781 research outputs found
Blood Pressure and Cognitive Decline Over 8 Years in Middle-Aged and Older Black and White Americans
Although the association between high blood pressure (BP), particularly in midlife, and late-life dementia is known, less is known about variations by race and sex. In a prospective national study of 22 164 blacks and whites ≥45 years without baseline cognitive impairment or stroke from the REGARDS cohort study (Reasons for Geographic and Racial Differences in Stroke), enrolled 2003 to 2007 and followed through September 2015, we measured changes in cognition associated with baseline systolic and diastolic BP (SBP and DBP), as well as pulse pressure (PP) and mean arterial pressure, and we tested whether age, race, and sex modified the effects. Outcomes were global cognition (Six-Item Screener; primary outcome), new learning (Word List Learning), verbal memory (Word List Delayed Recall), and executive function (Animal Fluency Test). Median follow-up was 8.1 years. Significantly faster declines in global cognition were associated with higher SBP, lower DBP, and higher PP with increasing age ( P<0.001 for age×SBP×follow-up-time, age×DBP×follow-up-time, and age×PP×follow-up-time interaction). Declines in global cognition were not associated with mean arterial pressure after adjusting for PP. Blacks, compared with whites, had faster declines in global cognition associated with SBP ( P=0.02) and mean arterial pressure ( P=0.04). Men, compared with women, had faster declines in new learning associated with SBP ( P=0.04). BP was not associated with decline of verbal memory and executive function, after controlling for the effect of age on cognitive trajectories. Significantly faster declines in global cognition over 8 years were associated with higher SBP, lower DBP, and higher PP with increasing age. SBP-related cognitive declines were greater in blacks and men
Ultrasonic Methods for Characterizing the Interface in Composites
Micromechanical modeling studies of composite materials have highlighted the need for better characterization of the interface zone in composite materials. Bulk behavior in composites has been predicted to be strongly influenced by the local elastic properties, residual stresses, and adhesion of the interface. Techniques to nondestructively measure these newly perceived quantities of importance do not exist. Thus it is not possible experimentally to (i) confirm the micromechanical model predictions, (ii) explore the relationships between interface properties and processing variables, and (iii) ensure acceptable interface properties in commercially fabricated composites. We report here the current status of a SDIO/ONR funded research program directed at developing experimental techniques for characterizing the interface zone in composites through the use of ultrasonic interface waves [1]
The First Space-Based Gravitational-Wave Detectors
Gravitational waves provide a laboratory for general relativity and a window
to energetic astrophysical phenomena invisible with electromagnetic radiation.
Several terrestrial detectors are currently under construction, and a
space-based interferometer is envisioned for launch early next century to
detect test-mass motions induced by waves of relatively short wavelength.
Very-long-wavelength gravitational waves can be detected using the plasma in
the early Universe as test masses; the motion induced in the plasma by a wave
is imprinted onto the cosmic microwave background (CMB). While the signature of
gravitational waves on the CMB temperature fluctuations is not unique, the
polarization pattern can be used to unambiguously detect gravitational
radiation. Thus, forthcoming CMB polarization experiments, such as MAP and
Planck, will be the first space-based gravitational-wave detectors.Comment: 5 pages, 3 postscript figure
Past environmental proxies from the Middle Stone Age at Sibudu, Kwazulu-Natal, South Africa
Middle Stone Age technological and behavioural developments
in southern Africa are central to understanding the
emergence of modern humans, and elucidating the role of
environmental change in this trajectory is dependent on
emerging palaeoclimatic reconstructions. Climate proxies
from Middle Stone Age sites are often poorly preserved,
coarsely resolved or subject to anthropogenic selection and
are not considered in favour of global environmental proxies
despite the fact that the modern climate regimes at the
relevant archaeological sites differ profoundly. Sibudu has a
well-preserved Middle Stone Age sequence that has yielded
abundant palaeoclimate proxy data. Isotopic analysis of
charcoal, charcoal anatomy and species representation, macro-
and micro-faunal remains, sediment texture, mineralogy
and magnetic susceptibility, pollen and macrobotanical
remains provide evidence for the environmental succession
specific to this site. The isotopic data suggest that archaeological
charcoal was not significantly post-depositionally
altered. During the Howiesons Poort (65–62 ka) the local
environment was thickly forested, moist and more humid
than during the 58 ka occupations. The environment changes
during the post-Howiesons Poort occupation (~58 ka) into the
late MSA occupation (~48 ka); conditions became drier and
colder than present with vegetation shifting to open savanna
grassland or woodlands.Les Ă©volutions technologiques et comportementales du Middle
Stone Age dans le sud de l’Afrique sont essentielles pour comprendre
l’émergence de l’Homme moderne, et la compréhension
du rĂ´le des changements environnementaux dans cette
trajectoire dépend des reconstitutions paléo-climatiques émergentes.
