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991.
Pier A Mello 《Pramana》2001,56(2-3):425-437
Universal statistical aspects of wave scattering by a variety of physical systems ranging from atomic nuclei to mesoscopic systems and microwave cavities are described. A statistical model for the scattering matrix is employed to address the problem of quantum chaotic scattering. The model, introduced in the past in the context of nuclear physics, discusses the problem in terms of a prompt and an equilibrated component: it incorporates the average value of the scattering matrix to account for the prompt processes and satisfies the requirements of flux conservation, causality and ergodicity. The main application of the model is the analysis of electronic transport through ballistic mesoscopic cavities: it describes well the results from the numerical solutions of the Schrödinger equation for two-dimensional cavities. 相似文献
992.
We have compared the resistivity, ρ, of sulfonated polyaniline (SPAN) prepared via three different synthetic routes: electrochemical synthesis with a supporting
electrolyte (camphorsulfonic acid), ρ
=340 Ω·m; electrochemical synthesis without a supporting electrolyte, ρ
=530 Ω·m, and; chemical synthesis, ρ
=166 Ω·m. Independent of the metal contact (Al, Au, Cu), SPAN forms ohmic contacts with the metal and the contact resistance r
c
~5 Ω does not correlate with the metal's work function.
Electronic Publication 相似文献
993.
Dried almonds, raisins, dates and pistachio were irradiated using either gamma radiation or electron beam, at an average absorbed dose of 5 kGy. To detect the previous irradiation different parts of the dried fruits were analyzed by ESR spectroscopy: almonds: skin; raisins: dried pulp; dates: dried pulp and stone; pistachio: nutshell. Analyses were carried out 2–3 months and 6 months after irradiation. A series of signals tentatively described as “cellulose-like”, “sugar-like” and “complex” radical were observed, and some slight differences between spectra from samples irradiated with gamma rays and electrons were evident. 相似文献
994.
995.
A new method that combines phase shifting photoelasticity and transmission Coherent Gradient Sensing (CGS) is developed to
determine the tensorial stress field in thin plates of photoelastic materials. A six step phase shifting photoelasticity method
determines principal stress directions and the difference of principal stresses. The transmission CGS method utilizes a standard
four step phase shifting method to measure the x and y first derivatives of the sum of principal stresses. These stress derivatives are numerically integrated using a weighted
preconditioned conjugate gradient (PCG) algorithm, which is also used for the phase unwrapping of the photoelastic and CGS
phases. With full-field measurement of the sum and difference of principal stresses, the principal stresses may be separated,
followed by the Cartesian and polar coordinate stresses using the principal stress directions. The method is demonstrated
for a compressed polycarbonate plate with a side V-shaped notch. The experimental stress fields compare well with theoretical
stress fields derived from Williams solution for a thin plate with an angular corner. 相似文献
996.
We consider interpolatory quadrature rules with nodes and weights satisfying symmetric properties in terms of the division operator. Information concerning these quadrature rules is obtained using a transformation that exists between these rules and classical symmetric interpolatory quadrature rules. In particular, we study those interpolatory quadrature rules with two fixed nodes. We obtain specific examples of such quadrature rules. 相似文献
997.
P. Castellini G. M. Revel L. Scalise R. M. De Andrade 《Optics and Lasers in Engineering》2000,32(6):525-581
In this paper it has been described part of the research devoted to the development of a complete non-intrusive experimental modal analysis procedure based on laser techniques both for excitation and for measurement. In particular, attention has been focused on the thermal effects generated by laser pulses on the excited structure. An analytical model of the energy exchange between the light pulse and the target surface is proposed together with a finite element model of thermal and mechanical behaviour of the structure under excitation. Both the models (analytical and numerical) have been experimentally validated by measuring the thermal and the vibration responses induced by the laser pulses. The experimental part of the study has been performed on a cantilever beam excited with laser pulses from an Nd : YAG source (532 nm, 100 mJ/pulse) using an high-speed infrared camera and a scanning laser Doppler vibrometer. Results from this work can be used to improve understanding concerning the features of laser excitation and to establish a mechanical equivalent system of forces and moments, useful in order to increase the accuracy in the measurements of modal parameters when laser pulses are used as excitation sources. 相似文献
998.
