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Heavy metal pollution has spread around the world with the development of industry, posing a major threat to human health. It is urgent to design and fabricate bifunctional materials for detection and adsorption of heavy metal ions. Herein, poly(glycidyl methacrylate-ico/i-ethylene glycol dimethacrylate) microspheres, a kind of common macroporous adsorption resin (MAR), were employed as the matrix, and carbon dots (CDs) with excellent optical properties were grafted onto the surface of MAR by surface-initiated atom transfer radical polymerization (SI-ATRP) and photo-initiated "thiol-yne" click chemistry. The synthesized MAR@poly(PA)@CD could produce fluorescence quenching with Fesup3+/sup. A simple fluorescence spectrometric method for detection of Fesup3+/supwas established. The fluorescence intensity of MAR@poly(PA)@CD decreased linearly with the concentration of Fesup3+/supin the range of 0-70 nmol Lsup-1/sup, with a limit of detection (LOD) of 6.6 nmol Lsup-1/sup, which had the potential for trace detection. In addition, after SI-ATRP modification, many adsorption sites were generated on the surface of MAR, and the adsorption capacity for Fesup3+/supwas 23.8 mg gsup-1/sup. Isothermal and kinetic adsorption experiments were more consistent with the Langmuir model (ir/i= 0.9992) and pseudo-second-order model (ir/i= 0.9902), indicating that the adsorption was monolayer adsorption and chemical adsorption, respectively. MAR@poly(PA)@CD with dual functions of detecting and adsorbing Fesup3+/supwas successfully prepared, showing great application prospects in the environmental field.

Climate warming has advanced the spring phenology of many plant species by accelerating heat accumulation. However, delayed phenophases due to insufficient chilling have also been reported. Based on phenological observation data (1963-2010), we compared the effects of preseason chill and heat accumulation on leaf unfolding dates of four deciduous woody species (Lagerstroemia indica, Robinia pseudoacacia, Sophora japonica, and Ulmus pumila) in temperate and subtropical regions of China. Daily chill and heat accumulation were calculated by two chilling models (the Positive Utah Model and the Dynamic Model) and the Growing Degree Hour (GDH) Model. We determined the temporal trends in chill and heat accumulations for leaf unfolding of the four species. The results showed that there were shorter chilling periods in the subtropics than in temperate sites because the chilling period typically started later and ended earlier. There was no significant difference in the length of the forcing period in the different regions. The chilling requirements for leaf unfolding were higher in temperate regions (1344.9-1798.9 chilling units (CU) or 64.7-79.4 chilling portions (CP)) than in the subtropics (1145.9-1828.1 CU or 47.9-75.2 CP). Plants in the subtropics needed higher forcing temperatures (4135.8-10084.8 GDH) than those in temperate regions (3292.0-8383.6 GDH). The earlier-leafing species (e.g., U. pumila) had a lower heat requirement for leaf unfolding than the later-leafing species (e.g., L. indica). A significant increase in heat accumulation was found at all sites except Guiyang, while chill accumulation only increased in Beijing.

The climate warming that has occurred over the past decades may benefit plant growth and development because it reduces the severity of frost events. However, these rising temperatures may also lead to diminished frost hardiness in plants due to their insufficient hardening. Despite climate warming exerting such dual effects on frost damage, how this might change the frost damage of woody plants remains unknown. Here, we conducted a laboratory experiment that used the relative electrolyte leakage method to derive species-specific model parameters for frost hardiness and a damage model. Then we simulated the daily frost hardiness and damage of five typical temperate tree species (Ulmus pumila, Robinia pseudoacacia, Fraxinus chinensis, Salix babylonica, and Armeniaca vulgaris), from 1980 to 2015, in Beijing, China. The root mean square error (RMSE) between observed and predicted frost damage ranged from 3.58% to 7.65%. According to our simulation results, frost hardiness has declined over this 36-year period due to insufficient cold hardening of plants in autumn coupled with rapid dehardening in spring; however, the percentage of frost damage incurred by the five species showed a declining trend because of the reduced frequency and intensity of frost events. Thus, decreased frost severity may, to a large extent, offset the negative effects of diminished frost hardiness such that the frost risk faced by temperate forests may well remain constant or decline with continued climate warming.

