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排序方式: 共有1017条查询结果,搜索用时 31 毫秒
931.
Balázs Imre Dániel Bedő Attila Domján Peter Schön G. Julius Vancso Béla Pukánszky 《European Polymer Journal》2013
Polyurethane elastomers are promising candidates for the impact modification of PLA producing blends for example for biomedicine. Poly(lactic acid) (PLA)/polyurethane elastomer (PU) blends were prepared by reactive processing and physical blending as comparison. The blends were characterized by a number of techniques including microscopy (scanning electron microscopy, SEM, and atomic force microscopy, AFM), rotational viscometry, thermal (dynamic mechanical analysis, DMA), and mechanical (tensile) measurements. The analysis and comparison of the structure and properties of physical and reactor blends proved the successful coupling of the phases. Coupling resulted in more advantageous structure and superior mechanical properties compared to those of physical blends as confirmed by morphology, macroscopic properties and the quantitative estimation of interfacial interactions. Structural studies and the composition dependence of properties indicated the formation of a submicron, phase-in-phase structure which positively influenced properties at large PU contents. The results strongly support that reactive processing is a convenient, cost-effective and environmentally friendly technique to obtain blends with superior properties. 相似文献
932.
Jean-Pierre Cuif Azzedine Bendounan Yannicke Dauphin Julius Nouet Fausto Sirotti 《Analytical and bioanalytical chemistry》2013,405(27):8739-8748
Organic compounds have been extracted from calcium carbonate skeletons produced by three invertebrate species belonging to distinct phyla. The soluble parts of these skeleton matrices were isolated and analysed by synchrotron-based X-ray spectroscopy (XPS). The presence of calcium associated with these organic materials was revealed in every sample studied, with important variations in Ca 2p binding energy from species to species. Measured Ca 2p binding energy values are more related to compositional diversity of the mineralizing matrices of the skeletons, whose taxonomic dependence has long been established, than to the Ca carbonate polymorph selected to build the skeletal units. This suggests a physical bond between species-specific mineralizing organic assemblages and the associated calcium. Remarkably, the binding energy of 2p electrons in calcium associated with mineralizing matrices is consistently higher than Ca 2p values obtained in purely mineral carbonate (both calcite and aragonite). The ability both to identify and measure the effect of organic matrices on their mineral counterpart in calcareous biominerals opens a new perspective for a functional approach to the biomineralization process. 相似文献
933.
Embrechts A Velders AH Schönherr H Vancso GJ 《Langmuir : the ACS journal of surfaces and colloids》2011,27(23):14272-14278
The recognition of self-complementary quadruple urea-aminotriazine (UAT)-based hydrogen-bonded arrays was investigated in solution and at surfaces. For this purpose, an UAT-based donor-acceptor-donor-acceptor (DADA) array and complementary receptors were synthesized. Two-dimensional proton nuclear magnetic resonance ((1)H NMR) measurements in CDCl(3) pointed at an intramolecular hydrogen-bond stabilization of the UAT, which promotes a planar molecular geometry and, thereby, results in a significant stabilization of the dimeric complex. The bond strength of the UAT dimers at surfaces was determined by atomic force microscopy-based single molecule force spectroscopy (AFM-SMFS) in hexadecane. The UAT receptor was immobilized on gold surfaces using an ultrathin layer of ethylene glycol terminated lipoic acid and isocyanate chemistry. The layers obtained and the reversible self-complementary recognition were thoroughly characterized with contact angle measurements, grazing angle Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and AFM. Loading rate-dependent SMFS measurements yielded a barrier width x(β) and a bond lifetime at zero force t(off)(0) of 0.29 ± 0.02 nm and 100 ± 80 ms, respectively. The value of the corresponding off-rate constant k(off) suggests a substantially larger value of the dimerization constant compared to theoretical predictions, which is fully in line with the additional intramolecular hydrogen-bond stabilization detected in solution by (1)H NMR spectroscopy. 相似文献
934.
The study of polynomial solutions to the classical Lamé equation in its algebraic form, or equivalently, of double-periodic solutions of its Weierstrass form has a long history. Such solutions appear at integer values of the spectral parameter and their respective eigenvalues serve as the ends of bands in the boundary value problem for the corresponding Schrödinger equation with finite gap potential given by the Weierstrass $\wpThe study of polynomial solutions to the classical Lamé equation in its algebraic form, or equivalently, of double-periodic
solutions of its Weierstrass form has a long history. Such solutions appear at integer values of the spectral parameter and
their respective eigenvalues serve as the ends of bands in the boundary value problem for the corresponding Schr?dinger equation
with finite gap potential given by the Weierstrass -function on the real line. In this paper we establish several natural (and equivalent) formulas in terms of hypergeometric
and elliptic type integrals for the density of the appropriately scaled asymptotic distribution of these eigenvalues when
the integer-valued spectral parameter tends to infinity. We also show that this density satisfies a Heun differential equation
with four singularities. 相似文献
935.
