1,562 research outputs found
s- and d-wave Symmetries in Nonadiabatic Theory of Superconductivity
High- superconductors have Fermi energies much smaller than
conventional metals comparable to phonon frequencies. In such a situation
nonadiabatic effects are important. A generalization of Eliashberg theory in
the nonadiabatic regime has previously been shown to reproduce some anomalous
features of the high- superconductors as for istance the enhancement of
or the isotopic effects on and . In this contribution we
address the issue of the symmetry of the gap in the context of nonadiabatic
superconductivity. We show that vertex corrections have a momentum structure
which favours d-wave superconductivity when forward scattering is predominant.
An additional increase of is also found.Comment: 6 pages, 3 eps figure, ijmpb-macros, proceeding of SATT10, to appear
on Int. Journ. Mod. Phys.
Isotope effects in the Hubbard-Holstein model within dynamical mean-field theory
We study the isotope effects arising from the coupling of correlated
electrons with dispersionless phonons by considering the Hubbard-Holstein model
at half-filling within the dynamical mean-field theory. In particular we
calculate the isotope effects on the quasi-particle spectral weight , the
renormalized phonon frequency, and the static charge and spin susceptibilities.
In the weakly correlated regime , where is the Hubbard
repulsion and is the bare electron half-bandwidth, the physical properties
are qualitatively similar to those characterizing the Holstein model in the
absence of Coulomb repulsion, where the bipolaronic binding takes place at
large electron-phonon coupling, and it reflects in divergent isotope responses.
On the contrary in the strongly correlated regime , where the
bipolaronic metal-insulator transition becomes of first order, the isotope
effects are bounded, suggesting that the first order transition is likely
driven by an electronic mechanism, rather then by a lattice instability. These
results point out how the isotope responses are extremely sensitive to phase
boundaries and they may be used to characterize the competition between the
electron-phonon coupling and the Hubbard repulsion.Comment: 10 pages, 8 figures. The paper has been already accepted on Phys.
Rev.
Nonadiabatic high-Tc superconductivity in hole-doped fullerenes
In this paper we address the possibility of high-T-c superconductivity (T(c)similar to100 K) in hypothetical hole doped C-60 within the context of the nonadiabatic theory of superconductivity. Our analysis shows that electron doped fullerenes, represented by the A(3)C(60) family, are characterized by relatively small values of the electron-phonon coupling constant lambda, which can thus be further increased by hole doping before lattice instabilities occur. In particular we show that T-c larger than 100 K are compatible in the nonadiabatic context with microscopic parameters lambda(h)similar or equal to0.5-1.0, mu(*)similar or equal to0.3-0.5 and phonon frequencies omega(ph)similar or equal to1500-2000 K. These results provide a stimulus for material engineering and optimization along the lines indicated
Relevance of multiband Jahn-Teller effects on the electron-phonon interaction in C
Assessing the effective relevance of multiband effects in the fullerides is
of fundamental importance to understand the complex superconducting and
transport properties of these compounds. In this paper we investigate in
particular the role of the multiband effects on the electron-phonon (el-ph)
properties of the bands coupled with the Jahn-Teller intra-molecular
vibrational modes in the C compounds. We show that, assuming
perfect degeneracy of the electronic bands, vertex diagrams arising from the
breakdown of the adiabatic hypothesis, are one order of magnitude smaller than
the non-crossing terms usually retained in the Migdal-Eliashberg (ME) theory.
These results permit to understand the robustness on ME theory found by
numerical calculations. The effects of the non degeneracy of the in
realistic systems are also analyzed. Using a tight-binding model we show that
the el-ph interaction is mainly dominated by interband scattering within a
single electronic band. Our results question the reliability of a degenerate
band modeling and show the importance of these combined effects in the
C family.Comment: 5 pages, 3 eps figure
Polaronic and nonadiabatic phase diagram from anomalous isotope effects
Isotope effects (IEs) are powerful tool to probe directly the dependence of
many physical properties on the lattice dynamics. In this paper we invenstigate
the onset of anomalous IEs in the spinless Holstein model by employing the
dynamical mean field theory. We show that the isotope coefficients of the
electron effective mass and of the dressed phonon frequency are sizeable also
far away from the strong coupling polaronic crossover and mark the importance
of nonadiabatic lattice fluctuations in the weak to moderate coupling region.
