2,186 research outputs found
Matching structure and bargaining outcomes in buyer–seller networks
We examine the relationship between the matching structure of a bipartite (buyer-seller) network and the (expected) shares of the unit surplus that each connected pair in this network can create. We show that in different bargaining environments, these shares are closely related to the Gallai-Edmonds Structure Theorem. This theorem characterizes the structure of maximum matchings in an undirected graph. We show that the relationship between the (expected) shares and the tructure Theorem is not an artefact of a particular bargaining mechanism or trade centralization. However, this relationship does not necessarily generalize to non-bipartite networks or to networks with heterogeneous link values
Fine-Structure FeII* Emission and Resonant MgII Emission in z = 1 Star-Forming Galaxies
We present a study of the prevalence, strength, and kinematics of ultraviolet
FeII and MgII emission lines in 212 star-forming galaxies at z = 1 selected
from the DEEP2 survey. We find FeII* emission in composite spectra assembled on
the basis of different galaxy properties, indicating that FeII* emission is
prevalent at z = 1. In these composites, FeII* emission is observed at roughly
the systemic velocity. At z = 1, we find that the strength of FeII* emission is
most strongly modulated by dust attenuation, and is additionally correlated
with redshift, star-formation rate, and [OII] equivalent width, such that
systems at higher redshifts with lower dust levels, lower star-formation rates,
and larger [OII] equivalent widths show stronger FeII* emission. We detect MgII
emission in at least 15% of the individual spectra and we find that objects
showing stronger MgII emission have higher specific star-formation rates,
smaller [OII] linewidths, larger [OII] equivalent widths, lower dust
attenuations, and lower stellar masses than the sample as a whole. MgII
emission strength exhibits the strongest correlation with specific
star-formation rate, although we find evidence that dust attenuation and
stellar mass also play roles in the regulation of MgII emission. Future
integral field unit observations of the spatial extent of FeII* and MgII
emission in galaxies with high specific star-formation rates, low dust
attenuations, and low stellar masses will be important for probing the
morphology of circumgalactic gas.Comment: 29 pages, 22 figures, 2 tables; accepted to Ap
The Origin of [O II] Emission in Recently Quenched Active Galaxy Nucleus Hosts
We have employed emission-line diagnostics derived from DEIMOS and NIRSPEC spectroscopy to determine the origin of the [O II] emission line observed in six active galactic nucleus (AGN) hosts at z ~ 0.9. These galaxies are a subsample of AGN hosts detected in the Cl1604 supercluster that exhibit strong Balmer absorption lines in their spectra and appear to be in a post-starburst or post-quenched phase, if not for their [O II] emission. Examining the flux ratio of the [N II] to Hα lines, we find that in five of the six hosts the dominant source of ionizing flux is AGN continuum emission. Furthermore, we find that four of the six galaxies have over twice the [O II] line luminosity that could be generated by star formation alone given their Hα line luminosities. This strongly suggests that AGN-excited narrow-line emission is contaminating the [O II] line flux. A comparison of star formation rates calculated from extinction-corrected [O II] and Hα line luminosities indicates that the former yields a five-fold overestimate of the current activity in these galaxies. Our findings reveal the [O II] line to be a poor indicator of star formation activity in a majority of these moderate-luminosity Seyferts. This result bolsters our previous findings that an increased fraction of AGN at high redshifts is hosted by galaxies in a post-starburst phase. The relatively high fraction of AGN hosts in the Cl1604 supercluster that show signs of recently truncated star formation activity may suggest that AGN feedback plays an increasingly important role in suppressing ongoing activity in large-scale structures at high redshift
The Keck Lyman Continuum Spectroscopic Survey (KLCS): The Emergent Ionizing Spectrum of Galaxies at
We present results of a deep spectroscopic survey designed to quantify the
statistics of the escape of ionizing photons from star-forming galaxies at z~3.
We measure the ratio of ionizing to non-ionizing UV flux density
_obs, where f900 is the mean flux density evaluated over the range
[880,910] A. We quantify the emergent ratio of ionizing to non-ionizing UV flux
density by analyzing high-S/N composite spectra formed from sub-samples with
common observed properties and numbers sufficient to reduce the statistical
uncertainty in the modeled IGM+CGM correction to obtain precise values of
_out, including a full-sample average
_out=. We further show that _out
increases monotonically with Ly rest equivalent width, inducing an
inverse correlation with UV luminosity as a by-product. We fit the composite
spectra using stellar spectral synthesis together with models of the ISM in
which a fraction f_c of the stellar continuum is covered by gas with column
density N(HI). We show that the composite spectra simultaneously constrain the
intrinsic properties of the stars (L900/L1500)_int along with f_c, N(HI),
E(B-V), and , the absolute escape fraction of ionizing photons. We
find a sample-averaged , and that subsamples fall
along a linear relation . We use the FUV luminosity function, the distribution function
, and the relationship between and
_out to estimate the total ionizing emissivity of
star-forming galaxies with Muv < -19.5:
ergs/s/Hz/Mpc, exceeding the contribution of QSOs by a factor of ,
and accounting for % of the total at
estimated using indirect methods.Comment: 45 pages, 31 figures, ApJ, in pres
Community repair: how does attending pop-up repair events impact on individuals' understanding and behaviour toward repair?
The Restart Project is a community-based repair initiative which seeks to extend the lifetime of, and reduce the waste from, electrical and electronic devices, thus reducing carbon emissions and enabling
sustainable resource consumption. It does so by various means of community engagement. Research reported here focuses on their pop-up repair events, or ‘Restart Parties’.
