Tools for Controlling Activity of Neural Circuits Can Boost Gastrointestinal Research

We thank Prof U. G. Knaus and T. C. Collin for critical reading of the manuscript. GA is supported by the European Crohn's and Colitis Organization (ECCO) (J/15/2) and by the National Childrens' Research Centre (K/12/1). GD is supported by the University of Aberdeen Wellcome Trust Institutional Support Fund (105625/Z/14Z).Peer reviewedPublisher PD

Fluctuations of fragment observables

This contribution presents a review of our present theoretical as well as experimental knowledge of different fluctuation observables relevant to nuclear multifragmentation. The possible connection between the presence of a fluctuation peak and the occurrence of a phase transition or a critical phenomenon is critically analyzed. Many different phenomena can lead both to the creation and to the suppression of a fluctuation peak. In particular, the role of constraints due to conservation laws and to data sorting is shown to be essential. From the experimental point of view, a comparison of the available fragmentation data reveals that there is a good agreement between different data sets of basic fluctuation observables, if the fragmenting source is of comparable size. This compatibility suggests that the fragmentation process is largely independent of the reaction mechanism (central versus peripheral collisions, symmetric versus asymmetric systems, light ions versus heavy ion induced reactions). Configurational energy fluctuations, that may give important information on the heat capacity of the fragmenting system at the freeze out stage, are not fully compatible among different data sets and require further analysis to properly account for Coulomb effects and secondary decays. Some basic theoretical questions, concerning the interplay between the dynamics of the collision and the fragmentation process, and the cluster definition in dense and hot media, are still open and are addressed at the end of the paper. A comparison with realistic models and/or a quantitative analysis of the fluctuation properties will be needed to clarify in the next future the nature of the transition observed from compound nucleus evaporation to multi-fragment production.Comment: Contribution to WCI (World Consensus Initiative) Book " "Dynamics and Thermodynamics with Nuclear Degrees of Freedom", to appear on Euorpean Physics Journal A as part of the Topical Volume. 9 pages, 12 figure

A Cavitation Susceptability Meter with Optical Cavitation Monitoring-Part One: Design Concepts

This work is concerned with the design of a Cavitation Susceptibility Meter based on the use of a venturi tube for the measurement of the active cavitation nuclei concentration in water samples as a function of the applied tension. The operation of the Cavitation Susceptibility Meter is analyzed and the main considerations leading to the proposed design are illustrated and critically discussed. The results of this analysis indicate that the operational range is mainly limited by nuclei interference, flow separation and saturation (choking), and suggest to develop a Cavitation Susceptibility Meter where; (1) the flow possesses a laminar potential core throughout the venturi throat section in all operational conditions; (b) the pressure at the venturi throat is determined from the upstream pressure and the local flow velocity; (c) the detection of cavitation and the measurement of the flow velocity are carried out optically by means of a Laser Doppler Velocimeter; (d) a custom-made electronic Signal Processor incorporating a frequency counter is used for real time data generation and temporary storage; (e) a computerized system performs the final acquisition and reduction of the data

Separation and Surface Nuclei Effects in a Cavitation Susceptibility Meter

This work is concerned with the effects of flow separation and surface nuclei on the operation of a fixed geometry Cavitation Susceptibility Meter (CSM) with laminar flow. Cavitation is induced under controlled conditions at the throat of a glass venturi tube for the measurement of the active nuclei concentration in water samples as a function of the applied tension. Both cavitation and flow velocity are monitored optically by a Laser Doppler Velocimeter. The throat pressure is determined indirectly from the upstream pressure and the local flow velocity. The results show that laminar flow separation and surface nuclei effects are the most stringent operational limitations. Separation in the diffuser increases the minimum attainable throat pressure above the susceptibility of most cavitation nuclei commonly found in technical waters. Surface nuclei can generate extensive sheet or spot cavitation at relatively high tensions even on optically finished glass surfaces. These phenomena are difficult to eliminate and bring therefore into question the practical utility of CSM's with laminar flow and fixed geometry for the measurement of the dependence of the cavitating nuclei concentration over wide ranges of the applied tension, as required for cavitation studies

On the Acoustical Dynamics of Bubble Clouds

Recently, Morch [1,2,3,4] Chahine [5,6] and others have focused attention on the dynamics of a cloud or cluster of cavitating bubbles and have expanded on the work of van Wijngaarden [7,8] and others. Unfortunately, there appear to be a number of inconsistencies in this recent work which will require further study before a coherent body of knowledge on the dynamics of clouds of bubbles is established. For example, Morch and his co-workers [1,2,3] have visualized the collapse of a cloud of cavitating bubbles as involving the inward propagation of a shock wave; it is assumed that the bubbles collapse virtually completely when they encounter the shock. This implies the virtual absense of non-condensable gas in the bubbles and the predominance of vapor. Yet in these circumstances the mixture in the the cloud will not have any real sonic speed. As implied by a negative L.H.S. of equation (9), the fluid motion equations for the mixture would be elliptic not hyperbolic and hence shock wave solutions are inappropriate

A Cavitation Susceptibility Meter with Optical Cavitation Monitoring -- Part Two: Experimental Apparatus and Results

This work in concerned with the development and operation of a Cavitation Susceptibility Meter based on the use of a venturi tube for the measurement of the active cavitation nuclei concentration in water samples as a function of the applied tension. The pressure at the venturi throat is determined from the upstream pressure and the local flow velocity without corrections for viscous effects because the flow possesses a laminar potential core in all operational conditions. The detection of cavitation and the measurement of the flow velocity are carried out optically by means of a Laser Doppler Velocimeter. A custom-made electronic Signal Processor is used for real time data generation and temporary storage and a computerized system for final data acquisition and reduction. The implementation of the whole system is described and the results of the application of the Cavitation Susceptibility Meter to the measurement of the water quality of tap water samples are presented and critically discussed with reference to the current state of knowledge on cavitation inception