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Investment casting is an effective method for fabricating dimensionally accurate metal components of complex shape. In the process of casting nickel superalloys, slurries based on Ludox® SK and zircon silicate (ZrSiO4) are widely used in casting shops. Ceramic moulds based on Ludox SK and ZrSiO4alone have a major disadvantage, as they interact with the molten metal. This interaction significantly reduces the production yield. In the present study causes of the most common blade defects are explained, based on extensive examinations of slurry components by scanning electron microscopy, high-resolution electron microscope, and zeta potential analyser. Slurry rheology via changes of pH and addition of alumina or aluminium oxide (Al2O3) powders is presented. It is found that Al2O3powder as a rheology modifier allows ceramic slurries based on Ludox SK and ZrSiO4to be modified deliberately.

Background:The aim of the study is to prospectively determine the incidence of inflow stenoses in dysfunctional hemodialysis access arteriovenous fistulae (AVFs) and grafts (AVGs). Methods:Contrast-enhanced magnetic resonance angiography (CE-MRA) was performed of 66 dysfunctional AVFs and 35 AVGs in 56 men and 45 women (mean age, 62 years; age range, 31 to 86 years). Complete inflow (from the subclavian artery), shunt region, and complete outflow (including subclavian vein) were shown at CE-MRA. In addition to standard digital subtraction angiography (DSA) of the shunt region and outflow, DSA of the complete inflow was obtained through access catheterization of all cases in which CE-MRA showed an inflow stenosis. Vascular stenosis is defined as greater than 50% decrease in luminal diameter compared with an uninvolved vascular segment located adjacent to the stenosis. Endovascular intervention of stenoses was performed in connection with DSA. Results:CE-MRA showed 19 arterial stenoses in 14 patients (14%). DSA confirmed 18 of these lesions in 13 patients and showed no additional inflow lesions. Of the 13 patients, 7 patients had arterial stenoses only and 6 patients had accompanying stenoses in the shunt region and/or outflow. Referral criteria for the 13 patients to undergo access evaluation had been decreased flow rates (9 patients), steal symptoms (2 patients), and insufficient access maturation (2 patients). Access flow of the 9 patients with a low-flow access improved from 477 ± 74 mL/min to 825 ± 199 mL/min after angioplasty. One patient with steal symptoms became symptom free after angioplasty. Endovascular intervention in 3 patients proved to be unsuccessful. Conclusion:Inflow stenoses are not uncommon in dysfunctional hemodialysis access shunts. We suggest that radiological evaluation comprise assessment of the complete arterial inflow.

The investigation presented in this paper was carried out on ribbon ring samples annealed for 1 hour at various temperatures (Ta = 410, 440, 470, 500 and 580 °C) in order to achieve different stages of nanocrystallization and different magnetic properties. To achieve the full description of crystallization process, both X-ray diffraction method (XRD) as well as differential scanning calorimetry (DSC) were utilized. For magnetoelastic tests, nonmagnetic cylindrical backings were used in order to obtain uniform compressive stresses and enable sample to be wound. In this paper the changes of flux density B as a function of compressive stresses σ (for constant values of the magnetizing field H) for samples at different stages of nanocrystallization are presented. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Quantitative analysis of carotene accumulation in white, pink, pumpkin, orange, and yellow haploid strains ofUstilago violacea by high-performance liquid chromatography indicated that specific patterns of carotene accumulation are primarily responsible for the white, pumpkin, orange, and yellow phenotypes. The yellow strains accumulated primarily ß-zeacarotene and ß-carotene. The white strains accumulated primarily the colorless carotene, phytoene, or did not accumulate any carotene at all. Carotene accumulation in pink haploid strains followed the same patterns as for the white, pumpkin, orange, or yellow strains. Pink diploid and disomic strains ofU. violacea with various parental combinations of the color mutations accumulated either cis-ß-zeacarotene and ß-carotene or only ß-carotene. The pattern of carotene accumulation in conjunction with the available genetic information for the carotene loci inU. violacea was used as a basis for the construction of a new genetic model for carotene biosynthesis inU. violacea. The model employs three dehydrogenases and one cyclase for the synthesis of ß-carotene from phytoene, and accounts for the carotene accumulation patterns of either cis-ß-zeacarotene and ß-carotene or lycopene, ?-carotene, and ß-carotene.

The first synthesis of two conagenin analogs is described.

C18:juvenile hormone is quite soluble in water, yielding a monomeric solution greater than 10-5M. In vivoinjection or addition of aqueous juvenile hormone to the hemolymph in vitroshows the complexation of juvenile hormone to a protein, as demonstrated by gel permeation chromatography and disc-gel electrophoresis. The protein has an apparent molecular weight of 3.4 × 104and is present in the hemolymph at a concentration in the micromolar range. The binding of the hormone to the protein can be described as a simple thermodynamic equilibrium with a dissociation constant of 3 × 10-7M, and the protein has a much higher affinity for the hormone than for the hydrolysis products.

