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

Trend analysis using non-stationary time series clustering based on the finite element method

In order to analyze low-frequency variability of climate, it is useful to model the climatic time series with multiple linear trends and locate the times of significant changes. In this paper, we have used non-stationary time series clustering to find change points in the trends. Clustering in a multi-dimensional non-stationary time series is challenging, since the problem is mathematically ill-posed. Clustering based on the finite element method (FEM) is one of the methods that can analyze multidimensional time series. One important attribute of this method is that it is not dependent on any statistical assumption and does not need local stationarity in the time series. In this paper, it is shown how the FEM-clustering method can be used to locate change points in the trend of temperature time series from in situ observations. This method is applied to the temperature time series of North Carolina (NC) and the results represent region-specific climate variability despite higher frequency harmonics in climatic time series. Next, we investigated the relationship between the climatic indices with the clusters/trends detected based on this clustering method. It appears that the natural variability of climate change in NC during 1950–2009 can be explained mostly by AMO and solar activity

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

Do contaminants originating from state-of-the-art treated wastewater impact the ecological quality of surface waters?

Since the 1980s, advances in wastewater treatment technology have led to considerably improved surface water quality in the urban areas of many high income countries. However, trace concentrations of organic wastewater-associated contaminants may still pose a key environmental hazard impairing the ecological quality of surface waters. To identify key impact factors, we analyzed the effects of a wide range of anthropogenic and environmental variables on the aquatic macroinvertebrate community. We assessed ecological water quality at 26 sampling sites in four urban German lowland river systems with a 0–100% load of state-of-the-art biological activated sludge treated wastewater. The chemical analysis suite comprised 12 organic contaminants (five phosphor organic flame retardants, two musk fragrances, bisphenol A, nonylphenol, octylphenol, diethyltoluamide, terbutryn), 16 polycyclic aromatic hydrocarbons, and 12 heavy metals. Non-metric multidimensional scaling identified organic contaminants that are mainly wastewater-associated (i.e., phosphor organic flame retardants, musk fragrances, and diethyltoluamide) as a major impact variable on macroinvertebrate species composition. The structural degradation of streams was also identified as a significant factor. Multiple linear regression models revealed a significant impact of organic contaminants on invertebrate populations, in particular on Ephemeroptera, Plecoptera, and Trichoptera species. Spearman rank correlation analyses confirmed wastewater-associated organic contaminants as the most significant variable negatively impacting the biodiversity of sensitive macroinvertebrate species. In addition to increased aquatic pollution with organic contaminants, a greater wastewater fraction was accompanied by a slight decrease in oxygen concentration and an increase in salinity. This study highlights the importance of reducing the wastewater-associated impact on surface waters. For aquatic ecosystems in urban areas this would lead to: (i) improvement of the ecological integrity, (ii) reduction of biodiversity loss, and (iii) faster achievement of objectives of legislative requirements, e.g., the European Water Framework Directive

Combined and single effects of pesticide carbaryl and toxic Microcystis aeruginosa on the life history of Daphnia pulicaria

The combined influence of a pesticide (carbaryl) and a cyanotoxin (microcystin LR) on the life history of Daphnia pulicaria was investigated. At the beginning of the experiments animals were pulse exposed to carbaryl for 24 h and microcystins were delivered bound in Microcystis’ cells at different, sub-lethal concentrations (chronic exposure). In order to determine the actual carbaryl concentrations in the water LC–MS/MS was used. For analyses of the cyanotoxin concentration in Daphnia’s body enzyme-linked immunosorbent assay (ELISA) was used. Individual daphnids were cultured in a flow-through system under constant light (16 h of light: 8 h of dark), temperature (20°C), and food conditions (Scenedesmus obliquus, 1 mg of C l−1). The results showed that in the treatments with carbaryl egg numbers per female did not differ significantly from controls, but the mortality of newborns increased significantly. Increasing microcystin concentrations significantly delayed maturation, reduced size at first reproduction, number of eggs, and newborns. The interaction between carbaryl and Microcystis was highly significant. Animals matured later and at a smaller size than in controls. The number of eggs per female was reduced as well. Moreover, combined stressors caused frequent premature delivery of offspring with body deformations such as dented carapax or an undeveloped heart. This effect is concluded to be synergistic and could not be predicted from the effects of the single stressors.

