Dynamical yield criterion for granular matter from first principles.

We investigate, using a recently developed model of liquid state theory describing the rheology of dense granular flows, how a yield stress appears in granular matter at the yielding transition. Our model allows us to predict an analytical equation of the corresponding dynamical yield surface, which is compared to the usual models of solid fracture. In particular, this yield surface interpolates between the typical failure behaviors of soft and hard materials. This work also underlines the central role played by the effective friction coefficient at the yielding transition.

Space hardware for concrete sample production on ISS "MASON concrete mixer".

Advances in space flight technology will enable the construction of Moon or even Mars bases in the not-too-distant future. Thus, materials will be needed that are suitable for building in microgravity environments. One idea is to use concrete, the most used construction material on Earth, for these challenging tasks. The hardening and the properties of concrete under the boundary conditions prevailing on Earth are well understood, but there is only limited research on concrete produced in microgravity. Hence, a research project called MASON was established, which aims to mix and harden concrete on the ISS and to investigate the properties of the specimens made in microgravity extensively. Since a defined geometry of the specimens would be favorable for these investigations, a special hardware was developed, called the MASON Concrete Mixer (MCM), which allows the production of concrete specimens fulfilling the requirements on the geometry as well as the safety requirements. Subsequently, the development, design, tests, and qualification of the MCM as well as its usage are presented.

Rheology of granular liquids in extensional flows: Beyond the µ(I)-law.

The Granular Integration Through Transients (GITT) formalism gives a theoretical description of the rheology of moderately dense granular flows and suspensions. In this work, we extend the GITT equations beyond the case of simple shear flows studied before. Applying this to the particular example of extensional flows, we show that the predicted behavior is somewhat different from that of the more frequently studied simple shear case, as illustrated by the possibility of nonmonotonous evolution of the effective friction coefficient µ with the inertial number I. By the reduction of the GITT equations to simple toy models, we provide a generalization of the µ(I)-law true for any type of flow deformation. Our analysis also includes a study of the Trouton ratio, which is shown to behave quite similarly to that of dense colloidal suspensions.

Soft matter dynamics: A versatile microgravity platform to study dynamics in soft matter.

We describe an experiment container with light scattering and imaging diagnostics for experiments on soft matter aboard the International Space Station (ISS). The suite of measurement capabilities can be used to study different materials in exchangeable sample cell units. The currently available sample cell units and future possibilities for foams, granular media, and emulsions are presented in addition to an overview of the design and the diagnostics of the experiment container. First results from measurements performed on ground and during the commissioning aboard the ISS highlight the capabilities of the experiment container to study the different materials.

Integration through transients approach to the µ(I) rheology.

This work generalizes the granular integration through transients formalism introduced by Kranz et al. [Phys. Rev. Lett. 121, 148002 (2018)10.1103/PhysRevLett.121.148002] to the determination of the pressure. We focus on the Bagnold regime and provide theoretical support to the empirical µ(I) rheology laws that have been successfully applied in many granular flow problems. In particular, we confirm that the interparticle friction is irrelevant in the regime where the µ(I) laws apply.

Temperature expansions in the square-shoulder fluid. I. The Wiener-Hopf function.

We investigate the spatial structure of dense square-shoulder fluids. To this end, we derive analytical perturbative solutions of the Ornstein-Zernike equation in the low- and high-temperature limits as expansions around the known hard sphere solutions. We then discuss the suitability of perturbative approaches in relation to the Ornstein-Zernike equation. Our analytical expressions are shown to reproduce reasonably well numerical data in the appropriate regimes.

Temperature expansions in the square-shoulder fluid. II. Thermodynamics.

In Paper I [O. Coquand and M. Sperl, J. Chem. Phys. 152, 124112 (2020)], we derived analytical expressions for the structure factor of the square-shoulder potential in a perturbative way around the high- and low-temperature regimes. Here, various physical properties of these solutions are derived. In particular, we investigate the large wave number sector and relate it to the contact values of the pair-correlation function. Then, the thermoelastic properties of the square-shoulder fluids are discussed.

EAC-1A: A novel large-volume lunar regolith simulant.

The European Astronaut Centre (EAC) is currently constructing the European Lunar Exploration Laboratory (LUNA), a large training and operations facility to be located adjacent to EAC at the DLR (German Aerospace Centre) campus in Cologne, Germany. With an estimated representative lunar testbed area of approximately 660 m2, a large volume of lunar regolith simulant material is needed for this purpose. In this study, a basanitic sandy silt from a quarry located in the Siebengebirge Volcanic Field is evaluated as a large-volume source of material. The focus of this project has been to conduct a physical and chemical characterisation of the fine-grained material to be used in LUNA; the European Astronaut Centre lunar regolith simulant 1 (EAC-1 A). The physical characterisation tests undertaken include sphericity, density measurements, cohesion and static angle of repose, with mineralogical investigations via petrographical analysis with optical microscope and SEM, XRF, XRD and DSC measurements. The results of the EAC-1A tests are compared to published data on existing widely used lunar regolith simulants, namely JSC-1A, JSC-2A, NU-LHT-3M, DNA and FJS-1.

