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Since optimal portfolio strategy depends heavily on the distribution of uncertain returns, this article proposes a new method for the portfolio optimization problem with respect to distribution uncertainty. When the distributional information of the uncertain return rate is only observable through a finite sample dataset, we model the portfolio selection problem with a robust optimization method from the data-driven perspective. We first develop an ambiguous mean-CVaR portfolio optimization model, where the ambiguous distribution set employed in the distributionally robust model is a Wasserstein ball centered within the empirical distribution. In addition, the computationally tractable equivalent model of the worst-case expectation under the uncertainty set of a cone is derived, and some theoretical conclusions of the box, budget and ellipsoid uncertainty set are obtained. Finally, to demonstrate the effectiveness of our mean-CVaR portfolio optimization method, two practical examples concerning the Chinese stock market and United States stock market are considered. Furthermore, some numerical experiments are carried out under different uncertainty sets. The proposed data-driven distributionally robust portfolio optimization method offers some advantages over the ambiguity-free stochastic optimization method. The numerical experiments illustrate that the new method is effective.

We propose and design a hollow As2S3 ring-core photonic crystal fiber (PCF) with 514 radially fundamental orbital angular momentum (OAM) modes over 360 nm communications bandwidth across all the O, E, S, C, and L bands. The designed PCF with 40 $\mu \text{m}$ -radius air core and 150 nm-width As2S3 ring can support eigenmodes up to HE130,1 and EH128,1. The numerical analysis shows that the designed ring PCF has large effective refractive index contrast, and can transmit up to 874 OAM modes near 1.55 $\mu \text{m}$ . Simulation results show that in the C and L bands, the PCF with a hollow-core radius of 40 $\mu \text{m}$ and a ring width of 0.15 $\mu \text{m}$ can retain an $2.5\times 10 ^{-3}$ effective refractive index difference between the two highest order OAM modes, which achieves effective mode separation, thereby achieving stable OAM mode transmission. The $n_{eff}$ difference between the even and odd fiber eigenmodes and the intra-mode walk-off are also carefully studied under different bending radii. The results show that higher-order OAM modes has better tolerance to the fiber bending, compared with the lower-order modes. The fiber has the potential to support ultra-high capacity OAM mode division multiplexing in the optical fiber communication systems.

Determining the land surface temperature (LST) variations in urban surfaces using high spatiotemporal resolution thermal infrared data is necessary for urban microthermal environmental modeling. An unmanned aerial vehicle (UAV) equipped with a thermal infrared imager was used to monitor the high-precision spatiotemporal variation of LSTs for six typical urban surfaces, including water, tree canopy, grass, brick pavement, asphalt pavement, and marble pavement, in the Jiangning district, Nanjing. An estimation of sensible heat release was further conducted to quantitatively describe the fine characteristics of the LSTs of these surfaces. The factors influencing LST were investigated by correlating LSTs with the meteorological factors. The results showed that there were significant differences in LSTs and sensible heat release for six typical urban surfaces in sunny and cloudy days, respectively. On sunny days, the diurnal variations in different surfaces fluctuated substantially, which was not evident on cloudy days. The artificial surfaces always represented as the main source of sensible heat release. Solar radiation and air temperature, among the meteorological factors, were positively correlated with the LSTs of the surfaces. The air humidity was negatively correlated with the LSTs and played a role in cooling the land surface.

