New insights into the morphology of Trypanosoma cruzi reservosome

Reservosomes are late endosomes present only in members of the Schizotrypanum subgenus of the Trypanosoma genus and are defined as the site of storage of endocytosed macromolecules and lysosomal enzymes. They have been extensively described in Trypanosoma cruzi epimastigote: are bounded by a membrane unit, present an electron-dense protein matrix with electron-lucent lipid inclusions, being devoid of inner membranes. Here we performed a detailed ultrastructural analysis of these organelles using a variety of electron microscopy techniques, including ultrathin sectioning, uranyl acetate stained preparations, and freeze fracture, either in intact epimastigotes or in isolated reservosomes. New informations were obtained. First, both isolated and in situ reservosomes presented small profiles of inner membranes that are morphologically similar to the membrane surrounding the organelle. In uranyl acetate stained preparations, internal membrane profiles turned out to be longer than they appeared in ultrathin section images and traversed the organelle diameter. Internal vesicles were also found. Second, endocytosed cargo are not associated with internal vesicles and reach reservosomes on board of vesicles that fuse with the boundary membrane, delivering cargo directly into reservosome lumen. Third, electron-lucent bodies with saturated lipid core surrounded by a membrane monolayer and with unusual rectangular shape were also observed. Fourth, it was possible to demonstrate the presence of intramembranous particles on the E face of both internal vesicles and the surrounding membrane. Collectively, these results indicate that reservosomes have a complex internal structure, which may correlate with their multiple functions.     

A nonlinear position and attitude observer on SE(3) using landmark measurements

This paper addresses the problem of position and attitude estimation, based on landmark readings and velocity measurements. A derivation of a nonlinear observer on SE(3) is presented, using a Lyapunov function conveniently expressed as a function of the difference between the estimated and the measured landmark coordinates. The resulting feedback laws are explicit functions of the landmark measurements and velocity readings, exploiting the sensor information directly in the observer. The proposed observer yields almost global asymptotic stabilization of the position and attitude errors and exponential convergence in any closed ball inside the region of attraction. Also, it is shown that the asymptotic convergence of the estimation error trajectories is shaped by the landmark geometry and observer design parameters. The problem of non-ideal velocity readings is also considered, and the observer is augmented to compensate for bias in the angular and linear velocity measurements. The resulting position, attitude, and bias estimation errors are shown to converge exponentially fast to the desired equilibrium points, for bounded initial estimation errors. Simulation results are presented to illustrate the stability and convergence properties of the observer.     

On the design of multi‐rate tracking controllers: Application to rotorcraft guidance and control

This paper presents a new methodology for the design and implementation of gain‐scheduled controllers for multi‐rate systems. The proposed methodology provides a natural way to address the integrated guidance and control problem for autonomous vehicles when the outputs are sampled at different instants of time. A controller structure is first proposed for the regulation of non‐square multi‐rate systems with more measured outputs than inputs. Based on this structure, an implementation for a gain‐scheduled controller is obtained that satisfies an important property known as the linearization property. The implementation resembles the velocity implementation for single‐rate systems. The method is then applied to the problem of steering an autonomous rotorcraft along a predefined trajectory defined in terms of space and time coordinates. By considering a convenient error vector to describe the vehicle's dynamics, the trajectory tracking problem is reduced to that of regulating the error variables to zero. Because of the periodic multi‐rate nature of the onboard sensor suite, the controller synthesis is dealt with under the scope of linear periodic systems theory. Simulation results obtained with a full non‐linear rotorcraft dynamic model are presented and discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

New simple and efficient heuristics for the uncapacitated single allocation hub location problem

Hub-and-spoke networks are widely studied in the area of location theory. They arise in several contexts, including passenger airlines, postal and parcel delivery, and computer and telecommunication networks. Hub location problems usually involve three simultaneous decisions to be made: the optimal number of hub nodes, their locations and the allocation of the non-hub nodes to the hubs. In the uncapacitated single allocation hub location problem (USAHLP) hub nodes have no capacity constraints and non-hub nodes must be assigned to only one hub. In this paper, we propose three variants of a simple and efficient multi-start tabu search heuristic as well as a two-stage integrated tabu search heuristic to solve this problem. With multi-start heuristics, several different initial solutions are constructed and then improved by tabu search, while in the two-stage integrated heuristic tabu search is applied to improve both the locational and allocational part of the problem. Computational experiments using typical benchmark problems (Civil Aeronautics Board (CAB) and Australian Post (AP) data sets) as well as new and modified instances show that our approaches consistently return the optimal or best-known results in very short CPU times, thus allowing the possibility of efficiently solving larger instances of the USAHLP than those found in the literature. We also report the integer optimal solutions for all 80 CAB data set instances and the 12 AP instances up to 100 nodes, as well as for the corresponding new generated AP instances with reduced fixed costs.     

Traffic analysis and synthetic models of second life

Virtual Worlds (VW), such as Massive Multiplayer Online Social Games, have been gaining increasing attention in the last few years, mainly due to the new way users interact with them. However, little effort has been devoted to understand their traffic profile and the implications to the traffic management area. With the current growing rate of VWs’ usage, their traffic demand could eventually impose a significant burden on the operation of a typical Internet Service Provider (ISP) network. In this paper, we seek to understand the traffic behavior of an increasingly popular VW application, namely Second Life (SL), from both the connection and network level perspectives. We also show results of a traffic analysis of a SL client, when an avatar performs different actions in the VW, at different places and under different network conditions. Our results show that SL makes intensive use of network resources (mostly bandwidth), since the capacity needed for having a full SL experience (listening to live music) may reach 500 kbps. We then extend the traffic analysis work on SL by providing analytical models for its traffic profile. We aim at helping the network management and planning area to estimate the impact of an intense use of such VW on access links or core networks. Such synthetic models are also useful to the networking research community for the use in network simulations.     