An instrument for studying granular media in low-gravity environment.

A new experimental facility has been designed and constructed to study driven granular media in a low-gravity environment. This versatile instrument, fully automatized, with a modular design based on several interchangeable experimental cells, allows us to investigate research topics ranging from dilute to dense regimes of granular media such as granular gas, segregation, convection, sound propagation, jamming, and rheology-all without the disturbance by gravitational stresses active on Earth. Here, we present the main parameters, protocols, and performance characteristics of the instrument. The current scientific objectives are then briefly described and, as a proof of concept, some first selected results obtained in low gravity during parabolic flight campaigns are presented.

[Pediatric knee injuries]. / Kindliche Kniebinnenverletzungen.

Patella dislocations are the most common knee injuries causing hemarthrosis in children. Flake fractures represent the main complication of these injuries and require fixation. First time dislocations are treated conservatively. Recurrent dislocations are managed operatively. Precise analysis of the underlying dispositional and pathological factors is important to determine the appropriate operative procedure. To protect the growth plate, special techniques are required. Tibial spine fractures are bony avulsions of the anterior cruciate ligament (ACL). Management includes closed reduction in hyperextension and immobilization in a knee cast. Tibial spine fractures which cannot be reduced require operative treatment using either arthroscopic or open reduction and stabilization without injuring the growth plate. Intraligamentous ACL injuries are increasingly observed in children and adolescents. The risk of meniscus tears or chondral damage is high in these injuries. In case of persistent ACL instability, early reconstruction is recommended. Various techniques have been described; however, there is no consensus regarding the most favorable technique. The attending physician must be familiar with different ACL reconstruction techniques and with the anatomy of the growth plate. Meniscus tears require early suturing. Healing rates are good in children.

Identifying the electronic character and role of the Mn states in the valence band of (Ga,Mn)As.

We report high-resolution hard x-ray photoemission spectroscopy results on (Ga,Mn)As films as a function of Mn doping. Supported by theoretical calculations we identify, for both low (1%) and high (13%) Mn doping values, the electronic character of the states near the top of the valence band. Magnetization and temperature-dependent core-level photoemission spectra reveal how the delocalized character of the Mn states enables the bulk ferromagnetic properties of (Ga,Mn)As.

Glass transition in driven granular fluids: a mode-coupling approach.

We consider the stationary state of a fluid comprised of inelastic hard spheres or disks under the influence of a random, momentum-conserving external force. Starting from the microscopic description of the dynamics, we derive a nonlinear equation of motion for the coherent scattering function in two and three space dimensions. A glass transition is observed for all coefficients of restitution, ε, at a critical packing fraction φ(c)(ε) below random close packing. The divergence of timescales at the glass transition implies a dependence on compression rate upon further increase of the density-similar to the cooling-rate dependence of a thermal glass. The critical dynamics for coherent motion as well as tagged particle dynamics is analyzed and shown to be nonuniversal with exponents depending on space dimension and degree of dissipation.

Growth of ultrathin epitaxial Fe/MgO spin injector on (0, 0, 1) (Ga, Mn)As.

We have grown an ultrathin epitaxial Fe/MgO bilayer on (Ga, Mn)As by e-beam evaporation in UHV. The system structure has been investigated by high resolution transmission electron microscopy (TEM) experiments which show that the Fe and MgO films, covering completely the (Ga, Mn)As, grow with the epitaxial relationship Fe[100](001) [parallel] MgO[110](001) [parallel] (Ga,Mn)As[110](001). The magnetic reversal process, studied by the magneto-optical Kerr effect (MOKE) at room temperature, demonstrates that the iron is ferromagnetic and possesses a cubic anisotropy, confirming the epitaxy relationship found with TEM. Resistivity measurements across the barrier display a non-Ohmic behavior characterized by cubic conductance as a function of the applied voltage suggesting tunneling-dominated transport across the barrier.

Identification of different electron screening behavior between the bulk and surface of (Ga,Mn)As.

We report x-ray photoemission spectroscopy results on (Ga,Mn)As films as a function of both temperature and Mn doping. Analysis of Mn 2p core level spectra reveals the presence of a distinct electronic screening channel in the bulk, hitherto undetected in more surface sensitive analysis. Comparison with model calculations identifies the character of the Mn 3d electronic states and clarifies the role, and the difference between surface and bulk, of hybridization in mediating the ferromagnetic coupling in (Ga,Mn)As.

Proximity induced enhancement of the Curie temperature in hybrid spin injection devices.

We investigate the increase of the Curie temperature T(C) in a lateral spin injection geometry where the ferromagnetic (Ga,Mn)As injector and detector contacts are capped by a thin iron film. Because of interlayer coupling between Fe and (Ga,Mn)As T(C) gets enhanced by nearly 100% for the thinnest (Ga,Mn)As films. The use of the proximity effect might pave the way for practical implementation of spintronic devices.

