156 research outputs found
The High Cost of Free Highways
It is widely but not universally held that more roads mean more traffic. In spite of this evidence we are continually seduced by the notion that we can zone for low density to preclude traffic from occurring, that we can move far away from traffic that we can avoid it, and/or that we can build our way out of traffic. This low density race to the edge results in the ill-defined but expensive condition of sprawl. In a counter vein, New Urbanists, Advocates of Transit Oriented Development (TOD), and smart growth advocates have embraced the notion that traffic has always been with us and is here to stay, but we can make the most of our activity spaces by concentrating development, arresting the creation of new roads, and investing wisely in high capacity transportation systems
Men, Women, Job Sprawl and Journey to Work in the Philadelphia Region
The observation that increasing dispersion of employment opportunities leads to decreased travel times is reflective of a short-rem/phenomenon. Census-reported journey-to-work travel time is examined for the greater Philadelphia region, showing that more people are commuting by automobile, a mode usually associated with shorter journey times, but are reporting longer trip times. The finding is counterintuitive as it coincides with a period when new jobs were established in outlying areas and the region experienced a net loss in jobs. The study concludes that as job opportunities disperse into lower density areas, Philadelphia\u27s existing high-capacity systems are underutilized, and transportation systems throughout the region that were designed for relatively low demand are becoming overwhelmed in time. The net effect is a breakdown of both the urban mass transit systems and the suburban and rural highway networks, the latter because of overuse and the former because of underuse
BostonBRT Initiative Report
The Barr Foundation's BostonBRT initiative was convened in 2013 as part of Barr's climate program. Acknowledging that any serious efforts to address climate change must advance solutions for mobility, BostonBRT sought to determine technical feasibility of Bus Rapid Transit (BRT) in the Boston Region, and, in the event that BRT was feasible, to advance a conversation within the Greater Boston community to build regional support for BRT.In 2018, Barr hired Weinberger & Associates to conduct a systematic review of the BRT initiative. The review was to measure Barr's progress and to assess the appropriate role for the Barr Foundation as BRT implementation continues. The work was conducted by and the report authored by Weinberger & Associates.The document describes the transportation and climate crises facing Boston and the Boston region, looking closely at the impetus for the BostonBRT initiative. It then looks at the planning context for BRT projects, contrasting the US experience with apparent "overnight" successes abroad. It discusses Barr grantmaking to date and the resulting achievements of the BostonBRT initiative. It highlights some apparent challenges to BRT implementation in the Boston region and points to potential scenarios that might facilitate the goal of implementing Gold Standard BRT in Greater Boston. The concluding section summarizes the consultant's analysis and provides recommendations to the Barr Foundation on how to move the initiative forward
Linking galaxy structural properties and star formation activity to black hole activity with IllustrisTNG
We study the connection between active galactic nuclei (AGN) and their host
galaxies through cosmic time in the large-scale cosmological IllustrisTNG
simulations. We first compare BH properties, i.e. the hard X-ray BH luminosity
function, AGN galaxy occupation fraction, and distribution of Eddington ratios,
to available observational constraints. The simulations produce a population of
BHs in good agreement with observations, but we note an excess of faint AGN in
hard X-ray (L_x ~ 10^{43-44} erg/s), and a lower number of bright AGN
(L_x>10^{44} erg/s), a conclusion that varies quantitatively but not
qualitatively with BH luminosity estimation method. The lower Eddington ratios
of the 10^{9} Msun BHs compared to observations suggest that AGN feedback may
be too efficient in this regime. We study galaxy star formation activity and
structural properties, and design sample-dependent criteria to identify
different galaxy types (star-forming/quiescent, extended/compact) that we apply
both to the simulations and observations from the candels fields. We analyze
how the simulated and observed galaxies populate the specific star formation
rate - stellar mass surface density diagram. A large fraction of the z=0
M_{star}>10^{11} Msun quiescent galaxies first experienced a compaction phase
(i.e. reduction of galaxy size) while still forming stars, and then a quenching
event. We measure the dependence of AGN fraction on galaxies' locations in this
diagram. After correcting the simulations with a redshift and AGN
luminosity-dependent model for AGN obscuration, we find good qualitative and
quantitative agreement with observations. The AGN fraction is the highest among
compact star-forming galaxies (16-20% at z~1.5-2), and the lowest among compact
quiescent galaxies (6-10% at z~1.5-2).Comment: 35 pages, 22 figures, accepted for publication in MNRA
The relationship between black hole mass and galaxy properties: Examining the black hole feedback model in IllustrisTNG
Supermassive black hole feedback is thought to be responsible for the lack of
star formation, or quiescence, in a significant fraction of galaxies. We
explore how observable correlations between the specific star formation rate
(sSFR), stellar mass (M), and black hole mass (M) are
sensitive to the physics of black hole feedback in a galaxy formation model. We
use the IllustrisTNG simulation suite, specifically the TNG100 simulation and
ten model variations that alter the parameters of the black hole model.
