841 research outputs found
Chiral-symmetry restoration in the linear sigma model at nonzero temperature and baryon density
We study the chiral phase transition in the linear sigma model with 2 quark
flavors and colors. One-loop calculations predict a first-order phase
transition at both and . We also discuss the phase diagram
and make a comparison with a thermal parametrization of existing heavy-ion
experimental data.Comment: 12 pages, 6 ps-figures, LaTe
On the Quantum Computational Complexity of the Ising Spin Glass Partition Function and of Knot Invariants
It is shown that the canonical problem of classical statistical
thermodynamics, the computation of the partition function, is in the case of
+/-J Ising spin glasses a particular instance of certain simple sums known as
quadratically signed weight enumerators (QWGTs). On the other hand it is known
that quantum computing is polynomially equivalent to classical probabilistic
computing with an oracle for estimating QWGTs. This suggests a connection
between the partition function estimation problem for spin glasses and quantum
computation. This connection extends to knots and graph theory via the
equivalence of the Kauffman polynomial and the partition function for the Potts
model.Comment: 8 pages, incl. 2 figures. v2: Substantially rewritte
Star cluster formation and evolution in Mrk 930: properties of a metal-poor starburst
We present a HST multiband analysis of the large population of star clusters
in the blue compact galaxy (BCG) Mrk 930. We have reconstructed the spectral
energy distributions of the star clusters and estimated age, mass, and
extinction for a representative sample. We observe a very young cluster
population with 70% of the systems formed less than 10 Myr ago. The peak in the
star cluster age distribution at 4 Myr is corroborated by the presence of
Wolf-Rayet spectral features, and by the observed optical and IR lines ratios
[OIII]/H_beta and [NeIII]/[NeII]. The recovered extinction in these very young
clusters shows large variations, with a decrease at older ages. It is likely
that our analysis is limited to the optically brightest objects (i.e. systems
only partially embedded in their natal cocoons). We map the extinction across
the galaxy using low-resolution spectra and the H_alpha/H_beta ratio, as
obtained from ground-based narrow band imaging. We find that the mean optical
extinction derived in the starburst regions is close to the averaged value
observed in the clusters, but locally, do not trace the more extinguished
clusters. Previous HST studies of BCGs have revealed a population of young and
extremely red super star clusters. We detect a considerable fraction of
clusters affected by a red excess also in Mrk 930. The nature of the red
excess, which turns up at near-IR wavelengths remains unknown. We compare the
cluster and the star formation history, the latter derived from the fit of
spectral population synthesis models to the spectra. We find a general
agreement between the two independently estimated quantities. Using the cluster
properties we perform a study of the host environmental properties. We find
that the cluster formation efficiency is significantly higher, suggesting a key
role of the environment for the formation of these massive objects.[Abridged]Comment: 21 pages, 16 figures, accepted for publication in MNRAS. For
high-resolution figures ask the author
Male reproductive health and environmental xenoestrogens
EHP is a publication of the U.S. government. Publication of EHP lies in the public domain and is therefore without copyright.
Research articles from EHP may be used freely; however, articles from the News section of EHP may contain photographs or figures copyrighted by other commercial organizations and individuals that may not be used without obtaining prior approval from both the EHP editors and the holder of the copyright.
Use of any materials published in EHP should be acknowledged (for example, "Reproduced with permission from Environmental Health Perspectives") and a reference provided for the article from which the material was reproduced.Male reproductive health has deteriorated in many countries during the last few decades. In the 1990s, declining semen quality has been reported from Belgium, Denmark, France, and Great Britain. The incidence of testicular cancer has increased during the same time incidences of hypospadias and cryptorchidism also appear to be increasing. Similar reproductive problems occur in many wildlife species. There are marked geographic differences in the prevalence of male reproductive disorders. While the reasons for these differences are currently unknown, both clinical and laboratory research suggest that the adverse changes may be inter-related and have a common origin in fetal life or childhood. Exposure of the male fetus to supranormal levels of estrogens, such as diethlylstilbestrol, can result in the above-mentioned reproductive defects. The growing number of reports demonstrating that common environmental contaminants and natural factors possess estrogenic activity presents the working hypothesis that the adverse trends in male reproductive health may be, at least in part, associated with exposure to estrogenic or other hormonally active (e.g., antiandrogenic) environmental chemicals during fetal and childhood development. An extensive research program is needed to understand the extent of the problem, its underlying etiology, and the development of a strategy for prevention and intervention.Supported by EU Contract BMH4-CT96-0314
Strange metals and the AdS/CFT correspondence
I begin with a review of quantum impurity models in condensed matter physics,
in which a localized spin degree of freedom is coupled to an interacting