Increasing incidence rates of soft tissue sarcomas? A population-based epidemiologic study and literature review.

BACKGROUND: Increasing incidence rates of soft tissue sarcomas (STS) have been reported. In the present study, the authors have analyzed the incidence of STS in Austria in a population-based study for the period 1984-2004. PATIENTS AND METHODS: Age-adjusted incidence rates, gender and age predilection and geographic differences were analyzed, comprising data from the Austrian National Cancer Registry. RESULTS: A total of 5333 cases were registered; male-to-female ratio was 0.8. The most common histotypes were sarcoma not otherwise specified (36%), leiomyosarcoma (24%), liposarcoma (12%), malignant fibrous histiocytoma (9%) and fibrosarcoma (5%). Age-adjusted incidence rate was 2.4 per 100,000 per year. Analysis of annual incidence rates and 3-year periods showed no increase (annual increasing gradient = -0.0025). CONCLUSIONS: This study has analyzed the most recent data from a European population in comparison with seven international studies. An increase, as postulated elsewhere, could not be confirmed. The incidence rate of STS in Austria ranges in the lower half of the international incidence rates (1.8-5.0 per 100,000 per year). Different inclusion criteria (Kaposi's sarcoma and dermatofibrosarcoma) and classifications in the various studies explain the increase of incidence in some studies rather than true increase of STS due to new or accumulated risk factors.

Evidence for a magnetic proximity effect up to room temperature at Fe/(Ga, Mn)As interfaces.

We report x-ray magnetic circular dichroism and superconducting quantum interference device magnetometry experiments to study magnetic order and coupling in thin Fe/(Ga, Mn)As(100) films. We observe induced magnetic order in the (Ga, Mn)As layer that extends over more than 2 nm, even at room temperature. We find spectroscopic evidences of a hybridized d configuration of Mn atoms in Fe/(Ga, Mn)As, with negligible Mn diffusion and/or MnFe intermixing. We show by experiment as well as by theory that the magnetic moment of the Mn ions couples antiparallel to the moment of the Fe overlayer.

Bond formation and slow heterogeneous dynamics in adhesive spheres with long-ranged repulsion: quantitative test of mode coupling theory.

A colloidal system of spheres interacting with both a deep and narrow attractive potential and a shallow long-ranged barrier exhibits a prepeak in the static structure factor. This peak can be related to an additional mesoscopic length scale of clusters and/or voids in the system. Simulation studies of this system have revealed that it vitrifies upon increasing the attraction into a gel-like solid at intermediate densities. The dynamics at the mesoscopic length scale corresponding to the prepeak represents the slowest mode in the system. Using mode coupling theory with all input directly taken from simulations, we reveal the mechanism for glassy arrest in the system at 40% packing fraction. The effects of the low-q peak and of polydispersity are considered in detail. We demonstrate that the local formation of physical bonds is the process whose slowing down causes arrest. It remains largely unaffected by the large-scale heterogeneities, and sets the clock for the slow cluster mode. Results from mode-coupling theory without adjustable parameters agree semiquantitatively with the local density correlators but overestimate the lifetime of the mesoscopic structure (voids).

Dynamic glass transition in two dimensions.

The question of the existence of a structural glass transition in two dimensions is studied using mode coupling theory (MCT). We determine the explicit d dependence of the memory functional of mode coupling for one-component systems. Applied to two dimensions we solve the MCT equations numerically for monodisperse hard disks. A dynamic glass transition is found at a critical packing fraction phi(c)d=2 approximately equal 0.697 which is above phi(c)d=3 approximately equal 0.516 by about 35%. Phi(c)d scales approximately with phi(rcp)d, the value for random close packing, at least for d=2, 3. Quantities characterizing the local, cooperative "cage motion" do not differ much for d=2 and d=3, and we, e.g., find the Lindemann criterion for the localization length at the glass transition. The final relaxation obeys the superposition principle, collapsing remarkably well onto a Kohlrausch law. The d=2 MCT results are in qualitative agreement with existing results from Monte Carlo and molecular dynamics simulations. The mean-squared displacements measured experimentally for a quasi-two-dimensional binary system of dipolar hard spheres can be described satisfactorily by MCT for monodisperse hard disks over four decades in time provided the experimental control parameter Gamma (which measures the strength of dipolar interactions) and the packing fraction phi are properly related to each other.

Jamming transition in granular systems.

Recent simulations have predicted that near jamming for collections of spherical particles, there will be a discontinuous increase in the mean contact number Z at a critical volume fraction phi(c). Above phi(c), Z and the pressure P are predicted to increase as power laws in phi-phi(c). In experiments using photoelastic disks we corroborate a rapid increase in Z at phi(c) and power-law behavior above phi(c) for Z and P. Specifically we find a power-law increase as a function of phi-phi(c) for Z-Z(c) with an exponent beta around 0.5, and for P with an exponent psi around 1.1. These exponents are in good agreement with simulations. We also find reasonable agreement with a recent mean-field theory for frictionless particles.