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71.
Manuel Belmonte Vitor A. Silva Antonio José Fernandes Florinda Costa Rui Silva 《Journal of the American Ceramic Society》2003,86(5):749-754
The efficiency of different surface pretreatments (four standard chemical etchings and four diamond powder abrasive procedures) on silicon nitride (Si3 N4 ) substrates for chemical vapor deposition (CVD) of diamond has been systematically investigated. Blank Si3 N4 samples were polished with colloidal silica (∼0.25 μm). Diamond nucleation and growth runs were conducted in a microwave plasma chemical vapor deposition apparatus for 10 min and 6 h, respectively. Superior results concerning nucleation density ( N d ∼ 1010 cm−2 after 10 min), film uniformity, and grain size (below 2 μm after 6 h) were obtained for the mechanically microflawed samples, revealing that chemical etchings (hot and cold strong acids, molten base or CF4 plasma) are not crucial for good CVD diamond quality on Si3 N4 . 相似文献
72.
A study of modified carbon paste electrode employing Nile blue (NB) adsorbed on silica gel modified with niobium oxide (SN) for electrocatalytic oxidation of reduced nicotinamide adenine dinucleotide (NADH) is described. The adsorbed organic dye on SN was used to prepare a modified carbon paste electrode to investigate its electrochemical properties. The formal potential (E°′) of the adsorbed NB (−230 mV vs. saturated calomel electrode, SCE) showed a shift of 70 mV towards a more positive potential value, compared to NB dissolved in aqueous solution. In solutions with pH between 6.0 and 8.0 did stability and E°′ remained almost constant. However, for a solution pH lower than 6.0 the E°′ was affected by the acidity of the contacting solution, shifting the E°′ towards more positive values. For the solution pHs between 6.0 and 8.0 the electrocatalytic activity remained almost constant. A linear response range for NADH between 1.0×10−5 and 5.2×10−4 mol l−1, at pH 7.0, was observed for the electrode, with an applied potential of −200 mV versus SCE. The formation of an intermediate charge transfer (CT) complex was proposed to the CT reaction between NADH and adsorbed NB. The heterogeneous electron transfer rate, kobs, was 1400 M−1 s−1 and the apparent Michaelis-Menten constant, was 0.21 mM at pH 7.0 evaluated from rotating disk electrode (RDE) experiments with an electrode coverage of about 5.2×10−9 mol cm−2. The increase in the reaction rate between NADH and the immobilized NB compared to those obtained with dissolved NB was assigned to the shift of the E°′ towards more positive values. 相似文献
73.
74.
Blends of polyamide 6 (PA6) and polycarbonate (PC) have been investigated, over a full range of composition, to check interactions between them. SEM observations show that the mixtures are characterized by domains of clearly segregated homophases and voids between the two polymers. DSC and DMTA data indicate the presence of two Tg' s, corresponding to two separate phases, with the Tg of the PC phase decreasing on increasing the PA6 amount. Moreover, the crystallization kinetics of PA6 is slightly showed down by the PC. Chemical reactions between the two polymers are supposed to give rise to low molar mass compounds, as shown by GPC; these species plasticize the PC and partially dissolve into the molten polyamide, causing decrease of PC Tg and reduction of overall crystallization rate of PA6. Apparent influence of PC on melting temperature and enthalpy of PA6 is also discussed. 相似文献
75.
Rana M. Tubaileh Antonio Garrido-Fernández M. Victoria Ruiz-Méndez Manuel León-Camacho Enrique Graciani-Constante 《Journal of the American Oil Chemists' Society》2002,79(1):101-104
Changes in the contents of waxes and fatty alcohols during deodorization/physical refining of bleached olive oil were studied.
