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Picosecond ultrasonic laser sonar (PULSE), one of the noninvasive technologies with a high thickness sensitivity, is capable of probing multilayer films directly on the production wafers. To reach ...

Under the sun insolation in the daytime, the partially shaded effect would easily happen in a photovoltaic (PV) array due to clouds, trees, buildings, etc. To deal with the partially shaded effect, this paper proposes solar global maximum power point tracking (GMPPT) method based on Deep Q-Network. Maximum power point tracking (MPPT) is often used to achieve the maximum power in the PV system. The Perturbation and Observation (P&O) method is one of the most popular MPPT techniques in practice. However, due to the use of fixed step size, the P&O method may cause undesired oscillation around the maximum power point (MPP). With the partially shaded effect, the characteristic P-V curve of a PV array may possess multi-peaks, which often results in tracking of a local maximum, not the expected global maximum. Demonstrated by experiment results, the proposed Deep Q-Network based solar GMPPT method indeed can track the global MPP faster and more precisely without oscillation.

Maximum power point tracking technique is often used in photovoltaic (PV) system to extract the maximum power at any environment condition. In this paper, a reinforcement learning based variable step size maximum power point tracking (RL MPPT) method is proposed. Q-learning is used as the algorithm of the proposed methods and is implemented by constructing the Q-table (RL-QT MPPT). A Q-network approach (RL-QN MPPT) is also proposed as a more general representation of the RL MPPT method. Implementing of the algorithm doesn't require the information of the actual PV module in advance, and the proposed system is able to track the MPP offline. With smaller ripples and faster tracking speed, the experiment results of the RL-QT MPPT method and the RL-QN MPPT method are presented.

In this study, numerical calculations using single- and two-phase models of CuO/water nanofluid forced convection in a three-dimensional C-shaped channel with constant heat flux are investigated. The laminar heat transfer enhancement using a nanofluid in a chaotic flow is first validated with the available data in the literature and the maximum discrepancy is within 3%; then further it is extended to design the C-shaped geometry. In addition, after comparisons of the numerical results with single- and two-phase models, the multiparameter constrained the optimization procedure integrating the design of experiments (DOE), response surface methodology (RSM), genetic algorithm (GA), and computational fluid dynamics (CFD) is proposed to design the nanofluid laminar convection of three-dimensional C-shaped channels. The thermal performance factors predicted by the regression function for the C-shaped channel case are in good agreement with the numerical results of CFD, with the difference being within 10%.

Through the femtosecond-time-resolved study of photoacoustic pulse generation in ultra-thin gold nanofilms, we observed a time delay of 0.5–0.7 ps in the formation of thermal-expansion pulses after photoexcitation. Our observation indicates that lattice anharmonicity dominates over hot electron pressure in the thermal expansion of Au nanofilms under ultrashort-pulsed photoexcitation.

We investigate the effects of surface tunneling on electrostatics and transport properties of two-dimensional electron gases (2DEGs) in undoped Si/SiGe heterostructures with different 2DEG depths. By varying the gate voltage, four stages of density-mobility dependence are identified with two density saturation regimes observed, which confirms that the system transitions between equilibrium and nonequilibrium. Mobility is enhanced with an increasing density at low biases and, counterintuitively, with a decreasing density at high biases as well. The density saturation and mobility enhancement can be semiquantitatively explained by a surface tunneling model in combination with a bilayer screening theory.

We investigate DC characteristics of a two-dimensional electron gas (2DEG) in an undoped Si/SiGe heterostructure and its temperature dependence. An insulated-gate field-effect transistor was fabricated, and transfer characteristics were measured at 4 K–300 K. At low temperatures (T 45 K, the current saturation and negative transconductance disappear and the device acts as a normal transistor.