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Inherent Variability (inherent + variability)
Selected AbstractsDefining and measuring braiding intensityEARTH SURFACE PROCESSES AND LANDFORMS, Issue 14 2008Roey Egozi Abstract Geomorphological studies of braided rivers still lack a consistent measurement of the complexity of the braided pattern. Several simple indices have been proposed and two (channel count and total sinuosity) are the most commonly applied. For none of these indices has there been an assessment of the sampling requirements and there has been no systematic study of the equivalence of the indices to each other and their sensitivity to river stage. Resolution of these issues is essential for progress in studies of braided morphology and dynamics at the scale of the channel network. A series of experiments was run using small-scale physical models of braided rivers in a 3 m , 20 m flume. Sampling criteria for braid indices and their comparability were assessed using constant-discharge experiments. Sample hydrographs were run to assess the effect of flow variability. Reach lengths of at least 10 times the average wetted width are needed to measure braid indices with precision of the order of 20% of the mean. Inherent variability in channel pattern makes it difficult to achieve greater precision. Channel count indices need a minimum of 10 cross-sections spaced no further apart than the average wetted width of the river. Several of the braid indices, including total sinuosity, give very similar numerical values but they differ substantially from channel-count index values. Consequently, functional relationships between channel pattern and, for example, discharge, are sensitive to the choice of braid index. Braid indices are sensitive to river stage and the highest values typically occur below peak flows of a diurnal (melt-water) hydrograph in pro-glacial rivers. There is no general relationship with stage that would allow data from rivers at different relative stage to be compared. At present, channel count indices give the best combination of rapid measurement, precision, and range of sources from which measurements can be reliably made. They can also be related directly to bar theory for braided pattern development. Copyright © 2008 John Wiley & Sons, Ltd. [source] Short-term plasticity in children's speech motor systemsDEVELOPMENTAL PSYCHOBIOLOGY, Issue 8 2006Bridget Walsh Abstract Speech production is a highly skilled behavior that requires rapid and coordinated movements of the orofacial articulators. Previous studies of speech development have shown that children have more variable articulatory movements compared to adults, and cross-sectional studies have revealed that a gradual transition to more stable movement patterns occurs with age. The focus of the present investigation is on the potential role of short-term changes in speech motor performance related to practice. Thus we developed a paradigm to examine the influences of phonological complexity and practice on children (9 and 10-year-olds) and adults' production of novel nonwords. Using two indices that reflect the degree of trial-to-trial consistency of articulatory movements, we analyzed the first and last five productions of the novel nonwords. Both children and adults accurately produced the novel nonwords; however, children showed a practice effect; their last five trials were more consistently produced than their first five trials. Adults did not show this practice effect. This study provides new evidence that children show short-term changes in their speech coordinative patterns with practice. In addition, the present findings support the contribution of neuromotor noise or background, inherent variability to speech motor development. © 2006 Wiley Periodicals, Inc. Dev Psychobiol 48: 660,674, 2006. [source] Seasonal trophic dynamics affect zooplankton community variabilityFRESHWATER BIOLOGY, Issue 11 2009BEATRIX E. BEISNER Summary 1. The degree to which communities are variable may be affected by the ecological conditions to which they are exposed and can affect their propensity to form alternative states. We examined the influence of two common ecological factors, predation and seasonal successional stage, on the variability in community composition of herbivorous pond plankton. In a highly replicated, two factor, mesocosm experiment we determined whether beta diversity was affected by seasonal successional stage of the community (two levels), by fish predation (presence/absence) or by their interaction. 2. Several significant changes were found in the composition of the rotifer, cladoceran and copepod assemblages. Most cladoceran abundances showed sharp declines in the presence of fish, while some rotifers, as well as their assemblage species richness, responded favourably to fish. The copepod assemblage was composed of omnivorous and carnivorous species, which added invertebrate predation to the experiment and which intensified as the season progressed. Copepods showed responses to fish predation that depended on seasonal successional stage of the initial community, because of changes in their stage structure and edibility as they grew from nauplii to adults. 