Institute for Advanced Simulation

Jülich, Germany

Institute for Advanced Simulation

Jülich, Germany
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In experiments and computer simulations, researchers repeatedly deformed red blood cells, let them “wriggle” and then analysed their behaviour. Three tiny spheres hold the cells in place during the process, while the movements of the cell membrane are measured with the help of a fourth sphere. The “wrapper” of the blood cell consists of a lipid double layer and a cytoskeleton; active forces, produced for example by an ion pump, move the membrane (red arrows) and fluids (green arrows) locally in opposite directions. Credit: Forschungszentrum Jülich For the first time, and using physical methods, scientists have demonstrated how red blood cells move. There had been real fights between academics over the question of whether these cells are moved by external forces or whether they actively "wriggle". An international team of biophysicists from Münster, Paris and Jülich have now proven that both opinions are correct. Linking physical principles and biological reality, they recognized that fast molecules in the vicinity make the cell membrane of the blood cells wriggle – but that the cells themselves also become active when they have enough reaction time. This process can be defined exactly by comparing innovative experiments with new theoretical models. The study was published in Nature Physics. The function of red blood cells (erythrocytes) is to transport oxygen in the blood of vertebrates. Up to now, scientists had only seen the reason for their constant wriggling in thermal (i.e. external) forces. On the other hand, biological considerations suggest that internal forces caused by proteins are also responsible for the cell membrane in blood cells changing its shape. "So we started with the following question: As blood cells are living cells, why shouldn't internal forces inside the cell also have an impact on the membrane?" says Dr. Timo Betz from Münster University. "For biologists, this is all clear – but these forces were just never a part of any physical equation." The researchers even have a suspicion already as to which forces inside the cell cause the cell membrane to change shape. "Transport proteins could generate such forces in the membrane by moving ions from one side of the membrane to the other," says Prof. Gerhard Gompper, a Director at the Jülich Institute of Complex Systems. Timo Betz has been doing research as a biophysicist at Münster University since 2015 and is head of the Mechanics of Cellular Systems research group within the Excellence Cluster "Cells in Motion". Research into the activity of red blood cells started as an international collaboration between the prestigious Institut Curie in Paris and two institutes in Jülich – the Institute of Complex Systems and the Institute for Advanced Simulation – and the work has now been completed in Münster, Paris and Jülich. "The key to our success was the interaction of Hervé Turlier's physical theories, the computer simulations made by Dmitry Fedosov and Thorsten Auth, and my experimental results," Timo Betz explains. The combination of experimental work, theory and computer simulations is essential for gaining new insights, says Gerhard Gompper. "Nowadays, modern simulations are able to quantify chemical and biological processes which do not lend themselves to direct experimental observation," he adds. The researchers want to find out more about the mechanics of blood cells and gain a detailed understanding of the forces which move and shape cells. In the case of red cells in particular, it is important to know precisely about their properties and their internal forces – because they are unusually soft and elastic and change their shape in order to be able to pass through the sometimes minute blood vessels in our body. It is precisely because blood cells are normally so soft that, in previous studies, physicists measured large thermal fluctuations at the outer membrane of the cells. These natural movements of molecules are defined by the ambient temperature. In other words, the cell membrane of the blood cells moves because molecules in the vicinity jog it. Under the microscope, this makes the blood cells appear to be wriggling. Although this explains why blood cells move, it does not address the question of possible internal forces being a contributory factor. So the research team led by Timo Betz has been using a new method to take a close look at the fluctuations of blood cells. Using so-called optical tweezers – a concentrated laser beam – the researchers stretched blood cells in a petri dish and analysed the behaviour of the cell. The result was that if the blood cells had enough reaction time they became active themselves and were able to counteract the force of the optical tweezers. If they did not have this time, they were at the mercy of their environment, and only temperature-related forces were measured. "By comparing both sets of measurements we can exactly define how fast the cells become active themselves and what force they generate in order to change shape," Betz explains. "Now it's up to the biologists, because we physicists only have a rough idea about which proteins might be the drivers for this movement. On the other hand, we can predict exactly how fast and how strong they are." Explore further: Putting the squeeze on a cell's nucleus More information: H. Turlier et al. Equilibrium physics breakdown reveals the active nature of red blood cell flickering, Nature Physics (2016). DOI: 10.1038/NPHYS3621


