Coherent patterns and self-induced diffraction of electrons on a thin nonlinear layer

Electron scattering on a thin layer where the potential depends self-consistently on the wave function has been studied. When the amplitude of the incident wave exceeds a certain threshold, a soliton-shaped brightening (darkening) appears on the layer causing diffraction of the wave. Thus the spontaneously formed transverse pattern can be viewed as a self-induced nonlinear quantum screen. Attractive or repulsive nonlinearities result in different phase shifts of the wave function on the screen, which give rise to quite different diffraction patterns. Among others, the nonlinearity can cause self-focusing of the incident wave into a ``beam'', splitting in two ``beams'', single or double traces with suppressed reflection or transmission, etc.Comment: RevTex, 4 pages, epsf.sty to insert figures, to appear in Phys.Rev.

Chaos in resonant-tunneling superlattices

Spatio-temporal chaos is predicted to occur in n-doped semiconductor superlattices with sequential resonant tunneling as their main charge transport mechanism. Under dc voltage bias, undamped time-dependent oscillations of the current (due to the motion and recycling of electric field domain walls) have been observed in recent experiments. Chaos is the result of forcing this natural oscillation by means of an appropriate external microwave signal.Comment: 3 pages, LaTex, RevTex, 3 uuencoded figures (1.2M) are available upon request from [email protected], to appear in Phys.Rev.

Nonlinear stochastic discrete drift-diffusion theory of charge fluctuations and domain relocation times in semiconductor superlattices

A stochastic discrete drift-diffusion model is proposed to account for the effects of shot noise in weakly coupled, highly doped semiconductor superlattices. Their current-voltage characteristics consist of a number stable multistable branches corresponding to electric field profiles displaying two domains separated by a domain wall. If the initial state corresponds to a voltage on the middle of a stable branch and a sudden voltage is switched so that the final voltage corresponds to the next branch, the domains relocate after a certain delay time. Shot noise causes the distribution of delay times to change from a Gaussian to a first passage time distribution as the final voltage approaches that of the end of the first current branch. These results agree qualitatively with experiments by Rogozia {\it et al} (Phys. Rev. B {\bf 64}, 041308(R) (2001)).Comment: 9 pages, 12 figures, 2 column forma

"Cayas" un nuevo asentamiento celtibérico en Malón (Aragón, España)

En el presente trabajo se presenta el estudio de un pequeño asentamiento rural celtibérico inédito documentado mediante prospección arqueológica en el término municipal de Malón perteneciente a la Comunidad Autónoma de Aragón. La cultura material estudiada y la tipología del asentamiento indican que se trata de una pequeña unidad de producción rural tipo granja vinculada al modelo social de las ciudades-estado celtibéricas, lo que nos lleva a proponer una cronología para este asentamiento entre finales del siglo III a.C. y la primera mitad del siglo II a.C.In the present work we present the study of a small unpublished Celtiberian rural settlement documented by archaeological survey in the municipality of Malón, belonging to the Autonomous Community of Aragon. The material culture studied and the settlement typology indicate that it is a small unit of rural farm production linked to the social model of Celtiberian city-states, which leads us to propose a chronology for this settlement between the end of the third century BC. And the first half of the second century BC

A study on the variability of Kappa (κ) in a borehole: Implications of the computation process

Knowledge of the acceleration spectral shape is crucial to various applications in engineering seismology. Spectral amplitude decays rapidly at high frequencies. Anderson and Hough (1984) introduced the empirical factor κ to model this attenuation. This is the first time κ is studied in a vertical array consisting of more than two stations. We use 180 earthquakes recorded at a downhole array with five stations in soils and rock to investigate the effect of soil conditions on κ. Given that κ computation processes vary across literature when following the classic Anderson–Hough method, we investigate its variability with the different assumptions that can be made when applying the method. The estimates of κ0 range between 0.017 and 0.031 s at the surface and between 0.004 and 0.024 s at rock. This variability due to the assumptions made is larger than the error of each estimate and larger than the average difference in values between sediment and rock. For this data set, part of it can be attributed to the type of distance used. Given this variability, κ0 values across literature may not always be comparable; this may bias the results of applications using κ0 as an input parameter, such as ground‐motion prediction equations. We suggest ways to render the process more homogeneous. We also find that κ at rock level is not well approximated by surface records from which we deconvolved the geotechnical transfer function. Finally, we compute κ on the vertical component and find a dependence of the vertical‐to‐horizontal κ ratio on site conditions

Symmetric hyperbolic systems for Bianchi equations

We obtain a family of first-order symmetric hyperbolic systems for the Bianchi equations. They have only physical characteristics: the light cone and timelike hypersurfaces. In the proof of the hyperbolicity, new positivity properties of the Bel tensor are used.Comment: latex, 7 pages, accepted for publication in Class. Quantum Gra

Effects of noise on hysteresis and resonance width in graphene and nanotubes resonators

We investigate the role that noise plays in the hysteretic dynamics of a suspended nanotube or a graphene sheet subject to an oscillating force. We find that not only the size but also the position of the hysteresis region in these systems can be controlled by noise. We also find that nano-resonators act as noise rectifiers: by increasing the noise in the setup, the resonance width of the characteristic peak in these systems is reduced and, as a result, the quality factor is increased.Comment: 15 pages, 6 figures. Sent to PRB (in revision

Giovanni BRIZZI: Ribelli contro Roma. Gli schiavi, Spartaco, l'altra Italia, Il Mu-lino, Bologna, 2017, 231 pp.

Reseña de la obra de Giovanni BRIZZI: Ribelli contro Roma. Gli schiavi, Spartaco, l''altra Italia, Il Mulino, Bologna, 2017, 231 pp. ISBN: 978-88-15-27378-9. A cargo de Óscar Bonilla Santander. De Aníbal a Espartaco: La desintegración del modelo social romano republicano Hablar de Espartaco y de su revuelta es trasladarnos a uno de los episodios más visitados de la antigüedad romana por la sociedad actual y a la vez uno de los más manipulados en el presente. La figura de Espartaco en el imaginario popular emerge de entre el resto de los que se rebelaron contra el dominio y la opresión de Roma debido sin duda a las producciones audiovisuales que giran en torno al personaje. Son numerosos los rebeldes y revolucionarios que dieron batalla a las legiones romanas pero a Espartaco se le ha brindado un espacio singular tanto en la filmografía como en el fenómeno más actual de las series de televisión. Aunque el cine italiano dedicó producciones al esclavo tracio desde muy temprano con la película “Spartaco” de Giovanni Enrico Vidali en 1913, la toma del poder de Benito Mussolini en Italia no favoreció que este tema fuese abordado por el cine fascista dada la incitación revolucionaria que se le suponía, centrando los esfuerzos de la industria cinematográfica italiana en potenciar los episodios más gloriosos de la expansión imperial de Roma desde los estudios de Cinecittà..