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81.
The following varieties of natural quartz, as the blue, the green, the red, the pink, the black, the sulphurous and the milky quartz, have been investigated concerning their thermoluminescence properties. For comparison sake natural colorless alpha quartz has been include. Since X-rays diffraction analysis has shown that all of them have the same crystal structure as the alpha quartz, it is expected that no great change in the TL property should be found, however, that was not the case. The TL peaks at 110, 175, 220, 325 and 375 °C observed in the alpha quartz are not found in all the varieties of quartz, for instance, the sulphurous quartz presented only 110° and 245° peaks, the pink one presented just 110, 220 and 375 °C peaks and so on. In respect to TL response as function of gamma ray dose a quite varied behavior has been observed and discussed. 相似文献
82.
A tight-binding model is used to study the energy band of graphene and graphene ribbon under simple shear strain. The ribbon consists of lines of carbon atoms in an armchair or zigzag orientation where a simple shear strain is applied in the x-direction keeping the atomic distances in the y-direction unchanged. Such modification in the lattice gives an energy band that differs in several aspects from the one without any shear and with pure shear. The changes in the spectrum depend on the line displacement of the ribbon, and also on the modified hopping parameter. It is also shown that this simple shear strain tunes the electronic properties of both graphene and graphene ribbon, opening and closing energy gaps for different displacements of the system. The modified density of states is also shown. 相似文献
83.
110 °C thermoluminescence (TL) peak in quartz is well known due to its pre-dose effect, which is used in dating technique. The generally accepted mechanism for the production of this peak is based on Ge impurity contained in quartz. Its role is to substitute for Si in SiO4 tetrahedron and under irradiation gives rise to [GeO4/e?]? electron centre. Heating for TL read out liberates electron that recombines with hole in [AlO4/h]° or [H3O4/h]° centres emitting photon. The investigation, carried out on blue quartz, green quartz, black quartz, pink quartz, red quartz, sulphurous quartz, milky quartz, alpha quartz and synthetic quartz, has shown that the 110 °C TL peak in all these varieties of quartz has no correlation with the respective Ge content. Electron paramagnetic resonance (EPR) measurements on any of these varieties of quartz revealed a signal with g1=2.0004, g2=1.9986 and g3=1.974 and this signal does not appear to correspond to any known EPR signals in alpha quartz. Furthermore, isothermal decay measurements are carried out on the above mentioned EPR signal and 110 °C TL peak in alpha, blue and green quartz. A close correlation has been observed in the decay behavior. A new mechanism is proposed based on an interstitial O? centre. 相似文献
84.
M. Brandalise R. W. R. Verjulio-Silva M. M. Tusi O. V. Correa L. A. Farias M. Linardi E. V. Spinacé A. Oliveira Neto 《Ionics》2009,15(6):743-747
Pt/C, PtRu/C, PtBi/C, and PtRuBi/C electrocatalysts (20 wt.% metal loading) were prepared by borohydride reduction using H2PtCl6·6H2O, RuCl3·xH2O, and Bi(NO3)3·5H2O as metal sources and Vulcan XC 72 as support. The electrocatalysts were characterized by energy-dispersive X-ray analysis,
X-ray diffraction, and thermogravimetric analysis. The electro-oxidation of ethanol was studied in sulfuric acid solution
by cyclic voltammetry and chronoamperometry. The electrochemical studies showed that PtRuBi/C (50:40:10) electrocatalyst has
superior performance for ethanol electro-oxidation at room temperature compared to the other electrocatalysts. Preliminary
tests at 100 °C on a single direct ethanol fuel cell also confirm the results obtained by electrochemical techniques. 相似文献
85.
Bruno Fonsêca Feitosa Charlene Maria de Alcntara Amanda Beatriz Sales de Lima Adriano SantAna Silva Alfredina dos Santos Araújo Mnica Tejo Cavalcanti Edna Mori Isaac Moura Araújo Pablo Antonio Maia de Farias Polrat Wilairatana Henrique Douglas Melo Coutinho 《Molecules (Basel, Switzerland)》2022,27(18)
The inappropriate use of synthetic antibiotics has become a global public health problem. Therefore, the study of new alternatives for the treatment of infectious diseases is relevant and natural bioactive products are on the rise. This study conducted a scientific prospection of bioactive natural products with promising applications in the chemical control of microorganisms. A systematic review of the most recent articles was performed according to the following three steps: (i) eligibility assessment, (ii) screening, and (iii) inclusion of articles and information extraction. There has been an increase in the number of scientific publications on bioactive natural products for microbial control in the CAPES and SciELO databases (2001–2021). Seventeen relevant articles were included, most of which focused on extracts. Ascorbic acid, chlorogenic acid, chrysin, and quercetin were the most cited compounds. Natural products were shown to be effective in inhibiting more than 30 microorganisms. A discussion was presented on the research trends. 相似文献
86.
