On a Mixture Model for Directional Data on the Sphere

We consider mixtures of general angular central Gaussian distributions as models for multimodal directional data. We prove consistency of the maximum‐likelihood estimates of model parameters and convergence of their numerical approximations based on an expectation–maximization algorithm. Then, we focus on mixtures of special angular central Gaussian distributions and discuss the details of a fast numerical algorithm, which allows to fit multimodal distributions to massive data, occurring, for example, in the study of the microstructure of materials. We illustrate the applicability with some data from fibre composites and from ceramic foams.     

Heuristics for the network design problem with connectivity requirements

We consider the NP-complete problem of finding a spanning \(k\)-tree of minimum weight in a complete weighted graph. This problem has a number of applications in designing reliable backbone telecommunication networks. We propose effective algorithms based on a greedy strategy and several variable neighborhood search metaheuristics. We also develop an integer linear programming model for calculating a lower bound. Preliminary numerical experiments using random and real-word data sets are reported to show the effectiveness of our approach. In addition, we compare our approach with known metaheuristics.     

Cognitive antecedents of business models: Exploring the link between attention and business model design over time

A firm's ability to conceive performance-enhancing business models (BMs) has become a cornerstone of competitive advantage. There is consensus that external triggers spur such BM change, but the literature has remained silent on the role of internal and cognitive antecedents such as managerial attention. In our inductive case study of four corporate spin-offs, we find that top management teams (TMTs) with a specific set of attention patterns are more likely to develop performance-enhancing BM designs. However, our findings provide evidence that specific attention foci are not sufficient to enhance particular BM designs, as it is also a matter of the intensity of attention. We further find that, over time, TMTs attention patterns shift and cause changes in BM designs. The emergent theoretical framework highlights that attention is an antecedent in explaining BM designs.     

How to improve urban greenspace for woodland birds: site and local-scale determinants of bird species richness

Wooded habitats represent hotspots of urban biodiversity, however, urban development imposes pressure on biota in these refuges. Identification of the most influential habitat attributes and the role of local urban characteristics is crucial for proper decisions on management practices supporting biodiversity. We aimed to identify well manageable fine-scale habitat attributes to suggest specific, feasible and affordable management recommendations for green space in cities. We analysed species richness of woodland-associated bird communities and incidence of individual species at 290 sites in a wide variety of green areas scattered across the city of Prague, Czech Republic. Generalized linear mixed models (GLMM) and regression tree analyses were used to identify site-scale (100 m radius sampling sites) and local-scale (200 m and 500 m radius plots) habitat attributes shaping the bird communities at individual sites. Logistic regression was used to assess the responses of individual species to habitat characteristics. Our results imply that at the site scale, management practices should focus on maintenance and promoting species-diverse and older tree stands, with a mixture of coniferous and deciduous trees. Water-bodies and accompanying riparian habitats should be maintained and carefully managed to preserve high-quality remnants of natural vegetation. Presence of a few old trees (about 12 % of tree cover with DBH?>?50 cm) or small urban standing water and watercourses enrich the bird community by at least two species. Species richness of woodland avifauna at particular sites is further supported by the total amount of tree cover in the surroundings, including scattered greenery of public spaces and private gardens. We conclude that proper management at site scale has the potential to increase biodiversity of the urban environment.     

Least squares and generalized least squares in models with orthogonal block structure

Besides the basic model, Kronecker products of rotated models are used to isolate the variance components as parameters of a linear model. A characterization of BLUE given by Zmy?lony (1980) is applied to the different models. Generalized least squares are used to complete the estimation.     

Achtsamkeit im organisationalen Kontext: Der Einfluss individueller und organisationaler Achtsamkeit auf resilientes Verhalten,psychische Gesundheit und Arbeitsengagement

This article in the journal Gruppe. Interaktion. Organisation (GIO) presents mindfulness as a starting point for coping with the increasing and changing demands of today’s workplaces. Based on a differentiated analysis of mindfulness on the individual and organizational level, we discuss their separate contribution to resilient behavior in the workplace as well as on psychological well-being and work engagement. These assumptions were empirically verified. Overall, 172 persons participated in the study, which was implemented as a web-based questionnaire. The results showed that individual and organizational mindfulness independently contributed to resilient behavior in the workplace. Furthermore, individual mindfulness and resilient behavior promoted psychological well-being. Both individual and organizational mindfulness were significantly associated with work engagement. Additional analyses revealed that these effects were mediated by resilient behavior. In summary, the results demonstrated that individual and organizational mindfulness are distinct constructs whose influence on psychological well-being and work engagement could be partly explained by resilient behavior in the workplace.     

L models and multiple regressions designs

Given an orthogonal model

${{\bf \lambda}}=\sum_{i=1}^m{{{\bf X}}_i}{\boldsymbol{\alpha}}_i$

an L model

${{\bf y}}={\bf L}\left(\sum_{i=1}^m{{{\bf X}}_i}{\boldsymbol{\alpha}}_i\right)+{\bf e}$

is obtained, and the only restriction is the linear independency of the column vectors of matrix L. Special cases of the L models correspond to blockwise diagonal matrices L = D(L ₁, . . . , L _c ). In multiple regression designs this matrix will be of the form

${\bf L}={\bf D}(\check{{\bf X}}_1,\ldots,\check{{\bf X}}_{c})$

with \({\check{{\bf X}}_j, j=1,\ldots,c}\) the model matrices of the individual regressions, while the original model will have fixed effects. In this way, we overcome the usual restriction of requiring all regressions to have the same model matrix.

     

Differences in fish harvest,fishing effort,and angling guard activities between urban and natural fishing grounds

Recreational fishing is a very popular outdoor leisure activity. Assessing differences in basic metrics in recreational fishing on different types of fishing grounds is very important for effective fisheries management. This study aimed to discover how basic metrics in recreational fishing (harvest, fishing effort, angling guard activities) differ between urban fishing grounds (located in a densely populated city) and natural fishing grounds (located in the countryside). Data were obtained from individual angling logbooks collected by the Czech Fishing Union on the River Elbe and the River Vltava (Prague and Central Bohemia, Czechia, Central Europe). Study shows that urban and natural fishing grounds showed significant differences in basic metrics in recreational fishing. Urban fishing grounds displayed higher fish harvest in general and higher dominance of intensively stocked fish species in catches of anglers (mainly common carp Cyprinus carpio). High harvest rates of common carp can be mostly explained by intensive fish stocking. The only fish species that showed higher harvest on natural fishing grounds were large-growing piscivorous fish with high ecological demands. However, anglers were harvesting larger fish (average body weight) on natural fishing grounds. In addition, fishing effort was similar on both types of fishing grounds. Inversely, angling guards were more active on natural fishing grounds. In conclusion, differences in basic fisheries metrics between urban and natural fishing grounds seem to be partially driven by intensive fish stocking.