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| 1.
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Yoshioka, H ; Tada, Yukio ; Kunimine, K ; Furuichi, T ; Hayashi, Yujiro
概要:
The solidification process of undercooled alloy melts has been clarified experimentally in Part I of this paper. In the
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present paper, using the experimental evidence, a solidification model linking macroscopic heat transfer and microscopic solidification is presented. The model reflects the microscopic solidification phenomena occurring until the thermodynamically unstable field shifts to equilibrium, consisting of three fundamental processes: (first stage) free growth, (second stage) crystal expansion with relaxation, and (third stage) equilibrium solidification. Based on this model, a numerical simulation is carried out for the temperature change, interface movement, and solute concentration distribution during the solidification of an undercooled Bi-Sn melt. Theoretical predictions of the temperature changes involving the recalescence, terminal time of the relaxation process, and microsegregation for the solidified texture agree quantitatively with experimental observations. © 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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| 2.
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Yoshioka, H ; Tada, Yukio ; Kunimine, K ; Furuichi, T ; Hayashi, Yujiro
概要:
The solidification process of Pb-Sn and Bi-Sn alloy melts is discussed to obtain a basic understanding of the essential
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phenomena of solidification with undercooling. First, from macroscopic observations, it is shown that the solidification process consists of the following three stages: (1) free growth with recalescence dissipation of thermal undercooling, (2) expansion of crystals with the relaxation of constitutional undercooling or with the recovering process of interrupted quasi-steady heat conduction, and (3) equilibrium solidification. The specific features of free growth under non-uniform undercooling are also shown by comparison with the Lipton, Glicksman, and Kurz model. Next, from microscopic observations, the distribution of the solute concentration and the change of crystal morphology in the solidified materials were investigated quantitatively using scanning electron microscopy and energy-dispersive spectroscopy. Finally, the solidification path during the above three fundamental processes is dynamically represented on phase diagrams. © 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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Yoshioka, H ; Tada, Yukio ; Hayashi, Yujiro
概要:
In the solidification of multicomponent alloys, a mushy zone appears between the solid and liquid regions and promotes s
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table solidification by accepting the rejected solute regionally. In this study, the link between heat transfer and microstructures of the mushy zone has been studied experimentally and theoretically. First, the crystal morphology of the mushy zone at a microscale was observed by using succinonitrile–acetone solution and Bi–Sn alloys melts. It was found that the mushy zone consists of a leading front, in which the microstructures originate, and a growing region, where solidification proceeds with the fattening of the crystals. Next, the mechanism of dendritic sidebranch evolution was studied, taking into account the interfacial instability. To summarize these results, a macro–microscopic model is presented, and the change of crystal morphology at the microscale level was analyzed in relation to cooling rate, initial concentration, and distance from a cold wall.
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| 4.
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多田, 幸生 ; Tada, Yukio
概要:
金沢大学理工研究域機械工学系<br />超音波振動と変動磁場を利用した食品の高品質冷凍技術の開発を目的に，超音波振動と交番電場が水および細胞の過冷却に及ぼす影響を実験的に追究した．1MHzの高周波超音波振動を5W以上の出力で付与すると，過冷
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却度の分散が小さくなり、また低過冷却度における核生成が抑制される傾向が見出された．また，交番電場の効果について検討し，微少電流印加により玉ねぎの表皮組織細胞の過冷却度が最大2K程度促進されたが，さらなる電流印加による過冷却促進は得られなかった．さらに，魚肉を対象に凍結・解凍による損傷度を数値計算により予測する手法が構築された．以上により，外部力を利用した食品の高品質冷凍技術の開発の基礎が得られた．<br />A method to actively controlling crystallization is one of promising technique for cryopreservation of food. The object of this project is to study the effects of ultrasonic vibration and alternating electric field on supercooling of water and biological tissue. By applying ultrasonic vibration at frequency of 1MHz to a water, a weak enhancement of supercooling was found at ultrasonic power larger than 5W. On the other hand, as for alternating electric field, it was found that the load effects of low electric current on onion cell enhanced supercooling degree, but also those of high electric current reduced supercooling degree. Furthermore, a muscle tissue of tuna fish was cooled by air-blast method. By linking the numerical model and experimentally determined correlation equations, the drip loss of tuna fish after freezing and thawing was quantitatively estimated. Summarizing these results, basic of knowledge for development of high-quality cryopreservation was obtained.<br />研究課題/領域番号:26420141, 研究期間(年度):2014-04-01 - 2017-03-31
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| 5.
