Application of a PCA-DBN-based surrogate model to robust aerodynamic design optimization

An efficient method employing a Principal Component Analysis(PCA)-Deep Belief Network(DBN)-based surrogate model is developed for robust aerodynamic design optimization in this study.In order to reduce the number of design variables for aerodynamic optimizations,the PCA technique is implemented to the geometric parameters obtained by parameterization method.For the purpose of predicting aerodynamic parameters,the DBN model is established with the reduced design variables as input and the aerodynamic parameters as output,and it is trained using the k-step contrastive divergence algorithm.The established PCA-DBN-based surrogate model is validated through predicting lift-to-drag ratios of a set of airfoils,and the results indicate that the PCA-DBN-based surrogate model is reliable and obtains more accurate predictions than three other surrogate models.Then the efficient optimization method is established by embedding the PCA-DBN-based surrogate model into an improved Particle Swarm Optimization(PSO)framework,and applied to the robust aerodynamic design optimizations of Natural Laminar Flow(NLF)airfoil and transonic wing.The optimization results indicate that the PCA-DBN-based surrogate model works very well as a prediction model in the robust optimization processes of both NLF airfoil and transonic wing.By employing the PCA-DBN-based surrogate model,the developed efficient method improves the optimization efficiency obviously.

An innovative study on low surface energy micronano coatings with multilevel structures for laminar flow design

Laminar flow design is one of the most effective ways to reduce the drag of a commercial aircraft by expanding the laminar flow region on the surface of the aircraft. As material science develops, the emergence of new materials such as low surface energy materials has offered new choices for laminar flow design of commercial aircraft. Different types of low surface energy micro-nano coatings are prepared to verify the effects on the boundary layer transition position and the drag of the airfoil through wind tunnel tests. The infrared thermal imaging technology is adopted for measuring the boundary layer transition, while the momentum integral approach is employed to measure the drag coefficient through a wake rake. Infrared thermal imaging results indicate that the coatings are capable of moving backward the boundary layer transition position at both a low velocity of Mach number 0.15 and a high velocity of Mach number 0.785. Results of the momentum integral approach demonstrate that the drag coefficients are reduced obviously within the cruising angle of attack range from 1° and 5° by introducing the low surface energy micro-nano coating technology.

Flexible Oxide-Based Thin-Film Transistors on Plastic Substrates for Logic Applications

Phosphorus doped（P-doped） nanogranular SiO2 films have been deposited by plasma-enhanced chemical vapor deposition. A high proton conductivity of;.2x10-4S/cm and a large electric double layer（EDL） capacitance of;.2μF/cm2 have been obtained. Flexible coplanar-gate EDL thin film transistors（TFTs） gated by P-doped nanogranular SiO2 films are self-assembled on plastic substrates at room temperature. Due to the big EDL capacitance,such TFTs show ultra-low voltage operation of 1 V,a large field-effect mobility of 18.9 cm2/Vs,a small subthreshold swing of 85 m V/decade and a high current on/off ratio of 107. Furthermore,the EDL TFT could work in dual coplanar gate mode. AND logic operation is realized. Our results demonstrate that such TFTs gated by P-doped nanogranular SiO2 films have potential applications in low-power flexible electronics.

Surface Passivation Performance of Atomic-Layer-Deposited Al_2O_3 on p-type Silicon Substrates

Surface passivation performances of Al2O3 layers deposited on p-type Czochralski Si wafers by atomic layer deposition（ALD） were investigated as a function of post-deposition annealing conditions.The maximal minority carrier lifetime of 4.7 ms was obtained for AI2O3 passivated p-type Si.Surface passivation mechanisms of Al2O3 layers were investigated in terms of interfacial state density（Dit） and negative fixed charge densities（Qfix） through capacitance—voltage（C— V） characterization.High density of Qfix and low density of Dit were needed for high passivation performances,while high density of Dit and low density of Qfixdegraded the passivation performances.A low Dit was a prerequisite to benefit from the strong field effect passivation induced by high density of negative fixed charges in the Al2O3 layer.

Short-Term Synaptic Plasticity Mimicked on Ionic/Electronic Hybrid Oxide Synaptic Transistor Gated by Nanogranular SiO_2 Films

An indium-zinc-oxide （IZO） based ionic/electronic hybrid synaptic transistor gated by field-configurable nanogranular SiO2 films was reported. The devices exhibited a high current ON/OFF ratio of above 107, a high electron mobility of ～14 cm2 V^-1 s^-1 and a low subthreshold swing of ～80 mV/decade. The gate bias would modulate the interplay between protons and electrons at the channel/dielectric interface. Due to the dynamic modulation of the transient protons flux within the nanogranular SiO2 films, the channel current would be modified dynamically. Short-term synaptic plasticities, such as short-term potentiation and short- term depression, were mimicked on the proposed IZO synaptic transistor. The results indicate that the synaptic transistor proposed here has potential applications in future neuromorphic devices.

n-type Polycrystalhne Si Thick Films Deposited on SiN_x-coated Metallurgical Grade Si Substrates

For photovoltaic applications,low-cost SiNx-coated metallurgical grade silicon（MG-Si） wafers were used as substrates for polycrystalline silicon（poly-Si） thick films deposition at temperatures ranging from 640 to880 ℃ by thermal chemical vapor deposition.X-ray diffraction and Raman results indicated that high-quality poly-Si thick films were deposited at 880 ℃.To obtain n-type poly-Si,the as-deposited poly-Si films were annealed at 880 ℃ capped with a phosphosilicate glass.Electrical properties of the n-type poly-Si thick films were investigated by four-probe and Hall measurements.The carrier concentration and electron mobility of the n-type poly-Si film was estimated to be 1.7 x 1019cm-3and 68.1 cm2V-1s-1,respectively.Highquality poly-Si thick films deposited on MG-Si wafers are very promising for photovoltaic applications.