Initial rise of bubbles in cohesive sediments by a process of viscoelastic fracture

Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 116 (2011): B04207, doi:10.1029/2010JB008133.An understanding of the mechanics of bubble rise in sediments is essential because of the role of bubbles in releasing methane to the atmosphere and the formation and melting of gas hydrates. Past models to describe and predict the rise of other buoyant geological bodies through a surrounding solid (e.g., magmas and hydrofractures) appear not to be applicable to bubbles in soft sediments, and this paper presents a new model for gas bubble rise in soft, fine-grained, cohesive sediments. Bubbles in such sediments are essentially “dry” (little if any free water) and grow through a process of elastic expansion and fracture that can be described using the principles of linear elastic fracture mechanics, which assume the existence of a spectrum of flaws within the sediment fabric. By extending this theory, we predict that bubbles initially rise by preferential propagation of a fracture in a (sub) vertical direction. We present a criterion for initial bubble rise. Once rise is initiated, the speed of rise is controlled by the viscoelastic response of the sediments to stress. Using this new bubble rise model, we estimate rise velocities to be of the order of centimeters per second. We again show that capillary pressure plays no substantive role in controlling bubble growth or rise.This research was funded by the U.S. Office of Naval research through grants N00014‐08‐0818 and N00014‐05‐1‐0175 (project managers J. Eckman and T. Drake). Support was also provided by the Natural Sciences and Engineering Council of Canada and by the Killam Trust

What is the clinical workup for failure to thrive?

The clinical evaluation of failure to thrive (FTT) includes a thorough history and physical examination; observation of parent-child interactions; observation and documentation of the child's feeding patterns; and a home visit by an appropriately trained health care professional (Strength of Recommendation [SOR]: C). Further diagnostic testing should be performed as indicated by positive findings from the history and physical exam or if the child's weight has not improved at follow-up (SOR: C)

Mortality in Aransas-Wood Buffalo Whooping Cranes: Timing, Location, and Causes

The Aransas-Wood Buffalo Population (AWBP) of Whooping Cranes (Grus americana) has experienced a population growth rate of approximately 4% for multiple decades (Butler et al., 2014a; Miller et al., 1974). Population growth for long-lived species of birds is generally highly sensitive to variation in adult mortality rates (Sæther and Bakke, 2000). A population model for endangered Red-crowned Cranes (Grus japonensis) in Japan conforms to this pattern, where growth rate is most sensitive to adult mortality (Masatomi et al., 2007). Earlier analyses observed that the AWBP growth rate increased in the mid-1950s and that this increase was likely caused by reduced annual mortality rates, even while the population experienced slightly decreasing natality (Binkley and Miller, 1988; Miller et al., 1974). A more contemporary analysis of the AWBP determined that approximately 50% of variation in annual population growth could be explained by variation in annual mortality (Butler et al., 2014a). Therefore, as a vital rate, mortality is critical to the maintained growth of the AWBP

Mortality in Aransas-Wood Buffalo Whooping Cranes: Timing, Location, and Causes

The Aransas-Wood Buffalo Population (AWBP) of Whooping Cranes (Grus americana) has experienced a population growth rate of approximately 4% for multiple decades (Butler et al., 2014a; Miller et al., 1974). Population growth for long-lived species of birds is generally highly sensitive to variation in adult mortality rates (Sæther and Bakke, 2000). A population model for endangered Red-crowned Cranes (Grus japonensis) in Japan conforms to this pattern, where growth rate is most sensitive to adult mortality (Masatomi et al., 2007). Earlier analyses observed that the AWBP growth rate increased in the mid-1950s and that this increase was likely caused by reduced annual mortality rates, even while the population experienced slightly decreasing natality (Binkley and Miller, 1988; Miller et al., 1974). A more contemporary analysis of the AWBP determined that approximately 50% of variation in annual population growth could be explained by variation in annual mortality (Butler et al., 2014a). Therefore, as a vital rate, mortality is critical to the maintained growth of the AWBP

