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A novel strategy was developed to fabricate FeNx-doped carbon quantum dots (Fe-N-CQDs) to detect Cu2+ ions selectively as a fluorescence probe. The Fe-N-CQDs were synthesized by an efficient electrolysis of a carbon cloth electrode, which was coated with monoatomic iron-anchored nitrogen-doped carbon (Fe-N-C). The obtained Fe-N-CQDs emitted blue fluorescence and possessed a quantum yield (QY) of 7.5%. An extremely wide linear relationship between the Cu2+ concentration and the fluorescence intensity was obtained in the range from 100 nM to 1000 nM (R2 = 0.997), and the detection limit was calculated as 59 nM. Moreover, the Fe-N-CQDs demonstrated wide range pH compatibility between 2 and 13 due to the coordination between pyridine nitrogen and Fe3+, which dramatically reduced the affection of the protonation and deprotonation process between H+ and Fe-N-CQDs. It is notable that the Fe-N-CQDs exhibited a rapid response in Cu2+ detection, where stable quenching can be completed in 7 s. The mechanism of excellent selective detection of Cu2+ was revealed by energy level simulation that the LUMO level of Fe-N-CQDs (−4.37 eV) was close to the redox potential of Cu2+, thus facilitating the electron transport from Fe-N-CQDs to Cu2+.

Rational design of advanced structure for transition metal oxides (TMOs) is attractive for achieving high-performance supercapacitors. However, it is hampered by sluggish reaction kinetics, low mass loading, and volume change upon cycling. Herein, hierarchical NiCo2O4 architectures with 2D-nanosheets-shell and 3D-nanocages-core (2D/3D h-NCO) are directly assembled on nickel foam via a facile one-step way. The 2D nanosheets are in-situ generated from the self-evolution of initial NCO nanospheres. This 2D/3D hierarchical structures ensure fast ion/electron transport and maintain the structural integrity to buffer the volume expansion. The 2D/3D h-NCO electrode with an ultrahigh mass loading (30 mg cm−2) achieves a high areal capacity of 4.65 C cm−2 (equivalent to 1.29 mAh cm−2) at a current density of 4 mA cm−2, and retains 3.7 C cm−2 even at 50 mA cm−2. Furthermore, the assembled solid-state hybrid supercapacitor yields a high volumetric energy density of 4.25 mWh cm−3 at a power density of 39.3 mW cm−3, with a high capacity retention of 92.4% after 5000 cycles. Therefore, this work provides a new insight to constuct hierarchical electrodes for energy storage application.

The accurate and rapid acquisition of the soil salt content and spatial distribution is of great significance for effectively monitoring cropland soil salinization. Using OLI/Landsat-8 images as da...

Rechargeable aqueous zinc-ion batteries (ZIBs) have become a research hotspot in recent years, due to their huge potential for high-energy, fast-rate, safe and low-cost energy storage. To realize good electrochemical properties of ZIBs, cathode materials with prominent Zn2+ storage capability are highly needed. Herein, we report a promising ZIB cathode material based on electrochemically induced transformation of vanadium oxides. Specifically, K2V6O16·1.5H2O nanofibers were synthesized through a simple stirring method at near room temperature and then used as cathode materials for ZIBs in different electrolytes. The cathode presented superior Zn2+ storage capability in Zn(OTf)2 aqueous electrolyte, including high capacity of 321 mAh/g, fast charge/discharge ability (96 mAh/g delivered in 35 s), high energy density of 235 Wh/kg and good cycling performance. Mechanism analysis evidenced that in Zn(OTf)2 electrolyte, Zn2+ intercalation in the first discharge process promoted K2V6O16·1.5H2O nanofibers to transform into Zn3+xV2O7(OH)2·2H2O nanoflakes, and the latter served as the Zn2+-storage host in subsequent charge/discharge processes. Benefiting from open-framework crystal structure and sufficiently exposed surface, the Zn3+xV2O7(OH)2·2H2O nanoflakes exhibited high Zn2+ diffusion coefficient, smaller charge-transfer resistance and good reversibility of Zn2+ intercalation/de-intercalation, thus leading to superior electrochemical performance. While in ZnSO4 aqueous electrolyte, the cathode material cannot sufficiently transform into Zn3+xV2O7(OH)2·2H2O, thereby corresponding to inferior electrochemical behaviors. Underlying mechanism and influencing factors of such a transformation phenomenon was also explored. This work not only reports a high-performance ZIB cathode material based on electrochemically induced transformation of vanadium oxides, but also provides new insights into Zn2+-storage electrochemistry.

Nowadays, rational yet high value-added utilization of low-cost petroleum asphalt still faces a significant challenge. In light of its high carbon content and abundant sulfur atoms, here, an in-situ bonding sulfur strategy is proposed to fabricate transition metal (Mn, Mo, Fe, or Co)-based/carbon composites (TM-based/C). This strategy successfully achieves the conversion from thiophenic-S of asphalt into transition metal sulfides (TMSs). When tested as anodes for lithium-ion batteries (LIBs), the TM-based/C electrodes deliver better specific capacity and cycling performance than those of sulfur-doped carbon nanosheets (SCN) electrode. As a typical example, a 3D network-nanosheets structure of Mn-based/C composite is constructed, and the optimized MnO2/MnS2/C-2 electrode achieves low charging/discharging voltage platform of 1.2 V/0.58 V, and delivers long-term life of 827 mAh g−1 after 400th cycle at 0.5 A g−1. These excellent electrochemical properties benefit from its structural integrity upon cycling and the formation of MnS2/MnO2 phases. Furthermore, LiFePO4/(MnO2/MnS2/C-2) full cell exhibits a remarkably reversible capacity of 168 mAh g−1 at 0.8C, and impressive cycling stability of 78% after 400 cycles at 1 C, better than those of LiFePO4/(commercial graphite). This work may provide a new perspective for the high value-added utilization of low-cost petroleum asphalt for efficient anodes toward LIBs.

