Search

Aims: Mesenchymal stem cells (MSCs) are usually cultured in a normoxic atmosphere (21%) in vitro, while the oxygen concentrations in human tissues and organs are 1% to 10% when the cells are transplanted in vivo. However, the impact of hypoxia on MSCs has not been deeply studied, especially its translational application. Methods: In the present study, we investigated the characterizations of human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) in hypoxic (1%) and normoxic (21%) atmospheres with a long-term culture from primary to 30 generations, respectively. The comparison between both atmospheres systematically analyzed the biological functions of MSCs, mainly including stemness maintenance, immune regulation, and resistance to chondrocyte apoptosis, and studied their joint function and anti-inflammatory effects in osteoarthritis (OA) rats constructed by collagenase II. Results: We observed that long-term hypoxic culture surpassed normoxic atmosphere during hUC-MSCs culture in respect of promoting proliferation, anti-tumorigenicity, maintaining normal karyotype and stemness, inhibiting senescence, and improving immunoregulatory function and the role of anti-apoptosis in chondrocytes. Furthermore, we demonstrated that the transplantation of long-term hypoxic hUC-MSCs (Hy-MSCs) had a better therapeutic effect on OA rats compared with the hUC-MSCs cultured in the normoxic atmosphere (No-MSCs) in terms of the improved function and swelling recovery in the joints, and substantially inhibited the secretion of pro-inflammatory factors, which effectively alleviated cartilage damage by reducing the expression of matrix metallopeptidase 13 (MMP-13). Conclusion: Our results demonstrate that Hy-MSCs possess immense potential for clinical applications via promoting stemness maintenance and enhancing immunoregulatory function. Cite this article: Bone Joint Res 2024;13(12):763–777.

Tiny and affordable computers (e.g. Raspberry Pi and Arduino) have been widely applied to technology-enhanced hands-on learning (THL). However, little scholarly attention has been devoted to the key factors behind students' performance in THL contexts. Therefore, this study not only helped the participants learn computer science through THL, but also devised a research model to investigate the major factors affecting their learning performance. In this model, self-efficacy and social support serve as the independent variables, and perceived usefulness, perceived enjoyment and behavioral intention act as the mediating variables, while learning performance functions as the dependent variable. The research findings reveal that (1) self-efficacy is a more significantly influential factor than social support behind learning performance; and (2) perceived enjoyment is more significantly influential than perceived usefulness in affecting learning performance via the mediation of behavioral intention. These findings imply that students' self-efficacy in using technologies is more important than others' assistance in THL contexts, since the latter may not be offered in a timely manner, whereas the former will prompt students to solve problems independently and ergo deliver better performance.

Flipped civic education has attracted many educators' attention, because it can be employed to increase students' interest in learning civic literacy. However, very few researches investigated students' continuance intention to participate in flipped civic education. It is a truly important issue since flipped civic education can be more effectively applied and developed if the factors behind students' continuance intention can be identified. Therefore, in order to identify these key factors, this study adopted social cognitive theory to devise a research model. The research findings showed that social interaction ties occupy a dominant role in affecting students' continuous participation in flipped civic education through hedonic and utilitarian outcome expectations. The results suggested that fostering the collaborative activities like debates or discussions is the top priority for teachers who want to promote students' engagement in flipped civic education, because it will help students construct knowledge and experience pleasure from interpersonal interaction.

Abstract We investigate gravitational collapse of a spherically symmetric thin shell in the Einstein–Gauss–Bonnet (EGB) gravity. Under the recently proposed 4D limit, we find that the collapsing shell will be bounced back at a small radius, without forming a singularity. This bouncing behavior is similar to those of a test particle and a homogeneous spherical dust star, in accordance with the expectation that the Gauss–Bonnet term will modify the small scale behavior of the Einstein gravity. We analyze the causal structure of the dynamic spacetime that represents the bouncing process, finding that the thin shell has an oscillation behavior on the Penrose diagram, which means that the thin shell results in a novel type of black hole with respect to observers outside the event horizon that the collapse forms. We also find that the weak cosmic censorship conjecture holds in this model. Further implications of such a regular gravitational collapse are discussed.

