26,214 research outputs found
Open clusters in AurOB2
We study the area around the HII region Sh 2-234, including the young open
cluster Stock 8, to investigate the extent and definition of the association
Aur OB2 and the possible role of triggering in massive cluster formation. We
obtained Str\"omgren and J,H,Ks photometry for Stock 8 and Str\"omgren
photometry for two other cluster candidates in the area, which we confirm as
young open clusters and name Alicante 11 and Alicante 12. We took spectroscopy
of 33 early-type stars in the area, including the brightest cluster members. We
calculate a common distance of kpc for the three open
clusters and surrounding association. We derive an age 4-6 Ma for Stock 8, and
do not find a significantly different age for the other clusters or the
association. The star LSV +34 23, with spectral type O8 II(f), is likely the
main source of ionization of Sh 2-234. We observe an important population of
pre-main sequence stars, some of them with disks, associated with the B-type
members lying on the main-sequence. We interpret the region as an area of
recent star formation with some residual and very localized ongoing star
formation. We do not find evidence for sequential star formation on a large
scale. The classical definition of Aur OB2 has to be reconsidered, because its
two main open clusters, Stock 8 and NGC 1893, are not at the same distance.
Stock 8 is probably located in the Perseus arm, but other nearby HII regions
whose distances also place them in this arm show quite different distances and
radial velocities and, therefore, are not connected.Comment: 29 pages, 17 figures Accepted for publication in MNRA
Electron density distribution and screening in rippled graphene sheets
Single-layer graphene sheets are typically characterized by long-wavelength
corrugations (ripples) which can be shown to be at the origin of rather strong
potentials with both scalar and vector components. We present an extensive
microscopic study, based on a self-consistent Kohn-Sham-Dirac
density-functional method, of the carrier density distribution in the presence
of these ripple-induced external fields. We find that spatial density
fluctuations are essentially controlled by the scalar component, especially in
nearly-neutral graphene sheets, and that in-plane atomic displacements are as
important as out-of-plane ones. The latter fact is at the origin of a
complicated spatial distribution of electron-hole puddles which has no evident
correlation with the out-of-plane topographic corrugations. In the range of
parameters we have explored, exchange and correlation contributions to the
Kohn-Sham potential seem to play a minor role.Comment: 13 pages, 13 figures, submitted. High-quality figures can be
requested to the author
Diagnosis and management of treatment-refractory hypothyroidism: an expert consensus report
There is a frequently encountered subset of hypothyroid patients who are refractory to standard thyroid hormone replacement treatment and require unexpectedly high doses of levothyroxine. In addition to clinical situations where hypothyroid patients are non-compliant, or where there is the possibility of excipient-induced disease exacerbation (gluten/celiac disease), therapeutic failure may be due to impaired absorption of the administered drug. The common approach to managing patients with unusual thyroxine needs is to escalate the dose of levothyroxine until targeted TSH levels are achieved. This approach can increase the risk for prolonged exposure to supratherapeutic doses of levothyroxine, which increase the chances of adverse outcomes. Repeated adjustments of levothyroxine can also escalate the costs of treatment, as frequent office visits and laboratory tests are required to determine and maintain the desired dose. Clinicians should take a systematic approach to managing patients whom they suspect of having treatment-refractory hypothyroidism. This may include searching for, and adjusting, occult medical conditions and/or other factors that may affect the absorption of levothyroxine, before up-titrating the dose of traditional levothyroxine therapy. Depending on the underlying pathology, another approach that may be considered is to try alternative formulations of levothyroxine that are less susceptible to intolerance issues related to excipients, or, in some cases, to malabsorption. The early discovery of these factors via a thoughtful patient work-up may avoid unnecessary thyroid medication adjustments and their consequences for both patients and clinicians
Spectrum in the broken phase of a theory
We derive the spectrum in the broken phase of a theory, in
the limit , showing that this goes as even integers of a
renormalized mass in agreement with recent lattice computations.Comment: 4 pages, 1 figure. Accepted for publication in International Journal
of Modern Physics
On Integrability of spinning particle motion in higher-dimensional black hole spacetimes
We study the motion of a classical spinning particle (with spin degrees of
freedom described by a vector of Grassmann variables) in higher-dimensional
general rotating black hole spacetimes with a cosmological constant. In all
dimensions n we exhibit n bosonic functionally independent integrals of
spinning particle motion, corresponding to explicit and hidden symmetries
generated from the principal conformal Killing--Yano tensor. Moreover, we
demonstrate that in 4-, 5-, 6-, and 7-dimensional black hole spacetimes such
integrals are in involution, proving the bosonic part of the motion integrable.
We conjecture that the same conclusion remains valid in all higher dimensions.
Our result generalizes the result of Page et. al. [hep-th/0611083] on complete
integrability of geodesic motion in these spacetimes.Comment: Version 2: revised version, added references. 5 pages, no figure
Recurrence for persistent random walks in two dimensions
We discuss the question of recurrence for persistent, or Newtonian, random
walks in Z^2, i.e., random walks whose transition probabilities depend both on
the walker's position and incoming direction. We use results by Toth and
Schmidt-Conze to prove recurrence for a large class of such processes,
including all "invertible" walks in elliptic random environments. Furthermore,
rewriting our Newtonian walks as ordinary random walks in a suitable graph, we
gain a better idea of the geometric features of the problem, and obtain further
examples of recurrence.Comment: 20 pages, 7 figure
Electron-hole puddles in the absence of charged impurities
It is widely believed that carrier-density inhomogeneities ("electron-hole
puddles") in single-layer graphene on a substrate like quartz are due to
charged impurities located close to the graphene sheet. Here we demonstrate by
using a Kohn-Sham-Dirac density-functional scheme that corrugations in a real
sample are sufficient to determine electron-hole puddles on length scales that
are larger than the spatial resolution of state-of-the-art scanning tunneling
microscopy.Comment: 5 pages, 3 figures, published versio
Qualitative analysis of the dynamics of the time delayed Chua's circuit
IEEE TRANS. CIRCUITS SYST.
- …