Another approach to the spherical Stark problem in hydrogen

The factorized wave function method of Hall is successfully applied to the spherical Stark problem in hydrogen. The results are in excellent agreement as compared to stabilization technique and accurate Padé approximants. This is the case even for large values of the field strength where the Rayleigh-Schrödinger perturbation theory becomes strongly divergent.     

Corticomuscular synchronization with small and large dynamic force output

Background  

Over the last few years much research has been devoted to investigating the synchronization between cortical motor and muscular activity as measured by EEG/MEG-EMG coherence. The main focus so far has been on corticomuscular coherence (CMC) during static force condition, for which coherence in beta-range has been described. In contrast, we showed in a recent study [1] that dynamic force condition is accompanied by gamma-range CMC. The modulation of the CMC by various dynamic force amplitudes, however, remained uninvestigated. The present study addresses this question. We examined eight healthy human subjects. EEG and surface EMG were recorded simultaneously. The visuomotor task consisted in isometric compensation for 3 forces (static, small and large dynamic) generated by a manipulandum. The CMC, the cortical EEG spectral power (SP), the EMG SP and the errors in motor performance (as the difference between target and exerted force) were analyzed.     

Talbot effect in metallic gratings under Gaussian illumination

Metallic gratings can be found in applications such as optical metrology. Due to their fabrication process, the surface presents a certain roughness. In this work, the effect of roughness on Talbot effect has been analyzed when the grating is illuminated with a Gaussian beam. A model based on Fresnel regime is used in order to determine the intensity distribution in the near field. Contrast of the self-images is obtained and it is found that it decreases in terms of the distance between the grating and the observation plane. When the autocorrelation function of roughness presents a Gaussian behaviour, the diffracted beams are still Gaussian although some of their properties change. For example, the width of the diffracted beams increases with respect to the case of the standard chrome on glass gratings. On the other hand, the power of each diffracted beam is independent on the roughness properties of the surface.     

Internal magnetic field effects on the photochemistry of a xanthone derivate covalently anchored to magnetite nanoparticles

Irradiation of azaxanthone in the presence of colloidal magnetite nanoparticles gives rise to the generation of the corresponding azaxanthone triplet, whose lifetime is influenced by internal magnetic field effects. In contrast, covalent tethering between magnetite and azaxanthone promotes photoinduced electron transfer leading to the observation of azaxanthone radical anion.     

Monodisperse DNA restriction fragments II. Sedimentation velocity and equilibrium experiments

We report sedimentation velocity and equilibrium measurements performed with an analytical ultracentrifuge to elucidate the effects of limited flexibility on the transport properties of semiflexible, monodisperse, double-stranded, blunt-ended DNA restriction fragments. We study a homologous series of fragments with 400, 800, and 1600 base pairs (3 to 11 persistence lengths), which are specifically designed and synthesized for this purpose (Part I). The molecular weights following from the sedimentation measurements agree well with the values expected on the basis of the number of base pairs. The sedimentation coefficients at infinite dilution are in good agreement with theoretical predictions for wormlike cylinders. The first order in volume fraction (varphi) coefficient K of the varphi-dependent sedimentation coefficient s(varphi)=1-Kvarphi decreases from 1178 for the shortest fragment to 882 for the longest fragment. These values are much larger than predicted for uncharged rigid rods, indicating the presence of associates with an enhanced aspect ratio and excluded volume. The precise match of the molecular weights obtained from exponential sedimentation-diffusion equilibrium distributions with weights calculated from the number of base pairs shows that any association is reversible and disappears at sufficiently low DNA concentration.     

