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101.
F. Flores P. L. de Andres F. J. Garcia-Vidal L. Jurczyszyn N. Mingo R. Perez 《Progress in Surface Science》1995,48(1-4):27-38
Physisorption on metal surfaces, and the tunneling currents through the adsorbed species, are calculated using a unified formalism that presents both problems on the same footing. Our method is based on a self-consistent LCAO approach whereby the different interaction parameters defining the bonds, and the tunneling currents, are calculated using the atomic properties of the atomic species forming the interface. Green function methods and the Keldish formalism are used to calculate the different physical properties. We present results for xenon adsorbed on aluminum. 相似文献
102.
The synthesis and X-ray structures of gold(I) adducts supported by beta-diketiminates have been reported. {[HC{(H)C(2,4,6-Br(3)C(6)H(2))N}(2)]Au}(2) and {[HC{(H)C(Dipp)N}(2)]Au}(2) [Dipp = 2,6-(i-Pr)(2)C(6)H(3)] are easily isolable solids and feature 12-membered macrocyclic ring structures. beta-Diketiminate ligands adopt a W-shaped conformation. Gold atoms are bonded to the nitrogen atoms in a linear fashion. (1)H NMR signals corresponding to the protons at the beta-diketiminate ligand beta-C position of the gold adducts appear at a notably high downfield region. 相似文献
103.
J.T. Elizalde Galindo A.H. Adair C.E. Botez V. Corral Flores D. Bueno Baques L. Fuentes Cobas J.A. Matutes-Aquino 《Applied Physics A: Materials Science & Processing》2007,87(4):743-747
Measurements of ac-susceptibility and dc-magnetization were carried out on samples of Ni1-xZnxFe2O4 nanoparticles (x=0, 0.25, 0.5, 0.75) with average diameters 〈D〉≈7 nm. Values of the superparamagnetic blocking temperature
T̄B were obtained from the characteristic temperature behavior of the imaginary susceptibility χimag. An Arrhenius-type law, which accurately describes the relationship between the observation time τobs and the blocking temperature, was used to determine the effective energy barrier to magnetization reversal Ueff. A Zn-content dependence of the energy barrier is observed, where Ueff changes little for 0≤x≤0.25, it peaks at x=0.5, and decreases back upon further Zn-doping. The large increase of Ueff at x=0.5 is attributed to an enhanced magnetic anisotropy induced by the crossover between two spatial arrangements of spins
in the A and B sub-lattices of the ferrimagnetic inverse spinel.
PACS 75.50.Bb; 75.50.Gg; 75.30.Et 相似文献
104.
A stochastic methodology was used to analyze the field-scale transport of solutes in heterogeneous aquifers with first-order biodegradation. Spectral methods and perturbation techniques were utilized to develop expressions for the field-scale effective parameters in the mean transport model. Expressions were obtained for the longitudinal and transverse macrodispersivity coefficients, and effective velocity and an effective decay parameter for statistically anisotropic, and isotropic, heterogeneous porous medium, respectively. The behavior of these parameters was described as function of time and log K correlation scale. The expressions for asymptotic values of the dispersivity coefficients and effective velocity and decay parameters were also derived for the isotropic case. 相似文献
105.
106.
Remedios Fernández-Fernández Juan Carlos López-Martínez Roberto Romero-González José Luis Martínez-Vidal María Isabel Alarcón Flores Antonia Garrido Frenich 《Chromatographia》2010,72(1-2):55-62
A rapid, reliable and sensitive method has been developed to determine malic and citric acid in fruits and vegetables. The methodology is based on simple extraction with an aqueous solution of ethanol (80% v/v) and subsequent chromatographic analysis by liquid chromatography coupled to mass spectrometry. Electrospray ionization in negative mode was used. The best response for citric and malic acid was provided by molecular ions [M?H]? at m/z 191 and 133 respectively. These ions were used for quantification, whereas other fragments were used as confirmation ions. Different variables involved in the separation and detection process, such as mobile phase, gradient profile and flow rate have been optimised. Linearity, repeatability, recovery and limits of quantification were evaluated. Good linearity was obtained up to 5,000 mg kg?1. Recovery ranged from 90.0 to 104.6%, repeatability (expressed as RSD) was <8% for tested matrices, and limits of quantification were equal or lower than 65 mg kg?1. Finally, the method was applied to the analysis of samples of orange, tomato and pepper. 相似文献
107.
