The finite-element （FE） model and the Rosenthal equation are used to study the thermal and microstructural phenomena in the laser powder-bed fusion of lnconel 718. A primary aim is to comprehend the advantages and d...The finite-element （FE） model and the Rosenthal equation are used to study the thermal and microstructural phenomena in the laser powder-bed fusion of lnconel 718. A primary aim is to comprehend the advantages and disadvantages of the Rosenthal equation （which provides an analytical alternative to FE analysis）, and to investigate the influence of underlying assumptions on estimated results. Various physical characteristics are compared among the FE model, Rosenthal equation, and experiments. The predicted melt pool shapes compared with reported experimental results from the literature show that both the FE model and the analytical （Rosenthal） equation provide a reasonably accurate estimation. At high heat input, under conditions leading to keyholing, the reported melt width is narrower than predicted by the analytical equation. Moreover, a sensitivity analysis based on choices of the absorptivity is performed, which shows that the Rosenthal approach is more sensitive to absorptivity, compared with the FE approach. The primary reason could be the effect of radiative and convective losses, which are assumed to be negligible in the Rosenthal equation. In addition, both methods predict a columnar solidification microstructure, which agrees well with experimental reports, and the primary dendrite arm spacing （PDAS） predicted with the two approaches is comparable with measurements.展开更多
Among-population differences in morphology and behaviors such as boldness have been shown to co-vary with eco- logical conditions, including predation regime. However, between- and within-population covariation of pre...Among-population differences in morphology and behaviors such as boldness have been shown to co-vary with eco- logical conditions, including predation regime. However, between- and within-population covariation of predator defense mor- phology with variation in behaviors relevant to ecology and evolution （boldness, exploration, activity, sociability and aggressive- ness, often defined as personality traits when they are consistent across time and contexts） have never been quantified together in a single study in juvenile fish from populations found in contrasting environments. We measured predator defense morphology differences between adults from two freshwater populations of threespine sticklebacks with different ecological conditions. We then quantified five behaviors in juveniles from both populations raised in a common environment. Wild-caught adults showed significant differences in predator defense morphology. One population had significantly lower lateral plate number, shorter dorsal spine, pelvic spine and pelvic girdle. Furthermore, 61% of individuals from that population showed an absence of pelvic spine and girdle. At the population level, we found that differences in defense morphology in adults between the two lakes were coupled with differences in behaviors in juveniles raised in a common environment. Levels of activity, aggressiveness and boldness were higher in juveniles from the population lacking predator defense structures. At the individual level, anti-predator morphology of adult females could not predict their offspring＇s behavior, but juvenile coloration predicted individual boldness in a popula- tion-specific manner. Our results suggest that ecological conditions, as reflected in adult predator defense morphology, also affect juvenile behavior in threespine sticklebacks, resulting in trait co-specialization, and that there is a genetic or epigenetic compo- nent to these behavioral differences [Current Zoology 58 （1）： 53-65, 2012].展开更多
In the structures where long-term behavior should be monitored and controlled, creep and shrinkage effects have to be included precisely in the analysis and design procedures. Shrinkage varies with the constituent and...In the structures where long-term behavior should be monitored and controlled, creep and shrinkage effects have to be included precisely in the analysis and design procedures. Shrinkage varies with the constituent and mixture proportions, and depends on the curing conditions and the work environment as well. Self-compacting concrete (SCC) contains combinations of various components, such as aggregate, cement, superplasticizer, water-reducing agent and other ingredients which affect the properties of the SCC including shrinkage. Hence, the realistic prediction shrinkage strains of SCC are an important requirement of the design process for this type of concrete structures. This study reviews the accuracy of the conventional concrete (CC) shrinkage prediction models proposed by the international codes of practice, including CEB-FIP (1990), ACI 209R (1997), Eurocode 2 (2001), JSCE (2002), AASHTO (2004; 2007) and AS 3600 (2009). Also, SCC shrinkage prediction models proposed by Poppe and De Schutter (2005), Larson (2007), Cordoba (2007) and Khayat and Long (2010) are reviewed. Further, a new shrinkage prediction model based on the comprehensive analysis on both of the available models, i.e., the CC and the SCC is proposed. The predicted shrinkage strains are compared with the actual measured shrinkage strains in 165 mixtures of SCC and 21 mixtures of CC.展开更多
This paper presents a self-assembly control strategy for the swarm modular robots. Simulated and physical experiments are conducted based on the Sambot platform, which is a novel self-assembly modular robot having the...This paper presents a self-assembly control strategy for the swarm modular robots. Simulated and physical experiments are conducted based on the Sambot platform, which is a novel self-assembly modular robot having the characteristics of both the chain-type and the mobile self-reconfigurable robots. Multiple Sambots can autonomously move and connect with one another through self-assembly to form robotic organisms. The configuration connection state table is used to describe the configuration of the robotic structure. A directional self-assembly control model is proposed to perform the self-assembly experiments. The self-assembly process begins with one Sambot as the seed, and then the Docking Sambots use a behavior-based controller to achieve connection with the seed Sambot. The controller is independent of the target configuration. The seed and connected Sambots execute a configuration comparison algorithm to control the growth of the robotic structure. Furthermore, the simul- taneous self-assembly of multiple Sambots is discussed. For multiple configurations, self-assembly experiments are conducted in simulation platform and physical platform of Sambot. The experimental results verify the effectiveness and scalability of the self-assembly algorithms.展开更多
基金support from the Royal Thai Government and the Bertucci Graduate Fellowship for this research. P. Chris Pistoriussupport from Early Stage Innovations under National Aeronautics and Space Administration (NASA)’s Space Technology Research Grants Program (NNX 17AD03G)
文摘The finite-element （FE） model and the Rosenthal equation are used to study the thermal and microstructural phenomena in the laser powder-bed fusion of lnconel 718. A primary aim is to comprehend the advantages and disadvantages of the Rosenthal equation （which provides an analytical alternative to FE analysis）, and to investigate the influence of underlying assumptions on estimated results. Various physical characteristics are compared among the FE model, Rosenthal equation, and experiments. The predicted melt pool shapes compared with reported experimental results from the literature show that both the FE model and the analytical （Rosenthal） equation provide a reasonably accurate estimation. At high heat input, under conditions leading to keyholing, the reported melt width is narrower than predicted by the analytical equation. Moreover, a sensitivity analysis based on choices of the absorptivity is performed, which shows that the Rosenthal approach is more sensitive to absorptivity, compared with the FE approach. The primary reason could be the effect of radiative and convective losses, which are assumed to be negligible in the Rosenthal equation. In addition, both methods predict a columnar solidification microstructure, which agrees well with experimental reports, and the primary dendrite arm spacing （PDAS） predicted with the two approaches is comparable with measurements.
