We present photometric and spectroscopic observations of SN 2007if, an overluminous (M_V = -20.4), red (B-V = 0.16 at B-band maximum), slow-rising (t_rise = 24 days) type Ia supernova in a very faint ...(M_g = -14.10) host galaxy. A spectrum at 5 days past B-band maximum light is a direct match to the super-Chandrasekhar-mass candidate SN Ia 2003fg, showing Si II and C II at ~9000 km/s. A high signal-to-noise co-addition of the SN spectral time series reveals no Na I D absorption, suggesting negligible reddening in the host galaxy, and the late-time color evolution has the same slope as the Lira relation for normal SNe Ia. The ejecta appear to be well mixed, with no strong maximum in I-band and a diversity of iron-peak lines appearing in near-maximum-light spectra. SN2007 if also displays a plateau in the Si II velocity extending as late as +10 days, which we interpret as evidence for an overdense shell in the SN ejecta. We calculate the bolometric light curve of the SN and use it and the \ion{Si}{2} velocity evolution to constrain the mass of the shell and the underlying SN ejecta, and demonstrate that SN2007 if is strongly inconsistent with a Chandrasekhar-mass scenario. Within the context of a "tamped detonation" model appropriate for double-degenerate mergers, and assuming no host extinction, we estimate the total mass of the system to be 2.4 +/- 0.2 solar masses, with 1.6 +/- 0.1 solar masses of nickel-56 and with 0.3-0.5 solar masses in the form of an envelope of unburned carbon/oxygen. Our modeling demonstrates that the kinematics of shell entrainment provide a more efficient mechanism than incomplete nuclear burning for producing the low velocities typical of super-Chandrasekhar-mass SNeIa.
Accumulation of α-synuclein (α-syn) fibrils in Lewy bodies and Lewy neurites is the pathological hallmark of Parkinson disease (PD). Ligands that bind α-syn fibrils could be utilized as imaging ...agents to improve the diagnosis of PD and to monitor disease progression. However, ligands for α-syn fibrils in PD brain tissue have not been previously identified and the feasibility of quantifying α-syn fibrils in brain tissue is unknown. We report the identification of the (125)I-labeled α-syn radioligand SIL23. (125)ISIL23 binds α-syn fibrils in postmortem brain tissue from PD patients as well as an α-syn transgenic mouse model for PD. The density of SIL23 binding sites correlates with the level of fibrillar α-syn in PD brain tissue, and (125)ISIL23 binding site densities in brain tissue are sufficiently high to enable in vivo imaging with high affinity ligands. These results identify a SIL23 binding site on α-syn fibrils that is a feasible target for development of an α-syn imaging agent. The affinity of SIL23 for α-syn and its selectivity for α-syn versus Aβ and tau fibrils is not optimal for imaging fibrillar α-syn in vivo, but we show that SIL23 competitive binding assays can be used to screen additional ligands for suitable affinity and selectivity, which will accelerate the development of an α-syn imaging agent for PD.
Neural activity and learning lead to myelin sheath plasticity in the intact central nervous system (CNS), but this plasticity has not been well‐studied after CNS injury. In the context of spinal cord ...injury (SCI), demyelination occurs at the lesion site and natural remyelination of surviving axons can take months. To determine if neural activity modulates myelin and axon plasticity in the injured, adult CNS, we electrically stimulated the contralesional motor cortex at 10 Hz to drive neural activity in the corticospinal tract of rats with sub‐chronic spinal contusion injuries. We quantified myelin and axonal characteristics by tracing corticospinal axons rostral to and at the lesion epicenter and identifying nodes of Ranvier by immunohistochemistry. Three weeks of daily stimulation induced very short myelin sheaths, axon branching, and thinner axons outside of the lesion zone, where remodeling has not previously been reported. Surprisingly, remodeling was particularly robust rostral to the injury which suggests that electrical stimulation can promote white matter plasticity even in areas not directly demyelinated by the contusion. Stimulation did not alter myelin or axons at the lesion site, which suggests that neuronal activity does not contribute to myelin remodeling near the injury in the sub‐chronic period. These data are the first to demonstrate wide‐scale remodeling of nodal and myelin structures of a mature, long‐tract motor pathway in response to electrical stimulation. This finding suggests that neuromodulation promotes white matter plasticity in intact regions of pathways after injury and raises intriguing questions regarding the interplay between axonal and myelin plasticity.
Main Points
Electrical stimulation of motor cortex induces white matter plasticity far from the lesion after adult spinal cord injury.