Random numbers play a vital role in communications and cryptography. However, most existing true random number generators have difficulty in satisfying the requirements of high-speed communications due to their complexity and bulkiness, or low speed limitations due to equipment bandwidth. Then, the all-electron true random number generator was presented based on GaAs/Al0.45Ga0.55As superlattices conducted under direct current bias at room temperature, which not only possesses the characteristics of miniaturization but also generates random numbers at rates up to the Gbit/s. However, the bit rate of random number generators based on superlattices is still much slower compared to chaotic laser random number generators. In order to generate higher-rate random numbers, we modified a DC-excited superlattice and then redirected the signal generated by the superlattice back into itself, thus introducing a self-feedback, and achieved a self-feedback superlattice true random number generator. This improvement makes the superlattice have a more detailed signal shape, a more effective signal amplitude, and with lower power consumption. Therefore, these advances made the self-feedback superlattice more suitable for generating random numbers. Moreover, we propose a new post-processing method, called the adjacent bits reversal exclusive-or. This method can reduce the sequence bias and correlation without discarding any random bit. The random number obtained by the self-feedback superlattice at a sampling rate of 10 GS/s passed the triple standard deviation test and the random number standard test (NIST SP 800-22), indicating that it possessed good statistical properties as a miniaturized random number generator.

At present, there are two main problems with fruit-and vegetable-picking robots. One is that complex scenes (with backlighting, direct sunlight, overlapping fruit and branches, blocking leaves, etc.) obviously interfere with the detection of fruits and vegetables; the other is that an embedded platform needs a lighter detection method due to performance constraints. To address these problems, a fast tomato detection method based on improved YOLOv3-tiny is proposed. First, we improve the precision of the model by improving the backbone network; second, we use image enhancement to improve the detection ability of the algorithm in complex scenes. Finally, we design several groups of comparative experiments to prove the rationality and feasibility of this method. The experimental results show that the f1-score of the tomato recognition model proposed in this paper is 91.92%, which is 12% higher than that of YOLOv3-tiny; the detection speed on a CPU can reach 25 frames/s, and the inferential speed is 40.35 ms, equivalent to that of YOLOv3-tiny. Through comparative experiments, we can see that the comprehensive performance of our method is better than that of other state-of-the-art methods.

In this work, an air-core ring fiber is designed with a record high 1322 orbital angular momentum (OAM) modes at 1550 nm while maintaining radially single-mode condition. Moreover, it can support over 1004 OAM modes across all O, E, S, C, and L bands, exploiting to our knowledge the highest number of OAM modes ever supported in the optical fiber within a wide wavelength range. Simulations show that, across the C and L bands, the fiber with 55-μm air-core radius and 0.45-μm ring width can preserve 3.3 × 10-3 effective refraction index difference between the two highest-order OAM modes HE340,1 and EH271,1. This enables efficient mode separation, and thus achieving stable OAM modes transmission. The effective refractive index differences between the even and odd fiber eigenmodes are also analyzed in the elliptical and bent fibers. We note that higher-order OAM modes are more tolerant to the fiber ellipticity and bending. This ring fiber design has the potential to increase the spectral efficiency and the overall capacity in fiber-based communications system.

This paper proposes a new phase-modular three-phase single-stage rectifier based on the LLC resonant converter. The proposed rectifier provides power factor correction, output voltage regulation, and electrical isolation in a single-stage modular-designed approach. The proposed rectifier has minimal switching loss due to the ZVS and ZCS operations of all the switches and diodes. Moreover, the proposed AC-DC converter does not use any bulky passive components and hence is suitable for high power density applications that also require high power conversion efficiency. Design notes and specifications of a single module are provided in this paper. Computer simulation results verified the unity PFC performance and output voltage regulation using a small output capacitance without any low-frequency ripple. Furthermore, the feasibility of the proposed rectifier is validated by the experimental results of a digitally implemented GaN-based laboratory prototype.

The Linear Extended State Observer (LESO) with model mismatch for Linear Active Disturbance Rejection Control (LADRC) is investigated in this paper, which is different from the existed results that only consider the unknown disturbances. Not only the uncertain disturbances in system are considered, but the model mismatch between the observer and the actual system is also considered. In Bounded-Input Bounded-Output stability scheme, the observer is analyzed in the time domain, and the observer error under a certain degree model mismatch is given. It is proved that for LESO, the observer error caused by the model mismatch is bounded and related to the bandwidth (w 0 ), and the error caused by model mismatch can be decreased by increasing bandwidth of the observer.

