Electrical characteristics of anodic tantalum pentoxide thin films under thermal stress

In this work, we report on electrical characteristics of tantalum oxide films fabricated by anodic oxidation of tantalum nitride and tantalum silicide with thicknesses ranging from 100 to 4500 Å. These films exhibit greatly improved leakage currents, breakdown voltage and a very low defect density, thus allowing the fabrication of large area capacitors. Leakage currents in the insulator under thermal stress have been carefully studied in order to determine the nature and physical origin of the dominant conduction mechanisms in the insulator. We have found noticeable differences in the dominant conduction mechanisms for thin and thick anodic tantalum pentoxide films. These differences are explained in terms of the thickness dependence of the insulator layer structure.     

Polypropylene/elastomer/poly(styrene-co-acrylonitrile) blends: Manifestation of the critical volume fraction of SAN in dynamic mechanical, tensile and impact properties

The effect of the critical volume fraction v_cr of poly(styrene-co-acrylonitrile) (SAN) on the mechanical properties of its blends with rubber-toughened polypropylene (RTPP) containing about 12% grafted ethylene-propylene copolymer was studied. To encompass a wide spectrum of mechanical properties, blend components were selected which are characterized with rather different viscoelastic, tensile and ultimate properties. The SAN volume fraction in blends covers the interval 0∼0.30; concentration dependencies of measured mechanical properties indicate v_cr = 0.13. Experimental data on storage modulus E_b′, loss modulus E_b″, tensile modulus E_b, yield S_yb and tensile S_ub strength are in plausible accord with their simultaneous prediction based on a predictive scheme which operates with a two-parameter equivalent box model and the data on the phase continuity of components obtained from modified equations of the percolation theory. Strain at break, tensile energy to break and total impact energy of blends show a conspicuous drop in the interval 0∼15 % of SAN where SAN forms a discontinuous component; further growth of the SAN fraction accounts for a reduction of the blend ultimate properties to the values typical of brittle polymers.     

Localization of the gene encoding the human heat shock cognate protein, HSP73, to chromosome 11

The heat shock cognate protein HSP73 (or HSC70) is a member of the HSP70 multigene family. This protein has several functions, including binding to nascent polypeptides to facilitate correct folding and the uncoating of clathrin-coated vesicles. Analysis of somatic cell hybrids by two-dimensional protein gel electrophoresis revealed the presence of a 73-kDa protein in two hybrids containing human chromosomes 5, 6, 9, and 11 in common. Using Western blot analysis, we demonstrate that this protein is a member of the HSP70 family and, by Southern blot analysis, that the HSP73 gene is located on human chromosome 11. Fluorescence in situ hybridization further localized HSP73 to the region 11q23.3-q25. This region is involved in a number of genetic rearrangements and is associated with several well-characterized tumours.     

Use of a flow deflector to protect rheophilic fish spawning grounds during hydropeaking

Rheophilic fishes are one of the ecological groups of fishes declining most quickly in number due to various habitat modifications and discharge regulations. Artificial rapid increases and decreases in discharge (hydropeaking) can cause severe damage to the eggs of rheophilic fishes. We investigated whether the effects of a water increase in hydropeaking on a spawning ground may be mitigated by a deflector installed at the top of the weir that diverts flow to other sections. At the research site, rheophilic asp (Leuciscus aspius) spawn annually in early spring, and their success might be affected by hydropeaking, with base discharge ranging from 3 to 7 m³ × s⁻¹ and peak discharge ranging from 16 to 25 m³ × s⁻¹ occurring 4 to 7 times during the asp spawning season and egg development period. To protect the adhesive eggs from detachment during peak discharge, a flow deflector (a wooden wall at the selected part of the weir) was installed to regulate discharge on the protected spawning ground. This measure allowed normal discharge under base flow conditions. During peak flow, a significant portion of the additional water was directed to the part of the river channel where egg abundance was lower and to the mill channel, where asp spawning was not present. While the total discharge increased 4.1 times compared to the base flow, the water discharge in the protected spawning ground increased only 2.7 times. This resulted in more than half of the asp eggs being retained in the protected channel. Although the use of such a measure is limited to specific local conditions where eggs are located just downstream of the weir, it can be a valid solution in highly fragmented rivers with hydropeaking and can lead to higher recruitment of rheophilic fishes.     

