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Search Results: 1 - 10 of 665331 matches for " L. M. R. Albuquerque "
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PET Oligomer Waste to Modify CAP Characteristics  [PDF]
L. C. Mendes, M. L. Dias, P. S. C. Pereira, L. M. R. Albuquerque
Materials Sciences and Applications (MSA) , 2012, DOI: 10.4236/msa.2012.38082
Abstract: To develop an improved method of reusing poly(ethylene terephthalate) (PET) waste in the production chain, it was chemically modified with pentaerythritol (PENTE), resulting in PET/PENTE (60/40) oligomer. This was added to petroleum asphalt cement (CAP) in different proportions—5, 10 and 20 wt%—as a modifier of bitumen characteristics. The mixture was evaluated by thermogravimetry (TG/DTG), differential scanning calorimetry (DSC), infrared spectroscopy (FT-IR), optical microscopy (OM) and the adhesion-peel test. The oligomer enhanced substantially the asphalt thermal stability-Tonset. OM images showed strong compatibility between components and PET’s amorphization. PET oligomer increased CAP’s wettability and the mixture presented cohesive fracture through the peel test. The mixture has excellent potential as paving material.
Spin wave specific heat in quasiperiodic Fibonacci structures
C. G. Bezerra,E. L. Albuquerque,A. M. Mariz,L. R. da Silva,C. Tsallis
Physics , 2001, DOI: 10.1016/S0378-4371(01)00017-6
Abstract: The energy spectra of a variety of collective modes on quasiperiodic structures exhibit a complex fractal profile. Among the modes that have attracted particular attention in this context, are the spin wave spectra of quasiperiodic magnetic multilayers that obey a substitutional sequence of the Fibonacci type. They are described within the framework of the Heisenberg theory. In order to have a deep insight on the relevant thermodynamical implications of the above mentioned energy spectra's fractal profile, we have performed analytical and numerical calculations of the spin wave specific heat associated with successive hierarchical sequences of the Fibonacci quasiperiodic structures. The spectra show interesting oscillatory behavior in the low-temperature region, which can be traced back to the spin wave's self-similar energy spectrum.
Exponential behavior of the interlayer exchange coupling across non-magnetic metallic superlattices
M. S. Ferreira,J. d'Albuquerque e Castro,R. B. Muniz,L. C. Lopes
Physics , 1998, DOI: 10.1103/PhysRevB.58.8198
Abstract: It is shown that the coupling between magnetic layers separated by non-magnetic metallic superlattices can decay exponentially as a function of the spacer thickness $N$, as opposed to the usual $N^{-2}$ decay. This effect is due to the lack of constructive contributions to the coupling from extended states across the spacer. The exponential behavior is obtained by properly choosing the distinct metals and the superlattice unit cell composition.
Inductorless Chua's Circuit: Experimental Time Series Analysis
R. M. Rubinger,A. W. M. Nascimento,L. F. Mello,C. P. L. Rubinger,N. Manzanares Filho,H. A. Albuquerque
Mathematical Problems in Engineering , 2007, DOI: 10.1155/2007/83893
Abstract: We have implemented an operational amplifier inductorless realization of the Chua's circuit. We have registered time series from its dynamical variables with the resistor R as the control parameter and varying from 1300 Ω to 2000 Ω. Experimental time series at fixed R were used to reconstruct attractors by the delay vector technique. The flow attractors and their Poincaré maps considering parameters such as the Lyapunov spectrum, its subproduct the Kaplan-Yorke dimension, and the information dimension are also analyzed here. The results for a typical double scroll attractor indicate a chaotic behavior characterized by a positive Lyapunov exponent and with a Kaplan-Yorke dimension of 2.14. The occurrence of chaos was also investigated through numerical simulations of the Chua's circuit set of differential equations.
Modeling chaotic current oscillations in semi-insulating GaAs with rate-equations of impact ionization and field-enhanced trapping
Albuquerque, H. A.;Silva, R. L. da;Rubinger, R. M.;Oliveira, A. G. de;Ribeiro, G. M.;Rodrigues, W. N.;
Brazilian Journal of Physics , 2006, DOI: 10.1590/S0103-97332006000300003
Abstract: we investigated the effect of adding the field-dependent recombination process, namely field-enhanced trapping, to the generation-recombination processes of charge carriers that model current oscillations in semiconductors. the main new features arising from this modification are identified in bifurcation diagrams with the electric field as the control parameter. the characteristic of the bifurcation diagrams is a function of impurity energy. thus, we generated a set of bifurcation diagrams for a range of the impurity energy and applied bias. the energy dependence of the bifurcation diagrams is discussed considering the context of the competition between the generation-recombination mechanisms impact ionization and field-enhanced trapping.
Low frequency oscillations and bifurcation diagram in semi-insulating GaAs samples
Silva, R. L. da;Albuquerque, H. A.;Rubinger, R. M.;Oliveira, A. G. de;Ribeiro, G. M.;Rodrigues, W. N.;
Brazilian Journal of Physics , 2006, DOI: 10.1590/S0103-97332006000300006
Abstract: we present an experimental study of bifurcation diagrams from low frequency current oscillations (lfo) measurements obtained from semi-insulating gaas samples grown by low temperature molecular beam epitaxy (lt-mbe). the considered growth temperatures were 215oc and 265oc. lfo are considered to be spontaneously generated oscillations under constant applied bias v. these oscillations were measurement and recorded in the form of time series. the bifurcation diagrams were obtained from the sequence of minima as a function of the applied bias. the standard measurement procedure was described elsewhere. as the control parameter, the bias allows the identification of a bifurcation route to chaos.
