1,732,609 research outputs found
Nonlinear dynamics of large-scale coherent structures in free shear layers
No full textIt is well known that fully developed turbulent free shear layers exhibit a high degree of order, characterized by large-scale coherent structures, i.e. spanwise vortex rollers. Extensive experimental investigations show that such organised motions bear remarkable resemblance to inviscid instability waves, and their main characteristics, including the length scales, propagation speeds and transverse structure, are reasonably well predicted by inviscid linear stability analysis of the mean flow. In this paper, we present a mathematical theory to describe the nonlinear dynamics of coherent structures. The theory is adapted from the nonlinear non-equilibrium critical-layer approach for laminar-flow instabilities by accounting for (a) the enhanced non-parallelism associated with fast spreading of the mean flow, and (b) the influence of small-scale turbulence on coherent structures. The combination of these factors with nonlinearity leads to an interesting evolution system, consisting of the coupled amplitude and vorticity equations, in which non-parallelism contributes the so-called translational critical-layer effect. Numerical solutions of the evolution system captures vortex roll-up, which is the hallmark of turbulent mixing layer, and the predicted amplitude development closely mimics what was measured in experiments. Key words: turbulence, coherent structures, instability, nonlinearit
Towards the standardization of a testing method for the end-stop impacts of suspension seats
No full textStandard tests of the vibration isolation efficiency of suspension seats currently use narrow-band input spectra representing the motions of specific vehicles. The motions used in these tests have near-Gaussian amplitude distributions, whereas vehicle motions include occasional extreme movements causing end-stop impacts of the seat suspension which increase the exposure of the seat occupant to vibration and shock. Tests have been conducted with various vibration magnitudes so as to quantify suspension seat isolation efficiency in terms of the ratios of the vibration dose values (VDVs) at the base of the seat, above the seat suspension and above the seat cushion. It is shown that the vibration response of a seat suspension occurs in five stages according to the magnitude of the input vibration, and that the cushion of a suspension seat may reduce the severity of severe end-stop impacts. The dynamic performance of a suspension seat when supporting a human subject and when supporting a sand bag is compared and the effect of mid-position adjustment is demonstrated. The form of an end-stop impact test which could supplement existing tests so as to evaluate the overall performance of suspension seats is discussed.</p
Business risks and opportunities from climate change in large developing countries - a case study focusing on China
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
A multi-stage genome-wide association study of bladder cancer identifies multiple susceptibility loci.
Full text linkWe conducted a multi-stage, genome-wide association study of bladder cancer with a primary scan of 591,637 SNPs in 3,532 affected individuals (cases) and 5,120 controls of European descent from five studies followed by a replication strategy, which included 8,382 cases and 48,275 controls from 16 studies. In a combined analysis, we identified three new regions associated with bladder cancer on chromosomes 22q13.1, 19q12 and 2q37.1: rs1014971, (P = 8 × 10⁻¹²) maps to a non-genic region of chromosome 22q13.1, rs8102137 (P = 2 × 10⁻¹¹) on 19q12 maps to CCNE1 and rs11892031 (P = 1 × 10⁻⁷) maps to the UGT1A cluster on 2q37.1. We confirmed four previously identified genome-wide associations on chromosomes 3q28, 4p16.3, 8q24.21 and 8q24.3, validated previous candidate associations for the GSTM1 deletion (P = 4 × 10⁻¹¹) and a tag SNP for NAT2 acetylation status (P = 4 × 10⁻¹¹), and found interactions with smoking in both regions. Our findings on common variants associated with bladder cancer risk should provide new insights into the mechanisms of carcinogenesis
The influence of end-stop buffer characteristics on the severity of suspension seat end-stop impacts
No full textSuspension seat end-stop impacts may be a source of increased risk of injury for the drivers of some machines and work vehicles, such as off-road vehicles. Most suspension seats use rubber buffers to reduce the severity of end-stop impacts, but they still result in a high magnitude of acceleration being transmitted to drivers when an end-stop impact occurs. An experimental study has been conducted to investigate the effect of buffer stiffness and buffer damping on the severity of end-stop impacts. The results show that the end-stop impact performance of suspension seats with only bottom buffers can be improved by the use of both top and bottom buffers. The force-deflection characteristics of rubber buffers had a significant influence on the severity of end-stop impacts. The optimum buffer should have medium stiffness which is nearly linear and occurs over a long deflection, without being compressed to its high stiffness stage. It is shown, theoretically, that buffer damping is capable of significantly reducing the severity of end-stop impacts. However, since current rubber material provides only low damping, alternative materials to those in current use, or either passive or active damping devices, are required.</p
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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