1,763 research outputs found
The Neuropsychiatric Factor in Allergic Disease
A concept of the causation of allergic disease herewith is presented in which, in addition to the allergic factors, emotional states and psychic stimuli are introduced as integral parts of every case. The adoption of the terms intrinsic for the neuropsychiatric factors and extrinsic for the organic factors in the production of allergic disease is suggested
Factors Associated With Retinal Vessel Diameters in an Elderly Population: the Thessaloniki Eye Study
Purpose: To identify the factors associated with retinal vessel diameters in the population of the Thessaloniki Eye Study.
Methods: Cross-sectional population-based study (age â„ 60 years). Subjects with glaucoma, late age-related macular degeneration, and diabetic retinopathy were excluded from the analyses. Retinal vessel diameters were measured using the IVAN software, and measurements were summarized to central retinal artery equivalent (CRAE), central retinal vein equivalent (CRVE), and arteriole to venule ratio (AVR).
Results: The analysis included 1614 subjects. The hypertensive group showed lower values of CRAE (P = 0.033) and AVR (P = 0.0351) compared to the normal blood pressure (BP) group. On the contrary, the group having normal BP under antihypertensive treatment did not have different values compared to the normal BP group. Diastolic BP (per mm Hg) was negatively associated with CRAE (P < 0.0001) and AVR (P < 0.0001), while systolic BP (per mm Hg) was positively associated with CRAE (P = 0.001) and AVR (P = 0.0096). Other factors significantly associated included age, sex, alcohol, smoking, cardiovascular disease history, ophthalmic medication, weight, and IOP; differences were observed in a stratified analysis based on BP medication use.
Conclusions: Our study confirms previous reports about the association of age and BP with vessel diameters. The negative correlation between BP and CRAE seems to be guided by the effect of diastolic BP as higher systolic BP is independently associated with higher values of CRAE. The association of BP status with retinal vessel diameters is determined by diastolic BP status in our population. Multiple other factors are also independently associated with retinal vessel diameters
Disordered loops in the two-dimensional antiferromagnetic spin-fermion model
The spin-fermion model has long been used to describe the quantum-critical
behavior of 2d electron systems near an antiferromagnetic (AFM) instability.
Recently, the standard procedure to integrate out the fermions to obtain an
effective action for spin waves has been questioned in the clean case. We show
that in the presence of disorder, the single fermion loops display two
crossover scales: upon lowering the energy, the singularities of the clean
fermionic loops are first cut off, but below a second scale new singularities
arise that lead again to marginal scaling. In addition, impurity lines between
different fermion loops generate new relevant couplings which dominate at low
energies. We outline a non-linear sigma model formulation of the single-loop
problem, which allows to control the higher singularities and provides an
effective model in terms of low-energy diffusive as well as spin modes.Comment: 22 pages, 8 figure
How old are the stars in the halo of NGC 5128 (Centaurus A)?
NGC 5128 (Centaurus A) is, at the distance of just 3.8 Mpc, the nearest
easily observable giant elliptical galaxy. Therefore it is the best target to
investigate the early star formation history of an elliptical galaxy. Our aims
are to establish when the oldest stars formed in NGC 5128, and whether this
galaxy formed stars over a long period. We compare simulated colour-magnitude
diagrams with the deep ACS/HST photometry. We find that that the observed
colour-magnitude diagram can be reproduced satisfactorily only by simulations
that have the bulk of the stars with ages in excess of ~10 Gyr, and that the
alpha-enhanced models fit the data much better than the solar scaled ones. Data
are not consistent with extended star formation over more than 3-4 Gyr. Two
burst models, with 70-80% of the stars formed 12+/-1 Gyr ago and with 20-30%
younger contribution with 2-4 Gyr old stars provide the best agreement with the
data. The old component spans the whole metallicity range of the models
(Z=0.0001-0.04), while for the young component the best fitting models indicate
higher minimum metallicity (~1/10 - 1/4 Z_sun). The bulk of the halo stars in
NGC5128 must have formed at redshift z>=2 and the chemical enrichment was very
fast, reaching solar or even twice-solar metallicity already for the ~11-12 Gyr
old population. The minor young component, adding ~20-30% of the stars to the
halo, and contributing less than 10% of the mass, may have resulted from a
later star formation event ~2-4 Gyr ago. (abridged)Comment: 36 pages, 14 figures, accepted for publication in A&
The Nature of the Density Clump in the Fornax Dwarf Spheroidal Galaxy
We have imaged the recently discovered stellar overdensity located
approximately one core radius from the center of the Fornax dwarf spheroidal