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多田, 幸生 ; Tada, Yukio
概要:
金沢大学理工研究域機械工学系<br />超音波振動と交番磁場を利用した過冷却の促進とそれを利用した食品の高品質冷凍技術の開発を目的に，超音波振動と交番電場が水および組織体の過冷却に及ぼす影響を実験的に追究した．1MHzの高周波超音波振動を水
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に付与すると，低過冷却度での核生成の抑制および過冷却度の分散を小さくする傾向が見られたが，平均的には有意な過冷却促進効果は得られなかった．一方，模擬食品としての寒天ゲルに対しては超音波の吸収に伴う発熱作用が顕著に現れ，この効果を利用した温度制御により組織全域を過冷却状態へ移行させ，それを解除することで組織体全域を急速凍結できることが示された．<br />A method to actively controlling crystallization is one of promising technique for cryopreservation of food. The object of this project is to study the effects of ultrasonic vibration and alternating electric field on supercooling of water and biological tissue. Firstly, water in a test tube was cooled at constant cooling rate with ultrasonic vibration at frequency of 1 MHz. As the results, release of supercooling at higher temperature was suppressed by applying ultrasonic vibration, although the average supercooling degree was not enhanced. Next, we focus on the thermal effect of ultrasound as changing temperature distribution in tissue, directional freezing experiments of cylindrical agar gel immersed in low temperature solution were carried out. It was found that ultrasound at high frequency is effective to enlarge supercooled region in the tissue. The lengths of supercooled region were clarified in relation to ultrasonic power and cooling condition.<br />研究課題/領域番号:17K06192, 研究期間(年度):2017-04-01 - 2020-03-31<br />出典：「高周波超音波振動と交番磁場を併用した過冷却の促進による食品の高品質冷凍技術の開発」研究成果報告書 課題番号17K06192（KAKEN：科学研究費助成事業データベース（国立情報学研究所））（https://kaken.nii.ac.jp/report/KAKENHI-PROJECT-17K06192/17K06192seika/)を加工して作成
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| 6.
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多田, 幸生 ; Tada, Yukio
概要:
金沢大学機械工学系<br />超音波振動を利用した食品の高品質冷凍技術の開発を目的に，超音波振動が水の過冷却と氷晶形成に及ぼす影響を実験的・理論的に追究した．超音波振動を高出力で付与した場合には過冷却の解除効果が顕在化するが，低出力で照射し
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た場合には弱い過冷却の促進効果が見出された．また，超音波振動の振幅に20～25kHzの周期的な変動を付与することで過冷却促進効果が若干向上する結果を得た．さらに変動磁場の併用による促進効果が示された．また，分子動力学計算を行い，水分子に交番電場による攪乱を付与することで，氷晶成長の遅れを誘起できる可能性が示された．以上により，外部力を利用した食品の高品質冷凍技術の開発の基礎が得られた.<br />A method to actively controlling crystallization is one of promising technique for cryopreservation of food. The object of this project is to study the effects of ultrasonic vibration on supercooling of water. Two types of ultrasonic vibration; (a)amplitude-regulated vibration at frequency of 1MHz and (b)amplitude-modulated vibration, were tested. Regarding the case of amplitude-regulated vibration, the supercooling degree decreased with increasing ultrasonic power. On the other hand, as for amplitude-modulated vibration, a weak enhancement of supercooling was found at amplitude-modulated frequency of 20-25kHz. Furthermore, it was indicated that there is optimum value of ultrasonic power for enhancing supercooling degree, since the action of ultrasonic vibration would have two aspects as to promote and reduce nucleation. Summarizing these results, the mechanism of sonocrystalization in biological tissue was discussed in relation to method of ultrasonic irradiation.<br />研究課題/領域番号:23560221, 研究期間(年度):2011-2013
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| 7.
