156 research outputs found
Understanding User Triads on Facebook
Contemporary approaches that analyze user behavior on online social networks only consider interactions among dyads, which are pairs of directly connected users. A large body of sociological work, however, suggests that mutual connections among users can influence their activities, leading to differences between two- and three-way interactions. This paper explores the dynamics of triads among Facebook users based on the wall posts from the New Orleans regional network. Initially, each connection is categorized as a close friendship or an acquiantance, contingent on the number of wall posts exchanged. Subsequently, the impact of different types of connections comprising triads is examined on the post volume and inter-post times. The analysis finds that these two properties are influenced by the number of close friendships constituting triads
Astrophysics datamining in the classroom: Exploring real data with new software tools and robotic telescopes
Within the efforts to bring frontline interactive astrophysics and astronomy
to the classroom, the Hands on Universe (HOU) developed a set of exercises and
platform using real data obtained by some of the most advanced ground and space
observatories. The backbone of this endeavour is a new free software Web tool -
Such a Lovely Software for Astronomy based on Image J (Salsa J). It is
student-friendly and developed specifically for the HOU project and targets
middle and high schools. It allows students to display, analyze, and explore
professionally obtained astronomical images, while learning concepts on
gravitational dynamics, kinematics, nuclear fusion, electromagnetism. The
continuous evolving set of exercises and tutorials is being completed with real
(professionally obtained) data to download and detailed tutorials. The
flexibility of the Salsa J platform tool enables students and teachers to
extend the exercises with their own observations. The software developed for
the HOU program has been designed to be a multi-platform, multi-lingual
experience for image manipulation and analysis in the classroom. Its design
enables easy implementation of new facilities (extensions and plugins), minimal
in-situ maintenance and flexibility for exercise plugin. Here, we describe some
of the most advanced exercises about astrophysics in the classroom, addressing
particular examples on gravitational dynamics, concepts currently introduced in
most sciences curricula in middle and high schools.Comment: 10 pages, 12 images, submitted to the special theme issue Using
Astronomy and Space Science Research in Physics Courses of the American
Journal of Physic
The age-redshift relation for Luminous Red Galaxies in the Sloan Digital Sky Survey
We present a detailed analysis of 17,852 quiescent, Luminous Red Galaxies
(LRGs) selected from Sloan Digital Sky Survey (SDSS) Data Release Seven (DR7)
spanning a redshift range of 0.0 < z < 0.4. These galaxies are co-added into
four equal bins of velocity dispersion and luminosity to produce high
signal-to-noise spectra (>100A^{-1}), thus facilitating accurate measurements
of the standard Lick absorption-line indices. In particular, we have carefully
corrected and calibrated these indices onto the commonly used Lick/IDS system,
thus allowing us to compare these data with other measurements in the
literature, and derive realistic ages, metallicities ([Z/H]) and alpha-element
abundance ratios ([alpha/Fe]) for these galaxies using Simple Stellar
Population (SSP) models. We use these data to study the relationship of these
galaxy parameters with redshift, and find little evidence for evolution in
metallicity or alpha-elements (especially for our intermediate mass samples).
This demonstrates that our subsamples are consistent with pure passive evolving
(i.e. no chemical evolution) and represent a homogeneous population over this
redshift range. We also present the age-redshift relation for these LRGs and
clearly see a decrease in their age with redshift (5 Gyrs over the redshift
range studied here) which is fully consistent with the cosmological lookback
times in a concordance Lambda CDM universe. We also see that our most massive
sample of LRGs is the youngest compared to the lower mass galaxies. We provide
these data now to help future cosmological and galaxy evolution studies of
LRGs, and provide in the appendices of this paper the required methodology and
information to calibrate SDSS spectra onto the Lick/IDS system.Comment: 26 pages, with several appendices containing data. Accepted for
publication in MNRA
Interior of a Schwarzschild black hole revisited
The Schwarzschild solution has played a fundamental conceptual role in
general relativity, and beyond, for instance, regarding event horizons,
spacetime singularities and aspects of quantum field theory in curved
spacetimes. However, one still encounters the existence of misconceptions and a
certain ambiguity inherent in the Schwarzschild solution in the literature. By
taking into account the point of view of an observer in the interior of the
event horizon, one verifies that new conceptual difficulties arise. In this
work, besides providing a very brief pedagogical review, we further analyze the
interior Schwarzschild black hole solution. Firstly, by deducing the interior
metric by considering time-dependent metric coefficients, the interior region
is analyzed without the prejudices inherited from the exterior geometry. We
also pay close attention to several respective cosmological interpretations,
and briefly address some of the difficulties associated to spacetime
singularities. Secondly, we deduce the conserved quantities of null and
timelike geodesics, and discuss several particular cases in some detail.
Thirdly, we examine the Eddington-Finkelstein and Kruskal coordinates directly
from the interior solution. In concluding, it is important to emphasize that
the interior structure of realistic black holes has not been satisfactorily
determined, and is still open to considerable debate.Comment: 15 pages, 7 figures, Revtex4. V2: Version to appear in Foundations of
Physic
Exceeding the nonlinear-shannon limit using Raman laser based amplification and optical phase conjugation
We demonstrate that a combination of Raman laser based amplification and optical phase conjugation enables transmission beyond the nonlinear-Shannon limit. We show nonlinear compensation of 7x114Gbit/s DP-QPSK channels, increasing system reach by 30%
Оптимізація паралельного ітераційного процесу для лінійних систем з розрідженими матрицями
Розглядається один із підходів до побудови передобумовлювача для методу спряжених градієнтів розв'язування СЛАР з розрідженими матрицями нерегулярної структури. Запропоновано та досліджено передобумовлювачі на основі методу паралельних перерізів.Рассматривается один из подходов к построению предобуславливателя для метода сопряженных градиентов решения СЛАУ с разреженными матрицами нерегулярной структуры. Предложены и исследованы предобуславливатели на основе метода параллельных сечений.Considered is one of approaches for construction a preconditioner for method of conjunctive gradients for solution SLAE with sparse matrices of irregular structure. Preconditioners, which are based on method of parallel section, is proposed and investigated
rEHR: An R package for manipulating and analysing Electronic Health Record data
Research with structured Electronic Health Records (EHRs) is expanding as data becomes more accessible; analytic methods advance; and the scientific validity of such studies is increasingly accepted. However, data science methodology to enable the rapid searching/extraction, cleaning and analysis of these large, often complex, datasets is less well developed. In addition, commonly used software is inadequate, resulting in bottlenecks in research workflows and in obstacles to increased transparency and reproducibility of the research. Preparing a research-ready dataset from EHRs is a complex and time consuming task requiring substantial data science skills, even for simple designs. In addition, certain aspects of the workflow are computationally intensive, for example extraction of longitudinal data and matching controls to a large cohort, which may take days or even weeks to run using standard software. The rEHR package simplifies and accelerates the process of extracting ready-for-analysis datasets from EHR databases. It has a simple import function to a database backend that greatly accelerates data access times. A set of generic query functions allow users to extract data efficiently without needing detailed knowledge of SQL queries. Longitudinal data extractions can also be made in a single command, making use of parallel processing. The package also contains functions for cutting data by time-varying covariates, matching controls to cases, unit conversion and construction of clinical code lists. There are also functions to synthesise dummy EHR. The package has been tested with one for the largest primary care EHRs, the Clinical Practice Research Datalink (CPRD), but allows for a common interface to other EHRs. This simplified and accelerated work flow for EHR data extraction results in simpler, cleaner scripts that are more easily debugged, shared and reproduced
Lipid analogs reveal features critical for hemolysis and diminish granadaene mediated Group B Streptococcus infection
Although certain microbial lipids are toxins, the structural features important for cytotoxicity
remain unknown. Increased functional understanding is essential for developing therapeutics
against toxic microbial lipids. Group B Streptococci (GBS) are bacteria associated with preterm
births, stillbirths, and severe infections in neonates and adults. GBS produce a pigmented,
cytotoxic lipid, known as granadaene. Despite its importance to all manifestations of
GBS disease, studies towards understanding granadaene’s toxic activity are hindered by its
instability and insolubility in purified form. Here, we report the synthesis and screening of
lipid derivatives inspired by granadaene, which reveal features central to toxin function,
namely the polyene chain length. Furthermore, we show that vaccination with a non-toxic
synthetic analog confers the production of antibodies that inhibit granadaene-mediated
hemolysis ex vivo and diminish GBS infection in vivo. This work provides unique structural
and functional insight into granadaene and a strategy to mitigate GBS infection, which will be
relevant to other toxic lipids encoded by human pathogens.This work was supported by funding from the National Institutes of Health
Grants R01AI112619, R01AI133976, R01AI100989, and R21AI125907 and seed funds
from Seattle Childrens Research Institute to L.
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