Local Structural Variability Research Articles

Modeling of the temporal and local spatial structure variability in mixed settlements of Mytilus edulis and Mytilus trossulus

Modeling of the temporal and local spatial structure variability in mixed settlements of Mytilus edulis and Mytilus trossulus

Prescribing of Sick Leave by Surgeons: A Survey Based on Hypothetical Patient Cases

Physicians regard the tasks of sick-listing and work ability assessments problematic and among the most challenging duties in their practice. Few studies have analyzed sick leave prescribing practices, and the practices have been shown to vary among physicians. The aim of this study was to examine the prescribing of sick leave by surgeons and factors that affect these prescribing practices. A questionnaire study with 19 hypothetical patient cases was conducted among 338 Finnish surgeons. The effects of both physician-related and local structural background variables on sick leave prescribing were studied using univariate and multiple linear regression models. The economic consequences of the variation in sick leave prescribing were estimated. The overall number of days of sick leave prescribed for the entire group of 19 patient cases averaged 281.4 days (range = 134-490 days). With the same diagnosis, surgeons prescribed more days of sick leave for patients who do physical work than for those who work in an office. Older surgeons with more working experience and those working in smaller municipalities or in smaller hospitals prescribed longer sick leave than others. Clinical specialists tended to prescribe longer sick leave than those still in specialty training. Structured education for surgeons on prescribing sick leave, together with defined guidelines, could produce more uniform practices and improve equality among patients.

A multiscale MDCT image-based breathing lung model with time-varying regional ventilation

A novel algorithm is presented that links local structural variables (regional ventilation and deforming central airways) to global function (total lung volume) in the lung over three imaged lung volumes, to derive a breathing lung model for computational fluid dynamics simulation. The algorithm constitutes the core of an integrative, image-based computational framework for subject-specific simulation of the breathing lung. For the first time, the algorithm is applied to three multi-detector row computed tomography (MDCT) volumetric lung images of the same individual. A key technique in linking global and local variables over multiple images is an in-house mass-preserving image registration method. Throughout breathing cycles, cubic interpolation is employed to ensure C1 continuity in constructing time-varying regional ventilation at the whole lung level, flow rate fractions exiting the terminal airways, and airway deformation. The imaged exit airway flow rate fractions are derived from regional ventilation with the aid of a three-dimensional (3D) and one-dimensional (1D) coupled airway tree that connects the airways to the alveolar tissue. An in-house parallel large-eddy simulation (LES) technique is adopted to capture turbulent-transitional-laminar flows in both normal and deep breathing conditions. The results obtained by the proposed algorithm when using three lung volume images are compared with those using only one or two volume images. The three-volume-based lung model produces physiologically-consistent time-varying pressure and ventilation distribution. The one-volume-based lung model under-predicts pressure drop and yields un-physiological lobar ventilation. The two-volume-based model can account for airway deformation and non-uniform regional ventilation to some extent, but does not capture the non-linear features of the lung.

LOCAL MICROSTRUCTURE EVOLUTION OF BISMUTH SODIUM TITANATE-BASED LEAD-FREE PIEZOELECTRIC SYSTEMS ACROSS THE MORPHOTROPIC PHASE BOUNDARY REGION

Morphotropic phase boundary (MPB) containing piezoelectric systems generally exhibit enhanced piezoelectric performance at compositions within, or close to, the MPB region. The mechanism/s underlying such enhancement, however, are still contentious due to complex micro/nanostructure and apparently inherent local structural variability associated with octahedral tilt disorder/platelet precipitates in such piezoelectric materials. This paper reviews some recent structural analysis results from Bi0.5Na0.5TiO3 (BNT) and other binary, lead-free, piezoelectric materials systems derived from it via electron diffraction and in situ neutron diffraction. The results suggest that intrinsically existing local microstructure (LMS) in BNT essentially continues across the MPB region. The LMS, originating from inherent octahedral tilt disorder, is strongly temperature-, electric field-, pressure- and chemical composition-dependent, and may help to explain a series of phenomena observed in BNT-based binary materials systems, including the enhanced piezoelectric effect in the region of the MPB.

