Observation of superconductivity (Tc = 50 K) in a new tetragonal alkaline-earth cuprate Sr0.8Ba1.2CuO3+δ, synthesised at ambient pressure

The ambient-pressure synthesis of a new tetragonal alkaline-earth superconducting cuprate, Sr_0.8Ba_1.2CuO_3+δ, from a cupro-oxycarbonate is reported. Magnetic-susceptibility measurements show the presence of a superconducting transition 50 K in a post-annealed sample. The crystal structure, refined from time-of-flight powder neutron-diffraction data was found to have an oxygen-deficient La₂CuO₄-type tetragonal T structure (a = 3.8988(3) Å and C = 12.815(3) Å) with oxygen vacancies located within the CuO₂ planes. Ordering of these oxygen vacancies is responsible for the observation of a superlattice in both neutron- and electron-diffraction measurements. An interpretation of the electron-diffraction patterns suggests that the superlattice in Sr_0.8Ba_1.2CuO_3+δ and also in the isostructural superconductor Sr₂CuO_3+δ are of an identical nature.     

Uniform distribution of polynomial-generated sequences inGF[q,x]

Summary Analogs are proved for sequences in Φ=GF[q, x], the ring of polynomials in x over a finite field of q elements, of results of Niven, Zane, and Cavior concerning uniform distribution of sequences of integers generated by polynomials with integer coefficients. The uniform distribution (mod m), m an integer, in these papers is replaced here by a concept called weak uniform distribution (mod M), M ε Φ. Supported byNSF Research GrantGP 6515. Entrata in Redazione il 21 settembre 1968.     

Beitr?ge zur Ultramikro-und Spurenanalyse organischer Stoffe

Zusammenfassung Zur Ultramikrobestimmung von Brom in schwerflüchtigen organischen Verbindungen werden 1–5 g Substanz (mit dieser Methode sind auch größere Substanzmengen analysierbar) durch Lösungsteilung abgemessen und nach Absaugen des Lösungsmittels im Wasserstoffstrom bei einer konstanten Temperatur von etwa 900°C pyrolysiert, wobei sich Brom quantitativ zu Bromwasserstoff umsetzt, der in einer Vorlage in Eisessig absorbiert und argentometrisch titriert wird. Die Endpunktsanzeige erfolgt bipotentiometrisch. Bei Abwesenheit von anderen Halogeniden und Sulfid werden Silberbromid-Elektroden benutzt, andernfalls SilberElektroden. Die relative Standardabweichung der Methode beträgt im ersten Fall ±1.4% und erhöht sich auf etwa ±3%, wenn gleichzeitig Chlor, Jod oder Schwefel vorliegen.

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Summary For the determination of bromine in ultramicro amounts of non-volatile organic compounds 1–5 g of the substance (this method can be used for larger amounts as well) are measured by taking an aliquot of a solution of known concentration. After evaporation of the solvent the sample is pyrolyzed in a hydrogen stream at a constant temperature of about 900°C. Hydrogen bromide obtained in a quantitative reaction, is absorbed in glacial acetic acid and titrated argentometrically. The endpoint of the titration is found by a bipotentiometric method. In the absence of other halogenides or sulphide silver bromide electrodes are used, otherwise silver electrodes. The relative standard deviation is ±1.4% in the first case and about ±3% in the latter.

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Herzlicher Dank gilt Herrn Prof. Dr. R. Bock für wertvolle Diskussionen. Der Deutschen Forschungsgemeinschaft, Bad Godesberg, sowie dem Verband der chemischen Industrie Düsseldorf, danken wir für ihre Unterstützung. Herrn cand. chem. H.-J. Anhuth sei vielmals für sorgfältig durchgeführte Messungen zur Bestimmung von Bromid neben anderen Halogeniden gedankt.

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Herrn Prof. Dr. F. Strassmann zum 65. Geburtstag gewidmet.