BACKGROUND Bone-marrow mesenchymal stem cells (BMSCs) are pluripotent stem cells with potent self-renewal and differentiation ability that are widely used in transplantation of cell therapy. But the mechanism on microRNA (miRNA) regulating stem cell differentiation is complicated and unclear. The aim of this study was to investigate whether miR-199b-5p is involved in differentiation of cardiomyocyte-like cells and identify potential signal pathways in BMSCs. MATERIAL AND METHODS Mouse BMSCs were treated with 5-azacytidine and transfected by miR-199b-5p mimic and inhibitor, respectively. qRT-PCR was used to detect the expression of miR-199b-5p in BMSCs, 5-azacytidine treated BMSCs, and neonatal murine cardiomyocytes. The expression of cardiac specific genes and the HSF1/HSP70 signal pathway were examined by qRT-PCR or western blotting. The proliferation and migration of BMSCs were evaluated by CCK-8 assay and wound-healing assay. RESULTS The expression of miR-199b-5p decreased gradually in the process of differentiation of BMSCs toward cardiomyocyte-like cells. The expression of cardiac specific genes and HSF1/HSP70 were increased in the miR-199b-5p inhibitor group; however, the miR-199b-5p mimic group presented an opposite result. Both the miR-199b-5p inhibitor group and the miR-199b-5p mimic group had no influence on BMSCs proliferation and migration. Using lentivirus vectors bearing HSF1 shRNA to silence HSF1 and HSP70, the anticipated elevated expression effect of cardiac specific genes induced by miR-199b-5p inhibitor was suppressed. CONCLUSIONS Downregulation of miR-199b-5p induced differentiation of BMSCs toward cardiomyocyte-like cells partly via the HSF1/HSP70 signaling pathway, and had no influence on BMSCs proliferation and migration.

This paper studies a simultaneous wireless information and power transfer system with multiple external eavesdroppers and internal curious users. We model the random network by Poisson cluster process in consideration of the case where eavesdroppers hide around certain targets. Focusing on the users that work in harvesting-transmitting mode with time switching receivers, we establish communication model via time division multiple access. On this basis, we propose a lightweight secure transmission scheme based on dual-thresholds for physical-layer security enhancement, which consists of two protocols applied to the downlink (DL) and uplink (UL) transmission respectively. In the DL, we design a dynamic information-power switching transmission protocol based on signal-to-noise ratio threshold, which provides an opportunistic approach to reform the fixed period allocation of information and power transfer; in the UL, an energy threshold is proposed for users to control the transmission, which is called a user-led on-off transmission protocol. Furthermore, we give a comprehensive performance analysis for the proposed scheme in terms of delay, reliability, security and secrecy throughput. Based on the analysis results, we optimize the two thresholds and the DL-UL allocation coefficient to maximize the secrecy throughput. Simulation results show the proposed scheme can bring about a substantial secrecy gain.

Plant phenology is influenced by various climatic factors such as temperature, precipitation, insolation, and humidity, etc. Among these factors, temperature and precipitation are proved to be the most important. However, the relative importance of these two factors is different among various phenophases and regions and is seldom discussed along environmental gradients. Based on normalized difference vegetation index NDVI data from the NDVI3g dataset and using the mid-point method, we extracted the start date of the growing season SOG and the end date of the growing season EOG in northern China during 1982–2012. To determine which climate factor was more influential on plant phenology, partial correlation analysis was applied to analyse the spatial difference between the response of SOG and EOG to temperature and precipitation. Finally, we calculated the temperature and precipitation sensitivities of the SOG and EOG. The results showed that: 1 SOG displayed an advancing trend in most regions, while EOG was delayed for all the vegetation types during 1982–2012. 2 SOG was mainly triggered by preseason temperature. The increase in temperature caused an overall advance in SOG. However, the relationship between SOG and precipitation varied among different vegetation types. Regarding EOG, precipitation had greater impacts than temperature in relatively arid environments, such as deserts, steppes and meadow biomes. 3 The response of vegetation phenology both SOG and EOG to temperature became stronger with increasing preseason precipitation across space. The response of EOG to precipitation became weaker from arid regions to relatively humid regions. These results provide a better understanding of the spatial pattern of the phenological response along the precipitation gradient and a reference for assessing impacts of future climate change on vegetation phenology, especially in transitional and fragile zones.

