Showing papers by "Ocean University of China published in 2018"

El Niño–Southern Oscillation complexity

Abstract: El Nino events are characterized by surface warming of the tropical Pacific Ocean and weakening of equatorial trade winds that occur every few years Such conditions are accompanied by changes in atmospheric and oceanic circulation, affecting global climate, marine and terrestrial ecosystems, fisheries and human activities The alternation of warm El Nino and cold La Nina conditions, referred to as the El Nino–Southern Oscillation (ENSO), represents the strongest year-to-year fluctuation of the global climate system Here we provide a synopsis of our current understanding of the spatio-temporal complexity of this important climate mode and its influence on the Earth system

Detection of Malicious Code Variants Based on Deep Learning

Abstract: With the development of the Internet, malicious code attacks have increased exponentially, with malicious code variants ranking as a key threat to Internet security. The ability to detect variants of malicious code is critical for protection against security breaches, data theft, and other dangers. Current methods for recognizing malicious code have demonstrated poor detection accuracy and low detection speeds. This paper proposed a novel method that used deep learning to improve the detection of malware variants. In prior research, deep learning demonstrated excellent performance in image recognition. To implement our proposed detection method, we converted the malicious code into grayscale images. Then, the images were identified and classified using a convolutional neural network (CNN) that could extract the features of the malware images automatically. In addition, we utilized a bat algorithm to address the data imbalance among different malware families. To test our approach, we conducted a series of experiments on malware image data from Vision Research Lab. The experimental results demonstrated that our model achieved good accuracy and speed as compared with other malware detection models.

High-Purity Inorganic Perovskite Films for Solar Cells with 9.72 % Efficiency.

Abstract: All-inorganic perovskite solar cells with high efficiency and improved stability are promising for commercialization. A multistep solution-processing method was developed to fabricate high-purity inorganic CsPbBr3 perovskite films for use in efficient solar cells. By tuning the number of deposition cycles (n) of a CsBr solution, the phase conversion from CsPb2 Br5 (n ≤3), to CsPbBr3 (n=4), and Cs4 PbBr6 (n≥5) was optimized to achieve vertical- and monolayer-aligned grains. Upon interfacial modification with graphene quantum dots, the all-inorganic perovskite solar cell (without a hole-transporting layer) achieved a power conversion efficiency (PCE) as high as 9.72 % under standard solar illumination conditions. Under challenging conditions, such as 90 % relative humidity (RH) at 25 °C or 80 °C at zero humidity, the optimized device retained 87 % PCE over 130 days or 95 % over 40 days, compared to the initial efficiency.

Increased variability of eastern Pacific El Niño under greenhouse warming

Abstract: The El Nino–Southern Oscillation (ENSO) is the dominant and most consequential climate variation on Earth, and is characterized by warming of equatorial Pacific sea surface temperatures (SSTs) during the El Nino phase and cooling during the La Nina phase. ENSO events tend to have a centre—corresponding to the location of the maximum SST anomaly—in either the central equatorial Pacific (5° S–5° N, 160° E–150° W) or the eastern equatorial Pacific (5° S–5° N, 150°–90° W); these two distinct types of ENSO event are referred to as the CP-ENSO and EP-ENSO regimes, respectively. How the ENSO may change under future greenhouse warming is unknown, owing to a lack of inter-model agreement over the response of SSTs in the eastern equatorial Pacific to such warming. Here we find a robust increase in future EP-ENSO SST variability among CMIP5 climate models that simulate the two distinct ENSO regimes. We show that the EP-ENSO SST anomaly pattern and its centre differ greatly from one model to another, and therefore cannot be well represented by a single SST ‘index’ at the observed centre. However, although the locations of the anomaly centres differ in each model, we find a robust increase in SST variability at each anomaly centre across the majority of models considered. This increase in variability is largely due to greenhouse-warming-induced intensification of upper-ocean stratification in the equatorial Pacific, which enhances ocean–atmosphere coupling. An increase in SST variance implies an increase in the number of ‘strong’ EP-El Nino events (corresponding to large SST anomalies) and associated extreme weather events. Despite inter-model differences in predicting the details of the eastern Pacific El Nino, a robust increase in the corresponding sea surface temperature variability under greenhouse warming is found across models.

ENSO Atmospheric Teleconnections and Their Response to Greenhouse Gas Forcing

Abstract: S. W. Y. is supported by the KoreaMeteorological Administration Researchand Development Program under grant KMIPA2015-2112. Wenju Cai is supported by Earth System and Climate Change Hub of the Australia National Environmental Science Programme, and Centre for Southern Hemisphere Oceans Research, an international collaboration between CSIRO and Qingdao National Laboratory for Marine Sciences and Technology. B. Dewitte acknowledges supports from FONDECYT(1151185) and from LEFE-GMMC. Dietmar Dommenget is supported by ARC Centre of Excellence for Climate System Science (CE110001028).

