Periodic and solitary waves in systems of coherently coupled nonlinear envelope equations

Exact solutions for two classes of coherently coupled nonlinear envelope equations are derived in terms of products of Jacobi elliptic functions. Physical applications are illustrated in the context of nonlinear optics, namely, polarization of light beams and quadratic (or parametric) solitons. Stabilities of these double-humped solitary pulses are studied by direct numerical simulations. The use of computer is crucial, both in terms of symbolic manipulation in the derivation process and in the implementation of numerical schemes in stability consideration. © 2010 Taylor & Francis.postprin

Fast-response Receiver-driven Layered Multicast

In this paper, a new layered multicast protocol, called Fast-response Receiver-driven Layered Multicast (FRLM), is proposed. The differences between our FRLM and the original RLM are only at the receivers. Our design allows the receivers to track the available network bandwidth faster; this enables the receivers to converge to their optimal number of subscribed layers quicker, and to respond to the network congestion prompter. An early trigger mechanism for shortening IGMP leave latency is also designed. We show that FRLM can avoid several potential problems with the original RLM, which have been overlooked previously. Last but not the least, FRLM is a practical scheme that can be readily implemented in today's best-effort Internet.published_or_final_versio

Maximizing multicast call acceptance rate in multi-channel multi-interface wireless mesh networks

In this paper, we consider the problem of constructing bandwidth-guaranteed multicast tree in multi-channel multi-interface wireless mesh networks. We focus on the scenario of dynamic multicast call arrival, where each call has a specific bandwidth requirement. A call is accepted if a multicast tree with sufficient bandwidth on each link can be constructed. Intuitively, if the carried load on both the most-heavily loaded channel and the most-heavily loaded node is minimized, the traffic load in the network will be balanced. If the network load is balanced, more room will be available for accommodating future calls. This would maximize the call acceptance rate in the network. With the above notion of load balancing in mind, an Integer Linear Programming (ILP) formulation is formulated for constructing bandwidth-guaranteed tree. We show that the above problem is NP-hard, and an efficient heuristic algorithm called Largest Coverage Shortest-Path First (LC-SPF) is devised. Simulation results show that LC-SPF yields comparable call acceptance rate as the ILP formulation, but with much shorter running time. © 2010 IEEE.published_or_final_versio

Fast-response receiver-driven layered multicast with multiple servers

Almost all the proposed layered multicast algorithms support a single server, i.e. a receiver can only subscribe to at most one server. A common restriction to single server approach Is that the maximum number of subscribed layers, as well as the maximum achievable throughput Is limited by the specific bottleneck link between a receiver and the server. In this paper, a new layered multicast protocol, called Fast-response Receiver-driven Layered Multicast with Multiple Servers (FRLM-MS) Is proposed. Our design allows a receiver to subscribe to more than one servers. A FRLM-MS receiver can benefit from multiple paths to the multiple servers, resulting In a higher achievable bandwidth. It In turn allows the receiver to have a higher layer subscription, and thus a better playback performance. © 2005 IEEE.published_or_final_versio

A joint routing and scheduling algorithm for efficient broadcast in wireless mesh networks

With the increasing popularity of wireless mesh networks (WMNs), broadcasting traffic (e.g. IP-TV) will contribute a large portion of network load. In this paper, we consider a multi-channel multi-interface WMN with real time broadcast call arrivals. Aiming at maximizing the call acceptance rate of the network, an efficient broadcast tree construction algorithm, called Schedule-based Greedy Expansion (S-Expand), is designed. Unlike the existing time fraction approach, which focuses on assigning time fractions to tree links to guarantee the existence of a feasible schedule, we follow the approach of joint routing and scheduling. The proposed S-Expand algorithm packs non-interfering transmissions to use the same time slots; this would allow more flexibility in accepting future calls. Simulation results show that S-Expand achieves higher call acceptance rate than the traditional time fraction approach. ©2010 IEEE.published_or_final_versionThe 2010 IEEE Wireless Communications and Networking Conference (WCNC), Sydney, Australia, 18-21 April 2010. In Proceedings of WCNC, 2010, p. 1-

Interface placement in constructing widest spanning tree for multi-channel multi-interface wireless mesh networks

Proceedings of the IEEE Wireless Communications and Networking Conference, 2009, p. 2560-2564Widest spanning tree is a broadcast tree with its bottleneck link bandwidth maximized. It provides a cost effective broadcasting solution in multi-channel multi-interface wireless mesh networks. To find the widest spanning tree, existing algorithms jointly consider channel assignment, routing and scheduling while assuming the number of network interface cards (NICs) at each node is given. In this paper, we treat the number of NICs at each node as a design parameter, whereas the total number of NICs in the system is given. By properly placing more NICs to more "critical" nodes, the bandwidth of the spanning tree can be further increased. To this end, a new Integer Linear Programming (ILP) is formulated for solving the widest spanning tree problem based on joint optimization of interface placement, channel assignment, routing and scheduling. Numerical results show that interface placement provides a significant boost to the bandwidth of the widest spanning tree found. © 2009 IEEE.published_or_final_versio

