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As one of the promising configurations of the next generation of commercial aircraft, research on departure characteristics of the Blended-Wing-Body (BWB) is of great signification to safe flight limits. A three-degree-of-freedom (3-DOF) virtual flight test in a wind tunnel has been implemented for a candidate configuration to predict the departure characteristics. The support mechanism, the test model and the control law of the virtual flight test are introduced. In order to show the relationship between virtual flight test and actual flight test, the similarity criterion is also given. In open loop, the model has mild oscillations in the longitudinal and lateral directions, which are stable in closed-loop. The effect of flight control has been verified in virtual flight and actual subscale flight test. The analysis of system identification results indicate that the model has a good response to the excitation signal, and the response is in reasonable agreement with the flight test. Finally, the virtual flight departure test results are compared with the flight test. It shows that there is a good correspondence between the angle of attack and the elevator deflection at departure. This gives promising evidence of the practicability of virtual flight testing to predict departure of a BWB.

The optimal yawing angle of sun-tracking solar aircraft is tightly related to the solar azimuth angle, which results in a large arc flight path to dynamically track the sun position. However, the limited detection range of payload usually requires solar aircraft to loiter over areas of interest for persistent surveillance missions. The large arc sun-tracking flight may cause the target area on the ground to be outside the maximum coverage area of payload. The present study therefore develops an optimal flight control approach for planning the flight path of sun-tracking solar aircraft within a mission region. The proposed method enables sun-tracking solar aircraft to maintain the optimal yawing angle most of the time during daylight flight, except when the aircraft reverses its direction by turning flight. For a circular region with a mission radius of 50 km, the optimal flight trajectory and controls of an example Λ-shaped sun-tracking solar aircraft are investigated theoretically. Results demonstrate the effectiveness of the proposed approach to optimize the flight path of the sun-tracking aircraft under the given circular region while maximizing the battery input power. Furthermore, the effects of varying the mission radius on energy performance are explored numerically. It has been proved that both net energy and energy balance remain nearly constant as the radius constraint varies, which enables the solar aircraft to achieve perpetual flight at almost the same latitude as the large arc flight. The method and results presented in this paper can provide reference for the persistent operation of sun-tracking solar aircraft within specific mission areas.

We study linear and nonlinear topological edge states on the domain wall (DW) of two helical waveguide arrays with opposite helicities. This composite helical structure is constructed by using the ...

Due to its layout, there are difficulties in realizing heading attitude control of a flying-wing unmanned aerial vehicle. In this paper, a reverse jet control scheme has been designed: (1) to replace the resistance rudders that are used for the yaw control of a conventional flying-wing unmanned aerial vehicle, (2) to assist and optimize heading attitude control, eliminate the adverse effects of the control surface and enhance stealth performance, and (3) to promote the use of rudderless flight for flying-wing unmanned aerial vehicles. To explore the control mechanism and the flow field of the reverse jet scheme, three-dimensional numerical simulations and low-speed wind tunnel experiments were carried out. First, the numerical simulations evaluated the feasibility and effectiveness of the reverse jet control scheme and explored and optimized the excitation parameters for the scheme. Then the forces were measured in a wind tunnel, and particle image velocimetry experiments were carried out. A reverse jet actuator was independently designed to verify the results of the numerical simulation. The results show that when the reverse jet excitation is applied, the jet obstructs the mainstream, destroys the flow field at the excitation position, and causes early separation of the flow, which increases the pressure drag on the wings and produces a control effect. The control effect mainly depends on the separation degree of the leeward surface. The larger the jet momentum coefficient is, the smaller the jet angle is, and the closer the excitation position is to the leading edge, the greater the separation degree of the leeward surface is, the better the heading attitude control effect is.

The absorption properties of wave-absorbing coatings can easily fail; therefore, a layer of corrosion-resistant topcoat is often added to the surface to increase the service life of the absorbing coating. In this study, we compare the changes in samples without or with a topcoat, namely fluorinated polyurethane, at 25 °C with a NaCl solution and at 35 °C with a neutral salt spray. Morphological characterization and composition analysis show that the topcoat can indeed greatly improve the corrosion resistance of the samples, but the absorption of the coatings still decreases in a short time. The reasons for this are indicated by electrochemical impedance spectroscopy. For the samples without a topcoat, the corrosion of the wave-absorbing coatings results in the failure of wave absorption. For the samples with a topcoat, it is likely that the state of the interface between the topcoat and absorbing coatings leads to the decline of the resistance of the wave-absorbing coatings, causing them to fail quickly.

