12,271 research outputs found
Lessons from resurgent cities
In 2008, the Federal Reserve Bank of Boston began a project to help reinvigorate the city of Springfield, Massachusetts. This cross-departmental initiative uses the Boston Fed's research and convening capabilities to complement the efforts of other organizations dedicated to improving economic and social conditions in New England's fourth-largest city. As noted in an earlier joint Federal Reserve-Brookings Institution study, Springfield has one of the highest rates of concentrated poverty in the country: one-third of the city's poor live in neighborhoods where poverty rates exceed 40 percent. Thus, a particular focus of the Boston Fed project has been to support revitalization strategies that would enable more city residents, particularly those located in poor areas, to prosper. While the Boston Fed project focuses on the city of Springfield, we hope to devise approaches that can be replicated in other struggling mid-sized cites around New England and the nation. To this end, this essay reports on lessons learned from our research on older industrial cities that have adapted relatively well to economic challenges, and are recognized as vital communities today. We believe these "resurgent cities" provide relevant, inspiring insights on development strategies for urban America.Cities and towns ; Cities and towns - Massachusetts ; Economic conditions ; Economic conditions - Massachusetts ; Economic policy ; Economic policy - Massachusetts
The evolution of the disc variability along the hard state of the black hole transient GX 339-4
We report on the analysis of hard-state power spectral density function (PSD)
of GX 339-4 down to the soft X-ray band, where the disc significantly
contributes to the total emission. At any luminosity probed, the disc in the
hard state is intrinsically more variable than in the soft state. However, the
fast decrease of disc variability as a function of luminosity, combined with
the increase of disc intensity, causes a net drop of fractional variability at
high luminosities and low energies, which reminds the well-known behaviour of
disc-dominated energy bands in the soft state. The peak-frequency of the
high-frequency Lorentzian (likely corresponding to the high-frequency break
seen in active galactic nuclei, AGN) scales with luminosity, but we do not find
evidence for a linear scaling. In addition, we observe that this characteristic
frequency is energy-dependent. We find that the normalization of the PSD at the
peak of the high-frequency Lorentzian decreases with luminosity at all
energies, though in the soft band this trend is steeper. Together with the
frequency shift, this yields quasi-constant high frequency (5-20 Hz) fractional
rms at high energies, with less than 10 percent scatter. This reinforces
previous claims suggesting that the high frequency PSD solely scales with BH
mass. On the other hand, this constancy breaks down in the soft band (where the
scatter increases to ~30 percent). This is a consequence of the additional
contribution from the disc component, and resembles the behaviour of optical
variability in AGN.Comment: 12 pages, 8 figures, accepted for publication in MNRA
Tracing the reverberation lag in the hard state of black hole X-ray binaries
We report results obtained from a systematic analysis of X-ray lags in a
sample of black hole X-ray binaries, with the aim of assessing the presence of
reverberation lags and studying their evolution during outburst. We used
XMM-Newton and simultaneous RXTE observations to obtain broad-band energy
coverage of both the disc and the hard X-ray Comptonization components. In most
cases the detection of reverberation lags is hampered by low levels of
variability signal-to-noise ratio (e.g. typically when the source is in a soft
state) and/or short exposure times. The most detailed study was possible for GX
339-4 in the hard state, which allowed us to characterize the evolution of
X-ray lags as a function of luminosity in a single source. Over all the sampled
frequencies (~0.05-9 Hz) we observe the hard lags intrinsic to the power law
component, already well-known from previous RXTE studies. The XMM-Newton soft
X-ray response allows us to detail the disc variability. At low-frequencies
(long time scales) the disc component always leads the power law component. On
the other hand, a soft reverberation lag (ascribable to thermal reprocessing)
is always detected at high-frequencies (short time scales). The intrinsic
amplitude of the reverberation lag decreases as the source luminosity and the
disc-fraction increase. This suggests that the distance between the X-ray
source and the region of the optically-thick disc where reprocessing occurs,
gradually decreases as GX 339-4 rises in luminosity through the hard state,
possibly as a consequence of reduced disc truncation.Comment: 15 pages, 9 figures, 2 tables, accepted for publication in Ap
Tuning surface metallicity and ferromagnetism by hydrogen adsorption at the polar ZnO(0001) surface
The adsorption of hydrogen on the polar Zn-ended ZnO(0001) surface has been
investigated by density functional {\it ab-initio} calculations. An on top
H(1x1) ordered overlayer with genuine H-Zn chemical bonds is shown to be
energetically favorable. The H covered surface is metallic and spin-polarized,
with a noticeable magnetic moment at the surface region. Lower hydrogen
coverages lead to strengthening of the H-Zn bonds, corrugation of the surface
layer and to an insulating surface. Our results explain experimental
observations of hydrogen adsorption on this surface, and not only predict a
metal-insulator transition, but primarily provide a method to reversible switch
surface magnetism by varying the hydrogen density on the surface.Comment: 4 pages, 3 figure
Understanding the Observed Evolution of the Galaxy Luminosity Function from z=6-10 in the Context of Hierarchical Structure Formation
Recent observations of the Lyman-break galaxy (LBG) luminosity function (LF)
from z~6-10 show a steep decline in abundance with increasing redshift.
