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[en] A facile CTAB-assisted sol-gel route has been successfully established to synthesize Y2Sn2O7 nanocrystals with pyrochlore structure. The route involves first the formation of CTAB-inorganics mesostructures as precursors and then their thermal decomposition to yield the final product. Well-crystallized and phase-pure Y2Sn2O7 particles of ∼40 nm in size can be readily obtained at 600 deg. C, a temperature much lower than that of the conventional solid-state method. Furthermore, photoluminescence characterization of the Y2Sn2O7 nanocrystals doped with 5 mol% Eu3+ was carried out and the results show that the as-synthesized material display intense and prevailing emission at 589 nm belonging to the 5D0→7F1 magnetic dipole transition
[en] Raman spectra of TiO2 nanoparticles (NPs) have a very strong finite-size dependency due to the phonon confinement effect. This provides a convenient way to characterize NPs size by simply using Raman spectroscopy. Together with fast grain growth kinetics and high stability under high temperature and pressure, these NPs have the potential to forensically retain the complete thermal history (temperature and time) of an event that they went through. Here, we demonstrate that both temperature and time can be determined simultaneously by using these thermosensors in the range of 400-700 deg. C and 5-60 s, assuming that the temperature is constant (a step-function approximation to a thermal spike) during a thermal event.
[en] To ensure the safety of the pilot, the design scheme of a ground experiment platform for testing the performance of oxygen supply system under rapid decompression was presented. Detail design process of the subsystems such as vacuum system, rapid decompression system and temperature control system was introduced. Numerical simulations were carried out for the latter two subsystems. The results show that, the requirements both for the temperature uniformity of the experiment cabin and for the rapid decompression time can be achieved, based on the design of the present work which is very valuable for constructing the rapid decompression test platform of oxygen supply system. (paper)
[en] Thermal stability of nanocrystalline anatase TiO2 against coarsening and anatase–rutile phase transformation was studied using both a pyroprobe heater and a conventional furnace. The pyroprobe heater, because of the programmable control and the ultra-fast heating rate (up to 20 000 °C s−1), for the first time, allows us to access the very early stage of the sintering and phase-transformation processes. Our short time (0–30 s) heat treatments reveal that rapid grain growth takes place first in anatase nanoparticles (NPs) upon the initial heating due to the lower activation energy compared with that for the anatase–rutile phase transformation. Meanwhile, rutile-like structural elements develop at the interface between anatase NPs during the fast grain growth period, which evolve into rutile nuclei with time, followed by nuclei growth, to convert nanocrystalline anatase into rutile rapidly in the temperature range where the phase transformation does not occur in coarse anatase TiO2. Overall, both grain growth and phase transformation in smaller anatase NPs happen at lower temperatures and faster than in bigger ones. The coupled sintering–phase-transformation mechanism can be exploited to design thermally stable nanocrystalline anatase TiO2 by reducing the sintering kinetics, for example, via minority additives. (paper)
[en] Synchronization of fractional-order nonlinear systems has received considerable attention for many research activities in recent years. In this Letter, we consider the synchronization between two nonidentical fractional-order systems. Based on the open-plus-closed-loop control method, a general coupling applied to the response system is proposed for synchronizing two nonidentical incommensurate fractional-order systems. We also derive a local stability criterion for such synchronization behavior by utilizing the stability theory of linear incommensurate fractional-order differential equations. Feasibility of the proposed coupling scheme is illustrated through numerical simulations of a limit cycle system, a chaotic system and a hyperchaotic system.
[en] Synchronization in chaotic fractional-order differential systems is studied both theoretically and numerically. Two schemes are designed to achieve chaos synchronization of so-called unified chaotic systems and the corresponding numerical algorithms are established. Some sufficient conditions on synchronization are also derived based on the Laplace transformation theory. Computer simulations are used for demonstration
[en] The topic of fractional calculus is enjoying growing interest among mathematicians, physicists and engineers in recent years. For complex network consisting of more than two fractional-order systems, however, it is difficult to establish its synchronization behavior. In this Letter, we study the synchronized motions in a star network of coupled fractional-order systems in which the major element is coupled to each of the noninteracting individual elements. On the basis of the stability theory of linear fractional-order differential equations, we derive a sufficient condition for the stability of the synchronization behavior in such a network. Furthermore, we verify our theoretical results by numerical simulations of star-coupled network with fractional-order chaotic nodes.
[en] This paper introduces contraction principle. Based on such a principle, a novel scheme is proposed to synchronize coupled systems with global diffusive coupling. A rigorous sufficient condition on chaos synchronization is derived. As an example, coupled Lorenz systems with nearest-neighbor diffusive coupling are investigated, and numerical simulations are given to validate the proposed synchronization approach
[en] Previous studies showed that a single negative feedback structure should be sufficient for robust circadian oscillations. It is thus pertinent to ask why current cellular clock models almost universally have interlocked negative feedback loop (NFL) and positive feedback loop (PFL). Here, we propose a molecular model that reflects the essential features of the Drosophila circadian clock to clarify the different roles of negative and positive feedback loops. In agreement with experimental observations, the model can simulate circadian oscillations in constant darkness, entrainment by light-dark cycles, as well as phenotypes of per01 and clkJrk mutants. Moreover, sustained oscillations persist when the PFL is removed, implying the crucial role of NFL for rhythm generation. Through parameter sensitivity analysis, it is revealed that incorporation of PFL increases the robustness of the system to regulatory processes in PFL itself. Such reduced models can aid understanding of the design principles of circadian clocks in Drosophila and other organisms with complex transcriptional feedback structures.
[en] With the rapid development of the rail vehicle industry, SUS301L austenitic stainless steel becomes the main material of rail vehicles, due to its cold processing performance, which has attracted much attention. In order to study the effect of grain boundary feature distribution on the properties of 301L stainless steel during cold deformation. 301L stainless steel samples with a cold rolling reduction of 3%, 5%, 9%, and 24% were prepared. The microstructure, mechanical properties and corrosion resistance of samples with different grain boundary characteristics were studied by means of OM, EBSD, universal testing machine and three-electrode electrochemical workstation. The result shows that with the increasing of the cold rolling reduction, grain orientation 〈111〉 is significantly weakened, the grain boundary of small angles gradually increases. Meanwhile, the grain boundary of large angle the strong grain boundary of Σ ≤ 29 gradually decreases. 301L stainless steel high ductility and toughness can be improved by obtaining a frequency of low Σ values in the coincident site lattice(CSL) grain boundaries. The microstructure and grain size is gradually getting smaller. The strength increased, while ductility, toughness, and the corrosion resistance reduced. The grain boundary of Σ3 gradually decreases with the increase of cold rolling reduction, but the reduction range of 9%∼24% is not significant. (paper)