523 research outputs found
Close binary evolution I. The tidally induced shear mixing in rotating binaries
We study how tides in a binary system induce some specific internal shear
mixing, able to substantially modify the evolution of close binaries prior to
mass transfer. We construct numerical models accounting for tidal interactions,
meridional circulation, transport of angular momentum, shears and horizontal
turbulence and consider a variety of orbital periods and initial rotation
velocities. Depending on orbital periods and rotation velocities, tidal effects
may spin down (spin down Case) or spin up (spin up Case) the axial rotation. In
both cases, tides may induce a large internal differential rotation. The
resulting tidally induced shear mixing (TISM) is so efficient that the internal
distributions of angular velocity and chemical elements are greatly influenced.
The evolutionary tracks are modified, and in both cases of spin down and spin
up, large amounts of nitrogen can be transported to the stellar surfaces before
any binary mass transfer. Meridional circulation, when properly treated as an
advection, always tends to counteract the tidal interaction, tending to spin up
the surface when it is braked down and vice versa. As a consequence, the times
needed for the axial angular velocity to become equal to the orbital angular
velocity may be larger than given by typical synchronization timescales. Also,
due to meridional circulation some differential rotation remains in tidally
locked binary systems.Comment: 10 pages, 18 figures, Accepted for publication in Astronomy and
Astrophysic
Localized magnetoplasmon modes arising from broken translational symmetry in semiconductor superlattices
The electromagnetic propagator associated with the localized collective
magnetoplasmon excitations in a semiconductor superlattice with broken
translational symmetry, is calculated analytically within linear response
theory. We discuss the properties of these collective excitations in both
radiative and non-radiative regimes of the electromagnetic spectra. We find
that low frequency retarded modes arise when the surface density of carriers at
the symmetry breaking layer is lower than the density at the remaining layers.
Otherwise a doublet of localized, high-frequency magnetoplasmon-like modes
occurs.Comment: Revtex file + separate pdf figure
Formalism for obtaining nuclear momentum distributions by the Deep Inelastic Neutron Scattering technique
We present a new formalism to obtain momentum distributions in condensed
matter from Neutron Compton Profiles measured by the Deep Inelastic Neutron
Scattering technique. The formalism describes exactly the Neutron Compton
Profiles as an integral in the momentum variable . As a result we obtain a
Volterra equation of the first kind that relates the experimentally measured
magnitude with the momentum distributions of the nuclei in the sample. The
integration kernel is related with the incident neutron spectrum, the total
cross section of the filter analyzer and the detectors efficiency function. A
comparison of the present formalism with the customarily employed approximation
based on a convolution of the momentum distribution with a resolution function
is presented. We describe the inaccuracies that the use of this approximation
produces, and propose a new data treatment procedure based on the present
formalism.Comment: 11 pages, 8 figure
Simultaneous J-, H-, K- and L-band spectroscopic observations of galactic Be stars. I. IR atlas
It is already accepted that Be stars are surrounded by circumstellar
envelopes, which are mostly compatible with a disc geometry in Keplerian
rotation. We aim to obtain a more complete characterisation of the properties
of the circumstellar environment of Be stars that helps to constrain the
theoretical models of the Be phenomenon. We present near-infrared,
medium-resolution spectra of a sample of galactic Be stars with different
spectral subtypes and luminosity classes. We measure different parameters of
the hydrogen recombination lines from the Paschen, Brackett, Pfund, and
Humphreys series, and use them to diagnose physical conditions in the
circumstellar environment. We analysed the equivalent-width (EW) ratio between
Br and Br lines and different diagrams of flux ratios. We also
identify lines from He I, C I, N I, O I, Na I, Mg I, Mg II, Si I, Fe I, and Fe
II. Analysing the EW measurements of particular He I, Mg II, Fe I, Fe II and O
I lines, we find that for some lines they correlate with the spectral type of
the star. Particularly, the emission of the O I~m line
decreases towards the later spectral types. We present an atlas of 22 Be stars,
that covers a wide infrared (IR) spectral range with quasi-simultaneous
observations. From a detailed analysis, we define new complementary criteria to
Mennickent's classification of Be stars according to their disc opacity. Some
objects in our sample present compact thick envelopes, while in others the
envelope is extended and optically thin. The correlation between the full
widths at half maximum (FWHM) and the peak separation ()
versus for the Br10, Br, and Hu14 lines reveals that the
broadening mechanism is rotational. The Ly fluorescence is a key
mechanism to explain the intensity of the emission of Mg II and O I lines.Comment: 27 pages, 14 figures. Accepted for publication in A&
