1,774 research outputs found
Reynolds number effect on the velocity increment skewness in isotropic turbulence
Second and third order longitudinal structure functions and wavenumber
spectra of isotropic turbulence are computed using the EDQNM model and compared
to results of the multifractal formalism. At the highest Reynolds number
available in windtunnel experiments, , both the multifractal
model and EDQNM give power-law corrections to the inertial range scaling of the
velocity increment skewness. For EDQNM, this correction is a finite Reynolds
number effect, whereas for the multifractal formalism it is an intermittency
correction that persists at any high Reynolds number. Furthermore, the two
approaches yield realistic behavior of second and third order statistics of the
velocity fluctuations in the dissipative and near-dissipative ranges.
Similarities and differences are highlighted, in particular the Reynolds number
dependence
Profiling invasive Plasmodium falciparum merozoites using an integrated omics approach
The symptoms of malaria are brought about by blood-stage parasites, which are established when merozoites invade human erythrocytes. Our understanding of the molecular events that underpin erythrocyte invasion remains hampered by the short-period of time that merozoites are invasive. To address this challenge, a Plasmodium falciparum gamma-irradiated long-lived merozoite (LLM) line was developed and investigated. Purified LLMs invaded erythrocytes by an increase of 10โ300 fold compared to wild-type (WT) merozoites. Using an integrated omics approach, we investigated the basis for the phenotypic difference. Only a few single nucleotide polymorphisms within the P. falciparum genome were identified and only marginal differences were observed in the merozoite transcriptomes. By contrast, using label-free quantitative mass-spectrometry, a significant change in protein abundance was noted, of which 200 were proteins of unknown function. We determined the relative molar abundance of over 1100 proteins in LLMs and further characterized the major merozoite surface protein complex. A unique processed MSP1 intermediate was identified in LLM but not observed in WT suggesting that delayed processing may be important for the observed phenotype. This integrated approach has demonstrated the significant role of the merozoite proteome during erythrocyte invasion, while identifying numerous unknown proteins likely to be involved in invasion
Characterizing the Adaptive Optics Off-Axis Point-Spread Function - I: A Semi-Empirical Method for Use in Natural-Guide-Star Observations
Even though the technology of adaptive optics (AO) is rapidly maturing,
calibration of the resulting images remains a major challenge. The AO
point-spread function (PSF) changes quickly both in time and position on the
sky. In a typical observation the star used for guiding will be separated from
the scientific target by 10" to 30". This is sufficient separation to render
images of the guide star by themselves nearly useless in characterizing the PSF
at the off-axis target position. A semi-empirical technique is described that
improves the determination of the AO off-axis PSF. The method uses calibration
images of dense star fields to determine the change in PSF with field position.
It then uses this information to correct contemporaneous images of the guide
star to produce a PSF that is more accurate for both the target position and
the time of a scientific observation. We report on tests of the method using
natural-guide-star AO systems on the Canada-France-Hawaii Telescope and Lick
Observatory Shane Telescope, augmented by simple atmospheric computer
simulations. At 25" off-axis, predicting the PSF full width at half maximum
using only information about the guide star results in an error of 60%. Using
an image of a dense star field lowers this error to 33%, and our method, which
also folds in information about the on-axis PSF, further decreases the error to
19%.Comment: 29 pages, 9 figures, accepted for publication in the PAS
Dependence of inner accretion disk stress on parameters: the Schwarzschild case
We explore the parameter dependence of inner disk stress in black hole
accretion by contrasting the results of a number of simulations, all employing
3-d general relativistic MHD in a Schwarzschild spacetime. Five of these
simulations were performed with the intrinsically conservative code HARM3D,
which allows careful regulation of the disk aspect ratio, H/R; our simulations
span a range in H/R from 0.06 to 0.17. We contrast these simulations with two
previously reported simulations in a Schwarzschild spacetime in order to
investigate possible dependence of the inner disk stress on magnetic topology.
In all cases, much care was devoted to technical issues: ensuring adequate
resolution and azimuthal extent, and averaging only over those time-periods
when the accretion flow is in approximate inflow equilibrium. We find that the
time-averaged radial-dependence of fluid-frame electromagnetic stress is almost
completely independent of both disk thickness and poloidal magnetic topology.
It rises smoothly inward at all radii (exhibiting no feature associated with
the ISCO) until just outside the event horizon, where the stress plummets to
zero. Reynolds stress can also be significant near the ISCO and in the plunging
region; the magnitude of this stress, however, depends on both disk thickness
and magnetic topology. The two stresses combine to make the net angular
momentum accreted per unit rest-mass 7-15% less than the angular momentum of
the ISCO.Comment: Accepted for publication in ApJ, 52 pages, 38 figures, AASTEX.
