5,067 research outputs found
Assessing Dynamic Efficiency: Theory and Evidence
The issue of dynamic efficiency is central to analyses of capital accumulation and economic growth. Yet the question of what operating characteristics of an economy subject to productivity shocks should be examined to determine whether or not it is efficient has not been resolved. This paper develops criterion based on observables for determining whether or not an economy is dynamically efficient. The criterion involves a comparison of the cash flows generated by capital with the volume of investment. Its application to the United States economy and the economies of other major OECD nations suggests that they are dynamically efficient.
Cylindrical gravitational waves in expanding universes: Models for waves from compact sources
New boundary conditions are imposed on the familiar cylindrical gravitational
wave vacuum spacetimes. The new spacetime family represents cylindrical waves
in a flat expanding (Kasner) universe. Space sections are flat and nonconical
where the waves have not reached and wave amplitudes fall off more rapidly than
they do in Einstein-Rosen solutions, permitting a more regular null inifinity.Comment: Minor corrections to references. A note added in proo
Meta-stable SUSY Breaking Model in Supergravity
We analyze a supersymmetry (SUSY) breaking model proposed by Intriligator,
Seiberg and Shih in a supergravity (SUGRA) framework. This is a simple and
natural setup which demands neither extra superpotential interactions nor an
additional gauge symmetry. In the SUGRA setup, the U(1)R symmetry is explicitly
broken by the constant term in the superpotential, and pseudo-moduli field
naturally takes non-zero vacuum expectation value through a vanishing
cosmological constant condition. Sfermions tend to be heavier than gauginos,
and the strong-coupling scale is determined once a ratio of sfermion to gaugino
masses is fixed.Comment: 13 page
Classifying Crises-Information Relevancy with Semantics
Social media platforms have become key portals for sharing and consuming information during crisis situations. However, humanitarian organisations and affected communities often struggle to sieve through the large volumes of data that are typically shared on such platforms during crises to determine which posts are truly relevant to the crisis, and which are not. Previous work on automatically classifying crisis information was mostly focused on using statistical features. However,
such approaches tend to be inappropriate when processing data on a type of crisis that the model was not trained on, such as processing information about a train crash, whereas the classifier was trained on floods, earthquakes, and typhoons. In such cases, the model will need to be retrained, which is costly and time-consuming. In this paper, we explore the impact of semantics in classifying Twitter posts across same, and different, types of crises. We experiment with 26 crisis events, using a hybrid system that combines statistical features with various semantic features extracted from external knowledge bases. We show that adding semantic features has no noticeable benefit over statistical features when classifying same-type crises, whereas it enhances the classifier performance by up to 7.2% when classifying information about a new type of crisis
Simplicity of eigenvalues in the Anderson model
We give a simple, transparent, and intuitive proof that all eigenvalues of
the Anderson model in the region of localization are simple
Five-dimensional Monopole Equation with Hedge-Hog Ansatz and Abel's Differential Equation
We review the generalized monopole in the five-dimensional Euclidean space. A
numerical solution with the Hedge-Hog ansatz is studied. The Bogomol'nyi
equation becomes a second order autonomous non-linear differential equation.
The equation can be translated into the Abel's differential equation of the
second kind and is an algebraic differential equation.Comment: 4 pages, 4 figures, typos correcte
An excursion set model of the cosmic web: The abundance of sheets, filaments and halos
We discuss an analytic approach for modeling structure formation in sheets,
filaments and knots. This is accomplished by combining models of triaxial
collapse with the excursion set approach: sheets are defined as objects which
have collapsed along only one axis, filaments have collapsed along two axes,
and halos are objects in which triaxial collapse is complete. In the simplest
version of this approach, which we develop here, large scale structure shows a
clear hierarchy of morphologies: the mass in large-scale sheets is partitioned
up among lower mass filaments, which themselves are made-up of still lower mass
halos. Our approach provides analytic estimates of the mass fraction in sheets,
filaments and halos, and its evolution, for any background cosmological model
and any initial fluctuation spectrum. In the currently popular CDM
model, our analysis suggests that more than 99% of the cosmic mass is in
sheets, and 72% in filaments, with mass larger than at the
present time. For halos, this number is only 46%. Our approach also provides
analytic estimates of how halo abundances at any given time correlate with the
morphology of the surrounding large-scale structure, and how halo evolution
correlates with the morphology of large scale structure.Comment: 22 pages, 7 figures, Accepted for publication in Ap
Fermion Masses and Mixing in Four and More Dimensions
We give an overview of recent progress in the study of fermion mass and
flavor mixing phenomena. Mass matrix ansatze are considered within the SM and
SUSY GUTs where some predictive frameworks based on SU(5) and SO(10) are
reviewed. We describe a variety of schemes to construct quark mass matrices in
extra dimensions focusing on four major classes: models with the SM residing on
3-brane, models with universal extra dimensions, models with split fermions and
models with warped extra dimensions. We outline how realistic patterns of quark
mass matrices could be derived from orbifold models in heterotic superstring
theory. Finally, we address the fermion mass problem in intersecting D-branes
scenarios, and present models with D6-branes able to give a good quantitatively
description of quark masses and mixing. The role of flavor/CP violation problem
as a probe of new physics is emphasized.Comment: a review based on seminars presented by S.K. in different places, 34
pages, late
Algunas soluciones exactas para una ecuación de Klein Gordon
In solving practical problems in science and engineering arises as a direct consequence differential equations that explains the dynamics of the phenomena. Finding exact solutions to this equations provides importan information about the behavior of physical systems. The Lie symmetry method allows tofind invariant solutions under certain groups of transformations for differential equations.This method not very well known and used is of great importance in the scientific community. By this approach it was possible to find several exactinvariant solutions for the Klein Gordon Equation uxx − utt = k(u). A particularcase, The Kolmogorov equation uxx − utt = k1u + k2un was considered.These equations appear in the study of relativistic and quantum physics. The general solutions found, could be used for future explorations on the study for other specific K(u) functions.Al resolver problemas prácticos en ciencia e ingeniería surge como consecuencia directa las ecuaciones diferenciales que explican la dinámica de los fenómenos. Encontrar soluciones exactas a estas ecuaciones proporciona información importante sobre el comportamiento de los sistemas físicos. El método de simetría de Lie permite encontrar soluciones invariantes bajo ciertos grupos de transformaciones para ecuaciones diferenciales. Este método, poco conocido y utilizado, es de gran importancia en la comunidad científica. Mediante este enfoque, fue posible encontrar varias soluciones exactas invariables para la ecuación de Klein Gordon uxx - utt = k (u). Un caso particular, se consideró la ecuación de Kolmogorov uxx - utt = k1u + k2un. Estas ecuaciones aparecen en el estudio de la física relativista y cuántica. Las soluciones generales encontradas podrían utilizarse para futuras exploraciones en el estudio para otras funciones específicas de K (u)
- …