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Recent numerical studies have shown that forced, statistically isotropic turbulence develops a 'thermal-equilibrium' spectrum, E(k) ∝ k², at large scales. This behaviour presents a puzzle, as it appears to imply the growth of a non-zero Saffman integral, which would require the longitudinal velocity correlation function, ∝ (r), to satisfy ∝ (r → 8) ∝ r-3. As is well known, the Saffman integral is an invariant of decaying turbulence, precisely because non-local interactions (i.e. interactions via exchange of pressure waves) are too weak to generate such correlations. Subject to certain restrictions on the nature of the forcing, we argue that the same should be true for forced turbulence. We show that long-range correlations and a k² spectrum arise as a result of the turbulent diffusion of linear momentum, and extend only up to a maximum scale that grows slowly with time. This picture has a number of interesting consequences. First, if the forcing generates eddies with significant linear momentum (as in so-called Saffman turbulence), a thermal spectrum is not reached - instead, a shallower spectrum develops. Secondly, the energy of turbulence that is forced for a while and then allowed to decay obeys Saffman's decay laws for a period that is much longer than the duration of the forcing stage. [ABSTRACT FROM AUTHOR]

Byline: M. J. Grainge (1), C. A. C. Coupland (1), S. J. Cliffe (1), C. E. D. Chilvers (1), D. J. Hosking (2) Keywords: Key words:Bone density -- Cross-sectional study -- Menopause -- Osteoporosis -- Postmenopausal -- Reproduction Abstract: The associations between a number of reproductive and menopausal factors and bone mineral density (BMD) were studied in a sample of early postmenopausal women. The study included 580 women aged 45--61 years who completed a risk factor questionnaire containing sections on obstetric and menstrual history. BMD measurements were taken at the anteroposterior (AP) spine, greater trochanter, femoral neck, total radius and whole body, along with whole body bone mineral content (BMC). In analyses adjusting for key confounders, number of pregnancies was more strongly associated with increased BMD than number of live births at all sites (p&lt 0.05 at femoral neck and total radius), and menstrual years was more strongly associated with increased BMD than years since menopause (p&lt 0.05 at all sites). Hysterectomized women had a significantly higher adjusted mean BMD than non-hysterectomized women at all sites (AP spine: 0.999 g/cm.sup.2 vs 0.941 g/cm.sup.2, p&lt 0.001), although there were no significant differences in BMD between hysterectomized women who had a bilateral oophorectomy and those whose ovaries were preserved. Negative associations between the duration of hot flushes and BMD were statistically significant (p&lt 0.05) at the three non-hip sites. In multiple regression analyses containing all reproductive terms, duration of hormone replacement therapy (HRT) use, menstrual years and hysterectomy status were significantly associated with BMD at all five sites, whilst oral contraceptive use before the age of 23 years was significantly associated with increased BMD at all sites except the total radius. Breastfeeding duration, the duration of oral contraceptive use and premenopausal amenorrhea were found to have no association with BMD. Results for whole body BMC were consistent with those for the five BMD sites, across all the variables considered here. These findings confirm the importance of HRT use and duration of menses as predictors of BMD, whilst the results for hysterectomy status and early oral contraceptive use require further consideration. Author Affiliation: (1) Division of Public Health Medicine and Epidemiology, School of Community Health Sciences, University of Nottingham Medical School, Queen's Medical Centre , GB (2) Division of Mineral Metabolism, Nottingham City Hospital, Nottingham, UK, GB Article note: Received: 26 July 2000 / Accepted: 5 April 2001

