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Horiuchi H.,Osaka University | Horiuchi H.,International Institute for Advanced Studies
Lecture Notes in Physics | Year: 2010

In this lecture I first review present knowledge about the actual coexistence features of cluster states and mean-field-type states in nuclei. I then discuss how nuclear structure changes from shell-model-like ground state to cluster states. About the actual coexistence features I review them in two parts. In the first part I discuss 8Be, 12C, 16O, and 20Ne. In the second part I discuss 44Ti and 32S where superdeformed atates are observed. The investigation in 32S suggests strong interrelation of 16O + 16O molecular states and superdeformed states. For the discussions of 20Ne, 44Ti and 32S systems, I utilize the results of the detailed studies with antisymmetrized molecular dynamics (AMD). On the basis of these studies of actual coexistence features, I discuss the mechanism of the structure-change between cluster structure and mean-field-type structure and indicate that it comes from the dual nature of nuclear wave functions which have both characters of cluster wave function and mean-field-type wave function. Observed strong E0 transitions between cluster states and the ground state are explained to be a good verification of dual nature of nuclear wave function. © 2010 Springer-Verlag Berlin Heidelberg.

Zhou B.,Nanjing University | Zhou B.,Osaka University | Zhou B.,Accelerator Centre | Funaki Y.,Accelerator Centre | And 10 more authors.
Physical Review Letters | Year: 2013

We investigate the α+O16 cluster structure in the inversion-doublet band (Kπ=01±) states of Ne20 with an angular-momentum-projected version of the Tohsaki-Horiuchi-Schuck-Röpke (THSR) wave function, which was successful "in its original form" for the description of, e.g., the famous Hoyle state. In contrast with the traditional view on clusters as localized objects, especially in inversion doublets, we find that these single THSR wave functions, which are based on the concept of nonlocalized clustering, can well describe the Kπ=01- band and the Kπ=01+ band. For instance, they have 99.98% and 99.87% squared overlaps for 1- and 3- states (99.29%, 98.79%, and 97.75% for 0+, 2+, and 4 + states), respectively, with the corresponding exact solution of the α+O16 resonating group method. These astounding results shed a completely new light on the physics of low energy nuclear cluster states in nuclei: The clusters are nonlocalized and move around in the whole nuclear volume, only avoiding mutual overlap due to the Pauli blocking effect. © 2013 American Physical Society.

Suzuki K.W.,Laval University | Nakayama K.,Kyoto University | Tanaka M.,International Institute for Advanced Studies
Journal of Oceanography | Year: 2013

Copepods are considered to be a vital component connecting the unique macrotidal environment to the high productivity and high biodiversity of the Ariake Sea. To examine the spatiotemporal succession of copepod communities, we conducted monthly sampling (vertical hauls of a 100-μm mesh plankton net) in three neighboring macrotidal estuaries between 2005 and 2006. Irrespective of the season, three copepod communities were recognized in relation to the relatively long gradients of salinity and turbidity along the Chikugo and Midori River estuaries. The oligohaline community (salinity 1-10) was observed at higher turbidities (>100 NTU), whereas the freshwater (salinity <1) and meso/polyhaline (salinity >10) communities were associated with lower turbidities (<100 NTU). The oligohaline calanoid Sinocalanus sinensis occurred only in the Chikugo River estuary, maintaining a large biomass (dry weight >10 mg m-3) in or close to the well-developed estuarine turbidity maximum (ETM) throughout the year. In the Midori River estuary, the oligohaline community lacked S. sinensis and showed a minimum biomass during winter (<10 mg m-3). In both estuaries, the freshwater community always remained at a small biomass (<1 mg m-3), whereas the meso/polyhaline community showed marked seasonal changes in biomass (0.1-657 mg m-3). The prevalence of higher salinities allowed only the meso/polyhaline community to occur in the Kuma River estuary. In summary, S. sinensis characterized the copepod community distinctive of the well-developed ETM, potentially serving as an important link to higher trophic levels during winter when copepods are scarce in other areas. © 2012 The Oceanographic Society of Japan and Springer Japan.

Suzuki K.W.,Laval University | Kasai A.,Kyoto University | Nakayama K.,Kyoto University | Tanaka M.,International Institute for Advanced Studies
Journal of Oceanography | Year: 2012

The inner part of the Ariake Sea is one of the most productive estuarine systems in Japan. To examine potential food items for estuarine organisms, we conducted monthly observations of the dynamics of particulate organic matter along the macrotidal Chikugo River estuary in 2005 and 2006. In the neighboring macrotidal Midori and Kuma River estuaries, comparative observations were made. High turbidity and strong vertical mixing were observed only at low salinities (<10) in the Chikugo River estuary. In contrast, the Midori and Kuma River estuaries were characterized by less turbid and less mixed waters. Concentrations of particulate organic carbon often exceeded 5 mg l -1 in or close to the estuarine turbidity maximum (ETM) of the Chikugo River estuary. However, such high concentrations were rarely observed in the other two estuaries. The observed differences could be attributable to different hydrodynamic processes related to the different lengths of tidal reaches: 23, 8, and 6 km in the Chikugo, Midori, and Kuma Rivers, respectively. In the Chikugo River estuary, spatiotemporal changes of chlorophyll a suggested that phytoplankton occurred abundantly up- and/or downstream from the ETM especially during the warm season. In contrast, pheophytin (i. e., plant detritus) always accumulated in or close to the ETM. Carbon stable isotope ratios and carbon to nitrogen ratios indicated that the plant detritus was derived from phytoplankton and terrestrial plants. The Chikugo River estuary has a high potential to support the production of estuarine organisms through abundant plant detritus in the well-developed ETM all the year round. © 2012 The Oceanographic Society of Japan and Springer.

Suzuki K.W.,Laval University | Ueda H.,Kochi University | Nakayama K.,Kyoto University | Tanaka M.,International Institute for Advanced Studies
Journal of Plankton Research | Year: 2012

Stage-specific horizontal distribution was compared between two sympatric oligohaline copepods to elucidate their life-history strategies related to reproduction: free-spawning Sinocalanus sinensis and egg-carrying Pseudodiaptomus inopinus. Copepods were sampled by vertical hauls of a 100-μm mesh plankton net along the macrotidal Chikugo River estuary in southwestern Japan from 2005 to 2006. Sinocalanus sinensis dominated throughout the year except for the warm season, when P. inopinus outnumbered S. sinensis. The spatiotemporal correspondence of peak densities with the estuarine turbidity maximum was evident for S. sinensis but ambiguous for P. inopinus. Nauplii of S. sinensis were always distributed on average downstream from copepodids and adults, whereas P. inopinus usually showed the opposite pattern of stage-specific horizontal distribution. During large freshwater discharges, S. sinensis was more subject to washout from the estuary. In addition, the potential vulnerability of S. sinensis to droughts was suggested by low tolerance for high salinities. Consequently, egg-carrying P. inopinus has higher flexibility to live under varying estuarine conditions especially during the warm season. In contrast, ecological specializations, such as tidal vertical migration and detritivorous feeding, are considered to underlie the dominance of the free-spawning S. sinensis under the conditions prevailing in the macrotidal environment. © 2012 The Author.

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