Experiments were carried out with 1.85% acidity oil, which was physically refined in a discontinuous deodorizer of 250-kg
maximum capacity using nitrogen as stripping gas instead of steam. The variables studied were load and temperature of oil
in the deodorizer as well as N2 flow. Analyses of waxes and alcohols were carried out at different operation times. The maximum content of wax was always
observed when the oil reached the deodorization temperature. The variation in the wax content depended on temperature and
N2 flow. Wax decomposition started and continued during the operating time, and a progressive decrease, which was pronounced
between 3 and 4 h, was observed. Small changes in waxes were observed between 4 and 5 h. Total content of fatty alcohols diminished
throughout the operating time, and changes did not depend on the variables studied. 相似文献
76.
Antonio M. Ortiz Fernando Royo Teresa Olivares Jose Carlos Castillo Luis Orozco‐Barbosa 《Expert Systems》2014,31(2):154-162
ZigBee is the primary standard solution for wireless sensor networks, implementing the Ad hoc On‐Demand Distance Vector (AODV) protocol in the network layer and supported by the standard IEEE 802.15.4. This study is focused on mesh topologies and the critical problems encountered when AODV is executed in conjunction with the Carrier Sense Multiple Access with Collision Avoidance protocol. These problems are mainly related to the packet overhead required to carry out route creation. To perform preliminary experiments to be able to implement AODV in a real network, a new metric is proposed herein. This metric uses fuzzy logic to help in the decision‐making process. The objective of the fuzzy routine is to determine, during the route‐discovery process, the best node to forward request/reply packets, with the aim of reducing packet overhead and energy consumption. Moreover, minor changes are also added to the discovery procedure of AODV to improve the performance of the route‐creation process. This intelligent version of AODV has provided promising experimental results, greatly reducing the number of packets required, with the consequent energy saving while selecting the best nodes to be part of the routes. 相似文献
77.
Manuel J. Castro José M. Gallardo Antonio Marquina 《Journal of scientific computing》2014,60(2):363-389
In this paper we propose a new class of incomplete Riemann solvers, based on approximations in the \(L^\infty \) -norm to the absolute value function in \([-1,1]\) by means of rational functions, for the numerical approximation of the solution of hyperbolic systems of conservation laws. The main idea relies on the construction of a numerical approximation to the viscosity matrix by using an appropriate rational real function \(R(x)\) , that approximates the function \(|x|\) uniformly in \([-1,1]\) , evaluated at the Jacobian of the fluxes of the hyperbolic system computed at some average value (for example, Roe averages). In addition to the Jacobians of the fluxes we shall use either the maximum in absolute value of the characteristic speeds in each cell or an upper bound of them. Thus, the resulting approximate Riemann solver is incomplete in the sense that we do not use the complete spectral decomposition of the Jacobian. Moreover, the new class of Riemann solvers consists of a hierarchy of schemes running from the more dissipative to the less dissipative ones, and having as limiting case a Roe-like scheme. According to the order of the approximation of the generating rational function used, the degree of dissipation can be dosed for particular applications. We study different rational approximations: Newman-type functions, iterative generated Halley functions, and also Chebyshev polynomial approximants. We test our basic algorithms for different initial value Riemann problems for ideal gas dynamics (HD) and magnetohydrodynamics (MHD) to observe their behavior with respect to challenging scenarios in numerical simulations, including some standard numerical pathologies (e. g., heat conduction, postshock oscillations and overheating) and the formation of compound waves in ideal MHD. We also examine our proposed schemes, by computing the numerical approximation of different initial value problems for nonconservative multilayer shallow water equations, where it has been observed that intermediate waves can be properly captured for an appropriate degree of approximation of the generating rational function used. Our numerical tests indicate that the proposed schemes are robust, running stable and accurate with a satisfactory time step restriction (CFL constant), and the computational cost is more advantageous with respect to schemes that use a complete spectral decomposition of the Jacobians. 相似文献
78.
