Search

Understanding the topological characteristics of complex networks and how they affect navigability is one of the most important goals in science today, as it plays a central role in various economic, biological, ecological and social systems. Here, we apply First Passage analysis tools to investigate the properties and characteristics of random walkers in networks with different topology. Starting with the simplest two-dimensional square lattice, we modify its topology incrementally by randomly reconnecting links between sites. We characterize these networks by First Passage Time from a significant number of random walkers without interaction, varying the departure and arrival locations. We also apply the concept of First Passage Simultaneity, which measures the likelihood of two walkers reaching their destination together. These measures, together with the site occupancy statistics during the processes, allowed to differentiate the studied networks, especially the random networks from the scale-free networks, by their navigability. We also show that small world features can also be highlighted with the proposed technique., Comment: 17 pages and 9 figures

This work is focused on the phase diagrams and physical properties of Y-doped and Lu-doped EuMnO3. The differences in the corresponding phase boundaries in the (x,T) phase diagram could be overcome by considering a scaling of the Y3+ and Lu3+ concentrations to the tolerance factor. This outcome evidences that the tolerance factor is in fact a more reliable representative of the lattice deformation induced by doping. The normalization of the phase boundaries using the tolerance factor corroborates previous theoretical outcomes regarding the key role of competitive FM and AFM exchanges in determining the phase diagrams of manganite perovskites. Though, significant differences in the nature and number of phases at low temperatures and concentrations could not be explained by just considering the normalization to the tolerance factor. The vertical phase boundary observed just for Lu-doped EuMnO3, close to 10%Lu, is understood considering a low temperature Peierls-type spin-phonon coupling, which stabilizes the AFM4 phase in Lu-doped EuMnO3., Comment: 15 pages, 6 figures

In this work we investigate the magnetic field dependence of Ag octahedra rotation (tilt) and B2g symmetric stretching modes frequency at different temperatures. Our field-dependent Raman investigation at 10K is interpreted by an ionic displacive nature of the magnetically induced ferroelectric phase transition. The frequency change of the Ag tilt is in agreement with the stabilization of the Mn-Gd spin arrangement, yielding the necessary conditions for the onset of ferroelectricity on the basis of the inverse Dzyaloshinskii-Moriya interaction. The role of the Jahn-Teller cooperative interaction is also evidenced by the change of the B2g mode frequency at the ferroelectric phase transition. This frequency change allows estimating the shift of the oxygen position at the ferroelectric phase transition and the corresponding spontaneous polarization of 480 {\mu}C/m2, which agrees with earlier reported values in single crystals. Our study also confirms the existence of a large magnetic hysteresis at the lowest temperatures, which is a manifestation of magnetrostiction., Comment: 5 pages, 3 figures

This work reports an experimental investigation of the magneto-elastic coupling and polarization character of magnetic phases of the orthorhombic Eu1-xYxMnO3 system at low temperatures. The temperature dependence of the polarization reversal curves clearly reveals the existence of a reentrant improper ferroelectric phase for x = 0.2 and 0.3. Although a ferroelectric phase is also stable for x = 0.4, we have no experimental evidence that it vanishing at finite temperatures. From these results and those obtained from other experimental techniques, the corresponding (x,T) phase diagram was traced, yet yielding significant differences with regard to previous reports. An expressive magneto-elastic coupling is revealed by changes observed in both Mn-O bond lengths and Mn-O1-Mn bond angle at the magnetic phase transitions, obtained by temperature dependence of synchrotron x-ray diffraction experiments. Furthermore, signatures of the lattice deformations across the magnetic phase transitions were evidenced by anomalies in the temperature dependence of the lattice mode involving rotations of the MnO6 octahedra. These anomalies confirm the important role of the spin-phonon coupling in these materials., Comment: 12 Figures, 2 Tables

Local oscillatory and other properties of source-type solutions of doubly nonlinear sixth-order parabolic thin film equations are studied., Comment: 27 pages, 5 figures

Eu1-xYxMnO3 exhibits, unlike other magnetoelectric systems, very distinctive features. Its magnetoelectric properties is driven by the magnetic spin of the Mn3+ ion, but they can be drastically changed by varying the content of Y3+, which it does not carry any magnetic moment. Though the x = 0.40 composition has been studied extensively, some basic questions still remain to be thoroughly understood. Thus, this work is aimed at studying some of its polar properties and their magnetic field dependence as well. The experimental results here reported have shown that this material is very easily polarisable under external electric fields, and so, whenever the polarization is obtained from time integration of the displacement currents, an induced polarization is superposed to the spontaneous one, eventually masking the occurrence of ferroelectricity. We have found clear evidence for the influence of a magnetic field in the polar properties of Eu0.6Y0.4MnO3. The study of electric polarization of Eu0.6Y0.4MnO3 under an external magnetic field yields a value with the same order of magnitude of the remanent polarization determined from polarization reversal experiments. The comparison of the magnetic induced changes on the polarization obtained in polycrystalline samples and single crystals confirms the threshold magnetic field value for the polarization rotation from the a- to the c-direction, and evidencing the importance of the granular nature of the samples in the polar response to magnetic field., Comment: 28 pages, 12 figures. Accepted for publication in J. Phys.: Condens. Matter