Byline: O. Sahota (1), I. Fowler (3), P. J. Blackwell (3), N. Lawson (3), S. A. Cawte (4), P. San (2), T. Masud (5), D. J. Hosking (2) Keywords: Key words:Alendronate -- Bone mineral density -- Calcitriol -- Established osteoporosis -- Etidronate Abstract: A number of drugs are now available for the treatment of established osteoporosis and have been shown to significantly increase bone mineral density (BMD). There are, however, few comparative treatment studies and, furthermore, adverse events remain a problem with some of the newer agents, particularly in the elderly, in everyday clinical practice. We report a 12 month, open labeled, randomized controlled, prospective treatment study in 140 postmenopausal women with established vertebral osteoporosis, comparing the effect of continuous alendronate, cyclical alendronate and cyclical etidronate with calcitriol in terms of gain in BMD, reduction in bone turnover markers and adverse event profile. The mean percentage increases in BMD at 12 months, at the spine and hip respectively, were: continuous alendronate 5.7%, 2.6% cyclical alendronate 4.1%, 1.6% cyclical etidronate 4.9%, 2.0% (p&lt 0.01) and calcitriol 2.0%, 0.4% (NS). In comparison with calcitriol, the mean changes in BMD at the spine and hip respectively were greater in the other groups continuous alendronate: 3.7% (95% CI 1.4 to 8.3), 2.2% (95% CI 0.7 to 4.0) cyclical alendronate: 2.1% (95% CI 1.2 to 6.4), 1.2% (95% CI -0.3 to 3.0) cyclical etidronate: 2.9% (95% CI 1.9 to 6.5), 1.6% (95% CI 0.9 to 3.1)). The reduction in bone turnover markers was between 26% and 32% in the alendronate and etidronate groups (p&lt 0.01), with a trend toward greater reduction in the continuous alendronate group. Eight patients discontinued the study: 6 in the continuous alendronate group, 1 in the cyclical alendronate group and 1 in the calcitriol group. Two patients in the cyclical etidronate group were unable to tolerate the Cacit component, but continued on substituting Cacit with Calcichew. In summary, 12 months of treatment with continuous alendronate, cyclical alendronate and cyclical etidronate are effective in terms of the gain in BMD at the anteroposterior spine and total hip in a comparable treatment population. These treatments are more effective than calcitriol and were generally well tolerated. Continuous alendronate showed a trend toward a larger gain in BMD and greater suppression of bone turnover markers than the other treatment groups, but had a higher incidence of adverse events, particularly within the older subgroup. Cyclical alendronate offers a lower adverse event profile and appears to be effective in comparison with continuous treatment, and may possibly be an alternative in the elderly. However, further studies are necessary, but more importantly with fracture end-points. Author Affiliation: (1) Ageing and Disability Research Unit (ADRU), University Hospital, Nottingham Divisions of (2) Mineral Metabolism, GB (3) Clinical Chemistry, GB (4) Nuclear Medicine, GB (5) Geriatric Medicine, City Hospital, Nottingham, UK, GB Article note: Received: 6 April 1999 / Accepted: 8 June 2000

Byline: C. A. C. Coupland (1), M. J. Grainge (1), S. J. Cliffe (1), D. J. Hosking (2), C. E. D. Chilvers (1) Keywords: Key words:Bone density -- Occupation -- Occupational activity -- Osteoporosis -- Postmenopausal Abstract: Few studies have assessed the relationship between occupational activity and bone mineral density (BMD), although two case--control studies have reported a protective effect of occupational activity on hip fracture. In the present study 580 postmenopausal women aged 45--61 years completed a risk factor questionnaire including a detailed occupational history. For each job, hours spent sitting, standing, walking, lifting and carrying were recorded these measures, evaluated at ages 20, 30, 40 years, in the current job and over the working lifetime, were used in the analysis. BMD was measured with dual-energy X-ray absorptiometry, and measurements at five sites were used in a multiple regression analysis adjusting for potential confounding variables. There was a significant negative association between sitting at age 20 years and BMD at the radius (p= 0.037), with negative relationships of borderline significance at the anteroposterior spine (pa=a0.091) and whole body (p= 0.078). There were significant positive associations between standing at age 30 years and BMD at all five sites (p&lt 0.05), but no significant linear associations for standing at ages 20 and 40 years. No significant associations were found for lifetime or current occupational measures of sitting, standing, walking and lifting or carrying. The lack of consistency of these significant findings suggests that they may have occurred by chance, and that occupational activity has little if any effect on BMD in postmenopausal women. Author Affiliation: (1) Division of Public Health Medicine and Epidemiology, University of Nottingham Medical School, Nottingham , GB (2) Division of Mineral Metabolism, Nottingham City Hospital, Nottingham, UK, GB Article note: Received: 12 March 1999 / Accepted: 17 September 1999