Browsing by Author "Yang, F."
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Item Bayesian Optimization Approach for Analog Circuit Synthesis Using Neural Network(Institute of Electrical and Electronics Engineers Inc., 2019-03-25) Zhang, S.; Lyu, W.; Yang, F.; Yan, C.; Zhou, Dian; Zeng, X.; Zhou, DianBayesian optimization with Gaussian process as surrogate model has been successfully applied to analog circuit synthesis. In the traditional Gaussian process regression model, the kernel functions are defined explicitly. The computational complexity of training is O(N³), and the computation complexity of prediction is O(N²), where N is the number of training data. Gaussian process model can also be derived from a weight space view, where the original data are mapped to feature space, and the kernel function is defined as the inner product of nonlinear features. In this paper, we propose a Bayesian optimization approach for analog circuit synthesis using neural network. We use deep neural network to extract good feature representations, and then define Gaussian process using the extracted features. Model averaging method is applied to improve the quality of uncertainty prediction. Compared to Gaussian process model with explicitly defined kernel functions, the neural-network-based Gaussian process model can automatically learn a kernel function from data, which makes it possible to provide more accurate predictions and thus accelerate the follow-up optimization procedure. Also, the neural-network-based model has O(N) training time and constant prediction time. The efficiency of the proposed method has been verified by two real-world analog circuits. © 2019 EDAA.Item Decoupling the Influence of Surface Structure and Intrinsic Wettability on Boiling Heat Transfer(American Institute of Physics Inc.) Dai, Xianming (Simon); Wang, P.; Yang, F.; Li, X.; Li, C.; 0000-0001-5050-2867 (Dai, X); 308247739 (Dai, X; Dai, Xianming (Simon)Surface structure and intrinsic wettability are both important for boiling heat transfer. While superhydrophilic micro, nano, and hierarchical surfaces are widely used for boiling enhancement, in which the surface structure and intrinsic wettability usually couple together. This study aims to decouple their influences on boiling heat transfer. Copper meshes are utilized as the microporous structures, and conformal superhydrophilic films of TiO₂ are deposited by atomic layer deposition (ALD). Although ALD coatings for boiling have been done on flat surfaces, this study separates the influence of surface structure from that of intrinsic wettability on a three-dimensional microporous surface. By comparing two and four layer meshes, we show that the surface structure has no obvious influence on the critical heat flux (CHF), but can significantly enhance the heat transfer coefficient (HTC). The intrinsic superhydrophilicity dramatically increases the CHF due to the fast rewetting of dryout regions. Our conclusion is that fast rewetting is critical to increase the CHF, while large surface areas are vital to enhance the HTC. © 2018 Author(s).Item Maternal Hyperuricemia Superimposed on Maternal Hypertension Aggravates the Risk of Small-for-Gestational-Age Fetus(Elsevier Inc., 2019-04-16) Liu, L.; Yu, Chunxiao; Yang, F.; Yuan, Z.; Wang, Q.; Liu, S.; Zuo, C.; Guan, Q.; Yu, ChunxiaoAims: Small-for-gestational-age (SGA) fetus is an important public health issue because of its high mortality and long-term effects on health. Maternal hyperuricemia is associated with diverse adverse pregnant outcomes and neonatal disturbance. We aimed to evaluate whether maternal hyper-uric acid (HUA) is associated with the risk of SGA fetus and to explore whether it can modify the association between maternal hyper-blood pressure (HBP) and SGA fetus. Materials and methods: We performed a population-based cross-section retrospective study, a total of 6715 pregnant females were recruited. Multiple logistic regression analysis was performed to identify risk factors significantly correlated with SGA fetus, and then studied the effect of maternal HUA on the association between maternal HBP and SGA fetus. Key findings: We collected 537 SGA fetuses among 6715 pregnant females. Maternal HUA was an independent risk factor for SGA delivery (odds ratio (OR), 2.737; 95% confidence interval (CI), 2.110–3.551). A dose–response association between maternal uric acid and SGA delivery was found among normotensive and hypertensive group. Compared with those whose uric acid was lower than 270 µmo/L with normal–blood pressure (NBP), the risk for SGA delivery in those whose uric acid was higher than 370 