Renato Mariz de Moraes

Nd isotopic study of the Neoproterozoic Mara Rosa Arc, central Brazil: implications for the evolution of the Brası́lia Belt

Abstract The Goias Magmatic Arc is a 0.9–0.64 Ga island arc underlying large areas of the western part of the Brasilia Belt, in central Brazil. It is exposed in two separate sections, known as the Arenopolis Arc in the south and the Mara Rosa Arc in the north. It is made of island arc volcanic–sedimentary sequences forming narrow NNE to NNW belts, separated from each other by tonalitic–granodioritic–granitic orthogneisses. All rocks are metamorphosed under upper greenschist to amphibolite facies conditions, but have kept major geochemical and isotopic features indicating the juvenile nature of the igneous protoliths. The meta-igneous and metasedimentary rocks are intruded by a number of late- to post-orogenic granites ( e Nd (850) ranging from +1.5 to +4.6, with T DM values between 1.0 and 1.1 Ga. Metasedimentary rocks in the Mara Rosa supracrustal belts display geochemical features suggesting that they represent first cycle, immature sediments which preserve chemical characteristics of their igneous sources. Their Nd isotopic characteristics support this interpretation. T DM model ages for detrital metasediments are mostly in the interval between 0.9 and 1.2 Ga, indicating that they are a product of erosion of the arc rocks. The absence of older contributions to these sediments seems to indicate an intraoceanic setting. This is also suggested by the Nd isotopic composition of the ≈0.8 Ga old tholeiitic amphibolites, which display positive initial e Nd (+4.9), indicating derivation from a depleted mantle source. Syn–orogenic deformed granites forming small intrusions within the supracrustal belts have T DM ages ranging from 0.77 to 2.54 Ga. The older model age values indicate the presence of hidden fragments of ancient crust, which were probably tectonically interleaved with younger rocks during accretion of the arc. The post-orogenic granites are moderately peraluminous and the Nd model ages between 1.0 and 1.3 Ga indicate that their parental magmas were predominantly re-melts of the arc rocks. Their peraluminous nature reflects the incorporation of substantial amounts of arc sediments in the original magma. Garnet-whole rock Sm–Nd ages for the metasediments may be interpreted to refer to two metamorphic events: an older event at ≈0.76–0.73 Ga and a younger event at ≈604–610 Ma. Mineral chemistry indicate that the older episode was characterized by higher P/T and the younger by lower P/T . The older metamorphic event is interpreted preliminarily as the result of the accretion of island arc terranes to the western edge of the orogen and the younger event, as a result of final ocean closure and continental collision between the Amazon and Sao Francisco continents. The Goias Arc formation and accretion is partially coeval with Rodinia break up, suggesting that the western margin of the Sao Francisco–Congo was peripheral in that supercontinent and faced a wide oceanic basin during most of the Neoproterozoic.

Mobility–capacity–delay trade-off in wireless ad hoc networks

We show that there is a trade off among mobility, capacity, and delay in ad hoc networks. More specifically, we consider two schemes for the mobility of nodes in ad hoc networks. We divide the entire network into cells whose sizes can vary with the total number of nodes or whose size is independent of the number of nodes. By restricting the movement of nodes within these cells, we calculate throughput and delay for randomly chosen pairs of source-destination nodes, and show that mobility is an entity that can be exchanged with capacity and delay. We also investigate the effect of directional antennas in a static network in which packet relaying is done through the closest neighbor, and verify that this approach attains better throughput than static networks employing omnidirectional antennas.

A comparative analysis of AODV route recovery mechanisms in wireless Ad Hoc networks

This work investigates the behavior of the Ad Hoc On-Demand Distance Vector (AODV) routing protocol in situations of link failures due to the mobility of nodes and consequent route recovery in ad hoc networks. Here, the AODV performance is compared when the failure repair happens locally, at the node before the link break, to the case where the repair is started from the source node considering three performance metrics: packet delivey fraction, overhead and packet delivery delay. It was observed that for source repair the packet delivery fraction has better performance, while overhead and delay were better for local repair, in the sparse network and low traffic scenarios studied. For the denser network cases, it was observed that the source repair mechanism behaves better for overhead and delay metrics. These results are important to applications that tolerate few losses but are more restringent to delay and suggest that either one or another recovering mechanism may be used depending on the network parameters and user application information, instead of adopting a hybrid recovery implementation of both mechanisms based only on the number of hops between the link break and the destination as described in the AODV protocol Request for Comments (RFC).

