172 research outputs found

    Cesare Pavese : return to the classicism in the Italy post war

    Get PDF
    En la vasta y variada producción de Cesare Pavese (1908-1950), sobresale la obra Dialoghi con Leucó (Diálogos con Leucó), publicada en el año 1947, a dos años de finalizada la Segunda Guerra Mundial, época que Italia vivió de modo trascendente y trágico al mismo tiempo. La obra mencionada evidencia la madurez de lecturas e influencias del mundo mítico-etnológico en el que Pavese había indagado y en el cual había decidido permanecer, a fin de explicar y explicarse el sentido de la existencia del hombre contemporáneo y de su destino. La investigación se propone poner en valor un texto clave del corpus pavesiano, además de situarlo en su contexto de producción, de publicación y de recepción. La valoración mencionada supondrá el acercamiento y la comprensión de ciertos factores que confluyeron en la creación de una rara avis dentro de su repertorio autorial, ya que el escrito, bajo el formato discursivo dialógico, retoma personajes de la tradición clásica para situarlos en circunstancias y problemáticas contemporáneas a la situación ítalo-europea de la guerra. Tales sucesos son vividos por Pavese como artista emergente de la década del ’40 y como ciudadano de un territorio asediado por la violencia del período mencionado.In the vast and diverse literary production of Cesare Pavese (1908-1950), it stands out the work Dialoghi con Leucó (Diálogos con Leucó), published in 1947, two years after the Second World War, a tragic period for Italy. The referred work demonstrates the maturity of readings and influences of the ethnological and mythical universe in which Pavese had investigated and in which he had decided to remain, with the purpuse of explain for himself and to others the meaning of the existence of modern man and his destiny. The research pretends to value a fundamental text of pavesian corpus and recognize it in its production, publication and reception context. The mentioned valuation will involve the approachment and understanding of certain factors that came together in the creation of a rara avis inside its authorial repertoire, because the writing, under the dialogic discursive format, recovers characters from the classical tradition to situates them into circumstances and troubles, both of them contemporary to the Italian-European war situation. Such events are experienced by Pavese as an emerging artist of the 40s years and as a citizen of a territory besieged by the violence of the period mentioned.Fil: Caram de Bataller, Graciela B.. Universidad Nacional de Cuyo. Facultad de Filosofía y Letra

    Size Segregation of Granular Matter in Silo Discharges

    Full text link
    We present an experimental study of segregation of granular matter in a quasi-two dimensional silo emptying out of an orifice. Size separation is observed when multi-sized particles are used with the larger particles found in the center of the silo in the region of fastest flow. We use imaging to study the flow inside the silo and quantitatively measure the concentration profiles of bi-disperse beads as a function of position and time. The angle of the surface is given by the angle of repose of the particles, and the flow occurs in a few layers only near the top of this inclined surface. The flowing region becomes deeper near the center of the silo and is confined to a parabolic region centered at the orifice which is approximately described by the kinematic model. The experimental evidence suggests that the segregation occurs on the surface and not in the flow deep inside the silo where velocity gradients also are present. We report the time development of the concentrations of the bi-disperse particles as a function of size ratios, flow rate, and the ratio of initial mixture. The qualitative aspects of the observed phenomena may be explained by a void filling model of segregation.Comment: 6 pages, 10 figures (gif format), postscript version at http://physics.clarku.edu/~akudrolli/nls.htm

    Excitation energy transfer in light-harvesting system: Effect of initial state

    Full text link
    The light-harvesting is a problem of long interest. It becomes active again in recent years stimulated by suggestions of quantum effects in energy transport. Recent experiments found evidence that BChla 1 and BChla 6 are the first to be excited in the Fenna-Matthews-Olson(FMO) protein, theoretical studies, however, are mostly restricted to consider the exciton in BChla 1 initially. In this paper, we study the energy transport in the FMO complex by taking different initial states into account. Optimizations are performed for the decoherence rates as to maximal transport efficiency. Dependence of the energy transfer efficiency on the initial states is given and discussed. Effects of fluctuations in the site energies and couplings are also examined.Comment: 6 pages, 6 figures, J Phys B accepte

    Distribution of entanglement in light-harvesting complexes and their quantum efficiency

    Full text link
    Recent evidence of electronic coherence during energy transfer in photosynthetic antenna complexes has reinvigorated the discussion of whether coherence and/or entanglement has any practical functionality for these molecular systems. Here we investigate quantitative relationships between the quantum yield of a light-harvesting complex and the distribution of entanglement among its components. Our study focusses on the entanglement yield or average entanglement surviving a time scale comparable to the average excitation trapping time. As a prototype system we consider the Fenna-Matthews-Olson (FMO) protein of green sulphur bacteria and show that there is an inverse relationship between the quantum efficiency and the average entanglement between distant donor sites. Our results suggest that longlasting electronic coherence among distant donors might help modulation of the lightharvesting function.Comment: Version accepted for publication in NJ