µmo/L with stage 2 or 3 hypertension increased 12.695–fold. Significance: Our results suggest that maternal HUA could increase the risk of neonatal SGA, and maternal HUA could be superimposed upon pre-existing maternal HBP and increase the risk for SGA fetus. © 2019 The AuthorsItem Multi-Objective Bayesian Optimization for Analog/RF Circuit Synthesis(Institute of Electrical and Electronics Engineers Inc.) Lyu, W.; Yang, F.; Yan, C.; Zhou, Dian; Zeng, X.; Zhou, DianIn this paper, a novel multi-objective Bayesian optimization method is proposed for the sizing of analog/RF circuits. The proposed approach follows the framework of Bayesian optimization to balance the exploitation and exploration. Gaussian processes (GP) are used as the online surrogate models for the multiple objective functions. The lower confidence bound (LCB) functions are taken as the acquisition functions to select the data point with best Pareto-dominance and diversity. A modified non-dominated sorting based evolutionary multi-objective algorithm is proposed to find the Pareto Front (PF) of the multiple LCB functions, and the next simulation point is chosen from the PF of the multiple LCB functions. Compared with the multi-objective evolutionary algorithms (MOEA) and the state-of-the-art online surrogate model based circuit optimization method, our method can better approximate the Pareto Front while significantly reduce the number of circuit simulations. © 2018 Association for Computing Machinery.Item Multi-Objective Bayesian Optimization for Analog/RF Circuit Synthesis(Institute of Electrical and Electronics Engineers Inc., 2019) Zeng, X.; Lyu, W.; Yang, F.; Yan, C.; Zhou, Dian; Zhou, DianIn this paper, a novel multi-objective Bayesian optimization method is proposed for the sizing of analog/RF circuits. The proposed approach follows the framework of Bayesian optimization to balance the exploitation and exploration. Gaussian processes (GP) are used as the online surrogate models for the multiple objective functions. The lower confidence bound (LCB) functions are taken as the acquisition functions to select the data point with best Pareto-dominance and diversity. A modified non-dominated sorting based evolutionary multi-objective algorithm is proposed to find the Pareto Front (PF) of the multiple LCB functions, and the next simulation point is chosen from the PF of the multiple LCB functions. Compared with the multi-objective evolutionary algorithms (MOEA) and the state-of-the-art online surrogate model based circuit optimization method, our method can better approximate the Pareto Front while significantly reduce the number of circuit simulations. © 2018 Association for Computing Machinery.Item Static and Dynamic Properties of Shell-Shaped Condensates(American Physical Society) Sun, Kuei; Padavić, K.; Yang, F.; Vishveshwara, S.; Lannert, C.; Sun, KueiStatic, dynamic, and topological properties of hollow systems differ from those that are fully filled as a result of the presence of a boundary associated with an inner surface. Hollow Bose-Einstein condensates (BECs) naturally occur in various ultracold atomic systems and possibly within neutron stars but have hitherto not been experimentally realized in isolation on Earth because of gravitational sag. Motivated by the expected first realization of fully closed BEC shells in the microgravity conditions of the Cold Atomic Laboratory aboard the International Space Station, we present a comprehensive study of spherically symmetric hollow BECs as well as the hollowing transition from a filled sphere BEC into a thin shell through central density depletion. We employ complementary analytic and numerical techniques in order to study equilibrium density profiles and the collective mode structures of condensate shells hosted by a range of trapping potentials. We identify concrete and robust signatures of the evolution from filled to hollow structures and the effects of the emergence of an inner boundary, inclusive of a dip in breathing-mode-type collective mode frequencies and a restructuring of surface mode structure across the transition. By extending our analysis to a two-dimensional transition of a disk to a ring, we show that the collective mode signatures are an essential feature of hollowing, independent of the specific geometry. Finally, we relate our work to past and ongoing experimental efforts and consider the influence of gravity on thin condensate shells. We identify the conditions under which gravitational sag is highly destructive and study the mode-mixing effects of microgravity on the collective modes of these shells. ©2018 American Physical Society.