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多田, 幸生 ; Tada, Yukio
概要:
金沢大学機械工学系<br />超音波照射を利用した食品の高品質冷凍技術の開発を目的に,超音波振動が水および模擬食品(寒天ゲル)の過冷却状態と氷晶形成に及ぼす影響を実験的・理論的に追究した.超音波を高出力で照射した場合には過冷却の解除効果が顕
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在化するが,低出力で照射した場合には弱い過冷却の促進効果が見出された.また,高い過冷却度の状態から凍結が開始する場合には,超音波照射による氷晶の微細化効果が見られた.実験データ数が不足しているため,より詳細な検証が必要であるが,超音波照射を利用した食品の高品質冷凍技術の開発の基礎が得られた.<br />A method to actively controlling crystallization is one of promising technique for cryopreservation of food. The object of this project is to study the effects of ultrasonic irradiation on ice formation during freezing of food. In the experiments, agar gel or pure water was frozen under various irradiation methods of ultrasound. It was found that the supercooling state was released by applying ultrasound at high intensity level, since ultrasonic cavitation effects augmented. On the other hand, a delay in the nucleation temperature was caused by applying ultrasound at low intensity level. Secondly, ice structure size decreased with increasing ultrasonic power under given initial-supercooling degree. Summarizing these results, the mechanism of sonocrystalization in biological tissue was discussed in relation to method of ultrasonic irradiation.<br />研究課題/領域番号:20560183, 研究期間(年度):2008-2010
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| 8.
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多田, 幸生 ; Tada, Yukio
概要:
金沢大学機械工学系<br />医療技術やバイオテクノロジーの発達に伴って生体細胞・組織を凍結保存する技術の確立が求められている.凍結保存は低温化と活性水分の低減により生化学反応の抑制を図るものであるが,凍結の過程で細胞内外に氷晶が形成され,
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それが各種の機械的損傷や膠質的損傷を発生させる要因となる.このような凍結損傷を完全に回避するためには,細胞内の水が結晶化せず,液体構造がそのまま固定化されるガラス化現象を発現させるのが理想的である.そこで本研究では,超音波を付与することにより凍結過程における核生成の能動的制御を追究した.すなわち,超音波の付与により,超音波キャビテーションによる衝撃波を発生させ,それにより水素結合で凝集している水分子のクラスターを解離させ,過冷却の促進を図り,最終目標としてガラス化を目指すものである.具体的には,生体模擬組織として寒天ゲルを供試した凍結実験を行い,過冷却度および氷晶の生成状態を超音波出力および冷却速度と関連づけて実験的に追究し,以下の結果を得た.(1)本装置では超音波照射による過冷却の促進効果は認められなかった.冷却速度が小さすぎること,超音波の周波数が低いこと,および超音波出力が不足していることなどが原因と考えられる.今後,装置系について見直しが必要である.(2)組織体表層部において超音波照射による氷晶の微細化の効果が認められた.また,音響流に基づく氷晶の微細化の効果は小さく,氷結晶の微細化は主に超音波キャビテーションの効果であることが示された.(3)冷却熱流束に対して超音波出力が過大になると,音波吸収による発熱作用が顕在化し,逆に氷結晶の肥大化を招くことが判った.(4)この対策として,超音波の間欠照射方式を提案し,その有効性が検証された.<br />Freezing can slow down or stop some biological reactions for preserving biological cell. It is also true that the freezing is lethal to the living system. During freezing, the extra- and intra-cellular ice formation, osmotic water permeation through cell membrane, deformation of the cell and other behavior occur at microscale and they bring serious injuries connecting to life-and-death of living cell.A method to actively controlling crystallization is one of promising technique for cryopreservation. The object of this project is to study the effects of ultrasonic irradiation on ice formation during freezing of biological materials. In the experiments, agar gel was frozen under various irradiation methods of ultrasound at frequency of 28 kHz. The measurements of temperature and the microscopic observation of ice crystals by using fluorescent indicator were carried out.Firstly, it was found that ultrasound released the supercooling states, and reduced ice crystal size in the tissue. However, the fattning of ice crystal was observed by irradiation of higher ultrasonic power, since the cooling rate was reduced due to absorption of the ultrasonic wave. The ice crystal size in the tissue was clarified in relation to ultrasonic power and tissue size. Secondly, various irradiation methods were tested. It was found that the pulsed irradiation is useful for reducing ice crystal size, since the fattening of ice crystal due to absorption of ultrasonic wave is reduced. The mechanism of sonocrystallization in biological tissue was discussed in relation to ultrasonic power, on-off frequency and irradiation duration.<br />研究課題/領域番号:18560195, 研究期間(年度):2006-2007<br />出典：「超音波を利用した凝固制御による生体組織のガラス化保存技術の開発」研究成果報告書 課題番号18560195 (KAKEN：科学研究費助成事業データベース（国立情報学研究所）) 本文データは著者版報告書より作成
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| 9.
