Rapid consolidation of powdered materials by induction hot pressing

A rapid hot press system in which the heat is supplied by RF induction to rapidly consolidate thermoelectric materials is described. Use of RF induction heating enables rapid heating and consolidation of powdered materials over a wide temperature range. Such rapid consolidation in nanomaterials is typically performed by spark plasma sintering (SPS) which can be much more expensive. Details of the system design, instrumentation, and performance using a thermoelectric material as an example are reported. The Seebeck coefficient, electrical resistivity, and thermal diffusivity of thermoelectric PbTe material pressed at an optimized temperature and time in this system are shown to agree with material consolidated under typical consolidation parameters.     

A high temperature apparatus for measurement of the Seebeck coefficient

A high temperature Seebeck coefficient measurement apparatus with various features to minimize typical sources of error is designed and built. Common sources of temperature and voltage measurement error are described and principles to overcome these are proposed. With these guiding principles, a high temperature Seebeck measurement apparatus with a uniaxial 4-point contact geometry is designed to operate from room temperature to over 1200 K. This instrument design is simple to operate, and suitable for bulk samples with a broad range of physical types and shapes.     

Synthesis and Characterization of <Emphasis Type="Italic">p</Emphasis>-Type Pb<Subscript>0.5</Subscript>Sn<Subscript>0.5</Subscript>Te Thermoelectric Power Generation Elements by Mechanical Alloying

A mechanical alloying (MA) process to transform elemental powders into solid Pb_0.5Sn_0.5Te with thermoelectric functionality comparable to melt-alloyed material is described. The room-temperature doping level and mobility as well as temperature-dependent electrical conductivity, Seebeck coefficient, and thermal conductivity are reported. Estimated values of lattice thermal conductivity (0.7 W m⁻¹ K⁻¹) are lower than some reports of functional melt-alloyed PbSnTe-based material, providing evidence that MA can engender the combination of properties resulting in highly functional thermoelectric material. Though doping level and Sn composition have not been optimized, this material exhibits a ZT value >0.5 at 550 K.     

The crystal structure of human procathepsin K

Cathepsin K is a cysteine protease present in human osteoclasts that plays an important role in bone resorption. Cathepsin K is synthesized as an inactive proenzyme and activated under conditions of low pH. Autoproteolytic processing of the N-terminal 99 amino acid propeptide produces the active, mature form of cathepsin K. It is presumed that the activation of procathepsin K in vivo occurs in the bone resorption pit, which has a low-pH environment. We have determined the structure of human procathepsin K at 2.8 A resolution. The structure of the mature enzyme domain within procathepsin K is virtually identical to that of mature cathepsin K. The fold of the propeptide of procathepsin K is similar to that observed in procathepsins B and L despite differences in length and sequence. A portion of the propeptide occupies the active site cleft of cathepsin K. Hydrophobic interactions, salt bridges, and hydrogen-bonding interactions are observed in the structure of the propeptide and between the propeptide and the mature enzyme of procathepsin K. These interactions suggest an explanation for the stability of the proenzyme. The structure of procathepsin K contributes to an understanding of the molecular basis of inhibition by the propeptide portion of the molecule and activation of this important member of the cysteine protease family.     

Stabilizing the optimal carrier concentration for high thermoelectric efficiency

The band structure of PbTe can be manipulated by alloying with MgTe to control the band degeneracy. This is used to stabilize the optimal carrier concentration, making it less temperature dependent, demonstrating a new strategy to improve overall thermoelectric efficiency over a broad temperature range.     

Constructing LR parsers for regular right part grammars

Summary Regular right part (RRP) grammars differ from context free (CF) grammars by virtue of the fact that the production right parts are nondeterministic finite automatons (FAs). LR(k) parsers for RRP grammars are linear time parsers which can determine the right end of each handle by considering at most k terminal symbols to its right and the left end (after the right end has been found) by considering at most one parse stack state to its left. This paper is concerned with the construction of a class of LR(k) parsers for RRP grammars which makes use of FAs for determining both the right and left ends of the handle.This work has been supported by a Carleton University grant and National Research Council of Canada grant no. A3585     

The Criteria for Beneficial Disorder in Thermoelectric Solid Solutions

Forming solid solutions has long been considered an effective approach for good thermoelectrics because the lattice thermal conductivities are lower than those of the constituent compounds due to phonon scattering from disordered atoms. However, this effect could also be compensated by a reduction in carrier mobility due to electron scattering from the same disorder. Using a detailed study of n‐type (PbTe)_1–x (PbSe)_x solid solution (0 ≤ x ≤ 1) as a function of composition, temperature, and doping level, quantitative modeling of transport properties reveals the important parameters characterizing these effects. Based on this analysis, a general criterion for the improvement of zT due to atomic disorder in solid solutions is derived and can be applied to several thermoelectric solid solutions, allowing a convenient prediction of whether better thermoelectric performance could be achieved in a given solid solution. Alloying is shown to be most effective at low temperatures and in materials that are unfavorable for thermoelectrics in their unalloyed forms: high lattice thermal conductivity (stiff materials with low Grüneisen parameters) and high deformation potential.     

Comparison between lung and liver lipid peroxidation and mortality after zymosan peritonitis in the rat

The author presents a 3-year study of 10 cases of revisional arthroplasty utilizing the Biomet Total Toe System. The procedure is performed to eliminate pain and restore function in cases of metatarsophalangeal joint silicone elastomer implant failure. The surgeon should be familiar with the Total Toe System before attempting revision.     

A high-performance line source feed for the AIO spherical reflector

An aberration-correcting line source feed has been designed, modeled, constructed, and tested in the Arecibo reflector. The feed is a linearly polarized flat wavegnide 40-foot-long array illuminating 700 feet of the 1000-foot-diameter spherical reflector at 318 MHz. The antenna, illuminated by the new feed, yields an aperture efficiency of 70 percent with a peak gain near 56 dB, half-power beamwidth of 16.2 minutes of arc, and sidelobe levels below 4 percent of the on-axis gain. Vignetting losses are approximately 30 percent at the highest zenith angle.