3,734 research outputs found

    Effect of Fractional Kinetic Helicity on Turbulent Magnetic Dynamo Spectra

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    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, fh,critf_{h,crit} above which the magnetic spectrum develops maxima at wavenumber =1= 1 scale {\it and} at the forcing scale, For f<fh,critf< f_{h,crit} 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 (‚ȧ\le 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

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    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 ‚Č•1012\ge 10^{12}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

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    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

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    Functional sequences of monodisperse, sequence‚Äźdefined oligo(amide‚Äźurethane)s are designed based on a peptide sequence as blueprint. The translation of a discrete side‚Äźchain functionality sequence from a known peptide‚Äźbased solubilizer of the photosensitizer meta‚Äźtetra(hydroxyphenyl)‚Äźchlorin, into a non‚Äźpeptidic 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

    Measuring Accuracy of Triples in Knowledge Graphs

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    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

    Prevalence of suspected hypertrophic cardiomyopathy or left ventricular hypertrophy based on race and gender in teenagers using screening echocardiography

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    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]

    The divergence of neighboring magnetic field lines and fast-particle diffusion in strong magnetohydrodynamic turbulence, with application to thermal conduction in galaxy clusters

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    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

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    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

    Speciation in Golden-Plovers, Pluvialis dominica and P. fulva: Evidence from the Breeding Grounds

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    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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