Journal of Venomous Animals and Toxins , 1996, DOI: 10.1590/S0104-79301996000200003
Abstract: two scorpion species of medical importance occur in the state of s?o paulo: the native brown scorpion tityus bahiensis (perty) and the highly toxic yellow scorpion tityus serrulatus lutz and mello, which was brought into the state. the study of accident data of patients admitted to the vital brazil hospital of the butantan institute from l982 to l993 revealed a gradual increase in stings by t. serrulatus in contrast to those by t. bahiensis with a variation from 5.2% to 29.7%. also, an inventory of the scorpions sent to the laboratory of venomous arthropods of the butantan institute over the same period showed an expressive growth in the number of t. serrulatus specimens in contrast to that of t. bahiensis. these data suggest a significative proliferation of t. serrulatus in the state of s?o paulo over the past 12 years, and a probable interspecific competition between t. serrulatus and the endemic t. bahiensis. the analysis of scorpion accidents reported to the state of s?o paulo health department (secretaria de estado da saúde de s?o paulo) corroborated the higher severity of t. serrulatus envenoming. the results pointed to the possibility of an increase in severe envenoming and deaths by scorpion stings in the state of s?o paulo. aiming to contribute to scorpion prevention and control programs, the present geographical distribution of both dangerous species was mapped, pointing to the areas of higher risk of scorpionism in the state.
Lisina digestível para frangos de corte machos entre 12 e 22 dias de idade
Takeara, P;Toledo, A.L;Gandra, E.R.S;Albuquerque, R;Trindade Neto, M.A;
Arquivo Brasileiro de Medicina Veterinária e Zootecnia , 2010, DOI: 10.1590/S0102-09352010000600023
Abstract: the lysine level was evaluated for 1,050 male broilers from 12 to 22 days of age. the experimental design was completely randomized with five treatments, seven replications, and 30 birds per experimental unit. the treatments were: 1.05, 1.10, 1.15, 1.20, and 1.25% of digestible lysine. weight gain, feed intake, feed: gain ratio, body composition, and nutrient deposition were measured. there were quadratic effects of digestible lysine on feed intake and an ascendant linear effect on carcass weight. in the carcass chemical composition, there was a quadratic response of lysine level in protein concentration. the deposition rates in carcass protein, carcass water, and whole body had a linear increase as response to lysine addition to diet. the lysine level increase however coincided with the mineral decrease on blood, offal, and whole body. basing on performance, the digestible lysine 1.1% level attended the broiler needs from 12 to 22 days of age. on the other hand, considering the chemical composition and the nutrient accretion rates, the need for digestible amino acid was equal or higher than 1.25%
Sazonalidade dos ductos secretores e óleo essencial de Foeniculum vulgare var. vulgare Mill. (Apiaceae)
Sousa, L.A.;Albuquerque, J.C.R.;Leite, M.N.;Stefanini, M.B.;
Revista Brasileira de Farmacognosia , 2005, DOI: 10.1590/S0102-695X2005000200015
Abstract: this work aimed to analyze the secretory ducts and the essential oil of the leaves of foeniculum vulgare in different periods of the year. for this purpose, the anatomic characterization, and histochemical tests of the leaves were performed as well as the comparative anatomy of the secretory ducts. the essential oil was obtained from the leaves and fruits by hidrodistillation in a clevenger-type apparatus and analyzed by gas chromatography coupled to a mass spectrometer, each analysis was repeated three times for leaves collected during the winter and spring, and for fruits collected in the summer. the results obtained for the secretory ducts, corresponded to the yield reduction of essential oil in the leaves collected in the end of the spring. the major substance of the essential oil of the leaves and fruits, in all seasons of the year was trans-anetol. therefore, it was evidenced that the secretory ducts and yield of essential oils are related, and also that the substances are subject to the seasonality, according to the phenologic stage of the plant.
Variable range hopping conduction in low-temperature molecular beam epitaxy GaAs
Rubinger, R. M.;Albuquerque, H. A.;Silva, R. L. da;Oliveira, A. G. de;Ribeiro, G. M.;Rodrigues, W. N.;Rubinger, C. P. L;Moreira, M. V. B.;
Brazilian Journal of Physics , 2006, DOI: 10.1590/S0103-97332006000300004
Abstract: electric transport properties measured by van der pauw resistivity experiments of low-temperature molecular beam epitaxy (lt-mbe) gaas samples are used to identify a method to improve the resistivity of gaas material. we present results on five samples grown at 265, 310, 315, 325, and 345 oc. the electric measurements were carried out at temperatures ranging from 130 to 300 k. in this temperature range the dominant transport process is identified as variable range hopping. the hopping parameter plotted against the growth temperature is shown to present a maximum. the mechanisms responsible for this behavior are discussed in relation to the compensation ratio.
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