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The petrology of fine-grained micrometeorites: Evidence for the diversity of primitive asteroids
We report the discovery by analytical TEM of serpentine and phases interpreted as dehydroxylates of serpentine in ultramicrotomed sections of a number of fine-grained Antarctic micrometeorites
Tectonic evolution of the Plymouth Bay Basin
A synthesis of offshore seismic data in the Plymouth Bay and Western Approaches, and onshore basement structures and mineralisation history has allowed new constraints to be placed on the structural evolution of the late Carboniferous- Triassic Plymouth Bay Basin. These data have been combined to produce a model for the late- and post- Variscan tectonics of the Plymouth Bay area. Additional controls on the timing and magnitude of Variscan uplift and late-Variscan low-angle extensional deformation onshore are used to infer a late Carboniferous age for the earliest basin fill. These sediments were accommodated in a northeast — south-west oriented basin formed during late-orogenic extension. A change in the orientation of the depocentre in the early Permian signalled a switch to a north-west — south-east, strike-slip dominated tectonic environment
Mission Concept for the Single Aperture Far-Infrared (SAFIR) Observatory
The Single Aperture Far-InfraRed (SAFIR) Observatory's science goals are
driven by the fact that the earliest stages of almost all phenomena in the
universe are shrouded in absorption by and emission from cool dust and gas that
emits strongly in the far-infrared and submillimeter. Over the past several
years, there has been an increasing recognition of the critical importance of
this spectral region to addressing fundamental astrophysical problems, ranging
from cosmological questions to understanding how our own Solar System came into
being. The development of large, far-infrared telescopes in space has become
more feasible with the combination of developments for the James Webb Space
Telescope and of enabling breakthroughs in detector technology. We have
developed a preliminary but comprehensive mission concept for SAFIR, as a 10
m-class far-infrared and submillimeter observatory that would begin development
later in this decade to meet the needs outlined above. Its operating
temperature (<4K) and instrument complement would be optimized to reach the
natural sky confusion limit in the far-infrared with diffraction-limited
peformance down to at least 40 microns. This would provide a point source
sensitivity improvement of several orders of magnitude over that of Spitzer or
Herschel, with finer angular resolution, enabling imaging and spectroscopic
studies of individual galaxies in the early universe. We have considered many
aspects of the SAFIR mission, including the telescope technology, detector
needs and technologies, cooling method and required technology developments,
attitude and pointing, power systems, launch vehicle, and mission operations.
The most challenging requirements for this mission are operating temperature
and aperture size of the telescope, and the development of detector arrays.Comment: 36 page
Four Dimensional String/String/String Triality
In six spacetime dimensions, the heterotic string is dual to a Type
string. On further toroidal compactification to four spacetime dimensions, the
heterotic string acquires an SL(2,\BbbZ)_S strong/weak coupling duality and
an SL(2,\BbbZ)_T \times SL(2,\BbbZ)_U target space duality acting on the
dilaton/axion, complex Kahler form and the complex structure fields
respectively. Strong/weak duality in interchanges the roles of and
in yielding a Type string with fields . This suggests
the existence of a third string (whose six-dimensional interpretation is more
obscure) that interchanges the roles of and . It corresponds in fact to
a Type string with fields leading to a four-dimensional
string/string/string triality. Since SL(2,\BbbZ)_S is perturbative for the
Type string, this triality implies -duality for the heterotic
string and thus fills a gap left by duality. For all three strings the
total symmetry is SL(2,\BbbZ)_S \times O(6,22;\BbbZ)_{TU}. The
O(6,22;\BbbZ) is {\it perturbative} for the heterotic string but contains the
conjectured {\it non-perturbative} SL(2,\BbbZ)_X, where is the complex
scalar of the Type string. Thus four-dimensional triality also
provides a (post-compactification) justification for this conjecture. We
interpret the Bogomol'nyi spectrum from all three points of view. In
particular we generalize the Sen-Schwarz formula for short multiplets to
include intermediate multiplets also and discuss the corresponding black hole
spectrum both for the theory and for a truncated ---- symmetric
theory. Just as the first two strings are described by the
four-dimensional {\it elementary} and {\it dual solitonic} solutions, so theComment: 36 pages, Latex, 2 figures, some references changed, minor changes in
formulas and tables; to appear in Nucl. Phys.