Design and evaluation of an osteogenesis-on-a-chip microfluidic device incorporating 3D cell culture
Microfluidic-based tissue-on-a-chip devices have generated significant research interest for biomedical applications, such as pharmaceutical development, as they can be used for small volume, high throughput studies on the effects of therapeutics on tissue-mimics. Tissue-on-a-chip devices are evolving from basic 2D cell cultures incorporated into microfluidic devices to complex 3D approaches, with modern designs aimed at recapitulating the dynamic and mechanical environment of the native tissue. Thus far, most tissue-on-a-chip research has concentrated on organs involved with drug uptake, metabolism and removal (e.g., lung, skin, liver, and kidney); however, models of the drug metabolite target organs will be essential to provide information on therapeutic efficacy. Here, we develop an osteogenesis-on-a-chip device that comprises a 3D environment and fluid shear stresses, both important features of bone. This inexpensive, easy-to-fabricate system based on a polymerized High Internal Phase Emulsion (polyHIPE) supports proliferation, differentiation and extracellular matrix production of human embryonic stem cell-derived mesenchymal progenitor cells (hES-MPs) over extended time periods (up to 21 days). Cells respond positively to both chemical and mechanical stimulation of osteogenesis, with an intermittent flow profile containing rest periods strongly promoting differentiation and matrix formation in comparison to static and continuous flow. Flow and shear stresses were modeled using computational fluid dynamics. Primary cilia were detectable on cells within the device channels demonstrating that this mechanosensory organelle is present in the complex 3D culture environment. In summary, this device aids the development of ‘next-generation’ tools for investigating novel therapeutics for bone in comparison with standard laboratory and animal testing
Anticoagulation in Patients With COVID-19: JACC Review Topic of the Week.
Clinical, laboratory, and autopsy findings support an association between coronavirus disease-2019 (COVID-19) and thromboembolic disease. Acute COVID-19 infection is characterized by mononuclear cell reactivity and pan-endothelialitis, contributing to a high incidence of thrombosis in large and small blood vessels, both arterial and venous. Observational studies and randomized trials have investigated whether full-dose anticoagulation may improve outcomes compared with prophylactic dose heparin. Although no benefit for therapeutic heparin has been found in patients who are critically ill hospitalized with COVID-19, some studies support a possible role for therapeutic anticoagulation in patients not yet requiring intensive care unit support. We summarize the pathology, rationale, and current evidence for use of anticoagulation in patients with COVID-19 and describe the main design elements of the ongoing FREEDOM COVID-19 Anticoagulation trial, in which 3,600 hospitalized patients with COVID-19 not requiring intensive care unit level of care are being randomized to prophylactic-dose enoxaparin vs therapeutic-dose enoxaparin vs therapeutic-dose apixaban. (FREEDOM COVID-19 Anticoagulation Strategy [FREEDOM COVID]; NCT04512079).Dr Farkouh has received research grants from Amgen, Novo Nordisk,
and Novartis. Dr Stone has received speaker honoraria from Infraredx; has served as a consultant to Valfix, TherOx, Robocath, HeartFlow, Ablative Solutions, Miracor, Neovasc, Abiomed, Ancora,
Vectorious, Elucid Bio, Occlutech, CorFlow, Apollo Therapeutics,
Impulse Dynamics, Cardiomech, Gore, and Amgen; and has equity/
options from Ancora, Cagent, Applied Therapeutics, Biostar family of
funds, SpectraWave, Orchestra Biomed, Aria, Cardiac Success, Valfix,
and Xenter. Dr Godoy is supported by the Frederick Banting and
Charles Best Canada Graduate Scholarship (Doctoral Research Award)
from the Canadian Institutes of Health Research. All other authors
have reported that they have no relationships relevant to the contents of this paper to disclose.S
Technical Confrontation of Two Prototypes of Dielectric Drying Wood using Radio Frequency
Partiendo de la premisa de que el secado endógeno dieléctrico es el que mejores resultados proporciona al aplicarlo a madera, se confrontaron dos prototipos diferentes desde las perspectivas de la filosofía de diseño de la tecnología de 50Ω y la de bomba de calor; de los resultados obtenidos en un proceso de secado para una probeta de madera, se identificó que el prototipo implementado con tecnología de 50Ω obtuvo mejores resultados con respecto a la eficiencia del proceso de secado. Este trabajo abre la brecha a futuras investigaciones en torno a este tipo de aplicaciones industriales de la Radiofrecuencia (RF), con miras al diseño a escala de un prototipo de horno industrial de bajo costo para el secado de madera.Starting from the premise that dielectric endogenous drying method is the one that gives better results on wood, there will be a confrontation between two different prototypes from the perspectives of the design philosophy and outcome results in a wooden probe. This work opens the gap for future research around this type of industrial RF applications, in order to design a prototype scale industrial furnace for wood drying
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