13,625 research outputs found
The StarScan plate measuring machine: overview and calibrations
The StarScan machine at the U.S. Naval Observatory (USNO) completed measuring
photographic astrograph plates to allow determination of proper motions for the
USNO CCD Astrograph Catalog (UCAC) program. All applicable 1940 AGK2 plates,
about 2200 Hamburg Zone Astrograph plates, 900 Black Birch (USNO Twin
Astrograph) plates, and 300 Lick Astrograph plates have been measured. StarScan
comprises of a CCD camera, telecentric lens, air-bearing granite table, stepper
motor screws, and Heidenhain scales to operate in a step-stare mode. The
repeatability of StarScan measures is about 0.2 micrometer. The CCD mapping as
well as the global table coordinate system has been calibrated using a special
dot calibration plate and the overall accuracy of StarScan x,y data is derived
to be 0.5 micrometer. Application to real photographic plate data shows that
position information of at least 0.65 micrometer accuracy can be extracted from
course grain 103a-type emulsion astrometric plates. Transformations between
"direct" and "reverse" measures of fine grain emulsion plate measures are
obtained on the 0.3 micrometer level per well exposed stellar image and
coordinate, which is at the limit of the StarScan machine.Comment: 24 pages, 8 figures, accepted for PAS
A Salmonella virulence factor activates the NOD1/NOD2 signaling pathway.
The invasion-associated type III secretion system (T3SS-1) of Salmonella enterica serotype Typhimurium (S. Typhimurium) activates the transcription factor NF-ÎșB in tissue culture cells and induces inflammatory responses in animal models through unknown mechanisms. Here we show that bacterial delivery or ectopic expression of SipA, a T3SS-1-translocated protein, led to the activation of the NOD1/NOD2 signaling pathway and consequent RIP2-mediated induction of NF-ÎșB-dependent inflammatory responses. SipA-mediated activation of NOD1/NOD2 signaling was independent of bacterial invasion in vitro but required an intact T3SS-1. In the mouse colitis model, SipA triggered mucosal inflammation in wild-type mice but not in NOD1/NOD2-deficient mice. These findings implicate SipA-driven activation of the NOD1/NOD2 signaling pathway as a mechanism by which the T3SS-1 induces inflammatory responses in vitro and in vivo
LOCAL VARIABILITY IN THE ORBIT OF SATURN'S F RING
This work was supported by the Science and Technology Facilities Council (grant number ST/F007566/1)
Plate-impact loading of cellular structures formed by selective laser melting
Porous materials are of great interest because of improved energy absorption over their solid counterparts. Their properties, however, have been difficult to optimize. Additive manufacturing has emerged as a potential technique to closely define the structure and properties of porous components, i.e. density, strut width and pore size; however, the behaviour of these materials at very high impact energies remains largely unexplored. We describe an initial study of the dynamic compression response of lattice materials fabricated through additive manufacturing. Lattices consisting of an array of intersecting stainless steel rods were fabricated into discs using selective laser melting. The resulting discs were impacted against solid stainless steel targets at velocities ranging from 300 to 700 m s-1 using a gas gun. Continuum CTH simulations were performed to identify key features in the measured wave profiles, while 3D simulations, in which the individual cells were modelled, revealed details of microscale deformation during collapse of the lattice structure. The validated computer models have been used to provide an understanding of the deformation processes in the cellular samples. The study supports the optimization of cellular structures for application as energy absorbers. © 2014 IOP Publishing Ltd
What Does Trump Really Want?
Donald Trumpâs 2017 inaugural address was scored with a content analysis measure of implicit motives. The results show that compared to other 20th and 21st century U.S. presidents, he scores very high in achievement and power motive imagery, but only about average in affiliation imagery. Based on previous research on presidentsâ motive imagery, this profile suggests some predictions about the Trump presidency and possible problems for it. In political leaders, high achievement motivation often leads to frustration with the political process. Power motivation, while associated with rated greatness, is related to polarization of public opinion and war. The effects of motives are further channel by temperament and traitsâin Trumpâs case, high extraversion and low agreeableness.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/146992/1/asap12154.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/146992/2/asap12154_am.pd
Thermal activation between Landau levels in the organic superconductor -(BEDT-TTF)SFCHCFSO
We show that Shubnikov-de Haas oscillations in the interlayer resistivity of
the organic superconductor -(BEDT-TTF)SF
CHCFSO become very pronounced in magnetic fields ~60~T.
The conductivity minima exhibit thermally-activated behaviour that can be
explained simply by the presence of a Landau gap, with the
quasi-one-dimensional Fermi surface sheets contributing negligibly to the
conductivity. This observation, together with complete suppression of chemical
potential oscillations, is consistent with an incommensurate nesting
instability of the quasi-one-dimensional sheets.Comment: 6 pages, 4 figure
On the de Haas - van Alphen oscillations in quasi-two-dimensional metals: effect of the Fermi surface curvature
Here, we present the results of theoretical analysis of the de Haas-van
Alphen oscillations in quasi-two-dimensional normal metals. We had been
studying effects of the Fermi surface (FS) shape on these oscillations. It was
shown that the effects could be revealed and well pronounced when the FS
curvature becomes zero at cross-sections with extremal cross-sectional areas.
In this case both shape and amplitude of the oscillations could be
significantly changed. Also, we analyze the effect of the FS local geometry on
the angular dependencies of the oscillation amplitudes when the magnetic field
is tilted away from the FS symmetry axis by the angle We show that a
peak appears at whose height could be of the same order as
the maximum at the Yamaji angle. This peak emerges when the FS includes zero
curvature cross-sections of extremal areas. Such maximum was observed in
experiments on the The obtained results could be
applied to organic metals and other quasi-two-dimensional compounds.Comment: 9 pages, 4 figures, text added, references adde
Spatiotemporal profile of emission from oscillating dc micro discharges
The axial light distributions in parallel-plate dc microdischarges in argon
show similar behavior to large scale discharges. Between the low-current
Townsend mode and the high current glow mode exists a large region of currents
where different oscillations appear and the dynamic Volt-Ampere characteristic
shows hysteresis behavior. During the oscillations the maximum peak intensity
moves closer to the cathode, which is characteristic for the abnormal glow
regime even though the average current is considerably smaller.Comment: submitted to: IEEE Trans. Plasma Sci., Spec. Issue on Images in
Plasma Sc
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