Enhanced vertical confinement in angled-wall slot waveguides

Optical confinement in slot waveguides with angled sidewalls is studied. Improved vertical optical confinement is observed. Different mode solvers are compared in the modeling of slot waveguides with varying sidewall angles. The finite element method was found best suitable for this task. The effect of the slot waveguide geometry on the vertical optical confinement is studied. The reduced effective mode area is beneficial in all-optical applications due to enhancement of nonlinear effects in the waveguide.     

Limitations of superoscillation filters in microscopy applications

The idea of superresolving pupil filters comes from the concept of superoscillations that may occur in regions of a band-limited signal with small amplitude having oscillations faster than the fastest Fourier component of the signal. In optical microscopy, superresolution can be achieved by appropriate design of pupil functions where the angular aperture determines the ultimate focal spot smaller than the Abbe diffraction limit outside the evanescent field region. The angular aperture cannot be increased indefinitely and the huge sidelobes cannot be avoided that are present in superresolving filters. The limitations of using such kind of filters in microscopy applications are discussed through computational examples.     

The application of solid sorbents for the purification of aluminum contaminated chemicals used as modifiers in electrothermal atomic absorption spectrometry

Various microcolumns with solid sorbents (ion exchange resins, functionalised cellulose sorbents, chelating resins) have been tested with respect to their ability for the purification of aluminum contaminated chemicals used as modifiers in electrothermal atomic absorption spectrometry. The purification of NaNO₃, Mg(NO₃)₂, K₂SO₄ and (NH₄)₂HPO₄ has been the most effective with an almost 100% efficiency, when Spheron-Oxine was used as chelating resin. The sorption of aluminum from KOH solution has been found to be very high (around 90%) for all investigated sorbents. However, the best results have been obtained with anion-exchange resins. It has been difficult to purify concentrated mineral acids (HCl, H₂SO₄). A retention of aluminum above 80% has been achieved only when Cellex P, Chelex 100 or Amberlite XAD-2 have been used.     

Constraints on sparticle spectrum in different supersymmetry breaking models

We derive sum rules for the sparticle masses in different models of supersymmetry breaking. This includes the gravity-mediated models (SUGRA models) as well as models in which supersymmetry breaking terms are induced by super-Weyl anomaly (AMSB models). These sum rules can help in distinguishing between these models. In particular, we obtain an upper bound on the mass of the lightest neutralino as a function of the gluino mass in SUGRA and AMSB models.     

Asymptotical behaviour of a class of semilinear diffusion equations

We improve the existing results of the long time asymptotical behaviour of some basic semilinear diffusion equations (with space variable in the whole space ). Our method is elementary: it is based on explicit calculations, weighted sup–norm estimates and a fixed point argument.     

Multipole interference in the second-harmonic optical radiation from gold nanoparticles

We provide experimental evidence of higher multipole (magnetic dipole and electric quadrupole) radiation in second-harmonic (SH) generation from arrays of metal nanoparticles. Fundamental differences in the radiative properties of electric dipoles and higher multipoles yield opposite interference effects observed in the SH intensities measured in the reflected and transmitted directions. These interference effects clearly depend on the polarization of the fundamental field, directly indicating the importance of multipole effects in the nonlinear response. We estimate that higher multipoles contribute up to 20% of the total emitted SH field amplitude for certain polarization configurations.     

Noncovalent attachment of pyro-pheophorbide a to a carbon nanotube

Pyrene mediated noncovalent attachment of a chlorophyll derivative, pyro-pheophorbide a, to a soluble single wall carbon nanotube is reported and the resultant CD, UV-Vis absorbance, fluorescence and 1H NMR spectra are discussed.     

From calls to communities: a model for time-varying social networks

Social interactions vary in time and appear to be driven by intrinsic mechanisms thatshape the emergent structure of social networks. Large-scale empirical observations ofsocial interaction structure have become possible only recently, and modelling theirdynamics is an actual challenge. Here we propose a temporal network model which builds onthe framework of activity-driven time-varying networks with memory. Themodel integrates key mechanisms that drive the formation of social ties – socialreinforcement, focal closure and cyclicclosure, which have been shown to give rise to community structure andsmall-world connectedness in social networks. We compare the proposed model with areal-world time-varying network of mobile phone communication, and show that they shareseveral characteristics from heterogeneous degrees and weights to rich communitystructure. Further, the strong and weak ties that emerge from the model follow similarweight-topology correlations as real-world social networks, including the role of weakties.     

Computational methods for analysis of an unsaturated carbocycle: heptafulvene

With respect to geometric optimizations, harmonic vibrational frequencies and single point conformational energies, various computational methods [HF, MP2, CCSD(T), BD(T), CASSCF, CASPT2, and DFT] were evaluated for their suitability to describe the heptafulvene system. We found that a significant number of basis sets lead to wrong predictions of folded minima, when ab initio methods including dynamic electron correlation are used. Possible explanations for these inconsistencies, such as wave function instabilities, near linear dependences of the basis sets and inadequate inclusion of polarization functions in the basis set, are discussed. Such concerns are likewise important for other classes of π-conjugated compounds, such that the results are expected to be of interest not only for heptafulvenes.