Independent Data Points Research Articles

An Experimental Study on Truck Side-Skirt Flow

The underbody of a truck is responsible for an appreciable portion of the vehicle’s aerodynamic drag, and thus its fuel consumption. This paper investigates experimentally the flow around side-skirts, a common underbody aerodynamic device which is known to be effective at reducing vehicle drag. A full, 1/10 scale European truck model is used. The chassis of the model is designed to represent one that would be found on a typical trailer, and is fully reconfigurable. Testing is carried out in a water towing tank, which allows the correct establishment of the ground flow and rotating wheels. Optical access into the underbody is possible through the clear working section of the facility. Stereoscopic and planar Particle Image Velocimetry (PIV) set-ups are used to provide both qualitative images of and quantitative information on the flow field. The planar PIV set-up employs novel techniques developed in-house, including the use of two laser sheets to reduce shadow regions, and frame averaging such that presented results are produced using an average of up to 1800 independent data points. It is shown that one drag-reducing mechanism of side-skirts at zero-degree yaw is the prevention of high-momentum flow at the side of the vehicle entering the upper half of the underbody. However, the flow topology varies significantly with vertical position, and side-skirts are shown to have effects on near-ground flow which could have a detrimental effect on vehicle drag. It is therefore likely that an optimum value exists for the height of a side-skirt from the ground.

Constraints on a ϕCDM model from strong gravitational lensing and updated Hubble parameter measurements

We constrain the scalar field dark energy model with an inverse power-law potential, i.e., V(ϕ) ∝ ϕ−α (α > 0), from a set of recent cosmological observations by compiling an updated sample of Hubble parameter measurements including 30 independent data points. Our results show that the constraining power of the updated sample of H(z) data with the HST prior on H0 is stronger than those of the SCP Union2 and Union2.1 compilations. A recent sample of strong gravitational lensing systems is also adopted to confine the model even though the results are not significant. A joint analysis of the strong gravitational lensing data with the more restrictive updated Hubble parameter measurements and the Type Ia supernovae data from SCP Union2 indicates that the recent observations still can not distinguish whether dark energy is a time-independent cosmological constant or a time-varying dynamical component.

Consistency of a phylogenetic tree maximum likelihood estimator

Phylogenetic trees represent the order and extent of genetic divergence of a fixed collection of organisms. Order of divergence is represented via the tree structure, and extent of divergence by the branch lengths. Both the tree’s structure and branch lengths are unknown parameters and the tree is estimated using sequence information sampled at a number of genetic sites. Under the model of genetic Brownian motion, we prove that as the number of genetic sites that are sampled becomes large, the maximum likelihood estimator of the tree is consistent. (Our maximum likelihood estimator treats each site as an independent data point, which is different from concatenating the sites.) Existing arguments for consistency rely on the assumption of a finite parameter space or only apply to transition probability matrix-based models, and do not hold here due to the continuous model for branch lengths. The metric space of Billera et al. (2001) is central to the proof. We conclude with some comments on the role of parametric methods in tree estimation.

Board interlocking network and the design of executive compensation packages

The standard approach used to model interlocks in the business and management literature is to treat each interlock of a network as an independent data point. However, such an approach ignores the complex inter-dependencies among the common director interlocks. We propose that an interlocking board network is an important inter-corporate setting that has bearing on how company boards make corporate decisions. Using a sample of 725 large U.S.-based public companies over the period 2007–2010, board member information, executive compensation information, and exponential random graph modeling (ERGM) techniques for social networks, we present evidence that board interlocks are positively linked with similarities in the design of executive compensation packages in interlocked firms, particularly the proportions of the options component. We also find evidence that board interlocks are positively linked with similarities in a number of board characteristics.

Correlational Studies in Typological and Historical Linguistics

We review a number of recent studies that have identified either correlations between different linguistic features (e.g., implicational universals) or correlations between linguistic features and nonlinguistic properties of speakers or their environment (e.g., effects of geography on vocabulary). We compare large-scale quantitative studies with more traditional theoretical and historical linguistic research and identify divergent assumptions and methods that have led linguists to be skeptical of correlational work. We also attempt to demystify statistical techniques and point out the importance of informed critiques of the validity of statistical approaches. Finally, we describe various methods used in recent correlational studies to deal with the fact that, because of contact and historical relatedness, individual languages in a sample rarely represent independent data points, and we show how these methods may allow us to explore linguistic prehistory to a greater time depth than is possible with orthodox comparative reconstruction.

Constraining duty cycles through a Bayesian technique

The duty cycle (DC) of astrophysical sources is generally defined as the fraction of time during which the sources are active. However, DCs are generally not provided with statistical uncertainties, since the standard approach is to perform Monte Carlo bootstrap simulations to evaluate them, which can be quite time consuming for a large sample of sources. As an alternative, considerably less time-consuming approach, we derived the theoretical expectation value for the DC and its error for sources whose state is one of two possible, mutually exclusive states, inactive (off) or flaring (on), as based on a finite set of independent observational data points. Following a Bayesian approach, we derived the analytical expression for the posterior, the conjugated distribution adopted as prior, and the expectation value and variance. We applied our method to the specific case of the inactivity duty cycle (IDC) for supergiant fast X-ray transients. We also studied IDC as a function of the number of observations in the sample. Finally, we compare the results with the theoretical expectations. We found excellent agreement with our findings based on the standard bootstrap method. Our Bayesian treatment can be applied to all sets of independent observations of two-state sources, such as active galactic nuclei, X-ray binaries, etc. In addition to being far less time consuming than bootstrap methods, the additional strength of this approach becomes obvious when considering a well-populated class of sources ($N_{\rm src} \geq 50$) for which the prior can be fully characterized by fitting the distribution of the observed DCs for all sources in the class, so that, through the prior, one can further constrain the DC of a new source by exploiting the information acquired on the DC distribution derived from the other sources. [Abridged]

PO-0459 Fat Mass(fm) And Fat Free Mass(ffm) Indices In Preterm And Term Infants During First 6 Months Of Life

Background The development of normative reference Body Composition (BC) data in infancy, is an important step towards evaluation of postnatal growth in clinical practice. Weight gain fails to differentiate lean body mass (constitution) from fat mass (nutrition). Percentile ranks and length normalised indices of FFM and FM can define nutritional depletion or obesity. We present longitudinal data from a large dataset of stable growing infants. Methods BC data (n = 857) from 574 infants (22–42 wks) enrolled in 4 longitudinal studies, 2/3rd were preterm, was considered as independent data points. Preterms on fortified breast milk or formula (80 kcal/dL), term infants on breast milk or formula (67 kcal/dL). Time points of measurement : after reaching full enteral feeding, at term and two further time points until a maximum of 6 months of corrected age. BC was measured by Dual energy X-ray absorptiometry (QDR 1500; Hologic). R software (GAMLSS) used for construction of growth curves. Results Length of preterms remain shorter than terms, both increases linearly at 0.7 cm/wk. Median FM/FFM in preterm is 500 g/2450 g (40 wks) and 1700 g/4500 g (60 wks) compared to 430 g/2790 g (40 wks) and 2400 g/4700 g (60 wks) for term. Preterm FMI centiles are higher than terms till 45–50 wks corrected. Preterm FFMI increases progressively till 40 wks, then remains constant over time like terms (Figure 1). Conclusion Growth pattern for preterm vary from term, justifying their higher nutritional requirement to support rapid FFM growth initially. FM being inverse of FFM, length normalised indices rather than percentages allow independent assessment of growth in each body compartment, while compensating for difference in body size of term and preterm infants.

The risk of heart failure associated with the use of noninsulin blood glucose-lowering drugs: systematic review and meta-analysis of published observational studies.

BackgroundPatients with type 2 diabetes mellitus (T2DM) are at high risk of heart failure. A summary of the effects of blood glucose-lowering drugs other than glitazones on the risk of heart failure in routine clinical practice is lacking. The objective of this study was to conduct a systematic review and meta-analysis of observational studies on the risk of heart failure when using blood glucose-lowering drugs.MethodsWe systematically identified and reviewed cohort and case–control studies in which the main exposure of interest was noninsulin blood glucose-lowering medications in patients with T2DM. We searched Medline, Embase, and the Cochrane Library to identify publications meeting prespecified eligibility criteria. The quality of included studies was assessed with the Newcastle-Ottawa Scale and the RTI item bank. Results were combined using fixed and random-effects models when at least 3 independent data points were available for a drug-drug comparison.ResultsThe summary relative risk of heart failure in rosiglitazone users versus pioglitazone users (95% CI) was 1.16 (1.05-1.28) (5 cohort studies). Heterogeneity was present (I2 = 66%). For new users (n = 4) the summary relative risk was 1.21 (1.14-1.30) and the heterogeneity was reduced (I2 = 31%);. The summary relative risk for rosiglitazone versus metformin was 1.36 (95% CI, 1.17-1.59) (n = 3). The summary relative risk (95% CI) of heart failure in sulfonylureas users versus metformin users was 1.17 (95% CI, 1.06-1.29) (5 cohort studies; I2 = 24%) and 1.22 (1.02-1.46) when restricted to new users (2 studies).Information on other comparisons was very scarce. Information on dose and duration of treatment effects was lacking for most comparisons. Few studies accounted for disease severity; therefore, confounding by indication might be present in the majority of the within-study comparisons of this meta-analysis.ConclusionsUse of glitazones and sulfonylureas was associated with an increased risk of heart failure compared with metformin use. However, indication bias cannot be ruled out. Ongoing large multidatabase studies will help to evaluate the risk of heart failure in treated patients with diabetes, including those using newer blood glucose-lowering therapies.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2261-14-129) contains supplementary material, which is available to authorized users.

De novo reconstruction of gene regulatory networks from time series data, an approach based on formal methods

Reverse engineering of gene regulatory relationships from genomics data is a crucial task to dissect the complex underlying regulatory mechanism occurring in a cell. From a computational point of view the reconstruction of gene regulatory networks is an undetermined problem as the large number of possible solutions is typically high in contrast to the number of available independent data points. Many possible solutions can fit the available data, explaining the data equally well, but only one of them can be the biologically true solution. Several strategies have been proposed in literature to reduce the search space and/or extend the amount of independent information.In this paper we propose a novel algorithm based on formal methods, mathematically rigorous techniques widely adopted in engineering to specify and verify complex software and hardware systems. Starting with a formal specification of gene regulatory hypotheses we are able to mathematically prove whether a time course experiment belongs or not to the formal specification, determining in fact whether a gene regulation exists or not. The method is able to detect both direction and sign (inhibition/activation) of regulations whereas most of literature methods are limited to undirected and/or unsigned relationships.We empirically evaluated the approach on experimental and synthetic datasets in terms of precision and recall. In most cases we observed high levels of accuracy outperforming the current state of art, despite the computational cost increases exponentially with the size of the network.We made available the tool implementing the algorithm at the following url: http://www.bioinformatics.unisannio.it.

Exploring the effects of spatial autocorrelation when identifying key drivers of wildlife crop-raiding.

Few universal trends in spatial patterns of wildlife crop-raiding have been found. Variations in wildlife ecology and movements, and human spatial use have been identified as causes of this apparent unpredictability. However, varying spatial patterns of spatial autocorrelation (SA) in human–wildlife conflict (HWC) data could also contribute. We explicitly explore the effects of SA on wildlife crop-raiding data in order to facilitate the design of future HWC studies. We conducted a comparative survey of raided and nonraided fields to determine key drivers of crop-raiding. Data were subsampled at different spatial scales to select independent raiding data points. The model derived from all data was fitted to subsample data sets. Model parameters from these models were compared to determine the effect of SA. Most methods used to account for SA in data attempt to correct for the change in P-values; yet, by subsampling data at broader spatial scales, we identified changes in regression estimates. We consequently advocate reporting both model parameters across a range of spatial scales to help biological interpretation. Patterns of SA vary spatially in our crop-raiding data. Spatial distribution of fields should therefore be considered when choosing the spatial scale for analyses of HWC studies. Robust key drivers of elephant crop-raiding included raiding history of a field and distance of field to a main elephant pathway. Understanding spatial patterns and determining reliable socio-ecological drivers of wildlife crop-raiding is paramount for designing mitigation and land-use planning strategies to reduce HWC. Spatial patterns of HWC are complex, determined by multiple factors acting at more than one scale; therefore, studies need to be designed with an understanding of the effects of SA. Our methods are accessible to a variety of practitioners to assess the effects of SA, thereby improving the reliability of conservation management actions.

Sympatric sister species in rodents are more chromosomally differentiated than allopatric ones: implications for the role of chromosomal rearrangements in speciation

AbstractA meta‐analysis approach was used to test for chromosomal speciation in rodents. Forty‐one pairs of sister species, identified in the two most species‐rich rodent families (Cricetidae andMuridae), were used as phylogenetically independent data points, each resulting from a speciation event. About 30% of sister species have an identical karyotype. There was a significant difference in the number of chromosomal differences between sympatric and allopatric sister species, compatible with a direct role of chromosomal rearrangements in speciation.

Implicit measurement of the latent heat in a magnetocaloric NiMnIn Heusler alloy

The latent heat linked with the first-order transformation of a NiMnIn Heusler alloy has been studied through direct measurements of the adiabatic temperature change, ΔTad, during magnetization process. The experimental procedure used guarantees independent data points and negates any contribution of hysteretic losses to the magnetocaloric effect. Thus, the differences between the magnitudes of ΔTad measurements during the magnetization with the initial temperature change directions from low-to-high and high-to-low are solely attributed to the latent heat exchange, which accompanies the irreversible structural first-order transformation. An estimate of the latent heat inducing such differences is about 0.292 J/g.

Protocol for a Systematic Review: Behavioral, Psychological, Educational, and Vocational Interventions to Facilitate Employment Outcomes for Cancer Survivors

Protocol for a Systematic Review: Behavioral, Psychological, Educational, and Vocational Interventions to Facilitate Employment Outcomes for Cancer Survivors

A New Maximum Likelihood Approach for Free Energy Profile Construction from Molecular Simulations

A novel variational method for construction of free energy profiles from molecular simulation data is presented. The variational free energy profile (VFEP) method uses the maximum likelihood principle applied to the global free energy profile based on the entire set of simulation data (e.g from multiple biased simulations) that spans the free energy surface. The new method addresses common obstacles in two major problems usually observed in traditional methods for estimating free energy surfaces: the need for overlap in the re-weighting procedure and the problem of data representation. Test cases demonstrate that VFEP outperforms other methods in terms of the amount and sparsity of the data needed to construct the overall free energy profiles. For typical chemical reactions, only ~5 windows and ~20-35 independent data points per window are sufficient to obtain an overall qualitatively correct free energy profile with sampling errors an order of magnitude smaller than the free energy barrier. The proposed approach thus provides a feasible mechanism to quickly construct the global free energy profile and identify free energy barriers and basins in free energy simulations via a robust, variational procedure that determines an analytic representation of the free energy profile without the requirement of numerically unstable histograms or binning procedures. It can serve as a new framework for biased simulations and is suitable to be used together with other methods to tackle with the free energy estimation problem.

Allometric Scaling of the Optic Tectum in Cartilaginous Fishes

In cartilaginous fishes (Chondrichthyes; sharks, skates and rays (batoids), and holocephalans), the midbrain or mesencephalon can be divided into two parts, the dorsal tectum mesencephali or optic tectum (analogous to the superior colliculus of mammals) and the ventral tegmentum mesencephali. Very little is known about interspecific variation in the relative size and organization of the components of the mesencephalon in these fishes. This study examined the relative development of the optic tectum and the tegmentum in 75 chondrichthyan species representing 32 families. This study also provided a critical assessment of attempts to quantify the size of the optic tectum in these fishes volumetrically using an idealized half-ellipsoid approach (method E), by comparing this method to measurements of the tectum from coronal cross sections (method S). Using species as independent data points and phylogenetically independent contrasts, relationships between the two midbrain structures and both brain and mesencephalon volume were assessed and the relative volume of each brain area (expressed as phylogenetically corrected residuals) was compared among species with different ecological niches (as defined by primary habitat and lifestyle). The relatively largest tecta and tegmenta were found in pelagic coastal/oceanic and oceanic sharks, benthopelagic reef sharks, and benthopelagic coastal sharks. The smallest tecta were found in all benthic sharks and batoids and the majority of bathyal (deep-sea) species. These results were consistent regardless of which method of estimating tectum volume was used. We found a highly significant correlation between optic tectum volume estimates calculated using method E and method S. Taxon-specific variation in the difference between tectum volumes calculated using the two methods appears to reflect variation in both the shape of the optic tectum relative to an idealized half-ellipsoid and the volume of the ventricular cavity. Because the optic tectum is the principal termination site for retinofugal fibers arising from the retinal ganglion cells, the relative size of this brain region has been associated with an increased reliance on vision in other vertebrate groups, including bony fishes. The neuroecological relationships between the relative size of the optic tectum and primary habitat and lifestyle we present here for cartilaginous fishes mirror those established for bony fishes; we speculate that the relative size of the optic tectum and tegmentum similarly reflects the importance of vision and sensory processing in cartilaginous fishes.

Extraction of complex refractive index of absorbing films from ellipsometry measurement

Numerical extraction of complex refractive index of an unknown absorbing layer inside a multilayer sample from ellipsometry measurement is discussed. The approach of point by point extraction considering all points of spectroscopic data as independent data points is investigated. This problem has typically multiple solutions and the standard method consisting in fitting calculated to experimental point is likely to converge to a wrong solution if a precise guess value is not given. An alternate method is proposed, based on the determination of contours of the ellipsometric function, to provide all solutions in an as extended as wanted range of complex refractive index values. The method is tested through different kinds of sample examples. Errors relative to any of the parameters used in the sample model are calculated and discussed. This method should be helpful in many practical cases of ellipsometry data interpretation.

Linkages between the life-history evolution of tropical and temperate birds and the resistance of their cells to oxidative and non-oxidative chemical injury

A fundamental challenge facing physiological ecologists is to understand how variation in life history at the whole-organism level might be linked to cellular function. Thus, because tropical birds have higher annual survival and lower rates of metabolism, we hypothesized that cells from tropical species would have greater cellular resistance to chemical injury than cells from temperate species. We cultured dermal fibroblasts from 26 tropical and 26 temperate species of birds and examined cellular resistance to cadmium, H(2)O(2), paraquat, thapsigargin, tunicamycium, methane methylsulfonate (MMS) and UV light. Using ANCOVA, we found that the values for the dose that killed 50% of cells (LD(50)) from tropical birds were significantly higher for H(2)O(2) and MMS. When we tested for significance using a generalized least squares approach accounting for phylogenetic relationships among species to model LD(50), we found that cells from tropical birds had greater tolerance for Cd, H(2)O(2), paraquat, tunicamycin and MMS than cells from temperate birds. In contrast, tropical birds showed either lower or no difference in tolerance to thapsigargin and UV light in comparison with temperate birds. These findings are consistent with the idea that natural selection has uniquely fashioned cells of long-lived tropical bird species to be more resistant to forms of oxidative and non-oxidative stress than cells from shorter-lived temperate species.

