Fatores envolvidos na migração das endopróteses em pacientes submetidos ao tratamento endovascular do aneurisma da aorta abdominal

A migração da endoprótese é complicação do tratamento endovascular definida como deslocamento da ancoragem inicial. Para avaliação da migração, verifica-se a posição da endoprótese em relação a determinada região anatômica. Considerando o aneurisma da aorta abdominal infrarrenal, a área proximal de referência consiste na origem da artéria renal mais baixa e, na região distal, situa-se nas artérias ilíacas internas. Os pacientes deverão ser monitorizados por longos períodos, a fim de serem identificadas migrações, visto que estas ocorrem normalmente após 2 anos de implante. Para evitar migrações, forças mecânicas que propiciam fixação, determinadas por características dos dispositivos e incorporação da endoprótese, devem predominar sobre forças gravitacionais e hemodinâmicas que tendem a arrastar a prótese no sentido caudal. Angulação, extensão e diâmetro do colo, além da medida transversa do saco aneurismático, são importantes aspectos morfológicos do aneurisma relacionados à migração. Com relação à técnica, não se recomenda implante de endopróteses com sobredimensionamento excessivo (> 30%), por provocar dilatação do colo do aneurisma, além de dobras e vazamentos proximais que também contribuem para a migração. Por outro lado, endopróteses com mecanismos adicionais de fixação (ganchos, farpas e fixação suprarrenal) parecem apresentar menos migrações. O processo de incorporação das endopróteses ocorre parcialmente e parece não ser suficiente para impedir migrações tardias. Nesse sentido, estudos experimentais com endopróteses de maior porosidade e uso de substâncias que permitam maior fibroplasia e aderência da prótese à artéria vêm sendo realizados e parecem ser promissores. Esses aspectos serão discutidos nesta revisão.

Effect of a frictional force on the Fermi-Ulam model

The dynamical properties of a classical particle bouncing between two rigid walls, in the presence of a drag force, are studied for the case where one wall is fixed and the other one moves periodically in time. The system is described in terms of a two-dimensional nonlinear map obtained by solution of the relevant differential equations. It is shown that the structure of the KAM curves and the chaotic sea is destroyed as the drag force is introduced. At high energy, the velocity of the particle decreases linearly with increasing iteration number, but with a small superimposed sinusoidal modulation. If the motion passes near enough to a fixed point, the particle approaches it exponentially as the iteration number evolves, with a speed of approach that depends on the strength of the drag force. For a simplified version of the model it is shown that, at low energies corresponding to the region of the chaotic sea in the non-dissipative model, the particle wanders in a chaotic transient that depends on the strength of the drag coefficient. However, the KAM islands survive in the presence of dissipation. It is confirmed that the fixed points and periodic orbits go over smoothly into the orbits of the well-known (non-dissipative) Fermi-Ulam model as the drag force goes to zero.

Influences of the load centre of gravity on heavy vehicle acceleration

The aim of this paper is to analyse the influence of the load centre of gravity on heavy vehicle acceleration. This analysis is done through a method in which a vehicle centre of gravity map is used. A model for the driving force is presented for bus, truck and tractor-semi trailer combinations. The proposed model takes into consideration the resistance forces (drag, rolling resistance, translation and rotation acceleration, climbing resistance) and the 4 X 2 traction system. The positions of the vehicle centre of gravity as a function of the position of the load centre of gravity are determined. The vehicle acceleration is calculated based on the position of the load centre of gravity. This study analyses the acceleration of one of the Mercedes-Benz do Brasil tractor-semitrailer vehicle. A comparison of the acceleration for different maximum adhesion coefficients and ramps are presented, showing new results. An example showing the variations of the load centre of gravity position with the acceleration time and distance is provided. The load centre of gravity position is important for vehicle safety and the efficiency and economy in the transportation of the load.