Continuous long-term temperature sensitivity (ST) of leaf unfolding date (LUD) and main impacting factors in spring in the period 1978–2014 for 40 plant species in Mudanjiang, Heilongjiang Province, Northeast China, were analyzed by using observation data from the China Phenological Observation Network (CPON), together with the corresponding meteorological data from the China Meteorological Data Service Center. Temperature sensitivities, slopes of the regression between LUD and mean temperature during the optimum preseason (OP), were analyzed using 15-year moving window to determine their temporal trends. Major factors impacting ST were then chosen and evaluated by applying a random sampling method. The results showed that LUD was sensitive to mean temperature in a defined period before phenophase onset for all plant species analyzed. Over the period 1978–2014, the mean ST of LUD for all plant species was − 3.2 ± 0.49 days °C−1. The moving window analysis revealed that 75% of species displayed increasing ST of LUD, with 55% showing significant increases (P

Based on Continuous Tabu Search with Sine map and Staged strategy (CTS-SS) algorithm, an improved CTS-SS (iCTS-SS) algorithm is proposed to achieve rapid convergence and enhance the robustness of the CTS-SS algorithm with strategies of adaptive neighborhood radius and awarding search iterations. Unlike a fixed neighborhood radius used in the CTS-SS algorithm, the iCTS-SS algorithm utilizes the adaptive neighborhood radius to improve the search capabilities. According to whether the optimal result is replaced, it could be narrowed for centralized search or expanded for decentralized search. By this way, the result can be better than using regular iterations. The experiments adopt various typical functions as numerical experiment cases to evaluate the robustness, accuracy and efficiency of iCTS-SS. And for comparison, these functions are also solved by CTS-SS and Modified Staged Continuous Tabu Search (MSCTS), which is one of the latest continuous tabu search algorithms. Experimental results show that iCTS-SS outperforms both CTS-SS and MSCTS in statistical significance.

This paper investigates the physical layer security in simultaneous wireless information and power transfer (SWIPT)-enabled cooperative non-orthogonal multiple access (NOMA) transmissions. Taking the malicious eavesdropper into account, we study on the problem of artificial noise (AN)-aided transceiver optimization. To guarantee the quality of service (QoS) at cell-edge users and promote the average performance of system, we consider the multi-cell beam-forming (MCBF) and formulate the problem of maximizing the secrecy spectral efficiency fairness (SSEF) among multiple coordinated cells. As the formulated problem is nonconvex and difficult to solve with existing methods, we apply the semi-definition relaxation (SDR) technique and propose an iterative algorithm based on successive convex approximation (SCA) for complexity reduction. Furthermore, we analyze the complexity of the proposed algorithm. Finally, simulations results demonstrate our analysis and illustrate the validity of AN-aided MCBF transmission scheme.

Due to dense and random deployment of dense heterogeneous cellular networks (HetNets), the systems are more susceptible to channel estimation errors, which effect secure and reliable transmission. To solve this problem, we propose a secure and reliable transmission scheme for dense HetNets based on secure Energy Efficiency (EE) Optimization. Firstly, the system model with channel estimation error is established. Then, transmission threshold selection algorithm is designed to maximize secure EE, and emission control is achieved by comparing the receiving signal-to-interference-plus-noise ratio (SINR) with the transmission threshold. Finally, secure EE constrained by the connection and secrecy probabilities is derived. Numerical results verify that the transmission scheme can increase secure EE by at least 50%.