We demonstrate an optical technique to derive the two-dimensional energy conversion efficiency (ηCE), fill factor (FF) and external quantum efficiency (ηQE) distributions across the surface of photovoltaic devices. A compact, inexpensive optical-feedback laser diode microscope is constructed to acquire the confocal reflectance and efficiency maps enabling the observation of the local parametric behavior in silicon photodiodes in photovoltaic mode and single-junction solar cells. The ηCE and ηQE distributions are greatly influenced by local parasitic resistances that depend on laser irradiance. These parasitic resistances decrease the ηCE and ηQE values with distance from the contact electrode at high laser irradiance. The optical technique enables microscopic comparison of ηCE and ηQE within the pn-overlay region of the photodiode sample, revealing its optimization for photodetection rather than power generation. The technique also elucidates the decreasing local ηCE of the solar cell under intense irradiation. 相似文献
936.
Atom reflection is studied in the presence of a non-Abelian vector potential proportional to a spin-1/2 operator. The potential is produced by a relatively simple laser configuration for atoms with a tripod level scheme. We show that the atomic motion is described by two different dispersion branches with positive or negative chirality. As a consequence, atom reflection shows unusual features, since an incident wave may split into two reflected ones at a barrier, an ordinary specular reflection, and an additional nonspecular one. Remarkably, the latter wave can exhibit negative reflection and may become evanescent if the angle of incidence exceeds a critical value. These reflection properties are crucial for future designs in non-Abelian atom optics. 相似文献
937.
Structure and Computational Studies of New Sulfonamide Compound: {(4-nitrophenyl)sulfonyl}tryptophan
Florence Uchenna Eze Chigozie Julius Ezeorah Blessing Chinweotito Ogboo Obinna Chibueze Okpareke Lydia Rhyman Ponnadurai Ramasami Sunday Nwankwo Okafor Groutso Tania Simeon Atiga Thomas Ugochukwu Ejiyi Mirabel Chinasa Ugwu Chiamaka Peace Uzoewulu Jude Ikechukwu Ayogu Ogechi Chinelo Ekoh David Izuchukwu Ugwu 《Molecules (Basel, Switzerland)》2022,27(21)
Synthesis of sulfonamide through an indirect method that avoids contamination of the product with no need for purification has been carried out using the indirect process. Here, we report the synthesis of a novel sulfonamide compound, ({4-nitrophenyl}sulfonyl)tryptophan (DNSPA) from 4-nitrobenzenesulphonylchloride and L-tryptophan precursors. The slow evaporation method was used to form single crystals of the named compound from methanolic solution. The compound was characterized by X-ray crystallographic analysis and spectroscopic methods (NMR, IR, mass spectrometry, and UV-vis). The sulfonamide N-H NMR signal at 8.07–8.09 ppm and S-N stretching vibration at 931 cm−1 indicate the formation of the target compound. The compound crystallized in the monoclinic crystal system and P21 space group with four molecules of the compound in the asymmetric unit. Molecular aggregation in the crystal structure revealed a 12-molecule aggregate synthon sustained by O-H⋯O hydrogen bonds and stabilised by N-H⋯O intermolecular contacts. Experimental studies were complemented by DFT calculations at the B3LYP/6-311++G(d,p) level of theory. The computed structural and spectroscopic data are in good agreement with those obtained experimentally. The energies of interactions between the units making up the molecule were calculated. Molecular docking studies showed that DNSPA has a binding energy of −6.37 kcal/mol for E. coli DNA gyrase (5MMN) and −6.35 kcal/mol for COVID-19 main protease (6LU7). 相似文献
938.
939.
940.
Martens Dana L. Motuzas Julius Smart Simon Diniz da Costa João C. 《Journal of Sol-Gel Science and Technology》2021,98(3):470-477
Journal of Sol-Gel Science and Technology - This work reports the hydrothermal treatment effect on cobalt silica-seeded xerogels under harsh conditions at 550?°C for 100?h in a... 相似文献