Influence of microbubble diameter and distribution on frictional resistance reduction

Investigations into frictional resistance reduction by microbubbles were carried out using a two-dimensional channel. The flow velocity and the amount of air injected were varied, and the frictional resistance reduction was measured. The frictional resistance reduction increased with increasing mean void ratio. When the bubble diameter was changed, the influence on frictional resistance reduction was negligible. The influence of bubble distribution near a wall was also investigated. Although it is thought that the influence of microbubbles near a wall is large, further investigations are required. Received: February 6, 2002 / Accepted: April 30, 2002 Acknowledgments. This research was supported by a special research program of Toyo University, SR239 Research Committee of the Shipbuilding Research Association of Japan, and the Research Project on Smart Control of Turbulence. The authors express their sincere gratitude for these supports. Address correspondence to: H. Kato (kato@eng.toyo.ac.jp)     

东海道新干线电气设备的变迁及维修

介绍了日本东海道新干线伴随科技发展和市场需求，为保证大量、高效、安全运输，在电力和通信信号设备方面所做的主要改进内容。     

Applications of a new ecosystem model to study the dynamics of phytoplankton and nutrients in the Ariake Sea,west coast of Kyushu,Japan

In this study, we present the development and application of a new ecosystem model coupled with a hydrodynamic model to describe the important physical, chemical and biological processes of an ecosystem in the marine environment, the Ariake Sea in the west coast of Kyushu, Japan. The model was calibrated and validated using in-situ field measurements from various monitoring stations in the sea. The presented results covered the period from January 1991 to December 2000. The results showed that chlorophyll-a, nutrients and dissolved oxygen levels varied seasonally in response to weather and boundary condition. Through this study, the model was shown to be able to handle the flooding and drying processes that usually exist and play an essential role over the estuarine-tidal flats of the sea.     

Reduction of skin friction by microbubbles and its relation with near-wall bubble concentration in a channel

Determination of the flow structure near the wall is essential for a clear insight into the phenomenon of skin friction reduction by microbubbles in a turbulent boundary layer. An important parameter, is the bubble concentration or void fraction in the wall region in drag-reducing conditions. The purpose of this paper is to show drag-reducing effects due to microbubbles in a water channel and, more importantly, to show the dependence of the drag-reduction values on the near-wall void fraction. A two-dimensional channel with an aspect ratio of 10 was specially built for this purpose with provisions for air injection through porous plates. Skin friction was directly measured by a miniature floating element transducer with a 5-mm circular sensing disk mounted flush on the top wall 67 channel-heights downstream of the injector. The wall friction in the presence of air bubbles was found to be reduced under the same bulk velocity when compared with the value without air. Detailed void fraction profiles across the channel were obtained by a sampling probe and a fiber-optic probe. Better collapse of the drag reduction data, independent of different profile shapes, was found when plotted against the near-wall void fraction than against a cross-sectional mean void fraction. While this dependence reconfirms that the phenomena are essentially inner-region dependent, the lack of influence of the bubble distribution patterns away from the wall implies lack of outer region influence.     

Development of a hull form definition tool with a related knowledge-based advisory system

The development of a parametric hull form design system utilizing combined knowledge-based and objectoriented methodologies, approaches, and techniques is the major purpose of this research. One objective was the development of a powerful, intuitive, and parameter-based hull definition system with a related hull definition advisory system that would provide useful and necessary advice to the user. Object and knowledge modeling activities were conducted during the analysis and design stage to facilitate the implementation of a hull design program and advisory system. The hull design system includes the generation of a geometric model from a process of aggregating simple user-selected shapes representing different boundaries. Design involves the capability to vary simple parameters such as entrance angles, length-breadth ratios, and radii to define local and general surface geometries. Hydrostatic calculations are included for analysis; results are referred to an advisory system for evaluation and the determination of the acceptability of parameters and analysis results. The advisory system includes a knowledge bases consisting of hull form databases, results of the statistical analysis of data, design parameter constraints, and expert knowledge acquired from designers, reference materials, and technical reports. Use of the design tool with the advisory system results in the rapid generation of hull forms and associated design evaluations. Flexibility in decision making results from the separation of the design system from the advisory system. The independence of the two systems allows for a wide range of user experience with experts using the design tool with minimal reference to the advisory system. On the other hand, the expertise and knowledge stored in the advisory system is fully available to inexperienced designers and users.     

