444 research outputs found
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
A rigorous comparison of different planet detection algorithms
The idea of finding extrasolar planets (ESPs) through observations of drops
in stellar brightness due to transiting objects has been around for decades. It
has only been in the last ten years, however, that any serious attempts to find
ESPs became practical. The discovery of a transiting planet around the star HD
209458 (Charbonneau et al. 2000) has led to a veritable explosion of research,
because the photometric method is the only way to search a large number of
stars for ESPs simultaneously with current technology. To this point, however,
there has been limited research into the various techniques used to extract the
subtle transit signals from noise, mainly brief summaries in various papers
focused on publishing transit-like signatures in observations. The scheduled
launches over the next few years of satellites whose primary or secondary
science missions will be ESP discovery motivates a review and a comparative
study of the various algorithms used to perform the transit identification, to
determine rigorously and fairly which one is the most sensitive under which
circumstances, to maximize the results of past, current, and future
observational campaigns.Comment: Accepted for publications by Astronomy and Astrophysic
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
Microbial diversity in fecal samples depends on DNA extraction method: easyMag DNA extraction compared to QIAamp DNA stool mini kit extraction
BACKGROUND: There are challenges, when extracting bacterial DNA from specimens for molecular diagnostics, since fecal samples also contain DNA from human cells and many different substances derived from food, cell residues and medication that can inhibit downstream PCR. The purpose of the study was to evaluate two different DNA extraction methods in order to choose the most efficient method for studying intestinal bacterial diversity using Denaturing Gradient Gel Electrophoresis (DGGE). FINDINGS: In this study, a semi-automatic DNA extraction system (easyMag®, BioMérieux, Marcy I’Etoile, France) and a manual one (QIAamp DNA Stool Mini Kit, Qiagen, Hilden, Germany) were tested on stool samples collected from 3 patients with Inflammatory Bowel disease (IBD) and 5 healthy individuals. DNA extracts obtained by the QIAamp DNA Stool Mini Kit yield a higher amount of DNA compared to DNA extracts obtained by easyMag® from the same fecal samples. Furthermore, DNA extracts obtained using easyMag® seemed to contain inhibitory compounds, since in order to perform a successful PCR-analysis, the sample should be diluted at least 10 times. DGGE performed on PCR from DNA extracted by QIAamp DNA Stool Mini Kit DNA was very successful. CONCLUSION: QIAamp DNA Stool Mini Kit DNA extracts are optimal for DGGE runs and this extraction method yields a higher amount of DNA compared to easyMag®
Orbital parameters, masses and distance to Beta Centauri determined with the Sydney University Stellar Interferometer and high resolution spectroscopy
The bright southern binary star beta Centauri (HR 5267) has been observed
with the Sydney University Stellar Interferometer (SUSI) and spectroscopically
with the ESO CAT and Swiss Euler telescopes at La Silla. The interferometric
observations have confirmed the binary nature of the primary component and have
enabled the determination of the orbital parameters of the system. At the
observing wavelength of 442 nm the two components of the binary system have a
magnitude difference of 0.15. The combination of interferometric and
spectroscopic data gives the following results: orbital period 357 days,
semi-major axis 25.30 mas, inclination 67.4 degrees, eccentricity 0.821,
distance 102.3 pc, primary and secondary masses M1 = M2 = 9.1 solar masses and
absolute visual magnitudes of the primary and secondary M1V = -3.85 and M2V =
-3.70. The high accuracy of the results offers a fruitful starting point for
future asteroseismic modelling of the pulsating binary components.Comment: 10 pages, 4 figures. Accepted for publication in MNRA
Ornamental plants, 1985: a summary of research
Field transplant survival of Amelanchier liners produced by tissue culture / Daniel K. Struve and R. Daniel Lineberger -- An evaluation of strawdust - an alternative growing media / Elton M. Smith and Sharon A. Treaster -- Growth of container grown nursery stock produced in composted municipal sludge amended media / Elton M. Smith and Sharon A. Treaster -- Soil temperature effects on root regeneration of scarlet oak seedlings / Daniel K. Struve arid Bruno C. Moser -- Lighting Viburnum opulus 'Nanum' cuttings to increase winter survival / Elton M. Smith and Sharon A. Treaster -- Treatments of etiolated dormant rose shoots / Elton M. Smith and Sharon A. Treaster -- Evaluation of flowering crabapple susceptibility to apple scab in Ohio – 1984 / Elton M. Smith and Sharon A. Treaster -- Tolerance of azalea, cotoneaster, and euonymus to Devrinol, Goal, and Goal Combinations / Elton M. Smith and Sharon A. Treaster -- Micropropagation of chimeral african violets / R. Daniel Lineberger and Mark Druckenbrod -- capital requirements of overwintering structures for nurseries in Ohio - 1984 / Reed D. Taylor, Daryl T. Gillette, and Elton M. Smith -- annual fixed costs of overwintering plants in nurseries differentiated by type of structure for Ohio - 1984 / Daryl T. Gillette, Reed D. Taylor, and Elton M. Smith -- Comparative costs of overwintering plants in nurseries differentiated by system for Ohio - 1984 / Reed D. Taylor, Daryl T. Gillette, and Elton M. Smit
Neodymium isotope analyses after combined extraction of actinide and lanthanide elements from seawater and deep-sea coral aragonite
Neutral Gas Outflows and Inflows in Infrared-Faint Seyfert Galaxies
Previous studies of the Na I D interstellar absorption line doublet have
shown that galactic winds occur in most galaxies with high infrared
luminosities. However, in infrared-bright composite systems where a starburst
coexists with an active galactic nucleus (AGN), it is unclear whether the
starburst, the AGN, or both are driving the outflows. The present paper
describes the results from a search for outflows in 35 infrared-faint Seyferts
with 10^9.9 < L_IR/L_sun < 10^11, or, equivalently, star formation rates (SFR)
of ~0.4 -- 9 solar masses per year, to attempt to isolate the source of the
outflow. We find that the outflow detection rates for the infrared-faint
Seyfert 1s (6%) and Seyfert 2s (18%) are lower than previously reported for
infrared-luminous Seyfert 1s (50%) and Seyfert 2s (45%). The outflow kinematics
of infrared-faint and infrared-bright Seyfert 2 galaxies resemble those of
starburst galaxies, while the outflow velocities in Seyfert 1 galaxies are
significantly larger. Taken together, these results suggest that the AGN does
not play a significant role in driving the outflows in most infrared-faint and
infrared-bright systems, except the high-velocity outflows seen in Seyfert 1
galaxies. Another striking result of this study is the high rate of detection
of inflows in infrared-faint galaxies (39% of Seyfert 1s, 35% of Seyfert 2s),
significantly larger than in infrared-luminous Seyferts (15%). This inflow may
be contributing to the feeding of the AGN in these galaxies, and potentially
provides more than enough material to power the observed nuclear activity over
typical AGN lifetimes.Comment: 17 pages, 12 figures, published in ApJ (article updated 12/30/09
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