9,993 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
Growth of quasiconvex subgroups
We prove that non-elementary hyperbolic groups grow exponentially more
quickly than their infinite index quasiconvex subgroups. The proof uses the
classical tools of automatic structures and Perron-Frobenius theory.
We also extend the main result to relatively hyperbolic groups and cubulated
groups. These extensions use the notion of growth tightness and the work of
Dahmani, Guirardel, and Osin on rotating families.Comment: 28 pages, 1 figure. v3 is the final version, to appear in Math Proc.
Cambridge Philos. So
Growing dust grains in protoplanetary discs - I. Radial drift with toy growth models
In a series of papers, we present a comprehensive analytic study of the
global motion of growing dust grains in protoplanetary discs, addressing both
the radial drift and the vertical settling of the particles. Here we study how
the radial drift of dust particles is affected by grain growth. In a first
step, toy models in which grain growth can either be constant, accelerate or
decelerate are introduced. The equations of motion are analytically integrable
and therefore the grains dynamics is easy to understand.
The radial motion of growing grains is governed by the relative efficiency of
the growth and migration processes which is expressed by the dimensionless
parameter Lambda, as well as the exponents for the gas surface density and
temperature profiles, denoted p and q respectively. When Lambda is of order
unity, growth and migration are strongly coupled, providing the most efficient
radial drift. For the toy models considered, grains pile up when -p+q+1/2<0.
Importantly, we show the existence of a second process which can help discs to
retain their solid materials. For accelerating growth, grains end up their
migration at a finite radius, thus avoiding being accreted onto the central
star.Comment: 12 pages, 9 figures. Accepted for publication in MNRAS. v2: typos
correcte
Breaking anchored droplets in a microfluidic Hele-Shaw cell
We study microfluidic self digitization in Hele-Shaw cells using pancake
droplets anchored to surface tension traps. We show that above a critical flow
rate, large anchored droplets break up to form two daughter droplets, one of
which remains in the anchor. Below the critical flow velocity for breakup the
shape of the anchored drop is given by an elastica equation that depends on the
capillary number of the outer fluid. As the velocity crosses the critical
value, the equation stops admitting a solution that satisfies the boundary
conditions; the drop breaks up in spite of the neck still having finite width.
A similar breaking event also takes place between the holes of an array of
anchors, which we use to produce a 2D array of stationary drops in situ.Comment: 5 pages, 4 figures, to appear in Phys. Rev. Applie
Doeblin Trees
This paper is centered on the random graph generated by a Doeblin-type
coupling of discrete time processes on a countable state space whereby when two
paths meet, they merge. This random graph is studied through a novel subgraph,
called a bridge graph, generated by paths started in a fixed state at any time.
The bridge graph is made into a unimodular network by marking it and selecting
a root in a specified fashion. The unimodularity of this network is leveraged
to discern global properties of the larger Doeblin graph. Bi-recurrence, i.e.,
recurrence both forwards and backwards in time, is introduced and shown to be a
key property in uniquely distinguishing paths in the Doeblin graph, and also a
decisive property for Markov chains indexed by . Properties related
to simulating the bridge graph are also studied.Comment: 44 pages, 4 figure
Updated estimate of the duration of the meningo-encephalitic stage in gambiense human African trypanosomiasis
Background:
The duration of the stages of HAT is an important factor in epidemiological studies and intervention planning. Previously, we published estimates of the duration of the haemo-lymphatic stage 1 and meningo-encephalitic stage 2 of the gambiense form of human African trypanosomiasis (HAT), in the absence of treatment. Here we revise the estimate of stage 2 duration, computed based on data from Uganda and South Sudan, by adjusting observed infection prevalence for incomplete case detection coverage and diagnostic inaccuracy.
Findings:
The revised best estimate for the mean duration of stage 2 is 252 days (95% CI 171–399), about half of our initial best estimate, giving a total mean duration of untreated gambiense HAT infection of approximately 2 years and 2 months.
Conclusions:
Our new estimate provides improved information on the transmission dynamics of this neglected tropical disease in Uganda and South Sudan. We stress that there remains considerable variability around the estimated mean values, and that one must be cautious in applying these results to other foci
Advances in Feature Selection with Mutual Information
The selection of features that are relevant for a prediction or
classification problem is an important problem in many domains involving
high-dimensional data. Selecting features helps fighting the curse of
dimensionality, improving the performances of prediction or classification
methods, and interpreting the application. In a nonlinear context, the mutual
information is widely used as relevance criterion for features and sets of
features. Nevertheless, it suffers from at least three major limitations:
mutual information estimators depend on smoothing parameters, there is no
theoretically justified stopping criterion in the feature selection greedy
procedure, and the estimation itself suffers from the curse of dimensionality.
This chapter shows how to deal with these problems. The two first ones are
addressed by using resampling techniques that provide a statistical basis to
select the estimator parameters and to stop the search procedure. The third one
is addressed by modifying the mutual information criterion into a measure of
how features are complementary (and not only informative) for the problem at
hand
Rayleigh-Taylor instability under an inclined plane
We revisit the canonical Rayleigh-Taylor instability and investigate the case
of a thin film of fluid upon the underside of an inclined plane. The presence
of a natural flow along the plane competes with the conventional droplet
forming instability. In particular, experiments reveal that no drops form for
inclinations greater than a critical value. These features are rationalized in
the context of the absolute/convective analysis conducted in this article
Crosstalk between nanotube devices: contact and channel effects
At reduced dimensionality, Coulomb interactions play a crucial role in
determining device properties. While such interactions within the same carbon
nanotube have been shown to have unexpected properties, device integration and
multi-nanotube devices require the consideration of inter-nanotube
interactions. We present calculations of the characteristics of planar carbon
nanotube transistors including interactions between semiconducting nanotubes
and between semiconducting and metallic nanotubes. The results indicate that
inter-tube interactions affect both the channel behavior and the contacts. For
long channel devices, a separation of the order of the gate oxide thickness is
necessary to eliminate inter-nanotube effects. Because of an exponential
dependence of this length scale on dielectric constant, very high device
densities are possible by using high-k dielectrics and embedded contacts
- …