As a unique class of molecular electronic materials, organic donor–acceptor complexes now exhibit tantalizing prospect for heat–electricity interconversion. Over the past decades, in design of these materials for thermoelectric applications, consistent efforts have been made to synthesize a wide variety of structures and to characterize their properties. However, hitherto, one of the paramount conundrums, namely lack of systematic molecular design principles, has not been addressed yet. Here, based on ab initio calculations, and by comprehensively examining the underlying correlation among thermoelectric power factors, non-intuitive transport processes, and fundamental chemical structures for 13 prototypical organic donor–acceptor complexes, we establish a unified roadmap for rational development of these materials with increased thermoelectric response. We corroborate that the energy levels of frontier molecular orbitals in the isolated donor and acceptor molecules control the charge transfer, electronic property, charge transport, and thermoelectric performance in the solid-state complexes. Our results demonstrate that tailoring a suitable energy-level difference between donor’s highest occupied molecular orbital and acceptor’s lowest unoccupied molecular orbital holds the key to achieving an outstanding power factor. Moreover, we reveal that the charge-transfer-caused Coulomb scattering governs the charge and thermoelectric transport in organic donor–acceptor complexes.

A multi-mode flapping wing micro air vehicle (FWMAV) that uses a figure eight wingtip motion trajectory with wing flapping, rotation, and swing motion is presented in this paper. The flapping wing vehicle achieves three active degrees of freedom (DOF) wing movements only with one driving micromotor which has a good balance in the mechanism design (that is inspired by natural fliers) and total weight. Owing to these characteristics being integrated into the simple mechanism design, the aerodynamic force is improved. The aerodynamic performance of the thrust force is improved by 64.3 % compared to one that could only flap up and down with one active DOF under the condition of routine flapping frequency.

In Named Data Networking (NDN) architecture, data can be obtained from multiple content sources (i.e., producers or caching nodes) with multiple paths, making the traditional end-to-end (i.e., TCP/IP) congestion control scheme invalid. In addition, the NDN multi-path discovery and management are still an open issue as the dynamic network topology changes. In this article, we propose a multi-path congestion control mechanism, named MPCC, which includes two major components, i.e., multi-path discovery and multi-path congestion control. Particularly, for multi-path discovery, we first devise a path tag to uniquely mark each sub-path in the forwarding process, and then propose a tag-aware forwarding strategy to discover and manage sub-paths. For multi-path selection and congestion control, we first integrate the metrics of packet loss, bandwidth, round trip time, and path centrality, for path assessment, based on which, we then leverage the Upper Confidence Bound (UCB) algorithm to select sub-paths in order to maximize the network throughput. In addition, for selected sub-paths, we have devised a sub-path window adaptation algorithm to avoid multi-path congestions. At last, we implement MPCC in ndnSIM and conduct extensive experiments for performance evaluation. Our results demonstrate that MPCC can discover all sub-paths in real-time for the multi-path scenario, and can effectively avoid multi-path congestions with improving throughput and reducing transmission time.

The grid-connected inverter is the vital energy conversion device in renewable energy power generation. With the increasing installed capacity of renewable energy, the grid presents characteristics of weak grids with large grid impedance. In general, the inverter often obtains grid synchronization information by the phase-locked loop (PLL) and to suppress the background harmonic and amplitude disturbance of grid voltage, the grid voltage feedforward (GVF) control is also needed. However, previous researches revealed that the PLL and the GVF would shape the quadrature-axis ( $\boldsymbol {q}$ -axis) output impedance of the inverter into a negative resistance in the low-frequency band, and this would be responsible for the instability of the inverter under a weak grid. To resolve this instability issue, this article proposes an impedance controller for reshaping the $\boldsymbol {q}$ -axis impedance into a positive resistance in the low-frequency band, which eliminates the negative effect introduced by the PLL and the GVF; therefore, the inverter will operate under very weak grids. Moreover, the proposed control strategy is only for $\boldsymbol {q}$ -axis impedance reshaping, and it does not affect the output characteristics of $\boldsymbol {d}$ -axis, thus ensuring the ability of the inverter to suppress background harmonics and amplitude disturbance of the grid voltage. The conclusions are verified by experimental results.

The integration of the massive multiple-input multiple-output (MIMO) and millimeter-wave (mmWave) communication can increase the throughput of 5G networks. As an attractive technique in the MIMO systems, hybrid beamforming (HBF) can improve the 5G capacity by employing spatial domain resources. However, with the increase of the number of antennas, the traditional beamforming algorithms fail to efficiently keep a balance between the hardware complexity and beamforming gains. In this paper, with the aid of bidirectional location information, a bidirectional positioning assisted HBF (BPA-HBF) scheme is proposed. Specifically, we first propose a new scheme to decouple the optimal problem of traditional HBF as two phases. In the analog beamforming (ABF) phase, the dominated path among the multi-path components is determined by the transmitter and receiver. In addition, the codebook-based beamforming weight vectors are bidirectionally and synchronously determined according to the angle parameters of the dominated path. In the second phase, based on the ABF matrices, the digital beamformers are designed to maximize the energy efficiency. Simulation results indicate that the proposed BPA-HBF scheme can lead to a lower convergence time and complexity than the conventional schemes. In addition, the results show that the algorithm convergence time can be significantly reduced by increasing the positioning precision.

Nitride coatings have been generally applied on light alloys like titanium and aluminium to promote their multiple performances, including hardness, thermal stability and wear resistance. In this work, TiAlSiN/TiN multilayered (ML) coating and TiAlSiN single-layer (SL) coating were deposited on TC18 (Ti5Al5Mo5V1CrFe) alloy by Multi-arc ion plating technique. The microstructure and chemical composition of the coatings were evaluated by SEM, XRD and XPS. Additionally, hardness, adhesion and wear resistance were measured through nanoindentation, scratch spectrometer and ball-on-disk tribometer. The results present that both ML and SL coating contain three main phases of TiN, Al2O3 and Si3N4. Nevertheless, the adhesion of ML coating is 62.4 N, compared to that of the SL coating is 51.8 N. The parameter H3/E2 as an indication of plastic deformation to evaluate wear resistance shows that the ML coating has high hardness and high toughness concurrently. The tribological study indicated that the wear rate of the ML coated specimen was 1/7 of the SL coated counterpart.

Thermal or photochemical 1,4-coupling reactions of butadiyne units can be employed to cross-link polymers. Poly(arylenebutadiynylene)s are solution-processable organic semiconducting polymers which...

