Electro-optical properties of Er-doped SnO2 thin films

Photoconductivity of SnO2 sol-gel films is excited, at low temperature, by using a 266 nm line-fourth harmonic-of a Nd:YAG laser. This line has above bandgap energy and promotes generation of electron-hole pairs, which recombines with oxygen adsorbed at grain boundary. The conductivity increases up to 40 times. After removing the illumination on an undoped SnO2 film, the conductivity remains unchanged, as long as the temperature is kept constant. Adsorbed oxygen ions recombine with photogenerated holes and are continuously evacuated from the system, leaving a net concentration of free electrons into the material, responsible for the increase in the conductivity. For Er doped SnO2, the excitation of conductivity by the laser line has similar behavior, however after removing illumination, the conductivity decreases with exponential-like decay. (C) 2003 Elsevier Ltd. All rights reserved.

Residue decay of insecticides applied with mineral oil on clementine fruits

Three insecticides (chlorpyrifos methyl, dimethoate and fenthion) were applied on clementine fruits with and without mineral oil to assess the effect of mineral oil on pesticide residues. In both experiments the residues on the fruits after the last treatment and at harvest time were not significantly different.

Determination of the U-238 spontaneous fission decay constant without neutron irradiation

We have developed a methodology for measuring the decay constant of the spontaneous fission of U-238, lambda(f), using nuclear particle track detectors where thermal neutron irradiation is unnecessary. This methodology is based on the fact that the radiation damage caused by spontaneous fission of trans-uranium elements bearing a mass number close to 238 are similar to U-238 spontaneous-fission ones. Loading a thick source of uranium (thickness greater than the fission fragment range) with a small amount of a suitable trans-uranium element (for instance, Pu-242, which presents a spontaneous fission half-life of 6.75(.)10(10) y), it is possible to determine the observation efficiency of a particle-track detector for fission fragments. Procedures concerning our thick source manufacture and uniformity tests of the trans-uranium distribution are also presented. These results make it possible for the exposure of thick uranium sources (without trans-uranium element) to lead to a lambda(f) value.

Asymmetry parameter for nonmesonic hypernuclear decay

We give general expressions for the vector asymmetry in the angular distribution of protons in the nonmesonic weak decay of polarized hypernuclei. From these we derive an explicit expression for the calculation of the asymmetry parameter, a(Lambda), which is applicable to the specific cases of He-5(Lambda) and C-12(Lambda) described within the extreme shell model. In contrast to the approximate formula widely used in the literature, it includes the effects of three-body kinematics in the final states of the decay and correctly treats the contribution of transitions originating from single-proton states beyond the s-shell. This expression is then used for the corresponding numerical computation of a(Lambda) within several one-meson-exchange models. Besides the strictly local approximation usually adopted for the transition potential, we also consider the addition of the first-order nonlocality terms. We find values for a(Lambda) ranging from -0.62 to -0.24, in qualitative agreement with other theoretical estimates but in contradiction with some recent experimental determinations.

Erbium-activated HfO2-based waveguides for photonics

Silica-based sol-gel waveguides activated by Er3+ ions are attractive materials for integrated optic devices. 70SiO(2)-30HfO(2) planar waveguides, doped with Er3+ concentrations ranging from 0.01 to 4 mol%, were prepared by sol-get route. The films were deposited on v-SiO2 and silica-on-silicon substrates, using dip-coating technique. The waveguides show a homogeneous surface morphology, high densification degree and uniform refractive index across the thickness. Emission in the C-telecommunication band was observed at room temperature for ill the samples upon excitation at 980 nm. The shape is found to be almost independent on erbium content, with a FWHM between 44 and 48 nm. The I-4(13/2) level decay curves presented a single-exponential profile, with a lifetime ranging between 1.1 and 6.7 ms, depending on the erbium concentration. The waveguide deposited on silica-on-silicon substrate supports one single propagation mode at 1.5 mum with a confinement coefficient of 0.85, and a losses of about 0.8 dB/cm at 632.8 nm. (C) 2003 Elsevier B.V. All rights reserved.