Chitosan-Based Nanomaterials for Drug Delivery.

Abstract: This review discusses different forms of nanomaterials generated from chitosan and its derivatives for controlled drug delivery. Nanomaterials are drug carriers with multiple features, including target delivery triggered by environmental, pH, thermal responses, enhanced biocompatibility, and the ability to cross the blood-brain barrier. Chitosan (CS), a natural polysaccharide largely obtained from marine crustaceans, is a promising drug delivery vector for therapeutics and diagnostics, owing to its biocompatibility, biodegradability, low toxicity, and structural variability. This review describes various approaches to obtain novel CS derivatives, including their distinct advantages, as well as different forms of nanomaterials recently developed from CS. The advanced applications of CS-based nanomaterials are presented here in terms of their specific functions. Recent studies have proven that nanotechnology combined with CS and its derivatives could potentially circumvent obstacles in the transport of drugs thereby improving the drug efficacy. CS-based nanomaterials have been shown to be highly effective in targeted drug therapy.

Improved light-harvesting and thermal management for efficient solar-driven water evaporation using 3D photothermal cones

Abstract: Solar-driven evaporation based on photothermal membrane has been proved to be promising in the field of fresh water generation, and it is considered as an emerging strategy both in laboratory and in industrial scales. However, further research efforts have to be made on light harvesting and thermal management to improve water evaporation. In this study, an extensive research was carried out to develop a bio-inspired 3D photothermal cone for high-efficiency solar-driven evaporation with minimum light reflection and heat loss to bulk water. The artificial photothermal cone with a polypyrrole (PPy) coating layer was facilely fabricated via chemical vapor deposition polymerization (CVDP). The present 3D cone with a rationally designed conical structure exhibited satisfactory absorbance around 99.2% in the entire solar spectrum, which is comparable with the performances of super-black materials. Additionally, the heat loss has been minimized by elevating the photothermal cone to narrow the contact area between water and the PPy-based cone with good wettability, thus achieving a highly efficient interface heating. The solar conversion efficiency up to 93.8% for evaporation was achieved for the photothermal cone under one sun illumination, which is about 1.7 times as high as the result obtained for a plane film. Based on our results, controlling the 3D morphology can be considered as an important strategy for designing a novel high-efficiency photothermal membrane and also, it provides new opportunities in practical application.

A facile nanocomposite strategy to fabricate a rGO–MWCNT photothermal layer for efficient water evaporation

Abstract: Solar-driven water evaporation assisted by photothermal membranes is considered as one of the sustainable and cost-effective strategies for pure water generation and wastewater treatment. Herein, we report a facile but effective approach to improve the photothermal performance by combining 2D reduced graphene oxide (rGO) and 1D multi-walled carbon nanotubes (MWCNTs), which have different nanomorphologies. The photothermal layer can be easily deposited on different substrate materials via simple vacuum assistance. Such a composite photothermal layer shows a rough surface with a controllable nano-structure, which can thus optimize solar light harvesting. On the other hand, the formation of a loose internal porous structure and suitable wettability ensure water transport inside the photothermal layer during evaporation. The surface temperature reaches as high as 78 °C even under one sun irradiation (1 kW m−2), which is 10 °C higher than the result of pure rGO membranes. When loaded on a PVDF substrate, the rGO–MWCNT based membrane is flexible and shows an obvious improvement in the evaporation rate, about 79.0% and 8.9% higher than those of pure rGO and MWCNT membranes, respectively. The solar thermal conversion efficiency can reach up to 80.4% without any extra accessory for thermal management. Based on our results, the nanocomposite strategy is facile and effective for the development of novel photothermal membranes for high-efficiency evaporation, and contributes to the widespread application in the fields of desalination and wastewater treatment.

