3,771 research outputs found
Effect of Fractional Kinetic Helicity on Turbulent Magnetic Dynamo Spectra
Magnetic field amplification in astrophysics ultimately requires an
understanding of magnetohydrodynamic turbulence. Kinetic helicity has long been
known to be important for large scale field growth in forced MHD turbulence,
and has been recently demonstrated numerically to be asymptotically consistent
with slow mean field dynamo action in a periodic box. Here we show numerically
that the magnetic spectrum at and below the forcing scale is also strongly
influenced by kinetic helicity. We identify a critical value,
above which the magnetic spectrum develops maxima at wavenumber scale
{\it and} at the forcing scale, For the field peaks only at the
resistive scale. Kinetic helicity may thus be important not only for generating
a large scale field, but also for establishing observed peaks in magnetic
spectra at the forcing scale. The turbulent Galactic disk provides an example
where both large scale ( supernova forcing scale) fields and small scale
( forcing scale, with peak at forcing scale) fields are observed. We
discuss this, and the potential application to the protogalaxy, but also
emphasize the limitations in applying our results to these systems.Comment: version accepted to ApJL, 10 pages, 3 fig
On the role of stochastic Fermi acceleration in setting the dissipation scale of turbulence in the interstellar medium
We consider the dissipation by Fermi acceleration of magnetosonic turbulence
in the Reynolds Layer of the interstellar medium. The scale in the cascade at
which electron acceleration via stochastic Fermi acceleration (STFA) becomes
comparable to further cascade of the turbulence defines the inner scale. For
any magnetic turbulent spectra equal to or shallower than Goldreich-Sridhar
this turns out to be cm, which is much larger than the shortest
length scales observed in radio scintillation measurements. While STFA for such
spectra then contradict models of scintillation which appeal directly to an
extended, continuous turbulent cascade, such a separation of scales is
consistent with the recent work of \citet{Boldyrev2} and \citet{Boldyrev3}
suggesting that interstellar scintillation may result from the passage of radio
waves through the galactic distribution of thin ionized boundary surfaces of
HII regions, rather than density variations from cascading turbulence. The
presence of STFA dissipation also provides a mechanism for the non-ionizing
heat source observed in the Reynolds Layer of the interstellar medium
\citep{Reynolds}. STFA accommodates the proper heating power, and the input
energy is rapidly thermalized within the low density Reynolds layer plasma.Comment: 12 Pages, no figures. Accepted for publication in MNRA
Thermal conduction and particle transport in strong MHD turbulence, with application to galaxy-cluster plasmas
We investigate field-line separation in strong MHD turbulence analytically
and with direct numerical simulations. We find that in the
static-magnetic-field approximation the thermal conductivity in galaxy clusters
is reduced by a factor of about 5-10 relative to the Spitzer thermal
conductivity of a non-magnetized plasma. We also estimate how the thermal
conductivity would be affected by efficient turbulent resistivity.Comment: Major revision: higher resolution simulations lead to significantly
different conclusions. 26 pages, 10 figure
Peptide-Assisted Design of Precision Polymer Sequences
Functional sequences of monodisperse, sequence‐defined oligo(amide‐urethane)s are designed based on a peptide sequence as blueprint. The translation of a discrete side‐chain functionality sequence from a known peptide‐based solubilizer of the photosensitizer meta‐tetra(hydroxyphenyl)‐chlorin, into a non‐peptidic precision polymer backbone is demonstrated. The resulting peptidomimetic precision polymers retain the functions of the parent peptide sequence, showing analogues sensitivity toward single monomer mutations/exchanges and even exceeding the parent peptide equivalent by reaching up to 69% higher payload capacities and more favored release kinetics.Peer Reviewe
Prevalence of suspected hypertrophic cardiomyopathy or left ventricular hypertrophy based on race and gender in teenagers using screening echocardiography
