Observational examination of aggregation and migration during early phase of neurosphere culture of mouse neural stem cells

Neural stem cells (NSCs) form cell aggregates called neurospheres during serum-free culture, and this aggregation contributes primarily to neurosphere development. In the present study, we conducted an observational examination of the cell clustering of mouse NSCs in relation to their migration potential. The cell clustering became significant from 12 h after the inoculation of NSCs during the examined culture period of 48 h. Three types of clustering were observed, that is, aggregation between two single cells, and coalescence between a cell and an aggregate and that between two aggregates. The aggregation between single cells occurred during the early phase (0-24 h after inoculation). Six hours after inoculation, the average migration rate of single cells that resulted in aggregation within the subsequent 12 h was higher than that of cells that did not aggregate. Fluorescent stainings of the cytoplasm and F-actin revealed the existence of mini podia and long podia, which were possible elements that produce the driving force for the migration of singly occurring NSCs.     

Production of extracellular bifidogenic growth stimulator by anaerobic and aerobic cultivations of several propionibacterial strains

Production of a bifidogenic growth stimulator (BGS) by propionic acid bacteria was investigated under anaerobic and aerobic culture conditions. To measure the concentration of extracellular BGS produced by propionic acid bacteria, we evaluated the effects of bioassay conditions using Bifidobacterium longum as a test microorganism on the formation of a growth-stimulation zone. The diameter of the growth-stimulation zone was significantly affected by both the component concentrations and the pH of a bioassay medium. The optimum component concentrations and pH of a bioassay medium were one-half of the normal values and 8.5, respectively. Using the bioassay method, we can measure the concentration of BGS produced by propionic acid bacteria ranging in concentrations from 0.1 microg/l to 1 mg/l using 1,4-dihydroxy-2-naphthoic acid (DHNA) and 2-amino-3-carboxy-1,4-naphthoquinone (ACNQ) as standards. Of six dairy propionic acid bacterial strains tested, the four strains (Propionibacterium freudenreichii ET-3, P. shermanii PZ-3, P. acidipropionici JCM 6432, and P. jensenii JCM 6433) produced BGS at a concentration range of 4-23 mg/l under the anaerobic culture conditions. Analysis of high performance liquid chromatography (HPLC) showed that more than 70% of total BGS produced in supernatant samples was DHNA and no ACNQ was produced by the strains. The effect of oxygen supply on BGS production was investigated for the four BGS-producing strains. The aerobic conditions exerted in positive effects on BGS production by only P. acidipropionici JCM 6432. The concentration of BGS obtained in the aerobic cultivation of P. acidipropionici JCM 6432 was 1.3-fold than that in anaerobic cultivation. Different properties (BGS production as well as cell growth and glucose metabolism) occurring in response to the aerobic conditions were observed, depending on the propionic acid bacterial strain used. This paper is the first report on BGS production by propionibacterial strains except for P. freudenreichii.     

Time flexibility to reduce climate change mitigation costs for Japanese electricity supply sector

The idea of greenhouse‐gas credit borrowing in global or national context faces severe problems such as international and intergenerational equity issues. Though the merit of cost reduction is obvious, the possibility is small for such a scheme to be massively allowed in future international negotiations. Still, there is a good chance for each specific player to use the idea of time flexibility. Through analytic and numerical model analysis, this paper demonstrates the merits of time flexibility on a sector base. First, the derived analytic solution for time paths of marginal mitigation costs gives an insight to the relation between timing and costs of mitigation action. Second, the numerical model analysis for the Japanese electricity supply sector shows that time flexibility can drastically reduce costs for mitigation in the sector. Time flexibility is important specifically to the Japanese electricity supply sector because (1) the sector is capital intensive and has long capital turnover time and (2) available mitigation option is limited for the near future. A sector like the Japanese utility sector needs some kind of mechanism to virtually realize the merits of using time flexibility. Domestic and international emission trading systems are the most promising candidate to date. © 2000 Scripta Technica, Electr Eng Jpn, 131(1): 68–77, 2000     

A Phylogenetic Analysis of Saccharomyces Species by the Sequence of 18S–28S rRNA Spacer Regions

Sequences of two internally transcribed spacer regions between 18S and 28S rRNA genes were determined to assess the phylogenetic relationship in the strains belonging to the genus Saccharomyces. The sequences of S. bayanus and S. pastorianus were quite similar, but not identical. Two phylogenetic trees constructed by the neighbor-joining method showed that all the species examined were distinguished from one another. The Saccharomyces sensu stricto species: S. cerevisiae, S. bayanus, S. paradoxus and S. pastorianus, were closely related and far from the Saccharomyces sensu lato species including S. barnetti, S. castellii, S. dairensis, S. exiguus, S. servazzii, S. spencerorum and S. unisporus, and an outlying species, S. kluyveri. © 1997 John Wiley & Sons, Ltd.     

