Design and Control of Upper Limb Rehabilitation Training Robot Based on a Magnetorheological Joint Damper.

In recent years, rehabilitation robots have been developed and used in rehabilitation training for patients with hemiplegia. In this paper, a rehabilitation training robot with variable damping is designed to train patients with hemiplegia to recover upper limb function. Firstly, a magnetorheological joint damper (MR joint damper) is designed for the rehabilitation training robot, and its structural design and dynamic model are tested theoretically and experimentally. Secondly, the rehabilitation robot is simplified into a spring-damping system, and the rehabilitation training controller for human movement is designed. The rehabilitation robot dynamically adjusts the excitation current according to the feedback speed and human-machine interaction torque, so that the rehabilitation robot always outputs a stable torque. The magnetorheological joint damper acts as a clutch to transmit torque safely and stably to the robot joint. Finally, the upper limb rehabilitation device is tested. The expected torque is set to 20 N, and the average value of the output expected torque during operation is 20.02 N, and the standard deviation is 0.635 N. The output torque has good stability. A fast (0.5 s) response can be achieved in response to a sudden motor speed change, and the average expected output torque is 20.38 N and the standard deviation is 0.645 N, which can still maintain the stability of the output torque.

Experimental Study on the Skyhook Control of a Magnetorheological Torsional Vibration Damper.

This study proposes a dual-coil magnetorheological torsional vibration damper (MRTVD) and verifies the effectiveness of semi-active damping control to suppress the shaft system's torsional vibration via experimental research. Firstly, the mechanical model of the designed MRTVD and its coupling mechanical model with the rotating shaft system are established. Secondly, the torsional response of the shaft system is obtained via resonance experiments, and the influence of the current on the torsional characteristics of the magnetorheological torsional damper is analyzed. Finally, the MRTVD is controlled using the skyhook control approach. The experimental results demonstrate that when the main shaft passes through the critical speed range at various accelerations, the amplitude of the shaft's torsional vibration decreases by more than 15%, and the amplitude of the shaft's torsional angular acceleration decreases by more than 22%. These conclusions validate the inhibitory effect of MRTVD on the main shaft's torsional vibrations under skyhook control.

Artificial SiNz:H Synapse Crossbar Arrays with Gradual Conductive Pathway for High-Accuracy Neuromorphic Computing.

Inspired by its highly efficient capability to deal with big data, the brain-like computational system has attracted a great amount of attention for its ability to outperform the von Neumann computation paradigm. As the core of the neuromorphic computing chip, an artificial synapse based on the memristor, with a high accuracy in processing images, is highly desired. We report, for the first time, that artificial synapse arrays with a high accuracy in image recognition can be obtained through the fabrication of a SiNz:H memristor with a gradient Si/N ratio. The training accuracy of SiNz:H synapse arrays for image learning can reach 93.65%. The temperature-dependent I-V characteristic reveals that the gradual Si dangling bond pathway makes the main contribution towards improving the linearity of the tunable conductance. The thinner diameter and fixed disconnection point in the gradual pathway are of benefit in enhancing the accuracy of visual identification. The artificial SiNz:H synapse arrays display stable and uniform biological functions, such as the short-term biosynaptic functions, including spike-duration-dependent plasticity, spike-number-dependent plasticity, and paired-pulse facilitation, as well as the long-term ones, such as long-term potentiation, long-term depression, and spike-time-dependent plasticity. The highly efficient visual learning capability of the artificial SiNz:H synapse with a gradual conductive pathway for neuromorphic systems hold great application potential in the age of artificial intelligence (AI).

Structural Design and Controllability of Magnetorheological Grease Buffers under Impact Loading.

