2,186 research outputs found
The GREATS H+[OIII] Luminosity Function and Galaxy Properties at : Walking the Way of JWST
The James Webb Space Telescope will allow to spectroscopically study an
unprecedented number of galaxies deep into the reionization era, notably by
detecting [OIII] and H nebular emission lines. To efficiently prepare
such observations, we photometrically select a large sample of galaxies at
and study their rest-frame optical emission lines. Combining data from
the GOODS Re-ionization Era wide-Area Treasury from Spitzer (GREATS) survey and
from HST, we perform spectral energy distribution (SED) fitting, using
synthetic SEDs from a large grid of photoionization models. The deep
Spitzer/IRAC data combined with our models exploring a large parameter space
enables to constrain the [OIII]+H fluxes and equivalent widths for our
sample, as well as the average physical properties of galaxies, such
as the ionizing photon production efficiency with
. We
find a relatively tight correlation between the [OIII]+H and UV
luminosity, which we use to derive for the first time the [OIII]+H
luminosity function (LF) at . The [OIII]+H LF is higher
at all luminosities compared to lower redshift, as opposed to the UV LF, due to
an increase of the [OIII]+H luminosity at a given UV luminosity from
to . Finally, using the [OIII]+H LF, we make
predictions for JWST/NIRSpec number counts of galaxies. We find that
the current wide-area extragalactic legacy fields are too shallow to use JWST
at maximal efficiency for spectroscopy even at 1hr depth and JWST
pre-imaging to mag will be required.Comment: 13 pages, 9 figures, accepted for publication in MNRA
Field-theoretic description of ionic crystallization in the restricted primitive model
Effects of charge-density fluctuations on a phase behavior of the restricted
primitive model (RPM) are studied within a field-theoretic formalism. We focus
on a -line of continuous transitions between charge-ordered and
charge-disordered phases that is observed in several mean-field (MF) theories,
but is absent in simulation results. In our study the RPM is reduced to a
theory, and a fluctuation contribution to a grand thermodynamic
potential is obtained by generalizing the Brazovskii approach. We find that in
a presence of fluctuations the -line disappears. Instead, a
fluctuation-induced first-order transition to a charge-ordered phase appears in
the same region of a phase diagram, where the liquid -- ionic-crystal
transition is obtained in simulations. Our results indicate that the
charge-ordered phase should be identified with an ionic crystal.Comment: 31 pages, 10 figure
Investigation of the Domain Wall Fermion Approach to Chiral Gauge Theories on the Lattice
We investigate a recent proposal to construct chiral gauge theories on the
lattice using domain wall fermions. We restrict ourselves to the finite volume
case, in which two domain walls are present, with modes of opposite chirality
on each of them. We couple the chiral fermions on only one of the domain walls
to a gauge field. In order to preserve gauge invariance, we have to add a
scalar field, which gives rise to additional light mirror fermion and scalar
modes. We argue that in an anomaly free model these extra modes would decouple
if our model possesses a so-called strong coupling symmetric phase. However,
our numerical results indicate that such a phase most probably does not exist.
---- Note: 9 Postscript figures are appended as uuencoded compressed tar file.Comment: 27p. Latex; UCSD/PTH 93-28, Wash. U. HEP/93-6
Magnetic phenomena in 5d transition metal nanowires
We have carried out fully relativistic full-potential, spin-polarized,
all-electron density-functional calculations for straight, monatomic nanowires
of the 5d transition and noble metals Os, Ir, Pt and Au. We find that, of these
metal nanowires, Os and Pt have mean-field magnetic moments for values of the
bond length at equilibrium. In the case of Au and Ir, the wires need to be
slightly stretched in order to spin polarize. An analysis of the band
structures of the wires indicate that the superparamagnetic state that our
calculations suggest will affect the conductance through the wires -- though
not by a large amount -- at least in the absence of magnetic domain walls. It
should thus lead to a characteristic temperature- and field dependent
conductance, and may also cause a significant spin polarization of the
transmitted current.Comment: 7 pages, 5 figure
Conductance and persistent current of a quantum ring coupled to a quantum wire under external fields
The electronic transport of a noninteracting quantum ring side-coupled to a
quantum wire is studied via a single-band tunneling tight-binding Hamiltonian.
We found that the system develops an oscillating band with antiresonances and
resonances arising from the hybridization of the quasibound levels of the ring
and the coupling to the quantum wire. The positions of the antiresonances
correspond exactly to the electronic spectrum of the isolated ring. Moreover,
for a uniform quantum ring the conductance and the persistent current density
were found to exhibit a particular odd-even parity related with the ring-order.
The effects of an in-plane electric field was also studied. This field shifts
the electronic spectrum and damps the amplitude of the persistent current
density. These features may be used to control externally the energy spectra
and the amplitude of the persistent current.Comment: Revised version, 7 pages and 9 figures. To appear in Phys. Rev.
