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

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

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

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

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

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

Interparticle normal force in highly porous granular matter during compression

We perform a numerical simulation of compression of a highly porous dust aggregate of monodisperse spheres. We find that the average interparticle normal force within the aggregate is inversely proportional to both the filling factor and the average coordination number, and we also derive this relation theoretically. Our findings would be applicable for granular matter of arbitrary structures, as long as the constituent particles are monodisperse spheres.Comment: 9 pages, 7 figures. Accepted for publication in PR

Flexibility and Productivity in IoT Programming: A Case Study with Mruby

This paper explores the use of data flow-based design in IoT application development and its integration with the Node-RED programming tool. Node-RED provides a visual interface for creating programs based on the flow of data between nodes. However, Node-RED is not suitable for resource-constrained devices like micro-controllers. To address this, we propose a method of generating mruby code from Node-RED’s data flow programs. The generated mruby code can be compiled into device-independent byte-code and executed on the mruby VM. To facilitate the implementation, we introduce the RBoard, a prototyping micro-controller board equipped with the mruby VM firmware. This approach combines the intuitive data flow design of Node-RED with the power of mruby for embedded systems. Through this integration, developers can rapidly prototype IoT applications and leverage the flexibility of scripting languages. Our findings demonstrate the feasibility and benefits of using data flow-based design and mruby code generation in IoT application development. This research contributes to the advancement of efficient and scalable IoT programming methodologies and enables the creation of innovative IoT solutions on micro-controller platforms.International Conference on Advanced Research in Technologies, Information, Innovation and Sustainability, ARTIIS 2023, October 18–20, 2023, Madrid, Spainjournal articl

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