Krewald S.,Institute For Kernphysik | Krewald S.,Institute for Advanced Simulation | Epelbaum E.,Ruhr University Bochum | Meissner U.-G.,Institute For Kernphysik | And 3 more authors.
Progress in Particle and Nuclear Physics | Year: 2012

The two- and three-nucleon interactions derived in chiral effective field theory at next-to-next-to-leading order are used to obtain the binding energy of nuclear matter. Saturation is found at a binding energy per particle EA=-16.2±0.3 MeV and a Fermi momentum k F=1.30±0. 03fm -1, where the uncertainty is due to the cut-off dependence of the two-nucleon interaction. The sensitivity of these values to the three-nucleon force is also studied. © 2012 Elsevier B.V. All rights reserved.


Jin F.,Zernike Institute for Advanced Materials | De Raedt H.,Zernike Institute for Advanced Materials | Michielsen K.,Institute for Advanced Simulation
Communications in Computational Physics | Year: 2010

We present a computer simulation model for the Hanbury Brown-Twiss experiment that is entirely particle-based and reproduces the results of wave theory. The model is solely based on experimental facts, satisfies Einstein's criterion of local causality and does not require knowledge of the solution of a wave equation. The simulation model is fully consistent with earlier work and provides another demonstration that it is possible to give a particle-only description of wave phenomena, rendering the concept of wave-particle duality superfluous. © 2010 Global-Science Press.


Physicists at The University of Nottingham, working in collaboration with researchers in the Czech Republic, Germany and Poland, and Hitachi Europe, have published new research in the prestigious academic journal Science which shows how the 'magnetic spins' of these antiferromagnets can be controlled to make a completely different form of digital memory. Lead researcher Dr Peter Wadley, from the School of Physics and Astronomy at The University of Nottingham, said: "This work demonstrates the first electrical current control of antiferromagnets. It utilises an entirely new physical phenomenon, and in doing so demonstrates the first all-antiferromagnetic memory device. This could be hugely significant as antiferromagnets have an intriguing set of properties, including a theoretical switching speed limit approximately 1000 times faster than the best current memory technologies." This entirely new form of memory has a set of properties which could make it extremely useful in modern electronics. It does not produce magnetic fields, meaning the individual elements can be packed more closely, leading to higher storage density. Antiferromagnet memory is also insensitive to magnetic fields and radiation making it particularly suitable for niche markets, such as satellite and aircraft electronics. If all of this potential could be realised, antiferromagnetic memory would be an excellent candidate for a so-called "universal memory", replacing all other forms of memory in computing, and transforming our electronic devices. How did they do it? Using a very specific crystal structure, CuMnAs, grown in almost complete vacuum, atomic layer by atomic layer—the research team has demonstrated that the alignment of the 'magnetic moments' of certain types of antiferromagnets can be controlled with electrical pulses through the material. Dr Frank Freimuth of the Peter Grünberg Institute and the