We discuss linear and nonlinear topological edge states on the bearded-bearded edge (BBE) and armchair-armchair edge (AAE) of two helical waveguide arrays with opposite helicity. The robustness of the linear topological edge state can be controlled by the helix radius, the angle of the incidence, and the amplitude of lattice potentials. In the nonlinear regime, multipole-like lattice quasisolitons may be found with a certain saturable nonlinear factor for AAE. The long-distance propagation dynamics of such quasisolitons are numerically studied from the evolution of their intensity patterns and the “center of mass”. On the contrary, no quasisoltion exists for BBE under the same conditions.

To achieve perpetual flight, solar-powered UAVs (SPUAVs) need to convert sufficient solar energy into electricity during daylight flight. However, perpetual flight at middle and high latitude regions in winter days still poses great challenges for gaining enough solar energy due to the low sun elevation angle and short daylight duration. Among measures for flight endurance enhancement, tracking the sun through changing geometry of wing and orienting flight direction may be an effective design scheme for gaining more solar energy. In this paper, the energy optimization method for Z-shaped sun-tracking morphing-wing SPUAV is developed and used to investigate the advantages on energy performance of the optimal Z-shaped wing over the conventional planar wing. Energy optimization for a whole year's flight shows that the optimal Z-shaped wing is capable of achieving longer flight endurance, improving perpetual flight latitude and extending perpetual flight date efficiently compared with the planar wing, especially for the middle and high latitude regions during winter days. The investigation on implications of conversion efficiency of solar cells indicates that, with higher conversion efficiency of solar cells, the optimal Z-shaped wing is more effective to collect more net energy, retain more energy margin and achieve perpetual flight at higher latitude. The Z-shaped sun-tracking morphing-wing design combined with the energy optimization method proposed is helpful to increase flight endurance and improve perpetual flight latitude for SPUAVs.

The path following control of quad-rotors transporting uncertain payloads, whose control system is featured with time-variation, high nonlinearity and strong couplings among state variables and inputs, is investigated. Targeting this, an internal model frame-based disturbance attenuation control scheme that requires only rough model information is proposed. Firstly, a novel disturbance estimator (DE) for general single-input-single-output (SISO) system is proposed. Secondly, the DE proposed is applied in transporting unknown payloads by quad-rotors, to estimate the disturbances caused by the payloads for feedback compensation. Lastly, the control scheme based on internal model frame is designed to further reduce the remaining disturbances from disturbance estimation error.

Aiming at the LED (Light Emitting Diode) point sources with Lambertian distribution, we propose an improved mesh method to design a free form lens. For this method, a free-form surface is divided into two parts. A part is designed to be a refraction surface by using mesh method. Based on the refraction, the other part is designed to be a reflection surface. The combination of two parts forms a free-form surface lens. To take a petal-shaped lens as an example, simulation results show that the lens designed by using the improved mesh method can be higher illumination uniformity by comparing our method with the tradition method. When the radius of the light shape increases, the illumination uniformity increases, but the efficiency has no obvious change. When the distance between the point light source and the target plane increases, the illumination uniformity does not change significantly and the efficiency increases. Thus, the improved method can realize the limited illumination of light shape in the far and near field, so it will has broad application prospects in LED lighting.

Coal pyrolysis is generally considered to initiate by cleavage of weak covalent bonds bridged between aromatic rings. The C–C covalent bonds are predominant bridged linkages among the framework of coal, which have a critical influence on coal pyrolysis reaction but lack of direct online observation. Five representative coal-related model compounds containing C–C bridged bonds, polypropylene (PP), polyvinylpyrrolidone (PVP), poly-4-vinylpyridine (P4VP), polystyrene (PS) and poly-4-vinylphenol, were selected to pyrolyze in an in-situ pyrolysis vacuum ultraviolet photoionization mass spectrometry (Py-VUV-PIMS). The soft ionized mass spectral detection can provide product distribution and evolved information of original products and intermediates, which are the key evidence to understand the initiation, recombination and reaction routes during pyrolysis process. Online analysis of pyrolysis reaction was found to be priority with cracking of C–C bond in the five polymer samples, and homologous free radicals and original products, which mainly include monomers, dimers and their alkyl and alkenyl radicals, were detected. The results reveal the cleavage temperature of C–C covalent bond is deeply related to its chemical environment, and obvious conjugation effect and steric effect for the bridged linkage were observed. In addition, the effect of hydrogen bond was also observed during the pyrolysis of model compounds containing hydroxyl groups, and intramolecular or intermolecular hydrogen bonding reduced the temperature at which C–C bridged bonds break. The analogous fracture mode and pyrolysis behavior of coal-related model compounds, which are beneficial to understand the reaction route and mechanism of coal pyrolysis, were discussed based on the experimental observations and theoretical calculation.

