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Full-Text Articles in Physics
Writing And Deleting Single Magnetic Skyrmions, Niklas Romming, Christian Hanneken, Matthias Menzel, Jessica E. Bickel, Boris Wolter, Kirsten Von Bergmann, André Kubetzka, Roland Wiesendanger
Writing And Deleting Single Magnetic Skyrmions, Niklas Romming, Christian Hanneken, Matthias Menzel, Jessica E. Bickel, Boris Wolter, Kirsten Von Bergmann, André Kubetzka, Roland Wiesendanger
Physics Faculty Publications
Topologically nontrivial spin textures have recently been investigated for spintronic applications. Here, we report on an ultrathin magnetic film in which individual skyrmions can be written and deleted in a controlled fashion with local spin-polarized currents from a scanning tunneling microscope. An external magnetic field is used to tune the energy landscape, and the temperature is adjusted to prevent thermally activated switching between topologically distinct states. Switching rate and direction can then be controlled by the parameters used for current injection. The creation and annihilation of individual magnetic skyrmions demonstrates the potential for topological charge in future information-storage concepts.
Automated Tracking Of Shallow Cumulus Clouds In Large Domain, Long Duration Large Eddy Simulations, Thijs Heus, Axel Seifert
Automated Tracking Of Shallow Cumulus Clouds In Large Domain, Long Duration Large Eddy Simulations, Thijs Heus, Axel Seifert
Physics Faculty Publications
This paper presents a method for feature tracking of fields of shallow cumulus convection in large eddy simulations (LES) by connecting the projected cloud cover in space and time, and by accounting for splitting and merging of cloud objects. Existing methods tend to be either imprecise or, when using the full three-dimensional (3-D) spatial field, prohibitively expensive for large data sets. Compared to those 3-D methods, the current method reduces the memory footprint by up to a factor 100, while retaining most of the precision by correcting for splitting and merging events between different clouds. The precision of the algorithm …
Direct Numerical Simulation Of Evaporative Cooling At The Lateral Boundary Of Shallow Cumulus Clouds, Dick Abma, Thijs Heus, Juan Pedro Mellado
Direct Numerical Simulation Of Evaporative Cooling At The Lateral Boundary Of Shallow Cumulus Clouds, Dick Abma, Thijs Heus, Juan Pedro Mellado
Physics Faculty Publications
This study investigates the dynamics of the subsiding shell at the lateral boundary of cumulus clouds, focusing on the role of evaporative cooling. Since the size of this shell is well below what large-eddy simulations can resolve, the authors have performed direct numerical simulations of an idealized subsiding shell. The system develops a self-similar, Reynolds number–independent flow that allows for the determination of explicit scaling laws relating the characteristic length, time, and velocity scales of the shell. It is found that the shell width grows quadratically in time, linearly with the traveled distance. The magnitude of these growth rates shows …
Visco-Elastic Properties Of Duct Tape, Ashley Brown, Ulrich Zurcher
Visco-Elastic Properties Of Duct Tape, Ashley Brown, Ulrich Zurcher
Physics Faculty Publications
A simple experiment for determining the nonlinear stress–strain relation of duct tape is described. After weights are added and subsequently removed, the tape does not return to its original state and is no longer taut. The tape exhibits hysteresis, which implies the loss of work during the cyclical process. The exponent describing the nonlinearity is related to the fractional work loss.
Large-Eddy Simulation Of Organized Precipitating Trade Wind Cumulus Clouds, Axel Seifert, Thijs Heus
Large-Eddy Simulation Of Organized Precipitating Trade Wind Cumulus Clouds, Axel Seifert, Thijs Heus
Physics Faculty Publications
Trade wind cumulus clouds often organize in along-wind cloud streets and across-wind mesoscale arcs. We present a benchmark large-eddy simulation which resolves the individual clouds as well as the mesoscale organization on scales of O(10 km). Different methods to quantify organization of cloud fields are applied and discussed. Using perturbed physics large-eddy simulation experiments, the processes leading to the formation of cloud clusters and the mesoscale arcs are revealed. We find that both cold pools as well as the sub-cloud layer moisture field are crucial to understand the organization of precipitating shallow convection. Further sensitivity studies show that microphysical assumptions …
Marine Low Cloud Sensitivity To An Idealized Climate Change: The Cgils Les Intercomparison, Peter N. Blossey, Christopher S. Bretherton, Minghua Zhang, Anning Cheng, Satoshi Endo, Thijs Heus, Yangang Liu, Adrian P. Lock, Stephan R. De Roode, Kuan Man Xu
Marine Low Cloud Sensitivity To An Idealized Climate Change: The Cgils Les Intercomparison, Peter N. Blossey, Christopher S. Bretherton, Minghua Zhang, Anning Cheng, Satoshi Endo, Thijs Heus, Yangang Liu, Adrian P. Lock, Stephan R. De Roode, Kuan Man Xu
Physics Faculty Publications
Subtropical marine low cloud sensitivity to an idealized climate change is compared in six large-eddy simulation (LES) models as part of CGILS. July cloud cover is simulated at three locations over the subtropical northeast Pacific Ocean, which are typified by cold sea surface temperatures (SSTs) under well-mixed stratocumulus, cool SSTs under decoupled stratocumulus, and shallow cumulus clouds overlying warmer SSTs. The idealized climate change includes a uniform 2 K SST increase with corresponding moist-adiabatic warming aloft and subsidence changes, but no change in free-tropospheric relative humidity, surface wind speed, or CO2. For each case, realistic advective forcings and boundary conditions …
Cgils: Results From The First Phase Of An International Project To Understand The Physical Mechanisms Of Low Cloud Feedbacks In Single Column Models, Minghua Zhang, Christopher S. Bretherton, Peter N. Blossey, Phillip H. Austin, Julio T. Bacmeister, Sandrine Bony, Florent Brient, Suvarchal K. Cheedela, Anning Cheng, Anthony D. Del Genio, Stephan R. De Roode, Satoshi Endo, Charmaine N. Franklin, Jean Christophe Golaz, Cecile Hannay, Thijs Heus
Cgils: Results From The First Phase Of An International Project To Understand The Physical Mechanisms Of Low Cloud Feedbacks In Single Column Models, Minghua Zhang, Christopher S. Bretherton, Peter N. Blossey, Phillip H. Austin, Julio T. Bacmeister, Sandrine Bony, Florent Brient, Suvarchal K. Cheedela, Anning Cheng, Anthony D. Del Genio, Stephan R. De Roode, Satoshi Endo, Charmaine N. Franklin, Jean Christophe Golaz, Cecile Hannay, Thijs Heus
Physics Faculty Publications
CGILS—the CFMIP-GASS Intercomparison of Large Eddy Models (LESs) and single column models (SCMs)—investigates the mechanisms of cloud feedback in SCMs and LESs under idealized climate change perturbation. This paper describes the CGILS results from 15 SCMs and 8 LES models. Three cloud regimes over the subtropical oceans are studied: shallow cumulus, cumulus under stratocumulus, and well-mixed coastal stratus/stratocumulus. In the stratocumulus and coastal stratus regimes, SCMs without activated shallow convection generally simulated negative cloud feedbacks, while models with active shallow convection generally simulated positive cloud feedbacks. In the shallow cumulus alone regime, this relationship is less clear, likely due to …