3,637 research outputs found
A Global Perspective On The Effects Of Eutrophication And Hypoxia On Aquatic Biota And Water Quality
Development associated with human populations has led to the globalization of many environmental problems. In marine systems, the most serious of these problems are directly related to the process of eutrophication. The increased production of organic matter in these marine systems associated with eutrophication is the primary factor impacting species abundance and composition and dissolved oxygen budgets. Oxygen, which is essential to maintaining balance in ecosystem processes through its role in mediating microbial and metazoan activities, has declined to critically low levels in many systems, which has led to the development of hypoxia (/l) and anoxia (0 ml O2/l). Currently, most oxygen depletion events are seasonal, but trends toward longer periods that could eventually lead to persistent hypoxic or anoxic conditions are emerging. Over the last 50 years, there has been an increase in the number of systems reporting problems associated with low dissolved oxygen. Currently there are over 100 hypoxic/anoxic areas around the globe, ranging in size fromkm2, that exhibit a graded series of responses to oxygen depletion, ranging from no obvious change to mass mortality of bottom fauna. Ecosystems currently severely stressed by eutrophication induced hypoxia continue to be threatened with the loss of fisheries, loss of biodiversity, alteration of food webs, and simplification of energy flows.https://scholarworks.wm.edu/vimsbooks/1014/thumbnail.jp
The source structure of 0642+449 detected from the CONT14 observations
The CONT14 campaign with state-of-the-art VLBI data has observed the source
0642+449 with about one thousand observables each day during a continuous
observing period of fifteen days, providing tens of thousands of closure
delays---the sum of the delays around a closed loop of baselines. The closure
delay is independent of the instrumental and propagation delays and provides
valuable additional information about the source structure. We demonstrate the
use of this new "observable" for the determination of the structure in the
radio source 0642+449. This source, as one of the defining sources in the
second realization of the International Celestial Reference Frame (ICRF2), is
found to have two point-like components with a relative position offset of -426
microarcseconds in right ascension and -66 microarcseconds in declination. The
two components are almost equally bright with a flux-density ratio of 0.92. The
standard deviation of closure delays for source 0642+449 was reduced from 139
ps to 90 ps by using this two-component model. Closure delays larger than one
nanosecond are found to be related to the source structure, demonstrating that
structure effects for a source with this simple structure could be up to tens
of nanoseconds. The method described in this paper does not rely on a priori
source structure information, such as knowledge of source structure determined
from direct (Fourier) imaging of the same observations or observations at other
epochs. We anticipate our study to be a starting point for more effective
determination of the structure effect in VLBI observations.Comment: 14 pages, 13 figures, Accepted by Astronomical Journal on 12 Jul,
201
The impacts of source structure on geodetic parameters demonstrated by the radio source 3C371
Closure quantities measured by very long baseline interferometry (VLBI)
observations are independent of instrumental and propagation instabilities and
antenna gain factors, but are sensitive to source structure. A new method is
proposed to calculate a structure index based on the median values of closure
quantities rather than the brightness distribution of a source. The results are
comparable to structure indices based on imaging observations at other epochs
and demonstrate the flexibility of deriving structure indices from exactly the
same observations as used for geodetic analysis and without imaging analysis. A
three-component model for the structure of source 3C371 is developed by
model-fitting closure phases. It provides a real case of tracing how the
structure effect identified by closure phases in the same observations as the
delay observables affects the geodetic analysis, and investigating which
geodetic parameters are corrupted to what extent by the structure effect. Using
the resulting structure correction based on the three-component model of source
3C371, two solutions, with and without correcting the structure effect, are
made. With corrections, the overall rms of this source is reduced by 1 ps, and