galaxy using the Magellan Clay 6.5m telescope with the Magellan Instant Camera
(MagIC). Superb seeing conditions allowed us to probe the stellar populations
of this overdensity and of a control field within Fornax to a limiting
magnitude of R=26. The color-magnitude diagram of the overdensity field is
virtually identical to that of the control field with the exception of the
presence of a population arising from a very short (less than 300 Myr in
duration) burst of star formation 1.4 Gyr ago. Coleman et al. have argued that
this overdensity might be related to a shell structure in Fornax that was
created when Fornax captured a smaller galaxy. Our results are consistent with
this model, but we argue that the metallicity of this young component favors a
scenario in which the gas was part of Fornax itself.Comment: 24 pages including 8 figures and 3 tables. Accepted by Astronomical
Journa
Effective Lorentz Force due to Small-angle Impurity Scattering: Magnetotransport in High-Tc Superconductors
We show that a scattering rate which varies with angle around the Fermi
surface has the same effect as a periodic Lorentz force on magnetotransport
coefficients. This effect, together with the marginal Fermi liquid inelastic
scattering rate gives a quantitative explanation of the temperature dependence
and the magnitude of the observed Hall effect and magnetoresistance with just
the measured zero-field resistivity as input.Comment: 4 pages, latex, one epsf figure included in text. Several revisions
and corrections are included. Major conclusions are the sam
Kagom{\'e} Lattice Antiferromagnet Stripped to Its Basics
We study a model of a spin S = 1/2 Heisenberg antiferromagnet on a one
dimensional lattice with the local symmetry of the two dimensional kagom{\'e}
lattice. Using three complementary approaches, it is shown that the low energy
spectrum can be described by two critical Ising models with different
velocities. One of these velocities is small, leading to a strongly localized
Majorana fermion. These excitations are singlet ones whereas the triplet sector
has a spectral gap.Comment: 4 page
High Energy gamma-rays From FR I Jets
Thanks to Hubble and Chandra telescopes, some of the large scale jets in
extragalactic radio sources are now being observed at optical and X-ray
frequencies. For the FR I objects the synchrotron nature of this emission is
surely established, although a lot of uncertainties - connected for example
with the particle acceleration processes involved - remain. In this paper we
study production of high energy gamma-rays in FR I kiloparsec-scale jets by
inverse-Compton emission of the synchrotron-emitting electrons. We consider
different origin of seed photons contributing to the inverse-Compton
scattering, including nuclear jet radiation as well as ambient, stellar and
circumstellar emission of the host galaxies. We discuss how future detections
or non-detections of the evaluated gamma-ray fluxes can provide constraints on
the unknown large scale jet parameters, i.e. the magnetic field intensity and
the jet Doppler factor. For the nearby sources Centaurus A and M 87, we find
measurable fluxes of TeV photons resulting from synchrotron self-Compton
process and from comptonisation of the galactic photon fields, respectively. In
the case of Centaurus A, we also find a relatively strong emission component
due to comptonisation of the nuclear blazar photons, which could be easily
observed by GLAST at energy ~10 GeV, providing important test for the
unification of FR I sources with BL Lac objects.Comment: 39 pages, 6 figures included. Modified version, accepted for
publication in Astrophysical Journa
The structural properties and star formation history of Leo T from deep LBT photometry
We present deep, wide-field g and r photometry of the transition type dwarf
galaxy Leo T, obtained with the blue arm of the Large Binocular Telescope. The
data confirm the presence of both very young (5
Gyr) stars. We study the structural properties of the old and young stellar
populations by preferentially selecting either population based on their color
and magnitude. The young population is significantly more concentrated than the
old population, with half-light radii of 104+-8 and 148+-16 pc respectively,
and their centers are slightly offset. Approximately 10% of the total stellar
mass is estimated to be represented by the young stellar population. Comparison
of the color-magnitude diagram (CMD) with theoretical isochrones as well as
numerical CMD-fitting suggest that star formation began over 10 Gyr ago and
continued in recent times until at least a few hundred Myr ago. The CMD-fitting
results are indicative of two distinct star formation bursts, with a quiescent
period around 3 Gyr ago, albeit at low significance. The results are consistent
with no metallicity evolution and [Fe/H] ~ -1.5 over the entire age of the
system. Finally, the data show little if any sign of tidal distortion of Leo T.Comment: 8 pages, 9 figures, some small textual changes, accepted for
publication in the Astrophysical Journa
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