Influence of forest structure and experimental green-tree retention on northern flying squirrel (Glaucomys sabrinus) abundance

In many regions of the world, forest management has shifted from practices emphasizing timber production to more sustainable harvesting that integrates ecological values, including maintenance of biodiversity, wildlife habitat, and ecological goods and services. To this end, management strategies emphasize retention of stand structures that meet the needs of forest-obligate wildlife species and enhance connectivity across landscapes. However, little is known about the effects on arboreal rodents of varying the amount or spatial distribution of retained structures. We quantified the responses of northern flying squirrels (Glaucomys sabrinus) to retention harvests of varying levels (15%, 40%, 75%, and 100% of original basal area) and spatial patterns (trees uniformly dispersed vs. aggregated in 1-ha patches), using six experimental treatments replicated at three locations in southwestern Oregon and Washington. Relative abundance of northern flying squirrels decreased following harvest; minimum number of squirrels known alive (MNKA) in the control (100%) and 75% retention treatment was significantly higher than in the 15% or 40% treatments. In mixed-effects regression models, MNKA increased with treatment-unit basal area and amount of surrounding mature (>80-year-old) forest, suggesting that squirrel abundance was influenced by local structure and landscape-scale variables. However, only basal area contributed to best-fit models of reproductive female abundance. Our results suggest a threshold response of northern flying squirrels to green-tree retention somewhere between 40% and 75% that is likely to be influenced by the spatial pattern of retention and landscape context. This study underscores previous conclusions that northern flying squirrels are sensitive to logging at both local and larger landscape scales, and demonstrates the current minimum retention standard of 15% will not provide suitable habitat for this species.

Factors affecting sick leave prescribing by dentists

The aim was to examine the prescribing of sick leave by dentists and factors affecting prescribing practices. A questionnaire study covering sick leave-prescribing practice during the preceding year and in response to 16 hypothetical patient cases was conducted among 1132 Finnish dentists. The effects of both dentist-related and local structural background variables on sick leave prescribing were studied. During the preceding year, dentists who were young, male, or practicing in small municipalities prescribed more days of sick leave than comparator groups. In response to the 16 hypothetical cases, dentists prescribed a mean of 31.6days of sick leave (range, 0-98days). The dentists with a specialty degree in oral and maxillofacial surgery prescribed longer sick leave than other dentists. Dentists working only in public dental services (PDS) and older dentists prescribed significantly less sick leave than others. There is considerable variation among dentists in sick leave-prescribing practices. The most significant factors affecting this variation are having a specialty in oral and maxillofacial surgery and working only in PDS. Further education and guidelines on dental sick leave prescribing are needed.

Variations in primary care physicians’ sick leave prescribing practices

Several studies have shown great differences in physicians' way to sick list. The roles of physician-related factors and local structural factors on the length of the sick leaves have been ambiguous. The aim was to examine the variation in short-term sick-listing practices among primary care physicians. A questionnaire study with 19 hypothetical patient cases was conducted among 300 Finnish primary care physicians. The effects of both physician related and local structural background variables on sick leave prescribing were studied using univariate and multiple linear regression models. Economic consequences of the variation in sick leave prescribing were estimated. On an average, the overall number of sick leave days prescribed for the entire group of the 19 patient cases was 97.4, varying between 42 and 165 days. The economic consequences to the society of the sick leaves prescribed to them would be €29,442 on average, varying between €11,837 and €51,613. Clinical specialists prescribed shorter sick leaves than general practitioners, with estimated costs of €27,888 and €30,789, respectively. More days of sick leave was prescribed in smaller municipalities than in larger ones. There is a lot of variation in physicians' sick leave prescribing practices and it depends both on physician-related factors and local structural factors. The speciality status of a physician was the most significant single factor affecting the variation. Notable savings for the society might be possible to achieve by increasing sick-listing education and training.

Construction of multi-region-multi-reference atlases for neonatal brain MRI segmentation

Neonatal brain MRI segmentation is a challenging problem due to its poor image quality. Atlas-based segmentation approaches have been widely used for guiding brain tissue segmentation. Existing brain atlases are usually constructed by equally averaging pre-segmented images in a population. However, such approaches diminish local inter-subject structural variability and thus lead to lower segmentation guidance capability. To deal with this problem, we propose a multi-region-multi-reference framework for atlas-based neonatal brain segmentation. For each region of a brain parcellation, a population of spatially normalized pre-segmented images is clustered into a number of sub-populations. Each sub-population of a region represents an independent distribution from which a regional probability atlas can be generated. A selection of these regional atlases, across different sub-regions, will in the end be adaptively combined to form an overall atlas specific to the query image. Given a query image, the determination of the appropriate set of regional atlases is achieved by comparing the query image regionally with the reference, or exemplar, of each sub-population. Upon obtaining an overall atlas, an atlas-based joint registration–segmentation strategy is employed to segment the query image. Since the proposed method generates an atlas which is significant more similar to the query image than the traditional average-shape atlas, better tissue segmentation results can be expected. This is validated by applying the proposed method on a large set of neonatal brain images available in our institute. Experimental results on a randomly selected set of 10 neonatal brain images indicate that the proposed method achieves higher tissue overlap rates and lower standard deviations (SDs) in comparison with manual segmentations, i.e., 0.86 (SD 0.02) for GM, 0.83 (SD 0.03) for WM, and 0.80 (SD 0.05) for CSF. The proposed method also outperforms two other average-shape atlas-based segmentation methods.

How Homogeneous is the Boreal Forest? Characteristics and Variability of Old-Growth Forest on aHylocomium—MyrtillusSite Type in the Pallas-Yllästunturi National Park, Northern Finland

An adequate understanding of an old-growth forest structure and its variability is needed for forest conservation and restoration. We studied the local scale structural variability of boreal old-growth forests on a Hylocomium—Myrtillus site type in the Pallas-Yllästunturi National Park in northern Finland. Principal component analysis (PCA) revealed that the main directions of structural and compositional variability were related to variables describing the total volume of coarse woody debris (CWD), volumes of living and dead Pinus sylvestris and volume of deciduous CWD. An average, living tree volume was 141.5 m3 ha-1, varying among the 252 sample plots from 15.3 to 442.0 m3 ha-1. The mean CWD volume was 30.0 m3 ha-1 (0–99.3 m3 ha-1). Downed and standing CWD comprised on average 64.6% and 35.4% of the total CWD volume, respectively. In general, the diameter distributions of living, standing and downed dead trees followed a negative exponential shape. Our results demonstrate high variability in structure and composition of old-growth forests on a northern boreal mesic Hylocomium—Myrtillus site type. This natural variability should be taken into account in forest restoration and management at landscape level.

Local properties of random mappings with exchangeable in-degrees

In this paper we investigate the ‘local’ properties of a random mapping model, TnD̂, which maps the set {1, 2, …, n} into itself. The random mapping TnD̂, which was introduced in a companion paper (Hansen and Jaworski (2008)), is constructed using a collection of exchangeable random variables D̂1, …, D̂n which satisfy In the random digraph, GnD̂, which represents the mapping TnD̂, the in-degree sequence for the vertices is given by the variables D̂1, D̂2, …, D̂n, and, in some sense, GnD̂ can be viewed as an analogue of the general independent degree models from random graph theory. By local properties we mean the distributions of random mapping characteristics related to a given vertex v of GnD̂ - for example, the numbers of predecessors and successors of v in GnD̂. We show that the distribution of several variables associated with the local structure of GnD̂ can be expressed in terms of expectations of simple functions of D̂1, D̂2, …, D̂n. We also consider two special examples of TnD̂ which correspond to random mappings with preferential and anti-preferential attachment, and determine, for these examples, exact and asymptotic distributions for the local structure variables considered in this paper. These distributions are also of independent interest.

Local properties of random mappings with exchangeable in-degrees

In this paper we investigate the ‘local’ properties of a random mapping model, T n D̂, which maps the set {1, 2, …, n} into itself. The random mapping T n D̂ , which was introduced in a companion paper (Hansen and Jaworski (2008)), is constructed using a collection of exchangeable random variables D̂ 1, …, D̂ n which satisfy In the random digraph, G n D̂ , which represents the mapping T n D̂ , the in-degree sequence for the vertices is given by the variables D̂ 1, D̂ 2, …, D̂ n , and, in some sense, G n D̂ can be viewed as an analogue of the general independent degree models from random graph theory. By local properties we mean the distributions of random mapping characteristics related to a given vertex v of G n D̂ - for example, the numbers of predecessors and successors of v in G n D̂ . We show that the distribution of several variables associated with the local structure of G n D̂ can be expressed in terms of expectations of simple functions of D̂ 1, D̂ 2, …, D̂ n . We also consider two special examples of T n D̂ which correspond to random mappings with preferential and anti-preferential attachment, and determine, for these examples, exact and asymptotic distributions for the local structure variables considered in this paper. These distributions are also of independent interest.

Local structural variability and the intermediate phase window in network glasses

Recent experimental work has shown that the width of the intermediate phase varies considerably in chalcogenide glasses containing $\mathrm{Ge}∕\mathrm{As}∕\mathrm{Se}$. As the chemical composition is varied within a series of glasses, three phases are observed. As the mean coordination of the glass is increased, the floppy phase evolves through the intermediate phase (rigid but unstressed) into the rigid and stressed phase. Here, using an extensive study of computer-generated networks, we show that the intermediate phase is caused by self-organization. This is only possible on networks where the single transition, from the floppy to the rigid and stressed phase, is second order in the absence of self-organization, which leads the network to be responsive to self-organization. This occurs when the structural variability---a measure of inhomogeneities within the glasses---exceeds a threshold value. The width of the intermediate phase is associated with the local structural variability. Above the threshold value, a large structural variability leads to a wider intermediate phase, which we refer to as the intermediate phase window.

