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71.
Sam Fletcher Mike J. S. Lowe Madis Ratassepp Colin Brett 《Journal of Nondestructive Evaluation》2012,31(1):56-64
The implementation of synthetic guided wave focusing to locate axially aligned defects in pipes has been investigated. Results
from both finite element computer models and experiments on real pipes are presented and the data show good agreement. Focusing
is necessary to improve the reflection coefficient from axially aligned defects, as the signals are very weak. The Common
Source Method (CSM) of synthetic focusing has been applied which makes it possible to apply focusing via post processing to
previously collected data. The dependence of reflection coefficient on crack length was measured for both through thickness
and part depth axially aligned defects, at a range of frequencies, using the torsional guided wave family. The results show
that the reflection coefficient is approximately doubled when focusing is employed, compared to the sensitivity for unfocused
fundamental torsional waves. However the sensitivity is still very low, so in practise this approach could only be used to
find severe defects. 相似文献
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Sam van Haute Liesbeth Jacxsens Mieke Uyttendaele 《Critical reviews in food science and nutrition》2015,55(11):1529-1551
This paper comprises a selection tool for water disinfection methods for fresh produce pre- and postharvest practices. A variety of water disinfection technologies is available on the market and no single technology is the best choice for all applications. It can be difficult for end users to choose the technology that is best fit for a specific application. Therefore, the different technologies were characterized in order to identify criteria that influence the suitability of a technology for pre- or postharvest applications. Introduced criteria were divided into three principal components: (i) criteria related to the technology and which relate to the disinfection efficiency, (ii) attention points for the management and proper operation, and (iii) necessities in order to sustain the operation with respect to the environment. The selection criteria may help the end user of the water disinfection technology to obtain a systematic insight into all relevant aspects to be considered for preliminary decision making on which technologies should be put to feasibility testing for water disinfection in pre- and postharvest practices of the fresh produce chain. 相似文献
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How have changes in communications technology affected the way that misinformation spreads through a population and persists? To what extent do differences in the architecture of social networks affect the spread of misinformation, relative to the rates and rules by which individuals transmit or eliminate different pieces of information (cultural traits)? Here, we use analytical models and individual-based simulations to study how a ‘cultural load’ of misinformation can be maintained in a population under a balance between social transmission and selective elimination of cultural traits with low intrinsic value. While considerable research has explored how network architecture affects percolation processes, we find that the relative rates at which individuals transmit or eliminate traits can have much more profound impacts on the cultural load than differences in network architecture. In particular, the cultural load is insensitive to correlations between an individual''s network degree and rate of elimination when these quantities vary among individuals. Taken together, these results suggest that changes in communications technology may have influenced cultural evolution more strongly through changes in the amount of information flow, rather than the details of who is connected to whom. 相似文献
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Analytical and numerical assessments of local overpressure from hydrogen gas explosions in petrochemical plants
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Boohyoung Bang Hyunsu Park Jonghun Kim Salem S. Al‐Deyab Alexander L. Yarin Sam S. Yoon 《火与材料》2017,41(6):587-597
Accurate prediction of pressure rise is important for safety assessments of a petrochemical plant in the event of an explosion accident. The sudden pressures arising from gas explosions at various hydrogen concentrations in air have been predicted analytically and numerically. These solutions were compared against experimental data. The analytical solution, based on the self‐similar solution for pointwise strong explosions in an open space, which assumed no energy loss and premixed fuel‐air mixture, reasonably predicted the explosive‐ignition detonation case while the numerical solutions were more suitable to model spark‐ignition deflagration cases that accounted for the effect of turbulence arising from three‐dimensionality and presence of obstacles in the computational domain. Comparison of both analytical and numerical results against experimental data indicates that their differences are within a 30% margin. The analytical model presented herein can be useful for field engineers who want conservative estimates of the overpressure resulting from explosive‐ignition detonation. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
79.
Pisith Sam Pruettha Nanakorn Kasem Theerakittayakorn Pana Suttakul 《International Journal of Mechanics and Materials in Design》2017,13(3):363-383
In this study, the effective elastic constants of several 2D and 3D frame-like periodic cellular solids with different unit-cell topologies are analytically derived using the homogenization method based on equivalent strain energy. The analytical expressions of strain energy of a unit cell under different strain modes are determined using a generic symbolic object-oriented finite element (FE) program written in MATLAB. The obtained analytical expressions of the strain energy are then used to symbolically compute the effective elastic constants that include Young’s moduli, Poisson’s ratios, and shear moduli. The obtained analytical effective elastic constants are numerically verified using results from an ordinary numerical FE program. The obtained closed-form effective elastic constants are also compared with some existing solutions from the literature. This study demonstrates that symbolic computation platforms can be properly used to provide efficient methodologies for finding useful analytical solutions of mechanical problems. Without the symbolic object-oriented FE program in this study, elaborate and tedious analytical analysis has to be manually performed for each different unit cell. The symbolic object-oriented FE program provides analytical analysis of unit cells that is accurate and fast. The object-oriented programming technique allows the symbolic FE program in this study to be efficiently implemented. 相似文献
80.
Erik Berg Schmidt Jeppe Hagstrup Christensen Inge Aardestrup Trine Madsen Sam Riahi Vibeke Ellegaard Hansen Helle Aarup Skou 《Lipids》2001,36(1):S65-S68
There is some evidence from epidemiology that intake of n-3 polyunsaturated fatty acids (PUFA) from seafood may protect against coronary artery disease (CAD). This hypothesis is further supported from animal data showing a beneficial effect of n-3 PUFA on thrombosis and atherosclerosis in animals fed fish oils in most, but not all, studies. There are several mechanisms by which an increased intake of marine n-3 PUFA may protect against CAD; the most universal finding is a reduction of plasma triglycerides. It is puzzling, however, that a very low amount of n-3 PUFA, with no known beneficial biochemical effects, seems to be cardioprotective. It has therefore been of paramount interest to perform clinical trials. Such evidence and trials are discussed in later chapters, and the results have been very encouraging. 相似文献