56,793 research outputs found
A similarity criterion for forest growth curves
Comparison of forest growth curves has led many to the conclusion that there is a similarity between forest stands growing in different conditions. Here we treat the same subject from the viewpoint of similarity theory. Our goal is to form a dimensionless ratio of biophysical entities that could parameterize the diversity of forest growth curves. (Such ratios are called similarity criteria.) Pursuing this goal, we focus on the analogy between tree crown growth and atomic explosion. A blast wave is formed when the rate of energy release is much higher than the rate of energy dissipation. The difference between the rates of energy release and dissipation is the essence of this phenomenon. The essential feature of crown growth is the difference between the rates of non-structural carbohydrate supply and demand. Since the rate of supply is much higher than the rate of demand, the flow of non-structural carbohydrates achieves the tips of branches and enables the radial growth of crown. Proceeding from these ideas, we derived the similarity criterion which supposedly captures the “essence of growth” that emerges from the geometric similarity of tree crowns
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Toward a physiological explanation of juvenile growth curves
Juvenile growth curves are generally sigmoid in shape: Growth is initially nearly exponential, but it slows to near zero as the animal approaches maturity. The dropâoff in growth rate is puzzling because, everything else being equal, selection favors growing as fast as possible. Existing theory posits sublinear scaling of resource acquisition with juvenile body mass and linear scaling of the requirement for maintenance, so the difference, fuel for growth, decreases as the juvenile increases in size. Experimental evidence, however, suggests that maintenance metabolism increases sublinearly not linearly with size. Here, we develop a new theory consistent with the experimental evidence. Our theory is based on the plausible assumption that there is a tradeâoff in the capacity of capillaries to supply growing and developed cells. As the proportion of nonâgrowing cells increases, they take up more macromolecules from the capillaries, leaving fewer to support growing cells. The predicted growth curves are realistic and similar to those of previous models (Bertalanffy, Gompertz, and Logistic) but have the advantage of being derived from a plausible physiological model. We hope that our focus on resource delivery in capillaries will encourage new experimental work to identify the detailed physiological basis of the tradeâoff underlying juvenile growth curves
grofit: Fitting Biological Growth Curves with R
The grofit package was developed to fit many growth curves obtained under different conditions in order to derive a conclusive dose-response curve, for instance for a compound that potentially affects growth. grofit fits data to different parametric models and in addition provides a model free spline method to circumvent systematic errors that might occur within application of parametric methods. This amendment increases the reliability of the characteristic parameters (e.g.,lag phase, maximal growth rate, stationary phase) derived from a single growth curve. By relating obtained parameters to the respective condition (e.g.,concentration of a compound) a dose response curve can be derived that enables the calculation of descriptive pharma-/toxicological values like half maximum effective concentration (EC50). Bootstrap and cross-validation techniques are used for estimating confidence intervals of all derived parameters.
Growth curves for algebras
This paper studies matrix representations of algebras (over a field) using countably-infinite matrices which are both row and column finite, and in which the
bandwidth growth is controlled. The ideas lead naturally to a concept of "growth of
an algebra", somewhat analogous to the growth associated with GK-dimension. They
also lead in a similar way to a dimension function on general algebras, which we term
bandwidth dimension. For each real number r â [0,1], we construct an algebra having
bandwidth dimension precisely r. Since the free algebra turns out to have bandwidth
dimension 0, our new dimension promises to distinguish among algebras of infinite
GK-dimension
Quantifying innovation in surgery
Objectives: The objectives of this study were to assess the applicability of patents and publications as metrics of surgical technology and innovation; evaluate the historical relationship between patents and publications; develop a methodology that can be used to determine the rate of innovation growth in any given health care technology. Background: The study of health care innovation represents an emerging academic field, yet it is limited by a lack of valid scientific methods for quantitative analysis. This article explores and cross-validates 2 innovation metrics using surgical technology as an exemplar. Methods: Electronic patenting databases and the MEDLINE database were searched between 1980 and 2010 for âsurgeonâ OR âsurgicalâ OR âsurgery.â Resulting patent codes were grouped into technology clusters. Growth curves were plotted for these technology clusters to establish the rate and characteristics of growth. Results: The initial search retrieved 52,046 patents and 1,801,075 publications. The top performing technology cluster of the last 30 years was minimally invasive surgery. Robotic surgery, surgical staplers, and image guidance were the most emergent technology clusters. When examining the growth curves for these clusters they were found to follow an S-shaped pattern of growth, with the emergent technologies lying on the exponential phases of their respective growth curves. In addition, publication and patent counts were closely correlated in areas of technology expansion. Conclusions: This article demonstrates the utility of publically available patent and publication data to quantify innovations within surgical technology and proposes a novel methodology for assessing and forecasting areas of technological innovation
Analysis of Balmer Profiles of early type stars
The spectral energy distribution (SED) of recent star formation regions is
dominated by the more massive and early stars (O and B types). These stars show
large and very significant absorption features, the most prominent being the
recombination lines of H, HeI and HeII. In particular, the shape of their
profiles are very dependent on the luminosity of the star. We have explored the
potential use of high resolution profiles to discriminate between different
luminosity classes and spectral types, by using profiles of the He and Balmer
lines. We have calculated growth curves for each of the lines and their
dependence on gravity and effective temperature. We show some of these
theoretical growth curves and our preliminary conclusions are analyzed and
discussed.Comment: 1 pag, Contribution to the conference "Cosmic Evolution and Galaxy
Formation: Structure, Interactions and Feedback", Nov. 1999 (Puebla, Mexico),
to be published in ASP. Conf. Series, Eds. J. Franco, E. Terlevich. O.
