Space groups P1 and Cc: how are they doing?

A survey of recent entries in the Cambridge Structural Database suggests that the percentage of structures described in space groups of inappropriately low symmetry has decreased from about 10% in the early 2000s to less than 5% today for space group Cc, but that for space group P1 it remains close to 8%

1,6-Diazabicyclo[4.4.4]tetradecane and its lnside-protonated lon: Changes in Space Groups

The crystal structures of 1,6-diazabicyclo[4.4.4]tetradecane (1) and of its inside-protonated ion (2), which were originally described in space group C2/c, should be described instead in trigonal space groups, (1) in R3c and (2) in P31c; both moieties have crystallographically imposed point symmetry D_3 rather than C_2

The impact of higher education institutions on the UK economy

This study presents an up-to-date analysis of the impact of UK higher education institutions on the economy of the United Kingdom during the academic and financial year 1999/2000. It examines the role of higher education as a conventional industry and the economic activity generated in the UK as a result of higher education activity.The UK higher education institutions (HEIs) included in this study are the 170 institutions returned to the Higher Education Statistics Agency (HESA) in the academic and financial year 1999/2000. The higher education sector is defined as comprising the UK HEIs plus all overseas students and overseas visitors to UK HEIs in the study year.Key economic aspects of UK higher education institutions, in terms of income, expenditure and employment, are examined together with the secondary or 'knock-on' effects of UKHEI activity and that of the expenditure of overseas students and overseas visitors attracted to the UK by HEIs. The study additionally highlights the skills profile of employment generated by UK HEIs and by overseas student and visitor expenditure. The overall impact of the higher education sector on the economy was estimated using aspecially constructed type 11 UK input-output model, with data derived from the 1998 UK input-output tables together with 1998 Labour Force Survey data

Overview of the labour market [January 2001]

The most recent labour market data indicates continued employment growth. The number of unfilled vacancies appears to be rising apace indicating that as the number of unemployed continues to fall, employers are finding it increasingly difficult to recruit staff. The rise in the level of those economically active (and a corresponding fall in economic inactivity) is reassuring. This suggests that both government policy and opportunity has spurred people into the labour market who othewise might not have taken part. Rising wage levels and further vacancy information will indicate whether this injection into the labour market is sufficient to prevent any labour shortages, thus enabling the current run of growth to continue

Defining and identifying the knowledge economy in Scotland: a regional perspective on a global phenomenon

The development and growth of a knowledge economy has become a key policy aim forgovernments in all advanced economies. This is based on recognition that technologicalchange, the swift growth of global communications, and the ease of mobility of capital across national borders has dramatically changed the patterns of international trade and investment. The economic fate of individual nations is now inseparably integrated into the ebb and flow of the global economy. When companies can quickly move capital to those geographical locations which offer the best return, a country's long term prosperity is now heavily dependent on its abilityto retain the essential factors of production that are least mobile. This has led to apremium being placed on the knowledge and skills embodied in a country's labourforce, as it has become a widely accepted view that a country which possesses a high level of knowledge and skills in its workforce will have a competitive advantage overothers with a lower domestic skill base. Knowledge and skills are thought to be thebasis for the development of a knowledge economy

A revised structure for α-dicalcium silicate hydrate

The structure of α-dicalcium silicate hydrate, Ca_2(SiO_3OH)(OH), has recently been described and refined [Y ano, Urabe, Ikawa, Teraushi, Ishizawa & Udagawa (1993). Acta Cryst. C49, 1555-1559] in space group P2_12_12_1 (orthorhombic; a = 9.487 (4), b = 9.179 (4), c = 10.666 (7) Å, Z = 8). It is better described in Pbca. Revised coordinates are given

Competitive partitioning of rotational energy in gas ensemble equilibration

A wide-ranging computational study of equilibration in binary mixtures of diatomic gases reveals the existence of competition between the constituent species for the orbital angular momentum and energy available on collision with the bath gas. The ensembles consist of a bath gas AB(v;j), and a highly excited minor component CD(v';j'), present in the ratio AB:CD = 10:1. Each ensemble contains 8000 molecules. Rotational temperatures (T(r)) are found to differ widely at equilibration with T(r)(AB)/T(r)(CD) varying from 2.74 to 0.92, indicating unequal partitioning of rotational energy and angular momentum between the two species. Unusually, low values of T(r) are found generally to be associated with diatomics of low reduced mass. To test effects of the equi-partition theorem on low T(r) we undertook calculations on HF(6;4) in N(2)(0;10) over the range 100-2000 K. No significant change in T(r)(N2)/T(r)(HF) was found. Two potential sources of rotational inequality are examined in detail. The first is possible asymmetry of -Δj and +Δj probabilities for molecules in mid- to high j states resulting from the quadratic dependence of rotational energy on j. The second is the efficiency of conversion of orbital angular momentum, generated on collision with bath gas molecules, into molecular rotation. Comparison of these two possible effects with computed T(r)(AB)/T(r)(CD) shows the efficiency factor to be an excellent predictor of partitioning between the two species. Our finding that T(r) values for molecules such as HF and OH are considerably lower than other modal temperatures suggests that the determination of gas ensemble temperatures from Boltzmann fits to rotational distributions of diatomics of low reduced mass may require a degree of caution

On the structure of 9-amino-2,7-di-tert-butylacridine

The crystal structure of 9-amino-2,7-di-tert-butylacridine hydrochloride monohydrate, C_(21)H_(27)N_2^+.Cl^-.H_2O, has been described in space group P3_1 [trigonal, a = 11.086 (2), c = 14.367 (4) Å, Z = 3; McKenna, Agbandje & Neidle (1992). Acta Cryst. C48, 188-190]. It is properly described in space group P3_121. Further refinement in P3_121, based on the original F values, leads to an improved R (0.049 vs 0.067) and to a revised position for the Cl^- ion

On the structure of 'potassium nitroprusside 0·8 hydrate'

The crystal structure of the compound reported as K_2[Fe(CN)_5NO].0·8H_2O, potassium pentacyanonitrosylferrate hydrate (1/0·8), recently described and refined in the non-centrosymmetric space group Pna2_1 [orthorhombic; a = 30·000 (8), b = 11·272 (3), c = 16·053 (4) Å, Z = 20; Castellano, Rivero, Piro & Amalvy (1989). Acta Cryst. C45, 1207-1210], is properly described as centrosymmetric, space group Pnma. Refinement in Pnma shows that one of the K atoms is, instead, an Na atom and that three of the sites of the water molecules are partially occupied; the proper formulation of the compound is K_9Na[Fe(CN)_5NO]_5.nH_2O (n = 4·8)

The importance of weak reflections in resolving the centrosymmetric-noncentrosymmetric ambiguity: a cautionary tale

The weak diffraction intensities are crucially important in determining whether a crystal structure has a real or only an approximate, center of symmetry; if these intensities are deleted from the data set, an intelligent conclusion may be impossible. In addition, statistical distribution tests, if based only on the stronger intensities, may be strongly biased toward a noncentrosymmetric indication. In one recently published structure determination [Cotton & Fanwick (1980), Acta Cryst. B36, 457-459] a distribution test led to the assignment of the noncentrosymmetric space group Cc to a structure which can be better described and refined in the centrosymmetric space group C2/c