signals was achieved by 2D NMR experiments: HSQC, HMBC, DQF-COSY and NOESY. 相似文献
54.
A novel procedure was developed for the preparation of 2,3-disubstituted 4,1-benzothiazepines, via the ring transformation of (2R∗,2aS∗)-2-chloro-2a-phenyl-2,2a-dihydro-2H,4H-azeto[1,2-a][3,1]benzothiazin-1-one (1) with sodium ethoxide in ethanol. The tautomeric products (R∗)-3-ethoxycarbonyl-2-phenyl-3,5-dihydro-4,1-benzothiazepine (4) and 3-ethoxycarbonyl-2-phenyl-1,5-dihydro-4,1-benzothiazepine (5) exhibit the rare phenomenon of desmotropy of the condensed seven-membered heterocycles. Surprisingly, these desmotropes could be separated by column chromatography. The products are unexpectedly stable in solution and their structures were proved by means of NMR and mass spectrometry. 相似文献
55.
Yaar Dürüst Cevher Altu Jari Sinkkonen Olli Martiskainen Kalevi Pihlaja 《Journal of heterocyclic chemistry》2006,43(5):1267-1274
56.
Peeters M Verschaffelt G Speybrouck J Thienpont H Danckaert J Turunen J Vahimaa P 《Optics letters》2006,31(9):1178-1180
Recently we observed a strong reduction of spatial coherence of the emission of large-aperture vertical-cavity surface-emitting lasers when they are driven by microsecond electrical pulses [Opt. Express 13, 9337 (2005)]. We study the influence of this partial spatial coherence on the propagation characteristics. The spatial decoherence manifests itself in the formation of a Gaussian far-field intensity distribution. We measure the transverse pulse profile from near to far field and see that the shape-invariant far-field regime starts after 140 microm in the pulsed regime as opposed to several centimeters in continuous wave operation. This value matches quantitatively calculations made with a novel partially coherent propagation model without any free fitting parameters. 相似文献
57.
Anna-Leena Erkkilä Teemu Leppänen Jari Hämäläinen 《International Journal of Solids and Structures》2013,50(14-15):2151-2179
The rheological nature of paper or board is usually treated either as elasto-plastic or as viscoelastic depending on the studied paper making process or behavior in converting and end use. In this paper we study several stress–strain curve models and the determination of material parameters from an elasto-plastic point of view. Finally, a suitable approach for all stress–strain curves measured from 180 strips is constructed using a linear function for an elastic region and a nonlinear function for a strain hardening region. This model determines a proportional limit (elastic limit) and gives fairly elegant dependencies between material/fitting parameters and two important factors of mechanical properties of paper: dry solids content and anisotropy. In this paper the dependency of a plastic strain on dry solids content and anisotropy is estimated using the introduced stress–strain curve model. Correspondingly, the model can be used to estimate many other mechanical behaviors, for example, the tension differences arising from non-uniform moisture content of the paper web profile. However, the main target of this study is to produce competent parameters based on modeled stress–strain curves for further construction of a material model. This elasto-plastic material model will be utilized in out-of-plane deformation and fracture models. 相似文献
58.
Jari M. J. Nuutinen Ritva Romppanen Silja Mäkinen Pirjo Vainiotalo 《Journal of the American Society for Mass Spectrometry》1999,10(4):339-346
Five differently substituted 1-(2-benzothiazolyl)-3,5-diphenyl formazans were studied by laser desorption ionization (LDI) and matrix assisted laser desorption/ionization (MALDI) mass spectrometry. The best explanation of the results is that the formazan molecules are photoionized to molecular radical ions, which then further react by ion-molecule reactions. Supporting this proposal was the abundant formation of [M − H]+ ions under LDI. These ions are not observed at all under either electron or chemical ionization. Under MALDI, the extent of the oxidation process is clearly dependent on the ability of the matrix to act as a reducing agent. With transition metals the formazans formed singly charged 1:2 metal:formazan complexes. The most stable electronic configuration of the complex determined the oxidation state of the metal regardless of its initial oxidation state. In some cases, this process also demanded a gas-phase reduction of the formazan. The ionization efficiency and affinity for complex formation depended on the substituent at the 3-phenyl group; both were increased by an electron donating substituent. The formazans were also tested as potential matrices for MALDI. Reasonable results were observed for several groups of compounds; however, only the piperazine ligands produced higher quality spectra with formazans than with common commercial matrices. 相似文献
59.
P Sundberg A Sood X Liu LS Johansson M Karppinen 《Dalton transactions (Cambridge, England : 2003)》2012,41(35):10731-10739
By combining atomic layer deposition (ALD) and molecular layer deposition (MLD) thin-film techniques, the latter being a variant of the former in which organic precursors are used, it is possible to deposit thin films containing precisely controlled portions of inorganic and organic constituents. This in turn enables the adjustment of material properties by changing the number of ALD and MLD cycles applied during the deposition. In this work, the properties of such thin-film "alloys" prepared by varying the portions of Ti-4,4'-oxydianiline (Ti-ODA) inorganic-organic hybrid and TiO(2) in the structure were investigated. The films were deposited at 280 °C using TiCl(4) and water as precursors for TiO(2), and TiCl(4) and ODA for the Ti-ODA hybrid. The results demonstrate excellent tunability of the film properties such as degree of crystallinity, roughness, refractive index, and hardness depending on the relative number of TiO(2) and Ti-ODA cycles employed. 相似文献
60.
The effect of absorber saturation on pulse shaping was studied both numerically and experimentally in a semiconductor disk laser. It was found that steady-state mode locking can be achieved even with very weak saturation of the absorber when the pulse energy is well below the saturation energy of absorption. The study discloses for the first time the direct impact of absorber modulation depth on the pulse width. Numerical analysis confirms that partial bleaching of absorption is adequate for formation of stable mode locking in SDLs. The fast gain dynamics of the semiconductor medium approach the dynamics of a slow gain medium at low pulse energies and high repetition rates with a pulse period much shorter than the gain recovery time. The presented results are of practical importance for multigigahertz repetition rate lasers, indicating that sufficient pulse shaping can occur when the saturable absorber is not fully bleached. 相似文献