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  • 1
    Electronic Resource
    Electronic Resource
    Exact classical simulation of hydrogen migration on Ni(100): The role of fluctuations, recrossing, and multiple jumps (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 3614-3634 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We examine the migration of a classical hydrogen atom adsorbed on a Ni(100) surface, in a temperature range when the motion consists of jumps between lattice sites. We view these jumps as isomerization reactions and calculate exactly their rate constants by using the correlation function theory. We examine in detail the effect of lattice motion, lattice fluctuations and lattice distortion on the jumping rates and test the accuracy of the transition state theory. We propose a new approximation to the rate constant which includes all the effects incorporated in the transition state theory and calculates approximately the dynamic correction due to recrossing. We find that the magnitude of the diffusion coefficient is affected by multiple jumps.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459674
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Adsorbate migration on a solid surface: The connection between hopping dynamics and the atom-surface interaction energy (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 2087-2098 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The migration of an adsorbed atom at moderate temperatures is described in terms of uncorrelated jumps between lattice sites which lead to diffusion. It is widely believed that a jumping rate coefficient and therefore a diffusion coefficient can be defined only if energy exchange with the moving lattice or collisions with randomly distributed impurities give the motion of the adsorbate a random character. In this paper we examine systematically a suggestion of Haug, Wanhstrom, and Metiu, who conjectured that coupling between the adsorbate motion along the surface and its motion perpendicular to it can provide the necessary randomization and, in particular, make possible the definition of a hopping rate coefficient. We calculate the flux–flux correlation functions needed for describing the dynamics of single and double jumps by using a set of simple, but reasonably realistic, adsorbate-surface interactions. In all these calculations the lattice atoms are held fixed. We show that in spite of this, the correlation functions converge and rate constants can be defined for many of the potentials. We study in detail those features of the potential energy surface (PES) that lead to convergence and also how the shape of the PES influences the amount of recrossing (i.e., the accuracy of the transition state theory) and multiple jumping. Our results indicate that it is possible to develop a correction to the transition state theory which includes the effect of thermal fluctuations and calculates the recrossing correction by holding the lattice atoms fixed. This saves substantial computer time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459034
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  • 3
    Electronic Resource
    Electronic Resource
    AN ATOMISTIC VIEW OF Si(001) HOMOEPITAXY1 (1997)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Materials Research 27 (1997), S. 525-553 
    Details
    ISSN: 0084-6600
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Growth of thin films from atoms deposited from the gas phase is intrinsically a non-equilibrium phenomenon dictated by a competition between kinetics and thermodynamics. Precise control of the growth becomes possible only after achieving an understanding of this competition. In this review, we present an atomistic view of the various kinetic aspects in a model system, the epitaxy of Si on Si(001), as revealed by scanning tunneling microscopy and total-energy calculations. Fundamentally important issues investigated include adsorption dynamics and energetics, adatom diffusion, nucleation, sticking, and detachment. We also briefly discuss the inverse process of growth, removal by sputtering or etching. We aim our discussions to an understanding at a quantitative level whenever possible.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.matsci.27.1.525
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  • 4
    Electronic Resource
    Electronic Resource
    Materials science Thin-film cliffhanger (2002)
    [s.l.] : Nature Publishing Group
    Nature 417 (2002), S. 907-910 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Many modern technologies depend on our ability to grow thin films. In highly refined semiconductor technologies (such as solid-state lasers in compact-disc players or fast electronic components in mobile phones), films must be nearly perfect, grown seemingly one atom at a time, and individual ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/417907a
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  • 5
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    Role of reservoir regulation and groundwater feedback in a simulated ground‐soil‐vegetation continuum: A long‐term regional scale analysis (2021)
    John Wiley & Sons, Inc. | Hoboken, USA
    Details
    Publication Date: 2022-03-24
    Description: The regional terrestrial water cycle is strongly altered by human activities. Among them, reservoir regulation is a way to spatially and temporally allocate water resources in a basin for multi‐purposes. However, it is still not sufficiently understood how reservoir regulation modifies the regional terrestrial‐ and subsequently, the atmospheric water cycle. To address this question, the representation of reservoir regulation into the terrestrial component of fully coupled regional Earth system models is required. In this study, an existing process‐based reservoir network module is implemented into NOAH‐HMS, that is, the terrestrial component of an atmospheric–hydrologic modelling system, namely, the WRF‐HMS. It allows to quantitatively differentiate role of reservoir regulation and of groundwater feedback in a simulated ground‐soil‐vegetation continuum. Our study focuses on the Poyang Lake basin, where the largest freshwater lake of China and reservoirs of different sizes are located. As compared to streamflow observations, the newly extended NOAH‐HMS slightly improves the streamflow and streamflow duration curves simulation for the Poyang Lake basin for the period 1979–1986. The inclusion of reservoir regulation leads to major changes in the simulated groundwater recharges and evaporation from reservoirs at local scale, but has minor effects on the simulated soil moisture and surface runoff at basin scale. The performed groundwater feedback sensitivity analysis shows that the strength of the groundwater feedback is not altered by the consideration of reservoir regulation. Furthermore, both reservoir regulation and groundwater feedback modify the partitioning of the simulated evapotranspiration, thus affecting the atmospheric water cycle in the Poyang Lake region. This finding motivates future research with our extended fully coupled atmospheric–hydrologic modelling system by the community.
