3,403 research outputs found

    Biomass burning and urban air pollution over the Central Mexican Plateau

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    Observations during the 2006 dry season of highly elevated concentrations of cyanides in the atmosphere above Mexico City (MC) and the surrounding plains demonstrate that biomass burning (BB) significantly impacted air quality in the region. We find that during the period of our measurements, fires contribute more than half of the organic aerosol mass and submicron aerosol scattering, and one third of the enhancement in benzene, reactive nitrogen, and carbon monoxide in the outflow from the plateau. The combination of biomass burning and anthropogenic emissions will affect ozone chemistry in the MC outflow

    The Topology of Branching Universes

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    The purpose of this paper is to survey the possible topologies of branching space-times, and, in particular, to refute the popular notion in the literature that a branching space-time requires a non-Hausdorff topology

    Partitioning of evapotranspiration using a stable isotope technique in an arid and high temperature agricultural production system

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    Agricultural production in the hot and arid low desert systems of southern California relies heavily on irrigation. A better understanding of how much and to what extent irrigated water is transpired by crops relative to being lost through evaporation would improve the management of increasingly limited water resources. In this study, we examined the partitioning of evapotranspiration (ET) over a field of forage sorghum (Sorghum bicolor), which was under evaluation as a potential biofuel feedstock, based on isotope measurements of three irrigation cycles at the vegetative stage. This study employed customized transparent chambers coupled with a laser-based isotope analyzer to continuously measure near-surface variations in the stable isotopic composition of evaporation (E, δE), transpiration (T, δT) and ET (δET) to partition the total water flux. Due to the extreme heat and aridity, δE and δT were very similar, which makes this system highly unusual. Contrary to an expectation that the isotopic signatures of T, E, and ET would become increasingly enriched as soils became drier, our results showed an interesting pattern that δE, δT, and δET increased initially as soil water was depleted following irrigation, but decreased with further soil drying in mid to late irrigation cycle. These changes are likely caused by root water transport from deeper to shallower soil layers. Results indicate that about 46% of the irrigated water delivered to the crop was used as transpiration, with 54% lost as direct evaporation. This implies that 28 − 39% of the total source water was used by the crop, considering the typical 60 − 85% efficiency of flood irrigation. The stable isotope technique provided an effective means of determining surface partitioning of irrigation water in this unusually harsh production environment. The results suggest the potential to further minimize unproductive water losses in these production systems

    Adiposity, Cardiometabolic Risk, and Vitamin D Status: The Framingham Heart Study

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    OBJECTIVE: Because vitamin D deficiency is associated with a variety of chronic diseases, understanding the characteristics that promote vitamin D deficiency in otherwise healthy adults could have important clinical implications. Few studies relating vitamin D deficiency to obesity have included direct measures of adiposity. Furthermore, the degree to which vitamin D is associated with metabolic traits after adjusting for adiposity measures is unclear. RESEARCH DESIGN AND METHODS: We investigated the relations of serum 25-hydroxyvitamin D (25[OH]D) concentrations with indexes of cardiometabolic risk in 3,890 nondiabetic individuals; 1,882 had subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) volumes measured by multidetector computed tomography (CT). RESULTS: In multivariable-adjusted regression models, 25(OH)D was inversely associated with winter season, waist circumference, and serum insulin (P < 0.005 for all). In models further adjusted for CT measures, 25(OH)D was inversely related to SAT (−1.1 ng/ml per SD increment in SAT, P = 0.016) and VAT (−2.3 ng/ml per SD, P < 0.0001). The association of 25(OH)D with insulin resistance measures became nonsignificant after adjustment for VAT. Higher adiposity volumes were correlated with lower 25(OH)D across different categories of BMI, including in lean individuals (BMI <25 kg/m2). The prevalence of vitamin D deficiency (25[OH]D <20 ng/ml) was threefold higher in those with high SAT and high VAT than in those with low SAT and low VAT (P < 0.0001). CONCLUSIONS: Vitamin D status is strongly associated with variation in subcutaneous and especially visceral adiposity. The mechanisms by which adiposity promotes vitamin D deficiency warrant further study.National Institutes of Health's National Heart, Lung, and Blood Institute (N01-HC-25195, R01-DK-80739): American Heart Associatio