We investigate the existence and stability of nonlocal surface solitons at the interface between linear media and nonlocal nonlinear media with two-dimensional (2D) parity-time ( PT )-symmetric optical lattices. We analytically obtain the nonlinearity-induced change of the refractive index by introducing a reasonable step function with the method of Fourier transform, and carry out the linear stability analysis for the surface solitons based on the response function of the infinite nonlocal medium. Numerical results show that nonlocal PT surface solitons can exist and be stable in 2D PT -symmetric optical lattices.

Baiyinhua coal was subjected to catalytic pyrolysis over HZSM-5 and Ni-modified HZSM-5 (Ni/HZSM-5) with a novel pyrolysis time-of-flight mass spectrometers (Py-TOF-MS) equipped with vacuum ultraviolet photoionization (VUVPI). The soft ionization of VUVPI allowed the detection of volatile organic compounds. The effect of HZSM-5 and Ni/HZSM-5 on distribution of coal pyrolysis products was online investigated. The coal pyrolysis products including alkanes, phenols, aromatics and sulfur containing compounds (H2S and CH3SH) were detected. In the presence of HZSM-5 and Ni/HZSM-5, the products from coal pyrolysis have higher content of substituted benzene and alkenes and lower content of phenols in comparison with that without catalyst. The catalysts promote the conversion of phenols products to aromatic hydrocarbons via dehydroxylation reaction. Ni/HZSM-5 exhibits better catalytic performance for generating products with higher aromatic content and less oxygen species than HZSM-5 alone. Temperature-evolved profiles of pyrolysis products were also measured. It was found that the peak temperature of alkenes and substituted benzene of catalytic pyrolysis shifts to lower temperature region while that of dihydroxybenzenes moves to higher temperature. This work demonstrates the good performance of Py-TOF-MS for the online study of the coal catalytic pyrolysis process.

With the significant development of Internet, cyberspace has become one of the most important national sovereignties. To secure national cyberspace, it is essential to know the amount of cyberspace resources and understand the state and risk of the resources. Recently, researchers have developed enormous effort to devising new algorithms, strategies and tools to help detect and analyze cyberspace resources. Based on the relevant literature we surveyed, we defined the basic concepts of cyberspace resources and the framework of related techniques. Then we classified the main techniques and make a comparison between them, based on which we made an inductive review about the key technologies, the critical problems and possible solutions. We conclude with some research subjects that we hope will help improve the development of cyberspace resources scanning and analyzing, providing with more support for cyberspace security.

The high-angle-of-attack uncommanded roll oscillations are dangerous and cause significant challenges in flight control. This paper focuses on investigating the feasibility and performance of an artificial-intelligence method - “model-free reinforcement learning” (MFRL) on this issue, in both simulation and experiment. In simulation, two algorithms TD3 and SAC were used to learn the policies to suppress the roll oscillations of a widely used mathematical model. The agents only utilized current states as observation vector, and achieved perfect results. In the experiments, these two algorithms were used to learn the policies to suppress the roll oscillations of a flying-wing model which utilized spanwise blowing as its roll effectors. It is worth noting that unlike in simulation, the experiments investigated the influence of the observation vectors' memory size on training results. The results show that for both algorithms, the agents cannot learn good-enough policies when their observation spaces were constructed only by the current sensor data. This phenomenon, which is a big difference between experiments and simulations of MFRL, is due to the non-Markovian characteristic of the real-world dynamics caused by inevitable latencies. However, constructing the observation space using current and past sensor data help both the TD3 and SAC agents to learn great policies to suppress the oscillations using spanwise blowing in real world. Surprisingly, the trained agents showed some counterintuitive “smart” behaviors in tests.