To examine the coral reef limestone–concrete shear failure characteristics, we conducted large-scale direct shear tests to study five types of interfaces: planar, sloped, arc shaped, stepped, and t...

Developing microwave absorption (MA) materials with satisfied comprehensive performance is a great challenge for tackling severe electromagnetic pollution. In particular, the magnetic component/carbon hybrids absorbers always suffer from high filler loading. Herein, we propose a feasible strategy to construct hierarchical porous carbon with tightly embedded Ni nanoparticles (Ni@NPC). These highly dispersed Ni nanoparticles produce strong magnetic coupling networks to enhance magnetic loss abilities. Moreover, the interconnected hierarchical dielectric carbon network affords favorable dipolar/interfacial polarization, conduction loss, multiple reflection and scattering. Impressively, with an ultralow filler loading of 5 wt.%, the resultant Ni@NPC/paraffin composite achieves an excellent MA performance with a minimum reflection loss of as high as -72.4 dB and a broad absorption bandwidth of 5.0 GHz. This capability outperforms most current magnetic-dielectric hybrids counterparts. Furthermore, the MA capacity can be easily tuned with adjustments in thickness, content and type of magnetic material. Thus, this work opens up new avenues for the development of high-performance and lightweight MA materials.

Sustainable bioconversion of glycerol into 3-hydroxypropionic acid (3-HP) and 1,3-propanediol (1,3-PDO) is often bottlenecked by the accumulation of a toxic metabolic intermediate, 3-hydroxypropana...

Microalgae consists a promising feedstock for biofuel production due to their high growth rates and lipid content. Microalgal wastewater remediation can achieve both organic matters removal and biodiesel production, leading to economic benefits. In this study, immobilized microalgae and algae-bacteria consortia were used to treat synthetic fracturing wastewater. Organic matter removal, biomass production and lipid synthesis by co-culture of Chlorella vulgaris and Bacillus bacteria were investigated in comparison with an algae immobilization system during the process. The chemical oxygen demand removal rate and lipid concentration of the co-culture were both lower than those of the immobilized C. vulgaris, while algal biomass under the two cultivation conditions was similar. The immobilized algae provided higher amount of fatty acids, especially mono-unsaturated fatty acids, than the algae-bacteria consortia. Most of the fuel properties of biodiesel produced in both immobilized and co-cultured C. vulgaris complied with the specifications for standard biodiesel. The comparative results of enzyme activity showed that immobilization can enhance the activity of acetyl-CoA carboxylase, the key enzyme for fatty acids synthesis, leading to the formation of more fatty acids and lipids. Furthermore, immobilization decreased the ADP-glucose pyrophosphorylase activity and inhibited starch formation. Immobilization favors lipid production and removal of organics by C. vulgaris.

Named Data Networking (NDN) is considered as a prominent architecture towards future Wireless Local Area Networks (WLAN), and multicast plays an important role in data delivery such as media streaming, multipoint videoconferencing, etc. However, to achieve high-efficiency multicast in NDN WLAN is challenging for two significant reasons. First, without feedback mechanism in IEEE 802.11 standards, to guarantee reliability, the current multicast scheme transmits the multicast data with the basic rate (e.g., 1 Mbps for IEEE 802.11b), which inevitably increases the transmission delay for high-speed consumers. Second, as a NDN multicast group is constituted by consumers who are requesting the same content, multicast groups are easy to form and evolve rapidly, where a data rate adaptation scheme is requisite to accommodate differential multicast groups. In this paper, we propose a multi-stage multicast rate adaptation scheme for NDN WLAN, named NDN-MMRA , to minimize the total transmission time with reliability guarantee for multicast group members. In NDN-MMRA , by checking the Pending Interest Table (PIT) status information, the number of consumers in each multicast group as well as their receiving capabilities are known ahead; with the available data rates in a specific 802.11 standard, NDN-MMRA determines: 1) how many transmission stages are required; and 2) in each stage, which data rate should be adopted. The merit is that with multi-stage transmissions, the data rate can be adapted in descending order to accommodate high-speed consumers with delay minimized, and low-speed consumers with reliability guaranteed. We implement NDN-MMRA in NS-3 by adopting the ndnSIM module, and conduct extensive experiments to demonstrate its efficacy under different IEEE 802.11 standards and various underlying WLAN topologies.

This paper investigated the problem of multi-target tracking (MTT) over a vehicle sensor network. A novel adaptive square root cubature joint probabilistic data association (ASRCJPDA) was proposed. Motivated by enhancing the stability of joint probabilistic data association (JPDA) in practical application, the proposed methodology implemented a numerically stabled cubature Kalman filter for JPDA state estimate process. It improved numerical stability and acquired more accurate estimated results. Additionally, enlightened by enhancing the real time efficiency of JPDA, an adaptive tracking gate designed for the JPDA measurement associate process was proposed. It combined with the kinematics of vehicle to reduce the computational complexity of data association, which improved the robustness of MTT in complex scenarios. The virtual vehicle target tracking scenarios were built in PreScan software in order to better simulate the real traffic condition. Simulations of target tracking examples are presented to show great effectiveness and superiority of the proposed method.

Graph convolutional network (GCN) has been proved to be an effective framework for graph-based semi-supervised learning applications. The core operation block of GCN is the convolutional layer, which enables the network to construct node embeddings by fusing both attributes of nodes and relationships between nodes. Different features or feature interactions inherently have various influences on the convolutional layers. However, there are very limited studies about the impact of feature importance in GCN-related communities. In this work, we attempt to augment convolutional layers in GCNs with statistical attention-based feature importance by modeling the latent interactions of features, which is complementary to the standard GCNs and only needs simple calculations with statistics rather than heavy trainings. To this end, we treat the feature input of each convolutional layer as a separate multi-layer heterogeneous graph, and propose Graph Statistical Self-Attention (GSSA) method to automatically learn the hierarchical structure of feature importance. More specifically, we propose two modules in GSSA, Channel-wise Self-Attention (CSA) to capture the dependencies between feature channels, and Mean-based Self-Attention (MSA) to reweight similarities among features. Aiming at each graph convolutional layer, GSSA can be applied in a ”plug and play” way for a wide range of GCN variants. To the best of our knowledge, this is the first implementation that optimizes GCNs from the feature importance perspective. Extensive experiments demonstrate that GSSA can promote existing popular baselines remarkably in semi-supervised node classification tasks. We further employ multiple qualitative evaluations to get deep insights into our method.