Cadmium determination in biological samples by direct solid sampling flame atomic absorption spectrometry 总被引:1,自引:0,他引:1
rico Marlon de Moraes Flores Jos Neri Gottfried Paniz Ayrton Figueiredo Martins Valderi L. Dressler Edson Irineu Müller Adilson Ben da Costa 《Spectrochimica Acta Part B: Atomic Spectroscopy》2002,57(12):2187-2193
A direct solid sampling flame atomic absorption spectrometric procedure for trace determination of cadmium in biological samples has been developed. Test samples (0.05–2.00 mg) were ground and weighed into small polyethylene vials, which were connected to the device for solid sample introduction into a conventional air/acetylene flame. Test samples were carried as a dry aerosol to a quartz cell, placed between the burner and the optical path, which had a perpendicular entrance and a slit in the upper part. The atomic vapor generated in the flame produced a transient signal that was totally integrated within 1 s. The effect of operating conditions and the extent of grinding on the analytical signal were evaluated. Background signals were always low and a characteristic mass of 0.29 ng Cd was obtained. Calibration was performed using different masses of solid certified reference materials. Results obtained for certified and in-house reference materials were typically within the 95% confidence interval of the certified and/or reference value, and the precision, expressed as relative standard deviation, was between 3.8 and 6.7%. The proposed system is simple and it might be adapted to conventional atomic absorption spectrometers allowing the determination of Cd in more than 80 test samples per hour, excluding weighing. 相似文献
108.
A p-version finite element method has been used to calculate second-order pair and total correlation energies for closed-shell Mg and Ar. Comparison with the best results found in the literature suggests that the present values are the most accurate and that the method should perform comparatively better for heavier elements. © 1993 John Wiley & Sons, Inc. 相似文献
109.
Cholant C. M. Westphal T. M. Balboni R. D. C. Moura E. A. Gündel A. Flores W. H. Pawlicka A. Avellaneda C. O 《Journal of Solid State Electrochemistry》2017,21(5):1509-1515
Journal of Solid State Electrochemistry - Pure and doped vanadium pentoxide (V2O5, V2O5/MoO3) thin films were prepared by sol-gel method and dip coating technique. Furthermore, they were... 相似文献
110.
Deng Z Tong L Flores M Lin S Cheng JX Yan H Liu Y 《Journal of the American Chemical Society》2011,133(14):5389-5396
We report a simple, fast and green phosphine-free colloidal chemistry to synthesize high-quality wurtzite-type Mn-doped ZnS quantum rods (QRs) with tunable diameters (1.6-5.6 nm), high aspect ratios (up to 50), variable Mn doping levels (0.18-1.60%), and high quantum yields (up to 45%). The electron paramagnetic resonance spectra with modeling reveal the successful doping of paramagnetic Mn(2+) ions in the host ZnS QRs. The Mn-doped ZnS QRs demonstrate tunable dual-color (orange and blue) emissions by tuning the doping levels and UV excitation wavelengths. The orange emission with long decay lifetime (3.3 ms) originates from the doped Mn(2+) states, while the blue emission with fast decay lifetime (0.31 ns) is attributed to the QR surface states. The bright two- and three-photon excitation upconversion luminescence from the Mn-doped ZnS QRs have been observed using tunable near-infrared femtosecond laser. Our strategy provides a versatile route to programmably control the optical properties of anisotropic semiconductor nanomaterials, which may create new opportunities for photonic devices and bioimaging applications. 相似文献