Acoustic mode at low frequencies in marine sediments: Derivation from first principles using the method of homogenization

We present a systematic first-principles modelling study of the structural dynamics and thermal transport in the CoSb3 skutterudites with a series of noble-gas filler atoms. A range of analysis techniques are proposed to estimate the filler rattling frequencies, to quantify the separate impacts of filling on the phonon group velocities and lifetimes, and to show how changes to the phonon spectra and interaction strengths lead to suppressed lifetimes. The fillers are found to reduce the thermal conductivity of the CoSb3 framework by up to 15 % primarily by suppressing the group velocities of low-lying optic modes. Calculations show that the filler rattling frequencies are determined by a detailed balance of increasing atomic mass and stronger interactions with the framework, and are a good predictor of their impact on the heat transport. Lowering the rattling frequency below ~1.5 THz by selecting heavy fillers that interact weakly with the framework is predicted to produce a much larger suppression of the thermal transport, by inducing avoided crossings in the acoustic-mode dispersion and facilitating resonant scattering with a consequent large reduction in the lifetimes. Approximate rattling frequencies determined from the harmonic force constants may therefore provide a useful metric for selecting filler atoms to optimise the thermal transport in skutterudites and other cage compounds such as clathrates.

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Uncertainty estimation of sound attenuation in marine sediments at low frequencies.

The Journal of the Acoustical Society of America ◽

10.1121/1.4784592 ◽

2009 ◽

Vol 125 (4) ◽

pp. 2747-2747

Author(s):

Yong‐Min Jiang ◽

N. Ross Chapman

Keyword(s):

Marine Sediments ◽

Uncertainty Estimation ◽

Sound Attenuation ◽

Low Frequencies

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Microscopic origin of pressure-induced phase-transitions in urea: a detailed investigation through first principles calculations

Physical Chemistry Chemical Physics ◽

10.1039/c8cp04827d ◽

2019 ◽

Vol 21 (2) ◽

pp. 884-900 ◽

Cited By ~ 7

Author(s):

B. Moses Abraham ◽

B. Adivaiah ◽

G. Vaitheeswaran

Keyword(s):

Phase Transitions ◽

First Principles ◽

Acoustic Mode ◽

First Principles Calculations ◽

Stability Criteria ◽

Mode Softening ◽

Microscopic Origin

Pressure induced phase transitions of urea are identified. The violation of Born stability criteria in the P212121 structure along with acoustic mode softening in the U–R direction are responsible for P212121 → P21212.

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Impact of Noble-Gas Filler Atoms on the Lattice Thermal Conductivity of CoSb3 Skutterudites: First-Principles Modelling

10.26434/chemrxiv.13227836.v2 ◽

2020 ◽

Author(s):

Jianqin Tang ◽

Jonathan Skelton

Keyword(s):

Thermal Conductivity ◽

First Principles ◽

Thermal Transport ◽

Noble Gas ◽

Detailed Balance ◽

Acoustic Mode ◽

Cage Compounds ◽

Idealised Model ◽

The Impact ◽

Group Velocities

We present a systematic first-principles modelling study of the structural dynamics and thermal transport in the CoSb3 skutterudites with a series of noble-gas filler atoms. Filling with chemically-inert atoms provides an idealised model for isolating the effects of the fillers from the impact of redox changes to the host electronic structure. A range of analysis techniques are proposed to estimate the filler rattling frequencies, to quantify the separate impacts of the filler on the phonon group velocities and lifetimes, and to show how changes to the phonon spectra and interaction strengths lead to suppressed lifetimes. The noble-gas fillers are found to reduce the thermal conductivity of the CoSb3 framework by up to 15 % primarily by suppressing the group velocities of low-lying optic modes. The filler rattling frequencies are determined by a detailed balance of increasing atomic mass and stronger interactions with the framework, and are found to be a good predictor of the impact on the heat transport. Lowering the rattling frequency below ~1.5 THz by selecting heavy fillers that interact weakly with the framework is predicted to lead to a much larger suppression of the thermal transport, by inducing avoided crossings in the acoustic-mode dispersion and facilitating enhanced scattering and a consequent large reduction in phonon lifetimes. Approximate rattling frequencies determined from the harmonic force constants may therefore provide a useful metric for selecting filler atoms to optimise the thermal transport in skutterudites and other cage compounds such as clathrates.

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Measurements of attenuation of sound in marine sediments at low frequencies.

