| 1. |
- Chen, F., et al.
(author)
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Reply to "comment on 'Ultrafast terahertz-field-driven ionic response in ferroelectric BaTiO3 ' "
- 2018
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In: Physical Review B. - 2469-9950. ; 97:22
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Journal article (peer-reviewed)abstract
- In this reply to S. Durbin's comment on our original paper "Ultrafast terahertz-field-driven ionic response in ferroelectric BaTiO3," we concur that his final equations 8 and 9 more accurately describe the change in diffracted intensity as a function of Ti displacement. We also provide an alternative derivation based on an ensemble average over unit cells. The conclusions of the paper are unaffected by this correction.
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| 2. |
- Chen, F., et al.
(author)
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Ultrafast terahertz-field-driven ionic response in ferroelectric BaTiO3
- 2016
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In: Physical Review B. - 1098-0121. ; 94:18
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Journal article (peer-reviewed)abstract
- The dynamical processes associated with electric field manipulation of the polarization in a ferroelectric remain largely unknown but fundamentally determine the speed and functionality of ferroelectric materials and devices. Here we apply subpicosecond duration, single-cycle terahertz pulses as an ultrafast electric field bias to prototypical BaTiO3 ferroelectric thin films with the atomic-scale response probed by femtosecond x-ray-scattering techniques. We show that electric fields applied perpendicular to the ferroelectric polarization drive large-amplitude displacements of the titanium atoms along the ferroelectric polarization axis, comparable to that of the built-in displacements associated with the intrinsic polarization and incoherent across unit cells. This effect is associated with a dynamic rotation of the ferroelectric polarization switching on and then off on picosecond time scales. These transient polarization modulations are followed by long-lived vibrational heating effects driven by resonant excitation of the ferroelectric soft mode, as reflected in changes in the c-axis tetragonality. The ultrafast structural characterization described here enables a direct comparison with first-principles-based molecular-dynamics simulations, with good agreement obtained.
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| 3. |
- Duffy, J. Emmett, et al.
(author)
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Toward a Coordinated Global Observing System for Seagrasses and Marine Macroalgae
- 2019
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In: Frontiers in Marine Science. - : Frontiers Media S.A.. - 2296-7745. ; 6
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Research review (peer-reviewed)abstract
- In coastal waters around the world, the dominant primary producers are benthic macrophytes, including seagrasses and macroalgae, that provide habitat structure and food for diverse and abundant biological communities and drive ecosystem processes. Seagrass meadows and macroalgal forests play key roles for coastal societies, contributing to fishery yields, storm protection, biogeochemical cycling and storage, and important cultural values. These socio-economically valuable services are threatened worldwide by human activities, with substantial areas of seagrass and macroalgal forests lost over the last half-century. Tracking the status and trends in marine macrophyte cover and quality is an emerging priority for ocean and coastal management, but doing so has been challenged by limited coordination across the numerous efforts to monitor macrophytes, which vary widely in goals, methodologies, scales, capacity, governance approaches, and data availability. Here, we present a consensus assessment and recommendations on the current state of and opportunities for advancing global marine macrophyte observations, integrating contributions from a community of researchers with broad geographic and disciplinary expertise. With the increasing scale of human impacts, the time is ripe to harmonize marine macrophyte observations by building on existing networks and identifying a core set of common metrics and approaches in sampling design, field measurements, governance, capacity building, and data management. We recommend a tiered observation system, with improvement of remote sensing and remote underwater imaging to expand capacity to capture broad-scale extent at intervals of several years, coordinated with strati fied in situ sampling annually to characterize the key variables of cover and taxonomic or functional group composition, and to provide ground-truth. A robust networked system of macrophyte observations will be facilitated by establishing best practices, including standard protocols, documentation, and sharing of resources at all stages of work flow, and secure archiving of open-access data. Because such a network is necessarily distributed, sustaining it depends on close engagement of local stakeholders and focusing on building and long-term maintenance of local capacity, particularly in the developing world. Realizing these recommendations will producemore effective, efficient, and responsive observing, a more accurate global picture of change in vegetated coastal systems, and stronger international capacity for sustaining observations.
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| 4. |
- Hart, James L., et al.
(author)
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Electron-beam-induced ferroelectric domain behavior in the transmission electron microscope : Toward deterministic domain patterning
- 2016
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In: Physical Review B. - 2469-9950 .- 2469-9969. ; 94:17
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Journal article (peer-reviewed)abstract
- We report on transmission electron microscope beam-induced ferroelectric domain nucleation and motion. While previous observations of this phenomenon have been reported, a consistent theory explaining induced domain response is lacking, and little control over domain behavior has been demonstrated. We identify positive sample charging, a result of Auger and secondary electron emission, as the underlying mechanism driving domain behavior. By converging the electron beam to a focused probe, we demonstrate controlled nucleation of nanoscale domains. Molecular dynamics simulations performed are consistent with experimental results, confirming positive sample charging and reproducing the result of controlled domain nucleation. Furthermore, we discuss the effects of sample geometry and electron irradiation conditions on induced domain response. These findings elucidate past reports of electron beam-induced domain behavior in the transmission electron microscope and provide a path towards more predictive, deterministic domain patterning through electron irradiation.
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| 5. |
- Marklund, Stellan, 1949-, et al.
(author)
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Determination of PCDDs and PCDFs in incineration samples and pyrolytic products
- 2018
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In: Chlorinated dioxins and dibenzofurans in perspective. - Boca Raton : CRC Press. - 9781351070645 - 9781315891545 ; , s. 79-92
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Book chapter (peer-reviewed)abstract
- The formation of polychlorinated dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in municipal solid waste (MSW) incinerators is now well documented and not controversial. It is interesting to compare the PCDD and the PCDF emissions from MSW incinerators with other energy sources. The identification of lower chlorinated PCDFs like penta-CDFs in pyrolysis of hexachloroethane indicates dechlorination to be an important pathway for the formation of PCDDs and PCDFs. The environmental and human health impact of the emissions of PCDDs and PCDFs from MSW incinerators have been discussed in Umea as well as at other places in Sweden and in other countries. The laboratory pyrolysis of PVC and Saran clearly shows that PVC and other organochlorine polymers can be precursors to the PCDDs and PCDFs found in various incinerators. The chapter discusses some of the data collected so far for various types of incinerators or incineration models.
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| 6. |
- Wieder, Benjamin J., et al.
(author)
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Wallpaper fermions and the nonsymmorphic Dirac insulator
- 2018
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In: Science. - : American Association for the Advancement of Science. - 0036-8075 .- 1095-9203. ; 361:6399, s. 246-
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Journal article (peer-reviewed)abstract
- Materials whose gapless surface states are protected by crystal symmetries include mirror topological crystalline insulators and nonsymmorphic hourglass insulators. There exists only a very limited set of possible surface crystal symmetries, captured by the 17 "wallpaper groups." Here we show that a consideration of symmetry-allowed band degeneracies in the wallpaper groups can be used to understand previously described topological crystalline insulators and to predict phenomenologically distinct examples. In particular, the two wallpaper groups with multiple glide lines, pgg and p4g, allow for a topological insulating phase whose surface spectrum consists of only a single, fourfolddegenerate, true Dirac fermion, representing an exception to a symmetry-enhanced fermion-doubling theorem. We theoretically predict the presence of this phase in Sr2Pb3 in space group 127 (P4/mbm).
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