Specific heat and anisotropic superconducting and normal-state magnetization of HoNi2B2C

The magnetization of single-crystal HoNi₂B₂C has been measured as a function of applied field (H) and temperature in order to probe the interplay between superconductivity and magnetism in this complex layered system. The normal-state magnetic susceptibility of HoNi₂B₂C is highly anisotropic with a Curie-Weiss-like temperature dependence for H applied perpendicular to the c-axis and with a much weaker temperature dependence for H applied parallel to the c-axis, indicating that the Ho⁺³ magnetic moments lie predominately in the tetragonal a−b plane below 20 K. High-field magnetization (2000 Oe), low-field magnetization (20 Oe) and zero-field specific heat all give an antiferromagnetic ordering temperature of T_N=5.0 K. Remarkably, in 20 Oe applied field both superconductivity (T_c=8.0 K) and antiferromagnetism (T_N=5.0 K) clearly make themselves manifest in the magnetization data. From these magnetization data a phase diagram in the H−T plane was constructed for both directions of applied field. This phase diagram shows a non-monotonic temperature dependence of H_c2 with a deep minimum at T_N=5 K. The high-field magnetization data for H applied perpendicular to the c-axis also reveal a cascade of three phase transitions for T < 5 K and H < 15 000 Oe, contributing to the rich H versus T phase diagram for HoNi₂B₂C at low temperatures.     

A modal separation measurement technique for broadband noise propagating inside circular ducts

A measurement technique which separates broadband noise propagating inside circular ducts into the acoustic duct modes is developed. The technique is also applicable to discrete frequency noise. The acoustic modes are produced by weighted combinations of the instantaneous outputs of microphones spaced around the duct circumference. The technique is compared with the cross spectral density approach presently available and found to have certain advantages, and disadvantages. Considerable simplification of both the new technique and the cross spectral density approach occurs when no correlation exists between different circumferential mode orders. The properties leading to uncorrelated modes and experimental tests which verify this condition are discussed. The modal measurement technique-is applied to the case of broadband noise generated by flow through a coaxial obstruction (nozzle or orifice) in a pipe. Different circumferential mode orders are shown to be uncorrelated for this type of noise source.     

The Definition of Parliamentary Constituencies in Great Britain: A Computer-Based Information System

The periodic reviews of parliamentary constituencies in Great Britain require the Parliamentary Boundary Commission in each country to propose any necessary changes in order that constituencies shall be as near the electoral quota (i.e. the average electorate per constituency) as possible, within certain constraints. For each unit (county, London borough etc.) with which they work, the number of potential solutions to their problem is very large. This paper describes a computer program that can be used to inform the Commission about all those solutions, so improving the information base from which they select the new set of constituencies.     

Reactions of unsaturated acid halides—IV: Competitive friedel-crafts acylations and alkylations of monohalogenobenzenes by the bifunctional cinnamoyl chloride

Aluminium chloride-catalysed acylations and alkylations of monohalogenobenzenes with cinnamoyl chloride has been studied. Under strictly homogeneous conditions, alkylation was increasingly favoured relative to acylation as the primary reaction along the series: benzene <fluorobenzene<bromobenzene<chlorobenzene. Changing to heterogeneous conditions (excess catalyst with CS₂ as diluent) preserved this order but primary alkylation was relatively enhanced. The addition of nitrobenzene to the homogeneous reaction restrained alkylation more than acylation.Primary acylation may be followed by alkylation giving asymmetrical 1,3,3-triarylpropan-1-ones but the possibility that these are formed by alkylation followed by acylation is ruled out. These ketones may subsequently undergo α,β-ketonic fission.Primary alkylation may be followed by cycliacylation producing 3-arylindan-l-ones with the halogeno substituent at the side-chain aryl group and this observation rules out their alternative mode of formation, cyclialkylation of the primary acylation product.An example of a para → meta bromine shift is discussed.     

Regioselectivity of the halolactonization of γ,δ-unsaturated acids

Bromolactonization of 4-hexenoic acids gives a greater percentage of δ-lactones than does iodolactonization. Substituents in the 3-position favor the formation of δ-lactones while substituents in the 6-position favor the formation of γ-lactones.     

Effects of the separating shear layer on the reattachment flow structure Part 1: Pressure and turbulence quantities

The effect of the separating shear-layer thickness and shape on the structure of the flow in the reattachment region of a backward-facing step is examined using wall static-pressure profiles and turbulence data for a range of Reynolds number (800 < Re _H< 40,000) and upstream boundary-layer thickness (0 < δ/H < 2). The reattachment pressure and the peak pressure in the reattachment zone decrease in a continuous manner as the upstream boundary layer thickens. The thinnest boundary layers follow the correlation of Roshko and Lau. Using the pressure data, correlations are developed which can be used to predict the level of turbulent shear stress in the near-wall region at reattachment, a location in which experimental data are extremely difficult to obtain.     

Hydrostatic pressure effects on the superconducting properties of Ag1−xSn1+xSe2

The superconducting transition temperature, T_c, of NaCl structure compounds in the series Ag_1?xSn_1+xSe₂ is found to be exceptionally sensitive to hydrostatic pressures up to 21 kbar. For five samples of varying composition, T_c is suppressed smoothly at a rate of ?(6?8)×10^?5K·bar^?1. These results are discussed with respect to the volume sensitivity of the electron-phonon interaction responsible for superconductivity.