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

Relaxation energies and excited state structures of poly(para-phenylene)

We investigate the relaxation energies and excited state geometries of the light emitting polymer, poly(para-phenylene). We solve the Pariser-Parr-Pople-Peierls model using the density matrix renormalization group method. We find that the lattice relaxation of the dipole-active $1^1B_{1u}^-$ state is quite different from that of the $1^3B_{1u}^+$ state and the dipole-inactive $2^1A_g^+$ state. In particular, the $1^1B_{1u}^-$ state is rather weakly coupled to the lattice and has a rather small relaxation energy ca. 0.1 eV. In contrast, the $1^3B_{1u}^+$ and $2^1A_g^+$ states are strongly coupled with relaxation energies of ca. 0.5 and ca. 1.0 eV, respectively. By analogy to linear polyenes, we argue that this difference can be understood by the different kind of solitons present in the $1^1B_{1u}^-$, $1^3B_{1u}^+$ and $2^1A_g^+$ states. The difference in relaxation energies of the $1^1B_{1u}^-$ and $1^3B_{1u}^+$ states accounts for approximately one-third of the exchange gap in light-emitting polymers.Comment: Submitted to Physical Review

Traits and stress: keys to identify community effects of low levels of toxicants in test systems

Community effects of low toxicant concentrations are obscured by a multitude of confounding factors. To resolve this issue for community test systems, we propose a trait-based approach to detect toxic effects. An experiment with outdoor stream mesocosms was established 2-years before contamination to allow the development of biotic interactions within the community. Following pulse contamination with the insecticide thiacloprid, communities were monitored for additional 2 years to observe long-term effects. Applying a priori ecotoxicological knowledge species were aggregated into trait-based groups that reflected stressor-specific vulnerability of populations to toxicant exposure. This reduces inter-replicate variation that is not related to toxicant effects and enables to better link exposure and effect. Species with low intrinsic sensitivity showed only transient effects at the highest thiacloprid concentration of 100 μg/l. Sensitive multivoltine species showed transient effects at 3.3 μg/l. Sensitive univoltine species were affected at 0.1 μg/l and did not recover during the year after contamination. Based on these results the new indicator SPEARmesocosm was calculated as the relative abundance of sensitive univoltine taxa. Long-term community effects of thiacloprid were detected at concentrations 1,000 times below those detected by the PRC (Principal Response Curve) approach. We also found that those species, characterised by the most vulnerable trait combination, that were stressed were affected more strongly by thiacloprid than non-stressed species. We conclude that the grouping of species according to toxicant-related traits enables identification and prediction of community response to low levels of toxicants and that additionally the environmental context determines species sensitivity to toxicants

Two-photon absorption spectra of luminescent conducting polymers measured over wide spectral range

Optical Science, Engineering and Instrumentation '97, 1997, San Diego, CA, United StatesRon K. Meyer, Martin Liess, Robert E. Benner, Werner Gellermann, Z. Valy Vardeny, Masanori Ozaki, Katsumi Yoshino, Yi Wei Ding, and Thomas J. Barton "Two-photon absorption spectra of luminescent conducting polymers measured over wide spectral range", Proc. SPIE 3145, Optical Probes of Conjugated Polymers, (1 December 1997). DOI: https://doi.org/10.1117/12.27927

A theoretical investigation of the low lying electronic structure of poly(p-phenylene vinylene)

The two-state molecular orbital model of the one-dimensional phenyl-based semiconductors is applied to poly(p-phenylene vinylene). The energies of the low-lying excited states are calculated using the density matrix renormalization group method. Calculations of both the exciton size and the charge gap show that there are both Bu and Ag excitonic levels below the band threshold. The energy of the 1Bu exciton extrapolates to 2.60 eV in the limit of infinite polymers, while the energy of the 2Ag exciton extrapolates to 2.94 eV. The calculated binding energy of the 1Bu exciton is 0.9 eV for a 13 phenylene unit chain and 0.6 eV for an infinite polymer. This is expected to decrease due to solvation effects. The lowest triplet state is calculated to be at ca. 1.6 eV, with the triplet-triplet gap being ca. 1.6 eV. A comparison between theory, and two-photon absorption and electroabsorption is made, leading to a consistent picture of the essential states responsible for most of the third-order nonlinear optical properties. An interpretation of the experimental nonlinear optical spectroscopies suggests an energy difference of ca. 0.4 eV between the vertical energy and ca. 0.8 eV between the relaxed energy, of the 1Bu exciton and the band gap, respectively.Comment: LaTeX, 19 pages, 7 eps figures included using epsf. To appear in Physical Review B, 199

Round table on morbilliviruses in marine mammals.

Since 1988 morbilliviruses have been increasingly recognized and held responsible for mass mortality amongst harbour seals (Phoca vitulina) and other seal species. Virus isolations and characterization proved that morbilliviruses from seals in Northwest Europe were genetically distinct from other known members of this group including canine distemper virus (CDV), rinderpest virus, peste des petits ruminants virus and measles virus. An epidemic in Baikal seals in 1987 was apparently caused by a morbillivirus closely related to CDV so that two morbilliviruses have now been identified in two geographically distant seal populations, with only the group of isolates from Northwest Europe forming a new member of the genus morbillivirus: phocid distemper virus (PDV). Because of distemper-like disease, the Baikal seal morbillivirus was tentatively named PDV-2 in spite of its possible identity with CDV. The appearance of morbilliviruses in the Mediterranean Sea causing high mortality amongst dolphins should further increase the research activities on protection strategies for endangered species of marine mammals

Theory of nonlinear optical properties of phenyl-substituted polyacetylenes

In this paper we present a theoretical study of the third-order nonlinear optical properties of poly(diphenyl)polyacetylene (PDPA) pertaining to the third-harmonic-generation (THG) process. We study the aforesaid process in PDPA's using both the independent electron Hueckel model, as well as correlated-electron Pariser-Parr-Pople (P-P-P) model. The P-P-P model based calculations were performed using various configuration interaction (CI) methods such as the the multi-reference-singles-doubles CI (MRSDCI), and the quadruples-CI (QCI) methods, and the both longitudinal and the transverse components of third-order susceptibilities were computed. The Hueckel model calculations were performed on oligo-PDPA's containing up to fifty repeat units, while correlated calculations were performed for oligomers containing up to ten unit cells. At all levels of theory, the material exhibits highly anisotropic nonlinear optical response, in keeping with its structural anisotropy. We argue that the aforesaid anisotropy can be divided over two natural energy scales: (a) the low-energy response is predominantly longitudinal and is qualitatively similar to that of polyenes, while (b) the high-energy response is mainly transverse, and is qualitatively similar to that of trans-stilbene.Comment: 13 pages, 7 figures (included), to appear in Physical Review B (April 15, 2004