We describe Chromium, a system for manipulating streams of graphics API commands on clusters of workstations. Chromium's stream filters can be arranged to create sort-first and sort-last parallel graphics architectures that, in many cases, support the same applications while using only commodity graphics accelerators. In addition, these stream filters can be extended programmatically, allowing the user to customize the stream transformations performed by nodes in a cluster. Because our stream processing mechanism is completely general, any cluster-parallel rendering algorithm can be either implemented on top of or embedded in Chromium. In this paper, we give examples of real-world applications that use Chromium to achieve good scalability on clusters of workstations, and describe other potential uses of this stream processing technology. By completely abstracting the underlying graphics architecture, network topology, and API command processing semantics, we allow a variety of applications to run in different environments.

We report the observation, by transmission electron microscopy, that single-crystal silicon and germanium are converted to an amorphous state at room temperature directly under both Vickers and Knoop indentations. The effect is seen for crystal orientations of [001], [Oil], and [111], and with applied loads between 0.1 and 0.5 N. We also observe that the materials become electrically conducting under load and that the process is reversible on subsequent unloading and reloading. Furthermore, the transformed phase is found to make Ohmic contact to the surrounding, untransformed, semiconductor.PACS numbers: 64.70.Dv, 64.70.Kb, 72.60.+g It has long been recognized that extremely high (hydrostatic and deviatoric) stresses are generated when a sharp indenter is loaded onto a flat surface of a solid. The exact details of the stress fields depend on the shape of the indenter and on the constitutive equations describing flow in the particular material, a subject that has now become the province of the theories of the hardness of materials and its measurement by indentation methods.' The existence of high hydrostatic stress has led investigators to suggest that the indentation experiment could be used to study high-pressure phase transformations, although it is recognized that the large deviatoric stresses make calculations difficult. Indeed Eremenko and Nikitenko, 2 and more recently Pirouz, Chaim, and Samuels, 3 report the formation of the hexagonal polymorph (Si IV) when silicon is indented at temperatures of 450-700 °C. Similarly, there is the suggestion by Gerk and Tabor 4 that silicon, germanium, and diamond may undergo a semiconductor-to-metal transition, as the pressures under an indenter are similar to those predicted for such a transition. We report here our findings of a rather different phase transformation in both silicon and germanium, the transition, through an electrically conducting state under load, to a metastable amorphous form after unloading, directly under an indentation. Such a crystailine-to-amorphous transition has not been observed in conventional high-pressure experiments.As part of our studies of cracks in brittle solids we have prepared samples containing arrays of small indentations together with their attendant cracks for transmission electron microscopy. Single crystals, mechanically ground and polished to a thickness of -100 /zm, were patterned with arrays of regularly spaced indentations with typically 100 indentations in a 3-mm-diam disk. The indentation impressions, produced by pyramidal diamond indenters having either the Vickers (148° included edge angle) or Knoop (asymmetric pyramid with included edge angles of 130° and 172.5°) configuration, were formed with loads in the range 0.1 and 0.5 N. In all cases the constant loading and unloading rates were 16.67 Ns" 1 . With the top, indented, surface protected by a glass cover slip, the samples were then ion thinned from the back until suitably thin for viewing in the transmission electron microscope. Figure 1 is a transmission electro...

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Compositionally graded films of SiGe/Si(100) and GaInAs/GaAs were grown under different conditions in order to investigate the different modes of strain relaxation associated with the compositional grading. We show that, when the growth conditions are very clean and the gradient is shallow enough (about 1% misfit per half micron), very good, relaxed films are obtained. This coincides with the introduction of large numbers of dislocations in the substrate itself, which is counter-intuitive at first since the substrate is under negligible strain. We show that this introduction of dislocations is the result of the activation of novel Frank–Read-like sources located in the graded region, and is directly correlated to the lack of other low energy nucleation sites for dislocations. We detail the conditions of growth necessary for this phenomenon to occur, and show that it operates both for the SiGe/Si system and the GaInAs/GaAs system. Pure, relaxed Ge films have been grown in this manner on Si(100), with a defect density as low as 106/cm2.

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