Polar amplification dominated by local forcing and feedbacks

Abstract: The surface temperature response to greenhouse gas forcing displays a characteristic pattern of polar-amplified warming1–5, particularly in the Northern Hemisphere. However, the causes of this polar amplification are still debated. Some studies highlight the importance of surface-albedo feedback6–8, while others find larger contributions from longwave feedbacks4,9,10, with changes in atmospheric and oceanic heat transport also thought to play a role11–16. Here, we determine the causes of polar amplification using climate model simulations in which CO2 forcing is prescribed in distinct geographical regions, with the linear sum of climate responses to regional forcings replicating the response to global forcing. The degree of polar amplification depends strongly on the location of CO2 forcing. In particular, polar amplification is found to be dominated by forcing in the polar regions, specifically through positive local lapse-rate feedback, with ice-albedo and Planck feedbacks playing subsidiary roles. Extra-polar forcing is further shown to be conducive to polar warming, but given that it induces a largely uniform warming pattern through enhanced poleward heat transport, it contributes little to polar amplification. Therefore, understanding polar amplification requires primarily a better insight into local forcing and feedbacks rather than extra-polar processes. Model simulations with CO2 forcing prescribed in discrete geographical regions reveal that polar amplification arises primarily due to local lapse-rate feedback, with ice-albedo and Planck feedbacks playing subsidiary roles.

Stability and Stabilization for Singular Switching Semi-Markovian Jump Systems With Generally Uncertain Transition Rates

Abstract: This paper studies the problems of stability and stabilization for a class of singular switching semi-Markovian jump systems. The general transition rates in the semi-Markov process cover completely unknown and uncertain bounded as two special cases. First, sufficient conditions are developed to ensure the unforced system to be regular, impulse-free, and exponentially mean-square stable. Then, by proposing a state feedback controller, sufficient conditions in terms of strict linear matrix inequalities are derived to guarantee the closed-loop system to be stochastically stabilziable. Finally, a numerical example is provided to show the effectiveness of the obtained results.

A Novel Robust Fuzzy Integral Sliding Mode Control for Nonlinear Semi-Markovian Jump T–S Fuzzy Systems

Abstract: This paper addresses the issue of robust fuzzy sliding mode control for continuous-time nonlinear Takagi–Sugeno fuzzy systems with semi-Markovian switching. The focus is on designing a novel fuzzy integral sliding surface without assuming that the input matrices are the same with full column rank and then developing a fuzzy sliding-mode controller for stochastic stability purpose. Based on Lyapunov theory, a set of newly developed linear matrix inequality conditions are established for stochastic stability of the sliding-mode dynamics with generally uncertain transition rates, and then extended to where the input matrix is plant-rule-independent, as discussed in most existing literatures. Furthermore, finite-time reachability of the sliding surface is also guaranteed by the proposed fuzzy sliding-mode control laws. A practical example is provided to demonstrate the effectiveness of the established method numerically.

Molecular Imprinting: Materials Nanoarchitectonics with Molecular Information

Abstract: Combining nanotechnology with the other science disciplines is necessary to produce various materials with nanoscale structural and functional information, which is nanoarchitectonics as a novel paradigm to create useful materials. One of the basic ideas in the nanoarchitectonics concept is use of molecular-level information to architect functional materials. This kind of strategy is indeed used in some pre-existing science fields and technical methods. For example, molecular imprinting technique provides functional materials possessing molecular information in insides of fabricated materials. Revisiting such known concept with the nanoarchitectonics concept would have great meaning in unification of individual research disciplines into one key concept. In this review, we survey fundamentals and recent trends of the molecular imprinting approaches upon consideration with the nanoarchitectonics. Here, aspects and examples of molecular imprinting are surveyed from fundamentals to advanced applications: (i) ...

Enhanced growth of halophyte plants in biochar-amended coastal soil: roles of nutrient availability and rhizosphere microbial modulation.

Abstract: Soil health is essential and irreplaceable for plant growth and global food production, which has been threatened by climate change and soil degradation. Degraded coastal soils are urgently required to reclaim using new sustainable technologies. Interest in applying biochar to improve soil health and promote crop yield has rapidly increased because of its multiple benefits. However, effects of biochar addition on the saline–sodic coastal soil health and halophyte growth were poorly understood. Response of two halophytes, Sesbania (Sesbania cannabina) and Seashore mallow (Kosteletzkya virginica), to the individual or co-application of biochar and inorganic fertilizer into a coastal soil was investigated using a 52 d pot experiment. The biochar alone or co-application stimulated the plant growth (germination, root development, and biomass), primarily attributed to the enhanced nutrient availability from the biochar-improved soil health. Additionally, the promoted microbial activities and bacterial community shift towards the beneficial taxa (e.g. Pseudomonas and Bacillus) in the rhizosphere also contributed to the enhanced plant growth and biomass. Our findings showed the promising significance because biochar added at an optimal level (≤5%) could be a feasible option to reclaim the degraded coastal soil, enhance plant growth and production, and increase soil health and food security.

