16,778 research outputs found
Characterization of Active Main Belt Object P/2012 F5 (Gibbs): A Possible Impacted Asteroid
In this work we characterize the recently discovered active main belt object
P/2012 F5 (Gibbs), which was discovered with a dust trail > 7' in length in the
outer main belt, 7 months prior to aphelion. We use optical imaging obtained on
UT 2012 March 27 to analyze the central condensation and the long trail. We
find nuclear B-band and R-band apparent magnitudes of 20.96 and 19.93 mag,
respectively, which give an upper limit on the radius of the nucleus of 2.1 km.
The geometric cross-section of material in the trail was ~ 4 x 10^8 m^2,
corresponding to a dust mass of ~ 5 x 10^7 kg. Analysis of infrared images
taken by the Wide-Field Infrared Survey Explorer in September 2010 reveals that
the object was below the detection limit, suggesting that it was less active
than it was during 2012, or possibly inactive, just 6 months after it passed
through perihelion. We set a 1-sigma upper limit on its radius during this time
of 2.9 km. P/2012 F5 (Gibbs) is dynamically stable in the outer main belt on
timescales of ~ 1 Gyr, pointing towards an asteroidal origin. We find that the
morphology of the ejected dust is consistent with it being produced by a single
event that occurred on UT 2011 July 7 20 days, possibly as the result of
a collision with a small impactor.Comment: 29 pages, 5 figures. Accepted for publication in Ap
Twisted K-theory and K-theory of bundle gerbes
In this note we introduce the notion of bundle gerbe K-theory and investigate
the relation to twisted K-theory. We provide some examples. Possible
applications of bundle gerbe K-theory to the classification of D-brane charges
in non-trivial backgrounds are discussed.Comment: 29 pages, corrected typos, added references, included new section on
twisted Chern character in non-torsion cas
Concept design and alternate arrangements of orbiter mid-deck habitability features
The evaluations and recommendations for habitability features in the space shuttle orbiter mid-deck are summarized. The orbiter mission plans, the mid-deck dimensions and baseline arrangements along with crew compliments and typical activities were defined. Female and male anthropometric data based on zero-g operations were also defined. Evaluations of baseline and alternate feasible concepts provided several recommendations which are discussed
Lingering grains of truth around comet 17P/Holmes
Comet 17P/Holmes underwent a massive outburst in 2007 Oct., brightening by a
factor of almost a million in under 48 hours. We used infrared images taken by
the Wide-Field Survey Explorer mission to characterize the comet as it appeared
at a heliocentric distance of 5.1 AU almost 3 years after the outburst. The
comet appeared to be active with a coma and dust trail along the orbital plane.
We constrained the diameter, albedo, and beaming parameter of the nucleus to
4.135 0.610 km, 0.03 0.01 and 1.03 0.21, respectively. The
properties of the nucleus are consistent with those of other Jupiter Family
comets. The best-fit temperature of the coma was 134 11 K, slightly
higher than the blackbody temperature at that heliocentric distance. Using
Finson-Probstein modeling we found that the morphology of the trail was
consistent with ejection during the 2007 outburst and was made up of dust
grains between 250 m and a few cm in radius. The trail mass was 1.2
- 5.3 10 kg.Comment: Accepted to ApJ. 2 tables, 4 figure
NEOWISE observations of comet C/2013 A1 (Siding Spring) as it approaches Mars
The Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) mission
observed comet C/2013 A1 (Siding Spring) three times at 3.4 {\mu}m and 4.6
{\mu}m as the comet approached Mars in 2014. The comet is an extremely
interesting target since its close approach to Mars in late 2014 will be
observed by various spacecraft in-situ. The observations were taken in 2014
Jan., Jul. and Sep. when the comet was at heliocentric distances of 3.82 AU,
1.88 AU, and 1.48 AU. The level of activity increased significantly between the
Jan. and Jul. visits but then decreased by the time of the observations in
Sep., approximately 4 weeks prior to its close approach to Mars. In this work
we calculate Af\r{ho} values, and CO/CO2 production rates.Comment: 9 pages, 3 figures, accepted by Astrophysical Journal Letter
The Non-Trivial Effective Potential of the `Trivial' lambda Phi^4 Theory: A Lattice Test
The strong evidence for the `triviality' of (lambda Phi^4)_4 theory is not
incompatible with spontaneous symmetry breaking. Indeed, for a `trivial' theory
the effective potential should be given exactly by the classical potential plus
the free-field zero-point energy of the shifted field; i.e., by the one-loop
effective potential. When this is renormalized in a simple, but nonperturbative