BACKGROUND:The goal of this study was to evaluate the prevalence of suspected hypertrophic cardiomyopathy (HCM) in a population of teenagers undergoing screening echocardiography for the detection of HCM.METHOD:The Anthony Bates Foundation performs screening echocardiography for the prevention of sudden death. A total of 2,066 students were studied between the ages of 13 to 19 years. Suspected HCM was defined as any wall thickness greater than or equal to] 15 mm. LVH was defined as wall thickness greater than or equal to] 13 mmRESULTS:Prevalence of suspected HCM was 0.7% (14/2066). After adjusting for hypertension (HTN), the total prevalence was 0.5% (8/1457). In a subgroup analysis, 551 teenagers with documented race and LV wall thickness were identified between the ages of 13 - 19 years. African American teenagers 6% (3/50)] had higher prevalence of suspected HCM 0.8% (4/501), OR 7.93, CI 1.72-36.49, p = 0.002]. After multivariate adjustment for age, gender, BMI and HTN (systolic BP >140 and diastolic BP of > 90), African American race remained independently associated with suspected HCM (OR 4.89, CI 1.24-39.62, p = 0.02).CONCLUSION:The prevalence of suspected HCM in young teenagers is approximately 0.2%. This prevalence appears to be higher in African Americans. However, due to small number of African Americans in our population, our result needs to be confirmed in larger trials.This item is part of the UA Faculty Publications collection. For more information this item or other items in the UA Campus Repository, contact the University of Arizona Libraries at [email protected]
Measuring Accuracy of Triples in Knowledge Graphs
An increasing amount of large-scale knowledge graphs have been constructed in recent years. Those graphs are often created from text-based extraction, which could be very noisy. So far, cleaning knowledge graphs are often carried out by human experts and thus very inefficient. It is necessary to explore automatic methods for identifying and eliminating erroneous information. In order to achieve this, previous approaches primarily rely on internal information i.e. the knowledge graph itself. In this paper, we introduce an automatic approach, Triples Accuracy Assessment (TAA), for validating RDF triples (source triples) in a knowledge graph by finding consensus of matched triples (among target triples) from other knowledge graphs. TAA uses knowledge graph interlinks to find identical resources and apply different matching methods between the predicates of source triples and target triples. Then based on the matched triples, TAA calculates a confidence score to indicate the correctness of a source triple. In addition, we present an evaluation of our approach using the FactBench dataset for fact validation. Our findings show promising results for distinguishing between correct and wrong triples
The divergence of neighboring magnetic field lines and fast-particle diffusion in strong magnetohydrodynamic turbulence, with application to thermal conduction in galaxy clusters
We investigate field-line separation in strong MHD turbulence using direct
numerical simulations. We find that in the static-magnetic-field approximation
the thermal conductivity in galaxy clusters is reduced by a factor of about 50
relative to the Spitzer thermal conductivity of a non-magnetized plasma. This
value is too small for heat conduction to balance radiative cooling in
clusters.Comment: Major revision: higher resolution simulations lead to significantly
different conclusions. 4 pages, 4 figures, submitted to Physical Review
Letter
Acceleration of energetic particles by large-scale compressible magnetohydrodynamic turbulence
Fast particles diffusing along magnetic field lines in a turbulent plasma can
diffuse through and then return to the same eddy many times before the eddy is
randomized in the turbulent flow. This leads to an enhancement of particle
acceleration by large-scale compressible turbulence relative to previous
estimates in which isotropic particle diffusion is assumed.Comment: 13 pages, 3 figures, accepted for publication in Ap
Making Colony Pcr Easier By Adding Gel-loading Buffer To The Amplification Reaction.
28424, 42
Speciation in Golden-Plovers, Pluvialis dominica and P. fulva: Evidence from the Breeding Grounds
Two forms of golden-plover have long been considered subspecies, Pluvialisdominica dominica and P. d. fulva. Prior studies have shown differences between forms in breeding distributions, wintering distributions, plumage, morphology, molt, and maturation schedules. We report clear and consistent differences in breeding vocalizations and nesting habitat, and strict assortative mating in areas of sympatry in western Alaska. These results indicate a greater degree of differentiation between the forms than was previously appreciated. They are appropriately treated as separate species and should be referred to under the names Pluvialis dominica, for the American Golden-Plover, and Pluvialis fulva, for the Pacific Golden-Plover
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