Baiyinhua (BYH) coal, a kind of lignite, was hydrothermally treated in an autoclave reactor at 200–350 °C for 30 min and the liquefaction behavior of the treated samples were investigated. To uncouple the complex behavior of the changes in structural characteristics and functional groups of treated samples, the structural change in BYH coal was investigated by thermogravimetry, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Results reveal that oxygen content and volatile matter in treated sample reduce and carbon content increases. The decrease in atomic ratio of oxygen to carbon and hydrogen to carbon of treated sample indicates the improvement in coalification degree. CO 2 and CO account for the overwhelming majority of gaseous products from hydrothermal treatment, which can be attributed to the significantly decrease of carboxyl and carbonyl content. The hydrothermal treatment involves the breakup of some weak bonds within coal structure, and the main structure of BYH coal does not change significantly. A desirable upgraded coal was obtained by hydrothermal treatment of BYH raw coal at 250 °C. The liquefaction behavior of coal can be improved by hydrothermal treatment at 250 °C, and the oil yield increases from 32.9 wt% (dry ash-free basis) of raw coal to 37.8 wt% (dry ash-free basis). This work illustrates that hydrothermal treatment is a promising approach for upgrading of low rank coal.

Direct coal liquefaction (DCL) was investigated using a deuterium tracer method which makes it possible to determine which structural positions in the coal react with H 2 or hydrogen-donor solvents, i.e. hydrogen-transfer mechanism. D 2 and/or 1,2,3,4-d 4 -tetralin (tetralin-d 4 ) were used in DCL of Bulianta coal at 7.0 MPa (initial charge pressure) and 445 °C for 0 or 60 min in a tubing-bomb microreactor. 2 H NMR and isotope ratio mass spectrometry (IRMS) were used to determine the distribution of deuterium in liquefaction solvent and products qualitatively and quantitatively. The 2 H NMR of solvents after DCL under a variety of conditions showed that the α-radical of tetralin is an important intermediate in hydrogen transfer to and exchange with coal, and the de/re-hydrogenation cycle of tetralin is not a dominating approach of hydrogen transfer in DCL. The distribution of deuterium in each structural position and the D/ 1 H in preasphaltenes and asphaltenes (PAA) under a variety of conditions showed that both hydrogen atoms in tetralin and H 2 could enter alkyl groups remote from aromatic nucleus of PAA in preference to aromatic nucleus and α to aromatic groups of PAA. The hydrogen atoms in tetralin are more easily to stabilize radicals from coal cracking to form PAA than those in H 2 during the heating-up stage of DCL. Both the kinetic isotope effect and electrophilic aromatic substitution reaction in DCL, indicating the existence of ionic reaction process besides a radical reaction process in DCL.

Hypersonic aircraft represent an important area of aerospace development. Raising the aircraft lift-to-drag ratio, improving the efficiency of attitude control, and optimizing aerodynamic performance are important goals. Active flow control technology can improve the aerodynamic performance of the aircraft while optimizing its control attitude. In the field of low speed, subsonic speed, and supersonic speed, many experiments and numerical simulations have been carried out to verify the excellent auxiliary or control effects of active flow control technology on aircraft. In this paper, a two-dimensional hypersonic airfoil is selected to analyze the feasibility and control effect of jet flow control technology under hypersonic inflow, and a flow control scheme is designed to make the jet eject from the wing surface. First, the influence of different jet excitation parameters on the scheme is explored through numerical simulation, mainly including the Mach number, the jet location, the jet angle, and the change with the angle of attack. After that, typical excitation states of numerical simulation are selected for hypersonic wind tunnel experiment verification, whose results are in good agreement with those of the numerical simulation. The results prove that, under the condition of high altitude and low pressure, if jet excitation is applied on the surface of the hypersonic airfoil, a local high pressure area will be formed in front of the excitation port, and the differential pressure between upper and lower wings will be changed. It can optimize the aerodynamic characteristics, increase or reduce lift, produce pitching moment simultaneously, enhance the efficiency of the rudder surface, and assist attitude control.

In this paper, the liquefaction of a Bulianta coal, from China Shenhua Group, was carried out in a hydrogen donor solvent, tetralin, or a non-hydrogen donor solvent, 1-methylnaphthalene, with or without catalyst to clarify the mechanism of hydrogen transfer. And roles of solvent and a nano-size iron catalyst from Shenhua Group in the heating-up stage of DCL were also investigated by using mixed solvent of decalin, phenanthrene, pyrene or fluoranthene and tetralin. The results show that tetralin inhibits the reaction of coal macromolecule to oil and the transfer of H2. The major transfer approach of H2 may be directly from H2 to coal rather than via the hydrogen donor solvents in the presence of the nano-sized iron catalyst. In the heating-up stage of DCL, the major role of solvent is to provide activated hydrogen for coal. High dissolving capability of the liquefaction solvent that has high enough hydrogen donor capacity is beneficial for improving liquefaction performance. The dominant function of the catalyst is to promote the activation of H2, which can improve coal liquefaction performance in the heating-up stage of DCL.

