1,235 research outputs found
Planet gaps in the dust layer of 3D proto-planetary disks: Observability with ALMA
Among the numerous known extrasolar planets, only a handful have been imaged
directly so far, at large orbital radii and in rather evolved systems. The
Atacama Large Millimeter/submillimeter Array (ALMA) will have the capacity to
observe these wide planetary systems at a younger age, thus bringing a better
understanding of the planet formation process. Here we explore the ability of
ALMA to detect the gaps carved by planets on wide orbits.Comment: 2 pages, 2 figures, to appear in the Proceedings of IAU Symp. 299:
Exploring the Formation and Evolution of Planetary Systems (Victoria, Canada
The accumulation and trapping of grains at planet gaps: effects of grain growth and fragmentation
We model the dust evolution in protoplanetary disks with full 3D, Smoothed
Particle Hydrodynamics (SPH), two-phase (gas+dust) hydrodynamical simulations.
The gas+dust dynamics, where aerodynamic drag leads to the vertical settling
and radial migration of grains, is consistently treated. In a previous work, we
characterized the spatial distribution of non-growing dust grains of different
sizes in a disk containing a gap-opening planet and investigated the gap's
detectability with the Atacama Large Millimeter/submillimeter Array (ALMA).
Here we take into account the effects of grain growth and fragmentation and
study their impact on the distribution of solids in the disk. We show that
rapid grain growth in the two accumulation zones around planet gaps is strongly
affected by fragmentation. We discuss the consequences for ALMA observations.Comment: Accepted for publication in Planetary and Space Science. 13 pages, 4
figure
Gravitational Lensing as Signal and Noise in Lyman-alpha Forest Measurements
In Lyman-alpha forest measurements it is generally assumed that quasars are
mere background light sources which are uncorrelated with the forest.
Gravitational lensing of the quasars violates this assumption. This effect
leads to a measurement bias, but more interestingly it provides a valuable
signal. The lensing signal can be extracted by correlating quasar magnitudes
with the flux power spectrum and with the flux decrement. These correlations
will be challenging to measure but their detection provides a direct measure of
how features in the Lyman-alpha forest trace the underlying mass density field.
Observing them will test the fundamental hypothesis that fluctuations in the
forest are predominantly driven by fluctuations in mass, rather than in the
ionizing background, helium reionization or winds. We discuss ways to
disentangle the lensing signal from other sources of such correlations,
including dust, continuum and background residuals. The lensing-induced
measurement bias arises from sample selection: one preferentially collects
spectra of magnified quasars which are behind overdense regions. This
measurement bias is ~0.1-1% for the flux power spectrum, optical depth and the
flux probability distribution. Since the effect is systematic, quantities such
as the amplitude of the flux power spectrum averaged across scales should be
interpreted with care.Comment: 22 pages, 8 figures; v2: references added, discussion expanded,
matches PRD accepted versio
Two-dimensional topological superconductivity in Pb/Co/Si(111)
Just like insulators can host topological Dirac states at their edges,
superconductors can also exhibit topological phases characterized by Majorana
edge states. Remarkable zero-energy states have been recently observed at the
two ends of proximity induced superconducting wires, and were interpreted as
localized Majorana end states in one-dimensional (1D) topological
superconductor. By contrast, propagating Majorana states should exist at the 1D
edges of two-dimensional (2D) topological superconductors. Here we report the
direct observation of dispersive in-gap states surrounding topological
superconducting domains made of a single atomic layer of Pb covering magnetic
islands of Co/Si(111). We interpret the observed continuous dispersion across
the superconducting gap in terms of a spatial topological transition
accompanied by a chiral edge mode and residual gaped helical edge states. Our
experimental approach enables the engineering and control of a large variety of
novel quantum phases. This opens new horizons in the field of quantum materials
and quantum electronics where the magnetization of the domains could be used as
a control parameter for the manipulation of topological states.Comment: 12 pages, 3 figure
Hybrid treatment of small droplets in atomized jet
