Phase Coherence in Multiple Pulse Optical Spectroscopy

In this paper we describe a new technique for the generation of multiple pulse phase coherent sequences in optical spectroscopy. The technique is an extension of the acousto-optic modulation and fluorescence detection methods developed for optical transitions by Zewail and Orlowski (Zewail et al., Chem. Phys. Lett. 48, 256 (1977); Orlowski et al., Chem. Phys. Lett. 54, 197 (1978)). Application of these multiple pulse trains (of different phases) to optical transitions of two-level and multilevel systems is demonstrated experimentally. It is shown that they can be used to (i) suppress spontaneous emission background, (ii) enhance coherent transients such as photon echoes, (iii) measure additional relaxation parameters in systems with complex rotational-vibrational levels, and (iv) enhance the effective laser bandwidths through composite pulse trains, as demonstrated on I2 gas. Finally, the potential of this development is extended to the possibility of observing selective multiquantum excitation in molecules

Method of making contamination-free ceramic bodies

Ceramic structures having high strength at temperatures above 1000 C after sintering are made by mixing ceramic powders with binder deflocculants such as guanidine salts of polymeric acids, guanidine salts of aliphatic organic carboxylic acids or guanidine alkylsulfates with the foregoing guanidine salts. The novelty of the invention appears to lie in the substitution of guanidine salts for the alkalai metal salt components or organic fatty acids of the prior art binder-deflocculant, ceramic processing aids whereby no undesirable metal contaminants are present in the final ceramic structure. Guanidine alkylsulfates also replace the Na or K alkylsulfates commonly used with binder-deflocculants in making high temperature ceramic structures

Use of extendible boom devices for space shuttle and EVA operations

Extended boom devices for orbital maintenance and safety of space shuttl

Polysiloxanes derived from the controlled hydrolysis of tetraethoxysilane as precursors to silica for use in ceramic processing

Synthesis, properties, and potential applications in ceramic processing for two polysiloxane silica precursors derived from the controlled hydrolysis of tetraethoxysilane (TEOS) are presented. The higher molecular weight TEOS-A is a thick adhesive liquid of viscosity 8000 to 12,000 c.p. having a SiO2 char yield of about 55 percent. The lower molecular weight TEOS-B is a more fluid liquid of viscosity 150 to 200 c.p. having a SiO2 char yield of about 52 percent. The acid catalyzed hydrolysis of TEOS to hydrated silica gel goes through a series of polysiloxane intermediates. The rate of this transition increases with the quantity of water added to the TEOS; thus, for ease of polymer isolation, the amount of water added must be carefully determined so as to produce the desired polymer in a reasonable time. The water to TEOS mole ratio falls in the narrow range of 1.05 for TEOS-A and 0.99 for TEOS-B. Further polymerization or gelation is prevented by storing at -5 C in a freezer. Both polysiloxanes thermoset to a glassy solid at 115 C. The liquid polymers are organic in nature in that they are miscible with toluene and ethanol, slightly souble in heptane, but immiscible with water. For both polymers, results on viscosity versus time are given at several temperatures and water additions. Based on these results, some examples of practical utilization of the precursors for ceramic fabrication are given

The Sudbury-Serenitatis analogy and 'so-called' pristine nonmare rocks

The Serenitatis Basin is the one lunar basin from which we confidently identify a suite of samples as pieces of the impact melt sheet: the distinctive Apollo 17 noritic breccias. Recent studies of the Sudbury Complex indicate that its 'irruptive' is almost entirely of impact-melt origin, making it the closest terrestrial analog to the Serenitatis melt sheet. Any attempt to model the evolution of the Moon's crust should be compatible with the relatively well-understood Sudbury Complex. However, the Sudbury-Moon analogy might be a misleading oversimplification, if applied too rigidly. The cause of evolutionary differences between the Serenitatis impact melt and the Sudbury impact melt is discussed

Mars regolith versus SNC meteorites: Evidence for abundant crustal carbonates

Viking XRF analyses are compared with those for terrestrial and lunar basalt samples, and eucritic meteorites (of possible Mars origin). The comparison indicates depletion of Ca relative to Si in the Mars regolith. It is suggested that carbonate formation during a warmer, wetter epoch early in Mars' history could have been responsible