We characterize the polaronic regime by the appearence of huge IEs. We draw a
nonadiabatic phase diagram in which we identify a novel crossover, not related
to polaronic features, where the IEs attain their largest anomalies.Comment: 5 pages, 4 figure
Characterization of DNA methylation as a function of biological complexity via dinucleotide inter-distances
We perform a statistical study of the distances between successive
occurrencies of a given dinucleotide in the DNA sequence for a number of
organisms of different complexity. Our analysis highlights peculiar features of
the dinucleotide CG distribution in mammalian DNA, pointing towards a
connection with the role of such dinucleotide in DNA methylation. While the CG
distributions of mammals exhibit exponential tails with comparable parameters,
the picture for the other organisms studied (e.g., fish, insects, bacteria and
viruses) is more heterogeneous, possibly because in these organisms DNA
methylation has different functional roles. Our analysis suggests that the
distribution of the distances between dinucleotides CG provides useful insights
in characterizing and classifying organisms in terms of methylation
functionalities.Comment: 13 pages, 5 figures. To be published in the Philosophical
Transactions A theme issue "DNA as information
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Drag produced by waves trapped at a density interface in non-hydrostatic flow over an axisymmetric hill
Linear non-hydrostatic theory is used to evaluate the drag produced by 3D trapped lee waves forced by an axisymmetric hill at a density interface. These waves occur at atmospheric temperature inversions, for example at the top of the boundary layer, and contribute to low-level drag possibly misrepresented as turbulent form drag in large-scale numerical models. Unlike in 2D waves, the drag has contributions from a continuous range of wavenumbers forced by the topography, because the waves can vary their angle of incidence to match the resonance condition. This leads to non-zero drag for Froude numbers (Fr) both 1, and a drag maximum typically for Fr slightly below 1, with lower magnitude than in hydrostatic conditions due to wave dispersion. These features are in good agreement with laboratory experiments using two axisymmetric obstacles, particularly for the lower obstacle, if the effects of a rigid lid above the upper layer and friction are taken into account. Quantitative agreement is less satisfactory for the higher obstacle, as flow nonlinearity increases. However, even in that case the model still largely outperforms both 3D hydrostatic and 2D non-hydrostatic theories, emphasizing the importance of both 3D and non-hydrostatic effects. The associated wave signatures are dominated by transverse waves for Fr lower than at the drag maximum, a dispersive ‘Kelvin ship wave’ pattern near the maximum, and divergent waves for Fr beyond the maximum. The minimum elevation at the density interface depression existing immediately downstream of the obstacle is significantly correlated with the drag magnitude
Investigation on the genetic variability of the american pit bull terrier dogs belonging to an italian breeder using microsatellite markers and genealogical data
The genetic variability of 18 American Pit Bull Terriers bred in Italy was studied using 21 STR markers from the panels recommended for the 2006, 2008 and 2010 ISAG canine comparison test and the genealogical information. As expected, all statistical analysis showed a reduced genetic variability. It is there-fore recommended greater attention in the programming of mating with an increase of gene flow among farmers, which would reduce the average inbreeding in the population and increase genetic variability.Генетическая изменчивость 18 американских питбультерьеров, выведенных в Италии, была изучена с использованием 21 STR маркеров из панелей, рекомендованных Международной ассоциацией генетики животных (ISAG canine) (2006, 2008, 2010). Как и ожидалось, все статистические анализы подтвердили невысокую генетическую изменчивость. Поэтому желательно уделять больше внимания пла-нированию скрещиваний с увеличением потока генов, чтобы уменьшить средний инбридинг в популяции и увеличить генетическую изменчивость.Генетична мінливість 18 американських пітбультер’єрів, виведених в Італії, була вивчена з використанням 21 STR маркерів з панелей, рекомендованих Міжнародною асоціацією генетики тварин (ISAG canine) (2006,2008 і 2010). Як і очікувалося, всі статистичні аналізи підтвердили невисоку генетичну мінливість. Тому бажано приділяти більше уваги плануванню схрещувань із збільшенням потоку генів, щоб зменшити середній інбридинг в популяції і збільшити генетичну мінливість
Abstracts of the Giornate di Coniglicoltura ASIC 2007
(2008). Abstracts of the Giornate di Coniglicoltura ASIC 2007. World Rabbit Science. 16(2). doi:10.4995/wrs.2008.634SWORD16
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Cataract and optic disk drusen in a patient with glycogenosis and di George syndrome: clinical and molecular report
Background
We report the ophthalmic findings of a patient with type Ia glycogen storage disease (GSD Ia), DiGeorge syndrome (DGS), cataract and optic nerve head drusen (ONHD).
Case presentation
A 26-year-old white woman, born at term by natural delivery presented with a post-natal diagnosis of GSD Ia. Genetic testing by array-comparative genomic hybridization (CGH) for DGS was required because of her low levels of serum calcium. The patient has been followed from birth, attending the day-hospital every six months at the San Paolo Hospital, Milan, outpatient clinic for metabolic diseases and previously at another eye center. During the last day-hospital visit, a complete eye examination showed ONHD and cataract in both eyes. Next Generation Sequencing (NGS) was subsequently done to check for any association between the eye problems and metabolic aspects.
Conclusions
This is the first description of ocular changes in a patient with GSD Ia and DGS. Mutations explaining GSD Ia and DGS were found but no specific causative mutation for cataract and ONHD. The metabolic etiology of her lens changes is known, whereas the pathogenesis of ONHD is not clear. Although the presence of cataract and ONHD could be a coincidence; the case reported could suggest that hypocalcemia due to DGS could be the common biochemical pathway
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