Design and characterization of optical heads for interferometric ballistic velocity measurements

The design of optical fiber based heads offering high accuracy and bandwidth for use in VISAR (velocity interferometer system for any reflector) experiments measuring ballistic velocities is described. A new, expanded, model for predicting the distance-dependent collection efficiency of the heads is presented. The model is shown to agree very well with experimental results, both within and outside the "depth of field". Various optical heads are demonstrated, to suit different experimental setups and conditions. Designs offering options for high bandwidths, accurate prealignment, and large stand-off distances are discussed. Results from a typical VISAR experiment are presented, verifying that our designs yield high-quality data.     

Scanning and tracking with independent cameras—a biologically motivated approach based on model predictive control

This paper presents a framework for visual scanning and target tracking with a set of independent pan-tilt cameras. The approach is systematic and based on Model Predictive Control (MPC), and was inspired by our understanding of the chameleon visual system. We make use of the most advanced results in the MPC theory in order to design the scanning and tracking controllers. The scanning algorithm combines information about the environment and a model for the motion of the target to perform optimal scanning based on stochastic MPC. The target tracking controller is a switched control combining smooth pursuit and saccades. Min-Max and minimum-time MPC theory is used for the design of the tracking control laws. We make use of the observed chameleon’s behavior to guide the scanning and the tracking controller design procedures, the way they are combined together and their tuning. Finally, simulative and experimental validation of the approach on a robotic chameleon head composed of two independent Pan-Tilt cameras is presented.

Neutronic analysis of hydride fueled PWR cores

The neutronic properties of U-ZrH_1.6 fuelled PWR cores are investigated and compared against those of the currently used UO₂ fuelled cores. In the first part of this work a parametric study is performed to quantify the neutronically achievable burnup for both hydride and oxide fuels at a number of enrichment levels and for a large number of geometries covering a wide design space of fuel rod outer diameter, D, and lattice pitch, P. The fuel temperature and coolant temperature reactivity coefficients as well as the small and large void reactivity coefficients are calculated for hydride fuel with 5% and 12.5% enriched uranium. For this purpose a simplified procedure was developed that can, using single unit cell or assembly calculations, (1) account for non-linear burnup dependent k_∞ and thus to adequately predict the discharge burnup; (2) estimate the burnup dependent soluble boron concentration and; (3) estimate the reactivity coefficients; all of the above for a multi-batch core. In the second part of this work a detailed neutronic analysis is carried out for the six most economical geometries of both oxide and hydride fuels, with the purpose of designing the U-ZrH_1.6 fueled PWR cores to have negative reactivity coefficients. The preferred design found is replacement of 25 ^v/_o of the ZrH_1.6 by thorium hydride, along with addition of some IFBA burnable poison. It is also found that the conversion from oxide to hydride fueled PWR cores could be done without modifications in the control system.     

Power flattening options for the ENHS (encapsulated nuclear heat source) core

The feasibility of power flattening while maintaining a nearly constant k_eff over the core life is assessed for the Encapsulated Nuclear Heat Source (ENHS). A couple of approaches are considered — using different fuel dimensions and using different enrichment levels across the core. Three new cores with flattened power distribution are successfully designed: Design-I uses different fuel rod diameters but uniform fuel composition; Design-II uses different fuel enrichment in the radial direction but uniform fuel rod dimensions; Design-III is similar to Design-II but uses enrichment splitting also in the axial direction. Relative to the reference ENHS core, the BOL peak-to-average channel power ratio is reduced from 1.50 to 1.15, 1.22 and 1.15 and the average discharge burnup increases by 8.5%, 27.9% and 41.2% for, respectively, Design-I, -II and -III. The corresponding burnup reactivity swings over 20 years of full power operation are 0.37%, 0.52% and 0.60% relative to 0.22% of the reference design. Design-II and -III have a negative coolant expansion reactivity defect while in the reference design this defect is positive. The radial power flattening increases the reactivity worth of the peripheral absorbers of the three new designs while the central absorber reactivity worth is reduced but their sum is nearly maintained. The newly designed cores have slightly more positive coolant void reactivity worth than the reference ENHS core.     

