3,559 research outputs found
A Multivariable Empirical Algorithm for Estimating Particulate Organic Carbon Concentration in Marine Environments From Optical Backscattering and Chlorophyll-a Measurements
Accurate estimates of the oceanic particulate organic carbon concentration (POC) from optical measurements have remained challenging because interactions between light and natural assemblages of marine particles are complex, depending on particle concentration, composition, and size distribution. In particular, the applicability of a single relationship between POC and the spectral particulate backscattering coefficient bbp(λ) across diverse oceanic environments is subject to high uncertainties because of the variable nature of particulate assemblages. These relationships have nevertheless been widely used to estimate oceanic POC using, for example, in situ measurements of bbp from Biogeochemical (BGC)-Argo floats. Despite these challenges, such an in situbased approach to estimate POC remains scientifically attractive in view of the expanding global-scale observations with the BGC-Argo array of profiling floats equipped with optical sensors. In the current study, we describe an improved empirical approach to estimate POC which takes advantage of simultaneous measurements of bbp and chlorophyll-a fluorescence to better account for the effects of variable particle composition on the relationship between POC and bbp. We formulated multivariable regression models using a dataset of field measurements of POC, bbp, and chlorophyll-a concentration (Chla), including surface and subsurface water samples from the Atlantic, Pacific, Arctic, and Southern Oceans. The analysis of this dataset of diverse seawater samples demonstrates that the use of bbp and an additional independent variable related to particle composition involving both bbp and Chla leads to notable improvements in POC estimations compared with a typical univariate regression model based on bbp alone. These multivariable algorithms are expected to be particularly useful for estimating POC with measurements from autonomous BGC-Argo floats operating in diverse oceanic environments. We demonstrate example results from the multivariable algorithm applied to depth-resolved vertical measurements from BGC-Argo floats surveying the Labrador Sea.publishedVersio
Brief Report: Which Came First? Exploring Crossmodal Temporal Order Judgements and Their Relationship with Sensory Reactivity in Autism and Neurotypicals
Previous studies have indicated that visual-auditory temporal acuity is reduced in children with autism spectrum conditions (ASC) in comparison to neurotypicals. In the present study we investigated temporal acuity for all possible bimodal pairings of visual, tactile and auditory information in adults with ASC (n = 18) and a matched control group (n = 18). No group differences in temporal acuity for crossmodal stimuli were observed, suggesting that this may be typical in adults with ASC. However, visual-tactile temporal acuity and bias towards vision when presented with visual-auditory information were both predictors of self-reported sensory reactivity. This suggests that reduced multisensory temporal acuity and/or attention towards vision may contribute to atypical sensory reactivity
A Detailed Thermal Analysis of the Binospec Spectrograph
Refractive optics in astronomical instruments are potentially sensitive to
temperature gradients and temperature transients. This sensitivity arises from
thermally dependent refractive indices, lens spacings, and lens dimensions. We
have therefore undertaken a detailed thermal analysis of Binospec, a wide-field
optical spectrograph under development for the converted MMT. Our goals are to
predict the temperature gradients that will be present in the Binospec optics
and structure under realistic operating conditions and to determine how design
choices affect these gradients. We begin our analysis by deriving thermal time
constants for instrument subassemblies. We then generate a low-resolution
finite difference model of the entire instrument and high-resolution models of
sensitive subassemblies. This approach to thermal analysis is applicable to a
variety of other instruments. We use measurements of the ambient temperature in
the converted MMT's dome to model Binospec's thermal environment. During
moderate conditions we find that the Binospec lens groups develop 0.14 C axial
and radial temperature gradients and that lens groups of different mass develop
0.5 C temperature differences; these numbers are doubled for the extreme
conditions. Internal heat sources do not significantly affect these results;
heat flow from the environment dominates. The instrument must be periodically
opened to insert new aperture masks, but we find that the resulting temperature
gradients and thermal stresses in the optics are small. Image shifts at the
detector caused by thermal deflections of the Binospec optical bench structure
are approx 0.1 pixel/hr. We conclude that the proposed Binospec design has
acceptable thermal properties, and briefly discuss design changes to further
reduce temperature gradients.Comment: 11 pages, to appear in PASP v114 Dec 200
Tissue Glycogen and Extracellular Buffering Limit the Survival of Red-Eared Slider Turtles during Anoxic Submergence at 3°C
The goal of this study was to identify the factors that limit the survival of the red-eared slider turtle Trachemys scripta during long-term anoxic submergence at 3°C. We measured blood acid-base status and tissue lactate and glycogen contents after 13, 29, and 44 d of submergence from ventricle, liver, carapace (lactate only), and four skeletal muscles. We also measured plasma Ca2+, Mg2+, Na+, K+, Cl-, inorganic phosphate (Pi), lactate, and glucose. After 44 d, one of the six remaining turtles died, while the other turtles were in poor condition and suffered from a severe acidemia (blood pH = 7.09 from 7.77) caused by lactic acidosis (plasma lactate 91.5 mmol L-1). An initial respiratory acidosis attenuated after 28 d. Lactate rose to similar concentrations in ventricle and skeletal muscle (39.3–46.1 μmol g-1). Liver accumulated the least lactate (21.8 μmol g-1), and carapace accumulated the most lactate (68.9 μmol g-1). Plasma Ca2+ and Mg2+ increased significantly throughout submergence to levels comparable to painted turtles at a similar estimated lactate load. Glycogen depletion was extensive in all tissues tested: by 83% in liver, by 90% in ventricle, and by 62%–88% in muscle. We estimate that the shell buffered 69.1% of the total lactate load, which is comparable to painted turtles. Compared with painted turtles, predive tissue glycogen contents and plasma HCO3- concentrations were low.We believe these differences contribute to the poorer tolerance to long-term anoxic submergence in red-eared slider turtles compared with painted turtles
