2,501 research outputs found
Connexins and pannexins in the skeleton: gap junctions, hemichannels and more
Regulation of bone homeostasis depends on the concerted actions of bone-forming osteoblasts and bone-resorbing osteoclasts, controlled by osteocytes, cells derived from osteoblasts surrounded by bone matrix. The control of differentiation, viability and function of bone cells relies on the presence of connexins. Connexin43 regulates the expression of genes required for osteoblast and osteoclast differentiation directly or by changing the levels of osteocytic genes, and connexin45 may oppose connexin43 actions in osteoblastic cells. Connexin37 is required for osteoclast differentiation and its deletion results in increased bone mass. Less is known on the role of connexins in cartilage, ligaments and tendons. Connexin43, connexin45, connexin32, connexin46 and connexin29 are expressed in chondrocytes, while connexin43 and connexin32 are expressed in ligaments and tendons. Similarly, although the expression of pannexin1, pannexin2 and pannexin3 has been demonstrated in bone and cartilage cells, their function in these tissues is not fully understood
X-ray and Multiwavelength Insights into the Nature of Weak Emission-Line Quasars at Low Redshift
(Abridged) We report on the X-ray and multiwavelength properties of 11
radio-quiet quasars with weak or no emission lines identified by the Sloan
Digital Sky Survey (SDSS) with redshift z=0.4-2.5. The distribution of relative
X-ray brightness for our low-redshift weak-line quasar (WLQ) candidates is
significantly different from that of typical radio-quiet quasars, having an
excess of X-ray weak sources, but it is consistent with that of high-redshift
WLQs. The X-ray weak sources generally show similar UV emission-line properties
to those of the X-ray weak quasar PHL 1811; they may belong to the notable
class of PHL 1811 analogs. The average X-ray spectrum of these sources is
somewhat harder than that of typical radio-quiet quasars. Several other
low-redshift WLQ candidates have normal ratios of X-ray-to-optical/UV flux, and
their average X-ray spectral properties are also similar to those of typical
radio-quiet quasars. The X-ray weak and X-ray normal WLQ candidates may belong
to the same subset of quasars having high-ionization "shielding gas" covering
most of the wind-dominated broad emission-line region, but be viewed at
different inclinations. The mid-infrared-to-X-ray spectral energy distributions
(SEDs) of these sources are generally consistent with those of typical SDSS
quasars, showing that they are not likely to be BL Lac objects with
relativistically boosted continua and diluted emission lines. However, one
source in our X-ray observed sample is remarkably strong in X-rays, indicating
that a small fraction of low-redshift WLQ candidates may actually be BL Lacs
residing in the radio-faint tail of the BL Lac population. We also investigate
universal selection criteria for WLQs over a wide range of redshift, finding
that it is not possible to select WLQ candidates in a fully consistent way
using different prominent emission lines as a function of redshift.Comment: ApJ in press; 26 pages, 11 figures and 7 tables. The full Table 3 is
available upon reques
Heteropolymer Sequence Design and Preferential Solvation of Hydrophilic Monomers: One More Application of Random Energy Model
In this paper, we study the role of surface of the globule and the role of
interactions with the solvent for designed sequence heteropolymers using random
energy model (REM). We investigate the ground state energy and surface monomer
composition distribution. By comparing the freezing transition in random and
designed sequence heteropolymers, we discuss the effects of design. Based on
our results, we are able to show under which conditions solvation effect
improves the quality of sequence design. Finally, we study sequence space
entropy and discuss the number of available sequences as a function of imposed
requirements for the design quality
The Ultraviolet-to-Mid-Infrared Spectral Energy Distribution of Weak Emission Line Quasars
We present Spitzer Space Telescope photometry of 18 Sloan Digital Sky Survey
(SDSS) quasars at 2.7 <= z <= 5.9 which have weak or undetectable
high-ionization emission lines in their rest-frame ultraviolet (UV) spectra
(hereafter weak-lined quasars, or WLQs). The Spitzer data are combined with
SDSS spectra and ground-based, near-infrared (IR) photometry of these sources
to produce a large inventory of spectral energy distributions (SEDs) of WLQs
across the rest-frame ~0.1-5 mum spectral band. The SEDs of our sources are
inconsistent with those of BL Lacertae objects which are dominated by
synchrotron emission due to a jet aligned close to our line-of-sight, but are
consistent with the SED of ordinary quasars with similar luminosities and
redshifts that exhibit a near-to-mid-IR 'bump', characteristic of hot dust
emission. This indicates that broad emission lines in WLQs are intrinsically
weak, rather than suffering continuum dilution from a jet, and that such
sources cannot be selected efficiently from traditional photometric surveys.Comment: 10 pages (emulateapj), 4 figures. Accepted for publication in Ap
Preventing Successor Liability for Defective Products: Safeguards for Acquiring Corporations
In recent years, many courts have determined longstanding limitations on successor liability to be insufficiently sensitive to the compensation needs of products liability claimants. In response, courts in several jurisdictions have eroded traditional corporate law immunities to successor liability for defective products. Although this liberalization of the principles of successor liability has expanded the range of potential defendants in many tort lawsuits, the expansion of liability has caused an increase in uncertainty in corporate transactions, and an increase in complex legal and logistical maneuvering to avoid the growing liability web. This Article seeks to outline the expansion of successor liability in the products area, note the negative implications of that expansion, and identify mechanisms to prevent the attachment of successor liability under both the traditional and expanded regimes. The Article also prescribes a statutory alternative to create much needed stability and certainty in this area through a straightforward allocation of liabilities between purchasers and sellers
Sound and complete axiomatizations of coalgebraic language equivalence
Coalgebras provide a uniform framework to study dynamical systems, including
several types of automata. In this paper, we make use of the coalgebraic view
on systems to investigate, in a uniform way, under which conditions calculi
that are sound and complete with respect to behavioral equivalence can be
extended to a coarser coalgebraic language equivalence, which arises from a
generalised powerset construction that determinises coalgebras. We show that
soundness and completeness are established by proving that expressions modulo
axioms of a calculus form the rational fixpoint of the given type functor. Our
main result is that the rational fixpoint of the functor , where is a
monad describing the branching of the systems (e.g. non-determinism, weights,
probability etc.), has as a quotient the rational fixpoint of the
"determinised" type functor , a lifting of to the category of
-algebras. We apply our framework to the concrete example of weighted
automata, for which we present a new sound and complete calculus for weighted
language equivalence. As a special case, we obtain non-deterministic automata,
where we recover Rabinovich's sound and complete calculus for language
equivalence.Comment: Corrected version of published journal articl
A systematically coarse-grained model for DNA, and its predictions for persistence length, stacking, twist, and chirality
We introduce a coarse-grained model of DNA with bases modeled as rigid-body
ellipsoids to capture their anisotropic stereochemistry. Interaction potentials
are all physicochemical and generated from all-atom simulation/parameterization
with minimal phenomenology. Persistence length, degree of stacking, and twist
are studied by molecular dynamics simulation as functions of temperature, salt
concentration, sequence, interaction potential strength, and local position
along the chain, for both single- and double-stranded DNA where appropriate.
The model of DNA shows several phase transitions and crossover regimes in
addition to dehybridization, including unstacking, untwisting, and collapse
which affect mechanical properties such as rigidity and persistence length. The
model also exhibits chirality with a stable right-handed and metastable
left-handed helix.Comment: 30 pages, 20 figures, Supplementary Material available at
http://www.physics.ubc.ca/~steve/publications.htm
- …