7,139 research outputs found
A comparison of minimum distance and maximum likelihood techniques for proportion estimation
The estimation of mixing proportions P sub 1, P sub 2,...P sub m in the mixture density f(x) = the sum of the series P sub i F sub i(X) with i = 1 to M is often encountered in agricultural remote sensing problems in which case the p sub i's usually represent crop proportions. In these remote sensing applications, component densities f sub i(x) have typically been assumed to be normally distributed, and parameter estimation has been accomplished using maximum likelihood (ML) techniques. Minimum distance (MD) estimation is examined as an alternative to ML where, in this investigation, both procedures are based upon normal components. Results indicate that ML techniques are superior to MD when component distributions actually are normal, while MD estimation provides better estimates than ML under symmetric departures from normality. When component distributions are not symmetric, however, it is seen that neither of these normal based techniques provides satisfactory results
Climate change and the selective signature of the Late Ordovician mass extinction
Selectivity patterns provide insights into the causes of ancient extinction events. The Late Ordovician mass extinction was related to Gondwanan glaciation; however, it is still unclear whether elevated extinction rates were attributable to record failure, habitat loss, or climatic cooling. We examined Middle Ordovician-Early Silurian North American fossil occurrences within a spatiotemporally explicit stratigraphic framework that allowed us to quantify rock record effects on a per-taxon basis and assay the interplay of macrostratigraphic and macroecological variables in determining extinction risk. Genera that had large proportions of their observed geographic ranges affected by stratigraphic truncation or environmental shifts at the end of the Katian stage were particularly hard hit. The duration of the subsequent sampling gaps had little effect on extinction risk, suggesting that this extinction pulse cannot be entirely attributed to rock record failure; rather, it was caused, in part, by habitat loss. Extinction risk at this time was also strongly influenced by the maximum paleolatitude at which a genus had previously been sampled, a macroecological trait linked to thermal tolerance. A model trained on the relationship between 16 explanatory variables and extinction patterns during the early Katian interval substantially underestimates the extinction of exclusively tropical taxa during the late Katian interval. These results indicate that glacioeustatic sea-level fall and tropical ocean cooling played important roles in the first pulse of the Late Ordovician mass extinction in Laurentia
Impact of single nucleotide polymorphisms in leptin, leptin receptor, growth hormone receptor, and diacylglycerol acyltransferase (DGAT1) gene loci on milk production, feed, and body energy traits of UK dairy cows
Epitaxial Thin Films of the Giant-Dielectric-Constant Material CaCu_3Ti_4O_{12} Grown by Pulsed-laser Deposition
Pulsed-laser deposition has been used to grow epitaxial thin films of the
giant-dielectric-constant material CaCu_3Ti_4O_{12} on LaAlO_3 and SrTiO_3
substrates with or without various conducting buffer layers. The latter include
YBa_2Cu_3O_7, La_{1.85}Sr_{0.15}CuO_{4+\delta} and LaNiO_3. Above 100K - 150K
the thin films have a temperature independent dielectric constant as do single
crystals. The value of the dielectric constant is of the order of 1500 over a
wide temperature region, potentially making it a good candidate for many
applications. The frequency dependence of its dielectric properties below 100K
- 150K indicates an activated relaxation process.Comment: 11 pages, 4 figure
Long-term storage and ageābiased export of fluvial organic carbon: field evidence from West Iceland
Terrestrial organic carbon (OC) plays an important role in the carbon cycle, but questions remain regarding the controls and timescale(s) over which atmospheric COā remains sequestered as particulate OC (POC). Motivated by observations that terrestrial POC is physically stored within soils and other shallow sedimentary deposits, we examined the role that sediment storage plays in the terrestrial OC cycle. Specifically, we tested the hypothesis that sediment storage impacts the age of terrestrial POC. We focused on the Efri HaukadalsĆ” River catchment in Iceland as it lacks ancient sedimentary bedrock that would otherwise bias radiocarbonābased determinations of POC storage duration by supplying preāaged āpetrogenicā POC.
