Statistical evaporation of rotating clusters. II. Angular momentum distribution

The change in the angular momentum of an atomic cluster following evaporation is investigated using rigorous phase space theory and molecular dynamics simulations, with an aim at the possible rotational cooling and heating effects. Influences of the shape of the interaction potential, anharmonicity of the vibrational density of states (DOS), and the initial distribution of excitation energies are systematically studied on the example of the Lennard-Jones cluster LJ_14. For this system, the predictions of PST are in quantitative agreement with the results of the simulations, provided that the correct forms for the vibrational density of states and the interaction potential are used. The harmonic approximation to the DOS is used to obtain explicit forms for the angular momentum distribution in larger clusters. These are seen to undergo preferential cooling when thermally excited, and preferential heating when subject to a strong vibrational excitation.Comment: 10 pages, 7 figure

Antiferromagnetic spin chain behavior and a transition to 3D magnetic order in Cu(D,L-alanine)2: Roles of H-bonds

We study the spin chain behavior, a transition to 3D magnetic order and the magnitudes of the exchange interactions for the metal-amino acid complex Cu(D,L-alanine)2.H2O, a model compound to investigate exchange couplings supported by chemical paths characteristic of biomolecules. Thermal and magnetic data were obtained as a function of temperature (T) and magnetic field (B0). The magnetic contribution to the specific heat, measured between 0.48 and 30 K, displays above 1.8 K a 1D spin-chain behavior that can be fitted with an intrachain antiferromagnetic (AFM) exchange coupling constant 2J0 = (-2.12 $\pm$ 0.08) cm$^{-1}$, between neighbor coppers at 4.49 {\AA} along chains connected by non-covalent and H-bonds. We also observe a narrow specific heat peak at 0.89 K indicating a phase transition to a 3D magnetically ordered phase. Magnetization curves at fixed T = 2, 4 and 7 K with B0 between 0 and 9 T, and at T between 2 and 300 K with several fixed values of B0 were globally fitted by an intrachain AFM exchange coupling constant 2J0 = (-2.27 $\pm$ 0.02) cm$^{-1}$ and g = 2.091 $\pm$ 0.005. Interchain interactions J1 between coppers in neighbor chains connected through long chemical paths with total length of 9.51 {\AA} are estimated within the range 0.1 < |2J1| < 0.4 cm$^{-1}$, covering the predictions of various approximations. We analyze the magnitudes of 2J0 and 2J1 in terms of the structure of the corresponding chemical paths. The main contribution in supporting the intrachain interaction is assigned to H-bonds while the interchain interactions are supported by paths containing H-bonds and carboxylate bridges, with the role of the H-bonds being predominant. We compare the obtained intrachain coupling with studies of compounds showing similar behavior and discuss the validity of the approximations allowing to calculate the interchain interactions.Comment: 10 pages, 4 figure

Statistical evaporation of rotating clusters. IV. Alignment effects in the dissociation of nonspherical clusters

Unimolecular evaporation in rotating, non-spherical atomic clusters is investigated using Phase Space Theory in its orbiting transition state version. The distributions of the total kinetic energy release epsilon_tr and the rotational angular momentum J_r are calculated for oblate top and prolate top main products with an arbitrary degree of deformation. The orientation of the angular momentum of the product cluster with respect to the cluster symmetry axis has also been obtained. This statistical approach is tested in the case of the small 8-atom Lennard-Jones cluster, for which comparison with extensive molecular dynamics simulations is presented. The role of the cluster shape has been systematically studied for larger, model clusters in the harmonic approximation for the vibrational densities of states. We find that the type of deformation (prolate vs. oblate) plays little role on the distributions and averages of epsilon_tr and J_r except at low initial angular momentum. However, alignment effects between the product angular momentum and the symmetry axis are found to be significant, and maximum at some degree of oblateness. The effects of deformation on the rotational cooling and heating effects are also illustrated.Comment: 15 pages, 9 figure

Spatiotemporal instability of a confined capillary jet

Recent experimental studies on the instability appearance of capillary jets have revealed the capabilities of linear spatiotemporal instability analysis to predict the parametrical map where steady jetting or dripping takes place. In this work, we present an extensive analytical, numerical and experimental analysis of confined capillary jets extending previous studies. We propose an extended, accurate analytic model in the limit of low Reynolds flows, and introduce a numerical scheme to predict the system response when the liquid inertia is not negligible. Theoretical predictions show a remarkable accuracy with results from the extensive experimental exploration provided.Comment: Submitted to the Physical Review E (20-March-2008

Time Reversal Mirror and Perfect Inverse Filter in a Microscopic Model for Sound Propagation

