1,141 research outputs found
Laboratory Testing of a Lyot Coronagraph Equipped with an Eighth-Order Notch Filter Image Mask
We have built a series of notch filter image masks that make the Lyot
coronagraph less susceptible to low-spatial-frequency optical aberrations. In
this paper, we present experimental results of their performance in the lab
using monochromatic light. Our tests show that these ``eighth-order'' masks are
resistant to tilt and focus alignment errors, and can generate contrast levels
of 2 x 10^-6 at 3 lambda/D and 6 x 10^-7 at 10 lambda/D without the use of
corrective optics such as deformable mirrors. This work supports recent
theoretical studies suggesting that eighth-order masks can provide the
Terrestrial Planet Finder Coronagraph with a large search area, high off-axis
throughput, and a practical requisite pointing accuracy.Comment: Accepted to ApJ. 16 pages, 7 figures, Contact [email protected]
for high resolution image
Substructures in WINGS clusters
We search for and characterize substructures in the projected distribution of
galaxies observed in the wide field CCD images of the 77 nearby clusters of the
WIde-field Nearby Galaxy-cluster Survey (WINGS). This sample is complete in
X-ray flux in the redshift range 0.04<z<0.07. We search for substructures in
WINGS clusters with DEDICA, an adaptive-kernel procedure. We test the procedure
on Monte-Carlo simulations of the observed frames and determine the reliability
for the detected structures. DEDICA identifies at least one reliable structure
in the field of 55 clusters. 40 of these clusters have a total of 69
substructures at the same redshift of the cluster (redshift estimates of
substructures are from color-magnitude diagrams). The fraction of clusters with
subclusters (73%) is higher than in most studies. The presence of subclusters
affects the relative luminosities of the brightest cluster galaxies (BCGs).
Down to L ~ 10^11.2 L_Sun, our observed differential distribution of subcluster
luminosities is consistent with the theoretical prediction of the differential
mass function of substructures in cosmological simulations.Comment: A&A accepted - figure 6 is available from
http://adlibitum.oats.inaf.it/ramella/WINGSfig
Antecedents and consequences of effectuation and causation in the international new venture creation process
The selection of the entry mode in an international market is of key importance for the venture. A process-based perspective on entry mode selection can add to the International Business and International Entrepreneurship literature. Framing the international market entry as an entrepreneurial process, this paper analyzes the antecedents and consequences of causation and effectuation in the entry mode selection. For the analysis, regression-based techniques were used on a sample of 65 gazelles. The results indicate that experienced entrepreneurs tend to apply effectuation rather than causation, while uncertainty does not have a systematic influence. Entrepreneurs using causation-based international new venture creation processes tend to engage in export-type entry modes, while effectuation-based international new venture creation processes do not predetermine the entry mod
Rolling Deck to Repository: Supporting the marine science community with data management services from academic research expeditions
Direct observations of the oceans acquired on oceanographic research ships operated across the international community support fundamental research into the many disciplines of ocean science and provide essential information for monitoring the health of the oceans. A comprehensive knowledge base is needed to support the responsible stewardship of the oceans with easy access to all data acquired globally. In the United States, the multidisciplinary shipboard sensor data routinely acquired each year on the fleet of coastal, regional and global ranging vessels supporting academic marine research are managed by the Rolling Deck to Repository (R2R, rvdata.us) program. With over a decade of operations, the R2R program has developed a robust routinized system to transform diverse data contributions from different marine data providers into a standardized and comprehensive collection of global-ranging observations of marine atmosphere, ocean, seafloor and subseafloor properties that is openly available to the international research community. In this article we describe the elements and framework of the R2R program and the services provided. To manage all expeditions conducted annually, a fleet-wide approach has been developed using data distributions submitted from marine operators with a data management workflow designed to maximize automation of data curation. Other design goals are to improve the completeness and consistency of the data and metadata archived, to support data citability, provenance tracking and interoperable data access aligned with FAIR (findable, accessible, interoperable, reusable) recommendations, and to facilitate delivery of data from the fleet for global data syntheses. Findings from a collection-level review of changes in data acquisition practices and quality over the past decade are presented. Lessons learned from R2R operations are also discussed including the benefits of designing data curation around the routine practices of data providers, approaches for ensuring preservation of a more complete data collection with a high level of FAIRness, and the opportunities for homogenization of datasets from the fleet so that they can support the broadest re-use of data across a diverse user community
The transmission spectrum of Earth through lunar eclipse observations
Of the 342 planets discovered so far orbiting other stars, 58 "transit" the
stellar disk, meaning that they can be detected by a periodic decrease in the
starlight flux. The light from the star passes through the atmosphere of the
planet, and in a few cases the basic atmospheric composition of the planet can
be estimated. As we get closer to finding analogues of Earth, an important
consideration toward the characterization of exoplanetary atmospheres is what
the transmission spectrum of our planet looks like. Here we report the optical
and near-infrared transmission spectrum of the Earth, obtained during a lunar
eclipse. Some biologically relevant atmospheric features that are weak in the
reflected spectrum (such as ozone, molecular oxygen, water, carbon dioxide and
methane) are much stronger in the transmission spectrum, and indeed stronger
than predicted by modelling. We also find the fingerprints of the Earth's
ionosphere and of the major atmospheric constituent, diatomic nitrogen (N2),
which are missing in the reflected spectrum.Comment: Published in Nature, 11 July 2009. This file also contains the
on-line materia
The Spin of the Near-Extreme Kerr Black Hole GRS 1915+105
Based on a spectral analysis of the X-ray continuum that employs a fully
relativistic accretion-disk model, we conclude that the compact primary of the
binary X-ray source GRS 1915+105 is a rapidly-rotating Kerr black hole. We find
a lower limit on the dimensionless spin parameter of a* greater than 0.98. Our
