Influence of Grain Growth on Dielectric Properties of Nb-Doped BaTiO3

Effects of grain size and grain growth in Nb-doped BaTiO₃ on temperature and frequency dependencies of the dielectric constant were investigated. When 0.65 μm powder is sintered to an average grain size of 1 μm, two dielectric constant peaks indicate the presence of Nb-free BaTiO₃ and of Nb-containing material. Single peaks are observed above room temperature after additional grain growth or when 0.07 μm powder is sintered to an average grain size of 1 μm. The Curie point of pure BaTiO₃ with 1 μm grains is 4 to 6°C lower than that of material with grains >10 μm. Thermodynamically, this behavior is accounted for by a phase inversion stress ∼ the room-temperature stress.     

Optical and Magnetic Properties of Some Transition Metal Ions in Barium Phosphate Glass

In barium phosphate glass containing first-row transition metal ions, the ions appear to possess normal oxidation states: Cr³⁺, Mn³⁺, Fe^2+,3+, Co²⁺, Ni²⁺, and Cu²⁺. Room temperature and 77°K spectra for Cr³⁺-, Mn³⁺-, Fe^2+,3+-, Ni²⁺-, and Cu²⁺-containing glasses can be interpreted, on the, basis of octahedrally coordinated metal ions, whereas the spectrum of the Co²⁺ glass correlates with a tetrahedrally coordinated metal ion. Magnetic moments for the glasses are similar to those for the spin-only values of the various metal ions.     

Effects of Grain Growth on the Distribution of Nb in BaTiO3 Ceramics

Measurements of Nb diffusion into large- and small-grained BaTiO₃ disks show a high ratio of grain boundary to bulk diffusivity. Well defined X-ray diffraction lines are found in Nb-doped BaTiO₃ only when significant grain growth occurs during sintering. When grain growth of a 0.65 μm grain size powder is limited at ∼1 μm, excess line broadening results. This is attributed to the simultaneous presence of Nb-free and Nb-rich regions. Because of its low bulk diffusivity little Nb penetrates into the original BaTiO₃ grain cores, and a solid solution forms only in the regions of recrystallization. When grain growth is limited, the "sintering reaction" results in a non-homogeneous system; when appreciable grain growth occurs, most of the original grain cores are eliminated and an essentially uniform system is obtained.     

CIPHER MACHINE INVENTOR - BORIS HAGELIN DIES

Abstract

The article discusses the late Cold War joint Polish security and East German Stasi signals intelligence operation against U.S. wireless communications lines in light of the files available at the Polish Institute of National Remembrance. It emphasizes the factors that contributed to the unsuccessful outcome of their efforts. The text also briefs measures related to signals intelligence and operational security applied by the communist secret services.     

EFFECT OF SALICYLHYDROXAMIC ACID (SHAM) ON DL-DOPA OXIDATION BY MUSHROOM TYROSINASE AND BY NaIO4

Salicylhydroxamic acid (SHAM) inhibits very effectively the rate of DL‐DOPA oxidation by mushroom tyrosinase. SHAM also affects the spectrum of the initial produces) formed when DL‐DOPA is oxidized by mushroom tyrosinase or by NaIO4. Moreover, at certain concentrations, SHAM prevents the polymerization of dopaquinone formed enzymaticatty or nonenzymatically probably due to a chemical interaction between dopaquinone and SHAM.     

2,3-DIHYDROXYBENZOIC ACID AS A SUBSTRATE FOR MUSHROOM TYROSINASE1,2

When 2, 3-dihydroxybenzoic acid (2, 3-DBA) is acted upon by mushroom tyrosinase, a yellow intermediate, 2, 3-DBA-o-quinone, characterized by a peak at 415 nm, is the first product detected. 2, 3-DBA-o-quinone gives rise to a “final blue product” (λmax = 230, 410, 620 nm), and to “soluble oxidation product(s)” (λmax = 275–280, 350–360 nm). Kinetic data (assayed spectrophotometrically and polarographically) obtained when different concentrations of 2, 3-DBA were oxidized by a fixed amount of mushroom tyrosinase, deviated from classic Michaelis-Menten kinetics. Reduction of the “final blue product” with ascorbate resulted in the loss of the blue chromophore at 620 nm and the concomitant appearance of a “yellowish reduced final product.” The “yellowish reduced final product” could be reoxidized with either mushroom tyrosinase or with NaIO4 to the “final blue product,” indicating that the latter has carbonylic quinonoid groups in ortho position to each other.     

THE VALUTON: AN AUTOMATION MODEL OF A SOCIOLOGICAL THEORY OF VALUE GENESIS

Abstract

Theories of value are legion, few axe satisfactory, however. Scarcity as source of value is too relativistic and also unable to explain negative evaluation of scarce objects. Labor as a basis of value cannot take account of observed variations of the value of goods. The present approach is an attempt to see value as the result of two sociological processes: proliferation and status association. The first process determines the value of a commodity by its information content, the other by a perceptional process, the halo-effect. The value of a commodity is hence the result of its history, a string of inputs. They lend themselves to be represented in form of an automaton. A prototype of such an automaton is presented, the valuton. A critical assessment concludes the article.     

Preparation of Small-Grained and Large-Grained Ceramics from Nb-Doped BaTiO3

Barium titanate powders with average grain sizes of 0.07 and 0.65 μm were coated with an organic Nb ester, using a liquid-solid mixing process. Small-grained (1 to 3 μm) ceramic dielectrics from both powders and large-grained (>50 μm) dielectrics from the 0.65 μm powder were fired using 0 to 2 at.% Nb. Microstructures, densities, and electrical resistivities were investigated.