Artefacts in statistical analyses of network motifs: general framework and application to metabolic networks

Few-node subgraphs are the smallest collective units in a network that can be investigated. They are beyond the scale of individual nodes but more local than, for example, communities. When statistically over- or under-represented, they are called network motifs. Network motifs have been interpreted as building blocks that shape the dynamic behaviour of networks. It is this promise of potentially explaining emergent properties of complex systems with relatively simple structures that led to an interest in network motifs in an ever-growing number of studies and across disciplines. Here, we discuss artefacts in the analysis of network motifs arising from discrepancies between the network under investigation and the pool of random graphs serving as a null model. Our aim was to provide a clear and accessible catalogue of such incongruities and their effect on the motif signature. As a case study, we explore the metabolic network of Escherichia coli and show that only by excluding ever more artefacts from the motif signature a strong and plausible correlation with the essentiality profile of metabolic reactions emerges.     

Two-dimensional modulation transfer function: a new perspective

One-dimensional templates, such as the U.S. Air Force resolution target or the circular spoke target, are commonly used for the characterization of imaging systems via the modulation transfer function response. It is shown in this paper that one needs a new family of templates for a true characterization of imaging systems that acquire two-dimensional (2D) high-density images or handle 2D information, such as 2D bar code detection and identification. The contrast provided by the newly defined 2D templates is the "true" contrast of the acquired image that the electronic processors are challenged with.     

Pulse profile and metal transfer in pulsed gas metal arc welding: droplet formation,detachment and velocity

The influence of current profile and pulse parameters on droplet formation and transfer was investigated. One profile has an exponential ramp up and down in the current pulse shape, while the second is nearly square shaped. High-speed photography, synchronised with a high-speed data acquisition system, was used to monitor the droplet formation and transfer. It was found that for long-tail current profile, most of droplet formation and detachment occurs before background current is reached. While, for the nearly square pulse, most of droplet formation and transfer occurs during background current, giving a stable and smooth metal transfer. The arc attachment position was found to vary for the different profiles. Droplet speed was measured, and it was found that it is proportional to the peak current and inversely proportional to background current. Dimensionless process parameters were defined and used to predict droplet speed using a neural networks algorithm.     

Analysis of foundation sliding of an arch dam considering the hydromechanical behavior

This paper presents the application of a methodology which can be used to assess arch dam foundation stability,using the discrete element method (DEM) and the code 3DEC.A global three-dimensional model...     

Strong influence of polymer architecture on the microstructural evolution of hafnium-alkoxide-modified silazanes upon ceramization

The present study focuses on the synthesis and ceramization of novel hafnium-alkoxide-modified silazanes as well as on their microstructure evolution at high temperatures. The synthesis of hafnia-modified polymer-derived SiCN ceramic nanocomposites is performed via chemical modification of a polysilazane and of a cyclotrisilazane, followed by cross-linking and pyrolysis in argon atmosphere. Spectroscopic investigation (i.e., NMR, FTIR, and Raman) shows that the hafnium alkoxide reacts with the N-H groups of the cyclotrisilazane; in the case of polysilazane, reactions of N-H as well as Si-H groups with the alkoxide are observed. Consequently, scanning and transmission electron microscopy studies reveal that the ceramic nanocomposites obtained from cyclotrisilazane and polysilazane exhibited markedly different microstructures, which is a result of the different reaction pathways of the hafnium alkoxide with cyclotrisilazane and with polysilazane. Furthermore, the two prepared ceramic nanocomposites are unexpectedly found to exhibit extremely different high-temperature behavior with respect to decomposition and crystallization; this essential difference is found to be related to the different distribution of hafnium throughout the ceramic network in the two samples. Thus, the homogeneous distribution of hafnium observed in the polysilazane-derived ceramic leads to an enhanced thermal stability with respect to decomposition, whereas the local enrichment of hafnium within the matrix of the cyclotrisilazane-based sample induces a pronounced decomposition upon annealing at high temperatures. The results indicate that the chemistry and architecture of the precursor has a crucial effect on the microstructure of the resulting ceramic material and consequently on its high-temperature behavior.     

Poly(3-hexylthiophene)/C60 heterojunction solar cells: Implication of morphology on performance and ambipolar charge collection

The performance of heterojunction organic solar cells is critically dependent on the morphology of the donor and acceptor components in the active film. We report results of photovoltaic devices consisting of bilayers and bulk heterojunctions using poly(3-hexylthiophene) (P3HT) and Buckminsterfullerene C₆₀. White light power efficiencies of η2.2% (bulk heterojunction) and 2.6% (bilayer) were measured after a thermal annealing step on completed devices. Optical and structural investigations on non-annealed bilayer thin films indicated a distinct porosity of the spin-coated polymer, which allows C₆₀ to penetrate the P3HT layer and to touch the anode. This resulted for these bilayer solar cells in the experimental observation that electrons were collected predominantly at the cathode after photo-excitation of P3HT, but predominantly at the anode after C₆₀ excitation. A morphological model to explain the ambipolar charge collection phenomenon is proposed.     

A better approach to goodness: Reply to Wagemans (1999).

In P. A. van der Helm and E. L. J. Leeuwenberg (see record 1996-01780-002), the authors presented a representation model for the goodness, or detectability, of visual regularities such as mirror symmetry and repetition. J. Wagemans (see record 1999-03499-009) acknowledged that this holographic goodness model has considerable explanatory power, but he also argued that it is not good enough yet. He challenged van der Helm and Leeuwenberg to qualify some open ends of their representation model, in particular those concerning its process assumptions. He also questioned the authors' assessment of previous goodness accounts such as S. E. Palmer's (1982, 1983) transformational approach and his own bootstrap model. He concluded that it is expedient to aim at a synthesis of useful aspects of diverse accounts of goodness, but he did not establish such a synthesis. Van der Helm and Leeuwenberg agree with his conclusion that such a synthesis is a worthy cause, but they disagree with his evaluation of the issues involved. This article is a reply with an alternative evaluation of these issues, advancing the discussion to a process-representation synthesis called holographic bootstrapping. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

How to Pack a Punch – Why 3D Batteries are Essential

The miniaturization of implantable medical devices, remote microsensors and transmitters, “smart” cards, and Internet of Things (IoT) systems is impeded by the absence of high‐performance micro‐size power sources. Insufficient areal energy density from thin‐film planar microbatteries has inspired a search for three‐dimensional microbatteries (3DMB) with the use of low‐cost and efficient micro‐ and nano‐scale materials and techniques. In our short review, we present our outlook on the state‐of‐the‐art development of advanced 3D‐microbattery designs and methods of the fabrication of electrode materials. Special attention is given to the 3D‐printing approach, which holds many opportunities for the mass production of microbatteries and their direct integration with electronic devices.