the impacts of the structure effect introduced by this single source are up to
1.4 mm on station positions and up to 4.4 microarcseconds on Earth orientation
parameters. This study is considered as a starting point for handling the
source structure effect on geodetic VLBI from geodetic sessions themselves.Comment: 5 figures, 15 pages, accepted by Journal of Geodesy at 19 Dec., 201
Volume-Based Care among Young Women Diagnosed with Uterine Cancer
Purpose. To characterize volume-based care of uterine cancer among women aged ≤50 years. Methods. The Maryland Health Service Cost Review Commission database was accessed for uterine cancer surgical cases from 1994 to 2005. Cross-tabulations and logistic regression models were used to evaluate for significant associations among volume-based care and other variables comparing women ≤50 years with those aged >50 years. Results. Women ≤50 years comprised 13.6% of the cases. Women ≤50 years were less likely to be managed by high-volume surgeons (31.6% versus 35.1%, P = 0.02). For women ≤50 years, there was a trend toward management at low-volume hospitals (52.0% versus 54.0%, P = 0.22). No deaths were reported among the group of women ≤50 years treated by high-volume providers or at high-volume centers. Women ≤50 years managed by high-volume surgeons had longer length of stay (P < 0.001) and higher adjusted cost of hospital-related care (P < 0.00). Women ≤50 years managed at high-volume centers had higher adjusted cost of hospital-related care (P = 0.01). Conclusion. Primary surgical care of young women with uterine cancer is often performed by low-volume providers
A Vacuum-driven Origami “Magic-ball” Soft Gripper
Soft robotics has yielded numerous examples of soft grippers that utilize compliance to achieve impressive grasping performances with great simplicity, adaptability, and robustness. Designing soft grippers with substantial grasping strength while remaining compliant and gentle is one of the most important challenges in this field. In this paper, we present a light-weight, vacuum-driven soft robotic gripper made of an origami “magic-ball” and a flexible thin membrane. We also describe the design and fabrication method to rapidly manufacture the gripper with different combinations of lowcost materials for diverse applications. Grasping experiments demonstrate that our gripper can lift a large variety of objects, including delicate foods, heavy bottles, and other miscellaneous items. The grasp force on 3D-printed objects is also characterized through mechanical load tests. The results reveal that our soft gripper can produce significant grasp force on various shapes using negative pneumatic pressure (vacuum). This new gripper holds the potential for many practical applications that require safe, strong, and simple graspingUnited States. Defense Advanced Research Projects Agency (award number FA8650-15-C-7548)National Science Foundation (U.S.) (award number 1830901)Wyss Institute for Biologically Inspired EngineeringJD.co
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Risk of Ischemic Cerebrovascular and Coronary Events in Adult Users of Anticonvulsant Medications in Routine Care Settings
Background: Older‐generation anticonvulsants that highly induce cytochrome P450 enzyme system activity produce metabolic abnormalities that may increase cardiovascular risk. The objective of this study was to evaluate the risk of ischemic cerebrovascular and coronary events in adult new users of anticonvulsants that highly induce cytochrome P450 activity compared with other anticonvulsant agents, as observed in a routine care setting. Methods and Results: This was a cohort study of patients 40 to 64 years old from the HealthCore Integrated Research Database who had initiated an anticonvulsant medication between 2001 and 2006 and had no recorded major coronary or cerebrovascular condition in the 6 months before treatment initiation. Propensity score (PS) matching was used to evaluate ischemic cerebrovascular and coronary risk among anticonvulsant new users. High‐dimensional propensity score (hdPS)–matched analyses were used to confirm adjusted findings. The study identified 913 events in 166 031 unmatched new treatment episodes with anticonvulsant drugs. In a PS‐matched population of 22 864 treatment episodes, the rate ratio (RR) for ischemic coronary or cerebrovascular events associated with highly inducing agents versus other agents was 1.22 (95% CI, 0.90‐1.65). The RR moved to 0.99 (95% CI, 0.73‐1.33) with adjustment for hdPS matching (RR, 1.47; 95% CI, 0.95‐2.28 for cerebrovascular events; RR, 0.70; 95% CI, 0.47‐1.05 for coronary events). Conclusions: In this exploratory analysis, there was no evidence of a consistent and statistically significant effect of initiating anticonvulsants that highly induce cytochrome P450 activity on ischemic coronary or cerebrovascular outcomes compared with other agents, given routine care utilization patterns
