Variation of the glass transition temperature with rigidity and chemical composition

The effects of flexibility and chemical composition in the variation of the glass transition temperature are obtained by using the Lindemann criteria, that relates melting temperature with atomic vibrations. Using this criteria and that floppy modes at low frequencies enhance in a considerable way the average cuadratic displacement, we show that the consequence is a modified glass transition temperature. This approach allows to obtain in a simple way the empirically modified Gibbs-DiMarzio law, which has been widely used in chalcogenide glasses to fit the changes in the glass transition temperature with the chemical composition . The method predicts that the constant that appears in the law depends upon the ratio of two characteristic frequencies (or temperatures). Then, the constant for the Se-Ge-As glass is estimated by using the experimental density of vibrational states, and the result shows a very good agreement with the experimental fit from glass transition temperature variation

Self-organized criticality in the intermediate phase of rigidity percolation

Experimental results for covalent glasses have highlighted the existence of a new self-organized phase due to the tendency of glass networks to minimize internal stress. Recently, we have shown that an equilibrated self-organized two-dimensional lattice-based model also possesses an intermediate phase in which a percolating rigid cluster exists with a probability between zero and one, depending on the average coordination of the network. In this paper, we study the properties of this intermediate phase in more detail. We find that microscopic perturbations, such as the addition or removal of a single bond, can affect the rigidity of macroscopic regions of the network, in particular, creating or destroying percolation. This, together with a power-law distribution of rigid cluster sizes, suggests that the system is maintained in a critical state on the rigid/floppy boundary throughout the intermediate phase, a behavior similar to self-organized criticality, but, remarkably, in a thermodynamically equilibrated state. The distinction between percolating and non-percolating networks appears physically meaningless, even though the percolating cluster, when it exists, takes up a finite fraction of the network. We point out both similarities and differences between the intermediate phase and the critical point of ordinary percolation models without self-organization. Our results are consistent with an interpretation of recent experiments on the pressure dependence of Raman frequencies in chalcogenide glasses in terms of network homogeneity.Comment: 20 pages, 18 figure

Self-organization with equilibration: a model for the intermediate phase in rigidity percolation

Recent experimental results for covalent glasses suggest the existence of an intermediate phase attributed to the self-organization of the glass network resulting from the tendency to minimize its internal stress. However, the exact nature of this experimentally measured phase remains unclear. We modify a previously proposed model of self-organization by generating a uniform sampling of stress-free networks. In our model, studied on a diluted triangular lattice, an unusual intermediate phase appears, in which both rigid and floppy networks have a chance to occur, a result also observed in a related model on a Bethe lattice by Barre et al. [Phys. Rev. Lett. 94, 208701 (2005)]. Our results for the bond-configurational entropy of self-organized networks, which turns out to be only about 2% lower than that of random networks, suggest that a self-organized intermediate phase could be common in systems near the rigidity percolation threshold.Comment: 9 pages, 6 figure

X-Linked Deafness in a South African Kindred

The X-linked deafness of Nance is present in a South African kindred. Recognition of the familial pattern of the disorder, together with the characteristic clinical and audiometric features, permits diagnostic precision, thereby facilitating accurate genetic counselling and rational management. Linkage studies indicated that the loci for the Xg blood group and the deafness gene are unlikely to be very close to each other.S. Afr. Med. J., 48, 587 (1974)

X-linked deafness in a South African kindred

The X-linked deafness of Nance is present in a South African kindred. Recognition of the familial pattern of the disorder, together with the characteristic clinical and audiometric features, permits diagnostic precision, thereby facilitating accurate genetic counselling and rational management. Linkage studies indicated that the loci for the Xg blood group and the deafness gene are unlikely to be very close to each other.S. Afr. Med. J., 48, 587 (1974)

The interfascicular matrix enables fascicle sliding and recovery in tendon, and behaves more elastically in energy storing tendons

While the predominant function of all tendons is to transfer force from muscle to bone and position the limbs, some tendons additionally function as energy stores, reducing the cost of locomotion. Energy storing tendons experience extremely high strains and need to be able to recoil efficiently for maximum energy storage and return. In the equine forelimb, the energy storing superficial digital flexor tendon (SDFT) has much higher failure strains than the positional common digital extensor tendon (CDET). However, we have previously shown that this is not due to differences in the properties of the SDFT and CDET fascicles (the largest tendon subunits). Instead, there is a greater capacity for interfascicular sliding in the SDFT which facilitates the greater extensions in this particular tendon (Thorpe et al., 2012). In the current study, we exposed fascicles and interfascicular matrix (IFM) from the SDFT and CDET to cyclic loading followed by a test to failure. The results show that IFM mechanical behaviour is not a result of irreversible deformation, but the IFM is able to withstand cyclic loading, and is more elastic in the SDFT than in the CDET. We also assessed the effect of ageing on IFM properties, demonstrating that the IFM is less able to resist repetitive loading as it ages, becoming stiffer with increasing age in the SDFT. These results provide further indications that the IFM is important for efficient function in energy storing tendons, and age-related alterations to the IFM may compromise function and predispose older tendons to injury

How Do State–Business Relations Shape Sustainable Development?

The achievement of the UN Sustainable Development Goals will depend on the ways in which states and businesses engage with one another. While state–business interactions can take many forms, they inherently involve processes of negotiation through which actors in both camps pursue their own interests. Successfully accelerating sustainability, generating inclusion or reducing inequalities will depend on whether such negotiations build on and support interdependencies, create trust, and develop shared ideas about challenges and potential solutions. But the factors that determine the nature and outcomes of state–business relations are not yet well-enough understood, particularly in relation to goals beyond economic growth, where trade-offs are often more apparent.UK Department for International Developmen

The w0(p)–w0(q) mapping problem for factorable matrices II

AbstractWe find necessary and sufficient conditions for the class of factorable matrices M(a,b) to map w0(p) into w0(q) for 0<q<p⩽1

Addressing Market Constraints to Providing Nutrient-Rich Foods: An Exploration of Market Systems Approaches

This Evidence Report asks how a market systems approach could be applied to improve poor households’ access to nutrient-dense foods. By ‘market systems approach’ we mean methods that identify and address underlying constraints in market transactions, their supporting functions and the institutional environment in which markets operate, and which are preventing markets from delivering desired outcomes. The report builds on a developing body of research on value chain approaches to nutrition, which has highlighted challenges in developing commercially viable business models that can deliver affordable, available, appropriate and acceptable foods. It explores how market systems approaches could be used to improve the diagnosis of constraints preventing a market from achieving these outcomes, and to develop interventions that change the way the market system works. The report does not seek to make specific recommendations for policy or practice, but rather sets out how a market systems approach could be applied to nutrition in different contexts in order to develop such recommendations.UK Department for International Developmen