Characterization of NOx species in dehydrated and hydrated Na- and Ba-Y, FAU zeolites formed in NO2 adsorption

Adsorbed ionic NO_x species formed upon the interaction of NO₂ with dehydrated or hydrated Na- and Ba-Y, FAU zeolites were characterized using FT-IR/TPD, solid state NMR, and XANES techniques. NO₂ disproportionates on both dehydrated catalyst materials forming NO⁺ and NO₃⁻ species. These ionic species are stabilized by their interactions with the negatively charged zeolite framework and the charge compensating cations (Na⁺ and Ba²⁺), respectively. Although the nature of the adsorbed NO_x species formed on the two catalysts is similar, their thermal stabilities are strongly dependent on the charge compensating cations. In the presence of water in the channels of these zeolite materials new paths open for reactions between NO⁺ and H₂O, and NO₂ and H₂O, resulting in significant changes in the adsorbed ionic species observed. These combined spectroscopic investigations afforded the understanding of the interactions between water and NO₂ on these zeolite catalysts.     

Squeezing and Quantum Canonical Transformations

In this paper we present an approach to quantum mechanical canonical transformations. Our main result is that time-dependent quantum canonical transformations can always be cast in the form of squeezing operators. We revise the main properties of these operators in regard to its Lie group properties, how two of them can be combined to yield another operator of the same class and how can also be decomposed and fragmented. In the second part of the paper we show how this procedure works extremely well for the time-dependent quantum harmonic oscillator. The issue of the systematic construction of quantum canonical transformations is also discussed along the lines of Dirac, Wigner, and Schwinger ideas and to the more recent work by Lee. The main conclusion is that the classical phase space transformation can be maintained in the operator formalism but the construction of the quantum canonical transformation is not clearly related to the classical generating function of a classical canonical transformation. We hereby propose the much more efficient method given by the squeezing operators. This method has also been proved to be very useful, by one of the authors, in the framework of the dynamical symmetries (Cerveró, J. M. (1999). International Journal of Theoretical Physics 38, 2095–2109).     

Phase-object analysis with a speckle interferometer

We describe the characteristics of a double-exposure specklegram obtained through a double-aperture system, by introduction of a wedge in front of one aperture in one exposure. It is assumed that a uniform displacement of the diffuser is produced between exposures. The average intensity distribution and visibility of the interferometric fringes in the Fourier plane are analyzed. An alternative interferometric technique for phase-object detection is proposed.     

Hopping of chaotic dynamics in a doubly resonant parametric oscillator

We study a doubly resonant optical parametric oscillator where the pump can feed two pairs of signal-idler modes. We assume the presence of gain at the pump frequency. We investigate the various oscillation states of interest, namely, when only the first pair oscillates with the other pair having null amplitudes and vice versa. We demonstrate the exchange of dynamics between the mode pairs when the relevant parameters of the cavity, namely, the phase mismatch factors or the decay rates switch because of fluctuations. The exchange of dynamics is shown to be independent of the nature of dynamics, i.e. independent of whether the motion isn-periodic or chaotic. We also investigate the case where both the pairs can exhibit chaotic dynamics though these states are difficult to realize because of fluctuations.     

Determination of strain and stress distribution on shearwalls by using the speckle photography technique

Speckle photography (SP) is a powerful tool that is adequate to determine small displacements in micrometer range. This information shows other characteristics of structure deformation under loads and can be determined as stress and strain distribution. In this paper we present the results of the application of the SP technique used to study the behaviour of discontinuities in a shearwall model. These structural elements are very important to the stability of buildings. The displacement whole field around the discontinuities and loading points was determined using the pointwise method. This allows us to determine stress distribution at the point of interest by means of the suitable equations. We also present the stress distribution obtained through the finite element method in order to compare the results obtained by means of these two techniques. Good correspondence was found between the displacements determined by both techniques (r=0.982) and also between the stress values we obtained.     

Synthesis and characterization of hollow ��-Fe2O3 sub-micron spheres prepared by sol�Cgel

In this work we report the preparation of magnetic hematite hollow sub-micron spheres (??-Fe₂O₃) by colloidal suspensions of ferric nitrate nine-hydrate (Fe(NO₃)₃·9H₂O) particles in citric acid solution by following the sol?Cgel method. After the gel formation, the samples were annealed at different temperatures in an oxidizing atmosphere. Annealing at 180°C resulted in an amorphous phase, without iron oxide formation. Annealing at 250°C resulted in coexisting phases of hematite, maghemite and magnetite, whereas at 400°C, only hematite and maghemite were found. Pure hematite hollow sub-micron spheres with porous shells were formed after annealing at 600°C. The characterization was performed by X-ray diffraction (XRD), Mössbauer spectroscopy (MS) and scanning electron microscopy (SEM).     

High-pressure crystal structure of elastically isotropic CaTiO3 perovskite under hydrostatic and non-hydrostatic conditions

The structural evolution of orthorhombic CaTiO3 perovskite has been studied using high-pressure single-crystal x-ray diffraction under hydrostatic conditions up to 8.1 GPa and under a non-hydrostatic stress field formed in a diamond anvil cell (DAC) up to 4.7 GPa. Under hydrostatic conditions, the TiO6 octahedra become more tilted and distorted with increasing pressure, similar to other 2:4 perovskites. Under non-hydrostatic conditions, the experiments do not show any apparent difference in the internal structural variation from hydrostatic conditions and no additional tilts and distortions in the TiO6 octahedra are observed, even though the lattice itself becomes distorted due to the non-hydrostatic stress. The similarity between the hydrostatic and non-hydrostatic cases can be ascribed to the fact that CaTiO3 perovskite is nearly elastically isotropic and, as a consequence, its deviatoric unit-cell volume strain produced by the non-hydrostatic stress is very small; in other words, the additional octahedral tilts relevant to the extra unit-cell volume associated with the deviatoric unit-cell volume strain may be totally neglected. This study further addresses the role that three factors--the elastic properties, the crystal orientation and the pressure medium--have on the structural evolution of an orthorhombic perovskite loaded in a DAC under non-hydrostatic conditions. The influence of these factors can be clearly visualized by plotting the three-dimensional distribution of the deviatoric unit-cell volume strain in relation to the cylindrical axis of the DAC and indicates that, if the elasticity of a perovskite is nearly isotropic as it is for CaTiO3, the other two factors become relatively insignificant.     

Manganese-enhanced magnetic resonance microscopy of mineralization

Paramagnetic manganese (II) can be employed as a calcium surrogate to sensitize magnetic resonance microscopy (MRM) to the processing of calcium during bone formation. At high doses, osteoblasts can take up sufficient quantities of manganese, resulting in marked changes in water proton T(1), T(2) and magnetization transfer ratio values compared to those for untreated cells. Accordingly, inductively coupled plasma mass spectrometry (ICP-MS) results confirm that the manganese content of treated cell pellets was 10-fold higher than that for untreated cell pellets. To establish that manganese is processed like calcium and deposited as bone, calvaria from the skull of embryonic chicks were grown in culture medium supplemented with 1 mM MnCl(2) and 3 mM CaCl(2). A banding pattern of high and low T(2) values, consistent with mineral deposits with high and low levels of manganese, was observed radiating from the calvarial ridge. The results of ICP-MS studies confirm that manganese-treated calvaria take up increasing amounts of manganese with time in culture. Finally, elemental mapping studies with electron probe microanalysis confirmed local variations in the manganese content of bone newly deposited on the calvarial surface. This is the first reported use of manganese-enhanced MRM to study the process whereby calcium is taken up by osteoblasts cells and deposited as bone.