Machine learning models have achieved state-of-the-art performance in various fields, from image classification to speech recognition. However, such models are trained with a large amount of sensitive training data, and are typically computationally expensive to build. As a result, many cloud providers (e.g., Google) have launched machine-learning-as-a-service, which helps clients benefit from the sophisticated cloud-based machine learning models via accessing public APIs. Such a business paradigm significantly expedites and simplifies the development circles. Unfortunately, the commercial value of such cloud-based machine learning models motivates attackers to conduct model extraction attacks for free use or as a springboard to conduct other attacks (e.g., craft adversarial examples in black-box settings). In this article, we conduct a thorough investigation of existing approaches to model extraction attacks and defenses on cloud-based models. We classify the state-of-the-art attack schemes into two categories based on whether the attacker aims to steal the property (i.e., parameters, hyperparameters, and architecture) or the functionality of the model. We also categorize defending schemes into two groups based on whether the scheme relies on output disturbance or query observation. We not only present a detailed survey of each method, but also demonstrate the comparison of both attack and defense approaches via experiments. We highlight several future directions in both model extraction attacks and its defenses, which shed light on possible avenues for further studies.

Laser dynamic flexible forming (LDFF) is a novel high velocity forming (HVF) technology, in which the foil metal is loaded by laser shock wave. Strain localization is readily to occur around the bulge edge, which will result in the ultimate dynamic failure. In this work, the microstructures before and after dynamic fracture are characterized by transmission electron microscopy (TEM) to investigate the dynamic failure mechanism. The plastic deformation regions of copper foil are composed of shock compression, strain localization and bulge. Microstructure refinement was observed in three different plastic deformation regions, particularly, dynamic recrystallization (DRX) occurs in the strain localization and bulge regions. In bulge region, extremely thin secondary twins in the twin/matrix (T/M) lamellae are formed. The microstructure features in the strain localization region show that superplastic flow of material exists until fracture, which may be due to DRX and subsequent grain boundary sliding (GBS) of the recrystallized grains. The grain coarsening in strain localization region may degrade the material flowing ability which results in the dynamic fracture.

Background: The high permeability of Distributed Generation (DG) and the development of DC load represented by electric vehicle Battery Swapping Station (BSS) pose new challenges to the reliable and economic operation of DC distribution system. Methods: In order to improve the wind and solar absorption rate and the reliable operation of DC distribution network and coordinate the interests and demands of BSS and DC distribution company, the upper level takes the abandonment rate and the minimum variance of BSS charging and discharging net load as two objective functions, and the lower level takes the minimum operation cost of DC distribution network and BSS as the objective function. Secondly, this paper proposes a method that combines Genetic Algorithm (GA) with Wind-Driven Optimization algorithm (WDO). CPLEX and hybrid GA-WDO are used to solve the upper and lower models, respectively. Results: Finally, an example shows that the proposed optimization model can reduce the operation cost of DC distribution network with BSS and improve the utilization rate of wind and light, which shows the rationality and effectiveness of the optimization model. Conclusion: In this paper, considering the randomness and uncertainty of wind power generation and photovoltaic power generation, this paper establishes the upper objective function with the minimum abandonment rate and load variance and the lower objective function with the minimum operation cost of DC distribution network and BSS operators.

Service migration is an often-used approach in cloud computing to minimize the access cost by moving the service close to most users. Although it is effective in a certain sense, the service migration in existing research still suffers from some deficiencies in its evolutionary abilities in scalability , sensitivity , and adaptability to effectively react to the dynamically changing environments. This article proposes an evolutionary framework based on deep reinforcement learning for virtual service migration in large-scale mobile cloud centers. To enhance the spatio-temporal sensitivity of the algorithm, we design a scalable reward function for virtual service migration, redefine the input state, and add a Recurrent Neural Network ( RNN ) to the learning framework. Additionally, in order to enhance the adaptability of the algorithm, we also decompose the action space and exploit the network cost to adjust the number of virtual machine (VMs). The experimental results show that, compared with the existing results, the migration strategy generated by the algorithm can not only significantly reduce the total service cost and achieve the load balancing at the same time, but also address the burst situations with low cost in dynamic environments.

Zeolitic imidazolate framework (ZIF-8) in three particle sizes (40, 70 and 100 nm) was prepared through both solvothermal and hydrothermal methods and employed to decorate polyvinylidene fluoride (PVDF). The finger-like macro-voids, sponge-like poly-porous morphology and surface roughness of prepared membranes were characterized by SEM and AFM microscopy. The FTIR spectrum and XPS analysis bear out the chemical component. ZIF-8 has the characteristics of higher porosity and appropriate pore size, which is a condition for improving the permeability and pollution resistance of the modified membrane. Results indicated that different ZIF-8s have different enhancement effects on PVDF MMM. 100 nm ZIF-8 membrane possessed pure water flux (PWF) of 350 L m−2h−1, which was 10 times more than the bare membrane (30 L m−2h−1), and OVA flux recovery ration (FRR%) is 98%. 40 nm ZIF-8 membrane owned BSA FRR% of 98.4%. The 70 nm ZIF-8 showed the best mechanical properties. The dynamic contact angles of UP-Z70 ranged from 104.5° to 62.5° within 180 s. Furthermore, pore size distribution, molecular weight cut-off (MWCO) and porosity were also researched to evaluate the MMM. The dislodge of Reactive Black KN-B, Reactive Red 3BS and Reactive Brilliant Blue KN-R dyes by MMM were studied under different dye concentrations and transmembrane pressures. The membrane can provide selective separation methods for dyes and Reactive Brilliant Blue KN-R up to 99%. Overall, the permeability, hydrophilicy, anti-fouling performance and wastewater treatment of modified membranes were regulated by the ZIF-8 in a steerable blending reaction modification process.

