There is limited information regarding the effects of spaceflight on the anatomical configuration of the brain and on cerebrospinal fluid (CSF) spaces.
We used magnetic resonance imaging (MRI) to ...compare images of 18 astronauts' brains before and after missions of long duration, involving stays on the International Space Station, and of 16 astronauts' brains before and after missions of short duration, involving participation in the Space Shuttle Program. Images were interpreted by readers who were unaware of the flight duration. We also generated paired preflight and postflight MRI cine clips derived from high-resolution, three-dimensional imaging of 12 astronauts after long-duration flights and from 6 astronauts after short-duration flights in order to assess the extent of narrowing of CSF spaces and the displacement of brain structures. We also compared preflight ventricular volumes with postflight ventricular volumes by means of an automated analysis of T
-weighted MRIs. The main prespecified analyses focused on the change in the volume of the central sulcus, the change in the volume of CSF spaces at the vertex, and vertical displacement of the brain.
Narrowing of the central sulcus occurred in 17 of 18 astronauts after long-duration flights (mean flight time, 164.8 days) and in 3 of 16 astronauts after short-duration flights (mean flight time, 13.6 days) (P<0.001). Cine clips from a subgroup of astronauts showed an upward shift of the brain after all long-duration flights (12 astronauts) but not after short-duration flights (6 astronauts) and narrowing of CSF spaces at the vertex after all long-duration flights (12 astronauts) and in 1 of 6 astronauts after short-duration flights. Three astronauts in the long-duration group had optic-disk edema, and all 3 had narrowing of the central sulcus. A cine clip was available for 1 of these 3 astronauts, and the cine clip showed upward shift of the brain.
Narrowing of the central sulcus, upward shift of the brain, and narrowing of CSF spaces at the vertex occurred frequently and predominantly in astronauts after long-duration flights. Further investigation, including repeated postflight imaging conducted after some time on Earth, is required to determine the duration and clinical significance of these changes. (Funded by the National Aeronautics and Space Administration.).
Abstract
BACKGROUND
Endovascular thrombectomy is currently the standard of care for acute ischemic stroke (AIS). Although earlier trials on endovascular thrombectomy were performed using stent ...retrievers, recently completed the contact aspiration vs stent retriever for successful revascularization (ASTER) and a comparison of direct aspiration versus stent retriever as a first approach (COMPASS) trials have shown the noninferiority of direct aspiration.
OBJECTIVE
To report the largest experience with ADAPT thrombectomy and compare the impact of advancement in reperfusion catheter technologies on outcomes.
METHODS
We reviewed a retrospective database of AIS patients who underwent ADAPT thrombectomy between January 2013 and November 2017 at the Medical University of South Carolina. Demographics and baseline characteristics, technical variables, and radiological and clinical outcomes were reviewed.
RESULTS
Among 510 patients (mean age: 67.7, 50.6% females), successful recanalization at first pass was achieved in 61.8%, and with aspiration only in 77.5%. Mean procedure time was 27.4 min, and the rate of good outcomes (mRS 0-2) at 90 d was 42.9%. The rate of recanalization with aspiration only was significantly higher, and procedure time was significantly lower in patients treated with larger catheters (ACE 064 and ACE 068) compared to smaller catheters (5 MAX and ACE, P < .05). There were no differences in complication rates or postoperative parenchymal hemorrhage across groups (P > .05); however, use of ACE 068 was an independent predictor of good outcomes at 90 d on multivariate regression analysis (odds ratio = 1.6, P < .05).
CONCLUSION
Refinement of ADAPT thrombectomy by incorporating reperfusion catheters with higher inner diameters and thus higher aspiration forces is associated with better outcomes, shorter procedure times, and lower likelihood of using additional devices without impacting complication rates.
The particle swarm optimization (PSO) is a relatively new generation of combinatorial metaheuristic algorithms which is based on a metaphor of social interaction, namely bird flocking or fish ...schooling. Although the algorithm has shown some important advances by providing high speed of convergence in specific problems it has also been reported that the algorithm has a tendency to get stuck in a near optimal solution and may find it difficult to improve solution accuracy by fine tuning. The present paper proposes a new variation of PSO model where we propose a new method of introducing nonlinear variation of inertia weight along with a particle's old velocity to improve the speed of convergence as well as fine tune the search in the multidimensional space. The paper also presents a new method of determining and setting a complete set of free parameters for any given problem, saving the user from a tedious trial and error based approach to determine them for each specific problem. The performance of the proposed PSO model, along with the fixed set of free parameters, is amply demonstrated by applying it for several benchmark problems and comparing it with several competing popular PSO and non-PSO combinatorial metaheuristic algorithms.
NASA's Orbiting Carbon Observatory-2 (OCO-2) mission was motivated by the need to diagnose how the increasing concentration of atmospheric carbon dioxide (CO
) is altering the productivity of the ...biosphere and the uptake of CO
by the oceans. Launched on 2 July 2014, OCO-2 provides retrievals of the column-averaged CO
dry-air mole fraction (Formula: see text) as well as the fluorescence from chlorophyll in terrestrial plants. The seasonal pattern of uptake by the terrestrial biosphere is recorded in fluorescence and the drawdown of Formula: see text during summer. Launched just before one of the most intense El Niños of the past century, OCO-2 measurements of Formula: see text and fluorescence record the impact of the large change in ocean temperature and rainfall on uptake and release of CO
by the oceans and biosphere.
Bootstrapping Lasso Estimators Chatterjee, A.; Lahiri, S. N.
Journal of the American Statistical Association,
06/2011, Letnik:
106, Številka:
494
Journal Article
Recenzirano
In this article, we consider bootstrapping the Lasso estimator of the regression parameter in a multiple linear regression model. It is known that the standard bootstrap method fails to be ...consistent. Here, we propose a modified bootstrap method, and show that it provides valid approximation to the distribution of the Lasso estimator, for all possible values of the unknown regression parameter vector, including the case where some of the components are zero. Further, we establish consistency of the modified bootstrap method for estimating the asymptotic bias and variance of the Lasso estimator. We also show that the residual bootstrap can be used to consistently estimate the distribution and variance of the adaptive Lasso estimator. Using the former result, we formulate a novel data-based method for choosing the optimal penalizing parameter for the Lasso using the modified bootstrap. A numerical study is performed to investigate the finite sample performance of the modified bootstrap. The methodology proposed in the article is illustrated with a real data example.
In the present work we have studied ion transport and their correlation with network structure of Li2O-P2O5 glasses. We have measured the ac conductivity of the glasses for wide ranges of temperature ...and frequency. The conductivity shows a crossover from dc to dispersive behavior with the increase in frequency. We have observed that the dc conductivity and the crossover frequency obey Arrhenius relation with same activation energy. We have calculated characteristic lengths of ion transport, such as the characteristic mean square displacement of mobile ions and the spatial extent of localized motion, within the framework of linear response theory. We have observed that both the length scales decrease with the increase in Li2O content in the glasses. We have also investigated FTIR and Raman spectra to study the structure of glassy network and established a simple correlation between transport properties and network structure of the glasses.
•Characteristics lengths of ion transport for Li2O-P2O5 glasses are calculated.•Different structural units are evaluated from FTIR spectra.•Correlation between ion transport and structure are established.
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