The noise of contra-rotating propellers contributes a major part to the underwater vehicle. The special noise properties often become an important basis for detecting and identifying targets. This paper establishes the numerical simulation and calculation approach on the radiated noise properties of contra-rotating propellers, which was set up based on the theory of acoustic analogy and the large eddy simulation approach, and then the numerical simulation results are verified. Taking the DTMB contra-rotating propellers which consist of DTMB3689 and DTMB3849 as an example, the numerical calculation of the hydrodynamic performance of the contra-rotating propellers is carried out based on the solving method of Reynolds stress turbulence model and the results agree well with the experimental results. The disk velocity distribution, blade pressure distribution and hydrodynamic wake distribution of the contra-rotating propellers are analyzed. Analyzing the acoustic signature of contra-rotating propellers shows that the low frequency line spectrum not only reflects the multiplicative frequency feature, but also the additive frequency feature, and the relationship between the radiated noise of the contra-rotating propellers and its inherent structure and its motion state is correlated.

The switched-capacitor converter (SCC) topology has been gaining attention in recent years because of their advantages of higher power density, switch utilization, and reduced component stress compared to existing converter topologies. However, SCCs have a major drawback in which capacitor charge redistribution results in significant current spikes. One method of addressing charge redistribution is split-phase operation, which accomplishes this by imposing voltage control on the SCC’s flying capacitors. However, an important design consideration was identified regarding the implementation of the split-phase Dickson SCC in high-current applications. Mismatched flying capacitors exhibit uneven charge rates, resulting in incomplete elimination of charge redistribution by split-phase control. This paper presents a discussion of the effects of mismatched flying capacitors on the operation of the split-phase Dickson SCC. Furthermore, design processes and test results of a prototype high-current split-phase Dickson SCC will be presented.

This study attempts to investigate the crucial factors affecting the warpage behavior of flip chip package on package (fcPoP) during fabrication. To characterize the process-induced warpage, a process-dependent simulation methodology that integrates ANSYS element death/birth technique and finite element analysis (FEA) is introduced. For modeling simplicity, the core and coreless substrates are transformed into an equivalent homogenized material, and their effective thermal-mechanical properties are determined using a proposed effective model based on FEA and trace mapping feature in ANSYS. The predicted effective mechanical properties are compared with those obtained by the rule-of-mixture analytical model and also the detailed FEA as a benchmark. Besides, the predicted process- induced warpages during the fabrication process are validated against experimental data.

In order to design a programmable multipath waveform generator, VHDL is used to design every module. It is consisted with the waveform input, FPGA module, digital-to-analog conversion (D/A) module, display circuit. By pressing the keys, eight waves can be chosen and shown in the oscilloscope. With the characteristics of low cost, portable and expandable, it can be widely used in electronic circuit system.

Convolutional Neural Networks (CNNs) achieve excellent in traffic sign detection and recognition with sufficient annotated training data. The quality of the whole vision system based on neural networks depend on the dataset. However, it is complicated to find traffic sign datasets from most of the countries of the world. In this context, Deep Convolutional Generative Adversarial Networks (DCGAN) can synthesize realistic and diverse additional training images to fill the data lack in the real image distribution. This paper mainly discusses how is the quality of the pictures generated by the DCGAN with various parameters. We use an image with a different number and size for training. Further, the Structural Similarity Index (SSIM) and MSE were used to evaluate the quality of the image. Our work measured SSIM values between generated images and corresponding real images. The generated images show high similarity with the actual image while using more images for training. The highest SSIM values reached when using 200 total images as input and images size 32×32.

A new method for solving volume-surface integral equation is proposed. The four sub-blocks of the impedance matrix are compressed in a form of hierarchical semi-separable (HSS) structure by randomized low-rank decompositions. To accelerate the convergence of the iterative solution, an HSS-based preconditioner is also proposed. Numerical experiments are conducted on an on-chip power grid model to study the performance of the method. This method can be further extended to the multilevel fast multipole algorithm for solving large-scale problems.