Our radiocarbon measurements of riverine suspended sediments and deposits implicated millennialāscale storage times. Comparison between the sample types (suspended and deposits) suggested an age offset between transported (suspended sediments) and stored (deposits) POC at the time of sampling, which is predicted by theory for the sediment age distribution in floodplains. We also observed that POC in suspended sediments is younger than the predicted mean storage duration generated from independent geomorphological data, which suggested an additional role for OC cycling. Consistent with this, we observed interparticle heterogeneity in the composition of POC by imaging our samples at the microscale using Xāray absorption spectroscopy. Specifically, we found that particles within individual samples differed in their sulfur oxidation state, which is indicative of multiple origins and/or diagenetic histories. Altogether, our results support recent coupled sediment storage and OC cycling models and indicate that the physical drivers of sediment storage are important factors controlling the cadence of carbon cycling
Implementation of a Standardized Handoff System for a General Surgery Residency Program
Introduction:
The I-PASS Handoff Bundle is an evidence based standardized set of educational materials designed to decrease handoff failures in patient care.
Two of every three sentinel events , the most serious events reported to the Joint Commission, are due to failures of communication, including miscommunication during patient care handoffs.
Implementation of the I-PASS method results in decreased medical errors and preventable adverse events
There are few studies that evaluate this validated method in the context of a General Surgery resident program
We aim to implement the I-PASS system into the transition of care process for General Surgery residents at our institution, and to analyze of the quality of the handoff process before and after the implementation.https://jdc.jefferson.edu/patientsafetyposters/1047/thumbnail.jp
Effects of temperature and carbon source on the isotopic fractionations associated with O_2 respiration for ^(17)O/^(16)O and ^(18)O/^(16)O ratios in E. coli
^(18)O/^(16)O and ^(17)O/^(16)O ratios of atmospheric and dissolved oceanic O_2 are used as biogeochemical tracers of photosynthesis and respiration. Critical to this approach is a quantitative understanding of the isotopic fractionations associated with production, consumption, and transport of O_2 in the ocean both at the surface and at depth. We made measurements of isotopic fractionations associated with O_2 respiration by E. coli. Our study included wild-type strains and mutants with only a single respiratory O_2 reductase in their electron transport chains (either a heme-copper oxygen reductase or a bd oxygen reductase). We tested two common assumptions made in interpretations of O_2 isotope variations and in isotope-enabled models of the O_2 cycle: (i) laboratory-measured respiratory ^(18)O/^(16)O isotopic fractionation factors (^(18)Ī±) of microorganisms are independent of environmental and experimental conditions including temperature, carbon source, and growth rate; And (ii) the respiratory āmass lawā exponent, Īø, between ^(18)O/^(16)O and ^(17)O/^(16)O, ^(17)Ī±āÆ=āÆ(^(18)Ī±)^Īø, is universal for aerobic respiration. Results demonstrated that experimental temperatures have an effect on both ^(18)Ī± and Īø for aerobic respiration. Specifically, lowering temperatures from 37 to 15āÆĀ°C decreased the absolute magnitude of ^(18)Ī± by 0.0025 (2.5ā°), and caused the mass law slope to decrease by 0.005. We propose a possible biochemical basis for these variations using a model of O_2 reduction that incorporates two isotopically discriminating steps: the reversible binding and unbinding of O_2 to a terminal reductase, and the irreversible reduction of that O_2 to water. Finally, we cast our results in a one-dimensional isopycnal reaction-advection-diffusion model, which demonstrates that enigmatic Ī“^(18)O and Ī^(17)O variations of dissolved O_2 in the dark ocean can be understood by invoking the observed temperature dependence of these isotope effects
Environmental effects of SPS: The middle atmosphere
The heavy lift launch vehicle associated with the solar power satellite (SPS) would deposit in the upper atmosphere exhaust and reentry products which could modify the composition of the stratosphere, mesosphere, and lower ionosphere. In order to assess such effects, atmospheric model simulations were performed, especially considering a geographic zone centered at the launch and reentry latitudes
Study of the volume and spin collapse in orthoferrite LuFeO_3 using LDA+U
Rare earth (R) orthoferrites RFeO_3 exhibit large volume transitions
associated with a spin collapse. We present here ab initio calculations on
LuFeO_3. We show that taking into account the strong correlation among the
Fe-3d electrons is necessary. Indeed, with the LDA+U method in the Projector
Augmented Wave (PAW), we are able to describe the isostructural phase
transition at 50 GPa, as well as a volume discontinuity of 6.0% at the
transition and the considerable reduction of the magnetic moment on the Fe
ions. We further investigate the effect of the variation of U and J and find a
linear dependence of the transition pressure on these parameters. We give an
interpretation for the non-intuitive effect of J. This emphasizes the need for
a correct determination of these parameters especially when the LDA+U is
applied to systems (e.g in geophysical investigations) where the transition
pressure is a priori unknown
Weed and Disease Control and Peanut Response Following PostāEmergence Herbicide and Fungicide Combinations
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