Focusing on central galaxies at with M
M, we find that the sSFR of galaxies in IllustrisTNG decreases once
the energy from black hole kinetic winds at low accretion rates becomes larger
than the gravitational binding energy of gas within the galaxy stellar radius.
This occurs at a particular M threshold above which galaxies are
found to sharply transition from being mostly star-forming to mostly quiescent.
As a result of this behavior, the fraction of quiescent galaxies as a function
of M is sensitive to both the normalization of the
M-M relation and the M threshold for
quiescence in IllustrisTNG. Finally, we compare these model results to
observations of 91 central galaxies with dynamical M measurements
with the caveat that this sample is not representative of the whole galaxy
population. While IllustrisTNG reproduces the observed trend that quiescent
galaxies host more massive black holes, the observations exhibit a broader
scatter in M at a given M and show a smoother decline
in sSFR with M.Comment: 20 pages, submitted to MNRA
Simulations of black hole fueling in isolated and merging galaxies with an explicit, multiphase ISM
We study gas inflows onto supermassive black holes using hydrodynamics
simulations of isolated galaxies and idealized galaxy mergers with an explicit,
multiphase interstellar medium (ISM). Our simulations use the recently
developed ISM and stellar evolution model called Stars and MUltiphase Gas in
GaLaxiEs (SMUGGLE). We implement a novel super-Lagrangian refinement scheme
that increases the gas mass resolution in the immediate neighborhood of the
black holes (BHs) to accurately resolve gas accretion. We do not include black
hole feedback in our simulations. We find that the complex and turbulent nature
of the SMUGGLE ISM leads to highly variable BH accretion. BH growth in SMUGGLE
converges at gas mass resolutions . We show
that the low resolution simulations combined with the super-Lagrangian
refinement scheme are able to produce central gas dynamics and BH accretion
rates very similar to that of the uniform high resolution simulations. We
further explore BH fueling by simulating galaxy mergers. The interaction
between the galaxies causes an inflow of gas towards the galactic centres and
results in elevated and bursty star formation. The peak gas densities near the
BHs increase by orders of magnitude resulting in enhanced accretion. Our
results support the idea that galaxy mergers can trigger AGN activity, although
the instantaneous accretion rate depends strongly on the local ISM. We also
show that the level of merger-induced enhancement of BH fueling predicted by
the SMUGGLE model is much smaller compared to the predictions by simulations
using an effective equation of state model of the ISM.Comment: 16 pages, 10 figure
Did people really drink bleach to prevent COVID-19? A guide for protecting survey data against problematic respondents
Survey respondents who are non-attentive, respond randomly, or misrepresent who they are can impact the outcomes of surveys. Prior findings reported by the CDC have suggested that people engaged in highly dangerous cleaning practices during the COVID-19 pandemic, including ingesting household cleaners such as bleach. In our attempts to replicate the CDC’s results, we found that 100% of reported ingestion of household cleaners are made by problematic respondents. Once inattentive, acquiescent, and careless respondents are removed from the sample, we find no evidence that people ingested cleaning products to prevent a COVID-19 infection. These findings have important implications for public health and medical survey research, as well as for best practices for avoiding problematic respondents in all survey research conducted online
Spatially resolved star formation and inside-out quenching in the TNG50 simulation and 3D-HST observations
We compare the star-forming main sequence (SFMS) of galaxies – both integrated and resolved on 1 kpc scales – between the high-resolution TNG50 simulation of IllustrisTNG and observations from the 3D-HST slitless spectroscopic survey at z ∼ 1. Contrasting integrated star formation rates (SFRs), we find that the slope and normalization of the star-forming main sequence in TNG50 are quantitatively consistent with values derived by fitting observations from 3D-HST with the Prospector Bayesian inference framework. The previous offsets of 0.2–1 dex between observed and simulated main-sequence normalizations are resolved when using the updated masses and SFRs from Prospector. The scatter is generically smaller in TNG50 than in 3D-HST for more massive galaxies with M*> 1010 M⊙, by ∼10–40 per cent, after accounting for observational uncertainties. When comparing resolved star formation, we also find good agreement between TNG50 and 3D-HST: average specific star formation rate (sSFR) radial profiles of galaxies at all masses and radii below, on, and above the SFMS are similar in both normalization and shape. Most noteworthy, massive galaxies with M*> 1010.5 M⊙, which have fallen below the SFMS due to ongoing quenching, exhibit a clear central SFR suppression, in both TNG50 and 3D-HST. In contrast, the original Illustris simulation and a variant TNG run without black hole kinetic wind feedback, do not reproduce the central SFR profile suppression seen in data. In TNG, inside-out quenching is due to the supermassive black hole (SMBH) feedback model operating at low accretion rates
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