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The carnivorous Venus flytrap catches prey by an ingenious snapping mechanism. Based on work over nearly 200 years, it has become generally accepted that two touches of the trap’s sensory hairs within 30 s, each one generating an action potential, are required to trigger closure of the trap. We developed an electromechanical model, which, however, suggests that under certain circumstances one touch is sufficient to generate two action potentials. Using a force-sensing microrobotic system, we precisely quantified the sensory-hair deflection parameters necessary to trigger trap closure and correlated them with the elicited action potentials in vivo. Our results confirm the model’s predictions, suggesting that the Venus flytrap may be adapted to a wider range of prey movements than previously assumed., It is generally accepted that two touches of the Venus flytrap’s sensory hairs within 30 seconds are required to trigger closure of the trap. Here, however, quantification of the plant’s sensory hair deflection parameters reveals that one stimulus is sufficient.

It is important for many animal model studies, particularly with rodents, to be performed in a well standardized and controlled physical environment. Otherwise the observations and measurements done might create difficulties in interpretation, or the results might even be impossible to reproduce or verify in another laboratory. In the animal department of BISAM at Umea university the ventilation system was modernized in 1983-84 in the rodent facilities, with supply of air through new devices in the ceiling and exhaust of air through perforated walls on two sides of the rooms. The supply air comes from a climat chamber where the incoming air should be properly heated and humidified, as controlled by thermo- and hygrostats in the chamber outlet. The animal rooms are also equipped with a sprinkler system for additional humidification as necessary. This report presents results on controls made on temperature and humidity stability in these rebuilt rodent facilities during summer (1984) as well as winter (early 1985) conditions. The capacity of the air supply system was also controlled. In summary, the temperature in the animal rooms tended to be high during summer, and increased in periods of high out of door temperature so that in the animal cages the temperature could exceed 31 °C. The relative humidity was above accepted levels most of the time. On the other hand, during winter it seemed to be possible to keep the temperature within the desired levels, but the relative humidity was unacceptably low. With these results at hand, the air supply system was controlled for its ability mainly to humidify the air. This control was done during autumn and showed that at that time of the year the capacity was just at limit to give the desired humidity in the animal rooms. The main >>function<< of the room sprinkler system was in fact to decrease room temperature and to give unstable temperature and humidity. During winter when very cold, dry air should be heated and humidified the capacity of the climat chamber is far from sufficient. The high temperature in the rooms during summer depend upon the lack of cooling possibilities in the chamber., Scandinavian Journal of Laboratory Animal Sciences, Vol. 14 No. 4 (1987)

The growing timber manufacturing industry faces challenges due to increasing geometric complexity of architectural designs. Complex and structurally efficient curved geometries are nowadays easily designed but still involve intensive manufacturing and excessive machining. We propose an efficient form-giving mechanism for large-scale curved mass timber by using bilayered wood structures capable of self-shaping by moisture content changes. The challenge lies in the requirement of profound material knowledge for analysis and prediction of the deformation in function of setup and boundary conditions. Using time- and moisture-dependent mechanical simulations, we demonstrate the contributions of different wood-specific deformation mechanisms on the self-shaping of large-scale elements. Our results outline how to address problems such as shape prediction, sharp moisture gradients, and natural variability in material parameters in light of an efficient industrial manufacturing., Science Advances, 5 (9), ISSN:2375-2548

Physical Review Letters, 123 (5), ISSN:0031-9007, ISSN:1079-7114

The carnivorous Venus flytrap catches prey by an ingenious snapping mechanism. Based on work over the past 190 years, it has become generally accepted that two touches of the trap’s sensory hairs within 30 seconds, each one generating an action potential, are required to trigger closure of the trap. We developed an electromechanical model which, however, suggests that under certain circumstances one touch is sufficient to generate two action potentials. Using a force-sensing microrobotics system, we precisely quantified the sensory hair deflection parameters necessary to trigger trap closure, and correlated them with the elicited action potentials in vivo. Our results confirm the model’s predictions, suggesting that the Venus flytrap may be adapted to a wider range of prey movement than previously assumed.

We investigate the mechanical behavior of a confined granular packing of irregular polyhedral particles under repeated heating and cooling cycles by means of numerical simulations with the non-smooth contact dynamics method. Assuming a homogeneous temperature distribution as well as constant temperature rate, we study the effect of the container shape, and coefficients of thermal expansions on the pressure buildup at the confining walls and the density evolution. We observe that small changes in the opening angle of the confinement can lead to a drastic peak pressure reduction. Furthermore, the displacement fields over several thermal cycles are obtained and we discover the formation of toroidal convection cells inside the granular material. The root mean square of the vorticity is then calculated from the displacement fields and a quadratic dependency on the ratio of thermal expansion coefficients is established.

