A removable and reusable filter attachment system is disclosed. A filter medium is fixed to, and surrounded by, a filter frame having a coaxial, longitudinally extending, annular rim. The rim engages an annular groove which surrounds the opening of a filter housing. The annular groove contains a fusible material and a heating mechanism for melting the fusible material. Upon resolidifying, the fusible material forms a hermetic bond with the rim and groove. Remelting allows detachment and replacement of the filter frame.

A coaxial high voltage, high current switch having a solid cylindrical cold cathode coaxially surrounded by a thin hollow cylindrical inner electrode and a larger hollow cylindrical outer electrode is described. A high voltage trigger between the cathode and the inner electrode causes electrons to be emitted from the cathode and flow to the inner electrode preferably through a vacuum. Some of the electrons penetrate the inner electrode and cause a volumetric discharge in the gas (which may be merely air) between the inner and outer electrodes. The discharge provides a low impedance path between a high voltage charge placed on the outer electrode and a load (which may be a high power laser) coupled to the inner electrode. For high repetition rate the gas between the inner and outer electrodes may be continuously exchanged or refreshed under pressure.

An improved downhole steam injector has an angled water orifice to swirl the water through the device for improved heat transfer before it is converted to steam. The injector also has a sloped diameter reduction in the steam chamber to throw water that collects along the side of the chamber during slant drilling into the flame for conversion to steam. In addition, the output of the flame chamber is beveled to reduce hot spots and increase efficiency, and the fuel-oxidant inputs are arranged to minimize coking.

The present invention is directed to a fuel-air control system for a combustor in which coal-derived gas of varying heat content is used. To maintain the temperature in the combustor at an essentially constant value the fuel-to-air ratio is adjusted by using a temperature actuated variable pressure regulator in the gas feed line to compensate for the variability of the heat content of the gas. The velocity of the products of combustion is maintained at an essentially constant flow rate by controlling the mass flow of the air and fuel through linked valves on the gas and air feed lines.

A method is described for the preparation of defined, isomerically pure phospholipid-nucleoside conjugates as a prodrug in which the drug (araC) is attached to the phospholipid by a monophosphate linkage. Key intermediates in the process involve selective blocking and deblocking of the nucleoside derivative. These particular monophosphate-linked derivatives represent a new class of prodrug, which are useful by themselves or in combination with diphosphate linked derivatives. Several new compositions involving diphosphate linked derivatives are described in which the products are isomerically pure and having defined fatty acid chain lengths.

A new composition of matter has been discovered which is an explosive addition compound of ammonium nitrate (AN) and diethylenetriamine trinitrate (DETN) in a 50:50 molar ratio. the compound is stable over extended periods of time only at temperatures higher than 46/sup 0/C, decomposing to a fine-grained eutectic mixture (which is also believed to be new) of AN and DETN at temperatures lower than 46/sup 0/C. The compound of the invention has an x-ray density of 1.61 g/cm/sup 3/, explodes to form essentially only gaseous products, has higher detonation properties (i.e., detonation velocity and pressure) than those of any mechanical mixture having the same density and composition as the compound of the invention, is a quite insensitive explosive material, can be cast at temperatures attainable by high pressure steam, and is prepared from inexpensive ingredients. Methods of preparing the compound and the fine-grained eutectic composition of the invention are given.

This invention is directed to a process of generating silicon tetrafluoride (SiF/sub 4/) from aqueous solutions of hexafluorosilicic acid (H/sub 2/SiF/sub 6/), comprising reacting an aqueous solution of H/sub 2/SiF/sub 6/ with a concentrated aqueous salt solution to produce a precipitate, separating and drying the precipitate, and heating the precipitate in an inert atmosphere to decompose the precipitate producing SiF/sub 4/.

Rhenium is recovered from an alloy containing that metal and either one or both of the metals molybdenum and tungsten by the following steps: (1) heating the alloy in the presence of O/sub 2/ to remove the Re from the alloy as gaseous Re/sub 2/O/sub 7/; (2) condensing the gaseous Re/sub 2/O/sub 7/; (3) dissolving the obtained solid Re/sub 2/O/sub 7/ in H/sub 2/O; (4) treating the solution of Re/sub 2/O/sub 7/ and H/sub 2/O with KCl to form KReO/sub 4/; and (5) heating the KReO/sub 4/ in the presence of H/sub 2/ to form Re.