Institute for Advanced Simulation in Jülich said: "The electric current brings about a quantum mechanical torque on individual spins and allows each of them to tilt 90 degrees". An effect first predicted by Dr Jakub Zelezny in Prague, Professor Tomas Jungwirth and colleagues at Nottingham. What makes antiferromagnets better than ferromagnets? Ferromagnets react to external magnetic fields. For magnetic strips on credit cards or hard drives on computers, this effect is useful as it allows data to be written. But it is necessary to shield these materials from unwanted magnetic fields, generated for instance by certain kinds of medical equipment, so that data is not deleted by mistake. Antiferromagnetic materials are not influenced by magnetic fields, and are of no use in magnetic data writing methods commonly utilised today. Until now, it has only been possible for them to be used in the field of information technology in combination with other classes of materials. But antiferromagnets are magnetically more robust and can, in principle, be switched much faster than ferromagnets, so the research team decided to look for a way to develop them into an independent data storage material class. As a result, they have succeeded in electrically controlling the switching and read-out of the magnetic moment of an antiferromagnetic material. Dr Wadley said: "In contrast to current (ferromagnetic) memory technologies, our antiferromagnetic memory cannot be erased even by large magnetic fields. It also does not generate magnetic fields, meaning that the individual memory elements could be packed more closely together, leading to denser memory storage. Another foreseen advantage, which is yet to be established, is the speed by which information can be written in antiferromagnetic memories. Its physical limit is hundreds to thousands of times greater than in ferromagnets. "The potential increase in speed of operation, robustness, energy efficiency and storage density could have a huge commercial and societal impact." This research, funded by the Grant Agency of the Czech Republic, the Engineering and Physical Sciences Research Council (EPSRC) in the UK and an EU 7th Framework Programme Grant. Dr Wadley, working with Dr Kevin Edmonds, Dr Richard Campion, Dr Andrew Rushforth, Professor Tomas Jungwirth and Professor Bryan Gallagher in the School of Physics and Astronomy in Nottingham now intends to fully explore this new effect and to produce prototype USB demonstrator memory devices. On the day this research is published (Thursday 14 January 2016) Dr Wadley will be presenting his work at the MMM Intermag conference in San Diego—the largest conference on magnetism, which is held in the USA. He said: "In August 2013 Nature Communications we published our first paper on this relatively unexplored area of applied physics. This latest study has taken 2 years to complete. A few years ago the field of antiferromagnetic spintronics was a very niche area. In the last year myself and colleagues have given upward of 20 invited talks at major international conferences. In this coming year there are symposia and sessions dedicated entirely to this exciting new emergent area of electronics research." Explore further: Spinning out the future of our electronic devices More information: "Electrical switching of an antiferromagnet" www.science.sciencemag.org/content/early/2015/12/14/science.aab1031


