833 research outputs found
On curvature-squared invariants of minimal five-dimensional supergravity from superspace
We elaborate on the off-shell superspace construction of curvature-squared
invariants in minimal five-dimensional supergravity. This is described by the
standard Weyl multiplet of conformal supergravity coupled to two compensators
being a vector multiplet and a linear multiplet. In this set-up, we review the
definition of the off-shell two-derivative gauged supergravity together with
the three independent four-derivative superspace invariants defined in
arXiv:1410.8682. We provide the explicit expression for the linear multiplet
based on a prepotential given by the logarithm of the vector multiplet primary
superfield. We then present for the first time the primary equations of motion
for minimal gauged off-shell supergravity deformed by an arbitrary combination
of these three four-derivative locally superconformal invariants. We also
identify a four-derivative invariant based on the linear multiplet compensator
and the kinetic superfield of a vector multiplet which can be used to engineer
an alternative supersymmetric completion of the scalar curvature squared.Comment: 35 pages. v2: minor corrections, typos correcte
Backreaction of Schwinger pair creation in massive QED
Particle-antiparticle pairs can be produced by background electric fields via
the Schwinger mechanism provided they are unconfined. If, as in QED in
(3+1)- these particles are massive, the particle production rate is
exponentially suppressed below a threshold field strength. Above this
threshold, the energy for pair creation must come from the electric field
itself which ought to eventually relax to the threshold strength. Calculating
this relaxation in a self-consistent manner, however, is difficult. Chu and
Vachaspati addressed this problem in the context of capacitor discharge in
massless QED [1] by utilizing bosonization in two-dimensions. When the bare
fermions are massless, the dual bosonized theory is free and capacitor
discharge can be analyzed exactly [1], however, special care is required in its
interpretation given that the theory exhibits confinement. In this paper we
reinterpret the findings of [1], where the capacitors Schwinger-discharge via
electrically neutral dipolar meson-production, and generalize this to the case
where the fermions have bare masses. Crucially, we note that when the initial
charge of the capacitor is large compared to the charge of the fermions, , the classical equation of motion for the bosonized model accurately
characterizes the dynamics of discharge. For massless QED, we find that the
discharge is suppressed below a critical plate separation that is commensurate
with the length scale associated with the meson dipole moment. For massive
QED, we find in addition, a mass threshold familiar from (3+1)-, and
show the electric field relaxes to a final steady state with a magnitude
proportional to the initial charge. We discuss the wider implications of our
findings and identify challenges in extending this treatment to higher
dimensions.Comment: 21 pages, 2 figures; several additional references and enhanced
discussion. Matches JHEP versio
Paleoproterozoic sterol biosynthesis and the rise of oxygen
Natural products preserved in the geological record can function as ‘molecular fossils’, providing insight into organisms and physiologies that existed in the deep past. One important group of molecular fossils is the steroidal hydrocarbons (steranes), which are the diagenetic remains of sterol lipids. Complex sterols with modified side chains are unique to eukaryotes, although simpler sterols can also be synthesized by a few bacteria. Sterol biosynthesis is an oxygen-intensive process; thus, the presence of complex steranes in ancient rocks not only signals the presence of eukaryotes, but also aerobic metabolic processes. In 1999, steranes were reported in 2.7 billion year (Gyr)-old rocks from the Pilbara Craton in Australia, suggesting a long delay between photosynthetic oxygen production and its accumulation in the atmosphere (also known as the Great Oxidation Event) 2.45–2.32 Gyr ago. However, the recent reappraisal and rejection of these steranes as contaminants pushes the oldest reported steranes forward to around 1.64 Gyr ago (ref. 6). Here we use a molecular clock approach to improve constraints on the evolution of sterol biosynthesis. We infer that stem eukaryotes shared functionally modern sterol biosynthesis genes with bacteria via horizontal gene transfer. Comparing multiple molecular clock analyses, we find that the maximum marginal probability for the divergence time of bacterial and eukaryal sterol biosynthesis genes is around 2.31 Gyr ago, concurrent with the most recent geochemical evidence for the Great Oxidation Event. Our results therefore indicate that simple sterol biosynthesis existed well before the diversification of living eukaryotes, substantially predating the oldest detected sterane biomarkers (approximately 1.64 Gyr ago), and furthermore, that the evolutionary history of sterol biosynthesis is tied to the first widespread availability of molecular oxygen in the ocean–atmosphere system
A Last Look at the Microwave Haze/Bubbles with WMAP
The microwave "haze" was first discovered with the initial release of the
full sky data from the Wilkinson Microwave Anisotropy Probe. It is diffuse
emission towards the center of our Galaxy with spectral behavior that makes it