The television ratings provide an effective way to analyze the popularity of TV programs and audiences’ watching habits. Most previous studies have analyzed the ratings from a single perspective. Few efforts have integrated analysis from different perspectives and explored the reasons for changes in ratings. In this paper, we design a visual analysis system called TVseer to analyze audience ratings from three perspectives: TV channels, TV programs, and audiences. The system can help users explore the factors that affect ratings, and assist them in decisions about program productions and schedules. There are six linked views in TVseer: the channel ratings view and program ratings view show ratings change information from the perspective of TV channels and programs respectively; the overlapping program competition view and the same-type program competition view indicate the competitive relationships among programs; the audience transfer view shows how audiences are moving among different channels; the audience group view displays audience groups based on their watching behavior. Besides, we also construct case studies and expert interviews to prove our system is useful and effective.

In this work, we have studied the thermal diffusivity of saturated liquids in the temperature range from 303.15 to 393.15 K for trans-1-chloro-3,3,3-trifluoropropene (R1233zd(E)) and dodecafluoro-2...

Developing efficient and cheap electromagnetic wave absorption (EWA) materials is highly desirable in modern information society. Herein, based on the abundant and low-cost petroleum asphalt, hierarchical porous carbon nanosheets (PCNs) have been rationally fabricated via one-step carbonization process by using water-removable NaCl templates. The NaCl can provide crystal planes for the growth of graphitized carbon layers, and promote the formation of interconnected porous architectures. The porous nanosheets structures realize the multiple reflections and scattering in the void space. The presence of dipole polarization and interfacial polarization in PCNs facilitates the dielectric loss. Remarkably, the EWA performance of optimized PCNs with a low filler content of 20 wt% reaches a strong reflection loss of −53.7 dB and a broad absorption bandwidth of 5.3 GHz at a thin thickness of 1.8 mm. This encouraging performance considerably outperforms most of reported dielectric materials, which also meets the demands of thin, light weight, strong and broad features for new-type EWA materials. Therefore, our strategy may open up new avenues for development of promising EWA materials and realizing the high value-added utilization of petroleum asphalt by considering the facile process and low production cost.

Titanium nitride (TiN) buffer is generally applied to improve the epitaxial growth quality of MgO(100) on Si(100) substrate, despite lacking integral and comprehensive description of the mechanism ...

When a dump truck brakes, it is difficult to effectively absorb the braking energy due to the transient mutation of braking energy. At the same time, braking energy production is too high to store easily. Focusing on these problems, this paper proposes a new type of two-stage series supercapacitor and battery (SP&B) hybrid energy storage system (ESS). Using the characteristics of supercapacitors, which can charge and discharge quickly with large currents, the system combines the supercapacitors with a battery with a high energy storage capacity. This allows sudden large currents to be absorbed and released rapidly, while large amounts of energy can be stored. This system can also reduce the charge and discharge times of the SP&B to meet the working requirements of dump truck braking while improving the service life of the system. After completion of the research and implementation of the proposed SP&B hybrid ESS, a laboratory dynamic model was set up as an experimental platform and vehicle operation experiments were performed. The obtained results show that the energy recovery efficiency of the hybrid ESS can reach 53.5%, which can realize both security and stability for dump truck braking energy recovery and utilization (BER&U) systems.

Starch, being one of the most abundant polysaccharides in nature, has been modified as starch-based thermoplastic materials for decades. In this work, we have demonstrated a green and facile method...

The high value-added utilization of fluid catalytic cracking (FCC) slurry has always been full of challenges and has important practical significance. Ultralight N-rich porous graphene nanosheets (...

Braking safety of heavy-duty engines has always been the focus of the research, and the fuel economy and after-treatment thermal management during low-load operation of heavy-duty engines have also received much attention in recent years. A variable mode valve actuation system which can realize switching between four-stroke driving, two-stroke compression release braking and cylinder deactivation modes on a traditional four-stroke engine was proposed in this article. Two-stroke compression release braking mode of the variable mode valve actuation system can greatly enhance the braking safety, while the overload of valve train was a great challenge, especially during the release event. The effects of different release opening timing on cylinder pressure and the braking performance were studied. The results indicated that a higher cylinder pressure does not always lead to higher braking power. When the release opening timing was advanced by 6 °CA, the braking power reduced by only 9 kW (2.65%) at 1900 r/min compared with the initial value, while the maximum cylinder pressure reduced by 11.4 bar (20.8%). Besides, the variable mode valve actuation system can realize alternate three-cylinder cylinder deactivation mode on a six-cylinder turbocharged engine, which can improve the brake-specific fuel consumption by 14.67% and increase the turbine outlet temperature by 63.6 °C and reduce the exhaust flow rate by 50.66% at lightly load idle. Meanwhile, when the engine load is less than 50% at the rated speed, the three-cylinder cylinder deactivation mode can improve the brake-specific fuel consumption, increase the turbine outlet temperature and reduce the exhaust flow rate. The increase of the turbine outlet temperature and the decrease of the exhaust flow rate are very beneficial to improve the efficiency of the after-treatment thermal management of heavy-duty engines.

The conceptual understanding of charge transport in conducting polymers is still ambiguous due to a wide range of paracrystallinity (disorder). Here, we advance this understanding by presenting the relationship between transport, electronic density of states and scattering parameter in conducting polymers. We show that the tail of the density of states possesses a Gaussian form confirmed by two-dimensional tight-binding model supported by Density Functional Theory and Molecular Dynamics simulations. Furthermore, by using the Boltzmann Transport Equation, we find that transport can be understood by the scattering parameter and the effective density of states. Our model aligns well with the experimental transport properties of a variety of conducting polymers; the scattering parameter affects electrical conductivity, carrier mobility, and Seebeck coefficient, while the effective density of states only affects the electrical conductivity. We hope our results advance the fundamental understanding of charge transport in conducting polymers to further enhance their performance in electronic applications., Obtaining a complete picture for charge transport in conducting polymers is vital to designing new organic electronic materials. Here, the authors show that a gaussian density of states clarifies the transport physics in conducting polymers by revealing the role of carrier scattering on transport.

