1,888 research outputs found
A modified protocol to improve the detection of enhancing brain and spinal cord lesions in multiple sclerosis
No full textQUANTITATIVE BRAIN MRI LESION LOAD PREDICTS THE COURSE OF CLINICALLY ISOLATED SYNDROMES SUGGESTIVE OF MULTIPLE-SCLEROSIS
No full textMRS shows abnormalities before symptoms in familial Alzheimer disease.
No full textBACKGROUND: Pathologic change in Alzheimer disease (AD) begins some years before symptoms. MRS has the potential to detect metabolic abnormalities reflecting this early pathologic change. Presenilin 1 (PS1) and amyloid precursor protein (APP) mutation carriers have a nearly 100% risk of developing AD and may be studied prior to symptom onset. METHODS: Short echo time proton MR spectra were acquired from a midline posterior cingulate voxel in presymptomatic carriers of PS1 or APP mutations ("presymptomatic mutation carriers" [PMCs]; n = 7) and age- and sex-matched control subjects (n = 6). Ratios of N-acetyl aspartate (NAA), myo-inositol (MI), and choline-containing compounds (Cho) to creatine (Cr) were measured and NAA/MI calculated. Regression analyses and t tests were performed after log transformation. RESULTS: PMC and control subjects were matched for age and sex. PMC subjects were 1.7 to 21.6 years (mean 9.8 years) before expected symptom onset, predicted from family-specific mean age at onset. Age did not significantly affect metabolite ratios. Geometric mean ratios in control subjects were as follows: NAA/Cr = 1.75, MI/Cr = 0.59, and NAA/MI = 2.95. NAA/Cr and NAA/MI were significantly reduced in PMC relative to controls (NAA/Cr mean decrease 10% [95% CI 2 to 18%]; NAA/MI mean decrease 25% [95% CI 3 to 44%]). MI/Cr was increased in PMC, but the differences did not achieve significance (19% increase [95% CI 1% decrease to 41% increase]; p = 0.07)). In PMCs, reduction in NAA/MI (p = 0.001) and MI/Cr (p = 0.002) were related to proximity of expected age at onset. CONCLUSIONS: Metabolic changes are detectable in presymptomatic mutation carriers years before expected onset of Alzheimer disease. Their magnitude is related to proximity of expected age at onset
Discontinuous Galerkin Methods for Numerical Weather Prediction: DG in a large-eddy simulation
No full textThe coarse grid of numerical weather prediction and climate models requires parametrization models to resolve atmospheric processes that are smaller than the grid size. For parametrization development, these processes are simulated by a high resolution model. At the Royal Netherlands MeteorologicalInstitute, the Dutch Atmospheric Large-Eddy Simulation (DALES) is used. This three-dimensional high resolution model uses advection schemes that are too diffusive when steep gradients are present. In this thesis, an advection scheme based on the Discontinuous Galerkin (DG) method is implementedfor DALES.The DG method is known to be dispersive. To remove those non-physical oscillations, the moment limiter of Krivodonova is used. Krivodonova constructed the limiter for one- and two-dimensions. In this thesis the moment limiter and limiting order are derived for three-dimensions. DALES is a model based on the finite difference method and uses operational splitting. Therefore, the DG advection scheme needs a mapping from each cell average to all nodal values that are needed for one DG cell, and a mapping back, which we called mapping a and b respectively. Mappings a that are discussed are taking the cell average as value for all nodal points of the DG cell (cell average a), and taking the L -projection of the cell average to the continuous finite element space (L -projection). This thesis describes mappings b that calculate cell averages of nodal DG values (cell average b)and calculate the cell averages of the tendencies of DG values (cell average of tendency). Using cell average a combined with cell average of tendency, made the DG method as diffusive as the first order upwind scheme. Substituting the cell average a method with the L -projection, the DG method becamevery dispersive, meaning that there was not enough diffusion. At last, cell average b was tested with the L -projection. Its numerical results showed that the speed of the advection was slower than the theoretical velocity. Therefore, a method is suggested which does not need mappings. An option couldbe a supergrid that takes multiple DALES cells as a DG cell.Applied Mathematic
Increasing Distributed Generation Penetration using Soft Normally-Open Points
