28 resultados para 74.20.Fg BCS theory and its development
em Repositório Institucional UNESP - Universidade Estadual Paulista "Julio de Mesquita Filho"
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The solutions of a renormalized BCS equation are studied in three space dimensions in s, p and d waves for finite-range separable potentials in the weak to medium coupling region. In the weak-coupling limit, the present BCS model yields a small coherence length ξ and a large critical temperature, T c, appropriate for some high-T c materials. The BCS gap, T c, ξ and specific heat C s(T c) as a function of zero-temperature condensation energy are found to exhibit potential-independent universal scalings. The entropy, specific heat, spin susceptibility and penetration depth as a function of temperature exhibit universal scaling below T c in p and d waves.
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It is shown that the appearance of a fixed-point singularity in the kernel of the two-electron Cooper problem is responsible for the formation of the Cooper pair for an arbitrarily weak attractive interaction between two electrons. This singularity is absent in the problem of three and few superconducting electrons at zero temperature on the full Fermi sea. Consequently, such three- and few-electron systems on the full Fermi sea do not form Cooper-type bound states for an arbitrarily weak attractive pair interaction.
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Soil acidity is one of the most important factors limiting agricultural production in the tropics. For this reason, the objective of this research work was to evaluate the effects of soil liming on the performance of carambola (Averrhoa carambola) trees. The experiment took place at the Citrus Experimental Station in Bebedouro, state of São Paulo, Brazil. The soil was a Typic Haplustox (V = 26% at the 0- to 20-cm layer) between August 1999 and July 2003. The following doses of limestone were employed: 0, 1.85, 3.71, 5.56, and 7.41 t ha(-1). During 40 months after the experiment was set up, soil chemical attributes were periodically examined. For a period of 2 years, the trees had their leaves analyzed for micro-and macronutrients; their trunk diameter, height, and crown volume measured; and the production of fruits determined. Liming improved in evaluated chemical attributes of the soil: pH, calcium (Ca), magnesium (Mg), BS, V, and hydrogen and aluminium (H + At) from the upper 60 cm of soil when the samples were taken from both the line and between the lines of plants. In the leaves, the levels of Ca and Mg also increased. The highest fruit yields were observed when soil base saturations reached 45% on the lines and 50% between the lines, as well as when foliar levels of 8.0 g of Ca and 4.7 a of Mg per kilogram of leaves were attained.
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
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The characteristics, performance, and application of an electrode, namely, Pt vertical bar Hg vertical bar Hg-2(FF)(2)vertical bar Graphite, where FF stands for flufenamate ion, are described. This electrode responds to FF with sensitivity of (-58.6 +/- 1.2) mV decade(-1) over the range 1.0 x 10(-6) - 1.0 x 10(-2) mol L-1 at pH 6.0-9.0 and a detection limit of 7.1 x 10(-7) mol L-1. The electrode is easily constructed at a relatively low cost with fast response time (within 10-25 s) and can be used for a period of 5 months without any considerable change in its performance characteristics. The proposed electrode displayed good selectivity for flufenamate in the presence of several substances as well as in the presence of some carboxylate and inorganic anions. The electrode was successfully applied to the determination of flufenamic acid in pharmaceuticals and human serum samples.
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We consider arbitrary U (1) charged matter non-minimally coupled to the self-dual field in d = 2 + 1. The coupling includes a linear and a rather general quadratic term in the self-dual field. By using both Lagragian gauge embedding and master action approaches we derive the dual Maxwell Chern-Simons-type model and show the classical equivalence between the two theories. At the quantum level the master action approach in general requires the addition of an awkward extra term to the Maxwell Chern-Simons-type theory. Only in the case of a linear coupling in the self-dual field can the extra term be dropped and we are able to establish the quantum equivalence of gauge invariant correlation functions in both theories.
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The aim of this paper was to apply a multiresidue method using Supercritical Fluid Extraction (SFE) and capillary gas chromatography with electron capture and mass spectrometry detections in the analysis of the levels of pesticide residues in fruits and vegetables. Single laboratory validation of both solid-liquid and supercritical fluid extraction methods was carried out for 32 compounds selected from four pesticide classes (organochlorine, organonitrogen, organophosphorus and pyretroid) in blank and fortified samples of fresh lettuce, potato, apple and tomato. Recoveries for the majority of pesticides from fortified samples at fortification level of 0.04-0.10 mg kg -1 ranged 74-96% for both methods and confirmation of pesticide identity was performed by gas-chromatography-mass spectrometry in a selected-ion monitoring mode. Both methods showed good limits of detection (less 0.01 mg kg-1, depending on the pesticide and matrix) and the SFE method minimized environmental concerns, time, and laboratory work. ©2005 Sociedade Brasileira de Química.