International audienceL'atomisation de combustible a un impact direct sur l'émission de polluants dans l'atmosphère. Face au besoin de caractériser l'atomisation primaire, l'étude numérique de l'intéraction liquide-gaz croît dans le but de maîtriser la création de particules polluantes et de la réduire. Elle est effectuée sur l'ensemble du spray, de son injection dans la chambre de combustion jusqu'à l'évaporation des gouttes créées suite au secondary breakup. Notre but est d'augmenter la précision du transport des gouttes au sein des jets atomisés, typiquement, une goutte est 100 fois plus petite que le diamètre d'injection. Cette différence d'échelle rend la définition de l'interface liquide-gaz complexe et crééer des zones sous résolues. Pour résoudre ce probleme d'échelle, un coupling entre un suivi Eulérien et un suivi Lagrangian a été proposé, voir Hermann, [1]. Cette communication se concentre sur les critères de transformation d'une goutte eulérienne en particule lagrangienne et les modifications physiques et numériques entourant cette transformation. Cette communication se concentre sur l'implémentation d'une méthode de suivi de particule polydisperse basée sur des critères géometriques. Ils sont finalement appliqués sur l'étude d'un jet atomisé. Abstract : Atomization of liquid fuel has a direct impact on the production of pollutant emission in engineering propulsion devices. Due to the multiple challenges in experimental investigations, motivation for numerical study is increasing on liquid/gas interaction from injection till dispersed spray zone. Our purpose is to increase the accuracy of the treatment of droplets in atomized jet, which are typically 100 times smaller than the injection size. As the size of the droplets reduces with the primary breakup of liquid fuel, it is increasingly challenging to track the interface of the droplets accurately. To solve this multis-cale issue, a coupled tracking Eulerian-Lagrangian Method is proposed, see Hermann, [1]. This communication focuses on the criteria of transformation of this coupling from interface captured droplets to Lagrangian particles and numerical/physical reconstruction during this process. From the literature, interaction criteria of transformation are all geometric, implementation of physical parameter is made in this communication. Those criteria are finally applied on a liquid jet atomization
Measuring Omega_0 with higher-order Quasar-Galaxy Correlations induced by Weak Lensing
Via the magnification bias, gravitational lensing by large-scale structures
causes angular cross-correlations between distant quasars and foreground
galaxies on angular scales of arc minutes and above. We investigate the
three-point cross-correlation between quasars and galaxy pairs measurable via
the second moment of the galaxy counts around quasars and show that it reaches
the level of a few per cent on angular scales near one arc minute. Combining
two- and three-point correlations, a skewness parameter can be defined which is
shown to be virtually independent on the shape and normalisation of the
dark-matter power spectrum. If the galaxy bias is linear and deterministic, the
skewness depends on the cosmic matter density parameter Omega_0 only;
otherwise, it can be used to probe the linearity and stochasticity of the bias.
We finally estimate the signal-to-noise ratio of a skewness determination and
find that around twenty thousand distant quasars e.g. from the Sloan Digital
Sky Survey should suffice for a direct measurement of Omega_0.Comment: 11 pages, 6 figures, submitted to Astronomy and Astrophysic
The accumulation and trapping of grains at planet gaps: effects of grain growth and fragmentation
13 pages, 4 figures.International audienceWe model the dust evolution in protoplanetary disks with full 3D, Smoothed Particle Hydrodynamics (SPH), two-phase (gas+dust) hydrodynamical simulations. The gas+dust dynamics, where aerodynamic drag leads to the vertical settling and radial migration of grains, is consistently treated. In a previous work, we characterized the spatial distribution of non-growing dust grains of different sizes in a disk containing a gap-opening planet and investigated the gap's detectability with the Atacama Large Millimeter/submillimeter Array (ALMA). Here we take into account the effects of grain growth and fragmentation and study their impact on the distribution of solids in the disk. We show that rapid grain growth in the two accumulation zones around planet gaps is strongly affected by fragmentation. We discuss the consequences for ALMA observations
Ar/Cl-2 etching of GaAs optomechanical microdisks fabricated with positive electroresist
FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESA method to fabricate GaAs microcavities using only a soft mask with an electrolithographic pattern in an inductively coupled plasma etching is presented. A careful characterization of the fabrication process pinpointing the main routes for a smooth devic1015767FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES2012/17610-32012/17765-72016/18308-02018/15577-52018/15580-62019/01402-100
From droplets to particles: Transformation criteria
