192 research outputs found
The Positive Impacts of Service Dogs on Individuals with Disabilities
This poster presentation examines multiple research studies justifying beneficial effects of service dogs on persons with physical and mental disabilities. To better understand the positive effects of service dogs and their capabilities, a comprehensive literature review was conducted to recount firsthand validation where their assistance has been valuable to these individuals. With over fifty million people in the United States currently living with a disability and that number rapidly increasing, the need for assistance with daily tasks can be achieved with the intervention of a service dog (Iezzoni, 2011). Existing research supports the benefits of service dogs for individuals with a disability. To further investigate this topic and the significant impact that service dogs have on the life and welfare of those with a disability, a survey will be conducted to evaluate the impact of service dogs on persons with disabilities in Iowa
1/2-Anyons in small atomic Bose-Einstein condensates
We discuss a way of creating, manipulating and detecting anyons in rotating
Bose-Einstein condensates consisting of a small number of atoms . By achieving
a quasidegeneracy in the atomic motional states we drive the system into a
1/2--Laughlin state for fractional quantum Hall bosons. Localized
1/2--quasiholes can be created by focusing lasers at the desired positions. We
show how to manipulate these quasiholes in order to probe directly their
1/2--statistics.Comment: 4 pages, 3 figure
Behavioral Health in Rural America: Understanding Citizen Perceptions and Willingness to Respond to Community Needs
Amid nationwide efforts to address behavioral health needs, rural communities often face unique challenges and a lack of resources. This study presents a bottom-up approach used by one rural community in the Midwest to respond to their needs regarding mental health and substance use. A survey instrument was developed from interviews with community stakeholders and disseminated in both online and paper formats. The survey sought to understand citizen perspectives regarding quality of life, barriers to treatment, and willingness to engage in efforts to address the community’s needs. Data from 1,303 respondents (71.5% women, 54.7% income \u3c$42,000) were analyzed using descriptive statistics and chi-square analyses. Results indicate that cost of treatment, shame, and lack of privacy were a barrier for most citizens’ treatment-seeking behavior. In addition, many citizens were willing to engage in strategies to address the community’s needs, including increased county spending, forming a neighborhood watch, and donating money. Differences associated with gender and income emerged across perceptions and willingness to support efforts. Implications for community efforts are discussed
Structural Controls on Shallow Cenozoic Fluid Flow in the Otago Schist, New Zealand
The Otago Schist in the South Island of New Zealand represents an exhumed Mesozoic accretionary prism. Two coastal areas (Akatore Creek and Bruce Rocks) south of Dunedin preserve structural and geochemical evidence for the development of postmetamorphic hydrothermal systems that involved widespread fluid-rock reaction at shallow crustal depths. The Jurassic to Triassic pumpellyite-actinolite (Akatore Creek) to upper greenschist facies (Bruce Rocks) metamorphic fabrics were crosscut by sets of regionally extensive Cretaceous exhumation joints. Many of the joints were subsequently reactivated to form networks of small-displacement (<metres) strike-slip faults containing cemented fault breccias and veins composed of hydrothermal calcite, siderite, and ankerite. Paleostress analysis performed on infrequent fault slickenlines indicates an overall strike-slip paleostress regime and a paleo-σ1 orientation (azimuth 094°) similar to the contemporary σ1 orientation in Otago and Canterbury (azimuth c. 110°-120°). High δ18O values in vein calcite (δ18OVPDB=21 to 28‰), together with the predominance of Type I calcite twins, suggest that vein formation occurred at low temperatures (<200°C) in the shallow crust and was associated with strongly channelized fluid flow along the joint and fault networks. Mass-balance calculations performed on samples from carbonate alteration zones show that significant mobilisation of elements occurred during fluid flow and fluid-rock reaction. Whole-rock and in situ carbonate 87Sr/86Sr data indicate varying