On energy transfer between linear and nonlinear oscillators

In this paper energy transfer in a dissipative mechanical system is analysed. Such system is composed of a linear and a nonlinear oscillator with a nonlinearizable cubic stiffness. Depending on initial conditions, we find energy transfer either from linear to nonlinear oscillator (energy pumping) or from nonlinear to linear. Such results are valid for two different potentials. However, under resonance and absence of external excitation, if the mass of the nonlinear oscillator is adequately small then the linear oscillator always loses energy. Our approach uses rigorous Regular Perturbation Theory. Besides, we have included the case of two linear oscillators under linear or cubic interactions. Comparisons with the earlier case are made. (c) 2008 Elsevier Ltd. All rights reserved.

Activation energy for the reverse eutectoid reaction in hypo-eutectoid Cu-Al alloys

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Influence of microwave energy on structural and photoluminescent behavior of CaTiO3 powders

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Time dependence and energy-transfer mechanisms in Tm3+Ho3+ and Tm3+-Ho3+ co-doped alkali niobium tellurite glasses sensitized by Yb3+

Glass samples with the composition (mol%) 80TeO(2)-10Nb(2)O(5)-5K(2)O-5Li(2)O, stable against crystallization, were prepared containing Yb3+, Tm3+ and Ho3+. The energy transfer and energy back transfer mechanisms in samples containing 5% Yb3+-5% Tm3+ and 5% Yb3+-5% Tm3+-0.5% Ho3+ were estimated by measuring the absorption and fluorescence spectra together with the time dependence of the Yb3+ F-2(5/2) excited state. A good fit for the luminescence time evolution was obtained with the Yokota-Tanimoto's diffusion-limited model. The up-conversion fluorescence was also studied in 5% Yb-5% Tm. 5% Yb-0.5% Ho and 5% Yb-5% Tm-0.5% Ho tellurite glasses under laser excitation at 975 nm. Strong emission was observed from (1)G(4) and F-3(2) Tm3+ energy levels in all samples. The S-5(2) Ho3+ emission was observed only in Yb3+Ho3+ samples being completely quenched in Yb3+/Tm3+/Tm3+ samples. (C) 2001 Elsevier B.V. B.V. All rights reserved.

Ytterbium-induced energy-transfer upconversion enhancement in Nd3+/Pr3+-codoped PbGeO3-PbF2-CdF2 glass excited at 810nm

The effect of ytterbium ions upon energy transfer (ET) excited upconversion emission in Nd3+/Pr3+ -codoped PbGeO3-PbF2-CdF2 glass under 810 nm diode laser excitation is investigated. The results revealed that the presence of Yb3+ ions in the Nd3+/Pr3+-doped sample yields a fourfold enhancement in the visible and near infrared upconversion luminescence. The dependence of the upconversion process upon the excitation power, Nd3+, and Yb3+ concentrations is examined. The results indicated that ytterbium plays a major role in the ET upconversion process by bridging the 810nm neodymium excitation to praseodymium ions. The population of the Pr3+ ions P-3(0) emitting level was accomplished through a multi-ion interaction involving ground-state and excited-state absorption of pump photons at 810 nm by the Nd3+ followed by successive ET involving the Nd3+-Yb3+ and Yb3+-Pr3+ pairs. There is also direct ET Nd3+-Pr3+. (c) 2005 Elsevier B.V. All rights reserved.

Mechanism of the Yb-Er energy transfer in fluorozirconate glass

The mechanism of the Yb(3+)-->Er(3+) energy transfer as a function of the donor and the acceptor concentration was investigated in Yb(3+)-Er(3+) codoped fluorozirconate glass. The luminescence decay curves were measured and analyzed by monitoring the Er(3+)((4)I(11/2)) fluorescence induced by the Yb(3+)((2)F(5/2)) excitation. The energy transfer microparameters were determined and used to estimate the Yb-Er transfer rate of an energy transfer process assisted by excitation migration among donors state (diffusion model). The experimental transfer rates were determined from the best fitting of the acceptor luminescence decay obtained using a theoretical approach analog to that one used in the Inokuti-Hirayama model for the donor luminescence decay. The obtained values of transfer parameter gamma [gamma(exp)] were always higher than that predicted by the Inokuti-Hirayama model. Also, the experimental transfer rate, gamma(2)(exp), was observed to be higher than the transfer rate predicted by the migration model. Assuming a random distribution among excited donors at the initial time (t=0) and that a fast excitation migration, which occurs in a very short time (t

Red-green-blue upconversion emission and energy-transfer between Tm3+ and Er3+ ions in tellurite glasses excited at 1.064 mu m

Red, green, and blue emission through frequency upconversion and energy-transfer processes in tellurite glasses doped with Tm3+ and Er3+ excited at 1.064 mum is investigated. The Tm3+/Er3+-codoped samples produced intense upconversion emission signals at around 480, 530, 550 and 660 nm. The 480 nm blue emission was originated from the (1)G(4)-->H-3(6) transition of the Tm3+ ions excited by a multiphoton stepwise phonon-assisted excited-state absorption process. The 5 30, 5 50 nm green and 660 mn red upconversion luminescences were identified as originating from the H-2(11/2), S-4(3/2) --> I-4(15/2) and F-4(9/2) --> I-4(15/2) transitions of the Er3+ ions, respectively, populated via efficient cross-relaxation processes and excited-state absorption. White light generation employing a single infrared excitation source is also examined. (C) 2003 Elsevier B.V. (USA). All rights reserved.