Excellent corrosion protection performance of epoxy composite coatings filled with silane functionalized silicon nitride

Abstract: Silicon nitride was firstly used as anticorrosive pigment in organic coatings. An effective strategy by combining inorganic fillers and organosilanes was used to enhance the dispersibility of silicon nitride in epoxy resin. The formed nanocomposites were applied to protect Q235 carbon steel from corrosion. The anticorrosive performance of modified silicon nitride with silane (KH-570) was investigated by electrochemical impedance spectroscopy (EIS), water absorption and pull-off adhesion methods. With the increase of immersion time, the corrosion resistance as well as adhesion strength of epoxy resin coating and unmodified silicon nitride coating decreased significantly. However, for the modified silicon nitride coating, the corrosion resistance and adhesion strength still maintained 5.7×1010 Ω cm2 and 7.6 MPa after 2400-h and 1200-h immersion, respectively. The excellent corrosion resistance performance could be attributed to the chemical interactions between KH-570 functional groups and silicon nitride powders, which mainly came from the easy formation of Si-O-Si bonds. Furthermore, the modified silicon nitride coating formed a strong barrier to corrosive electrolyte due to the hydrophobic of modified silicon nitride powder and increased bonds.

Prescribing Functional Additives for Treating the Poor Performances of High-Voltage (5 V-class) LiNi0.5Mn1.5O4/MCMB Li-Ion Batteries

Abstract: In this paper, tris(trimethylsilyl) phosphite (TMSP) and 1,3-propanediolcyclic sulfate (PCS) are unprecedentedly prescribed as binary functional additives for treating the poor performances of high-voltage (5 V-class) LiNi0.5Mn1.5O4/MCMB (graphitic mesocarbon microbeads) Li-ion batteries at both room temperature and 50 degrees C. The high-voltage LiNi0.5Mn1.5O4/MCMB cell with binary functional additives shows a preponderant discharge capacity retention of 79.5% after 500 cycles at 0.5 C rate at room temperature. By increasing the current intensity from 0.2 to 5 C rate, the discharge capacity retention of the high-voltage cell with binary functional additives is approximate to 90%, while the counterpart is only approximate to 55%. By characterizations, it is rationally demonstrated that the binary functional additives decompose and participate in the modification of solid-electrolyte interface layers (both electrodes), which are more conductive, protective, and resistant to electrolyte oxidative/reductive decompositions (accompanying active-Li+ consuming parasitic reactions) due to synergistic effects. Specifically, the TMSP additive can stabilize LiPF6 salt and scavenge erosive hydrofluoric acid. More encouragingly, at 50 degrees C, the high-voltage cell with binary functional additives holds an ultrahigh discharge capacity retention of 79.5% after 200 cycles at 1 C rate. Moreover, a third designed self-extinguishing flame-retardant additive of (ethoxy)-pentafluoro-cyclo-triphosphazene (PFPN) is introduced for reducing the flammability of the aforementioned binary functional additives containing electrolyte.

An overview of metamaterials and their achievements in wireless power transfer

Abstract: Metamaterials have been deployed for a wide range of fields including invisible cloak, superlens, electromagnetic wave absorption and magnetic resonance imaging, owing to their peculiar electromagnetic properties. However, few investigations on metamaterials were focused on wireless power transfer (WPT). WPT is the transmission of electrical energy from a power source to an electrical load without conductors like wires or cables. Metamaterials can enhance the transfer efficiency and enlarge the transfer distance due to their ability of focusing magnetic flux, which opens up a novel approach to promoting the development and application of WPT. This review paper aims to provide an overview of the fabrications, exotic properties, and their applications especially in the WPT field. Meanwhile, the perspective and future challenges of metamaterials and WPT are proposed.

Formation and Physicochemical Characteristics of Nano Biochar: Insight into Chemical and Colloidal Stability.

Abstract: Nano biochar (N-BC) attracts increasing interest due to its unique environmental behavior. However, understanding of its formation, physicochemical characteristics, and stability of N-BC is limited. We therefore examined N-BC formation from bulk biochars (B-BCs) produced from peanut shell, cotton straw, Chinese medicine residues, and furfural residues at 300–600 °C. Carbon stability and colloidal processes of nano peanut shell biochars (N-PBCs) were further investigated. N-BCs formed from pore collapse and skeleton fracture during biomass charring, breakup due to grinding, and sonication. Amorphous fraction in B-BCs was more readily degraded into N-BCs than graphitic component. The sonication-formed N-PBCs contained 19.2–31.8% higher oxygen and fewer aromatic structures than the bulk ones, leading to lower carbon stability, but better dispersibility in water. Heteroaggregation of N-PBCs with goethite/hematite destabilized initially and then restabilized with increasing concentrations of N-PBCs. Compared w...