28,740 research outputs found
Approximation by the Dickman distribution and quasi-logarithmic combinatorial structures
Quasi-logarithmic combinatorial structures are a class of decomposable
combinatorial structures which extend the logarithmic class considered by
Arratia, Barbour and Tavar\'{e} (2003). In order to obtain asymptotic
approximations to their component spectrum, it is necessary first to establish
an approximation to the sum of an associated sequence of independent random
variables in terms of the Dickman distribution. This in turn requires an
argument that refines the Mineka coupling by incorporating a blocking
construction, leading to exponentially sharper coupling rates for the sums in
question. Applications include distributional limit theorems for the size of
the largest component and for the vector of counts of the small components in a
quasi-logarithmic combinatorial structure.Comment: 22 pages; replaces earlier paper [arXiv:math/0609129] with same title
by Bruno Nietlispac
Tabulation of PVI Transcendents and Parametrization Formulas (August 17, 2011)
The critical and asymptotic behaviors of solutions of the sixth Painlev\'e
equation PVI, obtained in the framework of the monodromy preserving deformation
method, and their explicit parametrization in terms of monodromy data, are
tabulated.Comment: 30 pages, 1 figure; Nonlinearity 201
Superconducting states of pure and doped graphene
We study the superconducting phases of the two-dimensional honeycomb lattice
of graphene. We find two spin singlet pairing states, s-wave and an exotic
that is possible because of the special structure of the honeycomb
lattice. At half filling, the phase is gapless and superconductivity is
a hidden order. We discuss the possibility of a superconducting state in metal
coated graphene.Comment: 4 pages, 6 figure
On the Logarithmic Asymptotics of the Sixth Painleve' Equation (Summer 2007)
We study the solutions of the sixth Painlev\'e equation with a logarithmic
asymptotic behavior at a critical point. We compute the monodromy group
associated to the solutions by the method of monodromy preserving deformations
and we characterize the asymptotic behavior in terms of the monodromy itself.Comment: LaTeX with 8 figure
Strong D* -> D+pi and B* -> B+pi couplings
We compute g_{D* D pi} and g_{B* B pi} using a framework in which all
elements are constrained by Dyson-Schwinger equation studies of QCD, and
therefore incorporates a consistent, direct and simultaneous description of
light- and heavy-quarks and the states they may constitute. We link these
couplings with the heavy-light-meson leptonic decay constants, and thereby
obtain g_{D* D pi}=15.9+2.1/-1.0 and g_{B* B pi}=30.0+3.2/-1.4. From the latter
we infer \hat-g_B=0.37+0.04/-0.02. A comparison between g_{D* D pi} and g_{B* B
pi} indicates that when the c-quark is a system's heaviest constituent,
Lambda_{QCD}/m_c-corrections are not under good control.Comment: 5 pages, 1 table, 2 figure
Coulomb force effects in low-energy -deuteron scattering
The -proton Coulomb interaction is included in the description of
-deuteron scattering using the screening and renormalization approach
in the framework of momentum-space three-particle equations. The technical
reliability of the method is demonstrated. Large Coulomb-force effects are
found.Comment: To be published in Phys. Rev.
1/N Expansion in Correlated Graphene
We examine the 1/N expansion, where N is the number of two-component Dirac
fermions, for Coulomb interactions in graphene with a gap of magnitude . We find that for , where is graphene's "fine
structure constant", there is a crossover as a function of distance from
the usual 3D Coulomb law, , to a 2D Coulomb interaction, , for . This effect
reflects the weak "confinement" of the electric field in the graphene plane.
The crossover also leads to unusual renormalization of the quasiparticle
velocity and gap at low momenta. We also discuss the differences between the
interaction potential in gapped graphene and usual QED for different coupling
regimes.Comment: 7 pages, 2 figures; expanded presentation, references adde
Quantum size effects in the low temperature layer-by-layer growth of Pb on Ge(001)
The electronic properties of thin metallic films deviate from the
corresponding bulk ones when the film thickness is comparable with the
wavelength of the electrons at the Fermi level due to quantum size effects
(QSE). QSE are expected to affect the film morphology and structure leading to
the low temperature (LT) ``electronic growth'' of metals on semiconductors. In
particular, layer-by-layer growth of Pb(111) films has been reported for
deposition on Ge(001) below 130 K. An extremely flat morphology is preserved
throughout deposition from four up to a dozen of monolayers. These flat films
are shown to be metastable and to reorganize into large clusters uncovering the
first Pb layer, pseudomorphic to the substrate, already at room temperature.
Indications of QSE induced structural variations of the growing films have been
reported for Pb growth on Ge(001), where the apparent height of the Pb(111)
monatomic step was shown to change in an oscillatory fashion by He atom
scattering (HAS) during layer-by-layer growth. The extent of the structural QSE
has been obtained by a comparison of the HAS data with X-ray diffraction (XRD)
and reflectivity experiments. Whereas step height variations as large as 20 %
have been measured by HAS reflectivity, the displacement of the atomic planes
from their bulk position, as measured by XRD, has been found to mainly affect
the topmost Pb layer, but with a lower extent, i.e. the QSE observed by HAS are
mainly due to a perpendicular displacement of the topmost layer charge density.
The effect of the variable surface relaxation on the surface vibration has been
studied by inelastic HAS to measure the acoustic dispersion of the low energy
phonons.Comment: 28 pages (laTex,elsart) and 13 figures (eps); updated reference
- …