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41.
Santiago MB Vélez MM Borrero S Díaz A Casillas CA Hofmann C Guadalupe AR Colón JL 《Electroanalysis》2006,18(6):559-572
We present a carbon paste electrode (CPE) modified using the electron mediator bis(1,10‐phenanthroline‐5,6‐dione)(2,2′‐bipyridine)ruthenium(II) ([Ru(phend)2bpy]2+) exchanged into the inorganic layered material zirconium phosphate (ZrP). X‐Ray powder diffraction showed that the interlayer distance of ZrP increases upon [Ru(phend)2bpy]2+ intercalation from 10.3 Å to 14.2 Å. The UV‐vis and IR spectroscopies results showed the characteristic peaks expected for [Ru(phend)2bpy]2+. The UV‐vis spectrophotometric results indicate that the [Ru(phend)2bpy]2+ concentration inside the ZrP layers increased as a function of the loading level. The exchanged [Ru(phend)2bpy]2+ exhibited luminescence even at low concentration. Modified CPEs were constructed and analyzed using cyclic voltammetry. The intercalated mediator remained electroactive within the layers (E°′=–38.5 mV vs. Ag/AgCl, 3.5 M NaCl) and electrocatalysis of NADH oxidation was observed. The kinetics of the modified CPE shows a Michaelis–Menten behavior. This CPE was used for the oxidation of NADH in the presence of Bakers' yeast alcohol dehydrogenase. A calibration plot for ethanol is presented. 相似文献
42.
The diluted-field Ising model, a random nonnegative field ferromagnetic model, is shown to have a unique Gibbs measure with probability I when the field mean is positive. Our methods involve comparisons with ordinary uniform field Ising models. They yield as a corollary a way of obtaining spontaneous magnetization through the application of a vanishing random magnetic field. The correlation lengths of this model defined as (lim
n-(1/n) log 0;
n)-1, wheren is the site on the first coordinate axis at distancen from the origin and 0;
n
is the origin ton two-point truncated correlation function, is non-random. We derive an upper bound for it in terms of the correlation length of an ordinary nonrandom model with uniform field related to the field distribution of the diluted model. 相似文献
43.
G. Marest A. Fontes J. Roigt A. Faussemagne S. Fayeulle M. Jeandin A. Benyagoub N. Moncoffre M. Frainais 《Hyperfine Interactions》1995,95(1):227-245
Nodular iron of martensitic structure was treated by means of a XeCl laser prototype. The energy density varied from 0.3 to 5 J/cm2 and the number of shots from 4 to 40. Conversion electron Mössbauer spectroscopy, conversion X-ray Mössbauer spectroscopy and grazing incidence X-ray diffraction were used to characterize the irradiated surface. Some Rutherford backscattering spectrometry measurements were performed to control surface oxidation and carbon distribution. It is shown that after irradiation austenite formed in a rather deep heat affected zone (10–20 m) compared to the thickness of the melted zone ( 1 m). The austenite amount as well as its carbon content increase with energy density and number of shots up to a threshold of carbide formation. Beyond the threshold Fe2C, Fe3C and Fe5C2 formed only in the melted zone. The carbon content as a function of depth is constant in the melted layer, then decreases quickly from the melted layer-heat affected zone interface down its initial value. The carbon content is shown to govern the evolution of phases content in the melted layer depending on the laser treatment conditions. 相似文献
44.
J. Miguel Vadillo M. Esther Gonzalez Isabel Carretero J. Javier Laserna 《Mikrochimica acta》1995,118(3-4):273-282
Micellar liquid chromatography (MLC) and capillary zone electrophoresis (CZE) have been evaluated for the analysis of twelve banned drugs in sport including diuretics and -blockers. In MLC, a sodium dodecylsulphate aqueous solution has been used as mobile phase using an octadecylsilica column. In CZE, a pH 8 buffer solution and a silica capillary have been employed. Parameters of retention and efficiency have been compared. Limits of detection with UV detection at 254 nm and relative standard deviations for atenolol, furosemide, nadolol, spironolactone and triamterene were established and compared in both techniques. Examples of direct urine injection into the separation systems are presented. Drugs overlapping in MLC are well resolved in CZE, while the opposite is true for a limited number of drugs. Some interferences from urine may arise in CZE. The selectivity of analysis would be greatly enhanced by using both techniques, which require only filtration as pre-treatment. 相似文献
45.
We study a class of quasilinear elliptic equations on the unit ball of ℝ
n
in the divergence form ∑
j=1
n
D
j{G(|x|2,|Du|2)D
j
u} =H(|x|) and get estimates on the boundary by using a modified barrier-function technique of Bernstein. We establish a maximum principle
for the gradients of solutions and get a global gradient estimate. We prove that solutions with constant boundary condition
must be radial. Finally, we apply these results to graphs {(x,u(x)):x∈H
n
} whereu:H
n
→ℝ is a smooth map of then-hyperbolic spaceH
n
=B(0,1) with the metric
to get the existence of graphs with radial prescribed mean curvature. 相似文献
46.
Summary We consider the one dimensional nearest neighbors asymmetric simple exclusion process with ratesq andp for left and right jumps respectively;q<p. Ferrari et al. (1991) have shown that if the initial measure isv
,
, a product measure with densities and to the left and right of the origin respectively, <, then there exists a (microscopic) shock for the system. A shock is a random positionX
t
such that the system as seen from this position at timet has asymptotic product distributions with densities and to the left and right of the origin respectively, uniformly int. We compute the diffusion coefficient of the shockD=lim
t
t
–1(E(X
t
)2–(EX
t
)2) and findD=(p–q)(–)–1((1–)+(1–)) as conjectured by Spohn (1991). We show that in the scale
the position ofX
t
is determined by the initial distribution of particles in a region of length proportional tot. We prove that the distribution of the process at the average position of the shock converges to a fair mixture of the product measures with densities and . This is the so called dynamical phase transition. Under shock initial conditions we show how the density fluctuation fields depend on the initial configuration. 相似文献
47.
48.
49.
50.
Cristina Otero Eitel Pastor Antonio Ballesteros 《Applied biochemistry and biotechnology》1990,26(1):35-44
Transesterification between ethyl butyrate and glycerol using very different lipase preparations (native, modified, and immobilized) in a two-phase system—no extra solvent added—has been investigated. Optimal conversion was obtained with the presence of 5% water in the reaction mixture. Only monobutyrin was produced in all conditions tested. The best enzyme preparations were nativeCandida cylindracea lipase,Mucor miehei lipase immobilized on a phenol-formaldehyde exchange resin (Lipozyme?), andC. cylindracea lipase immobilized on Celite. 相似文献