Chemical potential oscillations from a single nodal pocket in the underdoped high-Tc superconductor YBa2Cu3O6+x

The mystery of the normal state in the underdoped cuprates has deepened with the use of newer and complementary experimental probes. While photoemission studies have revealed solely `Fermi arcs' centered on nodal points in the Brillouin zone at which holes aggregate upon doping, more recent quantum oscillation experiments have been interpreted in terms of an ambipolar Fermi surface, that includes sections containing electron carriers located at the antinodal region. To address the question of whether an ambipolar Fermi surface truly exists, here we utilize measurements of the second harmonic quantum oscillations, which reveal that the amplitude of these oscillations arises mainly from oscillations in the chemical potential, providing crucial information on the nature of the Fermi surface in underdoped YBa2Cu3O6+x. In particular, the detailed relationship between the second harmonic amplitude and the fundamental amplitude of the quantum oscillations leads us to the conclusion that there exists only a single underlying quasi-two dimensional Fermi surface pocket giving rise to the multiple frequency components observed via the effects of warping, bilayer splitting and magnetic breakdown. A range of studies suggest that the pocket is most likely associated with states near the nodal region of the Brillouin zone of underdoped YBa2Cu3O6+x at high magnetic fields.Comment: 7 pages, 4 figure

Search for gamma-ray emission from magnetars with the Fermi Large Area Telescope

We report on the search for 0.1-10 GeV emission from magnetars in 17 months of Fermi Large Area Telescope (LAT) observations. No significant evidence for gamma-ray emission from any of the currently-known magnetars is found. The most stringent upper limits to date on their persistent emission in the Fermi-LAT energy range are estimated between ~10^{-12}-10^{-10} erg/s/cm2, depending on the source. We also searched for gamma-ray pulsations and possible outbursts, also with no significant detection. The upper limits derived support the presence of a cut-off at an energy below a few MeV in the persistent emission of magnetars. They also show the likely need for a revision of current models of outer gap emission from strongly magnetized pulsars, which, in some realizations, predict detectable GeV emission from magnetars at flux levels exceeding the upper limits identified here using the Fermi-LAT observations.Comment: ApJ Letters in press; Corresponding authors: Caliandro G. A., Hadasch D., Rea N., Burnett

Enhanced progression of human prostate cancer PC3 cells induced by the microenvironment of the seminal vesicle

The objective of this study was to characterise the mechanism mediating the prostate cancer progression induced by the microenvironment of seminal vesicle (SV). The invasive potential of PC3 cells significantly increased after treatment with extract from SV of NOD/SCID mouse. Among several growth factors and cytokines that were present in the SV extract, transforming growth factor-β1 (TGF-β1) significantly enhanced the invasive potential of PC3 cells; however, the additional treatment with neutralising antibody against TGF-β1 suppressed the enhanced invasive potential induced by the SV extract. Changes in the invasive potential in PC3 cells after treatment with the SV extract and/or TGF-β1 were in proportion to those in the production of urokinase-type plasminogen activator (uPA) by PC3 cells. Tumour growth as well as the incidence of lymph node metastasis in NOD/SCID mice after the injection of PC3 cells into the SV were significantly greater than those after the injection into the prostate. These findings suggest that the microenvironment of SV enhances the progression of prostate cancer through a stimulated invasive potential, and that enhanced uPA production in prostate cancer cells induced by TGF-β1 could therefore be one of the most important mechanisms involved in the progression of prostate cancer after SV invasion

Detection of Gamma-Ray Emission from the Starburst Galaxies M82 and NGC 253 with the Large Area Telescope on Fermi

We report the detection of high-energy gamma-ray emission from two starburst galaxies using data obtained with the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. Steady point-like emission above 200 MeV has been detected at significance levels of 6.8 sigma and 4.8 sigma respectively, from sources positionally coincident with locations of the starburst galaxies M82 and NGC 253. The total fluxes of the sources are consistent with gamma-ray emission originating from the interaction of cosmic rays with local interstellar gas and radiation fields and constitute evidence for a link between massive star formation and gamma-ray emission in star-forming galaxies.Comment: Submitted to ApJ Letter

