Enhancement of optical luminescence of solids using a capillary lens

The Advanced Photon Source (APS) at Argonne National Laboratory is a 1-km-circumference, 7-GeV, third generation synchrotron light source. It is the largest light source in the Western Hemisphere and attracts about 3,500 users every year from around the globe. The APS is currently preparing for a major upgrade, a goal of which is to focus on high brightness at photon energies of around 20 keV and higher. The APS is particularly well suited for this high photon energy range due to its higher-energy, 7-GeV electron beam, but it also needs new insertion devices with short periods and high fields, i.e., superconducting devices.     

Reduced limits for nonlinear equations with measures

We consider equations (E) −Δu+g(u)=μ in smooth bounded domains Ω⊂RN, where g is a continuous nondecreasing function and μ is a finite measure in Ω. Given a bounded sequence of measures (μk), assume that for each k?1 there exists a solution uk of (E) with datum μk and zero boundary data. We show that if uk→u# in L¹(Ω), then u# is a solution of (E) relative to some finite measure μ#. We call μ# the reduced limit of (μk). This reduced limit has the remarkable property that it does not depend on the boundary data, but only on (μk) and on g. For power nonlinearities g(t)=|t|^q−1t, ∀t∈R, we show that if (μk) is nonnegative and bounded in W−2,q(Ω), then μ and μ# are absolutely continuous with respect to each other; we then produce an example where μ#≠μ.     

An Alternative Approach to the Electric Charge Quantization with Non-global Potentials

We present an alternative approach to justify the electric charge quantization by means of non-global electromagnetic potentials. We adopt a non-global potential whose singularity does not goes over to infinity and can be entirely embedded into an arbitrarily small closed ball.     

Ion distribution preferences in ternary crystals ZnxCd1−xTe, Zn1−xHgxTe and Cd1−xHgxTe

Similar ternary semiconductors are sometimes associated with widely different structures characterized by different site occupation preferences. We have used far-infrared (FIR) spectra to determine the site occupation preference coefficients for three ternary semiconductor alloys: ZnCdTe, ZnHgTe and CdHgTe and, in the case of ZnHgTe, have validated it by X-ray absorption fine structure (EXAFS) analysis. While ZnCdTe spectra exhibit the canonical configuration with eight phonon lines free of vibrational defect lines and only a slight departure from a random ion distribution, CdHgTe spectra show the eight canonical phonon modes plus an additional vibrational defect line and constant preference coefficients. In contrast, two defect lines and only four modes characterize ZnHgTe spectra, as extreme preferences prevent the formation of two of the five expected tetrahedral configuration arrangements. Moreover, for this system, comparison with EXAFS data points out the vibrational nature of both the extra lines. The analysis clearly shows that assuming a Bernoulli distribution of the component configurations of semiconductors may lead to wrong assessments of the evolution of its properties with relative content.     

Ethylene‐norbornene copolymers prepared with metallocene‐ based catalysts: new sequence assignments by 13C NMR

A series of ethylene‐norbornene copolymers were synthesized in the presence of zirconocenes with different symmetries and ligand patterns and at different norbornene (N)/ethylene (E) mole ratios. Copolymers were characterized by ¹³C NMR spectroscopy; Inadequate NMR sequences were used also. The comparison of ¹³C NMR spectra of copolymers prepared with different norbornene content and the correlation between ¹³C NMR chemical shifts and conformational structures of the chain on the basis of molecular mechanics calculations were performed. Preliminary assignments were revised and new comonomer sequences such as ENNE which contain meso and racemo NN dyads were assigned.     

Crosslinking of a fibrous sample to a macro-oriented mesomorphic network

Preliminary results on the synthesis and characterization of anisotropic networks, oriented on a macroscopic scale, are reported. Fiber samples of segmented thermotropic liquid-crystalline polymers bearing the oxypentenyl lateral substituent have been crosslinked via thermally activated radical reaction. This was made possible by immersion of fiber samples in dichloromethane containing t-butylperoxybenzoate as activating agent, thus allowing its diffusion in the samples. Subsequent annealing at 145°C brings us to an anisotropic network with no loss of the original orientation. A mesophase is stabilized and no structural modification is observed by heating samples from room temperature up to 400°C, where thermal decomposition takes place. Crosslinked fibers exhibit good tensile properties, at both room temperature and at 150°C. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 433–438, 1998     

Effect of Non-Calcined Sugarcane Bagasse Ash as an Alternative Precursor on the Properties of Alkali-Activated Pastes

BFS-MK-based alkali-activated materials are well established as an alternative for sustainable and green construction. This work aims to collaborate and encourage the use of biomass ashes, such as sugarcane bagasse ash (SCBA), as a precursor in alkali-activated materials (AAM). This ash is a rich source of aluminosilicate, which is a primary requirement for this application. In addition, this waste is still an environmental liability, especially in developing countries, and with a large volume of annual production. Thus, in this research, alkali-activated pastes (AA) were produced using sugarcane bagasse ash (SCBA), granulated blast furnace slag (BFS) and metakaolin (MK) as precursors. In addition, environmental gains were encouraged with energy savings, with no extra reburn or calcination steps in the SCBA. Thus, the precursors were characterized by laser granulometry, X-ray fluorescence spectrometry (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The pastes were produced by mixing the precursors with the activator, composed of a mixture of sodium hydroxide 8 mol/L and sodium silicate. Aiming to study the incorporation of SCBA, all samples have a precursor/activator ratio and a BFS/(BFS + MK) ratio constant of 0.6. The compressive strength analysis, FTIR, XRD, TGA, SEM and isothermal calorimetry analyses pointed out the occurrence of alkaline activation in all proposed samples for curing times of 7, 28 and 91 days. The sample GM0.6-BA0 (15% SCBA) achieved the highest compressive strength among the samples proposed (117.7 MPa, at 91 days), along with a good development of strength throughout the curing days. Thus, this work presents the properties of alkaline-activated pastes using SCBA as a sustainable and alternative precursor, seeking to encourage the use of raw materials and alternative waste in civil construction.