Pure Significance Tests of the Unit Root Hypothesis Against Nonlinear Alternatives

Abstract. This paper describes artificial neural network based pure significance tests for the unit root hypothesis against nonlinear alternatives. The theoretical properties of the tests are discussed and a Monte Carlo investigation of their small sample properties is undertaken.     

Stress in Leached Phase-Separated Glass

When a phase-separated glass is leached, stresses develop because of release of thermal stresses, creation of surface area, ion exchange, and hydration. Analyses are presented for the thermal stresses, including the portion that develops on cooling from the heat-treatment temperature to the setting temperature of the less viscous phase. During leaching, the interfacial energy of the residual phase increases, so that phase tends to contract. A more important effect is the contraction caused by removal of alkali and B₂O₃ from the residual phase during leaching. The extent of removal of B₂O₂ decreases with heat-treatment time, t_H , because the scale of the microstructure increases as t^1/3_H. The change in residual B₂O₂ content with t_H is shown to be consistent with diffusion-controlled ion exchange. The dependence of stress on t_H in partially leached glasses, measured by Drexhage and Gupta, results principally from the change in extent of ion exchange; the reduction in surface area with increasing t_H also has a significant effect on the stresses.     

Low-cycle fatigue in silicon: comparison with fcc metals

Undoped FZ silicon single crystals were cyclically loaded in tension‐compression under plastic strain amplitude control in a temperature and strain rate domain where the glide of dislocations is still controlled by the lattice friction: 1073–1173 K and (1.5–6) × 10⁻⁴s⁻¹; the plastic strain amplitude being varied from 6 × 10⁻⁴ to 10⁻². Cyclic hardening curves display logarithmic then linear hardening and pass through a maximum before the peak stress per cycle stabilizes. The maximum and stabilized stresses decrease when temperature increases. Microscopical observations suggest that strain localization takes place near the maximum cyclic stress and beyond. But, contrary to what is observed in fcc metals, the maximum or saturation stress decreases when the strain amplitude per cycle increases. Several types of dislocation arrangements, rather different from those found in copper, but looking more similar to Ni fatigued at low temperatures, were revealed by transmission electron microscopy. Before mechanical saturation, edge dislocation dipoles gather in thick stripes forming more or less corrugated walls, depending on the amplitude per cycle, when viewed normal to the primary slip plane. Once the maximum stress is reached, it seems that parts of the microstructure cease to participate in the imposed plastic strain, while others concentrate it. In active areas, thick walls condense into much thinner ones, forming chevrons when viewed normal to the slip plane. In areas which seem to be inactive, dipolar walls anneal out leaving a rather homogeneous distribution of prismatic loops. Thin PSBs with a well‐characterized ‘ladder‐structure’ are very rare. Characteristic lengths of the observed patterns are given and briefly discussed using current theories of cyclic deformation.     

A Search for Hidden Relationships: Data Mining with Genetic Algorithms

This paper presents an algorithm that permits the search for dependencies among sets of data (univariate or multivariate time-series, or cross-sectional observations). The procedure is modeled after genetic theories and Darwinian concepts, such as natural selection and survival of the fittest. It permits the discovery of equations of the data-generating process in symbolic form. The genetic algorithm that is described here uses parts of equations as building blocks to breed ever better formulas. Apart from furnishing a deeper understanding of the dynamics of a process, the method also permits global predictions and forecasts. The algorithm is successfully tested with artificial and with economic time-series and also with cross-sectional data on the performance and salaries of NBA players during the 94–95 season.     

In Vivo and In Vitro Assessment of Antinutritional Factors in Peanut and Soy

Raw and heat processed peanut flours were found to contain higher in vitro trypsin inhibitor activity and lectin content than similarly processed soy flour. When fed to weanling rats at a level of 10% protein, the response pattern in food consumption, growth, liver function, and serum chemistries was not consistent among or between the groups. It is concluded that the levels of antinutritional factors in legumes do not correlate with their overall biological impact in feeding studies with the rat.     

NITRITE REDUCTASE IN SALMONELLA TYPHIMURIUM

A nitrite reductase was identified and purified 11 -fold from the cytoplasmic fraction of Salmonella typhimurium grown anaerobically with nitrite as the sole nitrogen source. The enzyme required NADH as a cofactor and showed maximum in vitro reductase activity at pH 8.0.
S. typhimurium, grown anaerobically in glucose-limited minimal medium containing peptone and nitrite, showed shorter generation times and increased cell yields in comparison to nitrite-free cultures. The presence of nitrite had no effect on aerobic cultures. The nitrite reductase functions in a dissimilatory manner and appears to be primarily involved in physiological energy generation during anaerobic growth. The nitrite reductase may function to remove excess reducing power in the form of NADH from the cell thus increasing ATP production during the anaerobic fermentation of glucose. The formation and subsequent assimilation of ammonia from nitrite is of secondary importance to the organism.     

DETECTION OF BACILLUS CEREUS DIARRHEAGENIC TOXIN USING A RAT LIGATED INTESTINAL LOOP ASSAY

A study was performed to determine if the rat ligated intestinal loop assay could detect Bacillus cereus diarrheagenic toxin. The results obtained indicated that this assay system could be used for such a purpose but it was not as sensitive as the young rabbit ligated ileal loop assay. When rats were used, concentrating the cell free culture filtrate of B. cereus 30- to 40-fold was necessary to detect diarrheagenic toxin activity with the intestinal loop assay.     

Demonstration of the Performance of an Inclined Anaerobic Digester in Wine Stillage and Pea Blancher Wastewater Treatment

Disposal of high strength wastes has been a problem in the fruit and vegetable processing industries. We have designed and tested an inclined continuous anaerobic digester for the rapid treatment of unmodified wine stillage (21,000–25,000 mg COD per liter) and waste water from a pea blancher (20,000 mg COD per liter). The digester was successfully operated for periods up to 9 months using feed rates as high as 10.7g COD per liter per day (hydraulic detention time of 2.4 days). COD removal efficiency ranged from 95.9% to 99.5%, and effluent suspended solids were less than 800 mg per liter.     

Strength of a Ceramic at High Temperatures Under Biaxial and Uniaxial Tension

A design is presented for a fixture to test concentric-ring loaded disks and four-point loaded plates at high temperatures. In this fixture the loading plunger is guided by flexure plates to determine the load path with accuracy. The uniaxial and equibiaxial tensile strengths of a brittle material were measured at 982°C with this fixture. For lapped surfaces, the equibiaxial tensile strength of dense, isostatically pressed, sintered alumina was 16.0% lower than the uniaxial tensile strength. The uniaxial strength at 982°C was 42.3% lower than the previously reported value for comparable tests at room temperature. The effect of frictional forces and lateral constraint, of specimen and loading geometry, and of local stresses on the nominal stress are discussed.     

Precipitation in Microscopic Cracks

It is shown that precipitation occurs in Griffith-type surface cracks in solids from solutions or from vapors under conditions in which a plane surface would be dissolved or vaporized. A reduction in the equilibrium vapor pressure at the crack tip from that of a plane surface is produced by the driving force to reduce the surface energy of the crack. An equation is derived relating vapor pressure at the tip of the crack to vapor pressure over an infinite plane. This relation is used in deriving an expression for the fill-up of cracks with time. Experimental data on the measurement of the retreat of the crack edge with time appear to be in good agreement with the derived expression. A discussion of the effect of such crack healing on the mechanical properties of the solids is included.