1,460 research outputs found
A Relation-Based Page Rank Algorithm for Semantic Web Search Engines
With the tremendous growth of information available to end users through the Web, search engines come to play ever a more critical role. Nevertheless, because of their general-purpose approach, it is always less uncommon that obtained result sets provide a burden of useless pages. The next-generation Web architecture, represented by the Semantic Web, provides the layered architecture possibly allowing overcoming this limitation. Several search engines have been proposed, which allow increasing information retrieval accuracy by exploiting a key content of Semantic Web resources, that is, relations. However, in order to rank results, most of the existing solutions need to work on the whole annotated knowledge base. In this paper, we propose a relation-based page rank algorithm to be used in conjunction with Semantic Web search engines that simply relies on information that could be extracted from user queries and on annotated resources. Relevance is measured as the probability that a retrieved resource actually contains those relations whose existence was assumed by the user at the time of query definitio
Accretion flow properties in low-mass X-ray binaries
Accretieschijf dubbelstersystemen onderzocht In zijn proefschrift onderzoekt Andrea Sanna de eigenschappen van de accretiestroom in lage-massa röntgendubbelstersystemen (LMXBs, low-mass X-ray binaries). Dat zijn systemen waarin een neutronenster of een stellair zwart gat zich via een zogenoemde accretieschijf voedt met materie afkomstig van een lage massa begeleidende ster. Röntgendubbelstersystemen vormen een uniek laboratorium voor onderzoek van de fysica in een sterk zwaartekrachtsveld en in zeer dichte materie; extreme condities die niet na te bootsen zijn op de Aarde. Effecten rond deze compacte objecten, die voorspeld worden in de algemene relativiteitstheorie, zijn vele ordes van grootte sterker dan die waarin de algemene relativiteitstheorie succesvol is getest (het zwakke veld domein). De precieze aard en de collectieve eigenschappen van de elementaire deeltjes waaruit de neutronenster is opgebouwd, zijn nog steeds niet goed genoeg begrepen om de toestandsvergelijkingen (die de toestand van de materie in de neutronenster beschrijven) te voorspellen. Door de baanbeweging rond een neutronenster te onderzoeken, kunnen zowel de massa als de straal van het object bepaald worden. Dat kan weer gebruikt worden om de toestandsvergelijking en vervolgens de fundamentele eigenschappen van het materiaal in de neutronenster vast te stellen. Om röntgendubbelstersystemen te begrijpen, bestudeerde Sanna fotonen die worden uitgezonden door deze systemen. Hij richt zich op röntgenemissie die zijn oorsprong vindt in de nabije omgeving van het compacte object. âMomenteel zijn we nog niet in staat om via directe beeldvormende technieken de LMXBs ruimtelijk op te lossen in het röntgengebied,â zegt hij. âDaarom zijn spectrale- en tijdsanalyses van röntgenfotonen de voornaamste methodes die gebruikt worden om de spectrale evolutie van de röntgenbron te begrijpen en om de intrinsieke parameters van het compacte object te onthullen. In dit proefschrift richt ik me in het bijzonder op het bestuderen van de kilohertz quasi-periodieke oscillaties en de relativistische ijzeremissielijnen; twee karakteristieken die respectievelijk de variabiliteit en de spectrale eigenschappen van LMXBs weergeven.â
Relation between the properties of the kilohertz quasi-periodic oscillations and spectral parameters in 4U 163653
We investigate the relation between the parameters of the energy spectrum and
the frequency and amplitude of the kilohertz quasi-periodic oscillations (kHz
QPOs) in the low-mass X-ray binary 4U 163653. We fit the -keV
spectrum of this source with a model that includes a thermal Comptonisation
component. We show that the frequencies of both kHz QPOs follow the same
relation as a function of the parameters of this spectral component, except for
a systematic frequency shift, whereas the rms fractional amplitude of each QPO
follows a different relation with respect to those same parameters. This
implies that, while the dynamical mechanism that sets the frequencies of the
QPO can be the same for both kHz QPOs, the radiative mechanisms that set the
amplitudes of the lower and the upper kHz QPO are likely different. We discuss
the implications of these results to the modelling of the kHz QPOs and the
