208 research outputs found
Relevance of phonon dynamics in strongly correlated systems coupled to phonons: A Dynamical Mean Field Theory analysis
The properties of the electron-phonon interaction in the presence of a
sizable electronic repulsion at finite doping are studied by investigating the
metallic phase of the Hubbard-Holstein model with Dynamical Mean Field Theory.
Analyzing the quasiparticle weight at finite doping, we find that a large
Coulomb repulsion reduces the effect of electron-phonon coupling at low-energy,
while this reduction is not present at high energy. The renormalization of the
electron-phonon coupling induced by the Hubbard repul sion depends in a
surprisingly strong and non-trivial way on the phonon frequency. Our results
suggest that phonon might affect differently high-energy and low-energy
properties and this, together with the effect of phonon dynamics, should be
carefully taken into account when the effects of the electron-phonon
interaction in a strongly correlated system, like the superconducting cuprates,
are discussed.Comment: 10 pages, 7 figures - revised version with minor change
Strongly Correlated Superconductivity rising from a Pseudo-gap Metal
We solve by Dynamical Mean Field Theory a toy-model which has a phase diagram
strikingly similar to that of high superconductors: a bell-shaped
superconducting region adjacent the Mott insulator and a normal phase that
evolves from a conventional Fermi liquid to a pseudogapped semi-metal as the
Mott transition is approached. Guided by the physics of the impurity model that
is self-consistently solved within Dynamical Mean Field Theory, we introduce an
analytical ansatz to model the dynamical behavior across the various phases
which fits very accurately the numerical data. The ansatz is based on the
assumption that the wave-function renormalization, that is very severe
especially in the pseudogap phase close to the Mott transition, is perfectly
canceled by the vertex corrections in the Cooper pairing channel.A remarkable
outcome is that a superconducting state can develop even from a pseudogapped
normal state, in which there are no low-energy quasiparticles. The overall
physical scenario that emerges, although unraveled in a specific model and in
an infinite-coordination Bethe lattice, can be interpreted in terms of so
general arguments to suggest that it can be realized in other correlated
systems.Comment: 14 pages, 11 figure
Quantifying the relevance of different mediators in the human immune cell network
Immune cells coordinate their efforts for the correct and efficient
functioning of the immune system (IS). Each cell type plays a distinct role and
communicates with other cell types through mediators such as cytokines,
chemokines and hormones, among others, that are crucial for the functioning of
the IS and its fine tuning. Nevertheless, a quantitative analysis of the
topological properties of an immunological network involving this complex
interchange of mediators among immune cells is still lacking. Here we present a
method for quantifying the relevance of different mediators in the immune
network, which exploits a definition of centrality based on the concept of
efficient communication. The analysis, applied to the human immune system,
indicates that its mediators significantly differ in their network relevance.
We found that cytokines involved in innate immunity and inflammation and some
hormones rank highest in the network, revealing that the most prominent
mediators of the IS are molecules involved in these ancestral types of defence
mechanisms highly integrated with the adaptive immune response, and at the
interplay among the nervous, the endocrine and the immune systems.Comment: 10 pages, 3 figure
Local cone approximations in mathematical programming
We show how to use intensively local cone approximations to obtain results in some fields of optimization theory as optimality conditions, constraint qualifications, mean value theorems and error bound
Existence and solution methods for equilibria
Equilibrium problems provide a mathematical framework which includes optimization, variational inequalities, fixed-point and saddle point problems, and noncooperative games as particular cases. This general format received an increasing interest in the last decade mainly because many theoretical and algorithmic results developed for one of these models can be often extended to the others through the unifying language provided by this common format. This survey paper aims at covering the main results concerning the existence of equilibria and the solution methods for finding them
X-Ray Resonant Scattering as a Direct Probe of Orbital Ordering in Transition-Metal Oxides
X-ray resonant scattering at the K-edge of transition metal oxides is shown
to measure the orbital order parameter, supposed to accompany magnetic ordering
in some cases. Virtual transitions to the 3d-orbitals are quadrupolar in
general. In cases with no inversion symmetry, such as VO, treated in
detail here, a dipole component enhances the resonance. Hence, we argue that
the detailed structure of orbital order in VO is experimentally
accessible.Comment: LaTex using RevTex, 4 pages and two included postscript figure
An Innovative Configuration for CO2 Capture by High Temperature Fuel Cells
Many technological solutions have been proposed for CO 2 capture in the last few years. Most of them are characterized by high costs in terms of energy consumption and, consequently, higher fossil fuel use and higher economic costs. High temperature fuel cells are technological solutions currently developed for energy production with low environmental impact. In CIRIAF—University of Perugia labs, cylindrical geometry, small-sized molten carbonate fuel cell (MCFC) prototypes were built and tested with good energy production and lifetime performances. In the present work, an innovative application for MCFCs is proposed, and an innovative configuration for CO 2 capture/separation is investigated. The plant scheme is based on a reformer and a cylindrical MCFC. MCFCs are the most suitable solutions, because CO 2 is used in their operating cycle. An analysis in terms of energy consumption/kgCO 2 captured is made by coupling the proposed configuration with a gas turbine plant. The proposed configuration is characterized by a theoretical energy consumption of about 500 kJ/kgCO 2 , which is quite lower than actual sequestration technologies. An experimental campaign will be scheduled to verify the theoretical findings
Impact of Lentiviral Vector-Mediated Transduction on the Tightness of a Polarized Model of Airway Epithelium and Effect of Cationic Polymer Polyethylenimine
Lentiviral (LV) vectors are promising agents for efficient and long-lasting gene transfer into the lung and for gene therapy of genetically determined pulmonary diseases, such as cystic fibrosis, however, they have not been evaluated for cytotoxicity and impact on the tightness of the airway epithelium. In this study, we evaluated the transduction efficiency of a last-generation LV vector bearing Green Fluorescent Protein (GFP) gene as well as cytotoxicity and tight junction (TJ) integrity in a polarized model of airway epithelial cells. High multiplicities of infection (MOI) showed to be cytotoxic, as assessed by increase in propidium iodide staining and decrease in cell viability, and harmful for the epithelial tightness, as demonstrated by the decrease of transepithelial resistance (TER) and delocalization of occludin from the TJs. To increase LV efficiency at low LV:cell ratio, we employed noncovalent association with the polycation branched 25 kDa polyethylenimine (PEI). Transduction of cells with PEI/LV particles resulted in 2.5–3.6-fold increase of percentage of GFP-positive cells only at the highest PEI:LV ratios (1×107 PEI molecules/transducing units with 50 MOI LV) as compared to plain LV. At this dose PEI/LV transduction resulted in 6.5 ± 2.4% of propidium iodide-positive cells. On the other hand, PEI/LV particles did not determine any alteration of TER and occludin localization. We conclude that PEI may be useful for improving the efficiency of gene transfer mediated by LV vectors in airway epithelial cells, in the absence of high acute cytotoxicity and alteration in epithelial tightness
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