Temporal dynamics of two species of Chaetophoraceae (Chlorophyta) in tropical streams of São Paulo State, Southeastern Brazil

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Optimal space manoeuvres in a non-Keplerian force field

In this work the problem of a spacecraft bi-impulsive transfer between two given non coplanar elliptical orbits, with minimum fuel consumption, is solved considering a non-Keplerian force field (the perturbing forces include Earth gravity harmonics and atmospheric drag). The problem is transformed in the Two Point Boundary Value Problem. It is developed and implemented a new algorithm, that uses the analytical expressions developed here. A dynamics that considered a Keplerian force field was used to produce an initial guess to solve the Two Point Boundary Value Problem. Several simulations were performed to observe the spacecraft orbital behaviour by different kind of perturbations and constraints, on a fuel consumption optimization point of view. (C) 2002 COSPAR. Published by Elsevier B.V. Ltd. All rights reserved.

A note on the horseshoe confinement model: the Poynting-Robertson effect

In the present work we numerically simulated the motion of particles coorbital to a small satellite under the Poynting-Robertson light drag effect in order to verify the symmetry suggested by Dermott et al. (1979, 1980) on their ring confinement model. The results reveal a more complex scenario, especially for very small particles (micrometer sizes), which present chaotic motion. Despite the complexity of the trajectories the particles remain confined inside the coorbital region. However, the dissipative force caused by the solar radiation also includes the radiation pressure component which can change this configuration. Our results show that the inclusion of the radiation pressure, which is not present in the original confinement model, can destroy the configuration in a time much shorter than the survival time predicted for a dust particle in a horseshoe orbit with a satellite.

Some comments on the F ring-Prometheus-Pandora environment

The system formed by the F ring and two close satellites, Prometheus and Pandora, has been analysed since the time that Voyager visited the planet Saturn. During the ring plane crossing in 1995 the satellites were found in different positions as predicted by the Voyager data. Besides the mutual effects of Prometheus and Pandora, they are also disturbed by a massive F ring. Showalter et al. [Icarus 100 (1992) 394] proposed that, the core of the ring has a mass which corresponds to a moonlet varying in size from 15 to 70 kin in radius which can prevent the ring from spreading due to dissipative forces, such as Poynting-Robertson drag and collisions. We have divided this work into two parts. Firstly we analysed the secular interactions between Prometheus-Pandora and a massive F ring using the secular theory. Our results show the variation in eccentricity and inclination of the satellites and the F ring taking into account a massive ring corresponding to a moonlet of different sizes. There is also a population of dust particles in the ring in the company of moonlets at different sizes [Icarus 109 (1997) 304]. We also analysed the behaviour of these particles under the effects of the Poynting-Robertson drag and radiation pressure. Our results show that the time scale proposed for a dust particle to leave the ring is much shorter than predicted before even in the presence of a coorbital moonlet. This result does not agree with the confinement model proposed by Dermott et al. [Nature 284 (1980) 309]. In 2004, Cassini mission will perform repeated observations of the whole system, including observations of the satellites and the F ring environment. These data will help us to better understand this system. (C) 2003 COSPAR. Published by Elsevier Ltd. All rights reserved.

Photoinduced phenomena in layer-by-layer films of poly(allylamine hydrochloride) and Brilliant Yellow azodye

The nanoscale interactions between adjacent layers of layer-by-layer (LBL) films from poly(allylamine hydrochloride) (PAH) and azodye Brilliant Yellow (BY) have been investigated, with the films employed for optical storage and the formation of surface-relief gratings. Using Fourier transform infrared spectroscopy, we identified interactions involving SO3- groups from BY and NH3+ groups from PAH. These electrostatic interactions were responsible for the slow kinetics of writing in the optical storage experiments, due to a tendency to hinder photoisomerization and the subsequent reorientation of the azochromophores. The photoinduced birefringence did not saturate after one hour of exposure to the writing laser, whereas in azopolymer films, saturation is normally reached within a few minutes. on the other hand, the presence of such interactions prevented thermal relaxation of the chromophores after the writing laser was switched off, leading to a very stable written pattern. Moreover, the nanoscale interactions promoted mass transport for photoinscription of surface-relief gratings on PAH/BY LBL films, with the azochromophores being able to drag the inert PAH chains when undergoing the trans-cis-trans photoisomerization cycles. A low level of chromophore degradation was involved in the SRG photoinscription, which was confirmed with micro-Raman and fluorescence spectroscopies.