Fermi Gamma-ray Imaging of a Radio Galaxy

The Fermi Gamma-ray Space Telescope has detected the gamma-ray glow emanating from the giant radio lobes of the radio galaxy Centaurus A. The resolved gamma-ray image shows the lobes clearly separated from the central active source. In contrast to all other active galaxies detected so far in high-energy gamma-rays, the lobe flux constitutes a considerable portion (>1/2) of the total source emission. The gamma-ray emission from the lobes is interpreted as inverse Compton scattered relic radiation from the cosmic microwave background (CMB), with additional contribution at higher energies from the infrared-to-optical extragalactic background light (EBL). These measurements provide gamma-ray constraints on the magnetic field and particle energy content in radio galaxy lobes, and a promising method to probe the cosmic relic photon fields.Comment: 27 pages, includes Supplementary Online Material; corresponding authors: C.C. Cheung, Y. Fukazawa, J. Knodlseder, L. Stawar

Fermi Large Area Telescope observations of PSR J1836+5925

The discovery of the gamma-ray pulsar PSR J1836+5925, powering the formerly unidentified EGRET source 3EG J1835+5918, was one of the early accomplishments of the Fermi Large Area Telescope (LAT). Sitting 25 degrees off the Galactic plane, PSR J1836+5925 is a 173 ms pulsar with a characteristic age of 1.8 million years, a spindown luminosity of 1.1$\times10^{34}$ erg s$^{-1}$, and a large off-peak emission component, making it quite unusual among the known gamma-ray pulsar population. We present an analysis of one year of LAT data, including an updated timing solution, detailed spectral results and a long-term light curve showing no indication of variability. No evidence for a surrounding pulsar wind nebula is seen and the spectral characteristics of the off-peak emission indicate it is likely magnetospheric. Analysis of recent XMM observations of the X-ray counterpart yields a detailed characterization of its spectrum, which, like Geminga, is consistent with that of a neutron star showing evidence for both magnetospheric and thermal emission.Comment: Accepted to Astrophysical Journa

Mechanisms of seawater acclimation in a primitive, anadromous fish, the green sturgeon

Relatively little is known about salinity acclimation in the primitive groups of fishes. To test whether physiological preparative changes occur and to investigate the mechanisms of salinity acclimation, anadromous green sturgeon, Acipenser medirostris (Chondrostei) of three different ages (100, 170, and 533 dph) were acclimated for 7 weeks to three different salinities (<3, 10, and 33 ppt). Gill, kidney, pyloric caeca, and spiral intestine tissues were assayed for Na+, K+-ATPase activity; and gills were analyzed for mitochondria-rich cell (MRC) size, abundance, localization and Na+, K+-ATPase content. Kidneys were analyzed for Na+, K+-ATPase localization and the gastro-intestinal tract (GIT) was assessed for changes in ion and base content. Na+, K+-ATPase activities increased in the gills and decreased in the kidneys with increasing salinity. Gill MRCs increased in size and decreased in relative abundance with fish size/age. Gill MRC Na+, K+-ATPase content (e.g., ion-pumping capacity) was proportional to MRC size, indicating greater abilities to regulate ions with size/age. Developmental/ontogenetic changes were seen in the rapid increases in gill MRC size and lamellar length between 100 and 170 dph. Na+, K+-ATPase activities increased fourfold in the pyloric caeca in 33 ppt, presumably due to increased salt and water absorption as indicated by GIT fluids, solids, and ion concentrations. In contrast to teleosts, a greater proportion of base (HCO3− and 2CO32−) was found in intestinal precipitates than fluids. Green sturgeon osmo- and ionoregulate with similar mechanisms to more-derived teleosts, indicating the importance of these mechanisms during the evolution of fishes, although salinity acclimation may be more dependent on body size

A change in the optical polarization associated with a gamma-ray flare in the blazar 3C 279

It is widely accepted that strong and variable radiation detected over all accessible energy bands in a number of active galaxies arises from a relativistic, Doppler-boosted jet pointing close to our line of sight. The size of the emitting zone and the location of this region relative to the central supermassive black hole are, however, poorly known, with estimates ranging from light-hours to a light-year or more. Here we report the coincidence of a gamma-ray flare with a dramatic change of optical polarization angle. This provides evidence for co-spatiality of optical and gamma-ray emission regions and indicates a highly ordered jet magnetic field. The results also require a non-axisymmetric structure of the emission zone, implying a curved trajectory for the emitting material within the jet, with the dissipation region located at a considerable distance from the black hole, at about 10^5 gravitational radii.Comment: Published in Nature issued on 18 February 2010. Corresponding authors: Masaaki Hayashida and Greg Madejsk