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Elasticity Values (elasticity + value)

Distribution by Scientific Domains

Medical Sciences	50%

Selected Abstracts

Comparative assessment of time-related bioactive glass and calcium hydroxide effects on mechanical properties of human root dentin

DENTAL TRAUMATOLOGY, Issue 1 2009
Monika Marending
These materials have a disinfecting capacity similar to Ca(OH)2, but bear the advantage of bioactivity. However, because bioactive glasses initially act as alkaline biocides just as Ca(OH)2 does, they may also negatively affect mechanical dentin properties over time. This was assessed in the current study using standardized human root dentin bars. Specimens were immersed in 1:20 (wt vol,1) suspensions of nanometric bioactive glass 45S5 or calcium hydroxide for 1, 10, or 30 days. Control specimens were immersed in pure saline for 30 days (n = 20 per group). Subsequently, modulus of elasticity (E) and flexural strength (FS) of the specimens were determined. Results were compared between groups using one-way anova and Scheffé's post-hoc test. Ca(OH)2 caused a significant (P < 0.001) 35% drop in mean flexural strength values compared to the control treatment after 10 days. No further change was observed between 10 days and 30 days. Bioactive glass caused a 20% drop in mean flexural strength as compared to the control after 10 days. However, this difference did not reach statistical significance (P > 0.05). No effects of either material on dentin modulus of elasticity values were observed. It was concluded that the calcium hydroxide suspension affected the dentin more than the bioactive glass counterpart; however, the effect was self-limiting and probably restricted to superficial dentin layers, as suggested by the mere decrease in flexural strength but not in modulus of elasticity values. [source]

Tourism demand response by residents of Latin American countries

INTERNATIONAL JOURNAL OF TOURISM RESEARCH, Issue 1 2009
Manuel Vanegas Sr
Abstract A general-to-specific methodology was used to build international tourism demand models by residents from Argentina, Brazil, Colombia and Venezuela to Aruba. We seek to evaluate demand parameters, especially elasticity values, which were disaggregated on a country-to-country basis. We also aim to learn more about the structure and important variables and investigate the process of adjustment. The study has provided new and compelling evidence that, in the short run, residents in developing countries respond rationally and substantially to economic stimulus. The short-run income elasticity ranges from the low of 1.52 for Venezuela to the high of 2.34 for Argentina. These results indicate that Aruba will benefit differently from income increases in these four Latin American countries. The coefficients of the price variable had the expected negative signs, inelastic in the short-run for all countries but significant at the 5% level for Venezuela only. Any deliberate effort to expand tourist arrivals will require a much larger decline in prices than would be the case in the presence of short-run elastic response. The adjustment elasticity, being less than one, suggests that a period of more than one year is required for Latin American residents to fully adjust their tourism decisions in response to demand shocks. This study would seem to provide some useful information about international tourism demand from developing to developing countries that could form a very good and solid basis for analyses and policy action. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Which demographic traits determine population growth in the invasive brown seaweed Sargassum muticum?

JOURNAL OF ECOLOGY, Issue 4 2009
Aschwin Engelen
Summary 1Life-history traits commonly associated with plant invasiveness are vegetative reproduction or r -selected traits such as short generation times and high rates of reproduction and individual growth. 2We used matrix modelling to assess which demographic traits are important for the population growth of an invasive seaweed lacking vegetative reproduction and whether demographic and life-history strategies shift with increased dominance of the invader. The vital rates of one of the most successful invading seaweeds, Sargassum muticum, were investigated monthly for 2 years in intertidal pools dominated by the native brown seaweed Cystoseira humilis and by S. muticum, respectively. In order to speculate about the demographic mechanisms that determine invasiveness of S. muticum, and as the study sites were recently colonized, we assumed that C. humilis and S. muticum pools are proxies for early and late phases of invasion, respectively. 3Both deterministic and stochastic matrix models showed positive rates of population growth, and rates were significantly higher in the pools dominated by S. muticum than in the ones dominated by C. humilis, indicating demographic changes with invader dominance. The variability of population growth rates and of reproductive and elasticity values of S. muticum was higher in the pools dominated by C. humilis, suggesting invader-driven stabilization of environmental conditions. Generation times of the species increased with invader dominance, supporting invader-stabilized environmental conditions. 4Elasticity analyses revealed that the most important demographic trait for population growth rate at both levels of invader dominance was the persistence of the non-fertile adult fronds rather than reproduction or growth. No major shifts in the life-history strategy of S. muticum between levels of invader dominance were detected. 5Synthesis. This study suggests that the invasiveness of S. muticum, a perennial invader without vegetative reproduction, relies on K - rather than r -selected traits and without drastic changes in life-history strategy between phases of invasion. [source]

In vivo elasticity measurements of extremity skeletal muscle with MR elastography

NMR IN BIOMEDICINE, Issue 4 2004
Kai Uffmann
Abstract MR elastography (MRE) has been shown to be capable of non-invasively measuring tissue elasticity even in deep-lying regions. Although limited studies have already been published examining in vivo muscle elasticity, it is still not clear over what range the in vivo elasticity values vary. The present study intends to produce further information by examining four different skeletal muscles in a group of 12 healthy volunteers in the age range of 27,38 years. The examinations were performed in the biceps brachii, the flexor digitorum profundus, the soleus and the gastrocnemius. The average shear modulus was determined to be 17.9 (,±,5.5), 8.7 (,±,2.8), 12.5 (,±,7.3) and 9.9 (,±,6.8) kPa for each muscle, respectively. To ascertain the reproducibility of the examination, the stiffness measurements in two volunteers were repeated seven times for the biceps brachii. These examinations yielded a mean shear modulus of 11.3,±,.7 and 13.3,±,4.7,kPa for the two subjects. For elasticity reconstruction, an automated reconstruction algorithm is introduced which eliminates variation due to subjective manual image analysis. This study yields new information regarding the expected variation in muscle elasticity in a healthy population, and also reveals the expected variability of the MRE technique in skeletal muscle. Copyright © 2004 John Wiley & Sons, Ltd. [source]