Expression of Adhesion Molecules during Tooth Resorption in Feline Teeth: A Model System for Aggressive Osteoclastic Activity
Tooth resorption, a common feline dental problem, is often initiated at the cemento-enamel junction and hence is called cat 'neck' lesion. Studies have demonstrated that osteoclasts/odontoclasts are increased and activated at resorption sites, and that areas of resorption are partly repaired by formation of tissues resembling bone, cementum, and possibly dentin. However, the cellular/molecular mechanisms/factors involved in resorption and repair are unknown. In this study of tissues from cats with 'neck' lesions, we used specific antibodies and immunohistochemical analyses to examine adhesion molecules associated with mineralized tissues, bone sialoprotein (BSP) and osteopontin (OPN), and a cell-surface receptor linked with these molecules, α vβ3, for their localization in these lesions. In addition, to determine general cellular activity during repair, we performed in situ hybridization using a type I collagen riboprobe. Results showed OPN localized to resorption fronts and reversal lines, while BSP was localized to reversal lines. However, some osteoclasts and odontoblasts "sat" on mineralized surfaces not associated with OPN. The cell-surface receptor, αvβ 3, was localized to surfaces of osteoclasts/odontoclasts. Type I collagen mRNA was expressed where osteoblasts attempted to repair mineralized tissue. In contrast, odontoblasts did not express mRNA for type I collagen. This study suggests that osteoclastic resorption is the predominant activity in 'neck' lesions and that this activity was accompanied, at least in part, by increased concentrations of OPN and an associated integrin, α vβ3, at resorption sites. Lack of collagen expression by odontoblasts indicates that odontoblasts do not play an active role in attempts at repair.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66661/2/10.1177_00220345960750090601.pd
Classical and Thermodynamic Stability of Black Branes
It is argued that many non-extremal black branes exhibit a classical
Gregory-Laflamme instability if, and only if, they are locally
thermodynamically unstable. For some black branes, the Gregory-Laflamme
instability must therefore disappear near extremality. For the black -branes
of the type II supergravity theories, the Gregory-Laflamme instability
disappears near extremality for but persists all the way down to
extremality for (the black D3-brane is not covered by the analysis of
this paper). This implies that the instability also vanishes for the
near-extremal black M2 and M5-brane solutions.Comment: 21 pages, LaTeX. v2: Various points clarified, typos corrected and
reference adde
Solitonic Strings and BPS Saturated Dyonic Black Holes
We consider a six-dimensional solitonic string solution described by a
conformal chiral null model with non-trivial superconformal transverse
part. It can be interpreted as a five-dimensional dyonic solitonic string wound
around a compact fifth dimension. The conformal model is regular with the
short-distance (`throat') region equivalent to a WZW theory. At distances
larger than the compactification scale the solitonic string reduces to a dyonic
static spherically-symmetric black hole of toroidally compactified heterotic
string. The new four-dimensional solution is parameterised by five charges,
saturates the Bogomol'nyi bound and has nontrivial dilaton-axion field and
moduli fields of two-torus. When acted by combined T- and S-duality
transformations it serves as a generating solution for all the static
spherically-symmetric BPS-saturated configurations of the low-energy heterotic
string theory compactified on six-torus. Solutions with regular horizons have
the global space-time structure of extreme Reissner-Nordstrom black holes with
the non-zero thermodynamic entropy which depends only on conserved (quantised)
charge vectors. The independence of the thermodynamic entropy on moduli and
axion-dilaton couplings strongly suggests that it should have a microscopic
interpretation as counting degeneracy of underlying string configurations. This
interpretation is supported by arguments based on the corresponding
six-dimensional conformal field theory. The expression for the level of the WZW
theory describing the throat region implies a renormalisation of the string
tension by a product of magnetic charges, thus relating the entropy and the
number of oscillations of the solitonic string in compact directions.Comment: 27 Pages, uses RevTeX (solution for the axion field corrected,
erratum to appear in Phys. Rev. D
The Octonionic Membrane
We generalize the supermembrane solution of D=11 supergravity by permitting
the 4-form to be either self-dual or anti-self-dual in the eight dimensions
transverse to the membrane. After analyzing the supergravity field equations
directly, and also discussing necessary conditions for unbroken supersymmetry,
we focus on two specific, related solutions. The self-dual solution is not
asymptotically flat. The anti-self-dual solution is asymptotically flat, has
finite mass per unit area and saturates the same mass=charge Bogomolnyi bound
as the usual supermembrane. Nevertheless, neither solution preserves any
supersymmetry. Both solutions involve the octonionic structure constants but,
perhaps surprisingly, they are unrelated to the octonionic instanton 2-form
, for which is neither self-dual nor anti-self-dual.Comment: 17 pages, Latex; enhanced discussion on supersymmetry, some
references adde
Open Heterotic Strings
We classify potential cosmic strings according to the topological charge
measurable outside the string core. We conjecture that in string theory it is
this charge that governs the stability of long strings. This would imply that
the SO(32) heterotic string can have endpoints, but not the E_8 x E_8 heterotic
string. We give various arguments in support of this conclusion.Comment: 15 pages. v.2: typos, references correcte
Gauge Dyonic Strings and Their Global Limit
We show that six-dimensional supergravity coupled to tensor and Yang-Mills
multiplets admits not one but two different theories as global limits, one of
which was previously thought not to arise as a global limit and the other of
which is new. The new theory has the virtue that it admits a global
anti-self-dual string solution obtained as the limit of the curved-space gauge
dyonic string, and can, in particular, describe tensionless strings. We
speculate that this global model can also represent the worldvolume theory of
coincident branes. We also discuss the Bogomol'nyi bounds of the gauge dyonic
string and show that, contrary to expectations, zero eigenvalues of the
Bogomol'nyi matrix do not lead to enhanced supersymmetry and that negative
tension does not necessarily imply a naked singularity.Comment: Latex, 22 pages, References added and discussion altere
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