On non-ideal simple portal frame structural model: Experimental results under a non-ideal excitation

We present measurements of the non-linear oscillations of a portal frame foundation for a non-ideal motor. We consider a three-time redundant structure with two columns, clamped in their bases and a horizontal beam. An electrical unbalanced motor is mounted at mid span of the beam. Two non-linear phenomena are studied: a) mode saturation and energy transfer between modes; b) interaction between high amplitude motions of the structure and the rotation regime of a real limited power motor. The dynamic characteristics of the structure were chosen to have one-to-two internal resonance between the anti-symmetrical mode (sway motions) and the first symmetrical mode natural frequencies. As the excitation frequency reaches near resonance conditions with the 2nd natural frequency, the amplitude of this mode grows up to a certain level and then it saturates. The surplus energy pumped into the system is transferred to the sway mode, which experiences a sudden increase in its amplitude. Energy is transformed from low amplitude high frequency motion into high amplitude low frequency motion. Such a transformation is potentially dangerous.We consider the fact that real motors, such as the one used in this study, have limited power output. In this case, this energy source is said to be non-ideal, in contrast to the ideal source whose amplitude and frequency are independent of the motion of the structure. Our experimental research detected the Sommerfeld Effect: as the motor accelerates to reach near resonant conditions, a considerable part of its output energy is consumed to generate large amplitude motions of the structure and not to increase its own angular speed. For certain parameters of the system, the motor can get stuck at resonance not having enough power to reach higher rotation regimes. If some more power is available, jump phenomena may occur from near resonance to considerably higher motor speed regimes, no stable motions being possible between these two.

Efficient energy upconversion emission in Tm3+/Yb3+-codoped TeO2-based optical glasses excited at 1.064 mu m

Efficient energy upconversion of cw radiation at 1.064 mum into blue, red, and near infrared emission in Tm3+-doped Yb3+-sensitized 60TeO(2)-10GeO(2)-10K(2)O-10Li(2)O-10Nb(2)O(5) glasses is reported. Intense blue upconversion luminescence at 485 nm corresponding to the Tm3+ (1)G(4)--> H-3(6) transition with a measured absolute power of 0.1 muW for 800 mW excitation power at room temperature is observed. The experimental results also revealed a sevenfold enhancement in the upconversion efficiency when the sample was heated from room temperature to 235 degreesC yielding 0.7 muW of blue absolute fluorescence power for 800 mW pump power. High brightness emission around 800 nm (F-3(4)--> H-3(6)) in addition to a less intense 655 nm ((1)G(4)--> H-3(4) and F-3(2,3)--> H-3(6)) fluorescence is also recorded. The energy upconversion excitation mechanism for thulium emitting levels is assigned to multiphonon-assisted anti-Stokes excitation of the ytterbium-sensitizer followed by multiphonon-assisted sequential energy-transfer processes. (C) 2001 American Institute of Physics.

Efficient plasmonic coupling between Er3+:(Ag/Au) in tellurite glasses

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

Upconversion luminescence and thermal effects in terbium-ytterbium codoped fluorogermanate glass-ceramic

Cooperative energy transfer upconversion luminescence is investigated in Tb(3+)/Yb(3+)-codoped PbGeO(3)-PbF(2)-CdF(2) glass-ceramic and its precursor glass under resonant and off resonance infrared excitation. Bright UV-visible emission signals around 384, 415, 438 nm, and 473-490, 545, 587, and 623 nm are identified as due to the (5)D(3)((5)G(6))->(7)F(1) (J=6,5,4) and (5)D(4)->(7)F(1) (J=6,5,4,3) transitions, respectively, and readily observed. The results indicate that cooperative energy transfer between ytterbium and terbium. ions followed by excited state absorption are the dominant upconversion excitation mechanisms involved. Comparison of the upconversion process in a glass-ceramic sample and its glassy precursor revealed that the former present much higher upconversion efficiency. The dependence of the upconversion emission upon pump power, temperature, and doping content is also examined.

Infrared-to-visible upconversion in Yb3+/Er3+ co-doped PbO-GeO2 glass with silver nanoparticles

Enhanced frequency upconversion (UC) emission was studied in Yb3+/Er3+ co-doped PbO-GeO2 glass containing silver nanoparticles (NPs). Optical excitation was achieved with a laser operating at 980 nm in resonance with the Yb3+ transition F-4(5/2)-> F-4(7/2). The intensity of the whole UC spectrum from 400 to 700 nm was intensified due to the influence of silver NPs. The green and red emissions were enhanced by more than 300%. Emission bands centered at 408 nm and 480 nm were also detected corresponding to the H-2(9/2)-> I-4(15/2) and F-4(7/2)-> I-4(15/2) transitions of Er3+ ion. An intensity enhancement of approximate to 150% due to the NPs was measured. For the first time the influence of silver NPs on the blue emission of Yb3+/Er3+ co-doped PbO-GeO2 glass is reported. The large enhancement in the whole UC spectrum is due to the increased local field in the Er3+ ions locations and the proximity between the luminescence wavelengths and the NPs surface plasmon resonance. (C) 2010 Elsevier B.V. All rights reserved.

