A New Linear Inductive Voltage Adder Driver for the Saturn Accelerator

Saturn is a dual-purpose accelerator. It can be operated as a large-area flash x-ray source for simulation testing or as a Z-pinch driver especially for K-line x-ray production. In the first mode, the accelerator is fitted with three concentric-ring 2-MV electron diodes, while in the Z-pinch mode the current of all the modules is combined via a post-hole convolute arrangement and driven through a cylindrical array of very fine wires. We present here a point design for a new Saturn class driver based on a number of linear inductive voltage adders connected in parallel. A technology recently implemented at the Institute of High Current Electronics in Tomsk (Russia) is being utilized[1]. In the present design we eliminate Marx generators and pulse-forming networks. Each inductive voltage adder cavity is directly fed by a number of fast 100-kV small-size capacitors arranged in a circular array around each accelerating gap. The number of capacitors connected in parallel to each cavity defines the total maximum current. By selecting low inductance switches, voltage pulses as short as 30-50-ns FWHM can be directly achieved.Comment: 3 pages, 4 figures. This paper is submitted for the 20th Linear Accelerator Conference LINAC2000, Monterey, C

Direct Observation of the Fourth Star in the Zeta Cancri System

Direct imaging of the zeta Cnc system has resolved the fourth star in the system, which is in orbit around zeta Cnc C. The presence of the fourth star has been inferred for many years from irregularities in the motion of star C, and recently from C's spectroscopic orbit. However, its mass is close to that of C, making its non-detection puzzling. Observing at wavelengths of 1.2, 1.7, and 2.2 microns with the adaptive-optics system of the CFHT, we have obtained images which very clearly reveal star D and show it to have the color of an M2 star. Its brightness is consonant with its being two M stars, which are not resolved in our observations but are likely to be in a short-period orbit, thereby accounting for the large mass and the difficulty of detection at optical wavelengths, where the magnitude difference is much larger. The positions and colors of all four stars in the system are reported and are consistent with the most recent astrometric observations.Comment: 7 pages including 3 tables, 1 figure; To appear in PAS

Homozygous disruption of P450 side-chain cleavage (CYP11A1) is associated with prematurity, complete 46,XY sex reversal, and severe adrenal failure

Disruption of the P450 side-chain cleavage cytochrome (P450scc) enzyme due to deleterious mutations of the CYP11A1 gene is thought to be incompatible with fetal survival because of impaired progesterone production by the fetoplacental unit. We present a 46, XY patient with a homozygous disruption of CYP11A1.The child was born prematurely with complete sex reversal and severe adrenal insufficiency. Laboratory data showed diminished or absent steroidogenesis in all pathways. Molecular genetic analysis of the CYP11A1 gene revealed a homozygous single nucleotide deletion leading to a premature termination at codon position 288. This mutation will delete highly conserved regions of the P450scc enzyme and thus is predicted to lead to a nonfunctional protein. Both healthy parents were heterozygous for this mutation.Our report demonstrates that severe disruption of P450scc can be compatible with survival in rare instances. Furthermore, defects in this enzyme are inherited in an autosomal-recessive fashion, and heterozygote carriers can be healthy and fertile. The possibility of P450scc-independent pathways of steroid synthesis in addition to the current concept of luteoplacental shift of progesterone synthesis in humans has to be questioned

Structural and functional studies of Escherichia coli Aggregative Adherence Fimbriae (AAF/V) reveal a deficiency in extracellular matrix binding

Enteroaggregative Escherichia coli (EAEC) is an emerging cause of acute and persistent diarrhea worldwide. The pathogenesis of different EAEC stains is complicated, however, the early essential step begins with attachment of EAEC to intestinal mucosa via aggregative adherence fimbriae (AAFs). Currently, five different variants have been identified, which all share a degree of similarity in the gene organization of their operons and sequences. Here, we report the solution structure of Agg5A from the AAF/V variant. While preserving the major structural features shared by all AAF members, only Agg5A possesses an inserted helix at the beginning of the donor strand, which together with altered surface electrostatics, renders the protein unable to interact with fibronectin. Hence, here we characterize the first AAF variant with a binding mode that varies from previously described AAF