Giovanny Carvalho dos Santos Roberta Oliveira Servilha Eliézer Fernando de Oliveira Francisco Carlos Lavarda Valdecir Farias Ximenes Luiz Carlos da Silva-Filho 《Journal of fluorescence》2017,27(5):1709-1720
This paper describes the investigations on the solvatochromic effect and the photophysical properties of quinoline derivatives, compounds with potential applicability in optoelectronic devices. Using an experimental and theoretical approach, the effect of the solvent and the insertion of the phenyl, nitro, amino and dimethylamino group in the quinoline backbone were investigated. The use of Density Functional Theory (DFT) calculations provided the bases for the understanding of the energetic transitions observed in the absorption and fluorescence experiments. In general, it was observed a change in the wavelength of maximum absorption and fluorescence quantum yield of the studied compounds caused by the substituents in the quinoline core. This effect was correlated with the solvent dielectric constants. 相似文献
87.
The dispersion relation for a surface plasmon, propagating across a corrugated metal film on a dielectric substrate, is obtained by the method of reduced Rayleigh equations. It is found that the surface plasmon dispersion curve has an infinite number of branches. Numerical solutions of the dispersion relation are obtained for a film, characterized by a free-electron metal dielectric function and a sinusoidal profile function. 相似文献
88.
A cardinality constrained knapsack problem is a continuous knapsack problem in which no more than a specified number of nonnegative
variables are allowed to be positive. This structure occurs, for example, in areas such as finance, location, and scheduling.
Traditionally, cardinality constraints are modeled by introducing auxiliary 0-1 variables and additional constraints that
relate the continuous and the 0-1 variables. We use an alternative approach, in which we keep in the model only the continuous
variables, and we enforce the cardinality constraint through a specialized branching scheme and the use of strong inequalities
valid for the convex hull of the feasible set in the space of the continuous variables. To derive the valid inequalities,
we extend the concepts of cover and cover inequality, commonly used in 0-1 programming, to this class of problems, and we
show how cover inequalities can be lifted to derive facet-defining inequalities. We present three families of non-trivial
facet-defining inequalities that are lifted cover inequalities. Finally, we report computational results that demonstrate
the effectiveness of lifted cover inequalities and the superiority of the approach of not introducing auxiliary 0-1 variables
over the traditional MIP approach for this class of problems.
Received: March 13, 2003
Published online: April 10, 2003
Key Words. mixed-integer programming – knapsack problem – cardinality constrained programming – branch-and-cut 相似文献
89.
J. S. de Sousa E. W. S. Caetano J. R. Gonalves G. A. Farias V. N. Freire E. F. da Silva Jr. 《Applied Surface Science》2002,190(1-4):166-170
The effects imposed to the electron energy levels of Si/SiO2 quantum dots by the presence of smooth graded interfaces and interfacial carriers trap is studied. For small diameter quantum dots, while the existence of graded interfaces strongly blue shifts the carrier energy states (up to a few hundred meV), the effect of the interfacial carriers trap is to red shift the energies, but to a lesser extend (under 50 meV). In addition, slight changes in the distance of the carriers trap in relation to the center of the dot does not alter significantly the energy spectrum. 相似文献
90.
The adsorptive collection of the molybdenum (VI) complexed with 2-(2-benzothiazolylazo)-p-cresol (BTAC) coupled with the catalytic current of the adsorbed complex at a static mercury drop electrode yields an ultrasensitive voltammetric procedure for the determination of molybdenum. Optimal experimental conditions were: a stirred acetate buffer 0.2 M (pH 3.5) as supporting electrolyte, a BTAC concentration of 1.0 x 10(-6) M as ligand, and a concentration of 0.1 M potassium nitrate as the oxidizing agent. In addition, a preconcentration potential of -0.080 V vs Ag/AgCl (3 M KCl), equilibration time of 15 s, a frequency of 30 Hz, a scan increment of 2 mV, a pulse amplitude of 0.050 mV, and a drop area of 0.032 cm2 were used. The cyclic voltammogram was recorded using a staircase wave with a scan rate of 100 mV/s. The forward scan starts at the initial potential of -0.080 V and is reversed at -0.90 V. Using the catalytic current at approximately -0.55 V the response to the Mo(VI) was found to be linear over a concentration range of 1.0-10.0 microg/L. The limit of detection is as low as 6.2 x 10(-10) M with 4 min of preconcentration time. The possible interference of other trace ions was investigated. The merits of this procedure are demonstrated using of reference samples. 相似文献