way, one finds, self-consistently, that the shifted field does become
non-interacting in the continuum limit. For a classically scale-invariant (CSI)
lambda Phi^4 theory one finds m_h^2 = 8 pi^2 v^2, predicting a 2.2 TeV Higgs
boson. Here we extend our earlier work in three ways: (i) we discuss the
analogy with the hard-sphere Bose gas; (ii) we extend the analysis from the CSI
case to the general case; and (iii) we propose a test of the predicted shape of
the effective potential that could be tested in a lattice simulation.Comment: 22 pages, LaTeX, DE-FG05-92ER40717-
The four-fermion interaction in D=2,3,4: a nonperturbative treatment
A new nonperturbative approach is used to investigate the Gross-Neveu model
of four fermion interaction in the space-time dimensions 2, 3 and 4, the number
of inner degrees of freedom being a fixed integer. The spontaneous symmetry
breaking is shown to exist in and the running coupling constant is
calculated. The four dimensional theory seems to be trivial.Comment: a minor correction: one more acknowledgement is added. Latex 2.09
file, 15 pages, no figures, accepted for publication to Int.J.Mod.Phys.
The economic value of remote sensing by satellite: An ERTS overview and the value of continuity of service. Volume 2: Source document
The economic value of an ERS system with a technical capability similar to ERTS, allowing for increased coverage obtained through the use of multiple active satellites in orbit is presented. A detailed breakdown of the benefits achievable from an ERS system is given and a methodology for their estimation is established. The ECON case studies in agriculture, water use, and land cover are described along with the current ERTS system. The cost for a projected ERS system is given
Asteroid family identification using the Hierarchical Clustering Method and WISE/NEOWISE physical properties
Using albedos from WISE/NEOWISE to separate distinct albedo groups within the
Main Belt asteroids, we apply the Hierarchical Clustering Method to these
subpopulations and identify dynamically associated clusters of asteroids. While
this survey is limited to the ~35% of known Main Belt asteroids that were
detected by NEOWISE, we present the families linked from these objects as
higher confidence associations than can be obtained from dynamical linking
alone. We find that over one-third of the observed population of the Main Belt
is represented in the high-confidence cores of dynamical families. The albedo
distribution of family members differs significantly from the albedo
distribution of background objects in the same region of the Main Belt, however
interpretation of this effect is complicated by the incomplete identification
of lower-confidence family members. In total we link 38,298 asteroids into 76
distinct families. This work represents a critical step necessary to debias the
albedo and size distributions of asteroids in the Main Belt and understand the
formation and history of small bodies in our Solar system.Comment: Accepted to ApJ. Full version of Table 3 to be published
electronically in Ap
Genomic variations associated with attenuation in Mycobacterium avium subsp paratuberculosis vaccine strains
BACKGROUND: Mycobacterium avium subspecies paratuberculosis (MAP) whole cell vaccines have been widely used tools in the control of Johne's disease in animals despite being unable to provide complete protection. Current vaccine strains derive from stocks created many decades ago; however their genotypes, underlying mechanisms and relative degree of their attenuation are largely unknown.
RESULTS: Using mouse virulence studies we confirm that MAP vaccine strains 316 F, II and 2e have diverse but clearly attenuated survival and persistence characteristics compared with wild type strains. Using a pan genomic microarray we characterise the genomic variations in a panel of vaccine strains sourced from stocks spanning over 40 years of maintenance. We describe multiple genomic variations specific for individual vaccine stocks in both deletion (26-32 Kbp) and tandem duplicated (11-40 Kbp) large variable genomic islands and insertion sequence copy numbers. We show individual differences suitable for diagnostic differentiation between vaccine and wild type genotypes and provide evidence for functionality of some of the deleted MAP-specific genes and their possible relation to attenuation.
CONCLUSIONS: This study shows how culture environments have influenced MAP genome diversity resulting in large tandem genomic duplications, deletions and transposable element activity. In combination with classical selective systematic subculture this has led to fixation of specific MAP genomic alterations in some vaccine strain lineages which link the resulting attenuated phenotypes with deficiencies in high reactive oxygen species handling
- …