Regional and local environmental correlates of native Iberian fish fauna

Abstract – Knowledge of fishes’ habitat requirements is an essential tool for species conservation. We examined the habitat requirements of nine native freshwater fish species using 165 undisturbed or minimally disturbed sites from eight river basins in western Iberia (northern and central Portugal). Six environmental descriptors were considered at the regional level, and six descriptors at a local scale. Statistical associations between local assemblage structure and environmental variables were quantified by canonical correspondence analyses. Logistic regression was performed for each species to identify regional and local factors related to its distribution at the sample sites. The results suggested a reasonable degree of specialisation in the use of local variables and dependence on regional variables. Logistic regression models showed a good adjustment (0.75 < AUC < 0.93). Results of habitat modelling using minimally disturbed sites helped to clarify species preferences for specific abiotic drivers.

Estimation of Elastic Properties of Particle Reinforced Metal‐Matrix Composites Based on Tomographic Images

The structure of a real particle reinforced metal‐matrix composite, Al/Al2O3, was retrieved by high resolution X‐ray tomography. The paper presents a study of the influence of local structure variability on the elastic properties of the composite. The results are in good agreement with theoretical two‐point bounds.

Local-structural diversity and protein folding: Application to all-β off-lattice protein models

Global measures of structural diversity within a distribution of biopolymers, such as the radius of gyration and percent native contacts, have proven useful in the analysis of simulation data for protein folding. In this paper we describe a statistical-based methodology to quantify the local structural variability of a distribution of biopolymers, applied to 46- and 69-"residue" off-lattice, three-color model proteins. Each folds into beta-barrel structures. First we perform a principal component analysis of all interbead distance variables for a large number of independent, converged Boltzmann-distributed samples of conformations collected at each of a wide range of temperatures. Next, the principal component vectors are subjected to orthogonal (varimax) rotation. The results are displayed on so-called "squared-loading" plots. These provide a quantitative measure of the contribution to the sample variance of the position of each residue relative to the others. Dominant structural elements, those having the largest structural diversity within the sampled distribution, are responsible for peaks and shoulders observed in the specific heat versus temperature curves, generated using the weighted histogram analysis method. The loading plots indicate that the local-structural diversity of these systems changes gradually with temperature through the folding transition but radically changes near the collapse transition temperature. The analysis of the structural overlap order statistic suggests that the 46-mer thermodynamic folding transition involves the native state and at least three other nearly native intermediates. In the case of the 46-mer protein model, data are generated at sufficiently low temperatures that squared-loading plots, coupled with cluster analysis, provide a local and energetic description of its glassy state.

Determining The Geographical Variation In Danish Farming

Change in agricultural structure may have impact on employment in rural areas, environment, wildlife and landscape. Normally Administrative units have been used in describing the agricultural structure. T h s article describes a method to determine the geographical variation in agricultural structures from single farm data and shows how this knowledge can be used in determining the correlation between local structure variables and trends in farm development. In Denmark information about all farms are registered together with address coordinates. Through GIS and geo-statistical analyses the observations are generalised to maps showing the geographical variation of e.g. mean farm size, mean live stock hold or number of animal pr. acre. Comparing information for several years gives the opportunity to classify farms after their owners behaviour. By point inspection, information of the behaviour is related to the local structure variables and a potential correlation between these is analysed.

Molecular mechanics studies on poly(purine).poly(pyrimidine) sequences in DNA: polymorphism and local variability.

Energy minimization has been carried out on three poly(purine).poly(pyrimidine) sequences--d(G)10.d(C)10, d(A)10.d(T)10, and d(AG)5.d(CT)5--using the molecular mechanics program AMBER (Assisted Model Building and Energy Refinement). In order to extensively scan the conformational space available, five different helical models were studied, three of them being right-handed helices while the other two were left helical. For all three sequences the right-handed A- and B-type helices are energetically slightly preferred over the left helices, but the energy difference between the various right-handed helices is only marginal. A detailed analysis has been carried out to characterize the local structural variability in the refined structures, both in terms of torsion angles as well as other parameters such as base-pair tilt, wedge roll, and wedge tilt, etc. All three sequences exhibit similar structural features for a particular form, but both the forms A and B show significant deviations from fiber models. In particular, the A-form structures have higher unit rise (2.7 A), and lower unit twist (31 degrees) and base-pair tilt (12 degrees), compared to the fiber model, which has corresponding values of 2.56 A, 32.7 degrees, and 20 degrees, respectively. All these changes indicate that the refined models are closer to the A-form structure observed in crystals of oligonucleotides. In the refined B-for models, the helical parameters are close to the fiber B-form, although the torsion angles show considerable variations. None of the three sequences examined, including the d(A)n.d(T)n sequence, show any pronounced curvature for the B-form structure.