However, the LF is a convolution of the mass function of dark matter halos
(HMF)--which also declines sharply over this redshift range--and the
galaxy-formation physics that maps halo mass to galaxy luminosity. We consider
the strong observed evolution in the LF from z~6-10 in this context and
determine whether it can be explained solely by the behavior of the HMF. From
z~6-8, we find a residual change in the physics of galaxy formation
corresponding to a ~0.5 dex increase in the average luminosity of a halo of
fixed mass. On the other hand, our analysis of recent LF measurements at z~10
shows that the paucity of detected galaxies is consistent with almost no change
in the average luminosity at fixed halo mass from z~8. The LF slope also
constrains the variation about this mean such that the luminosity of galaxies
hosted by halos of the same mass are all within about an order-of-magnitude of
each other. We show that these results are well-described by a simple model of
galaxy formation in which cold-flow accretion is balanced by star formation and
momentum-driven outflows. If galaxy formation proceeds in halos with masses
down to 10^8 Msun, then such a model predicts that LBGs at z~10 should be able
to maintain an ionized intergalactic medium as long as the ratio of the
clumping factor to the ionizing escape fraction is C/f_esc < 10.Comment: 15 pages, 2 figures; results unchanged; accepted by JCA
Residents' perceptions of airport construction impacts: a negativity bias approach
Airports have significant implications for regional and local tourism development, so their impacts need to be assessed. Based on in-depth interviews with local residents, this study examined the effects of an airport development project in Mexico. Negativity bias theory was adopted as a theoretical framework to gain a fuller understanding of host communities’ perceptions. In accordance with this theory, even though the economic impacts of the airport’s construction are recognised as positive, its environmental and social effects on locals’ everyday lives are perceived more negatively. As a result, most locals interviewed do not support the airport project. This is because, in line with negativity bias theory, when perceived negative impacts outweigh positive ones, a holistic evaluation that integrates negative and positive events will ultimately be unfavourable. Practical implications in terms of public consultation, perceived impacts and tourism development are discussed
Low-Temperature Miniemulsion-Based Routes for Synthesis of Metal Oxides
Dedicated to Professor Gerhard Wegner on the occasion of his 80th anniversar
Fixed-Energy Sandpiles Belong Generically to Directed Percolation
Fixed-energy sandpiles with stochastic update rules are known to exhibit a
nonequilibrium phase transition from an active phase into infinitely many
absorbing states. Examples include the conserved Manna model, the conserved
lattice gas, and the conserved threshold transfer process. It is believed that
the transitions in these models belong to an autonomous universality class of
nonequilibrium phase transitions, the so-called Manna class. Contrarily, the
present numerical study of selected (1+1)-dimensional models in this class
suggests that their critical behavior converges to directed percolation after
very long time, questioning the existence of an independent Manna class.Comment: article (4 pages, 9 eps figures) + Supplement (8 pages, 9 eps
figures); Phys. Rev. Lett. 201
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