To study wing-body rock, various tests were used for the canard-configuration models in the wind tunnel, including free rolling, disturbance on free rolling, static moment measurements, dynamic derivative measurements, smoke wire method and particle image velocimetry. The models also have a chine forebody, strake wings, main wings and a vertical tail. In the tests, the canard deflection angles are 0° and 20° relative to the axis of the body. First, the roll angle time histories were obtained by free rolling motion and disturbed motion; the results demonstrate that both canard-configuration models have nonzero mean roll angles. In particular, the existence of the other larger nonzero mean roll angles on the same side is a curious aspect at the critical pitch angle, such as at θ = 37° for the model with canard deflection of 20°. Next, static moment tests and dynamic derivative tests demonstrate that although the roll angle time histories are non-limit cycle motions, they are irregularly self-excited oscillation under the influence of multi-vortex structures. Finally, the constituent parts of structures over wing bodies and the flow mechanism of abruptly jumping from an equilibrium roll angle to the other on the same roll side were revealed by the smoke wire and particle image velocimetry measurements.

Multi-field coupling simulation method based on the physical principles is used to simulate the discharge characteristics of nanosecond pulsed plasma synthetic jet actuator. Considering the effect of the energy transferring for air, the flow characteristics of nanosecond pulsed plasma synthetic jet actuator are simulated. The elastic heating sources and ion joule heating sources are the two main sources of energy. Through the collisions, the energy of ions is transferred to the neutral gas quickly. The flow characteristics of a series of blast waves and the synthetic jet which erupt from the plasma synthetic jet (PSJ) actuator are simulated. The blast wave not only promotes outward, but also accelerates the gas mixing the inhaled gas from the outside cavity with the residual gas inside the cavity. The performances of PSJ actuator fluctuate in the first three incentive cycles and become stable after that.

The surface dielectric barrier discharge plasma actuator driven by nanosecond pulses is recognized as an effective fluid actuator for flow separation control. The operation condition of nanosecond dielectric barrier discharge actuators for separated flow control still requires further study, particularly prioritizing the improvement of the effectiveness and reducing energy consumption in flow separation control implementation. In this study, experiments are conducted using a two-dimensional NASA SC(2)-0712 airfoil in a wind tunnel with a Reynolds number of 0.5 × 106 (25 m/s). The pressure measurement experiments show that the location of actuators affects the efficiency of separation control. Particle image velocimetry results indicate that the most efficient location of the actuator is upstream of the separation point and near the original point of the separated shear layer. Meanwhile, the particle image velocimetry results show the vorticity attaches to the airfoil wall after discharge, which suggests that the reattachment is due to the generation of large-scale vortices. These present structures result in the mixing of the shear layer with the main flow thereby delaying separation and reattaching a separated flow. This study shows the most efficient location related to the separation point. Furthermore, it indicates the reattachment of flow is attributed to the motion of vortexes coherent structure.

The modern high performance air vehicles are required to have extreme maneuverability, which includes the ability of controlled maneuvers at high angle of attack. However, the nonlinear and unsteady aerodynamic phenomena, such as flow separation, vortices interaction, and vortices breaking down, will occur during the flight at high angle of attack, which could induce the uncommanded motions for the air vehicles. For the high maneuverable and agile air missile, the nonlinear roll motions would occur at the high angle of attack. The present work is focused on the self-induced nonlinear roll motion for a missile configuration and discusses the influence of the strake wings on the roll motion according to the results from free-to-roll test and PIV measurement using the models assembled with different strake wings at α = 60°. The free-to-roll results show that the model with whole strake wings (baseline), the model assembled with three strake wings (Case A) and the model assembled with two opposite strake wings (Case C) experience the spinning, while the model assembled with two adjacent strake wings (Case B), the model assembled with one strake wing (Case D) and the model with no strake wing (Case E) trim or slightly vibrate at a certain “×” rolling angle, which mean that the rolling stability can be improved by dismantling certain strake wings. The flow field results from PIV measurement show that the leeward asymmetric vortices are induced by the windward strake wings. The vortices would interact the strake wings and induce crossflow on the downstream fins to degrade the rolling stability of the model. This could be the main reason for the self-induced roll motion of the model at α = 60°.

