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Aiming to circumvent the severe large-scale fading and the energy scarcity dilemma in high-altitude platform (HAP) networks, this paper investigates the benefits of the reconfigurable intelligent surface (RIS) and simultaneous wireless information and power transfer (SWIPT) on HAP communications. Specifically, we propose a concept of multi-layer refracting RIS-assisted receiver to achieve concurrent transmission of the information and energy, which is conducive to overcoming the severe fading effect induced by extreme long-distance HAP links and fully exploits RIS’s degrees-of-freedom (DoFs) for the SWIPT design. Based on the RIS-enhanced receiver, we then formulate a worst-case sum-rate maximization problem by considering the channel state information (CSI) error, the information rate requirements, and the energy harvesting constraint. To handle the intractable non-convex problem, a scalable robust optimization framework is proposed to obtain semi-closed-form solutions. Specifically, a discretization method is adopted to convert the imperfect CSI into a robust one. Then, by utilizing the LogSumExp inequality to smooth the objective and constraints, we develop a dual method to obtain the optimal solution for the HAP transmit precoder. In addition, a modified cyclic coordinate descent (M-CCD) is adopted to update the block-wise RIS coefficients. Moreover, closed-form solutions for power splitting (PS) ratios and the receive decoder are derived. Finally, the asymptotic performance of our proposed RIS-enhanced receiver is provided to reveal the substantial capacity gain for HAP communications. Numerical simulations demonstrate that the proposed architecture and optimization framework are capable of achieving superior performance with low complexity compared to state-of-the-art schemes in HAP networks.

Integrating sparse code multiple access (SCMA) and mobile edge computing (MEC) into the Internet of Things (IoT) networks can enable efficient connectivity and timely computation for resource-limited IoT users. This paper studies the computation rate maximization problem under task deadline constraints in dynamic SCMA-MEC networks. Specifically, we propose a predictive deep Q-network for SCMA resource allocation and computation offloading (PQ-RACO) algorithm for single-cell scenarios, where IoT devices use long short-term memory (LSTM) networks to predict the states and actions of other agents. However, the PQ-RACO algorithm is not scalable for increasing numbers of IoT devices. To address this issue, an improved multi-agent deep Q-network for SCMA resource allocation and computation offloading algorithm (MQ-RACO) is proposed for multi-cell scenarios. The algorithm is a centralized training and decentralized execution (CTDE) multi-agent reinforcement learning (MARL) algorithm with explicit rewards, which is tailored to the special structure of joint rewards. Simulation results demonstrate that the proposed algorithm outperforms several state-of-the-art MARL algorithms and other benchmark schemes in terms of convergence speed and computation rate.

• Voronoi-based trabecular-like scaffolds (VBTSs) were successfully fabricated by Electron-beam melting (EBM). • VBTSs favored bone regeneration more than cubic scaffolds. • For VBTSs, an average pore size of 596 μm was most favorable for bone regeneration. The Voronoi-tessellation method is a promising technique for porous implant design as it mimics the irregular structure of bone trabeculae very well. However, the optimal pore size distribution of Voronoi-based trabecular-like scaffolds (VBTSs) remains unknown. In this study, three VBTSs with different pore size distributions were fabricated by Electron-beam melting (EBM), with a regular cubic scaffold as a control. Compression experiments showed that the elastic modulus of all the fabricated scaffolds was within the range of human bone. The biocompatibility of the porous scaffolds was evaluated by Cell Counting Kit-8, live/dead staining, phalloidin staining, and scanning electron microscope. The effects of scaffolds on osteogenic differentiation were evaluated by alkaline phosphatase (ALP) assay, Alizarin Red S (ARS) assay, and Real-time quantitative polymerase chain reaction (RT-qPCR). In vivo experiments were performed to evaluate the performance of bone regeneration in the scaffolds. The results showed that all scaffolds were nontoxic with good biosafety, and VBTSs were more conducive to promoting cell proliferation, osteogenic differentiation, and bone regeneration within the scaffolds. Among the 596–1044 μm range, the VBTS with an average pore size of 596 μm performed best. This study showed that bone regeneration could be regulated by controlling the porous structure and provided a reference for applying VBTSs in bone implants. [Display omitted] [ABSTRACT FROM AUTHOR]

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The utilization of a large-scale antenna array has led to substantial performance improvements in anti-jamming communications. However, due to the practical constraints of hardware cost and power consumption, deploying such a large-scale antenna array at the user side is impractical. Inspired by the remarkable advantages of reconfigurable intelligent surfaces (RIS), we propose an active-passive cascaded RIS-aided receiver architecture that facilitates the cost- and energy-efficient deployment of a large-scale antenna array at the user side, while also providing additional degrees-of-freedom for effective beamforming design. Building upon this architectural framework and taking into account the practical imperfections in the angular channel state information (CSI), we formulate a worst-case achievable rate maximization problem for anti-jamming communications. To address the challenges posed by the intractable non-convex design problem, we present a low-complexity optimization framework that obtains semi-closed-form solutions. Specifically, we first develop a Pareto-dual scheme to handle the general power constraints in devising the optimal precoder for the base station. Subsequently, by introducing a novel anti-jamming criterion and employing the discretization method to transform the imperfect CSI of jammers into a robust form, we derive two jamming-nulling feasibility conditions and a unified unit-modulus zero-forcing scheme to determine the coefficients of the passive RIS. To strike a satisfactory balance between complexity and performance, we further design three computationally-efficient algorithms based on alternating majorization-minimization (AMM) and conventional/modified cyclic coordinate descent (C/M-CCD) methods to obtain the coefficients of the active RIS. Finally, through comprehensive numerical simulations, we validate the effectiveness of the proposed architecture and optimization framework, demonstrating their capacity to achieve exceptional performance in a cost-effective manner.

Neural regeneration after spinal cord injury (SCI) closely relates to the microvascular endothelial cell (MEC)-mediated neurovascular unit formation. However, the effects of central nerve system-derived MECs on neovascularization and neurogenesis, and potential signaling involved therein, are unclear. Here, we established a primary spinal cord-derived MECs (SCMECs) isolation with high cell yield and purity to describe the differences with brain-derived MECs (BMECs) and their therapeutic effects on SCI. Transcriptomics and proteomics revealed differentially expressed genes and proteins in SCMECs were involved in angiogenesis, immunity, metabolism, and cell adhesion molecular signaling was the only signaling pathway enriched of top 10 in differentially expressed genes and proteins KEGG analysis. SCMECs and BMECs could be induced angiogenesis by different stiffness stimulation of PEG hydrogels with elastic modulus 50-1650 Pa for SCMECs and 50-300 Pa for BMECs, respectively. Moreover, SCMECs and BMECs promoted spinal cord or brain-derived NSC (SNSC/BNSC) proliferation, migration, and differentiation at different levels. At certain dose, SCMECs in combination with the NeuroRegen scaffold, showed higher effectiveness in the promotion of vascular reconstruction. The potential underlying mechanism of this phenomenon may through VEGF/AKT/eNOS- signaling pathway, and consequently accelerated neuronal regeneration and functional recovery of SCI rats compared to BMECs. Our findings suggested a promising role of SCMECs in restoring vascularization and neural regeneration.

Multi-access edge computing (MEC) is regarded as a promising approach for providing resource-constrained mobile devices with computing resources through task offloading. Sparse code multiple access (SCMA) is a code-domain non-orthogonal multiple access (NOMA) scheme that can meet the demands of multi-cell MEC networks for high data transmission rates and massive connections. In this paper, we propose an optimization framework for SCMA-enabled multi-cell MEC networks. The joint resource allocation and computation offloading problem is formulated to minimize the system cost, which is defined as the weighted energy cost and latency. Due to the nonconvexity of the proposed optimization problem induced by the coupled optimization variables, we first propose an algorithm based on the block coordinate descent (BCD) method to iteratively optimize the transmit power and edge computing resources allocation by deriving closed-form solutions, and further develop an improved low-complexity simulated annealing (SA) algorithm to solve the computation offloading and multi-cell SCMA codebook allocation problem. To solve the problem of partial state observation and timely decision-making in long-term optimization environment, we put forward a multiagent deep deterministic policy gradient (MADDPG) algorithm with centralized training and distributed execution. Furthermore, we extend the framework to the partial offloading case and propose an algorithm based on alternating convex search for solving the task offloading ratio. Numerical results show that the proposed multi-cell SCMA-MEC scheme achieves lower energy consumption and system latency in comparison to the orthogonal frequency division multiple access (OFDMA) and power-domain (PD) NOMA techniques.

