ABSTRACT
We report the detection of pulsed gamma rays from the Crab pulsar at energies above 100 giga-electron volts (GeV) with the Very Energetic Radiation Imaging Telescope Array System (VERITAS) array of atmospheric Cherenkov telescopes. The detection cannot be explained on the basis of current pulsar models. The photon spectrum of pulsed emission between 100 mega-electron volts and 400 GeV is described by a broken power law that is statistically preferred over a power law with an exponential cutoff. It is unlikely that the observation can be explained by invoking curvature radiation as the origin of the observed gamma rays above 100 GeV. Our findings require that these gamma rays be produced more than 10 stellar radii from the neutron star.
ABSTRACT
The accretion of matter onto a massive black hole is believed to feed the relativistic plasma jets found in many active galactic nuclei (AGN). Although some AGN accelerate particles to energies exceeding 10(12) electron volts and are bright sources of very-high-energy (VHE) gamma-ray emission, it is not yet known where the VHE emission originates. Here we report on radio and VHE observations of the radio galaxy Messier 87, revealing a period of extremely strong VHE gamma-ray flares accompanied by a strong increase of the radio flux from its nucleus. These results imply that charged particles are accelerated to very high energies in the immediate vicinity of the black hole.
ABSTRACT
The vesicular-arbuscular (VA) mycorrhizal status of three alfalfa (Medicago sativa L.) nodulation genotypes (nod+ fix+ , nod+ fix- and nod- fix- ) was investigated using pot cultures of three fungal species from two genera (Glomus monosporum Gerd. & Trappe, Glomus fasciculatum (Thaxter) Gerd. & Trappe emend. Walker & Koske and Gigaspora margarita Becker & Hall). Roots of the nod+ fix+ genotype developed complete VA mycorrhizas with each fungus. Roots of the nod+ fix- and nod- fix- genotypes did not develop normal VA mycorrhizal symbioses. Roots of the nod- fix- genotype had significantly more appressoria than roots of the other genotypes. Aborted appressoria were unable to penetrate the cortical cells of roots of nod+ fix- and nod- fix- genotypes. Measurement of appressorium length, width and approximate contact area revealed significant differences in the size of appressoria produced by each VA mycorrhizal fungus on each alfalfa nodulation genotype. Histological studies of nod+ fix+ and nod- fix- genotypes colonized by Glomus versiforme (Karsten) Berch showed the presence of electron-dense material in aborted appressoria on roots of the nod- fix- genotype but not in appressoria on roots of the nod+ fix+ genotype.
ABSTRACT
Seedlings of a non-nodulating alfalfa (Medicago sativa L.) genotype (nod- fix- ) and an ineffectively nodulating alfalfa genotype (nod+ fix- ) exhibited resistance to vesiscular-arbuscular mycorrhizal (VA mycorrhizal) colonization, when grown in pot cultures inoculated with either Glomus versiforme (Daniels and Trappe) Berth or Glomus intraradices Schenck and Smith. Appressoria, showing considerable variation in size and shape, developed on the root surface, but failed to form any internal structures such as arbuscules and vesicies. Wild-type (nod+ fix- ) alfalfa seedlings developed normal colonization. This phenomenon will be extremely useful in studying the processes of recognition and compatibility between plant species and VA mycorrhizal fungal species.
ABSTRACT
The usefulness of preparatory vulval cleansing before urine specimen collection was evaluated in women aged 16 to 75 years attending a general practice. A total of 316 specimens were examined, 158 from women with symptoms of cystitis and 158 from controls. No significant differences were found in the numbers of contaminated or unreliable results between the specimens collected with and those collected without preparatory cleansing.