3,453 research outputs found
Recommendations for research design and reporting in computer-assisted diagnosis to facilitate meta-analysis
AbstractComputer-assisted diagnosis (CAD) describes a diverse, heterogeneous range of applications rather than a single entity. The aims and functions of CAD systems vary considerably and comparing studies and systems is challenging due to methodological and design differences. In addition, poor study quality and reporting can reduce the value of some publications. Meta-analyses of CAD are therefore difficult and may not provide reliable conclusions. Aiming to determine the major sources of heterogeneity and thereby what CAD researchers could change to allow this sort of assessment, this study reviews a sample of 147 papers concerning CAD used with imaging for cancer diagnosis. It discusses sources of variability, including the goal of the CAD system, learning methodology, study population, design, outcome measures, inclusion of radiologists, and study quality. Based upon this evidence, recommendations are made to help researchers optimize the quality and comparability of their trial design and reporting
Cambrian edrioasteroid reveals new mechanism for secondary reduction of the skeleton in echinoderms
Echinoderms are characterized by a distinctive high-magnesium calcite endoskeleton as adults, but elements of this have been drastically reduced in some groups. Herein, we describe a new pentaradial echinoderm, Yorkicystis haefneri n. gen. n. sp., which provides, to our knowledge, the oldest evidence of secondary non-mineralization of the echinoderm skeleton. This material was collected from the Cambrian Kinzers Formation in York (Pennsylvania, USA) and is dated as ca 510 Ma. Detailed morphological observations demonstrate that the ambulacra (i.e. axial region) are composed of flooring and cover plates, but the rest of the body (i.e. extraxial region) is preserved as a dark film and lacks any evidence of skeletal plating. Moreover, X-ray fluorescence analysis reveals that the axial region is elevated in iron. Based on our morphological and chemical data and on taphonomic comparisons with other fossils from the Kinzers Formation, we infer that the axial region was originally calcified, while the extraxial region was non-mineralized. Phylogenetic analyses recover Yorkicystis as an edrioasteroid, indicating that this partial absence of skeleton resulted from a secondary reduction. We hypothesize that skeletal reduction resulted from lack of expression of the skeletogenic gene regulatory network in the extraxial body wall during development. Secondary reduction of the skeleton in Yorkicystis might have allowed for greater flexibility of the body wall
Identification of single-site gold catalysis in acetylene hydrochlorination
There remains considerable debate over the active form of gold under operating conditions of a recently validated gold catalyst for acetylene hydrochlorination. We have performed an in situ x-ray absorption fine structure study of gold/carbon (Au/C) catalysts under acetylene hydrochlorination reaction conditions and show that highly active catalysts comprise single-site cationic Au entities whose activity correlates with the ratio of Au(I):Au(III) present. We demonstrate that these Au/C catalysts are supported analogs of single-site homogeneous Au catalysts and propose a mechanism, supported by computational modeling, based on a redox couple of Au(I)-Au(III) species.
View Full Tex
The solvation and dissociation of 4-benzylaniline hydrochloride in chlorobenzene
A reaction scheme is proposed to account for the liberation of 4-benzylaniline from 4-benzylaniline hydrochloride, using chlorobenzene as a solvent at a temperature of 373 K. Two operational regimes are explored: âclosedâ reaction conditions correspond to the retention of evolved hydrogen chloride gas within the reaction medium, whereas an âopenâ system permits gaseous hydrogen chloride to be released from the reaction medium. The solution phase chemistry is analyzed by 1H NMR spectroscopy. Complete liberation of solvated 4-benzylaniline from solid 4-benzylaniline hydrochloride is possible under âopenâ conditions, with the entropically favored conversion of solvated hydrogen chloride to the gaseous phase thought to be the thermodynamic driver that effectively controls a series of interconnecting equilibria. A kinetic model is proposed to account for the observations of the open system
Observational consequences of fine structure line optical depths on infrared spectral diagnostics
It has long been known that infrared fine structure lines of abundant ions,
like the [O III] 88 micron line, can become optically thick in H II regions
under certain high luminosity conditions. This could mitigate their potential
as diagnostic tools, especially if the source is too dusty for optical
spectroscopy to otherwise determine the system's parameters. We examined a
series of photoionization calculations which were designed to push the nebulae
into the limit where many IR lines should be quite optically thick. We find
that radiative transfer effects do not significantly change the observed
emission line spectrum. This is due to a combination of grain absorption of the
hydrogen ionizing continuum and the fact that the correction for stimulated
emission in these lines is large. Given these results, and the likelihood that
real objects have non-thermal line broadening, it seems unlikely that line
optical depth presents a problem in using these lines as diagnostics of the
physical conditions or chemical composition.Comment: 16 pages, 4 figures, to be published in the February 2003 issue of
the PAS