F.W.S. Lima U.M.S. Costa M.P. Almeida J.S. Andrade Jr. 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(1):111-114
We use the single-histogram technique to study the critical behavior of the three-state Potts model on a (random) Voronoi-Delaunay
lattice with size ranging from 250 to 8 000 sites. We consider the effect of an exponential decay of the interactions with
the distance, , with a>0, and observe that this system seems to have critical exponents and which are different from the respective exponents of the three-state Potts model on a regular square lattice. However, the
ratio remains essentially the same. We find numerical evidences (although not conclusive, due to the small range of system size)
that the specific heat on this random system behaves as a power-law for a=0 and as a logarithmic divergence for a=0.5 and a=1.0
Received 5 April 2000 相似文献
999.
Alberto Federman Neto Joseph Miller Vnia Faria de Andrade Susana Yumi Fujimoto Mrcia Maísa de Freitas Afonso Fernando Costa Archanjo Vítor Andr Darin Mrcio Luís Andrade e Silva urea Donizete Lanchote Borges Gino Del Ponte 《无机化学与普通化学杂志》2002,628(1):209-216
An improved technique for the preparation of ferrocenecarboxaldehyde and two new methods for the synthesis of ferrocenemonocarboxylic acid from the aldehyde or from acetyl ferrocene are described. Using the aldehyde or the monocarboxylic acid as starting materials, some important ferrocene key intermediates were prepared: monochlorocarbonyl ferrocene, alkali metal and ammonium ferrocenoates, ferrocene carboxyaldehyde diethylacetal, ferrocenecarboxamide, et …, as well as a new ferrocene derivative: piperazinium diferrocenoate. 相似文献
1000.
Carla Monteiro Leal Suzana Guimares Leito Leonardo Luiz Oliveira de Mello Isabel de Castro Rangel Carlos Vinicius Azevedo da Silva Milene Dias Miranda Amanda Resende Tucci Camilla Blanco de Assis Carolina de Queiroz Sacramento Natalia Fintelman-Rodrigues Hector Henrique Ferreira Koolen Boniek Gontijo Vaz Rosineide Costa Simas Gilda Guimares Leito 《Molecules (Basel, Switzerland)》2022,27(2)
Siparuna glycycarpa occurs in the Amazon region, and some species of this genus are used in Brazilian folk medicine. A recent study showed the inhibitory effect of this species against influenza A(H1N1)pdm09 virus, and in order to acquire active fractions, a polar solvent system n-butanol-methanol-water (9:1:10, v/v) was selected and used for bioassay-guided fractionation of n-butanol extract by centrifugal partition chromatography (CPC). The upper phase was used as stationary phase and the lower phase as mobile (descending mode). Among the collected fractions, the ones coded SGA, SGC, SGD, and SGO showed the highest antiviral inhibition levels (above 74%) at 100 µg·mL−1 after 24 h of infection. The bioactive fractions chemical profiles were investigated by LC-HRMS/MS data in positive and negative ionization modes exploring the Global Natural Products Social Molecular Networking (GNPS) platform to build a molecular network. Benzylisoquinoline alkaloids were annotated in the fractions coded SGA, SGC, and SGD collected during elution step. Aporphine alkaloids, O-glycosylated flavonoids, and dihydrochalcones in SGO were acquired with the change of mobile phase from lower aqueous to upper organic. Benzylisoquinolinic and aporphine alkaloids as well as glycosylated flavonoids were annotated in the most bioactive fractions suggesting this group of compounds as responsible for antiviral activity. 相似文献