Location-Aware Computing, Virtual Networks

This issue includes four works in process on issues and applications in location-aware computing: letting users set and control privacy policies when they use location-aware applications, cold-starting recommender systems for mobile location-aware services, aggregating contextual information for location-based applications, and applying location-based services to public transportation environments. The department also includes a report on lightweight virtualization of low-power wireless personal area networks.     

Floating Textures

We present a novel multi‐view, projective texture mapping technique. While previous multi‐view texturing approaches lead to blurring and ghosting artefacts if 3D geometry and/or camera calibration are imprecise, we propose a texturing algorithm that warps (“floats”) projected textures during run‐time to preserve crisp, detailed texture appearance. Our GPU implementation achieves interactive to real‐time frame rates. The method is very generally applicable and can be used in combination with many image‐based rendering methods or projective texturing applications. By using Floating Textures in conjunction with, e.g., visual hull rendering, light field rendering, or free‐viewpoint video, improved rendering results are obtained from fewer input images, less accurately calibrated cameras, and coarser 3D geometry proxies.     

Evaluation of a vacuum collection system in the preparation of PAN fibers by forcespinning for application in ultrafine particle filtration

This study investigates the use of a vacuum collection system (VCS) in the forcespinning formation of polyacrylonitrile fibers. The surface of different filter media (substrates) has been modified for air filtration applications. The evaluation was made of the effects of collection time (60 and 180 s), VCS power (25, 50, 75, and 100%), needle size (30G ½″ and 26G ½″), and rotation speed (4,000 and 6,000 rpm). The main results were that higher substrate permeability constant in association with VCS led to a decrease in the porosity of the fiber layer, an increase of the VCS power led to increases in the collection efficiency and pressure drop, while the superficial porosity and fiber diameter decreased, and fiber collection time analysis showed that the longer collection time led to higher fiber diameter and smaller pressure drop. In all cases, the addition of the fiber layer caused increases in the pressure drop and collection efficiency, together with decreased permeability constant. Although the collection efficiency values for nanoparticles are not as expressive, these results are encouraging and indicate that VCS can be used to improve the performance of the filter medium.     

Naphthalene Containing Poly(urethane‐urea) for Volatile Memory Device Applications

Current or voltage controlled electrical switching in organic molecules and polymers is attracting attention due to its potential in organic electronic memory applications. The switching phenomenon under consideration in this article is characterized as a sudden transition from a low to a high conductivity condition at a threshold voltage. For the observed volatile switching phenomenon, the lower conductivity condition is restored as soon as the applied voltage becomes smaller than a holding voltage. This switching phenomenon presents the basic requirements for application in volatile memory devices. In this Communication we report on volatile electrical switching observed in a polyurethane derivative copolymerized with diaminonaphthalene.     

Niobium doped Bi4Ti3O12 ceramics obtained by the polymeric precursor method

Pure and niobium doped bismuth titanate ceramics (Bi₄Ti_3−xNb_xO₁₂ (BTN)), with x ranging from 0 to 0.4 were prepared by the polymeric precursor method. X-ray diffraction showed no secondary phases. Increasing niobium content leads to more resistive ceramics. The shape and size of the grains are strongly influenced by the niobium added to the system. The dielectric constant is not influenced by the niobium addition while hysteresis loops are significantly narrowed.     

Pharmacological aspects of mouse hind-paw oedema induced by Lachesis muta rhombeata venom

Pharmacological aspects of mouse hind-paw oedema induced by subplantar injections of Lachesis muta rhombeata (LMR) venom were investigated. The oedema induced by subplantar injections of 10 to 50 ng/g of LMR venom is dose dependent, with onset, peak and duration at 30, 60 and 180 min, respectively. Subplantar injection of 30 ng/g of Bothrops jararaca (BJ) venom induced oedema that has the same intensity as 30 ng/g of LMR venom but lasts for more than 4 h suggesting different time course. Systemic effects or haemorrhage were not observed with doses less than 50 ng/g. Oedema is not due to the presence of oedematogenic amines since dialysis did not change the oedema induced by 30 ng/g of LMR venom. Part of the oedema induced by LMR venom is due to a thermolabile fraction since pre-heating the venom at 100 degrees C for 15 min induced a significant reduction (56.19 +/- 6.8%) of the oedematogenic activity. The oedema induced by LMR venom is possibly induced by release of a pharmacological active substance at the site of injection. Histamine, arachidonate metabolites, nitric oxide and serotonin may play important roles in the oedematogenic effect of LMR venom since pre-treatment of mice with pyrilamine, indomethacin, dexamethasone, L-NAME and methysergide induced a significant reduction (49.86 +/- 10%; 51.06 +/- 5.9%; 77.66 +/- 3.6%; 73.30 +/- 6.1% and 93.77 +/- 2.8%, respectively) of the oedema formation. The present results demonstrate that the oedema induced by LMR and BJ venoms may be triggered and maintained by different pharmacological mechanisms. Since methysergide and L-NAME were the most active inhibitors of the oedema we can suggest that a link between serotonin release by the venom and a NO synthase activation may be an important step in the oedema formation induced by LMR venom.     

