Exploratory mean-variance portfolio selection with Choquet regularizers

In this paper, we study a continuous-time exploratory mean-variance (EMV) problem under the framework of reinforcement learning (RL), and the Choquet regularizers are used to measure the level of exploration. By applying the classical Bellman principle of optimality, the Hamilton-Jacobi-Bellman equation of the EMV problem is derived and solved explicitly via maximizing statically a mean-variance constrained Choquet regularizer. In particular, the optimal distributions form a location-scale family, whose shape depends on the choices of the Choquet regularizer. We further reformulate the continuous-time Choquet-regularized EMV problem using a variant of the Choquet regularizer. Several examples are given under specific Choquet regularizers that generate broadly used exploratory samplers such as exponential, uniform and Gaussian. Finally, we design a RL algorithm to simulate and compare results under the two different forms of regularizers

Effects of different hypertonic resuscitations on traumatic brain injuries and cranioencephalic trauma: A single centre, retrospective analysis

Purpose: To compare the efficacies of 3 % (w/v) hypertonic saline, 20 % (w/v) mannitol, and 10 % (w/v) mannitol plus 10 % (v/v) glycerol in the management of intracranial hypertension.Methods: Patients with intracranial pressure > 20 mmHg received 3 % (w/v) hypertonic saline (HT cohort, n = 78) or 20 % w/v mannitol (MT cohort, n = 82) or 10 % (w/v) mannitol plus 10 % (v/v) glycerol (MG cohort, n = 73) until intracranial pressure was reduced below 15 mmHg. Neurologic outcomes, hemodynamic parameters, and clinical biochemistry were evaluated as indices of intracranial pressure and pathological parameters.Results: Serum sodium levels and serum osmolarity were significantly increased by 3 % (w/ v) hypertonic saline, relative to the other hypertonic resuscitations. At the end of 1 h observation period, 60 (77 %), 36 (44 %), and 41 (56 %) of patients from HT, MT, and MG cohorts, respectively, had their cerebral perfusion pressure successfully maintained at > 70 mmHg. At the end of 1 h observation period, intracranial pressure ≤ 20 mmHg was successfully maintained in 78 (100 %), 81 (99 %), and 73 (100 %) patients from HT, MT, and MG cohorts, respectively. The mean values of arterial pressure of patients in HT, MT, and MG cohorts were increased after 1 h, 15 min, and 30 min of interventions, respectively.Conclusion: These results indicate that 3 % (w/v) hypertonic saline was the most rapid and most effective resuscitation for the management of intracranial hypertension in traumatic brain injuries or cranioencephalic trauma

Phase-change metasurfaces for dynamic image display and information encryption

Optical metasurfaces enable to engineer the electromagnetic space and control light propagation at an unprecedented level, offering a powerful tool to achieve modulation of light over multiple physical dimensions. Here, we demonstrate a Sb$_{2}$S$_{3}$ phase-change metasurface platform that allows active manipulation of both amplitude and phase. In particular, we implement dynamic nanoprinting and holographic image display through tuning crystallization levels of this phase-change material. The Sb$_{2}$S$_{3}$ nanobricks tailored to function the amplitude, geometric and propagation phase modulation constitute the dynamic meta-atoms in the multiplexed metasurfaces. Using the incident polarizations as decoding keys, the encoded information can be reproduced into a naonprinting grayscale image in the near field and two holographic images in the far field. These images can be switched on and off by taking advantages of the reversible tunability of Sb$_{2}$S$_{3}$ nanostructure between amorphous and crystalline states. The proposed phase-change metasurfaces featuring manifold information and multifold encryption promise ultracompact data storage with high capacity and high security, which suggests an exciting direction for modern cryptography and security applications

Energy Harvesting from Ultra-low-Frequency Vibrations Through a Quasi-zero Stiffness Electromagnetic Energy Harvester

Purpose: To scavenge vibrational energy from ultra-low frequency vibrations with low excitation levels, this paper presents a novel quasi-zero stiffness electromagnetic energy harvester (QZS-EMEH) by exploiting a rolling magnet system. Methods: By calculating the nonlinear restoring force exerted on the moving magnet, the parameter region that results in conditions of quasi-zero stiffness is determined, and a theoretical model of the QZS-EMEH is established. Based on the method of harmonic balance, the analytical solution of the QZS-EMEH is derived, and the influence of system parameters on the response characteristics and energy harvesting performance is discussed. Results: Numerical and theoretical results indicate that the QZS-EMEH can efficiently harness energy in a wide frequency range under low-level excitations. Furthermore, the nonlinear dynamics of the QZS-EMEH are investigated based on the bifurcation diagram, phase orbit, Poincaré map, and basin of attraction, demonstrating that appropriate initial conditions can lead to the high-energy orbit oscillation. Conclusions: Finally, realistic ambient vibration accelerations from a bus and a human body are applied to excite the QZS-EMEH, and the results illustrate that the QZS-EMEH can generate considerable electrical output power and has excellent application prospects.</p

Energy Harvesting from Ultra-low-Frequency Vibrations Through a Quasi-zero Stiffness Electromagnetic Energy Harvester

Purpose: To scavenge vibrational energy from ultra-low frequency vibrations with low excitation levels, this paper presents a novel quasi-zero stiffness electromagnetic energy harvester (QZS-EMEH) by exploiting a rolling magnet system. Methods: By calculating the nonlinear restoring force exerted on the moving magnet, the parameter region that results in conditions of quasi-zero stiffness is determined, and a theoretical model of the QZS-EMEH is established. Based on the method of harmonic balance, the analytical solution of the QZS-EMEH is derived, and the influence of system parameters on the response characteristics and energy harvesting performance is discussed. Results: Numerical and theoretical results indicate that the QZS-EMEH can efficiently harness energy in a wide frequency range under low-level excitations. Furthermore, the nonlinear dynamics of the QZS-EMEH are investigated based on the bifurcation diagram, phase orbit, Poincaré map, and basin of attraction, demonstrating that appropriate initial conditions can lead to the high-energy orbit oscillation. Conclusions: Finally, realistic ambient vibration accelerations from a bus and a human body are applied to excite the QZS-EMEH, and the results illustrate that the QZS-EMEH can generate considerable electrical output power and has excellent application prospects.</p

A New Processing Method Combined with BP Neural Network for Francis Turbine Synthetic Characteristic Curve Research

A BP (backpropagation) neural network method is employed to solve the problems existing in the synthetic characteristic curve processing of hydroturbine at present that most studies are only concerned with data in the high efficiency and large guide vane opening area, which can hardly meet the research requirements of transition process especially in large fluctuation situation. The principle of the proposed method is to convert the nonlinear characteristics of turbine to torque and flow characteristics, which can be used for real-time simulation directly based on neural network. Results show that obtained sample data can be extended successfully to cover working areas wider under different operation conditions. Another major contribution of this paper is the resampling technique proposed in the paper to overcome the limitation to sample period simulation. In addition, a detailed analysis for improvements of iteration convergence of the pressure loop is proposed, leading to a better iterative convergence during the head pressure calculation. Actual applications verify that methods proposed in this paper have better simulation results which are closer to the field and provide a new perspective for hydroturbine synthetic characteristic curve fitting and modeling