Enrichment of r-process elements in dwarf spheroidal galaxies in chemo-dynamical evolution model

The rapid neutron-capture process (r-process) is a major process to synthesize elements heavier than iron, but the astrophysical site(s) of r-process is not identified yet. Neutron star mergers (NSMs) are suggested to be a major r-process site from nucleosynthesis studies. Previous chemical evolution studies however require unlikely short merger time of NSMs to reproduce the observed large star-to-star scatters in the abundance ratios of r-process elements relative to iron, [Eu/Fe], of extremely metal-poor stars in the Milky Way (MW) halo. This problem can be solved by considering chemical evolution in dwarf spheroidal galaxies (dSphs) which would be building blocks of the MW and have lower star formation efficiencies than the MW halo. We demonstrate that enrichment of r-process elements in dSphs by NSMs using an N-body/smoothed particle hydrodynamics code. Our high-resolution model reproduces the observed [Eu/Fe] by NSMs with a merger time of 100 Myr when the effect of metal mixing is taken into account. This is because metallicity is not correlated with time up to ~ 300 Myr from the start of the simulation due to low star formation efficiency in dSphs. We also confirm that this model is consistent with observed properties of dSphs such as radial profiles and metallicity distribution. The merger time and the Galactic rate of NSMs are suggested to be <~ 300 Myr and ~ $10^{-4}$ yr$^{-1}$, which are consistent with the values suggested by population synthesis and nucleosynthesis studies. This study supports that NSMs are the major astrophysical site of r-process.Comment: 16 pages, 16 figures, accepted for publication in Ap

Nanometer Order Separation Control of Large Working Area Nanogap Created by Cleavage of Single-Crystal Silicon Along {111} Planes Using a MEMS Device

Nanogaps with a large working area and a precisely controlled separation of about 1 to 20 nm has important applications in nano photonics, thermal management, power generation, chemical sensing, etc. However, an effective method of fabricating such nanogaps has not yet been established. In addition, it has been necessary to evaluate the dependence of physical characteristics of nanogaps on the separation, but it has been technically and economically difficult to develop such a system. In this study, we developed a MEMS device, which can produce nanogaps with a large area and parallel smooth surfaces by the (111) plane cleavage of a single crystal silicon beam and can change and measure the separation of nanogaps. Using this device, nanogap fabrication by cleavage and separation control were uninterruptedly carried out while maintaining the cleanliness of the gap surfaces in vacuum; a nanogap with a large smooth surface area of 30 μ m² was successfully controlled in the range of 14 nm–1.5 μ m. For a small separation of less than 100 nm, the control resolution was sufficiently high at 1 nm. This method is fully compatible with conventional fabrication technologies for not only MEMS but also other semiconductor devices and should contribute to the fabrication of devices that exhibit useful quantum effects with only minor modifications. 2022-007

SIRIUS Project. IV. The formation history of the Orion Nebula Cluster driven by clump mergers

The Orion Nebula Cluster (ONC) is an excellent example for understanding the formation of star clusters. Recent studies have shown that ONC has three distinct age populations and anisotropy in velocity dispersions, which are key characteristics for understanding the formation history of the ONC. In this study, we perform a smoothed-particle hydrodynamics/$N$-body simulation of star cluster formation from a turbulent molecular cloud. In this simulation, stellar orbits are integrated using a high-order integrator without gravitational softening; therefore, we can follow the collisional evolution of star clusters. We find that hierarchical formation causes episodic star formation that is observed in the ONC. In our simulation, star clusters evolve due to mergers of subclumps. The mergers bring cold gas with the clumps into the forming cluster. This enhances the star formation in the cluster centre. The dense cold gas in the cluster centre continues to form stars until the latest time. This explains the compact distribution of the youngest stars observed in the ONC. Subclump mergers also contribute to the anisotropy in the velocity dispersions and the formation of runaway stars. However, the anisotropy disappears within 0.5 Myr. The virial ratio of the cluster also increases after a merger due to the runaways. These results suggest that the ONC recently experienced a clump merger. We predict that most runaways originated from the ONC have already been found, but walkaways have not.Comment: 15 pages, 21 figures, and 3 tables, accepted for MNRA

Estimation of catch efficiency of a small seine for larval and juvenile Japanese sea bass, Lateolabrax japonicus, in the Ohta estuary

