ORCID Profile
0000-0003-4282-756X
Current Organisations
IT University of Copenhagen
,
Københavns Universitet
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Publisher: American Physical Society (APS)
Date: 25-10-2019
Publisher: Springer Science and Business Media LLC
Date: 31-08-2008
DOI: 10.1038/NMAT2273
Abstract: Engineering of materials with specific physical properties has recently focused on the effect of nano-sized 'guest domains' in a 'host matrix' that enable tuning of electrical, mechanical, photo-optical or thermal properties. A low thermal conductivity is a prerequisite for obtaining effective thermoelectric materials, and the challenge is to limit the conduction of heat by phonons, without simultaneously reducing the charge transport. This is named the 'phonon glass-electron crystal' concept and may be realized in host-guest systems. The guest entities are believed to have independent oscillations, so-called rattler modes, which scatter the acoustic phonons and reduce the thermal conductivity. We have investigated the phonon dispersion relation in the phonon glass-electron crystal material Ba(8)Ga(16)Ge(30) using neutron triple-axis spectroscopy. The results disclose unambiguously the theoretically predicted avoided crossing of the rattler modes and the acoustic-phonon branches. The observed phonon lifetimes are longer than expected, and a new explanation for the low kappa(L) is provided.
Publisher: Springer Science and Business Media LLC
Date: 12-2002
Publisher: Elsevier BV
Date: 03-2000
Publisher: Elsevier BV
Date: 03-2020
Publisher: AIP Publishing
Date: 10-2023
DOI: 10.1063/5.0152136
Publisher: Elsevier BV
Date: 08-2016
Publisher: Elsevier BV
Date: 10-2014
DOI: 10.1016/J.JSB.2014.08.003
Abstract: Floods can completely submerge terrestrial plants but some wetland species can sustain O2 and CO2 exchange with the environment via gas films forming on superhydrophobic leaf surfaces. We used high resolution synchrotron X-ray phase contrast micro-tomography in a novel approach to visualise gas films on submerged leaves of common cordgrass (Spartina anglica). 3D tomograms enabled a hitherto unmatched level of detail regarding the micro-topography of leaf gas films. Gas films formed only on the superhydrophobic adaxial leaf side (water droplet contact angle, Φ=162°) but not on the abaxial side (Φ=135°). The adaxial side of the leaves of common cordgrass is plicate with a longitudinal system of parallel grooves and ridges and the vast majority of the gas film volume was found in large ∼180μm deep elongated triangular volumes in the grooves and these volumes were connected to each neighbouring groove via a fine network of gas tubules (∼1.7μm diameter) across the ridges. In addition to the gas film retained on the leaf exterior, the X-ray phase contrast micro-tomography also successfully distinguished gas spaces internally in the leaf tissues, and the tissue porosity (gas volume per unit tissue volume) ranged from 6.3% to 20.3% in tip and base leaf segments, respectively. We conclude that X-ray phase contrast micro-tomography is a powerful tool to obtain quantitative data of exterior gas features on biological s les because of the significant difference in electron density between air, biological tissues and water.
Publisher: American Physical Society (APS)
Date: 23-09-2010
No related grants have been discovered for Kim Lefmann.