Corticospinal tract internodes are shorter, axons are thinner, & more axons branch.
Myelin at the lesion is unaffected.
To investigate the specificity of in vivo amyloid imaging with (11)C-Pittsburgh Compound B (PIB) in Parkinson disease dementia (PDD).
We performed detailed neuropathologic examination for 3 ...individuals with PDD who had PIB PET imaging within 15 months of death.
We observed elevated cortical uptake of (11)C-PIB on in vivo PET imaging in 2 of the 3 cases. At autopsy, all 3 individuals had abundant cortical Lewy bodies (Braak PD stage 6), and were classified as low-probability Alzheimer disease (AD) based on NIA-Reagan criteria. The 2 PIB-positive individuals had abundant diffuse Abeta plaques but only sparse neuritic plaques and intermediate neurofibrillary tangle pathology. The PIB-negative individual had rare diffuse plaques, no neuritic plaques, and low neurofibrillary tangle burden.
(11)C-Pittsburgh Compound B (PIB) PET is specific for fibrillar Abeta molecular pathology but not for pathologic diagnosis of comorbid Alzheimer disease in individuals with Parkinson disease dementia. The ability to specifically identify fibrillar Abeta amyloid in the setting of alpha-synucleinopathy makes (11)C-PIB PET a valuable tool for prospectively evaluating how the presence of Abeta amyloid influences the clinical course of dementia in patients with Lewy body disorders.
To investigate the impact of neurologist care on Parkinson disease (PD)-related hospitalizations. Recent data indicate that neurologist treatment in PD may be associated with improved survival, yet ...is underutilized. Factors contributing to this improved survival remain unknown, but may be due in part to optimal disease treatment or avoidance of disease-related complications.
This was a retrospective cohort study of Medicare beneficiaries diagnosed with PD in 2002 and still living in 2006. Hospitalization for PD-related (neurodegenerative disease, psychosis, depression, urinary tract infection, and traumatic injury) and general medical (hypertension, diabetes, congestive heart failure, angina, and gastrointestinal obstruction) illnesses was compared by PD treating physician specialty using Cox proportional hazard models, adjusting for confounders. Secondary analyses included PD-related rehospitalization and cost stratified by frequency of neurologist care.
We identified 24,929 eligible incident PD cases; 13,489 had neurologist care. There were 9,112 PD-related hospitalizations, and these occurred and recurred less often among neurologist-treated patients. Neurologist PD care was associated with lower adjusted odds of both initial and repeat hospitalization for psychosis (hazard ratio HR 0.71, 95% confidence interval CI 0.59-0.86), urinary tract infection (HR 0.74, 0.63-0.87), and traumatic injury (HR 0.56, 0.40-0.78). PD-related outcomes improved with frequency of neurologist care in a stepwise manner. Odds of general illness hospitalization or hospitalization did not differ by neurologist involvement.
Regular neurologist care in PD is specifically associated with lower risk of hospitalization and rehospitalization for several PD-related illnesses. This may reflect an improved ability of neurologists to prevent, recognize, or treat PD complications.
We present Advanced Camera for Surveys, NICMOS, and Keck adaptive-optics-assisted photometry of 20 Type Ia supernovae (SNe Ia) from the Hubble Space Telescope (HST) Cluster Supernova Survey. The SNe ...Ia were discovered over the redshift interval 0.623 < z < 1.415. Of these SNe Ia, 14 pass our strict selection cuts and are used in combination with the world's sample of SNe Ia to derive the best current constraints on dark energy. Of our new SNe Ia, 10 are beyond redshift z = 1, thereby nearly doubling the statistical weight of HST-discovered SNe Ia beyond this redshift. Our detailed analysis corrects for the recently identified correlation between SN Ia luminosity and host galaxy mass and corrects the NICMOS zero point at the count rates appropriate for very distant SNe Ia. Adding these SNe improves the best combined constraint on dark-energy density, rho sub(DE)(z), at redshifts 1.0 < z < 1.6 by 18% (including systematic errors). For a flat LAMBDACDM universe, we find ohm sub(Lambda) = 0.729 + or - 0.014 (68% confidence level (CL) including systematic errors). For a flat wCDM model, we measure a constant dark-energy equation-of-state parameter w = -1.013 super(+0.068) sub(-0.073) (68% CL). Curvature is constrained to ~0.7% in the owCDM model and to 2% in a model in which dark energy is allowed to vary with parameters w sub(0) and w sub(a). Further tightening the constraints on the time evolution of dark energy will require several improvements, including high-quality multi-passband photometry of a sample of several dozen z > 1 SNe Ia. We describe how such a sample could be efficiently obtained by targeting cluster fields with WFC3 on board HST. The updated supernova Union2.1 compilation of 580 SNe is available at http://supernova.lbl.gov/Union.
