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1 Structural holes and bridging in two-mode networks 2018-04-25             

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Publication date: October 2018
Source:Social Networks, Volume 55

Author(s): Jake Burchard, Benjamin Cornwell

Social networks are often structured in such a way that there are gaps, or “structural holes,” between regions. Some actors are in the position to bridge or span these gaps, giving rise to individual advantages relating to brokerage, gatekeeping, access to non-redundant contacts, and control over network flows. The most widely used measures of a given actor’s bridging potential gauge the extent to which that actor is directly connected to others who are otherwise not well connected to each other. Unfortunately, the measures that have been developed to identify structural holes cannot be adapted directly to two-mode networks, like individual-to-organization networks. In two-mode networks, direct contacts cannot be directly connected to each other by definition, making the calculation of redundancy, effective size, and constraint impossible with conventional one-mode methods. We therefore describe a new framework for the measurement of bridging in two-mode networks that hinges on the mathematical concept of the intersection of sets. An actor in a given node class (“ego”) has bridging potential to the extent that s/he is connected to actors in the opposite node class that have unique profiles of connections to actors in ego’s own node class. We review the relevant literature pertaining to structural holes in two-mode networks, and we compare our primary bridging measure (effective size) to measures of bridging that result when using one-mode projections of two-mode data. We demonstrate the results of applying our approach to empirical data on the organizational affiliations of elites in a large U.S. city.





2 A study of some airflow resistivity models for multi-component polyester fiber assembly 2018-04-25             

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Publication date: October 2018
Source:Applied Acoustics, Volume 139

Author(s): Tao Yang, Rajesh Mishra, Kirill V. Horoshenkov, Alistair Hurrell, Ferina Saati, Xiaoman Xiong

The airflow resistivity is a key parameter to predict accurately the acoustical properties of fibrous media. There is a large number of theoretical and empirical models which can be used to predict the airflow resistivity of this type of porous media. However, there is a lack of experimental data on the accuracy of these models in the case of multi-component fibrous media. This paper presents a detailed analysis of the accuracy of several existing models to predict airflow resistivity which make use of the porosity, bulk density and mean fibre diameter information. Three types of polyester (PET) materials made using regular PET, hollow PET and bi-component PET with a range of densities are chosen for this study. It is shown that some existing models largely under- or overestimate the airflow resistivity when compared with the measured values. A novel feature of this work is that it studies the relative performance of airflow resistivity prediction models that are based on the capillary channel theory and drag force theory. These two groups of models are then compared to some purely empirical models. It is found that the prediction error by some models is unacceptably high (e.g. >20–30%). The results suggest that there are existing models which can predict the airflow resistivity of multi-component fibrous media with 8–10% accuracy.





3 Improved stability strategies for pseudo-potential models of lattice Boltzmann simulation of multiphase flow 2018-04-23             

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Publication date: October 2018
Source:International Journal of Heat and Mass Transfer, Volume 125

Author(s): Yongyong Wu, Nan Gui, Xingtuan Yang, Jiyuan Tu, Shengyao Jiang

Since the pseudo-potential lattice-Boltzmann (LB) model was proposed, it has been suffering from low density ratio, small Reynolds number and flow instabilities, which hamper its application in many science and engineering problems. In this work, we analyze the reasons of flow instabilities in the pseudo-potential LB models, and propose some methods to improve the simulation stability. It is shown that the inter-particle interaction force term and the equations of state (EOS) can result in numerical instability in the particle distribution functions and density. Some straightforward and universal techniques are proposed here in order to achieve larger density ratio, higher Reynolds number and lower temperature as well as suppressing spurious velocity in multiphase flow in the pseudo-potential LB models without additional influences on the equilibrium properties in most cases. These methods contribute to extending the pseudo-potential LB models to realistic multiphase flow further. Finally, we demonstrate the method application for droplet splashing with Re = 15000, We = 120 and density ratio = 4792 at 0.45Tc successfully.





4 The stratigraphic and structural record of the Cretaceous Jianghan Basin, central China: Implications for initial rifting processes and geodynamics 2018-04-20             

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Publication date: October 2018
Source:Cretaceous Research, Volume 90

Author(s): Lulu Wu, Lianfu Mei, Yunsheng Liu, Douglas A. Paton, Jin Luo, Lu Yu, Deliang Wang, Caizheng Min, Minghua Li, Libin Guo, Hui Wen