Electrochemical destruction of chlorophenoxy herbicides by anodic oxidation and electro-Fenton using a boron-doped diamond electrode 总被引:1,自引:0,他引:1
Enric Brillas Birame Boye José Antonio Garrido Conchita Arias Christos Comninellis 《Electrochimica acta》2004,49(25):4487-4496
The degradation of herbicides 4-chlorophenoxyacetic acid (4-CPA), 4-chloro-2-methylphenoxyacetic acid (MCPA), 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) in aqueous medium of pH 3.0 has been comparatively studied by anodic oxidation and electro-Fenton using a boron-doped diamond (BDD) anode. All solutions are totally mineralized by electro-Fenton, even at low current, being the process more efficient with 1 mM Fe2+ as catalyst. This is due to the production of large amounts of oxidant hydroxyl radical (OH) on the BDD surface by water oxidation and from Fenton’s reaction between added Fe2+ and H2O2 electrogenerated at the O2-diffusion cathode. The herbicide solutions are also completely depolluted by anodic oxidation. Although a quicker degradation is found at the first stages of electro-Fenton, similar times are required for achieving overall mineralization in both methods. The decay kinetics of all herbicides always follows a pseudo first-order reaction. Reversed-phase chromatography allows detecting 4-chlorophenol, 4-chloro-o-cresol, 2,4-dichlorophenol and 2,4,5-trichlorophenol as primary aromatic intermediates of 4-CPA, MCPA, 2,4-D and 2,4,5-T, respectively. Dechlorination of these products gives Cl−, which is slowly oxidized on BDD. Ion-exclusion chromatography reveals the presence of persistent oxalic acid in electro-Fenton by formation of Fe3+-oxalato complexes, which are slowly destroyed by OH adsorbed on BDD. In anodic oxidation, oxalic acid is mineralized practically at the same rate as generated. 相似文献
79.
Maria?Antonietta BresciaEmail author Vincenzo?Mazzilli Angela?Sgaramella Stefano?Ghelli Francesco?Paolo Fanizzi Antonio?Sacco 《Journal of the American Oil Chemists' Society》2004,81(5):431-436
Characterization of the lipid fraction of raw cow and buffalo milk samples, collected in different breeding areas in Apulia,
a region of southern Italy, were performed by means of 1H NMR. The aim of this work was to establish whether FA composition data obtained by 1H NMR can be used in the differentiation of buffalo and cow milk samples according to species. A complete assignment of the
signals present in the spectrum was attempted by COSY, heteronuclear coherence spectra. Quantification of FA was carried out
by inserting the integrals of particular peaks in suitable calculations. Multivariate statistical analysis, conducted on the
results of the quantification, permitted buffalo and cow milks to be distinguished. 相似文献
80.
Evandro Eduardo Broday Antonio Augusto de Paula XavierReginaldo de Oliveira 《International Journal of Industrial Ergonomics》2014
The incorrect determination of metabolic rate can be linked to discrepancies between the model of the PMV (Predicted Mean Vote) and real thermal sensation collected in field studies. Aiming to improve the correlation of the PMV model and the real thermal sensation, this work established new values for the metabolic rate: one way being called “calculated” using Newton's Method and the other called "measured" using a metabolic analyzer. Welder's activities were evaluated, through the measurements of environmental and personal variables. New values of metabolic rate were determined for this activity. The values found for the calculated form and the measured one were, respectively, 178.63 and 145.46 W/m2, different from the range provided by the table of ISO 8996 (2004) for this activity (75–125 W/m2). In order to verify which of the values of the metabolic rate was closer to the real thermal sensation of PMV, a linear regression was made between the PMV and the real thermal sensation in three ways: S × PMVtabulated (R2 = 0.1749), S × PMVcalculated (R ² = 0.7481) and S × PMVmeasured (R2 = 0.7854). It was found that the values measured by the instrument gave a higher coefficient of determination which was chosen for the correction of the table. The correction of the table provides a value of Mpredicted, that is a value of metabolic rate that corrects the values provided by the tables of ISO 8996 (2004), by means of a correction coefficient. For the welder's activities in a metal-mechanics industry, tabulated values can be multiplied by the correction coefficient 1.4648 in order to minimize inaccuracies. The PMVpredicted, obtained through the Mpredicted, when related to the actual thermal sensation, provides a coefficient of determination of 0.7511, thereby improving the model of the PMV. 相似文献