conformal field theory in d = 2 spatial dimensions. Their properties are
similar to those of supersymmetric generalizations which can be solved by the
AdS/CFT correspondence; the low energy limit of the latter models is described
by a AdS2 geometry. Then I turn to Kondo lattice models, which can be described
by a mean- field theory obtained by a mapping to a quantum impurity coupled to
a self-consistent environment. Such a theory yields a 'fractionalized Fermi
liquid' phase of conduction electrons coupled to a critical spin liquid state,
and is an attractive mean-field theory of strange metals. The recent
holographic description of strange metals with a AdS2 x R2 geometry is argued
to be related to such mean-field solutions of Kondo lattice models.Comment: 19 pages, 4 figures; Plenary talk at Statphys24, Cairns, Australia,
July 2010; (v2) added refs; (v3) more ref
Multiscale Feature Analysis of Salivary Gland Branching Morphogenesis
Pattern formation in developing tissues involves dynamic spatio-temporal changes in cellular organization and subsequent evolution of functional adult structures. Branching morphogenesis is a developmental mechanism by which patterns are generated in many developing organs, which is controlled by underlying molecular pathways. Understanding the relationship between molecular signaling, cellular behavior and resulting morphological change requires quantification and categorization of the cellular behavior. In this study, tissue-level and cellular changes in developing salivary gland in response to disruption of ROCK-mediated signaling by are modeled by building cell-graphs to compute mathematical features capturing structural properties at multiple scales. These features were used to generate multiscale cell-graph signatures of untreated and ROCK signaling disrupted salivary gland organ explants. From confocal images of mouse submandibular salivary gland organ explants in which epithelial and mesenchymal nuclei were marked, a multiscale feature set capturing global structural properties, local structural properties, spectral, and morphological properties of the tissues was derived. Six feature selection algorithms and multiway modeling of the data was performed to identify distinct subsets of cell graph features that can uniquely classify and differentiate between different cell populations. Multiscale cell-graph analysis was most effective in classification of the tissue state. Cellular and tissue organization, as defined by a multiscale subset of cell-graph features, are both quantitatively distinct in epithelial and mesenchymal cell types both in the presence and absence of ROCK inhibitors. Whereas tensor analysis demonstrate that epithelial tissue was affected the most by inhibition of ROCK signaling, significant multiscale changes in mesenchymal tissue organization were identified with this analysis that were not identified in previous biological studies. We here show how to define and calculate a multiscale feature set as an effective computational approach to identify and quantify changes at multiple biological scales and to distinguish between different states in developing tissues
Young Star Cluster Complexes in NGC 4038/39: Integral field spectroscopy using VIMOS-VLT
We present the first results of a survey to obtain Integral Field
Spectroscopy of merging galaxies along the Toomre Sequence. In the present
work, we concentrate on the star cluster complexes in the Antennae galaxies
(NGC 4038/39) in the overlap region as well as the nuclear region of NGC 4038.
Using optical spectroscopy we derive the extinction age, metallicity, velocity,
velocity dispersion of the gas and star formation rate for each of the eight
complexes detected. We supplement this study with archival HST-WFPC2 U, B, V,
H, and I band imaging. Correcting the observed colours of the star
clusters within the complexes for extinction, measured through our optical
spectra, we compare the clusters with simple stellar population models, with
which we find an excellent agreement. In five of the complexes we detect strong
Wolf-Rayet emission features, indicating young ages (3-5 Myr). The ionized gas
surrounding the complexes is expanding at speeds of 20-40 km/s. This slow
expansion can be understood as a bubble, caused by the stellar winds and
supernovae within the complexes, expanding into the remnant of the progenitor
giant molecular cloud. We also find that the complexes themselves are grouped,
at about the largest scale of which young star clusters are correlated,
representing the largest coherent star forming region. We show that the area
normalized star formation rates of these complexes clearly place them in the
regime of star forming regions in starburst galaxies, thereby justifying the
label of localized starbursts. Finally, we estimate the stability of the
complexes, and find that they will probably loose a large fraction of their
mass to the surrounding environment, although the central regions may merge
into a single large star cluster.Comment: 14 pages, accepted A&A. A high-resolution pdf version of the paper
can be found at http://www.star.ucl.ac.uk/~bastian/bastian-vimos.pd
MAPK Kinase Kinase-1 Is Essential for Cytokine-Induced c-Jun NH2-Terminal Kinase and Nuclear Factor-κB Activation in Human Pancreatic Islet Cells
OBJECTIVE—The transcription factor nuclear factor-κB (NF-κB) and the mitogen-activated protein kinases (MAPKs) c-Jun NH2-terminal kinase (JNK) 1/2 are known to play decisive roles in cytokine-induced damage of rodent β-cells. The upstream events by which these factors are activated in response to cytokines are, however, uncharacterized. The aim of the present investigation was to elucidate a putative role of the MAPK kinase kinase-1 (MEKK-1) in cytokine-induced signaling
- …