possibility that the lower kHz QPO reflects a resonance between the
Comptonising medium and the photons from the accretion disc and/or the neutron
star surface.Comment: 7 pages, 4 figures, 2 tables. Accepted for publication in MNRA
Abelhas, drones e outras Coisas no espaço pĂșblico: fazendo estratĂ©gias na cidade
In this article we explore some emerging strategizing practices that citizens use for the development of their immediate urban fabric. We make use of our experiences and engagements with two citizen-driven initiatives in Helsinki, the capital of Finland. The first case attempts to rethink uses and actors of public space by creating viable conditions for the emergence of urban gardening in public spaces. The second initiative is engaged in a political discussion of the boundaries of participation, cultural appropriation and ownership of city space. We discuss and reflectively analyze some of their strategizing practices, as forms of infrastructuring, commoning and patchworking. The cases shed light on forms of designing that are enacted collectively through mobilizing particular concerns and caring approaches. We conclude by highlighting aspects made visible in the cases that can give a sense of direction for exercising forms of continuous, open-ended design that are attentive to the collective construction of Things.Keywords: city-making, citizen participation, infrastructuring, patchworking, commoning.Neste artigo, exploramos algumas prĂĄticas estratĂ©gicas emergentes que os cidadĂŁos utilizam para o desenvolvimento do tecido urbano ao seu redor. Usamos nossas experiĂȘncias e engajamento em duas iniciativas lideradas pelos cidadĂŁos em Helsinki, capital da FinlĂąndia. O primeiro caso Ă© relativo Ă s tentativas de repensar os usos e os atores do espaço pĂșblico atravĂ©s da criação das condiçÔes de viabilidade para o surgimento de jardinagem urbana em espaços pĂșblicos. A segunda iniciativa faz parte de uma discussĂŁo polĂtica dos limites de participação, apropriação cultural e do espaço da cidade. Discutimos e analisamos algumas de suas prĂĄticas estratĂ©gicas, como formas de infraestrutura, commoning e patchworking. Os casos lançam luz sobre as formas de fazer design que sĂŁo realizadas coletivamente atravĂ©s da mobilização em torno de preocupaçÔes especĂficas e por meio de abordagens de cuidado. ConcluĂmos destacando aspectos tornados visĂveis nos casos que podem indicar um caminho para desenvolver processos de design contĂnuos, open-ended que focam na construção coletiva das Coisas.Palavras-chave: city-making, participação cidadĂŁ, infraestruturação, patchworking, commoning
Design of a Low-Cost Microstrip Directional Coupler with High Coupling for a Motion Detection Sensor
A coupled-line coupler based on the asymmetric cascade connection of two coupled line sections is used to achieve a high coupling factor using low-cost material and technology in the X frequency band, and its performance is compared with a standard quarter-wave, coupled-line coupler, showing an increase in the coupling factor of about 3 dB. The proposed coupler can be effectively used in a Doppler motion detection sensor, due to its strong coupling and relatively high isolation. The coupler is designed through a simple, yet rigorous, equivalent circuital model. Then,anoptimizationprocedurewasperformedusingthecommercialsoftwareAnsysHFSSinorder to compensate for losses and second order effects. A prototype of the designed coupler was realized, and the measured data show very good agreement with simulations
The reflection spectrum of the low-mass X-ray binary 4U 1636-53
We present 3-79 keV NuSTAR observations of the neutron star low-mass X-ray
binary 4U 1636-53 in the soft, transitional and hard state. The spectra display
a broad emission line at 5-10 keV. We applied several models to fit this line:
A GAUSSIAN line, a relativistically broadened emission line model, KYRLINE, and
two models including relativistically smeared and ionized reflection off the
accretion disc with different coronal heights, RELXILL and RELXILLLP. All
models fit the spectra well, however, the KYRLINE and RELXILL models yield an
inclination of the accretion disc of with respect to the line
of sight, which is at odds with the fact that this source shows no dips or
eclipses. The RELXILLLP model, on the other hand, gives a reasonable
inclination of . We discuss our results for these models in this
