227 research outputs found
Wave Dark Matter and the Tully-Fisher Relation
We investigate a theory of dark matter called wave dark matter, also known as
scalar field dark matter (SFDM) and boson star dark matter or Bose-Einstein
condensate (BEC) dark matter, in spherical symmetry and its relation to the
Tully-Fisher relation. We show that fixing the oscillation frequency of wave
dark matter near the edge of dark galactic halos implies a Tully-Fisher-like
relation for those halos. We then describe how this boundary condition, which
is roughly equivalent to fixing the half-length of the exponentially decaying
tail of each galactic halo mass profile, may yield testable predictions for
this theory of dark matter.Comment: 19 pages, 4 figure
The Einstein-Klein-Gordon Equations, Wave Dark Matter, and the Tully-Fisher Relation
We examine the Einstein equation coupled to the Klein-Gordon equation for a
complex-valued scalar field. These two equations together are known as the
Einstein-Klein-Gordon system. In the low-field, non-relativistic limit, the
Einstein-Klein-Gordon system reduces to the Poisson-Schr\"odinger system. We
describe the simplest solutions of these systems in spherical symmetry, the
spherically symmetric static states, and some scaling properties they obey. We
also describe some approximate analytic solutions for these states.
The EKG system underlies a theory of wave dark matter, also known as scalar
field dark matter (SFDM), boson star dark matter, and Bose-Einstein condensate
(BEC) dark matter. We discuss a possible connection between the theory of wave
dark matter and the baryonic Tully-Fisher relation, which is a scaling relation
observed to hold for disk galaxies in the universe across many decades in mass.
We show how fixing boundary conditions at the edge of the spherically symmetric
static states implies Tully-Fisher-like relations for the states. We also
catalog other "scaling conditions" one can impose on the static states and show
that they do not lead to Tully-Fisher-like relations--barring one exception
which is already known and which has nothing to do with the specifics of wave
dark matter.Comment: This is a posting of my PhD thesis (Duke University Department of
Mathematics, 2015). 73 pages, 17 figures, 3 table
Northern High-Latitude Ecosystems Respond to Climate Change
The northern high latitudes are an area of particular importance to global climate change. As a system dependent on freezing conditions, the top of the planet contains vast amounts of carbon in biomass, soils, and permafrost that have the potential to interact with the atmosphere through the biosphere, hydrosphere, lithosphere, and cryosphere. If released en masse, this carbon would greatly exacerbate the levels of greenhouse gases in the atmosphere.
Over the past 2 years, a growing body of research has provided evidence of substantial but idiosyncratic environmental changes, with some surprising aspects, across the region. This article reviews some recent findings and presents a new analysis of northern vegetation photosynthetic and productivity trends tracked from Earth observing satellites
Blip glitches in Advanced LIGO data
Blip glitches are short noise transients present in data from ground-based
gravitational-wave observatories. These glitches resemble the
gravitational-wave signature of massive binary black hole mergers. Hence, the
sensitivity of transient gravitational-wave searches to such high-mass systems
and other potential short duration sources is degraded by the presence of blip
glitches. The origin and rate of occurrence of this type of glitch have been
largely unknown. In this paper we explore the population of blip glitches in
Advanced LIGO during its first and second observing runs. On average, we find
that Advanced LIGO data contains approximately two blip glitches per hour of
data. We identify four subsets of blip glitches correlated with detector
auxiliary or environmental sensor channels, however the physical causes of the
majority of blips remain unclear
High-Latitude Tree Growth and Satellite Vegetation Indices: Correlations and Trends in Russia and Canada (1982-2008)
Vegetation in northern high latitudes affects regional and global climate through energy partitioning and carbon storage. Spaceborne observations of vegetation, largely based on the normalized difference vegetation index (NDVI), suggest decreased productivity during recent decades in many regions of the Eurasian and North American boreal forests. To improve interpretation of NDVI trends over forest regions, we examined the relationship between NDVI from the advanced very high resolution radiometers and tree ring width measurements, a proxy of tree productivity. We collected tree core samples from spruce, pine, and larch at 22 sites in northeast Russia and northwest Canada. Annual growth rings were measured and used to generate site-level ring width index (RWI) chronologies. Correlation analysis was used to assess the association between RWI and summer NDVI from 1982 to 2008, while linear regression was used to examine trends in both measurements. The correlation between NDVI and RWI was highly variable across sites, though consistently positive (r = 0.43, SD = 0.19, n = 27). We observed significant temporal autocorrelation in both NDVI and RWI measurements at sites with evergreen conifers (spruce and pine), though weak autocorrelation at sites with deciduous conifers (larch). No sites exhibited a positive trend in both NDVI and RWI, although five sites showed negative trends in both measurements. While there are technological and physiological limitations to this approach, these findings demonstrate a positive association between NDVI and tree ring measurements, as well as the importance of considering lagged effects when modeling vegetation productivity using satellite data
Psychometric properties of the revised children’s anxiety and depression scale (RCADS) for autistic youth without co-occurring intellectual disability
Autistic youth often present with comorbid anxiety and depression yet there is a dearth of validated assessment tools. The Revised Children’s Anxiety and Depression Scale (RCADS) assesses internalizing symptoms but there is little psychometric data in autistic youth. Treatment-seeking autistic youth with anxiety or obsessive-compulsive symptoms (N = 74; age 6–14 years), and caregivers, were administered the RCADS-Parent, RCADS-Child, and assessments of internalizing, externalizing symptoms and social impairment indicative of autism. RCADS-Parent and RCADS-Child total anxiety scores demonstrated excellent internal consistency, and the six subscales demonstrated acceptable-to-good internal consistency. The RCADS-Child and Parent total anxiety scores were weakly correlated, and neither child age nor gender altered the strength of this association. Convergent validity was supported by moderate-to-strong correlations with clinician and parent-reported anxiety symptoms. Support for divergent validity was mixed. Results provide support for the RCADS-Parent and RCADS-Child as reliable, valid measures of internalizing symptoms in autistic youth
Screening for coping style increases the power of gene expression studies
Background: Individuals of many vertebrate species show different stress coping styles and these have a striking influence on how gene expression shifts in response to a variety of challenges. Principal Findings: This is clearly illustrated by a study in which common carp displaying behavioural predictors of different coping styles (characterised by a proactive, adrenaline-based or a reactive, cortisol-based response) were subjected to inflammatory challenge and specific gene transcripts measured in individual brains. Proactive and reactive fish differed in baseline gene expression and also showed diametrically opposite responses to the challenge for 80% of the genes investigated. Significance: Incorporating coping style as an explanatory variable can account for some the unexplained variation that is common in gene expression studies, can uncover important effects that would otherwise have passed unnoticed and greatly enhances the interpretive value of gene expression data
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