International audienceAtomization of liquid fuel has a direct impact on the production of pollutant emission in engineering propulsion devices. Due to the multiple challenges in experimental investigations, motivation for numerical study is increasing on liquid-gas interaction from injection till dispersed spray zone. Our purpose is to increase the accuracy of the treatment of droplets in atomized jet, which are typically 100 times smaller than the characteristic injection length size. As the characteristic length reduces downstream to the jet, it is increasingly challenging to track the interface of the droplets accurately. To solve this multiscale issue, a coupled tracking Eulerian-Lagrangian Method exists [1]. It consists in transforming the small droplets to Lagrangian droplets that are transported with drag models. In addition to the size transformation criteria, one can consider geometric parameters to determine if a droplet has to be transformed. Indeed, the geometric criteria are there for two reasons. The first one is the case where the droplets can break if there are not spherical. The second one is about the drag models that are based on the assumption that the droplet is spherical. In this paper we make a review of the geometric criteria used in the literature. New geometric criteria are also proposed. Those criteria are validated and then discussed in academic cases and a 3D airblast atomizer simulation. Following the analysis of the results the authors advise the use of the deformation combined with surface criteria as the geometric transformation criteria. Introduction Atomization is a phenomenon encountered in many applications such as sprays in cosmetic engineering or aerospace engineering for jet propulsion [2]. In the combustion chamber, the total surface of the interface separating the two phases is a key parameter. Primary and secondary breakup have been extensively investigated in the literature. However, in order to fully describe the complete process, one has to capture droplets in dispersed zone 100 times smaller than jet diameter. Atomization is then a multiphase and a multiscale flow phenomenon which is still far from being understood. Due to this wide range of scale, the Direct Numerical Simulation (DNS) of such process requires robust and efficient codes. DNS is an important tool to analyse the experimental results and go further into the atomization understanding. In the past few years, numerical schemes of Interface Capturing Method (ICM) have been improved but faced numerical limitation. For instance, the treatment of the small droplets is the most challenging part when the entire process is treated in DNS. When dealing with unresolved structures we face different problems such as the dilution or the creation of numerical instabilities. To avoir them, a strategy is to remove small structures during the simulation, see Shinjo et al. [3]. But, those methods do not collect information on smallest droplets in atomization application. Introduction of Adaptive Mesh Refinement (AMR) in DNS is a first answer to this issue, it consists in refining unresolved area under numerical concept and focus on the interface between two phases instead of refining the entire domain. In dense spray, AMR tends to refine the entire zone and becomes as expensive as a full domain refinement. A solution is to transform the smallest droplets into point particles and remove AMR in this area. This strategy is called Eulerian-Lagrangian coupling [1], it assumes that small droplets will no longer break during the simulation and that the Lagrangian models reproduce correctly the droplet transport. These physical assumptions are implemented to answer numerical issue and improve the computational cost. This Eulerian-Lagrangian coupling is based on transformation criteria that defines when an ICM structure has to be transformed into Lagrangian particle and when a Lagrangian particle has to be transformed back into ICM. The main purpose of the present communication is to provide a detailed analysis of the ICM to Lagrangian transformation criteria. The geometri
Plasma Angiotensins, Renin, and Blood Pressure During Acute Renin Inhibition by CGP 38 560A in Hypertensive Patients
The new renin inhibitor CGP 38560A has been shown to block angiotensin (ANG) production in healthy volunteers. In order to determine its potential antihypertensive effect, the compound was administered in a 30-min infusion, in 12 hypertensive patients (mean blood pressure (BP): 112.8 ± 3.5 mm Hg). These patients were selected for their sensitivity to Captopril: a single oral dose of 50 mg Captopril lowered their mean BP by 8.8 ± 2.2 mm Hg after 30 min and by 15.3 ± 1.5 mm Hg after 90 min. At the end of the renin inhibitor infusion, mean blood pressure decreased by 5.7 ± 2.2 mm Hg in the six patients infused with the dose of 0.125 mg/kg and by 6.0 ± 1.8 mm Hg in the six patients infused with 0.250 mg/kg. The fall in blood pressure was correlated to the initial plasma renin activity (PRA) (r = 0.61, P < .05). A dose-dependent effect was observed on plasma ANG I which fell by 74% with 0.125 mg/kg and by 94% with 0.250 mg/kg. Identical falls were found for plasma ANG II (72% and 94%, respectively) and ANG I and ANG II were well correlated (r = 0.91, P < .001). The fall in BP was correlated to the fall in plasma ANG I (r = 0.77, P < .01). The time-course of the BP changes was parallel to the changes in plasma angiotensins, as were the slightly delayed rise and fall in active renin measured by a direct immunoradiometric assay. When measured by the conventional ANG I radioimmunoassay, PRA values indicated a long-lasting inhibition. The arte- factual nature of the latter result is demonstrated by the different results obtained with an ANG I antibody-trapping radioimmunoassay, which followed more closely plasma ANG I levels. Am J Hypertens 1989; 2:819-82
- …