Influence of the temperature on the nucleation of silver nanoparticles in Tm3+/Yb3+ codoped PbO-GeO2 glasses

The influence of the temperature on the nucleation of silver nanoparticles (NPs) in Tm3+/Yb3+ codoped PbO-GeO2 glasses was studied in this work. The infrared-to-visible frequency upconversion (UC) luminescence of Tm3+ ions was used to probe the NPs nucleation and the results were correlated with the increase of the heat-treatment temperature. Emission spectra in the blue-red region were measured by exciting the samples with a cw 980 nm diode laser in resonance with the Yb3+ transition (F-2(7/2) -> F-2(5/2)). The results were correlated with transmission electron microscopy measurements and revealed the different behavior of the nucleation process as a function of temperature.The enhanced UC emission in the visible region is attributed to the increased local field in the proximity of the silver NPs combined with the Yb3+ -> Tm3+ energy transfer. (C) 2010 Elsevier B.V. All rights reserved.

Frequency upconversion luminescence from Yb+3-Tm+3 codoped PbO-GeO2 glasses containing silver nanoparticles

Infrared-to-visible and infrared-to-infrared frequency upconversion processes in Yb3+-Tm3+ doped PbO-GeO2 glasses containing silver nanoparticles (NPs) were investigated. The experiments were performed by exciting the samples with a diode laser operating at 980 nm (in resonance with the Yb3+ transition F-2(7/2)-> F-2(5/2)) and observing the photoluminescence (PL) in the visible and infrared regions due to energy transfer from Yb3+ to Tm3+ ions followed by excited state absorption in the Tm3+ ions. The intensified local field in the vicinity of the metallic NPs contributes for enhancement in the PL intensity at 480 nm (Tm3+ :(1)G(4)-> H-3(6)) and at 800 nm (Tm3+ : H-3(4) -> H-3(6)). (C) 2009 American Institute of Physics. [doi:10.1063/1.3211300]

Stokes and anti-Stokes luminescence of Er3+ doped Ga10Ge25S65 glass excited at 980 and 532 nm

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Two thermal methods to measure the energy fluence of a brief exposure of diagnostic x rays

This paper describes two simple thermal methods for measuring the energy fluence in J/cm 2 from a diagnostic x-ray exposure. Both detectors absorb essentially 100% of the radiation and give a signal that is directly proportional to the energy fluence of the x-ray beam. One detector measures the thermal effect when a pulse of x rays is totally absorbed in the pyroelectric detector of lead-zirconium-titanate (PZT). The other detector measures the expansion of a gas surrounding a lead disk detector in a photoacoustic chamber. The increased pressure of the gas is transmitted through a 1-mm duct to a sensitive microphone. Both detectors have previously been used to measure the energy fluence rate of continuous x-ray beams in the same energy region using a chopped beam and a lock-in amplifier. Measurement of the energy fluence of a pulse of radiation eliminates the need for the beam chopper and lock-in amplifier and results in a simple, rugged, and inexpensive dosimeter. Either method can be combined with the area of the beam to give an estimate of the imparted energy to the patient from a diagnostic x-ray exposure.

Frequency upconversion in Nd3+-doped fluoroindate glass

We report the observation of frequency upconversion in fluoroindate glasses with the following compositions: (mol%) (39 - x)InF3-20ZnF2-20SrF2-16BaF 2-2GdF3-2NaF-1GaF3-xNdF3 (x = 0.05, 0.1, 0.5, 1, 2, 3). The excitation source was a dye laser in resonance with the 4I9/2→(2G5/2, 2G7/2) transition of the Nd3+ ions. The upconverted fluorescence spectra show emissions from ∼ 350 to ∼ 450 nm, corresponding to transitions 4D3/2→4I9/2 ;4D3/2→4I11/2; 2P3/2→ 4I9/2; 4D3/2→4I13/2; 2P3/2→4I11/2; 4D3/2→4I15/2; and 2P3/2 → 4I13/2. The dependence of the fluorescence signals on the laser intensity indicates that two laser photons participate in the process. The temporal behavior of the signal indicates that energy transfer among the Nd3+ ions is the main mechanism which contributes to upconversion at 354 and 382 nm.