Solvent plays two very important roles in coal liquefaction: (1) Physically, it serves as a medium for coal transport and heat transfer, and (2) chemically, it serves as an important source of transferable hydrogen (hydrogen donor) and hydrogen shuttle between hydrogen and coal. In this work, eight types of non-hydrogen-donor solvents, namely, decalin, 1-methylnaphthalene, naphthalene, fluorene, anthracene, phenanthrene, pyrene, and fluoranthene, were examined in combination with the hydrogen-donor solvent tetralin in the liquefaction of Bulianta coal to clarify the interactions between the hydrogen-donor and non-hydrogen-donor solvents and the mechanism of hydrogen transfer. In the absence of a catalyst, the mixed solvents of tetralin with phenanthrene, pyrene, and fluoranthene showed favorable effects on coal conversion and oil yield compared with pure tetralin, regardless of whether the reactions were conducted in a H2 or N2 atmosphere. The reactions of non-hydrogen-donor solvents with tetralin showed ...

A cruciform-finned slender body can excite a limit-cycle rolling oscillation at high angles of attack. To suppress the unwanted motions, flow control approaches should be employed if the aerodynamic control surfaces lose control efficiency at high angles of attack. As a promising technology, the ns-dielectric barrier discharge plasma actuator has been successfully used in high-speed and high-Reynolds-number flow control applications. The present work employs a π-type ns-dielectric barrier discharge plasma actuator and vortex generators to suppress self-excited rolling oscillation at α = 50°. The free-to-roll tests show that the plasma actuator ignited at F+ ∼ 1.5 and that the vortex generators can suppress rolling oscillation. The flow patterns from particle image velocimetry measurement at different cross-sections and rolling angles suggest that the vorticity decrease of the leeward vortices may be the control mechanism for the plasma actuator. For the vortex generators, evident modification of the flow field structure can be observed due to the vortices generated from the vortex generators, which decreases the rolling moment induced by the asymmetry vortices to suppress the self-excited rolling oscillation.

The method of symmetrical spanwise blowing was used to suppress the wing-body rock of a typical canard-configuration model in free-to-roll tests. The experimental results showed that the rock was successfully suppressed by symmetrical spanwise blowing when the pitch angle was between thirty degrees and thirty-four degrees. However, this kind of blowing failed to suppress the non-commanded motion once pitch angle exceeded thirty-four degrees. To analyze the mechanism under this phenomenon, surface-pressure measurements and PIV tests were carried out. The reason for the successful suppression was inferred as the success of the delaying of windward vortex breakdown at a small sideslip angle, while the failed results at larger pitch angles were due to the fact that the blowing cannot delay the windward breakdown anymore under very small sideslip.

This study explores the effects of wingtip connection on decreasing energy consumption and increasing flight endurance for solar aircraft. The Oswald efficiency factor, induced drag coefficient and power consumption are derived as the models of the number of wingtip connected aircraft. As the energy margin model is related to the number of connected solar aircraft, a flight endurance margin model is proposed to evaluate the advantages of wingtip connection quantitatively. With the numerical method developed, researches on the energy and flight endurance performance for a given example wingtip-connected solar aircraft are performed. Moreover, the impacts of solar cell efficiency, flight date and latitude on the advantages of wingtip connection for solar aircraft are explored. The results suggest that the wingtip connection design enables solar aircraft to decrease induced drag coefficient, increase flight endurance and range effectively when the aircraft is only powered by battery. The wingtip connection design is more effective to increase the flight endurance and improve the maximum perpetual flight latitude with more connected solar aircrafts and higher solar cell efficiency, especially in the flight condition with high solar elevation angle and more daylight hours. However, as the number of connected solar aircraft increases, the effect of one more connected aircraft on these advantages decreases because the effect of wingtip connection on decreasing induced drag coefficient decreases with increasing aspect ratio.