The stratigraphic and structural characteristics of the initial phase of continental rift basins have been widely studied. However, the initial rifting geodynamic processes in many rift basins remain poorly understood because the relevant structures and stratigraphic successions tend to be deeply buried in result of continued rift evolution. Using an extensive database of geological (stratigraphic and structural) and geophysical data we investigate when and how rift initiation occurred in the Jianghan Basin. The correlation of the Lower Cretaceous strata across the basin reveals that they were deposited within a series of localized depressions distributed on the basin margin while the Late Cretaceous tectonic stage was characterized by widespread rifting with a maximum stratal thickness of ∼4500 m. The major faults controlling this Late Cretaceous sediment distribution are radially striking, suggesting a distributed, transtensional stress system or multi-directional extension during the Late Cretaceous. It is a common feature that pre-rift basement strata of the major faults in the hanging wall are older than that in the footwall and become progressively older approaching the fault plane, indicating a reactivation of pre-existing unroofed fault-related folds. Together with the regional geodynamic context for the South China Block, we divide the initial rifting processes into two distinct stages. During the Early Cretaceous, the lithosphere beneath the Jianghan Basin got rapidly thinned under the influence of the large-scale roll-back and dehydration of the subducted Pacific slab. Meanwhile, the upwelling asthenosphere and intruded dykes/magma heated and weakened the lithosphere, leading to thermal doming of most of the Jianghan Basin. However, on the basin margin, which was relatively unaffected by the thermal doming event, a set of localized depression sequences were deposited. Due to the Early Cretaceous lithospheric thinning, the lithosphere was thin enough to rift during the Late Cretaceous. Under the diapirism of the continuously upwelling asthenospheric mantle, the pre-existing thrusts with radial strikes simultaneously underwent extensional reactivation, forming a series of normal faults with multiple orientations. By providing the detailed stratigraphic and structural evidence for active rifting model, this study provides new insights into the processes of early rift initiation.





5 Recent progress on the development of glutathione (GSH) selective fluorescent and colorimetric probes 2018-04-19             

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Publication date: 1 July 2018
Source:Coordination Chemistry Reviews, Volume 366

Author(s): Songyi Lee, Jun Li, Xin Zhou, Jun Yin, Juyoung Yoon

Glutathione (GSH) plays a key role in many cellular functions. Abnormal levels of GSH is considered to be sign of many diseases. As a result, various fluorescent imaging probes and/or chemosensors for GSH have been developed. Compared to other analytical methods, fluorescence has unique merits, such as excellent detection limits and sensitivity for use in imaging cells, tissues and small animals. However, colorimetric probes undergo distinct color changes, which in most cases can be detected by using the naked eye. This review of studies aimed at the development of GSH probes is presented in a format that is organized by structural features and chemical reactions of the probes. The topics include probes that are based on nanoparticles or nanocomposites, metal ion displacement and coordination and chemical reactions. The reaction based probes are further classified into probes that undergo cleavage of sulphonamide, sulfonate ester and related functional groups, SeN bond cleavage, aryl substitution reactions, disulfide bond cleavage followed by cyclization, Michael additions, and other processes.





6 Chapter Seventeen Brain Imaging Using Hyperpolarized 129Xe Magnetic Resonance Imaging 2018-04-19             

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Publication date: 2018
Source:Methods in Enzymology, Volume 603

Author(s): Simrun Chahal, Braedan R.J. Prete, Alanna Wade, Francis T. Hane, Mitchell S. Albert

Hyperpolarized (HP) 129Xe magnetic resonance imaging (MRI) is a novel iteration of traditional MRI that relies on detecting the spins of 1H. Since 129Xe is a gaseous signal source, it can be used for lung imaging. Additionally, 129Xe dissolves in the blood stream and can therefore be detectable in the brain parenchyma and vasculature. In this work, we provide detailed information on the protocols that we have developed to image 129Xe within the brains of both rodents and human subjects.





7 The Correlation of Regional Lung Ventilation and Gas Transfer to Red Blood Cells: Implications for Functional-Avoidance Radiation Therapy Planning 2018-04-16             

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Publication date: Available online 14 April 2018
Source:International Journal of Radiation Oncology*Biology*Physics

Author(s): Leith J. Rankine, Ziyi Wang, Bastiaan Driehuys, Lawrence B. Marks, Christopher Kelsey, Shiva K. Das

Background and Purpose: Interest in functionally-guided radiation therapy (RT) planning has been bolstered by the ability to derive lung ventilation maps from 4-Dimensional Computed Tomography. However, this assumes that regional lung ventilation is an accurate surrogate for true regional lung function, i.e., gas exchange between the airspaces and capillary Red Blood Cells (RBCs). This work uses the emerging technology of hyperpolarized (HP)-129Xe Magnetic Resonance Imaging (MRI) to investigate the degree to which lung ventilation and gas exchange are regionally correlated. Material and Methods HP-129Xe MRI studies were performed on 17 IRB-approved human subjects, including 13 healthy volunteers, one emphysema patient, and 3 non-small cell lung cancer (NSCLC) patients imaged prior to and ∼11 weeks following RT. Subjects inhaled 1 liter of HP-129Xe mixture, followed by the acquisition of interleaved ventilation and gas exchange images, from which maps of relative HP-129Xe distribution were obtained in: 1) the lung airspaces; 2) dissolved interstitially in alveolar barrier tissue; and 3) transferred to the capillary RBCs. The relative spatial distributions of HP-129Xe in airspaces (regional ventilation) and RBCs (regional gas transfer) were compared. Further, we investigated the degree to which ventilation and RBC images identified similar functional regions of interest (ROIs) suitable for functionally-guided RT. For the RT patients, both ventilation and RBC functional images were used to calculate differences in the lung dose-function histogram (DFH) and functional effective uniform dose (fEUD). Results The correlation of ventilation and RBC transfer was ρ=0.39±0.15 in healthy volunteers. For the RT patients, this correlation was ρ=0.53±0.02 pre-treatment and ρ=0.39±0.07 post-treatment; for the emphysema patient it was ρ=0.24. Comparing functional ROIs, ventilation and RBC transfer demonstrated poor spatial agreement: DSC=0.50±0.07 and 0.26±0.12 for the highest-33%- and highest-10%-function ROIs in healthy volunteers, and in RT patients (pre-treatment) these were 0.54±0.02 and 0.35±0.06. The average magnitude of the differences between RBC- and ventilation-derived fEUD, fV20Gy, fV10Gy, and f5Gy, were 1.5±1.4 Gy, 4.1%±3.8%, 5.0%±3.8%, and 5.3%±3.9%. Conclusions Ventilation may not be an effective surrogate for true regional lung function for all patients.

