9,319 research outputs found
Efficiently Clustering Very Large Attributed Graphs
Attributed graphs model real networks by enriching their nodes with
attributes accounting for properties. Several techniques have been proposed for
partitioning these graphs into clusters that are homogeneous with respect to
both semantic attributes and to the structure of the graph. However, time and
space complexities of state of the art algorithms limit their scalability to
medium-sized graphs. We propose SToC (for Semantic-Topological Clustering), a
fast and scalable algorithm for partitioning large attributed graphs. The
approach is robust, being compatible both with categorical and with
quantitative attributes, and it is tailorable, allowing the user to weight the
semantic and topological components. Further, the approach does not require the
user to guess in advance the number of clusters. SToC relies on well known
approximation techniques such as bottom-k sketches, traditional graph-theoretic
concepts, and a new perspective on the composition of heterogeneous distance
measures. Experimental results demonstrate its ability to efficiently compute
high-quality partitions of large scale attributed graphs.Comment: This work has been published in ASONAM 2017. This version includes an
appendix with validation of our attribute model and distance function,
omitted in the converence version for lack of space. Please refer to the
published versio
Tilting mutation of weakly symmetric algebras and stable equivalence
We consider tilting mutations of a weakly symmetric algebra at a subset of
simple modules, as recently introduced by T. Aihara. These mutations are
defined as the endomorphism rings of certain tilting complexes of length 1.
Starting from a weakly symmetric algebra A, presented by a quiver with
relations, we give a detailed description of the quiver and relations of the
algebra obtained by mutating at a single loopless vertex of the quiver of A. In
this form the mutation procedure appears similar to, although significantly
more complicated than, the mutation procedure of Derksen, Weyman and Zelevinsky
for quivers with potentials. By definition, weakly symmetric algebras connected
by a sequence of tilting mutations are derived equivalent, and hence stably
equivalent. The second aim of this article is to study these stable
equivalences via a result of Okuyama describing the images of the simple
modules. As an application we answer a question of Asashiba on the derived
Picard groups of a class of self-injective algebras of finite representation
type. We conclude by introducing a mutation procedure for maximal systems of
orthogonal bricks in a triangulated category, which is motivated by the effect
that a tilting mutation has on the set of simple modules in the stable
category.Comment: Description and proof of mutated algebra made more rigorous (Prop.
3.1 and 4.2). Okuyama's Lemma incorporated: Theorem 4.1 is now Corollary 5.1,
and proof is omitted. To appear in Algebras and Representation Theor
The Outbursts and Orbit of the Accreting Pulsar GS 1843-02 = 2S 1845-024
We present observations of a series of 10 outbursts of pulsed hard X-ray flux
from the transient 10.6 mHz accreting pulsar GS 1843-02, using the Burst and
Transient Source Experiment on the Compton Gamma Ray Observatory. These
outbursts occurred regularly every 242 days, coincident with the ephemeris of
the periodic transient GRO J1849-03 (Zhang et al. 1996), which has recently
been identified with the SAS 3 source 2S 1845-024 (Soffitta et al. 1998). Our
pulsed detection provides the first clear identification of GS 1843-02 with 2S
1845-024. We present a pulse timing analysis which shows that the 2S 1845-024
outbursts occur near the periastron passage of the neutron star's highly
eccentric (e = 0.88+-0.01) 242.18+-0.01 day period binary orbit about a high
mass (M > 7 solar masses) companion. The orbit and transient outburst pattern
strongly suggest the pulsar is in a binary system with a Be star. Our
observations show a long-term spin-up trend, with most of the spin-up occurring
during the outbursts. From the measured spin-up rates and inferred luminosities
we conclude that an accretion disk is present during the outbursts.Comment: Accepted for publication in Astrophysical Journa
Planck-LFI radiometers' spectral response
The Low Frequency Instrument (LFI) is an array of pseudo-correlation
radiometers on board the Planck satellite, the ESA mission dedicated to
precision measurements of the Cosmic Microwave Background. The LFI covers three
bands centred at 30, 44 and 70 GHz, with a goal bandwidth of 20% of the central
frequency.
The characterization of the broadband frequency response of each radiometer
is necessary to understand and correct for systematic effects, particularly
those related to foreground residuals and polarization measurements. In this
paper we present the measured band shape of all the LFI channels and discuss
the methods adopted for their estimation. The spectral characterization of each
radiometer was obtained by combining the measured spectral response of
individual units through a dedicated RF model of the LFI receiver scheme.