source and the possible primary source of the hard X-rays.Comment: 9 pages, 8 figure
Iron-line and continuum variations in the XMM-Newton and Suzaku spectra of the neutron-star low-mass X-ray binary 4U 1636-53
We used six simultaneous XMM-Newton and Rossi X-ray Timing Explorer plus five
Suzaku observations to study the continuum spectrum and the iron emission line
in the neutron-star low-mass X-ray binary 4U 1636-53. We modelled the spectra
with two thermal components (representing the accretion disc and boundary
layer), a Comptonised component (representing a hot corona), and either a
Gaussian or a relativistic line component to model an iron emission line at
about 6.5 keV. For the relativistic line component we used either the diskline,
laor or kyrline model, the latter for three different values of the spin
parameter. The fitting results for the continuum are consistent with the
standard truncated disc scenario. We also find that the flux and equivalent
width of the iron line first increase and then decrease as the flux of the
Comptonised component increases. This could be explained either by changes in
the ionisation state of the accretion disc where the line is produced by
reflection, or by light bending of the emission from the Comptonised component
if the height at which this component is produced changes with mass accretion
rate.Comment: Accepted for publication in MNRAS, 16 pages, 10 figures, 5 table
Relation between spectral changes and the presence of the lower kHz QPO in the neutron-star low-mass X-ray binary 4U 1636-53
We fitted the -keV spectrum of all the observations of the
neutron-star low-mass X-ray binary 4U 163653 taken with the {\it Rossi X-ray
Timing Explorer} using a model that includes a thermal Comptonisation
component. We found that in the low-hard state the power-law index of this
component, , gradually increases as the source moves in the
colour-colour diagram. When the source undergoes a transition from the hard to
the soft state drops abruptly; once the source is in the soft state
increases again and then decreases gradually as the source spectrum
softens further. The changes in , together with changes of the electron
temperature, reflect changes of the optical depth in the corona. The lower
kilohertz quasi-periodic oscillation (kHz QPO) in this source appears only in
observations during the transition from the hard to the soft state, when the
optical depth of the corona is high and changes depends strongly upon the
position of the source in the colour-colour diagram. Our results are consistent
with a scenario in which the lower kHz QPO reflects a global mode in the system
that results from the resonance between, the disc and/or the neutron-star
surface, and the Comptonising corona.Comment: 9 pages, 6 figures. Accepted for publication in MNRA
Broad iron emission line and kilohertz quasi-periodic oscillations in the neutron star system 4U 1636-53
Both the broad iron (Fe) line and the frequency of the kilohertz
quasi-periodic oscillations (kHz QPOs) in neutron star low-mass X-ray binaries
(LMXBs) can potentially provide independent measures of the inner radius of the
accretion disc. We use XMM-Newton and simultaneous Rossi X-ray Timing Explorer
observations of the LMXB 4U 1636-53 to test this hypothesis. We study the
properties of the Fe-K emission line as a function of the spectral state of the
source and the frequency of the kHz QPOs. We find that the inner radius of the
accretion disc deduced from the frequency of the upper kHz QPO varies as a
function of the position of the source in the colour-colour diagram, in
accordance with previous work and with the standard scenario of accretion disc
geometry. On the contrary, the inner disc radius deduced from the profile of
the Fe line is not correlated with the spectral state of the source. The values
of the inner radius inferred from kHz QPOs and Fe lines, in four observations,
do not lead to a consistent value of the neutron star mass, regardless of the
model used to fit the Fe line. Our results suggest that either the kHz QPO or
the standard relativistic Fe line interpretation does not apply for this
system. Furthermore, the simultaneous detection of kHz QPOs and broad Fe lines
is difficult to reconcile with models in which the broadening of the Fe line is
due to the reprocessing of photons in an outflowing wind.Comment: 12 pages, 6 figures, Accepted for publication in MNRA
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