On the generation of force required for actin-based motility.

The fundamental question of how forces are generated in a motile cell, a lamellipodium, and a comet tail is the subject of this note. It is now well established that cellular motility results from the polymerization of actin, the most abundant protein in eukaryotic cells, into an interconnected set of filaments. We portray this process in a continuum mechanics framework, claiming that polymerization promotes a mechanical swelling in a narrow zone around the nucleation loci, which ultimately results in cellular or bacterial motility. To this aim, a new paradigm in continuum multi-physics has been designed, departing from the well-known theory of Larché-Cahn chemo-transport-mechanics. In this note, we set up the theory of network growth and compare the outcomes of numerical simulations with experimental evidence.

Study on the Strength of the Brake Pad of a Freight Wagon under Uneven Loading in Operation.

The paper highlights the results of determining the strength of the brake pad of a freight wagon under uneven loading in operation. The main reasons for the uneven loading on the pad have been found. A mathematical tool for determining the strength of the pad unevenly loaded has been proposed. In the study, the pad is considered to be a rod system loaded with concentrated forces and bending moments. Sensors have been used in order to detect the load state of the brake pads. These sensors have been defined in the simulation software, and they have been placed on the working surface of the pad in the area of its interaction with the wheel. The operation of these sensors was simulated in the simulation software package. The results of the calculation have shown that the stresses in the pad are about 21.1 MPa; thus, they exceed the permissible values by 29%. Therefore, considering the uneven loading of the pad in operation, the strength of the pad is not ensured. To test the obtained results, the strength of the pad was determined using the finite element method. The Coulomb criterion was used for the calculation. It was found that the maximum stresses in the pad were about 19 MPa. These stresses were 21% higher than permissible values and occurred in the back of the pad. The study has proven that the uneven loading on the brake pad in operation can cause their destruction during braking. This may also cause traffic accidents with freight trains during their movement. The results of this study will contribute to the theoretical developments and recommendations aimed at improving the brake system of a freight wagon and rail traffic safety. It is considered that the tensometric sensors will be applied in future experimental tests for comparison and verification of the achieved results from the simulation computations.

Fundamentals of Hysteresis in Perovskite Solar Cells: From Structure-Property Relationship to Neoteric Breakthroughs.

Perovskite solar cells (PSC) have shown a rapid increase in efficiency than other photovoltaic technology. Despite its success in terms of efficiency, this technology is inundated with numerous challenges hindering the progress towards commercial viability. The crucial one is the anomalous hysteresis observed in the photocurrent density-voltage (J-V) response in PSC. The hysteresis phenomenon in the solar cell presents a challenge for determining the accurate power conversion efficiency of the device. A detailed investigation of the fundamental origin of hysteresis behavior in the device and its associated mechanisms is highly crucial. Though numerous theories have been proposed to explain the causes of hysteresis, its origin includes slow transient capacitive current, trapping, and de-trapping process, ion migrations, and ferroelectric polarization. The remaining issues and future research required toward the understanding of hysteresis in PSC device is also discussed.

Research into the Strength of an Open Wagon with Double Sidewalls Filled with Aluminium Foam.

The research is concerned with the use of double walls filled with aluminium foam for an open wagon in order to decrease the dynamic stresses during the operational modes. The research presents the strength calculation for the bearing structure of an open wagon with consideration of the engineering solutions proposed. It was found that the maximum equivalent stresses appeared in the bottom section of the centre sill behind the back support; they amounted to about 315 MPa and did not exceed the allowable values. The maximum displacements were detected in the middle section of the centre sill and amounted to 9.6 mm. The maximum deformations were 1.17 × 10-2. The research also presents the strength calculation for a weld joint in the maximum loaded zones of the bearing structure of an open wagon and gives the results of a modal analysis of the bearing structure of the improved open wagon. It was found that the critical oscillation frequencies did not exceed the allowable values. The results of the research may be useful for those who are concerned about designing innovative rolling stock units and improving the operational efficiency of railway transport.