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排序方式: 共有163条查询结果,搜索用时 390 毫秒
101.
Tadesse M Strøm MB Svenson J Jaspars M Milne BF Tørfoss V Andersen JH Hansen E Stensvåg K Haug T 《Organic letters》2010,12(21):4752-4755
Bioassay-guided fractionation of the sub-Arctic ascidian Synoicum pulmonaria collected off the Norwegian coast led to the isolation of a novel family of brominated guanidinium oxazolidinones named synoxazolidinones A and B (1 and 2). The backbone of the compounds contains a 4-oxazolidinone ring rarely seen in natural products. The structure of the compounds was determined by spectroscopic methods. The synoxazolidinones exhibited antibacterial and antifungal activities. 相似文献
102.
103.
Gazzano O Michaelis de Vasconcellos S Gauthron K Symonds C Bloch J Voisin P Bellessa J Lemaître A Senellart P 《Physical review letters》2011,107(24):247402
We demonstrate strong confinement of the optical field by depositing a micron sized metallic disk on a planar distributed Bragg reflector. Confined Tamm plasmon modes are evidenced both experimentally and theoretically, with a lateral confinement limited to the disk area and strong coupling to TE polarized fields. Single quantum dots controllably coupled to these modes are shown to experience acceleration of their spontaneous emission when spectrally resonant with the mode. For quantum dots spectrally detuned from the confined Tamm plasmon mode, an inhibition of spontaneous emission by a factor 40±4 is observed, a record value in the optical domain. 相似文献
104.
Savanier M Andronico A Lemaître A Galopin E Manquest C Favero I Ducci S Leo G 《Optics letters》2011,36(15):2955-2957
We report on CW second-harmonic generation in selectively oxidized AlGaAs multilayer waveguides. Frequency doubling of a 1.55 μm pump is observed with 2.8% W(-1) conversion efficiency and a maximum second-harmonic power around 0.3 mW. This is the strongest second-harmonic generation ever reported in semiconductor waveguides and an encouraging result toward integrated spontaneous parametric downconversion in the telecom range. 相似文献
105.
R.?SiragusaEmail author E.?Perret H.?V.?Nguyen P.?Lema?tre-Auger S.?Tedjini C.?Caloz 《Applied Physics A: Materials Science & Processing》2011,103(3):709-714
A fully automated tool for designing CRLH interdigital microstrip structures using a co-design synthesis computational approach
is proposed and demonstrated experimentally. This approach uses an electromagnetic simulator in conjunction with a genetic
algorithm to synthesize and optimize a balanced CRLH interdigital microstrip transmission line. The high sensitivity of a
long balanced transmission line to fabrication tolerances is controlled by the use of a high precision 3D simulator. The 2.5D
simulator used was found insufficient for a large number of unit cells. A 13 UC CRLH transmission line is designed with the
proposed approach. The response sensitivity of the balanced transmission lines to the over/under-etching factor is highlighted
by comparing the measurements of four lines with different factors. The effect of over/under-etching is significant for values
larger than 10 μm. 相似文献
106.
K. Lemański A. G?gor M. Kurnatowska R. P?zik P.J. Dereń 《Journal of solid state chemistry》2011,184(10):2713-2718
In this work, we present for the first time the spectroscopic properties of perovskite nanocrystals CaTiO3: Nd3+, measured at room and liquid nitrogen temperature. Samples were prepared by the sol–gel method and annealed at 700 and 1000 °C. The concentration of Nd3+ ranged from 0.5% to 5%. Average nanocrystallite size primarily depends on the annealed temperature and is about 25 and 50 nm for 700 and 1000 °C, respectively. The absorption, emission and excitation spectra (monitored at 1078 nm) as well as the decay time profile of the emission from the 4F3/2 energy level of Nd3+ are obtained. The increasing amount of Nd3+ ions decreases the lifetime of the 4F3/2 level and that changes from 146 μs for 0.5% to 50 μs for 5% of Nd3+ concentration. The strongest emission was observed at two regions: 1050–1120 nm and 865–930 nm and was assigned to the 4F3/2→4I11/2 and 4F3/2→4I9/2 transitions, respectively. The spectroscopic quality parameter of neodymium in the CaTiO3 lattice has been calculated from the emission spectra. The influence of luminescent properties depending on the annealing temperature and concentration of neodymium ions is discussed. 相似文献
107.
108.
Exploiting a spectral criterion for a system not to be AT we give some new examples of zero entropy systems without the AT property. Our examples include those with finite spectral multiplicity—in particular we show that the system arising from the Rudin–Shapiro substitution is not AT. We also show that some nil-rotations on a quotient of the Heisenberg group as well as some (generalized) Gaussian systems are not AT. All known examples of non AT-automorphisms contain a Lebesgue component in the spectrum. 相似文献
109.
Fermentation of Biologically Pretreated Wheat Straw for Ethanol Production: Comparison of Fermentative Microorganisms and Process Configurations 总被引:2,自引:0,他引:2
María López-Abelairas Thelmo Alejandro Lu-Chau Juan Manuel Lema 《Applied biochemistry and biotechnology》2013,170(8):1838-1852
The pretreatment of lignocellulosic biomass with white-rot fungi to produce bioethanol is an environmentally friendly alternative to the commonly used physico-chemical processes. After biological pretreatment, a solid substrate composed of cellulose, hemicellulose and lignin, the two latter with a composition lower than that of the initial substrate, is obtained. In this study, six microorganisms and four process configurations were utilised to ferment a hydrolysate obtained from wheat straw pretreated with the white-rot fungus Irpex lacteus. To enhance total sugars utilisation, five of these microorganisms are able to metabolise, in addition to glucose, most of the pentoses obtained after the hydrolysis of wheat straw by the application of a mixture of hemicellulolytic and cellulolytic enzymes. The highest overall ethanol yield was obtained with the yeast Pachysolen tannophilus. Its application in combination with the best process configuration yielded 163 mg ethanol per gram of raw wheat straw, which was between 23 and 35 % greater than the yields typically obtained with a conventional bioethanol process, in which wheat straw is pretreated using steam explosion and fermented with the yeast Saccharomyces cerevisiae. 相似文献
110.
R. Taboada-Puig T. A. Lú-Chau M. T. Moreira G. Feijoo J. M. Lema 《Applied biochemistry and biotechnology》2013,169(4):1262-1278
Enzymatic lignin activation may be an environmentally friendly alternative to the use of chemicals in the production of wood fibers composites. Most studies on enzymatic activation of lignin for improving the adhesion of lignocellulosic products have been carried out using laccases. In this work, the use of a versatile peroxidase (VP) from the white-rot fungus Bjerkandera sp. (anamorph R1) for activating Kraft lignin was studied. The effect of enzyme dosage, incubation time, and H2O2 addition profile on lignin activation was evaluated by quantifying the phenoxy radicals formed using electron paramagnetic resonance (EPR) spectroscopy. Two alternative enzymatic systems based on the use of VP (a two-stage and an enzymatic cascade system) were also assayed. At optimal conditions (dose of 15 U?g?1 and continuous addition of H2O2 (5.24 μmol?h?1) during 1 h) the content of phenoxy radicals was doubled as compared with an untreated control. Moreover, using the two-stage VP system, a lignin activation similar to that found at optimal conditions could be reached in a shorter time. 相似文献