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

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

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

Damage identification in composite panels using guided waves

A methodology for the identification of barely visible impact damage using guided waves on a typical aircraft composite structure is implemented. Delaminations and debondings have been introduced in two stiffened panels by means of impact loads

Quantum Diffusion on Molecular Tubes: Universal Scaling of the 1D to 2D Transition

The transport properties of disordered systems are known to depend critically on dimensionality. We study the diffusion coefficient of a quantum particle confined to a lattice on the surface of a tube, where it scales between the 1D and 2D limits. It is found that the scaling relation is universal and independent of the disorder and noise parameters, and the essential order parameter is the ratio between the localization length in 2D and the circumference of the tube. Phenomenological and quantitative expressions for transport properties as functions of disorder and noise are obtained and applied to real systems: In the natural chlorosomes found in light-harvesting bacteria the exciton transfer dynamics is predicted to be in the 2D limit, whereas a family of synthetic molecular aggregates is found to be in the homogeneous limit and is independent of dimensionality.Comment: 10 pages, 6 figure

An exact equilibrium reduced density matrix formulation I: The influence of noise, disorder, and temperature on localization in excitonic systems

An exact method to compute the entire equilibrium reduced density matrix for systems characterized by a system-bath Hamiltonian is presented. The approach is based upon a stochastic unraveling of the influence functional that appears in the imaginary time path integral formalism of quantum statistical mechanics. This method is then applied to study the effects of thermal noise, static disorder, and temperature on the coherence length in excitonic systems. As representative examples of biased and unbiased systems, attention is focused on the well-characterized light harvesting complexes of FMO and LH2, respectively. Due to the bias, FMO is completely localized in the site basis at low temperatures, whereas LH2 is completely delocalized. In the latter, the presence of static disorder leads to a plateau in the coherence length at low temperature that becomes increasingly pronounced with increasing strength of the disorder. The introduction of noise, however, precludes this effect. In biased systems, it is shown that the environment may increase the coherence length, but only decrease that of unbiased systems. Finally it is emphasized that for typical values of the environmental parameters in light harvesting systems, the system and bath are entangled at equilibrium in the single excitation manifold. That is, the density matrix cannot be described as a product state as is often assumed, even at room temperature. The reduced density matrix of LH2 is shown to be in precise agreement with the steady state limit of previous exact quantum dynamics calculations.Comment: 37 pages, 12 figures. To appear in Phys. Rev.

Efectividad de un audiovisual como preparación para la cirugía en pacientes pediátricos

Las investigaciones sobre los pacientes pediátricos quirúrgicos, ponen en evidencia la urgente necesidad de preparlos psicológicamente para la hospitalización y la intervención. A este respecto, estudios realizados fuera de nuestro país han demostrado que la visualización de un audiovisual acerca de la hospitalización y el proceso quirúrgico es una técnica eficaz para ayudar a los niños y a sus progenitores a afrontar dicha situación. El objetivo del presente trabajo ha consistido en comprobar la eficacia de esta técnica en nuestro contexto hospitalario. Los resultados indican que la proyección de un audiovisual antes de la hospitalización es muy recomendable, dado que: 1) aclara dudas; 2) da una imagen más familiar del hospital; 3) estimula a los padres a hablar con sus hijos y 4) aumenta la satisfacción de los padres respecto a la información. Uno de los datos obtenidos que mayor refleja la eficacia del audiovisual es que el 98.2% de los padres recomendaría la visualización del audiovisual a otras familias.Research on paediatric surgical patients points to the urgent need to prepare them psychologically for hospitalisation and surgery. In this respect, studies conducted outside Spain have shown that seeing a video on hospitalisation and procedures for surgery is an effective technique for helping children and their parents to deal with this situation. The aim of the present work was to verify the effectiveness of this technique within the context of our hospitals. The results indicate that it is highly advisable to show such a video to patients and their parents before admission to hospital, since this: 1) clears up any doubts they might have; 2) gives a friendlier image of the hospitil; 3) encourages parents to talk to their children and 4) increases satisfaction among parents concerning the information they receive. One of the dadta which most clearly reflects the effectiveness of using the type of the audiovisual described is that 98.2% of parents would recommend other families to see it

Identification of barely visible impact damages on a stiffened composite panel with a probability-based approach

A probability-based damage detection algorithm has been implemented in order to identify barely visible impact damages in two composite stiffened panels by means of Acousto Ultrasonics (AU). A modification of RAPID (reconstruction algorithm for probabilistic inspection of defects) has been implemented to adapt the algorithm to the current structures and transducer networks. An improvement of 40% in the localization accuracy is obtained with the new algorith

SIG para la gestión eficiente de la información urbanística local

La dificultad de hacer el seguimiento del grado de cumplimiento del planeamiento urbanístico con la realidad construida y cambiante en la ciudad, demanda el uso de herramientas de Sistemas de Información Geográfica (SIG) en la gestión local para desarrollar y mantener un conocimiento preciso de las características físicas, urbanas y económicas del parque inmobiliario, así como de las determinaciones de planeamiento que afectan a los valores de su potencial edificable y urbano. En este trabajo se propone implementar un nuevo proceso innovador para el estudio y la gestión de la ciudad con SIG, dónde se establecen las pautas para obtener el potencial urbanístico de un ámbito, un barrio o una ciudad, a partir de la comparación de la realidad existente con el planeamiento urbanístico, detectando de manera automática tanto las parcelas que no agotan su potencial como las que están sobreedificadas. Para ello se ha realizado un estudio piloto en el núcleo antiguo del barrio de Sant Andreu de Barcelona, el cual está en un proceso de modificación del planeamiento general vigente, afrontando el reto de desarrollar nuevas herramientas que permitan emular las consecuencias de las modificaciones y acometer una gestión eficiente de la información urbanística local.Peer Reviewe