Objective: To study the effect and mechanism of Huayu Wan (化瘀丸, HYW) in combination of chemotherapy of tumor treatment. Methods: HYW serum was added in Lewis cells to assess its impact on fluorescent doxorubicin delivery in vitro. Then, Lewis tumor cells was implanted in C57BL/6 mice via xenograft transplantation. Tumor growth was measured and signal intensity corresponding to blood flow was assessed by laser doppler perfusion imaging (LDPI). Finally, the effect of HYW on the effificacy of doxorubicin was studied. Results: HYW can improve the transfer of fluorescent doxorubicin into cells. The blood flow signal in the tumor tissues of the HYW group was higher than that of the control group (P

A new variable mode valve actuation system for a heavy-duty engine was proposed and designed in this paper. The variable mode valve actuation system can significantly enhance braking safety and improve fuel economy and emission of heavy-duty engines through flexible switching among four-stroke driving mode, two-stroke compression-release braking mode, and cylinder deactivation mode on a conventional four-stroke engine. The switching was controlled by four-stroke driving modules and two-stroke braking modules, both of which have two operation states: effective state and failure state. For the control of the multi-cylinder engine, all cylinders can be divided into several groups, and all the four-stroke driving modules in the same group were controlled by one solenoid valve, as well as all the two-stroke braking modules were controlled by another solenoid valve. A hydraulic-mechanical multi-body dynamics model was established to investigate the switching response of the variable mode valve actuation system. The results indicated that when the engine operated at 2000 r/min, the switching of the four-stroke driving module and the two-stroke braking module required 30 °CA and 101 °CA at most, respectively. In addition, to avoid the conflict between the four-stroke driving valve lift and the two-stroke braking valve lift, the switching between the four-stroke driving mode and the two-stroke compression-release braking mode must have a reasonable sequence. The variable mode valve actuation system has an excellent switching response and it is convenient for the control of the multi-cylinder engine. Therefore, the variable mode valve actuation system has a good application prospect for heavy-duty engines.

In this work, a class-AB operational amplifier is to be presented, which is developed in a 0.5 μm CDMOS technology. The proposed amplifier is composed of a folded cascade input stage and a class-AB output stage. Owing to the special design of the operational amplifier, the robustness of the whole circuit has been enhanced. The proposed system can drive a wide resistance load range from 10 Ω to 100 kΩ with a 10 pF capacitance load without distortion and stability problems. In addition, a current-limit technique that stems from the design of a low dropout linear regulator is adopted to protect the output stage of the operational amplifier from being damaged by a huge transient current under unexpected conditions (when the output terminal is shorted to ground or V DD). Measurement results show that the maximum output current is nearly 390 mA with an 800 mA DC current limiting protection circuit on the single 5 V power supply at room temperature. This design can stably work at the industrial temperature range from −40 to 125°C. What is more, the total static current consumption of the whole circuit is 624 μA and the chip area is 0.419 mm2.

Mahan and Sofo proved that the best thermoelectric performance could be found in materials with a sharp peak in the density-of-states (DOS) near the chemical potential, which may come from a localized electronic state. However, such a state usually results in a poor electrical conductivity. Therefore, such an idealized model leads to this question: is there a material which naturally possesses a narrow DOS peak near the band edge without a localized state? The answer is yes. From a number of covalent organic frameworks (COFs), we identified poly(tetrathienoanthracene) (PTTA), a purely organic 2D COF possessing such a DOS and subsequently achieves a significant thermoelectric performance with an enhanced Seebeck coefficient such that the peak n- and p-type power factors can reach up to 14.9 and 21.9 μW cm−1 K−2, respectively. This provided a feasible prototype of the Mahan–Sofo model and demonstrated for the first time that a purely organic 2D COF could exhibit high thermoelectric performance for functional applications.

Geometry and texture noise make it difficult to accurately describe road image rules, which leads to the low degree of automation of traditional template matching algorithms based on internal texture homogenization. We propose a semi-automatic road extraction method based on multiple descriptors to improve the degree of automation while ensuring the accuracy of road extraction. This method aims to address the problems of incomplete road image geometric information and poor homogeneity of internal road texture. The multiscale line segment orientation histogram model and sector descriptor are established. Road points are tracked by interpolation and extension, and postprocessing is used to fit the tracking points and extract the road routes. In this article, high-resolution remote sensing images of different types, different resolutions, and different scenes are selected, and the roads exhibit curvatures, vehicle and shadow occlusions, roundabouts, and variational features. Experiments show that for roads with a certain width, completeness, and correctness of the method are more than 98%. Additionally, as compared with other algorithms, the interactive human intervention of this method is reduced by more than 2/3.

MXenes are two-dimensional transition metal carbides, nitrides, and/or carbonitrides which display extensive versatility in their elemental composition for tuning and optimization of their functional properties. In this work, by using a multiscale approach of density functional theory calculations, cluster expansion method, and Monte Carlo simulations, we systematically investigate the Ti2(1−x)Mo2xCO2 alloy system of two-dimensional Ti2CO2 and Mo2CO2 MXenes with 0 < x < 1. From the alloy formation energies, we identify the stable ground-state and report the possible existence of an asymmetrically ordered Janus-like MXene alloy TiMoCO2. This alloy is theoretically validated to be stable thermodynamically, mechanically, and thermally, with a high order–disorder phase transition temperature of ∼640 K. Importantly, TiMoCO2 is a semiconductor with a band gap of 0.60 eV and its valence band maximum and conduction band minimum are located on opposite sides of the MXene monolayer. As such, the asymmetric configuration generates an intrinsic dipole moment, which realigns the conduction and valence band edges, permitting photocatalytic redox water-splitting to favorably occur with a higher solar absorption efficiency in the visible-infrared region due to the smaller band gap. From the transport calculations, we propose the TiMoCO2 MXene alloy to exhibit high room temperature n- and p-type power factors of 49.8 μW cm−1 K−2 and 15 μW cm−1 K−2, respectively, outperforming other related experimentally synthesized Ti–Mo based MXene alloys and even similar to that of p-doped SnSe which is one of the best performing thermoelectric materials. All these indicate the stable asymmetrically ordered Janus-like TiMoCO2 MXene alloy to be a promising high performance water-splitting photocatalyst and thermoelectric material, paving the way for more stable Janus-like MXenes with interesting and outstanding functional properties to be discovered.

