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Scaling Exponent (scaling + exponent)
Selected AbstractsCore Functionality and Scaling Behavior of Lysine DendrimersMACROMOLECULAR RAPID COMMUNICATIONS, Issue 20 2005Bernd Fritzinger Abstract Summary: A scaling exponent to describe the dependence of the hydrodynamic radius as a characteristic length of the molecule on the molecular weight, has been determined for low generation dendrimers with a thiacalixarene core and lysine dendrons. The hydrodynamic radius has been calculated from the diffusion coefficient measured by pulsed-field-gradient NMR spectroscopy. Scaling exponents of 2.0 for the lysine monodendron, 2.3 for a dendrimer with a bifunctional core, and 3.9 for a dendrimer with a tetrafunctional core have been determined. For a given structure of the dendrons, the scaling exponent reflects the functionality of the core of the dendrimers. Hydrodynamic radius of lysine dendrons as a function of molar mass. [source] Biochemical universality of living matter and its metabolic implicationsFUNCTIONAL ECOLOGY, Issue 4 2005A. M. MAKARIEVA Summary 1Recent discussions of metabolic scaling laws focus on the model of West, Brown & Enquist (WBE). The core assumptions of the WBE model are the size-invariance of terminal units at which energy is consumed by living matter and the size-invariance of the rate of energy supply to these units. Both assumptions are direct consequences of the biochemical universality of living matter. However, the second assumption contradicts the central prediction of the WBE model that mass-specific metabolic rate q should decrease with body mass with a scaling exponent µ = ,1/4, thus making the model logically inconsistent. 2Examination of evidence interpreted by WBE and colleagues in favour of a universal µ = ,1/4 across 15 and more orders of magnitude range in body mass reveals that this value resulted from methodological errors in data assortment and analysis. 3Instead, the available evidence is shown to be consistent with the existence of a size-independent mean value of mass-specific metabolic rate common to most taxa. Plotted together, q -values of non-growing unicells, insects and mammals in the basal state yield µ , 0. Estimated field metabolic rates of bacteria and vertebrates are also size-independent. 4Standard mass-specific metabolic rates of most unicells, insects and mammals studied are confined between 1 and 10 W kg,1. Plant leaves respire at similar rates. This suggests the existence of a metabolic optimum for living matter. With growing body size and diminishing surface-to-volume ratio organisms have to change their physiology and perfect their distribution networks to keep their q in the vicinity of the optimum. [source] Large-scale pattern of biomass partitioning across China's grasslandsGLOBAL ECOLOGY, Issue 2 2010Yuanhe Yang ABSTRACT Aim, To investigate large-scale patterns of above-ground and below-ground biomass partitioning in grassland ecosystems and to test the isometric theory at the community level. Location, Northern China, in diverse grassland types spanning temperate grasslands in arid and semi-arid regions to alpine grasslands on the Tibetan Plateau. Methods, We investigated above-ground and below-ground biomass in China's grasslands by conducting five consecutive sampling campaigns across the northern part of the country during 2001,05. We then documented the root : shoot ratio (R/S) and its relationship with climatic factors for China's grasslands. We further explored relationships between above-ground and below-ground biomass across different grassland types. Results, Our results indicated that the overall R/S of China's grasslands was larger than the global average (6.3 vs. 3.7). The R/S for China's grasslands did not show any significant trend with either mean annual temperature or mean annual precipitation. Above-ground biomass was nearly proportional to below-ground biomass with a scaling exponent (the slope of log,log linear relationship between above-ground and below-ground biomass) of 1.02 across various grassland types. The slope did not differ significantly between temperate and alpine grasslands or between steppe and meadow. Main conclusions, Our findings support the isometric theory of above-ground and below-ground biomass partitioning, and suggest that above-ground biomass scales isometrically with below-ground biomass at the community level. [source] Long-term memory of the hydrological cycle and river runoffs in China in a high-resolution climate modelINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 12 2006Richard Blender Abstract The hydrological cycle in China is analysed on the basis of a 250-years present-day climate simulation with a high-resolution (T63, ,2° × 2° ) coupled atmosphere-ocean circulation model (ECHAM5/MPI-OM). The analysis of the annual data in the model simulation reveals long-term memory (LTM) on decadal time scales in some components of the hydrological cycle. LTM is characterised by a scaling exponent , > 0 in the power spectrum S(f) , f,, for low frequencies f and