Robert Wilson

Escape of Mycobacterium tuberculosis from oxidative killing by neutrophils.

Neutrophils enter sites of infection, where they can eliminate pathogenic bacteria in an oxidative manner. Despite their predominance in active tuberculosis lesions, the function of neutrophils in this important human infection is still highly controversial. We observed that virulent Mycobacterium tuberculosis survived inside human neutrophils despite prompt activation of these defence cells microbicidal effectors. Survival of M.u2003tuberculosis was accompanied by necrotic cell death of infected neutrophils. Necrotic cell death entirely depended on radical oxygen species production since chronic granulomatous disease neutrophils were protected from M.u2003tuberculosis‐triggered necrosis. More, importantly, the M.u2003 tuberculosisΔRD1 mutant failed to induce neutrophil necrosis rendering this strain susceptible to radical oxygen species‐mediated killing. We conclude that this virulence function is instrumental for M.u2003tuberculosis to escape killing by neutrophils and contributes to pathogenesis in tuberculosis.

The Gamma-Ray Giant Flare from SGR 1806?20: Evidence of Crustal Cracking via Initial Timescales

Soft γ-ray repeaters (SGRs) are neutron stars that emit short (1 s) and energetic (1042 ergs s-1) bursts of soft γ-rays. Only four of them are currently known. Occasionally, SGRs have been observed to emit much more energetic giant flares (~1044-1045 ergs s-1). These are exceptional and rare events. We report here on serendipitous observations of the intense γ-ray flare from SGR 1806-20 that occurred on 2004 December 27. Unique data from the Cluster and Double Star TC-2 satellites, designed to study the Earths magnetosphere, provide the first observational evidence of three separate timescales within the early (first 100 ms) phases of this class of events. These observations reveal that in addition to the initial very steep (<0.25 ms) X-ray onset, there is first a 4.9 ms exponential rise timescale followed by a continued exponential rise in intensity on a timescale of 70 ms. These three timescales are a prominent feature of current theoretical models, including the timescale (several milliseconds) for fracture propagation in the crust of the neutron star.

STRUCTURE OF CHROMOSPHERE--CORONA TRANSITION REGION FROM LIMB AND DISK INTENSITIES.

During a racket flight in April 1969, spectra were obtained of a region of the solar disk and at the solar limb. The absolute disk intensities derived from these data have been used to compute models of the transition region, making the assumptions that the relative abundances of different elements remain constant throughout the atmosphere, and that the electron pressure varies according to the equation of hydrostatic equilibrium. The models obtained are characterized by very steep temperature gradients. The relative intensities of emission lines in the disk and limb spectra have enabled the height of the emitting regions to be determined independently of the above assumptions, and independently of atomic data and absolute intensities. A comparison is made of the structure found by the two methods, and within the accuracy of the present data these are consistent. Emission from low temperature ( ~ 10 4 K) material is observed from heights up to 10 4 km above the transition region, and this probably originates in spicules.

The history of IUE

The International Ultraviolet Explorer, in the form of its acronym, IUE, has become a household name to astronomers throughout the world. Launched on January 26, 1978, it is still operational at the time of writing (end 1986, its ninth year) making it the longest-lived astronomical satellite ever. Although it is now showing some signs of age, its scientific performance is essentially unimpaired; for example, its photometric sensitivity has declined by only a few percent since launch.

High resolution interferometric studies of the solar magnesium ii doublet spectral region

The resonance lines of M gn (A = 279.55 and 280.27 nm) are just beyond the extinction limit of the Earth’s atmosphere. Because of the high cosmic abundance of magnesium, these lines are particularly important in ultraviolet astronomy and with the extension of interference spectroscopy into the far ultraviolet (Bradley 1968), sophisticated optical techniques can now be employed at these wavelengths. On the Sun, the M gn resonance lines consist of a broad absorption with a pronounced emission core similar to the H and K lines of Ca 11, but with more prominent emission and absorption features, so that the Mg 11H and K lines are much more sensitive indicators of chromospheric phenomena. The discovery (Kachalov & Yakovleva, 1962) of structure in the emission core, giving a doubly reversed profile, confirmed the similarity with CAII. The structure of the emission core was well resolved in high resolution {ca. 3 pm) echelle spectrograms obtained with a Sun-pointed rocket (Purcell, Garrett & Tousey 1963). These echelle line profiles were, however, composite ones averaged over one third of the solar disk, so that it was not possible to distinguish between profiles from quiet and active regions, or to determine centre-to-limb variations.

A high resolution solar ultraviolet spectrum between 200 and 220 nm

A high resolution solar spectrum in the range 200 to 220 nm has been recorded with an echelle spectrograph launched in, a sun-pointing Skylark rocket. The data have been reduced and are presented as intensity-wavelength plots together with a wavelength list and proposed identifications. A broad absorption feature at 212.4 nm is assigned to a single source and an intensity analysis confirms this to be the non-resonance Sii line at 212.412 nm. The discontinuity in the continuum intensity near 208.7 nm is revealed with high resolution for the first time and is assigned to the photoionization edge of A11. An analysis shows that its intensity drop and wavelength position can only be explained by adjustments to the solar model in the region 0.001 < T 5000 < 0.2.

Hot Stars: Beyond the balmer jump

Abstract We review the contribution of ultraviolet astronomy to the study of OB stars. UV resonance lines of ions such as C 3+ , N 4+ , and Si 3+ provide sensitive indicators of mass loss for OB stars. We show how observations of the corresponding P Cygni profiles have tested basic predictions of stellar wind theory— that mass-loss rates should scale with luminosity, that maximum flow velocites should scale with surface escape velocities, and that both should scale with metallicity. We emphasize the role that IUE has played in providing an understanding of variability in stellar winds, and conclude with an outline of the likely significance of future observations made below the IUE (and HST) limit of ∼120nm, down to ∼10nm.

A Discussion on astronomy in the ultraviolet - Preliminary results of ultraviolet interstellar extinction from TD1 satellite observations

The interstellar extinction law in the far ultraviolet has been derived from observations of about 100 stars for three galactic regions in the direction of Cygnus, galactic centre and anticentre. For each region the weighted mean extinction curve has an accuracy of about 6 % and shows no variation for the different directions. The profile of the broad extinction band centred near 2200 A is derived and shown to be symmetrical. It is concluded that the extinction characteristics will need more than one type of particle for their explanation.