Different origins of green-light photoluminescence emission in structurally ordered and disordered powders of calcium molybdate

A strong greenish-light photoluminescence (PL) emission was measured at room temperature for disordered and ordered powders of CaMoO4 prepared by the polymeric precursor method. The structural evolution from disordered to ordered powders was accompanied by XRD. Raman spectroscopy, and TEM imagery. High-level quantum mechanical calculations in the density functional framework were used to interpret the formation of the structural defects of disorder powders in terms of band diagram and density of states. Complex cluster vacancies [MoO3 center dot V-O(z)] and [CaO7 center dot V-O(z)] (where V-O(z) = V-O(X), V-O(center dot), V-O(center dot center dot)) were suggested to be responsible to the appearance of new states shallow and deeply inserted in the band gap. These defects give rise to the PL in disordered powders. The natural PL emission of ordered CaMoO4 was attributed to an intrinsic slight distortion of the [MoO4] tetrahedral in the short range.

Effect of temperature on the interaction between the nonionic surfactant C(12)E(5) and poly(ethylene oxide) investigated by dynamic light scattering and fluorescence methods

The interaction between the nonionic surfactant C(12)E(5) and a high molar mass (M = 5.94 x 10(5)) poly(ethylene oxide) (PEG) in aqueous solution has been examined as a function of temperature by dynamic light scattering and fluorescence methods over a broad concentration range. Clusters of small surfactant micelles form within the PEO coil, leading to its extension. The hydrodynamic radius of the complex increases strongly with temperature as well as with the concentrations of surfactant and polymer. At high concentrations of the surfactant, the coil/micellar cluster complex coexists with free C(12)E(5) micelles in the solution. Fluorescence quenching measurements show a moderate micellar growth from 155 to 203 monomers in PEO-free solutions of C(12)E(5) over a wide concentration range (0.02-2.5%) at 8 degrees C. Below 0.25% C(12)E(5), the average aggregation number (N) of the micelles is smaller in the presence of PEO than in its absence. However, N increases with increasing surfactant concentration up to a plateau value of about 270 at about 1.2% (ca. 30 mM) C(12)E(5). At high surfactant concentrations, N is larger in the presence of polymer than in its absence, a finding which is connected to a significant lowering of the clouding temperature due to the PEO at these compositions. Similar results of increasing aggregation number followed by a plateau were also found at a fixed concentration of surfactant (2.5%) and varied PEO.

Interactions between the non-ionic surfactant C(12)E(5) and poly(ethylene oxide) studied using dynamic light scattering and fluorescence quenching

Dynamic light scattering measurements have been made to elucidate changes in the coil conformation of a high molecular weight poly(ethylene oxide) (PEG) fraction when the non-ionic surfactant C(12)E(5) is present in dilute solutions. The measurements were made at 20 degrees C as functions of(a) the C(12)E(5) concentration at constant PEO concentration, (b) the PEO concentration at constant C(12)E(5) concentration, and (c) the C(12)E(5)/PEO concentration ratio. The influence of temperature on the interactions in terms of the relaxation time distributions was also examined up to the cloud point. It was found that when the C(12)E(5)/PEO weight ratio was >2 and when the temperature was >14 degrees C, the correlation functions became bimodal with well-separated components. The fast mode derives fi om individual surfactant micelles which are present in the solution at high number density. The appearance of the slow mode, which dominates the scattering, is interpreted as resulting from the formation of micellar clusters due to an excluded-volume effect when the high molar mass (M = 6 x 10(5)) PEO is added to the surfactant solution. It is shown that the micellar clusters form within the PEO coils and lead to a progressive swelling of the latter for steric reasons. The dimensions of the PEO/C(12)E(5) complex increase with increasing surfactant concentration to a value of R(H) approximate to 94 nm (R(g) approximate to 208 nm) at C-C12E5 = 3.5%. Fluorescence quenching measurements show that the average aggregation number of C(12)E(5) increases significantly on addition of the high molar mass PEG. With increasing temperature toward the cloud point the clusters increase in number density and/or become larger. The cloud point is substantially lower than that for C12E5 in water solution and is strongly dependent on the PEO concentration.

