Coliseum is a multiuser immersive remote teleconferencing system designed to provide collaborative workers the experience of face-to-face meetings from their desktops. Five cameras are attached to each PC display and directed at the participant. From these video streams, view synthesis methods produce arbitrary-perspective renderings of the participant and transmit them to others at interactive rates, currently about 15 frames per second. Combining these renderings in a shared synthetic environment gives the appearance of having all participants interacting in a common space. In this way, Coliseum enables users to share a virtual world, with acquired-image renderings of their appearance replacing the synthetic representations provided by more conventional avatar-populated virtual worlds. The system supports virtual mobility-participants may move around the shared space-and reciprocal gaze, and has been demonstrated in collaborative sessions of up to ten Coliseum workstations, and sessions spanning two continents.Coliseum is a complex software system which pushes commodity computing resources to the limit. We set out to measure the different aspects of resource, network, CPU, memory, and disk usage to uncover the bottlenecks and guide enhancement and control of system performance. Latency is a key component of Quality of Experience for video conferencing. We present how each aspect of the system-cameras, image processing, networking, and display-contributes to total latency. Performance measurement is as complex as the system to which it is applied. We describe several techniques to estimate performance through direct light-weight instrumentation as well as use of realistic end-to-end measures that mimic actual user experience. We describe the various techniques and how they can be used to improve system performance for Coliseum and other network applications. This article summarizes the Coliseum technology and reports on issues related to its performance-its measurement, enhancement, and control.
We show that, on a short time scale, the dynamics of vibrational excitations in multimode ground-state molecular systems, linearly coupled to a laser field, can be expressed as a simple functional of the laser pulse area. The dependence of the vibrational system’s dynamics on a field area leads to simple algebraic equations for this area, in the formulation of the inverse problem associated with the time-resolved control (tracking) of vibrational excitations. The control equation to be solved is quadratic in the area, when the object of the time-resolved control is the total vibrational energy, and linear when the object to be controlled is an average elongation (position tracking), or the average energy of a remotely coupled mode. This yields a control algorithm which requires no iteration and is easy to implement. Numerical tests of the algorithm are performed on the energy and position trackings in simple one-dimensional model systems. An excellent analytical, approximate description of the laser-driven dynamics of these systems is obtained using the concept of Lewis invariant. This analytical description is used as a reference with which the field numerically generated by solving the inverse control problem, using the aforementioned algorithm, can be compared.
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