Studying the vibrational energy transfer pathways and dynamics in molecules is important for different areas of chemical research, with the range of potential applications in nanotechnology, organic chemistry and biochemistry. Two transport regimes, ballistic and diffusive, are recognized for the transport in molecules; while the latter is typically slow the former can be fast and efficient. The diffusive transport regime was observed in numerous compounds, whereas there are only a few cases where the ballistic transport has been suggested in molecules. The subject of this dissertation is to identify the factors influencing the ballistic transport, including the molecular chain organization, thermodynamic conditions and end-group functionalities. The research involves several types of oligomeric chains, such as polyethyleneglycol, perfluoroalkane, and alkane chains. The experiments were performed using the relaxation-assisted two-dimensional infrared spectroscopy method, which permits measuring the energy transport time between two vibrating groups. The transport via all three chain types was found to occur with a constant speed, although different speeds were found in different chain types. The fastest speed of 14.4 Å/ps was found in linear alkanes, the slowest, 3.9 Å/ps, in perfluoroalkanes. The difference in the transport speed was attributed to involvement of different chain optical bands. The temperature dependence of the transport speed and efficiency in perfluoroalkanes demonstrated that the ballistic transport, dominating at low temperatures, is switched to the diffusive transport at elevated temperatures; the observation was supported by the theoretical modeling. The energy transport in several compounds lacking periodic structure was found to occur with an effective speed of 1.2-1.4 Å/ps, which approximately matches the speed of passing one bond-length per mean lifetime of the excited vibrational mode (1 ps). This speed was found to be 3-10 fold smaller than the transport speed via oligomeric chains. Moreover both regimes, diffusive and ballistic, were distinguished within the same compound: the transport was ballistic via the chain and diffusive within the bulky end group. The two transport times were found additive, confirming the ballistic nature of the through-chain transport. This study develops a detailed picture of energy transport in molecules and provides new opportunities for designing molecular and nanoscale materials with tailored energy transport properties, potentially useful for making novel elements for molecular electronics. / 1 / Natalia I. Rubtcova

<p>The Arctic region attracts considerable scientific interest in these years. Some of the Earth's most pronounced signs of the recent climate change are found here. The summer sea-ice cover is shrinking at an alarming rate. At the same time the region warms faster than the rest of the globe.</p><p>The sea-ice reduction implies an increase of solar-radiation absorption at the surface leading to warming which is expected to be larger at higher than at lower latitudes. It is therefore often assumed that the sea-ice reduction is a major cause of the observed Arctic temperature amplification. However, results presented in this thesis suggest that the snow and ice-albedo feedbacks are a contributing but not dominating mechanism behind the Arctic amplification. A coupled climate-model experiment with a doubling of the atmospheric CO2 concentration reveals a considerable Arctic surface-air-temperature amplification in a world without surface-albedo feedback. The amplification is only 8 % larger when this feedback is included. Instead the greenhouse effect associated with an increase of humidity and cloud cover over the Arctic seems to play a major role for the amplification.</p><p>Reanalysis data, which are partly based on observations, show Arctic temperature amplification well above the surface in the troposphere. In the summer season, the amplification has its maximum at ~ 2 km height. These trends cannot be explained by the snow- and ice-albedo feedbacks which are expected to induce the largest amplification near the surface. Instead, a considerable part of the trends aloft can be linked to an increase of the atmospheric energy transport into the Arctic.</p><p>A major topic of this thesis is the linkage between the mid-latitude circulation and the Arctic warming. It is suggested that the atmospheric meridional energy transport is an efficient indicator of this linkage.</p>

The Arctic region attracts considerable scientific interest in these years. Some of the Earth's most pronounced signs of the recent climate change are found here. The summer sea-ice cover is shrinking at an alarming rate. At the same time the region warms faster than the rest of the globe. The sea-ice reduction implies an increase of solar-radiation absorption at the surface leading to warming which is expected to be larger at higher than at lower latitudes. It is therefore often assumed that the sea-ice reduction is a major cause of the observed Arctic temperature amplification. However, results presented in this thesis suggest that the snow and ice-albedo feedbacks are a contributing but not dominating mechanism behind the Arctic amplification. A coupled climate-model experiment with a doubling of the atmospheric CO2 concentration reveals a considerable Arctic surface-air-temperature amplification in a world without surface-albedo feedback. The amplification is only 8 % larger when this feedback is included. Instead the greenhouse effect associated with an increase of humidity and cloud cover over the Arctic seems to play a major role for the amplification. Reanalysis data, which are partly based on observations, show Arctic temperature amplification well above the surface in the troposphere. In the summer season, the amplification has its maximum at ~ 2 km height. These trends cannot be explained by the snow- and ice-albedo feedbacks which are expected to induce the largest amplification near the surface. Instead, a considerable part of the trends aloft can be linked to an increase of the atmospheric energy transport into the Arctic. A major topic of this thesis is the linkage between the mid-latitude circulation and the Arctic warming. It is suggested that the atmospheric meridional energy transport is an efficient indicator of this linkage.

archives@tulane.edu / 1 / Robert Mackin

No description available.