    Description: An existing process‐based reservoir network module is implemented into the terrestrial component NOAH‐HMS of the atmospheric–hydrologic modelling system WRF‐HMS. The inclusion of reservoir regulation leads to major changes in the simulated groundwater recharges and evaporation from reservoirs at local scale, but does not alter the strength of the groundwater feedback. Reservoir regulation and groundwater feedback play different roles in modifying the regional terrestrial water cycle for the Poyang Lake basin, particularly with respect to the partitioning of the simulated evapotranspiration.
    Description: German Federal Ministry of Science and Education
    Description: German Research Foundation http://dx.doi.org/10.13039/501100001659
    Description: National Key R&D Program of China
    Description: National Natural Science Foundation of China http://dx.doi.org/10.13039/501100001809
    Keywords: ddc:551.49
    Language: English
    Type: doc-type:article
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  • 6
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    Lateral terrestrial water flow contribution to summer precipitation at continental scale – A comparison between Europe and West Africa with WRF‐Hydro‐tag ensembles (2021)
    John Wiley & Sons, Inc. | Hoboken, USA
    Details
    Publication Date: 2021-09-29
    Description: It is well accepted that summer precipitation can be altered by soil moisture condition. Coupled land surface – atmospheric models have been routinely used to quantify soil moisture – precipitation feedback processes. However, most of the land surface models (LSMs) assume a vertical soil water transport and neglect lateral terrestrial water flow at the surface and in the subsurface, which potentially reduces the realism of the simulated soil moisture – precipitation feedback. In this study, the contribution of lateral terrestrial water flow to summer precipitation is assessed in two different climatic regions, Europe and West Africa, for the period June–September 2008. A version of the coupled atmospheric‐hydrological model WRF‐Hydro with an option to tag and trace land surface evaporation in the modelled atmosphere, named WRF‐Hydro‐tag, is employed. An ensemble of 30 simulations with terrestrial routing and 30 simulations without terrestrial routing is generated with random realizations of turbulent energy with the stochastic kinetic energy backscatter scheme, for both Europe and West Africa. The ensemble size allows to extract random noise from continental‐scale averaged modelled precipitation. It is found that lateral terrestrial water flow increases the relative contribution of land surface evaporation to precipitation by 3.6% in Europe and 5.6% in West Africa, which enhances a positive soil moisture – precipitation feedback and generates more uncertainty in modelled precipitation, as diagnosed by a slight increase in normalized ensemble spread. This study demonstrates the small but non‐negligible contribution of lateral terrestrial water flow to precipitation at continental scale.
    Description: Ensembles of coupled atmospheric ‐ hydrological simulations are presented for a summer season in Europe and West Africa. The model is enhanced with a water tagging procedure to evaluate the fate of land surface evaporation. The figure shows the change in continental precipitation recycling, that is the fraction of precipitation originating from land surface evaporation, induced by the consideration of lateral terrestrial water flow in the coupled simulations.
    Description: German Science Foundation
    Keywords: 551.48 ; continental scale ; coupled modelling ; ensemble ; feedback ; summer precipitation ; terrestrial hydrology
    Type: map
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  • 7
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    A Joint Soil-Vegetation-Atmospheric Water Tagging Procedure With WRF-Hydro: Implementation and Application to the Case of Precipitation Partitioning in the Upper Danube River Basin (2021)
    Details
    Publication Date: 2021-10-06
    Description: Atmospheric models such as the Weather Research and Forecasting (WRF) model provide a tool to evaluate the behavior of regional hydrological cycle components, including precipitation, evapotranspiration, soil water storage, and runoff. Recent model developments have focused on coupled atmospheric-hydrological modeling systems, such as WRF-Hydro, in order to account for subsurface, overland, and river flow and potentially improve the representation of land-atmosphere interactions. The aim of this study is to investigate the contribution of lateral terrestrial water flow to the regional hydrological cycle, with the help of a joint soil-vegetation-atmospheric water tagging procedure newly developed in the so-called WRF-tag and WRF-Hydro-tag models. An application of both models for the high precipitation event on 15 August 2008 in the German and Austrian parts of the upper Danube river basin (94,100 km2) is presented. The precipitation that fell in the basin during this event is considered as a water source, is tagged, and subsequently tracked for a 40-month period until December 2011. At the end of the study period, in both simulations, approximately 57% of the tagged water has run off, while 41% has evaporated back to the atmosphere, including 2% that has recycled in the upper Danube river basin as precipitation. In WRF-Hydro-tag, the surface evaporation of tagged water is slightly enhanced by surface flow infiltration and slightly reduced by subsurface lateral water flow in areas with low topography gradients. This affects the source precipitation recycling only in a negligible amount.