Net requirements of protein and energy for maintenance of wool and hair lambs in a tropical region

The objective of this work was to evaluate the total endogenous N losses, and protein and energy net requirements for maintenance in growing lambs. Thirty-four castrated lambs, 17 F1 Ideal X Ile de France wool and 17 Santa Inas hair lambs, averaging 20 +/- 0.14 kg BW, were used in the experiment. Five animals from each genotype were slaughtered at the beginning of the experiment and taken as controls. Diets (D) were composed of concentrate mix (C) and Cynodon sp. c.v. Tifton 85 hay (R), combined in three different ratios: D1 = 60C:40R; D2 = 40C:60R and D3 = 20C:80R. Animals of each group of three lambs, that showed BW of 20 kg at the beginning of the dietary regimen, were slaughtered when one of them reached 35 kg, what always happened to be the one fed with D1. Total endogenous N losses estimated for wool lambs were 250 mg N/kg BW0.75. For hair lambs, total endogenous N losses reached 324 mg N/kg BW0.75 . Hair lambs showed higher (P < 0.01) (29.9%) net requirements of protein for maintenance than wool lambs. In contrast, net energy (NE) requirement for maintenance was similar (P > 0.05) for both genotypes (74.27 kcal/kg BW0.75 per day), the average of the antilog of the two intercept values obtained from the estimated regression equations of heat production for zero metabolizable energy (ME) consumption. Further studies should be done to check if this trend is also true for metabolizable energy and protein in animals exhibiting BW gains in tropical region. (C) 2003 Elsevier B.V. B.V. All rights reserved.

Acoustic measurement of the low-energy excitations in Nd2-xCexCuO4+delta

The complex dynamic Young's modulus of ceramic Nd2-xCexCuO4 with x = 0, 0.05 and 0.20 has been measured from 1.5 to 100 K at frequencies of 1 - 10 kHz. In the undoped sample the modulus starts decreasing below similar to 20 K, instead of approaching a constant value as in a normal solid. The modulus minimum has been interpreted in terms of paraelastic contribution from the relaxation of the Nd3+ 4f electrons between the levels of the ground state doublet, which is split by the interaction with the antiferromagnetically ordered Cu sublattice. The value of the splitting is found to be 0.34 meV, in excellent agreement with inelastic neutron scattering, infrared and specific heat experiments. With doping, the anomaly shifts to lower temperature and decreases in amplitude, consistently with a reduction of the local field from the Cu sublattice. (C) 2003 Elsevier B.V. Ltd. All rights reserved.

Do all tannins have similar nutritional effects? A comparison of three Brazilian fodder legumes

Three tropical legumes, namely Leucaena leucocephala, Sesbania sesban and Cajanus cajan, were subjected to chemical analysis plus in vitro, in situ and in vivo evaluations. Three different assays were used to determine total tannins: adsorption to polyvinyl pyrrolidine (PVPP-tannins), radial diffusion (RD-tannins) and protein precipitation capacity (BSA-tannins). Total phenols, total tannins and condensed tannins were highest for Sesbania. RD-tannins were correlated with total phenols (r(2) = 0.93), PVPP-tannins (r(2) = 0.92) and condensed tannins (r(2) = 0.99). The protein precipitation capacity of Sesbania, Leucaena and Cajanus were 25.9, 6.13 and 4.05 mu g BSA/g DM, respectively.Gas production at 24h was negatively correlated with total phenols (r(2) = 0.99), PVPP-tannins (r(2) = 0.99) and condensed tannins (r(2) = 0.91). The RD-, PVPP-tannins and the response to polyethylene glycol (PEG) in the gas production assay appeared to be useful as a first screen for tannins.In situ degradability did not reflect any adverse effects of tannins. However, in vivo experiments showed that the apparent DM digestibility of Sesbania and Leucaena was lower than the basal diet. The apparent protein digestibility was lower for all legumes compared to the basal diet. Most treatments caused a negative nitrogen balance. The problems associated with browse feeding were not only related to tannin contents, other factors such as inherently poor digestibility and low energy intake may also have lead to the poor animal performance on these diets. We propose, given the limitations of current tannin assays, that it is not possible to predict beneficial or harmful nutritional effects from total tannin concentrations per se. (C) 2004 Elsevier B.V. All rights reserved.