Dual superconductivity in the SU(2) pure gauge vacuum: a lattice study
We investigate the dual superconductivity hypothesis in pure SU(2) lattice
gauge theory. We focus on the dual Meissner effect by analyzing the
distribution of the color fields due to a static quark-antiquark pair. We find
evidence of the dual Meissner effect both in the maximally Abelian gauge and
without gauge fixing. We measure the London penetration length. Our results
suggest that the London penetration length is a physical gauge-invariant
quantity. We put out a simple relation between the penetration length and the
square root of the string tension. We find that our extimation is quite close
to the extrapolated continuum limit available in the literature. A remarkable
consequence of our study is that an effective Abelian theory can account for
the long range properties of the SU(2) confining vacuum.Comment: 38 pages, uuencoded compressed (using GNU's gzip) tar file containing
1 LaTeX2e file (to be processed 3 times) + 16 encapsulated Postscript
figures. A full Postscript version of this paper is available at
http://www.ba.infn.it/disk$gruppo_4/cosmai/www/papers/195-95.P
Low-lying fermion modes, topology and light hadrons in quenched QCD
We explore the properties of low lying eigenmodes of fermions in the quenched
approximation of lattice QCD. The fermion action is a recently proposed overlap
action and has exact chiral symmetry. We find that chiral zero-eigenvalue modes
are localized in space and their positions correlate strongly with the
locations (as defined through the density of pure gauge observables) of
instantons of the appropriate charge. Nonchiral modes are also localized with
peaks which are strongly correlated with the positions of both charges of
instantons. These correlations slowly die away as the fermion eigenvalue rises.
Correlators made of quark propagators restricted to these modes closely
reproduce ordinary hadron correlators at small quark mass in many channels. Our
results are in qualitative agreement with the expectations of instanton liquid
models.Comment: 21 pages, Revtex, 21 postscript figures. COLO-HEP-45
Common Origin for Surface Reconstruction and the Formation of Chains of Metal Atoms
During the fracture of nanocontacts gold spontaneously forms freely suspended
chains of atoms, which is not observed for the iso-electronic noble metals Ag
and Cu. Au also differs from Ag and Cu in forming reconstructions at its
low-index surfaces. Using mechanically controllable break junctions we show
that all the 5d metals that show similar reconstructions (Ir, Pt and Au) also
form chains of atoms, while both properties are absent in the 4d neighbor
elements (Rh, Pd, Ag), indicating a common origin for these two phenomena. A
competition between s and d bonding is proposed as an explanation
A risk profile for identifying community-dwelling elderly with a highrisk of recurrent falling: results of a 3-year prospective study
Introduction: The aim of the prospective study reported here was to develop a risk profile that can be used to identify community-dwelling elderly at a high risk of recurrent falling. Materials and methods: The study was designed as a 3-year prospective cohort study. A total of 1365 community-dwelling persons, aged 65 years and older, of the population-based Longitudinal Aging Study Amsterdam participated in the study. During an interview in 1995/1996, physical, cognitive, emotional and social aspects of functioning were assessed. A follow-up on the number of falls and fractures was conducted during a 3-year period using fall calendars that participants filled out weekly. Recurrent fallers were identified as those who fell at least twice within a 6-month period during the 3-year follow-up. Results: The incidence of recurrent falls at the 3-year follow-up point was 24.9% in women and 24.4% in men. Of the respondents, 5.5% reported a total of 87 fractures that resulted from a fall, including 20 hip fractures, 21 wrist fractures and seven humerus fractures. Recurrent fallers were more prone to have a fall-related fracture than those who were not defined as recurrent fallers (11.9% vs. 3.4%; OR: 3.8; 95% CI: 2.3-6.1). Backward logistic regression analysis identified the following predictors in the risk profile for recurrent falling: two or more previous falls, dizziness, functional limitations, weak grip strength, low body weight, fear of falling, the presence of dogs/cats in the household, a high educational level, drinking 18 or more alcoholic consumptions per week and two interaction terms (high educationx18 or more alcohol consumptions per week and two or more previous falls x fear of falling) (AUC=0.71). Discussion: At a cut-off point of 5 on the total risk score (range 0-30), the model predicted recurrent falling with a sensitivity of 59% and a specificity of 71%. At a cut-off point of 10, the sensitivity and specificity were 31% and 92%, respectively. A risk profile including nine predictors that can easily be assessed seems to be a useful tool for the identification of community-dwelling elderly with a high risk of recurrent falling. © International Osteoporosis Foundation and National Osteoporosis Foundation 2006
Domain wall fermion zero modes on classical topological backgrounds
The domain wall approach to lattice fermions employs an additional dimension,
in which gauge fields are merely replicated, to separate the chiral components
of a Dirac fermion. It is known that in the limit of infinite separation in
this new dimension, domain wall fermions have exact zero modes, even for gauge
fields which are not smooth. We explore the effects of finite extent in the
fifth dimension on the zero modes for both smooth and non-smooth topological
configurations and find that a fifth dimension of around ten sites is
sufficient to clearly show zero mode effects. This small value for the extent
of the fifth dimension indicates the practical utility of this technique for
numerical simulations of QCD.Comment: Updated fig. 3-7, small changes in sect. 3, added fig. 8, added more
reference
- …