Increase in the Alpha to Gamma Transformation Temperature of Pure Iron upon Very Rapid Heating

In recent years, laser and electron beam welding techniques have been developed with heating rates reaching 1 million K/s, and nonequilibrium microstructures sometimes result. In the present study, the alpha (bcc) to gamma (fcc) transformation in pure iron is studied using a bank of storage batteries for heating and a high speed data acquisition system to monitor the temperature determined from a thermocouple spot welded to the specimen. Heating rates up to 300,000 K/s were obtained with the transformation temperature increasing from the equilibrium value of 1185 K (912 °C) to over 2200 K (1927 °C). The results are presented in terms of continuous heating and isothermal transformation curves.     

Full-wafer technology-A new approach to large-scale laserfabrication and integration

A concept for full-wafer processing (FWP) and full-wafer testing (FWT) for semiconductor laser fabrication in the AlGaAs-GaAs material system is presented. The approach is based on chemically assisted ion beam etching for the laser-mirror formation. Record values for mirror scattering, optimum mirror reflectivity, and equivalence to cleaved mirrors in terms of laser threshold and efficiency have been achieved. Promising results for uniformity and reproducibility for major laser diode characteristics on processed 2-in wafers have been found. The FWP technology has been extensively used for designing test sites to determine various materials, process, and laser parameters, such as sheet resistance, ridge dimensions, lithographic alignment errors, mirror surface leakage, etc     

Tensile properties of directionally solidified Al-4 wt pct Cu alloys with columnar and equiaxed grains

The tensile properties of directionally solidified Al-4 wt pct Cu-0.15-0.2 wt pct Ti alloys with equiaxed grains were determined and compared with the properties of directionally solidified Al-4 wt pct Cu columnar structures. The tensile properties of the equiaxed structure were isotropic, but varied with the distance from the chill face. The mechanical properties of the equiaxed structure were generally between those of the longitudinal and transverse columnar structures. The 0.2 pct offset yield stress(σ _y, MPa) is represented as a function of the grain size,d (mm), the average concentration, C_o (wt pct), and the local concentration, C (wt pct), by σ_y = [(15.7 + 22.6 C_o) + (1.24 + 1.04 C_o)d ^-1/2] + [15.7 △C], where △C = C - C_o. The equiaxed structure exhibits inverse segregation similar to that in the columnar structure.     

Expression, purification, and characterization of inosine 5'-monophosphate dehydrogenase from Borrelia burgdorferi

Inosine 5'-monophosphate dehydrogenase (IMPDH) is the rate-limiting enzyme in de novo guanine nucleotide biosynthesis. IMPDH converts IMP to xanthosine 5'-monophosphate with concomitant conversion of NAD+ to NADH. All IMPDHs characterized to date contain a 130-residue "subdomain" that extends from an N-terminal loop of the alpha/beta barrel domain. The role of this subdomain is unknown. An IMPDH homolog has been cloned from Borrelia burgdorferi, the causative agent of Lyme disease (Margolis, N., Hogan, D., Tilly, K., and Rosa, P. A. (1994) J. Bacteriol. 176, 6427-6432). This homolog has replaced the subdomain with a 50-residue segment of unrelated sequence. We have expressed and characterized the B. burgdorferi IMPDH homolog. This protein has IMPDH activity, which unequivocally demonstrates that the subdomain is not required for catalytic activity. The monovalent cation and dinucleotide binding sites of B. burgdorferi IMPDH are significantly different from those of human IMPDH. Therefore, these sites are targets for the design of specific inhibitors for B. burgdorferi IMPDH. Such inhibitors might be new treatments for Lyme disease.     

Spatial and temporal variability in excessive soil phosphorus levels in eastern North Carolina

Numerous studies have shown that accumulation of excessive soil phosphorus raises the potential for phosphorus export and eutrophication of adjacent surface waters. Soil phosphorus data from the North Carolina Agronomy Division's database were analyzed for two-year periods spanning the decades of the 1980s and 1990s for 39 eastern North Carolina counties. Eastern North Carolina supported extensive row crop agriculture, rapidly growing intensive livestock industries, and a growing human population during these decades. Excessive soil phosphorus levels, defined as having a soil phosphorus index (P-I, based on Mehlich III testing) > 100, occurred in over 40% of almost a million samples reported for the three two-year periods analyzed. Excessive soil P-I levels were most frequent in central eastern North Carolina, declined in the 1980s and rose again in the 1990s. The distribution of row crop area with excessive soil P-I levels was very similar in time and space. Increases in the area harvested for cotton (+635%) and pasture (+523%) with excessive soil P-I levels were particularly large during the 1990s, when crop areas harvested associated with excessive soil P-I levels for other major crops (corn, tobacco, peanuts) declined. Residential and recreational land uses were associated with similarly high frequencies of excessive soil P-I levels, but these land uses were relatively unimportant (<5% area) compared to agricultural land use (~34%) in the region. Recent increases in fertilizer shipments (approximately twofold in the late 1990s) likely reflected increased cotton production. Rapid growth in concentrated animal production (almost twofold increase in total animal units (AU) between 1992 and 2001), with accompanying land application of wastes, accounted for increases in soil P-I values in pasturelands in the 1990s, particularly in central eastern North Carolina, where these activities were concentrated. The potential threat to water quality from export of excessive soil phosphorus is therefore greatest in this region. North Carolina is currently developing a Phosphorus Loss Assessment Tool (PLAT) in an attempt to manage the challenge posed by excessive soil phosphorus levels.     

Creep regimes for directionally solidified Al-Al3Ni eutectic composite

Creep characteristics of Al-Al₃Ni eutectic composites directionally solidified at 2.2 × 10^-2 mm/s were determined over a wide range of stress and temperature. Four distinct regions of creep were observed. The rate controlling mechanisms for the four regions appear to be high-temperature dislocation climb in the Al matrix, low-temperature climb in the Al matrix, boundary sliding, and a mechanism involving deformation of the Al₃Ni fibers. Creep rates of the Al-Al₃Ni composite are several orders of magnitude smaller than for pure Al, and apparently, in the regions where deformation of the Al matrix is rate controlling, only a very small fraction of the matrix is deforming during creep of the composite. Formerly Graduate Student, Department of Mechanical and Industrial Engineering, University of Manitoba