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VI. Mitteilung: Tölg, G., and K. Ballschmiter: Microchem. J. 9, 257 (1965).     

Frequency-stabilized cavity ring-down spectroscopy measurements of carbon dioxide isotopic ratios

Carbon dioxide (CO₂) isotopic ratios on samples of pure CO₂ were measured in the 1.6 μm wavelength region using the frequency-stabilized cavity ring-down spectroscopy (FS-CRDS) technique. We present CO₂ absorption spectra with peak signal-to-noise ratios as high as 28,000:1. Measured single-spectrum signal-to-noise ratios were as high as 8900:1, 10,000:1, and 1700:1 for ¹³C/¹²C, ¹⁸O/¹⁶O, and ¹⁷O/¹⁶O, respectively. In addition, we demonstrate the importance of utilizing the Galatry line profile in the spectrum analysis. The use of the Voigt line profile, which neglects the observed collisional narrowing, leads to large systematic errors which are transition-dependent and vary with temperature and pressure. While the relatively low intensities of CO₂ transitions near λ=1.6 μm make this spectral region non-optimal, the sensitivity and stability of FS-CRDS enabled measurement precision of pure CO₂ samples which are comparable to those of other optical techniques which operate at far more propitious wavelengths. These results indicate that a FS-CRDS spectrometer designed to probe CO₂ bands near wavelengths of 2.0 μm or 4.3 μm could achieve significantly improved precision over the present instrument and likely be competitive with mass spectrometric methods.     

Structured Markov Chain Monte Carlo

Abstract

This article introduces a general method for Bayesian computing in richly parameterized models, structured Markov chain Monte Carlo (SMCMC), that is based on a blocked hybrid of the Gibbs sampling and Metropolis—Hastings algorithms. SMCMC speeds algorithm convergence by using the structure that is present in the problem to suggest an appropriate Metropolis—Hastings candidate distribution. Although the approach is easiest to describe for hierarchical normal linear models, we show that its extension to both nonnormal and nonlinear cases is straightforward. After describing the method in detail we compare its performance (in terms of run time and autocorrelation in the samples) to other existing methods, including the single-site updating Gibbs sampler available in the popular BUGS software package. Our results suggest significant improvements in convergence for many problems using SMCMC, as well as broad applicability of the method, including previously intractable hierarchical nonlinear model settings.     

Orthorhombic Polymorphs of 1-Phenyl-3-(3-Hydroxyphenyl)-2-Propen-1-One

Abstract  

Chalcones, 1,3-diphenyl-2-propene-1-ones, exist naturally and synthetically, and are characterized by the linkage of two aromatic rings joining a three carbon α-β-unsaturated carbonyl entity. We report the observation of two new polymorphs of a hydroxy chalcone, C₆H₅–CO–CH=CH–C₆H₄ (m-OH), identified as a result of a Claisen–Schmidt synthesis and manual screening technique. One polymorph of this compound has been reported previously and exists in the monoclinic system, space group P2/n, with unit cell parameters a = 13.295(6) ?, b = 5.659(2) ?, c = 16.144(8) ?, β = 109.73(5)°, V = 1143.3(9) ?³, and Z = 4. Two crystalline forms (II and III) reported herein, are polymorphs of the reported monoclinic form (I). Form II exists in the orthorhombic system, space group Pca2₁, with unit cell constants a = 11.631 (2) ?, b = 13.163 (3) ?, c = 7.3977 (14) ?, V = 1132.6 (4) ?³, and Z = 4. Form III also crystallizes in the orthorhombic system, however in space group Pbca, with unit cell parameters a = 11.8100(8) ?, b = 7.4075(5) ?, c = 25.8729(19) ?, V = 2263.4(3) ?³, and Z = 8. Variations in the hydrogen bonding connectivity help to distinguish these two forms from the monoclinic, whereas crystal packing differentiates the two orthorhombic forms. The conformation of the C=C (C2–C3) is E for both orthorhombic forms.