河口域における魚類群集の主要構成者であるスズキ仔稚魚に対する小型曳き網（幅2.3m，高さ1m）の採集効率を，地曳き網（幅16m，高さ1m）による採集結果と比較することにより推定した。2008年3月21日と4月7日に太田川放水路感潮域において合計15回の曳網を行い，合計1,502個体（標準体長14.5－24.0mm）のスズキ仔稚魚を採集した。地曳き網の網目からの逸出が生じる体長16mm未満と，個体密度が著しく低下する23mm以上については解析対象とせず，地曳き網による採集効率を100％と仮定した。体長1mmごとに区分した分布密度を採集具間で比較した結果，小型曳き網による体長16mm以上18mm未満のスズキ仔稚魚採集効率は約100％と推定された。体長18mm以上23mm未満では採集効率（C, ％）が体長（L, mm）に比例して直線的に減少した（C=－17.2*L+388.8，n=11，r2=0.77，p=0.0004）。In order to estimate catch efficiency of a small seine (1.0 by 2.3 m, 2 mm mesh aperture) for larval and juvenile Japanese sea bass Lateolabrax japonicus, results from experimental hauls of the small seine were compared with those from a large seines (1.0 by 16 m, 2.5 mm mesh aperture) in the Ohta Diversion Channel on March 21 and April 7, 2008. A total of 1,502 Japanese sea bass, ranging between 14.5 and 24.0 mm in standard length were collected. Data of fish <15.9 mm was excluded from the analysis since extrusion of these fish through the mesh of the large seine was possible. Comparison of the Japanese sea bass abundance at lengths between the small and large seines revealed that the catch efficiency of the small seine for Japanese sea bass <18.0 mm was approximately 100%. The catch efficiency decreased with the increase in fish body length between 18.0 and 22.9 mm. A linear model was fitted to the relationship between the catch efficiency (C, %) and body length (L, mm): C=－17.2*L+388.8 (n=11, r2=0.77, p=0.0004). Catch efficiency was not estimated for Japanese sea bass ＞ 23 mm since their abundance was quite low in the surveyed area probably due to migration to downriver or sea areas, which are considered as habitats for the following life stages

Up and Down Quark Contributions to Spin Content of Lambda from Fragmentation

We check the $u$ and $d$ quark contributions to the spin content of the $\Lambda$ by means of the $q\to\Lambda$ fragmentation and find that the $u$ and $d$ quarks of the $\Lambda$ are likely positively polarized. The parton distributions in the $\Lambda$ are given by a successful statistical model which can reproduce and correlate a vast body of polarized and unpolarized structure function and parton distribution data of the nucleon. With the Gribov-Lipatov relation between the quark distributions and fragmentation functions, the longitudinal spin transfer for the $\Lambda$ production in the polarized charged lepton deep inelastic scattering (DIS) process and the $\Lambda$-polarization in the neutrino (antineutrino) DIS process are predicted. The available experimental data suggests that the $u$ and $d$ quark contributions to the spin of the $\Lambda$ are positive. In addition, our results provide a collateral evidence for the SU(3) symmetry breaking in hyperon semileptonic decays of the octet baryons, which is very important for a deeper understanding of the proton 'spin crisis'.Comment: 14 pages, 3 figures, 1 tabl

Effects of Splenectomy on Spontaneously Chronic Pancreatitis in aly/aly Mice

Background and Aim. Mice with alymphoplasia (aly/aly) mutation characterized by a lack of lymph nodes, Peyer's patches, and well-defined lymphoid follicles in the spleen were found. In this study, we used splenectomized aly/aly mice to elucidate the effects of secondary lymphoid organs in the development of aly/aly autoimmune pancreatitis. Methods. Forty-eight 10-week-old aly/aly mice were divided into two groups for splenectomy and sham operation. Histological and immunohistochemical analyses of the pancreas were performed at the ages of 20, 30, and 40 weeks old after operation, respectively. Results. Our results showed that mononuclear cell infiltration was restricted to the interlobular connective tissues at the age of 20 weeks, and not increase obviously at the age of 30 and 40 weeks in splenectomized aly/aly mice. Furthermore, an apparent decrease in the expressions of CD4+ T, CD8+ T, and B cells was detected in the pancreatic tissues compared with sham aly/aly mice, however, no significant difference in macrophage expression between mice with and without a splenectomy. Conclusions. Inflammation infiltration and development of the pancreatitis in aly/aly mice were suppressed effectively after splenectomy, which was, at least partly, correlated to inhibition of the infiltration of T and B cells in pancreatic tissues but not to macrophages

Social Participation and the Prevention of Functional Disability in Older Japanese: The JAGES Cohort Study

Background: We examined the relationship between incident functional disability and social participation from the perspective of number of types of organizations participated in and type of social participation in a prospective cohort study. Method The study was based on the Aichi Gerontological Evaluation Study (AGES) Cohort Study data. We followed 13,310 individuals aged 65 years or older for 4 years. Analysis was carried out on 12,951 subjects, excluding 359 people whose information on age or sex was missing. Social participation was categorized into 8 types. Results: Compared to those that did not participate in any organizations, the hazard ratio (HR) was 0.83 (95% CI: 0.73–0.95) for participation in one, 0.72 (0.61–0.85) for participation in two, and 0.57 (0.46–0.70) for participation in three or more different types of organizations. In multivariable adjusted models, participation in the following types of organization was protective for incident disability: local community organizations (HR = 0.85, 95% CI: 0.76–0.96), hobby organizations (HR = 0.75, 95% CI: 0.64–0.87), and sports organizations (HR = 0.64, 95% CI: 0.54–0.81). Conclusion: Social participation may decrease the risk of incident functional disability in older people in Japan. This effect may be strengthened by participation in a variety of different types of organizations. Participating in a local community, hobby, or sports group or organization may be especially effective for decreasing the risk of disability