650 research outputs found
Simulating the Impact of X-ray Heating during the Cosmic Dawn
Upcoming observations of the 21-cm signal from the Epoch of Reionization will
soon provide the first direct detection of this era. This signal is influenced
by many astrophysical effects, including long range X-ray heating of the
intergalactic gas. During the preceding Cosmic Dawn era the impact of this
heating on the 21-cm signal is particularly prominent, especially before spin
temperature saturation. We present the largest-volume (349\,Mpc
comoving=244~Mpc) full numerical radiative transfer simulations to date
of this epoch that include the effects of helium and multi-frequency heating,
both with and without X-ray sources. We show that X-ray sources contribute
significantly to early heating of the neutral intergalactic medium and, hence,
to the corresponding 21-cm signal. The inclusion of hard, energetic radiation
yields an earlier, extended transition from absorption to emission compared to
the stellar-only case. The presence of X-ray sources decreases the absolute
value of the mean 21-cm differential brightness temperature. These hard sources
also significantly increase the 21-cm fluctuations compared the common
assumption of temperature saturation. The 21-cm differential brightness
temperature power spectrum is initially boosted on large scales, before
decreasing on all scales. Compared to the case of the cold, unheated
intergalactic medium, the signal has lower rms fluctuations and increased
non-Gaussianity, as measured by the skewness and kurtosis of the 21-cm
probability distribution functions. Images of the 21-cm signal with resolution
around 11~arcmin still show fluctuations well above the expected noise for deep
integrations with the SKA1-Low, indicating that direct imaging of the X-ray
heating epoch could be feasible.Comment: 13 pages, 8 figure
LargeScale Precursors to Major Lake Effect Snowstorms Lee of Lake Erie
Lakeâeffect snowstorms are primarily a mesoscale feature; however, major lakeeffect snowstorms are linked closely to their synoptic environment. Thus, a lakeeffect system which lasts for more than 24 h cannot only be explained by the boundary layer; it is also associated with the upper tropospheric flow. This research will address whether major lakeâeffect snow events off of Lake Erie can also be associated with largeâscale planetary features several days prior to event onset. The goal is to aid in the forecast process by increasing the accuracy and leadtime of lakeâeffect snow forecasts. This study includes 31 cases recorded from the National Weather Service at Buffaloâs lake effect database. These 31 cases were then stratified into categories depending on its: length, the time of year, and the type of event. This categorization allowed for comparison of the state of the atmosphere in the days prior to different types of events. In order to assess the largeâscale pattern, teleconnections were used as a proxy for the state of the atmosphere. For cases that lasted for greater than 42 hours, there was a correlation to the phase Madden Julian oscillation eight days prior to onset. The cases that occurred during the positive and negative states of the Arctic Oscillation had two different upper level trough patterns, the former originating in Southern Canada and the latter over the Southwestern United States
Innovating the Study of Context: Using a Qualitative Study on Subjugation and Resistance to Explore the Utility of Foucauldian Governmentality as a Framework for Enriching Situational Analyses
Situational analysis has, as an emerging poststructuralist approach to grounded theory, recently grown in use across a diverse range of disciplines and substantive areas. In this paper, we consider the complementarity of Foucauldian governmentality as a theoretical framework for supporting and enriching situational analyses. Our work is based on the findings of a recent study, informed by situational analysis, in which we interviewed 27 HIV-positive (n=16) and HIV-negative (n=11) gay men ages 50 and over about their health care experiences, and used these data to examine processes of subjugation and resistance reflected in their accounts. Drawing on our analytical process, we consider the utility of governmentality in identifying salient discursive forces within a situation of interest, in theorizing how contextual factors operate on and influence the experiences of key actors in a field of inquiry, and in generating insight on fluid uses of power within an area under examination
A Phenomenological Study of International Students in US Graduate Programs Through the Lens of Personal Growth Initiative Construct
Humans, unlike other creatures, have an inherent desire to develop and grow. This desire to grow, Personal Growth Initiative, is an intentional way that humans cognitively and behaviorally navigate their environment and resources to effect change. While many researchers argue that this construct works only in individualistic cultures, others contend that the construct is applicable to collectivist cultures as well. We therefore undertook an exploration of the lived experiences of eight international students from predominantly collectivist cultures, through the lens of the Personal Growth Initiative theory. Using a phenomenological qualitative methodology, we interviewed these doctoral students via semi-structured interview questions. Results of the data indicated that participants cycled through the four factors in the construct to handle both successes and challenges in school. Recommendations for international studentsâ offices and recruitment agencies are provided
Evaluating the QSO contribution to the 21-cm signal from the Cosmic Dawn
The upcoming radio interferometer Square Kilometre Array (SKA) is expected to directly detect the redshifted 21-cm signal from the neutral hydrogen present during the Cosmic Dawn. Temperature fluctuations from X-ray heating of the neutral intergalactic medium can dominate the fluctuations in the 21-cm signal from this time. This heating depends on the abundance, clustering, and properties of the X-ray sources present, which remain highly uncertain. We present a suite of three new large-volume, 349âMpc a side, fully numerical radiative transfer simulations including QSO-like sources, extending the work previously presented in Ross et al. (2017). The results show that our QSOs have a modest contribution to the heating budget, yet significantly impact the 21-cm signal. Initially, the power spectrum is boosted on large scales by heating from the biased QSO-like sources, before decreasing on all scales. Fluctuations from images of the 21-cm signal with resolutions corresponding to SKA1-Low at the appropriate redshifts are well above the expected noise for deep integrations, indicating that imaging could be feasible for all the X-ray source models considered. The most notable contribution of the QSOs is a dramatic increase in non-Gaussianity of the signal, as measured by the skewness and kurtosis of the 21-cm probability distribution functions. However, in the case of late Lyman-α saturation, this non-Gaussianity could be dramatically decreased particularly when heating occurs earlier. We conclude that increased non-Gaussianity is a promising signature of rare X-ray sources at this time, provided that Lyman-α saturation occurs before heating dominates the 21-cm signal
Redshift-space distortions in simulations of the 21-cm signal from the cosmic dawn
The 21-cm signal from the Cosmic Dawn (CD) is likely to contain large
fluctuations, with the most extreme astrophysical models on the verge of being
ruled out by observations from radio interferometers. It is therefore vital
that we understand not only the astrophysical processes governing this signal,
but also other inherent processes impacting the signal itself, and in
particular line-of-sight effects. Using our suite of fully numerical radiative
transfer simulations, we investigate the impact on the redshifted 21-cm from
the CD from one of these processes, namely the redshift-space distortions
(RSDs). When RSDs are added, the resulting boost to the power spectra makes the
signal more detectable for our models at all redshifts, further strengthening
hopes that a power spectra measurement of the CD will be possible. RSDs lead to
anisotropy in the signal at the beginning and end of the CD, but not while
X-ray heating is underway. The inclusion of RSDs, however, decreases
detectability of the non-Gaussianity of fluctuations from inhomogeneous X-ray
heating measured by the skewness and kurtosis. On the other hand, mock
observations created from all our simulations that include telescope noise
corresponding to 1000 h observation with the Square Kilometre Array telescope
show that we may be able image the CD for all heating models considered and
suggest RSDs dramatically boost fluctuations coming from the inhomogeneous
Ly- background.Comment: 16 pages, 10 figure
Associations between neighbourhood characteristics and depression: a twin study.