degrees of interaction between the hydrothermal fluids and the host rock schists. Fluids were likely derived from the breakdown of metamorphic Ca-rich mineral phases with low 87Rb in the host schists (e.g., epidote or calcite), as well as more radiogenic components such as mica. Overall, the field and geochemical data suggest that shallow fluid flow in the field areas was channelized along foliation surfaces, exhumation joints, and networks of brittle faults, and that these structures controlled the distribution of fluid-rock reactions and hydrothermal veins. The brittle fault networks and associated hydrothermal systems are interpreted to have formed after the onset of Early Miocene compression in the South Island and may represent the manifestation of fracturing and fluid flow associated with reverse reactivation of regional-scale faults such as the nearby Akatore Fault
The astrophysics of nanohertz gravitational waves
Pulsar timing array (PTA) collaborations in North America, Australia, and Europe, have been exploiting the exquisite timing precision of millisecond pulsars over decades of observations to search for correlated timing deviations induced by gravitational waves (GWs). PTAs are sensitive to the frequency band ranging just below 1 nanohertz to a few tens of microhertz. The discovery space of this band is potentially rich with populations of inspiraling supermassive black hole binaries, decaying cosmic string networks, relic post-inflation GWs, and even non-GW imprints of axionic dark matter. This article aims to provide an understanding of the exciting open science questions in cosmology, galaxy evolution, and fundamental physics that will be addressed by the detection and study of GWs through PTAs. The focus of the article is on providing an understanding of the mechanisms by which PTAs can address specific questions in these fields, and to outline some of the subtleties and difficulties in each case. The material included is weighted most heavily toward the questions which we expect will be answered in the near-term with PTAs; however, we have made efforts to include most currently anticipated applications of nanohertz GWs
The NANOGrav 11-Year Data Set: Limits on Gravitational Waves from Individual Supermassive Black Hole Binaries
Observations indicate that nearly all galaxies contain supermassive black
holes (SMBHs) at their centers. When galaxies merge, their component black
holes form SMBH binaries (SMBHBs), which emit low-frequency gravitational waves
(GWs) that can be detected by pulsar timing arrays (PTAs). We have searched the
recently-released North American Nanohertz Observatory for Gravitational Waves
(NANOGrav) 11-year data set for GWs from individual SMBHBs in circular orbits.
As we did not find strong evidence for GWs in our data, we placed 95\% upper
limits on the strength of GWs from such sources as a function of GW frequency
and sky location. We placed a sky-averaged upper limit on the GW strain of at nHz. We also developed a
technique to determine the significance of a particular signal in each pulsar
using ``dropout' parameters as a way of identifying spurious signals in
measurements from individual pulsars. We used our upper limits on the GW strain
to place lower limits on the distances to individual SMBHBs. At the
most-sensitive sky location, we ruled out SMBHBs emitting GWs with
nHz within 120 Mpc for , and
within 5.5 Gpc for . We also determined that
there are no SMBHBs with emitting
GWs in the Virgo Cluster. Finally, we estimated the number of potentially
detectable sources given our current strain upper limits based on galaxies in
Two Micron All-Sky Survey (2MASS) and merger rates from the Illustris
cosmological simulation project. Only 34 out of 75,000 realizations of the
local Universe contained a detectable source, from which we concluded it was
unsurprising that we did not detect any individual sources given our current
sensitivity to GWs.Comment: 10 pages, 11 figures. Accepted by Astrophysical Journal. Please send
any comments/questions to S. J. Vigeland ([email protected]
Multi-Messenger Gravitational Wave Searches with Pulsar Timing Arrays: Application to 3C66B Using the NANOGrav 11-year Data Set
When galaxies merge, the supermassive black holes in their centers may form
binaries and, during the process of merger, emit low-frequency gravitational
radiation in the process. In this paper we consider the galaxy 3C66B, which was
used as the target of the first multi-messenger search for gravitational waves.