In order to further study the inner characteristics of the plasma synthetic jet actuator (PSJA) which consists of a cavity, two electrodes and a lid with orifice, a two-dimensional numerical simulation is carried out with SST k-ω turbulence model. The evolutions of the flow parameters inside the cavity with a single pulse, such as pressure, density, temperature and velocity, are analyzed in detail. The oscillation mechanisms of the flow parameters at the orifice of the cavity is also investigated. To study the effects of geometric factors on the performance of the PSJA, five widths and heights of the cavities are considered. The results suggest that the base frequencies are inversely proportional to the width and height of the cavity respectively. The proportional constant is equal to the sound speed. Besides, shortening the width or height of the cavity can obtain a faster peak velocity of the jet. The peak of the jet velocity occurs earlier with a shorter height of the cavity.

Next-generation aircraft and missile are required to have extreme maneuverability, which should maintain stability at high angle of attack. However, the unsteady flow field surrounding the air vehicle would affect the aerodynamics loads and induce unwanted nonlinear motions, of which the rolling motions are usually generated. In order to investigate the unsteady rolling characteristics of a cruciform-finned slender body, the free-to-roll and force measurement tests including particle image velocimetry measurement have been conducted comprehensively. Different types of rolling motion, trimming at equilibrium positions, self-excited rolling oscillation, and self-excited spinning are observed during the free-to-roll experiment depending on the different angles of attack. The force measurement results show that the rolling motions are related to both the static and dynamic stabilities of the rolling moment at balance points. The stabilities of the rolling moment would change as the angle of attack for the model increases. At last, the flow field results from particle image velocimetry measurement indicate that the unsteady rolling motions may be induced by the interaction between the asymmetry vortices and strake wings, fins.

Controlling the morphology of nanostructured materials is critical for their use in technological applications including in sensing, electronics and energy harvesting. In this paper we investigate the reaction pathways involved and their dependence on reactant concentrations in the formation of ZnO nanomaterials on –COOH terminated self-assembled monolayers using a simple chemical bath deposition process which employs zinc acetate, which acts as the Zn source, and ethylenediamine, which acts as both the O source and a complexing agent for Zn2 +. At a deposition temperature of 318 K (45 °C) our data shows that the concentration of Zn2 + as well as the deposition bath pH, which is controlled by the ethylenediamine concentration, is critical in determining the ZnO morphology. Above 0.01 M zinc acetate at low bath pH (~ 7.7–8.5), nanorods and nanorockets are observed to form. The nanorods exhibit a clear interface in the middle indicating that they are composed of two crystals. At lower zinc acetate concentrations over a wide pH range (~ 8.0–10.5) nanoflowers form. The nanorockets and nanoflowers grow via a modified La Mer mechanism in which there are multiple nucleation and crystallization steps. The initial nuclei are sphelurites (nanoflowers) or nanocrystallites (nanorockets). Since the reagent concentrations limit the reaction, for these initial precursor crystallites to increase in size, it is required dissolution and re-precipitation must occur. Thus at later times nanorockets or nanoflowers develop.

Fatigue is one of the most common yet complicated failures that can cause damage to mechanical structures. Structural adhesively bonded joints are not exempt from this deleterious phenomenon and have to be assessed under vibration loads. In this work, fatigue characteristics of single-lap joints (SLJ) made of steel and carbon fibre reinforced plastic (CFRP) laminates under vibration loads are primarily investigated by experiments. The aim of this work is to analyze the changes in the ultimate load of the SLJ under vibration loads. The experimental results showed that SLJ will face cohesive failure after the uniaxial tensile loading test. In addition to the increase of vibration cycles, the ultimate load and failure displacement gradually decrease. In order to model the adhesive between joint components and simulate the damage propagation, a new traction–separation law called the embedded process zone (EPZ) and a damage factor are introduced and developed within the framework of cohesive zone Model...

Proteins are often an important component of many bulk surfaces in biological and environmental systems that are coated with complex organic compounds that may also interact with NPs. We investigated the deposition of bare hematite NPs onto various proteins adsorbed on either negatively- or positively-charged bottom surfaces. Bovine serum albumin (BSA), lysozyme, and ubiquitin were used as model proteins and total protein extracts from two bacterial strains, Escherichia coli and Pseudomonas fluorescens, were used as complex protein mixtures. The NP deposition extents and rates were shown to be significantly different depending on the protein. The maximum difference observed was 8.6 ± 3.2 fold between E. coli and P. fluorescens proteins adsorbed onto positively-charged planar surfaces. These differences in NP deposition characteristics are attributed to the differences in physicochemical features of the topmost surface of the protein layer, such as the amino acid profiles, surface charge, and hydrophilicity. Such differences were likely driven by differences in species, orientation, and conformation of the adsorbed proteins. In particular, NP deposition was driven by various combinations of electrostatic and hydrophobic interactions. This study indicates that NP deposition onto surface-adsorbed proteins is an important mechanism in protein–NP interactions and that the deposition is strongly dependent on both the conformation and chemical characteristics of the adsorbed protein layer.

