Heavy atom quantum diffraction by scattering from surfaces

Typically one expects that when a heavy particle collides with a surface, the scattered angular distribution will follow classical mechanics. The heavy mass assures that the de Broglie wavelength of the incident particle in the direction of the propagation of the particle (the parallel direction) will be much shorter than the characteristic lattice length of the surface, thus leading to a classical description. Recent work on molecular interferometry has shown that by increasing the perpendicular coherence length, one may observe interference of very heavy species passing through a grating. Here we show, using quantum mechanical simulations, that the same effect will lead to quantum diffraction of heavy particles colliding with a surface. We find that the effect is robust with respect to the incident energy, the angle of incidence and the mass of the particle. It may also be used to verify the quantum nature of the surface and its fluctuations at very low temperatures.Comment: 9 pages, 3 figure

Dissipating the Langevin equation in the presence of an external stochastic potential

In the Langevin formalism, the delicate balance maintained between the fluctuations in the system and their corresponding dissipation may be upset by the presence of a secondary, space-dependent stochastic force, particularly in the low friction regime. In prior work, the latter was dissipated self-consistently through an additional uniform (mean-field) friction [Shepherd and Hernandez, J. Chem. Phys., 115, 2430-2438 (2001).] An alternative approach to ensure that equipartition is satisfied relies on the use of a space-dependent friction while ignoring nonlocal correlations. The approach is evaluated with respect to its ability to maintain constant temperature for two simple one-dimensional, stochastic potentials of mean force wherein the friction can be evaluated explicitly when there is no memory in the barriers. The use of a space-dependent friction is capable of providing qualitatively similar results to those obtained previously, but in extreme cases, deviations from equipartition may be observed due to the neglect of the memory effects present in the stochastic potentials.Comment: 9 pages, 5 figures, to appear in J. Chem. Phy

Forster resonance energy transfer, absorption and emission spectra in multichromophoric systems: III. Exact stochastic path integral evaluation

A numerically exact path integral treatment of the absorption and emission spectra of open quantum systems is presented that requires only the straightforward solution of a stochastic differential equation. The approach converges rapidly enabling the calculation of spectra of large excitonic systems across the complete range of system parameters and for arbitrary bath spectral densities. With the numerically exact absorption and emission operators one can also immediately compute energy transfer rates using the multi-chromophoric Forster resonant energy transfer formalism. Benchmark calculations on the emission spectra of two level systems are presented demonstrating the efficacy of the stochastic approach. This is followed by calculations of the energy transfer rates between two weakly coupled dimer systems as a function of temperature and system-bath coupling strength. It is shown that the recently developed hybrid cumulant expansion is the only perturbative method capable of generating uniformly reliable energy transfer rates and spectra across a broad range of system parameters.Comment: 20 pages, 4 figure

Coherent quantum transport in disordered systems I: The influence of dephasing on the transport properties and absorption spectra on one-dimensional systems

Excitonic transport in static disordered one dimensional systems is studied in the presence of thermal fluctuations that are described by the Haken-Strobl-Reineker model. For short times, non-diffusive behavior is observed that can be characterized as the free-particle dynamics in the Anderson localized system. Over longer time scales, the environment-induced dephasing is sufficient to overcome the Anderson localization caused by the disorder and allow for transport to occur which is always seen to be diffusive. In the limiting regimes of weak and strong dephasing quantum master equations are developed, and their respective scaling relations imply the existence of a maximum in the diffusion constant as a function of the dephasing rate that is confirmed numerically. In the weak dephasing regime, it is demonstrated that the diffusion constant is proportional to the square of the localization length which leads to a significant enhancement of the transport rate over the classical prediction. Finally, the influence of noise and disorder on the absorption spectrum is presented and its relationship to the transport properties is discussed.Comment: 23 pages, 7 figure

Coherent quantum transport in disordered systems: A unified polaron treatment of hopping and band-like transport

Quantum transport in disordered systems is studied using a polaron-based master equation. The polaron approach is capable of bridging the results from the coherent band-like transport regime governed by the Redfield equation to incoherent hopping transport in the classical regime. A non-monotonic dependence of the diffusion coefficient is observed both as a function of temperature and system-phonon coupling strength. In the band-like transport regime, the diffusion coefficient is shown to be linearly proportional to the system-phonon coupling strength, and vanishes at zero coupling due to Anderson localization. In the opposite classical hopping regime, we correctly recover that the dynamics are described by the Fermi's Golden Rule (FGR) and establish that the scaling of the diffusion coefficient depends on the phonon bath relaxation time. In both the hopping and band-like transport regimes, it is demonstrated that at low temperature the zero-point fluctuations of the bath lead to non-zero transport rates, and hence a finite diffusion constant. Application to rubrene and other organic semiconductor materials shows a good agreement with experimental mobility data.Comment: 19 pages, 4 figure

Towards a New Methodology to evaluate the Urban structure of the Metropolitan Systems; Chicago and Barcelona Metropolitan Areas as Examples.