Type Ia Supernovae (SNe Ia) are standardizable candles that allow us to measure the recent expansion rate of the Universe. Due to uncertainties in progenitor physics, potential astrophysical ...dependencies may bias cosmological measurements if not properly accounted for. The dependency of the intrinsic luminosity of SNe Ia with their host-galaxy environment is often used to standardize SNe Ia luminosity and is commonly parameterized as a step function. This functional form implicitly assumes two-populations of SNe Ia. In the literature, multiple environmental indicators have been considered, finding different, sometimes incompatible, step function amplitudes. We compare these indicators in the context of a two-populations model, based on their ability to distinguish the two populations. We show that local H
α
-based specific star formation rate (lsSFR) and global stellar mass are better tracers than, for instance, host galaxy morphology. We show that tracer accuracy can explain the discrepancy between the observed SNe Ia step amplitudes found in the literature. Using lsSFR or global mass to identify the two populations can explain all other observations, though lsSFR is favoured. As lsSFR is strongly connected to age, our results favour a prompt and delayed population model. In any case, there exists two populations that differ in standardized magnitude by at least 0.121 ± 0.010 mag.
Abstract
We study the spectral diversity of Type Ia supernovae (SNe Ia) at maximum light using high signal-to-noise spectrophotometry of 173 SNe Ia from the Nearby Supernova Factory. We decompose the ...diversity of these spectra into different extrinsic and intrinsic components, and we construct a nonlinear parameterization of the intrinsic diversity of SNe Ia that preserves pairings of “twin” SNe Ia. We call this parameterization the “Twins Embedding.” Our methodology naturally handles highly nonlinear variability in spectra, such as changes in the photosphere expansion velocity, and uses the full spectrum rather than being limited to specific spectral line strengths, ratios, or velocities. We find that the time evolution of SNe Ia near maximum light is remarkably similar, with 84.6% of the variance in common to all SNe Ia. After correcting for brightness and color, the intrinsic variability of SNe Ia is mostly restricted to specific spectral lines, and we find intrinsic dispersions as low as ∼0.02 mag between 6600 and 7200 Å. With a nonlinear three-dimensional model plus one dimension for color, we can explain 89.2% of the intrinsic diversity in our sample of SNe Ia, which includes several different kinds of “peculiar” SNe Ia. A linear model requires seven dimensions to explain a comparable fraction of the intrinsic diversity. We show how a wide range of previously established indicators of diversity in SNe Ia can be recovered from the Twins Embedding. In a companion article, we discuss how these results can be applied to the standardization of SNe Ia for cosmology.
Denoising fMRI data requires assessment of frame-to-frame head motion and removal of the biases motion introduces. This is usually done through analysis of the parameters calculated during ...retrospective head motion correction (i.e., ‘motion’ parameters). However, it is increasingly recognized that respiration introduces factitious head motion via perturbations of the main (B0) field. This effect appears as higher-frequency fluctuations in the motion parameters (>0.1 Hz, here referred to as ‘HF-motion’), primarily in the phase-encoding direction. This periodicity can sometimes be obscured in standard single-band fMRI (TR 2.0–2.5 s) due to aliasing. Here we examined (1) how prevalent HF-motion effects are in seven single-band datasets with TR from 2.0 to 2.5 s and (2) how HF-motion affects functional connectivity. We demonstrate that HF-motion is more common in older adults, those with higher body mass index, and those with lower cardiorespiratory fitness. We propose a low-pass filtering approach to remove the contamination of high frequency effects from motion summary measures, such as framewise displacement (FD). We demonstrate that in most datasets this filtering approach saves a substantial amount of data from FD-based frame censoring, while at the same time reducing motion biases in functional connectivity measures. These findings suggest that filtering motion parameters is an effective way to improve the fidelity of head motion estimates, even in single band datasets. Particularly large data savings may accrue in datasets acquired in older and less fit participants.
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•Single-band fMRI motion traces show factitious high-frequency content (HF-motion).•The magnitude of HF-motion relates to age and other demographic factors.•HF-motion elevates framewise displacement (FD) and causes data loss.•Substantial fMRI data can be recovered from censoring by filtering motion traces.•Filtering motion traces reduces motion artifacts in functional connectivity.
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