926 research outputs found
Review of scaled Penning H- surface plasma source with slit emitters for high duty factor linacs
Commercial-off-the-shelf simulation package interoperability: Issues and futures
Commercial-Off-The-Shelf Simulation Packages (CSPs) are widely used in industry to simulate discrete-event models. Interoperability of CSPs requires the use of distributed simulation techniques. Literature presents us with many examples of achieving CSP interoperability using bespoke solutions. However, for the wider adoption of CSP-based distributed simulation it is essential that, first and foremost, a standard for CSP interoperability be created, and secondly, these standards are adhered to by the CSP vendors. This advanced tutorial is on an emerging standard relating to CSP interoperability. It gives an overview of this standard and presents case studies that implement some of the proposed standards. Furthermore, interoperability is discussed in relation to large and complex models developed using CSPs that require large amount of computing resources. It is hoped that this tutorial will inform the simulation community of the issues associated with CSP interoperability, the importance of these standards and its future
Association of the Dictyostelium 30 kDa actin bundling protein with contact regions
\u27Contact regions\u27 are plasma membrane domains derived from areas of intercellular contact between aggregating Dictyostelium amebae (H.M. Ingalls et al. (1986). Proc. Nat. Acad. Sci. USA 83, 4779). Purified contact regions contain a prominent actin-binding protein with an M(r) of 34,000. Immunoblotting with monoclonal antibodies identifies this polypeptide as a 34,000 M(r) actin-bundling protein (known as 30 kDa protein), previously shown to be enriched in filopodia (M. Fechheimer (1987). J. Cell Biol. 104, 1539). About four times more 30 kDa protein by mass is associated with contact regions than is found in total plasma membranes isolated from aggregating cells. In agreement with these observations, immunostaining of the 30 kDa protein in aggregating cells reveals a prominent localization along the plasma membrane at sites of intercellular contact. By contrast, alpha-actinin does not appear to be significantly enriched at sites of cell to cell contact. Binding experiments using purified plasma membranes, actin and 30 kDa protein indicate that the 30 kDa protein is associated with the plasma membrane primarily through interactions with actin filaments. Calcium ions are known to decrease the interaction of actin with 30 kDa protein in solution. Surprisingly, membrane-associated complexes of actin and the 30 kDa protein are much less sensitive to dissociation by micromolar levels of free calcium ions than are complexes in solutions lacking membranes
Improving our understanding of the Spitzer Space Telescope's pointing drifts
Spitzer observations of exoplanets routinely yield photometric accuracies of better than one part in 10,000. However, the attainable precision is limited in part by pointing drifts, which have the effect of moving the target to less stable or less-well characterized regions of Spitzer’s IRAC detector arrays. Here we examine a large sample of observing sequences in an effort to identify the causes of these pointing drifts. We find that short term and higher order drifts are correlated on various time scales to the temperatures of components in and around the spacecraft bus, and are most likely due to very slight angular displacements of the star trackers. Despite the constraints imposed by a limited pool of targets, such pointing drifts are best mitigated by optimal scheduling, minimizing large and/or lengthy excursions in telescope pitch angle within 24 hours of a high-precision photometry sequence. Such an effort is currently being initiated by the Spitzer Science Center
Using drift scans to improve astrometry with Spitzer
The Spitzer Space Telescope Infrared Array Camera (IRAC) is the only space-based instrument currently capable of continuous long duration monitoring of brown dwarfs to detect variability and characterize their atmospheres. Any such studies are limited, however, by the accuracy to which we know the positions and distances to these targets (most of which are newly discovered and therefore do not yet have multiple epochs of astrometric data). To that end, we have begun a new initiative to adapt the astrometric drift scanning technique employed by the Hubble Space Telescope to enhance Spitzer measurements of parallaxes and proper motions of brown dwarfs and other targets. A suite of images are taken with a set of sources scanned across the array. This technique reduces random noise by coaddition, and because each target covers multiple pixels we are able to average over residual instrumental distortion and intra-pixel variations. Although these benefits can be realized with appropriate dithering, scanning is much more effcient because we can take data concurrently with the spacecraft motion, covering many pixels without waiting to reposition and settle. In this contribution we demonstrate that the observing mode works and describe our software for analyzing the observations. We outline ongoing efforts towards simultaneously solving for source position and residual distortion. Initial testing shows a factor of more than 2 improvement in the astrometric precision can be obtained with Spitzer. We anticipate being able to measure parallaxes for sources out to about 50 pc, increasing the volume surveyed by a factor of 100 and enabling luminosity measurements of the young population of brown dwarfs in the β Pictoris moving group. This observing mode will be ready for public use around Winter of 2015
