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排序方式: 共有838条查询结果,搜索用时 15 毫秒
51.
Andreas J. Steiner Georg Schitter Arnold E. Stütz Tanja M. Wrodnigg Chris A. Tarling Stephen G. Withers Don J. Mahuran Michael B. Tropak 《Tetrahedron: Asymmetry》2009,20(6-8):832-835
Cyclisation by double reductive amination of 2-acetamino-2-deoxy-d-xylo-hexos-5-ulose with N-2 protected l-lysine derivatives provided 2-acetamino-1,2-dideoxynojirimycin derivatives without any observable epimer formation at C-5. Modifications on the lysine moiety gave access to lipophilic derivatives that exhibited improved hexosaminidase inhibitory activities. 相似文献
52.
In most papers establishing consistency for learning algorithms it is assumed that the observations used for training are realizations of an i.i.d. process. In this paper we go far beyond this classical framework by showing that support vector machines (SVMs) only require that the data-generating process satisfies a certain law of large numbers. We then consider the learnability of SVMs for α-mixing (not necessarily stationary) processes for both classification and regression, where for the latter we explicitly allow unbounded noise. 相似文献
53.
In this paper we consider what happens when Adams self maps are modified by adding certain unstable maps. The unstable maps which are added are trivial after a single suspension. We can choose the modification so that the maps are still K-theory equivalences but the loops on the map are no longer K-theory equivalences. As a corollary we note that the maps are K-theory equivalences but not v
1-periodic equivalences. Another consequence is the behavior of the cobar spectral sequences for generalized homology theories. Tamaki shows that in certain cases a cobar-type spectral sequence for generalized homology theories is well behaved. The maps we construct give an example where despite the connectivity of the spaces the cobar spectral sequence is still poorly behaved. Finally we use our maps to construct spaces whose Bousfield class is distinct from the cofiber of the Adams map but which becomes the same after one suspension. 相似文献
54.
55.
Low levels of water (limit of detection 2-5 mg kg1?)can be determined in a non-polar organic solvents such as benzene, 1,2-dichloroethane (DCE) and n-hexane by utilizing the reaction of water with SnCl4 or SbCl5. The reaction results of hydrolysis in halide and is accompanied by a decrease in optical absorption. With SnSl4, the reaction is monitored near 300 nm and with SbCl5 it is monitored at lower wavelengths (350-420). Niether reactons proceeds well in media containing only DCE and n-hexane. For this reason, the arrangemens involves a halide reagent dissolved in benzene which is merged with a benzene/n-hexane/DCE carrier stream into which samlpe is injected. A configuration in which only 2μl of a concentrated halide reagent solution is injected into the flowing sample stream is also shown to be viable for the determination of water in benzene. A membrane-permeation-based calibration method for preparing trace water standards is described. 相似文献
56.
Kapuruge Don Kunkuma Amila Somarathne Ekenechukwu C. Okafor Daiki Sugawara Akihiro Hayakawa Hideaki Kobayashi 《Proceedings of the Combustion Institute》2021,38(4):5163-5170
This study examined the effects of OH concentration and temperature on the NO emission characteristics of turbulent, non-premixed methane (CH4)/ammonia (NH3)/air swirl flames in two-stage combustors at high pressure. Emission data were obtained using large-eddy simulations with a finite-rate chemistry method from model flames based on the energy fraction of NH3 (ENH3) in CH4/NH3 mixtures. Although NO emissions at the combustor exit were found to be significantly higher than those generated by CH4/air and NH3/air flames under both lean and stoichiometric primary zone conditions, these emissions could be lowered to approximately 300 ppm by employing far-rich equivalence ratios (?) of 1.3 to 1.4 in the primary zone. This effect was possibly due to the lower OH concentrations under far-rich conditions. An analysis of local flame characteristics using a newly developed mixture fraction equation for CH4/NH3/air flames indicated that the local temperature and NO and OH concentration distributions with local ? were qualitatively similar to those in NH3/air flames. That is, the maximum local NO and OH concentrations appeared at local ? of 0.9, although the maximum temperature was observed at local ? of 1.0. Both the temperature and OH concentration were found to gradually decrease with the partial replacement of CH4 with NH3. Consequently, NO emissions from CH4/NH3 flames were maximized at ENH3 in the range of 20% to 30%, after which the emissions decreased. Above 2100 K, the NO emissions from CH4/NH3 flames increased exponentially with temperature, which was not observed in NH3/air flames because of the lower flame temperatures in the latter. But, the maximum NO concentration in CH4/NH3 flames was occurred at a temperature slightly below the maximum temperature, just as in NH3/air flames. The apparent exponential increase in NO emissions from CH4/NH3 flames is attributed to a similar trend in the OH concentration at high temperatures. 相似文献
57.