To clarify the controversy concerning the ferroelectricity of the lower temperature magnetic phases of Eu0.8Y0.2MnO3, hence its multiferroic character, we have studied in detail the temperature dependence of the electric polarization. The existence of a spontaneous polarization in 30K < T < 22K, provides clear evidence for the ferroelectric character of the re-entrant magnetic phase, stable in that temperature range. Both lower temperature magnetic phases allow easily-induced electric polarization, which actually mask any spontaneous polarization., Comment: 11 pages, 4 figures, submitted to Phys. Rev. Letters

In this work we present a detailed study of the structural and lattice dynamic properties of Y-doped EuMnO3 ceramics (Eu1-xYxMnO3, with 0

We consider a modified form of gravity, which has an extra term quadratic in the Riemann tensor. This term mimics a Yang-Mills theory. The other defining characteristic of this gravity is having the affine connection independent of the metric. (The metricity of the metric is rejected, too, since it implies a Levi-Civita connection.) It is then shown that, in the low density limit, this modified gravity does not differ from the General Theory of Relativity. We then point out that its Lagrangian does not contain partials of the metric, so that the metric is not a quantum field, nor does it contribute propagators to the Feynman diagrams of the theory. We also point out that the couplings of this theory (that determine the topological structure of the Feynman diagrams) all come from the term quadratic in the Riemann tensor. As a result of this situation, the diagrams of this theory and the diagrams of a Yang-Mills theory all have the same topology and degree of divergence, up to numerical coefficients. Since Yang-Mills theories are renormalizable, it follows that this theory should also be renormalizable., Comment: 10 pages

A few years ago H. Morales and the author introduced a type of generalized derivative that contained both vector and scalar boson fields. Here it is shown how to construct a full-fledged generalized Yang-Mills theory through the introduction of "extended field" multiplets. These are mixed fields that include both a vector and a scalar part. It is shown how the standard model of high energy physics appears naturally in a Yang-Mills theory that uses extended field multiplets through two spontaneous symmetry breakings, one due to the VEV of a scalar field and another to the VEV of a vector field., Comment: 7 pages; talk at X Marcel Grossmann Meeting on General Relativity, Rio de Janeiro, July 20-26, 2003

We present central velocity dispersions and Mg$_2$ line indices for an all-sky sample of $\sim$ 1178 elliptical and S0 galaxies, of which 984 had no previous measures. This sample contains the largest set of homogeneous spectroscopic data for a uniform sample of elliptical galaxies in the nearby universe. These galaxies were observed as part of the ENEAR project, designed to study the peculiar motions and internal properties of the local early-type galaxies. Using 523 repeated observations of 317 galaxies obtained during different runs, the data are brought to a common zero-point. These multiple observations, taken during the many runs and different instrumental setups employed for this project, are used to derive statistical corrections to the data and are found to be relatively small, typically $\lsim$ 5% of the velocity dispersion and 0.01 mag in the \mg line-strength. Typical errors are about 8% in velocity dispersion and 0.01 mag in \mg, in good agreement with values published elsewhere., Comment: 179 pages, 8 figures, 5 tables. Full tables 4 and 5 start on page 41

In Wilson's Theorem the primality of a number hinges on a congruence. We present a similar test where the primality of a number m hinges, instead, on the indivisibility of 4(m-5)! by m. One implication of this theorem is a necessary and sufficient condition for two numbers to be twin primes, a result reminiscent of Clement's theorem but involving indivisibility. MSC: 11A41 and 11A51., Comment: There are no changes in this version, except for added journal information: to be published in the July 2011 issue of the Math. Gaz. (4 pages, LATEX, amsfonts)