Low-energy correlations in the positronium-hydrogen-atom system

Employing a nonlocal model potential for electron exchange we study positronium-hydrogen-atom (Ps-H) scattering using a five-state coupled-channel model allowing for Ps(2s,2p)H(1s) and Ps(1s)H(2s,2p) excitations. We find remarkable correlations among S-wave Ps-H binding energy, scattering length, effective range, and resonance energy in the electronic singlet state. Using these correlations we predict fairly accurate values of singlet Ps-H scattering length (3.50a0) and effective range (1.65a0).

Specific and nonspecific collapse in protein folding funnels

Experiments with fast folding proteins are beginning to address the relationship between collapse and folding. We investigate how different scenarios for folding can arise depending on whether the folding and collapse transitions are concurrent or whether a nonspecific collapse precedes folding. Many earlier studies have focused on the limit in which collapse is fast compared to the folding time; in this work we focus on the opposite limit where, at the folding temperature, collapse and folding occur simultaneously. Real proteins exist in both of these limits. The folding mechanism varies substantially in these two regimes. In the regime of concurrent folding and collapse, nonspecific collapse now occurs at a temperature below the folding temperature (but slightly above the glass transition temperature).

Frequency upconversion in rare-earth doped fluoroindate glasses

We present recent results on frequency upconversion (UPC) obtained in fluoroindate glasses (FIG) doped with Ho3+, Tm3+ and Nd3+ ions and codoped with Pr3+/Nd3+ and Yb3+/Tb3+ ions. The results for the Ho3+-doped samples show strong evidence of energy transfer (ET) between Ho3+ ions resonantly excited at 640 nm. The origin of the blue-green upconverted fluorescence observed was identified and the dynamics of the signals revealed the pathways involved in the UPC process. In the case of Tm3+-doped FIG, the samples were resonantly excited at 650 nm and the main mechanism that contributes for the red-to-blue upconversion is excited-state absorption (ESA). The FIG samples codoped with Pr3+/Nd3+ were excited at 588 nm in resonance with transitions starting from the ground state of the Nd 3+ and the Pr3+ ions. It was observed that the presence of Nd3+ ions enhanced the Pr3+ emission at 480 nm by two orders of magnitude. Multiphonon (MP)-assisted upconversion is also discussed for Nd3+-doped FIG pumped at 866 nm. Emission at 750 nm with a peculiar linear dependence with the laser intensity was observed and explained. A rate-equation model that includes MP absorption via thermally coupled electronic excited states of Nd3+ was developed and describes well the experimental results. The role played by effective phonon modes is clearly demonstrated. MP-assisted UPC process was also studied in Yb3+/ Tb3+-codoped FIG samples excited at 1064 nm, which is off-resonance with electronic transitions starting from the ground state. It was determined that the mechanism leading to Tb3+ emission in the blue is due to ET from a pair of excited Yb3+ ions followed by ESA in the Tb 3+ ions. © 2002 Académie des sciences/Éditions scientifiques et médicales Elsevier SAS.

Efficient UV-visible upconversion luminescence and thermal effects in terbium-ytterbium codoped fluorogermanate vitroceramic

Cooperative energy-transfer upconversion luminescence in Tb 3+/Yb 3+-codoped PbGeO 3-PbF 2-CdF 2 vitroceramic and its precursor glass under resonant and off-resonance infrared excitation, is investigated. Bright UV-visible emission signals around 384, 415, 438 nm, and 473-490, 545, 587, and 623 nm, identified as due to the 5D 3( 5G 6 → 7F J(J=6,5,4) and 5D 4 → 7F J(J=6,5,4,3) transitions, respectively, were readily observed. The results indicate that cooperative energy-transfer between ytterbium and terbium ions followed by excited-state absorption are the dominant upconversion excitation mechanisms herein involved. The comparison of the upconversion process in a vitroceramic sample and its glassy precursor revealed that the former present much higher upconversion efficiency. The dependence of the upconversion emission upon pump power, temperature, and doping content is also examined.

On nonlinear dynamics in a free fluid surface of a tank excited by a non-ideal power source

We investigate the nonlinear oscillations in a free surface of a fluid in a cylinder tank excited by non-ideal power source, an electric motor with limited power supply. We study the possibility of parametric resonance in this system, showing that the excitation mechanism can generate chaotic response. Additionally, the dynamics of parametrically excited surface waves in the tank can reveal new characteristics of the system. The fluid-dynamic system is modeled in such way as to obtain a nonlinear differential equation system. Numerical experiments are carried out to find the regions of chaotic solutions. Simulation results are presented as phase-portrait diagrams characterizing the resonant vibrations of free fluid surface and the existence of several types of regular and chaotic attractors. We also describe the energy transfer in the interaction process between the hydrodynamic system and the electric motor. Copyright © 2011 by ASME.