Period doubling in glow discharges: local versus global differential conductivity

Short planar glow discharges coupled to a resistive layer exhibit a wealth of spontaneous spatio-temporal patterns. Several authors have suggested effective reaction-diffusion-models to explore similarities with other pattern forming systems. To test these effective models, we here investigate the temporal oscillations of a glow discharge layer coupled to a linear resistor. We find an unexpected cascade of period doubling events. This shows that the inner structure of the discharge is more complex than can be described by a reaction-diffusion-model with negative differential conductivity.Comment: 4 pages, 4 figures, submitted to PR

Evolutionary Genetics of an S-Like Polymorphism in Papaveraceae with Putative Function in Self-Incompatibility

Papaver rhoeas possesses a gametophytic self-incompatibility (SI) system not homologous to any other SI mechanism characterized at the molecular level. Four previously published full length stigmatic S-alleles from the genus Papaver exhibited remarkable sequence divergence, but these studies failed to amplify additional S-alleles despite crossing evidence for more than 60 S-alleles in Papaver rhoeas alone.Using RT-PCR we identified 87 unique putative stigmatic S-allele sequences from the Papaveraceae Argemone munita, Papaver mcconnellii, P. nudicuale, Platystemon californicus and Romneya coulteri. Hand pollinations among two full-sib families of both A. munita and P. californicus indicate a strong correlation between the putative S-genotype and observed incompatibility phenotype. However, we also found more than two S-like sequences in some individuals of A. munita and P. californicus, with two products co-segregating in both full-sib families of P. californicus. Pairwise sequence divergence estimates within and among taxa show Papaver stigmatic S-alleles to be the most variable with lower divergence among putative S-alleles from other Papaveraceae. Genealogical analysis indicates little shared ancestral polymorphism among S-like sequences from different genera. Lack of shared ancestral polymorphism could be due to long divergence times among genera studied, reduced levels of balancing selection if some or all S-like sequences do not function in incompatibility, population bottlenecks, or different levels of recombination among taxa. Preliminary estimates of positive selection find many sites under selective constraint with a few undergoing positive selection, suggesting that self-recognition may depend on amino acid substitutions at only a few sites.Because of the strong correlation between genotype and SI phenotype, sequences reported here represent either functional stylar S-alleles, tightly linked paralogs of the S-locus or a combination of both. The considerable complexity revealed in this study shows we have much to learn about the evolutionary dynamics of self-incompatibility systems

Spatiotemporal patterns in a dc semiconductor-gas-discharge system: Stability analysis and full numerical solutions

A system very similar to a dielectric barrier discharge, but with a simple stationary dc voltage, can be realized by sandwiching a gas discharge and a high-ohmic semiconductor layer between two planar electrodes. In experiments this system forms spatiotemporal and temporal patterns spontaneously, quite similarly to, e.g., Rayleigh-Benard convection. Here it is modeled with a simple discharge model with space charge effects, and the semiconductor is approximated as a linear conductor. In previous work, this model has reproduced the phase transition from homogeneous stationary to homogeneous oscillating states semiquantitatively. In the present work, the formation of spatial patterns is investigated through linear stability analysis and through numerical simulations of the initial value problem; the methods agree well. They show the onset of spatiotemporal patterns for high semiconductor resistance. The parameter dependence of temporal or spatiotemporal pattern formation is discussed in detail

Application of a linear finite-frequency theory to time-lapse crosswell tomography in ultrasonic and numerical experiments

Time-lapse seismic monitoring is the geophysical discipline whereby multiple data sets recorded at the same location but at different times are used to locate and quantify temporal changes in the elastic parameters of the subsurface. We validate a time-lapse monitoring method by crosswell tomography using two types of wavefield-modeling experiments: (1) a 3D real ultrasonic waveform experiment and (2) 2D synthetic finite-difference wavefield simulations. For both wavefield experiments, a time-lapse structure simulating a fluid sweep in a reservoir layer is applied. The time-lapse tomographic monitoring approach is based on the standard ray theory and a finite-frequency wavefield theory, where the latter takes into account the finite-frequency properties of recorded wavefields. The inverted time-lapse models compiled with either the ray theory or the finite-frequency wavefield theory locate and correctly quantify the flooding zone in the simulated fluid sweep model. Both wavefield theories provide an adequate result because the flooding zone is comparable in size to the Fresnel volume.GeotechnologyCivil Engineering and Geoscience