232 research outputs found
City rankings and the citizens: exposing representational and participatory gaps
Acritical reflection on the purposes, role and performance of city rankings through an holistic communicational approach is at the core of this article. Grounded on a conceptual framework that highlights the contemporary idea of the city—beyond the smart city and more as a co-intelligent, collaborative and co-creative entity, and on the performance outputs of city rankings as territorial and strategic communication tools that actually represent the state of cities, we address the citizens’ presence or contribute—as main city stakeholders—to city rankings. In order to make research tangible with a practical component, an exploratory comparative content analysis of three recognized city rankings: the CBI – City Brands Index 2017, the GCR – 2018 Global Cities Report, and the Global Liveability Index 2018—was carried out. Conclusive notes argue that in order to effectively represent cities, as they are lived, thought and built by their citizens in their everyday, city rankings must rely in more real-time, updated, people’s perception centred data, and embed more citizen participation and insights. Moreover, methodology transparency and accountability should be promoted in order to add trust value to city rankings.(undefined
Evolution of the UV Excess in Early-Type Galaxies
We examine the UV emission from luminous early-type galaxies as a function of
redshift. We perform a stacking analysis using Galaxy Evolution Explorer
(GALEX) images of galaxies in the NOAO Deep Wide Field Survey (NDWFS) Bo\"otes
field and examine the evolution in the UV colors of the average galaxy. Our
sample, selected to have minimal ongoing star formation based on the optical to
mid-IR SEDs of the galaxies, includes 1843 galaxies spanning the redshift range
. We find evidence that the strength of the UV excess
decreases, on average, with redshift, and our measurements also show moderate
disagreement with previous models of the UV excess. Our results show little
evolution in the shape of the UV continuum with redshift, consistent either
with the binary model for the formation of Extreme Horizontal Branch (EHB)
stars or with no evolution in EHB morphology with look-back time. However, the
binary formation model predicts that the strength of the UV excess should also
be relatively constant, in contradiction with our measured results. Finally, we
see no significant influence of a galaxy's environment on the strength of its
UV excess.Comment: 30 pages, 10 figures; accepted by ApJ. Modified from original version
to reflect referee's comment
The Mass of the Black Hole in the Quasar PG 2130+099
We present the results of a recent reverberation-mapping campaign undertaken
to improve measurements of the radius of the broad line region and the central
black hole mass of the quasar PG 2130+099. Cross correlation of the 5100
angstrom continuum and H-beta emission-line light curves yields a time lag of
22.9 (+4.4 - 4.3) days, corresponding to a central black hole mass MBH= 3.8
(+/- 1.5) x 10^7 Msun. This value supports the notion that previous
measurements yielded an incorrect lag. We re-analyzed previous datasets to
investigate the possible sources of the discrepancy and conclude that previous
measurement errors were apparently caused by a combination of undersampling of
the light curves and long-term secular changes in the H-beta emission-line
equivalent width. With our new measurements, PG 2130+099 is no longer an
outlier in either the R-L or the MBH-Sigma relationships.Comment: 21 pages, 7 figures; Accepted for publication in Ap
A Survey of UV Bright Sources Behind the Halo of M31
We have performed a wide-area ultraviolet (UV) imaging survey using the
GALaxy Evolution eXplorer (GALEX) to search for bright, point-like UV sources
behind M31's extended halo. Our survey consisted of 46 pointings covering an
effective area of ~50 deg^2, in both the far-UV and near-UV channels. We
combined these data with optical R-band observations acquired with the WIYN
Mosaic-1 imager on the Kitt Peak National Observatory 0.9m WIYN telescope. An
analysis of the brightness and colors of sources matched between our
photometric catalogs yielded ~100 UV-bright quasar candidates. We have obtained
discovery spectra for 76 of these targets with the Kast spectrometer on the
Lick 3m telescope and confirm 30 active galactic nuclei and quasars, 29
galaxies at z > 0.02 including several early-type systems, 16 Galactic stars
(hot main-sequence stars), and one featureless source previously identified as
a BL Lac object. Future UV spectroscopy of the brightest targets with the
Cosmic Origins Spectrograph on the Hubble Space Telescope will enable a
systematic search for diffuse gas in the extended halo of M31.Comment: 10 pages, 10 figures. Accepted to MNRA
Infrared Spectroscopy of Nearby Radio Active Elliptical Galaxies
In preparation for a study of their circumnuclear gas we have surveyed 60% of a complete sample of elliptical galaxies within 75 Mpc that are radio sources. Some 20% of our nuclear spectra have infrared emission lines, mostly Paschen lines, Brackett γ, and [Fe II]. We consider the influence of radio power and black hole mass in relation to the spectra. Access to the spectra is provided here as a community resource
Heat conduction in the disordered harmonic chain revisited
A general formulation is developed to study heat conduction in disordered
harmonic chains with arbitrary heat baths that satisfy the
fluctuation-dissipation theorem. A simple formal expression for the heat
current J is obtained, from which its asymptotic system-size (N) dependence is
extracted. It is shown that the ``thermal conductivity'' depends not just on
the system itself but also on the spectral properties of the fluctuation and
noise used to model the heat baths. As special cases of our heat baths we
recover earlier results which reported that for fixed boundaries , while for free boundaries . For other choices we
find that one can get other power laws including the ``Fourier behaviour'' .Comment: 5 pages, 3 figures, accepted for publication in Phys. Rev. Let
Disparate MgII Absorption Statistics towards Quasars and Gamma-Ray Bursts : A Possible Explanation
We examine the recent report by Prochter et al. (2006) that gamma-ray burst
(GRB) sight lines have a much higher incidence of strong MgII absorption than
quasar sight lines. We propose that the discrepancy is due to the different
beam sizes of GRBs and quasars, and that the intervening MgII systems are
clumpy with the dense part of each cloudlet of a similar size as the quasars,
i.e. < 10^16 cm, but bigger than GRBs. We also discuss observational
predictions of our proposed model. Most notably, in some cases the intervening
MgII absorbers in GRB spectra should be seen varying, and quasars with smaller
sizes should show an increased rate of strong MgII absorbers. In fact, our
prediction of variable MgII lines in the GRB spectra has been now confirmed by
Hao et al. (2007), who observed intervening FeII and MgII lines at z=1.48 to be
strongly variable in the multi-epoch spectra of z=4.05 GRB060206.Comment: 12 pages, 2 figures; substantially revised model calculation;
accepted for publication in Astrophysics & Space Science as a Lette
Turing instability in oscillator chains with non-local coupling
We investigate analytically and numerically the conditions for the Turing
instability to occur in a one-dimensional chain of nonlinear oscillators
coupled non-locally in such a way that the coupling strength decreases with the
spatial distance as a power-law. A range parameter makes possible to cover the
two limiting cases of local (nearest-neighbor) and a global (all-to-all)
couplings. We consider an example from a non-linear auto-catalytic
reaction-diffusion model
Bostonia: The Boston University Alumni Magazine. Volume 12
Founded in 1900, Bostonia magazine is Boston University’s main alumni publication
- …