Lipid exchange enhances geometric pinning in multicomponent membranes on patterned substrates

Theoretical Physic

Activity-induced interactions and cooperation of artificial microswimmers in one-dimensional environments

Biological microswimmers such as bacteria show collective motion that is made possible by an intricate interplay of sensing and signaling. Ketzetzi et al. reproduce this phenomenon in a catalytic system undergoing, for instance, cooperative speed-ups and dynamic reconfiguration of microswimmer chains.Cooperative motion in biological microswimmers is crucial for their survival as it facilitates adhesion to surfaces, formation of hierarchical colonies, efficient motion, and enhanced access to nutrients. Here, we confine synthetic, catalytic microswimmers along one-dimensional paths and demonstrate that they too show a variety of cooperative behaviours. We find that their speed increases with the number of swimmers, and that the activity induces a preferred distance between swimmers. Using a minimal model, we ascribe this behavior to an effective activity-induced potential that stems from a competition between chemical and hydrodynamic coupling. These interactions further induce active self-assembly into trains where swimmers move at a well-separated, stable distance with respect to each other, as well as compact chains that can elongate, break-up, become immobilized and remobilized. We identify the crucial role that environment morphology and swimmer directionality play on these highly dynamic chain behaviors. These activity-induced interactions open the door toward exploiting cooperation for increasing the efficiency of microswimmer motion, with temporal and spatial control, thereby enabling them to perform intricate tasks inside complex environments.Biological and Soft Matter Physic

IMPACT OF SKINFOLD THICKNESS ON WAVELET-BASED MECHANOMYOGRAPHIC SIGNAL

Surface mechanography (MMG) is a non-invasive technique that captures signs of low-frequency vibrations of skeletal muscles through the skin. However, subcutaneous structures may interfere with the acquisition of MMG signals. The objective of this study was to verify the influence of skinfold thickness (ST) on the MMG wavelet-based signal in the rectus femoris muscle during maximal voluntary contraction in two groups of individuals: group I (n = 10, ST 20 mm). Negative correlation was observed between the 19 Hz, 28 Hz and 39 Hz frequency bands with ST. There was a statistical difference in almost all frequency bands, especially in the X and Y axes. All MMG axes in group II presented higher magnitudes in frequency bands 2 and 6 Hz (like low-pass filter). Thus, these results can be applied to calibrate MMG responses as biofeedback systems

Seismic assessment of a heavy-timber frame structure with ring-doweled moment-resisting connections

The performance of heavy-timber structures in earthquakes depends strongly on the inelastic behavior of the mechanical connections. Nevertheless, the nonlinear behavior of timber structures is only considered in the design phase indirectly through the use of an R-factor or a q-factor, which reduces the seismic elastic response spectrum. To improve the estimation of this, the seismic performance of a three-story building designed with ring-doweled moment resisting connections is analyzed here. Connections and members were designed to fulfill the seismic detailing requirements present in Eurocode 5 and Eurocode 8 for high ductility class structures. The performance of the structure is evaluated through a probabilistic approach, which accounts for uncertainties in mechanical properties of members and connections. Nonlinear static analyses and multi-record incremental dynamic analyses were performed to characterize the q-factor and develop fragility curves for different damage levels. The results indicate that the detailing requirements of Eurocode 5 and Eurocode 8 are sufficient to achieve the required performance, even though they also indicate that these requirements may be optimized to achieve more cost-effective connections and members. From the obtained fragility curves, it was verified that neglecting modeling uncertainties may lead to overestimation of the collapse capacity

On the geometry of demixing: A study of lipid phase separation on curved surfaces

Like a mixture of oil and water, lipid membranes separate into two liquid phases. While it is known that on a flat surface coexisting liquid phases result in the formation of circular domains, little is known about liquid-liquid phase separation on curved surfaces. In this thesis, a collection of experimental tools are offered to unravel this problem. Novel model systems in vitro consisting of supported lipid bilayers, or bilayers stabilised on solid substrates, are developed by using colloidal particles and micro-printed structures. In this way, both the composition and the geometry of the membrane can be controlled allowing for a direct comparison with simulation and theory.Nanofront, NWOBiological and Soft Matter Physic

A component approach for non-linear behavior of cross-laminated solid timber panels

Many possible emergency conditions, including evacuations, negatively affect the urban transportation system by substantially increasing the travel demand and/or reducing the supplied capacity. A transportation model can be used to quantify and understand the impact of the underlying disasters and corresponding management strategies. To this end, we develop an efficient methodology suitable for simulating multimodal transportation systems affected by emergencies, based on the novel integration of an activity-based choice model with both pre-trip and en-route choices, and a macroscopic or mesoscopic dynamic network loading model. The model structure first estimates the daily equilibrium and then uses that result as a starting point to simulate the emergency situation without further iterations. Unlike previous efforts, our methodology satisfies all requirements identified from literature regarding transportation modeling for emergencies, and is sufficiently general to investigate a wide range of emergency situations and management strategies. An evacuation case study for Delft shows the feasibility of applying the methodology. Furthermore, it yields practical insights for urban evacuation planning that stem from complex system dynamics, such as important interactions among travel directions and among modes. This supports the need for a comprehensive modeling methodology such as the one we present in this paper

A novel method for non-linear design of CLT wall systems

Inthis paper,a non-linear procedure for the seismic design of metal connections in cross-laminated timber (CLT) walls subjected to bending and axial force is presented. Timber is conservatively modelled as an elasto-brittle material, whereas metal connections (hold-downs and angle brackets) are modelled withan elasto-plastic behavior. The reaction force in each connection is iteratively calculated by varyingthe position of the neutral axis at the base of the wall using a simple algorithm that was implemented\ufb01rst in a purposely developed spreadsheet, and then into a purposely developed software. This methodis based on the evaluation of \ufb01ve different failure mechanisms at ultimate limit state, starting from the fully tensioned wall to the fully compressed one,similarly to reinforced concrete (RC) section design.By setting the mechanical properties of timber and metal connections and the geometry of the CLT panel, the algorithm calculates, for every axial load value, the ultimate resisting moment of the entire wall and the position of the neutral axis. The procedure mainly applies to platform-type structures with hold-downs and angle brackets connections at the base of the wall and rocking mechanism as the prevalentway of dissipation. This method allows the designer to have information on the rocking capacity of thesystem and on the failure mechanism for a given distribution of external loads. The proposed methodwas validated on the results of FE analyses using SAP2000 and ABAQUS showing acceptable accuracy