Experiences with high definition interactive video conferencing

We review the design and implementation of UltraGrid, a new high definition video conferencing system, and present some experimental results. UltraGrid was the first system to support gigabit rate high definition interactive video conferencing on commodity systems and networks, and we present measurements to illustrate behavior of production networks subject to such real time traffic. We illustrate the benefits of hybrid IP/provisioned optical networks over best effort IP networks for this class of traffic, and motivate the development of congestion control algorithms for interactive conferencing on best effort IP networks

Mapping the dynamic interactions between vortex species in highly anisotropic superconductors

Here we use highly sensitive magnetisation measurements performed using a Hall probe sensor on single crystals of highly anisotropic high temperature superconductors $Bi_{2}Sr_{2}CaCu_{2}O_{8}$ to study the dynamic interactions between the two species of vortices that exist in such superconductors. We observe a remarkable and clearly delineated high temperature regime that mirrors the underlying vortex phase diagram. Our results map out the parameter space over which these dynamic interaction processes can be used to create vortex ratchets, pumps and other fluxonic devices.Comment: 7 pages, 3 figures, to be published in Supercond. Sci. Techno

The role of spatial and temporal radiation deposition in inertial fusion chambers: the case of HiPER¿

The first wall armour for the reactor chamber of HiPER will have to face short energy pulses of 5 to 20 MJ mostly in the form of x-rays and charged particles at a repetition rate of 5–10 Hz. Armour material and chamber dimensions have to be chosen to avoid/minimize damage to the chamber, ensuring the proper functioning of the facility during its planned lifetime. The maximum energy fluence that the armour can withstand without risk of failure, is determined by temporal and spatial deposition of the radiation energy inside the material. In this paper, simulations on the thermal effect of the radiation–armour interaction are carried out with an increasing definition of the temporal and spatial deposition of energy to prove their influence on the final results. These calculations will lead us to present the first values of the thermo-mechanical behaviour of the tungsten armour designed for the HiPER project under a shock ignition target of 48 MJ. The results will show that only the crossing of the plasticity limit in the first few micrometres might be a threat after thousands of shots for the survivability of the armour

The Fluctuations of the Quark Number and of the Chiral Condensate

The distributions of the quark number and chiral condensate over the gauge fields are computed for QCD in Euclidean space at nonzero quark chemical potential. As both operators are non-hermitian the distributions are in the complex plane. Moreover, because of the sign problem, the distributions are not real and positive. The computations are carried out within leading order chiral perturbation theory and give a direct insight into the delicate cancellations that take place in contributions to the total baryon number and the chiral condensate.Comment: 19 pages, 2 figure

Single polymer dynamics: coil-stretch transition in a random flow

By quantitative studies of statistics of polymer stretching in a random flow and of a flow field we demonstrate that the stretching of polymer molecules in a 3D random flow occurs rather sharply via the coil-stretch transition at the value of the criterion close to theoretically predicted.Comment: 4 pages, 5 figure

Band structure in classical field theory

Stability and instability bands in classical mechanics are well-studied in connection with systems such as described by the Mathieu equation. We examine whether such band structure can arise in classical field theory in the context of an embedded kink in 1+1 dimensions. The static embedded kink is unstable to perturbations but we show that if the kink is dynamic it can exhibit stability in certain parameter bands. Our results are relevant for estimating the lifetimes of various embedded defects and, in particular, loops of electroweak Z-string.Comment: 6 pages, 4 fig. Reference added, Fig. 3 updated with improved numerical code, minor comments added. Version to be published in Phys. Rev.

Optimal edge termination for high oxide reliability aiming 10kV SiC n-IGBTs

The edge termination design strongly affects the ability of a power device to support the desired voltage and its reliable operation. In this paper we present three appropriate termination designs for 10kV n-IGBTs which achieve the desired blocking requirement without the need for deep and expensive implantations. Thus, they improve the ability to fabricate, minimise the cost and reduce the lattice damage due to the high implantation energy. The edge terminations presented are optimised both for achieving the widest immunity to dopant activation and to minimise the electric field at the oxide. Thus, they ensure the long-term reliability of the device. This work has shown that the optimum design for blocking voltage and widest dose window does not necessarily give the best design for reliability. Further, it has been shown that Hybrid Junction Termination Extension structure with Space Modulated Floating Field Rings can give the best result of very high termination efficiency, as high as 99%, the widest doping variation immunity and the lowest electric field in the oxide

System model development for nuclear thermal propulsion

A critical enabling technology in the evolutionary development of nuclear thermal propulsion (NTP) is the ability to predict the system performance under a variety of operating conditions. This is crucial for mission analysis and for control subsystem testing as well as for the modeling of various failure modes. Performance must be accurately predicted during steady-state and transient operation, including startup, shutdown, and post operation cooling. The development and application of verified and validated system models has the potential to reduce the design, testing, and cost and time required for the technology to reach flight-ready status. Since Oct. 1991, the U.S. Department of Energy (DOE), Department of Defense (DOD), and NASA have initiated critical technology development efforts for NTP systems to be used on Space Exploration Initiative (SEI) missions to the Moon and Mars. This paper presents the strategy and progress of an interagency NASA/DOE/DOD team for NTP system modeling. It is the intent of the interagency team to develop several levels of computer programs to simulate various NTP systems. The first level will provide rapid, parameterized calculations of overall system performance. Succeeding computer programs will provide analysis of each component in sufficient detail to guide the design teams and experimental efforts. The computer programs will allow simulation of the entire system to allow prediction of the integrated performance. An interagency team was formed for this task to use the best capabilities available and to assure appropriate peer review