Community dynamics mining

In this paper we propose a model to analyze community dynamics. Recently, several methods and tools have been proposed to extract communities from static graphs. However, since communities are not static, but change over time, it is necessary to provide methods to determine and observe the community transitions and to extract the factors that cause the development. We regard a community as an object that exists over time and propose to observe community transitions along the time axis. For this we partition the time axis under observation by time windows. In each time window, a set of interactions between community participants is aggregated. These static networks are analyzed for subcommunities by applying community detection mechanisms. Through this we detect communities in each interval and can observe if communities persist over time or undergo a transition. We present community transitions and the observable indicators for the respective development. We furthermore present a software environment that incorporates several community detection and analysis methods to analyze community transitions. It supports a dynamic temporal community analysis and provides several forms of visualizations and analysis settings thus providing an interactive tool to observe community dynamics

Does functional soil microbial diversity contribute to explain within-site plant beta-diversity in an alpine grassland and a <i>dehesa</i> meadow in Spain?

Questions: Once that the effects of hydrological and chemical soil properties have been accounted for, does soil microbial diversity contribute to explain change in plant community structure (i.e. within-site beta-diversity)? If so, at which spatial scale does microbial diversity operate? Location: La Mina in Moscosa Farm, Salamanca, western Spain (dehesa community) and Laguna Larga in the Urbión Peaks, Soria, central-northern Spain (alpine grassland). Methods: The abundance of vascular plant species, soil gram-negative microbial functional types and soil chemical properties (pH, available phosphorus, and extractable cations) were sampled at both sites, for which hydrological models were available. Redundancy analysis (RDA) was used to partition variation in plant community structure into hydrological, chemical and microbial components. Spatial filters, arranged in scalograms, were used to test for the spatial scales at which plant community structure change. Results: In the case of the dehesa the diversity of soil gram-negative microbes, weakly driven by soil pH, contributed to a small extent (adj-R2 = 2%) and at a relative medium spatial scale to explain change in plant community structure. The abundance of a few dehesa species, both annual (Trifolium dubium, Vulpia bromoides) and perennial (Poa bulbosa, Festuca ampla), was associated with either increasing or decreasing soil microbial diversity. In the alpine meadow the contribution was negligible. Conclusions: Microbial diversity can drive community structure, though in the hierarchy of environmental factors structuring communities it appears to rank lower than other soil factors. Still, microbial diversity appears to promote or restrain individual plant species. This paper aims to encourage future studies to use more comprehensive and insightful techniques to assess microbial diversity and to combine this with statistical approaches such as the one used here

Application of an Inverse Design Method to the Design of Transonic Nacelles

This paper describes the extension and application of a design method to nacelles for turbofan engines under transonic flow conditions. Starting form a generic nacelle shape and a prescribed pressure or Mach number distribution, the inverse design problem for the unknown nacelle geometry is solved. The method uses an existing Euler solver to obtain solutions of the transonic, compressible flow field around the configuration. Examples show that the method os capable of handling axisymmetric and three dimensional flow conditions on isolated and installed nacelles, and that it can be used to design the external as well as the internal surfaces of a nacelle

Aggregative root placement: A feature during interspecific competition in inland sand-dune habitats

Bartelheimer M, Steinlein T, Beyschlag W. Aggregative root placement: A feature during interspecific competition in inland sand-dune habitats. PLANT AND SOIL. 2006;280(1-2):101-114.Segregation of roots is frequently observed in competing root systems. However, recently, intensified root growth in response to a neighbouring plant has been described in pot experiments [Gersani M, Brown J S, O'Brien E E, Maina G M and Abramsky Z 2001. J. Ecol. 89, 660-669]. This paper examines whether intense root growth towards a neighbour (aggregation) plays a role in competitive interactions between plant species from open nutrient-poor mid-European sand ecosystems. In a controlled field-competition experiment, root distribution patterns of intra- and interspecific pairs as well as single control plants of Corynephorus canescens, Festuca psammophila, Hieracium pilosella, Hypochoeris radicata and Conyza canadensis were investigated after one growing season. Under intraspecific competition plants tended to segregate their root systems, while under interspecific competition most species tended to aggregate roots towards their neighbours even at the expense of root development at the opposite competition-free side of the target. Preference of a root aggregation strategy over the occupation of competition-free soil in interspecific competition emphasizes the importance of contesting between individuals in relation to mere resource acquisition. It is suggested that in the presence of a competitor the plants might use root aggregation as a defensive reaction to maintain a strong competitive response and exclusive access to the resources of already occupied soil volumes

Handling images of patient postures in arms up and arms down position using a biomechanical skeleton model

Deformable image registration is gradually becoming the tool of choice for motion extraction during adaptive radiotherapy. Achieving a motion vector field that accurately represents the anatomical changes requires a tissue specific transformation model. Therefore, widely used spline based models most likely fail in appropriately reproducing large anatomical changes such as the arms of the patient being positioned up and down. We present the application of a tissue specific biomechanical model with the goal to mimic patient motion even in presence of large motion. Based on the planning CT, delineated bones are used to represent the rigid anatomy of the patient. We implement ball-and-socket joints between corresponding bones in order to achieve mobility of the skeleton. An inverse kinematics approach enables the propagation of motion between individual bones across their joints, leading to an articulated skeleton that can be controlled by feature points on one or more bones. The transformation of each bone initializes a chainmail based soft tissue model to also propagate the motion into the surrounding heterogeneous soft tissue. Representation of different postures like arms up and down can be achieved within less than 1 s for the skeleton and ∼10 s for the soft tissue. Especially for large anatomical changes, the kinematics approach benefits from the direct articulation at specific joints, considerably lowering the degrees of freedom for motion description. Being the input for the chainmail based soft tissue model, the transformed bones guarantee for its meaningful initialization. The proposed biomechanical skeleton model is promising to facilitate the registration of patients’ anatomy, being positioned with arms up and arms down. The results encourage further refinement of the joints and the soft tissue model