Thermal stream loadings from both natural and anthropogenic sources have significant relevance with respect to ecosystem health and water resources management, particularly in the context of future climate change. In recent years, there has been an increase in field-based research directed towards characterizing thermal energy transport exchange processes that occur at the surface water/groundwater interface of streams. In spite of this effort, relatively little work has been performed to simulate these exchanges and elucidate their roles in mediating surface water temperatures and to simultaneously take into account all the pertinent hydrological, meteorological and surface/variably-saturated subsurface processes. To address this issue, HydroGeoSphere, a fully-integrated surface/subsurface flow and transport model, was enhanced to include fully-integrated thermal energy transport. HydroGeoSphere can simulate water flow, evapotranspiration, and advective-dispersive heat and solute transport over the 2D land surface and water flow and heat and solute transport in 3D subsurface variably-saturated conditions. In this work, the new thermal capabilities of HydroGeoSphere are tested and verified by comparing HydroGeoSphere simulation results to those from a previous subsurface thermal groundwater injection study, and also by simulating an example of atmospheric thermal energy exchange. A proof of concept simulation is also presented which illustrates the ability of HydroGeoSphere to simulate fully-integrated surface/subsurface thermal energy transport. High-resolution 3D numerical simulations of a well-characterized reach of the Pine River in Ontario, Canada are also presented to demonstrate steady-state thermal energy transport in an atmosphere-groundwater-surface water system. The HydroGeoSphere simulation successfully matched the spatial variations in the thermal patterns observed in the river bed, the surface water and the groundwater. Transient simulations of the high-resolution Pine River domain are also presented. Diurnal atmospheric conditions were incorporated to illustrate the importance of fluctuations in atmospheric parameters on the entire hydrologic regime. The diurnal atmospheric input fluxes were found to not only change the temperatures of the surface and subsurface throughout the cycle, but also the magnitude and direction of the transfer of thermal energy between the surface and subsurface. Precipitation events were also simulated for the Pine River domain using three different rainfall rates. The surface temperatures responded quickly to the rainfall events, whereas the subsurface temperatures were slower to respond in regions where infiltration was not significant. A thermal energy signal from the precipitation event was evident in the subsurface, and dissipated once the rainfall ceased. This indicates that temperature can potentially be used as a tracer for hydrograph separation. The potential of a thermal energy tracer for hydrograph separation was investigated using HydroGeoSphere simulations of the Borden rainfall-runoff experiment. These results matched both measured and previous simulation results using a bromide tracer. The hydrograph separation results from the thermal energy tracer were sensitive to temperature conditions in the subsurface, although this sensitivity reduced considerably when the precipitation event and subsurface temperatures were significantly different. The contribution of each atmospheric component to thermal energy transport was investigated using the Pine River and Borden examples. Each atmospheric component was individually neglected from the simulation of both sites to investigate their impact on thermal energy transport. The results show that longwave radiation dominates the atmospheric inputs for the Borden example, whereas shortwave radiation dominates in the Pine River example. This indicates that the atmospheric contributions to the thermal energy distribution are site-specific and cannot be generalized. In addition, these results indicate that the atmospheric contributions should not be ignored; measuring atmospheric data in the field is an important component in developing an accurate thermal energy transport model. The addition of thermal energy transport to HydroGeoSphere provides a valuable tool for investigating the impact of anthropogenic and non-anthropogenic changes to the atmospheric and hydrological thermal energy system. This computational framework can be used to provide quantitative guidance towards establishing the conditions needed to maintain a healthy ecosystem.