3. Community variability was consistently high at the end of each month-long experimental period for both cladoceran and rotifer assemblages, except under two conditions. In the early season treatments, the rotifer assemblages were more consistent (lower beta diversity) in the presence of fish. This was attributed to high population growth rates for rotifers under these ecological conditions because of reduced copepod predation on them through a trophic cascade from fish. Low community variability was also observed in the late season for rotifers when fish were excluded and, as a result, they were exposed to high invertebrate predation from cyclopoid copepods. 4. Results from the early season support theoretical predictions that when community size increases, variability in composition should decline because of an increase in competitive processes over stochastic ones. Late season results suggest that a second mechanism, specialist predation, can also reduce prey community variability. Our study demonstrates that plankton communities may be more predictable under certain trophic web configurations and challenges ecologists to find ways to incorporate such inherent variability into experiments and community theory. [source] Probabilistic analysis of underground pillar stabilityINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 8 2002D. V. Griffiths The majority of geotechnical analyses are deterministic, in that the inherent variability of the materials is not modelled directly, rather some ,factor of safety' is applied to results computed using ,average' properties. In the present study, the influence of spatially varying strength is assessed via numerical experiments involving the compressive strength and stability of pillars typically used in underground construction and mining operations. The model combines random field theory with an elasto-plastic finite element algorithm in a Monte-Carlo framework. It is found that the average strength of the rock is not a good indicator of the overall strength of the pillar. The results of this study enable traditional approaches involving factors of safety to be re-interpreted as a ,probability of failure' in the context of reliability based design. Copyright © 2002 John Wiley & Sons, Ltd. [source] Use of the Sperm-Class Analyser® for objective assessment of human sperm morphologyINTERNATIONAL JOURNAL OF ANDROLOGY, Issue 5 2003C. Soler Summary The Sperm-Class Analyser® was validated for assessing morphometric parameters of the head and midpiece of unwashed and washed human ejaculated spermatozoa from volunteers providing a wide range of semen quality. A higher proportion of sperm could be assessed (86% fresh semen and 75% washed sperm) if Hemacolor staining was used rather than DiffQuik (80 and 73%) or Papanicolaou (78 and 68%). Different stains employed different fixatives and the area, length, width and perimeter of the sperm head was significantly larger for washed sperm stained by Hemacolor and DiffQuik. Acrosomal area ranged from 48 to 51% of the sperm head area and this percentage was larger for washed sperm stained with DiffQuik. Sperm at the end of the slide, distant from the initial semen droplet, were larger in area and perimeter than those at that site or in the middle. The high precision and reproducibility of the equipment required assessing only 50 sperm on the slide. Far greater variation was found in head width, relative acrosomal area and midpiece width between different slides prepared from the same ejaculate, highlighting the inherent variability within the ejaculate and smear preparation, and requiring more than one slide to be assessed. [source] Architectural properties of the first dorsal interosseous muscleJOURNAL OF ANATOMY, Issue 4 2010Benjamin W. Infantolino Abstract Muscle architecture is considered to reflect the function of muscle in vivo, and is important for example to clinicians in designing tendon-transfer and tendon-lengthening surgeries. The purpose of this study was to quantify the architectural properties of the FDI muscle. It is hypothesized that there will be consistency, that is low variability, in the architectural parameters used to describe the first dorsal interosseous muscle because of its clear functional role in index finger motion. The important architectural parameters identified were those required to characterize a muscle adequately by modeling. Specifically the mass, cross-sectional area, and length of the tendon and muscle were measured in cadavers along with the muscle fiber optimum length and pennation angle, and the moment arm of the first dorsal interosseous at the metacarpophalangeal joint. These parameters provide a characterization of the architecture of the first dorsal interosseous, and were used to indicate the inherent variability between samples. The results demonstrated a large amount of variability for all architectural parameters measured; leading to a rejection of the hypothesis. Ratios designed to describe the functioning of the muscles in vivo, for example the ratio of tendon to fiber optimum lengths, also demonstrated a large variability. The results suggest that function cannot be deduced from form for the first dorsal interosseous, and that subject-specific architectural parameters may be necessary for the formulation of accurate musculoskeletal models or making clinical