Thermal conductivity of porous aggregates

$\mathit{Context.}$ The thermal conductivity of highly porous dust aggregates is a key parameter for many subjects in planetary science; however, it is not yet fully understood. $\mathit{Aims.}$ In this study, we investigate the thermal conductivity of fluffy dust aggregates with filling factors of less than $10^{-1}$. $\mathit{Methods.}$ We determine the temperature structure and heat flux of the porous dust aggregates calculated by $N$-body simulations of static compression in the periodic boundary condition. $\mathit{Results.}$ We derive an empirical formula for the thermal conductivity through the solid network $k_{\rm sol}$ as a function of the filling factor of dust aggregates $\phi$. The results reveal that $k_{\rm sol}$ is approximately proportional to ${\phi}^{2}$, and the thermal conductivity through the solid network is significantly lower than previously assumed. In light of these findings, we must reconsider the thermal histories of small planetary bodies.Comment: 4 pages, 4 figures. Accepted for publication in Astronomy & Astrophysic

Impacts of viscous dissipation on collisional growth and fragmentation of dust aggregates

Understanding the collisional behavior of dust aggregates consisting of submicron-sized grains is essential to unveiling how planetesimals formed in protoplanetary disks. It is known that the collisional behavior of individual dust particles strongly depends on the strength of viscous dissipation force; however, impacts of viscous dissipation on the collisional behavior of dust aggregates have not been studied in detail, especially for the cases of oblique collisions. Here we investigated the impacts of viscous dissipation on the collisional behavior of dust aggregates. We performed numerical simulations of collisions between two equal-mass dust aggregates with various collision velocities and impact parameters. We also changed the strength of viscous dissipation force systematically. We found that the threshold collision velocity for the fragmentation of dust aggregates barely depends on the strength of viscous dissipation force when we consider oblique collisions. In contrast, the size distribution of fragments changes significantly when the viscous dissipation force is considered. We obtained the empirical fitting formulae for the size distribution of fragments for the case of strong dissipation, which would be useful to study the evolution of size and spatial distributions of dust aggregates in protoplanetary disks.Comment: 16 pages, 15 figures. Accepted for publication in Ap

平安時代における変体漢文の日本語学的研究

学位の種別: 課程博士審査委員会委員 : （主査）東京大学教授 月本 雅幸, 東京大学教授 井島 正博, 東京大学准教授 肥爪 周二, 熊本大学教授 堀畑 正臣, 白百合女子大学教授 山本 真吾University of Tokyo(東京大学

Spatial distribution of cryoconite granules and microorganisms on Qaanaaq Glacier, Greenland

第6回極域科学シンポジウム分野横断セッション：[IB2] 地球環境変動の解析と地球生命システム学の構築11月19日（木）　統計数理研究所 セミナー室1（D305

Comparison of soil macro-invertebrate communities in Malaysian oil palm plantations with secondary forest from the viewpoint of litter decomposition

Biodiversity decline in rapidly expanding oil palm plantations is of global concern. Many studies have demonstrated that fauna species diversity is lower in oil palm plantations than forests. However, information about the flow-on effects of these declines in species diversity on ecosystem functioning is scarce for oil palm plantations. Litter decomposition performed by soil organisms is a vital ecosystem function that regulates nutrient cycling and carbon sequestration. Some studies have found a high level of redundancy among litter decomposing species. In order to evaluate the effects of the conversion of forests to oil palm plantations on decomposition, we investigated the abundance and biomass of soil macro-invertebrates at sites in two oil palm plantations and a secondary forest in Malaysia. Biodiversity of soil macro-invertebrates were lower in the oil palm plantations than in the secondary forest. The abundance and biomass of surface–living litter transformers was lower in oil palm plantations than forest, probably due to the isolated piles of frond litter that occur in plantations, instead of the more continuous litter layer observed in forests. However, we found dense populations of wood (litter)–feeding termites in the thick rachises of fronds heaped on the ground surface. A pantropical earthworm species, Pontoscolex corethrurus, which buries the litter through cast deposition, abounded more in the oil palm plantations than in the secondary forest. These characteristics of soil macro-invertebrates have also been reported in other oil palm plantations. Thus, we conclude that the conversion of forests to oil palm plantations may reduce diversity of soil macro-invertebrates, increase the heterogeneity of macro-invertebrates distribution and decrease populations of some functional groups of soil macro-invertebrates. However, overall, forest conversion does not appear to have a negative impact on the decomposition process to a great extent, owing to the colonization of plantation sites by other groups of decomposer animals that are favored by disturbance and/or the great amount of localized input of fresh fronds pruned at the time of fruit harvesting

Soil characteristics in an oil palm field, Central Pahang, Malaysia with special reference to micro sites under different managements and slope positions

