Tensile Strength of Porous Dust Aggregates

Comets are thought to have information about the formation process of our solar system. Recently, detailed information about comet 67P/Churyumov-Gerasimenko has been found by a spacecraft mission Rosetta. It is remarkable that its tensile strength was estimated. In this paper, we measure and formulate the tensile strength of porous dust aggregates using numerical simulations, motivated by porous dust aggregation model of planetesimal formation. We perform three-dimensional numerical simulations using a monomer interaction model with periodic boundary condition. We stretch out a dust aggregate with a various initial volume filling factor between $10^{-2}$ and 0.5. We find that the tensile stress takes the maximum value at the time when the volume filling factor decreases to about a half of the initial value. The maximum stress is defined to be the tensile strength. We take an average of the results with 10 different initial shapes to smooth out the effects of initial shapes of aggregates. Finally, we numerically obtain the relation between the tensile strength and the initial volume filling factor of dust aggregates. We also use a simple semi-analytical model and successfully reproduce the numerical results, which enables us to apply to a wide parameter range and different materials. The obtained relation is consistent with previous experiments and numerical simulations about silicate dust aggregates. We estimate that the monomer radius of comet 67P has to be about 3.3--220 $\mathrm{\mu m}$ to reproduce its tensile strength using our model.Comment: 12 pages, 12 figures, accepted for publication in Ap

Formulating Compressive Strength of Dust Aggregates from Low to High Volume Filling Factors with Numerical Simulations

Compressive strength is a key to understanding the internal structure of dust aggregates in protoplanetary disks and their resultant bodies, such as comets and asteroids in the Solar System. Previous work has modeled the compressive strength of highly-porous dust aggregates with volume filling factors lower than 0.1. However, a comprehensive understanding of the compressive strength from low ($0.1$) volume filling factors is lacking. In this paper, we investigate the compressive strength of dust aggregates by using aggregate compression simulations resolving constituent grains based on JKR theory to formulate the compressive strength comprehensively. We perform a series of numerical simulations with moving periodic boundaries mimicking the compression behavior. As a result, we find that the compressive strength becomes sharply harder when the volume filling factor exceeds 0.1. We succeed in formulating the compressive strength comprehensively by taking into account the rolling motion of aggregates for low volume filling factors and the closest packing of aggregates for high volume filling factors. We also find that the dominant compression mechanisms for high volume filling factors are sliding and twisting motions, while rolling motion dominates for low volume filling factors. We confirm that our results are in good agreement with previous numerical studies. We suggest that our analytical formula is consistent with the previous experimental results if we assume the surface energy of silicate is $\simeq210\pm90\mathrm{\ mJ\ m^{-2}}$. Now, we can apply our results to properties of small compact bodies, such as comets, asteroids, and pebbles.Comment: 15 pages, 12 figures, accepted for publication in Ap

Snail1 expression in human colon cancer DLD-1 cells confers invasive properties without N-cadherin expression

AbstractThe epithelial-mesenchymal transition (EMT) is a fundamental characteristic of carcinoma cells. EMT is generally associated with a change in cellular morphology from cobblestone to spindle shape, reduced expression of epithelial markers such as E-cadherin, and enhanced expression of mesenchymal markers such as N-cadherin. This EMT-associated reciprocal expression of E-cadherin and N-cadherin has been called the “cadherin switch”. Downregulation of E-cadherin enables cells to dissociate from colonies while upregulation of N-cadherin is associated with increased invasiveness. The transcription factor Snail1 induces these changes in various epithelial cell lines, including canine MDCK cells and human A431 cells. In the present study, we introduced a Snail1 expression vector into human DLD-1 cells and isolated stable transfectants. These cells showed changes in morphology, reduced expression of epithelial marker E-cadherin and occludin, and elevated invasion and migration. However, neither expression of N-cadherin protein nor its corresponding mRNA was detected. Therefore, elevated N-cadherin expression is not required for invasiveness of the cells

