586 research outputs found
InfoFlow: Mining Information Flow Based on User Community in Social Networking Services
Online social networking services (SNSs) have emerged rapidly and have become huge data sources for social network analysis. The spread of the content generated by users is crucial in SNS, but there is only a handful of research works on information diffusion and, more precisely, information diffusion flow. In this paper, we propose a novel method to discover information diffusion processes from SNS data. The method starts preprocessing the SNS data using a user-centric algorithm of community detection based on modularity maximization with the purpose of reducing the complexity of the noisy data. After that, the InfoFlow miner generates information diffusion flow models among the user communities discovered from the data. The algorithm is an extension of a traditional process discovery technique called the Flexible Heuristics miner, but the visualization ability of the generated process model is improved with a new measure called response weight, which effectively captures and represents the interactions among communities. An experiment with Facebook data was conducted, and information flow among user communities was visualized. Additionally, a quality assessment of the models was carried out to demonstrate the effectiveness of the method. The final constructed models allowed us to identify useful information such as how the information flows between communities and information disseminators and receptors within communities.11Ysciescopu
Quantum bounds for gravitational de Sitter entropy and the Cardy-Verlinde formula
We analyze different types of quantum corrections to the Cardy-Verlinde
entropy formula in a Friedmann-Robertson-Walker universe and in an (anti)-de
Sitter space. In all cases we show that quantum corrections can be represented
by an effective cosmological constant which is then used to redefine the
parameters entering the Cardy-Verlinde formula so that it becomes valid also
with quantum corrections, a fact that we interpret as a further indication of
its universality. A proposed relation between Cardy-Verlinde formula and the
ADM Hamiltonian constraint is given.Comment: LaTeX file, 15 pages, reference is adde
Metagenomics and Social Inclusion in Peru
Metagenomics is the study of all the genetic material found in an ecosystem. Each part of the human body is an ecosystem with a distinct bacterial profile or microbiota whose metagenomic signature is called a human microbiome. The study of human microbiomes is a promising new area of biomedical research. Certain bacterial species are directly associated to specific diseases, suggesting their potential as biomarkers or even as therapeutic alternatives. As it has happened with genetics and genomics applications, most microbiome research is focused on urban human populations, thus providing a very biased set of study populations, both human and bacterial.The developing world harbors biological phenomena absent in the developed world. The study of traditional communities from developing countries provides unique opportunities for scientific advancement. At the same time, the knowledge obtained might impact public health programs and help to build research capacity in these countries. However, including traditional communities from developing countries in research has proved to be a sensitive matter.Research with indigenous populations carries the stigma of being exploitative, neocolonialist, and imperialist. Engaging communities in research can reduce the risk of exploitation and increase protection for these vulnerable populations. The biggest challenge to establishing meaningful partnerships with indigenous populations is distrust. The history of marginalization and constant friction between indigenous communities and outsiders has eroded any potential predisposition to trust. In absence of trust, any attempt to engage a community will be futile, superficial or pretendcommunity engagements without any real participation from the community. Real community engagement requires open dialog that results in real partnership which is impossible without a relationship of trust.Developing a relationship of trust with indigenous communities and the authorities that represent them is a demanding venture. Some unsuccessful research initiatives in the developing world have been credited to obstacles resulting from inefficient systems of research governance. Barriers that complicate inclusion of indigenous populations in biomedical research will contribute to the existing health disparities.Here, I discuss these topics from my own field experience and my efforts of implementing metagenomic research in Peru. Chapter 1 presents a case- study of the human gut microbiota of a hunter-gatherer community from the Peruvian Amazon region. The findings challenge some of the early conclusions of the study of human gut microbiome, highlighting the need to diversify the populations examined. Chapter 2 discusses distrust as the main barrier to effectively engage indigenous populations from developing countries in biomedical research. Chapter 3 offers the concept of intermediate research organizations as an alternative to overcome some of the barriers related to the implementation of international research with indigenous populations. The necessary process that researchers must undertake can be streamlined, while enhancing protection for human subjects within a system that lacks clear regulations for research
