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121.
Baffert C Boas JF Bond AM Kögerler P Long DL Pilbrow JR Cronin L 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(33):8472-8483
The synthesis, isolation and structural characterization of the sulfite polyoxomolybdate clusters alpha-(D(3h))(C(20)H(44)N)(4){alpha-[Mo(18)O(54)(SO(3))(2)]}CH(3)CN and beta-(D(3d))(C(20)H(44)N)(4){beta-[Mo(18)O(54)(SO(3))(2)]}CH(3)CN is presented. Voltammetric studies in acetonitrile (0.1 M Hx(4)NClO(4), Hx(4)N=tetra-n-hexylammonium) reveal the presence of an extensive series of six one-electron reduction processes for both isomers. Under conditions of bulk electrolysis, the initial [Mo(18)O(54)(SO(3))(2)](4-/5-) and [Mo(18)O(54)(SO(3))(2)](5-/6-) processes produce stable [Mo(18)O(54)(SO(3))(2)](5-) and [Mo(18)O(54)(SO(3))(2)](6-) species, respectively, and the same reduced species may be produced by photochemical reduction. Spectroelectrochemical data imply that retention of structural form results upon reduction, so that both alpha and beta isomers are available at each of the 4-, 5-, and 6-redox levels. However, the alpha isomer is the thermodynamically favored species in both the one- and two-electron-reduced states, with beta-->alpha isomerization being detected in both cases on long time scales (days). EPR spectra also imply that increasing localization of the unpaired electron occurs over the alpha- and beta-[Mo(18)O(54)(SO(3))(2)](5-) frameworks as the temperature approaches 2 K where the EPR spectra show orthorhombic symmetry with different g and hyperfine values for the alpha and beta isomers. Theoretical studies support the observation that it is easier to reduce the alpha cluster than the beta form and also provide insight into the driving force for beta-->alpha isomerization in the reduced state. Data are compared with that obtained for the well studied alpha-[Mo(18)O(54)(SO(4))(2))](4-) sulfate cluster. 相似文献
122.
Barros CN Arêas EP Figueiredo EN Arêas JA 《Colloids and surfaces. B, Biointerfaces》2006,48(2):119-127
A low-resolution 1H NMR relaxometry study on the dynamics of an n-decane/water emulsion stabilized by β-casein is presented. Spin–spin (transverse) relaxation time constants (T2) were used to assess relative mobilities of emulsion components, by a selective deuteration procedure. Data analysis allowed the emulsion investigated to be described by a heterogeneous collection of dynamically distinct populations. A major population of n-decane molecules presented an average mobility that very nearly approached that of pure solvent, which is compatible with its occurrence in the emulsion continuous microphase. β-Casein molecules displayed a prevalent population with significantly decreased mobility as compared to the free protein in solution, which is in accordance with the protein location at the oil/water interface. Also, a major H2O population with significantly lower average T2 as compared to the pure liquid was detected and has been assigned to interfacial water. 相似文献
123.
Amino alcohols are important synthons for N-heterocycles. We have developed an efficient method to activate hydroxyl groups, which avoids the use of toxic reagents and tolerates a wide variety of functional groups. Our strategy has been applied to the synthesis of functionalized p-methoxyphenyl-protected azetidines, pyrrolidines, and piperidines. The required amino alcohols were synthesized according to an optimized proline-catalyzed Mannich protocol. An azetidine analogue of ezetimibe was synthesized to demonstrate the potential for the synthesis of drug-like molecules. 相似文献
124.
Paulo JP Coelho JL Figueiredo MA 《The Journal of the Acoustical Society of America》2010,128(4):1747-1754
Low noise surfaces have been increasingly considered as a viable and cost-effective alternative to acoustical barriers. However, road planners and administrators frequently lack information on the correlation between the type of road surface and the resulting noise emission profile. To address this problem, a method to identify and classify different types of road pavements was developed, whereby near field road noise is analyzed using statistical learning methods. The vehicle rolling sound signal near the tires and close to the road surface was acquired by two microphones in a special arrangement which implements the Close-Proximity method. A set of features, characterizing the properties of the road pavement, was extracted from the corresponding sound profiles. A feature selection method was used to automatically select those that are most relevant in predicting the type of pavement, while reducing the computational cost. A set of different types of road pavement segments were tested and the performance of the classifier was evaluated. Results of pavement classification performed during a road journey are presented on a map, together with geographical data. This procedure leads to a considerable improvement in the quality of road pavement noise data, thereby increasing the accuracy of road traffic noise prediction models. 相似文献
125.