Modeling Reactive Wetting when Inertial Effects are Dominant
Recent experimental studies of molten metal droplets wetting high temperature
reactive substrates have established that the majority of triple-line motion
occurs when inertial effects are dominant. In light of these studies, this
paper investigates wetting and spreading on reactive substrates when inertial
effects are dominant using a thermodynamically derived, diffuse interface model
of a binary, three-phase material. The liquid-vapor transition is modeled using
a van der Waals diffuse interface approach, while the solid-fluid transition is
modeled using a phase field approach. The results from the simulations
demonstrate an O \left( t^{-\nicefrac{1}{2}} \right) spreading rate during
the inertial regime and oscillations in the triple-line position when the metal
droplet transitions from inertial to diffusive spreading. It is found that the
spreading extent is reduced by enhancing dissolution by manipulating the
initial liquid composition. The results from the model exhibit good qualitative
and quantitative agreement with a number of recent experimental studies of
high-temperature droplet spreading, particularly experiments of copper droplets
spreading on silicon substrates. Analysis of the numerical data from the model
suggests that the extent and rate of spreading is regulated by the spreading
coefficient calculated from a force balance based on a plausible definition of
the instantaneous interface energies. A number of contemporary publications
have discussed the likely dissipation mechanism in spreading droplets. Thus, we
examine the dissipation mechanism using the entropy-production field and
determine that dissipation primarily occurs in the locality of the triple-line
region during the inertial stage, but extends along the solid-liquid interface
region during the diffusive stage
Sloan Digital Sky Survey Spectroscopic Lens Search. I. Discovery of Intermediate-Redshift Star-Forming Galaxies Behind Foreground Luminous Red Galaxies
We present a catalog of 49 spectroscopic strong gravitational lens candidates
selected from a Sloan Digital Sky Survey sample of 50996 luminous red galaxies.
Potentially lensed star-forming galaxies are detected through the presence of
background oxygen and hydrogen nebular emission lines in the spectra of these
massive foreground galaxies. This multiline selection eliminates the ambiguity
of single-line identification and provides a very promising sample of candidate
galaxy-galaxy lens systems at low to intermediate redshift, with foreground
redshifts ranging from 0.16 to 0.49 and background redshifts from 0.25 to 0.81.
Any lenses confirmed within our sample would be important new probes of
early-type galaxy mass distributions, providing complementary constraints to
those obtained from currently known lensed high-redshift quasars.Comment: 23 pages; to appear in The Astronomical Journal, 2004 April. Version
with full-resolution figures available at
http://web.mit.edu/bolton/www/speclens.ps.gz (PostScript) or
http://web.mit.edu/bolton/www/speclens.pdf (PDF
A New Einstein Cross: A Highly Magnified, Intrinsically Faint Lyman-Alpha Emitter at z=2.7
We report the discovery of a new Einstein cross at redshift z_S = 2.701 based
on Lyman-alpha emission in a cruciform configuration around an SDSS luminous
red galaxy (z_L = 0.331). The system was targeted as a possible lens based on
an anomalous emission line in the SDSS spectrum. Imaging and spectroscopy from
the W. M. Keck Observatory confirm the lensing nature of this system. This is
one of the widest-separation galaxy-scale lenses known, with an Einstein radius
of ~1.84 arcsec. We present simple gravitational lens models for the system and
compute the intrinsic properties of the lensed galaxy. The total mass of the
lensing galaxy within the 8.8 +/- 0.1 kpc enclosed by the lensed images is (5.2
+/- 0.1) x 10^11 M_sun. The lensed galaxy is a low mass galaxy (0.2 L*) with a
high equivalent-width Lyman-alpha line (EW_Lya_rest = 46 +/- 5 Angstroms).
Follow-up studies of this lens system can probe the mass structure of the
lensing galaxy, and can provide a unique view of an intrinsically faint,
high-redshift, star-forming galaxy at high signal-to-noise ratio.Comment: ApJ Letters, in pres
Community dimensions and HPSA practice location: 30 years of family medicine training
BACKGROUND AND OBJECTIVES: Our objective was to assess practicing family physicians\u27 confidence and participation in a range of community-related activities. Additionally, we assessed the strength of the relationship between the physicians\u27 reported medical school and residency training in community-related activities and their current community activities, as well as whether they were practicing in an underserved location.
METHODS: All 347 graduates of the University of Massachusetts Family Medicine Residency were surveyed about practice location and type, involvement and training in community work, confidence in community-related skills, and sociodemographic characteristics. Analyses were conducted by residency graduation decade (1976-1985, 1986-1995, and 1996-2005).
RESULTS: Earlier graduates (19761985) were significantly more likely to engage in an array of community-related activities, but recent graduates (1996-2005) were more likely to report having been trained in these skills. There was a significant positive association between practice in an underserved area and confidence in issues related to sociocultural aspects of care. While recent graduates were more likely to locate both initial and current practices in a Health Professions Shortage Area (HPSA), 20.6% of all graduates reported an initial practice in a HPSA.
CONCLUSIONS: While family physician involvement in community-related activities increases with years out of residency, a higher proportion of recent graduates report having learned community-related skills while in medical school. Physician relocation tends to be away from HPSA toward non-HPSA sites
Effect of nozzle secondary flows on turbine performance as indicated by exit surveys of a rotor
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