The Journal of the Acoustical Society of America ◽

10.1121/1.4808984 ◽

2008 ◽

Vol 124 (4) ◽

pp. 2468-2468

Author(s):

Ross Chapman ◽

Yong‐min Jiang

Keyword(s):

Marine Sediments ◽

Low Frequencies

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Impact of Noble-Gas Filler Atoms on the Lattice Thermal Conductivity of CoSb3 Skutterudites: First-Principles Modelling

10.26434/chemrxiv.13227836 ◽

2020 ◽

Author(s):

Jianqin Tang ◽

Jonathan Skelton

Keyword(s):

Thermal Conductivity ◽

First Principles ◽

Thermal Transport ◽

Noble Gas ◽

Detailed Balance ◽

Acoustic Mode ◽

Cage Compounds ◽

Idealised Model ◽

The Impact ◽

Group Velocities

We present a systematic first-principles modelling study of the structural dynamics and thermal transport in the CoSb3 skutterudites with a series of noble-gas filler atoms. Filling with chemically-inert atoms provides an idealised model for isolating the effects of the fillers from the impact of redox changes to the host electronic structure. A range of analysis techniques are proposed to estimate the filler rattling frequencies, to quantify the separate impacts of the filler on the phonon group velocities and lifetimes, and to show how changes to the phonon spectra and interaction strengths lead to suppressed lifetimes. The noble-gas fillers are found to reduce the thermal conductivity of the CoSb3 framework by up to 15 % primarily by suppressing the group velocities of low-lying optic modes. The filler rattling frequencies are determined by a detailed balance of increasing atomic mass and stronger interactions with the framework, and are found to be a good predictor of the impact on the heat transport. Lowering the rattling frequency below ~1.5 THz by selecting heavy fillers that interact weakly with the framework is predicted to lead to a much larger suppression of the thermal transport, by inducing avoided crossings in the acoustic-mode dispersion and facilitating enhanced scattering and a consequent large reduction in phonon lifetimes. Approximate rattling frequencies determined from the harmonic force constants may therefore provide a useful metric for selecting filler atoms to optimise the thermal transport in skutterudites and other cage compounds such as clathrates.

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The S-SH Confusion Test and the Effects of Frequency Lowering

Journal of Speech Language and Hearing Research ◽

10.1044/2018_jslhr-h-18-0267 ◽

2019 ◽

Vol 62 (5) ◽

pp. 1486-1505

Author(s):

Joshua M. Alexander

Keyword(s):

Cognitive Processing ◽

Hearing Aids ◽

Response Times ◽

Nonlinear Frequency ◽

Low Frequencies ◽

Frequency Compression ◽

Negative Side ◽

Minimal Word ◽

Low Pass ◽

Negative Side Effects

PurposeFrequency lowering in hearing aids can cause listeners to perceive [s] as [ʃ]. The S-SH Confusion Test, which consists of 66 minimal word pairs spoken by 6 female talkers, was designed to help clinicians and researchers document these negative side effects. This study's purpose was to use this new test to evaluate the hypothesis that these confusions will increase to the extent that low frequencies are altered.MethodTwenty-one listeners with normal hearing were each tested on 7 conditions. Three were control conditions that were low-pass filtered at 3.3, 5.0, and 9.1 kHz. Four conditions were processed with nonlinear frequency compression (NFC): 2 had a 3.3-kHz maximum audible output frequency (MAOF), with a start frequency (SF) of 1.6 or 2.2 kHz; 2 had a 5.0-kHz MAOF, with an SF of 1.6 or 4.0 kHz. Listeners' responses were analyzed using concepts from signal detection theory. Response times were also collected as a measure of cognitive processing.ResultsOverall, [s] for [ʃ] confusions were minimal. As predicted, [ʃ] for [s] confusions increased for NFC conditions with a lower versus higher MAOF and with a lower versus higher SF. Response times for trials with correct [s] responses were shortest for the 9.1-kHz control and increased for the 5.0- and 3.3-kHz controls. NFC response times were also significantly longer as MAOF and SF decreased. The NFC condition with the highest MAOF and SF had statistically shorter response times than its control condition, indicating that, under some circumstances, NFC may ease cognitive processing.ConclusionsLarge differences in the S-SH Confusion Test across frequency-lowering conditions show that it can be used to document a major negative side effect associated with frequency lowering. Smaller but significant differences in response times for correct [s] trials indicate that NFC can help or hinder cognitive processing, depending on its settings.

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