5,548 research outputs found
A mesoscopic approach to diffusion phenomena in mixtures
The mesosocpic concept is applied to the theory of mixtures. The aim is to
investigate the diffusion phenomenon from a mesoscopic point of view. The
domain of the field quantities is extended by the set of mesoscopic variables,
here the velocities of the components. Balance equations on this enlarged space
are the equations of motion for the mesoscopic fields. Moreover, local
distribution functions of the velocities are introduced as a statistical
element, and an equation of motion for this distribution function is derived.
From this equation of motion differential equations for the diffusion fluxes,
and also for higher order fluxes are obtained. These equations are of balance
type, as it is postulated in Extended Thermodynamics. The resulting evolution
equation for the diffusion flux generalizes the Fick's law
Broad Line Radio Galaxies: Jet Contribution to the nuclear X-Ray Continuum
It is shown that, for Broad Line Radio Galaxies the strength of the
non-thermal beamed radiation, when present, is always smaller than the
accretion flow by a factor < 0.7 in the 2-10 keV band. The result has been
obtained using the procedure adopted for disentangling the Flat Spectrum Radio
Quasar 3C 273 (Grandi & Palumbo 2004). Although this implies a significantly
smaller non-thermal flux in Radio Galaxies when compared to Blazars, the jet
component, if present, could be important at very high energies and thus easily
detectable with GLAST.Comment: 12 pages including 2 figures (4 files), ApJ accepte
Chern-Simons theory and atypical Hall conductivity in the Varma phase
In this letter, we analyze the topological response of a fermionic model
defined on the Lieb lattice in presence of an electromagnetic field. The
tight-binding model is built in terms of three species of spinless fermions and
supports a topological Varma phase due to the spontaneous breaking of
time-reversal symmetry. In the low-energy regime, the emergent effective
Hamiltonian coincides with the so-called Duffin-Kemmer-Petiau (DKP)
Hamiltonian, which describes relativistic pseudospin-0 quasiparticles. By
considering a minimal coupling between the DKP quasiparticles and an external
Abelian gauge field, we calculate both the Landau-level spectrum and the
emergent Chern-Simons theory. The corresponding Hall conductivity reveals an
atypical quantum Hall effect, which can be simulated in an artificial Lieb
lattice.Comment: 5 pages, 3 figures; New version with an improved discussion about our
finding
Conformal QED in two-dimensional topological insulators
It has been shown recently that local four-fermion interactions on the edges
of two-dimensional time-reversal-invariant topological insulators give rise to
a new non-Fermi-liquid phase, called helical Luttinger liquid (HLL). In this
work, we provide a first-principle derivation of this non-Fermi-liquid phase
based on the gauge-theory approach. Firstly, we derive a gauge theory for the
edge states by simply assuming that the interactions between the Dirac fermions
at the edge are mediated by a quantum dynamical electromagnetic field. Here,
the massless Dirac fermions are confined to live on the one-dimensional
boundary, while the (virtual) photons of the U(1) gauge field are free to
propagate in all the three spatial dimensions that represent the physical space
where the topological insulator is embedded. We then determine the effective
1+1-dimensional conformal field theory (CFT) given by the conformal quantum
electrodynamics (CQED). By integrating out the gauge field in the corresponding
partition function, we show that the CQED gives rise to a 1+1-dimensional
Thirring model. The bosonized Thirring Hamiltonian describes exactly a HLL with
a parameter K and a renormalized Fermi velocity that depend on the value of the
fine-structure constant .Comment: (5+4) pages, 2 figure
ASCA view on High-Redshift Radio-Quiet Quasars
We briefly discuss the latest ASCA results on the X-ray spectral properties
of high-redshift radio-quiet quasars.Comment: 4 pages, 1 figure, to appear in the Proceedings of the Conference
"X-ray Astronomy '999: Stellar Endpoints, AGNs, and the Diffuse X-ray
Background (September 6-10 - 1999
Numerical study of the scaling properties of SU(2) lattice gauge theory in Palumbo non-compact regularization
In the framework of a non-compact lattice regularization of nonabelian gauge
theories we look, in the SU(2) case, for the scaling window through the
analysis of the ratio of two masses of hadronic states. In the two-dimensional
parameter space of the theory we find the region where the ratio is constant,
and equal to the one in the Wilson regularization. In the scaling region we
calculate the lattice spacing, finding it at least 20% larger than in the
Wilson case; therefore the simulated physical volume is larger.Comment: 24 pages, 7 figure
A deep look at the inner regions of the mini-BAL QSO PG 1126-041 with XMM-Newton
A long XMM-Newton observation of the mini-BAL QSO PG 1126-041 allowed us to
detect a highly ionized phase of X-ray absorbing gas outflowing at v~15000
km/s. Physical implications are briefly discussed.Comment: 2 pages, 2 figures. Proceedings of "X.ray Astronomy 2009", Bologna
09/7-11/2009, AIP Conference Series, Eds. A. Comastri, M. Cappi, L. Angelin
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