is determined by detrended fluctuation analysis (DFA). The simulated annual precipitation and atmospheric near-surface temperature fields show, as in the observations, a white low-frequency spectrum and, hence, no long-term memory in East Asia. However, simulated river flows of the Yangtze and the Huang He reveal LTM with scaling exponents , = 0.3,0.4 (similar to the observations and that of the river Nile) extending beyond the decadal time scale. The model soil temperature indicates restricted memory up to time scales of approximately 30 years. In addition, the model's soil wetness, evaporation, and local runoff show memory on this time scale in a zonal belt at the latitude of Mongolia. Copyright © 2006 Royal Meteorological Society. [source] Novel Measures of Heart Rate Variability Predict Cardiovascular Mortality in Older Adults Independent of Traditional Cardiovascular Risk Factors: The Cardiovascular Health Study (CHS)JOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 11 2008PHYLLIS K. STEIN Ph.D. Background: It is unknown whether abnormal heart rate turbulence (HRT) and abnormal fractal properties of heart rate variability identify older adults at increased risk of cardiovascular death (CVdth). Methods: Data from 1,172 community-dwelling adults, ages 72 ± 5 (65,93) years, who participated in the Cardiovascular Health Study (CHS), a study of risk factors for CV disease in people ,65 years. HRT and the short-term fractal scaling exponent (DFA1) derived from 24-hour Holter recordings. HRT categorized as: normal (turbulence slope [TS] and turbulence onset [TO] normal) or abnormal (TS and/or TO abnormal). DFA1 categorized as low (,1) or high (>1). Cox regression analyses stratified by Framingham Risk Score (FRS) strata (low = <10, mid = 10,20, and high >20) and adjusted for prevalent clinical cardiovascular disease (CVD), diabetes, and quartiles of ventricular premature beat counts (VPCs). Results: CVdths (N = 172) occurred over a median follow-up of 12.3 years. Within each FRS stratum, low DFA1 + abnormal HRT predicted risk of CVdth (RR = 7.7 for low FRS; 3.6, mid FRS; 2.8, high FRS). Among high FRS stratum participants, low DFA1 alone also predicted CVdth (RR = 2.0). VPCs in the highest quartile predicted CVdth, but only in the high FRS group. Clinical CV disease predicted CVdth at each FRS stratum (RR = 2.9, low; 2.6, mid; and 1.9, high). Diabetes predicted CVdth in the highest FRS group only (RR = 2.2). Conclusions: The combination of low DFA1 + abnormal HRT is a strong risk factor for CVdth among older adults even after adjustment for conventional CVD risk measures and the presence of CVD. [source] Core Functionality and Scaling Behavior of Lysine DendrimersMACROMOLECULAR RAPID COMMUNICATIONS, Issue 20 2005Bernd Fritzinger Abstract Summary: A scaling exponent to describe the dependence of the hydrodynamic radius as a characteristic length of the molecule on the molecular weight, has been determined for low generation dendrimers with a thiacalixarene core and lysine dendrons. The hydrodynamic radius has been calculated from the diffusion coefficient measured by pulsed-field-gradient NMR spectroscopy. Scaling exponents of 2.0 for the lysine monodendron, 2.3 for a dendrimer with a bifunctional core, and 3.9 for a dendrimer with a tetrafunctional core have been determined. For a given structure of the dendrons, the scaling exponent reflects the functionality of the core of the dendrimers. Hydrodynamic radius of lysine dendrons as a function of molar mass. [source] Predictors of Long-Term Risk for Heart Failure Hospitalization after Acute Myocardial InfarctionANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 3 2010Juha S. Perkiömäki M.D. Background: Data on the value of baseline brain natriuretic peptide (BNP) and autonomic markers in predicting heart failure (HF) hospitalization after an acute myocardial infarction (AMI) are limited. Methods: A consecutive series of patients with AMI without a previous history of HF (n = 569) were followed up for 8 years. At baseline, the patients had a blood sample for determination of BNP, a 24-hour Holter recording for evaluating heart rate variability (HRV) and heart rate turbulence (HRT), and an assessment of baroreflex sensitivity (BRS) using phenylephrine test. Results: During the follow-up, 79 (14%) patients were hospitalized due to HF. Increased baseline BNP, decreased HRV, HRT, and BRS had a significant association with HF hospitalization in univariate comparisons (P < 0.001 for all). After adjusting with all the relevant clinical parameters, BNP, HRV, and HRT still significantly predicted HF hospitalization (P < 0.001 for BNP and for the short-term scaling exponent ,1, P < 0.01 for turbulence slope). In the receiver operator characteristics curve analysis, the area under the curve for BNP was 0.77, for the short-term scaling exponent ,1 0.69, for turbulence slope 0.71, and for BNP/standard deviation of all N-N intervals ratio 0.80. Conclusion: Baseline increased BNP and impaired autonomic function after AMI yield significant information on the long-term risk