Nanosecond x-ray diffraction from polycrystalline and amorphous materials in a pinhole camera geometry suitable for laser shock compression experiments.

Nanosecond pulses of quasimonochromatic x-rays emitted from the K shell of ions within a laser-produced plasma are of sufficient spectral brightness to allow single-shot recording of powder diffraction patterns from thin foils of order millimeter diameter. Strong diffraction signals have been observed in a cylindrical pinhole camera arrangement from both polycrystalline and amorphous foils, and the experimental arrangement and foil dimensions are such that they allow for laser shocking or quasi-isentropic loading of the foil during the diffraction process.

Large acoustic transients induced by nonthermal melting of InSb.

We have observed large-amplitude strain waves following a rapid change in density of InSb due to nonthermal melting. The strain has been measured in real time via time-resolved x-ray diffraction, with a temporal resolution better than 2 ps. The change from the solid to liquid density of the surface layer launches a high-amplitude strain wave into the crystalline material below.

The effects of smoking on bone health.

Osteoporotic fractures are a major public health problem in most developed countries and an increasing concern in much of the developing world. This healthcare burden will increase significantly worldwide over the next 20 years due to aging of the population. Smoking is a key lifestyle risk factor for bone loss and fractures that appears to be independent of other risk factors for fracture such as age, weight, sex and menopausal status.

Genetic effects on bone loss in peri- and postmenopausal women: a longitudinal twin study.

Unlabelled: This longitudinal twin study was designed to assess the heritability of bone loss in peri- and postmenopausal women. A sample of 724 female twins was studied. Baseline and repeat BMD measurements were performed.

Shock waves in polycrystalline iron.

The propagation of shock waves through polycrystalline iron is explored by large-scale atomistic simulations. For large enough shock strengths the passage of the wave causes the body-centered-cubic phase to transform into a close-packed phase with most structure being isotropic hexagonal-close-packed (hcp) and, depending on shock strength and grain orientation, some fraction of face-centered-cubic (fcc) structure. The simulated shock Hugoniot is compared to experiments.

The vertebral fracture cascade in osteoporosis: a review of aetiopathogenesis.

Once an initial vertebral fracture is sustained, the risk of subsequent vertebral fracture increases significantly. This phenomenon has been termed the "vertebral fracture cascade". Mechanisms underlying this fracture cascade are inadequately understood, creating uncertainty in the clinical environment regarding prevention of further fractures.

In vivo quantification of fat content in mice using the Hologic QDR 4500A densitometer.

Purpose: Validation of dual-energy X-ray absorptiometry (DXA) with the Hologic QDR 4500A (QDR 4500) Fan Beam X-ray densitometer for in vivo assessment of body fat content in mice.

Methods: Precision of DXA fat measurement was assessed by repeated in vivo scanning and re-positioning of different sized mice (17.6, 24.

Alendronic acid produces greater effects than risedronic acid on bone density and turnover in postmenopausal women with osteoporosis : results of FACTS -international.

Background: The objective of the study was to evaluate the effects of alendronic acid once weekly relative to risedronic acid once weekly on bone mineral density (BMD), markers of bone turnover and tolerability in the treatment of osteoporosis in postmenopausal women.

Methods: This was a randomised, double-masked, double-dummy multicentre international study (75 centres in 27 countries in Europe, the Americas and Asia-Pacific). A total of 1303 women were screened and 936 with low bone density (T-score < or = -2.

Balance impairment is related to vertebral fracture rather than thoracic kyphosis in individuals with osteoporosis.

Introduction: Balance impairments have been identified in people with osteoporosis. Although an association between thoracic kyphosis and impaired balance has been reported, the specific role of vertebral fractures has not been considered. This study aimed to investigate the independent effects of osteoporotic vertebral fracture and thoracic kyphosis on balance characteristics in an osteoporotic population.

The influence of dance training on growth and maturation of young females: a mixed longitudinal study.

Background: The effects of systematic sports training during childhood and adolescence on subsequent growth and sexual maturation remains in dispute.

Aim: The study aimed to determine whether moderate-high volumes of dance training adversely influence linear growth and sexual maturation of young girls progressing through puberty.

Subjects And Methods: This 3-year mixed longitudinal study comprised 82 novice dancers and 61 controls, aged 8-11 years at baseline, who were assessed bi-annually for 3 consecutive years.

Anti-epileptic medication and bone health.

Background: Epilepsy is a common chronic neurological disorder, usually requiring long-term treatment with anti-epileptic drugs (AED). Many studies have reported that AED therapy is associated with metabolic bone disease and is a major iatrogenic risk factor for fractures. There remains uncertainty about the type(s) of bone disease due to AED treatment, and the pathogenesis of AED-associated fractures.

Shock deformation of face-centred-cubic metals on subnanosecond timescales.

Despite its fundamental importance for a broad range of applications, little is understood about the behaviour of metals during the initial phase of shock compression. Here, we present molecular dynamics (MD) simulations of shock-wave propagation through a metal allowing a detailed analysis of the dynamics of high strain-rate plasticity. Previous MD simulations have not seen the evolution of the strain from one- to three-dimensional compression that is observed in diffraction experiments.

