Diversity-induced resonance in a system of globally coupled linear oscillators

The purpose of this paper to analyze in some detail the arguably simplest case of diversity-induced reseonance: that of a system of globally-coupled linear oscillators subjected to a periodic forcing. Diversity appears as the parameters characterizing each oscillator, namely its mass, internal frequency and damping coefficient are drawn from a probability distribution. The main ingredients for the diversity-induced-resonance phenomenon are present in this system as the oscillators display a variability in the individual responses but are induced, by the coupling, to synchronize their responses. A steady state solution for this model is obtained. We also determine the conditions under which it is possible to find a resonance effect.Comment: Reported at the XI International Workshop "Instabilities and Nonequilibrium Structures" Vina del Mar (Chile

The Myth of the Frontier

One of the most salient explanations for the distinctive path of economic and political development of the United States is captured by the 'Frontier (or Turner) thesis'. Turner argued that it was the presence of the open frontier which explained why the United States became democratic and, at least implicitly, prosperous. In this paper we provide a simple test of this idea. We begin with the contradictory observation that almost every Latin American country had a frontier in the 19th century as well. We show that while the data does not support the Frontier thesis, it is consistent with a more complex 'conditional Frontier thesis.' In this view, the effect of the frontier is conditional on the way that the frontier was allocated and this in turn depends on political institutions at the time of frontier expansion. We show that for countries with the worst political institutions, there is a negative correlation between the historical extent of the frontier and contemporary income per-capita. For countries with better political institutions this correlation is positive. Though the effect of the frontier on democracy is positive irrespective of initial political institutions, it is larger the better were these institutions. In essence, Turner saw the frontier as having positive effects on development because he already lived in a country with good institutions.

Confirmation Via the Continuum-Fitting Method that the Spin of the Black Hole in Cygnus X-1 is Extreme

In Gou et al. (2011), we reported that the black hole primary in the X-ray binary Cygnus X-1 is a near-extreme Kerr black hole with a spin parameter a*>0.95(3{\sigma}). We confirm this result while setting a new and more stringent limit: a*>0.983 at the 3{\sigma}(99.7%) level of confidence. The earlier work, which was based on an analysis of all three useful spectra that were then available, was possibly biased by the presence in these spectra of a relatively strong Compton power-law component: The fraction of the thermal seed photons scattered into the power law was f_s=23-31%, while the upper limit for reliable application of the continuum-fitting method is f_s<25%. We have subsequently obtained six additional spectra of Cygnus X-1 suitable for the measurement of spin. Five of these spectra are of high quality with f_s in the range 10% to 19%, a regime where the continuum-fitting method has been shown to deliver reliable results. Individually, the six spectra give lower limits on the spin parameter that range from a*>0.95 to a*>0.98, allowing us to conservatively conclude that the spin of the black hole is a*>0.983 (3{\sigma}).Comment: 14 pages in emulated ApJ format, including 6 figures and 4 tables, ApJ in press. Discussion on the pileup effect to our spin measurement is added, including a subsection and a new figure, to reflect the referee's comments; the conclusions are unchange

The evolution of GX 339-4 in the low-hard state as seen by NuSTAR and Swift

We analyze eleven NuSTAR and Swift observations of the black hole X-ray binary GX 339-4 in the hard state, six of which were taken during the end of the 2015 outburst, five during a failed outburst in 2013. These observations cover luminosities from 0.5%-5% of the Eddington luminosity. Implementing the most recent version of the reflection model relxillCp, we perform simultaneous spectral fits on both datasets to track the evolution of the properties in the accretion disk including the inner edge radius, the ionization, and temperature of the thermal emission. We also constrain the photon index and electron temperature of the primary source (the "corona"). We find the disk becomes more truncated when the luminosity decreases, and observe a maximum truncation radius of $37R_g$. We also explore a self-consistent model under the framework of coronal Comptonization, and find consistent results regarding the disk truncation in the 2015 data, providing a more physical preferred fit for the 2013 observations.Comment: 15 pages, 8 figures, 6 tables, accepted for publication in The Astrophysical Journa

Dinámica y definición de pobreza en los Andes colombianos: enfoques participativos versus enfoques objetivos

El objetivo principal de este trabajo es el de examinar la consistencia de los resultados de una metodología participativa para evaluar la pobreza con las medidas de pobreza de carácter objetivo y con lo esperado para dos cuencas en Colombia, de acuerdo con sus características. Los resultados obtenidos permiten determinar que existe un conjunto de elementos básicos que son considerados tanto por las medidas de pobreza de carácter objetivo como por las de carácter participativo, pero que a su vez hay otros que dependen de las preferencias de los hogares. Además, muestran cómo, a partir de las percepciones locales, el concepto de pobreza adquiere un carácter diferente para cada lugar de acuerdo con su contexto: un hogar puede ser considerado como pobre en un lugar mientras en otro puede no serlo. Los resultados de la metodología participativa son útiles para identificar quiénes son pobres en las comunidades y por qué. Así mismo, permiten tener una mejor comprensión del fenómeno y dinámica de la pobreza; sin embargo, estos resultados no se pueden generalizar, ya que pueden diferir tanto en contenido como en magnitud con las medidas objetivas de pobrezapobreza, análisis rural, métodos participativos, Colombia

Coherent control of trapped ions using off-resonant lasers

In this paper we develop a unified framework to study the coherent control of trapped ions subject to state-dependent forces. Taking different limits in our theory, we can reproduce two different designs of a two-qubit quantum gate --the pushing gate [1] and the fast gates based on laser pulses from Ref. [2]--, and propose a new design based on continuous laser beams. We demonstrate how to simulate Ising Hamiltonians in a many ions setup, and how to create highly entangled states and induce squeezing. Finally, in a detailed analysis we identify the physical limits of this technique and study the dependence of errors on the temperature. [1] J.I. Cirac, P. Zoller, Nature, 404, 579, 2000. [2] J.J. Garcia-Ripoll, P. Zoller, J.I. Cirac, PRL 67, 062318, 200

STRONGER REFLECTION FROM BLACK HOLE ACCRETION DISKS IN SOFT X-RAY STATES

We analyze 15,000 spectra of 29 stellar-mass black hole (BH) candidates collected over the 16 year mission lifetime of Rossi X-ray Timing Explorer using a simple phenomenological model. As these BHs vary widely in luminosity and progress through a sequence of spectral states, which we broadly refer to as hard and soft, we focus on two spectral components: the Compton power law and the reflection spectrum it generates by illuminating the accretion disk. Our proxy for the strength of reflection is the equivalent width of the Fe–K line as measured with respect to the power law. A key distinction of our work is that for all states we estimate the continuum under the line by excluding the thermal disk component and using only the component that is responsible for fluorescing the Fe–K line, namely, the Compton power law. We find that reflection is several times more pronounced (~3) in soft compared to hard spectral states. This is most readily caused by the dilution of the Fe line amplitude from Compton scattering in the corona, which has a higher optical depth in hard states. Alternatively, this could be explained by a more compact corona in soft (compared to hard) states, which would result in a higher reflection fraction.United States. National Aeronautics and Space Administration (Einstein Fellowship Grant PF5-160144