Small animal dual modality microSPECT-micro CT has seen many technological advances during recent years. The design of small animal dual modality scanners is a multidisciplinary field, where several interrelated technological problems must be integrated in a complex instrument. This article describes the general concepts that must be taken into consideration during the design process of dual modality microSPECT- microCT scanners. A description of the contemporary scanner technology is presented using the recently designed dual modality micro SPECT -microCT at the Physics Research Laboratory at UCSF. The technology is described with a simple approach to introduce the reader to the complex process of the dual modality scanner design. This article includes a discussion of current technological challenges that have potential to improve or expand the microSPECT-microCT performance and its applications.
The dynamics of an electrooptic hybrid bistable device with feedback is analized when a discrete signal is used. Experimental results show be and eultistability period doubling chaos and type I intermittence. Numerical results of a model without aproximations show a very good agreement with the experiment. 1 . DESCRIPTION Feedback is used in control engineering to stabilize the output in a position defined by a control parameter. Non linear dynaMic analisys shows that systems with feedback can be chaotic when the control parameter is changed. Gibbs and co workers (1) have shown for tt first time the bistability behavior in a hybrid system with a delayed feedback signal. Later on a lot of work was done in systems with other devices like liquid crystals and acustooptic modulators. We have changed the system introducing a digital signal (pulsed) and delaying the feedback until the next pulse was present at the modulator. In this way the output is controled by the feedback loop and can be described without any aproximations (like small signal modulation) by a recurrence equation. Xn+1 A E I + cos ( R. Xn + B ) 3 (1) In order to analize completely the system three control parameters were introduced experimentally to have all the possible changes of an unidimensional map: a multiplicative parameter of amplitude (like in the logistic map) and two aditional parameters in the argument of
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