In situ Raman study on single- and double-walled carbon nanotubes as a function of lithium insertion

We investigated the electrochemical lithium ion (Li(+)) insertion/desertion behavior on highly pure and bundled single- and double-walled carbon nanotubes (SWNTs and DWNTs) using an in situ Raman technique. In general, two storage sites could host Li(+) in SWNT and DWNT bundles when varying an external potential: a) the outer surface sites, and b) the interstitial spaces within the bundles. The most sensitive changes in the tangential mode (TM) of the Raman spectra upon doping with Li(+) can be divided into two regions. The first region was found from 2.8 to 1.0 V (the coverage of Li(+) on the outer surface of a bundled nanotube) and was characterized by the loss of resonant conditions via partial charge transfer, where the G(+) line of the SWNT and the TM of the outer tube of DWNTs experienced a highly depressed intensity, but remained almost constant in frequency. The appearance of a Breit-Wigner-Fano (BWF) profile provided strong evidence of metallic inner tubes within DWNTs. The second region was observed when the applied potentials ranged from 0.9 to 0 V and was characterized by Li(+) diffusion into the interstitial sites of the bundled nanotube material. This phenomenon invoked a large downshift of the G(-) band in SWNTs, and a small downshift of the TM of the inner tube of DWNTs caused by expansion of the C--C bonds due to the charge transferred to the nanotubes, and the disappearance of the BWF profile through the screening effect of the interstitial Li(+) layers.     

Numerical analysis of residual stress distribution generated by welding after surface machining based on hardness variation in surface machined layer due to welding thermal cycle

Recently, stress corrosion cracking (SCC) has been observed near the welded zone of the primary loop recirculation pipes made of low-carbon austenitic stainless steel type 316L in boiling water reactors. SCC is initiated by superposition effect of three factors. They are material, environmental and mechanical factors. For non-sensitized material such as type 316L, residual stress as a mechanical factor of SCC is comparatively important. In the joining processes of pipes, butt welding is conducted after surface machining. Surface machining is performed in order to match the inside diameter and smooth surface finish of pipes. Residual stress is generated by both processes. Moreover, residual stress distribution generated by surface machining is varied by subsequent welding processes, and it has the maximum residual stress around 900 MPa near the weld metal. The variation of metallographic structure, such as recovery and recrystallization, in the surface machined layer due to the welding thermal cycle is an important factor for this residual stress distribution. In this study, thermal ageing tests were performed in order to evaluate hardness variation due to the thermal cycle in the surface machined layer. Results of thermal ageing tests were applied to the finite-element method as the additivity rule of the hardness variation. Varied hardness was converted into equivalent plastic strain. Then, thermo-elastic-plastic analysis was performed under residual stress fields generated by surface machining. As a result, analytical results of surface residual stress distribution generated by bead-on-plate welding after surface machining show good agreement with measured results by the X-ray diffraction method. The maximum residual stress near the weld metal is generated by the same mechanism as in the both-ends-fixed bar model in the surface machined layer that has high yield stress.     

High-Temperature Mechanical Behavior and Fracture Analysis of a Low-Carbon Steel Related to Cracking

Cracking in continuously cast steel slabs has been one of the main problems in casting for decades. In recent years, the use of computational models has led to a significant improvement in caster performance and product quality. However, these models require accurate thermomechanical properties as input data, which are either unreliable or nonexistent for many alloys of commercial interest. A major reason for this lack of reliable data is that high-temperature mechanical properties are difficult to measure. Several methods have been developed to assess the material strength during solidification, especially for light alloys. The tensile strength during solidification of a low carbon aluminum-killed (LCAK; obtained from Tata Steel Mainland Europe cast at the DSP plant in IJmuiden, the Netherlands) has been studied by a technique for high-temperature tensile testing, which was developed at Sumitomo Metal Industries in Japan. The experimental technique enables a sample to melt and solidify without a crucible, making possible the accurate measurement of load over a small solidification temperature range. In the current study, the tensile test results are analyzed and the characteristic zero-ductility and zero-strength temperatures are determined for this particular LCAK steel grade. The fracture surfaces are investigated following tensile testing, which provides an invaluable insight into the fracture mechanism and a better understanding with respect to the behavior of the steel during solidification. The role of minor alloying elements, like sulfur, in hot cracking susceptibility is also discussed.     

Synthesis of nanocrystalline rare earth oxides by glycothermal method

The reaction of yttrium acetate hydrate in 1,2-propanediol at 300 °C yielded a product containing acetate groups and glycol moieties. From this product, Y₂O₃ was directly crystallized at 400 °C without the formation of a carbonate oxide phase. The thus-obtained Y₂O₃ samples had a small crystallite size (2.2 nm) and significantly large surface area (280 m²/g). Other nanocrystalline rare earth (Gd-Yb) oxides were also obtained by this method.