Interaction between poly(ethylene glycol) and C12E8 investigated by dynamic light scattering, time-resolved fluorescence quenching, and calorimetry

Dynamic light scattering (DLS), time-resolved fluorescence quenching (TRFQ), and isothermal titration microcalorimetry have been used to show that, in dilute solution, low molecular weight poly(ethylene glycol) (PEG, M-w = 12 kDa) interacts with the nonionic surfactant octaethylene glycol n-dodecyl monoether, C12E8, to form a complex. Whereas the relaxation time distributions for the binary C12E8/water and PEG/water systems are unimodal, in the ternary mixtures they may be either uni- or bimodal depending on the relative concentrations of the components. At low concentrations of PEG or surfactant, the components of the relaxation time distribution are unresolvable, but the distribution becomes bimodal at higher concentrations of either polymer or surfactant. For the ternary system in excess surfactant, we ascribe, on the basis of the changes in apparent hydrodynamic radii and the scattered intensities, the fast mode to a single micelle, the surface of which is associated with the polymer and the slow mode to a similar complex but containing two or three micelles per PEG chain. Titration microcalorimetry results show that the interaction between C12E8, and PEG is exothermic and about 1 kJ mol(-1) at concentrations higher than the CMC of C12E8. The aggregation number, obtained by TRFQ, is roughly constant when either the PEG or the C12E8 concentration is increased at a given concentration of the second component, owing to the increasing amount of surfactant micelles inside the complex.

Yb3+, Tm3+ and Ho3+ triply-doped tellurite core-cladding optical fiber for white light generation

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Consistency between light-front quantization and covariantization for zero modes

In the light-cone gauge choice for Abelian and non-Abelian gauge fields, the vector boson propagator carries in it an additional spurious or unphysical pole intrinsic to the choice requiring a careful mathematical treatment. Research in this field over the years has shown us that mathematical consistency only is not enough to guarantee physically meaningful results. Whatever the prescription invoked to handle such an object, it has to preserve causality in the process. On the other hand, the covariantization technique is a well-suited one to tackle gauge-dependent poles in the Feynman integrals, dispensing the use of ad hoc prescriptions. In this work we show that the covariantization technique in the light-cone gauge is a direct consequence of the canonical quantization of the theory. © World Scientific Publishing Company.

Mandelstam-leibbrandt: Not really a prescription in the light-cone gauge

Since the very beginning of it, perhaps the subtlest of all gauges is the light-cone gauge, for its implementation leads to characteristic singularities that require some kind of special prescription to handle them in a. proper and consistent manner. The best known of these prescriptions is the Mandelstam-Leibbrandt one. In this work we revisit it showing that its status as a mere prescription is not appropriate but rather that its origin can be traced back to fundamental physical properties such as causality and covariantization methods. © World Scientific Publishing Company.

Light-cone fluctuations and the renormalized stress tensor of a massless scalar field

We investigate the effects of light-cone fluctuations over the renormalized vacuum expectation value of the stress-energy tensor of a real massless minimally coupled scalar field defined in a (d+1)-dimensional flat space-time with topology R×Td. For modeling the influence of light-cone fluctuations over the quantum field, we consider a random Klein-Gordon equation. We study the case of centered Gaussian processes. After taking into account all the realizations of the random processes, we present the correction caused by random fluctuations. The averaged renormalized vacuum expectation value of the stress-energy associated with the scalar field is presented. © 2013 World Scientific Publishing Company.

Critical Water Effect on the Plasmon Band and Visible Light Activity of Au/ZnO Nanocomposites

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

Light-Induced Structural Change in Iridium Complexes Studied by Electron Spin Resonance

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Greening a Brazilian cotton seed processing company: from challenges to strategic opportunities

This paper aims to shed light on a current and important theme that has been gaining increasing importance for governments, society and companies: the greening of agricultural companies in developing countries. The research objective is to classify a Brazilian cotton seed processing company in the evolutionary stages of environmental management: reactive, preventive or proactive. Design/methodology/approach– A case study was conducted in a Brazilian cotton seed processing company.Findings– The main results are: the studied company is positioned in the preventive stage of environmental management; this company is investing in operational green practices; environmental management in this company is motivated by various factors aiming at an increased competitive advantage. Finally, it can be concluded that this company is looking for green opportunities towards the proactive environmental management stage.