Use of anodic tantalum pentoxide for high-density capacitor fabrication

In this work we report on very thin (10 to 100 nm) tantalum oxide fabricated by anodic oxidation of tantalum nitride and tantalum silicide to be used as the dielectric of high density MIM and MIS capacitors. These films exhibit greatly improved leakage currents, breakdown voltage and very low defect density, thus allowing the fabrication of large area capacitors. Several counter and bottom electrodes have been used and compared. The effects of the different processing conditions (top-electrode metals, annealing conditions, bottom electrode stoichiometry) on the capacitor performances are extensively discussed throughout this work. The nitrogen content of tantalum nitride films seems to have an important influence on the insulator quality. Leakage currents in the insulator have been carefully studied in order to determine the nature and physical origin of the dominant conduction mechanisms in the insulator. The electrical behaviour of the resulting high-density MIM capacitors has been extensively characterized. Finally, we describe a new method to fabricate MIS diodes with anodic tantalum oxide as insulator.     

Cadmium uptake by a green alga can be predicted by equilibrium modelling

Short-term uptake of cadmium by a wild-type (2137) and a cell wall-less strain (CW-2) of Chlamydomonas reinhardtii was examined as a function of Cd speciation in a well-defined, aqueous medium. Internalization fluxes were determined for free cadmium concentrations ranging from 5 x 10(-10) M to 5 x 10(-4) M in the presence of ligands forming both labile and inert hydrophilic complexes. A first-order biological internalization, as predicted by the free ion activity model (FIAM), was observed for both strains. The maximum Cd internalization flux, Jmax, for the wild-type strain was 5-fold higher (1.3 x 10(-11) mol cm(-2) min(-1)) than for the CW-2 strain (2.3 x 10(-12) mol cm(-2) min(-1)) and was not influenced by the presence of competitors such as Ca in the experimental solution. The conditional stability constant for the adsorption of Cd to transport sites of the CW-2 strain was 5-fold higher (10(6.7) M(-1)) than for the wild-type strain (10(6) M(-1)). Competition experiments demonstrated that Mo, Mn, Cu, Co, Zn, Ni, Ca, and Pb inhibited, at least partially, Cd uptake, while no inhibition was observed for similar concentrations of Mg and Fe. The stability constant for the competitive binding of Ca to the Cd transport site was determined to be 10(4.5) M(-1). Cu and Zn competed with Cd uptake sites with stability constants of 10(5.6) and 10(5.2) M(-1), respectively. Protons also appeared to compete with Cd uptake sites as uptake could generally be predicted quantitatively in their presence. Finally, in the presence of low concentrations (<20 mg L(-1)) of Suwannee River fulvic acid, Cd internalization fluxes could be predicted from [Cd2+], in accordance with the FIAM.     

Varying the Directionality of Protein Catalysts for Aldol and Retro-Aldol Reactions

Natural aldolase enzymes and created retro-aldolase protein catalysts often catalyze both aldol and retro-aldol reactions depending on the concentrations of the reactants and the products. Here, we report that the directionality of protein catalysts can be altered by replacing one amino acid. The protein catalyst derived from a scaffold of a previously reported retro-aldolase catalyst, catalyzed aldol reactions more efficiently than the previously reported retro-aldolase catalyst. The retro-aldolase catalyst efficiently catalyzed the retro-aldol reaction but was less efficient in catalyzing the aldol reaction. The results indicate that protein catalysts with varying levels of directionality in usually reversibly catalyzed aldol and retro-aldol reactions can be generated from the same protein scaffold.