A Proposal to Stabilize the Random Waypoint Mobility Model for Ad Hoc Network Simulation

It has been recently shown that the instantaneous average node speed for the random waypoint (RWP) mobility model may not reach a steady state regime due to velocity gradual decaying which can cause inaccurate results in simulations and communication protocol validations for mobile ad hoc networks (MANETs). This paper presents a modification to the RWP model, in which we propose to choose node speeds from a BETA(2,2) distribution, demonstrating analytically and by simulations that our idea stabilizes the instantaneous average node speed and consequently other important network metrics, like control overhead, number of dropped data packets and delivery delay. The proposal of alteration not only eliminates the decaying problem of the average node speed but also provides average values closer to the commonly supposed average velocity

LatinCon05 - Comparative Analysis of AODV Route Recovery Mechanisms in Wireless Ad Hoc Networks

\frac{V_{max}+V_{min}}{2}

A new distributed cooperative MIMO scheme for mobile ad hoc networks

than those of the original RWP model. In addition, the proposed change for the RWP model can be readily incorporated into network simulators.

Evaluation of link lifetime for the Random Waypoint mobility model

This work investigates the behavior of the Ad Hoc On-Demand Distance Vector (AODV) routing protocol in situations of link failures due to the mobility of nodes in wireless ad hoc networks. The AODV performance is compared when the failure repair happens locally from the node before the link break to the case where the repair is performed from the source node for four metrics: throughput (as packet delivery fraction), overhead, average packet delivery delay and average hop count, the last being only used to validate throughput and delay analyses. From the scenarios studied, it was observed that the throughput and delay for source repair have better performance, while overhead was better for local repair in sparse networks.

Dynamic Timed Energy Efficient and Data Collision Free MAC Protocol for Wireless Sensor Networks

In this paper, we introduce a new communication scheme based on cooperative multiple-input multiple-output (MIMO) communication for mobile ad hoc networks (MANETs) in which nodes are endowed with M antennas. According to our new approach, adjacent nodes no longer interfere with each other but rather cooperate attempting to communicate concurrently. In our scheme, during transmissions, the nodes send packets from only one of their antennas, while during reception, they use all of their antennas to receive and decode packets from multiple close nodes simultaneously. Therefore, each distributed MIMO system in this scheme consists of multiple transmitting nodes acting as a single-array of multiple antennas. We derive upper and lower bounds on the receiver node ergodic capacity in the network where the wireless channel is modeled with both large and small-scale fluctuations. These bounds are compared with Monte-Carlo simulation of point-to-point and cooperative MIMO communications in MANETs. We demonstrate that the capacity of MANETs with multiple antennas is improved using cooperation compared to non-cooperative schemes, i.e., point-to-point MIMO communication. In addition, under the above communication model, we demonstrate that the lower and upper bounds of the ergodic capacity grows linearly with the number of receiving antennas M.

Channel capacity in dense MANETs for a propagation model considering the law of conservation of energy and fading

We propose an analytical expression to evaluate the distribution of link lifetimes in a mobile ad hoc network (MANET) under the Random Waypoint mobility model. We compare this model with a model found in the literature to derive residual link lifetimes. From the derived model, numerical results are evaluated and compared. We found that the residual link lifetime has link durations that last longer for the mobility in steady-state regime and can be used to appropriately devise new communication protocols for MANETs.

Capacity of MIMO MANETs with cooperation

This article proposes a new data collision free medium access control protocol for wireless sensor networks in automation environments based on time division multiple access (TDMA) with duty cycling, which presents less energy consumption than the S-MAC protocol while maintain high data throughput. The new protocol employs single channel and a carrier sense approach. Simulation results are presented and show how the new proposal outperforms the S-MAC protocol.