Dancing for bone health: a 3-year longitudinal study of bone mineral accrual across puberty in female non-elite dancers and controls.

Introduction: Weight-bearing exercise during growth enhances peak bone mass. However, the window of opportunity for optimizing positive effects of exercise on peak bone mass remains to be fully defined. Ballet dancing provides a model of mechanical loading patterns required to site-specifically modulate bone.

Genetic and environmental influences on variation in balance performance among female twin pairs aged 21-82 years.

Genetic and environmental influences on variation in balance performance were measured in 93 monozygous and 83 dizygous female twin pairs aged 21-82 years (mean age, 50.5 years) in Melbourne, Australia, between 1999 and 2003. The authors administered clinical (Lord's Balance Test and Step Test) and laboratory tests of static and dynamic balance from the Chattecx Balance System with and without distractor tasks.

Radiation transfer effects on the spectra of laser-generated plasmas.

Experimental x-ray spectra of the H-like 2p --> 1s (Lyman-alpha) doublet have been obtained using time-integrated high-resolution spectroscopy of a constrained-flow, laser-generated aluminum plasma. These spectra show monotonic alteration of the relative intensities of the doublet components with distance from the target surface. Excellent agreement between experiment and theory is found only if the modeling includes both ion collisional rates between the fine-structure components of the level and, more importantly, the radiative pumping of one Lyman-alpha component by the other component along the direction of the major velocity gradient (i.

Maternal 25-hydroxyvitamin D and parathyroid hormone concentrations and offspring birth size.

Context: There is inconsistent evidence that maternal 25-hydroxyvitamin D [25-(OH)D] deficiency may impair fetal growth.

Objective: The objective of the study was to examine the relationship between maternal 25-(OH)D and PTH concentrations at less than 16 and 28 wk gestation and offspring birth size.

Design: This was an observational study.

Effect of antiepileptic medication on bone mineral measures.

Objective: Long-term antiepileptic drug (AED) use has been associated with bone disease, but many previous studies have been limited by inadequate control subjects. We used a cotwin affected sib-pair model to investigate this issue.

Methods: The authors studied 31 female twin (15 monozygous and 16 dizygous) and four sibling pairs (< 3 years age difference) aged 21 to 75 years, in which one member had > 12 months of AED treatment.

Should older people in residential care receive vitamin D to prevent falls? Results of a randomized trial.

Objectives: To determine whether vitamin D supplementation can reduce the incidence of falls and fractures in older people in residential care who are not classically vitamin D deficient.

Design: Randomized, placebo-controlled double-blind, trial of 2 years' duration.

Setting: Multicenter study in 60 hostels (assisted living facilities) and 89 nursing homes across Australia.

Observation of structural anisotropy and the onset of liquidlike motion during the nonthermal melting of InSb.

The melting dynamics of laser excited InSb have been studied with femtosecond x-ray diffraction. These measurements observe the delayed onset of diffusive atomic motion, signaling the appearance of liquidlike dynamics. They also demonstrate that the root-mean-squared displacement in the [111] direction increases faster than in the [110] direction after the first 500 fs.

Direct observation of the alpha-epsilon transition in shock-compressed iron via nanosecond x-ray diffraction.

In situ x-ray diffraction studies of iron under shock conditions confirm unambiguously a phase change from the bcc (alpha) to hcp (epsilon) structure. Previous identification of this transition in shock-loaded iron has been inferred from the correlation between shock-wave-profile analyses and static high-pressure x-ray measurements. This correlation is intrinsically limited because dynamic loading can markedly affect the structural modifications of solids.

Is there overlap between the genetic determinants of mammographic density and bone mineral density?

Mammographic density and bone mineral density, risk factors for breast cancer and osteoporotic fractures, respectively, are both thought to reflect cumulative exposure to estrogen and are highly heritable. We asked if there was overlap between the genes that explain their variances. We studied 63 monozygous and 71 dizygous female twin pairs ages 38 to 71 years (mean, 50 years).

In vivo intrarater and interrater precision of measuring apparent bone mineral density in vertebral subregions using supine lateral dual-energy x-ray absorptiometry.

Analysis of apparent bone mineral density (BMD) in the lumbar spine is commonly based on anteroposterior (AP) scanning using dual-energy X-ray absorptiometry (DXA). Although not widely used, clinically important information can also be derived from lateral scanning. Vertebral bone density, and therefore strength, can may vary in different subregions of the vertebral body.

A review of anatomical and mechanical factors affecting vertebral body integrity.

Background: The aetiology of osteoporotic vertebral fracture is multifactorial and may be conceptualised using a systems framework. Previous studies have established several correlates of vertebral fracture including reduced vertebral cross-sectional area, weakness in back extensor muscles, reduced bone mineral density, increasing age, worsening kyphosis and recent vertebral fracture. Alterations in these physical characteristics may influence biomechanical loads and neuromuscular control of the trunk and contribute to changes in subregional bone mineral density of the vertebral bodies.