Towards an effective potential for the monomer, dimer, hexamer, solid and liquid forms of hydrogen fluoride

We present an attempt to build up a new two-body effective potential for hydrogen fluoride, fitted to theoretical and experimental data relevant not only to the gas and liquid phases, but also to the crystal. The model is simple enough to be used in Molecular Dynamics and Monte Carlo simulations. The potential consists of: a) an intra-molecular contribution, allowing for variations of the molecular length, plus b) an inter-molecular part, with three charged sites on each monomer and a Buckingham "exp-6" interaction between fluorines. The model is able to reproduce a significant number of observables on the monomer, dimer, hexamer, solid and liquid forms of HF. The shortcomings of the model are pointed out and possible improvements are finally discussed.Comment: LaTeX, 24 pages, 2 figures. For related papers see also http://www.chim.unifi.it:8080/~valle

Interaction between Attention and Bottom-Up Saliency Mediates the Representation of Foreground and Background in an Auditory Scene

Bottom-up (stimulus-driven) and top-down (attentional) processes interact when a complex acoustic scene is parsed. Both modulate the neural representation of the target in a manner strongly correlated with behavioral performance

HYCSOS: a chemical heat pump and energy conversion system based on metal hydrides. 1979 status report

The current status of the HYCSOS chemical heat pump and energy conversion system based on metal hydrides is described. Heat transfer fluid loops were insulated and modified for isothermal operation. Software development for HYCSOS manual mode operation was completed. Routines to handle data acquisition, logging, compression, correction and plotting, using a Tektronix Graphics system with flexible disk data storage, provide a rapid and versatile means of presenting HYCSOS data for analysis. Advanced concept heat exchangers to improve the heat transfer of the hydride bed with the heat transfer fluid are discussed. Preliminary tests made with a LaNi/sub 5/ loaded aluminum foam test unit showed that heat transfer properties are very markedly improved. Thermodynamic expressions are applied to the selection of alloys for use in HYCSOS. The substitution of aluminum for nickel in AB/sub 5/ type alloys is shown to reduce hysteresis and permits the use of potentially lower cost materials with added flexibility for the optimization of engineering design and performance characteristics of the hydride heat pump system. Transient thermal measurements on hydride beds of CaNi/sub 5/ and LaNi/sub 5/ show no deterioration with cycling. Relatively slow heat transfer between the hydride beds and heat transfer fluid in the coiled tube heat exchangers is indicated by temperature lag of the bed and heat transfer fluid. Improved heat transfer is anticipated with aluminum foam heat exchangers