29,994 research outputs found
Combinatorics of lattice paths with and without spikes
We derive a series of results on random walks on a d-dimensional hypercubic
lattice (lattice paths). We introduce the notions of terse and simple paths
corresponding to the path having no backtracking parts (spikes). These paths
label equivalence classes which allow a rearrangement of the sum over paths.
The basic combinatorial quantities of this construction are given. These
formulas are useful when performing strong coupling (hopping parameter)
expansions of lattice models. Some applications are described.Comment: Latex. 25 page
Confinement of electrons in layered metals
We analyze the out of plane hopping in models of layered systems where the
in--plane properties deviate from Landau's theory of a Fermi liquid. We show
that the hopping term acquires a non trivial energy dependence, due to the
coupling to in plane excitations, and can be either relevant or irrelevant at
low energies or temperatures. The latter is always the case if the Fermi level
lies close to a saddle point in the dispersion relation.Comment: 4 pages, 1 eps figur
Comparative aspects of phytase and xylanase effects on performance, mineral digestibility, and ileal phytate degradation in broilers and turkeys
Two experiments were performed, using broilers or turkeys, each utilizing a 3 × 2 factorial arrangement, to compare their response to phytase and xylanase supplementation with growth performance, nutrient digestibility, and ileal phytate degradation as response criteria. For both experiments, 960 Ross 308 or 960 BUT 10 (0-day-old) birds were allocated to 6 treatments: (1) control diet, containing phytase at 500 FTU/kg; (2) the control diet with xylanase (16,000 BXU/kg); (3) the control diet supplemented on top with phytase (1,500 FTU/kg); (4) diet supplemented with 1,500 FTU/kg phytase and xylanase (16,000 BXU/kg); (5) the control diet supplemented with phytase (3,000 FTU/kg); and (6) diet supplemented with 3,000 FTU/kg phytase and xylanase (16,000 BXU/kg). Each treatment had 8 replicates of 20 birds each. Water and diets based on wheat, soybean meal, oilseed rape meal, and barley were available ad libitum. Body weight gain and feed intake were measured from 0 to 28 D, and feed conversion ratio (FCR) corrected for mortality was calculated. Ileal digestibility for dry matter and minerals on day 7 and 28 were analyzed in addition to levels of inositol phosphate esters (InsP6-3) and myo-inositol. Statistical comparisons were performed using ANOVA. Xylanase supplementation improved 28D FCR in broilers and turkeys. Increasing doses of phytase reduced FI and improved FCR only in broilers. In broilers, the age × phytase interaction for phosphorous digestibility showed that increasing phytase dose was more visible on day 7, than on day 28. Mineral digestibility was lower in 28-day-old turkey compared with 7-day-old turkey. InsP6 disappearance increased with increasing phytase levels in both species, with lower levels analyzed in turkeys. InsP6 disappearance was greater in younger turkeys (day 7 compared with day 28). In conclusion, although broilers and turkeys shared several similarities in their growth and nutrient utilization responses, the outcomes of the 2 trials also differed in many aspects. Whether this is because of difference in diets (InsP or Ca level) or differences between species needs further investigation
Anisotropic Fermi surfaces and Kohn-Luttinger superconductivity in two dimensions
The instabilities induced on a two-dimensional system of correlated electrons
by the anisotropies of its Fermi line are analyzed on general grounds. Simple
scaling arguments allow to predict the opening of a superconducting gap with a
well-defined symmetry prescribed by the geometry of the Fermi line. The same
arguments predict a critical dimension of 3/2 for the transition of the
two-dimensional system to non-Fermi liquid behavior. The methods are applied to
the t-t' Hubbard model in a wide range of dopings.Comment: 25 pages, 13 postscript figure
On the families of orthogonal polynomials associated to the Razavy potential
We show that there are two different families of (weakly) orthogonal
polynomials associated to the quasi-exactly solvable Razavy potential V(x)=(\z
\cosh 2x-M)^2 (\z>0, ). One of these families encompasses the
four sets of orthogonal polynomials recently found by Khare and Mandal, while
the other one is new. These results are extended to the related periodic
potential U(x)=-(\z \cos 2x -M)^2, for which we also construct two different