Due to the observed periodicities present in the photometric and astrometric
data of the source of the source, it has been theorized to contain a
supermassive black hole binary. Its apparent 1.05-year orbital period would
place the gravitational wave emission directly in the pulsar timing band. Since
the first pulsar timing array study of 3C66B, revised models of the source have
been published, and timing array sensitivities and techniques have improved
dramatically. With these advances, we further constrain the chirp mass of the
potential supermassive black hole binary in 3C66B to less than using data from the NANOGrav 11-year data set. This
upper limit provides a factor of 1.6 improvement over previous limits, and a
factor of 4.3 over the first search done. Nevertheless, the most recent orbital
model for the source is still consistent with our limit from pulsar timing
array data. In addition, we are able to quantify the improvement made by the
inclusion of source properties gleaned from electromagnetic data to `blind'
pulsar timing array searches. With these methods, it is apparent that it is not
necessary to obtain exact a priori knowledge of the period of a binary to gain
meaningful astrophysical inferences.Comment: 14 pages, 6 figures. Accepted by Ap
The NANOGrav Nine-year Data Set:Limits on the Isotropic Stochastic Gravitational Wave Background
We compute upper limits on the nanohertz-frequency isotropic stochastic gravitational wave background (GWB) using the 9 year data set from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) collaboration. Well-tested Bayesian techniques are used to set upper limits on the dimensionless strain amplitude (at a frequency of 1 yr(-1)) for a GWB from supermassive black hole binaries of A(gw) <1.5 x 10(-15). We also parameterize the GWB spectrum with a broken power-law model by placing priors on the strain amplitude derived from simulations of Sesana and McWilliams et al. Using Bayesian model selection we find that the data favor a broken power law to a pure power law with odds ratios of 2.2 and 22 to one for the Sesana and McWilliams prior models, respectively. Using the broken power-law analysis we construct posterior distributions on environmental factors that drive the binary to the GW-driven regime including the stellar mass density for stellar-scattering, mass accretion rate for circumbinary disk interaction, and orbital eccentricity for eccentric binaries, marking the first time that the shape of the GWB spectrum has been used to make astrophysical inferences. Returning to a power-law model, we place stringent limits on the energy density of relic GWs, Omega(gw) (f)h(2) <4.2 x 10(-10). Our limit on the cosmic string GWB, Omega(gw) (f)h(2) <2.2 x 10(-10), translates to a conservative limit on the cosmic string tension with G mu <3.3 x 10(-8), a factor of four better than the joint Planck and high-l cosmic microwave background data from other experiments
Bayesian Solar Wind Modeling with Pulsar Timing Arrays
Using Bayesian analyses we study the solar electron density with the NANOGrav
11-year pulsar timing array (PTA) dataset. Our model of the solar wind is
incorporated into a global fit starting from pulse times-of-arrival. We
introduce new tools developed for this global fit, including analytic
expressions for solar electron column densities and open source models for the
solar wind that port into existing PTA software. We perform an ab initio
recovery of various solar wind model parameters. We then demonstrate the
richness of information about the solar electron density, , that can be
gleaned from PTA data, including higher order corrections to the simple
model associated with a free-streaming wind (which are informative probes of
coronal acceleration physics), quarterly binned measurements of and a
continuous time-varying model for spanning approximately one solar cycle
period. Finally, we discuss the importance of our model for chromatic noise
mitigation in gravitational-wave analyses of pulsar timing data and the
potential of developing synergies between sophisticated PTA solar electron
density models and those developed by the solar physics community.Comment: 22 pages, 7 figures, Submitted to Ap
The NANOGrav 11 Year Data Set: Pulsar-timing Constraints on the Stochastic Gravitational-wave Background
We search for an isotropic stochastic gravitational-wave background (GWB) in the newly released 11 year data set from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). While we find no evidence for a GWB, we place constraints on a population of inspiraling supermassive black hole (SMBH) binaries, a network of decaying cosmic strings, and a primordial GWB. For the first time, we find that the GWB constraints are sensitive to the solar system ephemeris (SSE) model used and that SSE errors can mimic a GWB signal. We developed an approach that bridges systematic SSE differences, producing the first pulsar-timing array (PTA) constraints that are robust against SSE errors. We thus place a 95% upper limit on the GW-strain amplitude of A GWB < 1.45 × 10−15 at a frequency of f = 1 yr−1 for a fiducial f −2/3 power-law spectrum and with interpulsar correlations modeled. This is a factor of ~2 improvement over the NANOGrav nine-year limit calculated using the same procedure. Previous PTA upper limits on the GWB (as well as their astrophysical and cosmological interpretations) will need revision in light of SSE systematic errors. We use our constraints to characterize the combined influence on the GWB of the stellar mass density in galactic cores, the eccentricity of SMBH binaries, and SMBH–galactic-bulge scaling relationships. We constrain the cosmic-string tension using recent simulations, yielding an SSE-marginalized 95% upper limit of Gμ < 5.3 × 10−11—a factor of ~2 better than the published NANOGrav nine-year constraints. Our SSE-marginalized 95% upper limit on the energy density of a primordial GWB (for a radiation-dominated post-inflation universe) is ΩGWB(f) h 2 < 3.4 × 10−10
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