131 research outputs found
Recommended from our members
Can Institutions Build Unity in Multiethnic States?
We investigate whether political institutions can promote attachment to the state in multiethnic
societies. Building on literatures on nationalism, democratization, and conflict resolution, we discuss the importance of attachment, understood as a psychological identification with, and pride in, the state. We construct a model of state attachment, specifying the individual-, group-, and state-level conditions that foster it. Then, using cross-national survey data from 51 multiethnic states, we show that, in general, ethnic minorities manifest less attachment to the states in which they reside than
do majorities. Combining the survey data with minority group attributes and country-level attributes,
we show that the attachment of minorities varies importantly across groups and countries. Our central
finding is that federalism and proportional electoral systems—–two highly touted solutions to ethnic
divisions—–have at best mixed effects. These results have implications for state-building and democratic
consolidation in ethnically heterogeneous states.Governmen
Racing Apart Partisan Shifts on Racial Attitudes Over the Last Decade
This report examines the ways Democrat and Republic voter attitudes toward race and related issues including inequality, the Black Lives Matter movement, and Immigration among others have changed over the past decade. The authors base their findings on analysis of two survey projects: one that has tracked over 3,300 Americans over almost 10 years and another that interviewed 500,000 Americans between July 2019 and February 2021.
Intercultural Interaction in architectural education
Fourteen case studies on architectural education - Intercultural Interactions is a theme that began within SCHOSA (The Standing Conference of Heads of Schools of Architecture) whilst Robert Mull was chair between 2008 and 2010. The theme and publication were then developed with the support of CEBE (The Centre for Education in the Built Environment) and the ASD Projects office at London Metropolitan University
Direct observation of active material concentration gradients and crystallinity breakdown in LiFePO4 electrodes during charge/discharge cycling of lithium batteries
The phase changes that occur during discharge of an electrode comprised of LiFePO4, carbon, and PTFE binder have been studied in lithium half cells by using X-ray diffraction measurements in reflection geometry. Differences in the state of charge between the front and the back of LiFePO4 electrodes have been visualized. By modifying the X-ray incident angle the depth of penetration of the X-ray beam into the electrode was altered, allowing for the examination of any concentration gradients that were present within the electrode. At high rates of discharge the electrode side facing the current collector underwent limited lithium insertion while the electrode as a whole underwent greater than 50% of discharge. This behavior is consistent with depletion at high rate of the lithium content of the electrolyte contained in the electrode pores. Increases in the diffraction peak widths indicated a breakdown of crystallinity within the active material during cycling even during the relatively short duration of these experiments, which can also be linked to cycling at high rate
How Quickly We Forget: The Duration of Persuasion Effects From Mass Communication
Scholars do not usually test for the duration of the effects of mass communication, but when they do, they typically find rapid decay. Persuasive impact may end almost as soon as communication ends. Why so much decay? Does mass communication produce any long-term effects? How should this decay color our understanding of the effects of mass communication? We examine these questions with data from the effects of advertising in the 2000 presidential election and 2006 subnational elections, but argue that our model and results are broadly applicable within the field of political communication. We find that the bulk of the persuasive impact of advertising decays quickly, but that some effect in the presidential campaign endures for at least 6 weeks. These results, which are similar in rolling cross-section survey data and county-level data on actual presidential vote, appear to reflect a mix of memory-based processing (whose effects last only as long as short-term memory lasts) and online processing (whose effects are more durable). Finally, we find that immediate effects of advertising are larger in subnational than presidential elections, but decay more quickly and more completely. [Supplementary material is available for this article. Go to the publisher's online edition of Political Communication for the following free supplemental resource(s): discussion of methodological issues; results for a alternative specifications of key models; full reports of model results.]. © 2013 Copyright Taylor & Francis Group, LLC
Detection of Cosmic Structures using the Bispectrum Phase. II. First Results from Application to Cosmic Reionization Using the Hydrogen Epoch of Reionization Array
Characterizing the epoch of reionization (EoR) at via the
redshifted 21 cm line of neutral Hydrogen (HI) is critical to modern
astrophysics and cosmology, and thus a key science goal of many current and
planned low-frequency radio telescopes. The primary challenge to detecting this
signal is the overwhelmingly bright foreground emission at these frequencies,
placing stringent requirements on the knowledge of the instruments and
inaccuracies in analyses. Results from these experiments have largely been
limited not by thermal sensitivity but by systematics, particularly caused by
the inability to calibrate the instrument to high accuracy. The interferometric
bispectrum phase is immune to antenna-based calibration and errors therein, and
presents an independent alternative to detect the EoR HI fluctuations while
largely avoiding calibration systematics. Here, we provide a demonstration of
this technique on a subset of data from the Hydrogen Epoch of Reionization
Array (HERA) to place approximate constraints on the brightness temperature of
the intergalactic medium (IGM). From this limited data, at we infer
"" upper limits on the IGM brightness temperature to be
"pseudo" mK at "pseudo" Mpc (data-limited)
and "pseudo" mK at "pseudo" Mpc
(noise-limited). The "pseudo" units denote only an approximate and not an exact
correspondence to the actual distance scales and brightness temperatures. By
propagating models in parallel to the data analysis, we confirm that the
dynamic range required to separate the cosmic HI signal from the foregrounds is
similar to that in standard approaches, and the power spectrum of the
bispectrum phase is still data-limited (at dynamic range)
indicating scope for further improvement in sensitivity as the array build-out
continues.Comment: 22 pages, 12 figures (including sub-figures). Published in PhRvD.