Teaser

Functionally-guided radiation therapy (RT) planning using 4-Dimensional Computed Tomography (4DCT)-derived ventilation is gaining momentum. However, an important question remains: is regional lung ventilation a good surrogate for end-to-end lung function, i.e., gas transfer to Red Blood Cells (RBCs). We acquired functional image data for N=17 human subjects, using state-of-the-art hyperpolarized (HP)-129Xe Magnetic Resonance Imaging (MRI). We analyzed the correlation of ventilation and RBC transfer, and calculated the similarity of planning optimization structures created from each.



8 Weak fault feature extraction of rolling bearings based on globally optimized sparse coding and approximate SVD 2018-04-15             

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Publication date: October 2018
Source:Mechanical Systems and Signal Processing, Volume 111

Author(s): Fatao Hou, Jin Chen, Guangming Dong

Fault feature extraction is crucial to condition monitoring and fault prognostics. However, when fault is in the initial stage, it is often very weak and submerged in the strong noise. This makes the fault feature very difficult to be extracted. In this paper, we propose a novel method based on sparse representation theory. It is inspired by the traditional K-SVD based de-noising method and can penetrate into the underlying structure of the signal. It learns sparse coefficients and dictionary from the noisy signal itself. The coefficients are globally optimized based on an l 1 -regularized least square problem solving method, which can locate the impulse coordinates more accurately compared with orthonormal matching pursuit (OMP) applied in the traditional K-SVD. The dictionary learning is based on an approximation of singular value decomposition (SVD). With the learned dictionary, we can capture the higher-level structure of the signal. Combining the sparse coefficients and the learned dictionary, we can de-noise the signal effectively and extract the incipient weak fault features of rolling bearings. The results of processing both simulated and experimental signals are illustrated and both validate the proposed method. All the experimental data are also processed by SpaEIAD, wavelet shrinkage, and fast kurtogram for comparison.

Graphical abstract

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9 Shift-equivalence of k-ary, one-dimensional cellular automata rules 2018-04-13             

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Publication date: October 2018
Source:Communications in Nonlinear Science and Numerical Simulation, Volume 63

Author(s): Eurico L.P. Ruivo, Pedro P.B. de Oliveira, Fabiola Lobos, Eric Goles

Cellular automata are locally-defined, synchronous, homogeneous, fully discrete dynamical systems. In spite of their typically simple local behaviour, many are capable of showing complex emergent behaviour. When looking at their time-evolution, one may be interested in studying their qualitative dynamical behaviour. One way to group rules that display the same qualitative behaviour is by defining symmetries that map rules to others, the simplest way being by means of permutations in the set of state variables and reflections in their neighbourhood definitions, therefore defining equivalence classes. Here, we introduce the notion of shift-equivalence as another kind of symmetry, now relative to the concept of translation. After defining the notion and showing it indeed defines an equivalence relation, we extend the usual characterisation of dynamical equivalence and use it to partition some specific binary cellular automata rule spaces. Finally, we give a characterisation of the class of shift-equivalent rules in terms of the local transition functions of the cellular automata in the class, by providing an algorithm to compute the members of the class, for any k-ary, one-dimensional rule.





10 A novel method to optimize electricity generation from wind energy 2018-04-09             

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Publication date: October 2018
Source:Renewable Energy, Volume 126

Author(s): E.E. Vogel, G. Saravia, S. Kobe, R. Schumann, R. Schuster

We present and discuss a new technique based on information theory to detect in advance favorable periods of wind activity (positive ramps) for electricity generation. In addition this technique could also help in the analysis of plant operation and management protocols design. Real data from wind power plants in Germany is used; this information is freely available in the internet with reliable registers every 15 min. A simple protocol to mix such wind energy production with electricity coming from conventional sources is proposed as a way to test the proposed algorithm. The eight-year period 2010–2017 is analyzed looking for different behaviors in wind activity. The first five years (2010–2014) are employed to calibrate the method, while the remaining three years (2015–2017) are used to test previous calibration without any further variation in the tuning possibilities described below. Thus, the proposed protocol is tried on under different seasonal wind conditions. Both the algorithm and the general protocol could be adjusted to optimize performances according to regional conditions. In addition, this algorithm can also be used in retrospective studies to adjust productivity to operational conditions.





 
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