577 research outputs found
Mapping the Asymmetric Thick Disk: The Hercules Thick Disk Cloud
The stellar asymmetry of faint thick disk/inner halo stars in the first
quadrant first reported by Larsen & Humphreys (1996) and investigated further
by Parker et al. (2003, 2004) has been recently confirmed by SDSS (Juric et al.
2008). Their interpretation of the excess in the star counts as a ringlike
structure, however, is not supported by critical complimentary data in the
fourth quadrant not covered by SDSS. We present stellar density maps from the
Minnesota Automated Plate Scanner (MAPS) Catalog of the POSS I showing that the
overdensity does not extend into the fourth quadrant. The overdensity is most
probably not a ring. It could be due to interaction with the disk bar, evidence
for a triaxial thick disk, or a merger remnant/stream. We call this feature the
Hercules Thick Disk Cloud.Comment: 11 pages, 5 figures, to be published in Astrophysical Journal Letter
D-branes and Strings as Non-commutative Solitons
The non-commutative geometry of a large auxiliary -field simplifies the
construction of D-branes as solitons in open string field theory. Similarly,
fundamental strings are constructed as localized flux tubes in the string field
theory. Tensions are determined exactly using general properties of non-BPS
branes, and the non-Abelian structure of gauge fields on coincident D-branes is
recovered.Comment: 31 pages, 2 figures, harvmac; v2: crucial sign error in vortex
solution corrected, additional comments on electric flux tube, references
adde
Wanted: a strategy to integrate deterrence
Integrated deterrence is a new term in the defence lexicon, introduced by members of the Biden administration to describe a key concept in current U.S. National Security Strategy. This article unpacks this concept by explaining why deterrence is no longer integrated. It identifies the technological, social, and environmental changes that produced this emergent demand for a fundamental assessment of the workings of deterrence today. The concept of deterrence itself, however, does not require reassessment. Rather, the focus here is on applying existing theory to a new strategic setting. The narrative surveys criteria suggested by various authors to guide the process of integration while explaining why some of these ideas are unsuitable as a starting point for integrating deterrence. The article then identifies several themes that should be incorporated into a future deterrence strategy and concludes with some observations about where the task of integrating deterrence might commence
Exact Noncommutative Solitons
We find exact solitons in a large class of noncommutative gauge theories
using a simple solution generating technique. The solitons in the effective
field theory description of open string field theory are interpreted as
D-branes for any value of the noncommutativity. We discuss the vacuum structure
of open string field theory in view of our results.Comment: 23 pages. v3: correction in section 3.
Mapping the Asymmetric Thick Disk I. A Search for Triaxiality
A significant asymmetry in the distribution of faint blue stars in the inner
Galaxy, Quadrant 1 (l = 20 to 45 degrees) compared to Quadrant 4 was first
reported by Larsen & Humphreys (1996). Parker et al (2003, 2004) greatly
expanded the survey to determine its spatial extent and shape and the
kinematics of the affected stars. This excess in the star counts was
subsequently confirmed by Juric et al. (2008) using SDSS data. Possible
explanations for the asymmetry include a merger remnant, a triaxial Thick Disk,
and a possible interaction with the bar in the Disk. In this paper we describe
our program of wide field photometry to map the asymmetry to fainter magnitudes
and therefore larger distances. To search for the signature of triaxiality, we
extended our survey to higher Galactic longitudes. We find no evidence for an
excess of faint blue stars at l > 55 degrees including the faintest magnitude
interval. The asymmetry and star count excess in Quadrant 1 is thus not due to
a triaxial Thick Disk.Comment: 36 pages, 8 figures. Accepted by Astronomical Journa
Mapping the Asymmetric Thick Disk: II Distance, Size and Mass of the Hercules Thick Disk Cloud
The Hercules Thick Disk Cloud (Larsen et al. 2008) was initially discovered
as an excess in the number of faint blue stars between quadrants 1 and 4 of the
Galaxy. The origin of the Cloud could be an interaction with the disk bar, a
triaxial thick disk or a merger remnant or stream. To better map the spatial
extent of the Cloud along the line of sight, we have obtained multi-color UBVR
photometry for 1.2 million stars in 63 fields approximately 1 square degree
each. Our analysis of the fields beyond the apparent boundaries of the excess
have already ruled out a triaxial thick disk as a likely explanation (Larsen,
Humphreys and Cabanela 2010) In this paper we present our results for the star
counts over all of our fields, determine the spatial extent of the over density
across and along the line of sight, and estimate the size and mass of the
Cloud. Using photometric parallaxes, the stars responsible for the excess are
between 1 and 6 kiloparsecs from the Sun, 0.5 -- 4 kpc above the Galactic
plane, and extends approximately 3-4 kiloparsecs across our line of sight. It
is thus a major substructure in the Galaxy. The distribution of the excess
along our sight lines corresponds with the density contours of the bar in the
Disk, and its most distant stars are directly over the bar. We also see through
the Cloud to its far side. Over the entire 500 square degrees of sky containing
the Cloud, we estimate more than 5.6 million stars and 1.9 million solar masses
of material. If the over density is associated with the bar, it would exceed
1.4 billion stars and more than than 50 million solar masses. Finally, we argue
that the Hercules-Aquila Cloud (Belokurov et al. 2007) is actually the Hercules
Thick Disk Cloud.Comment: 52 pages, 13 figure
Strategy and Conventional-Nuclear Integration for the Navy
NPS NRP Executive SummaryThe United States Navy must address how it will integrate conventional and nuclear weapons across the full spectrum of conflict, ranging from non-kinetic, gray zone-type encounters all the way up the escalatory chain to a nuclear exchange. At present the conception of warfare is considered in discrete areas: conventional, chemical, biological, cyber, and nuclear. It is imperative that the Navy develop a coherent conceptual framework that recognizes the linkages between all these domains of warfare. This study will develop a conceptual framework for the Navy to address the integration of conventional and nuclear weapons.N3/N5 - Plans & StrategyThis research is supported by funding from the Naval Postgraduate School, Naval Research Program (PE 0605853N/2098). https://nps.edu/nrpChief of Naval Operations (CNO)Approved for public release. Distribution is unlimited.
Strategy and Conventional-Nuclear Integration for the Navy
NPS NRP Project PosterThe United States Navy must address how it will integrate conventional and nuclear weapons across the full spectrum of conflict, ranging from non-kinetic, gray zone-type encounters all the way up the escalatory chain to a nuclear exchange. At present the conception of warfare is considered in discrete areas: conventional, chemical, biological, cyber, and nuclear. It is imperative that the Navy develop a coherent conceptual framework that recognizes the linkages between all these domains of warfare. This study will develop a conceptual framework for the Navy to address the integration of conventional and nuclear weapons.N3/N5 - Plans & StrategyThis research is supported by funding from the Naval Postgraduate School, Naval Research Program (PE 0605853N/2098). https://nps.edu/nrpChief of Naval Operations (CNO)Approved for public release. Distribution is unlimited.
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