decisions. [source] IN-LINE CONSISTENCY MONITORING OF TOMATO BASED PRODUCTS USING VIBRATIONAL PROCESS VISCOMETRYJOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 5 2001P. J. CULLEN A vibrational process viscometer was evaluated as an in-line consistency monitoring technique for tomato based products. This sensor was installed in both pilot and industry scale production processes. Accuracy of the sensor and its ability to distinguish between varying concentrations of non-Newtonian fluids was evaluated with flowrate and temperature closely controlled. The sensor was shown to have the least inherent variability when compared to off-line techniques. However it was found to be flowrate dependent for the tomato based products. Good correlations between the sensor and off-line techniques were developed for the pilot scale trials. Plant trials revealed a number of problems in developing such correlations under industrial process conditions, however the instrument proved capable of tracking out of specification sauce as determined by the off-line Brookfield viscometer. It was concluded that use of the sensor would result in increased measurement precision over the off-line instruments coupled with the benefits of in-line monitoring. [source] Spontaneously changing muscular activation pattern in patients with cervical dystoniaMOVEMENT DISORDERS, Issue 6 2001A. Münchau MD Abstract The objective of this study was to determine stability of the neck muscle activation pattern in a given dystonic head position in patients with cervical dystonia (CD). We assessed 26 patients with CD and botulinum toxin (BT) treatment failure before surgical denervation. None of them had received BT injections for at least 4 months. To relate dystonic head position to underlying neck muscle activity, we used synchronised video and poly-electromyographic (EMG) recording over a period of 10 minutes. The muscle activation pattern during constant ("stable") maximal dystonic excursions was analysed. EMG data of nine patients was excluded from the analysis, as these patients had a constantly changing head position or marked head tremor. In the remaining 17 patients, who had a fairly stable dystonic position, muscular activation patterns during the recording spontaneously changed in nine (Group A) while in eight it remained stable (Group B). There was no significant difference in demographic variables between the two groups other than a male predominance in Group A. However, the retrospectively determined initial response to BT treatment (before BT treatment failure had occurred) was significantly worse in Group A as compared with Group B. Neck muscle activation patterns can spontaneously change in CD patients despite constant dystonic head position, implying an inherent variability of the underlying central motor program in some patients. This should be considered when BT treatment response is unsatisfactory, and should also be taken into account when interpreting results of EMG recordings of neck muscles in these patients. © 2001 Movement Disorder Society. [source] Which traits promote persistence of feral GM crops?OIKOS, Issue 1 2005Part 1:implications of environmental stochasticity Transgenes in plants affect life history traits including seed survival and germination. With stochastic matrix models we predict population-level consequences of transgene induced life history changes. We assess systematically which changes in life history traits, resulting from genetic modification, may increase the risk of invasion and persistence of feral crops or increase fitness in case of introgression from arable fields into conspecific, feral populations. We apply our method to feral populations of oilseed rape. Like many annual weeds, oilseed rape depends critically on disturbance; in undisturbed habitats it is generally outcompeted by perennials. The associated inherent variability and unpredictability render deterministic models inappropriate. With a stochastic matrix model we study population growth rate, elasticities and quasi-extinction times. Our results indicate that changes in survival in the seed bank impact population growth and persistence most. Less important are dormancy, fecundity and seedling survival. The predicted distribution of extinction times is highly skewed, with some patches persisting for decades. [source] Estuarine eutrophication in the UK: current incidence and future trendsAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 1 2009Gerald Maier Abstract 1.Increased inputs of nutrients to estuaries can lead to undesirable effects associated with eutrophication, including algal blooms, changes in species composition and bottom anoxia. Several estuaries and coastal areas around the UK have increased nitrogen (N) and phosphorus (P) concentrations, elevated concentrations of chlorophyll a and changes in algal community composition and abundance. This paper reviews the pressures that lead to high nutrient concentrations in estuaries and considers the likely effectiveness of current and proposed regulatory actions. 