Regulation of male germline transmission patterns by the Trp53-Cdkn1a pathway

A small number of offspring are born from the numerous sperm generated from spermatogonial stem cells (SSCs). However, little is known regarding the rules and molecular mechanisms that govern germline transmission patterns. Here we report that the Trp53 tumor suppressor gene limits germline genetic diversity via Cdkn1a. Trp53-deficient SSCs outcompeted wild-type (WT) SSCs and produced significantly more progeny after co-transplantation into infertile mice. Lentivirus-mediated transgenerational lineage analysis showed that offspring bearing the same virus integration were repeatedly born in a non-random pattern from WT SSCs. However, SSCs lacking Trp53 or Cdkn1a sired transgenic offspring in random patterns with increased genetic diversity. Apoptosis of KIT⁺ differentiating germ cells was reduced in Trp53- or Cdkn1a-deficient mice. Reduced CDKN1A expression in Trp53-deficient spermatogonia suggested that Cdkn1a limits genetic diversity by supporting apoptosis of syncytial spermatogonial clones. Therefore, the TRP53-CDKN1A pathway regulates tumorigenesis and the germline transmission pattern

社会情勢の変化と環境意識の関連に関する研究 : ガソリン価格高騰による影響を事例に

The aim of this paper is to address the problem regarding the relation between socioeconomic circumstances and environmental awareness among people, and toclarify some conclusions reached. Research involved a questionnaire survey concerning the remarkable jump in gasoline prices experienced in 2008, and how it influenced automobile use among consumers. Some of the findings are as follows. (1) The frequency of automobile use decreased among more than half the respondents with the sharp rise of gasoline prices. (2) The half of respondents in(1), who had decreased the frequency of use, continued to reduce their use of automobiles even after prices fell to previous rates. (3) The group that reduced use, showed signs of gaining higher environmental awareness. (4) Also, in the group of people that did not reduce use, environmental awareness increased in relation to the jump in gasoline price. (5) The ways of coping with environmental considerations differ between the group that reduced automobile use, and the group that did not reduce

市町村都市計画策定における住民参加の現状と課題

Community participation is required when creating a master city plan under local governance, because the City Planning Law was amended in 1992. This paper presents questionnaire survey results on citizen participation. Administrative urban planners in Osaka Prefecture and Hyogo Prefecture were asked question regarding the actual conditions of community participation in development district planning and master city plans

解体業者アンケート調査からみた木造戸建住宅解体におけるリサイクルの現状について

One of the big problems in a recycling society is to reduce the amount of waste from construction. Specifically, construction waste accounts for 30 percent of the entire waste products. Various approaches to reduce the amount of construction waste have been realized, and positive results have been achieved. However, in the current situation, there is still not enough reduction, especially for wooden waste. Wooden detached houses were constructed in great numbers during the high growth period, but one by one they will need to be rebuilt in the future. In also considered the possibility of recycling and reuse of materials from a wooden detached house through a questionnaire given to dismantlement traders. As a result, the following became clear. There are a lot of small-scale, relatively unknown members of the demolition industry, and there is no even consideration of the environment in the industry. The most general feeling is that concrete structures are the most easily dismantled, but the industry\u27s attitude towards wooden detached houses has been divided. They report that the clearance price is low, and the recycling methods for wooden rubbish are advanced. I believe that it is necessary to examine the strategy for the making of manuals and other methods for the improvement of the methods which the demolition industries use as well as an appropriate 3R as a strategy for the future

都市の住宅ストックとしての3階建て戸建て住宅の現状と課題

This research considers whether the three-story detached houses currently located in urban areas is viable city housing stock. The method of research involved a questionnaire survey of residents living in single three-story houses to clarify their amenity, and degree of continued resident habitation intention. The results show that since plottage is narrow and cramped, barrier-free and other amenities are compromised, and clearly these houses lack functional elements to alleviate problems faced by their aging residents. Moreover, since there is much dissatisfaction with the extent of earthquake resistance, I think that an obligation to provide seismic reinforcement, and regulating the area of the site, and other safety or amenity features, are required in order for the single three-story house to become viable city housing stock