Trapping mechanism in overdamped ratchets with quenched noise

A trapping mechanism is observed and proposed as the origin of the anomalous behavior recently discovered in transport properties of overdamped ratchets subject to external oscillatory drive in the presence of quenched noise. In particular, this mechanism is shown to appear whenever the quenched disorder strength is greater than a threshold value. The minimum disorder strength required for the existence of traps is determined by studying the trap structure in a disorder configuration space. An approximation to the trapping probability density function in a disordered region of finite length included in an otherwise perfect ratchet lattice is obtained. The mean velocity of the particles and the diffusion coefficient are found to have a non-monotonic dependence on the quenched noise strength due to the presence of the traps.Comment: 21 pages, 6 figures, to appear in PR

Participación y escolarización de la política: Reflexiones sobre lo político en la escuela

In the following article we intend to reflect and discuss the conceptual link between youth, school and politics. We will focus on the student´s participative practices and the political conditions in middle schools. Our perspective integrates concepts which originate in the political theory and sociology of education. The latter will be the starting point from where we will discuss the difference between politics and political in the school context, while we consider the school as a specific institution. We set an interpretative hypothesis about the “scholarisation of politics” based on the complex relationship between two worlds in tension: the political and the middle school worlds. Lastly, we ask ourselves if every form of participation and politization has the same potential to describe and empirically interpret the aim of this study, but also for the protection and broadening of youth rights.En este artículo proponemos una discusión conceptual para el abordaje del vínculo entre jóvenes, escuela y política; centrando la mirada en las prácticas participativas de los estudiantes en la escuelas secundarias  y las condiciones de politización de las mismas. La perspectiva propuesta integra conceptos provenientes de la teoría política y la sociología de la educación, desde donde discutimos la  distinción entre la política y lo político; participación y política; concibiendo a la escuela como una institución específica. Planteamos una hipótesis interpretativa acerca de la “escolarización de la política” que surge del análisis de la compleja relación entre dos mundos constitutivamente en tensión: el de la política y el de la escuela secundaria.  Por último,  nos preguntamos si todas las formas de participación y politización  tienen las mismas potencialidades para describir e interpretar empíricamente este objeto de estudio, pero también para la protección y/o la ampliación de derechos de los jóvene

Spontaneous circadian rhythms in a cold-Adapted natural isolate of Aureobasidium pullulans

Indexación: Scopus.Circadian systems enable organisms to synchronize their physiology to daily and seasonal environmental changes relying on endogenous pacemakers that oscillate with a period close to 24 h even in the absence of external timing cues. The oscillations are achieved by intracellular transcriptional/translational feedback loops thoroughly characterized for many organisms, but still little is known about the presence and characteristics of circadian clocks in fungi other than Neurospora crassa. We sought to characterize the circadian system of a natural isolate of Aureobasidium pullulans, a cold-Adapted yeast bearing great biotechnological potential. A. pullulans formed daily concentric rings that were synchronized by light/dark cycles and were also formed in constant darkness with a period of 24.5 h. Moreover, these rhythms were temperature compensated, as evidenced by experiments conducted at temperatures as low as 10 °C. Finally, the expression of clock-essential genes, frequency, white collar-1, white collar-2 and vivid was confirmed. In summary, our results indicate the existence of a functional circadian clock in A. pullulans, capable of sustaining rhythms at very low temperatures and, based on the presence of conserved clock-gene homologues, suggest a molecular and functional relationship to well-described circadian systems.https://www.nature.com/articles/s41598-017-14085-

Transport and dynamical properties of inertial ratchets

In this paper we discuss the dynamics and transport properties of a massive particle, in a time dependent periodic potential of the ratchet type, with a dissipative environment. The directional currents and characteristics of the motion are studied as the specific frictional coefficient varies, finding that the stationary regime is strongly dependent on this parameter. The maximal Lyapunov exponent and the current show large fluctuations and inversions, therefore for some range of the control parameter, this inertial ratchet could originate a mass separation device. Also an exploration of the effect of a random force on the system is performed.Comment: PDF, 16 pages, 7 figure

Temperature-programmed reduction and dispersive X-ray absorption spectroscopy studies of CeO2-based nanopowders for intermediate-temperature Solid-Oxide Fuel Cell anodes