Time reversal of quantum dynamics can be achieved by a global change of the Hamiltonian sign (a hasty Loschmidt daemon), as in the Loschmidt Echo experiments in NMR, or by a local but persistent procedure (a stubborn daemon) as in the Time Reversal Mirror (TRM) used in ultrasound acoustics. While the first is limited by chaos and disorder, the last procedure seems to benefit from it. As a first step to quantify such stability we develop a procedure, the Perfect Inverse Filter (PIF), that accounts for memory effects, and we apply it to a system of coupled oscillators. In order to ensure a many-body dynamics numerically intrinsically reversible, we develop an algorithm, the pair partitioning, based on the Trotter strategy used for quantum dynamics. We analyze situations where the PIF gives substantial improvements over the TRM.Comment: Submitted to Physica

An Enactive Theory of Need Satisfaction

In this paper, based on the predictive processing approach to cognition, an enactive theory of need satisfaction is discussed. The theory can be seen as a first step towards a computational cognitive model of need satisfaction

The new body-objet: from the entrails to the @

Este artículo se enmarca dentro de los Proyectos de Investigación “Hacia una historia conceptual comprehensiva: giros filosóficos y culturales” (FFI2011-24473; investigador principal: Dr. Faustino Oncina Coves) y “Fenomenología del cuerpo y análisis del dolor” (FFI2013-43240-P; investigador principal: Dr. Agustín Serrano de Haro)En este artículo, proponemos el estudio de un nuevo cuerpo-objeto aparecido en las redes sociales: el cuerpo-@, diferente del tradicional conjunto de vísceras. Tras desligarlo del ciborg, del feminismo, etc., nos centramos en ver la construcción verbal de LiveJournal que destruye el diario clásico, así como nos ocupamos de su hiperexposición en FacebookIn this paper, we aim to study a new Body-Object displayed on the social networks: the Body-@, different from the traditional set of entrails. Away from the comparison with the cyborg and the feminism, we are going to focus on the oral construction of LiveJournal, the one that destroys the intimate notes. Also, we are going to discuss the Hyper-Exhibition on Faceboo

La percepción y la pintura moderna como inversiones del modelo epistemológico clásico. (una visión Merleau-Pontyana)

[Resumen] El presente artículo pretende mostrar cómo Merleau-Ponty intentó superar el modelo epistemológico clásico mediante la percepción y la pintura. El edificio conceptual elaborado alrededor de la no-teticidad perceptiva crea la ilusión de la superación, pero todos los cambios acometidos son insuficientes porque se basan en la antigua ontología. Por eso, Merleau-Ponty propone la (endo)ontología de la Carne que se pone de manifiesto en la pintura moderna en la que la dicotomía sujeto-objeto deja paso al co-nacimiento del être-au-monde — être-du-monde.[Sommaire] Notre objectif est montrer comment Merleau-Ponty poursuit surmonter le modèle épistémologique sujet-objet merci à la perception es à la peinture. Les concepts qu’entourent l’irréfléchi perceptive nous font croire au dépassement de cette dichotomie, mais Merleau-Ponty s’aperçois que ces changements se sont appuyés sur l’ancienne ontologie et, pour ça, il introduit l’ontologie de la Chair. Celle-là apparaît à la peinture moderne à laquelle la séparation sujet-objet disparaît pour laisser surgir le co-naître du être-au-monde — être-du-monde.[Abstract] The broad outlines of this paper is to show how Merleau-Ponty tried to overcome the epistemological dichotomy subject-object between the perception and the picture. The conceptual building elaborated around the character non-positional of perception is insufficient because its supposes the past ontology. For this reason, Merleau-Ponty proposes the ontology of the flesh that shows in the modern picture. In it, the classical dichotomy disappear and we can observe the co-birth of a being-in-the-world and a being-at-the-world

Sampling along reaction coordinates with the Wang-Landau method

The multiple range random walk algorithm recently proposed by Wang and Landau [Phys. Rev. Lett. 86, 2050 (2001)] is adapted to the computation of free energy profiles for molecular systems along reaction coordinates. More generally, we show how to extract partial averages in various statistical ensembles without invoking simulations with constraints, biasing potentials or unknown parameters. The method is illustrated on a model 10-dimensional potential energy surface, for which analytical results are obtained. It is then applied to the potential of mean force associated with the dihedral angle of the butane molecule in gas phase and in carbon tetrachloride solvent. Finally, isomerization in a small rocksalt cluster, Na4F4, is investigated in the microcanonical ensemble, and the results are compared to those of parallel tempering Monte Carlo.Comment: 6 pages, 5 figure

Dynamics of a 1-D model for the emergence of the plasma edge shear flow layer with momentum conserving Reynolds stress

A one-dimensional version of the second-order transition model based on the sheared flow amplification by Reynolds stress and turbulence supression by shearing is presented. The model discussed in this paper includes a form of the Reynolds stress which explicitly conserves momentum. A linear stability analysis of the critical point is performed. Then, it is shown that the dynamics of weakly unstable states is determined by a reduced equation for the shear flow. In the case in which the flow damping term is diffusive, the stationary solutions are those of the real Ginzburg-Landau equation.Comment: 21 pages, 8 figure