Effect of the surface temperature on surface morphology, deuterium retention and erosion of EUROFER steel exposed to low-energy, high-flux deuterium plasma

Samples of EUFROFER, a reduced activation ferritic martensitic steel, were exposed in the linear plasma device Pilot-PSI to a deuterium (D) plasma with incident ion energy of similar to 40 eV and incident D flux of 2-6 x10(23) D/m(2) s to fluences up to 10 27 D/m(2) at surface temperatures ranging from 400 K to 950 K. The main focus of the study lays on the surface morphology changes dependent on the surface temperature and the surface composition evolution, e.g., the enrichment in tungsten; but also the erosion and the D retention are studied. The created surface morphology varies strongly with surface temperature from needle-like to corral-like structures. The visible lateral length scale of the formed structures is in the range of tens of nanometres to above 1 mu m and exhibits two thermal activated regimes below and above similar to 770 K with activation energies of 0.2 eV and 1.3 eV, respectively. The lateral variation of the enrichment of heavy elements on the surface is correlated to this surface morphology at least in the high temperature regime, independent of the origin of the enrichment (intrinsic from the sample or deposited by the plasma). Also the erosion exhibits temperature dependence at least above similar to 770 K as well as a fluence dependence. The amount of deuterium retained in the top 500 nm is almost independent of the exposure temperature and is of the order of 10(18) D/m(2), which would correspond to a sub-monolayer D coverage on the surface. The retained D in the volume summing up over the complete samples exceeds the D retained close to the surface by one order of magnitude. (C) 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license

Focusing by blocking: repeatedly generating central density peaks in self-propelled particle systems by exploiting diffusive processes

Over the past few years the displacement statistics of self-propelled particles has been intensely studied, revealing their long-time diffusive behavior. Here, we demonstrate that a concerted combination of boundary conditions and switching on and off the self-propelling drive can generate and afterwards arbitrarily often restore a non-stationary centered peak in their spatial distribution. This corresponds to a partial reversibility of their statistical behavior, in opposition to the above-mentioned long-time diffusive nature. Interestingly, it is a diffusive process that mediates and makes possible this procedure. It should be straightforward to verify our predictions in a real experimental system.Comment: 6 pages, 6 figure

Cooperation of Sperm in Two Dimensions: Synchronization, Attraction and Aggregation through Hydrodynamic Interactions

Sperm swimming at low Reynolds number have strong hydrodynamic interactions when their concentration is high in vivo or near substrates in vitro. The beating tails not only propel the sperm through a fluid, but also create flow fields through which sperm interact with each other. We study the hydrodynamic interaction and cooperation of sperm embedded in a two-dimensional fluid by using a particle-based mesoscopic simulation method, multi-particle collision dynamics (MPC). We analyze the sperm behavior by investigating the relationship between the beating-phase difference and the relative sperm position, as well as the energy consumption. Two effects of hydrodynamic interaction are found, synchronization and attraction. With these hydrodynamic effects, a multi-sperm system shows swarm behavior with a power-law dependence of the average cluster size on the width of the distribution of beating frequencies

Hannover study on long-stay hospitalization – part I: prediction of long-stay hospitalisation in cases of chronic mental illness

BACKGROUND: The problem of long-stay hospitalization is still a pressing issue. In this study we examined the possibility of detecting and characterising the group at risk of long-stay hospitalization in advance. METHODS: This study examines the data of patients in the urban catchment area of the Medical University of Hannover, capital of Lower Saxony, Germany, during a period of 10 years. RESULTS AND CONCLUSION: The introduced "psychosocial risk-score", calculated at the first institutional contact, was able to predict the risk of long-term hospitalization. Characteristics of social disintegration, especially with regard to employment status, are of particular importance

Coherent Hydrodynamic Coupling for Stochastic Swimmers

A recently developed theory of stochastic swimming is used to study the notion of coherence in active systems that couple via hydrodynamic interactions. It is shown that correlations between various modes of deformation in stochastic systems play the same role as the relative internal phase in deterministic systems. An example is presented where a simple swimmer can use these correlations to hunt a non-swimmer by forming a hydrodynamic bound state of tunable velocity and equilibrium separation. These results highlight the significance of coherence in the collective behavior of nano-scale stochastic swimmers.Comment: 6 pages, 3 figure

LAS BATALLAS FESTIVAS DE ESPANA

Serving individual customer needs at reasonable prices can be a profitable target market in high-wage countries. The dilemma between scale and scope-oriented production is one major research topic within the Cluster of Excellence "Integrative Production Technology for High-Wage Countries" at the RWTH Aachen University. One main objective of this project is to bridge the existing gap between individual manufacturing and mass production. Modularization is a widely accepted approach in tool-based manufacturing processes. In this paper, we propose a flexible design methodology for modular tools and dies. The methodology will assist the design engineer in setting up a series of modularized tools in a conceptually closed manner. The described methodology covers modularization in a broad sense, i.e. it includes hardware modularization as well as modularization of the construction process. The methodology consists of three phases: initiation, analysis and design phase

Microstructure and defect analysis in the vicinity of blisters in polycrystalline tungsten

AbstractUp to now, analyzing the production of dislocation-type defects in the subsurface region of plasma or ion-exposed tungsten samples has been hampered by the challenging production of suitable cross-section samples for transmission electron microscopy. We present two reliable methods based on precision electropolishing to prepare cross-sections of tungsten that allow direct imaging of dislocation-type defects by scanning as well as by transmission electron microscopy. Using these methods, we are able to demonstrate a clear enhancement of the dislocation density in the caps of blisters on tungsten exposed to H isotope plasma, i.e., of surface morphologies that are correlated to subsurface cavities. As a benchmark, we also show a cross-section of tungsten irradiated by 20 MeV W6+ ions

How does a flexible chain of active particles swell?

We study the swelling of a flexible linear chain composed of active particles by analytical theory and computer simulation. Three different situations are considered: a free chain, a chain confined to an external harmonic trap, and a chain dragged at one end. First we consider an ideal chain with harmonic springs and no excluded volume between the monomers. The Rouse model of polymers is generalized to the case of self-propelled monomers and solved analytically. The swelling, as characterized by the spatial extension of the chain, scales with the monomer number defining a Flory exponent $\nu$ which is $\nu =1/2, 0, 1$ in the three different situations. As a result, we find that activity does not change the Flory exponent but affects the prefactor of the scaling law. This can be quantitatively understood by mapping the system onto an equilibrium chain with a higher effective temperature such that the chain swells under an increase of the self-propulsion strength. We then use computer simulations to study the effect of self-avoidance on active polymer swelling. In the three different situations, the Flory exponent is now $\nu = 3/4, 1/4, 1$ and again unchanged under self-propulsion. However, the chain extension behaves non-monotonic in the self-propulsion strength.Comment: (9 pages, 5 figures