    Keywords: 551.5 ; soil-vegetation-atmospheric moisture tagging ; precipitation partitioning ; coupled modeling ; Danube river basin
    Language: English
    Type: map
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  • 8
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    A Joint Soil‐Vegetation‐Atmospheric Modeling Procedure of Water Isotopologues: Implementation and Application to Different Climate Zones With WRF‐Hydro‐Iso (2021)
    Details
    Publication Date: 2022-03-29
    Description: Water isotopologues, as natural tracers of the hydrological cycle on Earth, provide a unique way to assess the skill of climate models in representing realistic atmospheric‐terrestrial water pathways. This study presents the newly developed WRF‐Hydro‐iso, which is a version of the coupled atmospheric‐hydrological WRF‐Hydro model enhanced with a joint soil‐vegetation‐atmospheric description of water isotopologue motions. It allows the consideration of isotopic fractionation processes during water phase changes in the atmosphere, the land surface, and the subsurface. For validation, WRF‐Hydro‐iso is applied to two different climate zones, namely Europe and Southern Africa under the present climate conditions. Each case is modeled with a domain employing a 5 km grid‐spacing coupled with a terrestrial subgrid employing a 500 m grid‐spacing in order to represent lateral terrestrial water flow. A 10‐year slice is simulated for 2003–2012, using ERA5 reanalyses as driving data. The boundary condition of isotopic variables is prescribed with mean values from a 10‐year simulation with the Community Earth System Model Version 1. WRF‐Hydro‐iso realistically reproduces the climatological variations of the isotopic concentrations δPO18 and δPH2 from the Global Network of Isotopes in Precipitation. In a sensitivity analysis, it is found that land surface evaporation fractionation increases the isotopic concentrations in the rootzone soil moisture and slightly decreases the isotopic concentrations in precipitation. Lateral terrestrial water flow minorly affects these isotopic concentrations through changes in evaporation‐transpiration partitioning.
    Description: Plain Language Summary: Global climate models are limited by their coarse resolution, which may reduce their meaningfulness. This problem can be circumvented for a specific region with regional climate models, which provide, for example, a detailed description of clouds and land‐atmosphere interactions. But it remains a question: How realistic is the model representation of water transport through the different compartments of the hydrological cycle, the atmosphere, the land, and the sea? A unique way to assess modeled water transport is the comparison to natural tracers, such as water isotopologues, which requires to include the fate of these water isotopologues in the model. This is what we pursue here with the newly developed WRF‐Hydro‐iso model. A model description and a proof of concept are provided for two climate zones, using the Global Network of Isotopes in Precipitation data set as reference.
    Description: Key Points: A new coupled atmospheric‐hydrological regional modeling system of water isotopologues is presented. Land surface evaporation fractionation increases the isotopic concentrations in the rootzone. Lateral terrestrial water flow has a minor effect on isotopic concentrations in the rootzone.
    Description: Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659
    Description: German Federal Ministry of Science and Education
    Description: Bavarian State Ministry of Science and the Arts
    Keywords: ddc:551.6
    Language: English
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  • 9
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    Magnetotransport signatures of Weyl physics and discrete scale invariance in the elemental semiconductor tellurium (2020)
    National Academy of Sciences
    Details
    Publication Date: 2020-05-12
    Description: The study of topological materials possessing nontrivial band structures enables exploitation of relativistic physics and development of a spectrum of intriguing physical phenomena. However, previous studies of Weyl physics have been limited exclusively to semimetals. Here, via systematic magnetotransport measurements, two representative topological transport signatures of Weyl physics, the negative longitudinal magnetoresistance and the planar Hall effect, are observed in the elemental semiconductor tellurium. More strikingly, logarithmically periodic oscillations in both the magnetoresistance and Hall data are revealed beyond the quantum limit and found to share similar characteristics with those observed in ZrTe5and HfTe5. The log-periodic oscillations originate from the formation of two-body quasi-bound states formed between Weyl fermions and opposite charge centers, the energies of which constitute a geometric series that matches the general feature of discrete scale invariance (DSI). Our discovery reveals the topological nature of tellurium and further confirms the universality of DSI in topological materials. Moreover, introduction of Weyl physics into semiconductors to develop “Weyl semiconductors” provides an ideal platform for manipulating fundamental Weyl fermionic behaviors and for designing future topological devices.
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 10
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    Chiral patterns arising from electrostatic growth models (1998)
    American Physical Society
    Details
    Publication Date: 1998-11-01
    Print ISSN: 1063-651X
    Electronic ISSN: 1095-3787
    Topics: Physics
    Published by American Physical Society
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