Shock loads can pose a great threat to personnel or instruments, and efficient control of the buffering process is an effective means of reducing damage from shock energy. In this paper, magneto-rheological grease was used as the internal controllable material of the buffer to address the turbulence and settling problems of conventional magneto-rheological fluid. A bending and folding back magnetic circuit is proposed, and the magnetic circuit simulation was verified. The corresponding dynamic mechanical model was established, and the mechanical response characteristics of the buffer under impact load were also simulated dynamically. The mechanical properties of the designed and processed device were tested, and a variable current control method was used to improve the performance of the shock resistance of the buffer. The response of the magnetorheological grease buffer under different drop hammer impacts was investigated. The buffering effect and controllability of the buffer were analyzed by comparing the acceleration, velocity, and top-end cap displacement at the same drop hammer height for different current magnitudes. The results show that the buffer performance of the buffer gradually improved as the current increased. The response time of the designed new magnetorheological buffer was determined by the jump time of the peak damping force to be 9 ms. Lastly, the controllability was verified by manually and automatically adjusting the current magnitude, and the results were compared with those at 300 mm drop hammer height and 0.5 A current magnitude, and the continuous variable current control was found to be effective. This provides a feasible reference for scholars to study optimal buffer control.

Multi-Objective Optimization Design and Performance Comparison of Magnetorheological Torsional Vibration Absorbers of Different Configurations.

The purpose of this study is to provide a convenient optimization design method for magnetorheological torsional vibration absorbers (MR-TVA) suitable for automotive engines, which is a damper matching design method that takes into account the needs of the engine operating conditions. In this study, three kinds of MR-TVA with certain characteristics and applicability are proposed: axial single-coil configuration, axial multi-coil configuration and circumferential configuration. The magnetic circuit model, damping torque model and response time model of MR-TVA are established. Then, under the constraints of weight, size and inertia ratio, according to different torsional vibration conditions, the MR-TVA mass, damping torque and response time are multi-objective optimized in two directions. The optimal configurations of the three configurations are obtained from the intersection of the two optimal solutions, and the performance of the optimized MR-TVA is compared and analyzed. The results show that the axial multi-coil structure has large damping torque and the shortest response time (140 ms), which is suitable for complex working conditions. The damping torque of the axial single coil structure is generally large (207.05 N.m), which is suitable for heavy load conditions. The circumferential structure has a minimum mass (11.03 kg) and is suitable for light load conditions.

Controlling the Carrier Injection Efficiency in 3D Nanocrystalline Silicon Floating Gate Memory by Novel Design of Control Layer.

Three-dimensional NAND flash memory with high carrier injection efficiency has been of great interest to computing in memory for its stronger capability to deal with big data than that of conventional von Neumann architecture. Here, we first report the carrier injection efficiency of 3D NAND flash memory based on a nanocrystalline silicon floating gate, which can be controlled by a novel design of the control layer. The carrier injection efficiency in nanocrystalline Si can be monitored by the capacitance-voltage (C-V) hysteresis direction of an nc-Si floating-gate MOS structure. When the control layer thickness of the nanocrystalline silicon floating gate is 25 nm, the C-V hysteresis always maintains the counterclockwise direction under different step sizes of scanning bias. In contrast, the direction of the C-V hysteresis can be changed from counterclockwise to clockwise when the thickness of the control barrier is reduced to 22 nm. The clockwise direction of the C-V curve is due to the carrier injection from the top electrode into the defect state of the SiNx control layer. Our discovery illustrates that the thicker SiNx control layer can block the transfer of carriers from the top electrode to the SiNx, thereby improving the carrier injection efficiency from the Si substrate to the nc-Si layer. The relationship between the carrier injection and the C-V hysteresis direction is further revealed by using the energy band model, thus explaining the transition mechanism of the C-V hysteresis direction. Our report is conducive to optimizing the performance of 3D NAND flash memory based on an nc-Si floating gate, which will be better used in the field of in-memory computing.

Artificial HfO2/TiOx Synapses with Controllable Memory Window and High Uniformity for Brain-Inspired Computing.