Les données indirectes liées au climat du MSA sont souvent
mal conservées, de résolution grossière ou soumis à une
sélection d’origine anthropique et sont abandonnées au profit
des données indirectes liées aux conditions environnementales
globales, en dépit du fait que les régimes climatiques modernes
sur les sites archéologiques étudiés diffèrent profondément.
Sibudu a une séquence bien conservée du Middle Stone
Age qui a fournit d’abondantes données paléoclimatiques indirectes.
L’analyse isotopique de charbons de bois, l’anatomie
du charbon de bois et la représentation des espèces, des restes
de faunes macroscopiques et microscopiques, la texture des
sédiments, la minéralogie et la susceptibilité magnétique, le
pollen et les restes macrobotaniques fournissent des indices de
l’évolution de l’environnement spécifique à ce site. Au cours
de la période Howiesons Poort (65–62 ka), l’environnement
local est couvert de forĂŞts Ă©paisses et humide, plus humide encore
lors des occupations de 58 ka. L’environnement change
au cours de l’occupation post-Howiesons Poort (~ 58 ka)
jusqu’a la fin de l’occupation MSA (~ 48 ka) : il devient plus
sec et plus froid qu’à présent et la végétation se mue en grande
savane herbeuse ou boisée.Palaeo-Anthropological Scientific Trust (PAST), the National Research Foundation
(NRF), the Council for Scientific and Industrial Research (CSIR) and the University of the Witwatersrand.http://www.african-archaeology.dehb201
Stochastic Simulation of Mudcrack Damage Formation in an Environmental Barrier Coating
The FEAMAC/CARES program, which integrates finite element analysis (FEA) with the MAC/GMC (Micromechanics Analysis Code with Generalized Method of Cells) and the CARES/Life (Ceramics Analysis and Reliability Evaluation of Structures / Life Prediction) programs, was used to simulate the formation of mudcracks during the cooling of a multilayered environmental barrier coating (EBC) deposited on a silicon carbide substrate. FEAMAC/CARES combines the MAC/GMC multiscale micromechanics analysis capability (primarily developed for composite materials) with the CARES/Life probabilistic multiaxial failure criteria (developed for brittle ceramic materials) and Abaqus (Dassault Systmes) FEA. In this report, elastic modulus reduction of randomly damaged finite elements was used to represent discrete cracking events. The use of many small-sized low-aspect-ratio elements enabled the formation of crack boundaries, leading to development of mudcrack-patterned damage. Finite element models of a disk-shaped three-dimensional specimen and a twodimensional model of a through-the-thickness cross section subjected to progressive cooling from 1,300 C to an ambient temperature of 23 C were made. Mudcrack damage in the coating resulted from the buildup of residual tensile stresses between the individual material constituents because of thermal expansion mismatches between coating layers and the substrate. A two-parameter Weibull distribution characterized the coating layer stochastic strength response and allowed the effect of the Weibull modulus on the formation of damage and crack segmentation lengths to be studied. The spontaneous initiation of cracking and crack coalescence resulted in progressively smaller mudcrack cells as cooling progressed, consistent with a fractal-behaved fracture pattern. Other failure modes such as delamination, and possibly spallation, could also be reproduced. The physical basis assumed and the heuristic approach employed, which involves a simple stochastic cellular automaton methodology to approximate the crack growth process, are described. The results ultimately show that a selforganizing mudcrack formation can derive from a Weibull distribution that is used to describe the stochastic strength response of the bulk brittle ceramic material layers of an EBC
Recruitment of Spiny Lobsters, Panulirus argus, to submerged sea cages off Puerto Rico, and its implication for the development of an aquaculture operation
- …