文摘Among-population differences in morphology and behaviors such as boldness have been shown to co-vary with eco- logical conditions, including predation regime. However, between- and within-population covariation of predator defense mor- phology with variation in behaviors relevant to ecology and evolution （boldness, exploration, activity, sociability and aggressive- ness, often defined as personality traits when they are consistent across time and contexts） have never been quantified together in a single study in juvenile fish from populations found in contrasting environments. We measured predator defense morphology differences between adults from two freshwater populations of threespine sticklebacks with different ecological conditions. We then quantified five behaviors in juveniles from both populations raised in a common environment. Wild-caught adults showed significant differences in predator defense morphology. One population had significantly lower lateral plate number, shorter dorsal spine, pelvic spine and pelvic girdle. Furthermore, 61% of individuals from that population showed an absence of pelvic spine and girdle. At the population level, we found that differences in defense morphology in adults between the two lakes were coupled with differences in behaviors in juveniles raised in a common environment. Levels of activity, aggressiveness and boldness were higher in juveniles from the population lacking predator defense structures. At the individual level, anti-predator morphology of adult females could not predict their offspring＇s behavior, but juvenile coloration predicted individual boldness in a popula- tion-specific manner. Our results suggest that ecological conditions, as reflected in adult predator defense morphology, also affect juvenile behavior in threespine sticklebacks, resulting in trait co-specialization, and that there is a genetic or epigenetic compo- nent to these behavioral differences [Current Zoology 58 （1）： 53-65, 2012].
文摘In the structures where long-term behavior should be monitored and controlled, creep and shrinkage effects have to be included precisely in the analysis and design procedures. Shrinkage varies with the constituent and mixture proportions, and depends on the curing conditions and the work environment as well. Self-compacting concrete (SCC) contains combinations of various components, such as aggregate, cement, superplasticizer, water-reducing agent and other ingredients which affect the properties of the SCC including shrinkage. Hence, the realistic prediction shrinkage strains of SCC are an important requirement of the design process for this type of concrete structures. This study reviews the accuracy of the conventional concrete (CC) shrinkage prediction models proposed by the international codes of practice, including CEB-FIP (1990), ACI 209R (1997), Eurocode 2 (2001), JSCE (2002), AASHTO (2004; 2007) and AS 3600 (2009). Also, SCC shrinkage prediction models proposed by Poppe and De Schutter (2005), Larson (2007), Cordoba (2007) and Khayat and Long (2010) are reviewed. Further, a new shrinkage prediction model based on the comprehensive analysis on both of the available models, i.e., the CC and the SCC is proposed. The predicted shrinkage strains are compared with the actual measured shrinkage strains in 165 mixtures of SCC and 21 mixtures of CC.
基金supported by the National High Technology Research and Development Program of China ("863" Program) (Grant Nos. 2009AA043901 and 2012AA041402)National Natural Science Foundation of China (Grant No. 61175079)+1 种基金Fundamental Research Funds for the Central Universities (Grant No. YWF-11-02-215)Beijing Technological New Star Project (Grant No. 2008A018)
文摘This paper presents a self-assembly control strategy for the swarm modular robots. Simulated and physical experiments are conducted based on the Sambot platform, which is a novel self-assembly modular robot having the characteristics of both the chain-type and the mobile self-reconfigurable robots. Multiple Sambots can autonomously move and connect with one another through self-assembly to form robotic organisms. The configuration connection state table is used to describe the configuration of the robotic structure. A directional self-assembly control model is proposed to perform the self-assembly experiments. The self-assembly process begins with one Sambot as the seed, and then the Docking Sambots use a behavior-based controller to achieve connection with the seed Sambot. The controller is independent of the target configuration. The seed and connected Sambots execute a configuration comparison algorithm to control the growth of the robotic structure. Furthermore, the simul- taneous self-assembly of multiple Sambots is discussed. For multiple configurations, self-assembly experiments are conducted in simulation platform and physical platform of Sambot. The experimental results verify the effectiveness and scalability of the self-assembly algorithms.
