The role of fixation in visual motion analysis

How does the ability of humans and primates to fixate at environmental points in the presence of relative motion help their visual systems in solving various tasks? To state the question in a more formal setting, we investigate in this article the following problem: Suppose that we have an active vision system, that is, a camera resting on a platform and being controlled through motors by a computer that has access to the images sensed by the camera in real time. The platform can move freely in the environment. If this machine can fixate on targets being in relative motion with it, can it solve visual tasks in an efficient and robust manner? By restricting our attention to a set of navigational tasks, we find that such an active observer can solve the problems of 3-D motion estimation, egomotion recovery, and estimation of time-to-contact in a very efficient manner, using as input the spatiotemporal derivatives of the image-intensity function (or normal flow). Fixation over time changes the input (motion field) in a controlled way and from this change additional information is derived making the previously mentioned tasks easier to solve.     

Incremental refinement of image salient-point detection

Low-level image analysis systems typically detect "points of interest", i.e., areas of natural images that contain corners or edges. Most of the robust and computationally efficient detectors proposed for this task use the autocorrelation matrix of the localized image derivatives. Although the performance of such detectors and their suitability for particular applications has been studied in relevant literature, their behavior under limited input source (image) precision or limited computational or energy resources is largely unknown. All existing frameworks assume that the input image is readily available for processing and that sufficient computational and energy resources exist for the completion of the result. Nevertheless, recent advances in incremental image sensors or compressed sensing, as well as the demand for low-complexity scene analysis in sensor networks now challenge these assumptions. In this paper, we investigate an approach to compute salient points of images incrementally, i.e., the salient point detector can operate with a coarsely quantized input image representation and successively refine the result (the derived salient points) as the image precision is successively refined by the sensor. This has the advantage that the image sensing and the salient point detection can be terminated at any input image precision (e.g., bound set by the sensory equipment or by computation, or by the salient point accuracy required by the application) and the obtained salient points under this precision are readily available. We focus on the popular detector proposed by Harris and Stephens and demonstrate how such an approach can operate when the image samples are refined in a bitwise manner, i.e., the image bitplanes are received one-by-one from the image sensor. We estimate the required energy for image sensing as well as the computation required for the salient point detection based on stochastic source modeling. The computation and energy required by the proposed incremental refinement approach is compared against the conventional salient-point detector realization that operates directly on each source precision and cannot refine the result. Our experiments demonstrate the feasibility of incremental approaches for salient point detection in various classes of natural images. In addition, a first comparison between the results obtained by the intermediate detectors is presented and a novel application for adaptive low-energy image sensing based on points of saliency is presented.     

Typical diffusion behaviour in packaging polymers - application to functional barriers

When plastics are collected for recycling, possibly contaminated articles might be recycled into food packaging, and thus the contaminants might subsequently migrate into the food. Multilayer functional barriers may be used to delay and to reduce such migration. The contribution of the work reported here is to establish reference values (at 40°C) of diffusion coefficients and of activation energies to predict the functional barrier efficiency of a broad range of polymers (polyolefins, polystyrene, polyamide, PVC, PET, PVDC, [ethylene vinyl alcohol copolymer], polyacrylonitrile and [ethylene vinyl acetate copolymer]). Diffusion coefficients (D) and activation energies (Ea) were measured and were compiled together with literature data. This allowed identification of new trends for the log D = f(molecular weight) relationships. The slopes were a function of the barrier efficiency of the polymer and temperature. The apparent activation energy of diffusion displayed two domains of variation with molecular weight (M). For low M (gases), there was little variation of Ea. Focusing on larger molecules, high barrier polymers displayed a larger dependence of Ea with M. The apparent activation energy decreased with T. These results suggest a discontinuity between rubbery and glassy polymers.     

Prediction of band discontinuities in semiconductor heterojunctions: A simple model

A simple model for the prediction of heterojunction valence band discontinuities is proposed in this paper. Only two properties of semiconductors are used in this model, namely the lattice constant and the energy gap.     

Comparative study of batch and continuous multi-stage fixed-bed tower (MFBT) bioreactor during wine-making using freeze-dried immobilized cells

A freeze-dried immobilized biocatalyst produced by immobilization of Saccharomyces cerevisiae AXAZ-1 yeast cells on gluten pellets and subsequent freeze-drying was used in a multistage fixed-bed tower (MFBT) bioreactor for batch and continuous wine-making. The MFBT bioreactor resulted in higher alcohol productivity compared to fermentations carried out in a packed bed (PB) bioreactor and showed an important operational stability and no decrease in activity, even at low fermentation temperature (5 °C) and after storage for 6 months at 4 °C. The production of amyl alcohols proved to be temperature dependent and was significantly reduced at low temperatures. Re-activation of the freeze-dried immobilized cells after storage for 6 months resulted in further decreased content of amyl alcohols. The SPME GC/MS analysis of volatile compounds revealed no significant differences in the wines produced by MFBT and PB bioreactors, while the preliminary sensory evaluation ascertained the overall improved quality of the produced wines. Potential industrial application of MFBT bioreactor is also assessed and discussed.     

Functionality of freeze-dried L. casei cells immobilized on wheat grains

Lactobacillus casei cells were immobilized on wheat grains and the effect of nine cryoprotectants during freeze-drying was investigated. Survival and fermentative activity of the freeze-dried immobilized biocatalysts was studied by monitoring pH, lactic acid and lactose content in successive fermentations batches of both synthetic lactose medium and milk. Freeze-dried L. casei cells immobilized on wheat grains without using cryoprotectants resulted in high cell survival and metabolic activity. The same biocatalysts were stored at room temperature for 9 months and at 4 °C and −18 °C for 12 months. Reactivation of the stored biocatalysts was carried out in synthetic lactose medium. Storage at room and low temperatures (4 °C and −18 °C) resulted in about 5.11, 4.9 and 4.3 final pH respectively during fermentations, indicating the suitability of the immobilized biocatalysts for the production of mild and low pH dairy products. The immobilization of a probiotic microorganism, such as L. casei, on boiled wheat which contains prebiotic compounds might provide a potential synbiotic preparation.