NEUTRINOLESS DOUBLE-BETA DECAY IN AN SU(3)(L)CIRCLE-TIMES-U(1)(N) MODEL

We consider a model for the electroweak interactions with the SU(3)(L) circle times U(1)(N) gauge symmetry. We show that the conservation of the quantum number F = L+B forbids the appearance of massive neutrinos and the neutrinoless double-beta decay (beta beta)(0 nu). Explicit or/and spontaneous breaking of F implies that the neutrinos have an arbitrary mass. In addition the (beta beta)(0 nu) decay also has some channels that do not depend explicitly on the neutrino mass.

Decay of photo-excited conductivity of Er-doped SnO2 thin films

Er-doped SnO2 thin films, obtained by sol-gel-dip-coating technique, were submitted to excitation with the 4th harmonic of a Nd:YAG laser (266 nm), at low temperature, and a conductivity decay is observed when the illumination is removed. This decay is modeled by considering a thermally activated cross section of an Er-related trapping center. Besides, grain boundary scattering is considered as dominant for electronic mobility. X-ray diffraction data show a characteristic profile of nanoscopic crystallite material (grain average size approximate to 5 nm) in agreement with this model. Temperature dependent and concentration dependent decays are measured and the capture barrier is evaluated from the model, yielding 100 meV for SnO2:0.1% Er and 148 meV for SnO2:4% Er.

Sequencing wasp venom peptides by endopeptidase digestion and nested collision-induced dissociation/post-source decay methods

A method incorporating nested collision-induced dissociation/post-source decay (CID/PSD) combined with endopeptidase digestion is described as an approach to determine the sequence of N-terminally modified peptides. The information from immonium and related ions observed in the CID/PSD spectrum was used for the selection of a suitable endopeptidase for the digestion of peptides. Rapid and reliable assignment of peptide sequence was performed by the comparison of CID/PSD spectra of both intact and endopeptidese-digested peptide fragments, since the assignments of the observed fragment ions to either N- or C-terminal ions can thus be carried out unambiguously. This nested CID/PSD method was applied to the sequence determination of two peptides from the solitary wasps Anoplius samariensis and Batozonellus maculifrons (pompilid wasps), which could not be sequenced by the Edman method due to N-terminal modification. Copyright (C) 2002 John Wiley Sons, Ltd.

Sol-gel Er-doped SiO(2)-HfO(2) planar waveguides: A viable system for 1.5 mu m application

70SiO(2)-30HfO(2) planar waveguides, doped with Er(3+) concentrations ranging from 0.3 to 1 mol %, were prepared by sol-gel route, using dip-coating deposition on silica glass substrates. The waveguides show high densification degree, effective intermingling of the two components of the film, and uniform surface morphology. Propagation losses of about 1 dB/cm were measured at 632.8 nm. When pumped with 987 or 514.5 nm continuous-wave laser light, the waveguides show the (4)I(13/2)-->(4)I(15/2) emission band with a bandwidth of 48 nm. The spectral features are found independent both on erbium content and excitation wavelength. The (4)I(13/2) level decay curves presented a single-exponential profile, with a lifetime between 2.9 and 5.0 ms, depending on the erbium concentration. (C) 2002 American Institute of Physics.

COMMENT ON THE TAU DECAY PUZZLE

We analyse the current data on tau-lepton decays and show that they are consistent with the standard model.

Kinetics of photoinduced birefringence in the guest-host system of poly(methyl methacrylate) doped with azobenzene-containing crown ethers

The kinetics of the buildup and decay of photoinduced birefringence was examined in a series of host-guest systems: azobenzene-containing crown ethers, differing in the size of the crowns, dissolved in a poly (methyl methacrylate) matrix. In all samples, the kinetics of the buildup of the birefringence was reasonably described by a sum of two exponential functions, the time constants being inversely proportional to the intensity of the pumping light and the magnitudes of the signals at the saturation level depending on the pumping light intensity and sample thickness. The dark decays were best described by the stretched exponential function, with the characteristic parameters (time constant and stretch coefficient) being practically independent of the type of crown ether. The time constants of the signal decay were orders of magnitude shorter than the respective constants of the dark isomerization of the azo crown ethers, thus indicating that the process controlling the decay was a relaxation of the polymer matrix and/or a rearrangement of the flexible parts of the crowns. (C) 2007 Wiley Periodicals, Inc.