difficult to categorize as any of the previously known emission mechanisms at
those wavelengths. With now seven years of WMAP data publicly available, we
have learned much about the nature of the haze, and with the release of data
from the Fermi Gamma-Ray Space Telescope and the discovery of the gamma-ray
haze/bubbles, we have had a spectacular confirmation of its existence at other
wavelengths. As the WMAP mission winds down and the Planck mission prepares to
release data, I take a last look at what WMAP has to tell us about the origin
of this unique Galactic feature. Much like the gamma-rays, the microwave
haze/bubbles is elongated in latitude with respect to longitude by a factor of
roughly two, and at high latitudes, the microwave emission cuts off sharply
above ~35 degrees (compared to ~50 degrees in the gammas). The hard spectrum of
electrons required to generate the microwave synchrotron is consistent with
that required to generate the gamma-ray emission via inverse Compton
scattering, though it is likely that these signals result from distinct regions
of the spectrum (~10 GeV for the microwaves, ~1 TeV for the gammas). While
there is no evidence for significant haze polarization in the 7-year WMAP data,
I demonstrate explicitly that it is unlikely such a signal would be detectable
above the noise.Comment: 9 pages, 6 figures; accepted in ApJ; matches published version with
significantly enhanced figure
On the Origins of the High-Latitude H-alpha Background
The diffuse high-latitude H-alpha background is widely believed to be
predominantly the result of in-situ recombination of ionized hydrogen in the
warm interstellar medium of the Galaxy. Instead, we show that both a
substantial fraction of the diffuse high-latitude H-alpha intensity in regions
dominated by Galactic cirrus dust and much of the variance in the high-latitude
H-alpha background are the result of scattering by interstellar dust of H-alpha
photons originating elsewhere in the Galaxy. We provide an empirical relation,
which relates the expected scattered H-alpha intensity to the IRAS 100um
diffuse background intensity, applicable to about 81% of the entire sky. The
assumption commonly made in reductions of CMB observations, namely that the
observed all-sky map of diffuse H-alpha light is a suitable template for
Galactic free-free foreground emission, is found to be in need of
reexamination.Comment: 26 pages, 5 figures, Accepted for publication in Ap
Cardiorespiratory Fitness Diminishes the Effects of Age on White Matter Hyperintensity Volume
White matter hyperintensities (WMHs) are among the most commonly observed marker of cerebrovascular disease. Age is a key risk factor for WMH development. Cardiorespiratory fitness (CRF) is associated with increased vessel compliance, but it remains unknown if high CRF affects WMH volume. This study explored the effects of CRF on WMH volume in community-dwelling older adults. We further tested the possibility of an interaction between CRF and age on WMH volume. Participants were 76 adults between the ages of 59 and 77 (mean age = 65.36 years, SD = 3.92) who underwent a maximal graded exercise test and structural brain imaging. Results indicated that age was a predictor of WMH volume (beta = .32, p = .015). However, an age-by-CRF interaction was observed such that higher CRF was associated with lower WMH volume in older participants (beta = -.25, p = .040). Our findings suggest that higher levels of aerobic fitness may protect cerebrovascular health in older adults
Major depressive disorder in a family study of obsessive–compulsive disorder with pediatric probands
Objective: This study examined the comorbidity of obsessive–compulsive disorder (OCD) with major depressive disorder (MDD) in a family study of OCD with pediatric probands. Method: This study assessed the lifetime prevalence of MDD in 141 first‐degree relatives (FDR) and 452 second‐degree relatives (SDR) of pediatric probands with OCD and healthy controls, and identified variables associated with MDD in case FDR. All available FDR were directly interviewed blind to proband status; parents were also interviewed to assess the family psychiatric history of FDR and SDR. Best‐estimate diagnoses were made using all sources of information. Data were analyzed with logistic regression and robust Cox regression models. Results: Lifetime MDD prevalence was significantly higher in case than in control FDR (30.4 versus 15.4%). Lifetime MDD prevalence was significantly higher in FDR of case probands with MDD than in FDR of case probands without MDD or control FDR (46.3 versus 19.7 versus 15.4%, respectively). MDD in case FDR was significantly associated with MDD in case probands and with age and OCD in those relatives. Lifetime MDD prevalence was similar in case and control SDR. However, lifetime MDD prevalence was significantly higher in SDR of case probands with MDD than in SDR of case probands without MDD or control SDR (31.9 versus 16.8 versus 15.4%, respectively). Conclusions: MDD prevalence was significantly higher in both FDR and SDR of case probands with MDD than in relatives of case probands without MDD or control relatives, suggesting that pediatric OCD comorbid with MDD is a complex familial syndrome. Depression and Anxiety, 2011. © 2011 Wiley‐Liss, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87090/1/20824_ftp.pd
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Short-Term Changes in Ambient Temperature and Risk of Ischemic Stroke