In this paper, a hardware-oriented lossless EEG compression algorithm including a two-stage prediction, voting prediction and tri-entropy coding is proposed. In two stages prediction, 27 conditions and 6 functions are used to decide how to predict the current data from previous data. Then, voting prediction finds optimal function according to 27 conditions for best function to produce best Error (the difference of predicted data and current data). Moreover, a tri-entropy coding technique is developed based on normal distribution. The two-stage Huffman coding and Golomb-Rice coding was used to generate the binary code of Error value. In CHB-MIT Scalp EEG Database, the novel EEG compression algorithm achieves average compression rate to 2.37. The proposed hardware-oriented algorithm is suitable for VLSI implementation due to its low complexity.

In this paper, the problem of adaptive neural networks (NNs) control for a class of uncertain flexible manipulator systems with variable loads and state constraints is discussed. The system is expressed by partial differential equation (PDE) model. The barrier Lyapunov function (BLF) is selected in the design process to ensure that the states of the system do not violate the constraints. The uncertainties caused by the unknow hub inertia of the system and varying payload are also considered, then a vibration inhibition control method on the basis of NNs is proposed in the framework of adaptive backstepping control design, which ensure that the control input forces $\varphi(t)$ and $U(t)$ satisfy the corresponding constraint condition, the closed-loop system is stable. Finally, the simulation results verify the effectiveness of the control strategy.

Current sharing in multiphase resonant converters is a serious concern as any small tolerance in the resonant tank components of different phases can lead to a large imbalance in the voltage gain and hence the load current imbalance. An interleaved LCLC resonant converter with four resonant components for wide input voltage range applications is studied in this paper. Because of the sharp voltage gain curve of the LCLC resonant converter, traditional current balancing approaches are not so successful. In this topology, the resonant tank impedances of each phase are tuned by a Switch-Controlled Capacitor (SCC) that is implemented in the resonant tank in both phases resulting in precise load current balancing among paralleled phases. The effect of different imbalance conditions on the interleaved LCLC resonant converter is studied, a minimum operating angle for the SCC circuit is identified and a control strategy is proposed for a reliable current sharing. The performance of the interleaved LCLC converter is validated by both computer simulation and experimental results of a two-phase 1kW prototype with 250V-400V input voltage. Further, a flat high-efficiency profile is achieved with different input voltage conditions over a wide load range.

Advancements in datacenter power architecture has led to 48V to 12V intermediate bus converters becoming a resurgent area of research interested. The 48 volt server architecture, proposed by companies such as Google, can offer significant benefits. This higher voltage reduces the distribution losses by 4x as compared with a 12V distribution, as well ad reducing the power conversion losses at the building level. However, increasing this server rack voltage to 48 volts presents a challenge when converting down to point of load voltages using conventional topologies. The Zero Inductor-Voltage converter that can achieve up to 2.5kW/in3 power density for 70A/12V output. The full load efficiency was measured to be 97.2% with a peak efficiency of 99.1%. This represents the highest efficiency and power density yet demonstrated. The design of the converter is also relatively straightforward as there is no need for active current sharing control, and the converter does not utilize resonant components.

The conduction loss becomes extremely large if applied LLC converter in high power electrical vehicle (EV) applications. Interleaving technique can help reduce the conduction loss and expand load capacity for LLC converter. However, component tolerance on resonant tanks causes load sharing problem, leading to severe performance degrading. To solve the problem, Switch-controlled Capacitor (SCC) circuit is added into resonant tanks to offset the component tolerance through reducing equivalent resonant capacitance. The load sharing characteristic of a three-phase LLC converter with and without SCC circuit is analyzed. The proposed control strategy reduces the SCC MOSFET voltage stress. Thus, lower voltage rating MOSFET which usually features of lower turn-on resistance can be used. Phase shedding technique is also performed to improve the light load efficiency. A prototype of a 250V – 430V input, 14V/260A output three-phase SCC-LLC prototype has been built and tested. Experimental results demonstrate the effectiveness of the SCC circuit and the proposed control strategy. Good current sharing performance among three phases is obtained. In addition, a peak efficiency of 96.7% and a full load efficiency of 95.8% are achieved at 380V input.