An analytical and numerical study of plane change maneuvers using aerodynamic force

The goal of the present work is to analyze space missions that use the terrestrial atmosphere to accomplish orbital maneuvers that involve a plane change. A set of analytical solutions is presented for the variation of the orbital elements due to a single passage through the atmosphere, assuming that the interval the spacecraft travels through the atmosphere is not too large. The study considers both the lift influence on the spacecraft orbit as well as drag. The final equations are tested with numerical integration and can be considered in accordance with the numerical results whenever the perigee height is larger than a critical value. Next, a numerical study of the ratio between the velocity increment required to correct the semimajor axis decay due to the atmospheric passage and the velocity variation required to obtain the change in the inclination is also presented. This analysis can be used to decide if a maneuver passing through the atmosphere can decrease the fuel consumption of the mission and, in the cases where this technique can be used, if a multiple passage is more efficient than a single passage.

Peculiar trajectories around the Lagrangian equilateral points

In the present work we analyse the behaviour of a particle under the gravitational influence of two massive bodies and a particular dissipative force. The circular restricted three body problem, which describes the motion of this particle, has five equilibrium points in the frame which rotates with the same angular velocity as the massive bodies: two equilateral stable points (L-4, L-5) and three colinear unstable points (L-1, L-2, L-3). A particular solution for this problem is a stable orbital libration, called a tadpole orbit, around the equilateral points. The inclusion of a particular dissipative force can alter this configuration. We investigated the orbital behaviour of a particle initially located near L4 or L5 under the perturbation of a satellite and the Poynting-Robertson drag. This is an example of breakdown of quasi-periodic motion about an elliptic point of an area-preserving map under the action of dissipation. Our results show that the effect of this dissipative force is more pronounced when the mass of the satellite and/or the size of the particle decrease, leading to chaotic, although confined, orbits. From the maximum Lyapunov Characteristic Exponent a final value of gamma was computed after a time span of 10(6) orbital periods of the satellite. This result enables us to obtain a critical value of log y beyond which the orbit of the particle will be unstable, leaving the tadpole behaviour. For particles initially located near L4, the critical value of log gamma is -4.07 and for those particles located near L-5 the critical value of log gamma is -3.96. (c) 2006 Elsevier B.V. All rights reserved.

Evaluation of Salmonella-Lytic Properties of Bacteriophages Isolated from Commercial Broiler Houses

Because of recent interest in bacteriophage therapy in poultry, information regarding the interaction of bacteriophages and potential host bacteria in the environment should be collected. The present studies were initiated with a rather typical commercial broiler integrator within the south-central United States to examine environmental Salmonella levels in two broiler complexes, attempt to isolate Salmonella-lytic bacteriophages, and elucidate a possible reason for differing apparent Salmonella prevalence. Significantly ( P<0.05) less Salmonella was isolated from houses in complex 1 ( 15/44 [ 34%] Salmonella-positive drag swabs) as compared to houses in complex 2 ( 22/24 [ 92%]). A total of seven Salmonella-lytic bacteriophages were isolated from Salmonella-positive environments, and two bacteriophages were isolated from a single Salmonella-negative house. During the initial bacteriophage isolation, individual bacteriophages did not replicate in the Salmonella host isolated from the same environment, and lysis of additional Salmonella hosts relied on high numbers of bacteriophage to be present. This suggests that the presence of these bacteriophages in the environment of a commercial broiler house had little to no effect on the presence of Salmonella. This study highlights the need to find additional bacteriophage sources, more effective isolation methods, and more innovative approaches to using bacteriophages to treat enteric disease.

