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121.
122.
A.C.A. Ramos G.A. Farias N.S. Almeida 《Physica E: Low-dimensional Systems and Nanostructures》2011,43(10):1878-1881
The effects of nonzero temperature, finite thickness and magnetic fields on an electron gas confined in a quasi-two-dimensional (Q2DEG) region are studied. Finite values of the thickness allow the existence of energy bands and give new characteristics to the system. Here we study some thermodynamic and transport properties to get a better understanding of these effects. For electronic densities of the order of 1012 electrons per cm2, and temperatures lower than 4 K, it is found that the chemical potential, free energy, magnetization, magnetic susceptibility and the inverse of Hall conductivity are independent of the thickness up to it reaches a threshold value. Systems with thicknesses a little above of the critical value lose the two-dimensional character, but they do not have the properties of a three-dimensional electron gas. 相似文献
123.
We present a simple measure of the conductance fluctuations in open ballistic chaotic quantum dots, extending the number of maxima method originally proposed for the statistical analysis of compound nuclear reactions. The average number of extreme points (maxima and minima) in the dimensionless conductance T as a function of an arbitrary external parameter Z is directly related to the autocorrelation function of T(Z). The parameter Z can be associated with an applied gate voltage causing shape deformation in quantum dot, an external magnetic field, the Fermi energy, etc. The average density of maxima is found to be <ρ(Z)>=α(Z)/Z(c), where α(Z) is a universal constant and Z(c) is the conductance autocorrelation length, which is system specific. The analysis of <ρ(Z)> does not require large statistic samples, providing a quite amenable way to access information about parametric correlations, such as Z(c). 相似文献
124.
We study the homology theory of ? - modal maps of the interval. We give another proof of the Milnor and Thurston results
about zeta-functions and we give a functorial approach to kneading theory. Our results give explicit methods for computing
the sequences of lap numbers ? (f
k
) and the sequences of numbers of periodic points in an arbitrary interval [x,y].
Received: 25 February 1998 / Accepted: 15 January 1999 相似文献
125.
Paula Gonçalves Fenga Nelson Ramos Stradiotto 《Journal of Solid State Electrochemistry》2011,15(6):1279-1286
In this work, the electrochemical quartz crystal microbalance has been employed to monitor directly the in situ growth of
the zinc hexacyanoferrate film during the electrodeposition. Mass changes of the platinum|crystal working electrode were correlated
with cyclic voltammetry data. Effects of the sorption of counter-cations (K+, Na+, and NH4+ {\hbox{NH}}_4^{+} and anions (Cl− and SO42 - {\hbox{SO}}_4^{2 - } ) during redox reactions were studied. The electrocatalytic oxidation properties of procaine by the zinc hexacyanoferrate
films were performed. 相似文献
126.
127.
9-Membered rings are readily constructed through a radical addition-cyclisation sequence on a 1,6-dien-3-ol system followed by a Grob-type fragmentation. 相似文献
128.
Miriam Beneito‐Cambra Virginia Bernabé‐Zafón Ernesto F. Simó‐Alfonso Guillermo Ramis‐Ramos 《Rapid communications in mass spectrometry : RCM》2010,24(14):2093-2100
A new derivatization procedure to increase the sensitivity of electrospray ionization mass spectrometry (ESI‐MS) to non‐ethoxylated and ethoxylated alcohols was investigated. The analytes were oxidized with chromium(VI) oxide and the resulting carboxylic and ethoxy‐carboxylic acids were isolated by extraction with ethyl acetate; the extracts were alkalinized and infused into the ESI‐MS system working in the negative‐ion mode. The yields of the combined oxidation‐extraction were ca. 100% for non‐ethoxylated fatty alcohols dissolved in acetone and they decreased moderately in samples containing increasing amounts of water (e.g., a 75% yield was obtained with 50% water). Ethoxylated alcohols with more than two ethylene oxide units resulted in yields of ca. 60%. Low limits of detection (LODs) were obtained when the procedure was applied to the analysis of body‐care products and cosmetics containing fatty alcohols, e.g., in a varicose‐vein cream, the LODs were 25 µg cetyl alcohol and 7.5 µg stearyl alcohol (detected as palmitic acid and stearic acid, respectively) per gram of sample. High molecular mass alcohols were also detected in seawater after pre‐concentration by solid‐phase extraction. Thus, the proposed method is particularly valuable for use in industrial samples having complex matrices and in environmental samples and it is competitive with other methods for the analysis of trace amounts of fatty alcohols. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
129.
130.
M. Ramos Suzarte N. Rodríguez J. P. Oliva N. Iznaga A. Perera A. Morales N. Gonzalez O. Torres T. Rodríguez 《Journal of Radioanalytical and Nuclear Chemistry》1999,240(2):499-503
Monoclonal antibody ior egf/r3 is a IgG2a, recognizes the epidermal growth factor receptor. The aim of the present work was
to evaluate the diagnostic efficacy of the99mTc-labeled ior egf/r3 for the detection of epithelial tumors, its metastasis and its recurrences. The sensitivity by organs
was: brain 100%, diegestive tract 90%, head and neck 89%, lung 84% and breast 79%. The overall sensitivity, specificity, accuracy,
positive predictive value and negative predictive value of the immunoscintigraphic imaging were 84.1%, 100%, 86.5%, 100% and
52.4%, respectively. Immunoscintigraphy with99mTc-ior egf/r3 is useful for the diagnosis and follow-up of epithelial tumors. 相似文献