1,276 research outputs found
Energy Dependence of the Delta Resonance: Chiral Dynamics in Action
There is an important connection between the low energy theorems of QCD and
the energy dependence of the Delta resonance in pi-N scattering, as well as the
closely related gamma^{*} N -> pi N reaction. The resonance shape is due not
only to the strong pi-N interaction in the p wave but the small interaction in
the s wave; the latter is due to spontaneous chiral symmetry breaking in QCD
(i.e. the Nambu-Goldstone nature of the pion). A brief overview of experimental
tests of chiral perturbation theory and chiral based models is presentedComment: 11 pages, 6 figures, Festschrift for S.N. yan
Background risk of breast cancer and the association between physical activity and mammographic density
This work is licensed under a Creative Commons Attribution 4.0
International License. The images or other third party material in this
article are included in the article’s Creative Commons license, unless indicated
otherwise in the credit line; if the material is not included under the Creative Commons
license, users will need to obtain permission from the license holder to reproduce the
material. To view a copy of this license, visit http://creativecommons.org/licenses/
by/4.0
A holographic model for the fractional quantum Hall effect
Experimental data for fractional quantum Hall systems can to a large extent
be explained by assuming the existence of a modular symmetry group commuting
with the renormalization group flow and hence mapping different phases of
two-dimensional electron gases into each other. Based on this insight, we
construct a phenomenological holographic model which captures many features of
the fractional quantum Hall effect. Using an SL(2,Z)-invariant
Einstein-Maxwell-axio-dilaton theory capturing the important modular
transformation properties of quantum Hall physics, we find dyonic diatonic
black hole solutions which are gapped and have a Hall conductivity equal to the
filling fraction, as expected for quantum Hall states. We also provide several
technical results on the general behavior of the gauge field fluctuations
around these dyonic dilatonic black hole solutions: We specify a sufficient
criterion for IR normalizability of the fluctuations, demonstrate the
preservation of the gap under the SL(2,Z) action, and prove that the
singularity of the fluctuation problem in the presence of a magnetic field is
an accessory singularity. We finish with a preliminary investigation of the
possible IR scaling solutions of our model and some speculations on how they
could be important for the observed universality of quantum Hall transitions.Comment: 86 pages, 16 figures; v.2 references added, typos fixed, improved
discussion of ref. [39]; v.3 more references added and typos fixed, several
statements clarified, v.4 version accepted for publication in JHE
Distributed Synthesis in Continuous Time
We introduce a formalism modelling communication of distributed agents
strictly in continuous-time. Within this framework, we study the problem of
synthesising local strategies for individual agents such that a specified set
of goal states is reached, or reached with at least a given probability. The
flow of time is modelled explicitly based on continuous-time randomness, with
two natural implications: First, the non-determinism stemming from interleaving
disappears. Second, when we restrict to a subclass of non-urgent models, the
quantitative value problem for two players can be solved in EXPTIME. Indeed,
the explicit continuous time enables players to communicate their states by
delaying synchronisation (which is unrestricted for non-urgent models). In
general, the problems are undecidable already for two players in the
quantitative case and three players in the qualitative case. The qualitative
undecidability is shown by a reduction to decentralized POMDPs for which we
provide the strongest (and rather surprising) undecidability result so far
Extragalactic Globular Clusters and Galaxy Formation
Globular cluster (GC) systems have now been studied in galaxies ranging from
dwarfs to giants and spanning the full Hubble sequence of morphological types.
Imaging and spectroscopy with the Hubble Space Telescope and large ground-based
telescopes have together established that most galaxies have bimodal color
distributions that reflect two subpopulations of old GCs: metal-poor and
metal-rich. The characteristics of both subpopulations are correlated with
those of their parent galaxies. We argue that metal-poor GCs formed in low-mass
dark matter halos in the early universe and that their properties reflect
biased galaxy assembly. The metal-rich GCs were born in the subsequent
dissipational buildup of their parent galaxies and their ages and abundances
indicate that most massive early-type galaxies formed the bulk of their stars
at early times. Detailed studies of both subpopulations offer some of the
strongest constraints on hierarchical galaxy formation that can be obtained in
the near-field.Comment: 74 pages, including 14 figures. In press for Annual Reviews of
Astronomy and Astrophysic
The formation of professional identity in medical students: considerations for educators
<b>Context</b> Medical education is about more than acquiring an appropriate level of knowledge and developing relevant skills. To practice medicine students need to develop a professional identity – ways of being and relating in professional contexts.<p></p>
<b>Objectives</b> This article conceptualises the processes underlying the formation and maintenance of medical students’ professional identity drawing on concepts from social psychology.<p></p>
<b>Implications</b> A multi-dimensional model of identity and identity formation, along with the concepts of identity capital and multiple identities, are presented. The implications for educators are discussed.<p></p>
<b>Conclusions</b> Identity formation is mainly social and relational in nature. Educators, and the wider medical society, need to utilise and maximise the opportunities that exist in the various relational settings students experience. Education in its broadest sense is about the transformation of the self into new ways of thinking and relating. Helping students form, and successfully integrate their professional selves into their multiple identities, is a fundamental of medical education
Ultraviolet Irradiation Induces the Accumulation of Chondroitin Sulfate, but Not Other Glycosaminoglycans, in Human Skin
Ultraviolet (UV) light alters cutaneous structure and function. Prior work has shown loss of dermal hyaluronan after UV-irradiation of human skin, yet UV exposure increases total glycosaminoglycan (GAG) content in mouse models. To more fully describe UV-induced alterations to cutaneous GAG content, we subjected human volunteers to intermediate-term (5 doses/week for 4 weeks) or single-dose UV exposure. Total dermal uronyl-containing GAGs increased substantially with each of these regimens. We found that UV exposure substantially increased dermal content of chondroitin sulfate (CS), but not hyaluronan, heparan sulfate, or dermatan sulfate. UV induced the accumulation of both the 4-sulfated (C4S) and 6-sulfated (C6S) isoforms of CS, but in distinct distributions. Next, we examined several CS proteoglycan core proteins and found a significant accumulation of dermal and endothelial serglycin, but not of decorin or versican, after UV exposure. To examine regulation in vitro, we found that UVB in combination with IL-1α, a cytokine upregulated by UV radiation, induced serglycin mRNA in cultured dermal fibroblasts, but did not induce the chondroitin sulfate synthases. Overall, our data indicate that intermediate-term and single-dose UVB exposure induces specific GAGs and proteoglycan core proteins in human skin in vivo. These molecules have important biologic functions and contribute to the cutaneous response to UV
- …