The effects of wet suits on physiological and biomechanical indices during swimming

The objectives of this study were to verify the effects of wet suits (WS) on the performance during 1500m swimming (V1500), on the velocity corresponding to the anaerobic threshold (VAT) and on the drag force (AD) as well as its coefficient (Cx). 19 swimmers randomly completed the following protocols on different days (with and without WS): 1) maximal performance of 1500m swimming; 2) VAT in field test, with fixed concentration of blood lactate (4 mM) and 3) determination of hydrodynamic indices (AD and Cx). The results demonstrated significant differences (p < 0.05) in the VAT (1.27±0.09; 1.21±0.06 m.s-1), and in the V1500 (1.21±0.08; 1.17±0.08 m.s-1), with and without WS, respectively. However the AD, and its Cx did not present significant differences (p>0.05) for the respective maximal speeds of swimming. In summary, we can conclude that WS allows swimmers to reach greater speeds in both, long- and short-course swims. This improvement can be related to the decrease of the AD, since with higher speeds (with WS) the subjects presented the same resistance, as they did when compared to speeds without a WS. Moreover, these data suggest that the methodology used in this study to determine the Cx is unable to detect the improvement caused by WS.

Mechanisms of surface-relief gratings formation in layer-by-layer films from azodyes

Surface-relief gratings are photoinscribed on ionically adsorbed layer-by-layer (LBL) films of an azodye, Brilliant Yellow (BY), which was layered alternately with a polyelectrolyte. Photoinscription is performed by impinging an interference pattern of p- or s-polarized laser light with moderate intensity onto the LBL film, which is unlikely to cause thermal effects. Large-scale mass transport occurs due to the force associated with the field gradient of the light pattern. The ionic interactions between adjacent layers appear to provide the means for the chromophores to drag the polymer chains upon photoizomerization. LBL films were produced from two different polyelectrolytes and under two distinct pH values leading to markedly different film properties especially concerning photodegradation. Exposure to the laser light, for instance, leads to higher photodegradation in the poly(dimethyl diallylammonium chloride)/BY system, in comparison to the poly(allylamine hydrochloride)/BY films. Mass transport in the latter case is predominantly light-driven, which is consistent with the higher amplitude of modulation for p-polarized light (70 nm) compared to that caused by s-polarized light (18 nm). © 2003 Elsevier Ltd. All rights reserved.

Effects of electroplated zinc-nickel alloy coatings on the fatigue strength of AISI 4340 high strength steel

It is well known that fatigue behaviour is an important parameter to be considered in mechanical components subjected to constant and variable amplitude loadings. In combination with corrosion phenomenon, fatigue effects were responsible for proximally 64% of fails that occur in metallic parts of aeronautical accidents in the last 30 years. Recovered substrates have been extensively used in the aerospace field. Cadmium electroplating has been widely applied to promote protective coatings in aeronautical components, resulting in excellent corrosion protection combined with a good performance in cyclic loading. Ecological considerations allied to the increasing demands for corrosion resistance, resulted in the search for possible alternatives. Zinc-nickel alloys received considerable interest recently, since these coatings showed some advantages such as a good resistance to white and red rust, high plating rates and acceptation in the market. In this study the effects of zinc-nickel coatings electroplated on AISI 4340 high strength steel were analysed on rotating bending and axial fatigue strength, corrosion and adhesion resistance. Compressive residual stress field was measured by a X-ray tensometry prior to fatigue tests. Optical microscopy images showed coating thicknesses, adhesion and the existence of an uniform coverage of nearly all substrates. The fractured fatigue specimens were investigated using a scanning electron microscope. Three different zinc-nickel coating thicknesses were tested and comparison with rotating bending fatigue data from specimens cadmium electroplated and heat treated at 190°C for 3, 8 and 24 hours to avoid the diffusion of hydrogen in the substrate, was performed. Experimental results showed effect of coatings on the AISI 4340 steel behaviour when submitted to fatigue testing and the existence of coating thickness influence on the fatigue strength.

The balloon flights in the tropics of the hibiscus project

HIBISCUS is a project for studying the dynamics, microphysics and chemistry of the Tropical Tropopause Layer based on balloon measurements. Thirteen heavy sondes and 18 short duration balloons of different types have been used for local process studies. Eight superpressure (BP) and 3 Infra Red Montgolfier (MIR) long duration balloons have been flown for extending the investigations at global scale around the world. Overall the campaign has been very successful operationally as well as scientifically. The paper provides a description of the balloons, the instruments and the strategy used for meeting at best the goals of the project.