A range of new datacenter switch designs combine wireless or optical circuit technologies with electrical packet switching to deliver higher performance at lower cost than traditional packet-switched networks. These "hybrid" networks schedule large traffic demands via a high-rate circuits and remaining traffic with a lower-rate, traditional packet-switches. Achieving high utilization requires an efficient scheduling algorithm that can compute proper circuit configurations and balance traffic across the switches. Recent proposals, however, provide no such algorithm and rely on an omniscient oracle to compute optimal switch configurations. Finding the right balance of circuit and packet switch use is difficult: circuits must be reconfigured to serve different demands, incurring non-trivial switching delay, while the packet switch is bandwidth constrained. Adapting existing crossbar scheduling algorithms proves challenging with these constraints. In this paper, we formalize the hybrid switching problem, explore the design space of scheduling algorithms, and provide insight on using such algorithms in practice. We propose a heuristic-based algorithm, Solstice that provides a 2.9× increase in circuit utilization over traditional scheduling algorithms, while being within 14% of optimal, at scale.

A novel holographic particle-image velocimeter system has been developed for the study of threedimensional (3-D) fluid velocity fields. The recording system produces 3-D particle images with a resolution, a signal-to-noise ratio, an accuracy, and derived velocity fields that are comparable to high-quality two-dimensional photographic particle-image velocimetry (PIV). The high image resolution is accomplished through the use of low f-number optics, a fringe-stabilized processing chemistry, and a phase conjugate play-back geometry that compensates for aberrations in the imaging system. In addition, the system employs a reference multiplexed, off-axis geometry for the determination of velocity directions with the cross-correlation technique, and a stereo camera geometry for the determination of the three velocity components. The combination of the imaging and reconstruction subsystems makes the analysis of volumetric PIV domains feasible.

Abstract. A 4-year (1993)(1994)(1995)(1996) temperature and wind data set obtained from over 2000 highresolution balloon soundings at South Pole is used to study gravity wave characteristics in the troposphere and lower stratosphere. Extensive a, nalyses of energy density, spectra, and static stability are performed to present a comprehensive view of the gravity wave characteristics in the lower atmosphere at South Pole. Our results show that the gravity waves are ubiquitous and often fairly strong at South Pole, even though the generation mechanisms are not clear. Gravity wave characteristics are, in general, similar to those obtained at other high-latitude southern hemisphere stations. Potential energies vary between about 0.5 J/kg and 5 J/kg with season and altitude. Variations in kinetic energies are not well correlated with potential energy variations and range from 1 J/kg to 11 J/kg. We observe significant seasonal variations of the slope and magnitude of the vertical wavenumber spectrum of temperature fluctuations, especially in the stratosphere. In general, the gravity waves in the stratosphere are stronger (weaker) in austral spring (fall). Wave activity in the troposphere has little seasonal dependence. Stability analysis shows that instabilities are more likely to occur in the troposphere than in the stratosphere. The probability of wave instability is 13.7% in the troposphere and 5.4% in the stratosphere. This is due to the less stable stratification in the troposphere, where the buoyancy period averages 8.3 rnin compared to 4.9 rnin in the stratosphere. Dynamic (shear) instability is more likely to occur than convective instability (11% versus 2.6% in the troposphere and 4.7% versus 0.7% in the stratosphere), due to the prevailing strong wind shear. The instability probabilities vary seasonally with the austral winter exhibiting the highest probability of instabilities (dynamic and convective instabilities combined) in both the troposphere and stratosphere.

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The design, development, and first measurements of a novel mesospheric temperature lidar are described. The lidar technique employs mesospheric Fe as a fluorescence tracer and relies on the temperature dependence of the population difference of two closely spaced Fe transitions. The principal advantage of this technique is that robust solid-state broadband laser source(s) can be used that enables the lidar to be deployed at remote locations and aboard research aircraft. We describe the system design and present a detailed analysis of the measurement errors. Correlative temperature observations, made with the Colorado State University Na lidar at Fort Collins, Colorado, are also discussed. Last, we present the initial range-resolved temperature measurements in the mesosphere and lower thermosphere over both the North and the South Poles obtained with this system.