Performance characteristics of a therapeutic ultrasound wire waveguide apparatus

Therapeutic ultrasound angioplasty has been investigated, clinically, by a number of researchers and represents a potentially promising therapy for the treatment of atherosclerotic lesions. To date, there has been no detailed analysis of the effect of mechanical design parameters, such as wire geometry or damping characteristics, on wire waveguide performance. An apparatus capable of delivering therapeutic ultrasound down small diameter nickel–titanium (NiTi) wire waveguides is described. The output peak-to-peak (p–p) displacements at the distal tip of a 1.0 mm diameter waveguide were measured experimentally, by means of an optical microscope and image analysis software. The output was measured for a range of waveguide lengths from 118 to 303 mm. Wire waveguide distal tip displacements as high as 98 μm (p–p) at 23.5 kHz were measured. For the range of lengths tested, the experimental measurements show the critical relationship between the length of the waveguide and the output distal tip displacements. A finite element model that can predict the resonant frequencies and distal tip displacements of various wire waveguide geometries and configurations, including the effect of damping, is presented. This numerical model has been validated against the experimental displacement data obtained. This will be a valuable design tool for ensuring the safety and effectiveness of therapeutic ultrasound angioplasty procedures.     

Propane conversion over zeolite catalysts: Comments on the role of Ga

The activation of propane using zeolite H-Y and Ga³⁺ exchanged zeolite Y indicates that in the presence of Ga³⁺ the mechanism of propane activation is changed from a cracking pathway to a dehydrogenation pathway. The presence of both Ga³⁺ and H⁺ are required to achieve this effect.     

Potent and selective bicyclic lactam inhibitors of thrombin: Part 2: P1 modifications

The synthesis and antithrombotic activity of a series of nonpeptide bicyclic thrombin inhibitors is described. We have explored the SAR with modifications to the P1 site. The introduction of arginine mimetics at the P1 site led to potent and selective thrombin inhibitors.     

Numerical and experimental study of a nonisothermal turbulent jet with a heavy impurity

Temperature and momentum distributions of the carrier phase are determined experimentally and compared to results of numerical calculations using the (k–) model.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 50, No. 5, pp. 735–743, May, 1986.     

Distribution of disperse impurity in turbulent jet

The concentration fields of disperse impurity are calculated on the basis of a k- model of turbulence in a wide range of Stokes numbers.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 49, No. 4, pp. 548–555, October, 1985.     

Copper Assisted Inverted Pyramids Texturization of Monocrystalline Silicon in a Nitrogen Bubbling Bath for Highly Efficient Light Trapping

Silicon - Inverted pyramid (IP) texturization on silicon wafers has recently attracted attention for the structure’s light trapping ability and low specific surface area. The later property...     

SULFUR RECOVERY WITH REDUCED EMISSIONS, LOW CAPITAL INVESTMENT AND HYDROGEN CO-PRODUCTION

The main disadvantage of the Claus process is that by introducing air as oxidant a large volume of tail gas is produced. This must be treated to reduce atmospheric emissions of sulfur-containing gases. The costs of the tail-gas unit are a significant fraction of the total capital and operating costs for sulfur recovery. A new process uses thermal decomposition of hydrogen sulfide in the presence of carbon dioxide instead of air oxidation. The products of this reaction are hydrogen, carbon monoxide, elemental sulfur, water vapor and carbonyl sulfide. Carbonyl sulfide is easily converted to H₂S and C0₂ by liquid- or vapor-phase hydrolysis. Unreacted H₂S and C0₂ are recovered by absorption and recycled to the reactor. Since no air is introduced, there is no tail gas and the tail-gas unit is eliminated, giving a substantial reduction in capital investment. The concentrations of sulfur-containing gases in the product streams depend only on the operation of the absorber and stripper units and can be controlled to very low levels by increasing stripper boil-up. Process operating costs depend on the level of sulfur recovery required and can also be much lower than those of the modified Claus Process.

The process chemistry depends on a shift in the equilibrium of H₂S decomposition caused by reaction of hydrogen with C0₂ by the reverse of the water-gas-shift reaction. Catalysts for this chemistry have been identified. Reactor conversion is further improved by rapid cooling of the reactor effluent gas. Other aspects of process design and operation confer further advantages with respect to the Claus process; however, the process equipment used is similar to that used in a Claus plant. Retrofit of existing plant to the new technology can therefore be considered.     

Polymer modification and synthesis using sulphenyl derivatives: 9. Addition of alkylsulphenyl chlorides to cis-1, 4-polybutadiene

Methanesulphenyl chloride and n-butanesulphenyl chloride add readily across the double bonds in cis-1,4-polybutadiene. The addition is highly regioselective so that long sequences of saturated units are formed. The products are very unstable, evolving hydrogen chloride on standing, but can be stabilized by replacing the labile chlorine atom with other nucleophiles in a phase transfer catalysed reaction.