Thermal stream loadings from both natural and anthropogenic sources have significant relevance with respect to ecosystem health and water resources management, particularly in the context of future climate change. In recent years, there has been an increase in field-based research directed towards characterizing thermal energy transport exchange processes that occur at the surface water/groundwater interface of streams. In spite of this effort, relatively little work has been performed to simulate these exchanges and elucidate their roles in mediating surface water temperatures and to simultaneously take into account all the pertinent hydrological, meteorological and surface/variably-saturated subsurface processes. To address this issue, HydroGeoSphere, a fully-integrated surface/subsurface flow and transport model, was enhanced to include fully-integrated thermal energy transport. HydroGeoSphere can simulate water flow, evapotranspiration, and advective-dispersive heat and solute transport over the 2D land surface and water flow and heat and solute transport in 3D subsurface variably-saturated conditions. In this work, the new thermal capabilities of HydroGeoSphere are tested and verified by comparing HydroGeoSphere simulation results to those from a previous subsurface thermal groundwater injection study, and also by simulating an example of atmospheric thermal energy exchange. A proof of concept simulation is also presented which illustrates the ability of HydroGeoSphere to simulate fully-integrated surface/subsurface thermal energy transport. High-resolution 3D numerical simulations of a well-characterized reach of the Pine River in Ontario, Canada are also presented to demonstrate steady-state thermal energy transport in an atmosphere-groundwater-surface water system. The HydroGeoSphere simulation successfully matched the spatial variations in the thermal patterns observed in the river bed, the surface water and the groundwater. Transient simulations of the high-resolution Pine River domain are also presented. Diurnal atmospheric conditions were incorporated to illustrate the importance of fluctuations in atmospheric parameters on the entire hydrologic regime. The diurnal atmospheric input fluxes were found to not only change the temperatures of the surface and subsurface throughout the cycle, but also the magnitude and direction of the transfer of thermal energy between the surface and subsurface. Precipitation events were also simulated for the Pine River domain using three different rainfall rates. The surface temperatures responded quickly to the rainfall events, whereas the subsurface temperatures were slower to respond in regions where infiltration was not significant. A thermal energy signal from the precipitation event was evident in the subsurface, and dissipated once the rainfall ceased. This indicates that temperature can potentially be used as a tracer for hydrograph separation. The potential of a thermal energy tracer for hydrograph separation was investigated using HydroGeoSphere simulations of the Borden rainfall-runoff experiment. These results matched both measured and previous simulation results using a bromide tracer. The hydrograph separation results from the thermal energy tracer were sensitive to temperature conditions in the subsurface, although this sensitivity reduced considerably when the precipitation event and subsurface temperatures were significantly different. The contribution of each atmospheric component to thermal energy transport was investigated using the Pine River and Borden examples. Each atmospheric component was individually neglected from the simulation of both sites to investigate their impact on thermal energy transport. The results show that longwave radiation dominates the atmospheric inputs for the Borden example, whereas shortwave radiation dominates in the Pine River example. This indicates that the atmospheric contributions to the thermal energy distribution are site-specific and cannot be generalized. In addition, these results indicate that the atmospheric contributions should not be ignored; measuring atmospheric data in the field is an important component in developing an accurate thermal energy transport model. The addition of thermal energy transport to HydroGeoSphere provides a valuable tool for investigating the impact of anthropogenic and non-anthropogenic changes to the atmospheric and hydrological thermal energy system. This computational framework can be used to provide quantitative guidance towards establishing the conditions needed to maintain a healthy ecosystem.

We use normal mode decomposition to obtain phonon properties from quasi-harmonic lattice dynamics calculations and classical molecular dynamics simulations in unstrained Lennard-Jones argon superlattices with perfect and mixed interfaces. Debye scaling of phonon lifetimes at low frequencies in both perfect and mixed superlattices and Rayleigh scaling for intermediate frequencies in mixed superlattices is observed. For short period mixed superlattices, lifetimes below the Ioffe-Regel limit are observed. The relaxation-time approximation of the Boltzmann transport equation is used to predict cross-plane and in-plane thermal conductivity. We find that using a dispersion relation which includes the secondary periodicity is required to predict thermal conductivity. The assumption of perturbative disorder, where Tamura elastic mass defect scattering theory can be applied, was found to be valid for predicting cross-plane thermal conductivities but not in-plane thermal conductivities in mixed superlattices.

We use normal mode decomposition to obtain phonon properties from quasi-harmonic lattice dynamics calculations and classical molecular dynamics simulations in unstrained Lennard-Jones argon superlattices with perfect and mixed interfaces. Debye scaling of phonon lifetimes at low frequencies in both perfect and mixed superlattices and Rayleigh scaling for intermediate frequencies in mixed superlattices is observed. For short period mixed superlattices, lifetimes below the Ioffe-Regel limit are observed. The relaxation-time approximation of the Boltzmann transport equation is used to predict cross-plane and in-plane thermal conductivity. We find that using a dispersion relation which includes the secondary periodicity is required to predict thermal conductivity. The assumption of perturbative disorder, where Tamura elastic mass defect scattering theory can be applied, was found to be valid for predicting cross-plane thermal conductivities but not in-plane thermal conductivities in mixed superlattices.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18776号 / 理博第4034号 / 新制||理||1581(附属図書館) / 31727 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)准教授 武末 真二, 教授 佐々 真一, 教授 早川 尚男 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM