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891.
An additional maximum has been detected in the differential potentiometric titration of mixtures of sodium hydroxide and sodium carbonate with hydrochloric acid using pH-responsive glass electrodes. This maximum is not detected under the following conditions: if ethanol (mol fraction >0.2) or t-butanol (mol fraction >0.1) is added; when the temperature is raised above 55°C; when hydrogen gas is bubbled through the solution; if a hydrogen gas electrode is used instead of the glass electrode; when carbonic anhydrase is added. The additional feature is ascribed to a new species HCO3·H2CO3- formed in solutions by a slow reaction. 相似文献
892.
Antonella Fontana Paolo De Maria Gabriella Siani Brian H. Robinson 《Colloids and surfaces. B, Biointerfaces》2003,32(4):365-374
Didodecyldimethylammonium bromide (DDAB) forms vesicles spontaneously by simple solubilization of the solid into water at a concentration of ≈2.5 mM. Vesicles can be observed by the increase in turbidity of the aqueous solution of DDAB and by the increase in absorbance (at λmax=490 nm) of a lipophilic dye (Sudan III) solubilized into the vesicular bilayer. This vesicle system has been perturbed by addition of single-chain surfactants in order to study the transition from a vesicle-stable region to a mixed-micelle region. Vesicle breakdown involves the initial incorporation of a single-chain surfactant into the vesicular bilayer, followed by subsequent disintegration of the vesicle. The progress of reaction has been observed by monitoring turbidity changes using a stopped-flow spectrophotometer. The rate of breakdown of vesicles depends on the concentration and hydrophobic properties of the added single-chain surfactant. In addition, hypertonic and hypotonic osmotic stresses have been investigated. 相似文献
893.
It is demonstrated that a closed symmetric derivation δ of aC?-algebra \(\mathfrak{A}\) generates a strongly continuous one-parameter group of automorphisms of aC?-algebra \(\mathfrak{A}\) if and only if, it satisfies one of the following three conditions
- (αδ+1)(D(δ))= \(\mathfrak{A}\) , α∈?\{0}.
- δ possesses a dense set of analytic elements.
- δ possesses a dense set of geometric elements.
- ∥(αδ+1)(A)∥≧∥A∥, α∈IR,A∈D(δ).
- If α∈IR andA∈D(δ) then (αδ+1)(A)≧0 impliesA≧0.
894.
It is pointed out that the linear scattering problem for a non-linear evolution equation which admits soliton solutions may be described in terms of a linear connection on a principal SL(2, ). The equation in question is satisfied if and only if the curvature of this connection vanishes. Some other properties of the curvature are identified. The sine-Gordon, Korteweg-de Vries and modified Korteweg-de Vries equations are treated explicitly.On leave of absence. Visit supported by NSF Grant 36217 and by the Norman Foundation. 相似文献
895.
896.
897.
898.
New Schiff bases of 5-aminouracil have been synthesized by the 1: 1 condensation with N-heterocyclic aldehydes. The new compounds were characterized by elemental analyses and 1H NMR spectroscopy. Under similar conditions, the condensation of 6-aminouracil with aldehydes failed to yield the desired Schiff base. Interestingly, the reaction of 6-aminouracil with 6-methylpyridine-2-carbaldehyde resulted in an unusual compound, 2-methyl-6-[7-(6-methylpyridin-2-yl)-2,4-dioxo-1,2,3,4-tetrahydropyrimido[4,5-d]pyrimidin-5-yl]-pyridinium methanesulfonate, whose crystal structure was elucidated by X-ray crystallography. 相似文献
899.
Electrochemical Characterization of Vertically Aligned Carbon Nanofiber Arrays Prepared by Hole‐mask Colloidal Lithography 下载免费PDF全文
Jendai E. Robinson William R. Heineman Laura B. Sagle M. Meyyappan Jessica E. Koehne 《Electroanalysis》2016,28(12):3039-3047
Nanoelectrode arrays consisting of vertically aligned carbon nanofibers were prepared through plasma enhanced chemical vapor deposition and patterned using hole‐mask colloidal lithography (HCL), a simple fabrication method employed as a cost‐effective patterning alternative to the conventional electron beam lithography. The density of the carbon nanofibers was easily altered by changing the concentration of the polystyrene spheres employed in HCL. Cyclic voltammetry and chronoamperometry were used to electrochemically characterize the arrays of different density. Results indicate that the density of the carbon nanofibers leads to differences in the macro/micro electroactive surface areas. 相似文献
900.
Low‐Temperature Solution Synthesis of Few‐Layer 1T ′‐MoTe2 Nanostructures Exhibiting Lattice Compression 下载免费PDF全文
Yifan Sun Yuanxi Wang Du Sun Bruno R. Carvalho Carlos G. Read Chia‐hui Lee Zhong Lin Kazunori Fujisawa Prof. Joshua A. Robinson Prof. Vincent H. Crespi Prof. Mauricio Terrones Prof. Raymond E. Schaak 《Angewandte Chemie (International ed. in English)》2016,55(8):2830-2834
Molybdenum ditelluride, MoTe2, is emerging as an important transition‐metal dichalcogenide (TMD) material because of its favorable properties relative to other TMDs. The 1T ′ polymorph of MoTe2 is particularly interesting because it is semimetallic with bands that overlap near the Fermi level, but semiconducting 2H‐MoTe2 is more stable and therefore more accessible synthetically. Metastable 1T ′‐MoTe2 forms directly in solution at 300 °C as uniform colloidal nanostructures that consist of few‐layer nanosheets, which appear to exhibit an approx. 1 % lateral lattice compression relative to the bulk analogue. Density functional theory calculations suggest that small grain sizes and polycrystallinity stabilize the 1T ′ phase in the MoTe2 nanostructures and suppress its transformation back to the more stable 2H polymorph through grain boundary pinning. Raman spectra of the 1T ′‐MoTe2 nanostructures exhibit a laser energy dependence, which could be caused by electronic transitions. 相似文献