Thermo-elasticity for anisotropic media in higher dimensions

In this note we develop tools to study the Cauchy problem for the system of thermo-elasticity in higher dimensions. The theory is developed for general homogeneous anisotropic media under non-degeneracy conditions. For degenerate cases a method of treatment is sketched and for the cases of cubic media and hexagonal media detailed studies are provided.Comment: 33 pages, 5 figure

Persistent disruption of interspecific competition after ultra-low esfenvalerate exposure

Field and mesocosm studies repeatedly show that higher tier process reduce the predictive accuracy of toxicity evaluation and consequently their value for pesticide risk assessment. Therefore, understanding the influence of ecological complexity on toxicant effects is crucial to improve realism of aquatic risk assessment. Here we investigate the influence of repeated exposure to ecologically realistic concentrations of esfenvalerate on the similarly sensitive species Daphnia magna and Culex pipiens in a food limited and highly competitive environment. We show that significant perturbations in population development are only present close to the EC50. In contrast, interspecific competition between species is already reduced at concentrations 3-4 orders of magnitude below the acute EC50. We conclude that extremely low, environmentally relevant concentrations can disrupt species interactions. This toxicant mediated alteration of competitive balances in ecological communities may be the underlying mechanism for shifts in species distribution at ultra-low pesticide concentrations. A realistic risk assessment should therefore consider these processes in order to predict potential pesticide effects on the structure of communities

Electroabsorption spectroscopy of luminescent and nonluminescent ∏-conjugated polymers

Journal ArticleWe have measured the quadratic electroabsorption (EA) spectrum of a variety of soluble luminescent and nonluminescent p-conjugated polymer films in the spectral range of 1.5-4.5 eV. The luminescent polymers include MEH and DOO derivatives of poly(phenylene-vinylene), poly(phenylene ethylene), and polythiophene; the nonluminescent polymers include poly(diethynyl silane) and monosubstituted polyacetylene. All EA spectra show a Stark shift of the low-lying odd-parity exciton (1Bu) and imply the presence of phonon sidebands. There are also higher-energy bands due to transfer of oscillator strength to even-parity exciton states (Ag), the strongest of which (mAg) is located at an energy about 1.3 times that of the 1Bu exciton in both luminescent and nonluminescent polymers; in the luminescent polymers the EA spectra also show a second prominent Ag state (kAg) at an energy of about 1.6 times that of the 1Bu. We have successfully fitted the EA spectra by calculating the imaginary part of the third order optical susceptibility, Im[x3(ω;ω,0,0)], using a summation over states model dominated by the ground state, the 1Bu exciton, two strongly coupled Ag states (mAg and kAg), and their most strongly coupled vibrations, using Frank-Condon overlap integrals

Optical probes of pristine and C60-doped silicon-bridged PT polymer; a novel highly luminescent, low bandgap polymer

Journal ArticleSilicon bridged PT polymer (PTSi) is a new soluble polymer with a strong luminescence in the infrared band (0-0 transition at 1.6 eV). We have applied various spectroscopies such as absorption, electroabsorption (EA), photo induced absorption (PA), electromodulated PA (EPA), photoluminescence (PL) and photo induced absorption detected magnetic resonance (PADMR) to pristine and C60- doped PTSi thin films in order to eluvidate the photoexcitation and electronic states this material.. The absorption spectrum consists of three bands, one in the visible with a peak at 2 eV and the others in the UV at 4.5 eV and 6.2 eV respectively. The PL band at 1.6 eV contains also three pronounced phonon replica, each 150 meV apart. An electric field reduces the luminescence due to dissociation of excitons into polarons. The PA spectrum is dominated by a broad PA band peaked at 1.1 eV which is due to triplet-triplet transitions, with a shoulder at 1.7 eV due to polaron pairs; there is also a distinctive band at 0.3 eV due to both, polarons and polaron pairs. Upon doping with C60- the 1.1 eV triplet band loses intensity, whereas the 0.3 eV feature dramatically increases and the typical signature of C60- HOMO to LUMO transition appears at 1.15 eV

Electromodulated photoinduced absorption; a new spectroscopy in ∏-conjugated polymer/C60-blends

Journal ArticleWe have applied the electromodulated photoinduced absorption (EPA) technique to a variety of C 6 0 -doped and pristine luminescent conducting polymer films. EPA measures the electric field-related change of the absorption in the sample as a result of above-gap illumination. An electric field leads to two major effects. One is a possible Stark shift of photoexcitation (polarons, polaron pairs, or C 6 0 ') energy levels, and the other is a change in the photoexcitation decay kinetics, which leads to reduction or enhancement of PA features. This can be due to an electric field enhanced dissociation of the 1Bu exciton or due to a lifetime reduction of polaron pairs