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排序方式: 共有321条查询结果,搜索用时 15 毫秒
81.
A porous, homochiral titanium‐phosphonate material based on a tripodal peptide scaffold was used as a heterogeneous reaction medium for the enantioselective hydration (>99%) of styrene oxide. This titanium‐phosphonate material, which was shown to contain confined chiral spaces, was prepared by polymerization of L ‐leucine onto a tris(2‐aminoethyl)amine initiator, followed by capping with phosphonate groups and completed by non‐aqueous condensation with titanium isopropoxide. Circular dichroism confirmed that the peptide tethers yielded a secondary structure. X‐ray powder diffraction and transmission electron microscopy supported by a semi‐empirical model showed the likely formation of a porous, lamellar material that was quantified by nitrogen adsorption. 相似文献
82.
Numan Almonasy Miloš Nepraš Šárka Hyková Antonin Lyčka Jiři Čermák Miroslav Dvořák Martin Michl 《Dyes and Pigments》2009,82(2):164-170
N-Acetyl and N-triazinyl 3-aminoperylenes were prepared. N-(4,6-Dichloro-1,3,5-triazin-2-yl)-3-aminoperylene was synthesized by the condensation of 3-aminoperylene with cyanuric chloride; other N-triazinyl derivatives were prepared by the successive substitution of chlorine atoms with methoxy or aniline groups. The structure and purity of the compounds were confirmed by elemental analysis, NMR spectroscopy and mass spectrometry. The UV/vis absorption, fluorescence and excitation spectra as well as the fluorescence quantum yields for the compounds were measured in dibutyl ether, 1,4-dioxane, ethyl acetate and acetonitrile; fluorescence lifetimes were measured in ethyl acetate and dimethyl sulfoxide. The influences of both the character of the N-substituent and the solvent polarity upon the spectra and quantum yields are discussed. 相似文献
83.
Spectral cytopathology (SCP) is a novel approach for disease diagnosis that utilizes infrared spectroscopy to interrogate the biochemical components of cellular samples and multivariate statistical methods, such as principal component analysis, to analyze and diagnose spectra. SCP has taken vast strides in its application for disease diagnosis over the past decade; however, fixation-induced changes and sample handling methods are still not systematically understood. Conversely, fixation and staining methods in conventional cytopathology, typically involving protocols to maintain the morphology of cells, have been documented and widely accepted for nearly a century. For SCP, fixation procedures must preserve the biochemical composition of samples so that spectral changes significant to disease diagnosis are not masked. We report efforts to study the effects of fixation protocols commonly used in traditional cytopathology and SCP, including fixed and unfixed methods applied to exfoliated oral (buccal) mucosa cells. Data suggest that the length of time in fixative and duration of sample storage via desiccation contribute to minor spectral changes where spectra are nearly superimposable. These findings illustrate that changes influenced by fixation are negligible in comparison to changes induced by disease. 相似文献
84.
Petr Kočí Šárka Bártová David Mráček Miloš Marek Jae-Soon Choi Mi-Young Kim Josh A. Pihl William P. Partridge 《Topics in Catalysis》2013,56(1-8):118-124
In this paper we propose an effective global kinetic model that allows prediction of N2O and NH3 formation during the reduction of stored NO x in dependence on the composition of the rich mixture (H2/CO/C3H6), actual operating temperature, and length of regeneration period. A bench flow reactor equipped with a high-speed FTIR was used to measure dynamic evolution of gas components during periodic lean/rich operation of a fully formulated NSRC catalyst (PtPdRh/Ba/Ce–Zr/Mg–Al/Al2O3). 相似文献
85.
Milan Dopita Miloš Janeček Radomír Kužel Hans Jürgen Seifert Sergey Dobatkin 《Journal of Materials Science》2010,45(17):4631-4644
The microstructure evolution of extruded Cu–0.18 wt% Zr polycrystals processed by high-pressure torsion (HPT) at room temperature
at the pressure of 4 GPa and the different number of the HPT revolutions (i.e. different strain) was investigated using the
combination of the electron back-scatter diffraction, microhardness measurements and the X-ray diffraction. A significant
transition from the inhomogeneous microstructure after few HPT revolutions into the homogeneous equiaxed microstructure with
increasing number of HPT rotations was observed. HPT straining leads to the grain size refinement by a factor more than 100
after the 25 HPT revolutions. Moreover, the EBSD revealed an increase in the fraction of high-angle grain boundaries (HAGBs)
with increasing HPT straining reaching the value of 70% after 25 revolutions. Additionally, a slight increase of the twin-related
CSL Σ3 grain boundaries occurred during the microstructure refinement. The microhardness measurements confirmed the billet
radial inhomogeneity at early stages of the HPT straining, whereas with increasing number of the HPT rotations, causing the
specimen fragmentation and homogenization, the microhardness values increased. The average crystallite size and the average
dislocation density in individual specimens determined by the XRD diffraction were in the range of approximately 100–200 nm
and 2 × 1015 m−2, respectively. Moreover, XRD measurements confirmed the absence of residual stresses in all specimens. 相似文献
86.
