Atomistic Investigation of Titanium Carbide Ti8C5 under Impact Loading

Titanium carbides attract attention from both academic and industry fields because of their intriguing mechanical properties and proven potential as appealing candidates in the variety of fields such as nanomechanics, nanoelectronics, energy storage and oil/water separation devices. A recent study revealed that the presence of Ti8C5 not only improves the impact strength of composites as coatings, but also possesses significant strengthening performance as an interlayer material in composites by forming strong bonding between different matrices, which sheds light on the design of impact protection composite materials. To further investigate the impact resistance and strengthening mechanism of Ti8C5, a pilot Molecular Dynamics (MD) study utilizing comb3 potential is carried out on a Ti8C5 nanosheet by subjecting it to hypervelocity impacts. The deformation behaviour of Ti8C5 and the related impact resist mechanisms are assessed in this research. At a low impact velocity ~0.5 km/s, the main resonance frequency of Ti8C5 is 11.9 GHz and its low Q factor (111.9) indicates a decent energy damping capability, which would eliminate the received energy in an interfacial reflection process and weaken the shock waves for Ti8C5 strengthened composites. As the impact velocity increases above the threshold of 1.8 km/s, Ti8C5 demonstrates brittle behaviour, which is signified by its insignificant out-of-plane deformation prior to crack initiation. When tracking atomic Von Mises stress distribution, the elastic wave propagation velocity of Ti8C5 is calculated to be 5.34 and 5.90 km/s for X and Y directions, respectively. These figures are inferior compared with graphene and copper, which indicate slower energy delocalization rates and thus less energy dissipation via deformation is expected prior to bond break. However, because of its relatively small mass density comparing with copper, Ti8C5 presents superior specific penetration. This study provides a fundamental understanding of the deformation and penetration mechanisms of titanium carbide nanosheets under impact, which is crucial in order to facilitate emerging impact protection applications for titanium carbide-related composites

Tracking the Yadong-Gulu Rift belt with multiple thermochronometers on modern detritus from Yarlung-Tsangpo River

Abstract HKT-ISTP 2013 A

Particle-number fractionalization of a one-dimensional atomic Fermi gas with synthetic spin-orbit coupling

published_or_final_versio

General Error-based Active Disturbance Rejection Control for Swift Industrial Implementations

In this article, a typical 2DOF active disturbance rejection control (ADRC) design is restructured into a 1DOF form, thus making it compatible with standard industrial control function blocks and enhancing its market competitiveness. This methodology integrates the previously separated components, such as the profile generator, state observer, feedback controller, feedforward terms, and disturbance rejection, into one unified structure. In doing so, certain ADRC components can be made simpler (or even obsolete) without sacrificing the nominal control performance, which further simplifies the control synthesis and tuning. A generalized version of the error-driven design is adopted and rigorously proved here using the singular perturbation theory. The experimental verification of the utilized approach is carried out using a disturbed DC–DC buck converter

Conjugate field and fluctuation-dissipation relation for the dynamic phase transition in the two-dimensional kinetic Ising model

The two-dimensional kinetic Ising model, when exposed to an oscillating applied magnetic field, has been shown to exhibit a nonequilibrium, second-order dynamic phase transition (DPT), whose order parameter Q is the period-averaged magnetization. It has been established that this DPT falls in the same universality class as the equilibrium phase transition in the two-dimensional Ising model in zero applied field. Here we study for the first time the scaling of the dynamic order parameter with respect to a nonzero, period-averaged, magnetic `bias' field, H_b, for a DPT produced by a square-wave applied field. We find evidence that the scaling exponent, \delta_d, of H_b at the critical period of the DPT is equal to the exponent for the critical isotherm, \delta_e, in the equilibrium Ising model. This implies that H_b is a significant component of the field conjugate to Q. A finite-size scaling analysis of the dynamic order parameter above the critical period provides further support for this result. We also demonstrate numerically that, for a range of periods and values of H_b in the critical region, a fluctuation-dissipation relation (FDR), with an effective temperature T_{eff}(T, P, H_0) depending on the period, and possibly the temperature and field amplitude, holds for the variables Q and H_b. This FDR justifies the use of the scaled variance of Q as a proxy for the nonequilibrium susceptibility, \partial / \partial H_b, in the critical region.Comment: revised version; 31 pages, 12 figures; accepted by Phys. Rev.

Vacuum Energy Density and Cosmological Constant in dS Brane World

We discuss the vacuum energy density and the cosmological constant of dS$_5$ brane world with a dilaton field. It is shown that a stable AdS$_4$ brane can be constructed and gravity localization can be realized. An explicit relation between the dS bulk cosmological constant and the brane cosmological constant is obtained. The discrete mass spectrum of the massive scalar field in the AdS$_4$ brane is used to acquire the relationship between the brane cosmological constant and the vacuum energy density. The vacuum energy density in the brane gotten by this method is in agreement with astronomical observations.Comment: 16 pages,4 figure