For materials with high ductility, malleability and conductivity, temperature will have significant impact on the material properties. This is especially true for pure elemental metals which have a wide range of applications due to their ultrahigh strengths. Recently, the study of damage mechanism at the nano- and micro level has attracted a significant interest and research. However, the current understanding of deformation mechanisms in nanocrystalline metals in relation to atomic structure and behavior is insufficient. In this study, atomistic simulation of uniaxial tension at nano-scale was performed at a fixed rate of loading (500 ms^-1) on some nano-crystalline face centered cubic metals (Al, Cu, and Ni), to study the nature of tensile deformation at different temperatures using the embedded-atomic method (EAM) potential function. The simulation results show a rapid increase in the stress up to a maximum value followed by a sharp drop when the nanocrystal fails by ductile dislocation. The drop in the stress-strain curves can be attributed to the rearrangement of atoms to a new or modified crystalline structure. Additional simulations were run to study the effects of temperature on the stress-strain curve of nano-crystals. The result shows that increasing temperature weakens the ductility of these nanomaterials. In this investigation, the strain corresponding to yielding stress is observed to be lower with increasing temperature. Finally, the evolution of crystalline microstructure during the entire tensile process was investigated. The atomistic simulation result of tensile deformation at nanoscale obtained in this study agree with plasticity phenomenon observed in macroscale.

Bulk solids have a microstructure that differs significantly from nanoscale materials. In modern era, new devices are always produced at nano-scale level and existing ones are quantized to fit the global demand. To achieve this, there is a need to understand the behaviour of materials at atomic level. As a result, examining the properties of nanoparticles can help in understanding the nature of small-scale material behavior. The cohesive energy and lattice constant are essential physical quantities that can be used to predict other material properties. In this research, the equilibrium cohesive energies and its corresponding lattice constants of three nanosized crystals (Al, Cu and Ni), were investigated using molecular dynamics simulation method with a semi-empirical embedded atom model (EAM) potential function. The simulated results reveal that the three nanocrystals’ lattice constant match the experimental data. Besides, Al, Cu and Ni have cohesive energies of -3.40 eV, -3.55 eV, -4.44 eV respectively. Cu’s cohesive energy differs from experimental data unlike Al and Ni. The findings in the current research are in good agreement with those obtained utilizing the First principle calculation method.

Bacteria can spontaneously develop collective motions by aligning their motions in dense systems. Here, we show that bacteria can also respond collectively to an alternating electrical field and form dynamic clusters oscillating at the same frequency of the field. As the dynamic clusters go beyond a critical size, they split into smaller ones spontaneously. The critical size for splitting depends on the frequency of electric field and the concentration of bacteria. We show that instead of their biological activity, the physical properties of bacteria as charged particles are responsible for the formation of dynamic clusters. Electroconvective flows across the system play the key role in stabilizing the clusters. However, to form clusters, collective hydrodynamic cooperation between bacteria is important such that no aggregation occurs in dilute suspensions. The findings in this study illustrate that bio-systems can respond collectively to an external field, promising an effective way to control and modulate the behavior of organisms. Moreover, the controlled aggregation and condensation of bacteria offer a robust approach to improve the local concentration of bacteria for early and rapid detection, which has wide applications in clinics.

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