Static compression of porous dust aggregates

Context: In protoplanetary disks, dust grains coagulate with each other and grow to form aggregates. As these aggregates grow by coagulation, their filling factor \phi decreases down to \phi << 1. However, comets, the remnants of these early planetesimals, have \phi ~ 0.1. Thus, static compression of porous dust aggregates is important in planetesimal formation. However, the static compression strength has been investigated only for relatively high density aggregates (\phi > 0.1). Aims: We investigate and find the compression strength of highly porous aggregates (\phi << 1). Methods: We perform three dimensional N-body simulations of aggregate compression with a particle-particle interaction model. We introduce a new method of static compression: the periodic boundary condition is adopted and the boundaries move with low speed to get closer. The dust aggregate is compressed uniformly and isotropically by themselves over the periodic boundaries. Results: We empirically derive a formula of the compression strength of highly porous aggregates (\phi << 1). We check the validity of the compression strength formula for wide ranges of numerical parameters, such as the size of initial aggregates, the boundary speed, the normal damping force, and material. We also compare our results to the previous studies of static compression in the relatively high density region (\phi > 0.1) and confirm that our results consistently connect to those in the high density region. The compression strength formula is also derived analytically.Comment: 12 pages, 14 figures, accepted for publication in A&

Public views of health insurance in Japan during the era of attaining universal health coverage: a secondary analysis of an opinion poll on health insurance in 1967

While Japan’s success in achieving universal health insurance over a short period with controlled healthcare costs has been studied from various perspectives, that of beneficiaries have been overlooked. We conducted a secondary analysis of an opinion poll on health insurance in 1967, immediately after reaching universal coverage. We found that people continued to face a slight barrier to healthcare access (26.8% felt medical expenses were a heavy burden) and had high expectations for health insurance (60.5% were satisfied with insured medical services and 82.4% were willing to pay a premium). In our study, younger age, having children before school age, lower living standards, and the health insurance scheme were factors that were associated with a willingness to pay premiums. Involving high-income groups in public insurance is considered to be the key to ensuring universal coverage of social insurance

Geometrical Cross Sections of Dust Aggregates and a Compression Model for Aggregate Collisions

Geometrical cross sections of dust aggregates determine their coupling with disk gas, which governs their motions in protoplanetary disks. Collisional outcomes also depend on geometrical cross sections of initial aggregates. In the previous paper, we performed three-dimensional N-body simulations of sequential collisions of aggregates composed of a number of sub-micron-sized icy particles and examined radii of gyration (and bulk densities) of the obtained aggregates. We showed that collisional compression of aggregates is not efficient and that aggregates remain fluffy. In the present study, we examine geometrical cross sections of the aggregates. Their cross sections decreases due to the compression as well as their gyration radii. It is found that a relation between the cross section and the gyration radius proposed by Okuzumi et al. is valid for the compressed aggregates. We also refine the compression model proposed in our previous paper. The refined model enables us to calculate the evolution of both gyration radii and cross sections of growing aggregates and reproduces well our numerical results of sequential aggregate collisions. The refined model can describe non-equal-mass collisions as well as equal-mass case. Although we do not take into account oblique collisions in the present study, oblique collisions would further hinder compression of aggregates

Comet 9P/Tempel 1: Interpretation with the Deep Impact Results

According to our common understandings, the original surface of a short-period comet nucleus has been lost by sublimation processes during its close approaches to the Sun. Sublimation results in the formation of a dust mantle on the retreated surface and in chemical differentiation of ices over tens or hundreds of meters below the mantle. In the course of NASA's Deep Impact mission, optical and infrared imaging observations of the ejecta plume were conducted by several researchers, but their interpretations of the data came as a big surprise: (1) The nucleus of comet 9P/Tempel 1 is free of a dust mantle, but maintains its pristine crust of submicron-sized carbonaceous grains; (2) Primordial materials are accessible already at a depth of several tens of cm with abundant silicate grains of submicrometer sizes. In this study, we demonstrate that a standard model of cometary nuclei explains well available observational data: (1) A dust mantle with a thickness of ~1-2 m builds up on the surface, where compact aggregates larger than tens of micrometers dominate; (2) Large fluffy aggregates are embedded in chemically differentiated layers as well as in the deepest part of the nucleus with primordial materials. We conclude that the Deep Impact results do not need any peculiar view of a comet nucleus.Comment: 11 pages, 1 figure, 1 table. ApJ letters, 673, L199-20

Immunoglobulin Production by Peripheral Blood Mononuclear Cells in IgA Nephropathy Patients and their Relatives

Immunoglobulin production by peripheral blood mononuclear cells of 27 patients of IgA nephropathy and 11 relatives was determined. In comparison with 15 healthy controls, no significant difference could be observed in both IgA nephropathy patients and relatives of the group not stimulated with PWM, but in the group stimulated with PWM a significant elevation in the production of IgA, IgG and IgM was seen in IgA nephropathy patients, while in the relatives a significant elevation in production of IgA and IgG was observed. It is speculated that immune complexes mainly IgA are the chief cause of development and progression of IgA nephropathy and that IgG and IgM are also involved. In also relatives, the presence of immunological abnormalities similar to those of IgA nephropathy patients is suggested

Regeneration of the acorn worm pygochord with the implication for its convergent evolution with the notochord

The origin of the notochord is a central issue in chordate evolution. This study examined the development of the acorn worm pygochord, a putative homologue of the notochord. Because the pygochord differentiates only after metamorphosis, the developmental was followed process by inducing regeneration after artificial amputation in Ptychodera flava. It was found that although the regeneration of the posterior part of the body did not proceed via formation of an obvious regeneration bud, pygochord regeneration was observed within a few weeks, possibly via trans‐differentiation of endoderm cells. The expression of the fibrillary collagen gene (Fcol) and elav in the pygochord during regeneration was detected. This indicates that pygochord cells are not part of gut epithelial cells, but that they differentiated as a distinct cell type. Our gene expression analyses do not provide supporting evidence for the homology between the pygochord and notochord, but rather favored the convergent evolution between them