An initial survey was conducted with 99 of 316 individuals who attended Restart Parties across London
between September and November 2016. This research explored environmental and repair-related topics and sought to establish the reasons why people attend Restart Parties. It was presented in a
report published in March 2017. The current report presents the findings of a follow-up survey which sought to establish if Restart Party attendance had:
● Increased engagement in repair activities
● Fostered new knowledge and skills
● Changed respondents’ attitudes and/or behaviour towards repair and obtaining electrical and electronic devices.
The research also examined respondents’ understanding of the broader issues around repair and how The Restart Project contributes to tackling them. The survey approached 74 of the previous 99 respondents and obtained 25 responses. Whilst this small sample size should be noted, the results show that:
● The majority of respondents (60%) had taken environmentally-responsible action with their
device since the events, such as continued use of the device or recycling it, but some stored
it (16%) or “threw it away” (8%)
● Three-quarters (75%) of respondents were more likely to “attend a community repair event”
● A small majority (56%) of respondents were more likely to attempt repairs at home
● Nearly a third of respondents were more likely to ‘‘volunteer at a community repair event’’
(30%), a higher proportion than those less likely to do so (22%)
● A small proportion of respondents (12%) had volunteered at a subsequent repair event
● Equal proportions of respondents were more likely to use a commercial repairer (39%) as
those less likely to do so (39%)
● Respondents gained a variety of knowledge and skills, including laptop servicing skills, device disassembly, how to locate repair manuals, and how to recycle devices
● Some respondents also reported that attendance at Restart Parties improved their
confidence to undertake repairs on their own
● Priorities when buying items have changed, although the average importance placed on
environmentally-responsible considerations has not
● There was little change in the order of actions taken by respondents when a device breaks
● Respondents did not have a full understanding of The Restart Project’s aims.
In summary, the results showed that respondents were more able to repair items and to dispose of those beyond repair responsibly. However, this ability is not consistently put into action. The priorities when buying items, the order of actions taken when a device breaks and recycling rates could be improved, whilst the rate at which items are stored could be decreased. Future work could focus on achieving sustained behaviour change
The Hubble Constant
Considerable progress has been made in determining the Hubble constant over
the past two decades. We discuss the cosmological context and importance of an
accurate measurement of the Hubble constant, and focus on six high-precision
distance-determination methods: Cepheids, tip of the red giant branch, maser
galaxies, surface brightness fluctuations, the Tully-Fisher relation and Type
Ia supernovae. We discuss in detail known systematic errors in the measurement
of galaxy distances and how to minimize them. Our best current estimate of the
Hubble constant is 73 +/-2 (random) +/-4 (systematic) km/s/Mpc. The importance
of improved accuracy in the Hubble constant will increase over the next decade
with new missions and experiments designed to increase the precision in other
cosmological parameters. We outline the steps that will be required to deliver
a value of the Hubble constant to 2% systematic uncertainty and discuss the
constraints on other cosmological parameters that will then be possible with
such accuracy.Comment: To be published in Annual Reviews of Astronomy and Astrophysics, Vol.
48, 2010, consisting of 79 pages, 13 figures, 2 table
A Candidate Brightest Proto-Cluster Galaxy at z = 3.03
We report the discovery of a very bright (m_R = 22.2) Lyman break galaxy at z
= 3.03 that appears to be a massive system in a late stage of merging. Deep
imaging reveals multiple peaks in the brightness profile with angular
separations of ~0.''8 (~25 h^-1 kpc comoving). In addition, high
signal-to-noise ratio rest-frame UV spectroscopy shows evidence for ~5
components based on stellar photospheric and ISM absorption lines with a
velocity dispersion of sigma ~460 km s^-1 for the three strongest components.
Both the dynamics and high luminosity, as well as our analysis of a LCDM
numerical simulation, suggest a very massive system with halo mass M ~ 10^13
M_solar. The simulation finds that all halos at z = 3 of this mass contain
sub-halos in agreement with the properties of these observed components and
that such systems typically evolve into M ~ 10^14 M_solar halos in groups and
clusters by z = 0. This discovery provides a rare opportunity to study the
properties and individual components of z ~ 3 systems that are likely to be the
progenitors to brightest cluster galaxies.Comment: 14 pages, 3 figures, submitted to ApJ Letter
Adaptive Regret Minimization in Bounded-Memory Games
Online learning algorithms that minimize regret provide strong guarantees in
situations that involve repeatedly making decisions in an uncertain
environment, e.g. a driver deciding what route to drive to work every day.
While regret minimization has been extensively studied in repeated games, we
study regret minimization for a richer class of games called bounded memory
games. In each round of a two-player bounded memory-m game, both players
simultaneously play an action, observe an outcome and receive a reward. The
reward may depend on the last m outcomes as well as the actions of the players
in the current round. The standard notion of regret for repeated games is no
longer suitable because actions and rewards can depend on the history of play.
To account for this generality, we introduce the notion of k-adaptive regret,
which compares the reward obtained by playing actions prescribed by the
algorithm against a hypothetical k-adaptive adversary with the reward obtained
by the best expert in hindsight against the same adversary. Roughly, a
hypothetical k-adaptive adversary adapts her strategy to the defender's actions
exactly as the real adversary would within each window of k rounds. Our
definition is parametrized by a set of experts, which can include both fixed
and adaptive defender strategies.
We investigate the inherent complexity of and design algorithms for adaptive
regret minimization in bounded memory games of perfect and imperfect
information. We prove a hardness result showing that, with imperfect
information, any k-adaptive regret minimizing algorithm (with fixed strategies
as experts) must be inefficient unless NP=RP even when playing against an
oblivious adversary. In contrast, for bounded memory games of perfect and
imperfect information we present approximate 0-adaptive regret minimization
algorithms against an oblivious adversary running in time n^{O(1)}.Comment: Full Version. GameSec 2013 (Invited Paper
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