News Article | January 17, 2016
Site: www.nanotech-now.com

Home > Press > First all-antiferromagnetic memory device could get digital data storage in a spin Abstract: If you haven't already heard of antiferromagnetic spintronics it won't be long before you do. This relatively unused class of magnetic materials could be about to transform our digital lives. They have the potential to make our devices smaller, faster, more robust and increase their energy efficiency. Physicists at The University of Nottingham, working in collaboration with researchers in the Czech Republic, Germany and Poland, and Hitachi Europe, have published (2pm US ET Thursday 14 January 2016) new research in the prestigious academic journal Science which shows how the 'magnetic spins' of these antiferromagnets can be controlled to make a completely different form of digital memory. Lead researcher Dr Peter Wadley, from the School of Physics and Astronomy at The University of Nottingham, said: "This work demonstrates the first electrical current control of antiferromagnets. It utilises an entirely new physical phenomenon, and in doing so demonstrates the first all-antiferromagnetic memory device. This could be hugely significant as antiferromagnets have an intriguing set of properties, including a theoretical switching speed limit approximately 1000 times faster than the best current memory technologies." This entirely new form of memory has a set of properties which could make it extremely useful in modern electronics. It does not produce magnetic fields, meaning the individual elements can be packed more closely, leading to higher storage density. Antiferromagnet memory is also insensitive to magnetic fields and radiation making it particularly suitable for niche markets, such as satellite and aircraft electronics. If all of this potential could be realised, antiferromagnetic memory would be an excellent candidate for a so-called "universal memory", replacing all other forms of memory in computing, and transforming our electronic devices. How did they do it? Using a very specific crystal structure, CuMnAs, grown in almost complete vacuum, atomic layer by atomic layer -- the research team has demonstrated that the alignment of the 'magnetic moments' of certain types of antiferromagnets can be controlled with electrical pulses through the material. Dr Frank Freimuth of the Peter Grünberg Institute and the Institute for Advanced Simulation in Jülich said: "The electric current brings about a quantum mechanical torque on individual spins and allows each of them to tilt 90 degrees". An effect first predicted by Dr Jakub Zelezny in Prague, Professor Tomas Jungwirth and colleagues at Nottingham. What makes antiferromagnets better than ferromagnets? Ferromagnets react to external magnetic fields. For magnetic strips on credit cards or hard drives on computers, this effect is useful as it allows data to be written. But it is necessary to shield these materials from unwanted magnetic fields, generated for instance by certain kinds of medical equipment, so that data is not deleted by mistake. Antiferromagnetic materials are not influenced by magnetic fields, and are of no use in magnetic data writing methods commonly utilised today. Until now, it has only been possible for them to be used in the field of information technology in combination with other classes of materials. But antiferromagnets are magnetically more robust and can, in principle, be switched much faster than ferromagnets, so the research team decided to look for a way to develop them into an independent data storage material class. As a result, they have succeeded in electrically controlling the switching and read-out of the magnetic moment of an antiferromagnetic material. The potential Dr Wadley said: "In contrast to current (ferromagnetic) memory technologies, our antiferromagnetic memory cannot be erased even by large magnetic fields. It also does not generate magnetic fields, meaning that the individual memory elements could be packed more closely together, leading to denser memory storage. Another foreseen advantage, which is yet to be established, is the speed by which information can be written in antiferromagnetic memories. Its physical limit is hundreds to thousands of times greater than in ferromagnets. "The potential increase in speed of operation, robustness, energy efficiency and storage density could have a huge commercial and societal impact." This research, funded by the Grant Agency of the Czech Republic, the Engineering and Physical Sciences Research Council (EPSRC) in the UK and an EU 7th Framework Programme Grant. Dr Wadley, working with Dr Kevin Edmonds, Dr Richard Campion, Dr Andrew Rushforth, Professor Tomas Jungwirth and Professor Bryan Gallagher in the School of Physics and Astronomy in Nottingham now intends to fully explore this new effect and to produce prototype USB demonstrator memory devices. MMM Intermag 2016 conference On the day this research is published (Thursday 14 January 2016) Dr Wadley will be presenting his work at the MMM Intermag conference in San Diego -- the largest conference on magnetism, which is held in the USA. He said: "In August 2013 Nature Communications we published our first paper on this relatively unexplored area of applied physics. This latest study has taken 2 years to complete. A few years ago the field of antiferromagnetic spintronics was a very niche area. In the last year myself and colleagues have given upward of 20 invited talks at major international conferences. In this coming year there are symposia and sessions dedicated entirely to this exciting new emergent area of electronics research." For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.


Hoth J.,Leibniz Institute for New Materials | Hoth J.,Saarland University | Hausen F.,Leibniz Institute for New Materials | Muser M.H.,Institute for Advanced Simulation | And 2 more authors.
Journal of Physics Condensed Matter | Year: 2014

The mechanical properties of the ionic liquid 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl) trifluorophosphate ([Py1,4][FAP]) in confinement between a SiOx and a Au(1 1 1) surface are investigated by means of atomic force microscopy (AFM) under electrochemical control. Up to 12 layers of ion pairs can be detected through force measurements while approaching the tip of the AFM to the surface. The particular shape of the force versus distance curve is explained by a model for the interaction between tip, gold surface and ionic liquid, which assumes an exponentially decaying oscillatory force originating from bulk liquid density correlations. Jumps in the tip-sample distance upon approach correspond to jumps of the compliant force sensor between branches of the oscillatory force curve. Frictional force between the laterally moving tip and the surface is detected only after partial penetration of the last double layer between tip and surface. © 2014 IOP Publishing Ltd.