In this paper, we test the weak cosmic censorship conjecture (WCCC) for n≥4 dimensional nearly extremal RN-AdS black holes with non-trivial topologies, namely plane and hyperbola, using the new version of gedanken experiment proposed by Sorce and Wald. Provided that the non-electromagnetic part of the stress tensor of matter fields satisfies the null energy condition and the linear stability condition holds, we find that the black holes cannot be overcharged under the second-order perturbation approximation, which includes the self-force and finite-size effects. As a result, we conclude that the violation of Hubeny type never occurs and the WCCC holds for the topological RN-AdS black hole.

A distributed energy efficient beamforming algorithm was studied for multicell multiuser downlink communication system.Firstly,the energy efficient optimization problem was first considered as the maximization of the ratio between the system sum rate and the system power consumption.The fractional programming optimization target was then transformed into a subtractive form via using the fractional programming theorem.Secondly,the problem was decomposed into some subproblems that can be solved respectively by introducing the concept of the interference temperature in cognitive radio networks.Finally,an effective distributed energy efficient beamforming algorithm was proposed by exploiting the Lagrangian duality theorem and optimization theorem.Compared to the classical energy efficient optimization algorithm,the proposed algorithm can achieve an obvious energy efficiency performance gain.

An algorithm is proposed for energy-efficient resource allocation scheme in massive MIMO OFDMA downlink mobile communication system.A mathematical formulation of optimization issue is provided with the objective of maximizing system energy efficiency lower bound under the minimum data rate requirement of user,meanwhile the BS uses a zero-forcing(ZF) precoding.And then for optimizing energy efficiency function,the bandwidth allocation,power allocation and the number of antenna arrays at the BS are adjusted synchronously.First,an iterative algorithm derived from optimality condition for bandwidth assignment is proposed.Second,the properties of fractional programming and convex optimization are used to maximize the energy efficiency.Specifically,both the number of antenna arrays at the BS and the transmit data rate at the user are adjusted.Simulation results show that the proposed schemes not only have less iteration number but also have good perform for system energy efficiency and throughput.

The outage probability and average BER (bit error ratio) of two-way relay system with network coding using relay selection were analyzed over Nakagami channels. The cooperative relay selection criterion of minimizing the worse user's BER was proposed based on three time slots network coding. The closed-form expressions of outage probability and average BER were derived through theoretical analysis from the point of two-way communication; meanwhile, the analytical expressions of outage probability and average BER of two-way relay system using network coding without cooperative relay selection were also obtained rigorously. By the analysis of two-way relay system without cooperative relay selection, it was found that the performance gains of the proposed scheme would increase gradually with the Naka-gami channel fading parameters decreasing. Simulation results verified the correctness of theoretical analysis and illus-trated that the performance of the proposed scheme can be improved significantly relative to the network coding without cooperative relay selection.

Root system morphology (RSM) in plants plays a key role in acquiring nutrients from the soil and is also altered by abiotic or biotic factors including soil microorganisms and signal molecules. The present study was made to evaluate the effects of an arbuscular mycorrhizal fungus (AMF, Glomus versiforme) and exogenous peroxide hydrogen (H2O2, 0, 1 and 100 μM) on root length, lateral root number and activities of polyamine-metabolized enzymes in trifoliate orange (Poncirus trifoliata) seedlings. After 5 months of inoculation with AMF, root mycorrhizal colonization was significantly increased by application of 1 μM H2O2, but markedly restrained by 100 μM H2O2. Inoculation with AMF significantly increased the taproot length and the number of second- and third-order lateral roots under 1 and 100 μM H2O2application. The AMF infection significantly increased 0-1 cm classed root length and total root length, regardless of H2O2 concentration. In general, inoculation with AMF increased arginine decarboxylase (ADC) and ornithine decarboxylase (ODC) activity of roots under 0, 1 and 100 μM H2O2, increased diamine oxidase (DAO) activity of roots under 0 μM H2O2 and decreased DAO activity of roots under 1 and 100 μM H2O2. Root polyamine oxidase (PAO) activity was similar between AMF and non-AMF seedlings, irrespectively of H2O2concentration. Results suggest that lower concentration of H2O2(1 μM) might be regarded as a signal to stimulate mycorrhizal and lateral root development through increase of ADC and ODC and decrease of DAO, while high concentration of 2O2 (100 μM) as a toxic compound of reactive oxygen species restricted AMF colonization.

