In vivo assessment of the mechanical properties of the child cortical bone using quantitative computed tomography

The mechanical properties of the rib cortical bone are extremely rare on children due to difficulties to obtain specimens to perform conventional tests. Some recent studies used cadaveric bones or bone tissues collected during surgery but are limited by the number of samples that could be collected. A non-invasive technique could be extremely valuable to overcome this limitation. It has been shown that a relationship exists between the mechanical properties (apparent Young’s modulus and ultimate strength) and the bone mineral density (assessed using Quantitative Computed Tomography, QCT), for the femur and recently by our group for the adult ribs ex vivo. Thus the aim of this study was to assess the mechanical properties of the child rib cortical bone using both QCT images in vivo and the previous relationship between bone mineral density and mechanical properties of the rib cortical bone. Twenty-eight children were included in this study. Seven age-groups have been considered (1, 1.5, 3, 6, 10, 15, 18 years old). The QCT images were prescribed for various thoracic pathologies at the pediatric hospital in Lyon. A calibration phantom was added to the clinical protocol without any modifications for the patient. The protocol was approved by the ethical committee. A 3D reconstruction of each thorax was performed using the QCT images. A custom software was then used to obtain cross-sections to the rib midline. The mean bone mineral density was then computed by averaging the Hounsfield Units in a specific cross-section and by converting the mean value (Hounsfield Units) in bone mineral density using the calibration phantom. This bone mineral density was assessed for the 6th rib of each subject. Our relationship between the bone mineral density and the mechanical properties of the rib cortical bone was used to derive the mechanical properties of the child ribs in vivo. The results give values for the apparent Young’s modulus and the ultimate strength. The mechanical properties increase along growth. As an example the apparent Young’s modulus in the lateral region ranges from 7 GPa +/-3 at 1 year old up to 13 GPa +/- 2 at 18 years old. These data are in agreement with the few previous values obtained from child tissues. This methodology opens the way to in vivo measurement of the mechanical properties of the child cortical bone based on calibrated QCT images

An advanced apparatus for the integration of nanophotonics and cold atoms

We combine nanophotonics and cold atom research in a new apparatus enabling the delivery of single-atom tweezer arrays in the vicinity of photonic crystal waveguides

Localized surface-plasmon resonances in periodic nondiffracting metallic nanoparticle and nanohole arrays

J. Parsons, Euan Hendry, C. P. Burrows, Baptiste Auguié, J. Roy Sambles, and William L. Barnes, Physical Review B, Vol. 79, article 073412 (2009). Copyright © 2009 by the American Physical Society.We compare the optical response of periodic nondiffracting metallic nanoparticle and nanohole arrays. Experimental data from both structures show a pronounced minimum in their wavelength-dependent transmittance that, through numerical modeling, we identify as being due to the excitation of localized surface-plasmon resonances associated with the nanoparticles/nanoholes. Our main finding is that, while the optical response of the nanoparticle arrays is largely independent of interparticle separation, the response from nanohole arrays shows a marked dependence on interhole separation. We attribute this effect to coupling between localized surface-plasmon resonances mediated by the symmetric surface plasmon-polaritons associated with the metal film. Further numerical modeling supports this view

Grit ingestion and size-related consumption of tubers by Graylag Geese

In herbivorous birds the processing rate of food is constrained by gizzard capacity. To enhance digestive processes, many species ingest grit to grind the food. Grit ingestion, however, may further limit the capacity of file gizzard. Graylag Geese (Anser anser) wintering in SW Spain fed mainly on Alkali Bulrush (Scirpus maritimus) tubers, showing a preference for small tubers. This preference may be due to a faster disintegration of small tubers than larger ones inside the gizzard. As larger tubers are likely coarser than smaller tubers, more grit would be necessary to process larger tubers. However, the ingestion of more grit to grind large tubers would be at the expense of ingesting additional tubers because of gizzard capacity limitations. Under these circumstances, there may be an inverse relationship between tuber size and amount of grit ingested to optimize food ingestion. Indeed, we found such a relationship. Grit facilitated the disintegration of tubers. This suggests that relying on some amount of grit to facilitate the grinding of food should outweigh the loss of gizzard capacity to the amount of food ingested.Peer Reviewe

Fluctuations of Fluctuation-Induced "Casimir" Forces

The force experienced by objects embedded in a correlated medium undergoing thermal fluctuations--the so-called fluctuation--induced force--is actually itself a fluctuating quantity. We compute the corresponding probability distribution and show that it is a Gaussian centered on the well-known Casimir force, with a non-universal standard deviation that can be typically as large as the mean force itself. The relevance of these results to the experimental measurement of fluctuation-induced forces is discussed, as well as the influence of the finite temporal resolution of the measuring apparatus.Comment: 4 pages, 2 figure

Duality and ontology

A ‘duality’ is a formal mapping between the spaces of solutions of two empirically equivalent theories. In recent times, dualities have been found to be pervasive in string theory and quantum field theory. Naïvely interpreted, duality-related theories appear to make very different ontological claims about the world—differing in e.g. space-time structure, fundamental ontology, and mereological structure. In light of this, duality-related theories raise questions familiar from discussions of underdetermination in the philosophy of science: in the presence of dual theories, what is one to say about the ontology of the world? In this paper, we undertake a comprehensive and non-technical survey of the landscape of possible ontological interpretations of duality-related theories. We provide a significantly enriched and clarified taxonomy of options—several of which are novel to the literature