Artificial neural networks, as a game-changer to break up the bottleneck of classical von Neumann architectures, have attracted great interest recently. As a unit of artificial neural networks, memristive devices play a key role due to their similarity to biological synapses in structure, dynamics, and electrical behaviors. To achieve highly accurate neuromorphic computing, memristive devices with a controllable memory window and high uniformity are vitally important. Here, we first report that the controllable memory window of an HfO2/TiOx memristive device can be obtained by tuning the thickness ratio of the sublayer. It was found the memory window increased with decreases in the thickness ratio of HfO2 and TiOx. Notably, the coefficients of variation of the high-resistance state and the low-resistance state of the nanocrystalline HfO2/TiOx memristor were reduced by 74% and 86% compared with the as-deposited HfO2/TiOx memristor. The position of the conductive pathway could be localized by the nanocrystalline HfO2 and TiO2 dot, leading to a substantial improvement in the switching uniformity. The nanocrystalline HfO2/TiOx memristive device showed stable, controllable biological functions, including long-term potentiation, long-term depression, and spike-time-dependent plasticity, as well as the visual learning capability, displaying the great potential application for neuromorphic computing in brain-inspired intelligent systems.

Design and Feasibility Study of MRG-Based Variable Stiffness Soft Robot.

The conventional pneumatic soft robot has the problem of insufficient stiffness, while in the magnetorheological soft robot, the magnetic field provided by electromagnet has the disadvantage of oversized structure and poor flexibility. This paper presents a variable stiffness pneumatic soft robot based on magnetorheological grease (MRG) to solve these problems. Its three soft fingers cooperate with the adjustable gripper to adjust the gripping range for the robot hand, and it is used to provide gripping driving force through the bending drive. The MRG layer is designed on the gripping surface to provide adaptivity and rigid support for the gripped objects. A magnetic-air structure consisting of a Halbach array and Halbach array actuator is designed inside the soft fingers to provide a flexible magnetic field for the MRG layer. Theoretical and simulation analysis is carried out, and the results show that the state of the MRG changes and the stiffness of the clamping surface changes under the working pressure of 30 kPa. Finally, the experiment further proves the variable and high adaptivity of the surface stiffness of the gripping surface to reduce the damage to the gripped objects.

Artificial Synapse Consisted of TiSbTe/SiCx:H Memristor with Ultra-high Uniformity for Neuromorphic Computing.

To enable a-SiCx:H-based memristors to be integrated into brain-inspired chips, and to efficiently deal with the massive and diverse data, high switching uniformity of the a-SiC0.11:H memristor is urgently needed. In this study, we introduced a TiSbTe layer into an a-SiC0.11:H memristor, and successfully observed the ultra-high uniformity of the TiSbTe/a-SiC0.11:H memristor device. Compared with the a-SiC0.11:H memristor, the cycle-to-cycle coefficient of variation in the high resistance state and the low resistance state of TiSbTe/a-SiC0.11:H memristors was reduced by 92.5% and 66.4%, respectively. Moreover, the device-to-device coefficient of variation in the high resistance state and the low resistance state of TiSbTe/a-SiC0.11:H memristors decreased by 93.6% and 86.3%, respectively. A high-resolution transmission electron microscope revealed that a permanent TiSbTe nanocrystalline conductive nanofilament was formed in the TiSbTe layer during the DC sweeping process. The localized electric field of the TiSbTe nanocrystalline was beneficial for confining the position of the conductive filaments in the a-SiC0.11:H film, which contributed to improving the uniformity of the device. The temperature-dependent I-V characteristic further confirmed that the bridge and rupture of the Si dangling bond nanopathway was responsible for the resistive switching of the TiSbTe/a-SiC0.11:H device. The ultra-high uniformity of the TiSbTe/a-SiC0.11:H device ensured the successful implementation of biosynaptic functions such as spike-duration-dependent plasticity, long-term potentiation, long-term depression, and spike-timing-dependent plasticity. Furthermore, visual learning capability could be simulated through changing the conductance of the TiSbTe/a-SiC0.11:H device. Our discovery of the ultra-high uniformity of TiSbTe/a-SiC0.11:H memristor devices provides an avenue for their integration into the next generation of AI chips.