Model studies of the tropical 30 to 60 day oscillation

The tropical 30-60 day oscillation, also referred to as the intraseasonal oscillation (IO) or Madden-Julian oscillation is an important phenomenon in the tropical atmosphere on the intraseasonal timescale. The dominant characteristic of the IO is the eastward propagation of convection cells that organize themselves to super cloud clusters over the Indian Ocean and the West Pacific. The correct simulation of the initiation and propagation of the IO in General Circulation Models (GCMs) is important for the representation of convective clouds and the resulting radiation budget and precipitation in the tropical eastern hemisphere. The IO is a possible trigger of the Asian summer monsoon (Lau et al., 1998) and the Australian monsoon (Hendon and Liebmann, 1990) and affects the position of subtropical jets (Knutson and Weickmann, 1987). The present study discusses the representation of the IO in observations, reanalyses data and GCM simulations. The Principal Oscillation Pattern analysis (von Storch, 1995; Hasselmann, 1988) is used to investigate IO activity. Case studies are performed to gain a detailed insight into the structure of the IO. The simulations are performed with (1) the fourth version of the European Centre Hamburg Atmospheric Model (ECHAM4; Roeckner et al., 1996) GCM; (2) the ECHAM4 GCM coupled to the third version of the ocean isopycnal (OPYC3) GCM to clarify possible air-sea interactions and connections of the IO and the El Niño/Southern Oscillation (ENSO) cycle; (3) ECHAM4 with increased vertical resolution and by this improved representation of the tropospheric stratification. To artificially force cooler (warmer) levels in the mid-troposphere and by this a changed stability, the melting rate for convective precipitation is doubled (halved) in two sensitivity studies. Additionally an experiment with suppressed snow melt for all precipitation is performed. (4) The horizontal resolution is increased to investigate the importance of a reasonable land-sea distribution over the maritime continent. (5) To distinguish this effect from general dynamical changes due to the changed resolution, the effects of the land-sea distribution are additionally studied in an experiment with land points associated with the maritime continent replaced by sea points. (6) The ECHAM4 GCM is forced by a T42 version of the Optimum Interpolated Sea Surface Temperature (OISST) dataset (Reynolds and Smith, 1994) to study the influence of the SST as a boundary condition. The main results are as follows: (1) The ECHAM4 T42 standard version simulates a too fast eastward propagation and an eastward shift of the main IO activity, as is common to many atmosphere GCMs (Slingo et al., 1996). (2) The coupled version reveals no improvements, although it is shown that the IO influences the ENSO cycle and ENSO influences the interannual variability of the IO. (3) The increase in vertical resolution slightly improves the simulation of the vertical moisture profile, and thus slightly slows down the propagation speed of the IO. This result is not confirmed by the studies with artificially changed stability in the mid-troposphere. (4) Increasing the horizontal resolution from T42 to T106 results in a more precise representation of convection over the maritime continent. A consequence is a reduction of the erroneous eastward shift of the simulated IO activity, although the phase speed of the IO is increased. (5) These results are also obtained by replacing the maritime continent with sea points. (6) ECHAM4 forced by a changed SST dataset leads to the strongest improvements, since convection driving the IO is highly sensitive to surface temperature with lower level convection leading to a slower IO due to an increased influence of surface friction. ECHAM4 forced by the changed SST, produces a reasonable IO with a mean period of 48 days and a main IO activity near 140E, as in the reanalysis. This illustrates the strong influence of the prescribed SST on the simulation of the I

Electron correlation effects in electron-hole recombination in organic light-emitting diodes

We develop a general theory of electron--hole recombination in organic light emitting diodes that leads to formation of emissive singlet excitons and nonemissive triplet excitons. We briefly review other existing theories and show how our approach is substantively different from these theories. Using an exact time-dependent approach to the interchain/intermolecular charge-transfer within a long-range interacting model we find that, (i) the relative yield of the singlet exciton in polymers is considerably larger than the 25% predicted from statistical considerations, (ii) the singlet exciton yield increases with chain length in oligomers, and, (iii) in small molecules containing nitrogen heteroatoms, the relative yield of the singlet exciton is considerably smaller and may be even close to 25%. The above results are independent of whether or not the bond-charge repulsion, X_perp, is included in the interchain part of the Hamiltonian for the two-chain system. The larger (smaller) yield of the singlet (triplet) exciton in carbon-based long-chain polymers is a consequence of both its ionic (covalent) nature and smaller (larger) binding energy. In nitrogen containing monomers, wavefunctions are closer to the noninteracting limit, and this decreases (increases) the relative yield of the singlet (triplet) exciton. Our results are in qualitative agreement with electroluminescence experiments involving both molecular and polymeric light emitters. The time-dependent approach developed here for describing intermolecular charge-transfer processes is completely general and may be applied to many other such processes.Comment: 19 pages, 11 figure

A smooth introduction to the wavefront set

The wavefront set provides a precise description of the singularities of a distribution. Because of its ability to control the product of distributions, the wavefront set was a key element of recent progress in renormalized quantum field theory in curved spacetime, quantum gravity, the discussion of time machines or quantum energy inequalitites. However, the wavefront set is a somewhat subtle concept whose standard definition is not easy to grasp. This paper is a step by step introduction to the wavefront set, with examples and motivation. Many different definitions and new interpretations of the wavefront set are presented. Some of them involve a Radon transform.Comment: 29 pages, 7 figure