    Panchromatic observations and modeling of the HV Tau C edge-on disk

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    We present new high spatial resolution (<~ 0.1") 1-5 micron adaptive optics images, interferometric 1.3 mm continuum and 12CO 2-1 maps, and 350 micron, 2.8 and 3.3 mm fluxes measurements of the HV Tau system. Our adaptive optics images reveal an unusually slow orbital motion within the tight HV Tau AB pair that suggests a highly eccentric orbit and/or a large deprojected physical separation. Scattered light images of the HV Tau C edge-on protoplanetary disk suggest that the anisotropy of the dust scattering phase function is almost independent of wavelength from 0.8 to 5 micron, whereas the dust opacity decreases significantly over the same range. The images further reveal a marked lateral asymmetry in the disk that does not vary over a timescale of 2 years. We further detect a radial velocity gradient in the disk in our 12CO map that lies along the same position angle as the elongation of the continuum emission, which is consistent with Keplerian rotation around an 0.5-1 Msun central star, suggesting that it could be the most massive component in the triple system. We use a powerful radiative transfer model to compute synthetic disk observations and use a Bayesian inference method to extract constraints on the disk properties. Each individual image, as well as the spectral energy distribution, of HV Tau C can be well reproduced by our models with fully mixed dust provided grain growth has already produced larger-than-interstellar dust grains. However, no single model can satisfactorily simultaneously account for all observations. We suggest that future attempts to model this source include more complex dust properties and possibly vertical stratification. (Abridged)Comment: 26 pages, 11 figures, editorially accepted for publication in Ap

    No Fossil Disk in the T Tauri Multiple System V773 Tau

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    We present new multi-epoch near-infrared and optical high-angular images of the V773 Tau pre-main sequence triple system, a weak-line T Tauri (WTTS) system in which the presence of an evolved, ``fossil'' protoplanetary disk has been inferred on the basis of a significant infrared excess. Our images reveal a fourth object bound to the system, V773 Tau D. While it is much fainter than all other components at 2 micron, it is the brightest source in the system at 4.7 micron. We also present medium-resolution K band adaptive optics spectroscopy of this object, which is featureless with the exception of a weak Br gamma emission line. Based on this spectrum and on the spectral energy distribution of the system, we show that V773 Tau D is another member of the small class of ``infrared companions'' (IRCs) to T Tauri stars. It is the least luminous, and probably the least massive, component of the system, as opposed to most other IRCs, which suggests that numerous low-luminosity IRCs such as V773 Tau D may still remain to be discovered. Furthermore, it is the source of the strong IR excess in the system. We therefore reject the interpretation of this excess as the signature of a fossil (or ``passive'') disk and further suggest that these systems may be much less frequent than previously thought. We further show that V773 Tau C is a variable classical T Tauri star (CTTS) and that its motion provides a well constrained orbital model. We show that V773 Tau D can be dynamically stable within this quadruple system if its orbit is highly inclined. Finally, V773 Tau is the first multiple system to display such a variety of evolutionary states (WTTS, CTTS, IRC), which may be the consequence of the strong star-star interactions in this compact quadruple system.Comment: Accepted for publication in Astrophysical Journal, 29 pages, 2 tables, 5 figure

    Behavioral intervention in adolescents improves bone mass, yet lactose maldigestion is a barrier

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    Calcium intake during adolescence is important for attainment of peak bone mass. Lactose maldigestion is an autosomal recessive trait, leading to lower calcium intake. The Adequate Calcium Today study aimed to determine if a school-based targeted behavioral intervention over one year could improve calcium intake and bone mass in early adolescent girls. The school-randomized intervention was conducted at middle schools in six states over one school year. A total of 473 girls aged 10–13 years were recruited for outcome assessments. Bone mineral content (BMC) was determined by dual energy X-ray absorptiometry. Dietary calcium intake was assessed with a semi-quantitative food frequency questionnaire. Baseline calcium intake and BMC were not significantly different between groups. After the intervention period, there were no differences in changes in calcium intake and BMC at any site between groups. An unanticipated outcome was a greater increase in spinal BMC among lactose digesters than lactose maldigesters in the intervention schools only (12 months) (6.9 ± 0.3 g vs. 6.0 ± 0.4 g, p = 0.03) and considering the entire study period (18 months) (9.9 ± 0.4 vs. 8.7 ± 0.5 g, p < 0.01). Overall, no significant differences between the intervention and control schools were observed. However, lactose digesters who received the intervention program increased bone mass to a greater extent than lactose maldigesters
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