As a consistency check, we also attempted end-to-end spectral measurements of
the integrated radiometer chain in a cryogenic chamber. However, due to
systematic effects in the measurement setup, only qualitative results were
obtained from these tests. The measured LFI bandpasses exhibit a moderate level
of ripple, compatible with the instrument scientific requirements.Comment: 16 pages, 9 figures, this paper is part of the Prelaunch status LFI
papers published on JINST:
http://www.iop.org/EJ/journal/-page=extra.proc5/jins
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Spectral Analysis of Airborne Effluents from Nuclear Facilities and Design of AOTF Spectroradiometer
This report summarizes the spectral analysis and design of an acousto optic tunable filter (AOTF) imaging spectroradiometer for the project SR003. This system will use passive open-path infrared absorption to detect the presence of various source gases
Solução Paralela em Agregado de PCs de um Código de Elementos Finitos Aplicado à Elasticidade Linear
Este trabalho apresenta os resultados comparativos de desempenho de cĂłdigos paralelos, baseados no mĂ©todo dos elementos finitos aplicado Ă Â elasticidade linear para problemas estruturais, que utilizam o mĂ©todo dos gradientes conjugados para solução do sistema de equaçÔes. Os programas foram executados em um agregado de PCs, por ser uma opção economicamente viĂĄvel, jĂĄ que utiliza tecnologia depurada de alta disponibilidade e confiabilidade e softwares de domĂnio pĂșblico. Foram implementadas duas versĂ”es utilizando PVM e MPI. O desempenho dos programas paralelos foi medido pelos tempos de execução e speedup relativo, em função do tamanho do problema e do nĂșmero de processadores
Prediction of Herbage Accumulation of \u3ci\u3eCynodon\u3c/i\u3e Grasses by an Empirical Model Based on Temperature and Daylength
The objective of this work was to estimate dry matter production of Cynodon grasses as a function of photothermal units (PU). Total PU values were calculated for the period from February 1 to April 24, 1996, from a location in southeastern Brazil. Regression analysis was run between PU and herbage production from a published data set on five Cynodon cultivars, with an r2 of 0.9983. Differences between measured and estimated values were under 5%. Model testing using an independent data set on herbage dry matter production from grazed Cynodon pastures showed an overestimation, probably due to water deficit during the experimental period. In addition, grazing intensity may have been a reason for the less than optimal fit. The model was adequate in predicting the variation in production potential throughout the periods studied although modifications to include the effect of water balance, nitrogen fertilization and defoliation intensity may allow for better predictions under sub-optimal environmental conditions and varying management strategies
Trapped lipopolysaccharide and LptD intermediates reveal lipopolysaccharide translocation steps across the Escherichia coli outer membrane
Lipopolysaccharide (LPS) is a main component of the outer membrane of Gram-negative bacteria, which is essential for the vitality of most Gram-negative bacteria and plays a critical role for drug resistance. LptD/E complex forms a N-terminal LPS transport slide, a hydrophobic intramembrane hole and the hydrophilic channel of the barrel, for LPS transport, lipid A insertion and core oligosaccharide and O-antigen polysaccharide translocation, respectively. However, there is no direct evidence to confirm that LptD/E transports LPS from the periplasm to the external leaflet of the outer membrane. By replacing LptD residues with an unnatural amino acid p-benzoyl-L-phenyalanine (pBPA) and UV-photo-cross-linking in E.coli, the translocon and LPS intermediates were obtained at the N-terminal domain, the intramembrane hole, the lumenal gate, the lumen of LptD channel, and the extracellular loop 1 and 4, providing the first direct evidence and âsnapshotsâ to reveal LPS translocation steps across the outer membrane
Reductionâoxidation (redox) system in radiation-induced normal tissue injury: molecular mechanisms and implications in radiation therapeutics
Every year, millions of cancer patients undergo radiation therapy for treating and destroying abnormal cell growths within normal cell environmental conditions. Thus, ionizing radiation can have positive therapeutic effects on cancer cells as well as post-detrimental effects on surrounding normal tissues. Previous studies in the past years have proposed that the reduction and oxidation metabolism in cells changes in response to ionizing radiation and has a key role in radiation toxicity to normal tissue. Free radicals generated from ionizing radiation result in upregulation of cyclooxygenases (COXs), nitric oxide synthase (NOSs), lipoxygenases (LOXs) as well as nicotinamide adenine dinucleotide phosphate oxidase (NADPH oxidase), and their effected changes in mitochondrial functions are markedly noticeable. Each of these enzymes is diversely expressed in multiple cells, tissues and organs in a specific manner. Overproduction of reactive oxygen radicals (ROS), reactive hydroxyl radical (ROH) and reactive nitrogen radicals (RNS) in multiple cellular environments in the affected nucleus, cell membranes, cytosol and mitochondria, and other organelles, can specifically affect the sensitive and modifying enzymes of the redox system and repair proteins that play a pivotal role in both early and late effects of radiation. In recent years, ionizing radiation has been known to affect the redox functions and metabolism of NADPH oxidases (NOXs) as well as having destabilizing and detrimental effects on directly and indirectly affected cells, tissues and organs. More noteworthy, chronic free radical production may continue for years, increasing the risk of carcinogenesis and other oxidative stress-driven degenerative diseases as well as pathologies, in addition to late effect complications of organ fibrosis. Hence, knowledge about the mechanisms of chronic oxidative damage and injury in affected cells, tissues and organs following exposure to ionizing radiation may help in the development of treatment and management strategies of complications associated with radiotherapy (RT) or radiation accident victims. Thus, this medically relevant phenomenon may lead to the discovery of potential antioxidants and inhibitors with promising results in targeting and modulating the ROS/NO-sensitive enzymes in irradiated tissues and organ injury systems
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