The spectral efficiency of the downlink of multi-user multiple-input and single-output (MU-MISO) was ana-lyzed in the time-division duplex (TDD) communication systems with large-scale antennas. Assuming that the number of users was fixed and the antenna number (M) of base station (BS) increases without limit, the conclusions through theo-retical derivations and analyses were drawn that, when the transmit power of the BS reduces to 1/M of that of BS with single antenna, the system spectral efficiency tends to a constant value with the increase of M if the BS acquires the per-fect channel state information (CSI). The adverse effects of the inter-user interferences and the fast fading could also be eliminated through simple pre-processings. Although the multicell system is affected by the pilot contamination, which is the reason why the inter-cell interferences cannot be eliminated, the reduced transmit power makes the system changed from interference-limited to noise-limited. The limit expression of the system spectral efficiency using zero-forcing (ZF) normalized precoding is equal to that using maximum ratio transmission (MRT) normalized precoding. Finally, the lower bound of the spectral efficiency of multi-user downlink applying space time block code was presented and the correctness of the above conclusions was confirmed by the simulation analyses.

Two pilot contamination reduction methods in very large MIMO cellular network were proposed by dividing all cells into two types of one-dimensional very large MIMO network.The same pilot sequences were used in cells in the same category while orthogonal pilot sequences were used between these two categorie.Then the pilot power control method can be used to achieve the purpose of alleviating pilot contamination.By coordinating among base stations,the nearly optimal length of pilot sequences and assignment of pilot transmission could be found through minimizing the sum of channel estimation mean square error of all base stations.Thus,much better performance of channel estimation could be obtained,greatly enhancing the sum rate in downlink in all cells.

Multi-cell multi-user downlink beamforming schemes considering transceiver impairments were developed,with the objective of minimizing the maximum mean square error (MSE) and the sum of MSE of all users.The optimiza-tion problem was transformed into a second-order cone programming(SOCP) standard form,and a hierarchical iterative algorithm was developed to solve the original problem.Compared with the traditional beamforming methods developed for ideal transceivers,numerical results show that our proposed optimization algorithms greatly reduce the impact of im-pairments and improve the system performance.

Arbuscular mycorrhizal fungi (AMF) can enhance tolerance of plants to soil water deficit, whereas morphological observations of reactive oxygen species and antioxidant enzyme system are poorly studied. The present study thereby evaluated temporal variations of the antioxidant enzyme system in citrus (Citrus tangerina) seedlings colonized by Glomus etunicatum and G. mosseae over a 12-day period of soil drying. Root colonization by G. etunicatum and G. mosseae decreased with soil drying days from 32.0 to 1.0% and 50.1 to 4.5% in 0-day to 12-day, respectively. Compared to the non-AM controls, the AMF colonized plants had significantly lower tissue (both leaves and roots) hydrogen peroxide (H2O2) and superoxide anion radical (O2•–) concentrations during soil water deficit, whereas 1.03–1.92, 1.25–1.84 and 1.18–1.69 times higher enzyme activity in superoxide dismutase, peroxidase (POD) and catalase. In situ leaf H2O2 and root POD location also showed that AM seedlings had less leaf H2O2 but higher root POD accumulation. Furthermore, significantly higher root infection and antioxidant enzymatic activities in plants colonized with G. mosseae expressed than with G. etunicatum during the soil drying. These results demonstrated that the AMs could confer greater tolerance of citrus seedlings to soil water deficit through an enhancement in their antioxidant enzyme defence system whilst an decrease level in H2O2 and O2•–.

The recent IEEE 802.11ac adopted a novel multi-user access technique,which was the downlink multi-user MIMO (MU-MIMO) transmission.This was very different from the former IEEE 802.11 standard's protocols.The MU-MIMO transmission technique in IEEE 802.11ac draft was studied and proposed some optimal designs.Finally,the performance of the IEEE 802.11ac MU-MIMO transmission schemes and gives the simulations.The simulation results show that the proposal transmission schemes can achieve gains of BER and throughput in theory and simulations.