Factors Influencing Pseudo-Accommodation—The Difference between Subjectively Reported Range of Clear Focus and Objectively Measured Accommodation Range
The key determinants of the range of clear focus in pre-presbyopes and their relative contributions to the difference between subjective range of focus and objective accommodation assessments have not been previously quantified. Fifty participants (aged 33.0 ± 6.4 years) underwent simultaneous monocular subjective (visual acuity measured with an electronic test-chart) and objective (dynamic accommodation measured with an Aston open-field aberrometer) defocus curve testing for lenses between +2.00 to −10.00 DS in +0.50 DS steps in a randomized order. Pupil diameter and ocular aberrations (converted to visual metrics normalized for pupil size) at each level of blur were measured. The difference between objective range over which the power of the crystalline lens changes and the subjective range of clear focus was quantified and the results modelled using pupil size, refractive error, tolerance to blur, and ocular aberrations. The subjective range of clear focus was principally accounted for by age (46.4%) and pupil size (19.3%). The objectively assessed accommodative range was also principally accounted for by age (27.6%) and pupil size (15.4%). Over one-quarter (26.0%) of the difference between objective accommodation and subjective range of clear focus was accounted for by age (14.0%) and spherical aberration at maximum accommodation (12.0%). There was no significant change in the objective accommodative response (F = 1.426, p = 0.229) or pupil size (F = 0.799, p = 0.554) of participants for levels of defocus above their amplitude of accommodation. Pre-presbyopes benefit from an increased subjective range of clear vision beyond their objective accommodation due in part to neural factors, resulting in a measured depth-of-focus of, on average, 1.0
Constraints on the Universal CIV Mass Density at z~6 from Early IR Spectra Obtained with the Magellan FIRE Spectrograph
We present a new determination of the intergalactic CIV mass density at 4.3 <
z < 6.3. Our constraints are derived from high signal-to-noise spectra of seven
quasars at z > 5.8 obtained with the newly commissioned FIRE spectrograph on
the Magellan Baade telescope, coupled with six observations of northern objects
taken from the literature. We confirm the presence of a downturn in the CIV
abundance at =5.66 by a factor of 4.1 relative to its value at =4.96, as
measured in the same sightlines. In the FIRE sample, a strong system previously
reported in the literature as CIV at z=5.82 is re-identified as MgII at z=2.78,
leading to a substantial downward revision in for these prior
studies. Additionally we confirm the presence of at least two systems with
low-ionization CII, SiII, and OI absorption but relatively weak signal from
CIV. The latter systems systems may be of interest if the downward trend in
at high redshift is driven in part by ionization effects.Comment: 14 pages, 6 figures, 2 tables. Submitted to Ap
Starburst99: Synthesis Models for Galaxies with Active Star Formation
Starburst99 is a comprehensive set of model predictions for
spectrophotometric and related properties of galaxies with active star
formation. The models are an improved and extended version of the data set
previously published by Leitherer & Heckman (1995). We have upgraded our code
by implementing the latest set of stellar evolution models of the Geneva group
and the model atmosphere grid compiled by Lejeune et al. (1997). Several
predictions which were not included in the previous publication are shown here
for the first time. The models are presented in a homogeneous way for five
metallicities between Z = 0.040 and 0.001 and three choices of the initial mass
function. The age coverage is 10^6 to 10^9 yr. We also show the spectral energy
distributions which are used to compute colors and other quantities. The full
data set is available for retrieval at
http://www.stsci.edu/science/starburst99/. This website allows users to run
specific models with non-standard parameters as well. We also make the source
code available to the community.Comment: 32 pages, LaTeX. All the Figures and the summary Table are located at
http://www.stsci.edu/science/starburst99/, ApJ accepte
Open versus laparoscopic retroperitoneal lymph node dissection: Assessing adequacy of dissection in a porcine model
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