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Mass Variation (mass + variation)
Selected AbstractsRelevance of the genes for bone mass variation to susceptibility to osteoporotic fractures and its implications to gene search for complex human diseasesGENETIC EPIDEMIOLOGY, Issue 1 2002Hong-Wen Deng Abstract We investigate the relevance of the genetic determination of bone mineral density (BMD) variation to that of differential risk to osteoporotic fractures (OF). The high heritability (h2) of BMD and the significant phenotypic correlations between high BMD and low risk to OF are well known. Little is reported on h2 for OF. Extensive molecular genetic studies aimed at uncovering genes for differential risks to OF have focussed on BMD as a surrogate phenotype. However, the relevance of the genetic determination of BMD to that of OF is unknown. This relevance can be characterized by genetic correlation between BMD and OF. For 50 Caucasian pedigrees, we estimated that h2 at the hip is 0.65 (P < 0.0001) for BMD and 0.53 (P < 0.05) for OF; however, the genetic correlation between BMD and OF is nonsignificant (P > 0.45) and less than 1% of additive genetic variance is shared between them. Hence, most genes found important for BMD may not be relevant to OF at the hip. The phenotypic correlation between high BMD and low risk to OF at the hip (approximately ,0.30) is largely due to an environmental correlation (,E = ,0.73, P < 0.0001). The search for genes for OF should start with a significant h2 for OF and should include risk factors (besides BMD) that are genetically correlated with OF. All genes found important for various risk factors must be tested for their relevance to OF. Ideally, employing OF per se as a direct phenotype for gene hunting and testing can ensure the importance and direct relevance of the genes found for the risk of OF. This study may have significant implications for the common practice of gene search for complex diseases through underlying risk factors (usually quantitative traits). Genet. Epidemiol. 22:12,25, 2002. © 2002 Wiley-Liss, Inc. [source] Body mass change strategies in blackbirds Turdus merula: the starvation,predation risk trade-offJOURNAL OF ANIMAL ECOLOGY, Issue 2 2005R. MACLEOD Summary 1It is theoretically well established that body mass in birds is the consequence of a trade-off between starvation risk and predation risk. There are, however, no studies of mass variation from sufficiently large wild populations to model in detail the range of diurnal and seasonal mass change patterns in natural populations and how these are linked to the complex environmental and biological variables that may affect the trade-off. 2This study used data on 17 000 individual blackbirds Turdus merula to model how mass changes diurnally and seasonally over the whole year and over a wide geographical area. Mass change was modelled in respect of temperature, rainfall, day length, geographical location, time of day and time of year and the results show how these mass changes vary with individual size, age and sex. 3The hypothesis that seasonal mass is optimized over the year and changes in line with predictors of foraging uncertainty was tested. As theory predicts, reduced day length and reduced temperature result in increased mass and the expected seasonal peak of mass in midwinter. 4The hypothesis that diurnal mass gain is optimized in terms of starvation,predation risk trade-off theory was also tested. The results provide the first empirical evidence for intraspecies seasonal changes in diurnal mass gain patterns. These changes are consistent with shifts in the relative importance of starvation risk and predation risk and with the theory of mass-dependent predation risk. 5In winter most mass was gained in the morning, consistent with reducing starvation risk. In contrast, during the August,November non-breeding period a bimodal pattern of mass gain, with increases just after dawn and before dusk, was adopted and the majority of mass gain occurred at the end of the day consistent with reducing mass-dependent predation risk. The bimodal diurnal mass gain pattern described here is the first evidence that bird species in the wild gain mass in this theoretically predicted pattern. [source] Seedling growth and morphology of three oak species along field resource gradients and seed mass variation: a seedling age-dependent responseJOURNAL OF VEGETATION SCIENCE, Issue 3 2010Ignacio M. Pérez-Ramos Abstract Question: What is the relative importance of seed mass and abiotic factors in species-specific seedling growth and morphology during the first and the second growing season? How do oak species respond along gradients of these factors? Location: Mediterranean oak forest in southern Spain. Methods: We analysed seedling growth components and morphology of three co-occurring Quercus species (two deciduous and one evergreen). Oak seeds with a wide variety of sizes were sown along broad gradients of abiotic conditions. Intra- and inter-specific differences were evaluated by calibrating maximum likelihood estimators of seedling growth during the first two years of life. Results: We found multiple resources and conditions affecting seedling morphology and biomass allocation. However, the integrative variables of seedling growth , total aboveground biomass and relative growth rate (RGR) , were affected by two main factors: seed mass and light conditions. The relative contribution of these two factors depended strongly on seedling age. Seed mass explained most of the growth and morphological variables during the first year, while light conditions were the best predictor in the second growing season. In contrast, soil factors did not play an important role in seedling growth. We found some evidence of regeneration niche partitioning between oak species along the light gradient, a reflection of their distribution patterns as adults at the study site. Conclusions: We conclude that inter-specific differences in seedling growth, arising from seed size variability and microsite heterogeneity, could be of paramount importance in oak species niche segregation, driving stand dynamics and composition along environmental gradients. [source] Growth and characterization of isotopic natGa15N by molecular-beam epitaxyPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009Yong-zhao Yao Abstract Isotopically enriched gallium nitride films, Ga14N and Ga15N, have been fabricated by molecular-beam epitaxy to study the effects of nitrogen atomic mass variation on structures and properties of GaN. The phonon frequency shift due to the isotopic substitution was clearly observed using Raman spectroscopy. The lattice constants of Ga15N differed from those of Ga14N; the unit cell volume of Ga15N was approximately 0.06% less than that of Ga14N. Temperature-dependent photoluminescence measurements revealed that the recombination mechanism in Ga14N and Ga15N was the same in the temperature range of 4-50 K, and the band gap energy difference was Eg15 -Eg14 = 6.0 ± 0.1 meV. This Eg difference is discussed in terms of volume shrinkage and change in phonon-electron interaction due to isotopic substitution. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Early warning of agglomeration in fluidized beds by attractor comparisonAICHE JOURNAL, Issue 11 2000J. Ruud van Ommen An enhanced monitoring method, based on pressure fluctuation measurements, for observing nonstationarities in fluidized-bed hydrodynamics is presented. Experiments show that it can detect small changes in the particle-size distribution. Such a monitoring method is useful to give an early warning of the onset of agglomeration in a fluidized bed. In contrast to earlier methods, this method is insensitive to small changes in superficial gas velocity and can handle multiple signals, making it relevant to industrial application. By carefully choosing the measurement position, the method becomes also insensitive to small bed mass variations. It uses the attractor reconstructed from a measured pressure signal, which is a "fingerprint" of the hydrodynamics of the fluidized bed for a certain set of conditions. Using this method statistically the reconstructed attractor of a reference time series of pressure fluctuations (representing the desired fluidization behavior) is compared with that of successive time series measured during the bed operation. [source] | ||||||||||