Acausality in Gowdy spacetimes
We present a parametrization of and Gowdy cosmological
models which allows us to study both types of topologies simultaneously. We
show that there exists a coordinate system in which the general solution of the
linear polarized special case (with both topologies) has exactly the same
functional dependence. This unified parametrization is used to investigate the
existence of Cauchy horizons at the cosmological singularities, leading to a
violation of the strong cosmic censorship conjecture. Our results indicate that
the only acausal spacetimes are described by the Kantowski-Sachs and the
Kerr-Gowdy metrics.Comment: Typos corrected, 10 pages. Dedicated to Michael P. Ryan on the
occasion of his 60-th birthda
Unified approach to study quantum properties of primordial black holes, wormholes and of quantum cosmology
We review the anomaly induced effective action for dilaton coupled spinors
and scalars in large N and s-wave approximation. It may be applied to study the
following fundamental problems: construction of quantum corrected black holes
(BHs), inducing of primordial wormholes in the early Universe (this effect is
confirmed) and the solution of initial singularity problem. The recently
discovered anti-evaporation of multiple horizon BHs is discussed. The existance
of such primordial BHs may be interpreted as SUSY manifestation. Quantum
corrections to BHs thermodynamics maybe also discussed within such scheme.Comment: LaTeX file and two eps files, to appear in MPLA, Brief Review
Isotopic δ\u3csup\u3e15\u3c/sup\u3eN Signature of Grass-Alone and Grass-Legume Tropical Pastures to Estimate Sources of Nitrogen to Grasses in Farmer Managed Pastures
Vast areas of tropical forest have been converted into pastures sown with introduced grasses (Urochloa spp.). The majority of pastures exist in some stage of degradation, which has dramatic ecological and economic consequences. Our objective was to determine isotopic 15N signature of grass alone and grass-legume pastures to estimate sources of nitrogen (N) to grasses in farmer managed pastures. This work contributes to enhancing the sustainability of tropical pastures in forest margins through the integration of legumes. The overarching hypothesis tested was that legumes associated with grasses will improve nutrient supply via symbiotic fixation and mobilization of soil phosphorus (P) reserves increasing belowground inputs and recycling of carbon (C), N and P. We have done preliminary research in ten paired plots of productive grass-alone vs. grass-legume pastures on farms located in the Caquetá region of Colombia. Pasture productivity and sources of plant N uptake using 15N isotope natural abundance methods have been analysed. The integration of legumes increased biomass production by about 74%, and N and P uptake by two-fold. The legumes derived about 80% of their N via symbiotic fixation, showing the significance of this process to N nutrition despite the acidic soil conditions. The isotopic 15N signature of grasses in grass-alone vs. grass-legume pastures suggested that sources of grass N are affected by pasture composition. Furthermore, low δ15N found in some grass-alone pastures, indicate that other N sources apart from soil mineral N are being exploited. The role of different processes like symbiosis with arbuscular mycorrhiza fungi, biological nitrification inhibition or associative N fixation need to be further studied to provide a more comprehensive interpretation of N exploitation in grass-alone pastures
(Non) singular Kantowski-Sachs Universe from quantum spherically reduced matter
Using s-wave and large N approximation the one-loop effective action for 2d
dilaton coupled scalars and spinors which are obtained by spherical reduction
of 4d minimal matter is found. Quantum effective equations for reduced Einstein
gravity are written. Their analytical solutions corresponding to 4d
Kantowski-Sachs (KS) Universe are presented. For quantum-corrected Einstein
gravity we get non-singular KS cosmology which represents 1) quantum-corrected
KS cosmology which existed on classical level or 2)purely quantum solution
which had no classical limit. The analogy with Nariai BH is briefly mentioned.
For purely induced gravity (no Einstein term) we found general analytical
solution but all KS cosmologies under discussion are singular. The
corresponding equations of motion are reformulated as classical mechanics
problem of motion of unit mass particle in some potential V.Comment: LaTeX file, 16 pages, a few misprints are correcte
Generating Gowdy cosmological models
Using the analogy with stationary axisymmetric solutions, we present a method
to generate new analytic cosmological solutions of Einstein's equation
belonging to the class of Gowdy cosmological models. We show that the
solutions can be generated from their data at the initial singularity and
present the formal general solution for arbitrary initial data. We exemplify
the method by constructing the Kantowski-Sachs cosmological model and a
generalization of it that corresponds to an unpolarized Gowdy model.Comment: Latex, 15 pages, no figure
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