Structural Evolution and Fluorescence Properties of Dy<Superscript>3+</Superscript>: Silica Matrix

Silica glasses doped with Dy³⁺ were prepared by sol–gel method. The FTIR and thermo gravimetric analysis (TGA) clearly show complete densification (density = 2.2 gm/cm³) of the gels around 1000C. The fluorescence properties of Dy³⁺ ion are utilized to study the structural changes during the gel to glass transition of the silica xerogels. The fluorescence intensity and full width at half maximum (FWHM) of the emission bands show an increasing tendency with heat treatment. This is attributed to a glassy silica network with an asymmetric environment. The (Y/B) ratio for the Dy³⁺ ion is found to be less sensitive to site symmetry effects.     

Novel phthalocyaninatobis(alkylcarboxylato)silicon(IV) compounds: NMR data and X-ray structures to study the spacing provided by long hydrocarbon tails that enhance their solubility

The reaction between trans-PcSiCl2 (1) and the potassium salts of six fatty acids (2 a-2 f) led to the trans-PcSi[OOC(CH2)nCH3]2 compounds (3 a-3 f), which were characterised by elemental analysis, IR, UV/Vis and 1H, 13C, and 29Si NMR spectroscopy. From a detailed study of the NMR spectra, the strong anisotropic currents of the Pc macrocycle were found to have an effect on up to the sixth methylenic group. As expected, the length of the hydrocarbon tail does not affect the chemical shift of the 29Si nucleus of any of the compounds, appearing at around -222.6. The structures of PcSi[OOC(CH2)nCH3]2, where n = 7, 10, 12, 13 and 20, were determined by X-ray crystallography. All the compounds were found to be triclinic with a P1 space group. In all cases the observed crystallographic pseudosymmetry is Ci and the asymmetric unit consists of half a molecule. The silicon atom is at the centre of a distorted octahedron and hence its coordination number is six. The carboxylate fragments are in a trans configuration with respect to the Pc macrocycle. The supramolecular structures are discussed in detail herein. The correlation between the 1H NMR chemical shifts and the position of the corresponding carbon atoms in the hydrocarbon tail reveals that the dicarboxylate substituents exhibit a spacer-like behaviour that enhances the solubility. A detailed study of the tail variable allowed us to evaluate the loss of radial shielding along the Pc2- ligand.     

Multicomponent domino processes based on the organocatalytic generation of conjugated acetylides: efficient synthetic manifolds for diversity-oriented molecular construction

The organocatalytic generation of a strong base by the action of a good nucleophile is the base for the in situ catalytic generation of conjugated acetylides in the presence of aldehydes or activated ketones. The method is affordable in a multicomponent, domino format able to generate a chemically diverse set of multifunctionalized adducts that are very well suited for diversity-oriented molecular construction. The domino process involves a nucleophile as catalyst and a terminal conjugated alkyne (H-C[triple chemical bond]C-Z) and an aldehyde or activated ketone as building blocks. The chemical outcome of this process changes dramatically as a function of the nucleophile (tertiary amine or phosphine), temperature, stoichiometry, and solvent. These multicomponent domino processes achieve molecular construction with good atom economy and, very importantly, with an exquisite chemo-differentiating incorporation of identical starting units into the products (nondegenerated chemical output). These properties convert the H-C[triple chemical bond]C-Z unit into a specific building block for diversity-oriented molecular construction. Applications to the modular and diversity-oriented synthesis of relevant heterocycles are discussed. A protocol involving two coupled domino processes linked in a one-pot manner will be discussed as an efficient synthetic manifold for the modular and diversity-oriented construction of multisubstituted nitrogen-containing heterocycles.     

Subphthalocyanines as fluoro-chromogenic probes for anions and their application to the highly selective and sensitive cyanide detection

The use of a subphthalocyanine derivative as a selective chromo-fluorogenic reporter for the anion cyanide in mixed aqueous solutions is reported.     

Aluminium(III) adsorption: a soft and simple method to prevent TiO2 deactivation during salicylic acid photodegradation

Deposition of poisoning species on TiO2 during salicylic acid photodegradation can be halted when Al(III) has been previously adsorbed on the catalyst surface; this widens the application of photocatalysis to more concentrated solutions.