951 research outputs found
ESTIMATING THE SUBJECT BY TREATMENT INTERACTION IN NON-REPLICATED CROSSOVER DIET STUDIES
Researchers in human nutrition commonly refer to the ‘consistent’ diet effect (i.e. the main effect of diet) and an ‘inconsistent’ diet effect (i.e. a subject by diet interaction). However, due to the non-replicated designs of most studies, one can only estimate the first part using ANOVA; the latter (interaction) is confounded with the residual noise. In many diet studies, it appears that subjects do respond differently to the same diet, so the subject by diet interaction may be large. In a search of over 40,000 published human nutrition studies, most using a crossover design, we found that in none was a subject by diet interaction effect estimated. For this paper, we examined LDL-cholesterol data from a non-replicated crossover study with four diets, the typical American diet, with and without added plant sterols, and a cholesterol-lowering Step-1 diet, with and without sterols. We also examined LDL-cholesterol data from a second crossover study with some replications with three diets, representing the daily supplement of 0, 1 or 2 servings of pistachio nuts. These two data sets were chosen because experience suggested that LDLcholesterol responses to diet tend to be subject-specific. The second data set, with some replication, allowed us to estimate the subject by diet interaction term in a traditional ANOVA framework. One approach to estimating an interaction effect in non-replicated studies is through the use of a multiplicative decomposition of the interaction (sometimes called AMMI―additive main effects, multiplicative interaction). In this type of analysis, residuals, formed after estimated main effects are subtracted from the data, are arrayed in a matrix with diets as columns and subjects as rows. A singular value decomposition of the matrix is performed and the first, or first and second, principal component(s) are used as estimates of the interaction, and can be tested for significance using approximate F-tests. Using the R gnm package, we found large and significant subject by diet interaction effects in both data sets; estimates of the interaction in the second data set were similar to interaction estimates from traditional ANOVA. Of an additional 26 dependent variables from the first and a third data set (the latter investigating the effect of mild alcohol consumption on blood variables), 19 had significant subject by diet interactions, based on the AMMI methodology. These results suggest that the subject by diet interaction is often important and should not be ignored when analyzing data obtained from non-replicated crossover designs―the AMMI methodology works well and is readily available in statistical software packages
CARMA Large Area Star Formation Survey: Project Overview with Analysis of Dense Gas Structure and Kinematics in Barnard 1
We present details of the CARMA Large Area Star Formation Survey (CLASSy),
while focusing on observations of Barnard 1. CLASSy is a CARMA Key Project that
spectrally imaged N2H+, HCO+, and HCN (J=1-0 transitions) across over 800
square arcminutes of the Perseus and Serpens Molecular Clouds. The observations
have angular resolution near 7" and spectral resolution near 0.16 km/s. We
imaged ~150 square arcminutes of Barnard 1, focusing on the main core, and the
B1 Ridge and clumps to its southwest. N2H+ shows the strongest emission, with
morphology similar to cool dust in the region, while HCO+ and HCN trace several
molecular outflows from a collection of protostars in the main core. We
identify a range of kinematic complexity, with N2H+ velocity dispersions
ranging from ~0.05-0.50 km/s across the field. Simultaneous continuum mapping
at 3 mm reveals six compact object detections, three of which are new
detections. A new non-binary dendrogram algorithm is used to analyze dense gas
structures in the N2H+ position-position-velocity (PPV) cube. The projected
sizes of dendrogram-identified structures range from about 0.01-0.34 pc.
