198,645 research outputs found
Focused beam routing protocol for underwater acoustic networks
No full textMulti-hop transmission is considered for large coverage areas in bandwidth-limited underwater acoustic networks. In this paper, we present a scalable routing technique based on location information, and optimized for minimum energy per bit consumption. The proposed Focused Beam Routing (FBR) protocol is suitable for networks containing both static and mobile nodes, which are not necessarily synchronized to a global clock. A source node must be aware of its own location and the location of its final destination, but not those of other nodes.
The FBR protocol can be defined as a cross-layer approach, in which the routing protocol, the medium access control and the physical layer functionalities are tightly coupled by power control. It can be described as a distributed algorithm, in which a route is dynamically established as the data packet traverses the network towards its final destination. The selection of the next relay is made at each step of the path after suitable candidates have proposed themselves.
The system performance is measured in terms of energy per bit consumption and average packet end-to-end delay. The results are compared to those obtained using pre-established routes, defined via Dijkstra's algorithm for minimal power consumption. It is shown that the protocol's performance is close to the ideal case, as the additional burden of dynamic route discovery is minimal
On Joint Frequency and Power Allocation in a Cross-Layer Protocol for Underwater Acoustic Networks
No full textPath loss in an underwater acoustic channel depends not only on the transmission distance, but also on the signal frequency. As a result, the useful bandwidth decreases with distance, a feature not normally present in terrestrial radio networks. This fact motivates the use of multihop communications in an acoustic network, and strongly influences its design, since the same set of protocols will exhibit different performance when operating in a different frequency range. Multihop transmission is considered for large area coverage in acoustic networks, with an eye towards efficient power and bandwidth allocation. Power control is used as a practical means of optimizing the overall performance across the physical, medium access control (MAC) and routing layers. A geographic routing technique, called the focused beam routing (FBR), which requires each node to know only its own location and that of the final destination, is coupled with the distance aware collision avoidance protocol, which regulates the channel access. Results show that the average energy per bit consumption is reduced by adjusting the power, center frequency, and bandwidth in accordance with the network node density. Specifically, as the density increases, greater bandwidths offer per-hop energy reduction as well as a reduced packet collision rate.United States. National Oceanic and Atmospheric Administration (Sea Grant NA060AR4170019)National Science Foundation (U.S.) (grant 0520075)National Science Foundation (U.S.) (grant 0831728
Underwater sensor networks: applications, advances and challenges
No full textThis paper examines the main approaches and challenges in the design and implementation of underwater wireless sensor networks. We summarize key applications and the main phenomena related to acoustic propagation, and discuss how they affect the design and operation of communication systems and networking protocols at various layers. We also provide an overview of communications hardware, testbeds and simulation tools available to the research community
Idle-time energy savings through wake-up modes in underwater acoustic networks
No full textInterest in underwater sensor networks has increased recently due to the possibility of using autonomous underwater vehicles and sensors to explore the oceans and monitor underwater equipment. Such networks, due to the need for long term deployments, must be energy efficient, like their terrestrial counterparts. However, there are fundamental differences between radio interfaces and acoustic modems, both in terms of achievable performance (e.g. bit rate and latency) and in terms of energy consumption (i.e. transmit power, receive power, sleep power, etc.). These differences may cause techniques that are highly effective for radios to perform poorly in acoustic scenarios. This paper considers asynchronous idle-time power management techniques and the effects of acoustic modem properties on the optimal solutions. Specifically, we compare two main techniques, a sleep cycling solution and a wakeup mode solution. We show that for traffic rates of greater than one packet every few hours, using a wakeup mode may be the most efficient way to save energy
Exploiting the Bandwidth-Distance Relationship in Underwater Acoustic Networks
No full textIn this paper we study the relationship between effective use of the available bandwidth, energy consumption, and transmission delay in a Underwater Wireless Acoustic Sensor Network (UWASN). We compare different solutions to transport data to a sink node, namely multihop transmissions through multiple relays and the use of direct relay-to-sink links that require more power but reach the sink in one hop. We also address the effects of different error control policies. Our analysis shows that the energy consumption can be traded off for delay by choosing different policies and by varying some key parameters in each policy
A Comparative Performance Evaluation of MAC Protocols for Underwater Sensor Networks
No full textA propagation-delay-aware MAC protocol, based on carrier sensing multiple access, is proposed. The design aims at maximizing the bandwidth utilization by keeping track of neighboring transmissions to avoid collisions, thus enabling interleaved packet transmission between different pairs of users. The performance is compared to several representative MAC protocols: the standard and slotted ALOHA, and three protocols designed specifically for the underwater acoustic environment, APCAP [1], DACAP [2] and T-Lohi [3]. Simulation results identify network settings (traffic load, node density, single/multi-hop topologies) in which each protocol offers the best performance. © 2008 IEEE
CD40 antisense oligonucleotide inhibition of trinitrobenzene sulphonic acid induced rat colitis
No full textBackground: CD154/CD40 interactions play a pivotal role both in humoral and cellular immune responses. Their involvement in the pathogenesis of chronic inflammatory bowel disease (IBD) has been revealed by increased expression of CD40 and CD154 in the inflamed mucosa of patients and the therapeutic effects of anti-CD154 antibodies in experimental colitis. Because of adverse side effects however, the use of such antibodies in patients with IBD may be limited. Aims: An alternative approach to blocking CD154/CD40 interactions by employing a CD40 antisense oligonucleotide (ODN) was explored. Results: After sequencing of the rat CD40 gene, five antisense ODNs were designed, of which one (rAS3) effectively downregulated CD40 expression in rat vascular smooth muscle cells as well as the subsequent changes in gene expression in response to CD40 stimulation. The therapeutic potency of rAS3 was evaluated in the 2,4,6-trinitrobenzene sulphonic acid (TNBS) induced colitis model of the rat. Single intracolonic injection of a liposomal formulation of rAS3 either prior to or post colitis induction markedly suppressed the inflammatory reaction in these animals monitored both macroscopically and microscopically over one week, while application of a scrambled control ODN had no such effects. Moreover, reverse transcription-polymerase chain reaction analyses revealed reduced expression of vascular cell adhesion molecule 1, interleukin 12 p40, and monocyte chemoatractive protein 1 in the inflamed mucosa, which in turn may have contributed to the decrease in leucocyte infiltration judged by immunohistochemistry. Conclusions: These results suggest that CD40 antisense ODNs effectively interfere with CD154/CD40 interactions in vivo and, therefore, may provide a novel approach to the treatment of patients with chronic IBD
Dr. Duane M. Jackson, Morehouse College, July 2011
No full textThis video is a conversation with Dr. Duane M. Jackson. Dr. Jackson talks about his paper, "Recall and the Serial Position Effect: The Role of Primacy and Recency on Accounting Students' Performance." Jackie Daniel, AUC Woodruff Library, is the interviewer
A tale of two partners: working with students during implementation of a new medical curriculum to enhance student experience
No full textPoster Presentation No. 347Introduction/Background: The University of Adelaide is sequentially rolling out a new 6-year Bachelor of Medical Studies/Doctor of Medicine (BMedSt/MD) program to replace the existing 6-year MBBS program. The pre-clinical structure (Y1-3) has undergone significant reform, with the curriculum changing from a spiral to a block model. The online structure within the learning management system has also required significant modification to provide an intuitive and engaging experience in a blended learning environment. To optimise the student experience, we prioritised working in partnership with students across this challenging transition.Dillon A, Billington A, Beckett E, Mingorance C, Stojanovic M, Katharesan V, Arnold M, Cann
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