7,869 research outputs found
Controlling the composition of a confined fluid by an electric field
Starting from a generic model of a pore/bulk mixture equilibrium, we propose
a novel method for modulating the composition of the confined fluid without
having to modify the bulk state. To achieve this, two basic mechanisms -
sensitivity of the pore filling to the bulk thermodynamic state and electric
field effect - are combined. We show by Monte Carlo simulation that the
composition can be controlled both in a continuous and in a jumpwise way. Near
the bulk demixing instability, we demonstrate a field induced population
inversion in the pore. The conditions for the realization of this method should
be best met with colloids, but being based on robust and generic mechanisms, it
should also be applicable to some molecular fluids.Comment: 9 pages, 5 figure
Data sources for rescuing the rich heritage of Mediterranean historical surface climate data
10.1002/gdj3.4Availability of long-term and high-quality instrumental climate records is still insufficient and the rich heritage of meteorological surface observations is largely underexploited in many parts of the world. This is particularly striking over the Greater Mediterranean region (GMR), where meteorological observations have been taken since the 18th century at some locations. The lack of high quality and long series here is despite this region being regarded as a climate change hot spot. This article mainly assesses relevant sources containing Mediterranean historical climate data and metadata either from online repositories worldwide or physical archives, with the emphasis here on the rich holdings kept at French archives. A particular case study is the data rescue (DARE) program undertaken by the Algerian National Meteorological Service, as well as some of the past and ongoing projects and initiatives aimed at enhancing climate data availability and accessibility over the GMR. Our findings point to the high potential for undertaking DARE activities over the GMR and the need for bringing longer and higher quality climate time series to support a diverse number of scientific and technical assessments and policies
Last passage percolation and traveling fronts
We consider a system of N particles with a stochastic dynamics introduced by
Brunet and Derrida. The particles can be interpreted as last passage times in
directed percolation on {1,...,N} of mean-field type. The particles remain
grouped and move like a traveling wave, subject to discretization and driven by
a random noise. As N increases, we obtain estimates for the speed of the front
and its profile, for different laws of the driving noise. The Gumbel
distribution plays a central role for the particle jumps, and we show that the
scaling limit is a L\'evy process in this case. The case of bounded jumps
yields a completely different behavior
Effect of selection on ancestry: an exactly soluble case and its phenomenological generalization
We consider a family of models describing the evolution under selection of a
population whose dynamics can be related to the propagation of noisy traveling
waves. For one particular model, that we shall call the exponential model, the
properties of the traveling wave front can be calculated exactly, as well as
the statistics of the genealogy of the population. One striking result is that,
for this particular model, the genealogical trees have the same statistics as
the trees of replicas in the Parisi mean-field theory of spin glasses. We also
find that in the exponential model, the coalescence times along these trees
grow like the logarithm of the population size. A phenomenological picture of
the propagation of wave fronts that we introduced in a previous work, as well
as our numerical data, suggest that these statistics remain valid for a larger
class of models, while the coalescence times grow like the cube of the
logarithm of the population size.Comment: 26 page
The Universal Gaussian in Soliton Tails
We show that in a large class of equations, solitons formed from generic
initial conditions do not have infinitely long exponential tails, but are
truncated by a region of Gaussian decay. This phenomenon makes it possible to
treat solitons as localized, individual objects. For the case of the KdV
equation, we show how the Gaussian decay emerges in the inverse scattering
formalism.Comment: 4 pages, 2 figures, revtex with eps
A rare early-type star revealed in the Wing of the Small Magellanic Cloud
Sk 183 is the visually-brightest star in the N90 nebula, a young star-forming
region in the Wing of the Small Magellanic Cloud (SMC). We present new optical
spectroscopy from the Very Large Telescope which reveals Sk 183 to be one of
the most massive O-type stars in the SMC. Classified as an O3-type dwarf on the
basis of its nitrogen spectrum, the star also displays broadened He I
absorption which suggests a later type. We propose that Sk 183 has a composite
spectrum and that it is similar to another star in the SMC, MPG 324. This
brings the number of rare O2- and O3-type stars known in the whole of the SMC
to a mere four. We estimate physical parameters for Sk 183 from analysis of its
spectrum. For a single-star model, we estimate an effective temperature of
46+/-2 kK, a low mass-loss rate of ~10^-7 Msun yr^-1, and a spectroscopic mass
of 46^+9_-8 Msun (for an adopted distance modulus of 18.7 mag to the young
population in the SMC Wing). An illustrative binary model requires a slightly
hotter temperature (~47.5 kK) for the primary component. In either scenario, Sk
183 is the earliest-type star known in N90 and will therefore be the dominant
source of hydrogen-ionising photons. This suggests Sk 183 is the primary
influence on the star formation along the inner edge of the nebula.Comment: Accepted by ApJ, 10 pages, 7 figures, v2 after proof
Fluctuations of the heat flux of a one-dimensional hard particle gas
Momentum-conserving one-dimensional models are known to exhibit anomalous
Fourier's law, with a thermal conductivity varying as a power law of the system
size. Here we measure, by numerical simulations, several cumulants of the heat
flux of a one-dimensional hard particle gas. We find that the cumulants, like
the conductivity, vary as power laws of the system size. Our results also
indicate that cumulants higher than the second follow different power laws when
one compares the ring geometry at equilibrium and the linear case in contact
with two heat baths (at equal or unequal temperatures). keywords: current
fluctuations, anomalous Fourier law, hard particle gasComment: 5 figure
Partially Observable Concurrent Kleene Algebra
We introduce partially observable concurrent Kleene algebra (POCKA), an algebraic framework to reason about concurrent programs with variables as well as control structures, such as conditionals and loops, that depend on those variables. We illustrate the use of POCKA through concrete examples. We prove that POCKA is a sound and complete axiomatisation of a model of partial observations, and show the semantics passes an important check for sequential consistency
Living IoT: A Flying Wireless Platform on Live Insects
Sensor networks with devices capable of moving could enable applications
ranging from precision irrigation to environmental sensing. Using mechanical
drones to move sensors, however, severely limits operation time since flight
time is limited by the energy density of current battery technology. We explore
an alternative, biology-based solution: integrate sensing, computing and
communication functionalities onto live flying insects to create a mobile IoT
platform.
Such an approach takes advantage of these tiny, highly efficient biological
insects which are ubiquitous in many outdoor ecosystems, to essentially provide
mobility for free. Doing so however requires addressing key technical
challenges of power, size, weight and self-localization in order for the
insects to perform location-dependent sensing operations as they carry our IoT
payload through the environment. We develop and deploy our platform on
bumblebees which includes backscatter communication, low-power
self-localization hardware, sensors, and a power source. We show that our
platform is capable of sensing, backscattering data at 1 kbps when the insects
are back at the hive, and localizing itself up to distances of 80 m from the
access points, all within a total weight budget of 102 mg.Comment: Co-primary authors: Vikram Iyer, Rajalakshmi Nandakumar, Anran Wang,
In Proceedings of Mobicom. ACM, New York, NY, USA, 15 pages, 201
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