families of weakly orthogonal polynomials. We prove that either of these two
families yields the ground state (when is odd) and the lowest lying gaps in
the energy spectrum of the latter periodic potential up to and including the
gap and having the same parity as . Moreover, we show
that the algebraic eigenfunctions obtained in this way are the well-known
finite solutions of the Whittaker--Hill (or Hill's three-term) periodic
differential equation. Thus, the foregoing results provide a Lie-algebraic
justification of the fact that the Whittaker--Hill equation (unlike, for
instance, Mathieu's equation) admits finite solutions.Comment: Typeset in LaTeX2e using amsmath, amssymb, epic, epsfig, float (24
pages, 1 figure
Soliton tunneling with sub-barrier kinetic energies
We investigate (theoretically and numerically) the dynamics of a soliton
moving in an asymmetrical potential well with a finite barrier. For large
values of the width of the well, the width of the barrier and/or the height of
the barrier, the soliton behaves classically. On the other hand, we obtain the
conditions for the existence of soliton tunneling with sub-barrier kinetic
energies. We apply these results to the study of soliton propagation in
disordered systems.Comment: 6 eps figures. To appear in Physical Review E (Rapid Communications
OTELO survey: optimal emission-line flux determination with OSIRIS/GTC
Emission-line galaxies are important targets for understanding the chemical
evolution of galaxies in the universe. Deep, narrow-band imaging surveys allow
to detect and study the flux and the equivalent widths (EW) of the emission
line studied. The present work has been developed within the context of the
OTELO project, an emission line survey using the Tunable Filters (TF) of
OSIRIS, the first generation instrument on the GTC 10.4m telescope located in
La Palma, Spain, that will observe through selected atmospheric windows
relatively free of sky emission lines. With a total survey area of 0.1 square
degrees distributed in different fields, reaching a 5 \sigma depth of 10^-18
erg/cm^2/s and detecting objects of EW < 0.3 A, OTELO will be the deepest
emission line survey to date. As part of the OTELO preparatory activities, the
objective of this study is to determine the best combination of sampling and
full width at half maximum (FWHM) for the OSIRIS tunable filters for deblending
H\alpha from [NII] lines by analyzing the flux errors obtained. We simulated
the OTELO data by convolving a complete set of synthetic HII galaxies in EW
with different widths of the OSIRIS TFs. We estimated relative flux errors of
the recovered H\alpha and [NII]6583 lines. We found that, for the red TF, a
FWHM of 12 A and a sampling of 5 A is an optimal combination that allow
deblending H\alpha from the [NII]6583 line with a flux error lower than 20%.
This combination will allow estimating SFRs and metallicities using the H\alpha
flux and the N2 method, respectively.Comment: 16 pages, 9 figures. Some authors added. Accepted for publication in
PAS
Present and future of the OTELO project
OTELO is an emission-line object survey carried out with the red tunable
filter of the instrument OSIRIS at the GTC, whose aim is to become the deepest
emission-line object survey to date. With 100% of the data of the first
pointing finally obtained in June 2014, we present here some aspects of the
processing of the data and the very first results of the OTELO survey. We also
explain the next steps to be followed in the near future.Comment: Oral contribution presented in the XI Scientific Meeting of the
Spanish Astronomical Society held on September 8-12, in Teruel, Spain (7
pages, 2 figures, 1 table). To appear in Highlights of Spanish Astrophysics
VIII, Proceedings of the XI Scientific Meeting of the Spanish Astronomical
Society. Eds. A. J. Cenarro, F. Figueras, C. Hern\'andez-Monteagudo, J.
Trujillo, L. Valdiviels
On Existence of a Biorthonormal Basis Composed of Eigenvectors of Non-Hermitian Operators
We present a set of necessary conditions for the existence of a biorthonormal
basis composed of eigenvectors of non-Hermitian operators. As an illustration,
we examine these conditions in the case of normal operators. We also provide a
generalization of the conditions which is applicable to non-diagonalizable
operators by considering not only eigenvectors but also all root vectors.Comment: 6 pages, no figures; (v2) minor revisions based on the comment
quant-ph/0603096; (v3) presentation improved, final version to appear in
Journal of Physics
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