The resistance of Gram−bacteria to the broad-spectrum antibiotic tetracycline (Tc) results from energy-dependent drug efflux mediated by the tetgene product, the cytoplasmic membrane Tet protein. Amino acid (aa) sequences deduced from total tetnucleotide sequences of three different resistance determinants (classes A, B and C) indicate that the protein products [Tet(A), Tet(B), and Tet(C)] share a common ancestor. Hydropathic analysis of Tet sequences predicts twelve transmembrane segments in each protein, with six occuring in each half of the molecule. More importantly, the linear distributions of these segments in the N- and C-terminal halves are nearly identical, suggesting that the two halves of each Tet protein are related by a process of tandem gene duplication and divergence. Indeed, a variable but significant conservation of sequence was detected among the N- and C-terminal halves for all possible comparisons of the three proteins. Such conservation was not observed within other prokaryotic integral membrane proteins or when other prokaryotic proteins were compared to Tet halves. Similarity, both in sequence and in predicted transmembrane structural organization, strongly suggests that a common aancestor of Tet(A), Tet(B), and Tet(C) arose by duplication of a gene reading frame specifying a transmembrane protein of approximately 200 aa residues. The two halves of Tet proteins correspond to the two domains, α and β, which have distinct, complementary roles in Tc efflux. Nevertheless, selective constraints to function in the cytoplasmic membrane have apparently led to maintenance of similar patterns of secondary structural organization in these complementary domains.

Two inhibitors of cynomolgus monkey cholesteryl ester transfer protein were evaluated. One, a monoclonal antibody made against purified cynomolgus monkey cholesteryl ester transfer protein, was capable of severely inhibiting triglyceride transfer, but had a variable effect on cholesteryl ester transfer. At low antibody to antigen ratios, there was what appeared to be a stoichiometric inhibition of cholesteryl ester transfer, but at high antibody to antigen ratios the inhibition of cholesteryl ester transfer was completely relieved, even though triglyceride transfer remained blocked. Fab fragments of the antibody had no effect whatsoever on cholesteryl ester transfer, but were capable of completely blocking triglyceride transfer. The other inhibitor, 6-chloromecuric cholesterol, severely inhibited cholesteryl ester transfer with minimal inhibition of triglyceride transfer. When both inhibitors were added to the assay, both cholesteryl ester and triglyceride transfer were inhibited; an indication that the inhibitors did not compete for the same binding site on cholesteryl ester transfer protein.

The enzymatic reaction of porcine pancreatic lipase with insoluble monolayers of either trioctanoin or 1,2-dioctanoin can be followed quantitatively by monitoring the considerable change in surface pressure which occurs during the course of the reaction. The rate of each reaction is proportional to the surface concentration of the substrate. The calculated pseudo-first order rate constants are proportional to the enzyme concentration in the bulk solution.

The reaction of porcine pancreatic lipase B (EC 3.1.1.3) with the soluble triglyceride, tripropionin, shows substantial stimulation in the presence of hydrophobic surfaces. The enhancement of the enzymatic rate can be correlated with the reversible binding of the enzyme to the hydrophobic surface with a dissociation constant K= 1.3 x10-8m. The binding of the enzyme to the surface is diffusion controlled with a rate constant of 1.8 x106m-1s-1. At saturation of the surface with enzyme each protein molecule occupies an average area of 6000 A2per molecule.

The pH dependence of the α-chymotrypsin-catalyzed hydrolysis of l-tryptophan methyl ester in H2O and D2O and of d-tryptophan methyl ester was determined by spectroscopic means (kcat, Kmand kcat/Km). No product inhibition or substrate activation was observed. The kinetic parameters of the α-chymotrypsin-catalyzed hydrolysis of l-tyrosine p-nitrophenyl ester were also determined. Values of kcatfor both the tyrosine and tryptophan derivatives depend on the ionization of the amino group. For the tryptophan derivatives which were investigated in most detail, the pH dependence of kcat/Km( = k2/Ks) yields a bell-shaped curve with a maximum at pH 7.2. The deuterium oxide kinetic solvent isotope effect and the dependency of the reaction on a base of pK ∼ 7 for the lderivative are comparable to that seen with the corresponding acylamino derivative. Thus, the mechanism of hydrolysis of the amino acid esters appear to be the same as that for the acylamino acid esters. However, the ionizability of the α-amino group in the former produces a markedly different pH dependency of the enzyme-catalyzed reaction, which can be attributed to the presence of a protonated and unprotonated substrate. The protonated substrate is about 20-fold faster than the unprotonated substrate in both acylation and deacylation of l-tryptophan methyl ester. Full specificity of the enzyme (lover d) is found for l-tryptophan methyl ester in its protonated form. This may be due to a hydrogen bond between the substrate and the enzyme with very strict orientational requirements.

The aim of this work was to produce a material with high strength and electrical conductivity. Two aluminium alloys: Al 6101 and 6201 were used for investigation. Improvement of mechanical properties was obtained by severe plastic deformation, using Hydrostatic Extrusion (HE). To examine mechanical properties of the materials microhardness and tensile tests were carried out. Furthermore, the microstructure analysis was carried out using TEM and light microscopy. Electrical conductivity of materials was measured by 4-wire method. It was found that in the material processed by HE tensile strength and microhardness increased about twice. The biggest strength of 356 MPa was obtained for alloy 6201 after HE. In this case the reduction of a diameters from 20 to 5 mm was used. Examination of the microstructure revealed that as a result of HE grain size refinement to 0.5 micrometer occurred. It was also found that the material has the electric conductivity of about 52% IACS.

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The crystal structure of d[Cp(CH3)G] has been determined as part of a project to study the mechanism of the B-Z transition in DNA. The asymmetric unit contains two dinucleotldes and the equivalent of 7.5 water molecules, partially disordered over 12 definable positions. The two symmetry-independent dinucleotides form a duplex with Watson-Crick basepairing and a right-handed helical sense. Comparison with previously determined structures of the B and A conformation showed that this duplex is closer to B than to A but significantly different from B. It corresponds to a stretched out helix with a 4 A rise per base pair and a helical twist of 32°. This structure may serve as a model for the bending of DNA in certain situations. The configuration at the methyl phosphonate is RP, and a mechanism, based on this assignment, is presented for the B–Z transition in DNA.