Dalian University of Technology

About: Dalian University of Technology is a education organization based out in Dalian, China. It is known for research contribution in the topics: Catalysis & Finite element method. The organization has 60890 authors who have published 71921 publications receiving 1188356 citations. The organization is also known as: Dàlián Lǐgōng Dàxué.

Robust Adaptive Tracking Control for Nonlinear Systems Based on Bounds of Fuzzy Approximation Parameters

Abstract: A robust adaptive fuzzy control approach is developed for a class of multi-input-multi-output (MIMO) nonlinear systems with modeling uncertainties and external disturbances by using both the approximation property of the fuzzy logic systems and the backstepping technique. The MIMO systems are composed of interconnected subsystems in the strict-feedback form. The main characteristics of the developed approach are that the online computation burden is alleviated and the robustness to dynamic uncertainties and external disturbances is improved. It is proven that all the signals of the resulting closed-loop system are uniformly bounded and that the tracking errors converge to a small neighborhood around zero. Two simulation experiments are presented to demonstrate the feasibility of the approach developed in this paper.

Effect of graphene oxide concentration on the morphologies and antifouling properties of PVDF ultrafiltration membranes

Abstract: Poly (vinylidene fluoride) (PVDF)/graphene oxide (GO) ultrafiltration (UF) membranes are prepared via immersion precipitation phase inversion process. Raman spectra results indicate the existence of GO in PVDF/GO UF membranes. SEM pictures show that the PVDF/GO UF membranes present developed finger-like pore substructure along with the increased porosity and mean pore size. As revealed by FT-IR spectra, large amount of OH groups are appeared due to the introduction of GO nanosheets that improve the surface hydrophilicity of the modified membrane. In permeation experiment, the water flux is improved after blending GO. With 2 wt% GO content, the pure water flux and permeation flux reach peak values of 26.49 L/m2 h and 14.21 L/m2 h, increasing 79% and 99% respectively. Furthermore, the flux recovery ratio (FRR) and the fouling resistance results suggest that PVDF/GO UF membranes have better antifouling properties than pure PVDF due to the changes of surface hydrophilicity and membrane morphologies. AFM images show that UF membranes have a smoother surface with a higher efficient filtration area, which would enhance antifouling properties.

Caching UAV Assisted Secure Transmission in Hyper-Dense Networks Based on Interference Alignment

Abstract: Unmanned aerial vehicles (UAVs) can help small-cell base stations (SBSs) offload traffic via wireless backhaul to improve coverage and increase rate. However, the capacity of backhaul is limited. In this paper, UAV assisted secure transmission for scalable videos in hyper-dense networks via caching is studied. In the proposed scheme, UAVs can act as SBSs to provide videos to mobile users in some small cells. To reduce the pressure of wireless backhaul, UAVs and SBSs are both equipped with caches to store videos at off-peak time. To facilitate UAVs, a single antenna is equipped at each UAV and thus, only the precoding matrices of SBSs should be cooperatively designed to manage interference by exploiting the principle of interference alignment. On the other hand, the SBSs replaced by UAVs will be idle. Thus, in order to guarantee secure transmission, the idle SBSs can be further exploited to generate jamming signal to disrupt eavesdropping. The jamming signal is zero-forced at the legitimate users through the precoding of the idle SBSs, without affecting the legitimate transmission. The feasibility conditions of the proposed scheme are derived, and the secrecy performance is analyzed. Finally, simulation results are presented to verify the effectiveness of the proposed scheme.

Enhanced piezoelectric effect in Janus group-III chalcogenide monolayers

Abstract: Piezoelectricity is a unique material property that converts mechanical energy into electricity or vice versa. Starting from the group-III monochalcogenide monolayers, we design a series of derivative Janus structures for piezoelectric materials, including Ga2SSe, Ga2STe, Ga2SeTe, In2SSe, In2STe, In2SeTe, GaInS2, GaInSe2, and GaInTe2. Our first-principles calculations show that these Janus structures are thermodynamically and dynamically stable. They have a bandgap in the range of 0.89–2.03 eV, lower than those of the perfect monolayers, and Ga2STe, Ga2SeTe, In2STe, and In2SeTe monolayers are direct gap semiconductors. They possess piezoelectric coefficients up to 8.47 pm/V, over four times the maximum value obtained in perfect group-III monochalcogenide monolayers. Moreover, the broken mirror symmetry of these Janus structures induces out-of-plane dipolar polarization, yielding additional out-of-plane piezoelectric coefficients of 0.07–0.46 pm/V. The enhanced piezoelectric properties enable the developme...