In this work, we study the influence of the average crystallite size and dopant oxide on the reducibility of CeO2-based nanomaterials. Samples were prepared from commercial Gd2O3-, Sm2O3- and Y2O3-doped CeO2 powders by calcination at different temperatures ranging between 400 and 900C and characterized by X-ray powder diffraction, transmission electron microscopy and BET specific surface area. The reducibility of the samples was analyzed by temperature-programmed reduction and in situ dispersive X-ray absorption spectroscopy techniques. Our results clearly demonstrate that samples treated at lower temperatures, of smallest average crystallite size and highest specific surface areas, exhibit the best performance, while Gd2O3-doped ceria materials display higher reducibility than Sm2O3- and Y2O3-doped CeO2

The Evolution of the Intracluster Medium Metallicity in Sunyaev-Zel'dovich-Selected Galaxy Clusters at 0 < z < 1.5

We present the results of an X-ray spectral analysis of 153 galaxy clusters observed with the Chandra, XMM-Newton, and Suzaku space telescopes. These clusters, which span 0 < z < 1.5, were drawn from a larger, mass-selected sample of galaxy clusters discovered in the 2500 square degree South Pole Telescope Sunyaev Zel'dovich (SPT-SZ) survey. With a total combined exposure time of 9.1 Ms, these data yield the strongest constraints to date on the evolution of the metal content of the intracluster medium (ICM). We find no evidence for strong evolution in the global (r<R500) ICM metallicity (dZ/dz = -0.06 +/- 0.04 Zsun), with a mean value at z=0.6 of = 0.23 +/- 0.01 Zsun and a scatter of 0.08 +/- 0.01 Zsun. These results imply that >60% of the metals in the ICM were already in place at z=1 (at 95% confidence), consistent with the picture of an early (z>1) enrichment. We find, in agreement with previous works, a significantly higher mean value for the metallicity in the centers of cool core clusters versus non-cool core clusters. We find weak evidence for evolution in the central metallicity of cool core clusters (dZ/dz = -0.21 +/- 0.11 Zsun), which is sufficient to account for this enhanced central metallicity over the past ~10 Gyr. We find no evidence for metallicity evolution outside of the core (dZ/dz = -0.03 +/- 0.06 Zsun), and no significant difference in the core-excised metallicity between cool core and non-cool core clusters. This suggests that strong radio-mode AGN feedback does not significantly alter the distribution of metals at r>0.15R500. Given the limitations of current-generation X-ray telescopes in constraining the ICM metallicity at z>1, significant improvements on this work will likely require next-generation X-ray missions.Comment: 11 pages, 8 figures, 2 tables. Submitted to ApJ. Comments welcome

Star-Forming Brightest Cluster Galaxies at 0.25 < z < 1.25: A Transitioning Fuel Supply

We present a multi-wavelength study of 90 brightest cluster galaxies (BCGs) in a sample of galaxy clusters selected via the Sunyaev Zel'dovich effect by the South Pole Telescope, utilizing data from various ground- and space-based facilities. We infer the star formation rate (SFR) for the BCG in each cluster, based on the UV and IR continuum luminosity, as well as the [O II] emission line luminosity in cases where spectroscopy is available, finding 7 systems with SFR > 100 Msun/yr. We find that the BCG SFR exceeds 10 Msun/yr in 31 of 90 (34%) cases at 0.25 < z < 1.25, compared to ~1-5% at z ~ 0 from the literature. At z > 1, this fraction increases to 92(+6)(-31)%, implying a steady decrease in the BCG SFR over the past ~9 Gyr. At low-z, we find that the specific star formation rate in BCGs is declining more slowly with time than for field or cluster galaxies, most likely due to the replenishing fuel from the cooling ICM in relaxed, cool core clusters. At z > 0.6, the correlation between cluster central entropy and BCG star formation - which is well established at z ~ 0 - is not present. Instead, we find that the most star-forming BCGs at high-z are found in the cores of dynamically unrelaxed clusters. We investigate the rest-frame near-UV morphology of a subsample of the most star-forming BCGs using data from the Hubble Space Telescope, finding complex, highly asymmetric UV morphologies on scales as large as ~50-60 kpc. The high fraction of star-forming BCGs hosted in unrelaxed, non-cool core clusters at early times suggests that the dominant mode of fueling star formation in BCGs may have recently transitioned from galaxy-galaxy interactions to ICM cooling.Comment: 20 pages, 10 figures. Submitted for publication in ApJ. Comments welcom