BACKGROUND: Frequently, the unimodal shape of size‐exclusion chromatography (SEC) elution curves is taken as evidence that the polymer sample being analysed contains no minority components in significant quantities. The legitimacy of this assumption, however, has never been checked systematically. RESULTS: An algorithm for the simulation of SEC elution curves of multi‐component polymer systems has been developed. Using the algorithm, the shapes of the overall SEC curves with a wide range of parameters describing binary systems were generated and scanned. The crucial parameters determining the shape of the elution curves are the ratio of the molecular weights of the components, the breadth of the molecular weight distribution of the components, the mass fractions of the components and the band broadening. CONCLUSION: A detailed inspection of the curves shows that the identification of the presence of minority components in such systems from the shapes of the elution curves is more difficult then generally assumed. The absence of peak irregularities, such as minima or inflection points, widely used as a proof of absence of minority components, is a highly unreliable criterion. Copyright © 2008 Society of Chemical Industry 相似文献
87.
Reliability of masonry walls subjected to in‐plane loading: A slip failure along head joints / Zuverlässigkeit von Mauerwerkswänden bei Belastung in der Ebene: Versagen entlang der Stoßfugenflucht 下载免费PDF全文
Masonry structures are a sustainable, economical and traditionally widely used type of construction. However, current masonry design codes are rather conservative, so there is a growing need for revision i.e. calibration of safety factors to improve the allocation of material resources. In this paper, we investigate the probability of occurrence of slip failure along head joints (perpends) in masonry subjected to in‐plane loading. An appropriate limit state function is established and the masonry material properties and loads are defined as random variables in order to simulate likelihood of occurrence of a slip failure regime along the head joints. Furthermore, an example of masonry wall with probabilistic analysis outcomes using Monte Carlo simulation is presented and recommendations for further work are provided. 相似文献
88.
Lukáš Fiala Miloš Jerman Pavel Reiterman Robert Černý 《International Journal of Thermophysics》2018,39(2):28
Silicate materials have an irreplaceable role in the construction industry. They are mainly represented by cement-based- or lime-based materials, such as concrete, cement mortar, or lime plaster, and consist of three phases: the solid matrix and air and water present in the pores. Therefore, their effective thermal conductivity depends on thermal conductivities of the involved phases. Due to the time-consuming experimental determination of the effective thermal conductivity, its calculation by means of homogenization techniques presents a reasonable alternative. In the homogenization theory, both volumetric content and particular property of each phase need to be identified. For porous materials the most problematic part is to accurately identify thermal conductivity of the solid matrix. Due to the complex composition of silicate materials, the thermal conductivity of the matrix can be determined only approximately, based on the knowledge of thermal conductivities of its major compounds. In this paper, the thermal conductivity of silicate matrix is determined using the measurement of a sufficiently large set of experimental data. Cement pastes with different open porosities are prepared, dried, and their effective thermal conductivity is determined using a transient heat-pulse method. The thermal conductivity of the matrix is calculated by means of extrapolation of the effective thermal conductivity versus porosity functions to zero porosity. Its practical applicability is demonstrated by calculating the effective thermal conductivity of a three-phase silicate material and comparing it with experimental data. 相似文献
89.
Milan Vukićević Kathrin Kirchner Boris Delibašić Miloš Jovanović Johannes Ruhland Milija Suknović 《Knowledge and Information Systems》2013,35(1):111-130
The analysis of microarray data is fundamental to microbiology. Although clustering has long been realized as central to the discovery of gene functions and disease diagnostic, researchers have found the construction of good algorithms a surprisingly difficult task. In this paper, we address this problem by using a component-based approach for clustering algorithm design, for class retrieval from microarray data. The idea is to break up existing algorithms into independent building blocks for typical sub-problems, which are in turn reassembled in new ways to generate yet unexplored methods. As a test, 432 algorithms were generated and evaluated on published microarray data sets. We found their top performers to be better than the original, component-providing ancestors and also competitive with a set of new algorithms recently proposed. Finally, we identified components that showed consistently good performance for clustering microarray data and that should be considered in further development of clustering algorithms. 相似文献
90.
Evgeny Senokos David B. Anthony Noelia Rubio Maria Crespo Ribadeneyra Emile S. Greenhalgh Milo S. P. Shaffer 《Advanced functional materials》2023,33(16):2212697
Multifunctional electrodes for structural supercapacitors are prepared by vacuum infiltration of single-walled carbon nanotubes (SWCNTs) into woven carbon fibers (CFs); the use of reductive charging chemistry to form nanotubide solutions ensured a high degree of individualization. The route is highly versatile, as shown by comparing four different commercial nanotube feedstocks. In film form, the pure nanotubide networks (“buckypapers”) are highly conductive (up to 2000 S cm−1) with high surface area (>1000 m2 g−1) and great electrochemical performance (capacitance of 101 F g−1, energy density of 27.5 Wh kg−1 and power density of 135 kW kg−1). Uniformly integrating these SWCNT networks throughout the CF fabrics significantly increased electrical conductivity (up to 318 S cm−1), surface area (up to 196 m2 g−1), and in-plane shear properties, all simultaneously. The CNT-infiltrated CFs electrodes exhibited intrinsically high specific energy (2.6–4.2 Wh kg−1) and power (6.0–8.7 kW kg−1) densities in pure 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM TFSI) electrolyte. Multifunctional structural supercapacitors based on CNT-coated CFs offer a substantial increase in capacitive performance while maintaining the tensile mechanical properties of the as-received CF-based composite. This non-damaging approach to modify CFs with highly graphitic, high surface area nanocarbons provides a new route to structural energy storage systems. 相似文献