Energy transfer between Tm3+ and Er3+ ions in a TeO2-based glass pumped at diode laser wavelength

In this paper we investigate the energy transfer processes in TM3+/Er3+ doped telluride glass pumped at the commercial diode laser pump wavelength similar to 800 nm. Tailoring the rare-earths content in the glass matrix, seven main energy transfer channels within the doping range considered were identified, A 6-fold enhancement of the Er3+ visible frequency upconversion fluorescence at similar to 660 nm is observed due to the inclusion of Tm3+ ions. This is evidence of the relevant contribution of the route Er-1(I-4(11/2)) + Er-2(I-4(13/2)) -> Er-1(I-4(15/2)) + Er-2(F-4(9/2)) to the process. Energy migration among pumped I-4(9/2) level reducing the efficiency of the upconversion emission rate (H-3(11/2), S-4(3/2), and F-4(9/2)) is observed for Er3+ above 1.5 wt%. The rate equations regarding the observed energy transfer routes are determined and a qualitative analysis of the observed processes is reported. (c) 2006 Elsevier B.V. All rights reserved.

Thermally enhanced cooperative energy-transfer frequency upconversion in terbium and ytterbium doped tellurite glass

Infrared-to-visible frequency upconversion through cooperative energy-transfer and thermal effects in Tb3+/Yb3+-codoped tellurite glasses excited at 1.064 mum is investigated. Bright luminescence emission around 485, 550, 590, 625 and 65 nm, identified as due to the D-5(4) --> F-7(J) (J= 6, 5, 4, 3, and 2) transitions of the terbium ions, respectively, was recorded. The excitation of the D-5(4) emitting level of the Tb3+ ions is assigned to cooperative energy-transfer from pairs of ytterbium ions.. The effect of temperature on the upconversion process was examined and the results revealed a fourfold upconversion enhancement in the 300-500 K interval. The enhancement of the upconversion process is due to the temperature dependence of the Yb3+-sensitizer absorption cross-section under anti-Stokes excitation. A rate-equation. model using multiphonon-assisted absorption for the ytterbium excitation combined with the energy migration effect between Yb-Yb pair, and Tb3+ ground-state depopulation via multiphonon excitation of the F-7(J) excited states describes quite well the experimental results. (C) 2003 Elsevier B.V. B.V. All rights reserved.

Energy upconversion luminescence in neodymium-doped tellurite glass

Infrared-to-visible upconversion luminescence emission in Nd3+-doped 60TeO(2)-10GeO(2)-10K(2)O-10Li(2)O-10Nb(2)O(5) tellurite glasses under cw excitation around 800 nm is investigated. Blue (430, and 475 nm), green (5 0 nm) and yellow-orange (590 nm) energy upconversion emission owing to the P-2(1/2) --> I-4(j) (j=9/2, 11/2, 13/2 and 15/2) transitions of the Nd3+ ions, respectively, was recorded. The dependence of the upconversion intensity upon the excitation wavelength and pump power is also studied. The upconversion excitation mechanism responsible for the observed emission signals is attributed to stepwise multiphoton absorption. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Potential of municipal solid waste (MSW) as a source of energy in São Paulo: Its impact on CO2 balance

Energy generation is needed in São Paulo and MSW represents a promising alternative, although it is more expensive than hydroelectric power. About 14 900 t/day of MSW is generated, of which 8433 t/day is domestic and commercial MSW. From this amount, 1800 t will be destined to generate 30 MW of power. The eco-balance of CO2 has been considered for incineration and recycling. The recycling program of plastics, metals, paper and glass would represent a significant reduction in energy and CO2 emission. The total CO2 released is 3.34 x 10(5) t/yr without recycling. and is 1.25 x 10(5) t/yr with a recycling program. Most of the CO2 comes from plastics and paper production. Economic aspects could probably favor Incineration with energy production as the best option. (C) 1998 Published by Elsevier B.V. Ltd. All rights reserved.

Energy-transfer frequency upconversion in neodymium-sensitized praseodymium-doped PbGeO3-PbF2-CdF2 glass excited at 810 nm

Visible frequency upconversion emission through resonant energy-transfer involving neodymium and praseodymium ions in PbGeO3-PbF2-CdF2 glass excited by a semiconductor laser at 8 10 nm is investigated. Luminescence emission centered around 485, 530, 610, and 645 nm, which correspond to the P-3(0) -> H-3(4), P-3(1) + I-1(6) -> H-3(5), P-3(0) -> H-3(6) and P-1(0) -> F-3(2) transitions of praseodymium ions, respectively, are observed. The upconversion excitation of the Pr3+ ions excited-state emitting levels was accomplished by means of an ion-pair interaction involving ground-state absorption, multiphonon relaxation, and excited-state absorption of pump photons at 8 10 nm by the Nd3+ (I-4(9/2) -> H-2(9/2), F-4(5/2); F-4(3/2) -> P-2(1/2)) and direct energy-transfer to Pr3+ ((4)G(11/2) + K-2(11/2), H-3(4) -> I-4(9/2), P-3(1) + I-1(6)). The dependence of the upconversion emission intensity upon the excitation power, and neodymium concentration are also examined. (c) 2004 Elsevier B.V. All rights reserved.