HST hot Jupiter transmission spectral survey: detection of water in HAT-P-1b from WFC3 near-IR spatial scan observations
We present Hubble Space Telescope near-infrared transmission spectroscopy of the transiting hot-Jupiter HAT-P-1b. We observed one transit with Wide Field Camera 3 using the G141 low-resolution grism to cover the wavelength range 1.087â1.678âÎŒm. These time series observations were taken with the newly available spatial-scan mode that increases the duty cycle by nearly a factor of 2, thus improving the resulting photometric precision of the data. We measure a planet-to-star radius ratio of Rp/R* = 0.117 09 ± 0.000 38 in the white light curve with the centre of transit occurring at 245 6114.345 ± 0.000 133 (JD). We achieve S/N levels per exposure of 1840 (0.061âperâcent) at a resolution of Îλ = 19.2 nm (R ⌠70) in the 1.1173â1.6549âÎŒm spectral region, providing the precision necessary to probe the transmission spectrum of the planet at close to the resolution limit of the instrument. We compute the transmission spectrum using both single target and differential photometry with similar results. The resultant transmission spectrum shows a significant absorption above the 5Ï level matching the 1.4âÎŒm water absorption band. In solar composition models, the water absorption is sensitive to the âŒ1 m bar pressure levels at the terminator. The detected absorption agrees with that predicted by a 1000âK isothermal model, as well as with that predicted by a planetary-averaged temperature model
Hubble Space Telescope hot Jupiter transmission spectral survey: a detection of Na and strong optical absorption in HAT-P-1b
We present an optical to near-infrared transmission spectrum of the hot Jupiter HAT-P-1b, based on Hubble Space Telescope observations, covering the spectral regime from 0.29 to 1.027âÎŒm with Space Telescope Imaging Spectrograph (STIS), which is coupled with a recent Wide Field Camera 3 (WFC3) transit (1.087 to 1.687âÎŒm). We derive refined physical parameters of the HAT-P-1 system, including an improved orbital ephemeris. The transmission spectrum shows a strong absorption signature shortward of 0.55âÎŒm, with a strong blueward slope into the near-ultraviolet. We detect atmospheric sodium absorption at a 3.3Ï significance level, but find no evidence for the potassium feature. The red data imply a marginally flat spectrum with a tentative absorption enhancement at wavelength longer than ⌠0.85âÎŒm. The STIS and WFC3 spectra differ significantly in absolute radius level (4.3 ± 1.6 pressure scaleheights), implying strong optical absorption in the atmosphere of HAT-P-1b. The optical to near-infrared difference cannot be explained by stellar activity, as simultaneous stellar activity monitoring of the G0V HAT-P-1b host star and its identical companion show no significant activity that could explain the result. We compare the complete STIS and WFC3 transmission spectrum with theoretical atmospheric models which include haze, sodium and an extra optical absorber. We find that both an optical absorber and a supersolar sodium to water abundance ratio might be a scenario explaining the HAT-P-1b observations. Our results suggest that strong optical absorbers may be a dominant atmospheric feature in some hot Jupiter exoplanets
Technology Readiness Levels for Machine Learning Systems
The development and deployment of machine learning (ML) systems can be
executed easily with modern tools, but the process is typically rushed and
means-to-an-end. The lack of diligence can lead to technical debt, scope creep
and misaligned objectives, model misuse and failures, and expensive
consequences. Engineering systems, on the other hand, follow well-defined
processes and testing standards to streamline development for high-quality,
reliable results. The extreme is spacecraft systems, where mission critical
measures and robustness are ingrained in the development process. Drawing on
experience in both spacecraft engineering and ML (from research through product
across domain areas), we have developed a proven systems engineering approach
for machine learning development and deployment. Our "Machine Learning
Technology Readiness Levels" (MLTRL) framework defines a principled process to
ensure robust, reliable, and responsible systems while being streamlined for ML
workflows, including key distinctions from traditional software engineering.
Even more, MLTRL defines a lingua franca for people across teams and
organizations to work collaboratively on artificial intelligence and machine
learning technologies. Here we describe the framework and elucidate it with
several real world use-cases of developing ML methods from basic research
through productization and deployment, in areas such as medical diagnostics,
consumer computer vision, satellite imagery, and particle physics
word~river literary review (2009)
wordriver is a literary journal dedicated to the poetry, short fiction and creative nonfiction of adjuncts and part-time instructors teaching in our universities, colleges, and community colleges. Our premier issue was published in Spring 2009. We are always looking for work that demonstrates the creativity and craft of adjunct/part-time instructors in English and other disciplines. We reserve first publication rights and onetime anthology publication rights for all work published. We define adjunct instructors as anyone teaching part-time or full-time under a semester or yearly contract, nationwide and in any discipline. Graduate students teaching under part-time contracts during the summer or who have used up their teaching assistant time and are teaching with adjunct contracts for the remainder of their graduate program also are eligible.https://digitalscholarship.unlv.edu/word_river/1002/thumbnail.jp
- âŠ