BACKGROUND: Depression is an important contributor to the global burden of disease. Besides several known individual-level factors that contribute to depression, there is a growing recognition that neighbourhood environment can also profoundly affect mental health. This study assessed associations between three neighbourhood constructs-socioeconomic deprivation, residential instability and income inequality-and depression among adult twin pairs. The twin design is used to examine the association between neighbourhood constructs and depression, controlling for selection factors (ie, genetic and shared environmental factors) that have confounded purported associations.
METHODS: We used multilevel random-intercept Poisson regression among 3738 same-sex twin pairs from a community-based twin registry to examine the association between neighbourhood constructs and depression. The within-pair association controls for confounding by genetic and environmental factors shared between twins within a pair, and is the main parameter of interest. Models were adjusted for individual-level income, education and marital status, and further by neighbourhood-level population density.
RESULTS: When twins were analysed as individuals (phenotypic model), all neighbourhood constructs were significantly associated with depression. However, only neighbourhood socioeconomic deprivation showed a significant within-pair association with depression. A 10-unit within-pair difference in neighbourhood socioeconomic deprivation was associated with 6% greater depressive symptoms (1.06, 95%âCI 1.01 to 1.11); the association did not substantially change in adjusted models.
CONCLUSION: This study provides new evidence linking neighbourhood socioeconomic deprivation with greater depression. Future studies should employ longitudinal designs to better test social causation versus social selection
The 21-cm bispectrum as a probe of non-Gaussianities due to X-ray heating
We present analysis of the normalized 21-cm bispectrum from fully-numerical simulations of intergalactic-medium heating by stellar sources and high-mass X-ray binaries (HMXBs) during the cosmic dawn.âLy-α coupling is assumed to be saturated, we therefore probe the nature of non-Gaussianities produced by X-ray heating processes. We find the evolution of the normalized bispectrum to be very different from that of the power spectrum. It exhibits a turnover whose peak moves from large to small scales with decreasing redshift, and corresponds to the typical separation of emission regions. This characteristic scale reduces as more and more regions move into emission with time. Ultimately, small-scale fluctuations within heated regions come to dominate the normalized bispectrum, which at the end of the simulation is almost entirely driven by fluctuations in the density field. To establish how generic the qualitative evolution of the normalized bispectrum we see in the stellar + HMXB simulation is, we examine several other simulations â two fully numerical simulations that include quasi-stellar object (QSO) sources, and two with contrasting source properties produced with the semi-numerical simulation 21CMFAST. We find the qualitative evolution of the normalized bispectrum during X-ray heating to be generic, unless the sources of X-rays are, as with QSOs, less numerous and so exhibit more distinct isolated heated profiles. Assuming mitigation of foreground and instrumental effects are ultimately effective, we find that we should be sensitive to the normalized bispectrum during the epoch of heating, so long as the spin temperature has not saturated by zâ19
Assessment of murine collagen-induced arthritis by longitudinal non-invasive duplexed molecular optical imaging
In the present study we evaluated the use of four commercially available fluorescent probes to monitor disease activity in murine CIA and its suppression during glucocorticoid therapy. Arthritis was induced in male DBA/1 mice by immunization with type II collagen in Complete Freund's Adjuvant, followed by a boost of collagen in PBS. Four fluorescent probes from PerkinElmer in combination [ProSense 750 fluorescent activatable sensor technology (FAST) with Neutrophil Elastase 680 FAST and MMPSense 750 FAST with CatK 680 FAST] were used to monitor disease development from day 5 through to day 40 post-immunization. Fluorescence generated in vivo by the probes was correlated with clinical and histological score and paw measurements. The fluorescence intensity emitted by each probe was shown to correlate with the conventional measurements of disease. The highest degree of correlation was observed with ProSense 750 FAST in combination with Neutrophil Elastase 680 FAST; these probes were then used to successfully assess CIA suppression during dexamethasone treatment. We have demonstrated that longitudinal non-invasive duplexed optical fluorescence imaging provides a simple assessment of arthritic disease activity within the joints of mice following the induction of CIA and may represent a powerful tool to monitor the efficacy of drug treatments in preclinical studies
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