第118回計算科学コロキウムを、10月25日（水）に開催します。
多数のご来聴をお願い致します。

場所：筑波大学　計算科学研究センター　会議室D
日時：2017年10月25日 （水）16:00-18:00
講演タイトル：Theoretical Vibrational Spectroscopy of Aqueous TMAO Solution under High Hydrostatic Pressure Conditions
講演者氏名：井本翔博士(ルール大学ボーフム)
使用言語：英語

 

要旨：Hydrogen bonds (H-bonds) play a significant role in liquid water, aqueous solutions, and bio-systems and, therefore, a deep understanding of H-bonds in liquid phases is of great importance. Although many theoretical and experimental studies have been devoted to understand their properties at ambient conditions, our knowledge of H-bonds under extreme conditions, such as high hydrostatic pressure (HHP) conditions in the kilo-bar regime, is not enough. Especially, the pressure response of aqueous trimethylamine N-oxide (TMAO) is of great interest because it works as a protecting osmolyte against high pressure denaturation. Vibrational spectroscopy is one of the most powerful methods to elucidate structure and dynamics of H-bonds. Concerning the theoretical side, quantitative analysis on IR spectra of H-bonding systems requires not only atomistic trajectories but also accurate dipole moments because the effects of induced dipole moments and charge transfer are not negligible in these cases. In this study, by using ab initio MD simulations, we analyzed IR spectra of TMAO(aq) under HHP conditions. The solvation structure of TMAO-oxygen changes dramatically under HHP conditions; threefold H-bonding structure is dominant at 1 bar, whereas three and fourfold H-bonding structures are almost equally populated at 10 kbar [1,2]. We found that the increase in the number of H-bonds can be observed as a skewness of the N-O stretch spectra since three and fourfold H-bonding structures have slightly different resonance frequencies [3]. 

[1] S. Imoto, H. Forbert, D. Marx, Phys. Chem. Chem. Phys. 17, 24224 (17). 
[2] C. Hölzl, P. Kibies, S. Imoto, R. Frach, S. Suladze, R. Winter, D. Marx, D. Horinek, S. M. Kast, J. Chem. Phys. 144, 144104 (2016).
[3] S. Imoto, P. Kibies, C. Rosin, R. Winter, S. M. Kast, D. Marx, Angew. Chem. Int. Ed. 55, 9534 (2016).

 

世話人：重田育照　

懇親会：　18:30からつくばセンター界隈で懇親会を行います。

参加希望なされる方は10/23までに庄司 (mshoji[at]ccs.tsukuba.ac.jp)まで、

ご連絡頂けますようお願い致します。

第117回計算科学コロキウムを、10月13日（金）に開催します。
多数のご来聴をお願い致します。

場所：筑波大学　総合研究棟B 110
日時：2017/10/13(金)　16:00-17：00
講演タイトル：Molecular Modeling of Water-Air and Ice-Air Interfaces
講演者氏名：永田勇樹　博士
講演者所属：Max Planck Institute for Polymer Research, Bonn Group

要旨：Structure and dynamics of Interfacial water  governs the atmospheric chemistry, chemical reactions on aqueous interface, and high surface tension of water. Nevertheless, molecular level insight into interfacial water is not fully gained. In this talk, I shall focus on the two topics – water evaporation and anomaly of ice surface around 200 K -. For water evaporation, I would reveal that water evaporation is -NOT- a completely stochastic process. The evaporation of water occurs in a time-ordered motion of multiple water molecules. [1] This challenges the variability of the free energy description for such an event. For anomaly of ice surface, we combined the molecular dynamics simulation with sum-frequency generation spectroscopy [2] and reveal that ice surface generates the maximum number of the hydrogen bond around 200 K, [3] which seems counterintuitive for the entropy increase in the thermodynamics second law. I will discuss how ice surface is melt with increasing temperature.

[1] Y. Nagata, K. Usui, and M. Bonn, Phys. Rev. Lett. 115, 236102 (2015)
[2] F. Perakis, …, Y. Nagata, Chem. Rev. 116, 7590 (2016)
[3] W. J. Smits, T. Fujie, …, Y. Nagata, Phys. Rev. Lett. 119, 133003 (2017)

第116回計算科学コロキウムを、9月26日（火）に開催します。
多数のご来聴をお願い致します。

場所：計算科学研究センター　会議室A
日時：2017/9/26(火), 13:30-15:30
講演タイトル：Downslope windstorms and foehn flows around the world: a historical overview and open research questions
講演者氏名：Dr. Annette Miltenberger
講演者所属：Institute for Climate and Atmospheric Science, University of Leeds, Leeds, UK

概要：

Foehn flows and downslope windstorms are prominent mesoscale weather phenomena in many mountain ranges across the globe. The climatology and characteristics of foehn flows in different geographic locations, ranging from the Alps to the Antarctic mountain ranges, are discussed and compared. Naturally, people living in mountainous regions have had a long standing interest in the formation and prediction of downslope windstorms and foehn flow. Accordingly, a number of mechanisms have been proposed to explain the warm nature of foehn flow and its descent into the lee side valleys. A brief historical overview on the evolution of these theories will be followed by a summary of our current understanding of the mechanisms for foehn air warming and downstream descent. Based on the discussion of the foehn flow climatologies, the relative importance of these mechanisms are investigated for different mountain ranges and various upstream conditions. The importance of regional difference will be highlighted with the example of foehn flows in the eastern and western sections of the Alpine range, which are often associated with weak and strong upstream ascent of the foehn air masses, respectively. Key open research questions regarding these aspects of foehn flow are highlighted in the discussion.

世話人：日下博幸