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多田, 幸生 ; Tada, Yukio
概要:
金沢大学機械工学系<br />食品の凍結保存は低温化と活性水分の低減により生化学反応の抑制を図るものであるが,凍結の過程で細胞(筋繊維)レベルでのミクロ現象が生じ,これが各種の機械的損傷や膠質的損傷を発生させる要因となる.したがって,食品の
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品質(風味,テクスチャー)を損なわない効果的な冷却技術の開発が必須となる.本謀題は以上の観点から進めるものであり,凍結過程で超音波を付与するととにより,超音波キャビテーションによる衝撃波を発生させ,それにより(1)細胞内過冷却の能動的解除と,(2)細胞内外の氷結晶の微細化を図るものである.最終的には,食品全城の氷晶を微細化させる新しい凍結技術の開発を目指すものである.具体的には模擬食品(寒天)および食品(馬鈴薯)を供試した凍結実験を行い,氷晶の生成状態を超音波出力および冷却速度と関連づけて追究し,以下の成果を得た.1.低温度城(0℃〜-5℃)において超音波キャビテーションの発生を確認した.2.冷却速度が大きい条件において超音波による氷結晶の微細化の効果を見出した.また,超音波出力の増加につれて氷晶径および長径/短径比は減少することを明らかにした.3.超音波による氷晶の微細化の機構について検討し,音響流による試料表面の熱伝達促進以外の要因がある可能性が示された.4.本実験範囲では,氷晶制御に及ぼす溶存気体の影響は小さい.5.超音波付与により,水溶液中で成長する氷結晶は高次アーム化することが示された.6.馬鈴薯の凍結・解凍実験を行い,超音波付与により,細胞内外の氷晶による機械的損傷の軽減が認められた.しかし,電気インピーダンス法による計測の結果,細胞膜の凍結損傷は防止できていないことが判った.<br />Freezing can slow down or stop some biological reactions for preserving food. It is also true that the freezing is lethal to keeping the taste of food. During freezing, the extra- and intra-cellular ice formation, osmotic water permeation through cell membrane, deformation of the cell and other behavior occur at microscale and they bring serious injuries connecting to drip and denaturation of protein.A method to actively controlling crystallization is one of promising technique for cryopreservation. The object of this project is to study the effects of ultrasonic irradiation on ice formation during freezing of biological materials. In the experiments, agar gel and/or potato tissue was frozen under irradiation of ultrasound at frequency of 28kHz. The measurements of temperature and the microscopic observation of ice crystals by using fluorescent indicator were carried out.Firstly, the cooling rate of sample augmented according to the increase of the ultrasonic power, since acoustic streaming and flow disturbance due to acoustic cavitation increased. Secondly, it was found that ice structure size decreased with increasing ultrasonic power in case of rapid cooling. Furthermore, the ultrasonically induced effects on freezing was analyzed using local cooling rate defined at freezing front. It was clarified that smaller ice crystals were formed by irradiating ultrasound, comparing with case without ultrasound, under being the same local cooling rate. Therefore, there are effects on ice formation through not only enhancing local cooling rate due to acoustic streaming, but also other relevant phenomena. The mechanism of sonocrystallisation in biological tissue was discussed in relation to ultrasonic power and cooling rate.<br />研究課題/領域番号:16560178, 研究期間(年度):2004-2005<br />出典：「パルス超音波を利用した凝固制御による生体・食品の低損傷・凍結保存技術の開発」研究成果報告書 課題番号16560178 (KAKEN：科学研究費助成事業データベース（国立情報学研究所）) 本文データは著者版報告書より作成
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| 10.