Multicomponent ion exchange isotherms in NaX zeolite: evaluation of Cr/Ca/Mg,Cr/Ca/K and Cr/Mg/K systems

BACKGROUND: One of the most important heavy metals is Cr³⁺, which is commonly found together with Ca²⁺, Mg²⁺ and K⁺ ions in tannery wastewaters. Such metals can be removed through ion exchange process using zeolite NaX. Unfortunately, with single exchange mechanisms it is impossible to predict muti‐component and competitive interactions. This work is aimed at overcoming this problem. Ion exchange isotherms of Cr³⁺, Mg²⁺, Ca²⁺ and K⁺ in ternary mixtures (Cr/Mg/Ca, Cr/Ca/K, Cr/Mg/K) using NaX zeolite at 30 °C, 45 °C and 60 °C are studied and reported. RESULTS: Ion exchange is dependent on temperature, and on the nature and interaction of ingoing cations. Sequential ion exchange occurs where one cation is able to displace another already located in the site. Values of the equilibrium constant of all cations investigated are close to each other, which indicates a weak preference for Cr⁺³. The affinity order is as follows: for Cr/Ca/Mg–NaX isotherms, Cr³⁺ > Ca²⁺ > Mg²⁺ at 30 °C, Ca²⁺ > Cr³⁺ > Mg²⁺ at 45 °C and Ca²⁺ > Mg²⁺ > Cr³⁺ at 60 °C. For Cr/Ca/K–NaX isotherms the sequence is Cr³⁺ > Ca²⁺ > K⁺ for the three temperatures and for Cr/Mg/K–NaX isotherms, Cr³⁺ > Mg²⁺ > K⁺ at 30 and 45 °C and Mg²⁺ > K⁺ > Cr³⁺ at 60 °C. CONCLUSION: It can be concluded that ions with a high charge such as Cr³⁺ are not always preferentially removed from multi‐component solution. Therefore, exchanges in NaX zeolite are useful when there is no need to have high chromium removal when compared to the competitive cations investigated here. Copyright © 2008 Society of Chemical Industry     

Spin-wave instabilities, auto-oscillations, and chaos inyttrium-iron-garnet

A review is presented of recent experimental results in yttrium-iron-garnet subject to three different spin-wave pumping mechanisms: parallel pumping, subsidiary resonance (first-order Suhl process), and premature saturation of the main resonance (second-order Suhl process). A theoretical model derived from first principles and leading to coupled nonlinear spin-wave equations, is used to interpret the observed spin-wave instabilities, auto-oscillations, and chaotic dynamics. It is shown that a two-mode model explains the main features of the experimental observations, both in parallel and perpendicular pumping. Improvements needed in the model are indicated     

Trajectory-Tracking and Path-Following of Underactuated Autonomous Vehicles With Parametric Modeling Uncertainty

We address the problem of position trajectory-tracking and path-following control design for underactuated autonomous vehicles in the presence of possibly large modeling parametric uncertainty. For a general class of vehicles moving in either 2- or 3-D space, we demonstrate how adaptive switching supervisory control can be combined with a nonlinear Lyapunov-based tracking control law to solve the problem of global boundedness and convergence of the position tracking error to a neighborhood of the origin that can be made arbitrarily small. The desired trajectory does not need to be of a particular type (e.g., trimming trajectories) and can be any sufficiently smooth bounded curve parameterized by time. We also show how these results can be applied to solve the path-following problem, in which the vehicle is required to converge to and follow a path, without a specific temporal specification. We illustrate our design procedures through two vehicle control applications: a hovercraft (moving on a planar surface) and an underwater vehicle (moving in 3-D space). Simulations results are presented and discussed.     

Orientation in manhattan: equiprojective classes and sequential estimation

The problem of inferring 3D orientation of a camera from video sequences has been mostly addressed by first computing correspondences of image features. This intermediate step is now seen as the main bottleneck of those approaches. In this paper, we propose a new 3D orientation estimation method for urban (indoor and outdoor) environments, which avoids correspondences between frames. The scene property exploited by our method is that many edges are oriented along three orthogonal directions; this is the recently introduced Manhattan world (MW) assumption. The main contributions of this paper are: the definition of equivalence classes of equiprojective orientations, the introduction of a new small rotation model, formalizing the fact that the camera moves smoothly, and the decoupling of elevation and twist angle estimation from that of the compass angle. We build a probabilistic sequential orientation estimation method, based on an MW likelihood model, with the above-listed contributions allowing a drastic reduction of the search space for each orientation estimate. We demonstrate the performance of our method using real video sequences.