New ground-based observational methods and instrumentation for asteroseismology

Space instrumentation like SOHO, MOST, CoRoT and Kepler has been and is being built to attain very high precision data to be used for asteroseismic analysis. Nonetheless, there is a very strong need for providing additional information, especially on mode identification. With this contribution I will review the efforts been put on new ground-based instrumentation and the methodology that can be used to achieve this aim.Comment: 6 pages. Review contribution to be published in Astrophysics and Space Science Proceedings series (ASSP), in the proceedings of "20th Stellar Pulsation Conference Series: Impact of new instrumentation and new insights in stellar pulsations", 5-9 September 2011, Granada, Spai

The EXPLORE Project I: A Deep Search for Transiting Extrasolar Planets

(Abridged) We discuss the design considerations of the EXPLORE (EXtra-solar PLanet Occultation REsearch) project, a series of transiting planet searches using 4-m-class telescopes to continuously monitor a single field of stars in the Galactic Plane in each ~2 week observing campaign. We discuss the general factors which determine the efficiency and the number of planets found by a transit search, including time sampling strategy and field selection. The primary goal is to select the most promising planet candidates for radial velocity follow-up observations. We show that with very high photometric precision light curves that have frequent time sampling and at least two detected transits, it is possible to uniquely solve for the main parameters of the eclipsing system (including planet radius) based on several important assumptions about the central star. Together with a measured spectral type for the star, this unique solution for orbital parameters provides a powerful method for ruling out most contaminants to transiting planet candidates. For the EXPLORE project, radial velocity follow-up observations for companion mass determination of the best candidates are done on 8-m-class telescopes within two or three months of the photometric campaigns. This same-season follow-up is made possible by the use of efficient pipelines to produce high quality light curves within weeks of the observations. We conclude by presenting early results from our first search, EXPLORE I, in which we reached <1% rms photometric precision (measured over a full night) on ~37,000 stars to I <= 18.2.Comment: accepted by ApJ. Main points unchanged but more thorough discussion of some issues. 36 pages, including 14 figure

A circumnuclear disk of atomic hydrogen in Centaurus A

We present new observations, performed with the Australia Telescope Compact Array, of the HI absorption in the central regions of Centaurus A. For the first time, absorption is detected against the radio core at velocities blueshifted with respect to the systemic velocity. Moreover, the data show that the nuclear redshifted absorption component is broader than reported before. With these new results, the kinematics of the HI in the inner regions of Cen A appears very similar to that observed in emission for the molecular circumnuclear disk. This suggests that the central HI absorption is not, as was previously claimed, evidence of gas infall into the AGN, but instead is due to a cold, circumnuclear disk.Comment: Accepted for publication in A&A Letter, 4 pages, 2 figure

Sub-milliarcsecond precision spectro-astrometry of Be stars

The origin of the disks around Be stars is still not known. Further progress requires a proper parametrization of their structure, both spatially and kinematically. This is challenging as the disks are very small. Here we assess whether a novel method is capable of providing these data. We obtained spectro astrometry around the Pa beta line of two bright Be stars, alpha Col and zeta Tau, to search for disk signatures. The data, with a pixel to pixel precision of the centroid position of 0.3..0.4 milliarcsecond is the most accurate such data to date. Artefacts at the 0.85 mas level are present in the data, but these are readily identified as they were non-repeatable in our redundant datasets. This does illustrate the need of taking multiple data to avoid spurious detections. The data are compared with simple model simulations of the spectro astrometric signatures due to rotating disks around Be stars. The upper limits we find for the disk radii correspond to disk sizes of a few dozen stellar radii if they rotate Keplerian. This is very close to observationally measured and theoretically expected disk sizes, and this paper therefore demonstrates that spectro-astrometry, of which we present the first such attempt, has the potential to resolve the disks around Be stars.Comment: 6 pages, A&A accepte