Nanoscale deformation irregularities of γ-irradiated poly(methyl methacrylate)

Development of deformation jumps in the creep of poly(methyl methacrylate) (PMMA) has been studied. The structural levels of deformation have been determined from the creep rate oscillation periods (deformation jumps) measured by the interferometric method. Special attention is given to a new method of data processing, which enables one to reveal previously undetectable nanoscale deformation jumps. By the example of PMMA specimens preliminarily exposed to γ radiation with doses D=55–330 kGy and unexposed specimens, the presence of nanoscale deformation jumps with the values dependent on the dose D and time of creep has been shown. The obtained results confirm the existence of 10–20-nm domains in amorphous polymers and make it possible to study the multilevel organization of the deformation process, starting from the nanoscale.     

Analytical approach for CRLH-based antennas design

This paper presents an analytical model for CRLH (Composite Right-Left Handed) antennas preliminary design. The objective of this work is to develop a tool to estimate quickly the scattering and radiating characteristics of these CRLH-based structures. The analytical model provides thus a set of parameters which roughly fulfill desired requirements. Afterwards, the antenna designer can refine the CRLH-based antenna performances with full 3D electromagnetic simulation software.     

Investigations on the wavelength dependence of optically induced long-period Bragg gratings

We numerically analyze the conversion of transverse modes with optically induced long-period Bragg gratings. These gratings are generated by a recently developed technique which uses a writing beam guided within the fiber to introduce a transient grating via the optical Kerr effect. We demonstrate several settings for conversion between different transverse modes, including conversion over a broad spectral range of up to 60?nm. The tunability of the grating parameters could promote novel applications.     

SU(1,1) Coherent States for Position-Dependent Mass Singular Oscillators

The Schr?dinger equation for position-dependent mass singular oscillators is solved by means of the factorization method and point transformations. These systems share their spectrum with the conventional singular oscillator. Ladder operators are constructed to close the su(1,1) Lie algebra and the involved point transformations are shown to preserve the structure of the Barut-Girardello and Perelomov coherent states.     

Interface Energy in the Edwards-Anderson Model

We numerically investigate the spin glass energy interface problem in three dimensions. We analyze the energy cost of changing the overlap from −1 to +1 at one boundary of two coupled systems (in the other boundary the overlap is kept fixed to +1). We implement a parallel tempering algorithm that simulates finite temperature systems and works with both cubic lattices and parallelepiped with fixed aspect ratio. We find results consistent with a lower critical dimension D _c =2.5. The results show a good agreement with the mean field theory predictions.     

Dissociative and molecular oxygen chemisorption channels on reduced rutile TiO2(110): An STM and TPD study

High-resolution scanning tunneling microscopy (STM) and temperature-programmed desorption (TPD) were used to study the interaction of O₂ with reduced TiO₂(110)–(1 × 1) crystals. STM is the technique of choice to unravel the relation between vacancy and non-vacancy assisted O₂ dissociation channels as a function of temperature. It is revealed that the vacancy-assisted, first O₂ dissociation channel is preferred at low temperature (~ 120 K), whereas the non-vacancy assisted, second O₂ dissociation channel operates at temperatures higher than 150 K–180 K. Based on the STM results on the two dissociative O₂ interaction channels and the TPD data, a new comprehensive model of the O₂ chemisorption on reduced TiO₂(110) is proposed. The model explains the relations between the two dissociative and the molecular O₂ interaction channels. The experimental data are interpreted by considering the available charge in the near-surface region of reduced TiO₂(110) crystals, the kinetics of the two O₂ dissociation channels as well as the kinetics of the diffusion and reaction of Ti interstitials.     

Low voltage TEM: Influences on electron energy loss spectrometry experiments

We discuss the advantages and disadvantages of electron energy loss spectrometry (EELS) a transmission electron microscope (TEM) at different high tensions. Instrumental effects such as energy resolution, spatial resolution, and point spread function of the detecting system, as well as physical effects like inelastic (Coloumb) delocalization and Cerenkov losses are dealt with. It is found that the actually available equipment is suitable for performing low voltage experiments. The energy resolution of a thermo-ionic emitter can be tremendously improved at lower energies, and the detector also has advantageous behaviour.     

Biphenyl-type sensing system in proton-rich environment by fluorescence and quantum-chemical calculations

Biphenyl derivative N-allyl-N′-(4′-nitro[1,1′-biphenyl]-4-yl)thiourea (BP1) was synthesized as a functional fluorescent sensor for protons and their photophysical properties were studied. The influence of environment protonation on photophysical properties of the biphenyls in solutions was investigated using UV absorption, steady-state and time-resolved fluorescence spectroscopy. Semi-empirical and DFT calculations and optimization of the molecular structure of the biphenyl derivatives in vacuum, in polar solvents and in a proton-rich environment were conducted using the HyperChem, Amsol and Gaussian3 software package. Fluorescence quenching with addition of acidic acid was observed and the Stern-Volmer quenching rate constant was about 3.0×10⁹ M⁻¹ s⁻¹. Intermolecular hydrogen bonds formations by the protons with the sulphur being substituted to the biphenyls generate charge movement and strong increase (×5) of the dipole moment of the fluorophore.     

Hamilton-Poisson formulation for the rotational motion of a rigid body in the presence of an axisymmetric force field and a gyroscopic torque

We give sufficient conditions for the rigid body in the presence of an axisymmetric force field and a gyroscopic torque to admit a Hamilton-Poisson formulation. Even if by adding a gyroscopic torque we initially lose one of the conserved Casimirs, we recover another conservation law as a Casimir function for a modified Poisson structure. We apply this frame to several well-known results in the literature.