The valuation of premium power based on perceived utility (PU, i.e., perceived effectiveness or satisfaction degree of customers) and their willingness to pay has been researched for years. One of the remaining challenges is the accurate evaluation of PU. PU is the foundation of premium power evaluation, and it is essential for the decision-making process of investments on premium power by high-tech manufacturers (HTMs). This paper presents a framework to effectively evaluate PU. In this framework, factors influencing PU were classified to be quantitative and qualitative. An indication system (IS) was then constructed based on those influencing factors. Finally, PU was evaluated by the IS, considering psychological perception and decision-making behavior of HTMs. The effectiveness of the proposed PU-evaluation framework was demonstrated through field case studies.

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), being the most popular conductive polymer, has been doped with various additives with the aim of improving its thermoelectric performance. Among all additives, dimethyl sulfoxide (DMSO) has been widely used for various treatments. In this work, we designed and synthesized a series of aliphatic- and aromatic-substituted sulfoxides as dopants to improve the thermoelectric properties of PEDOT:PSS. It was found that the substituents in the sulfoxides played a vital role in controlling the thermoelectric properties. Sulfoxides with relatively longer alkyl chains and large phenyl groups increased the electrical conductivity of PEDOT:PSS to more than 200 S cm−1 compared to the pristine PEDOT:PSS film. The sulfoxide with 4-nitrophenyl substituents, however, led to negligible changes in electrical conductivity but increased the Seebeck coefficient from 22 to 56 μV K−1. In contrast, the sulfoxide with 4-hydroxyphenyl substituents remarkably improved both the electrical conductivity and Seebeck coefficient, leading to a power factor of up to 69 μW m−1 K−2, much higher than that of the PEDOT:PSS film which was obtained by simply mixing with DMSO. Several simulation methods were used to evaluate various interactions between sulfoxides, PEDOT, and PSS to elucidate the mechanisms, revealing that the sulfoxide with 4-hydroxyphenyl groups exhibited additional interaction with the PSS phase, while the sulfoxide with 4-nitrophenyl groups showed strong interaction with the PEDOT phase instead and hence disrupted electrical conductivity. Our findings would uncover the mechanism of electrical conductivity enhancement, providing a general strategy for designing promising alternative additives for PEDOT:PSS treatment and eventually achieving better thermoelectric properties.

The breakage or fragmentation kinetic function (FKF) of a given father size floc breaking to form two specific daughter size flocs cannot be measured experimentally. Indirectly it can be determined from the FKF model used to solve the dimensionless log-form population balance (PB) equation for floc fragmentation subjected to meeting three conditions: i) the computed and experimental particle size distribution function (PSDF) matched at all fragmentation time, ii) the PSDF data at zero fragmentation time was the input in the computation and iii) the duration of the experimental fragmentation be used in making the PB equation dimensionless. The fragmentation of compact polyelectrolyte-bridged silica flocs in a narrow gap concentric cylinder flow cell was investigated in the laminar Taylor vortex flow regime. The FKF data was correlated with the Taylor number. The FKF values were much smaller for large flocs as they tend to migrate to the low shear region. Cryo-SEM images of the flocs at different fragmentation times showed compact fractal structure with dimension larger than 2.

The vortex electromagnetic (EM) wave carrying orbital angular momentum (OAM) has attracted much attention in radar applications. Aimed at the moving target detection application of vortex EM waves, the Doppler effect and the micro-Doppler (m-D) effect, both including the linear Doppler shift and the angular Doppler shift, are investigated. The theoretical analyses demonstrate that the Doppler effect and the m-D effect in vortex-EM-wave-based radar are significantly more complicated than those in traditional non-vortex-EM-wave-based radar, and can provide additional features for target identification and recognition. Simulations are given to validate the proposed theoretical analyses.

Donor–acceptor (D–A) copolymers are a type of prototypical conducting conjugated polymers with remarkably high mobility approaching 100 cm2 V−1 s−1, making them potential thermoelectric (TE) candidates. However, only limited pioneering experimental studies have been devoted to obtaining a microscopic understanding of the relationship between the atomic structure and TE properties of D–A copolymers, which hampered the effort to enhance their TE performance. As such, our work seeks to establish a comprehensive understanding of the intrinsic electronic, geometric, and TE properties of a series of D–A copolymer chains. By using density functional theory methods combined with Boltzmann transport and deformation potential theories, we found the strong intra-chain superexchange (SE) coupling to be a key indicator for high mobility and TE performance. Strong SE couplings induce not only small hole effective mass but also weak electron–phonon couplings, resulting in high mobility and high power factors. Furthermore, we provide a route to establish strong SE coupling and optimize the TE performance by minimizing the energy difference between the frontier molecular orbitals of the donor and acceptor moieties. Our work thus provides strong indications that D–A copolymers represent a class of systems with high potential in TE applications.

This paper focuses on the tracking control problem of Magnetic Levitation System (MLS). MLS is highly unstable nonlinear system, in the process of operation, MLS needs to have strong robustness and anti-interference ability. Due to disturbance and parameter uncertainties in MLS, it is complex to obtain the exact dynamics of MLS, and it is difficult to design a suitable controller. The dynamic equation of the system is established by Lagrange equation, and then we propose an adaptive Sliding Mode Control (SMC) based on Radial Basis Function Neural Network (RBFNN). Because of the parameter uncertainties and disturbance in MLS, RBFNN is used to approximate the unknown dynamics in MLS. The stability of the closed-loop system is strictly proved by using the Lyapunov stability theory, which can achieve the uniform ultimate boundedness (UUB) of the signals of the closed-loop MLS. MATLAB environment is used to verify the performance of the proposed controller. Considering disturbance, parameter change, or unmodeled dynamics in MLS, proposed controller is compared with other nonlinear controllers, simulation results verify the effectiveness of the proposed approach.

Interior permanent magnet synchronous motors (IPMSMs) have high power densities and speed control performance, and they are widely used in the industry. The problem of reducing the torque ripple of an IPMSM is one of the hot issues in the field of electrical machine design. In order to determine the optimal combination of the geometric parameters to reduce the torque ripple of an IPMSM, a range analysis was conducted on the data from the orthogonal experiments in this study, dividing the rotor geometric parameters into two categories (important and ordinary) based on their degree of impact on the torque ripples of the IPMSM. Thereafter, an optimization of the ordinary parameters was carried out based on the results of the range analysis, whereas the optimization of the important parameters was carried out through a method that combined a multi-island genetic algorithm (MIGA) and Radial Basis Function (RBF) neural networks. The torque ripple of the IPMSM was effectively reduced without materially affecting the output power. Finally, the results of this optimization process were verified using a finite element simulation. The optimization method used in this study divided the motor geometric parameters into two categories and applied a different method of optimization to each parameter type, so it was able to efficiently optimize multiple geometric parameters for the IPMSM.

The energy consumption of wireless interface is critical to power-constrained mobile devices. To improve energy efficiency for WLAN stations, power saving mode (PSM) is proposed, to manage the time spent in idle listening (IL) state. The hurdle is that the receiver has no knowledge about when the pending data will arrive under end-to-end communication protocols (TCP/IP), making each station spend enormous time in IL to wait for the pending data. To overcome this limitation, in this paper, we propose a named data networking (NDN) enabled PSM, namely, NDN-PSM, which leverages NDN communication architecture to cut down unnecessary IL time. In particular, we devise two new power states in NDN-PSM , i.e., light doze and deep doze, to precisely map to the underlying data arriving states. The inherent receiver-driven pattern of NDN can effectively drive the stations to the deep doze state for power saving, and to light doze state for timely data reception. Considering the IL time waste during channel contention, we further design a channel contention control mechanism in NDN-PSM , in which stations will switch to the light doze state if the channel is perceived to be busy. The power consumption model of the proposed NDN-PSM is theoretically analyzed and verified via numerical results. At last, we implement NDN-PSM in NS-3 by adopting the ndnSIM module and conduct extensive simulations to demonstrate the efficacy of NDN-PSM . Specifically, compared to the existing PSM mechanism, NDN-PSM reduces 56% power consumption by cutting down unnecessary IL time, and meanwhile enables low-delay transmission.

Thermoelectric (TE) polymers have unique advantages in converting heat into electricity. But their Seebeck coefficient is lower than that of inorganic TE materials by about one order of magnitude. Here, surface energy filtering is proposed to significantly enhance the Seebeck coefficient of TE polymers. The as-prepared poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS, the most popular TE polymer) films from aqueous solution have a low Seebeck coefficient of 15–18 μV K−1 and a power factor of ∼0.008 μW m−1 K−2. Depositing Rhodamine 101, a zwitterion, on PEDOT:PSS films can enhance the Seebeck coefficient to 47.2 μV K−1 and the power factor to 401.2 μW m−1 K−2. The Rhodamine 101 effect on the Seebeck coefficient is consistent with its effect on the work function of PEDOT:PSS. The enhancement in the Seebeck coefficient is ascribed to the dipole moment of Rhodamine 101 and the interfacial dipole moment formed at the surface of the PEDOT:PSS films. This is confirmed by theoretical simulations. We call this mechanism surface energy filtering. Surface energy filtering can increase the mean energy of the transporting carriers and thus the Seebeck coefficient of the PEDOT:PSS films while only slightly affecting the electrical conductivity. It can thus significantly enhance the Seebeck coefficient and the power factor simultaneously.

Background: As the multimedia service develops and the transmission rate in terrestrial communication systems increases rapidly, satellite communication needs to improve the transmission rate and throughput. Multiple Input Multiple Output (MIMO) techniques can increase the system capacity significantly by introducing the space dimension, as the system bandwidth remains the same. Therefore, utilization of MIMO for satellite communications to increase the capacity is an important research topic. So MIMO techniques for multibeam satellite communications are researched in the dissertation. Objective: The goal of this work is improving the capacity of the satellite system. Multi-beam and dual-polarized technologies are applied to a satellite system to improve the capacity further. Methods: In this paper, we first introduce a multi-beam dual-polarized satellite multi-put and multiout (MBDP-S-MIMO) system which combines the full frequency multiplexing and dual-polarization technologies. Then the system model and channel model are first constructed. At last, to improve the capacity further, BD and BD-ZF precoding algorithms are applied to MBDP-S-MIMO and their performance is verified by simulation. Results: Simulation results show the performance of the BD precoding algorithm gets better with the growth of the XPD at the receiver and is almost not affected by the growth of the channel polarization correlation coefficient. In addition, with the growth of the users’ speed, the performance becomes worse. Conclusion: The multi-beam dual-polarized satellite MIMO system has high capacity, and it has certain application prospects for satellite communication.

In order to enhance the braking safety and improve the fuel economy and emission of heavy-duty engines, a variable mode valve actuation system which can switch operation modes flexibly among four-stroke driving, two-stroke compression release braking, and cylinder deactivation modes on a four-stroke engine was developed in this article. The switching was controlled by the four-stroke driving module and the two-stroke braking module, both of which have two states: effective state and failure state. Besides, a full-cycle numerical model of a six-cylinder turbocharged engine was established for the performance analysis of two-stroke compression release braking mode. The orthogonal design method was introduced in the present study to obtain the optimum valve parameters which can result in high braking power and maintain the maximum cylinder pressure at a lower level at the same time. Then, the two-stroke compression release brake braking power with the optimum valve parameters was compared with four-stroke compression release braking power. Meanwhile, the two-stroke braking cam profile of the variable mode valve actuation system was designed according to the optimum valve parameters, and the two-stroke braking performance with the dynamic valve lift of the variable mode valve actuation system was validated by the numerical model including the hydraulic system. The results indicated that a higher engine speed leads to higher braking power at the same valve lift. Besides, two-stroke compression release brake braking power of the variable mode valve actuation system achieved 525.3 kW at 2600 r/min and 358.1 kW at 1900 r/min, 52.9% and 71.3% higher than four-stroke compression release braking power, respectively. Although the two-stroke compression release brake braking power with dynamic valve lift is slightly less than that with the optimum valve parameters, it is still much higher than that of the four-stroke compression release braking power. Therefore, it has a good application prospect for heavy-duty engines.