In this paper, the effects of the change in a tidal range on salinity intrusion in a tidal estuary were investigated with an experimental set-up which can realize an arbitrary change of tide and the transition of the mixing type.Then a vertically 2-dimensional numerical simulation of the above experimental results was carried out in order to verify its predictive ability. As a result, the following findings were obtained;
1) When the change in the salinity intrusion length due to the change in the tidal range spends a relatively long time for exchanging the fluid, salinity intrusion does not actually correspond to that of quasi-steady state and the change in salinity intrusion length has the phase shift compared with the tidal change.
2) It is confirmed that the vertically 2-dimensional numerical model developed can reproduce the experimental results of the unsteady change in the salinity intrusion with a good accuracy.

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In order to make clear the characteristics of water exchange at Nishisakura-jima strait in Kagoshima bay, the field observations on the velocity field was carried out utilizing an ADCP. It was observed that a flow pattern of residual current "outflow at the upper layer and inflow at the lower layer" dominated at the strait. Then 3D numerical simulations were carried out and it was confirmed that the residual currents at the strait were induced by the horizontal gradient of baroclinic pressure formed by the salinity distribution.

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Komatsu et al.(1997) have recently proposed a new water-purification method in a semi-enclosed coastal area. By means of this method, to activate the tidal exchange between the inner and outer sea area, installing many bottom structures “Bottom Roughness” controls a pattern of tidal residual current, which have an unsymmetrical 3-dimensional shape. In order to confirm the effect of the present method in an actual coastal area we started prototype test since May 2000 in New Nagasaki Fishery Port, Nagasaki, Japan. In this prototype test, 60 units of bottom roughness, whose height and width were 4m respectively, were installed on the bottom near two mouths of the port in May 2001. In this paper, some processes to apply this water-purification method to New Nagasaki Fishery Port were reported.

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本研究では小規模海域における現地観測の重要性を指摘し, 長崎県新長崎漁港での現地観測を実施した. これまでの研究成果から, 同海域の夏季の残差流構造は主に港内外の密度差によって説明できるということが明らかにされているため, 本論文では特に港内外の密度分布に違いが生じる要因に着目して検討を行った. その結果, 新長崎漁港の成層構造は風の影響を強く受けており, 流動構造と密度場が互いに影響を及ぼしながら非定常な変化を示していることが分かった. また, 数日周期の一方向に卓越する南風によって引き起こされる残差流構造が夏季の海水交換に大きな役割を果していることが示唆された.

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We proposed a method to reduce the salinity intrusion of well-mixed type by controlling artificially the pattern of river discharge with tidal phase in a tidal estuary. In order to examine the effect of this method, some experimental simulations were made under various conditions of river discharge.
In this study, the effect of the pattern of river discharge, the most effective timing of discharge when the water was stored, and the relation between the reduction of salinity intrusion and the ratio of the volume of fresh water flowing in during a tidal period to the tidal prism were examined. As a result, it was made clear that discharging the river water intensively during the flood tide could reduce the salinity intrusion effectively when the river discharge was relatively large.

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Directional characteristics of hydrodynamic force on a submerged asymmetrical roughness (we call this roughness BaNK block) in oscillatory flows were experimentally investigated. In this study, a quarter sphere or a half cylinder is used as a BaNK block which is set on the bottom of channel with an angle of attack θ to an oscillating flow direction. It is found that residual hydrodynamic force on half cylinder is much larger than that on quarter sphere because the substantial length of quarter sphere is smaller than that of half cylinder. Furthermore, residual hydrodynamic force on BaNK blocks is almost constant with the change of θ when Keulegan-Carpenter number KC is small. However, in large KC number, the force on quarter sphere decreases with the increase of θ because residual lift force decreases in θ=50°-90°.