Size-linewidth relations using those structures show that non-thermal
line-of-sight velocity dispersion varies weakly with projected size, while rms
variation in the centroid velocity rises steeply with projected size. Comparing
these relations, we propose that all dense gas structures in Barnard 1 have
comparable depths into the sky, around 0.1-0.2 pc; this suggests that
over-dense, parsec-scale regions within molecular clouds are better described
as flattened structures rather than spherical collections of gas. Science-ready
PPV cubes for Barnard 1 molecular emission are available for download.Comment: Accepted to The Astrophysical Journal (ApJ), 51 pages, 27 figures
(some with reduced resolution in this preprint); Project website is at
http://carma.astro.umd.edu/class
Estudio Microbiológico e Histopatológico en Peces Tetra Neón (Paracheirodon innesi) de la Amazonía Peruana
The aim of this study was to determine the presence of infectious agents by microbiological and histopathological studies in the neon tetra (Paracheirodon innesi), an Amazonian ornamental fish. A total of 168 fish were randomly collected from the aquarium of an ornamental fish retail collector in Iquitos, Peru. For the microbiological study, kidney and spleen samples were collected during the necropsy of 84 specimens, and bacteria were isolated in trypticase soy agar (TSA), Citophaga (AO) and Middlebrook 7H9, while identification was done through Gram staining and biochemical analysis. The histopathological study was conducted in the remaining 84 fish. Bacteria isolated were of genera Flavobacterium, Staphylococcus, Carnobacterium, Pseudomonas, Enterococcus, Bacillus and of the Enterobacteriaceae family. In gills was observed laminar hyperplasia, fusion of lamellae and Mixosporidia spores at the tips of the lamellae; in the intestine was observed epithelial hyperplasia of the bowel and spores of Microsporidium in the intestinal villi; in the liver was found hydropic and fatty degeneration and a parasitic granuloma; in kidneys was found peritubular edema and hydropic degeneration; and in the muscular skeletal was found necrosis, presence of Mixosporidium cysts, granulomas, and spores of Microsporidium, Pleistophora and Heterosporis.El objetivo del presente estudio fue determinar la presencia de agentes infecciosos mediante estudios microbiológicos e histopatológicos en tetra neón (Paracheirodon innesi), pez amazónico ornamental. Se colectaron 168 peces, al azar, del acuario de un acopiador minorista de peces ornamentales de Iquitos, Perú. En la necropsia de 84 peces se tomaron muestras de riñón y bazo para el aislamiento de bacterias en agar tripticasa de soya (TSA), Citophaga (AO) y Middlebrook 7H9, haciendo la identificación mediante coloración Gram y análisis bioquímico. El estudio histopatológico se hizo con los 84 peces restantes. Se aislaron bacterias de los géneros Flavobacterium, Staphylococcus, Carnobacterium, Pseudomonas, Enterococcus, Bacillus y de la familia Enterobacteriaceae. En branquias se observó hiperplasia lamelar, fusión de lamelas, aspi como presencia de esporas de Mixosporidia en los ápices de las lamelas; en intestino se encontró hiperplasia del epitelio y presencia de esporas de Microsporidium en enterocitos; en hígado se encontró degeneración hidrópica, grasa y presencia de un granuloma parasitario; en riñones se encontró edema peritubular y degeneración hidrópica tubular; y en músculo esquelético se encontró necrosis, granulomas y presencia de quistes de Mixosporidium y esporas de Microsporidium, Pleistophora y Heterosporis
The Green Bank Ammonia Survey (GAS): First Results of NH3 mapping the Gould Belt
We present an overview of the first data release (DR1) and first-look science
from the Green Bank Ammonia Survey (GAS). GAS is a Large Program at the Green
Bank Telescope to map all Gould Belt star-forming regions with
mag visible from the northern hemisphere in emission from NH and other key
molecular tracers. This first release includes the data for four regions in
Gould Belt clouds: B18 in Taurus, NGC 1333 in Perseus, L1688 in Ophiuchus, and
Orion A North in Orion. We compare the NH emission to dust continuum
emission from Herschel, and find that the two tracers correspond closely.
NH is present in over 60\% of lines-of-sight with mag in
three of the four DR1 regions, in agreement with expectations from previous
observations. The sole exception is B18, where NH is detected toward ~ 40\%
of lines-of-sight with mag. Moreover, we find that the NH
emission is generally extended beyond the typical 0.1 pc length scales of dense
cores. We produce maps of the gas kinematics, temperature, and NH column
densities through forward modeling of the hyperfine structure of the NH
(1,1) and (2,2) lines. We show that the NH velocity dispersion,
, and gas kinetic temperature, , vary systematically between
the regions included in this release, with an increase in both the mean value
and spread of and with increasing star formation activity.
The data presented in this paper are publicly available.Comment: 33 pages, 27 figures, accepted to ApJS. Datasets are publicly
available: https://dataverse.harvard.edu/dataverse/GAS_DR
Droplets I: Pressure-Dominated Sub-0.1 pc Coherent Structures in L1688 and B18
We present the observation and analysis of newly discovered coherent
structures in the L1688 region of Ophiuchus and the B18 region of Taurus. Using
data from the Green Bank Ammonia Survey (GAS), we identify regions of high
density and near-constant, almost-thermal, velocity dispersion. Eighteen
coherent structures are revealed, twelve in L1688 and six in B18, each of which
shows a sharp "transition to coherence" in velocity dispersion around its
periphery. The identification of these structures provides a chance to study
the coherent structures in molecular clouds statistically. The identified
coherent structures have a typical radius of 0.04 pc and a typical mass of 0.4
Msun, generally smaller than previously known coherent cores identified by
Goodman et al. (1998), Caselli et al. (2002), and Pineda et al. (2010). We call
these structures "droplets." We find that unlike previously known coherent
cores, these structures are not virially bound by self-gravity and are instead
predominantly confined by ambient pressure. The droplets have density profiles
shallower than a critical Bonnor-Ebert sphere, and they have a velocity (VLSR)
distribution consistent with the dense gas motions traced by NH3 emission.