for HF hospitalization. Ann Noninvasive Electrocardiol 2010;15(3):250,258 [source] Effects of pharmacological adrenergic and vagal modulation on fractal heart rate dynamicsCLINICAL PHYSIOLOGY AND FUNCTIONAL IMAGING, Issue 5 2001Mikko P. Tulppo Breakdown of short-term fractal-like behaviour of HR indicates an increased risk for adverse cardiovascular events and mortality, but the pathophysiological background for altered fractal HR dynamics is not known. Our aim was to study the effects of pharmacological modulation of autonomic function on fractal correlation properties of heart rate (HR) variability in healthy subjects. Short-term fractal scaling exponent (,1) along with spectral components of HR variability were analysed during the following pharmacological interventions in healthy subjects: (i) noradrenaline (NE) infusion (n=22), (ii) NE infusion after phentolamine (PHE) (n=8), (iii) combined NE + adrenaline (EPI) infusion (n=12), (iv) vagal blockade with high dose of atropine (n=10), (v) and vagal activation by low dose of atropine (n=10). Then ,1 decreased progressively during the incremental doses of NE (from 0·85 ± 0·250 to 0.55 ± 0·23, P<0·0001). NE also decreased the average HR (P<0·001) and increased the high frequency spectral power (P<0·001). Vagal blockade with atropine increased the ,1 value (from 0·82 ± 0·22 to 1·24 ± 0·41, P<0·05). Combined NE + EPI infusion and vagal activation with a low dose atropine did not result in any changes in ,1, and ,-adrenergic blockade by PHE did not completely reverse the effects of NE on ,1. Increased levels of circulating NE result in reduction of short-term correlation properties of HR dynamics. The results suggest that coactivation of cardiac vagal outflow at the time of high levels of a circulating sympathetic transmitter explains the breakdown of fractal-like behaviour of human HR dynamics. [source] Long-term memory of the hydrological cycle and river runoffs in China in a high-resolution climate modelINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 12 2006Richard Blender Abstract The hydrological cycle in China is analysed on the basis of a 250-years present-day climate simulation with a high-resolution (T63, ,2° × 2° ) coupled atmosphere-ocean circulation model (ECHAM5/MPI-OM). The analysis of the annual data in the model simulation reveals long-term memory (LTM) on decadal time scales in some components of the hydrological cycle. LTM is characterised by a scaling exponent , > 0 in the power spectrum S(f) , f,, for low frequencies f and is determined by detrended fluctuation analysis (DFA). The simulated annual precipitation and atmospheric near-surface temperature fields show, as in the observations, a white low-frequency spectrum and, hence, no long-term memory in East Asia. However, simulated river flows of the Yangtze and the Huang He reveal LTM with scaling exponents , = 0.3,0.4 (similar to the observations and that of the river Nile) extending beyond the decadal time scale. The model soil temperature indicates restricted memory up to time scales of approximately 30 years. In addition, the model's soil wetness, evaporation, and local runoff show memory on this time scale in a zonal belt at the latitude of Mongolia. Copyright © 2006 Royal Meteorological Society. [source] Multiple growth-correlated life history traits estimated simultaneously in individualsOIKOS, Issue 1 2010Fabian M. Mollet We present a new methodology to estimate rates of energy acquisition, maintenance, reproductive investment and the onset of maturation (four-trait estimation) by fitting an energy allocation model to individual growth trajectories. The accuracy and precision of the method is evaluated on simulated growth trajectories. In the deterministic case, all life history parameters are well estimated with negligible bias over realistic parameter ranges. Adding environmental variability reduces precision, causes the maintenance and reproductive investment to be confounded with a negative error correlation, and tends, if strong, to result in an underestimation of the energy acquisition and maintenance and an overestimation of the age and size at the onset of maturation. Assuming a priori incorrect allometric scaling exponents also leads to a general but fairly predictable bias. To avoid confounding in applications we propose to assume a constant maintenance (three-trait estimation), which can be obtained by fitting reproductive investment simultaneously to size at age on population data. The results become qualitatively more robust but the improvement of the estimate of the onset of maturation is not significant. When applied to growth curves back-calculated from otoliths of female North Sea plaice Pleuronectes platessa, the four-trait and three-trait estimation produced estimates for the onset of maturation very similar to those obtained by direct observation. The correlations between life-history traits match expectations. We discuss the potential of the methodology in studies of the ecology and evolution of life history parameters in wild populations. [source] | |||||||||||||