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Directional characteristics of wave-induced residual current and control of littoral sand drift depending on wave direction and an angle of plural asymmetrical bottom roughness (we call the asymmetrical bottom roughness BaNK block) were experimentally investigated. Firstly, the distribution of residual velocity on the fixed bed with the bended BaNK blocks was measured in a 3-dimensional wave field. Secondly, the deformation of movable bed due to the effect of blocks was measured in other fields. As a result, direction of wave-induced residual current could be arbitrarily changed by setting blocks with an angle. Furthermore, it was dmonstrated that the BaNK blocks are able to control littoral sand drift in a 3-dimensional wave field with movable bed.

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In this study, the salinity at the bottom-layer in the Chikugo estuary was measured by the automatic measuring instruments fixed at 7km and 15km upstream from the mouth in order to make clear the change of the salinity intrusion.
As a result, the following findings were obtained.
1) The salinity intrusion at the spring tide in the Chikugo estuary is of well-mixed type, while the mixing at the neap tide is generally moderately-mixed type and the salinity intrusion length in this mixing-type is shorter than that in a well-mixed type.
2) When both the diurnal inequality of tide and the decrease of the tidal range become remarkable, the fully-stratified type can be realized and then the salinity intrusion length becomes longest near the neap tide.

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In order to make clear the material flow mechanism and the eco-system in the northern region of Kagoshima Bay, we firstly investigated the seasonal change in the water quality and phytoplankton composition utilizing the observational results. Then, we constructed a lower-trophic level model on the basis of the observation and investigated the material flow mechanism. As a result, the following findings were obtained; 1) The biomass of Bacillariophyceae is dominant among various phytoplankton groups through a year, 2) The lower-trophic ecosystem model constructed can reproduce well the seasonal change of water quality and phytoplankton biomass, 3) The change in DO near the water surface is controlled mainly by the net primary production.

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流体力学が自然環境や生態系と直接向かい合うようになった昨今, 「抽象化された世界 (数物理学の世界) 」だけに閉じこもっていること事もはや許されない. 自然環境という生き生きとした実体の世界を真に理解し, 解明していくためには, 論理プラス「情緒力・直感力・感性・想像力」などが必要となってくる. また流体力学そのものも柔軟で色彩を持ったものになっていかなければならない. そこで著者がこの方向に添うと考えている「大規模振動流場における流れと物質輸送の創造・制御」に関する研究例を紹介する.

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Efficiency of a prevention method on saline wedge intrusion in rivers using an air curtain (a two-dimensional bubble flow) was experimentally investigated from a viewpoint of a flow mechanism. The behavior of saline wedges in the presence of an air curtain is governed by the three external forces: the buoyancy of an air curtain A, the intrusion force of a saline wedge B and the inertial force of a fresh water flow R. It was found that the flow behavior could be classified into three types both by A/B dominating the rising discharge of salt water due to an air curtain, and by A/R dominating the strength (circulation) of a convection cell induced by an air curtain in its upstream side. In addition, the efficiency of this method was evaluated using the newly introduced parameter α through the discussion on the appearance conditions of the three flow types.

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【背景・目的】activation-induced cytidine deaminase（AID）欠損によるB細胞クラススイッチ障害は，腸内細菌叢の変化を誘導する．ところがAID欠損は他のIgクラスの発現も阻害するため，この変化はIgA単独の欠損に直接起因するのか明確でない．そこで我々はCRISPR/Cas9システムを用いてIgA変異モデルを新たに樹立し，腸管粘膜におけるIgAの重要性を再検証した．【方法・結果】IgEとIgAの細胞内ドメイン間を標的としたguide RNAを構築し，Cas9 mRNAとともにC57BL/6胚に導入した結果，IgA遺伝子座全領域を欠損する系統（IgA^−/−）を樹立し，IgA以外のIgクラス発現には影響がないことを確認した．このIgA^−/−の小腸粘膜におけるsegmented filamentous bacteriaの著しい増殖を走査電子顕微鏡で観察した．腸管内容物から抽出した16S rRNAのメタゲノム解析から，回腸細菌叢の多様性変動を観察した．さらに全消化管のうち回腸粘膜に限局した炎症とともに，回腸粘膜固有層へのCD4⁺ T細胞浸潤，IFN-γやIL-17産生の亢進，IL-4産生の抑制が確認された．IgA^−/−をCD19 Cre-YC3.60 transgenicマウスと交配し生体イメージングで観察すると，IgA^−/−回腸パイエル板B細胞のCa²⁺流入はむしろ亢進していた．【結論】我々はIgA単独の欠損で腸内細菌叢の変化が誘導されることを再確認したばかりでなく，この変化によって腸管の恒常性破綻に起因する回腸粘膜特異的な炎症が誘発されることを見出した．

