The high-resolution microwave spectrum of cyclopropyl cyanide

The quadrupole hyperfine structure of six selected rotational transitions of cyclopropyl cyanide has been analyzed. The derived coupling constants are χ_aa = ?3.453(11) MHz and χ_bb = 1.759(16) MHz. The analysis yielded improved center frequencies for the multiplets and, in turn, led to slightly revised rotational constants: A = 15786.068(22), B = 3465.112(7), C = 3286.252(10) MHz; D_N = 1.18(30) kHz.     

The total synthesis of d1-dihydrocallitrisin

Bromodiene $\text{2}$ is converted to $\text{dl}$-dihydrocallitrisin ($\text{1}$), a sesquiterpene lactone recently isolated from the heartwood of $\text{Callitris}$$\text{columellaris}$.     

Power requirement for the mixing of thixotropic liquids

A procedure has recently been proposed by Godfrey et al. [1] for the calculation of the variation of power consumption with time when a thixotropic liquid is agitated from rest using an impeller which rotates at constant speed. This procedure requires a knowledge of the power requirement for Newtonian and time-independent non-Newtonian liquids together with viscometric data for the thixotropic liquid obtained under constant shear rate conditions.Experimental work to test the procedure has been carried out in a 0.126-m-diameter cylindrical vessel with anchor, helical ribbon and helical screw impellers. Power consumption data were obtained for a range of Newtonian and time-independent non-Newtonian liquids and this was then used to make predictions of the measured power input to the thixotropic liquids: salad cream, tomato ketchup, yoghurt, paint and Laponite solutions.The agreement between experiment and theory was usually better than 10%. However, for the case of the helical screws rotating in Laponite it was observed that regions existed close to the vessel wall where there was no fluid circulation. In such cases, the predicted power input was greatly in excess of the measured value. This is not a serious limitation of the predictive procedure since efficient industrial mixers would keep the entire fluid in circulation.     

A crystallographic, EPR and theoretical study of the Jahn-Teller distortion in [CuTp2] (Tp- = tris[pyrazol-1-yl]hydridoborate)

Crystals of the title compound (1) contain two independent, centrosymmetric half-molecules per asymmetric unit. While both of these show Jahn-Teller elongated six-coordinate geometries, the lengths of the elongated Cu-N bonds in the two molecules differ by 0.117(2) A at 30 K. The structure of one of these molecules (molecule A) does not vary with temperature below 350 K. The other molecule (molecule B) shows Cu-N bond lengths that are temperature-dependent between 225 and 375 K, but do not vary further at lower temperature. This indicates a fluxional axis of Jahn-Teller elongation in this molecule at these higher temperatures. Consideration of the thermal parameters in these structures implies that the fluxionality in molecule B is frozen out near 150 K. This conclusion is supported by a Q-band powder EPR study. The d-d transition energies of molecules A and B have been calculated by several density function (DF) methods, including a time-dependent DF calculation. The crystallographic data have been reproduced using the vibronic coupling model of Burgi and Hitchman. This has shown that the different fluxionality regimes for molecules A and B are not a consequence of their different static molecular structures, but rather reflect their different local environments in the crystal.     

Crystal engineering of microporous 'Chinese-lantern' compounds to improve their ability to reversibly adsorb sulfur dioxide

Three new 'Chinese lantern' complexes [XMn(mu-dppO2)4MnX](2+)2X-.4MeOH.Me2CO [X = Cl, Br, I; dppO2 = 1,3-bis(diphenylphosphinoyl)propane], have been structurally characterised using single-crystal X-ray diffraction and shown to have increasing affinity for SO2 across the series Cl < Br < I via thermogravimetric measurements.     

An evolutionary approach for finding optimal trees in undirected networks

In many utilities, such as water and gas, materials are distributed through networks of pipes. For efficiency, many such distribution networks are constructed as trees. The cost of construction and operation of these is generally a complex function of the edges which are used, so that it is impossible to use conventional algorithms for the optimisation of trees. This paper presents a method for identifying a tree which is close to optimal. This evolutionary method is based on ideas from genetic algorithms.     

Thermal smearing and screening in a strong magnetic field for Dirac materials in comparison with the two dimensional electron liquid

We compute and compare the effects due to a uniform perpendicular magnetic field as well as temperature on the static polarization functions for monolayer graphene (MLG), associated with the Dirac point, with that for the two-dimensional electron liquid (2DEL) with the use of comprehensive numerical calculations. The relevance of our study to the Friedel oscillations for the screening of the potential for a dilute distribution of impurities is reported too. Our results show substantial differences due to screening for the 2DEL and MLG which have not been given adequate attention previously.     

ASSESSING EARLY MATHEMATICAL DEVELOPMENT

The work discussed here is part of an international study involving Dutch, Belgian, German, Greek, Finnish and Slovenian as well as English children aged between 52 and 98 months. The project is coordinated by the University of Utrecht and employs the Utrecht Early Mathematical Competence Test. The full international data set is currently being analysed. This paper reports only the analysis of the English data, together with some international data already in the public domain. The data are interrogated to throw light upon (a) the comparison between England and other countries, (b) the relationship between age and mathematical attainment in the English sample, (c) differences between boys and girls and (d) the relationship between attainment in Piagetian tasks and more arithmetical tasks.