1,115 research outputs found
The dynamics of internal working surfaces in MHD jets
The dynamical effects of magnetic fields in models of radiative, Herbig-Haro
(HH) jets have been studied in a number of papers. For example, magnetized,
radiative jets from variable sources have been studied with axisymmetric and 3D
numerical simulations. In this paper, we present an analytic model describing
the effect of a toroidal magnetic field on the internal working surfaces that
result from a variability in the ejection velocity. We find that for parameters
appropriate for HH jets the forces associated with the magnetic field dominate
over the gas pressure force within the working surfaces. Depending on the ram
pressure radial cross section of the jet, the magnetic field can produce a
strong axial pinch, or, alternatively, a broadening of the internal working
surfaces. We check the validity of the analytic model with axisymmetric
numerical simulations of variable, magnetized jets.Comment: 14 pages, 4 figures. ApJ in pres
Automatic configuration of routing control platforms in OpenFlow networks
RouteFlow provides a way to run routing control platforms (e. g. Quagga) in OpenFlow networks. One of the issues of RouteFlow is that an administrator needs to devote a lot of time (typically 7 hours for 28 switches) in manual configurations. We propose and demonstrate a framework that can automatically configure RouteFlow. For this demonstration, we use an emulated pan-European topology of 28 switches. In the demonstration, we stream a video clip from a server to a remote client, and show that the video clip reaches at the remote client within 4 minutes (including the configuration time). In addition, we show automatic configuration of RouteFlow using a GUI (Graphical User Interface)
Simulation of dark lanes in post--flare supra--arcades
Using two simulations of 1.5D, for the first time, in Costa et al. (2009) and
Shulz et al. (2010) we numerically reproduce the observational dark inflows
described in Verwichte et al. (2005). We show that the dark tracks can be
explained as hot plasma vacuums generated upstream of a slow magnetoacoustic
shock wave produced by a localized deposition of energy. In this work, we show
that the overall 2D results are in agreement with the observational behaviour.
However they show a slight shift in the characteristic parameter with respect
to those found previously. Also, we confirm qualitatively the behaviour found
in the previous papers, i.e. for a given numerical domain the period of the
kink--like structure is a function of the magnetic field intensity: larger
periods are associated with lower magnetic field intensities. Contrary to the
1D result -where the sunward dynamic is independent of the magnetic field
intensity due to its exclusively waveguide role- in the 2D simulation the
sunward speed is larger for larger values of the magnetic field. This can be
interpreted as the capability of the low coronal plasma to collimate the
deposition of energy into the magnetic field direction. The moving features
consistent of low--density and high--temperature plasma cavities have larger
inside values of the structuring parameter beta than the neighboring media.
Thus, the voids seem to be the emergence structures of a whole nonlinear
interacting plasma context of shocks and waves more than voided plasma loops
magnetically structured.Comment: 5 pages, 5 figure
Single-bubble and multi-bubble cavitation in water triggered by laser-driven focusing shock waves
In this study a single laser pulse spatially shaped into a ring is focused
into a thin water layer, creating an annular cavitation bubble and cylindrical
shock waves: an outer shock that diverges away from the excitation laser ring
and an inner shock that focuses towards the center. A few nanoseconds after the
converging shock reaches the focus and diverges away from the center, a single
bubble nucleates at the center. The inner diverging shock then reaches the
surface of the annular laser-induced bubble and reflects at the boundary,
initiating nucleation of a tertiary bubble cloud. In the present experiments,
we have performed time-resolved imaging of shock propagation and bubble wall
motion. Our experimental observations of single-bubble cavitation and collapse
and appearance of ring-shaped bubble clouds are consistent with our numerical
simulations that solve a one dimensional Euler equation in cylindrical
coordinates. The numerical results agree qualitatively with the experimental
observations of the appearance and growth of bubble clouds at the smallest
laser excitation rings. Our technique of shock-driven bubble cavitation opens
novel perspectives for the investigation of shock-induced single-bubble or
multi-bubble cavitation phenomena in thin liquids
Multiplex STR amplification sensitivity in a silicon microchip
The demand for solutions to perform forensic DNA profiling outside of centralized laboratories is increasing. We here demonstrate highly sensitive STR amplification using a silicon micro-PCR (mu PCR) chip. Exploiting industry-standard semiconductor manufacturing processes, a device was fabricated that features a small form factor thanks to an integrated heating element covering three parallel micro-reactors with a reaction volume of 0.5 mu l each. Diluted reference DNA samples (1 ng-31 pg) were amplified on the mu PCR chip using the forensically validated AmpFISTR Identifier Plus kit, followed by conventional capillary electrophoresis. Complete STR profiles were generated with input DNA quantities down to 62 pg. Occasional allelic dropouts were observed from 31 pg downward. On-chip STR profiles were compared with those of identical samples amplified using a conventional thermal cycler for direct comparison of amplification sensitivity in a forensic setting. The observed sensitivity was in line with kit specifications for both mu PCR and conventional PCR. Finally, a rapid amplification protocol was developed. Complete STR profiles could be generated in less than 17 minutes from as little as 125 pg template DNA. Together, our results are an important step towards the development of commercial, mass-produced, relatively cheap, handheld devices for on-site testing in forensic DNA analysis
Construction and Test of a Flux Modulation Superconducting Machine for Aircraft
International audienceThe increasing of drives towards More Electric Aircraft (MEA) or the development of electric propulsion aircraft calls for MW-class electrical machines with more compact and power dense designs. One way is to explore the use of superconducting materials to create a high magnetic field in order to reduce the mass of ferromagnetic components. This paper presents the construction and the test of a brushless axial flux superconducting machine. The brushless topology satisfies the aeronautics industry requirements in terms of maintenance, while the axial configuration ensures an optimal use of the anisotropic HTS tapes. The machine is classed as partially superconducting, only the inductor is made with superconducting materials. A special design concerning the use of a stationary cryostat is presented. This improvement reduces significantly the electromagnetic air-gap length. A 50kW prototype is manufactured with a minimal mass objective. The prototype constitutes a first step to a scale-up MW-class machine design
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