Effect of heated solutions on decay control and residues of imazalil in lemons

Freshly harvested lemons [(Citrus limon (L.) Burm)] were dipped 3 min in water with and without imazalil (IMZ) at 50, 100, and 200 ppm at 50 degrees C and at 1000 ppm IMZ at 20 degrees C. Following treatments fruit were kept at 9 degrees C and 90%-95% relative humidity (RH) for 13 weeks and an additional week at 21 degrees C and ca. 75% RH, to simulate a marketing period (SMP). No decay control was observed with fruit dipped in water at 50 degrees C. In contrast, IMZ treatments provided 90%-96% control of Penicillium rots during cold storage and SMP. Fungi other than Penicillium spp. were also found in all samples as differences among treatments were negligible. IMZ treatment caused some external damage to the fruit (peel browning), and the percentage of damaged fruit was related to the amount of active ingredient (AI) present in it. Dipping in 200 or 1000 ppm IMZ promoted off-flavor development after 10 weeks of storage, and fruit were judged to be unacceptable for consumption after 13 weeks of cold storage. After 1000 ppm IMZ dipping at 20 degrees C, residue concentration in fruit was 8.20 ppm; this value doubled that found in a previous investigation on lemons treated with comparable IMZ levels. Residue concentrations in fruit after treatment at 50 degrees C was strictly related to the amount of fungicide employed. After 13 weeks Al residues in fruit decreased to average ca. 35% of the initial values. During the 1 week SMP, residue levels decreased by a further ca. 25%. It was concluded that it is possible to achieve significant control of decay in lemons during longterm storage by dipping fruit in 50 ppm IMZ mixtures at 50 degrees C. Such treatment should be advised to remarkably reduce potential pollution in the environment due to packinghouse wastewater disposal.

Photoluminescence in quantum-confined SnO2 nanocrystals: Evidence of free exciton decay

Nanocrystalline SnO2 quantum dots were synthesized at room temperature by hydrolysis reaction of SnCl2. The addition of tetrabutyl ammonium hydroxide and the use of hydrothermal treatment enabled one to obtain tin dioxide colloidal suspensions with mean particle radii ranging from 1.5 to 4.3 nm. The photoluminescent properties of the suspensions were studied. The particle size distribution was estimated by transmission electron microscopy. Assuming that the maximum intensity photon energy of the photoluminescence spectra is related to the band gap energy of the system, the size dependence of the band gap energies of the quantum-confined SnO2 particles was studied. This dependence was observed to agree very well with the weak confinement regime predicted by the effective mass model. This might be an indication that photoluminescence occurs as a result of a free exciton decay process. (C) 2004 American Institute of Physics.

The complementary exponential power lifetime model

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Bayesian estimation of generalized exponential distribution under noninformative priors

The generalized exponential distribution, proposed by Gupta and Kundu (1999), is a good alternative to standard lifetime distributions as exponential, Weibull or gamma. Several authors have considered the problem of Bayesian estimation of the parameters of generalized exponential distribution, assuming independent gamma priors and other informative priors. In this paper, we consider a Bayesian analysis of the generalized exponential distribution by assuming the conventional non-informative prior distributions, as Jeffreys and reference prior, to estimate the parameters. These priors are compared with independent gamma priors for both parameters. The comparison is carried out by examining the frequentist coverage probabilities of Bayesian credible intervals. We shown that maximal data information prior implies in an improper posterior distribution for the parameters of a generalized exponential distribution. It is also shown that the choice of a parameter of interest is very important for the reference prior. The different choices lead to different reference priors in this case. Numerical inference is illustrated for the parameters by considering data set of different sizes and using MCMC (Markov Chain Monte Carlo) methods.