Within an oil palm field, different micro sites are established for fertilizer application (weeded circle), organic matter addition (frond heap) and operation paths (harvest path). This study reports the soil characteristics on an oil palm field with special reference to the micro sites as well as slope positions. For this study purpose, a second generation oil palm field (average slope gradient of 8°) with 10 years old oil palm was selected. The soils (Typic Hapludox) could be generally characterized by acidic nature and low levels in exchangeable bases with high aluminum activity. Soil properties were significantly or tended to be different at the depth of 0-5 cm and 5-10 cm in terms of micro sites; total carbon (T-C), total nitrogen (T-N), exchangeable magnesium (Mg) and exchangeable calcium (Ca) contents were higher at the frond heap. On the other hand, higher amounts of available phosphorus were accumulated in the weeded circle due to fertilizer application. Meanwhile, between different slope positions, non-distinct soil particles movement was observed and no evidence of soil erosion was found

Oxygen Isotope Exchange Between Molten Silicate Spherules and Ambient Water Vapor with Nonzero Relative Velocity: Implication for Chondrule Formation Environment

Oxygen isotope compositions of chondrules reflect the environment of chondrule formation and its spatial and temporal variations. Here, we present a theoretical model of oxygen isotope exchange reaction between molten silicate spherules and ambient water vapor with finite relative velocity. We found a new phenomenon, that is, mass-dependent fractionation caused by isotope exchange with ambient vapor moving with nonzero relative velocity. We also discussed the plausible condition for chondrule formation from the point of view of oxygen isotope compositions. Our findings indicate that the relative velocity between chondrules and ambient vapor would be lower than several 100 m/s when chondrules crystallized.Comment: 15 pages, 8 figures. Accepted for publication in Icaru

Nutrient status of frond heaps and the underlying soils at an 18-year-old oil palm field in Central Pahang, Malaysia

In oil palm plantation, palm fronds are pruned off upon fruit bunch harvest and heaped up in-between palm trees, which is called as a frond heap. This study examined the amounts of nutrients contained in frond heaps and their influence on the underlying soil fertility at an 18-year-old oil palm field in Central Pahang, Malaysia. Based on biomass measurement and nutrient analysis, the amounts of C, N, P, K, Ca, and Mg in the frond heaps were estimated to be 697, 11.8, 0.810, 18.9, 8.05, and 2.73 g m-2, respectively. Meanwhile, the surface soils below the frond heaps showed higher levels of pH, EC, total C, N, exchangeable Ca, Mg, and K than those at harvest path, which is operation path for workers to harvest, while available P was more accumulated at weeded circle, to which fertilizer is applied under the palm canopy. These tendencies were more obvious compared with our previous study conducted at a 10-year-old field located in the same region. This study reveals that the nutrients released from decomposing frond heaps could contribute to build-up of the major nutrients except for P in the underlying soils to be recycled by palm trees

Examining pre-service teachers’ the selection and treatment of issues about teaching controversial issues in social studies: For the improvement of social studies teacher training curriculum

This paper examines how pre-service social studies teachers handle controversial issues in their practice. Based on the results, suggestions for improving the social studies teacher training curriculum are obtained. Previous social studies suggested that teacher training programs must be reformed in order to enhance the practice of controversial issues learning, but the specifics of the reforms have not been clarified. This is partly because, although previous studies focus on in-service teachers, there has been little research to clarify the perceptions of pre-service teachers regarding teaching about controversial issues. In this paper, we examined the selection and handling of controversial issues by prospective social studies teachers based on questionnaires and interviews with Japanese prospective social studies teachers. The results suggest the following two points. First, there is a need to visualize and verbalize the prospective teachers’ concerns and gatekeeping process with regard to the teacher training curriculum. Second, for teacher education research, there is a need to strengthen cooperation with outside social studies and to expand the role of teachers.本研究はJSPS科研費19K14239の助成を受けたものである

Effects of Acacia mangium on morphological and physicochemical properties of soil

This study was conducted in an industrial Acacia mangium plantation in Sarawak, Malaysia, to investigate the effects of planting and harvesting A. mangium on soil morphological and physicochemical properties. In A. mangium sites, the disruptive effect of planting practices extended to morphological properties in subsoil layers. The A horizon redeveloped during early stages after planting which could be ascribed to plentiful supply of organic matter through rapid decomposition of vegetation residues produced upon land preparation. However, soil C- And N-related properties appeared to decrease with stand age, while the levels of exchangeable bases and available P remained low even after 10 years. In post-harvest sites, distinct soil horizons were not observed due to severe disturbance. The levels of total C, N and exchangeable bases at depth of 0-5 cm for sites assessed 3 years after harvesting were higher than those of sites assessed 1 year after harvesting. This might be ascribed to relatively gradual release of organic matter and nutrients from harvest residues into soil due to low level of decomposition as well as low nutrient uptake of poor vegetation regrowth