Sergio de Oliveira

Direct production of carbon nanotubes/metal nanoparticles hybrids from a redox reaction between metal ions and reduced carbon nanotubes.

A method to decorate single-walled and multiwalled carbon nanotubes (CNTs) with metal nanoparticles (NPs) based on the formation of a CNT polyelectrolyte is reported. Such a method does not rely on CNT surface functionalization or the use of surfactants. It has been tested for gold (Au) and palladium (Pd). The resulting hybrids present metal NPs highly dispersed along the tube walls and with small size dispersion. The average diameters of the Au and Pd NPs were approximately 5 and approximately 3 nm, respectively. This method paves the way for large-scale decoration of CNTs with metal NPs.

An adaptive security management model for emergency networks

In disasters and emergency scenarios, due to a lack of network infrastructure, first-responders can build mobile ad hoc networks to send information and help disaster response coordination. However, the communication in these situations can suffer from long interruptions. This paper proposes a security management framework to dynamically configure or reconfigure emergency networks, in order to adapt the use of security components according to management information received by the decision-maker entities. The security management model includes the definition of security levels, the management information base, protocol messages and events. The emergency network activates the security mechanisms only when necessary, which avoid attacks effects and save resources.

Nano-engineered composites: interlayer carbon nanotubes effect

The concept of carbon nanotube interlayer was successfully introduced to carbon fiber/epoxy composites. This new hybrid laminated composites was characterized by Raman spectroscopy, X-ray diffraction, scanning electron microscopy and tensile tests. An increase on peak stress close to 85% was witnessed when CNTs interlayer with 206.30 mg was placed to carbon fiber/epoxy laminates. The failure mechanisms are associated to CNTs distribution between and around carbon fibers. These CNTs are also responsible for crack bridging formation and the increase on peak stress. Initial stiffness is strongly affected by the CNT interlayer, however, changes on stiffness is associated to changes on nano/micro-structure due to damage. Three different behaviors can be described, i.e. for interlayers with ≈ 60 mg of CNT the failure mode is based on cracks between and around carbon fibers, while for interlayers with CNT contents between 136 mg and 185 mg cracks were spotted on fibers and inside the CNT/matrix mix. Finally, the third failure mechanism is based on carbon fiber breakage, as a strong interface between CNT/matrix mix and carbon fibers is observed.

(CIA) 2 -ITS: Interconnecting mobile and ubiquitous devices for Intelligent Transportation Systems

This work-in-progress article presents the research objectives of the (CIA)2-ITS workgroup of the Brazilian project consortium called (CIA)2. The workgroup is developing an architecture and protocols to integrate the heterogeneous networks and devices that compose a city-wide (or even nation-wide) Intelligent Transportation System (ITS). The ITS architecture will support networks of wireless sensors and actuators, smart vehicle communication as well as PCs and PDAs generating and requesting ITS-related information. This network will be open, thus gaining more functionality and data as users and the government “log into” the system.

A policy based security management architecture for sensor networks

Wireless sensor networks are subjected to several types of attacks specially attacks of denial of service types (DoS). Several mechanisms and techniques were proposed to provide security to wireless sensor networks, like cryptographic process, key management protocols, intrusion detection systems, node revocation schemas, secure routing, and secure data fusion. A recent work proposes a security management framework to dynamically configure and reconfigure security components in sensor networks according to management information collected by sensor nodes and sent to decision-maker management entities. It turns on or off security components only when they are necessary, saving power and extend network lifetime. The architecture is policy based, what enable rules configuration specific for each application. We evaluate that security management framework, showing possibilities to save power and how that work can contribute to extend network lifetime. We propose some scenarios to evaluate the performance of the security management framework and estimate the cost of security components.

Social networks for certification in Vehicular Disruption Tolerant Networks

Vehicular Disruption Tolerant Networks appear due to the search of information by drivers, which build mobile ad hoc networks that may suffer from long interruptions. This paper proposes a certification mechanism by means of social networks, enabling cars to share keys through direct contacts between two acquaintances that warrant their identity, so they sign a reciprocal certificate. Certificates signed by a third party can be validated if the users public key is available to the other party. Further, the reputation mechanism can identify certificates of trusted users. The evaluation shows the behavior of a vehicular network that uses certificates in social networks as cryptographic security mechanism to establish a degree of trust between users.

Multiphase intrusion detection and revocation system for wireless sensor networks

Wireless sensor networks are subjected to several types of attacks specially attacks of denial of service types (DoS). A previous work proposes a routing strategy that considers alternative routes aiming to increase the resilience to the intrusion and allow efficient intrusion detection. This paper shows a revocation approach to reduce the number of intruders and enable new detection phase after a new route establishment phase. After the revocation, new intruders can be detected and revoked by their turn, minimising its effects over the network. After some turns, all of effective intruders can be revoked. The performance of the proposed approach was verified by simulation studies.

Veia gástrica posterior: hipertensão porta

The posterior gastric vein has not been mentioned very often neither in anatomy textbooks nor in portal hypertension papers. The authors studied the anatomy, frequency and confluence of this vein because is a huge variety in the presentation of esophageal varices. Twenty-six adult preserved corpses (twenty females and six males) had a wide abdominal incision allowing the dissection of the portal system, identifying the frequency and confluence of its tributaries, notably the posterior gastric vein. The portal vein, in all cases, was formed by the confluence of the superior mesenteric vein with the splenic vein and had a mean length of 6.4 cm. The splenic vein had a mean length of 6.5 cm. The left gastric vein was tributary of the portal vein in 50% of the cases and in 30% of the cases in the splenic vein. The right gastric vein had its confluence to portal vein in 30 % of the cases and to the splenic vein in 4 %. The inferior mesenteric vein was tributary of the splenic vein in 54% of the cases and in the superior mesenteric vein in 46%. The left gastro-omental vein had its confluence to the splenic vein in 50% of the cases and to the inferior polar vein in 34 %. The middle colic vein had its confluence to superior mesenteric vein in 42% of the cases, to inferior mesenteric vein in 12% and to splenic vein in 8%. The posterior gastric vein was found in 54% of the corpses, and in all cases it was a tributary of the splenic vein, in retropancreatic position, coming from the esophageal-gastric junction. These findings agree with previous papers describing a prevalence of 60% of posterior gastric vein in patients submitted to surgery in portal hypertension, and in all cases, this vein was tributary of the splenic vein. The identification of this vein may influence the treatment, because if left untied during cases of portal-azigos disconnection, they may predispose to postoperative bleeding, but in cases of splenorenal anastomosis may preserve its patency in cases of anastomosis occlusion, or can lead again to postoperative bleeding feeding the esophageal varices. To ligate or not this vein will depends on the surgeon s experience and common sense. Regarding to previous papers and to this data presented here, the authors believe that the prevalence of this vein is between 50 and 60% in the population.