793 research outputs found
Alien Registration- Bourgoin, Marie A. (Van Buren, Aroostook County)
https://digitalmaine.com/alien_docs/33235/thumbnail.jp
Induction in a von Karman flow driven by ferromagnetic impellers
We study magnetohydrodynamics in a von K\'arm\'an flow driven by the rotation
of impellers made of material with varying electrical conductivity and magnetic
permeability. Gallium is the working fluid and magnetic Reynolds numbers of
order unity are achieved. We find that specific induction effects arise when
the impeller's electric and magnetic characteristics differ from that of the
fluid. Implications in regards to the VKS dynamo are discussed.Comment: 14 pages, 7 figure
Testing Lorentz symmetry with Lunar Laser Ranging
Lorentz symmetry violations can be parametrized by an effective field theory
framework that contains both general relativity and the standard model of
particle physics called the standard-model extension (SME). We present new
constraints on pure gravity SME coefficients obtained by analyzing lunar laser
ranging (LLR) observations. We use a new numerical lunar ephemeris computed in
the SME framework and we perform a LLR data analysis using a set of 20721
normal points covering the period of August, 1969 to December, 2013. We
emphasize that linear combination of SME coefficients to which LLR data are
sensitive and not the same as those fitted in previous postfit residuals
analysis using LLR observations and based on theoretical grounds. We found no
evidence for Lorentz violation at the level of for ,
for and , for
and
and for
. We improve previous constraints on SME
coefficient by a factor up to 5 and 800 compared to postfit residuals analysis
of respectively binary pulsars and LLR observations
Turbulent transport of material particles: An experimental study of finite size effects
We use an acoustic Lagrangian tracking technique, particularly adapted to
measurements in open flows, and a versatile material particles generator (in
the form of soap bubbles with adjustable size and density) to characterize
Lagrangian statistics of finite sized, neutrally bouyant, particles transported
in an isotropic turbulent flow of air. We vary the size of the particles in a
range corresponding to turbulent inertial scales and explore how the turbulent
forcing experienced by the particles depends on their size. We show that, while
the global shape of the intermittent acceleration probability density function
does not depend significantly on particle size, the acceleration variance of
the particles decreases as they become larger in agreement with the classical
scaling for the spectrum of Eulerian pressure fluctuations in the carrier flow
Radio Occultation Data Analysis With Analytical Ray-Tracing
Radio occultation experiments are a sensing technique dedicated to the remote sounding of planetary atmospheres. The technique exploits the frequency shift of a radio signal due to refraction in a planetary atmosphere. The aim is to infer the physical properties of the neutral atmosphere (e.g., pressure and temperature) and ionosphere (e.g., the electron number density). For one-way occultations, the data processing usually relies on Abel transform algorithms when the atmosphere is spherically symmetric. For two-way occultations, such techniques require the introduction of approximate relationships for the bending experienced by the signal to be obtained. In this context, we introduce a new method to process two-way occultations data by spherically symmetric atmospheres using a ray-tracing approach. However, the numerical integration of the geometrical optics equation through the atmosphere requires a significant computational time due to initial pointing issues. For this reason, our novel algorithm exploits a closed-form solution to the equations of geometrical optics (Bourgoin et al., A&A, 624, A41, 2019, https://doi.org/10.1051/0004-6361/201834962) applied to a spherically symmetric atmosphere. Within this approach, the bending is directly provided by the analytical solution and no numerical integration is required. In addition, we develop a procedure enabling us to disentangle the contributions from dispersive and neutral media in the frequency shift. This procedure is validated by comparing our vertical profiles to those obtained using Abel inversion or numerical ray-tracing for Mars and Titan occultation experiments. We show that our algorithm provides similar results to purely numerical ray-tracing algorithms while significantly decreasing the computational time
First-principles calculation of intrinsic defect formation volumes in silicon
We present an extensive first-principles study of the pressure dependence of
the formation enthalpies of all the know vacancy and self-interstitial
configurations in silicon, in each charge state from -2 through +2. The neutral
vacancy is found to have a formation volume that varies markedly with pressure,
leading to a remarkably large negative value (-0.68 atomic volumes) for the
zero-pressure formation volume of a Frenkel pair (V + I). The interaction of
volume and charge was examined, leading to pressure--Fermi level stability
diagrams of the defects. Finally, we quantify the anisotropic nature of the
lattice relaxation around the neutral defects.Comment: 9 pages, 9 figure
A bibliographic catalogue of the Cicadomorpha and Fulgoromorpha of North East Spain (Aragon)
The knowledge of a large number of Iberian Peninsula Hemiptera such as Cicadomorpha and Fulgoromopha is still fragmentary.
Nevertheless, these two groups are especially remarkable because many species are endemic to this region while others are pests
and/or vectors of diseases to cultivated plants. Therefore, information on these Hemiptera is important not only for conservation
purposes, but also necessary for agricultural pest management. Within Spain, Aragon -located in the northeast of the country- is
especially interesting due to the great diversity of habitats, rich flora and the strategic geographic position. For this political re gion, a bibliographic catalogue of Cicadomorpha and Fulgoromopha is here compiled. The results show that 136 species of 12 of
the 15 families present in Iberian Peninsula have been reported in Aragon in previous works. Of these species, 17 percent are en demic to Spain and 15 percent were never mentioned in previous catalogues or checklists for the whole Iberian Peninsula. These
results although exciting are clearly insufficient if we consider that several hundreds of species should be expected in this area;
clearly more work should be done.info:eu-repo/semantics/publishedVersio
Flow dynamics and magnetic induction in the von-Karman plasma experiment
The von-Karman plasma experiment is a novel versatile experimental device
designed to explore the dynamics of basic magnetic induction processes and the
dynamics of flows driven in weakly magnetized plasmas. A high-density plasma
column (10^16 - 10^19 particles.m^-3) is created by two radio-frequency plasma
sources located at each end of a 1 m long linear device. Flows are driven
through JxB azimuthal torques created from independently controlled emissive
cathodes. The device has been designed such that magnetic induction processes
and turbulent plasma dynamics can be studied from a variety of time-averaged
axisymmetric flows in a cylinder. MHD simulations implementing
volume-penalization support the experimental development to design the most
efficient flow-driving schemes and understand the flow dynamics. Preliminary
experimental results show that a rotating motion of up to nearly 1 km/s is
controlled by the JxB azimuthal torque
Scaling Law in Carbon Nanotube Electromechanical Devices
We report a method for probing electromechanical properties of multiwalled
carbon nanotubes(CNTs). This method is based on AFM measurements on a doubly
clamped suspended CNT electrostatically deflected by a gate electrode. We
measure the maximum deflection as a function of the applied gate voltage. Data
from different CNTs scale into an universal curve within the experimental
accuracy, in agreement with a continuum model prediction. This method and the
general validity of the scaling law constitute a very useful tool for designing
actuators and in general conducting nanowire-based NEMS.Comment: 12 pages, 4 figures. To be published in Phys. Rev. Let
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