No full textThis paper considers the effects of various voltage control solutions on facilitating an increase in allowable levels of distributed generation installation before voltage violations occur. In particular, the voltage control solution that is focused on is the implementation of `soft' normally-open points (SNOPs), a term which refers to power electronic devices installed in place of a normally-open point in a medium-voltage distribution network which allows for control of real and reactive power flows between each end point of its installation sites. While other benefits of SNOP installation are discussed, the intent of this paper is to determine whether SNOPs are a viable alternative to other voltage control strategies for this particular application. As such, the SNOPs ability to affect the voltage profile along feeders within a distribution system is focused on with other voltage control options used for comparative purposes. Results from studies on multiple network models with varying topologies are presented and a case study which considers economic benefits of increasing feasible DG penetration is also given
Dg algebras with enough idempotents, their dg modules and their derived categories
No full textWe develop the theory dg algebras with enough idempotents and their dg modules and show their equivalence with that of small dg categories and their dg modules. We introduce the concept of dg adjunction and show that the classical covariant tensor-Hom and contravariant Hom-Hom adjunctions of modules over associative unital algebras are extended as dg adjunctions between categories of dg bimodules. The corresponding adjunctions of the associated triangulated functors are studied, and we investigate when they are one-sided parts of bifunctors which are triangulated on both variables. We finally show that, for a dg algebra with enough idempotents, the perfect left and right derived categories are dual to each other.The author is highly indebted to Alexander Zimmermann for the careful reading of these notes, for his comments and for his help in improving the presentation. This work is backed by reseach projects from the Ministerio de Economía y Competitividad of Spain(MTM201346837-P and MTM201677445-P) and the Fundación ’Séneca’ of Murcia(19880/GERM/15), both with a part of FEDER funds. We thank these institutions for their support
Life cycle comparison of petroleum- and bio-based paper binder from distillers grains (DG)
No full textAbstractThis study presents a comparative cradle-to-gate life cycle assessment (LCA) of distillers grain (DG) gum, a bio-based paper coating binder, and polyvinyl alcohol (PVA). Non-renewable energy use, greenhouse gas (GHG) emissions, and eutrophication potential were assessed for each binder. Economic, mass, and energy allocation were used to allocate the impacts of DG gum production with co-products (ethanol and livestock feed). DG production non-renewable energy use (269 to 183MJ) surpassed that associated with PVA production (168MJ). GHG emissions from DG gum production under mass and energy allocations were 28% and 37% lower than PVA production emissions, respectively. Corn cultivation is responsible for 55% to 78% of the eutrophication impacts of DG gum production under energy and economic allocation, respectively. Changes to natural gas consumption and fertilizer runoff had the largest influence on total energy use, GHG emissions, and eutrophication potential of DG gum production
Hypersonic interference heating in the vicinity of surface protuberances
No full textThe understanding of the behaviour of the flow around surface protuberances in
hypersonic vehicles is developed and an engineering approach to predict the
location and magnitude of the highest heat transfer rates in their vicinity is
presented. To this end, an experimental investigation was performed in a
hypersonic facility at freestream Mach numbers of 8.2 and 12.3 and Reynolds
numbers ranging from Re (a)/m = 3.35 x 10(6) to Re (a)/m = 9.35 x 10(6). The
effects of protuberance geometry, boundary layer state, freestream Reynolds
number and freestream Mach numbers were assessed based on thin-film heat
transfer measurements. Further understanding of the flowfield was obtained
through oil-dot visualizations and high-speed schlieren videos. The local
interference interaction was shown to be strongly 3-D and to be dominated by the
incipient separation angle induced by the protuberance. In interactions in which
the incoming boundary layer remains unseparated upstream of the protuberance,
the highest heating occurs adjacent to the device. In interactions in which the
incoming boundary layer is fully separated ahead of the protuberance, the
highest heating generally occurs on the surface just upstream of it except for
low-deflection protuberances under low Reynolds freestream flow conditions in
which case the heat flux to the side is greater
The DG-category of secondary cohomology operations
No full textWe study track categories (i.e., groupoid-enriched categories) endowed with additive structure similar to that of a 1-truncated DG-category, except that composition is not assumed right linear. We show that if such a track category is right linear up to suitably coherent correction tracks, then it is weakly equivalent to a 1-truncated DG-category. This generalizes work of the first author on the strictification of secondary cohomology operations. As an application, we show that the secondary integral Steenrod algebra is strictifiable
- …
