1,193 research outputs found
Anisotropic fluxes and nonlocal interactions in MHD turbulence
We investigate the locality or nonlocality of the energy transfer and of the
spectral interactions involved in the cascade for decaying magnetohydrodynamic
(MHD) flows in the presence of a uniform magnetic field at various
intensities. The results are based on a detailed analysis of three-dimensional
numerical flows at moderate Reynold numbers. The energy transfer functions, as
well as the global and partial fluxes, are examined by means of different
geometrical wavenumber shells. On the one hand, the transfer functions of the
two conserved Els\"asser energies and are found local in both the
directions parallel (-direction) and perpendicular (-direction)
to the magnetic guide-field, whatever the -strength. On the other
hand, from the flux analysis, the interactions between the two
counterpropagating Els\"asser waves become nonlocal. Indeed, as the -intensity is increased, local interactions are strongly decreased and the
interactions with small modes dominate the cascade. Most of the energy
flux in the -direction is due to modes in the plane at , while
the weaker cascade in the -direction is due to the modes with .
The stronger magnetized flows tends thus to get closer to the weak turbulence
limit where the three-wave resonant interactions are dominating. Hence, the
transition from the strong to the weak turbulence regime occurs by reducing the
number of effective modes in the energy cascade.Comment: Submitted to PR
A survey of transposable element classification systems--a call for a fundamental update to meet the challenge of their diversity and complexity.
The increase of publicly available sequencing data has allowed for rapid progress in our understanding of genome composition. As new information becomes available we should constantly be updating and reanalyzing existing and newly acquired data. In this report we focus on transposable elements (TEs) which make up a significant portion of nearly all sequenced genomes. Our ability to accurately identify and classify these sequences is critical to understanding their impact on host genomes. At the same time, as we demonstrate in this report, problems with existing classification schemes have led to significant misunderstandings of the evolution of both TE sequences and their host genomes. In a pioneering publication Finnegan (1989) proposed classifying all TE sequences into two classes based on transposition mechanisms and structural features: the retrotransposons (class I) and the DNA transposons (class II). We have retraced how ideas regarding TE classification and annotation in both prokaryotic and eukaryotic scientific communities have changed over time. This has led us to observe that: (1) a number of TEs have convergent structural features and/or transposition mechanisms that have led to misleading conclusions regarding their classification, (2) the evolution of TEs is similar to that of viruses by having several unrelated origins, (3) there might be at least 8 classes and 12 orders of TEs including 10 novel orders. In an effort to address these classification issues we propose: (1) the outline of a universal TE classification, (2) a set of methods and classification rules that could be used by all scientific communities involved in the study of TEs, and (3) a 5-year schedule for the establishment of an International Committee for Taxonomy of Transposable Elements (ICTTE)
Adaptive Covariance Estimation with model selection
We provide in this paper a fully adaptive penalized procedure to select a
covariance among a collection of models observing i.i.d replications of the
process at fixed observation points. For this we generalize previous results of
Bigot and al. and propose to use a data driven penalty to obtain an oracle
inequality for the estimator. We prove that this method is an extension to the
matricial regression model of the work by Baraud
Simulations for single-dish intensity mapping experiments
HI intensity mapping is an emerging tool to probe dark energy. Observations
of the redshifted HI signal will be contaminated by instrumental noise,
atmospheric and Galactic foregrounds. The latter is expected to be four orders
of magnitude brighter than the HI emission we wish to detect. We present a
simulation of single-dish observations including an instrumental noise model
with 1/f and white noise, and sky emission with a diffuse Galactic foreground
and HI emission. We consider two foreground cleaning methods: spectral
parametric fitting and principal component analysis. For a smooth frequency
spectrum of the foreground and instrumental effects, we find that the
parametric fitting method provides residuals that are still contaminated by
foreground and 1/f noise, but the principal component analysis can remove this
contamination down to the thermal noise level. This method is robust for a
range of different models of foreground and noise, and so constitutes a
promising way to recover the HI signal from the data. However, it induces a
leakage of the cosmological signal into the subtracted foreground of around 5%.
