Conduction mechanism in sputtered polycrystalline zinc oxide thin films

Conductivity and Hall effect data are reported for columnar polycrystalline zinc oxide films between 1 and 4 μm thick deposited onto insulating substrates by r.f. reactive sputtering. Crystallites are (00.1) oriented, typically a few hundred nanometers in diameter and 98%–99% packed. Resistivities between 10⁷ and 10¹¹ Ω cm at 300 K typically decrease by between one and three orders of magnitude for a 100 K temperature increase. The shallow oxygen vacancy donor is the only impurity level present in significant densities; IR absorption indicates densities greater than 10¹⁷ cm^-3, but Hall measurements show apparent carrier concentrations of between 10⁴ and 10⁸ cm^-3.This anomaly is resolved by invoking the Petritz diode model of conduction in discontinuous materials, modified to include the case of highly doped crystallites and applied to zinc oxide with deplectively chemisorbed intercrystalline states. Quantitative agreement is found for conductivity against temperature. The measurable Hall carrier concentration, deduced from the empirical intracrystallite carrier densities of between 1 × 10¹⁵ and 1 × 10¹⁹ cm^-3 and barrier heights of between 0.6 and 1.2 eV, agrees well with Hall effect measurements. Crystallite surface state densities of about 10¹³ cm^-2 are indicated as responsible for these effects.     

A bait and switch hapten strategy generates catalytic antibodies for phosphodiester hydrolysis

General base catalysis supplied by the histidine-12 (H-12) residue of ribonuclease (RNase) A has long been appreciated as a major component of the catalytic power of the enzyme. In an attempt to harness the catalytic power of a general base into antibody catalysis of phosphodiester bond hydrolysis, the quaternary ammonium phosphate 1 was used as a bait and switch hapten. Based on precedence, it was rationalized that this positively charged hapten could induce a counter-charged residue in the antibody binding site at a locus suitable for it to deprotonate the 2'-hydroxyl group of the anhydroribitol phosphodiester substrate 2. After murine immunization with hapten 1, mAb production yielded a library of 35 antibodies that bound to a BSA-1 conjugate. From this panel, two were found to catalyze the cyclization-cleavage of phosphodiester 2. Kinetic studies at pH 7.49 (Hepes, 20 mM) and 25 degreesC showed that the most active antibody, MATT.F-1, obeyed classical Michaelis-Menten kinetics with a Km = 104 microM, a kcat = 0.44 min-1, and a kcat/kuncat = 1.7 x 10(3). Hapten 1 stoichiometrically inhibits the catalytic activity of the antibody. MATT.F-1 is the most proficient antibody-catalyst (1.6 x 10(7) M-1) yet generated for the function of phosphodiester hydrolysis and emphasizes the utility of the bait and switch hapten paradigm when generating antibody catalysts for processes for which general-base catalysis can be exploited.     

Clinical and economic analysis of allogeneic peripheral blood progenitor cell transplants: a Canadian perspective

Allogeneic peripheral blood progenitor cell (PBPC) transplants are an alternative to BMT, although G-CSF mobilization dose, timing of pheresis and risk of GVHD are not well defined. We compared harvest characteristics, donor and recipient outcomes and costs of two PBPC transplant strategies with historical controls who received BMT. Twenty donors mobilized with four daily s.c. G-CSF doses (5 microg/kg/day) (group 1) and 20 mobilized with 10 microg/kg/day G-CSF (group 2) were compared with 20 BM controls (group 3). G-CSF and phereses were well tolerated. Four of 40 PBPC donors required femoral catheter placement. At least 2.5 x 10(6) CD34+/kg recipient weight were collected with two phereses in 19/20 donors (group 1) and 18/20 donors (group 2). Time to neutrophil (18 vs 20 vs 22 days, P = 0.02) and platelet (21 vs 24 vs 27 days, P = 0.005) engraftment was shorter in the PBPC groups (group 2 vs group 1 vs group 3) but secondary engraftment outcomes were not different. The incidence of grade 2-4 aGVHD was higher in the low-dose G-CSF group (group 1) but there was no difference in cGVHD, 100-day or 1-year survival. The mean PBPC transplant cost (group 1) at first hospital discharge was less than BM (group 3) ($34,643 vs $37,354) but the mean overall cost for both groups was similar at 100 days ($46,334 vs $46,083). Allogeneic PBPC transplant with short course, low-dose G-CSF mobilization is safe, feasible and cost equivalent to allogeneic BMT.     

Microstructure and tensile behavior of nitrogen-alloyed,dual-phase stainless steels

Two alloys of high-nitrogen stainless steel have been heat treated to produce dual-phase microstruc-tures. The first alloy, N10CrNiMol7 1, a Ni-containing stainless steel, was processed conventionally. The second alloy, N20CrMol7, a Ni-free stainless steel, was processed to obtain a higher nitrogen content by pressurized electroslag remelting. The martensite in N10CrNiMol7 1 was homogeneously distributed in the ferrite and obtained a near-constant volume fraction as a function of intercritical annealing temperature. Microprobe analysis and microhardness measurements of the martensite con-stituent suggested that up to 0.4 pct N was dissolved in the austenite before quenching. Austenite formation, martensite transformation, undissolved nitrides, and retained austenite were evaluated by transmission electron microscopy (TEM). The Ni-containing alloy exhibited classic dual-phase tensile behavior in that continuous yielding was observed together with good combinations of ultimate tensile strength and total elongation. The martensite constituent in alloy N20CrMol7 was concen-trated within bands. Comparison of tensile properties of the two alloys at similar volume fractions and hardness levels of martensite and ferrite showed that the microstructure containing banded mar-tensite had inferior combinations of strength and ductility. The degradation of tensile ductility was accompanied by a fracture mode transition from microvoid coalescence to transgranular cleavage. The deformation and fracture behavior of both alloys were related to the microstructure.     

A Tutorial on Satellite Graphics Systems

Satellite graphics terminals, which include a micro or minicomputer to perform interactive processing, present a number of advantages–not the least of which are accessibility and responsiveness. This paper describes two basic types of satellites and outlines techniques for best exploiting their capabilities.