1,809 research outputs found
Goos-Haenchen induced vector eigenmodes in a dome cavity
We demonstrate numerically calculated electromagnetic eigenmodes of a 3D dome
cavity resonator that owe their shape and character entirely to the
Goos-Haenchen effect. The V-shaped modes, which have purely TE or TM
polarization, are well described by a 2D billiard map with the Goos-Haenchen
shift included. A phase space plot of this augmented billiard map reveals a
saddle-node bifurcation; the stable periodic orbit that is created in the
bifurcation corresponds to the numerically calculated eigenmode, dictating the
angle of its "V". A transition from a fundamental Gaussian to a TM V mode has
been observed as the cavity is lengthened to become nearly hemispherical.Comment: 4 pages, 4 figure
Collisions of boosted black holes: perturbation theory prediction of gravitational radiation
We consider general relativistic Cauchy data representing two nonspinning,
equal-mass black holes boosted toward each other. When the black holes are
close enough to each other and their momentum is sufficiently high, an
encompassing apparent horizon is present so the system can be viewed as a
single, perturbed black hole. We employ gauge-invariant perturbation theory,
and integrate the Zerilli equation to analyze these time-asymmetric data sets
and compute gravitational wave forms and emitted energies. When coupled with a
simple Newtonian analysis of the infall trajectory, we find striking agreement
between the perturbation calculation of emitted energies and the results of
fully general relativistic numerical simulations of time-symmetric initial
data.Comment: 5 pages (RevTex 3.0 with 3 uuencoded figures), CRSR-107
The Large-Scale Extinction Map of the Galactic Bulge from the MACHO Project Photometry
We present a (V-R)-based reddening map of about 43 square degrees of the
Galactic bulge/bar. The map is constructed using template image photometry from
the MACHO microlensing survey, contains 9717 resolution elements, and is based
on (V-R)-color averages of the entire color-magnitude diagrams (CMDs) in 4 by 4
arc-minute tiles. The conversion from the observed color to the reddening
follows from an assumption that CMDs of all bulge fields would look similar in
the absence of extinction. Consequently, the difference in observed color
between various fields originates from varying contribution of the disk
extinction summed along different lines of sight. We check that our (V-R)
colors correlate very well with infrared and optical reddening maps. We show
that a dusty disk obeying a cosec|b| extinction law, E(V-R) = 0.0274 cosec|b|,
provides a good approximation to the extinction toward the MACHO bulge/bar
fields. The large-scale (V-R)-color and visual extinction map presented here is
publicly available in the electronic edition of the Journal and on the World
Wide Web.Comment: 24 pages, 3 tables, 7 figures (6 in color), version accepted to AJ,
added comparisons with Schlegel et al. (1998) and Dutra et al. (2003)
reddening map
Morphologic study of the ascending aorta and aortic arch in hypoplastic left hearts: Surgical implications
ObjectivesThe ascending aorta and aortic arch in patients with hypoplasia of the left heart are hypoplastic as a result of diminished blood flow. In this study, the presence and degree of obstruction owing to areas of narrowing or infolding within the diminutive aorta are quantified, and their surgical significance is discussed.MethodsNinety-six specimens with hypoplasia of the left heart were studied and measurements were taken at specified sites to evaluate areas of narrowing. Quantitative assessments of infoldings and their contribution to obstruction of flow are made.ResultsNarrowing of the distal ascending aorta was found in 60 (62.5%) specimens, with a decrease in circumference of the distal ascending aorta (0.72 ± 1.06 mm) present when compared with its midpoint (P < .05). Tissue infolding at the orifice of the brachiocephalic artery and its junction with the distal ascending aorta was observed in 56 (58.3%) hearts, with major infolding in 29 (30.2%) and minor infolding in 27 (28.5%). Tissue infolding at this site correlated with a smaller ascending aorta (P < .001) but not with narrowing in the distal ascending aorta (P = .53). Ductal coarctations were detected in 77 (81.1%) specimens. Their presence correlated with a smaller diameter of the ascending aorta (P < .05), and their severity correlated with the presence of aortic and mitral valvular atresia (P < .05).ConclusionsImportant areas of obstruction in the ascending aorta in patients with hypoplasia of the left heart were found, and their pathogenesis is discussed. The findings highlight the importance of incorporating the ascending aorta into the aortic reconstruction at the time of initial palliation for patients with hypoplasia of the left heart
The Star Formation History of LGS 3
We have determined the distance and star formation history of the Local Group
dwarf galaxy LGS 3 from deep Hubble Space Telescope WFPC2 observations. LGS 3
is intriguing because ground-based observations showed that, while its stellar
population is dominated by old, metal-poor stars, there is a handful of young,
blue stars. Also, the presence of HI gas makes this a possible ``transition
object'' between dwarf spheroidal and dwarf irregular galaxies. The HST data
are deep enough to detect the horizontal branch and young main sequence for the
first time. A new distance of D=620+/-20 kpc has been measured from the
positions of the TRGB, the red clump, and the horizontal branch. The mean
metallicity of the stars older than 8 Gyr is Fe/H = -1.5 +/- 0.3. The most
recent generation of stars has Fe/H ~ -1. For the first few Gyr the global star
formation rate was several times higher than the historical average and has
been fairly constant since then. However, we do see significant changes in
stellar populations and star formation history with radial position in the
galaxy. Most of the young stars are found in the central 63 pc (21''), where
the star formation rate has been relatively constant, while the outer parts
have had a declining star formation rate.Comment: To appear in The Astrophysical Journal, 26 pages, 14 figures, uses
