3,932 research outputs found
W-graph ideals
We introduce a concept of a W-graph ideal in a Coxeter group. The main goal
of this paper is to describe how to construct a W-graph from a given W-graph
ideal. The principal application of this idea is in type A, where it provides
an algorithm for the construction of W-graphs for Specht modules.Comment: 25 page
The Military Career of James Gettys
James Gettys was a Federalist, tried and true. From his role in the American Revolution to his final position as Vice Brigadier General during the War of 1812, James understood the necessity for “we the people” to remain united as one, power in numbers. He lived that way, worked that way, and built his town on that premise. Like most of the frontiersmen of his time, his life was difficult, and his rise to the top was not always met with valor. Much like his father, Samuel, James Gettys fought for everything he had, and his attainments were well earned. Until recently, discussion of James Gettys’ military career began with his 1781 role as a Cornet in a Light Horsemen of York County. While any role in the Revolutionary War was beneficial, his appeared fairly insignificant, as a Cornet was a lower ranked officer, and Gettys’ unit was never activated.1 Seemingly odd given his numerous promotions within the militia, James appeared to witness the fighting safely on the sidelines. New research, however, reveals, that this version of events is not entirely accurate. This article reviews that new evidence and narrates the postwar Revolutionary War life of Gettysburg’s founding father
Cosmology with Peculiar Velocities: Observational Effects
In this paper we investigate how observational effects could possibly bias
cosmological inferences from peculiar velocity measurements. Specifically, we
look at how bulk flow measurements are compared with theoretical predictions.
Usually bulk flow calculations try to approximate the flow that would occur in
a sphere around the observer. Using the Horizon Run 2 simulation we show that
the traditional methods for bulk flow estimation can overestimate the magnitude
of the bulk flow for two reasons: when the survey geometry is not spherical
(the data do not cover the whole sky), and when the observations undersample
the velocity distributions. Our results may explain why several bulk flow
measurements found bulk flow velocities that seem larger than those expected in
standard {\Lambda}CDM cosmologies. We recommend a different approach when
comparing bulk flows to cosmological models, in which the theoretical
prediction for each bulk flow measurement is calculated specifically for the
geometry and sampling rate of that survey. This means that bulk flow values
will not be comparable between surveys, but instead they are comparable with
cosmological models, which is the more important measure.Comment: 11 pages, 5 figures. Accepted for publication in MNRA
The Achilles Heel of Governance: Critical Capacity Deficits and Their Role in Governance Failures
10.2139/ssrn.24231661-2
Enhancing Policy Capacity for Better Policy Integration: Achieving the Sustainable Development Goals in a Post COVID-19 World
The adoption of the Sustainable Development Goals (SDGs) by the UN, in 2015, established a clear global mandate for greater integrated policymaking, but there has been little consensus on how to achieve them. The COVID-19 pandemic amplified the role of policy capacity in mounting this kind of integrated policy response; however, the relationship between pre- and post-pandemic SDG efforts remains largely unexplored. In this article, we seek to address this gap through a conceptual analysis of policy integration and the capacities necessary for its application to the current SDG situation. Building on the literature on policy design, we define policy integration as the process of effectively reconciling policy goals and policy instruments and we offer a typology of policy integration efforts based on the degree of goal and instrument consistency including: policy harmonization, mainstreaming, coordination, and institutionalization. These forms of policy integration dictate the types of strategies that governments need to adopt in order to arrive at a more coherent policy mix. Following the dimensions of policy capacity by Wu et al. (2015), policy capacities are identified that are critical to ensuring successful integration. This information, thus, contributes to both academic- and policy-related debates on policy integration, by advancing conceptual clarity on the different, and sometimes, diverging concepts used in the field
Standard siren speeds: improving velocities in gravitational-wave measurements of H0
We re-analyse data from the gravitational-wave event GW170817 and its host galaxy NGC 4993 to demonstrate the importance of accurate total and peculiar velocities when measuring the Hubble constant using this nearby standard siren. We show that a number of reasonable choices can be made to estimate the velocities for this event, but that systematic differences remain between these measurements depending on the data used. This leads to significant changes in the Hubble constant inferred from GW170817. We present Bayesian model averaging as one way to account for these differences, and obtain H-0 = 66.8(-9.2)(+13.4) km s(-1)Mpc(-1). Adding additional information on the viewing angle from high-resolution imaging of the radio counterpart refines this to H-0 = 64.8(-7.2)(+7.3) km s(-1) Mpc(-1). During this analysis, we also present an alternative Bayesian model for the posterior on H-0 from standard sirens that works more closely with observed quantities from redshift and peculiar velocity surveys. Our results more accurately capture the true uncertainty on the total and peculiar velocities of NGC 4993 and show that exploring how well different data sets characterize galaxy groups and the velocity field in the local Universe could improve this measurement further. These considerations impact any low-redshift distance measurement, and the improvements we suggest here can also be applied to standard candles like Type Ia supernovae. GW170817 is particularly sensitive to peculiar velocity uncertainties because it is so close. For future standard siren measurements, the importance of this error will decrease as (i) we will measure more distant standard sirens and (ii) the random direction of peculiar velocities will average out with more detections
Evaluating bulk flow estimators for CosmicFlows-4 measurements
For over a decade there have been contradictory claims in the literature
about whether the local bulk flow motion of galaxies is consistent or in
tension with the CDM model. While it has become evident that
systematics affect bulk flow measurements, systematics in the estimators have
not been widely investigated. In this work, we thoroughly evaluate the
performance of four estimator variants, including the Kaiser maximum likelihood
estimator (MLE) and the minimum variance estimator (MVE). We find that these
estimators are unbiased, however their precision may be strongly correlated
with the survey geometry. Small biases in the estimators can be present leading
to underestimated bulk flows, which we suspect are due to the presence of
non-linear peculiar velocities. The uncertainty assigned to the bulk flows from
these estimators is typically underestimated, which leads to an overestimate of
the tension with CDM. We estimate the bulk flow for the CosmicFlows-4
data and use mocks to ensure the uncertainties are appropriately accounted for.
Using the MLE we find a bulk flow amplitude of
at a depth of , in reasonable agreement with
CDM. However using the MVE which can probe greater effective depths,
we find an amplitude of at a depth of , in tension with the model, having only a 0.11%
probability of obtaining a larger . These measurements appear directed
towards the Great Attractor region where more data may be needed to resolve
tensions
Can Einstein (rings) surf Gravitational Waves?
How does the appearance of a strongly lensed system change if a gravitational
wave is produced by the lens? In this work we address this question by
considering a supermassive black hole binary at the center of the lens emitting
gravitational waves propagating either colinearly or orthogonally to the line
of sight. Specializing to an Einstein ring configuration (where the source, the
lens and the observer are aligned), we show that the gravitational wave induces
changes on the ring's angular size and on the optical path of photons. The
changes are the same for a given pair of antipodal points on the ring, but
maximally different for any pair separated by . For realistic
lenses and binaries, we find that the change in the angular size of the
Einstein ring is dozens of orders of magnitude smaller than the precision of
current experiments. On the other hand, the difference in the optical path
induced on a photon by a gravitational wave propagating \textit{orthogonally}
to the line of sight triggers, at peak strain, time delays in the range seconds, making the chance of their detection (and thus the use of
Einstein rings as gravitational wave detectors) less hopeless.Comment: v2. Version accepted for publication in the Open Journal of
Astrophysics. 8 pages, four figures. Comments are welcome
- …