Occlusion-resistant camera design for acquiring active environments.

In this article, we present a detailed theoretical analysis and a prototype implementation of a family of cameras designed with the explicit goal of detecting and removing interfering dynamic occluders in real time, during live capture, as opposed to fixing the resulting artifacts a posteriori. Such an early-acquisition approach improves efficiency: more valid samples are acquired faster without worrying about moving occluders. One option for designing a camera to be unaffected by moving occluders is to sample through the occluder, but true x-ray-like vision is technically impractical. Another option is to sample around the occluder using a camera with a large effective aperture, but such an approach requires a bulky acquisition device. Yet another possibility of sampling around an occluder is to rely on second and higher order reflected rays that indirectly sample surfaces not directly visible. However, devising an acquisition device sufficiently sensitive and efficient to capture large environments using reflected rays will remain challenging for the foreseeable future.     

Spatial navigation model based on chaotic attractor networks

We present a model of spatial navigation based on the non-convergent dynamics of brain activity. The system includes a hippocampal module that processes global spatial information and a cortical module that deals with local sensory information. We test the model using several spatial navigation paradigms: goal finding, shortcutting and detouring. Computer simulations show that the performance of the agent qualitatively matches that of animals and related models. This new approach provides a novel interpretation of how the brain accomplishes spatial navigation.     

Componentwise asymptotic stability of linear constant dynamical systems

This note deals with a special type of asymptotic stability, namely componentwise asymptotic stability with respect to the vectorgamma(t)(CWASγ) of systemS: dot{x} = Ax + Bu, t geq 0, wheregamma(t) > 0(componentwise inequality) andgamma(t) rightarrow 0ast rightarrow + infty.Sis CWASγ if for eacht_{0} geq 0and for each|x(t_{0})| leq gamma (t_{0}) (|x (t_{0})|with the components|x_{i}(t_{0})|the free response ofSsatisfies|x(t)| leq gamma (t)for eacht geq t_{0}. Forgamma(t){underline { underline delta} } alphae^{-beta t}, t geq 0, withalpha > 0andbeta > 0(scalar), the CWEAS (E= exponential) may be defined.Sis CWAS γ (CWEAS) if and only ifdot{gamma}(t) geq bar{A}gamma(t), t geq 0 (bar{A}alpha < 0); A {underline { underline delta} } (a_{ij})andbar{A}has the elements aijand|a_{ij}|, i neq j. These results may be used in order to evaluate in a more detailed manner the dynamical behavior ofSas well as to stabilizeScomponentwise by a suitable linear state feedback.     

IR and UV laser-assisted deposition from titanium tetrachloride: A comparative study

Laser-induced TiCl₄ decomposition at vapour pressure was performed and comparative study of the composition and structure of thermally (at 10.6 μm) and photolytically (at 248 nm) deposited Ti-based films is presented. Emphasis was given to the less explored titanium deposition process by CO₂ laser pyrolysis of TiCl₄. The detailed structure of films deposited on quartz substrates was examined by scanning electron microscopy and X-ray photoelectron spectroscopy. The influence of the incident laser energy on the chemical content of the films as well as on the film growth rate was demonstrated. The results indicate that in the thermal IR decomposition of TiCl₄ a multilayer structure is formed with unsaturated TiSi_x at the interface and oxidized phases at the surface. The photolytic process leads to films with increased purity and a specific growth morphology.     

Synthesis and characterization of collagen/hydroxyapatite: magnetite composite material for bone cancer treatment

Our purpose was obtaining and characterizing a complex composite system with multifunctional role: bone graft material and hyperthermia generator necessary for bone cancer therapy. The designed system was a magnetite enriched collagen/hydroxyapatite composite material, obtained by a co-precipitation method. Due to the applied electromagnetic field the magnetite will induce hyperthermia and cause tumoral cell apoptosis. The complex bone graft system was characterised by XRD, FTIR and SEM, while the hyperthermia was quantify by measuring the temperature increase due to the applied alternative electromagnetical field.     

Observing the state with componentwise exponentially decaying error

The componentwise exponential asymptotically stable (CWEAS) observer is defined. Its estimation error is componentwise and absolutely bounded by prespecified decaying exponentials. Using the notion of CWEAS introduced earlier, an existence condition for such an observer is proved. Via eigenvalues location and convexity of certain functions one states the maximization problem of the damping factor of the above exponentials and introduces and characterizes the CWEAS detectability. This is an explicit property of the observability pair (A, C), which, under a certain condition involving the pair (B, D), suffices for strong^* detectability and therefore for the existence of a strong observer.     

On the componentwise stability of linear systems

The componentwise asymptotic stability (CWAS) and componentwise exponential asymptotic stability (CWEAS) represent stronger types of asymptotic stability, which were first defined for symmetrical bounds constraining the flow of the state‐space trajectories, and then, were generalized for arbitrary bounds, not necessarily symmetrical. Our paper explores the links between the symmetrical and the general case, proving that the former contains all the information requested by the characterization of the CWAS/CWEAS as qualitative properties. Complementary to the previous approaches to CWAS/CWEAS that were based on the construction of special operators, we incorporate the flow‐invariance condition into the classical framework of stability analysis. Consequently, we show that the componentwise stability can be investigated by using the operator defining the system dynamics, as well as the standard ε?δ formalism. Although this paper explicitly refers only to continuous‐time linear systems, the key elements of our work also apply, mutatis mutandis, to discrete‐time linear systems. Copyright © 2004 John Wiley & Sons, Ltd.