A B S T R A C TIt was established that ideal, diffusion-controlled, steady-state segregation, never accomplished on earth, was achieved during the growth of Te-doped InSb crystals in Skylab. Surface tension effects led to nonwetting conditions u n d e r which free surface solidification took place in confined geometry. It was further found that, under forced contact conditions, surface tension effects led to the formation of surface ridges (not previously observed on earth) which isolated the growth system from its container. In addition, it was possi~ble, for the first time, to identify unambiguously: the origin of segregation discontinuities associated with facet growth, the mode of nucleation and propagation of rotational t w i n boundaries, and the specific effect of mechanical-shock perturbations on segregation. The results obtained prove the advantageous conditions provided by outer space. Thus, fundamental data on solidification thought to be unattainable on earth because of gravityinduced interference are now within reach.Structural and compositional control during solidification of materials is impeded by gravity-induced effects in the melt. Thermal gradients necessary for crystal growth lead, in the presence of gravitational forces, to thermal convection which in general causes uncontrolled variations in the solidification rate and in diffusion boundary layer thickness; such variations lead directly to periodic and/or random microscopic and macroscopic segregation inhomogeneities. F u rthermore, in the presence of gravity, establishing steep thermal gradients, frequently required to prevent constitutional supercooling, is often impossible and consequently interface breakdown is unavoidable.Gravity effects are, thus, primarily responsible for the present lack of reliable solidification data and the existing gap between theory and experiment. Consequently, crystal growth and associated segregation phenomena are still based on empiricism, and the properties and performance of solids are not at their theoretical limits.Gravity-free conditions made accessible through the space program provide a unique opportunity to obtain reliable crystal growth data and, therefore, to advance our quantitative understanding of solidification processes; in addition this program makes possible the exploration and assessment of the potential of outer space for materials processing.Indium antimonide was chosen for the presently reported Skylab experiment because its relatively low melting point (525~ made the experiment compatible with the available electrical power. In addition, chemical etching, the only high-resolution technique available, at the time, for the study of segregation inhomogeneities on a microscale, had been developed on InSb to its most advanced level.The experiments performed during the Skylab-III and -IV missions included the growth of undoped, tellurium-doped, and tin-doped indium antimonide. The present report is concerned primarily with results obtained on tellurium-doped InSb. ObjectivesThe objectives of...

Integrative and conjugative elements (ICEs) are mobile genetic elements that reside in a bacterial host chromosome and are prominent drivers of bacterial evolution. They are also powerful tools for genetic analyses and engineering. Transfer of an ICE to a new host involves many steps, including excision from the chromosome, DNA processing and replication, transfer across the envelope of the donor and recipient, processing of the DNA, and eventual integration into the chromosome of the new host (now a stable transconjugant). Interactions between an ICE and its host throughout the life cycle likely influence the efficiencies of acquisition by new hosts. Here, we investigated how different functional modules of two ICEs, Tn916 and ICEBs1, affect the transfer efficiencies into different host bacteria. We constructed hybrid elements that utilize the high-efficiency regulatory and excision modules of ICEBs1 and the conjugation genes of Tn916. These elements produced more transconjugants than Tn916, likely due to an increase in the number of cells expressing element genes and a corresponding increase in excision. We also found that several Tn916 and ICEBs1 components can substitute for one other. Using B. subtilis donors and three Enterococcus species as recipients, we found that different hybrid elements were more readily acquired by some species than others, demonstrating species-specific interactions in steps of the ICE life cycle. This work demonstrates that hybrid elements utilizing the efficient regulatory functions of ICEBs1 can be built to enable efficient transfer into and engineering of a variety of other species.

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A new configuration of LPEE is described in which the substrate is placed between two wells containing a solution. This configuration eliminates problems associated with the contact to the back‐side of the substrate. It also enables simultaneous observation of electroepitaxial growth and dissolution processes on the opposite sides of the substrate, and provides a unique means forin situ monitoring of the growth (and dissolution) kinetics.