39 research outputs found
Imaging the dynamics of cardiac fiber orientation in vivo using 3D Ultrasound Backscatter Tensor Imaging
The assessment of myocardial fiber disarray is of major interest for the
study of the progression of myocardial disease. However, time-resolved imaging
of the myocardial structure remains unavailable in clinical practice. In this
study, we introduce 3D Backscatter Tensor Imaging (3D-BTI), an entirely novel
ultrasound-based imaging technique that can map the myocardial fibers
orientation and its dynamics with a temporal resolution of 10 ms during a
single cardiac cycle, non-invasively and in vivo in entire volumes. 3D-BTI is
based on ultrafast volumetric ultrasound acquisitions, which are used to
quantify the spatial coherence of backscattered echoes at each point of the
volume. The capability of 3D-BTI to map the fibers orientation was evaluated in
vitro in 5 myocardial samples. The helicoidal transmural variation of fiber
angles was in good agreement with the one obtained by histological analysis.
3D-BTI was then performed to map the fiber orientation dynamics in vivo in the
beating heart of an open-chest sheep at a volume rate of 90 volumes/s. Finally,
the clinical feasibility of 3D-BTI was shown on a healthy volunteer. These
initial results indicate that 3D-BTI could become a fully non-invasive
technique to assess myocardial disarray at the bedside of patients
Frequency ratio method for seismic modeling of Gamma Doradus stars
A method for obtaining asteroseismological information of a Gamma Doradus
oscillating star showing at least three pulsation frequencies is presented.
This method is based on a first-order asymptotic g-mode expression, in
agreement with the internal structure of Gamma Doradus stars. The information
obtained is twofold: 1) a possible identification of the radial order n and
degree l of observed frequencies (assuming that these have the same l), and 2)
an estimate of the integral of the buoyancy frequency (Brunt-Vaisala) weighted
over the stellar radius along the radiative zone. The accuracy of the method as
well as its theoretical consistency are also discussed for a typical Gamma
Doradus stellar model. Finally, the frequency ratios method has been tested
with observed frequencies of the Gamma Doradus star HD 12901. The number of
representative models verifying the complete set of constraints (the location
in the HR diagram, the Brunt-Vaisala frequency integral, the observed
metallicity and frequencies and a reliable identification of n and l) is
drastically reduced to six.Comment: 11 pages, 12 figure
Imaging the dynamics of cardiac fiber orientation in vivo using 3D Ultrasound Backscatter Tensor Imaging
ABSTRACT: The assessment of myocardial fiber disarray is of major interest for the study of the progression of myocardial disease. However, time-resolved imaging of the myocardial structure remains unavailable in clinical practice. In this study, we introduce 3D Backscatter Tensor Imaging (3D-BTI), an entirely novel ultrasound-based imaging technique that can map the myocardial fibers orientation and its dynamics with a temporal resolution of 10 ms during a single cardiac cycle, non-invasively and in vivo in entire volumes. 3D-BTI is based on ultrafast volumetric ultrasound acquisitions, which are used to quantify the spatial coherence of backscattered echoes at each point of the volume. The capability of 3D-BTI to map the fibers orientation was evaluated in vitro in 5 myocardial samples. The helicoidal transmural variation of fiber angles was in good agreement with the one obtained by histological analysis. 3D-BTI was then performed to map the fiber orientation dynamics in vivo in the beating heart of an open-chest sheep at a volume rate of 90 volumes/s. Finally, the clinical feasibility of 3D-BTI was shown on a healthy volunteer. These initial results indicate that 3D-BTI could become a fully non-invasive technique to assess myocardial disarray at the bedside of patients
Kappa-mechanism excitation of retrograde mixed modes in rotating B-type stars
I examine the stability of retrograde mixed modes in rotating B-type stars.
These modes can be regarded as a hybrid between the Rossby modes that arise
from conservation of vorticity, and the Poincare modes that are gravity waves
modified by the Coriolis force. Using a non-adiabatic pulsation code based
around the traditional approximation, I find that the modes are unstable in
mid- to late-B type stars, due to the same iron-bump opacity mechanism usually
associated with SPB and Cep stars. At one half of the critical rotation
rate, the instability for modes spans the spectral types B4 to A0.
Inertial-frame periods of the unstable modes range from 100 days down to a
fraction of a day, while normalized growth rates can reach in excess of
.
I discuss the relevance of these findings to SPB and pulsating Be stars, and
to the putative Maia class of variable star. I also outline some of the
questions raised by this discovery of a wholly-new class of pulsational
instability in early-type stars.Comment: 11 pages, 6 figures, accepted by MNRA
Asteroseismology and Interferometry
Asteroseismology provides us with a unique opportunity to improve our
understanding of stellar structure and evolution. Recent developments,
including the first systematic studies of solar-like pulsators, have boosted
the impact of this field of research within Astrophysics and have led to a
significant increase in the size of the research community. In the present
paper we start by reviewing the basic observational and theoretical properties
of classical and solar-like pulsators and present results from some of the most
recent and outstanding studies of these stars. We centre our review on those
classes of pulsators for which interferometric studies are expected to provide
a significant input. We discuss current limitations to asteroseismic studies,
including difficulties in mode identification and in the accurate determination
of global parameters of pulsating stars, and, after a brief review of those
aspects of interferometry that are most relevant in this context, anticipate
how interferometric observations may contribute to overcome these limitations.
Moreover, we present results of recent pilot studies of pulsating stars
involving both asteroseismic and interferometric constraints and look into the
future, summarizing ongoing efforts concerning the development of future
instruments and satellite missions which are expected to have an impact in this
field of research.Comment: Version as published in The Astronomy and Astrophysics Review, Volume
14, Issue 3-4, pp. 217-36
AVONET: morphological, ecological and geographical data for all birds
Functional traits offer a rich quantitative framework for developing and testing theories in evolutionary biology, ecology and ecosystem science. However, the potential of functional traits to drive theoretical advances and refine models of global change can only be fully realised when species‐level information is complete. Here we present the AVONET dataset containing comprehensive functional trait data for all birds, including six ecological variables, 11 continuous morphological traits, and information on range size and location. Raw morphological measurements are presented from 90,020 individuals of 11,009 extant bird species sampled from 181 countries. These data are also summarised as species averages in three taxonomic formats, allowing integration with a global phylogeny, geographical range maps, IUCN Red List data and the eBird citizen science database. The AVONET dataset provides the most detailed picture of continuous trait variation for any major radiation of organisms, offering a global template for testing hypotheses and exploring the evolutionary origins, structure and functioning of biodiversity