The efficiency of the component separation methods depends heavily on the
smoothness of the frequency spectrum of the foreground and the 1/f noise. We
find that as, long as the spectral variations over the band are slow compared
to the channel width, the foreground cleaning method still works.Comment: 14 pages, 12 figures. Submitted to MNRA
Mesalazine: A Novel Etiology For Drug-Induced Urinary Calculi
We report the case of a 23-year-old woman treated by mesalazine for ulcerative colitis and who subsequently presented recurrent renal colic due to mesalazine urinary stones. This is the second case described in the literature.Mesalazine stones are soft, friable and have an orange-beige color. They are not visible on non-contrast computed tomography (CT). Their diagnosis is based on morpho-constitutional analysis and CT-urography. Patients treatedby mesalazine who present renal colic should undergo CT-urography in order to make the diagnosis
Three-dimensional interferometric, spectrometric, and planetary views of Procyon
We used a new realistic 3D radiative-hydrodynamical model atmosphere of
Procyon generated with the Stagger Code and synthetic spectra computed with the
radiative transfer code Optim3D to re-analyze interferometric and spectroscopic
data from the optical to the infrared of Procyon. We compute intensity maps in
two optical filters centered at 500 and 800 nm (MARK III) and one infrared
filter centered at 2200 nm (VINCI). We constructed stellar disk images
accounting for the center-to-limb variations and used them to derive visibility
amplitudes and closure phases. We provide 3D limb-darkening coefficients in the
optical as well as in the infrared. We show that visibility curves and closure
phases show clear deviations from circular symmetry from the 3rd lobe on. These
deviations are detectable with current interferometers using closure phases. We
derive new angular diameters at different wavelengths with two independent
methods based on 3D simulations. We find a diameter_Vinci = 5.390 \pm 0.03 mas
that this is confirmed by an independent asteroseismic estimation. The
resulting Teff is 6591 K, which is consistent with the infrared flux method
determinations. We find also a value of the surface gravity log g = 4.01 \pm
0.03 that is larger by 0.05 dex from literature values. Spectrophotometric
comparisons with observations provide very good agreement with the spectral
energy distribution and photometric colors, allowing us to conclude that the
thermal gradient of the simulation matches fairly well Procyon. Finally, we
show that the granulation pattern of a planet hosting Procyon-like star has a
non-negligible impact on the detection of hot Jupiters in the infrared using
interferometry closure phases. It is then crucial to have a comprehensive
knowledge of the host star to directly detect and characterize hot Jupiters. In
this respect, RHD simulations are very important to reach this aim.Comment: Accepted for publication on Astronomy and Astrophysics, 14 pages, 12
figure
MOST photometry of the roAp star 10 Aql
Context: We present 31.2 days of nearly continuous MOST photometry of the
roAp star 10Aql. Aims:The goal was to provide an unambiguous frequency
identification for this little studied star, as well as to discuss the detected
frequencies in the context of magnetic models and analyze the influence of the
magnetic field on the pulsation. Methods: Using traditional Fourier analysis
techniques on three independent data reductions, intrinsic frequencies for the
star are identified. Theoretical non-adiabatic axisymmetric modes influenced by
a magnetic field having polar field strengths Bp = 0-5kG were computed to
compare the observations to theory. Results: The high-precision data allow us
to identify three definite intrinsic pulsation frequencies and two other
candidate frequencies with low S/N. Considering the observed spacings, only one
(50.95microHz) is consistent with the main sequence nature of roAp stars. The
comparison with theoretical models yields a best fit for a 1.95Msun model
having solar metallicity, suppressed envelope convection, and homogenous helium
abundance. Furthermore, our analysis confirms the suspected slow rotation of
the star and sets new lower limits to the rotation period (Prot>1 month) and
inclination (i>30\pm10deg.). Conclusions:The observed frequency spectrum is not
rich enough to unambiguously identify a model. On the other hand, the models
hardly represent roAp stars in detail due to the approximations needed to
describe the interactions of the magnetic field with stellar structure and
pulsation. Consequently, errors in the model frequencies needed for the fitting
procedure can only be estimated. Nevertheless, it is encouraging that models
which suppress convection and include solar metallicity, in agreement with
current concepts of roAp stars, fit the observations best.Comment: accepted by A&
Calibrating photometric redshifts with intensity mapping observations
Imaging surveys of galaxies will have a high number density and angular resolution yet a poor
redshift precision. Intensity maps of neutral hydrogen (HI) will have accurate redshift resolution
yet will not resolve individual sources. Using this complementarity, we show how the clustering
redshifts approach, proposed for spectroscopic surveys can also be used in combination with intensity mapping observations to calibrate the redshift distribution of galaxies in an imaging survey
and, as a result, reduce uncertainties in photometric redshift measurements. We show how the
intensity mapping surveys to be carried out with the MeerKAT, HIRAX and SKA instruments can
improve photometric redshift uncertainties to well below the requirements of DES and LSST. The
effectiveness of this method as a function of instrumental parameters, foreground subtraction and
other potential systematic errors is discussed in detail.Scopu
A spectroscopic analysis of the chemically peculiar star HD207561
In this paper we present a high-resolution spectroscopic analysis of the
chemically peculiar star HD207561. During a survey programme to search for new
roAp stars in the Northern hemisphere, Joshi et al. (2006) observed significant
photometric variability on two consecutive nights in the year 2000. The
amplitude spectra of the light curves obtained on these two nights showed
oscillations with a frequency of 2.79 mHz [P~6-min]. However, subsequent
follow-up observations could not confirm any rapid variability. In order to
determine the spectroscopic nature of HD207561, high-resolution spectroscopic
and spectro-polarimetric observations were carried out. A reasonable fit of the
calculated Hbeta line profile to the observed one yields the effective
temperature (Teff) and surface gravity (log g) as 7300 K and 3.7 dex,
respectively. The derived projected rotational velocity (vsin i) for HD207561
is 74 km/sec indicative of a relatively fast rotator. The position of HD207561
in the H-R diagram implies that this is slightly evolved from the main-sequence
and located well within the delta-Scuti instability strip. The abundance
analysis indicates the star has slight under-abundances of Ca and Sc and mild
over-abundances of iron-peak elements. The spectro-polarimetric study of
HD207561 shows that the effective magnetic field is within the observational
error of 100 gauss (G). The spectroscopic analysis revealed that the star has
most of the characteristics similar to an Am star, rather than an Ap star, and
that it lies in the delta-Scuti instability strip; hence roAp pulsations are
not expected in HD207561, but low-overtone modes might be excited.Comment: 8 pages, 7 figures, 3 tables. Accepted for pubblication in MNRA
- âŠ