Background: Despite consistent evidence of a higher short-term risk of cardiovascular mortality associated with ambient temperature, there have been discrepant findings on the association between temperature and ischemic stroke. Moreover, few studies have considered potential confounding by ambient fine particulate matter air pollution <2.5 μm in diameter (PM2.5) and none have examined the impact of temperature changes on stroke in the subsequent hours rather than days. The aim of this study was to evaluate whether changes in temperature trigger an ischemic stroke in the following hours and days and whether humid days are particularly harmful. Methods: We reviewed the medical records of 1,705 patients residing in the metropolitan region of Boston, Mass., USA, who were hospitalized with neurologist-confirmed ischemic stroke, and we abstracted data on the time of symptom onset and clinical characteristics. We obtained hourly meteorological data from the National Weather Service station and hourly PM2.5 data from the Harvard ambient monitoring station. We used the time-stratified case-crossover design to assess the association between ischemic stroke and apparent temperature averaged over 1-7 days prior to stroke onset adjusting for PM2.5. We assessed whether differences in apparent temperature trigger a stroke within shorter time periods by examining the association between stroke onset and apparent temperature levels averaged in 2-hour increments prior to stroke onset (0-2 h through 36-38 h). We tested whether the association varied by health characteristics or by PM2.5, ozone or relative humidity. Results: The incidence rate ratio of ischemic stroke was 1.09 (95% confidence interval 1.01-1.18) following a 5°C decrement in average apparent temperature over the 2 days preceding symptom onset. The higher risk associated with cooler temperatures peaked in the first 14-34 h. There was no statistically significant difference in the association between temperature and ischemic stroke across seasons. The risk of ischemic stroke was not meaningfully different across subgroups of patients defined by health characteristics. The association between ischemic stroke and ambient temperature was stronger on days with higher levels of relative humidity. Conclusions: Lower temperatures are associated with a higher risk of ischemic stroke onset in both warm and cool seasons, and the risk is higher on days with higher levels of relative humidity. Based on this study and the body of literature on ambient temperature and cardiovascular events, identifying methods for mitigating cardiovascular risk may be warranted
Enlarged Perivascular Spaces are Negatively Associated with Montreal Cognitive Assessment Scores in Older Adults
Emerging evidence suggests that enlarged perivascular spaces (ePVS) may be a clinically significant neuroimaging marker of global cognitive function related to cerebral small vessel disease (cSVD). We tested this possibility by assessing the relationship between ePVS and both a standardized measure of global cognitive function, the Montreal Cognitive Assessment (MoCA), and an established marker of cSVD, white matter hyperintensity volume (WMH) volume. One hundred and eleven community-dwelling older adults (56–86) underwent neuroimaging and MoCA testing. Quantification of region-specific ePVS burden was performed using a previously validated visual rating method and WMH volumes were computed using the standard ADNI pipeline. Separate linear regression models were run with ePVS as a predictor of MoCA scores and whole brain WMH volume. Results indicated a negative association between MoCA scores and both total ePVS counts (P ≤ 0.001) and centrum semiovale ePVS counts (P ≤ 0.001), after controlling for other relevant cSVD variables. Further, WMH volumes were positively associated with total ePVS (P = 0.010), basal ganglia ePVS (P ≤ 0.001), and centrum semiovale ePVS (P = 0.027). Our results suggest that ePVS burden, particularly in the centrum semiovale, may be a clinically significant neuroimaging marker of global cognitive dysfunction related to cSVD
Water Exchange Rate across the Blood-Brain Barrier Is Associated with CSF Amyloid-β 42 in Healthy Older Adults
INTRODUCTION: We tested if water exchange across the blood-brain barrier (BBB), estimated with a noninvasive magnetic resonance imaging (MRI) technique, is associated with cerebrospinal fluid (CSF) biomarkers of Alzheimer\u27s disease (AD) and neuropsychological function.
METHODS: Forty cognitively normal older adults (67–86 years old) were scanned with diffusion‐prepared, arterial spin labeling (DP‐ASL), which estimates water exchange rate across the BBB (kw). Participants also underwent CSF draw and neuropsychological testing. Multiple linear regression models were run with kw as a predictor of CSF concentrations and neuropsychological scores.
RESULTS: In multiple brain regions, BBB kw was positively associated with CSF amyloid beta (Aβ)42 concentration levels. BBB kw was only moderately associated with neuropsychological performance.
DISCUSSION: Our results suggest that low water exchange rate across the BBB is associated with low CSF Aβ42 concentration. These findings suggest that kw may be a promising noninvasive indicator of BBB Aβ clearance functions, a possibility which should be further tested in future research
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