Vision-based control for rigid body stabilization

This paper addresses the problem of stabilizing to a desired equilibrium point an eye-in-hand system, which consists of a single camera mounted on a rigid body free to move on . It is assumed that there is a collection of landmarks fixed in the environment and that the image coordinates of those landmarks are provided to the system by an on-board CCD camera. The proposed method addresses not only the problem of stabilization but also that of maintaining feature visibility along the system’s trajectory. The resulting solution consists of a feedback control law based on the current and desired image coordinates and reconstructed attitude and depth ratio information, which guarantees that (i) the desired equilibrium point is an almost global attractor; (ii) a set of necessary conditions for feature visibility holds throughout the system’s trajectories; and (iii) the image of a predefined feature point is kept inside the camera’s field of view.     

Pollution of inland waters in Brazil: the case for goal-oriented initiatives

This article examines the use of output-based aid and payment for environmental services to reduce water pollution in Brazil. Two nationwide initiatives are reviewed. First, the output-based aid concept of the River Basin Clean-up Programme (PRODES) to tackle the problem of sanitation deficit in urban areas is presented. Second, the payment for environmental services scheme supported by Brazil’s National Water Agency (ANA) through the Water Producer Programme to promote water conservation on rural properties is discussed. Both programmes are evaluated not only as financing mechanisms for water conservation but also as strategies for implementing Brazil’s water policy.     

Spin Polarization by Tilted Magnetic Field in Wide Ga1?xAlxAs Parabolic Quantum Wells

Wide parabolic wells can be created by properly controlling the Al content during the growth of successive Ga_1–xAl_xAs thin layers. Under a tilted magnetic field these systems present interesting transport properties, which are associated to their composition dependent g-factor. We present an exact solution for the eigenstates of an electron gas inside such a quantum well. We calculate the renormalized cyclotron frequencies as functions of the angle of tilt, as well as the density of states, and the Fermi level. We discuss the conditions for the existence of spin-polarized charge.     

Post-cracking behaviour of steel fibre reinforced concrete

Recently, RILEM TC 162-TDF has proposed equivalent,f _eq , and residual,f _R , flexural tensile strength parameters to characterize and simulate the post-cracking behaviour of steel fibre reinforced concrete (SFRC) structures. In the current work, more than two hundred flexural tests are carried out according to the RILEM TC 162-TDF recommendations and the corresponding values off _eq andf _R parameters are evaluated. In series of specimens reinforced with fibres of a distinct length/diameter ratio, similar values off _eq andf _R parameters were obtained in these series. Although a strong correlation betweenf _eq andf _R was determined, a larger scatter off _R values was observed thereby revealingf _eq to be more appropriate for design purposes. A numerical strategy involving a cross sectional layered model and an inverse analysis was developed to evaluate the post-cracking stress-strain and the stress-crack opening diagrams for the tested SFRC. This strategy was also used to determine a relation between the post-cracking strain, ɛ ^pcr , and the crack opening displacement,w, (ɛ ^pcr =w/L _p ) which is useful for evaluating the crack opening when numerical strategies based on a stress-strain approach are used. The obtainedL _p values range from half the specimen cross section height to half the distance between the tip of the notch and the top of the cross section.

---

Résumé Récemment, pour caractériser et simuler le comportement post-fissuration en traction du béton renforcé des fibres d'acier, la Commission Technique 162-TDF de la RILEM a proposé des paramètres désignés par résistance équivalente, f_eq, et résistance résiduelle, f_R, à la contrainte en flexion. Dans le travail présent, des valeurs de ces paramètres sont obtenues sur plus de deux cents essais de flexion effectués en accord avec les recommandations du TC 162-TDF de la RILEM. Des valeurs semblables de f_eq et f_R ont été obtenues dans des séries d'éprouvettes renforcées avec des fibres d'un rapport longueur/diamètre distinct. Bien qu'une forte corrélation entre f_eq et f_R ait été déterminée, une plus grande dispersion de valeurs du f_R a été observée, en démontrant que f_eq est plus approprié pour les buts du projet. Pour évaluer les diagrammes contrainte-déformation et contrainte-ouverture après fissuration, une stratégie numérique a été développée, en utilisant un modèle de section et en effectuant une analyse inverse. Cette stratégie a aussi été utilisée pour déterminer une relation entre la contrainte après fissuration, ɛ ^pcr , et l'ouverture de fissure, w, (ɛ ^pcr =w/L _p ) utile pour évaluer l'ouverture de la fissure quand les stratégies numériques sont basées sur une approche contrainte-déformation. Les valeurs de L_p obtenues ont varié entre la demi-hauteur de la section de l'éprouvette et la demi-distance entre l'extrémité de l'entaille et le sommet de la section.

     

Automatic Visualization of Recursion Trees: a Case Study on Generic Programming

Although the principles behind generic programming are already well understood, this style of programming is not widespread and examples of applications are rarely found in the literature. This paper addresses this shortage by presenting a new method, based on generic programming, to automatically visualize recursion trees of functions written in Haskell. Crucial to our solution is the fact that almost any function definition can be automatically factorized into the composition of a fold after an unfold of some intermediate data structure that models its recursion tree. By combining this technique with an existing tool for graphical debugging, and by extensively using Generic Haskell, we achieve a rather concise and elegant solution to this problem.