444,797 research outputs found
Whole-stream metabolism: strategies for measuring and modeling diel trends of dissolved oxygen
Stream metabolism is used to characterize the allochthonous and autochthonous basis of stream foodweb production. The metabolic rates of respiration and gross primary production often are estimated from changes in dissolved O2 concentration in the stream over time. An upstream–downstream O2 accounting method (2-station) is used commonly to estimate metabolic rates in a defined length of stream channel. Various approaches to measuring and analyzing diel O2 trends have been used, but a detailed comparison of different approaches (e.g., required reach length, method of measuring aeration rate [k], and use of temperature-corrected metabolic rates) is needed. We measured O2 upstream and downstream of various reaches in Kings Creek, Kansas. We found that 20 m was the approximate minimum reach length required to detect a significant change in O2, a result that matched the prediction of a calculation method to determine minimum reach length. We assessed the ability of models based on 2-station diel O2 data and k measurements in various streams around Manhattan, Kansas, to predict k accurately, and we tested the importance of accounting for temperature effects on metabolic rates. We measured gas exchange directly with an inert gas and used a tracer dye to account for dilution and to measure velocity and discharge. Modeled k was significantly correlated with measured k (Kendall's τ, p < 0.001; regression adjusted R²  =  0.70), but 19 published equations for estimating k generally provided poor estimates of measured k (only 6 of 19 equations were significantly correlated). Temperature correction of metabolic rates allowed us to account for increases in nighttime O2, and temperature-corrected metabolic rates fit the data somewhat better than uncorrected estimates. Use of temperature-correction estimates could facilitate cross-site comparisons of metabolism
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Psychometric Evaluation of an Instrument to Measure Prospective Pregnancy Preferences: The Desire to Avoid Pregnancy Scale.
BACKGROUND:Existing approaches to measuring women's pregnancy intentions suffer important limitations, including retrospective assessment, overly simple categories, and a presumption that all women plan pregnancies. No psychometrically valid scales exist to prospectively measure the ranges of women's pregnancy preferences. MATERIALS AND METHODS:Using a rigorous construct modeling approach, we developed a scale to measure desire to avoid pregnancy. We developed 60 draft items from existing research, assessed comprehension through 25 cognitive interviews, and administered items in surveys with 594 nonpregnant women in 7 primary and reproductive health care facilities in Arizona, New Jersey, New Mexico, South Carolina, and Texas in 2016-2017. We used item response theory to reduce the item set and assess the scale's reliability, internal structure validity, and external validity. Items were included based on fit to a random effects multinomial logistic regression model (partial credit item response model), correspondence of item difficulty with participants' pregnancy preference levels, and consistency of each item's response options with overall scale scores. RESULTS:The 14 final items covered 3 conceptual domains: cognitive preferences, affective feelings, and practical consequences. Items fit the unidimensional model, with a separation reliability of 0.90 (Cronbach α: 0.95). The scale met established criteria for internal validity, including correspondence between each item's response categories and overall scale scores. We found no important differential item functioning by participant characteristics. CONCLUSIONS:A robust measure is available to prospectively measure desire to avoid pregnancy. The measure can aid in identifying women who could benefit from contraceptive care and research on less desired pregnancy
Evaluating Cascading Impact of Attacks on Resilience of Industrial Control Systems: A Design-Centric Modeling Approach
A design-centric modeling approach was proposed to model the behaviour of the
physical processes controlled by Industrial Control Systems (ICS) and study the
cascading impact of data-oriented attacks. A threat model was used as input to
guide the construction of the CPS model where control components which are
within the adversary's intent and capabilities are extracted. The relevant
control components are subsequently modeled together with their control
dependencies and operational design specifications. The approach was
demonstrated and validated on a water treatment testbed. Attacks were simulated
on the testbed model where its resilience to attacks was evaluated using
proposed metrics such as Impact Ratio and Time-to-Critical-State. From the
analysis of the attacks, design strengths and weaknesses were identified and
design improvements were recommended to increase the testbed's resilience to
attacks
Investigating the Feasibility of Integrating Pavement Friction and Texture Depth Data in Modeling for INDOT PMS
Under INDOT’s current friction testing program, the friction is measured annually on interstates but only once every three years on non-interstate roadways. The state’s Pavement Management System, however, would require current data if friction were to be included in the PMS. During routine pavement condition monitoring for the PMS, texture data is collected annually. This study explored the feasibility of using this pavement texture data to estimate the friction during those years when friction is not measured directly. After multi0ple approaches and a wide variety of ways of examining the currently available data and texture measuring technologies, it was determined that it is not currently feasible to use the texture data as a surrogate for friction testing. This is likely because the lasers used at this time are not capable of capturing the small-scale pavement microtexture. This situation may change, however, with advances in laser or photo interpretation technologies and improved access to materials data throughout the INDOT pavement network
Spectroastrometry of rotating gas disks for the detection of supermassive black holes in galactic nuclei. III. CRIRES observations of the Circinus galaxy
We present new CRIRES spectroscopic observations of BrGamma in the nuclear
region of the Circinus galaxy, obtained with the aim of measuring the black
hole (BH) mass with the spectroastrometric technique. The Circinus galaxy is an
ideal benchmark for the spectroastrometric technique given its proximity and
secure BH measurement obtained with the observation of its nuclear H2O maser
disk. The kinematical data have been analyzed both with the classical method
based on the analysis of the rotation curves and with the new method developed
by us and based on spectroastrometry. The classical method indicates that the
gas disk rotates in the gravitational potential of an extended stellar mass
distribution and a spatially unresolved mass of (1.7 +- 0.2) 10^7 Msun,
concentrated within r < 7 pc. The new method is capable of probing gas rotation
at scales which are a factor ~3.5 smaller than those probed by the rotation
curve analysis. The dynamical mass spatially unresolved with the
spectroastrometric method is a factor ~2 smaller, 7.9 (+1.4 -1.1) 10^6 Msun
indicating that spectroastrometry has been able to spatially resolve the
nuclear mass distribution down to 2 pc scales. This unresolved mass is still a
factor ~4.5 larger than the BH mass measurement obtained with the H2O maser
emission indicating that it has not been possible to resolve the sphere of
influence of the BH. Based on literature data, this spatially unresolved
dynamical mass distribution is likely dominated by molecular gas and it has
been tentatively identified with the circum-nuclear torus which prevents a
direct view of the central BH in Circinus. This mass distribution, with a size
of ~2pc, is similar in shape to that of the star cluster of the Milky Way
suggesting that a molecular torus, forming stars at a high rate, might be the
earlier evolutionary stage of the nuclear star clusters which are common in
late type spirals.Comment: A&A in press. We wish to honor the memory of our great friend and
colleague David Axon. He will be greatly missed by all of us. arXiv admin
note: text overlap with arXiv:1110.093
Top Quark Properties Measurements in CMS
Recent top quark properties measurements made with the CMS detector at the
LHC are presented. The measurements summarized include spin correlation of top
quark pairs, asymmetries, top quark mass, and the underlying event in top quark
pair events. The results are compared to the standard model predictions and new
physics models.Comment: 8 pages, 5 figures, To appear in the proceedings of LaThuile2016, Les
Rencontres de Physique de la Vallee d'Aoste, March 6-12, 2016, La Thuile,
Aosta Valley, Ital
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