    Traffic Equations and Granular Convection

    Full text link
    We investigate both numerically and analytically the convective instability of granular materials by two dimensional traffic equations. In the absence of vibrations the traffic equations assume two distinctive classes of fixed bed solutions with either a spatially uniform or nonuniform density profile. The former one exists only when the function V(\rho) that monitors the relaxation of grains assumes a cut off at the closed packed density, \rho_c, with V(\rho_c)=0, while the latter one exists for any form of V. Since there is little difference between the uniform and nonuniform solution deep inside the bed, the convective instability of the bulk may be studied by focusing on the stability of the uniform solution. In the presence of vibrations, we find that the uniform solution bifurcates into a bouncing solution, which then undergoes a supercritical bifurcation to the convective instability. We determine the onset of convection as a function of control parameters and confirm this picture by solving the traffic equations numerically, which reveals bouncing solutions, two convective rolls, and four convective rolls. Further, convective patterns change as the aspect ratio changes: in a vertically long container, the rolls move toward the surface, and in a horizontally long container, the rolls move toward the walls. We compare these results with those reported previously with a different continuum model by Hayakawa, Yue and Hong[Phys. Rev. Lett. 75,2328, 1995]. Finally, we also present a derivation of the traffic equations from Enskoq equation.Comment: 34 pages, 10 figure

    Liquid flyback booster pre-phase: A study assessment

    Get PDF
    The concept of a flyback booster has been around since early in the shuttle program. The original two-stage shuttle concepts used a manned flyback booster. These boosters were eliminated from the program for funding and size reasons. The current shuttle uses two Redesigned Solid Rocket Motors (RSRM's), which are recovered and refurbished after each flight; this is one of the major cost factors of the program. Replacement options have been studied over the past ten years. The conclusion reached by the most recent study is that the liquid flyback booster (LFBB) is the only competitive option from a life-cycle cost perspective. The purpose of this study was to assess the feasibility and practicality of LFBB's. The study provides an expansion of the recommendations made during the aforementioned study. The primary benefits are the potential for enhanced reusability and a reduction of recurring costs. The potential savings in vehicle turnaround could offset the up-front costs. Development of LFBB's requires a commitment to the shuttle program for 20 to 30 years. LFBB's also offer enhanced safety and abort capabilities. Currently, any failure of an RSRM can be considered catastrophic, since there are no intact abort capabilities during the burn of the RSRM's. The performance goal of the LFBB's was to lift a fully loaded orbiter under optimal conditions, so as not to be the limiting factor of the performance capability of the shuttle. In addition, a final benefit is the availability of growth paths for applications other than shuttle

    Exciton Dynamics in Photosynthetic Complexes: Excitation by Coherent and Incoherent Light

    Full text link
    In this paper we consider dynamics of a molecular system subjected to external pumping by a light source. Within a completely quantum mechanical treatment, we derive a general formula, which enables to asses effects of different light properties on the photo-induced dynamics of a molecular system. We show that once the properties of light are known in terms of certain two-point correlation function, the only information needed to reconstruct the system dynamics is the reduced evolution superoperator. The later quantity is in principle accessible through ultrafast non-linear spectroscopy. Considering a direct excitation of a small molecular antenna by incoherent light we find that excitation of coherences is possible due to overlap of homogeneous line shapes associated with different excitonic states. In Markov and secular approximations, the amount of coherence is significant only under fast relaxation, and both the populations and coherences between exciton states become static at long time. We also study the case when the excitation of a photosynthetic complex is mediated by a mesoscopic system. We find that such case can be treated by the same formalism with a special correlation function characterizing ultrafast fluctuations of the mesoscopic system. We discuss bacterial chlorosom as an example of such a mesoscopic mediator and propose that the properties of energy transferring chromophore-protein complexes might be specially tuned for the fluctuation properties of their associated antennae.Comment: 12 page

    Motional effects on the efficiency of excitation transfer

    Full text link
    Energy transfer plays a vital role in many natural and technological processes. In this work, we study the effects of mechanical motion on the excitation transfer through a chain of interacting molecules with application to biological scenarios of transfer processes. Our investigation demonstrates that, for various types of mechanical oscillations, the transfer efficiency is significantly enhanced over that of comparable static configurations. This enhancement is a genuine quantum signature, and requires the collaborative interplay between the quantum-coherent evolution of the excitation and the mechanical motion of the molecules; it has no analogue in the classical incoherent energy transfer. This effect may not only occur naturally, but it could be exploited in artificially designed systems to optimize transport processes. As an application, we discuss a simple and hence robust control technique.Comment: 25 pages, 11 figures; completely revised; version accepted for publicatio
    corecore