Modifications alter hygro-mechanical properties of wood in non-trivial ways that depend on modification treatment and wood microstructure. Generic micromechanical models with modifications on the cellular scale of spruce are proposed and studied, such as partial and entire lumen filling with isotropic materials, as well as modification of S2-layer properties. Based on a hierarchical micromechanical model, hygro-mechanical response surfaces of the modified, orthotropic material are predicted. Simulation results are compared to experimental data. The findings can be used for optimizing modification treatments, as well as for calculating the behavior in graded situations, common to treatments with limited modification depth.

This chapter focuses on Discrete Element models using Contact Dynamics, that capture the behavior of granular assemblies with fluid on the pore scale. The effect of the timescales, introduced by the fluid transport on relaxation, fluid migration, and failure are identified and studied in particle simulations and accompanying experiments. To extend the simulation capabilities to larger fluid contents, a discretization scheme for arbitrary liquid bodies with morphological evolution laws is employed, that combines experimental observations and results from small-scale Numerical Energy Minimization (NEM) simulations (part 1). We demonstrate that this way, fluid saturation in random packings can be simulated with arbitrary liquid contents ranging from dry to full saturation with good accuracy.

The early strength evolution of self-consolidating concrete (SCC) is studied by a set of non-standard mechanical tests for compressive, tensile, shear and bending failure. The results are applicable in an industrial environment for process control, e.g. of slip casting with adaptive molds in robotic fabrication. A procedure for collapsing data to a master evolution curve is presented that allows to distinguish two regimes in the evolution. In the first, the material is capable of undergoing large localized plastic deformation, as expected from thixotropic yield stress fluids. This is followed by a transition to cohesive frictional material behavior dominated by crack growth. The typical differences in tensile and compressive strength of hardened concrete are observed to originate at the transition. Finally, the evolution of a limit surface in principal stress space is constructed and discussed.

Wood-derived cellulose materials obtained by structure-retaining delignification are attracting increasing attention due to their excellent mechanical properties and great potential to serve as renewable and CO2 storing cellulose scaffolds for advanced hybrid materials with embedded functionality. Various delignification protocols and a multitude of further processing steps including polymer impregnation and densification are applied resulting in a large range of properties. However, treatment optimization requires a more comprehensive characterization of the developed materials in terms of structure, chemical composition, and mechanical properties for faster progress in the field. Herein, the current protocols for structure-retaining delignification are reviewed and the emphasis is placed on the mechanical characterization at different hierarchical levels of the cellulose scaffolds by experiments and modeling to reveal the underlying structure-property relationships.

We study fragment size distributions after crushing single and many particles under uniaxial compression inside a cylindrical container by means of numerical simulations. Under the assumption that breaking goes through the bulk of the particle we obtain the size distributions of fragments for both cases after large displacements. For the single-particle crushing, this fragmentation mechanism produces a log-normal size distribution, which deviates from the power-law distribution of fragment sizes for the packed bed. We show that as the breaking process evolves, a power-law dependency on the displacement is present for the single grain, while for the many-grains system, the distribution converges to a steady state. We further investigate the force networks and the average coordination number as a function of the particle size, which gives information about the origin of the power-law distributions for the granular assembly under uniaxial compression.

In recent architectural research, thin wooden bilayer laminates capable of self-actuation in response to humidity changes have been proposed as sustainable, programmed, and fully autonomous elements for facades or roofs for shading and climate regulation. Switches, humidistats, or motor elements represent further promising applications. Proper wood-adapted prediction models for actuation, however, are still missing. Here, a simple model that can predict bending deformation as a function of moisture content change, wood material parameters, and geometry is presented. We consider material anisotropy and moisture-dependency of elastic mechanical parameters. The model is validated using experimental data collected on bilayers made out of European beech wood. Furthermore, we present essential design aspects in view of facilitated industrial applications. Layer thickness, thickness-ratio, and growth ring angle of the wood in single layers are assessed by their effect on curvature, stored elastic energy, and generated axial stress. A sensitivity analysis is conducted to identify primary curvature-impacting model input parameters., PLoS ONE, 13 (10), ISSN:1932-6203

This work discusses the use of slipping domains to improve load support in water-lubricated microsystems through a multi-scale approach. A semi-analytical continuum formulation is developed to calculate changes in pressure distribution for a line contact with added slip. It is found that the slipping region maximizing hydrodynamic lift should favor inlet flow, but not be located at the contact outlet. Estimations for its positioning are provided. Slip on flat surfaces gives the largest gains in load support and friction reduction, but moderate improvements are also possible on circular geometries featuring high convergence ratios. Finally, Molecular Dynamics simulations are employed to quantify slip on hydrophobic surfaces. Among the considered topologies, graphene is an excellent candidate to generate slip in water-lubricated microsystems.

Flexible barriers are increasingly used for the protection from debris flow in mountainous terrain due to their low cost and environmental impact. How- ever, the development of a numerical tool for the ratio- nal design of such structures is still a challenge. In this work, a hybrid computational framework is presented, using a total Lagrangian formulation of the finite element method to represent aflexible barrier. The actions exerted on the structure by a debris flow are obtained from si- multaneous simulations of the flow of a fluid-grain mix- ture, using two conveniently coupled solvers: the discrete element method governs the motion of the grains, while the free-surface non-Newtonian fluid phase is solved us- ing the lattice Boltzmann method. Simulations on real- istic geometries show the dependence of the momentum transfer on the barrier on the composition of the debris flow, challenging typical assumptions made during the design process today. In particular, we demonstrate that both grains and fluid contribute in a nonnegligible way to the momentum transfer. Moreover, we show how the flexibility of the barrier reduces its vulnerability to struc- tural collapse, and how the stress is distributed on its fabric, highlighting potential weak points.

