Global dispersive solutions for the Gross-Pitaevskii equation in two and three dimensions

We study asymptotic behaviour at time infinity of solutions close to the non-zero constant equilibrium for the Gross-Pitaevskii equation in two and three spatial dimensions. We construct a class of global solutions with prescribed dispersive asymptotic behavior, which is given in terms of the linearized evolution

Investigation of radar backscattering from second-year sea ice

The scattering properties of second-year ice were studied in an experiment at Mould Bay in April 1983. Radar backscattering measurements were made at frequencies of 5.2, 9.6, 13.6, and 16.6 GHz for vertical polarization, horizontal polarization and cross polarizations, with incidence angles ranging from 15 to 70 deg. The results indicate that the second-year ice scattering characteristics were different from first-year ice and also different from multiyear ice. The fading properties of radar signals were studied and compared with experimental data. The influence of snow cover on sea ice can be evaluated by accounting for the increase in the number of independent samples from snow volume with respect to that for bare ice surface. A technique for calculating the snow depth was established by this principle and a reasonable agreement has been observed. It appears that this is a usable way to measure depth in snow or other snow-like media using radar

Enzyme-based DNA extraction from zoospores of ruminal fungi

We report here a rapid, efficient and simple method for the extraction of high molecular weight DNA from zoospores of Neocallimastix frontalis EB188. This anaerobic fungus, isolated from bovine digesta, effectively degrades plant fiber in vitro (Barichievich et al. 1990. Appl. Env. Micro. 56:43-48). Our interest in ruminal fungi stems from their ability to degrade wood materials (Joblin et al. 1989. FEMS Micro. Lett. 56:119-122) and their potential use in biomass saccharification. Zoospore DNA synthesis is of particular interest to our laboratory. It is these motile zoospores which colonize and degrade plant materials (Mountfort 1987. FEMS Micro. Rev. 46:501-508). To detail fully this metabolic event, it will be necessary to extract nucleic acids from zoospores. Such procedures have not been reported in the literature. Using acetone drying and enzymatic removal of cell walls, we have isolated high molecular weight DNA from very small amounts of culture. The procedure takes less than one hour and DNA yields are high. The DNA is readily cut with restriction endonucleases and religated efficiently but is otherwise stable. Electrophoretic analysis of the DNA confirmed the presence of repetitive sequences. This procedure will aid the study of DNA replication, DNA repair and DNA RFLP analysis of various strains using small (\u3c1 ml) cultures

Revealing common artifacts due to ferromagnetic inclusions in highly-oriented pyrolytic graphite

We report on an extensive investigation to figure out the origin of room-temperature ferromagnetism that is commonly observed by SQUID magnetometry in highly-oriented pyrolytic graphite (HOPG). Electron backscattering and X-ray microanalysis revealed the presence of micron-size magnetic clusters (predominantly Fe) that are rare and would be difficult to detect without careful search in a scanning electron microscope in the backscattering mode. The clusters pin to crystal boundaries and their quantities match the amplitude of typical ferromagnetic signals. No ferromagnetic response is detected in samples where we could not find such magnetic inclusions. Our experiments show that the frequently reported ferromagnetism in pristine HOPG is most likely to originate from contamination with Fe-rich inclusions introduced presumably during crystal growth.Comment: 8 pages, 7 figure

Stable directions for small nonlinear Dirac standing waves

We prove that for a Dirac operator with no resonance at thresholds nor eigenvalue at thresholds the propagator satisfies propagation and dispersive estimates. When this linear operator has only two simple eigenvalues close enough, we study an associated class of nonlinear Dirac equations which have stationary solutions. As an application of our decay estimates, we show that these solutions have stable directions which are tangent to the subspaces associated with the continuous spectrum of the Dirac operator. This result is the analogue, in the Dirac case, of a theorem by Tsai and Yau about the Schr\"{o}dinger equation. To our knowledge, the present work is the first mathematical study of the stability problem for a nonlinear Dirac equation.Comment: 62 page

Magnetic catalysis in QED_3 at finite temperature: beyond the constant mass approximation

We solve the Schwinger-Dyson equations for (2+1)-dimensional QED in the presence of a strong external magnetic field. The calculation is done at finite temperature and the fermionic self energy is not supposed to be momentum-independent, which is the usual simplification in such calculations. The phase diagram in the temperature-magnetic field plane is determined. For intermediate magnetic fields the critical temperature turns out to have a square root dependence on the magnetic field, but for very strong magnetic fields it approaches a B-independent limiting value.Comment: 21 pages, 10 figures, published versio