In generalized Yang-Mills theories scalar fields can be gauged just as vector fields in a usual Yang-Mills theory, albeit it is done in the spinorial representation. The presentation of these theories is aesthetic in the following sense: A physical theory using Yang-Mills theories requires several terms and irreducible representations, but with generalized Yang-Mills theories, only two terms and two irreducible representations are required. These theories are constructed based upon the maximal subgroups of the gauge Lie group. The two terms of the lagrangian are the kinetic energy of fermions and of bosons. A brief review of Yang-Mills theories and covariant derivatives is given, then generalized Yang-Mills theories are defined through a generalization of the covariant derivative. Two examples are given, one pertaining the Glashow-Weinberg-Salam model and another SU(5) grand unification. The first is based upon a $U(3)\supset U(1)\times U(1)\times SU(2)$ generalized Yang-Mills theory, and the second upon a $SU(6)\supset U(1)\times SU(5)$ theory. The possibility of expressing generalized Yang-Mills theories using a five-dimensional formalism is also studied. The situation is unclear in this case. At the end a list of comments and criticisms is given., Comment: 37 p., AMSLaTeX, Lectures, Summer School in Theoretical Physics, Zacatecas, August 2000. A few typos have been corrected

The asymptotic decay of passive scalar fields is solved analytically for the Kraichnan model, where the velocity has a short correlation time. At long times, two universality classes are found, both characterized by a distribution of the scalar -- generally non-Gaussian -- with global self-similar evolution in time. Analogous behavior is found numerically with a more realistic flow resulting from an inverse energy cascade., Comment: 4 pages, 3 Postscript figures, submitted to PRL

Generalized Yang-Mills theories have a covariant derivative that employs both scalar and vector bosons. Here we show how grand unified theories of the electroweak and strong interactions can be constructed with them. In particular the SU(5) GUT can be obtained from SU(6) with SU(5)xU(1) as a maximal subgroup. The choice of maximal subgroup also determines the chiral structure of the theory. The resulting Lagrangian has only two terms, and only two irreducible representations are needed, one for fermions and another for bosons., Comment: 10 pages, no figures

The generalized covariant derivative, that uses both scalar and vector bosons, is defined. It is shown how a grand unified theory of the Standard Model can be constructed using a generalized Yang-Mills theory., Comment: 8 pages, no figures. To be published in the proceedings of the International Workshop "Lorentz Group, CPT and Neutrinos", (Zacatecas, Mexico, June 23-26, 1999)

Software for the resolution of certain kind of problems, those that rate high in the Stringent Performance Objectives adjustment factor (IFPUG scheme), can be described using a combination of game theory and autonomous systems. From this description it can be shown that some of those problems exhibit chaotic behavior, an important fact in understanding the functioning of the related software. As a relatively simple example, it is shown that chess exhibits chaotic behavior in its configuration space. This implies that static evaluators in chess programs have intrinsic limitations., Comment: 7 pages, no figures

This paper has been withdrawn by the author because the conclusions reached in it are incorrect., Comment: This paper has been withdrawn by the author because the conclusions reached in it are incorrect

Generalized Yang-Mills theories are constructed, that can use fields other than vector as gauge fields. Their geometric interpretation is studied. An application to the Glashow-Weinberg-Salam model is briefly review, and some related mathematical and physical considerations are made., Comment: No figures. LaTeX 2.09. 12 pages. Contribution to Nova collection of papers on the Lorentz group (Ed. V. Dvoeglazov)

The inflaton field is assumed to possess electric charge. The effect of the charge upon inflation is studied using a parameter \omega_0 that acts as a measure of the quantity of inflaton present. It is shown that at the end of inflation the charged inflaton should produce a fractal electromagnetic structure, which could act as a seed for the development of macroscopic galactic structures. Another consequence would be the presence nowadays of residual electromagnetic fields that would encompass galaxies, clusters, and larger structures., Comment: 7 pages, no figures

It is odd that chess grandmasters often disagree in their analysis of positions, sometimes even of simple ones, and that a grandmaster can hold his own against an powerful analytic machine such as Deep Blue. The fact that there must exist pure winning strategies for chess is used to construct a control strategy function. It is then shown that chess strategy is equivalent to an autonomous system of differential equations, and conjectured that the system is chaotic. If true the conjecture would explain the forenamed peculiarities and would also imply that there cannot exist a static evaluator for chess., Comment: 7 pages, no figures

A generalization of the Yang-Mills covariant derivative, that uses both vector and scalar fields and transforms as a 4-vector contracted with Dirac matrices, is used to simplify and unify the Glashow-Weinberg-Salam model. Since SU(3) assigns the wrong hypercharge to the Higgs boson, it is necessary to use a special representation of U(3) to obtain all the correct quantum numbers. A surplus gauge scalar boson emerges in the process, but it uncouples from all other particles., Comment: 12 pages, no figures. To be published in Int. J. Mod. Phys. A

We show that a system of bosons in a T=0 quantum field theory can present metastable ground states with spontaneous symmetry breaking, even in the absence of an imaginary mass term. This gives a natural explanation to the Davis-Shellard background field \exp(-i \omega_0 t) and adds a new degree of freedom in boson systems, with possible applications in cosmology, condensed matter and high energy physics.