1,124 research outputs found
The Influence of Fallback Foods on Great Ape Tooth Enamel
Lucas and colleagues recently proposed a model based on fracture and deformation concepts to describe how mammalian tooth enamel may be adapted to the mechanical demands of diet (Lucas et al.: Bioessays 30[2008] 374-385). Here we review the applicability of that model by examining existing data on the food mechanical properties and enamel morphology of great apes (Pan, Pongo, and Gorilla). Particular attention is paid to whether the consumption of fallback foods is likely to play a key role in influencing great ape enamel morphology. Our results suggest that this is indeed the case. We also consider the implications of this conclusion on the evolution of the dentition of extinct hominins
Fracture in teeth—a diagnostic for inferring bite force and tooth function
Teeth are brittle and highly susceptible to cracking. We propose that observations of such cracking can be used as a diagnostic tool for predicting bite force and inferring tooth function in living and fossil mammals. Laboratory tests on model tooth structures and extracted human teeth in simulated biting identify the principal fracture modes in enamel. Examination of museum specimens reveals the presence of similar fractures in a wide range of vertebrates, suggesting that cracks extended during ingestion or mastication. The use of ‘fracture mechanics’ from materials engineering provides elegant relations for quantifying critical bite forces in terms of characteristic tooth size and enamel thickness. The role of enamel microstructure in determining how cracks initiate and propagate within the enamel (and beyond) is discussed. The picture emerges of teeth as damage-tolerant structures, full of internal weaknesses and defects and yet able to contain the expansion of seemingly precarious cracks and fissures within the enamel shell. How the findings impact on dietary pressures forms an undercurrent of the study
Pattern formation and selection in quasi-static fracture
Fracture in quasi-statically driven systems is studied by means of a discrete
spring-block model. Developed from close comparison with desiccation
experiments, it describes crack formation induced by friction on a substrate.
The model produces cellular, hierarchical patterns of cracks, characterized by
a mean fragment size linear in the layer thickness, in agreement with
experiments. The selection of a stationary fragment size is explained by
exploiting the correlations prior to cracking. A scaling behavior associated
with the thickness and substrate coupling, derived and confirmed by
simulations, suggests why patterns have similar morphology despite their
disparity in scales.Comment: 4 pages, RevTeX, two-column, 5 PS figures include
Making stillbirths count, making numbers talk - issues in data collection for stillbirths.
BACKGROUND: Stillbirths need to count. They constitute the majority of the world's perinatal deaths and yet, they are largely invisible. Simply counting stillbirths is only the first step in analysis and prevention. From a public health perspective, there is a need for information on timing and circumstances of death, associated conditions and underlying causes, and availability and quality of care. This information will guide efforts to prevent stillbirths and improve quality of care. DISCUSSION: In this report, we assess how different definitions and limits in registration affect data capture, and we discuss the specific challenges of stillbirth registration, with emphasis on implementation. We identify what data need to be captured, we suggest a dataset to cover core needs in registration and analysis of the different categories of stillbirths with causes and quality indicators, and we illustrate the experience in stillbirth registration from different cultural settings. Finally, we point out gaps that need attention in the International Classification of Diseases and review the qualities of alternative systems that have been tested in low- and middle-income settings. SUMMARY: Obtaining high-quality data will require consistent definitions for stillbirths, systematic population-based registration, better tools for surveys and verbal autopsies, capacity building and training in procedures to identify causes of death, locally adapted quality indicators, improved classification systems, and effective registration and reporting systems
Partial amino acid sequence of apolipoprotein(a) shows that it is homologous to plasminogen.
Stable Distributions in Stochastic Fragmentation
We investigate a class of stochastic fragmentation processes involving stable
and unstable fragments. We solve analytically for the fragment length density
and find that a generic algebraic divergence characterizes its small-size tail.
Furthermore, the entire range of acceptable values of decay exponent consistent
with the length conservation can be realized. We show that the stochastic
fragmentation process is non-self-averaging as moments exhibit significant
sample-to-sample fluctuations. Additionally, we find that the distributions of
the moments and of extremal characteristics possess an infinite set of
progressively weaker singularities.Comment: 11 pages, 5 figure
Tuberculosis incidence correlates with sunshine : an ecological 28-year time series study
Birmingham is the largest UK city after London, and central Birmingham has an annual tuberculosis incidence of 80 per 100,000. We examined seasonality and sunlight as drivers of tuberculosis incidence. Hours of sunshine are seasonal, sunshine exposure is necessary for the production of vitamin D by the body and vitamin D plays a role in the host response to tuberculosis.
Methods:
We performed an ecological study that examined tuberculosis incidence in Birmingham from Dec 1981 to Nov 2009, using publicly-available data from statutory tuberculosis notifications, and related this to the seasons and hours of sunshine (UK Meteorological Office data) using unmeasured component models.
Results:
There were 9,739 tuberculosis cases over the study period. There was strong evidence for seasonality, with notifications being 24.1% higher in summer than winter (p<0.001). Winter dips in sunshine correlated with peaks in tuberculosis incidence six months later (4.7% increase in incidence for each 100 hours decrease in sunshine, p<0.001).
Discussion and Conclusion:
A potential mechanism for these associations includes decreased vitamin D levels with consequent impaired host defence arising from reduced sunshine exposure in winter. This is the longest time series of any published study and our use of statutory notifications means this data is essentially complete. We cannot, however, exclude the possibility that another factor closely correlated with the seasons, other than sunshine, is responsible. Furthermore, exposure to sunlight depends not only on total hours of sunshine but also on multiple individual factors. Our results should therefore be considered hypothesis-generating. Confirmation of a potential causal relationship between winter vitamin D deficiency and summer peaks in tuberculosis incidence would require a randomized-controlled trial of the effect of vitamin D supplementation on future tuberculosis incidence
Failure Processes in Elastic Fiber Bundles
The fiber bundle model describes a collection of elastic fibers under load.
the fibers fail successively and for each failure, the load distribution among
the surviving fibers change. Even though very simple, the model captures the
essentials of failure processes in a large number of materials and settings. We
present here a review of fiber bundle model with different load redistribution
mechanism from the point of view of statistics and statistical physics rather
than materials science, with a focus on concepts such as criticality,
universality and fluctuations. We discuss the fiber bundle model as a tool for
understanding phenomena such as creep, and fatigue, how it is used to describe
the behavior of fiber reinforced composites as well as modelling e.g. network
failure, traffic jams and earthquake dynamics.Comment: This article has been Editorially approved for publication in Reviews
of Modern Physic
Incidence of WHO stage 3 and 4 conditions following initiation of Anti-Retroviral Therapy in resource limited settings
To determine the incidence of WHO clinical stage 3 and 4 conditions during early anti-retroviral therapy (ART) in resource limited settings (RLS)
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