Rearrangements and Tunneling Splittings in Small Water Clusters

Recent far-infrared vibration-rotation tunneling (FIR-VRT) experiments pose new challenges to theory because the interpretation and prediction of such spectra requires a detailed understanding of the potential energy surface (PES) away from minima. In particular we need a global description of the PES in terms of a complete reaction graph. Hence all the transition states and associated mechanisms which might give rise to observable tunneling splittings must be characterized. It may be possible to guess the detailed permutations of atoms from the transition state alone, but experience suggests this is unwise. In this contribution a brief overview of the issues involved in treating the large amplitude motions of such systems will be given, with references to more detailed discussions and some specific examples. In particular we will consider the effective molecular symmetry group, the classification of rearrangement mechanisms, the location of minima and transition states and the calculation of reaction pathways. The application of these theories to small water clusters ranging from water dimer to water hexamer will then be considered. More details can be found in recent reviews.Comment: 15 pages, 5 figures. This paper was prepared in August 1997 for the proceedings volume of the NATO-ASI meeting on "Recent Theoretical and Experimental Advances in Hydrogen Bonded Clusters" edited by Sotiris Xantheas, which has so far not appeare

Agglomeration mechanism during the preparation of nickel(0) and iron(0) zeolites

Magnetization measurements have been used to study the reduction process of Ni - zeolites and the thermal decomposition of iron pentacarbonyl adsorbed on NaY zeolites . The Ni(0) particle size distribution in H2»reduced NiNaA, Ni NaX, Ni NaY and NiNaM is bidisperse. The amount and the volume of particles exceeding the cage dimensions increases in the sequence Μ,Υ,Χ,Α zeolites. Particle fusion is found to be the rate determining step. With decomposition of Fe(C0)5/NaY adducts, up to 97 wt.% of the iron particles produced are smaller than 1.3 nm. Fluidized sample bed, inert gas atmosphere and fast heating up to 440 Κ are essential to reach mononodal dispersion

Aerodynamic Interference on Finned Slender Body

Aerodynamic interference can occur between high-speed slender bodies when in close proximity. A complex flowfield develops where shock and expansion waves from a generator body impinge upon the adjacent receiver body and modify its aerodynamic characteristics in comparison to the isolated case. The aim of this research is to quantify and understand the multibody interference effects that arise between a finned slender body and a second disturbance generator body. A parametric wind tunnel study was performed in which the effects of the receiver incidence and axial stagger were considered. Computational fluid dynamic simulations showed good agreement with the measurements, and these were used in the interpretation of the experimental results. The overall interference loads for a given multibody configuration were found to be a complex function of the pressure footprints from the compression and expansion waves emanating from the generator body as well as the flow pitch induced by the generator shockwave. These induced interference loads change sign as the shock impingement location moves aft over the receiver and in some cases cause the receiver body to become statically unstable. Overall, the observed interference effects can modify the subsequent body trajectories and may increase the likelihood of a collision

3D simulations of Einstein's equations: symmetric hyperbolicity, live gauges and dynamic control of the constraints

We present three-dimensional simulations of Einstein equations implementing a symmetric hyperbolic system of equations with dynamical lapse. The numerical implementation makes use of techniques that guarantee linear numerical stability for the associated initial-boundary value problem. The code is first tested with a gauge wave solution, where rather larger amplitudes and for significantly longer times are obtained with respect to other state of the art implementations. Additionally, by minimizing a suitably defined energy for the constraints in terms of free constraint-functions in the formulation one can dynamically single out preferred values of these functions for the problem at hand. We apply the technique to fully three-dimensional simulations of a stationary black hole spacetime with excision of the singularity, considerably extending the lifetime of the simulations.Comment: 21 pages. To appear in PR

Estimation of drift and diffusion functions from time series data: A maximum likelihood framework

Complex systems are characterized by a huge number of degrees of freedom often interacting in a non-linear manner. In many cases macroscopic states, however, can be characterized by a small number of order parameters that obey stochastic dynamics in time. Recently techniques for the estimation of the corresponding stochastic differential equations from measured data have been introduced. This contribution develops a framework for the estimation of the functions and their respective (Bayesian posterior) confidence regions based on likelihood estimators. In succession approximations are introduced that significantly improve the efficiency of the estimation procedure. While being consistent with standard approaches to the problem this contribution solves important problems concerning the applicability and the accuracy of estimated parameters.Comment: 18 pages, 2 figure

Einstein on the beach: A study in temporality

This is an Author's Accepted Manuscript of an article published in Performance Research, 17(5), 34 - 40, 2012, copyright @ Taylor & Francis, available online at: http://www.tandfonline.com/10.1080/13528165.2012.728438.In this paper I seek to examine and analyse the sense of duration induced by performances of Einstein on the Beach, and the entailed sense of time which its internal structure creates. I initially sketch out the stylistic context and artistic intentions of this work's creators, Glass and Wilson, and I briefly describe the process of its creation. Certain features of this process indicate how the work may be interpreted. Having cited the creators' thoughts on structure and temporality, I address directly aspects of Einstein's temporal effects, comparing it to works of similar lengths. I give the briefest synopsis of its staging and motifs. I then outline three kinds of devices which seem to inform our temporal sense of this work as spectators. In the final section I invoke two ideas which serve as analogies to help characterise this work's overall effect on us: Heidegger's notion of the ‘hermeneutic circle’ and, more speculatively, Nietzsche's ‘theory’ of Eternal Recurrence