Detailed understanding of the equation of state of light elements such as the hydrogen isotopes in the warm dense matter (WDM) regime is essential for the modeling of the inner structure of many astrophysical objects, in particular Jovian planets as well as inertial confinement fusion (ICF) research. In these systems quantum degeneracy and strong inter-particle forces play an important role making its theoretical description extremely challenging. The Omega laser was used to drive a planar shock wave in cryogenically cooled deuterium creating WDM conditions. We used a set of independent diagnostics to measure the thermodynamic conditions of WDM including velocity interferometry (VISAR), streaked optical pyrometry (SOP) and x-ray Thomson scattering (XRTS). With a narrow-band x-ray backlighter probe at backscattering geometry the spectrally resolved XRTS accessed the boundary of collective and non-collective regimes making our measurement sensitive to both electron temperature and density. This work presents a full set of measurements of the thermodynamic properties for different laser intensity drives creating warm dense deuterium at various degrees of degeneracy and coupling. The measured electron densities and temperatures ranged between 0.2 and 2.15×1023 cm−3 and 0.6 − 20 eV respectively. The scattering measurement confirmed the findings from the VISAR and SOP data and together densityfunctional molecular dynamics (DFT-MD) simulations provides a novel self-consistent approach for an accurate characterization of the microscopic structure of WDM. Complementary to the laser compression work, findings from project employing static compression hydrogen with the use of diamond anvil cells is also be presented. The first direct measurement of the local field correction to the Coulomb interactions in degenerate plasma was obtained from inelastic scattering (20 keV probe) at the Diamond Light Source synchrotron facility.

In particle-laden flows through porous media, porosity and permeability are significantly affected by the deposition and erosion of particles. Experiments show that the permeability evolution of a porous medium with respect to a particle suspension is not smooth, but rather exhibits significant jumps followed by longer periods of continuous permeability decrease. Their origin seems to be related to internal flow path reorganization by avalanches of deposited material due to erosion inside the porous medium. We apply neutron tomography to resolve the spatio-temporal evolution of the pore space during clogging and unclogging to prove the hypothesis of flow path reorganization behind the permeability jumps. This mechanistic understanding of clogging phenomena is relevant for a number of applications from oil production to filters or suffosion as the mechanisms behind sinkhole formation., Comment: 18 pages, 9 figures

A multi-scale scheme for the invasion percolation of rock fracture networks with heterogeneous fracture aperture fields is proposed. Inside fractures, fluid transport is calculated on the finest scale and found to be localized in channels as a consequence of the aperture field. The channel network is characterized and reduced to a vectorized artificial channel network (ACN). Different realizations of ACNs are used to systematically calculate efficient apertures for fluid transport inside differently sized fractures as well as fracture intersection and entry properties. Typical situations in fracture networks are parameterized by fracture inclination, flow path length along the fracture and intersection lengths in the entrance and outlet zones of fractures. Using these scaling relations obtained from the finer scales, we simulate the invasion process of immiscible fluids into saturated discrete fracture networks, which were studied in previous works., Comment: 21 pages

Parasite proteins containing repeats are essential invasion ligands, important for their ability to evade the host immune system and to induce immunosuppression. Here, the intrinsic suppressive potential of repetitive structures within parasite proteins was exploited to induce immunomodulation in order to establish self-tolerance in an animal model of autoimmune neurological disease. We tested the tolerogenic potential of fusion proteins containing repeat sequences of parasites linked to self-antigens. The fusion constructs consist of a recombinant protein containing repeat sequences derived from the S-antigen protein (SAg) of Plasmodium falciparum linked to a CD4 T cell epitope of myelin. They were tested for their efficacy to control the development of experimental autoimmune encephalomyelitis (EAE), In addition, we used the DO11.10 transgenic mouse model to study the immune mechanisms involved in tolerance induced by SAg fusion proteins. We found that repeated sequences of P. falciparum SAg protein linked to self-epitopes markedly protected mice from EAE. These fusion constructs were powerful tolerizing agents not only in a preventive setting but also in the treatment of ongoing disease. The tolerogenic effect was shown to be antigen-specific and strongly dependent on the physical linkage of the T cell epitope to the parasite structure and on the action of anti-inflammatory cytokines like IL-10 and TGF-{beta}. Other mechanisms include down-regulation of TNF-{alpha} accompanied by increased numbers of FoxP3(+) cells. This study describes the use of repetitive structures from parasites linked to defined T cell epitopes as an effective method to induce antigen-specific tolerance with potential applicability for the treatment and prevention of autoimmune diseases.