The hypothesis called "panspermia" proposes an interplanetary transfer of life. Experiments have exposed extremophilic organisms to outer space to test microbe survivability and the panspermia hypothesis. Microbes inside shielding material with sufficient thickness to protect them from UV-irradiation can survive in space. This process has been called "lithopanspermia," meaning rocky panspermia. We previously proposed sub-millimeter cell pellets (aggregates) could survive in the harsh space environment based on an on-ground laboratory experiment. To test our hypothesis, we placed dried cell pellets of the radioresistant bacteria Deinococcus spp. in aluminum plate wells in exposure panels attached to the outside of the International Space Station (ISS). We exposed microbial cell pellets with different thickness to space environments. The results indicated the importance of the aggregated form of cells for surviving in harsh space environment. We also analyzed the samples exposed to space from 1 to 3 years. The experimental design enabled us to get and extrapolate the survival time course to predict the survival time of Deinococcus radiodurans. Dried deinococcal cell pellets of 500 μm thickness were alive after 3 years of space exposure and repaired DNA damage at cultivation. Thus, cell pellets 1 mm in diameter have sufficient protection from UV and are estimated to endure the space environment for 2-8 years, extrapolating the survival curve and considering the illumination efficiency of the space experiment. Comparison of the survival of different DNA repair-deficient mutants suggested that cell aggregates exposed in space for 3 years suffered DNA damage, which is most efficiently repaired by the uvrA gene and uvdE gene products, which are responsible for nucleotide excision repair and UV-damage excision repair. Collectively, these results support the possibility of microbial cell aggregates (pellets) as an ark for interplanetary transfer of microbes within several years.
Nanosized cylindrical structures consisting of a SiC core and a crosslinked polysilane coating (see Figure and also inside front cover) are produced here by ion beam irradiation of a polysilane film. It is shown that both the radius and length of the nanowires can be controlled by altering the incident ion beam, molecular weight of the polymer, and thickness of the target film.
A method for creating a fast scintillator is proposed. Recently, much attention has been paid to pure semiconductors during development of subnanosecond fast solid scintillators. However, the bulky samples rarely exhibit high light yields at room temperature because of thermal instability at the excitonic levels. The authors employed the optimum three- and two-dimensional semiconducting systems provided by lead-halide-based compounds to demonstrate the advantage of low dimensionality in the scintillating efficiency. Their dimensional and temperature dependencies were investigated using a high-energy proton beam. Consequently, the quantum confinement system clearly prevented thermal quenching from excitonic level even at room temperature, and the result proposes the next breakthrough to create ultrafast solid scintillators.
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