The return of the Andromedids meteor shower

The Andromedid meteor shower underwent spectacular outbursts in 1872 and 1885, producing thousands of visual meteors per hour and described as `stars fell like rain' in Chinese records of the time. The shower originates from comet 3D/Biela whose disintegration in the mid-1800's is linked to the outbursts, but the shower has been weak or absent since the late 19th Century. This shower returned in December 2011 with a zenithal hourly rate of approximately 50, the strongest return in over a hundred years. Some 122 probable Andromedid orbits were detected by the Canadian Meteor Orbit Radar. The shower outburst occurred during 2011 Dec 3-5. The radiant at RA +$18\degree$ and Dec +$56\degree$ is typical of the `classical' Andromedids of the early 1800's, whose radiant was actually in Cassiopeia. The orbital elements indicate that the material involved was released before 3D/Biela's breakup prior to 1846. The observed shower in 2011 had a slow geocentric speed (16 km s$^{-1}$) and was comprised of small particles: the mean measured mass from the radar is $\sim5 \times 10^{-7}$ kg corresponding to radii of 0.5 mm at a bulk density of 1000 kg/m$^3$. Numerical simulations of the parent comet indicate that the meteoroids of the 2011 return of the Andromedids shower were primarily ejected during 3D/Biela's 1649 perihelion passage. The orbital characteristics, radiant, timing as well as the absence of large particles in the streamlet are all consistent with simulations. Predictions are made regarding other appearances of the shower in the years 2000-2047 based on our numerical model. We note that the details of the 2011 return can, in principle, be used to better constrain the orbit of 3D/Biela prior to the comets first recorded return in 1772.Comment: submitted to the Astronomical Journal Sep 22 201

Probing Magnetic Configurations in Co/Cu Multilayered Nanowires

Magnetic configurations in heterostructures are often difficult to probe when the magnetic entities are buried inside. In this study we have captured magnetic and magnetoresistance "fingerprints" of Co nanodiscs embedded in Co/Cu multilayered nanowires using a first-order reversal curve method. In 200nm diameter nanowires, the magnetic configurations can be tuned by adjusting the Co nanodisc aspect ratio. Nanowires with the thinnest Co nanodiscs exhibit single domain behavior, while those with thicker Co reverse via vortex states. A superposition of giant and anisotropic magnetoresistance is observed, which corresponds to the different magnetic configurations of the Co nanodiscs.Comment: 14 pages, 3 figure

Attenuated and Nonproductive Viral Transcription in the Lymphatic Tissue of HIV-1-Infected Patients Receiving Potent Antiretroviral Therapy

Human immunodeficiency virus type 1 (HIV-1) RNA that persists in the lymphoid tissue of patients despite treatment with highly active antiretroviral therapy (HAART) may represent extracellular virions or intracellular RNAs residing within HIV-infected cells. To further characterize residual viral transcription, tonsil biopsy specimens from patients receiving long-term HAART, untreated patients, and patients undergoing 2 weeks of structured treatment interruption were analyzed by polymerase chain reaction quantification of virion-encapsidated RNA, intracellular unspliced HIV RNA (HIV UsRNA), multiply spliced HIV RNA encoding tat and rev (HIV MsRNA), and HIV DNA. Tonsil biopsy specimens from viremic patients harbored high amounts of virions, which primarily stemmed from local production, as indicated by a strong correlation of extracellular tonsillar RNA with intracellular HIV-1 nucleic acid levels but not with plasma viremia, and as shown by phylogenetic analysis of clonal env sequences from lymphoid tissue and plasma. In patients receiving HAART, intracellular HIV UsRNA persisted at significantly decreased levels, whereas HIV MsRNA and lymphoid virion levels were depleted. Thus, residual lymphoid HIV-1 RNA in patients receiving HAART indicates attenuated viral transcription in HIV-1-infected cells that lack virion productio

Optical to near-infrared transmission spectrum of the warm sub-Saturn HAT-P-12b

We present the transmission spectrum of HAT-P-12b through a joint analysis of data obtained from the Hubble Space Telescope Space Telescope Imaging Spectrograph (STIS) and Wide Field Camera 3 (WFC3) and Spitzer, covering the wavelength range 0.3-5.0 $\mu$m. We detect a muted water vapor absorption feature at 1.4 $\mu$m attenuated by clouds, as well as a Rayleigh scattering slope in the optical indicative of small particles. We interpret the transmission spectrum using both the state-of-the-art atmospheric retrieval code SCARLET and the aerosol microphysics model CARMA. These models indicate that the atmosphere of HAT-P-12b is consistent with a broad range of metallicities between several tens to a few hundred times solar, a roughly solar C/O ratio, and moderately efficient vertical mixing. Cloud models that include condensate clouds do not readily generate the sub-micron particles necessary to reproduce the observed Rayleigh scattering slope, while models that incorporate photochemical hazes composed of soot or tholins are able to match the full transmission spectrum. From a complementary analysis of secondary eclipses by Spitzer, we obtain measured depths of $0.042\%\pm0.013\%$ and $0.045\%\pm0.018\%$ at 3.6 and 4.5 $\mu$m, respectively, which are consistent with a blackbody temperature of $890^{+60}_{-70}$ K and indicate efficient day-night heat recirculation. HAT-P-12b joins the growing number of well-characterized warm planets that underscore the importance of clouds and hazes in our understanding of exoplanet atmospheres.Comment: 25 pages, 19 figures, accepted for publication in AJ, updated with proof correction