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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
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We report the occurrence of aggressive vulvar carcinoma associated with condyloma acuminata in three patients: under 33 years old. Discussion of the role of the human papilloma virus (HPV) in the development of vulvar cancer is also presented. Three patients with condyloma associated with aggressive vulvar squamous cell carcinoma, in situ (1 case) and invasive (2 cases), documented by biopsy and/or vulvectomy are presented. In situ hybridization (ISH) was used to characterize the subtypes of HPV. One patient with erythematous systemic lupus developed in situ carcinoma after 5 years. The other two cases also developed aggressive multicentric, invasive squamous cell carcinoma after 10 years of diagnosis of condyloma. In all cases HPV cytological abnormalities were seen throughout the pathological examination. HPV 16 and 18 were present in cells of invasive squamous cell carcinoma in cases 2 and 3. HPV 6 and 11 were detected only in the condyloma area in case 2. HPV 30 was seen only in the condyloma area in case 3. This report emphasizes the need for biopsies of all unusually persistent or treatment-resistant condylomas, particularly in young and/or immunoisuppressed patients.
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Paracrine cell signaling is thought to be important for ovarian follicle development, and a role for some members of the fibroblast growth factor (FGF) family have been suggested. In the present study, we tested the hypothesis that FGF-8 and its cognate receptors (FGFR-3c and FGFR-4) are expressed in bovine preantral follicles. Reverse transcription-polymerase chain reaction was used to amplify bovine FGF-8, FGFR-3c, and FGFR-4 from preantral follicle samples and a variety of fetal and adult tissues. All three genes were widely expressed in fetal tissues, with a restricted expression pattern in adult tissues. FGF-8 and FGFR-3c were expressed in secondary follicles in 70% of fetuses examined, whereas FGFR-4 expression was significantly less frequent (20%). FGFR-3c expression frequency was significantly lower in primordial compared to secondary follicles, and FGF-8 expression showed a similar trend. FGFR-4 was only observed when all follicle classes of an individual were expressing both FGF-8 and FGFR-3c. We conclude that FGF-8 and its receptors are expressed in preantral follicles in a developmentally regulated manner. (C) 2005 Wiley-Liss, Inc.
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Six zoeal stages and the megalopa of the comestible crab Ucides cordatus cordatus (Linnaeus, 1763) are described and illustrated. The larvae were reared in the laboratory at temperature 25 ± 1ºC and water salinity of 24 ; duration of stages and survival rates were measured. Comparisons with the descriptions of the zoeal morphologic characters of Ocypodidae and Gecarcinidae permited to include definitively U. c. cordatus in the family Ocypodidae, subfamily Ocypodinae.
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Complex mass poles, or ghost poles, are present in the Hartree-Fock solution of the Schwinger-Dyson equation for the nucleon propagator in renormalizable models with Yukawa-type meson-nucleon couplings, as shown many years ago by Brown, Puff and Wilets (BPW), These ghosts violate basic theorems of quantum field theory and their origin is related to the ultraviolet behavior of the model interactions, Recently, Krein et.al, proved that the ghosts disappear when vertex corrections are included in a self-consistent way, softening the interaction sufficiently in the ultraviolet region. In previous studies of pi N scattering using ''dressed'' nucleon propagator and bare vertices, did by Nutt and Wilets in the 70's (NW), it was found that if these poles are explicitly included, the value of the isospin-even amplitude A((+)) is satisfied within 20% at threshold. The absence of a theoretical explanation for the ghosts and the lack of chiral symmetry in these previous studies led us to re-investigate the subject using the approach of the linear sigma-model and study the interplay of low-energy theorems for pi N scattering and ghost poles. For bare interaction vertices we find that ghosts are present in this model as well and that the A((+)) value is badly described, As a first approach to remove these complex poles, we dress the vertices with phenomenological form factors and a reasonable agreement with experiment is achieved, In order to fix the two cutoff parameters, we use the A((+)) value for the chiral limit (m(pi) --> 0) and the experimental value of the isoscalar scattering length, Finally, we test our model by calculating the phase shifts for the S waves and we find a good agreement at threshold. (C) 1997 Elsevier B.V. B.V.