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31.
We analytically describe the complex scenario of homoclinic bifurcations in the Chua's circuit. We obtain a general scaling law that gives the ratio between bifurcation parameters of different nearby homoclinic orbits. As an application of this theoretical approach, we estimate the number of higher order subsidiary homoclinic orbits that appear between two consecutive lower order subsidiary orbits. Our analytical finds might be valid for a large class of dynamical systems and are numerically confirmed in the parameter space of the Chua's circuit. 相似文献
32.
A.M. Baptista 《International Journal of Non》2012,47(9):1033-1044
In the recent codes for the design of steel structures, the elastic–plastic methods of analysis are recognised to provide an efficient estimation of the ultimate resistance of some of these structures. These methods are usually based on some basic hypotheses, such as the creation of plastic hinges in the most stressed cross-sections, for instance.As the development of these plastic hinges depends on the interaction between the internal forces and on the cross-section shape, specific equations are required for the analysis of different types of cross-sections. However, most frequently, these equations are not available, or they are expressed by means of simplified expressions; this is usually the case when biaxial bending is involved.This paper presents new interaction criteria for the analysis of steel rectangular hollow sections subjected to an axial force and biaxial bending moments, at the elastic or the plastic limit states (as long as buckling phenomena are not involved). The plastic interaction criteria are presented, in a first step, for some particular combinations of the internal forces, such as axial loading with bending about a main axis, and biaxial bending without axial loading. Then, the global solution for the simultaneous combination of an axial force and bending moments about both the main axes of inertia are described in detail. All these plastic interaction criteria are compared with the corresponding plastic criteria adopted in the Eurocode 3 (EC3). Some suggestions are presented in order to improve the results given by these EC3 criteria. 相似文献
33.
G. Vidal M.S. Baptista H. Mancini 《The European physical journal. Special topics》2014,223(8):1601-1610
We present a stream cipher based on a chaotic dynamical system. Using a chaotic trajectory sampled under certain rules in order to avoid any attempt to reconstruct the original one, we create a binary pseudo-random keystream that can only be exactly reproduced by someone that has fully knowledge of the communication system parameters formed by a transmitter and a receiver, sharing the same initial conditions. The plaintext is XOR’ed with the keystream creating the ciphertext, the encrypted message. This keystream passes the NIST’s randomness test and has been implemented in a videoconference App for smartphones, in order to show the fast and light nature of the proposed encryption system. 相似文献
34.
Joao M. Baptista 《Letters in Mathematical Physics》2014,104(6):731-747
We note that the Bogomolny equation for abelian vortices is precisely the condition for invariance of the Hermitian–Einstein equation under a degenerate conformal transformation. This leads to a natural interpretation of vortices as degenerate Hermitian metrics that satisfy a certain curvature equation. Using this viewpoint, we rephrase standard results about vortices and make new observations. We note the existence of a conceptually simple, non-linear rule for superposing vortex solutions, and we describe the natural behaviour of the L 2-metric on the moduli space upon restriction to a class of submanifolds. 相似文献
35.
Oliveira CS Branco KP Baptista MS Indig GL 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2002,58(13):2971-2982
We have characterized the spectroscopy properties of crystal violet (CV+) and ethyl violet (EV+) in liquid solutions as a function of the solvent type and dye concentration. The analysis of how solvent properties and dye concentration affects the electronic spectra of these tri-para-dialkylamino substituted tryarylmethane (TAM+) dyes was performed on the basis of two spectroscopic parameters, namely the difference in wavenumber (deltanu) between the maximum and the shoulder that appears in the short-wavelength side of the respective maximum visible band (deltanu = 1/lambda(shoulder)-1/lambda(max) cm(-1)), and the wavelength of the maximum absorption (lambda(max)). The solvent and the concentration effects on lambda(max) and deltanu have indicated that both solute/solute (ion-pairing and dye aggregation) and solute/solvent (H-bonding type) interactions modulate the shape of the visible electronic spectra of these dyes in solution. In solvent with small dieletric constant (epsilon < approximately 10), the formation of ion-pairs represents a major contribution to the shaping of these spectra. Upon increasing dye concentration the formation of ion-pairs was characterized by an increase in deltanu observed concomitantly with a red shift in lambda(max) In chloroform and chlorobenzene the ion-pair association constant of CV+ and EV+ with Cl- ions were found to be in the order of 10(6) and 10(5) M(-1), respectively. In trichloroethylene the association constant for the CV+Cl- pair was 10(8) M(-1). In water, dye aggregation instead of ion-pairing represents a major contribution to the shaping of the visible spectra of CV+ and EV+. Dye aggregation was indicated by an increase in deltanu observed concomitantly with a blue shift in lambda(max) upon increasing dye concentration. The distinct behavior of deltanu for dye aggregation and ion-pairing as a function of dye concentration can therefore assist in the characterization of these two distinct phenomena. The solute/solvent interactions were studied in a series of polar solvents in which solute/solute interactions do not occur in any detectable extent. The dependence found for deltanu as a function of the Kamlet-Tafts solvatochromic parameters (alpha, beta and pi*) is in keeping with previous inferences indicating that the splitting in the overlapped absorption band of CV+ and EV+ in hydroxilated solvents arises from a perturbation in the molecular symmetry induced by hydrogen bonding (donor-acceptor) type interactions with solvent molecules. A distinction between the effects of solute/solute and solute/solvent interactions on the visible spectra of these dyes is provided. 相似文献
36.
