Vacuum ultraviolet spectroscopy of Ce(3+)-doped SrMgF(4) with superlattice structure.

X-ray diffraction of Ce(3+)-doped SrMgF(4) (SMF:Ce) crystals shows a superlattice structure, reflecting the distribution of Ce(3+) polyhedra centres observed in optical experiments. Optical absorption bands and fluorescence bands from the Ce(3+) polyhedra centres overlap in the vacuum ultraviolet (VUV) and ultraviolet (UV) regions, respectively, so that wide pumping and tuning ranges are expected for laser operation. The SMF:Ce crystals, as well as the isomorphous BaMgF(4), are candidates for a tunable laser gain material with nonlinear properties. The optical absorption, excitation, and fluorescence bands observed in the SMF:Ce crystals at low temperatures are ascribed to five distinct fluorescent centres. Three centres have well-known Ce(3+) optical characters, for example, fluorescence with double peaks separated by 2000 cm(-1) and five resolved absorption/excitation bands. These centres are assigned to Ce(3+)-polyhedra classified by weak and strong crystal fields as a consequence of the superlattice structure. The other two fluorescence bands observed in the visible region have 1.5-2 times larger linewidths than those of the former three bands. These bands are interpreted as optical transitions from complexes consisting of Ce(3+) and one or two electrons trapped at a vacancy of the nearest neighbour F(-) ligand ions.

Polymorphism in 2,4,6-trinitrotoluene crystallized from solution.

An examination has been made of the role of solvent type in the definition of the polymorphic nature of 2,4,6-trinitrotoluene precipitated from solution. A combination of calorimetric and structural techniques including in situ crystallization studies using synchrotron radiation has shown that the variations in polymorphic form following precipitation from solution do not arise specifically from any stereospecific guidance that the nature of the solvent might impose on the structural form. Rather the differences are linked to the variations in solubility and hence supersaturation which might build up prior to nucleation and growth and to the isolation of the metastable orthorhombic phase from the solvent. The final conclusion is that the changes fit well with Ostwald's Law of Stages with the orthorhombic form always precipitating initially followed by its conversion to the stable monoclinic form. The previously observed tendency for some solvents to yield one or the other form then becomes attributable to kinetics in solution rather than structural control. It can be associated with the solubility of the material in the solvent used and the role of this factor in a solvent-mediated phase transformation. On this basis rules can be formulated for the isolation of the metastable forms of this and similarly related polymorphic systems.

Oral rehydration therapy: a Third World solution applied to intensive care.

Oral rehydration therapy (ORT)--World Health Organisation formula--has reduced the mortality of severe diarrhoea tenfold but its use in Intensive Care has not been reported. ORT was administered via a nasogastric tube to 3 adult intensive care patients who developed severe diarrhoea and post-operative acute renal impairment. The median intake of ORT was 2.21/day (range 1.5-3.0) and the mean duration of therapy was 7 days (range 6-10). Renal function improved (creatinine fell from 389 to 165 mmol/l) and both haemodynamic and metabolic stability (Na, K, Mg, PO4 and urea) were maintained. While it may not reduce the volume of diarrhoea, ORT provides a cheap, effective and physiological solution to severe gastrointestinal losses in intensive care and may have wider application in both adult and paediatric practice.

Cigarette smoking and the age at menopause.

In a sample of 15,464 apparently healthy Australian women, the mean age at natural menopause of women who smoke ten or more cigarettes a day was 1.3 years lower than that of other women. These distributions were well described by logistic distributions with the same variances. A parallel non-parametric Kaplan-Meier analysis confirmed that heavy smokers reached menopause earlier than other women, and also showed that the women accurately recalled their age at menopause. Logistic regression analyses were used to show that obesity, alcohol intake and regular use of aspirin and other analgesics, sedatives, tranquillizers or anti-depressants did not affect the distribution of the age at natural menopause. The age-specific probability of natural compared with surgically induced menopause was shown to be independent of smoking history and obesity. Logistic regression analysis is a powerful statistical technique for analysing data such as age-specific proportions of still menstrual women. It is easy to apply and interpret, and its aptness for any particular data set is readily assessed.

A multivariate assessment of alcohol consumption.

Subjects attending a large, multiphasic health screening centre in Sydney, Australia estimated their alcohol consumption and specimens of their blood were analysed. The most useful univariate estimates of alcohol consumption were erythrocyte mean corpuscular volume and plasma aspartate-aminotransferase, gamma-glutamyl-transpeptidase, triglycerides and uric acid. The most statistically significant of these tests have been combined to form a multivariate predictor of alcohol intake which is more successful in identifying heavy-drinkers than single tests. To describe this population further, and to aid comparisons between populations, information about non-drinkers has also been provided.