11,762 research outputs found
The colour of the narrow line Sy1-blazar 0324+3410
Aims. We investigate the properties of the host galaxy of the blazar
J0324+3410 (B2 0321+33) by the analysis of B and R images obtained with the NOT
under good photometric conditions. Methods: The galaxy was studied using
different methods: Sersic model fitting, unsharp-masked images, B-R image and
B-R profile analysis. Results: The images show that the host galaxy has a
ring-like morphology. The B-R colour image reveals two bluish zones: one that
coincides with the nuclear region, interpreted as the signature of emission
related to the active nucleus, the other zone is extended and is located in the
host ring-structure. We discuss the hypothesis that the later is thermal
emission from a burst of star formation triggered by an interacting/merging
process
Dynamics of capillary spreading along hydrophilic microstripes
We have studied the capillary spreading of a Newtonian liquid along hydrophilic microstripes that are chemically defined on a hydrophobic substrate. The front of the spreading film advances in time according to a power law x=Bt1/2. This exponent of 1/2 is much larger than the value 1/10 observed in the axisymmetric spreading of a wetting droplet. It is identical to the exponent found for wicking in open or closed microchannels. Even though no wicking occurs in our system, the influence of surface curvature induced by the lateral confinement of the liquid stripe also leads to an exponent of 1/2 but with a strongly modified prefactor B. We obtain excellent experimental agreement with the predicted time dependence of the front location and the dependence of the front speed on the stripe width. Additional experiments and simulations reveal the influence of the reservoir volume, liquid material parameters, edge roughness, and nonwetting defects. These results are relevant to liquid dosing applications or microfluidic delivery systems based on free-surface flow
Hard-Loop Dynamics of Non-Abelian Plasma Instabilities
Non-Abelian plasma instabilities may be responsible for the fast apparent
quark-gluon thermalization in relativistic heavy-ion collisions if their
exponential growth is not hindered by nonlinearities. We study the real-time
evolution of instabilities in an anisotropic non-Abelian plasma with an SU(2)
gauge group in the hard-loop approximation. We find exponential growth of
non-Abelian plasma instabilities both in the linear and in the strongly
nonlinear regime, with only a brief phase of subexponential behavior in
between.Comment: 4 pages REVTEX4, 3 figures; updated to match version published in
Phys. Rev. Lett. (shorter introduction, added details on quality of numerical
simulation
Marangoni driven turbulence in high energy surface melting processes
Experimental observations of high-energy surface melting processes, such as
laser welding, have revealed unsteady, often violent, motion of the free
surface of the melt pool. Surprisingly, no similar observations have been
reported in numerical simulation studies of such flows. Moreover, the published
simulation results fail to predict the post-solidification pool shape without
adapting non-physical values for input parameters, suggesting the neglect of
significant physics in the models employed. The experimentally observed violent
flow surface instabilities, scaling analyses for the occurrence of turbulence
in Marangoni driven flows, and the fact that in simulations transport
coefficients generally have to be increased by an order of magnitude to match
experimentally observed pool shapes, suggest the common assumption of laminar
flow in the pool may not hold, and that the flow is actually turbulent. Here,
we use direct numerical simulations (DNS) to investigate the role of turbulence
in laser melting of a steel alloy with surface active elements. Our results
reveal the presence of two competing vortices driven by thermocapillary forces
towards a local surface tension maximum. The jet away from this location at the
free surface, separating the two vortices, is found to be unstable and highly
oscillatory, indeed leading to turbulence-like flow in the pool. The resulting
additional heat transport, however, is insufficient to account for the observed
differences in pool shapes between experiment and simulations
Using Remote Access for Sharing Experiences in a Machine Design Laboratory
A new Machine Design Laboratory at Marquette University has been created to foster student exploration and promote “hands-on” and “minds-on” learning. Laboratory experiments have been developed to give students practical experiences and expose them to physical hardware, actual tools, and design challenges. Students face a range of real-world tasks: identify and select components, measure parameters (dimensions, speed, force), distinguish between normal and used (worn) components and between proper and abnormal behavior, reverse engineer systems, and justify design choices. The experiments serve to motivate the theory, spark interest, and promote discovery learning in the subject of machine design.
This paper presents details of the experiments in the Machine Design Laboratory and then explores the feasibility of sharing some of the experiences with students at other institutions through remote access technologies. The paper proposes steps towards achieving this goal and raises issues to be addressed for a pilot-study offering machine design experiences to students globally who have access to the internet
Atmospheric pressure glow discharge for CO2 conversion : model-based exploration of the optimum reactor configuration
We investigate the performance of an atmospheric pressure glow discharge (APGD) reactor for CO2 conversion in three different configurations, through experiments and simulations. The first (basic) configuration utilizes the well-known pin-to-plate design, which offers a limited conversion. The second configuration improves the reactor performance by employing a vortex-flow generator. The third, "confined" configuration is a complete redesign of the reactor, which encloses the discharge in a limited volume, significantly surpassing the conversion rate of the other two designs. The plasma properties are investigated using an advanced plasma model
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