High-resolution versions can be found at the following links:
http://ccrg.rit.edu/~scn/papers/schwarzstress.ps,
http://ccrg.rit.edu/~scn/papers/schwarzstress.pd
Fiber Bragg gratings of type I in SMF-28 and B/Ge fibre and type IIA B/Ge fibre under gamma radiation up to 0.54 MGy
The sensitivities of type I and IIA fibre Bragg gratings written to different reflectivities in SMF-28 and B/Ge fibres to ionizing radiation up to 0.54MGy are investigated. The Bragg wavelength shows a small and rapid increase at the start of irradiation followed by either a plateau (type I) or a decrease (type IIA)
Malate, citrate, and amino acids in tall fescue cultivars: Relationship to animal preference
Grazing animals depend on little-understood chemical and physical
cues when selecting forage diets. This study determined malate, citrate,
and amino acid concentrations in endophyte-free tall fescue (Festuca
arundinacea Schreb.) and related those concentrations to cultivar,
harvest time, and grazing-animal preference. Barcel', 'Kenhy', 'Kentucky-31',
'Missouri-96', `Mozark', `Stargrazer, and the two accessions
Cl and HiMag were established in three replicates within each of
three pastures. Organic acids were determined on regrowth within
each plot during four seasons and two years; amino adds were determined
on regrowth of four cultivars across three replicates during
both spring and fall seasons in one year. Malate and citrate were
extracted with boiling water and quantified by high-performance liquid
chromatography (HPLC) with an organic add column. Amino
adds were hydrolyzed, separated by ion-exchange HPLC, and quantified
as their ninhydrin derivatives. Both malate and citrate concentrations
differed between years. During one year only, malate concentrations
were higher in Kenhy (68 g kg-' dry matter [DM], most
preferred) than in Mozark (54 g kg-, DM, least preferred). Citrate
concentrations (13 g kg-' DM) were not different among cultivars.
Eighteen amino acids (including tryptophan) accounted for 75% of
total N. Thus, tissue N data were used as covariates to amino add
data in the ANOVA. Kenhy contained higher concentrations of eight
amino acids than did other cultivars. These differences may reflect
presence of Lolium genes in Kenhy. Cattle (Bos taurus L.) grazing
preference (0 = not eaten; 10 = completely eaten) was not related
to malate, citrate, or amino add concentrations among cultivars
Radiative efficiency and thermal spectrum of accretion onto Schwarzschild black holes
Recent general relativistic magneto-hydrodynamic (MHD) simulations of
accretion onto black holes have shown that, contrary to the basic assumptions
of the Novikov-Thorne model, there can be substantial magnetic stress
throughout the plunging region. Additional dissipation and radiation can
therefore be expected. We use data from a particularly well-resolved simulation
of accretion onto a non-spinning black hole to compute both the radiative
efficiency of such a flow and its spectrum if all emitted light is radiated
with a thermal spectrum whose temperature matches the local effective
temperature. This disk is geometrically thin enough (H/r ~= 0.06) that little
heat is retained in the flow. In terms of light reaching infinity (i.e., after
allowance for all relativistic effects and for photon capture by the black
hole), we find that the radiative efficiency is at least ~=6-10% greater than
predicted by the Novikov-Thorne model (complete radiation of all heat might
yield another ~6%). We also find that the spectrum more closely resembles the
Novikov-Thorne prediction for a/M ~= 0.2--0.3 than for the correct value,
a/M=0. As a result, if the spin of a non-spinning black hole is inferred by
model-fitting to a Novikov-Thorne model with known black hole mass, distance,
and inclination, the inferred a/M is too large by ~= 0.2--0.3.Comment: Submitted to ApJ, 26 pages, 12 figures (some in color), AASTE
Complete Genome Sequence and Comparative Metabolic Profiling of the Prototypical Enteroaggregative Escherichia coli Strain 042
Background \ud
Escherichia coli can experience a multifaceted life, in some cases acting as a commensal while in other cases causing intestinal and/or extraintestinal disease. Several studies suggest enteroaggregative E. coli are the predominant cause of E. coli-mediated diarrhea in the developed world and are second only to Campylobacter sp. as a cause of bacterial-mediated diarrhea. Furthermore, enteroaggregative E. coli are a predominant cause of persistent diarrhea in the developing world where infection has been associated with malnourishment and growth retardation. \ud
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Methods \ud
In this study we determined the complete genomic sequence of E. coli 042, the prototypical member of the enteroaggregative E. coli, which has been shown to cause disease in volunteer studies. We performed genomic and phylogenetic comparisons with other E. coli strains revealing previously uncharacterised virulence factors including a variety of secreted proteins and a capsular polysaccharide biosynthetic locus. In addition, by using Biologโข Phenotype Microarrays we have provided a full metabolic profiling of E. coli 042 and the non-pathogenic lab strain E. coli K-12. We have highlighted the genetic basis for many of the metabolic differences between E. coli 042 and E. coli K-12. \ud
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Conclusion \ud
This study provides a genetic context for the vast amount of experimental and epidemiological data published thus far and provides a template for future diagnostic and intervention strategies
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