These results point to a potential formation mechanism through pressure
compression and turbulent processes in the dense gas. We present a comparison
with a magnetohydrodynamic simulation of a star-forming region, and we
speculate on the relationship of droplets with larger, gravitationally bound
coherent cores, as well as on the role that droplets and other coherent
structures play in the star formation process.Comment: Accepted by ApJ in April, 201
Resonant Auger spectroscopy at the L2,3 shake-up thresholds as a probe of electron correlation effects in nickel
The excitation energy dependence of the three-hole satellites in the
L3-M4,5M4,5 and L2-M4,5M4,5 Auger spectra of nickel metal has been measured
using synchrotron radiation. The satellite behavior in the non-radiative
emission spectra at the L3 and L2 thresholds is compared and the influence of
the Coster-Kronig channel explored. The three-hole satellite intensity at the
L3 Auger emission line reveals a peak structure at 5 eV above the L3 threshold
attributed to resonant processes at the 2p53d9 shake-up threshold. This is
discussed in connection with the 6-eV feature in the x-ray absorption spectrum.Comment: 8 pages, 4 figures; http://prb.aps.org/abstract/PRB/v58/i7/p3677_
An ammonia spectral map of the L1495-B218 filaments in the Taurus molecular cloud. I. Physical properties of filaments and dense cores
We present deep NH3 observations of the L1495-B218 filaments in the Taurus molecular cloud covering over a 3° angular range using the K-band focal plane array on the 100 m Green Bank Telescope. The L1495-B218 filaments form an interconnected, nearby, large complex extending over 8 pc. We observed NH3 (1, 1) and (2, 2) with a spectral resolution of 0.038 km s−1 and a spatial resolution of 31''. Most of the ammonia peaks coincide with intensity peaks in dust continuum maps at 350 and 500 μm. We deduced physical properties by fitting a model to the observed spectra. We find gas kinetic temperatures of 8–15 K, velocity dispersions of 0.05–0.25 km s−1, and NH3 column densities of 5 × 1012 to 1 × 1014 cm−2. The CSAR algorithm, which is a hybrid of seeded-watershed and binary dendrogram algorithms, identifies a total of 55 NH3 structures, including 39 leaves and 16 branches. The masses of the NH3 sources range from 0.05 to 9.5 . The masses of NH3 leaves are mostly smaller than their corresponding virial mass estimated from their internal and gravitational energies, which suggests that these leaves are gravitationally unbound structures. Nine out of 39 NH3 leaves are gravitationally bound, and seven out of nine gravitationally bound NH3 leaves are associated with star formation. We also found that 12 out of 30 gravitationally unbound leaves are pressure confined. Our data suggest that a dense core may form as a pressure-confined structure, evolve to a gravitationally bound core, and undergo collapse to form a protostar
Second harmonic generation and birefringence of some ternary pnictide semiconductors
A first-principles study of the birefringence and the frequency dependent
second harmonic generation (SHG) coefficients of the ternary pnictide
semiconductors with formula ABC (A = Zn, Cd; B = Si, Ge; C = As, P) with
the chalcopyrite structures was carried out. We show that a simple empirical
observation that a smaller value of the gap is correlated with larger value of
SHG is qualitatively true. However, simple inverse power scaling laws between
gaps and SHG were not found. Instead, the real value of the nonlinear response
is a result of a very delicate balance between different intraband and
interband terms.Comment: 13 pages, 12 figure
Tracing the evolution of dust-obscured activity using sub-millimetre galaxy populations from STUDIES and AS2UDS
We analyse the physical properties of 121 SNR ≥ 5 sub-millimetre galaxies (SMGs) from the STUDIES 450 μm survey. We model their UV-to-radio spectral energy distributions using MAGPHYS+photo-z and compare the results to similar modelling of 850 μm-selected SMG sample from AS2UDS, to understand the fundamental physical differences between the two populations at the observed depths. The redshift distribution of the 450-μm sample has a median of z = 1.85 ± 0.12 and can be described by strong evolution of the far-infrared luminosity function. The fainter 450-μm sample has ∼14 times higher space density than the brighter 850-μm sample at z ≲ 2, and a comparable space density at z = 2–3, before rapidly declining, suggesting LIRGs are the main obscured population at z ∼ 1–2, while ULIRGs dominate at higher redshifts. We construct rest-frame ∼180-μm-selected and dust-mass-matched samples at z = 1–2 and z = 3–4 from the 450 and 850-μm samples, respectively, to probe the evolution of a uniform sample of galaxies spanning the cosmic noon era. Using far-infrared luminosity, dust masses, and an optically thick dust model, we suggest that higher redshift sources have higher dust densities due to inferred dust continuum sizes which are roughly half of those for the lower redshift population at a given dust mass, leading to higher dust attenuation. We track the evolution in the cosmic dust mass density and suggest that the dust content of galaxies is governed by a combination of both the variation of gas content and dust destruction time-scale
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