This paper presents a high power density LLC converter for Electric Vehicles (EVs) on-board low voltage DC-DC converter. The design specification imposes critical challenges on size and efficiency due to extremely high load current rating and wide input/output voltage range. The proposed design enables high switching frequency by using wide-band-gap (WBG) devices to significantly reduce the size of magnetic components and meet the power density requirement. A two-transformer configuration with series connected primary windings and parallel connected secondary windings is used to reduce the heavy I2R loss on the output side. The structures of parallel resonant inductor and transformers are carefully designed to reduce the fringing loss and AC conduction loss. A single phase 1.3kW LLC prototype with water cooling was built and experiment results verified the design considerations. The prototype achieved 3kW/L of power density and 97% peak efficiency. Full input voltage range from 250V to 430V and output voltage from 9V to 16V operation was verified with 96.5% efficiency achieved at nominal input and full load.

A single stage 1.65kW AC-DC LLC converter with Power Factor Correction (PFC) for OBC application is proposed. A boost inductor is not required since the LLC converter serves as both the AC-DC and DC-DC stage which provides all the functions of rectification, PFC, output voltage regulation and galvanic isolation. A design methodology is proposed in this paper to maintain the output voltage regulation and PFC over the entire AC input voltage range from zero to peak voltage. Benefiting from the true-single-stage structure, the quantity of active switches and magnetic components is reduced. Therefore, high power density and high efficiency can be achieved with an overall reduction in the number of components. An experimental prototype is designed based on the LLC PFC design methodology. Stable DC output voltage regulation is implemented with over 99% Power Factor. Experimental testing is conducted which achieves over 2.9kW/L power density and 96.9% overall efficiency.

The demand for internet and computing resources has led to datacenters and servers being one of the fastest growing consumers of power in the world today. While datacenter power architectures have improved over time, the majority of the loss still occurs at the server power supply, and board level voltage regulators. To attempt to improve this, Google has proposed and implemented a 48 volt server architecture that can significantly reduce both the upstream conversion losses, and the distribution losses within the server racks. To fully realize these benefits new technology is needed to convert 48 volts down to the point of load voltage levels. In this paper a regulation technique for the zero inductor-voltage converter is proposed. This modified control scheme allowed the ZIV converter topology to provide a regulated 12V output from 48/60V input range without sacrificing many of the key advantages that allow the ZIV converter to achieve the highest demonstrated power density and efficiency for intermediate bus converter technologies.

In order to study the properties of radiation noise of single-propeller and contra-rotating propellers, the numerical simulation and computing was accomplished by using RNG turbulence model, LES turbulence model, FW-H acoustic analog equation and dynamic grid model. The open water performance of single propeller and contra-rotating propellers is calculated respectively, and the calculated results are in good agreement with the published results. Then the flow field properties of single propeller and contralateral propeller are compared and analyzed, on this basis, acoustic signature analysis and computing on properties of radiation noise from underwater single-propeller and contra-rotating propellers was accomplished, the properties of pulsating sound pressure at the monitoring point are solved. From the computing results, it can be seen that there are line spectral components related to front and rear blade frequency in the noise power spectrum, the low frequency line spectrum of contra-rotating propellers is more abundant than that of single propeller.