Mortality in Aransas-Wood Buffalo Whooping Cranes: Timing, Location, and Causes

The Aransas-Wood Buffalo Population (AWBP) of Whooping Cranes (Grus americana) has experienced a population growth rate of approximately 4% for multiple decades (Butler et al., 2014a; Miller et al., 1974). Population growth for long-lived species of birds is generally highly sensitive to variation in adult mortality rates (Sæther and Bakke, 2000). A population model for endangered Red-crowned Cranes (Grus japonensis) in Japan conforms to this pattern, where growth rate is most sensitive to adult mortality (Masatomi et al., 2007). Earlier analyses observed that the AWBP growth rate increased in the mid-1950s and that this increase was likely caused by reduced annual mortality rates, even while the population experienced slightly decreasing natality (Binkley and Miller, 1988; Miller et al., 1974). A more contemporary analysis of the AWBP determined that approximately 50% of variation in annual population growth could be explained by variation in annual mortality (Butler et al., 2014a). Therefore, as a vital rate, mortality is critical to the maintained growth of the AWBP

U.S. Fresh Fruit and Vegetable Marketing: Emerging Trade Practices, Trends, and Issues

In the past year, trade practices between fresh produce shippers and food retailers gained national attention. Shippers are concerned that recent retail consolidation has led to market power and the growing incidence of fees and services. Retailers argue that these new trade practices reflect their costs of doing business and the demands of consumers. Trade practices include fees such as volume discounts and slotting fees, as well as services like automatic inventory replenishment, special packaging, and requirements for third-party food safety certification. Trade practices also refer to the overall structure of a transaction-for example, long-term relationships or contracts versus daily sales with no continuing commitment. This study compares trade practices in 1999 with those prevalent in 1994, placing them in the broader context of the evolving shipper/retailer relationship. Most shippers and retailers reported that the incidence and magnitude of fees and services associated with transactions has increased over the last 5 years. Fees paid to retailers are usually around 1-2 percent of sales for most of the commodities we examined, but 1-8 percent for bagged salads. Information on the incidence and magnitude of these new practices is scarce. To augment information that is publicly available, we interviewed a limited number of shippers, retailers, and wholesalers about their firms and trade practices. We received a high level of voluntary cooperation from the interviewed firms.produce, fresh fruit and vegetables, fresh-cut produce, trade practices, fees and services, slotting fees, retail consolidation, produce shipper consolidation, Crop Production/Industries, Marketing,

Mortality in Aransas-Wood Buffalo Whooping Cranes: Timing, Location, and Causes

The Aransas-Wood Buffalo Population (AWBP) of Whooping Cranes (Grus americana) has experienced a population growth rate of approximately 4% for multiple decades (Butler et al., 2014a; Miller et al., 1974). Population growth for long-lived species of birds is generally highly sensitive to variation in adult mortality rates (Sæther and Bakke, 2000). A population model for endangered Red-crowned Cranes (Grus japonensis) in Japan conforms to this pattern, where growth rate is most sensitive to adult mortality (Masatomi et al., 2007). Earlier analyses observed that the AWBP growth rate increased in the mid-1950s and that this increase was likely caused by reduced annual mortality rates, even while the population experienced slightly decreasing natality (Binkley and Miller, 1988; Miller et al., 1974). A more contemporary analysis of the AWBP determined that approximately 50% of variation in annual population growth could be explained by variation in annual mortality (Butler et al., 2014a). Therefore, as a vital rate, mortality is critical to the maintained growth of the AWBP

The relationship between tooth size discrepancy and archform classification in orthodontic patients

Background: To determine the relationship between clinically significant tooth size discrepancies (TSD) and archform classification in orthodontic patients. Material and Methods: Two hundred and forty consecutive sets of pre-treatment orthodontic study models were scanned and landmarked. All models had permanent teeth erupted from first molar to first molar in both arches. Sixty sets of images were classified into two groups of 30 according to the presence (group 1) or absence (group 2) of a clinically significant overall or anterior TSD (>2 SD from Bolton’s original means). Mean upper and lower archforms were created for each group using a fourth degree polynomial curve. Upper and lower archforms in each group were classified as square, tapering or ovoid; their distribution was analysed using the Fisher test with a 5% level of significance. To evaluate the intra-operator error when determining archform type, the 60 archforms were re-classified by the same operator two weeks later. The unweighted Kappa statistic at 95% confidence intervals was used to determine the similarity of the classification on the two occasions. Results: Reproducibility of the classification of archform was very good (unweighted Kappa statistic of 0.83 with a 95% confidence interval of 0.73, 0.93). There was no statistically significant difference in the distribution of archform type between group 1 and group 2 for the upper ( p =0.3305) or lower ( p =0.6310) arches. Conclusions: The presence of a clinically significant TSD and archform classification do not appear to be related