Lopez-Cruz, I. Aretxag
Analysis of logistic growth models
A variety of growth curves have been developed to model both unpredated, intraspecific
population dynamics and more general biological growth. Most successful predictive models are
shown to be based on extended forms of the classical Verhulst logistic growth equation. We further
review and compare several such models and calculate and investigate properties of interest for
these. We also identify and detail several previously unreported associated limitations and restrictions.
A generalized form of the logistic growth curve is introduced which is shown incorporate these
models as special cases. The reported limitations of the generic growth model are shown to be addressed
by this new model and similarities between this and the extended growth curves are identified.
Several of its properties are also presented. We furthermore show that additional growth characteristics
are accommodated by this new model, enabling previously unsupported, untypical population dynamics to
be modelled by judicious choice of model parameter values alone
Aperture effects on the oxygen abundance determinations from CALIFA data
This paper aims at providing aperture corrections for emission lines in a
sample of spiral galaxies from the Calar Alto Legacy Integral Field Area Survey
(CALIFA) database. In particular, we explore the behavior of the
log([OIII]5007/Hbeta)/([NII]6583/Halpha) (O3N2) and log[NII]6583/Halpha (N2)
flux ratios since they are closely connected to different empirical
calibrations of the oxygen abundances in star forming galaxies.
We compute median growth curves of Halpha, Halpha/Hbeta, O3N2 and N2 up to
2.5R_50 and 1.5 disk R_eff. The growth curves simulate the effect of observing
galaxies through apertures of varying radii. The median growth curve of the
Halpha/Hbeta ratio monotonically decreases from the center towards larger
radii, showing for small apertures a maximum value of ~10% larger than the
integrated one. The median growth curve of N2 shows a similar behavior,
decreasing from the center towards larger radii. No strong dependence is seen
with the inclination, morphological type and stellar mass for these growth
curves. Finally, the median growth curve of O3N2 increases monotonically with
radius. However, at small radii it shows systematically higher values for
galaxies of earlier morphological types and for high stellar mass galaxies.
Applying our aperture corrections to a sample of galaxies from the SDSS
survey at 0.02<=z<=0.3 shows that the average difference between fiber-based
and aperture corrected oxygen abundances, for different galaxy stellar mass and
redshift ranges, reaches typically to ~11%, depending on the abundance
calibration used. This average difference is found to be systematically biased,
though still within the typical uncertainties of oxygen abundances derived from
empirical calibrations. Caution must be exercised when using observations of
galaxies for small radii (e.g. below 0.5R_eff) given the high dispersion shown
around the median growth curves.Comment: Accepted for publication in Ap
Comparison between CDC and WHO BMI z-score and their relation with metabolic risk markers in Northern Portuguese obese adolescents
Growth-curves are an important tool for evaluating the anthropometric development in pediatrics. The different growth-curves available are based in different populations, what leads to different cut-offs. Pediatric obesity tracks into adulthood and is associated with increased cardiovascular risk. The accurate assessment of a child nutritional status using growth-curves can indicate individuals that are either obese or in risk of becoming obese, allowing an early intervention. Moreover, the association between the data obtained from growth-curves with specific metabolic risk factors further highlights the importance of these charts. This study aimed to evaluate the associations between body mass index z-score (BMIzsc), determined using the growth-curves from the Centre for Disease Control and Prevention (CDC) and from the World Health Organization (WHO), with cardiovascular risk factors, represented here by metabolic syndrome (MS) and insulin resistance (IR) related parameters. The study involved 246 obese adolescents (10-18 years, 122 females). MS was defined according to the International Diabetes Federation. IR was considered for HOMA-IR greater than 2.5
Retrieving Bulge and Disk Parameters and Asymptotic Magnitudes from the Growth Curves of Galaxies
We show that the growth curves of galaxies can be used to determine their
bulge and disk parameters and bulge-to-total luminosity ratios, in addition to
their conventional asymptotic magnitudes, provided that the point spread
function is accurately known and signal-to-noise ratio is modest
(S/N). The growth curve is a fundamental quantity that most future
large galaxy imaging surveys will measure. Bulge and disk parameters retrieved
from the growth curve will enable us to perform statistical studies of
luminosity structure for a large number of galaxies.Comment: 28 pages including 13 PS figures; accepted for publication in PAS
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