Search

While it is known that musculotendon units adapt to their load environments, there is only a limited understanding of tendon adaptation in vivo. Here we develop a computational model of tendon remodeling based on the premise that mechanical damage and tenocyte-mediated tendon damage and repair processes modify the distribution of its collagen fiber lengths. We explain how these processes enable the tendon to geometrically adapt to its load conditions. Based on known biological processes, mechanical and strain-dependent proteolytic fiber damage are incorporated into our tendon model. Using a stochastic model of fiber repair, it is assumed that mechanically damaged fibers are repaired longer, whereas proteolytically damaged fibers are repaired shorter, relative to their pre-damage length. To study adaptation of tendon properties to applied load, our model musculotendon unit is a simplified three-component Hill-type model of the human Achilles-soleus unit. Our model results demonstrate that the geometric equilibrium state of the Achilles tendon can coincide with minimization of the total metabolic cost of muscle activation. The proposed tendon model independently predicts rates of collagen fiber turnover that are in general agreement with in vivo experimental measurements. While the computational model here only represents a first step in a new approach to understanding the complex process of tendon remodeling in vivo, given these findings, it appears likely that the proposed framework may itself provide a useful theoretical foundation for developing valuable qualitative and quantitative insights into tendon physiology and pathology.

Since 1995 the eruption of the andesitic Soufrière Hills Volcano (SHV), Montserrat, has been studied in substantial detail. As an important contribution to this effort, the Seismic Experiment with Airgunsource-Caribbean Andesitic Lava Island Precision Seismo-geodetic Observatory (SEA-CALIPSO) experiment was devised to image the arc crust underlying Montserrat, and, if possible, the magma system at SHV using tomography and reflection seismology. Field operations were carried out in October–December 2007, with deployment of 238 seismometers on land supplementing seven volcano observatory stations, and with an array of 10 ocean-bottom seismometers deployed offshore. The RRS James Cook on NERC cruise JC19 towed a tuned airgun array plus a digital 48-channel streamer on encircling and radial tracks for 77 h about Montserrat during December 2007, firing 4414 airgun shots and yielding about 47 Gb of data. The main objecctives of the experiment were achieved. Preliminary analyses of these data published in 2010 generated images of heterogeneous high-velocity bodies representing the cores of volcanoes and subjacent intrusions, and shallow areas of low velocity on the flanks of the island that reflect volcaniclastic deposits and hydrothermal alteration. The resolution of this preliminary work did not extend beyond 5 km depth. An improved three-dimensional (3D) seismic velocity model was then obtained by inversion of 181 665 first-arrival travel times from a more-complete sampling of the dataset, yielding clear images to 7.5 km depth of a low-velocity volume that was interpreted as the magma chamber which feeds the current eruption, with an estimated volume 13 km3. Coupled thermal and seismic modelling revealed properties of the partly crystallized magma. Seismic reflection analyses aimed at imaging structures under southern Montserrat had limited success, and suggest subhorizontal layering interpreted as sills at a depth of between 6 and 19 km. Seismic reflection profiles col

It is estimated that more than 500 million people are at risk from the hazards posed by volcanoes. The potential therefore exists for major loss of life and damage to property in a number of regions, especially where large urban areas occur in proximity to dangerous volcanoes. As population pressures intensify, hazardous areas are likely to become increasingly developed, so raising the level of risk. In the case of major eruptions, losses to property, infrastructure and economic activity can run into hundreds of millions or even billions of dollars and high casualty rates may be inflicted, although even relatively minor activity can have adverse impacts through the disruption of economic activity, lack of investor confidence and harm to health. Eruptions may therefore seriously disrupt development plans by causing burdensome economic setbacks that divert precious resources into relief and reconstruction, which would otherwise be destined for development. This can be severe in developing nations with small, poorly diversified economies. Because disasters are inextricably linked to human and economic development, the most efficient way to prevent them or reduce their impact is to take natural hazards into routine consideration when formulating development plans. An integrated approach to hazard management and development planning will also result in more realistic cost-benefit analyses of potential development projects, by taking into account the estimated costs and benefits of hazard reduction measures. Although numerous volcanoes pose a high level of risk in many developing countries, relatively few have been the subject of hazard assessments. The main objective of the project has therefore been the development and evaluation of rapid and cost-effective methods for volcanic hazard mapping in developing countries. Volcanic hazard mapping methods are described and the role that these have to play within the broader framework of risk reduction is discussed. With respec

The cold tolerance mechanism of the Antarctic terrestrial mite Alaskozetes antarcticus (Michael) was investigated in cultured animals. Freezing is fatal in this species and winter survival occurs by means of supercooling, which is enhanced by the presence of glycerol in the body. There is an inverse, linear relationship between the concentration of glycerol and the supercooling point, which may be as low as −30°C. Feeding detracts from supercooling ability by providing ice nucleators in the gut which initiate freezing at relatively high sub-zero temperatures. Experiments on the effects of various environmental factors showed that low temperature acclimation gave rise to increased glycerol concentrations and suppressed feeding, while desiccation also stimulated glycerol production. Photoperiod had no effect on cold tolerance in this species. The juvenile instars of A. antarcticus were found to possess a greater degree of low temperature tolerance than adults.

Measurements of oxygen consumption in all post-embryonic life stages of U.K. cultured Alaskozetes antarcticus (Acari: Cryptostigmata) showed that log10 respiration rate was linearly related to log10 live weight, while loge metabolic rate was linearly related to the reciprocal of the absolute temperature over the range 273–283°K, although the magnitude of response to temperature shown by different life stages was found to vary. Differences were apparent between cultured animals and previous measurements made on field animals, especially in respect of the relationship between respiration rate and live weight. The data were found to support the hypothesis of cold adaptation by means of metabolic rate elevation and a possible mechanism in discussed.

1. Determinations of live weight-specific oxygen consumption (metabolic rate) in adults of the Antarctic terrestrial mite Alaskozetes antarcticus (Michael) showed that starvation resulted in metabolic suppression. 2. Food materials were shown to influence metabolic rates and depletion of oxygen concentration in Cartesian Divers resulted in decreased oxygen uptake. 3. The effects of sex and reproductive condition on metabolic rates were explicable on the basis of weight differences between males, gravid females and non-gravid females. 4. Long periods of laboratory culture tended to result in lower weights and metabolic rates, but short term temporal variation in weight-specific oxygen consumption within individuals was also demonstrated. 5. Oxygen consumption rates of adult A. antarcticus were measured at -4°C and found to be slightly lower than values previously measured at 0°C.