1,633 research outputs found
Hydrodynamic limits of kinetic equations for polyatomic and reactive gases
Abstract Starting from a kinetic BGK-model for a rarefied polyatomic gas, based on a molecular structure of discrete internal energy levels, an asymptotic Chapman-Enskog procedure is developed in the asymptotic continuum limit in order to derive consistent fluid-dynamic equations for macroscopic fields at Navier-Stokes level. In this way, the model allows to treat the gas as a mixture of mono-atomic species. Explicit expressions are given not only for dynamical pressure, but also for shear stress, diffusion velocities, and heat flux. The analysis is shown to deal properly also with a mixture of reactive gases, endowed for simplicity with translational degrees of freedom only, in which frame analogous results can be achieved
On the shock thickness for a binary gas mixture
We discuss the structure of the shock wave solution for a system of Navier–Stokes equations, obtained as hydrodynamic limit of a BGK description of the dynamics of monoatomic gases at kinetic level. We investigate first the thickness of the transition region of the shock profile for a monoatomic gas, for varying Mach number and different physical options for the viscosity coefficient. The analysis is then extended to a binary gas mixture. Some numerical results for noble gases are presented and discussed
Kinetic models for reactive mixtures: Problems and applications
Problems related to physical consistency and practical application of kinetic BGK models for reactive mixtures are investigated. In particular, two approximation strategies are discussed, relevant to the different physical scenarios
of slow and fast chemical reactions, respectively. The former is tested versus the steady shock problem in comparison to available hydrodynamic results. For the latter, allowing for an explicit proof of the H-theorem, a preliminary sample is shown of the space homogeneous calculations in progress
Shock wave structure of multi-temperature Euler equations from kinetic theory for a binary mixture
A multi-temperature hydrodynamic limit of kinetic equations is employed for the analysis of the steady shock problem in a binary mixture. Numerical results for varying parameters indicate possible occurrence of either smooth profiles or of weak solutions with one or two discontinuities. \ua9 2014 Springer Science+Business Media Dordrecht
Schwannoma vestibular (neurinoma do acústico) imitando desordens temporomandibulares: um relato de caso
Aproximadamente 6 a 16% dos pacientes com sintomas de neuralgia trigeminal apresentam tumores intracranianos, sendo mais comum o schwannoma vestibular (neurinoma do acústico). Alguns sintomas relatados pelos pacientes são perda da audição, zumbido, dores de cabeça, vertigens e distúrbios trigeminais. Uma resposta muscular aumentada na musculatura associada da cabeça e do pescoço também pode ser observada, o que pode mimetizar sinais e sintomas de desordens temporomandibulares. Nestes casos é de grande valia o uso de imagem de ressonância magnética (IRM) para detecção de tumores. É importante, também, a diferenciação de dores miofasciais e neurálgicas, pois ambas podem apresentar caracterÃsticas semelhantes, mas com origens e tratamentos diferentes. O objetivo desse trabalho foi demonstrar através de relato de caso clÃnico a associação entre sintomas de neuralgia trigeminal, tumores intracranianos e disfunção temporomandibular.Approximately 6 to 16% of patients with trigeminal neuralgia symptoms present intracranial tumors, the most common being the vestibular schwannoma (acoustic neuroma). Some symptoms reported by patients include hearing loss, tinnitus, headaches, vertigo and trigeminal disturbances. An increased muscle response in the surrounding head and neck musculature may also be observed, which mimics signs and symptoms of temporomandibular disorders. In these cases, magnetic resonance imaging (MRI) has proved to be a useful tool in tumor diagnosis. The differential diagnosis between myofascial and neuralgic pain is important, as both may present similar characteristics, while being of different origin, and demanding special treatment approaches. The purpose of this paper is to demonstrate the relationship among trigeminal neuralgia symptoms, intracranial tumors and temporomandibular dysfunction by presenting a clinical case
A BGK model for reactive mixtures of polyatomic gases with continuous internal energy
Versão dos autores para esta publicação.In this paper we derive a BGK relaxation model for a mixture of polyatomic gases with a continuous structure of internal energies. The emphasis of the paper is on the case of a quaternary mixture undergoing a reversible chemically reaction of bimolecular type. For such a mixture we prove an H-theorem and characterize the equilibrium solutions with related mass action law of chemical kinetics.
Further, a Chapman-Enskog asymptotic analysis is performed in view of computing the first-order non-equilibrium corrections to the distribution functions and investigating the transport properties of the reactive mixture. The chemical reaction rate is explicitly derived at the first-order and the balance equations for the constituent number densities are derived at the Euler level.The paper is partially supported by the Italian National Group GNFM of INdAM and by the Portuguese
Funds FCT Project UID/MAT/00013/2013. One of the Authors (AJS) thanks the Italian institution for
the financial support given in her visiting professor program in Italy.info:eu-repo/semantics/publishedVersio
Solar and Heliospheric Physics with the Square Kilometre Array
The fields of solar radiophysics and solar system radio physics, or radio
heliophysics, will benefit immensely from an instrument with the capabilities
projected for SKA. Potential applications include interplanetary scintillation
(IPS), radio-burst tracking, and solar spectral radio imaging with a superior
sensitivity. These will provide breakthrough new insights and results in topics
of fundamental importance, such as the physics of impulsive energy releases,
magnetohydrodynamic oscillations and turbulence, the dynamics of post-eruptive
processes, energetic particle acceleration, the structure of the solar wind and
the development and evolution of solar wind transients at distances up to and
beyond the orbit of the Earth. The combination of the high spectral, time and
spatial resolution and the unprecedented sensitivity of the SKA will radically
advance our understanding of basic physical processes operating in solar and
heliospheric plasmas and provide a solid foundation for the forecasting of
space weather events.Comment: 15 pages, Proceedings of Advancing Astrophysics with the Square
Kilometre Array (AASKA14). 9 -13 June, 2014. Giardini Naxos, Italy. Online at
http://pos.sissa.it/cgi-bin/reader/conf.cgi?confid=215, id.16
Modulations of Cortical Power and Connectivity in Alpha and Beta Bands during the Preparation of Reaching Movements
Planning goal-directed movements towards different targets is at the basis of common daily activities (e.g., reaching), involving visual, visuomotor, and sensorimotor brain areas. Alpha (8-13 Hz) and beta (13-30 Hz) oscillations are modulated during movement preparation and are implicated in correct motor functioning. However, how brain regions activate and interact during reaching tasks and how brain rhythms are functionally involved in these interactions is still limitedly explored. Here, alpha and beta brain activity and connectivity during reaching preparation are investigated at EEG-source level, considering a network of task-related cortical areas. Sixty-channel EEG was recorded from 20 healthy participants during a delayed center-out reaching task and projected to the cortex to extract the activity of 8 cortical regions per hemisphere (2 occipital, 2 parietal, 3 peri-central, 1 frontal). Then, we analyzed event-related spectral perturbations and directed connectivity, computed via spectral Granger causality and summarized using graph theory centrality indices (in degree, out degree). Results suggest that alpha and beta oscillations are functionally involved in the preparation of reaching in different ways, with the former mediating the inhibition of the ipsilateral sensorimotor areas and disinhibition of visual areas, and the latter coordinating disinhibition of the contralateral sensorimotor and visuomotor areas
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