Protein Supplements for Beef Calves on Winter Range
These trials were to compare the effect of different sources and levels of supplemental protein on the winter and subsequent summer gains of beef calves grazing native range at the Fort Robinson Beef Cattle Research Station, Crawford, Nebraska
Spitzer/IRAC Observations of the Variability of Sgr A* and the Object G2 at 4.5 microns
We present the first detection from the Spitzer Space Telescope of 4.5 micron
variability from Sgr A*, the emitting source associated with the Milky Way's
central black hole. The >23 hour continuous light curve was obtained with the
IRAC instrument in 2013 December. The result characterizes the variability of
Sgr A* prior to the closest approach of the G2 object, a putative infalling gas
cloud that orbits close to Sgr A*. The high stellar density at the location of
Sgr A* produces a background of ~250 mJy at 4.5 microns in each pixel with a
large pixel-to-pixel gradient, but the light curve for the highly variable Sgr
A* source was successfully measured by modeling and removing the variations due
to pointing wobble. The observed flux densities range from the noise level of
~0.7 mJy rms in a 6.4-s measurement to ~10 mJy. Emission was seen above the
noise level ~34% of the time. The light curve characteristics, including the
flux density distribution and structure function, are consistent with those
previously derived at shorter infrared wavelengths. We see no evidence in the
light curve for activity attributable to the G2 interaction at the observing
epoch, ~100 days before the expected G2 periapsis passage. The IRAC light curve
is more than a factor of two longer than any previous infrared observation,
improving constraints on the timescale of the break in the power spectral
distribution of Sgr A* flux densities. The data favor the longer of the two
previously published values for the timescale.Comment: 13 pages, 10 figures, 2 tables, accepted for publication in the Ap
Physical State of Molecular Gas in High Galactic Latitude Translucent Clouds
The rotational transitions of carbon monoxide (CO) are the primary means of
investigating the density and velocity structure of the molecular interstellar
medium. Here we study the lowest four rotational transitions of CO towards
high-latitude translucent molecular clouds (HLCs). We report new observations
of the J = (4-3), (2-1), and (1-0) transitions of CO towards eight
high-latitude clouds. The new observations are combined with data from the
literature to show that the emission from all observed CO transitions is
linearly correlated. This implies that the excitation conditions which lead to
emission in these transitions are uniform throughout the clouds. Observed
13CO/12CO (1-0) integrated intensity ratios are generally much greater than the
expected abundance ratio of the two species, indicating that the regions which
emit 12CO (1-0) radiation are optically thick. We develop a statistical method
to compare the observed line ratios with models of CO excitation and radiative
transfer. This enables us to determine the most likely portion of the physical
parameter space which is compatible with the observations. The model enables us
to rule out CO gas temperatures greater than 30K since the most likely
high-temperature configurations are 1 pc-sized structures aligned along the
line of sight. The most probable solution is a high density and low temperature
(HDLT) solution. The CO cell size is approximately 0.01 pc (2000 AU). These
cells are thus tiny fragments within the 100 times larger CO-emitting extent of
a typical high-latitude cloud. We discuss the physical implications of HDLT
cells, and we suggest ways to test for their existence.Comment: 19 pages, 13 figures, 2 tables, emulateapj To be published in The
Astrophysical Journa
MICROGRID RESILIENCE ANALYSIS SOFTWARE DEVELOPMENT
Military installation microgrids need to be resilient to a variety of potential disruptions (storms, attacks, et cetera). Various metrics for assessing microgrid resilience have been described in literature, and multiple tools for simulating microgrid performance have been constructed; however, it is often left to system owners and maintainers to bring these efforts together to identify and realize effective, efficient improvement strategies. Military microgrid stakeholders have expressed a desire for an integrated, unified platform that provides these multiple capabilities in a coordinated fashion. In support of these endeavors, analysis methods developed by NPS and NAVFAC Expeditionary Warfare Center researchers for measuring microgrid resilience have been integrated into an existing web-based microgrid power flow simulation and distributed energy resource rightsizing software tool. This was achieved by the development of additional functions and methods within the existing software platform code base, and expansion of the application programming interface (API). These API additions enabled access to the new calculation and analysis capabilities, as well as increased control over power flow simulation parameters. These analytical and functional contributions were validated through a design of experiments, including comparison to independently generated data, and factorial analysis.Outstanding ThesisCivilian, Department of the NavyCivilian, Department of the NavyCivilian, Department of the NavyCivilian, Department of the NavyCivilian, Department of the NavyApproved for public release. Distribution is unlimited
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