Abstract may be slightly abridged compared to the actual manuscript due to
length limitations on arXi
What does an interferometer really measure? Including instrument and data characteristics in the reconstruction of the 21cm power spectrum
Combining the visibilities measured by an interferometer to form a
cosmological power spectrum is a complicated process in which the window
functions play a crucial role. In a delay-based analysis, the mapping between
instrumental space, made of per-baseline delay spectra, and cosmological space
is not a one-to-one relation. Instead, neighbouring modes contribute to the
power measured at one point, with their respective contributions encoded in the
window functions. To better understand the power spectrum measured by an
interferometer, we assess the impact of instrument characteristics and analysis
choices on the estimator by deriving its exact window functions, outside of the
delay approximation. Focusing on HERA as a case study, we find that
observations made with long baselines tend to correspond to enhanced low-k
tails of the window functions, which facilitate foreground leakage outside the
wedge, whilst the choice of bandwidth and frequency taper can help narrow them
down. With the help of simple test cases and more realistic visibility
simulations, we show that, apart from tracing mode mixing, the window functions
can accurately reconstruct the power spectrum estimator of simulated
visibilities. We note that the window functions depend strongly on the
chromaticity of the beam, and less on its spatial structure - a Gaussian
approximation, ignoring side lobes, is sufficient. Finally, we investigate the
potential of asymmetric window functions, down-weighting the contribution of
low-k power to avoid foreground leakage. The window functions presented in this
work correspond to the latest HERA upper limits for the full Phase I data. They
allow an accurate reconstruction of the power spectrum measured by the
instrument and can be used in future analyses to confront theoretical models
and data directly in cylindrical space.Comment: 18 pages, 18 figures, submitted to MNRAS. Comments welcome
Characterization Of Inpaint Residuals In Interferometric Measurements of the Epoch Of Reionization
Radio Frequency Interference (RFI) is one of the systematic challenges
preventing 21cm interferometric instruments from detecting the Epoch of
Reionization. To mitigate the effects of RFI on data analysis pipelines,
numerous inpaint techniques have been developed to restore RFI corrupted data.
We examine the qualitative and quantitative errors introduced into the
visibilities and power spectrum due to inpainting. We perform our analysis on
simulated data as well as real data from the Hydrogen Epoch of Reionization
Array (HERA) Phase 1 upper limits. We also introduce a convolutional neural
network that capable of inpainting RFI corrupted data in interferometric
instruments. We train our network on simulated data and show that our network
is capable at inpainting real data without requiring to be retrained. We find
that techniques that incorporate high wavenumbers in delay space in their
modeling are best suited for inpainting over narrowband RFI. We also show that
with our fiducial parameters Discrete Prolate Spheroidal Sequences (DPSS) and
CLEAN provide the best performance for intermittent ``narrowband'' RFI while
Gaussian Progress Regression (GPR) and Least Squares Spectral Analysis (LSSA)
provide the best performance for larger RFI gaps. However we caution that these
qualitative conclusions are sensitive to the chosen hyperparameters of each
inpainting technique. We find these results to be consistent in both simulated
and real visibilities. We show that all inpainting techniques reliably
reproduce foreground dominated modes in the power spectrum. Since the
inpainting techniques should not be capable of reproducing noise realizations,
we find that the largest errors occur in the noise dominated delay modes. We
show that in the future, as the noise level of the data comes down, CLEAN and
DPSS are most capable of reproducing the fine frequency structure in the
visibilities of HERA data.Comment: 26 pages, 18 figure
Direct Optimal Mapping Image Power Spectrum and its Window Functions
The key to detecting neutral hydrogen during the epoch of reionization (EoR)
is to separate the cosmological signal from the dominating foreground
radiation. We developed direct optimal mapping (Xu et al. 2022) to map
interferometric visibilities; it contains only linear operations, with full
knowledge of point spread functions from visibilities to images. Here we
present an FFT-based image power spectrum and its window functions based on
direct optimal mapping. We use noiseless simulation, based on the Hydrogen
Epoch of Reionization Array (HERA) Phase I configuration, to study the image
power spectrum properties. The window functions show power leakage
from the foreground-dominated region into the EoR window; the 2D and 1D power
spectra also verify the separation between the foregrounds and the EoR.
Furthermore, we simulated visibilities from a -complete array and
calculated its image power spectrum. The result shows that the foreground--EoR
leakage is further suppressed below , dominated by the tapering
function sidelobes; the 2D power spectrum does not show signs of the horizon
wedge. The -complete result provides a reference case for future 21cm
cosmology array designs.Comment: Submitted to Ap
Direct Optimal Mapping for 21cm Cosmology: A Demonstration with the Hydrogen Epoch of Reionization Array
Motivated by the desire for wide-field images with well-defined statistical
properties for 21cm cosmology, we implement an optimal mapping pipeline that
computes a maximum likelihood estimator for the sky using the interferometric
measurement equation. We demonstrate this direct optimal mapping with data from
the Hydrogen Epoch of Reionization (HERA) Phase I observations. After
validating the pipeline with simulated data, we develop a maximum likelihood
figure-of-merit for comparing four sky models at 166MHz with a bandwidth of
100kHz. The HERA data agree with the GLEAM catalogs to <10%. After subtracting
the GLEAM point sources, the HERA data discriminate between the different
continuum sky models, providing most support for the model of Byrne et al.
2021. We report the computation cost for mapping the HERA Phase I data and
project the computation for the HERA 320-antenna data; both are feasible with a
modern server. The algorithm is broadly applicable to other interferometers and
is valid for wide-field and non-coplanar arrays.Comment: 16 pages, 10 figures, 2 tables, published on Ap
- …