368 research outputs found
Temporal tracking of mineralization and transcriptional developments of shell formation during the early life history of pearl oyster Pinctada maxima
Molluscan larval ontogeny is a highly conserved process comprising three principal developmental stages. A characteristic unique to each of these stages is shell design, termed prodissoconch I, prodissoconch II and dissoconch. These shells vary in morphology, mineralogy and microstructure. The discrete temporal transitions in shell biomineralization between these larval stages are utilized in this study to investigate transcriptional involvement in several distinct biomineralization events. Scanning electron microscopy and X-ray diffraction analysis of P. maxima larvae and juveniles collected throughout post-embryonic ontogenesis, document the mineralogy and microstructure of each shelled stage as well as establishing a timeline for transitions in biomineralization. P. maxima larval samples most representative of these biomineralization distinctions and transitions were analyzed for differential gene expression on the microarray platform PmaxArray 1.0. A number of transcripts are reported as differentially expressed in correlation to the mineralization events of P. maxima larval ontogeny. Some of those isolated are known shell matrix genes while others are novel; these are discussed in relation to potential shell formation roles. This interdisciplinary investigation has linked the shell developments of P. maxima larval ontogeny with corresponding gene expression profiles, furthering the elucidation of shell biomineralization
Global Charges in Chern-Simons theory and the 2+1 black hole
We use the Regge-Teitelboim method to treat surface integrals in gauge
theories to find global charges in Chern-Simons theory. We derive the affine
and Virasoro generators as global charges associated with symmetries of the
boundary. The role of boundary conditions is clarified. We prove that for
diffeomorphisms that do not preserve the boundary there is a classical
contribution to the central charge in the Virasoro algebra. The example of
anti-de Sitter 2+1 gravity is considered in detail.Comment: Revtex, no figures, 26 pages. Important changes introduced. One
section added
Semi-infinite Throat as the End-state Geometry of two-dimensional Black Hole Evaporation
We study a modified two-dimensional dilaton gravity theory which is exactly
solvable in the semiclassical approximation including back-reaction. The vacuum
solutions of this modified theory are asymptotically flat static space-times.
Infalling matter forms a black hole if its energy is above a certain threshold.
The black hole singularity is initially hidden behind a timelike apparent
horizon. As the black hole evaporates by emitting Hawking radiation, the
singularity meets the shrinking horizon in finite retarded time to become
naked. A natural boundary condition exists at the naked singularity such that
for general infalling matter-configuration the evaporating black hole
geometries can be matched continuously to a unique static end-state geometry.
This end-state geometry is asymptotically flat at its right spatial infinity,
while its left spatial infinity is a semi-infinite throat extending into the
strong coupling region.Comment: Tex + compressed uuencoded ps version with one figure included, 11
Touching Random Surfaces and Liouville Gravity
Large matrix models modified by terms of the form g(\Tr\Phi^n)^2
generate random surfaces which touch at isolated points. Matrix model results
indicate that, as is increased to a special value , the string
susceptibility exponent suddenly jumps from its conventional value to
. We study this effect in \L\ gravity and attribute it
to a change of the interaction term from for to
for ( and are the two roots
of the conformal invariance condition for the \L\ dressing of a matter operator
). Thus, the new critical behavior is explained by the unconventional branch
of \L\ dressing in the action.Comment: 15 pages, PUPT-1486 (last paragraph of sec. 2 revised
High Energy Neutrinos from Quasars
We review and clarify the assumptions of our basic model for neutrino
production in the cores of quasars, as well as those modifications to the model
subsequently made by other workers. We also present a revised estimate of the
neutrino background flux and spectrum obtained using more recent empirical
studies of quasars and their evolution. We compare our results with other
thoeretical calculations and experimental upper limits on the AGN neutrino
background flux. We also estimate possible neutrino fluxes from the jets of
blazars detected recently by the EGRET experiment on the Compton Gamma Ray
Observatory. We discuss the theoretical implications of these estimates.Comment: 14 pg., ps file (includes figures), To be published in Space Science
Review
M-Theory as a Holographic Field Theory
We suggest that M-theory could be non-perturbatively equivalent to a local
quantum field theory. More precisely, we present a ``renormalizable'' gauge
theory in eleven dimensions, and show that it exhibits various properties
expected of quantum M-theory, most notably the holographic principle of
't~Hooft and Susskind. The theory also satisfies Mach's principle: A
macroscopically large space-time (and the inertia of low-energy excitations) is
generated by a large number of ``partons'' in the microscopic theory. We argue
that at low energies in large eleven dimensions, the theory should be
effectively described by eleven-dimensional supergravity. This effective
description breaks down at much lower energies than naively expected, precisely
when the system saturates the Bekenstein bound on energy density. We show that
the number of partons scales like the area of the surface surrounding the
system, and discuss how this holographic reduction of degrees of freedom
affects the cosmological constant problem. We propose the holographic field
theory as a candidate for a covariant, non-perturbative formulation of quantum
M-theory.Comment: 27 pp. v2: typos corrected; a small paragraph on naturalness of small
cosmological constant in four dimensions added at end of sect 5.1; final
version to appear in Phys. Rev.
A novel role for Teneurin C-terminal Associated Peptide (TCAP) in the regulation of cardiac activity in the Sydney rock oyster, Saccostrea glomerata
Teneurin C-terminal associated peptide (TCAP) is an ancient bioactive peptide that is highly conserved in metazoans. TCAP administration reduces cellular and behavioural stress in vertebrate and urochordate models, yet despite numerous studies in higher animals, there is limited knowledge of its role in invertebrates. In particular, there are no studies on TCAPâs effects on the heart of any metazoan, which is a critical organ in the stress response. We used the Sydney rock oyster (SRO) as an invertebrate model to investigate a potential role for sroTCAP in regulating cardiac activity, including during stress. sroTCAP is localized to the neural innervation network of the SRO heart, and suggested binding with various heart proteins related to metabolism and stress, including SOD, GAPDH and metabotropic glutamate receptor. Intramuscular injection of sroTCAP (10 pmol) significantly altered the expression of heart genes that are known to regulate remodelling processes under different conditions, and modulated several gene families responsible for stress mitigation. sroTCAP (1 and 10 pmol) was shown to cause transient bradycardia (heart rate was reduced by up to 63% and for up to 40Â min post-administration), indicative of an unstressed state. In summary, this study has established a role for a TCAP in the regulation of cardiac activity through modulation of physiological and molecular components associated with energy conservation, stress and adaptation. This represents a novel function for TCAP and may have implications for higher-order metazoans
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