516 research outputs found
Ray tracing of ion-cyclotron waves in a coronal funnel
Remote observations of coronal holes have strongly implicated the kinetic
interactions of ion-cyclotron waves with ions as a principal mechanism for
plasma heating and acceleration of the fast solar wind. In order to study these
waves, a linear perturbation analysis is used in the work frame of the
collisionless multi-fluid model. We consider a non-uniform background plasma
describing a funnel region and use the ray tracing equations to compute the ray
path of the waves as well as the spatial variation of their properties.Comment: 4 pages, 3 figures Modern Solar Facilities, Advanced Solar Science,
Universitatsverlag Goettingen 200
On Minimizing ||S−(AX−XB)||Pp
In this paper, we minimize the map Fp (X)= ||S−(AX−XB)||Pp ,
where the pair (A, B) has the property (F P )Cp , S ∈ Cp , X varies such that
AX − XB ∈ Cp and Cp denotes the von Neumann-Schatten class
New values of gravitational moments J2 and J4 deduced from helioseismology
By applying the theory of slowly rotating stars to the Sun, the solar
quadrupole and octopole moments J2 and J4 were computed using a solar model
obtained from CESAM stellar evolution code (Morel, 1997) combined with a recent
model of solar differential rotation deduced from helioseismology (Corbard et
al., 2002). This model takes into account a near-surface radial gradient of
rotation which was inferred and quantified from MDI f-mode observations by
Corbard and Thompson (2002). The effect of this observational near-surface
gradient on the theoretical values of the surface parameters J2, J4 is
investigated. The results show that the octopole moment J4 is much more
sensitive than the quadrupole moment J2 to the subsurface radial gradient of
rotation
Coronal ion-cyclotron beam instabilities within the multi-fluid description
Spectroscopic observations and theoretical models suggest resonant
wave-particle interactions, involving high-frequency ion-cyclotron waves, as
the principal mechanism for heating and accelerating ions in the open coronal
holes. However, the mechanism responsible for the generation of the
ion-cyclotron waves remains unclear. One possible scenario is that ion beams
originating from small-scale reconnection events can drive micro-instabilities
that constitute a possible source for the excitation of ion-cyclotron waves. In
order to study ion beam-driven electromagnetic instabilities, the multi-fluid
model in the low-beta coronal plasma is used. While neglecting the electron
inertia this model allows one to take into account ion-cyclotron wave effects
that are absent from the one-fluid MHD model. Realistic models of density and
temperature as well as a 2-D analytical magnetic field model are used to define
the background plasma in the open-field funnel region of a polar coronal hole.
Considering the WKB approximation, a Fourier plane-wave linear mode analysis is
employed in order to derive the dispersion relation. Ray-tracing theory is used
to compute the ray path of the unstable wave as well as the evolution of the
growth rate of the wave while propagating in the coronal funnel. We demonstrate
that, in typical coronal holes conditions and assuming realistic values of the
beam velocity, the free energy provided by the ion beam propagating parallel
the ambient field can drive micro-instabilities through resonant ion-cyclotron
excitation.Comment: 8 pages, 6 figures, submitted to A&
Neural Network Monitoring Strategy of Cutting Tool Wear of Horizontal High Speed Milling
The wear of cutting tool degrades the quality of the product in the manufacturing processes. The online monitoring of the cutting tool wear level is very necessary to prevent the deterioration of the quality of machining. Unfortunately there is not a direct manner to measure the cutting tool wear online. Consequently we must adopt an indirect method where wear will be estimated from the measurement of one or more physical parameters appearing during the machining process such as the cutting force, the vibrations, or the acoustic emission etc. In this work, a neural network system is elaborated in order to estimate the flank wear from the cutting force measurement and the cutting conditions
Sviluppo di un modello orientato al controllo di un catalizzatore trivalente per applicazioni GDI
I sempre più stringenti vincoli normativi riguardanti le emissioni, richiedono lo sviluppo di modelli in grado stimare on-board le emissioni engine-out e le emissioni a valle del catalizzatore. Per modellare la chimica di un catalizzatore è richiesto un elevato sforzo computazione e questo va in contrapposizione con la necessità di lavorare real-time. La variabile che maggiormente influenza la dinamica del catalizzatore è l'ossigeno in esso contenuto, portando così a definire un modello oxygen storage dominated. Con questa tipologia di modellazione semplificata il catalizzatore viene descritto come un serbatoio di ossigeno con una sua dinamica di riempimento e svuotamento. Le possibili applicazioni su cui il modello potrebbe lavorare sono l’implementazione di una strategia di controllo lambda predittiva per i progetti con singolo brick e la modellazione del titolo a valle del GPF nei progetti con layout a cascata
Nanostructured Fe-N-C as bifunctional catalysts for oxygen reduction and hydrogen evolution
The development of electrocatalysts for energy conversion and storage devices is of paramount importance to promote sustainable development. Among the different families of materials, catalysts based on transition metals supported on a nitrogen-containing carbon matrix have been found to be effective catalysts toward oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) with high potential to replace conventional precious metal-based catalysts. In this work, we developed a facile synthesis strategy to obtain a Fe-N-C bifunctional ORR/HER catalysts, involving wet impregnation and pyrolysis steps. Iron (II) acetate and imidazole were used as iron and nitrogen sources, respectively, and functionalized carbon black pearls were used as conductive support. The bifunctional performance of the Fe-N-C catalyst toward ORR and HER was investigated by cyclic voltammetry, rotating ring disk electrode experiments, and electrochemical impedance spectroscopy in alkaline environment. ORR onset potential and half-wave potential were 0.95 V and 0.86 V, respectively, indicating a competitive performance in comparison with the commercial platinum-based catalyst. In addition, Fe-N-C had also a good HER activity, with an overpotential of 478 mV @10 mAcm(-2) and Tafel slope of 133 mVdec(-1), demonstrating its activity as bifunctional catalyst in energy conversion and storage devices, such as alkaline microbial fuel cell and microbial electrolysis cells
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