241 research outputs found
Outward Influence and Cascade Size Estimation in Billion-scale Networks
Estimating cascade size and nodes' influence is a fundamental task in social,
technological, and biological networks. Yet this task is extremely challenging
due to the sheer size and the structural heterogeneity of networks. We
investigate a new influence measure, termed outward influence (OI), defined as
the (expected) number of nodes that a subset of nodes will activate,
excluding the nodes in S. Thus, OI equals, the de facto standard measure,
influence spread of S minus |S|. OI is not only more informative for nodes with
small influence, but also, critical in designing new effective sampling and
statistical estimation methods.
Based on OI, we propose SIEA/SOIEA, novel methods to estimate influence
spread/outward influence at scale and with rigorous theoretical guarantees. The
proposed methods are built on two novel components 1) IICP an important
sampling method for outward influence, and 2) RSA, a robust mean estimation
method that minimize the number of samples through analyzing variance and range
of random variables. Compared to the state-of-the art for influence estimation,
SIEA is times faster in theory and up to several orders of
magnitude faster in practice. For the first time, influence of nodes in the
networks of billions of edges can be estimated with high accuracy within a few
minutes. Our comprehensive experiments on real-world networks also give
evidence against the popular practice of using a fixed number, e.g. 10K or 20K,
of samples to compute the "ground truth" for influence spread.Comment: 16 pages, SIGMETRICS 201
Importance Sketching of Influence Dynamics in Billion-scale Networks
The blooming availability of traces for social, biological, and communication
networks opens up unprecedented opportunities in analyzing diffusion processes
in networks. However, the sheer sizes of the nowadays networks raise serious
challenges in computational efficiency and scalability.
In this paper, we propose a new hyper-graph sketching framework for inflence
dynamics in networks. The central of our sketching framework, called SKIS, is
an efficient importance sampling algorithm that returns only non-singular
reverse cascades in the network. Comparing to previously developed sketches
like RIS and SKIM, our sketch significantly enhances estimation quality while
substantially reducing processing time and memory-footprint. Further, we
present general strategies of using SKIS to enhance existing algorithms for
influence estimation and influence maximization which are motivated by
practical applications like viral marketing. Using SKIS, we design high-quality
influence oracle for seed sets with average estimation error up to 10x times
smaller than those using RIS and 6x times smaller than SKIM. In addition, our
influence maximization using SKIS substantially improves the quality of
solutions for greedy algorithms. It achieves up to 10x times speed-up and 4x
memory reduction for the fastest RIS-based DSSA algorithm, while maintaining
the same theoretical guarantees.Comment: 12 pages, to appear in ICDM 2017 as a regular pape
Élaboration et propriétés des composites polypropylène recyclé/fibres de bambou
Cette étude présente des résultats obtenus sur l’élaboration de composites à base de polypropylène recyclé renforcé par des fibres végétales (fibres de bambou), fabriqués à l’aide d’une extrudeuse double vis modulaire pour produire un composite sous forme de granulés transformables. L’effet de la teneur en fibres de bambou, du compatibilisant et des méthodes de traitement chimique de la surface des fibres sur les propriétés mécaniques et rhéologiques du composite a été étudié. Nous avons montré que le traitement avec la soude enlève les impuretés et augmente la rugosité de surface des fibres, ce qui entraîne une meilleure adhésion des fibres dans la matrice polymère. Les composites fibres de bambou acétylées/polypropylène recyclé présentent de meilleures propriétés mécaniques, dues au greffage de groupes acétyles sur la surface des fibres et donc à l’amélioration de la compatibilité entre les fibres de bambou et la matrice polymère. Les propriétés rhéologiques des composites à différents taux de fibres de bambou et pour différentes méthodes de traitement de surface sont également analysées. Les facteurs prédominants qui influencent les propriétés des composites sont identifiés
Relationship between fiber chemical treatment and properties of recycled pp/bamboo fiber composites
