Measures Of Structural Diversity Research Articles

Structural diversity is a poor proxy for information diversity: Evidence from 25 scientific fields

Many empirical applications of structural holes theory rest on the assumption that there is a close relationship between network position, or ‘structural diversity,’ and access to complementary information, or ‘information diversity.’ Constraint, and to a lesser extent efficiency, are two measures that are typically used as measures of structural diversity, which is in turn used as a proxy for information diversity. In this article, we question the assumed relationship between structural and information diversity at the core of brokerage theory. We collected metadata for 864,450 journal articles from the Web of Science database, identified 1,192,488 authors, and constructed 13 different measures of information diversity that are based on the text data and co-authorship network structure. We correlated each of these measures with Burt’s constraint and efficiency as measures of structural diversity, finding only weak correlations and low R2 values. Efficiency performs slightly better than constraint, however the strongest correlation was 0.56, corresponding to an R2 of 0.3163. Furthermore, the variance in this relationship is non-uniform and indicates that, aside from the poor correlation, other factors are likely important mediators to the relationship between efficiency and information diversity. We argue that this shows that, even in the best cases, neither constraint nor efficiency should be used as proxies for information diversity and make suggestions for more diligent treatment of information in structural holes and brokerage research.

Changes in the Sector Employment Structure of the Silesian Voivodeship beetwen 2009-2017

Transformations of employment structures reflect changes in the economic structure. This structure is closely related to economic development. The importance and complexity of this field make structural changes one of the most important areas of scientific research. Detailed recognition and deepening of knowledge about sectoral transformations of employment structures, as well as current and future trends in this area, are necessary for finding optimal solutions that will accelerate changes in the economy. The purpose of the study is to identify and evaluate changes in the sectoral employment structure in the Silesian Voivodeship in the years 2009-2017, with particular emphasis on intra-sectoral changes in the service sector. In connection with this, an analysis of structural changes was carried out in the Silesian Voivodeship in the examined period. The research was based on data obtained from the Local Data Bank. The analysis of structural changes in employment was conducted using structure and dynamics indicators as well as one of the known measures of structure diversity. The results of the analysis allowed this study to recognize and assess changes within the sectoral employment structure within the studied region.

Assessing Forest Structure and Composition along the Altitudinal Gradient in the State of Sikkim, Eastern Himalayas, India

Understanding the structure and composition of native forests is a prerequisite in developing an adaptive forest management plan for Himalayan forest ecosystems where climate change is rapid. However, basic information on forest structure and composition are still limited in many places of the Eastern Himalayas. In this study, we aimed to understand the diversity, structure, and composition of forests and their variations along an altitudinal gradient in Himalayan forests. The study was conducted in the Indian federal state of Sikkim, Eastern Himalayas. We carried out a comprehensive and comparative evaluation of species diversity, stand basal area, and stem density along the altitudinal gradient from 900 m a.s.l. to 3200 m a.s.l. We used stratified random sampling to survey eighty-three plots each 0.1 ha in forest communities that occurred along the altitudinal gradient: (a) lower (900–1700 m) altitude forest (N = 24), (b) mid (1700–2500 m) altitude forests (N = 37), and (c) higher (2500–3200 m)altitude forests (N = 22). We measured and identified all living trees with a >3 cm diameter at breast height in each plot. We counted 10,344 individual plants, representing 114 woody species belonging to 42 families and 75 genera. The family Fagaceae and its species Lithocarpus pachyphyllus (Kurz) Rehder. were reported as the most dominant forest trees with the highest Importance Value Index. The Shannon diversity index was recorded as being the highest for the low-altitude forests, whereas measures of structural diversity varied among forests along with altitude: the mid-altitude forests recorded the highest stem density and the high-altitude forests showed the highest mean stem DBH (diameter at 1.3 m height). One significant finding of our study was the disparity of the size class distribution among forests along the altitudinal gradient. Overall, we found a reverse J-shape distribution of tree diameter signifying the uneven-agedness. However, we showed, for the first time, a complete lack of large trees (>93 cm DBH) in the lower altitude forests. Our study highlights conservation concerns for the low-altitude forests that record high species diversity, although lacked large-diameter trees. We anticipate that our study will provide a comprehensive understanding of forest diversity, composition, and structure along the altitudinal gradient to design conservation and sustainable management strategies

Using structural diversity to measure the complexity of technologies.

The paper introduces structural diversity as a new approach to quantify the complexity of technologies. By modeling technologies as combinatorial networks, a measure of technological complexity is derived that represents the diversity of (sub-)network topologies in these networks. It is further argued that this measure can be empirically approximated with the Network Diversity Score (NDS). The paper also presents an application of this approach to European patent data from 1980 to 2015. On this basis, the measure of structural diversity is shown to replicate a number of stylized facts commonly associated with technological complexity: Complexity increases over time and younger technologies are more complex than older technologies. Complex technologies are also associated to larger R&D efforts and require more collaborative R&D activities. Lastly, when controlling for technologies’ size, technologies scoring high on structural diversity are also shown to concentrate in space.

