Cross-layer opportunistic adaptation for voice over ad hoc networks

The support of voice communication is fundamental in the deployment of an ad hoc network for the battlefield or emergency response. We use the QoS requirements of voice to identify factors influencing its communication, and validate their significance through statistical analysis. Based on the results, we propose an opportunistic protocol within a cross-layer framework that adapts these factors at different time scales. Hop-by-hop adaptation exploits the PHY/MAC interaction to improve the use of the spectral resources through opportunistic rate-control and packet bursts, while end-to-end adaptation exploits the LLC/application interaction to control the demand per call through voice coding and packet size selection. Our objective is to maximize the number of calls admitted while minimizing loss of quality. We evaluate the performance of the protocol in simulation with real audio traces using both quantitative and mean opinion score (MOS) audio quality metrics, comparing to several standard voice codecs. The results indicate that: (i) compression and packet-size selection play a critical role in supporting QoS over ad hoc networks; (ii) header compression is needed to limit the overhead per packet especially over longer paths; (iii) good voice quality is achieved even in strenuous network conditions.     

Distinguishing the role of eating disturbance from depression in the sex role self-perceptions of anorexic and bulimic inpatients.

Previous research has linked specific sex role self-perceptions to two major eating disorders: anorexia nervosa and bulimia. To date, however, sex role self-perceptions and ideals unique to eating disturbance have not been distinguished from those related to depression and other concomitant psychopathology. The Bem Sex-Role Inventory was administered twice (self-ratings and ideal self-ratings) to 83 women: 37 eating disorder inpatients, 12 depressed inpatients, and 34 high school and college students. Results indicate that both patient groups scored significantly lower (p?p?     

An Adaptive Generalized Transmission Protocol for Ad Hoc Networks

Wireless networking and group communication in combination allows groups of dispersed mobile users to collaborate. This paper presents AGENT, a medium access control (MAC) protocol that unifies point-to-point and multi-point transmission services to facilitate group communication in ad hoc networks. Analysis and experiments performed in a simulated ad hoc network demonstrate that AGENT exhibits reliable and stable performance with high spatial bandwidth reuse. Moreover, variation in the proportion of point-to-point and multi-point traffic is shown to have little impact on the overall performance of AGENT. Comparison with the other tested MAC protocols reveals that the performance of AGENT is superior, achieving higher channel utilization and lower access delay.     

Co-Precipitation Method for the Preparation of Nanocrystalline Ferroelectric SrBi<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript> Ceramics

A simple co-precipitation technique had been successfully applied for the preparation of pure ultrafine single phase SrBi₂Nb₂O₉. Ammonium hydroxide and ammonium oxalate were used to precipitate Sr^{2 +}, Bi³⁺ and Nb⁵⁺ cations simultaneously. No pyrochlore phase was found while heating powder at 850C and pure SrBi₂Nb₂O₉ (SBN) phase was formed as revealed by the X-ray diffraction (XRD) studies. Particle size and morphology was studied by transmission electron microscopy (TEM). The room temperature dielectric constant at 1 kHz is 100. The ferroelectric hysteresis loop parameters of these samples were also studied.     

Solid Phase Enhanced Direct Spectrofluorometric Determination of Polychlorinated Biphenyls (PCBs) in Natural Waters

A method of detection of PCBs in water, based on extraction/concentration with chips cut from an SPE disk-shaped C18 inverse phase coupled with a fluorescence detection and quantification directly on the phase has been evaluated. Experiments were performed with PCBs congeners IUPAC N° 3, 35, 67 and 169. Within the experimental conditions used : Hitachi F-4500 fluorometer, band-paths: 2.5 nm and extraction time: 60 min. the limits of detection were estimated to be respectively : 0.07, 0.4, 0.3 and 0.2 ppb. These values are within the range of PCB concentrations found in highly polluted waters and thus confer some interest to the method. However its sensitivity is not sufficient for application to moderately polluted natural water and the method needs some further improvements. Moreover, fluorescence quenching by humic substances was shown to substantially affect PCB's fluorescence intensity and must be taken into consideration for quantitative analysis.     

Using local conditions to reduce control overhead

In this paper, we replace the periodic transmission of control information by transmissions that depend on local network conditions. As a case study, we consider the proactive link state routing protocol OLSR running in a wireless network without infrastructure. Each node maintains a time series on its betweenness, a metric widely used in social network analysis. We interpret an anomaly in a node’s time series as a change in its role and use it to trigger the transmission of link state. In order to ensure throughput does not degrade by the use of dated information, we use a keep-alive timer whose interval takes into account other local conditions including the node speed, packet arrival rate, and number of flows served. We also measure the number of local link breaks and use it to trigger the transmission of neighbour information. ns-2 simulations comparing our proposed A⁺-OLSR to OLSR, A-OLSR, and Adaptive OLSR show a statistically significant increase in throughput and a decrease in control overhead. Our evaluation also considers packet losses and the use of CRAWDAD wireless traces to drive node movement.     

Synthesis of nanocrystalline SnO<Subscript>2</Subscript> powder at 100°C

A simple gel to crystal conversion route has been followed for the preparation of nanocrystalline SnO₂ at 80–100°C under refluxing conditions. Freshly prepared stannic hydroxide gel is allowed to crystallize under refluxing and stirring conditions for 4–6 h. Formation of nano crystallites of SnO₂ is confirmed by X-ray diffraction (XRD) study. Transmission electron microscopic (TEM) investigations revealed that the average particle size is 30 nm for these powders.