Interface placement in constructing widest spanning tree for multi-channel multi-interface wireless mesh networks

Proceedings of the IEEE Wireless Communications and Networking Conference, 2009, p. 2560-2564Widest spanning tree is a broadcast tree with its bottleneck link bandwidth maximized. It provides a cost effective broadcasting solution in multi-channel multi-interface wireless mesh networks. To find the widest spanning tree, existing algorithms jointly consider channel assignment, routing and scheduling while assuming the number of network interface cards (NICs) at each node is given. In this paper, we treat the number of NICs at each node as a design parameter, whereas the total number of NICs in the system is given. By properly placing more NICs to more "critical" nodes, the bandwidth of the spanning tree can be further increased. To this end, a new Integer Linear Programming (ILP) is formulated for solving the widest spanning tree problem based on joint optimization of interface placement, channel assignment, routing and scheduling. Numerical results show that interface placement provides a significant boost to the bandwidth of the widest spanning tree found. © 2009 IEEE.published_or_final_versio

J-CAR: An efficient channel assignment and routing protocol for multi-channel multi-interface mobile ad hoc networks

In Session: Wireless Ad Hoc and Sensor Networks towards Anytime Anywhere Internetworking: WSN-15: Resource Allocation: article no. WSN15-2We propose an efficient joint channel assignment and routing protocol (J-CAR) for multi-channel multi-interface mobile ad hoc networks (MANETs). Aiming at overcoming the limitations of the existing channel assignment and routing algorithms, J-CAR negotiates a channel at each active link during the route setup process. It has the following major features: a) a pre-determined common control channel is used by every node for routing and channel negotiation; b) control packets for data transmission (RTS, CTS & ACK) are carried by the associated data channels; c) the spare capacity on the control channel can be used for data transmission; d) an interface is free to change its working modes between send and receive; and e) an interface can tune to any data channels for data sending or receiving at the cost of switching overhead. With J-CAR, a more flexible assignment of interfaces, channels, and the working mode of each interface can be rendered. The performance gain brought by J-CAR is substantiated by extensive simulation results. © 2006 IEEE.published_or_final_versionProceedings of the Global Telecommunications Conference, 2006 (GLOBECOM 2006), San Francisco, CA, USA, 27 November - 1 December 200

Mass of galaxy lenses in modified gravity: any need for dark mass?

Using strong lensing data, Milgrom's modified Newtonian dynamics (MOND) and its covariant TeVeS (tensor-vector-scalar theory) are examined here as an alternative to the conventional ΛCDM paradigm. We examine 10 double-image, gravitational lensing systems in which the lens masses have been estimated by stellar population synthesis models. While mild deviations exist, we find no strong case of outliers to the TeVeS theory. © 2011 American Physical Society.published_or_final_versio

Validation of Statistical Models for Estimating Hospitalization Associated with Influenza and Other Respiratory Viruses

BACKGROUND: Reliable estimates of disease burden associated with respiratory viruses are keys to deployment of preventive strategies such as vaccination and resource allocation. Such estimates are particularly needed in tropical and subtropical regions where some methods commonly used in temperate regions are not applicable. While a number of alternative approaches to assess the influenza associated disease burden have been recently reported, none of these models have been validated with virologically confirmed data. Even fewer methods have been developed for other common respiratory viruses such as respiratory syncytial virus (RSV), parainfluenza and adenovirus. METHODS AND FINDINGS: We had recently conducted a prospective population-based study of virologically confirmed hospitalization for acute respiratory illnesses in persons <18 years residing in Hong Kong Island. Here we used this dataset to validate two commonly used models for estimation of influenza disease burden, namely the rate difference model and Poisson regression model, and also explored the applicability of these models to estimate the disease burden of other respiratory viruses. The Poisson regression models with different link functions all yielded estimates well correlated with the virologically confirmed influenza associated hospitalization, especially in children older than two years. The disease burden estimates for RSV, parainfluenza and adenovirus were less reliable with wide confidence intervals. The rate difference model was not applicable to RSV, parainfluenza and adenovirus and grossly underestimated the true burden of influenza associated hospitalization. CONCLUSION: The Poisson regression model generally produced satisfactory estimates in calculating the disease burden of respiratory viruses in a subtropical region such as Hong Kong