Sandy cobble stratum is the most common unfavorable geology in the construction of subway tunnels. Grouting cement slurry is one of the main methods used to reinforce the sandy cobble stratum when shield tunneling in sandy cobble stratum. In order to study the reinforcement effect of cement slurry on sandy cobble stratum, water–cement ratio (w/c ratio) and nanomaterial percentages of slurry viscosity and compressive strength were studied by adding nano-SiO2, silica sol, nano-CaCO3, silica fume and other additives. The compressive strength, the pore characteristics and the porosity of slurry under the different nanomaterial were studied by pressure test, scanning electron microscopy (SEM) and micro-CT three-dimensional imaging. Both the microstructure of cement slurry after hydration and hardening and its influence on the macroscopic properties were analyzed. It is indicated that 1%–2% nano-SiO2and 1%–5% silica fume can improve the compressive strength of the hardened cement paste, but the compressive strength of the hardened cement paste is not obviously improved or even decreased by adding nano-CaCO3and silica sol. In addition, the slurry with 5% silica fume has the best performance, and its compressive strength is improved by more than 25% compared with the sample without nanomaterial. Moreover, the addition of silica fume reduces the porosity of the hardened cement paste and the average pore diameter.

The aim was to explore the effect of lateral recess decompression by percutaneous transforaminal endoscopic spine system (Tessys) technique combined with percutaneous transforaminal endoscopic discectomy (PTED) on pain medium, nerve function and stress response in patients suffering from contralateral symptoms of lumbar disc herniation. A total of 96 patients with contralateral symptoms of lumbar disc herniation treated in our hospital from February 2015 to April 2017 were randomly divided into control group and study group, with 48 cases in each group. The control group underwent PTED, and the study group underwent lateral recess decompression by Tessys technique combined with PTED. The visual analogue scale (VSA) score and Japanese Orthopaedic Association (JOA) score before surgery and 3 months after surgery were compared between the two groups. The levels of serum pain medium (prostaglandin E2 (PGE2), histamine (HA), 5-hydroxytryptamine (5-HT)) and oxidative stress indexes (malondialdehyde (MDA), myeloperoxidase (MPO), superoxide dismutase (SOD), total antioxidant capacity (TAC)) before surgery and 7 days after surgery were compared. The clinical efficacy of the two groups was compared at 1 month after treatment. One month after treatment, the excellent and good rate in the study group was significantly higher than that in the control group (85.4% vs 56.3%; P< 0.05). There was no significant difference between VAS and JOA score in the two groups preoperatively (P> 0.05). At 3 months after surgery, the VAS score in the study group was significantly lower than that in the control group (P< 0.05), and the JOA score in the study group was significantly higher than that in the control group (P< 0.05). There was no significant difference in serum PGE2, HA and 5-HT levels between the two groups preoperatively (P> 0.05). At 7 days after surgery, the serum PGE2, HA and 5-HT levels in the study group were significantly lower than those in the control group (P< 0.05). Preoperatively, the levels of serum MDA, MPO, SOD and TAC were not significantly different between the two groups (P> 0.05). On the seventh day after surgery, the levels of serum MDA and MPO in the study group were significantly lower than those in the control group (P< 0.05), and the levels of SOD and TAC were significantly higher than those in the control group (P< 0.05). In conclusion, the combined therapy of lateral recess decompression by Tessys technique and PTED in patients suffering from contralateral symptoms of lumbar disc herniation has a definite clinical effect, which can significantly alleviate the symptoms of low back pain and motor nerve function and reduce the contents of serum pain medium and the levels of oxidative stress. It is worthy of clinical promotion.