10,147 research outputs found
Measuring the Effects of Artificial Viscosity in SPH Simulations of Rotating Fluid Flows
A commonly cited drawback of SPH is the introduction of spurious shear
viscosity by the artificial viscosity term in situations involving rotation.
Existing approaches for quantifying its effect include approximate analytic
formulae and disc-averaged be- haviour in specific ring-spreading simulations,
based on the kinematic effects produced by the artificial viscosity. These
methods have disadvantages, in that they typically are applicable to a very
small range of physical scenarios, have a large number of simplifying
assumptions, and often are tied to specific SPH formulations which do not
include corrective (e.g., Balsara) or time-dependent viscosity terms. In this
study we have developed a simple, generally applicable and practical technique
for evaluating the local effect of artificial viscosity directly from the
creation of specific entropy for each SPH particle. This local approach is
simple and quick to implement, and it al- lows a detailed characterization of
viscous effects as a function of position. Several advantages of this method
are discussed, including its ease in evaluation, its greater accuracy and its
broad applicability. In order to compare this new method with ex- isting ones,
simple disc flow examples are used. Even in these basic cases, the very roughly
approximate nature of the previous methods is shown. Our local method pro-
vides a detailed description of the effects of the artificial viscosity
throughout the disc, even for extended examples which implement Balsara
corrections. As a further use of this approach, explicit dependencies of the
effective viscosity in terms of SPH and flow parameters are estimated from the
example cases. In an appendix, a method for the initial placement of SPH
particles is discussed which is very effective in reducing numerical
fluctuations.Comment: 15 pages, 9 figures, resubmitted to MNRA
The Last King of Scotland or the Last N----r on Earth? The Ethics of Race on Film
This paper undertakes four tasks. It examines a tradition of cinematic and narrative representation that we might call “the narrative of moral gentrification.” It insists on the importance of excavating the racialist and often racist images, motifs, and myths that constitute this tradition. It recommends a form of philosophical aesthetics, located at the intersection of aesthetics, ethical perfectionism, and critical race theory, as a resource for doing this work. And it insists on the importance of subjecting problematic or qualitatively inferior expressive objects to critical scrutiny for the sake of developing proper iconographies and archives of white supremacist expressive culture
Personalized medicine : the impact on chemistry
An effective strategy for personalized medicine requires a major conceptual change in the development and application of therapeutics. In this article, we argue that further advances in this field should be made with reference to another conceptual shift, that of network pharmacology. We examine the intersection of personalized medicine and network pharmacology to identify strategies for the development of personalized therapies that are fully informed by network pharmacology concepts. This provides a framework for discussion of the impact personalized medicine will have on chemistry in terms of drug discovery, formulation and delivery, the adaptations and changes in ideology required and the contribution chemistry is already making. New ways of conceptualizing chemistry’s relationship with medicine will lead to new approaches to drug discovery and hold promise of delivering safer and more effective therapies
Unexpected evolutionary proximity of eukaryotic and cyanobacterial enzymes responsible for biosynthesis of retinoic acid and its oxidation
Biosynthesis of retinoic acid from retinaldehyde (retinal) is catalysed by an aldehyde dehydrogenase (ALDH) and its oxidation by cytochrome P450 enzymes (CYPs). Herein we show by phylogenetic analysis that the ALDHs and CYPs in the retinoic acid pathway in animals are much closer in evolutionary terms to cyanobacterial orthologs than would be expected from the standard models of evolution
Matching of spatially homogeneous non-stationary space--times to vacuum in cylindrical symmetry
We study the matching of LRS spatially homogeneous collapsing dust
space-times with non-stationary vacuum exteriors in cylindrical symmetry. Given
an interior with diagonal metric we prove existence and uniqueness results for
the exterior. The matched solutions contain trapped surfaces, singularities and
Cauchy horizons. The solutions cannot be asymptotically flat and we present
evidence that they are singular on the Cauchy horizons.Comment: LaTeX, 15 pages, 1 figure, submitted for publicatio
Experimental measurement of focused wave group and solitary wave overtopping
Prediction of individual wave overtopping events is important in assessing danger to life and property, but data are sparse and hydrodynamic understanding is lacking. Laboratory-scale waves of three distinct types were generated at the Coastal Research Facility to model extreme waves overtopping a trapezoidal embankment. These comprised wave groups of compact form, wave groups embedded in a background wave field, and a solitary wave. The inshore wave propagation was measured and the time variation of overtopping rate estimated. The total volume overtopped was measured directly. The experiments provide well-defined data without uncertainty due to the effect of reflection on the incident wave train. The dependence of overtopping on a range of wave shapes is thus determined and the influence of wave-wave interactions on overtopping assessed. It was found that extreme overtopping may arise from focused waves with deep troughs rather than large crests. Furthermore, overtopping waves can be generated from small wave packets without affecting the applicability of results to cases in which there are surrounding waves. Finally, overtopping from a solitary wave is comparable with overtopping from focused wave groups of the same amplitude. © 2011 Copyright International Association for Hydro-Environment Engineering and Research
Depletion of atmospheric nitrate and chloride as a consequence of the Toba Volcanic Eruption
Continuous measurements of SO42− and electrical conductivity (ECM) along the GISP2 ice core record the Toba mega‐eruption at a depth 2590.95 to 2091.25 m (71,000±5000 years ago). Major chemical species were analyzed at a resolution of 1 cm per sample for this section. An ∼6‐year long period with extremely high volcanic SO42− coincident with a 94% depletion of nitrate and 63% depletion of chloride is observed at the depth of the Toba horizon. Such a reduction of chloride in a volcanic layer preserved in an ice core has not been observed in any previous studies. The nearly complete depletion of nitrate (to 5 ppb) encountered at the Toba level is the lowest value in the entire ∼250,000 years of the GISP2 ice core record. We propose possible mechanisms to explain the depletion of nitrate and chloride resulting from this mega‐eruption
Using the Man9(GlcNAc)2 – DC-SIGN pairing to probe specificity in photochemical immobilization
We demonstrate the expected preference of an immobilised oligosaccharide Man(9)(GlcNAc)(2) upon a 96-well photochemical array, for its known receptor, the cell-surface lectin Dendritic Cell-Specific ICAM3 Grabbing Nonintegrin (DC-SIGN) when compared to immobilised competing monosaccharides
FMRI Clustering and False Positive Rates
Recently, Eklund et al. (2016) analyzed clustering methods in standard FMRI
packages: AFNI (which we maintain), FSL, and SPM [1]. They claimed: 1) false
positive rates (FPRs) in traditional approaches are greatly inflated,
questioning the validity of "countless published fMRI studies"; 2)
nonparametric methods produce valid, but slightly conservative, FPRs; 3) a
common flawed assumption is that the spatial autocorrelation function (ACF) of
FMRI noise is Gaussian-shaped; and 4) a 15-year-old bug in AFNI's 3dClustSim
significantly contributed to producing "particularly high" FPRs compared to
other software. We repeated simulations from [1] (Beijing-Zang data [2], see
[3]), and comment on each point briefly.Comment: 3 pages, 1 figure. A Letter accepted in PNA
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