WFI Optimised PWGPS for Wireless IP Networks

The paper describes the design and analysis of a packet scheduler intended to operate over wireless channels with spatially selective error bursts. A particularly innovative aspect in the design is the optimization of the scheduler algorithm to minimize the worst-case fairness index (WFI) for real-time IP traffic.

Wavelets for the Analysis and Compression of Power System Disturbances

Wavelets introduce new classes of basis functions for time-frequency signal analysis and have properties particularly suited to the transient components and discontinuities evident in power system disturbances. Wavelet analysis involves representing signals in terms of simpler, fixed building blocks at different scales and positions. This paper examines the analysis and subsequent compression properties of the discrete wavelet and wavelet packet transforms and evaluates both transforms using an actual power system disturbance from a digital fault recorder. The paper presents comparative compression results using the wavelet and discrete cosine transforms and examines the application of wavelet compression in power monitoring to mitigate against data communications overheads.

Why does relativity allow quantum tunnelling to 'take no time'?

In quantum tunnelling, what appears to be an infinitely fast barrier traversal can be explained in terms of an Aharonov-like weak measurement of the tunnelling time, in which the role of the pointer is played by the particle's own coordinate. A relativistic wave packet is shown to be reshaped through a series of subluminal shifts which together produce an anomalous 'superluminal' result.

Is big best? Queen size, usurpation and nest closure in a primitively eusocial sweat bee (Lasioglossum malachurum).

For primitively eusocial insects in which a single foundress establishes a nest at the start of the colony cycle, the solitary provisioning phase before first worker emergence represents a risky period when other, nestless foundresses may attempt to usurp the nest. In the primitively eusocial sweat bee Lasioglossum malachurum (Hymenoptera, Halictidae), spring foundresses compete for nests which are dug into hard soil. Nest-searching foundresses (‘floaters’) frequently inspected nests during this solitary phase and thereby exerted a usurpation pressure on resident queens. Usurpation has been hypothesised to increase across the solitary provisioning phase and favour closure of nests at an aggregation, marking the termination of the solitary provisioning phase by foundresses, before worker emergence. However, our experimental and observational data suggest that usurpation pressure may remain constant or even decrease across the solitary provisioning phase and therefore cannot explain nest closure before first worker emergence. Levels of aggression during encounters between residents and floaters were surprisingly low (9% of encounters across 2 years), and the outcome of confrontations was in favour of residents (resident maintains residency in 94% of encounters across 2 years). Residents were significantly larger than floaters. However, the relationship between queen size and offspring production, though positive, was not statistically significant. Size therefore seems to confer a considerable advantage to a queen during the solitary provisioning phase in terms of nest residency, but its importance in terms of worker production appears marginal. Factors other than intraspecific usurpation need to be invoked to explain the break in provisioning activity of a foundress before first worker emergence.

Mapping the evolution of optically generated rotational wave packets in a room-temperature ensemble of D2

A coherent superposition of rotational states in D2 has been excited by nonresonant, ultrafast (12 fs), intense (2×1014 W cm-2) 800 nm laser pulses, leading to impulsive dynamic alignment. Field-free evolution of this rotational wave packet has been mapped to high temporal resolution by a time-delayed pulse, initiating rapid double ionization, which is highly sensitive to the angle of orientation of the molecular axis with respect to the polarization direction, . The detailed fractional revivals of the neutral D2 wave packet as a function of and evolution time have been observed and modeled theoretically.

An agent-based control mechanism for WFQ in IP networks

This paper presents a new packet scheduling scheme called agent-based WFQ to control and maintain QoS parameters in virtual private networks (VPNs) within the confines of adaptive networks. Future networks are expected to be open heterogeneous environments consisting of more than one network operator. In this adaptive environment, agents act on behalf of users or third-party operators to obtain the best service for their clients and maintain those services through the modification of the scheduling scheme in routers and switches spanning the VPN. In agent-based WFQ, an agent on the router monitors the accumulated queuing delay for each service. In order to control and to keep the end-to-end delay within the bounds, the weights for services are adjusted dynamically by agents on the routers spanning the VPN. If there is an increase or decrease in queuing delay of a service, an agent on a downstream router informs the upstream routers to adjust the weights of their queues. This keeps the end-to-end delay of services within the specified bounds and offers better QoS compared to VPNs using static WFQ. This paper also describes the algorithm for agent-based WFQ, and presents simulation results. (C) 2003 Elsevier Science Ltd. All rights reserved.

Single-Photon Excitation of Surface Plasmon Polaritons

We provide the quantum-mechanical description of the excitation of surface plasmon polaritons on metal surfaces by single photons. An attenuated-reflection setup is described for the quantum excitation process in which we find remarkably efficient photon-to-surface plasmon wave-packet transfer. Using a fully quantized treatment of the fields, we introduce the Hamiltonian for their interaction and study the quantum statistics during transfer with and without losses in the metal.

Rising time of entanglement between scattering spins

We investigate the time evolution of entanglement in a process where a mobile particle is scattered by static spins. We show that entanglement increases monotonically during a transient and then saturates to a steady-state value. For a quasimonochromatic mobile particle, the transient time depends only on the group velocity and width of the incoming wave packet and is insensitive to the interaction strength and spin number of the scattering particles. These features do not depend on the interaction model and can be seen in various physical settings.

A programmable architecture for layered multimedia streams in IPv6 networks

A new configurable architecture is presented that offers multiple levels of video playback by accommodating variable levels of network utilization and bandwidth. By utilizing scalable MPEG-4 encoding at the network edge and using specific video delivery protocols, media streaming components are merged to fully optimize video playback for IPv6 networks, thus improving QoS. This is achieved by introducing “programmable network functionality” (PNF) which splits layered video transmission and distributes it evenly over available bandwidth, reducing packet loss and delay caused by out-of-profile DiffServ classes. An FPGA design is given which gives improved performance, e.g. link utilization, end-to-end delay, and that during congestion, improves on-time delivery of video frames by up to 80% when compared to current “static” DiffServ.