Assessing the utility of structure in amorphous materials.

This paper presents a set of general strategies for the analysis of structure in amorphous materials and a general approach to assessing the utility of any selected structural description. Two measures of structure are defined, "diversity" and "utility," and applied to two model glass forming binary atomic alloys, Cu50Zr50 and a Lennard-Jones A80B20 mixture. We show that the change in diversity associated with selecting Voronoi structures with high localization or low energy, while real, is too weak to support claims that specific structures are the prime cause of these local physical properties. In addition, a new structure-free measure of incipient crystal-like organization in mixtures is introduced, suitable for cases where the stable crystal is a compound structure.

Canopy space filling rather than conventional measures of structural diversity explains productivity of beech stands

Silvicultural success in achieving, among other management goals, maximum productivity strongly depends on knowledge of the relationship between stand density and the resulting growth response of a stand. However, there are still controversial discussions whether wood production can be enhanced by silvicultural thinning or reaches its maximum in unmanaged forest stands if time plays no role. Moreover there is no universal answer whether structural diversity promotes or reduces productivity. In the present study we applied terrestrial laser scanning (TLS) to investigate the relationship between three-dimensional space filling, forest management intensity, productivity and conventional measures of structural diversity. We examined 35 beech-dominated forest plots along a gradient of management intensity in three regions of Germany. We found that space filling in leaf-on condition increased with management intensity, particularly in the shaded crown. Increased space filling in the shaded crown due to tree removals also resulted in higher stand productivity. We conclude that an increased space filling in the shaded canopy of managed European beech stands is responsible for the compensation of production losses in the upper canopy due to thinning activities. Conventional measures of structural diversity were not sensitive to the applied silvicultural activities. We also found no relationship between structural diversity described by conventional measures and stand productivity.

Physical Site Conditions and Land Use History as Factors Influencing the Conservation of Regrowth Forests in a Southwest Ohio Nature Reserve

Abstract Intensive agricultural practices across the midwestern United States cleared nearly all of the original broadleaf deciduous forest, and today restrict the selection of protected areas to regrowth stands across human-dominated landscapes. This study focused on the: (1) physical-site conditions and past land use influence woody plant diversity and the canopy structure of protected regrowth forests, and (2) relationships between these measures of structural diversity and community resistance to an invasive non-native shrub. We measured woody vegetation at 30 points in the 268 ha Bachelor Reserve, Southwest Ohio, and examined statistical relationships between physical-site conditions, historical land use since 1938, and the structural diversity of woody plants. Stand age, with topographic and soil attributes, provide unique and significant contributions to multiple regression models, explaining canopy species richness and height variability. Certain physical settings were managed in certain ways and ...

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.

The significance of different indices for stand structure and diversity in forests

Data from the so-called Level II Plots which were established within the frame of the Pan-European Programme for Intensive and Continuos Monitoring of Forest Ecosystems were used to quantify stand structure and species diversity by means of different indices. The calculations presented are based on species composition, spatial pattern as well as diameter and height distribution. The data assessed are suitable to calculate different measures of structural diversity, if a mapping of the stands is carried out. A comparison of the different indices by means of correlation analysis shows that there exist only few and weak correlations between species diversity of different vegetation layers, and between plant species diversity and diversity of stand structure, while among all the indices of stand structure a correlation exists. More complex indices of stand diversity perform quite well in characterising the specific situation. Mountain forests are compared with forests from lower elevations. They show a tendency towards irregular stand structures. No correlation between the naturalness of tree species composition and the calculated diversity indices can be found within the sample.

A computationally convenient diversity measure: Theory and application

This paper introduces a computationally convenient measure of structural diversity based on absolute deviations between relative shares of individual groups forming a community. A conceptual framework is developed, some theoretical properties of the measure are derived, and its close relation to the Shannon index, a widely used diversity measure, is explored. The paper also presents an empirical application involving this measure where optimum harvesting strategies are determined under diversity constraints, and investigates the trade off between economic and environmental objectives for a mixed forest in Indonesia.

Rapid Quantification of Molecular Diversity for Selective Database Acquisition

There is an increasing need to expand the structural diversity of the molecules investigated in lead-discovery programs. One way in which this can be achieved is by acquiring external datasets that will enhance an existing database. This paper describes a rapid procedure for the selection of external datasets using a measure of structural diversity that is calculated from sums of pairwise intermolecular structural similarities.

Una nota sulla distanza tra modelli ARIMA per serie storiche correlate

In this paper we consider a distance measure between ARIMA models which has been proposed as a measure of structural diversity between time series. Specifically, the metric is defined on the space of linear, convergent and Gaussian processes as the Euclidean distance between the weights of the corresponding AR(oo) representations. We discuss how the distribution properties of that measure are modified by the presence of correlation between time series.