A Green's function approach to transmission of massless Dirac fermions in graphene through an array of random scatterers

We consider the transmission of massless Dirac fermions through an array of short range scatterers which are modeled as randomly positioned $\delta$- function like potentials along the x-axis. We particularly discuss the interplay between disorder-induced localization that is the hallmark of a non-relativistic system and two important properties of such massless Dirac fermions, namely, complete transmission at normal incidence and periodic dependence of transmission coefficient on the strength of the barrier that leads to a periodic resonant transmission. This leads to two different types of conductance behavior as a function of the system size at the resonant and the off-resonance strengths of the delta function potential. We explain this behavior of the conductance in terms of the transmission through a pair of such barriers using a Green's function based approach. The method helps to understand such disordered transport in terms of well known optical phenomena such as Fabry Perot resonances.Comment: 22 double spaced single column pages. 15 .eps figure

Effect of temperature on behavior, glycogen content, and mortality in Limnoperna fortunei (Dunker, 1857) (Bivalvia: Mytilidae)

Limnoperna fortunei (Dunker 1857) is a freshwater mussel with physiological tolerance to different environmental conditions, which may explain its success as an invasive species. The role of abiotic factors in its establishment, abundance and projections of risk of further spread into several areas has been studied. These mussels may respond to multiple environmental stressors, such as temperature, through physiological mechanisms, behavioral responses, mortality or some combination of these. The aim of this study was to investigate the behavioral responses (valve closing), glycogen concentrations and mortality of L. fortunei under four different temperatures (5°C, 10°C, 20°C and 30° C) during a chronic test (30 days). Two-way analysis of variance (ANOVA) was used to compare glycogen concentrations across days of the experiment and at the different temperatures. Differences in valve-closing behavior and mortality among temperatures were tested using repeated-measures ANOVA. We observed that most of the mussels maintained at 5°C closed their valves (74.7 ± 15.3%), indicating that they remain inactive at low temperatures. The glycogen levels significantly differed among the temperatures tested. These differences occurred mainly due to the high glycogen values observed in mussels exposed to 10°C. Stability in glycogen concentrations was observed within each particular temperature. The cumulative mortality was higher at extreme temperatures (5°C and 30°C). The ideal temperature for laboratory maintenance and tests is approximately 20°C. Our data also show that L. fortunei can survive and maintain their energy reserves (glycogen) for several days at 5°C, an important feature related to its invasion success

The energy spectrum of cosmic rays beyond the turn-down around 10^17 eV as measured with the surface detector of the Pierre Auger Observatory

We present a measurement of the cosmic-ray spectrum above 100 PeV using the part of the surface detector of the Pierre Auger Observatory that has a spacing of 750 m. An inflection of the spectrum is observed, confirming the presence of the so-called second-knee feature. The spectrum is then combined with that of the 1500 m array to produce a single measurement of the flux, linking this spectral feature with the three additional breaks at the highest energies. The combined spectrum, with an energy scale set calorimetrically via fluorescence telescopes and using a single detector type, results in the most statistically and systematically precise measurement of spectral breaks yet obtained. These measurements are critical for furthering our understanding of the highest energy cosmic rays