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  我々の腸管粘膜には独特なリンパ組織gut-associated lymphoid tissues（GALT）が形成され，免疫寛容と賦活の適切なバランスが巧みに調節されている．一方，この腸管粘膜における免疫恒常性の破綻は過剰で病的な免疫応答の誘導を来たし，クローン病や潰瘍性大腸炎など本邦でも急増傾向にある炎症性腸疾患（IBD）の病態を誘導する．これまでに，クローン病をはじめとする腸管の慢性炎症性疾患は回盲部に好発すること，また潰瘍性大腸炎は虫垂切除術によって発症リスクが低下することなどが知られている．こうした事実は回盲部周辺における免疫応答がIBDの病態に深く関与することを暗示している．しかしその特殊な免疫調節機構の詳細，あるいは疾患における病態的意義はこれまで明らかにされていない．そこで我々は5D生体イメージングやFLET技術を応用しつつ，IBDモデル誘発時の回盲部周辺における免疫応答の解析を試みた．IBDにおけるB細胞機能の病態的意義としては，分化した形質細胞から分泌される異常な免疫グロブリン産生のみがこれまで注目されてきた．ところが我々の解析結果から見えてきたものは，特定のGALTにおけるB細胞の新たな機能であった．本講演では，生体イメージングによる解析から浮き彫りにされた，この腸管粘膜における新たな免疫調節機構について紹介したい．

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In recent years the upstream intrusion of salinity in a tidal estuary has become a serious social problem for river environment and water resources. In view of taking water resources durably and preserving the ecology, artificial control methods for preventing the salinity intrusion are required. Setting up a mound on a river bed has been proposed and applied to real estuaries. So we experimentally examined the effects of the height and the position of mound in a well-mixed estuary. In addition, we proposed the method to make vertical mixing strongly by using a bubble plume to decrease the intrusion length of saline wedge and also examined its effect experimentally.

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In the Sendai river which is located in the southwest part of Kyusyu, Japan, the trouble that the salinity concentration of water drawn from the intake is more than the water quality standard of city tap water has sometimes occurred in recent years and it has called people's attention. In this paper, it is made apparent with the use of field data that all the trouble occurred in two or three days after the neap tide and that the fresh water discharge, the M. W. L. in the mouth of estuary and the pattern of tidal curve determine the situation of salinity intrusion and the mixing of salinity with the water taken. Evaluation of these dominant factors makes it possible for us to predict easily whether the trouble will occur or not in the future.

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筑後川は, 流域内外に各種用水を供給している九州最大の河川である. 近年, 筑後大堰湛水域の内部生産や海面上昇に伴う筑後川感潮域における塩分の上昇傾向が指摘されつつあるが, 十分な機構解明には至っていないようである. 本論文は, 筑後川下流域に位置する筑後大堰湛水域, 筑後川感潮域における水質特性について考察したものである. 筑後大堰湛水域では, 取水に伴う滞留時間の長期化が夏期の高水温期と相侯って藻類増殖の一因となっていることが確認された. 筑後川感潮域の塩分変化が有明海の海面上昇と利水形態の変更の影響を受けていること, さらには感潮域停滞部における藻類増殖の可能性を指摘した. この感潮域の藻類増殖を有限容積モデルを用いた水質モデルにより確認した.

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