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MASSIVE GRAVITY WRAPPED IN THE COSMIC WEB
Shim, Junsup,Lee, Jounghun,Li, Baojiu IOP Publishing 2014 The Astrophysical journal Vol.784 No.1
<P>We study how the filamentary pattern of the cosmic web changes if the true gravity deviates from general relativity (GR) on a large scale. The f(R) gravity, whose strength is controlled to satisfy the current observational constraints on the cluster scale, is adopted as our fiducial model and a large, high-resolution N-body simulation is utilized for this study. By applying the minimal spanning tree algorithm to the halo catalogs from the simulation at various epochs, we identify the main stems of the rich superclusters located in the most prominent filamentary section of the cosmic web and determine their spatial extents per member cluster to be the degree of their straightness. It is found that the f (R) gravity has the effect of significantly bending the superclusters and that the effect becomes stronger as the universe evolves. Even in the case where the deviation from GR is too small to be detectable by any other observables, the degree of the supercluster straightness exhibits a conspicuous difference between the f (R) and the GR models. Our results also imply that the supercluster straightness could be a useful discriminator of f (R) gravity from the coupled dark energy since it is shown to evolve differently between the two models. As a final conclusion, the degree of the straightness of the rich superclusters should provide a powerful cosmological test of large scale gravity.</P>
DARK SECTOR COUPLING BENDS THE SUPERCLUSTERS
Shim, Junsup,Lee, Jounghun IOP Publishing 2013 The Astrophysical journal Vol.777 No.1
<P>Galaxy clusters exhibit a noticeably anisotropic pattern in their clustering, which is vividly manifested by the presence of rich filament-like superclusters. The more anisotropic the clustering of galaxy clusters is, the more straight the rich filament-like superclusters become. Given that the degree of the anisotropy in the largest-scale clustering depends sensitively on the nature of dark energy, the supercluster straightness may play a complimentary role in testing dynamic dark energy models. Here, we focus on the coupled dark energy (cDE) models which assume the existence of dark sector coupling between scalar field dark energy and nonbaryonic dark matter. By determining the spines of the superclusters identified in the publicly available group catalogs from the COupled Dark Energy Cosmological Simulations for four different cDE models as well as for the Lambda CDM model, we quantify the straightness of each supercluster as the spatial extent of its spine per member cluster, where a supercluster spine represents the main stem of the minimal spanning tree constructed out of the member clusters. It is shown that the dark sector coupling plays a role in making the supercluster less straight relative to the Lambda CDM case and that in a cDE model with supergravity potential the superclusters are least straight. We also find that the difference in the degree of the supercluster straightness between the cDE and the Lambda CDM cases increases with redshift. A physical interpretation of our result as well as its cosmological implication are discussed.</P>
중, 소형 디젤 차량에서 플라즈마와 후 분사를 통한 PM, NOx 동시 저감에 관한 실험적 연구
김종우(Jongwoo Kim),윤준섭(Junsup Yun),심우찬(Wochan Shim) 한국자동차공학회 2007 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
Due to the global warming problem, diesel engine is becoming a one of the most promising solutions for light-duty vehicles in the world. Compared to spark-ignition engines, diesel engines generally have lower unburned hydrocarbon and carbon monoxide, but they also produce still higher levels of NO x and smoke emissions even though using a common-rail injection system. To reduce the diesel emissions, DOC and DPF system have been developed to comply with tighten diesel emission regulations. This paper describes the NOx and smoke emission characteristics of current diesel vehicle with a post injection and plasma aftertreatment system in a transient driving mode. Emissions tests were performed according to New European Driving Cycle mode. Results from these tests show that NOx and smoke emissions with post injection and plasma treatment system is much lower than that without the system in the NEDC mode.