It is desirable to connect several LLC converters in parallel in high-power and/or high-current applications. However, component tolerance among resonant tank of different phases causes severe unbalanced load sharing, leading to performance degrading. In this paper, full-wave Switch-Controlled Capacitor (SCC) is added into resonant tank to compensate component tolerance and to achieve load sharing. An adaptive hysteresis comparison control scheme is proposed to adjust SCC angle α for current sharing. The proposed control strategy only occupies few digital controller resources; thus, low-cost Micro-Controller Unit (MCU) can be used. Experimental results of a 250V - 430V input, 14V/260A/3.6kW output, three-phase interleaved SCC-LLC EV DC-DC converter demonstrate the effectiveness and feasibility of the proposed method.

The demand for internet and computing resources has led to datacenters and servers being one of the fastest growing consumers of power in the world today. While datacenter power architectures have improved over time, the majority of the loss still occurs at the server power supply, and board level voltage regulators. To attempt to improve this, Google has proposed and implemented a 48 volt server architecture that can significantly reduce both the upstream conversion losses, and the distribution losses within the server racks. Google has estimated that this change can reduce their overall conversion losses by up to 30%, but to fully realize these benefits new technology is needed to convert 48 volts down to the point of load voltage levels. The Intermediate Bus Architecture, where a "bus converter" steps down the 48 volts to a lower bus voltage which is then stepped down by point-of-load regulators is a very attractive option to "bridge the gap" between the 48 volt architecture of cutting edge servers, and the existing 12 volt architecture. The proposed topology is a novel intermediate bus converter that can achieve up to 2500W/in3 power density, 99.1% peak efficiency, and 97.2% full load efficiency for 70A 12V output. Compared with other cutting edge designs this work achieves higher efficiency, and superior power density without the need for complex control, or a sensitive resonant based design.

In this paper, an interleaved LCLC converter with TO-220 enhancement mode GaN devices (e-mode GaN) and accurate current sharing performance is introduced for data center application. Any tolerance in the resonant tank elements can lead to large load imbalance between different phases. Due to the steep gain curve of LCLC converter, conventional current sharing methods are not so effective. In the proposed converter the impedances of the resonant networks are matched by switching a capacitor (i.e. Switch Controlled Capacitor SCC) in series with the resonant capacitor in one or some of the phases, which results in accurate load current sharing between phases (i.e. around 0.025% difference). The load share of each phase is sensed through the resonant current on each phase and the control logic is applied so current sharing between all phases can be achieved. By this method, an accurate current sharing is achieved for a wide input voltage range that is required for hold up time in data center application. Moreover, interleaving is applied in the proposed multi-phase LCLC converter resulting in low stress on the output capacitor allowing sole ceramic capacitor implementation. Moreover, phase shedding allows a flat high conversion efficiency curve for a wide load range. The performance of the proposed interleaved LCLC converter is verified by a two-phase 1 kW prototype with 250 V - 400 V input voltage and fixed 12 V output voltage.

This paper proposes a Chinese medical question answering system based on CNN s with self-attention embedded model. The key idea of the proposed framework is first understanding whole sentences via LSTM, obtaining the feature map by the convolution layer of CNN, then further-comprehending of question and answer by self-attention and finally pass through to polling layer of CNN to enhance accuracy. In addition, due to the word segmentation issue in the Chinese especially in medical field, character embedding is applied to enhance the accuracy. The experimental results show that the proposed framework improves the accuracy around 80%.

Blue phase liquid crystal films are quite useful in reflective displays, flexible photonic devices, and optical sensors. However, the effects of refractive index properties of refilled liquid crystals and environment temperature on reflection properties of blue phase liquid crystal films are far from fully exploration. Herein, we demonstrate blue phase liquid crystal films refilled with different nematic liquid crystals. The effects of birefringence and average refractive index of refilled nematic liquid crystals on the reflection properties such as reflectance, central wavelength, and linewidth of photonic band have been studies. The temperature effect on reflectance and central wavelength has been studied. A narrow linewidth (19.4 nm) and temperature insensitivity blue phase liquid crystal film has been fabricated by refilling liquid crystals of DYX8013 with small birefringence. The narrow linewidth and excellent temperature insensitivity properties of BPLC film can be applied in color reflective display and flexible photonic devices.