FOLLICULO-STELLATE CELLS OFTHE RAT ANTERIOR PITUITARY RESPONDED TO ANGIOTENSIN Ⅱ BY INCREASING INTRACELLULAR CONCENTRATION

Objective The main purpose of this study was to investigate whether the folliculo-stellate cells (FSC) respond to angiotensin(Ang) Ⅱ by increasing intracellular free concentration ([]i) ,and where the o-rigin of mobilization is if that has occurred. Methods Pituitary cells in primary culture were prepared from male Wister rats(250g) by a conventional method and cultured in MEM supplemented with 4％ normal rat serum. Af-ter 2 days in culutre,cells were loaded with 1 μmol/L fura-PE3/AM for 1 h and subjected to a ment with Quanti Cell 700 system. Excitation wavelengths of 340 and 380 nm were selected by means of a computer-controlled filterwheel. Results The of FSC in the rat anterior pituitary was elevated by Ang Ⅱ. The eleva-tion of of FSC induced by 0. 1,1.0,10 and 100 nmol/L Ang Ⅱ was (56.33±6.18), (117.07± 36.07), (175.59 ± 40.01 ) and (216.02 ±11.52) nmol/L, respectively. The increase of of FSC induced by 100nmol/L Ang Ⅱ was not influenced by the medium without (0Ca),but significantly suppressed by thapsigargin (TG),an inhibitor of ATPase. The rate of responsive FSC to Ang Ⅱ (100 nmol/L) was 61.84％ which was obviously higher than that of pituitary endocrine cells (43.49％). Conclusion The present experiment demonstrates that the FSC in the rat anterior pituitary responds to Ang Ⅱ by increasing [which raises the possibility that Ang Ⅱ re-leased from either lactotrophs or gonadotrophs affects FSC through paracrine mechanism. The elevation of [induced by Ang Ⅱ presents a dosage-dependent relation, and is possibly because of the release of from an intra-cellular pool (s). Fashions of release are relative to the concentration of Ang Ⅱ. The results indicate that Ang Ⅱ functions as a paracrine factor among pituitary cells including FSC.     

Vortex-induced vibration (VIV) dynamics of a tensioned flexible cylinder subjected to uniform cross-flow

This paper presents the experimental results of a study on the effects of axial applied tension on the vibration amplitude, the suppression of vibration, hydrodynamic force coefficients and in-line (IL) and cross-flow (CF) frequency responses during vortex-induced vibration of a horizontally mounted flexible cylinder with a low mass ratio (cylinder’s mass/mass of displaced water), low bending-stiffness, and high aspect ratio (length/diameter 200) in the subcritical Reynolds number regime (Re = 1000–16000). The effect of tension is studied by applying four different tensions. It was revealed that higher applied tensions, which reduce the vibration amplitude, could significantly raise the hydrodynamic lift force coefficient. In addition, higher applied tensions generate narrower lock-in bandwidths. After the highest vibration amplitude and during the region of lower vibration amplitudes, within the first lock-in region (in the first mode of vibration), power spectral densities show broad bandwidth, while within other regions and higher modes they appear narrow-banded. The ratio of the dominant IL to CF frequency is approximately equal to 2.0, except for the lower reduced velocities, where the ratio values reach 3.83 for the highest tension accompanied by widening of the region in which this ratio is over 2.0. This ratio is 2.76 for the lowest applied tension with a narrower region.     

Impacts of improvements in rural roads on household income through the enhancement of market accessibility in rural areas of Cambodia

Rural areas in low-income countries often face severe poverty typically caused by insufficient accessibility to basic facilities. Improvements in rural roads are expected to reduce poverty although the mechanism has not been investigated sufficiently. This study empirically analyzes the impacts of rural road improvements implemented from 2012 to 2014 in Cambodia, highlighting local residents’ accessibility to local markets. This study assumes two causal relationships: rural road improvements have upgraded the accessibility and travel frequency to local markets, and the upgraded accessibility and travel frequency to local markets have led to a growth in local residents’ income. The hypotheses are statistically tested with a dataset developed through a questionnaire survey conducted in three areas in 2016. The dataset contains responses from 400 local residents to questions concerning their social attributes, livelihoods, travel modes, travel frequency, and time/cost of travels to the basic facilities. The quasi-experimental design incorporating a difference-in-differences design and an inverse possibility of treatment weighting approach revealed that the improvements in rural roads did not affect travel time nor travel cost but significantly enhanced travel frequency to local markets, and that an increase in the travel frequency to local markets and travel time savings significantly contributed to the households’ income growth. The results suggest that the improvement of seasonal reliability in accessing local markets through an introduction of all-weather roads could be critical to enhance household income, particularly in areas where agriculture is a leading industry and weather conditions are unstable across seasons.