In the original publication [1] the name of author Yajun Chen was spelled wrong. The original article was updated to rectify this error.

Device-to-device (D2D) communication has been deemed as a promising technology in the next generation 5G wireless communication. Due to the openness nature of the transmission medium, secure transmission is also a critical issue in the D2D-enabled cellular network as well as other wireless systems. In this paper, we investigate secure communication for the cellular downlink in this hybrid network. We consider a case in which each base station has no channel state information (CSI) from D2D transmitters which are generally deployed in the cell edge. To guarantee the secure communication of the cellular link, each base station employs the artificial noise assisted transmission strategy. Firstly, we derive the close-form expression and asymptotic expression of the secrecy outage probability of the cellular link in different scenarios: (I) eavesdroppers having no multi-user decedability; (II) eavesdroppers having the multi-user decedability. Then, we comprehensively discuss the impacts of some main system parameters on the performance to provide some system design guidances. To characterize the reliable communication of the typical D2D link, the close-form expression and asymptotic expression of the connection outage probability are, respectively, derived and some comprehensive analysis are presented. Finally, simulation results are provided to validate the effectiveness of theoretical analysis.

This paper studies the physical-layer secrecy performance of the downlink transmission in Simultaneous Wireless Information and Power Transfer (SWIPT) deployed in Internet of Things (IoT), where the Energy Receivers (ERs) are curious about the confidential messages of Information Receivers (IRs). Firstly, the locations of IoT users are modeled as the Poisson Point Process (PPP) to characterize the random deployment. Then, the communication model among the Resource Center (RC) and multiple IoT users is established via Time Division Multiple Access (TDMA). Furthermore, considering the energy requirements of nodes that work in "harvesting-transmitting" mode, two thresholds of eavesdropping are proposed to analyze the eavesdropping behaviors of ERs in different scenarios, based on which the curiosity probabilities are respectively obtained. Finally, the average secrecy outage probability is derived through the comprehensive analysis on different links in an entire period. The simulation results show that there exits an optimal transmitting power that can achieve the best performance and the proposed thresholds can improve the accuracy of the analysis.

Due to the dense random deployment of heterogeneous cellular networks (HetNets), the system is more seriously affected by channel estimation errors. However, there is a lack of effective secure transmission scheme in this scenario. In order to solve this problem, a transmit antenna selection strategy based on channel estimation accuracy is proposed. First, the stochastic geometric tool is used to derive the secrecy outage probability of K-tier dense HetNets. Then the influence of channel estimation accuracy on secure performance of the system is analyzed. Finally, the validity of the theoretical derivation is verified and the influence of some parameters on the security performance of the system is analyzed.

Based on the phenological data from China Phenological Observation Network, we compiled the phenological calendars of 3 phenological observation stations (Shanghai, Nanjing, and Hefei) in East China for 1987–1996 and 2003–2012 according to the sequences of mean phenophases. We calculated the correlated coefficient and the root mean square error (RMSE) between phenophases and the beginning of meteorological seasons to determine the beginning date of phenological season. By comparing new phenological calendars with the old ones, we discussed the variation of phenophases and their responses to temperature. The conclusions are as follows. (1) The beginning dates of spring and summer advanced, while those of autumn and winter delayed. Thus, summers got longer and winters got shorter. (2) The beginning time of the four phenological seasons was advancing during 1987–1996, while it was delaying during 2003–2012. (3) Most spring and summer phenophases occur earlier and most autumn and winter phenophases occur later in 2003–2012 than in 1987–1996. (4) The beginning time of phenological seasons was significantly correlated with temperature. The phenological sensitivities to temperature ranged from −6.49 to −6.55 days/°C in spring, −3.65 to −5.02 days/°C in summer, 8.13 to 10.27 days/°C in autumn, and 4.76 to 10.00 days/°C in winter.