Inverse link between density and dispersal distance in butterflies: field evidence from six co‐occurring species

AbstractA pertinent question in animal population ecology is the relationship between population abundance, density, and mobility. Two extreme ways to reach sufficient abundance for long‐term persistence are to inhabit restricted locations at high densities, or large areas in low densities. The former case predicts low individual mobility, whereas the later predicts high one. This assumption is rarely tested using across‐species comparisons, due to scarcity of data on both mobility and population sizes for multiple species. We used data on dispersal and local population densities of six butterfly species gained by mark‐recapture, and data on their (relative) regional abundance obtained by walking transects in a landscape surrounding the mark‐recapture sites. We correlated both local density and regional abundance against slopes of the inverse power function, appropriate for describing the shape of dispersal kernel. Local densities correlated negatively with the dispersal kernel slopes both when sexes were treated as independent data points and if treated together. For regional abundance, the correlation was also negative but only marginally significant. Our results corroborate the notion that a trade‐off exists between living in dense populations and having poor dispersal, and vice versa. We link this observation to resource use by individual species, and distribution of such resources as host plants in the study landscape.

Traits and ecological strategies of Australian tropical and temperate climbing plants

Aim Understanding large scale patterns in trait variation in climbing plants (lianas, vines, scramblers, twiners) is important for the development of a stronger theoretical understanding of climbing plant ecology and for more applied issues such as prediction of community assembly under changing climatic conditions. We compared values of five key functional traits for 388 species of climbing plant from tropical and temperate regions of Australia to quantify variation between these two biogeographic regions. Location Australia. Methods Data on dispersal mode, growth habit, leaf form, leaf size and seed mass were compiled from field measurements and published sources. Comparative analyses were performed in three ways: (1) across species where each species was treated as an independent data point, (2) using evolutionary divergence analyses for each trait, and (3) in multidimensional space using a matrix of similarities between species. Results Tropical climbing plants had 22-fold greater seed mass and four times greater leaf size than did temperate species. Tropical climbers were more likely to be woody (63%) than were temperate species (40%). Surprisingly we found a similar proportion of animal-dispersed seeds in the two regions, although we expected animal-dispersed seeds to be more prevalent in the tropics. We also found similar proportions of simple- and compound-leaved species between the two regions. All of our findings were consistent between cross-species and phylogenetic analyses indicating that patterns in present-day species are reflected in the evolutionary history of Australian climbers. Multivariate analyses suggested that there is a spectrum of variation among climbing plants, with tropical species having greater seed mass, leaf size and woody growth compared with temperate climbing plant species. Main conclusions Tropical and temperate climbers of Australia exhibit a mixture of similar and contrasting traits and ecological strategies. Understanding strategy variation along latitudinal gradients will be particularly informative for predicting ecosystem and community structure with climate change.

Using scale-free processes to explain punctuated-change in management-relevant phenomena

The way organisations change shows evidence of ‘extreme dynamics’, but management research is based on Gaussian statistics that rule out these extremes. On occasion, deviation-amplifying mutual causal processes cause extreme events characterised by power laws. They seem ubiquitous; we list 103 kinds of them – social and/or organisational or managerial rank/frequency distributions. We draw a ‘line in the sand’ between scale-bound processes (characterised by Gaussian statistics and based on independent data points, finite variance and emphasising averages) and scale-free processes (characterised by Paretian statistics reflecting interdependence, positive feedback, infinite variance, and extreme outcomes). Quantitative journal publication depends almost entirely on the former type. We draw on complexity theory to propose redirecting management theory and research so as to make it more relevant to management practitioners. First, we propose a taxonomy of scale-free theories that explain the fractal properties of various kinds of organisational rank/frequency distributions and why they emerge. Second, we apply the scale-free theories to specific social/organisational examples.