This article reports the preparation of recycled polypropylene (RPP)/bamboo fiber (BF) composite via direct melt blends using a twin screw extruder. The effects of the chemical treatment of BF surface (alkaline and acetylation) on fiber structure and composite mechanical, thermal, rheological properties have been investigated. We showed that alkali treatment increases the contact surface of BF within composites, resulting in a more homogenous dispersion of fibers in the polymer matrix. Alkali treatment improves mechanical properties such as tensile strength as well as the Charpy impact strength. Reinforced composites obtained with acetylated BF show better mechanical properties due to grafting of acetyl groups onto the cellulose fiber surface and thus improve compatibility between BF and matrix. The rheological properties of RPP/BF composites depending on the BF content and treatment methods are also analyzed. Predominant factors that influence the properties of relevant materials are identified. Maleic anhydride grafted polypropylene is used as a compatibilizer to improve the adhesion between the cellulosic phase and the RPP matrix
The Evolution of the VASIMR Engine
Our future deep space explorers face many daunting challenges but three of these loom high above the rest: Physiological debilitation, radiation sickness and psychological stress. Many countermeasures are presently being considered to ameliorate these difficulties however, in the long run, two important new developments are required: abundant space power and advanced propulsion. The development of the Variable Specific Impulse Magnetoplasma Rocket (VASIMR) addresses these important areas of need. The VASIMR is a high power, radio frequency-driven magneto plasma rocket, capable of very high exhaust velocities. In addition, its unique architecture allows in-flight mission-optimization of thrust and specific impulse to enhance performance and reduce trip time. A NASA-led, research team, involving industry, academia and government facilities is pursuing the development of this concept in the United States. The technology can be validated, in the near term, in venues such as the International Space Station, where it can also serve as both a drag compensation device and a plasma contactor for the orbital facility. Other near-Earth applications in the commercial and scientific satellite sectors are also envisioned. This presentation covers the present status of the technology, plans for its near term deployment and a vision for its future evolution
Forages Improve Livelihoods of Smallholder Farmers with Beef Cattle in South Central Coastal Vietnam
In South Central Coastal Vietnam, on-farm research and farmer experience demonstrated the benefits of growing improved forages as a means of improving the year round quantity and quality of feed available for beef cattle. In Binh Dinh, Phu Yen and Ninh Thuan provinces, five new forage species (Panicum maximum, cv. TD58, Brachiaria hybrid cv. Mulato II, Pennisetum purpureum cv.VA06, Paspalum atratum cv. Terenos and Stylosanthes guianensis cv. CIAT 184) were evaluated for yield and crude protein concentration. There was not a consistent yield difference between locations for the forage grasses, but in Binh Dinh province P. maximum TD58 produced the highest yield. The grasses were comparable in crude protein concentration. Stylo CIAT 184 performed relatively well and had the highest crude protein concentration. All species have potential use, depending on the circumstances and site factors such as fertility, drainage and availability of irrigation. This work was expanded to a total of 45 farmers to gain feedback on farmer experience in growing different forages. The percentage of farmers who “liked” the introduced forages was Mulato II, 92%; TD58, 85%; VA06, 82%; Paspalum, 46%; and Stylo, 36%. By far the most important early socio-economic impact of developing perennial forage plots close to households was an average 50% reduction in the amount of labour and time that farmers spend supplying cut and carry forage to their animals. In addition, the growing of forages can meaningfully reduce the grazing pressure on common grazing lands, thereby lowering the potential for environmental degradation
Petrographic Characteristics and Depositional Environment Evolution of Middle Miocene Sediments in the Thien Ung - Mang Cau Structure of Nam Con Son Basin