Temperature Dependence of Excited-State Proton Transfer and Geminate Recombination Processes in Water and in Glycerol-Doped Ice

The reversible proton dissociation and geminate recombination of photoacids was studied as a function of temperature in neat water, binary water mixture containing 0.6 mol% glycerol, and doped ice containing 0.6 mol% glycerol. The deuterium isotope effect on both condensed phases was also studied. 8-hydroxypyrene-1,3,6 trisulfonate trisodium salt was used as the electronically-excited-state proton emitter. The experimental data are analyzed by the Debye–Smoluchowski equation solved numerically with boundary conditions to account for the reversibility of the reaction. We propose a qualitative model to describe the unusual temperature dependence of the proton transfer rate in the liquid phase. We also propose a model for proton transfer in solid ice based on L-defects transport as proton acceptors. While in the liquid phase at t > 10°C the proton dissociation rate constant is almost temperature independent, in glycerol-doped ice we find a large temperature dependence.     

Metaqueries: Semantics, complexity, and efficient algorithms

Metaquery (metapattern) is a data mining tool which is useful for learning rules involving more than one relation in the database. The notion of a metaquery has been proposed as a template or a second-order proposition in a language that describes the type of pattern to be discovered. This tool has already been successfully applied to several real-world applications.In this paper we advance the state of the art in metaquery research in several ways. First, we argue that the notion of a support value for metaqueries, where a support value is intuitively some indication to the relevance of the rules to be discovered, is not adequately defined in the literature, and, hence, propose our own definition. Second, we analyze some of the related computational problems, classify them as NP-hard and point out some tractable cases. Third, we propose some efficient algorithms for computing support and present preliminary experimental results that indicate the usefulness of our algorithms.     

Head Movements for Depth Perception: Praying Mantis versus Pigeon

Inspired by the abilities of both the praying mantis and the pigeon to judge distance by use of motion-based visually mediated odometry, we create miniature models for depth estimation that are similar to the head movements of these animals. We develop mathematical models of the praying mantis and pigeon visual behavior and describe our implementations and experimental environment. We investigate structure from motion problems when images are taken from a camera whose focal point is translating according to each of the biological models. This motion in the first case is reminiscent of a praying mantis peering its head left and right, apparently to obtain depth perception, hence the moniker mantis head camera. In the second case this motion is reminiscent of a pigeon bobbing its head back and forth, also apparently to obtain depth perception, hence the moniker pigeon head camera. We present the performance of the mantis head camera and pigeon head camera models and provide experimental results and error analysis of the algorithms. We provide the comparison of the definitiveness of the results obtained by both models. The precision of our mathematical model and its implementation is consistent with the experimental facts obtained from various biological experiments.     

Novel electrochemical biosensing platform using self-assembled peptide nanotubes

Here we describe a novel electrochemical biosensing platform based on biocompatible, well-ordered, self-assembled diphenylalanine peptide nanotubes. Voltammetric and time-based amperometric techniques were applied to demonstrate the ability of the peptide nanotubes to improve the electrochemical parameters of graphite electrodes. The findings clearly show that this novel class of peptide nanotubes provides an attractive component for future electroanalytical devices.     

Nurses’ reactions to alarms in a neonatal intensive care unit

Neonatal intensive care units (NICUs), like other intensive care units, are intended to provide immediate responses to any change in the patients condition. Patient-monitoring alarms and alarms from other medical equipment are very common in these units, and most alarms have no clinical significance. This study addresses the question of how alarms affect nurses actions by measuring the occurrence of alarms from different causes in a NICU, recording the nurses reactions, and analyzing the relationship between the alarms and the actions. The results show that nurses often do not respond directly to alarms, but, rather, use them as additional sources of information in their ongoing flow of actions. The probabilities for their responding to an alarm depend on the causes of the alarm, its duration, and the characteristics of the patient. These findings support the view that experienced nurses dynamically adjust their activities according to the information they receive from alarm systems and other sources, and that they combine their reactive actions with the periodic performance of routine tasks.     

Finding the focus of expansion and estimating range using optical flow images and a matched filter

The focus of expansion plays an important role in many vision applications such as three-dimensional reconstruction, range estimation, time-to-impact computation, and obstacle avoidance. Most current techniques are based on correspondence or on accurate flow estimation and are therefore considered computationally heavy. This paper presents an efficient technique to find the focus of expansion from optical flow. The technique utilizes a specially designed matched filter that does not require an exact estimation of the optical flow but rather can use a low-quality estimation of it. In addition, based on the location of the focus of expansion and its immediate neighborhood, the paper suggests a way to estimate the range to the focus of expansion. Based on the experimental results, the technique has proved to be both accurate and efficient.Received: 26 January 2003, Accepted: 18 March 2004, Published online: 14 September 2004 Correspondence to: Didi Sazbon