2.The main sources of nutrients to estuaries are river runoff, sewage discharges, atmospheric inputs and possibly submarine groundwater discharges, although little is known about the latter. Significant reductions in N and P inputs have been realized following application of the EU's Urban Waste Water Treatment Directive. Atmospheric NOx and NHx emissions have also decreased and are expected to decrease further in the next decade as implementation of existing legislation continues, and new controls are introduced for activities such as shipping. 3.Agricultural inputs reach estuaries principally through diffuse sources, either in surface water (and in some areas possibly groundwater) or, for N, via the atmosphere. Over 10 years ago the Nitrates Directive was introduced to tackle the problem of N discharges from agriculture but little change in N loads to estuaries has been recorded. 4.To meet the aims of the EU Water Framework Directive, for at least ,good' ecological status, more rigorous application and implementation of the Nitrates Directive, together with changes in the Common Agriculture Policy and farming practice are likely to be needed. Even then, the slow response of the natural environment to change and the inherent variability of estuaries means that their responses may not be as predicted. Research is needed into the relationship between policy drivers and environmental responses to ensure actions taken will achieve the planned results. Copyright © 2008 John Wiley & Sons, Ltd. [source] An analysis of variability in the manufacturing of dexosomes: Implications for development of an autologous therapy,BIOTECHNOLOGY & BIOENGINEERING, Issue 2 2005Sanjay Patel Abstract Dexosomes are nanometer-size vesicles released by dendritic-cells, possessing much of the cellular machinery required to stimulate an immune response (i.e. MHC Class I and II). The ability of patient-derived dexosomes loaded with tumor antigens to elicit anti-tumor activity is currently being evaluated in clinical trials. Unlike conventional biologics, where variability between lots of product arises mostly from the manufacturing process, an autologous product has inherent variability in the starting material due to heterogeneity in the human population. In an effort to assess the variability arising from the dexosome manufacturing process versus the human starting material, 144 dexosome preparations from normal donors (111) and cancer patients (33) from two Phase I clinical trials were analyzed. A large variability in the quantity of dexosomes (measured as the number of MHC Class II molecules) produced between individual lots was observed (,>,50-fold). An analysis of intra-lot variability shows that the manufacturing process introduces relatively little of this variability. To identify the source(s) of variability arising from the human starting material, distributions of the key parameters involved in dexosome production were established, and a model created. Computer simulations using this model were performed, and compared to the actual data observed. The main conclusion from these simulations is that the number of cells collected per individual and the productivity of these cells of are the principal sources of variability in the production of Class II. The approach described here can be extended to other autologous therapies in general to evaluate control of manufacturing processes. Moreover, this analysis of process variability is directly applicable to production at a commercial scale, since the large scale manufacture of autologous products entails an exact process replication rather than scale-up in volume, as is the case with traditional drugs or biologics. © 2005 Wiley Periodicals, Inc. [source] A population pharmacokinetic meta-analysis of maraviroc in healthy volunteers and asymptomatic HIV-infected subjectsBRITISH JOURNAL OF CLINICAL PHARMACOLOGY, Issue 2008Phylinda L. S. Chan AIMS To develop a population pharmacokinetic model for maraviroc, a noncompetitive CCR5 antagonist, after oral administration of tablets to healthy volunteers and asymptomatic HIV-infected subjects and to quantify the inherent variability and influence of covariates on the parameters of the model. METHODS Rich pharmacokinetic data available from 15 studies in healthy volunteers (n = 365) and two studies in asymptomatic HIV-infected subjects (n = 48) were analysed using NONMEM. Maraviroc was administered as single or multiple oral tablet doses under fasted and fed conditions. Doses ranged from 100 to 1800 mg day,1. RESULTS A two-compartment model parameterized to separate out absorption and clearance components on bioavailability was used. Absorption was described by a lagged first-order process. A sigmoid Emax model described the effect of dose on absorption. A visual predictive check and nonparametric bootstrap evaluation confirmed that the model was a good description of the data. Typical CL, Vc and Vp values for a 30-year-old non-Asian are 51.5 l h,1, 132 l and 277 l, respectively. CONCLUSIONS For the typical non-Asian subject, fasted bioavailability increased asymptotically with dose from 24% at 100 mg to 33% at 600 mg. A high-fat meal taken with maraviroc reduced exposure by 43% for a 100-mg dose to approximately 25% at doses of 600 mg. The typical Asian subject had a 26.5% higher AUC than the typical non-Asian subject irrespective of dose, a difference not considered to be clinically relevant. None of the other covariates tested had any clinically relevant effects on exposure. [source] | |||||||||||||