Haidenbauer J.,Institute for Advanced Simulation | Kang X.-W.,Institute for Advanced Simulation | Meissner U.-G.,Institute for Advanced Simulation | Meissner U.-G.,University of Bonn
Nuclear Physics A | Year: 2014

The reactions p-p→e+e- and e+e-→p-p are analyzed in the near-threshold region. Specific emphasis is put on the role played by the interaction in the initial or final antinucleon-nucleon (N-N) system which is taken into account rigorously. For that purpose a recently published N-N potential derived within chiral effective field theory and fitted to results of a new partial-wave analysis of p-p scattering data is employed. Our results provide strong support for the conjecture that the pronounced energy dependence of the e+e-↔p-p cross section, seen in pertinent experiments, is primarily due to the p-p interaction. Predictions for the proton electromagnetic form factors GE and GM in the timelike region, close to the N-N threshold, and for spin-dependent observables are presented. The steep rise of the effective form factor for energies close to the p-p threshold is explained solely in terms of the p-p interaction. The corresponding experimental information is quantitatively described by our calculation. © 2014 Elsevier B.V.


Singh S.P.,Institute for Advanced Simulation | Chatterji A.,Indian Institute of Science | Gompper G.,Institute for Advanced Simulation | Winkler R.G.,Institute for Advanced Simulation
Macromolecules | Year: 2013

The dynamical and rheological properties of ultrasoft colloids and star polymers are investigated in dilute and semidilute solutions under linear shear flow. We apply a hybrid mesoscale hydrodynamics simulation approach, which combines molecular dynamics simulations for the solute with the multiparticle collision dynamics approach for the solvent. We investigate the effect of concentration on relaxation, diffusion, and the rheological properties of the star polymers. We find that the relaxation time of a star-polymer arm is a universal function of a concentration-dependent Weissenberg number. The center-of-mass mean square displacements of the star polymers are anisotropic under shear flow. At high shear rate, we find shear-induced enhanced center-of-mass displacements along the vorticity and gradient directions. Moreover, we determine the shear viscosity and normal stress coefficients as a function of concentration. The shear viscosity exhibits shear thinning with a weak functionality dependence. © 2013 American Chemical Society.


Wysocki A.,Institute for Advanced Simulation | Winkler R.G.,Institute for Advanced Simulation | Gompper G.,Institute for Advanced Simulation
EPL | Year: 2014

The structural and dynamical properties of suspensions of self-propelled Brownian particles of spherical shape are investigated in three spatial dimensions. Our simulations reveal a phase separation into a dilute and a dense phase, above a certain density and strength of self-propulsion. The packing fraction of the dense phase approaches random close packing at high activity, yet the system remains fluid. Although no alignment mechanism exists in this model, we find long-lived cooperative motion of particles in the dense regime. This behavior is probably due to an interface-induced sorting process. Spatial displacement correlation functions are nearly scale free for systems with densities close to or above the glass transition density of passive systems. © Copyright EPLA, 2014.


Winkler R.G.,Institute for Advanced Simulation | Wysocki A.,Institute for Advanced Simulation | Gompper G.,Institute for Advanced Simulation
Soft Matter | Year: 2015

The pressure of suspensions of self-propelled objects is studied theoretically and by simulation of spherical active Brownian particles (ABPs). We show that for certain geometries, the mechanical pressure as force/area of confined systems can be equally expressed by bulk properties, which implies the existence of a nonequilibrium equation of state. Exploiting the virial theorem, we derive expressions for the pressure of ABPs confined by solid walls or exposed to periodic boundary conditions. In both cases, the pressure comprises three contributions: the ideal-gas pressure due to white-noise random forces, an activity-induced pressure ("swim pressure"), which can be expressed in terms of a product of the bare and a mean effective particle velocity, and the contribution by interparticle forces. We find that the pressure of spherical ABPs in confined systems explicitly depends on the presence of the confining walls and the particle-wall interactions, which has no correspondence in systems with periodic boundary conditions. Our simulations of three-dimensional ABPs in systems with periodic boundary conditions reveal a pressure-concentration dependence that becomes increasingly nonmonotonic with increasing activity. Above a critical activity and ABP concentration, a phase transition occurs, which is reflected in a rapid and steep change of the pressure. We present and discuss the pressure for various activities and analyse the contributions of the individual pressure components. This journal is © The Royal Society of Chemistry.

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