Overexpression and correlation of HIF-2α, VEGFA and EphA2 in residual hepatocellular carcinoma following high-intensity focused ultrasound treatment: Implications for tumor recurrence and progression.

Rapid growth of residual tumors can occur as a result of their recurrence and progression. The present study aimed to investigate the expression of hypoxia inducible factor-2 subunit α (HIF-2α), vascular endothelial growth factor A (VEGFA), erythropoietin-producing hepatocellular A2 (EphA2) and angiogenesis in residual hepatocellular carcinoma (HCC), following treatment with high-intensity focused ultrasound (HIFU) ablation, in order to investigate the association between protein expression and tumor recurrence and growth. Athymic BALB/c (nu/nu) mice were subcutaneously inoculated with the HCC cell line HepG2, in order to create xenograft tumors. Approximately 30 days post-inoculation, eight mice were treated with HIFU, whereas eight mice received no treatment and acted as the control group. Residual tumor tissues were obtained from the experimental groups after one month. Levels of HIF-2α, VEGFA, EphA2 and cluster of differentiation 31 (CD31) expression was measured by immunohistochemical staining. CD31-positive vascular endothelial cells were counted to calculate microvascular density (MVD), and western blot analysis was performed to determine levels of HIF-2α, VEGFA, and EphA2 protein. It was found that the expression levels of HIF-2α, VEGFA, EphA2, and MVD proteins in residual HCC tissues were significantly higher than in the control group tissues (P<0.05). Tumor MVD was strongly correlated with VEGFA (R=0.957, P<0.01) and EphA2 (R=0.993, P<0.01) protein expression levels. Furthermore, there was a significant positive correlation between HIF-2α and EphA2 expression (R=0.991, P<0.01). The correlation between VEGFA and EphA2 expression was also positive (R=0.985, P<0.01). These data suggest that overexpression of HIF-2α, VEGFA and EphA2 is related to angiogenesis in residual HCC following HIFU ablation, potentially via their association with key mediators of recurrence.

Expression of Oct4 in HCC and modulation to wnt/ß-catenin and TGF-ß signal pathways.

Hepatocellular carcinoma (HCC) is considered as a disease of dysfunction of the stem cells. Studies on stem cells have demonstrated that Oct4 plays a pivotal role in embryo regulation. In order to understand the role of Oct4 in HCC and the relationship among Oct4 and wnt/ß-catenin and TGF-ß signal pathways, we have detected the expression of Oct4, Nanog, Sox2, STAT3 as well as the genes in wnt/ß-catenin, and TGF-ß families in HCC cell lines and in tumor specimens from HCC patients. The authors found that Oct4 was expressed in all of the four HCC cell lines and the tumor specimens from HCC patients. Some other genes were also expressed in them with different level including Nanog, Sox2, STAT3 and TCF3, wnt10b, ß-catenin, ELF, Smad3 and Smad4. The ability of the clone formation and migration of the HepG2 decreased after Oct4 was knockdowned. Silencing of Oct4 and TCF3 in HCC cell line HepG2 revealed that there were complicated relationships among Oct4, wnt/ß-catenin family and TGF-ß family genes. Knockdowning Oct4 reduced the expression of TGF-ß family genes ELF, Smad3, Smad4 and wnt/ß-catenin family genes, wnt10b, and ß-catenin but increased TCF3. In reverse, knockdowning TCF3 led to the increased expression of Oct4 and TGF-ß family genes. In conclusion, the expression of Oct4 in HCC may play an important role as in stem cell. Because Oct4 improves not only the function of wnt/ß-catenin, but also the TGF-ß signal pathways, the significance of its expression in HCC might be more complicated than we evinced before.