Ali Izadi-Najafabadi Takeo Yamada Don N. Futaba Hiroaki Hatori Sumio Iijima Kenji Hata 《Electrochemistry communications》2010,12(12):1678-1681
We report the energy and power voltage-dependencies of supercapacitors using single-walled carbon nanotube electrodes. The energy density was dependent on the cell-voltage cubed (up to 4 V: E = 1.43 × V3). The cubic relationship was attributed to the linear increase of the capacitance as a function of voltage, enabled by electrochemical doping. Furthermore, while up to 3.5 V, the maximum power rating of the nanotube electrodes increased as a function of the cell-voltage squared, beyond 3.5 V, a decline in power was observed as a result of depletion of the electrolyte's ions. 相似文献
58.
Biotoxicity of nanoparticles: effect of natural organic matter 总被引:1,自引:0,他引:1
Sungyun Lee Kitae Kim H. K. Shon Sang Don Kim Jaeweon Cho 《Journal of nanoparticle research》2011,13(7):3051-3061
Various natural organic matters (NOM) with different characteristics in aquatic environment may affect toxicity of leased
nanoparticles, owing to interactions between NOM and nanoparticles. This study investigated the effect of NOM and physical
characteristics of the effluent organic matter (EfOM) on the ecotoxicity of quantum dots (QD) using Daphnia magna. Organic matter samples were obtained from: Yeongsan River (YR-NOM), Dongbuk Lake (DL-NOM), Damyang wastewater treatment
plant (EfOM), and Suwannee River NOM (SR-NOM). The QD was composed of a CdSe core, ZnS shell, and polyethylene glycol coating.
The average size of the investigated QD was 4.8, 56.5, and 25.0 nm determined by transmission electron microscopy, dynamic
light scattering, and asymmetric flow field-flow fractionation, respectively. The relative hydrophobicity of NOM was investigated
using both specific UV absorbance at 254 nm and XAD-8/4 resins. The sorption of NOM on the QD was measured using a fluorescence
quenching method. The highest hydrophobicity was exhibited by the SR-NOM, while the lowest was recorded for the DL-NOM. All
tested NOMs significantly reduced the acute toxicity of D. magna when adsorbed to QD, and the order of effectiveness for each NOM was as follows: SR-NOM > EfOM > YS-NOM > DL-NOM. The sorption
of NOM on the QD surface caused a decrease in the fluorescence intensity of QD at increasing NOM concentration. This suggests
that the NOM coating influenced the physicochemical characteristics of QD in the internal organs of D. magna by inducing a reduced bioavailability. Results from this study revealed that NOM with relatively high hydrophobicity had a greater capability of inducing toxicity
mitigation. 相似文献
59.
Abstract
The photoinduced electron transfer from chlorophyll a through the interface of positively charged dioctadecyltrimethylammonium chloride (DODAC), neutral dipalmitoylphosphatidylcholine (DPPC) and negatively charged dihexadecylphosphate (DHP) headgroup of the lipid bilayers was studied. The photoinduced radicals were identified by electron spin resonance (ESR) and radical yields of chlorophyll a were determined by double integration of the ESR spectra. The formation of vesicles was identified indirectly by measuring change of the λ max value of optical absorption spectrophotometer from diethyl ether solution to vesicle solutions, and observed directly with scanning and transmission electron microscopic images. The interaction distance between chlorophyll a and interface water (D2O) determined by deuterium modulation depth with electron spin echo modulation (ESEM) showed a decreasing order DODAC > DPPC > DHP. The interface charge of each vesicle was determined with zeta potential measurement. The interface charge of the lipid bilayers affected the radical yields of chlorophyll a more critically than the interaction distance between chlorophyll a and interface water. 相似文献60.
Don Zagier 《Proceedings Mathematical Sciences》1994,104(1):57-75
In 1956, Rankin described which polynomials in the derivatives of modular forms are again modular forms, and in 1977, H Cohen
defined for eachn ≥ 0 a bilinear operation which assigns to two modular formsf andg of weightk andl a modular form [f, g]n of weightk +l + 2n. In the present paper we study these “Rankin-Cohen brackets” from two points of view. On the one hand we give various explanations
of their modularity and various algebraic relations among them by relating the modular form theory to the theories of theta
series, of Jacobi forms, and of pseudodifferential operators. In a different direction, we study the abstract algebraic structure
(“RC algebra”) consisting of a graded vector space together with a collection of bilinear operations [,]n of degree + 2n satisfying all of the axioms of the Rankin-Cohen brackets. Under certain hypotheses, these turn out to be
equivalent to commutative graded algebras together with a derivationS of degree 2 and an element Φ of degree 4, up to the equivalence relation (∂,Φ) ~ (∂ - ϕE, Φ - ϕ2 + ∂(ϕ)) where ϕ is an element of degree 2 andE is the Fuler operator (= multiplication by the degree).
Dedicated to the memory of Professor K G Ramanathan 相似文献