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多田, 幸生 ; Tada, Yukio
概要:
金沢大学機械工学系<br />食品の凍結保存は,原理的には,低温化と活性水分の低減により生化学反応の抑制を図るものであるが,凍結の過程で細胞レベルでのミクロ現象が生じ,これが各種の機械的・膠質的損傷を廃生させる.したがって,食品の品質(食味
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,テクスチャー)を損なわない効果的な冷却技術の開発が必須となる.本課題は以上の観点に立って進めるものであり,パルスマイクロ波の付与により凍結過程における過冷却現象の能動的促進を追究した.すなわち,マイクロ波照射により,極性分子である水分子の回転運軌を励起し,それにより水素結合しているクラスターを解離させ,過冷却の促進を実現しようとするものである.最終的には,食品全域を過冷却状態から瞬時に凍結させる方式の開発を目指すものである.本研究で得られた主な成果は以下のとおりである.1.試験セル,液体窒素を封入した冷却部,パルスマイクロ波発生装置,熱電対を用いた温度測定系からなる装置が製作された.2.マイクロ波照射下でグリセロール水溶液の凍結実験を行い,マイクロ波は過冷却の促進と解除の2つの作用を内在する可能性があることが示された.3.食品としてリンゴ組織体を供試した凍結実験を行い,凍結組織をCryo-SEM観察した結果,マイクロ波出力が大きくなるにつれて組織体表層部において氷晶径が減少することが見いだされた.4.組織体内部ではマイクロ波による加熱効果などに起因する局所冷却速度の低下のため,氷晶径の微細化は難しく,適用サイズに制限があることが判った.5.食品凍結において生ずる氷晶形成とミクロ挙動が3次元観察により明らかにされ,マクロ伝熱,ミクロ現象,凍結後の品質変化を連結した速度論モデルが構築され,凍結による品質変化の定量的予測が実現された.<br />Freezing can slow down or stop some biological reactions for preserving food. It is also true that the freezing is lethal to keeping the taste of food. During freezing, the extra-and intra-cellular ice formation, osmotic water permeation through cell membrane, deformation of the cell and other behavior occur at microscale and they bring serious injuries connecting to drip and denaturation of protein.A method to actively enhancing the supercooling is one of promissing technique for cryopreservation of food The object of this project was to study the effects of microwave irradiation on supercoling and ice formation during freezing of food. In the experiments, glycerol solution and apple tissue were frozen under irradiation of microwave at 2.45GHz. The measurements of supecooling degree and observation of morophology of frozen cell by using cryo-rnicroscopy were carried out.Summarizing these results, it was found that microwave have two aspects ; enhacing and releasing supercooling in dependence on microwave power. Especially, in the case of cooling by immersion in liquid nitrogen, the ice crystal size near the cooling surface decreased with increasing microwave power. Therefore, a combined use of microwave, irradiation and rapid cooling is considered to be a approach to reduce freezing injury. Regarding case of core region in the tissue, the effects of microwave on ice crystal size was diminished, since local cooling rate decreased due to heating effect caused by microwave increased. Thus, the size effects on microwave irradiation was found to be important factor to be considered.<br />研究課題/領域番号:14550175, 研究期間(年度):2002-2003<br />出典：「パルスマイクロ波を用いた過冷却の促進による食品の低損傷・凍結保存技術の開発」研究成果報告書 課題番号14550175 (KAKEN：科学研究費助成事業データベース（国立情報学研究所）) 本文データは著者版報告書より作成
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