The specialized researches have proposed various approaches to the delimitation of urban and metropolitan systems. Administrative aspects (administrative units historically inherited), morphological (urban continuum), some linked to the economies of agglomeration (population and employment density, urban economic activities, …) or functional interaction (home-work commuting) have been used for the definition of a metropolitan area. At the same time it has developed in recent years, an extensive research that has come to reveal the progressive trend of the metropolitan areas to the polycentrism. There is no doubt that the monocentric city paradigm, structured around a single CBD, is broken. The contemporary metropolises have seen the emergence of the phenomenon of the sub centers. This changes in the internal structure of many cities has extended the hypothesis that the polycentric city is more efficient than traditional monocentric city, from an environmental perspective (ETE, 1999), representing usually shorter home-work trips, thus contributing to more sustainable mobility. However, few efforts have been directed to address the three aspects together: a) the metropolitan boundaries, b) analysis of its internal structure, and c) contrasting the hypothesis of the environmental efficiency of polycentric systems. This paper addresses the challenge of defining an integrated way of both metropolitan areas and their internal composition, structured or not around different sub centers. The methodology developed of the Interaction Value simultaneously allows delimiting these two levels of urban structure: the metropolitan system as a whole and the subsystems articulated around the emerging sub centers, by measuring the functional relationships between housing and workplaces. At the same time, the Interaction Value assesses the degree of polycentrism beyond the simple identification of sub centers developed in the literature. And, so, support the hypothesis that the polycentric city structure is more efficient, from an environmental perspective, than the monocentric. In this way, and taking the cases of Chicago and Barcelona metropolitan areas as examples of these types of organizations, the efficiency of metropolitan structures is evaluated from the dual perspective of land consumption and sustainable mobility.

A hybrid stochastic hierarchy equations of motion approach to treat the low temperature dynamics of non-Markovian open quantum systems

The hierarchical equations of motion technique has found widespread success as a tool to generate the numerically exact dynamics of non-Markovian open quantum systems. However, its application to low temperature environments remains a serious challenge due to the need for a deep hierarchy that arises from the Matsubara expansion of the bath correlation function. Here we present a hybrid stochastic hierarchical equation of motion (sHEOM) approach that alleviates this bottleneck and leads to a numerical cost that is nearly independent of temperature. Additionally, the sHEOM method generally converges with fewer hierarchy tiers allowing for the treatment of larger systems. Benchmark calculations are presented on the dynamics of two level systems at both high and low temperatures to demonstrate the efficacy of the approach. Then the hybrid method is used to generate the exact dynamics of systems that are nearly impossible to treat by the standard hierarchy. First, exact energy transfer rates are calculated across a broad range of temperatures revealing the deviations from the Forster rates. This is followed by computations of the entanglement dynamics in a system of two qubits at low temperature spanning the weak to strong system-bath coupling regimes.Comment: 20 pages, 6 figure

The History of Dog Training and Its Importance to Modern Day Training Techniques

A trainer must have a thorough understanding of history and its foundational principles to select and utilize modern techniques effectively. The world of dog training is a vast community that consists of many different methodologies, trainers, and philosophies, each with its own strengths and weaknesses. It is vital for any dog trainer, whether simply training their pet dog to come and sit or training a high-performance military working dog, to have a thorough understanding of today’s training philosophies and the philosophies that came before. Dog training is a living, breathing science that must be viewed as the sum of experiences and movements

Facilitación de la recuperación postquirúrgica mediante técnicas basadas en el procesamiento de información durante la anestesia general

Existe una línea creciente de investigación que parece mostrar que cuando los pacientes se encuentran bajo anestesia general son capaces de procesar información exterior. Basándose en este hallazgo, algunos estudios intentan comprobar si facilitar sugestiones de relajación y fácil recuperación mientras el paciente se encuentra anestesiado puede tener efectos beneficiosos en la convalecencia. Este trabajo constituye una revisión de dichas investigaciones. Sólamente se han revisado aquellos trabajos que cumplen dos criterios metodológicos: grupo control asignado al azar y doble ciego. Finalmente, se realizan algunas consideraciones de talante tanto básico como aplicado sobre este fenómeno.There is a growing field of research that seems to show that patients under anesthesia can process external information. On the basis of this evidence, some studies investigate whether intraoperative suggestions about relaxation and easy postoperative recovery can positively influence convalescence. This work is a review of the investigations which have this goal. The review only includes double-blind randomized studies. Finally, some basic and applied considerations of this phenomenon are made

Modulacion psicologica de la recuperacion postquirúrgica

En este trabajo se exponen los motivos por los que el estudio del paciente quirúrgico, desde un punto de vista psicológico, supone tanto una contribución en el campo básico -como paradigma para la investigación del estrés- como una contribución desde una óptica más aplicada con beneficios económicos y humanos. Se analizan las distintas líneas de investigación que se estan generando en este campo, describiendo nuestras propias investigaciones en las mismasIn this work wepoint out some reasons why the psychological study of surgical patients means a contribution to the basic area as apattern for stress research. We also show the reasons why this kind of research is interesting from a more applied point of view with economic and human benefits. The different research lines in thisfield are analyzed, describing our own research in these line