No Arabic abstract
In this letter we derive a universal law for nanoindentation, considering different sizes and shapes of the indenter. The law matches as limit cases all the well-known hardness scaling laws proposed in the literature. But our finding can also explain their deviations experimentally observed at the nanoscale. An even more general scaling law is then formulated, also in the fast and slow dynamics; it is based only on the surface over volume ratio of the domain in which the energy flux occurs: thus, its application in different fields, also for chaotic and complex (e.g., biological) systems, is demonstrated.
Due to high viscosity, glassy systems evolve slowly to the ordered state. Results of molecular dynamics simulation reveal that the structural ordering in glasses becomes observable over experimental (finite) time-scale for the range of phase diagram with high values of pressure. We show that the structural ordering in glasses at such conditions is initiated through the nucleation mechanism, and the mechanism spreads to the states at extremely deep levels of supercooling. We find that the scaled values of the nucleation time, $tau_1$ (average waiting time of the first nucleus with the critical size), in glassy systems as a function of the reduced temperature, $widetilde{T}$, are collapsed onto a single line reproducible by the power-law dependence. This scaling is supported by the simulation results for the model glassy systems for a wide range of temperatures as well as by the experimental data for the stoichiometric glasses at the temperatures near the glass transition.
We show how the periodicity of 180^{o} domains as a function of crystal thickness scales with the thickness of the domain walls both for ferroelectric and for ferromagnetic materials. We derive an analytical expression for the universal scaling factor and use this to calculate domain wall thickness and gradient coefficients (exchange constants) in some ferroic materials. We then use these to discuss some of the wider implications for the physics of ferroelectric nano-devices and periodically poled photonic crystals.
Violence detection has been studied in computer vision for years. However, previous work are either superficial, e.g., classification of short-clips, and the single scenario, or undersupplied, e.g., the single modality, and hand-crafted features based multimodality. To address this problem, in this work we first release a large-scale and multi-scene dataset named XD-Violence with a total duration of 217 hours, containing 4754 untrimmed videos with audio signals and weak labels. Then we propose a neural network containing three parallel branches to capture different relations among video snippets and integrate features, where holistic branch captures long-range dependencies using similarity prior, localized branch captures local positional relation using proximity prior, and score branch dynamically captures the closeness of predicted score. Besides, our method also includes an approximator to meet the needs of online detection. Our method outperforms other state-of-the-art methods on our released dataset and other existing benchmark. Moreover, extensive experimental results also show the positive effect of multimodal (audio-visual) input and modeling relationships. The code and dataset will be released in https://roc-ng.github.io/XD-Violence/.
Precise determination of the solid-state microstructure of semiconducting polymers is of paramount importance for the further development of these materials in various organic electronic technologies. Yet, prior characterization of the ordering of semiconducting polymers often resulted in conundrums in which X-ray scattering and microscopy yielded seemingly contradicting results. Here, based on fast scanning calorimetry, we introduce for the first time the concept of the semi-para-crystallinity and measurement of the degree of para-crystallinity (ordered volume/mass fraction) in a set of materials that previously eluded understanding. In combination with lattice distortion determination within para-crystals (g-parameter from X-ray scattering) and nanomorphology, the complete solid-state microstructure is correlated with device properties. Our data show that the long-range charge carrier transport in these materials is more sensitive to the interconnection of para-crystal units than to the amount of structural order itself.
Understanding the mechanisms of plasticity in structural steels is essential for the operation of next-generation fusion reactors. Elemental composition, particularly the amount of Cr present, and irradiation can have separate and synergistic effects on the mechanical properties of ferritic/martensitic steels. The study of ion-irradiated FeCr alloys is useful for gaining a mechanistic understanding of irradiation damage in steels. Previous studies of ion-irradiated FeCr did not clearly distinguish between the nucleation of dislocations to initiate plasticity, and their propagation through the material as plasticity progresses. In this study, Fe3Cr, Fe5Cr, and Fe10Cr were irradiated with 20 MeV Fe$^{3+}$ ions at room temperature to nominal doses of 0.01 dpa and 0.1 dpa. Nanoindentation was carried out with Berkovich and spherical indenter tips to study the nucleation of dislocations and their subsequent propagation. The presence of irradiation-induced defects reduced the theoretical shear stress and barrier for dislocation nucleation. The presence of Cr further enhanced this effect due to increased retention of irradiation defects. However, this combined effect is still small compared to dislocation nucleation from pre-existing sources such as Frank-Read sources and grain boundaries. The yield strength, an indicator of dislocation mobility, of FeCr increased with irradiation damage and Cr. The increased retention of irradiation defects due to the presence of Cr also further increased the yield strength. Reduced work hardening capacity was also observed following irradiation. The synergistic effects of Cr and irradiation damage in FeCr appear to be more important for the propagation of dislocations, rather than their nucleation.