J.P. Carvalho A. Anuszkiewicz G. Statkiewicz-Barabach J.M. Baptista O. Frazão P. Mergo J.L. Santos W. Urbanczyk 《Optics Communications》2012,285(3):264-268
In this work, we demonstrate the possibility of fabricating short-length long-period gratings and rocking filters in highly birefringent Photonic Crystal Fiber using a CO2 laser. In our experiments both kinds of gratings were made in the same Boron doped highly birefringent PCF using similar exposure parameters. We also present the sensing capabilities of both fabricated gratings to temperature, strain and hydrostatic pressure by interrogation of the wavelength shifts at different resonances. 相似文献
37.
Peña A Rojas L Aparicio R Alarcón L Baptista JG Velasco J Carmona J Usubillaga A 《Natural product communications》2012,7(5):661-662
The essential oil of the leaves of Espeletia nana Cuatrec., obtained by hydrodistillation, was analyzed by GC-MS, which allowed the identification of 24 components, which made up 99.9% of the oil. The most abundant compounds were a-pinene (38.1%), beta-pinene (17.2%), myrcene (15.0%), spathulenol (4.2%), bicyclogermacrene (4.0%), a-zingiberene (4.0%), and gamma-himachalene (3.7%). Antibacterial activity was tested against Gram-positive and Gram-negative bacteria using the agar disk diffusion method. Activity was observed only against Gram-positive bacteria. MIC values were determined for Staphylococcus aureus ATCC 25923 (200 microg/mL) and Enterococcusfaecalis ATCC 29212 (600 microg/mL). 相似文献
38.
The pressure dependence of T1 formation in acridine and phenazine vapours was studied between 0.05 torr and 40 torr of an added buffer gas, by microsecond flash photolysis. In contrast to the pressure dependence of anthracene triplet formation, in the heterocyclic compounds the triplet absorption increases slightly with pressure up to 1 torr and then decreases strongly with an increase in pressure up to 30–40 torr. These effects were confirmed by the slight increase followed by a decrease with time of the integrated areas of the T1 acridine spectra observed at much shorter times by means of nanosecond flash photolysis. The absorption of the lowest triplet was found to have an induction period more than one order of magnitude longer than the laser pulse or the singlet lifetimes revealing that the T1 state is not populated directly from S1 but via other electronic triplet states. The pressure effects on triplet formation are interpreted in terms of a reversible intersystem crossing S1 ? T1 associated with vibrational relaxation in the triplet states. 相似文献
39.
In this work, an alkoxide solution route to synthesize Ca phosphates was developed. For the precursors, a CaO2C2H4 solution was prepared by dissolving Ca metal powder into ethylene glycol, and a PO(OH)x(OBut)3–x solution was prepared by dissolving P2O5 inton -butanol under reflux conditions. In order to obtain a mixed solution of the two precursors, acetic acid was used as an additive. The experimental results show that (1) -2CaO · P2O5, -3CaO · P2O5, and hydroxyapatite can be easily synthesized by converting the corresponding mixed solutions to powder products in a hot plate, and calcining the as prepared products at 1100°C; (2) acetic acid behaves as a good agent for controlling the reactions between the two precursors by modifying the CaO2C2H4 species in solution and decreasing the reactivity of the PO(OH)x(OBut)3–x species. 相似文献
40.
Aiying Wu Isabel M. Miranda Salvado Paula M. Vilarinho João L. Baptista Armando J.D. Silvestre 《Journal of Sol-Gel Science and Technology》2000,19(1-3):671-676
Lead zirconate titanate (PZT) thin films were prepared by the sol-gel process using acetic acid and 1,2-propanediol as solvents. Acetone was used as final solvent and in this way a stable stock sol (for more than 12 months) was obtained. The PZT sols prepared were reproducible and suitable for the preparation of PZT thin films. To study the sol structure evolution gas chromatography mass spectrum (GC-MS) and Fourier-transform-infrared (FT-IR) spectra were recorded and analyzed on each step of the synthesis. The rheological behavior and the stability of the stock sol were checked using a rheometer. It is observed that the addition of acetone leads to a very stable stock sol. The preliminary investigation of the electric properties of the obtained PZT thin films showed that the crystallized films deposited from a fresh prepared sol and a 12 months aged sol exhibit similar ferroelectric properties and comparable to those reported in the literature. 相似文献