30,300 research outputs found
On the arcmin structure of the X-ray Universe
We present the angular correlation function of the X-ray population of 1063
XMM-Newton observations at high Galactic latitudes, comprising up to ~30000
sources over a sky area of ~125 sq. degrees in the energy bands: soft (0.5-2
keV) and hard (2-10 keV). This is the largest sample of serendipitous X-ray
sources ever used for clustering analysis purposes to date and the results have
been determined with unprecedented accuracy. We detect significant clustering
signals in the soft and hard bands (~10 sigma and ~5 sigma, respectively). We
deproject the angular correlation function via Limber's equation and calculate
the typical spatial lengths. We infer that AGN at redshifts ~1 are embedded in
dark matter halos with typical masses of log M ~ 12.6/h Msol and lifetimes in
the range ~3-5 x 10^8 years, which indicates that AGN activity is a transient
phase in the life of galaxies.Comment: 4 pages, 1 figure. Proc. of the conference "X-ray Astronomy 2009:
Present status, multiwavelength approach and future perspectives", September
2009, Bologna. To appear in AIP Conf. Proc. (editors: A. Comastri, M. Cappi,
L. Angelini)
Project management techniques for highly integrated programs
The management and control of a representative, highly integrated high-technology project, in the X-29A aircraft flight test project is addressed. The X-29A research aircraft required the development and integration of eight distinct technologies in one aircraft. The project management system developed for the X-29A flight test program focuses on the dynamic interactions and the the intercommunication among components of the system. The insights gained from the new conceptual framework permitted subordination of departments to more functional units of decisionmaking, information processing, and communication networks. These processes were used to develop a project management system for the X-29A around the information flows that minimized the effects inherent in sampled-data systems and exploited the closed-loop multivariable nature of highly integrated projects
Earth Observations Division version of the Laboratory for Applications of Remote Sensing System (EOD-LARSYS) user guide for the IBM 370/148. Volume 2: User reference manual
This document presents instructions for analysts who use the EOD-LARSYS as programmed on the Purdue University IBM 370/148 (recently replaced by the IBM 3031) computer. It presents sample applications, control cards, and error messages for all processors in the system and gives detailed descriptions of the mathematical procedures and information needed to execute the system and obtain the desired output. EOD-LARSYS is the JSC version of an integrated batch system for analysis of multispectral scanner imagery data. The data included is designed for use with the as built documentation (volume 3) and the program listings (volume 4). The system is operational from remote terminals at Johnson Space Center under the virtual machine/conversational monitor system environment
Does gravity prefer the Poincare dodecahedral space?
The missing fluctuations problem in cosmic microwave background observations
is naturally explained by well-proportioned small universe models. Among the
well-proportioned models, the Poincare dodecahedral space is empirically
favoured. Does gravity favour this space? The residual gravity effect is the
residual acceleration induced by weak limit gravity from multiple topological
images of a massive object on a nearby negligible mass test object. At the
present epoch, the residual gravity effect is about a million times weaker in
three of the well-proportioned spaces than in ill-proportioned spaces. However,
in the Poincare space, the effect is 10,000 times weaker still, i.e. the
Poincare space is about 10^{10} times "better balanced" than ill-proportioned
spaces. Both observations and weak limit dynamics select the Poincare space to
be special.Comment: 6 pages, Honorable Mention in 2009 Gravity Research Foundation essay
competitio
Statistical properties of an ensemble of vortices interacting with a turbulent field
We develop an analytical formalism to determine the statistical properties of
a system consisting of an ensemble of vortices with random position in plane
interacting with a turbulent field. We calculate the generating functional by
path-integral methods. The function space is the statistical ensemble composed
of two parts, the first one representing the vortices influenced by the
turbulence and the second one the turbulent field scattered by the randomly
placed vortices.Comment: Third version; Important corrections in the normalization for the gas
of vortices, et
Holocene-Neogene volcanism in northeastern Australia: chronology and eruption history
Quaternary and late Neogene volcanism is widespread in northeastern Australia, producing at least 397 eruptions covering more than 20,000 km2, including at least 20 flows over 50 km long. Despite this abundance of young volcanism, before this study numerous eruptions had tentative ages or were undated, and the area requires a comprehensive evaluation of eruption patterns through time. To help address these issues we applied multi-collector ARGUS-V 40Ar/39Ar geochronology to determine the age of four of the younger extensive flows: Undara (160 km long, 189 ± 4/4 ka; 2σ, with full analytical/external uncertainties), Murronga (40 km long, 153 ± 5/5 ka), Toomba (120 km long, 21 ± 3/3 ka), and Kinrara (55 km long, 7 ± 2/2 ka). Verbal traditions of the Gugu Badhun Aboriginal people contain features that may potentially describe the eruption of Kinrara. If the traditions do record this eruption, they would have been passed down for 230 ± 70 generations – a period of time exceeding the earliest written historical records. To further examine north Queensland volcanism through time we compiled a database of 337 ages, including 179 previously unpublished K-Ar and radiocarbon results. The compiled ages demonstrate that volcanic activity has occurred without major time breaks since at least 9 Ma. The greatest frequency of eruptions occurred in the last 2 Ma, with an average recurrence interval of <10–22 ka between eruptions. Activity was at times likely more frequent than these calculations indicate, as the geochronologic dataset is incomplete, with undated eruptions, and intraplate volcanism is often episodic. The duration, frequency, and youthfulness of activity indicate that north Queensland volcanism should be considered as potentially still active, and there are now two confirmed areas of Holocene volcanism in eastern Australia – one at each end of the continent. More broadly, our data provides another example of 40Ar/39Ar geochronology applied to Holocene and latest Pleistocene mafic eruptions, further demonstrating that this method has the ability to examine eruptions and hazards at the youngest volcanoes on Earth
Electronic structure and the glass transition in pnictide and chalcogenide semiconductor alloys. Part II: The intrinsic electronic midgap states
We propose a structural model that treats in a unified fashion both the
atomic motions and electronic excitations in quenched melts of pnictide and
chalcogenide semiconductors. In Part I (submitted to J. Chem. Phys.), we argued
these quenched melts represent aperiodic -networks that are highly
stable and, at the same time, structurally degenerate. These networks are
characterized by a continuous range of coordination. Here we present a
systematic way to classify these types of coordination in terms of discrete
coordination defects in a parent structure defined on a simple cubic lattice.
We identify the lowest energy coordination defects with the intrinsic midgap
electronic states in semiconductor glasses, which were argued earlier to cause
many of the unique optoelectronic anomalies in these materials. In addition,
these coordination defects are mobile and correspond to the transition state
configurations during the activated transport above the glass transition. The
presence of the coordination defects may account for the puzzling discrepancy
between the kinetic and thermodynamic fragility in chalcogenides. Finally, the
proposed model recovers as limiting cases several popular types of bonding
patterns proposed earlier, including: valence-alternation pairs, hypervalent
configurations, and homopolar bonds in heteropolar compounds.Comment: 17 pages, 15 figures, revised version, final version to appear in J.
Chem. Phy
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