A distributed contention-vector division multiple access (D-CVDMA) protocol for wireless networks

Traditional Time Division Multiple Access (TDMA) protocol provides deterministic periodic collision free data transmissions. However, TDMA lacks flexibility and exhibits low efficiency in dynamic environments such as wireless LANs. On the other hand contention-based MAC protocols such as the IEEE 802.11 DCF are adaptive to network dynamics but are generally inefficient in heavily loaded or large networks. To take advantage of the both types of protocols, a D-CVDMA protocol is proposed. It is based on the k-round elimination contention (k-EC) scheme, which provides fast contention resolution for Wireless LANs. D-CVDMA uses a contention mechanism to achieve TDMA-like collision-free data transmissions, which does not need to reserve time slots for forthcoming transmissions. These features make the D-CVDMA robust and adaptive to network dynamics such as node leaving and joining, changes in packet size and arrival rate, which in turn make it suitable for the delivery of hybrid traffic including multimedia and data content. Analyses and simulations demonstrate that D-CVDMA outperforms the IEEE 802.11 DCF and k-EC in terms of network throughput, delay, jitter, and fairness.

Synchrophasor Broadcast over Internet Protocol for Distributed Generator Synchronization

Synchronous islanded operation involves continuously holding an islanded power network in virtual synchronism with the main power system to aid paralleling and avoid potentially damaging out-of-synchronism reclosure. This requires phase control of the generators in the island and the transmission of a reference signal from a secure location on the main power system. Global positioning system (GPS) time-synchronized phasor measurements transmitted via an Internet protocol (IP) are used for the reference signal. However, while offering low cost and a readily available solution for distribution networks, IP communications have variable latency and are susceptible to packet loss, which can make time-critical control applications difficult. This paper investigates the ability of the phase-control system to tolerate communications latency. Phasor measurement conditioning algorithms that can tolerate latency are used in the phase-control loop of a 50-kVA diesel generator. © 2010 IEEE.

A Scalable and Programmable Modular Traffic Manager Architecture

A key issue in the design of next generation Internet routers and switches will be provision of traffic manager (TM) functionality in the datapaths of their high speed switching fabrics. A new architecture that allows dynamic deployment of different TM functions is presented. By considering the processing requirements of operations such as policing and congestion, queuing, shaping and scheduling, a solution has been derived that is scalable with a consistent programmable interface. Programmability is achieved using a function computation unit which determines the action (e.g. drop, queue, remark, forward) based on the packet attribute information and a memory storage part. Results of a Xilinx Virtex-5 FPGA reference design are presented.

Evidence for progressive Holocene aridification in southern Africa recorded in Namibian hyrax middens: Implications for African Monsoon dynamics and the

Presented here are stable nitrogen isotope data from a rock hyrax (Procavia capensis) middens from northwestern Namibia that record a series of rapid aridification events beginning at ca. 3800 cal yr BP, and which mark a progressive decrease in regional humidity across the Holocene. Strong correlations exist between this record and other terrestrial and marine archives from southern Africa, indicating that the observed pattern of climate change is regionally coherent. Combined, these data indicate hemispheric synchrony in tropical African climate change during the Holocene, with similar trends characterising the termination of the 'African Humid Period' (AHP) in both the northern and southern tropics. These findings run counter to the widely accepted model of direct low-latitude insolation forcing, which requires an antiphase relationship to exist between the hemispheres. The combined dataset highlights: 1) the importance of forcing mechanisms influencing the high northern latitudes in effecting low-latitude climate change in Africa, and 2) the potential importance of solar forcing and variations in the Earth's geomagnetic shield in determining both long-term and rapid centennial-scale climate changes, identifying a possible mechanism for the variations marking the AHP termination in both the southern and northern tropics. (C) 2010 University of Washington. Published by Elsevier Inc. All rights reserved.

Weakly nonlinear vertical dust grain oscillations in dusty plasma crystals in the presence of a magnetic field

The weakly nonlinear regime of transverse paramagnetic dust grain oscillations in dusty (complex) plasma crystals is discussed. The nonlinearity, which is related to the sheath electric/magnetic field(s) and to the intergrain (electrostatic/magnetic dipole) interactions, is shown to lead to the generation of phase harmonics and, in the case of propagating transverse dust-lattice modes, to the modulational instability of the carrier wave due to self-interaction. The stability profile depends explicitly on the form of the electric and magnetic fields in the plasma sheath. The long term evolution of the modulated wave packet, which is described by a nonlinear Schrodinger-type equation, may lead to propagating localized envelope structures whose exact forms are presented and discussed. Explicit suggestions for experimental investigations are put forward. (C) 2004 American Institute of Physics.

Nonlinearly coupled whistlers and dust-acoustic perturbations in dusty plasmas

The nonlinear interaction between magnetic-field-aligned coherent whistlers and dust-acoustic perturbations (DAPs) in a magnetized dusty plasma is considered. The interaction is governed by a pair of equations consisting of a nonlinear Schrodinger equation for the modulated whistler wave packet and an equation for the nonresonant DAPs in the presence of the ponderomotive force generated by the whistlers. The coupled equations are employed to investigate the occurrence of modulational instability, in addition to the formation of whistler envelope solitons. This investigation is relevant to amplitude modulated electron whistlers in magnetized space dusty plasmas. (c) 2005 American Institute of Physics.