Trigueiro João Paulo C. Figueiredo Rute C. Rojo Javier Viana Renato M. R. Schnitzler Mariane C. Silva Glaura G. 《Journal of Solid State Electrochemistry》2016,20(7):1991-2000
Journal of Solid State Electrochemistry - Carbon nanotubes (CNTs) were surface-modified by a glycodendrimer with four glucose units (4-Gl). Electrodes for supercapacitors based on CNT/4-Gl hybrids... 相似文献
126.
In this work, we performed Monte Carlo simulations on a lattice model for spontaneous amphiphilic aggregation, in order to study the orientational and hydrogen-bonding dynamics of water on different regions inside the micellar solution. We employed an associating lattice gas model that mimics the aqueous solvent, which presents a rich phase diagram with first- and second-order transition lines. Even though this is a simplified model, it makes possible to investigate the orientational dynamics of water in an equilibrium solution of amphiphiles, as well as the influence of the different phases of the solvent in the interfacial and bulk water dynamics. By means of extensive simulations, we showed that, at high temperatures, the behavior of the orientational relaxation and hydrogen bonding of water molecules in the bulk, first, and second hydration shells are considerable different. We observe the appearance of a very slow component for water molecules in the first hydration shell of micelles when the system reaches a high-density phase, consistent with previous theoretical and experimental studies concerning biological water. Also, at high temperatures, we find that water molecules in the second hydration shell of micelles have an orientational decay similar to that of bulk water, but with a generally slower dynamics. Otherwise, at low temperatures, we have two components for the orientational relaxation of bulk water in the low density liquid phase, and only a single component in the high density liquid (HDL) phase, which reflect the symmetry properties of the different phases of the solvent model. In the very dense region of water molecules in the first hydration shell of micelles at low temperatures, we find two components for the orientational relaxation on both liquid phases, one of them much slower than that in the single component of bulk water in the HDL phase. This happens even though our model does not present any hindrance to the water rotational freedom caused by the presence of the amphiphiles. 相似文献
127.
Rubens Figueiredo Camargo Edmundo Capelas de Oliveira Jayme Vaz Jr. 《Mathematical Physics, Analysis and Geometry》2012,15(1):1-16
The classical Mittag-Leffler functions, involving one- and two-parameter, play an important role in the study of fractional-order
differential (and integral) equations. The so-called generalized Mittag-Leffler function, a function with three-parameter
which generalizes the classical ones, appear in the fractional telegraph equation. Here we introduce some integral transforms
associated with this generalized Mittag-Leffler function. As particular cases some recent results are recovered. 相似文献
128.
Hidalgo C Silva C Carreras BA van Milligen B Figueiredo H García L Pedrosa MA Gonçalves B Alonso A 《Physical review letters》2012,108(6):065001
The dynamical coupling between density gradients and particle transport has been investigated using similar experimental tools in the plasma boundary of different tokamak (JET, ISTTOK) and stellarator (TJ-II) devices, showing that the size of turbulent events is minimum in the proximity of the most probable density gradient. Experimental results were found to be consistent with results from two very different models of plasma turbulence and transport. The present findings, common to several plasma devices, suggest the importance of self-regulation mechanisms between plasma transport and gradients in fusion devices. 相似文献
129.
Deepak?D.?Dicholkar Lalit?K.?Patil Vilas?G.?Gaikar Shekhar?KumarEmail author U.?Kamachi Mudali R.?Natarajan 《Journal of Radioanalytical and Nuclear Chemistry》2012,291(3):739-743
The high performance liquid chromatography and gas chromatography methods were investigated for their applicability in determining
micro-level concentrations of tri-n-butyl phosphate (TBP). A high performance liquid chromatograph (HPLC) equipped with refractive
index detector was used in determining TBP up to 2 ppm concentration level in the aqueous nitric acid solutions. The gas chromatography
incorporated with Thermionic Detector (NPD) and Flame Photometric Detector (FPD) were examined for their potential in analyzing
TBP in organic phase up to sub-ppm level. The results indicated that HPLC-RI technique is well suited for direct analysis
of aqueous phase. For organic phase analysis, gas chromatographic methods with the TID and FPD were suitable but performance
of detectors deteriorated often due to fouling. 相似文献
130.
Stochastic derivations of the Schrödinger equation are always developed on very general and abstract grounds. Thus, one is never enlightened which specific stochastic process corresponds to some particular quantum mechanical system, that is, given the physical system—expressed by the potential function, which fluctuation structure one should impose on a Langevin equation in order to arrive at results identical to those comming from the solutions of the Schrödinger equation. We show, from first principles, how to write the Langevin stochastic equations for any particular quantum system. We also show the relation between these Langevin equations and those proposed by Bohm in 1952. We present numerical simulations of the Langevin equations for some quantum mechanical problems and compare them with the usual analytic solutions to show the adequacy of our approach. The model also allows us to address important topics on the interpretation of quantum mechanics. 相似文献