AASTe
Use of methods for specifying the target difference in randomised controlled trial sample size calculations : Two surveys of trialists' practice
© The Author(s), 2014.Peer reviewedPublisher PD
Distributed System Contract Monitoring
The use of behavioural contracts, to specify, regulate and verify systems, is
particularly relevant to runtime monitoring of distributed systems. System
distribution poses major challenges to contract monitoring, from
monitoring-induced information leaks to computation load balancing,
communication overheads and fault-tolerance. We present mDPi, a location-aware
process calculus, for reasoning about monitoring of distributed systems. We
define a family of Labelled Transition Systems for this calculus, which allow
formal reasoning about different monitoring strategies at different levels of
abstractions. We also illustrate the expressivity of the calculus by showing
how contracts in a simple contract language can be synthesised into different
mDPi monitors.Comment: In Proceedings FLACOS 2011, arXiv:1109.239
Maturation Schedules of Walleye Populations in the Great Lakes Region: Comparison of Maturation Indices and Evaluation of Samplingâ Induced Biases
Maturation schedules, key determinants of fish stocks’ harvest potential and population dynamics, are influenced by both plastic and adaptive processes. Various indices are used to describe maturation schedules, and these have differential advantages for discriminating between plastic and adaptive processes. However, potential samplingâ related biases associated with different maturation indices have not been fully evaluated. We analyzed three maturation indices for walleyes Sander vitreus in Lake Erie; Saginaw Bay, Lake Huron; and Oneida Lake, New York: age and length at 50% maturity, midpoint of ageâ specific maturity ogives (ageâ specific length at which probability of maturity = 0.50), and midpoints of probabilistic maturation reaction norms (PMRNs; ageâ specific length at which probability of maturing in the following year = 0.50). We then compared estimated maturation indices to evaluate sensitivity of different maturation indices to samplingâ induced biases and to assess the relative importance of plastic versus adaptive processes in structuring interstock and temporal variation in maturation schedules. Our findings suggest that although small changes in sampling month, gear, and agencyâ related effects can bias estimates of age and length at 50% maturity and midpoints of maturity ogives, PMRN estimates appear to be robust to these biases. Furthermore, PMRN estimates are suggestive of potential adaptive variation in maturation schedules among walleye stocks and over time. For instance, Oneida Lake walleyes (which had relatively slow growth and low mortality rates) matured at a smaller size for a given age (smaller midpoints of PMRNs) than the other stocks. Temporally, walleyes in the western basin of Lake Erie matured at a larger size in recent years, as evidenced by increasing midpoints of PMRNs (1978â 1989 versus 1990â 2006 for Ohio Department of Natural Resources data and 1990â 1996 versus 1997â 2006 for Ontario Ministry of Natural Resources data). Our study highlights the necessity of monitoring maturation schedules via multiple maturation indices and the need to account for samplingâ induced biases when comparing maturation schedules.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141201/1/nafm1540.pd
Investigating molecular mechanisms of 2A-stimulated ribosomal pausing and frameshifting in Theilovirus.
Funder: Helmholtz AssociationFunder: Royal SocietyThe 2A protein of Theiler's murine encephalomyelitis virus (TMEV) acts as a switch to stimulate programmed -1 ribosomal frameshifting (PRF) during infection. Here, we present the X-ray crystal structure of TMEV 2A and define how it recognises the stimulatory RNA element. We demonstrate a critical role for bases upstream of the originally predicted stem-loop, providing evidence for a pseudoknot-like conformation and suggesting that the recognition of this pseudoknot by beta-shell proteins is a conserved feature in cardioviruses. Through examination of PRF in TMEV-infected cells by ribosome profiling, we identify a series of ribosomal pauses around the site of PRF induced by the 2A-pseudoknot complex. Careful normalisation of ribosomal profiling data with a 2A knockout virus facilitated the identification, through disome analysis, of ribosome stacking at the TMEV frameshifting signal. These experiments provide unparalleled detail of the molecular mechanisms underpinning Theilovirus protein-stimulated frameshifting
Canopy nitrogen, carbon assimilation, and albedo in temperate and boreal forests: Functional relations and potential climate feedbacks
The availability of nitrogen represents a key constraint on carbon cycling in terrestrial ecosystems, and it is largely in this capacity that the role of N in the Earth\u27s climate system has been considered. Despite this, few studies have included continuous variation in plant N status as a driver of broad-scale carbon cycle analyses. This is partly because of uncertainties in how leaf-level physiological relationships scale to whole ecosystems and because methods for regional to continental detection of plant N concentrations have yet to be developed. Here, we show that ecosystem CO2 uptake capacity in temperate and boreal forests scales directly with whole-canopy N concentrations, mirroring a leaf-level trend that has been observed for woody plants worldwide. We further show that both CO2 uptake capacity and canopy N concentration are strongly and positively correlated with shortwave surface albedo. These results suggest that N plays an additional, and overlooked, role in the climate system via its influence on vegetation reflectivity and shortwave surface energy exchange. We also demonstrate that much of the spatial variation in canopy N can be detected by using broad-band satellite sensors, offering a means through which these findings can be applied toward improved application of coupled carbon cycle–climate models
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