result is robust in the sense that it is independent of the details of the data
analysis and insensitive to the uncertainties in the mass and distance of the
black hole. Furthermore, our accretion-disk model includes an advanced
treatment of spectral hardening. Our data selection relies on a rigorous and
quantitative definition of the thermal state of black hole binaries, which we
used to screen all of the available RXTE and ASCA data for the thermal state of
GRS 1915+105. In addition, we focus on those data for which the accretion disk
luminosity is less than 30% of the Eddington luminosity. We argue that these
low-luminosity data are most appropriate for the thin alpha-disk model that we
employ. We assume that there is zero torque at the inner edge of the disk, as
is likely when the disk is thin, although we show that the presence of a
significant torque does not affect our results. Our model and the model of the
relativistic jets observed for this source constrain the distance and black
hole mass and could thus be tested by determining a VLBA parallax distance and
improving the measurement of the mass function. Finally, we comment on the
significance of our results for relativistic-jet and core-collapse models, and
for the detection of gravitational waves.Comment: 58 pages, 18 figures. Accepted for publication in ApJ. New in this
version is a proposed observational test of our spin model and the kinematic
model of the radio jet
An open-source database for the synthesis of soil radiocarbon data: International Soil Radiocarbon Database (ISRaD) version 1.0
Radiocarbon is a critical constraint on our estimates of the timescales of soil carbon cycling that can aid in identifying mechanisms of carbon stabilization and destabilization and improve the forecast of soil carbon response to management or environmental change. Despite the wealth of soil radiocarbon data that have been reported over the past 75 years, the ability to apply these data to global-scale questions is limited by our capacity to synthesize and compare measurements generated using a variety of methods. Here, we present the International Soil Radiocarbon Database (ISRaD; http://soilradiocarbon.org, last access: 16 December 2019), an open-source archive of soil data that include reported measurements from bulk soils, distinct soil carbon pools isolated in the laboratory by a variety of soil fractionation methods, samples of soil gas or water collected interstitially from within an intact soil profile, CO2 gas isolated from laboratory soil incubations, and fluxes collected in situ from a soil profile. The core of ISRaD is a relational database structured around individual datasets (entries) and organized hierarchically to report soil radiocarbon data, measured at different physical and temporal scales as well as other soil or environmental properties that may also be measured and may assist with interpretation and context. Anyone may contribute their own data to the database by entering it into the ISRaD template and subjecting it to quality assurance protocols. ISRaD can be accessed through (1) a web-based interface, (2) an R package (ISRaD), or (3) direct access to code and data through the GitHub repository, which hosts both code and data. The design of ISRaD allows for participants to become directly involved in the management, design, and application of ISRaD data. The synthesized dataset is available in two forms: the original data as reported by the authors of the datasets and an enhanced dataset that includes ancillary geospatial data calculated within the ISRaD framework. ISRaD also provides data management tools in the ISRaD-R package that provide a starting point for data analysis; as an open-source project, the broader soil community is invited and encouraged to add data, tools, and ideas for improvement. As a whole, ISRaD provides resources to aid our evaluation of soil dynamics across a range of spatial and temporal scales. The ISRaD v1.0 dataset is archived and freely available at https://doi.org/10.5281/zenodo.2613911 (Lawrence et al., 2019).Max Planck Institute for Biogeochemistry; European Research CouncilEuropean Research Council (ERC) [695101]; USGS Land Change Science mission area; US Department of AgricultureUnited States Department of Agriculture (USDA) [2018-67003-27935]; US Geological Survey Powell Center for the working group on Soil Carbon Storage and FeedbacksOpen access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
Dinosaur peptides suggest mechanisms of protein survival
Eleven collagen peptide sequences recovered from chemical extracts of dinosaur bones were mapped onto molecular models of the vertebrate collagen fibril derived from extant taxa. The dinosaur peptides localized to fibril regions protected by the close packing of collagen molecules, and contained few acidic amino acids. Four peptides mapped to collagen regions crucial for cell-collagen interactions and tissue development. Dinosaur peptides were not represented in more exposed parts of the collagen fibril or regions mediating intermolecular cross-linking. Thus functionally significant regions of collagen fibrils that are physically shielded within the fibril may be preferentially preserved in fossils. These results show empirically that structure-function relationships at the molecular level could contribute to selective preservation in fossilized vertebrate remains across geological time, suggest a ‘preservation motif’, and bolster current concepts linking collagen structure to biological function. This non-random distribution supports the hypothesis that the peptides are produced by the extinct organisms and suggests a chemical mechanism for survival
Challenges and Pitfalls in the Management of Parathyroid Carcinoma: 17-Year Follow-Up of a Case and Review of the Literature
A 29-year-old man presented to his primary care physician with nausea, severe weight loss and muscle weakness. He had a hard, fixed neck swelling. He was severely hypercalcaemic with 10-fold increased parathyroid hormone (PTH) concentrations. A diagnosis of primary hyperparathyroidism was established and the patient was referred for parathyroidectomy. At neck exploration, an enlarged parathyroid gland with invasive growth into the thyroid gland was found and removed, lymph nodes were cleared and hemithyroidectomy was performed. A suspected diagnosis of parathyroid carcinoma was confirmed histologically. Serum calcium and PTH levels normalised post-operatively, but hyperparathyroidism recurred within 3 years of surgery. Over the following 17 years, control of hypercalcaemia represented the most difficult challenge despite variable success achieved with repeated surgical interventions, embolisations, radiofrequency ablation of metastases and treatment with calcimimetics, bisphosphonates and haemodialysis using low-dialysate calcium. In this paper, we report the challenges and pitfalls we encountered in the management of our patient over nearly two decades of follow-up and review recent literature on the topic
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