This paper introduces the petrographic characteristics and depositional environment of Middle Miocene rocks of the Thien Ung - Mang Cau structure in the central area of Nam Con Son Basin based on the results of analyzing thin sections and structural characteristics of core samples. Middle Miocene sedimentary rocks in the studied area can be divided into three groups: (1) Group of terrigenous rocks comprising greywacke sandstone, arkosic sandstone, lithic-quartz sandstone, greywacke-lithic sandstone, oligomictic siltstone, and bitumenous claystone; (2) Group of carbonate rocks comprising dolomitic limestone and bituminous limestone; (3) Mixed group comprising calcareous sandstone, calcarinate sandstone, arenaceous limestone, calcareous claystone, calcareous silty claystone, dolomitic limestone containing silt, and bitumen. The depositional environment is expressed through petrographic characteristics and structure of the sedimentary rocks in core samples. The greywacke and arkosic sandstones are of medium grain size, poor sorting and roundness, and siliceous cement characterizing the alluvial and estuarine fan environment expressed by massive structure of core samples. The mixed calcareous limestone, arenaceous dolomitic limestone, and calcareous and bituminous clayey siltstone in the core samples are of turbulent flow structure characterizing shallow bay environment with the action of bottom currents. The dolomitic limestones are of relatively homogeneous, of microgranular and fine-granular texture, precipitated in a weakly reducing, semi-closed, and relatively calm bay environment
Mapping for engagement: setting up a community based participatory research project to reach underserved communities at risk for Hepatitis C in Ho Chi Minh City, Vietnam
Background: Approximately 1. 07 million people in Vietnam are infected with hepatitis C virus (HCV). To address this epidemic, the South East Asian Research Collaborative in Hepatitis (SEARCH) launched a 600-patient cohort study and two clinical trials, both investigating shortened treatment strategies for chronic HCV infection with direct-acting antiviral drugs. We conducted ethnographic research with a subset of trial participants and found that the majority were aware of HCV infection and its implications and were motivated to seek treatment. However, people who inject drugs (PWID), and other groups at risk for HCV were under-represented, although injecting drug use is associated with high rates of HCV. Material and Methods: We designed a community-based participatory research (CBPR) study to engage in dialogues surrounding HCV and other community-prioritized health issues with underserved groups at risk for HCV in Ho Chi Minh City. The project consists of three phases: situation analysis, CBPR implementation, and dissemination. In this paper, we describe the results of the first phase (i.e., the situation analysis) in which we conducted desk research and organized stakeholder mapping meetings with representatives from local non-government and community-based organizations where we used participatory research methods to identify and analyze key stakeholders working with underserved populations. Results: Twenty six institutions or groups working with the key underserved populations were identified. Insights about the challenges and dynamics of underserved communities were also gathered. Two working groups made up of representatives from the NGO and CBO level were formed. Discussion: Using the information provided by local key stakeholders to shape the project has helped us to build solid relationships, give the groups a sense of ownership from the early stages, and made the project more context specific. These steps are not only important preliminary steps for participatory studies but also for other research that takes place within the communities
Dynamic Limits on Planar Libration-Orbit Coupling Around an Oblate Primary
This paper explores the dynamic properties of the planar system of an
ellipsoidal satellite in an equatorial orbit about an oblate primary. In
particular, we investigate the conditions for which the satellite is bound in
librational motion or when the satellite will circulate with respect to the
primary. We find the existence of stable equilibrium points about which the
satellite can librate, and explore both the linearized and non-linear dynamics
around these points. Absolute bounds are placed on the phase space of the
libration-orbit coupling through the use of zero-velocity curves that exist in
the system. These zero-velocity curves are used to derive a sufficient
condition for when the satellite's libration is bound to less than 90 degrees.
When this condition is not satisfied so that circulation of the satellite is
possible, the initial conditions at zero libration angle are determined which
lead to circulation of the satellite. Exact analytical conditions for
circulation and the maximum libration angle are derived for the case of a small
satellite in orbits of any eccentricity.Comment: Submitted to Celestial Mechanics and Dynamical Astronom
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