Faraday Conversion in Turbulent Blazar Jets

Low ($\lesssim 1\%$) levels of circular polarization (CP) detected at radio frequencies in the relativistic jets of some blazars can provide insight into the underlying nature of the jet plasma. CP can be produced through linear birefringence, in which initially linearly polarized emission produced in one region of the jet is altered by Faraday rotation as it propagates through other regions of the jet with varying magnetic field orientation. Marscher has begun a study of jets with such magnetic geometries using the Turbulent Extreme Multi-Zone (TEMZ) model, in which turbulent plasma crossing a standing shock in the jet is represented by a collection of thousands of individual plasma cells, each with distinct magnetic field orientations. Here we develop a radiative transfer scheme that allows the numerical TEMZ code to produce simulated images of the time-dependent linearly and circularly polarized intensity at different radio frequencies. In this initial study, we produce synthetic polarized emission maps that highlight the linear and circular polarization expected within the model.Comment: 17 pages, 13 figures, accepted for publication in Ap

"Orphan" γ\gamma-ray Flares and Stationary Sheaths of Blazar Jets

Blazars exhibit flares across the entire electromagnetic spectrum. Many $\gamma$-ray flares are highly correlated with flares detected at longer wavelengths; however, a small subset appears to occur in isolation, with little or no correlated variability at longer wavelengths. These "orphan" $\gamma$-ray flares challenge current models of blazar variability, most of which are unable to reproduce this type of behavior. Macdonald et al. have developed the Ring of Fire model to explain the origin of orphan $\gamma$-ray flares from within blazar jets. In this model, electrons contained within a blob of plasma moving relativistically along the spine of the jet inverse-Compton scatter synchrotron photons emanating off of a ring of shocked sheath plasma that enshrouds the jet spine. As the blob propagates through the ring, the scattering of the ring photons by the blob electrons creates an orphan $\gamma$-ray flare. This model was successfully applied to modeling a prominent orphan $\gamma$-ray flare observed in the blazar PKS 1510$-$089. To further support the plausibility of this model, Macdonald et al. presented a stacked radio map of PKS 1510$-$089 containing the polarimetric signature of a sheath of plasma surrounding the spine of the jet. In this paper, we extend our modeling and stacking techniques to a larger sample of blazars: 3C 273, 4C 71$.$01, 3C 279, 1055$+$018, CTA 102, and 3C 345, the majority of which have exhibited orphan $\gamma$-ray flares. We find that the model can successfully reproduce these flares, while our stacked maps reveal the existence of jet sheaths within these blazars.Comment: 19 pages, 27 figures, accepted for publication in ApJ. arXiv admin note: text overlap with arXiv:1505.0123

Inter-band magnetoplasmons in mono- and bi-layer graphene

Collective excitations spectrum of Dirac electrons in mono and bilayer graphene in the presence of a uniform magnetic field is investigated. Analytical results for inter-Landau band plasmon spectrum within the self-consistent-field approach are obtained. SdH type oscillations that are a monotonic function of the magnetic field are observed in the plasmon spectrum of both mono- and bi-layer graphene systems. The results presented are also compared with those obtained in conventional 2DEG. The chiral nature of the quasiparticles in mono and bilayer graphene system results in the observation of $\pi$ and $2\pi$ Berry's phase in the SdH- type oscillations in the plasmon spectrum.Comment: 9 pages, 2 figure

Differences in radionuclide and heavy metal concentrations found in the kidneys of barren-ground caribou from the western Northwest Territories 1994/95 to 2000/01

Aluminum, nickel, cadmium, mercury, and lead concentrations were measured in the kidney tissue of known aged barren-ground caribou wintering in the western Northwest Territories harvested during winter 1994/1995 and during winters 2000/2001 and 2001/2002. 40K, 137Cs, and 210Pb concentrations were measured in the kidney tissue of known aged barren-ground caribou during winter 2000/2001 and compared to concentrations in winter 1993/1994 reported in Macdonald et al. (1996). Renal concentrations of aluminum were higher (P<0.001)in winter 2000/2001 than winter 1994/1995. Contrastingly renal concentrations of mercury were lower (P<0.001) in winter 2000/2001 than 1994/1995. 137Cs (P<0.02), 40K (P=0.01), 210Pb (P<0.01) had lower renal concentrations in winter 2000/2001 than 1993/1994. Renal concentrations of cadmium (P<0.001) and 137Cs (P<0.04) had a positive relationship with caribou age. We also document renal concentrations of arsenic, copper, selenium, zinc, 232Th, 226Ra, and 235U in the kidneys of caribou harvested in winters 2000/2001 and 2001/2002. Renal zinc concentrations were positively correlated with the age of caribou

Permanent annihilation of thermally activated defects which limit the lifetime of float-zone silicon

We have observed very large changes in the minority carrier lifetime when high purity float-zone (FZ) silicon wafers are subject to heat-treatments in the range of 200– 1100˚C. Recombination centres were found to become activated upon annealing at 450–700˚C, causing significant reductions in the bulk lifetime, detrimental for high efficiency solar cells and stable high powered devices. Photoluminescence imaging of wafers annealed at 500˚C revealed concentric circular patterns, with lower lifetimes occurring in the centre, and higher lifetimes around the periphery. Deep level transient spectroscopy measurements on samples extracted from the centre of an n-type FZ silicon wafer annealed at 500˚C revealed a large variety of defects with activation energies ranging between 0.16– 0.36eV. Our measurements indicate that vacancy related defects are causing the severe degradation in lifetime when FZ wafers are annealed at 450–700˚C. Upon annealing FZ silicon at temperatures >800°C, the lifetime is completely recovered, whereby the defect-rich regions vanish and do not reappear (permanently annihilated). Our results indicate that, in general, as-grown FZ silicon should not be assumed to be defect lean, nor can it be assumed that the bulk lifetime will remain stable during thermal processing, unless annealed at temperatures >1000°C

Dynamic changes in lung microRNA profiles during the development of pulmonary hypertension due to chronic hypoxia and monocrotaline

<b>Objective</b>: MicroRNAs (miRNAs) are small noncoding RNAs that have the capacity to control protein production through binding "seed" sequences within a target mRNA. Each miRNA is capable of potentially controlling hundreds of genes. The regulation of miRNAs in the lung during the development of pulmonary arterial hypertension (PAH) is unknown.<p></p> <b>Methods and Results</b>: We screened lung miRNA profiles in a longitudinal and crossover design during the development of PAH caused by chronic hypoxia or monocrotaline in rats. We identified reduced expression of Dicer, involved in miRNA processing, during the onset of PAH after hypoxia. MiR-22, miR-30, and let-7f were downregulated, whereas miR-322 and miR-451 were upregulated significantly during the development of PAH in both models. Differences were observed between monocrotaline and chronic hypoxia. For example, miR-21 and let-7a were significantly reduced only in monocrotaline-treated rats. MiRNAs that were significantly regulated were validated by quantitative polymerase chain reaction. By using in vitro studies, we demonstrated that hypoxia and growth factors implicated in PAH induced similar changes in miRNA expression. Furthermore, we confirmed miR-21 downregulation in human lung tissue and serum from patients with idiopathic PAH.<p></p> <b>Conclusion</b>: Defined miRNAs are regulated during the development of PAH in rats. Therefore, miRNAs may contribute to the pathogenesis of PAH and represent a novel opportunity for therapeutic intervention.<p></p&gt