Shin Yabushita

Bio: Shin Yabushita is an academic researcher from Kyoto University. The author has contributed to research in topics: Comet & Interstellar comet. The author has an hindex of 13, co-authored 60 publications receiving 485 citations. Previous affiliations of Shin Yabushita include Osaka Kyoiku University.

Thermal evolution of cometary nuclei by radioactive heating and possible formation of organic chemicals

Abstract: Thermal evolution of large cometary nuclei (radii ≥ 40 km) due to heating by decay of 238 U, 235 U, 40 K and 232 Th is investigated by adopting chemical models based on observations of P/Halley and mineral compositions of C1 chondrites. If the thermal diffusivity of crystallized ice is sufficiently small (k c ≤ 0.0015 cm s −1 ), the central temperature may reach the melting point of H 2 O in large nuclei (radii ≃ 200 km), while if the diffusivity is 0.003 or greater, the central temperature will not reach the melting point

A statistical test for periodicity hypothesis in the crater formation rate

Abstract: The hypothesis that the crater formation rate exhibits periodicity is examined by adopting a criterion proposed by Broadbent, which is more stringent than those adopted by previous authors. Data sets of Alvarez & Muller, Rampino & Stothers and of Grieve are tested. The data set of Rampino & Stothers is found to satisfy the adopted criterion for periodicity with period P = 30 Myr. Again, small craters (D < 10 km) in the data set of Grieve satisfy the criterion even better with P = 30 Myr and 50 Myr, but large craters do not satisfy the criterion.

Primary biological aerosol particles in the atmosphere: a review

Abstract: Atmospheric aerosol particles of biological origin are a very diverse group of biological materials and structures, including microorganisms, dispersal units, fragments and excretions of biological organisms. In recent years, the impact of biological aerosol particles on atmospheric processes has been studied with increasing intensity, and a wealth of new information and insights has been gained. This review outlines the current knowledge on major categories of primary biological aerosol particles (PBAP): bacteria and archaea, fungal spores and fragments, pollen, viruses, algae and cyanobacteria, biological crusts and lichens and others like plant or animal fragments and detritus. We give an overview of sampling methods and physical, chemical and biological techniques for PBAP analysis (cultivation, microscopy, DNA/RNA analysis, chemical tracers, optical and mass spectrometry, etc.). Moreover, we address and summarise the current understanding and open questions concerning the influence of PBAP on the atmosphere and climate, i.e. their optical properties and their ability to act as ice nuclei (IN) or cloud condensation nuclei (CCN). We suggest that the following research activities should be pursued in future studies of atmospheric biological aerosol particles: (1) develop efficient and reliable analytical techniques for the identification and quantification of PBAP; (2) apply advanced and standardised techniques to determine the abundance and diversity of PBAP and their seasonal variation at regional and global scales (atmospheric biogeography); (3) determine the emission rates, optical properties, IN and CCN activity of PBAP in field measurements and laboratory experiments; (4) use field and laboratory data to constrain numerical models of atmospheric transport, transformation and climate effects of PBAP. Keywords: primary biological atmospheric aerosol; climate; cloud condensation nuclei; biology; atmospheric ice nuclei (Published: 22 February 2012) Citation: Tellus B 2012, 64 , 15598, DOI: 10.3402/tellusb.v64i0.15598

Physics of the Primitive Solar Accretion Disk

Abstract: The theory of viscous accretion disks developed by Lynden-Bell and Pringle (1974) has been applied to the evolution of the primitive solar nebula The additional physical input needed to determine the structure of the disk is described A series of calculations was carried out using a steady flow approximation to explore the effects on the disk properties of variations in such parameters as the angular momentum and accretion rate of the infalling material from a collapsing interstellar cloud fragment The more detailed evolutionary calculations involved five cases with various combinations of parameters It was concluded that the late stages of evolution of the disks would be dominated by the effects of mass loss from the expansion of a hot disk corona into space, and the effects of this were included in the evolutionary calculations A new theory of comet formation is formulated upon these results The most important result is the conclusion that the primitive solar accretion disk was repeatedly unstable against axisymmetric perturbations, in which rings would form and collapse upon themselves, with the subsequent formation of giant gaseous protoplanets

The Newtonian gravitational constant: recent measurements and related studies

Abstract: Improvements in our knowledge of the absolute value of the Newtonian gravitational constant, G, have come very slowly over the years. Most other constants of nature are known (and some even predictable) to parts per billion, or parts per million at worst. However, G stands mysteriously alone, its history being that of a quantity which is extremely difficult to measure and which remains virtually isolated from the theoretical structure of the rest of physics. Several attempts aimed at changing this situation are now underway, but the most recent experimental results have once again produced conflicting values of G and, in spite of some progress and much interest, there remains to date no universally accepted way of predicting its absolute value. The review will assess the role of G in physics, examine the status of attempts to derive its value and provide an overview of the experimental efforts that are directed at increasing the accuracy of its determination. Regarding the latter, emphasis will be placed on describing the instrumentational aspects of the experimental work. Related topics that are also discussed include the search for temporal variation of G and recent investigations of possible anomalous gravitational effects that lie outside of presently accepted theories.