Uncommanded self-induced roll oscillations cause significant challenges in flight control and are ubiquitous in high-attack-angle flights in the flying-wing configuration. Spanwise blowing slots were designed in this article to suppress these roll oscillations with nonzero mean angles of a 53° swept flying-wing model. Three flow control strategies were proposed and studied successively. The open-loop symmetric blowing successfully suppressed oscillations below the nominal angle of attack of 24° before losing its effectiveness. Subsequently, adaptive continuous blowing using the proportion-integral-differential algorithm was performed with symmetric pre-blowing to eliminate the ineffective region with a small blowing coefficient. Using this strategy, roll oscillations under all tested nominal angles of attack were successfully addressed as the nonzero trim angles were eliminated and the oscillations were suppressed. However, the air consumption needed to maintain the model balance was too large, which necessitated the development of pulsed blowing. Static force measurements showed that the blowing-induced rolling moment had a linear relationship with the duty cycle of blowing. The results from the particle-image-velocimetry tests revealed that the mechanism of the linear relationship was the increased duration of coherent vortices over a period at longer duty cycles. Based on the static experimental results, the model was stabilized via proportion-integral-differential adaptive blowing, which utilized the duty cycle as the control variable. Compared to the second strategy, the last one reduced the required mean blowing momentum coefficient by two orders of magnitude while maintaining a great control effect.

In this study, we investigated the effects of surface sliding discharge of a dielectric barrier discharge (SL-DBD) plasma actuator on the boundary layer flow using the time-resolved particle image velocimetry (PIV) technique. According to the PIV measurements, the peak-shaped mean jet flow is induced by the SL-DBD plasma actuator in quiescent air. Under the freestream of U∞ = 6 m/s on the flat plate, the results show that the streamwise velocity fluctuation induced by SL-DBD plasma is increased pronouncedly at the downstream of the actuator. Meanwhile, the mean flow velocity increases obviously in the downstream of the actuator. The instantaneous results show the formation of the vorticity at the bottom of the boundary layer after the plasma excitation. In addition, the vorticity has the behavior to lift up, possibly because of the induced peak-shaped jet.

With the prosperity of the Internet of Things (IoT) industry environment, the variety and quantity of IoT devices have grown rapidly. IoT devices have been widely used in smart homes, smart wear, smart manufacturing, smart cars, smart medical care, and many other life-related fields. With it, security vulnerabilities of IoT devices are emerging endlessly. The proliferation of security vulnerabilities will bring severe risks to users&rsquo, privacy and property. This paper first describes the research background, including IoT architecture, device components, and attack surfaces. We review state-of-the-art research on IoT device vulnerability discovery, detection, mitigation, and other related works. Then, we point out the current challenges and opportunities by evaluation. Finally, we forecast and discuss the research directions on vulnerability analysis techniques of IoT devices.

We propose a design of a center high mounted stop lamp (CHMSL) based on Fresnel lens. The Fresnel lens is divided into four layers. The first layer collimates the beam of Light Emitting Diode (LED) along the direction perpendicular to optical axis; The second layer makes the output light uniformly distributed; The third layer collimates the beam along the optical axis direction; The fourth layer scatters the collimating light to make the last light distribution meet the relevant regulations. The simulation and test results show that the efficient of this CHMSL is 38.3 % and the uniformity is about 92.4 %. This CHMSL is practical and can applicable to vehicle lighting.

In this paper, we investigate the popular neural word embedding method word2vec as a source of evidence in short text similarity calculation, which has been applied to intention classification of user queries in our intelligent customer service system — Alime. For avoiding information loss on sentence-level vector representation, we design a Word Similarity Maximization (WSM) method, which utilize word-level embedding vectors to directly calculate query similarity. Experimental results on a dataset from real daily user query data from Alime system show WSM can better detect query-intention relation than baseline methods.

Word sense disambiguation (WSD) plays an important role in natural language processing, such as information retrieval, text summarization, question answering, machine translation, etc. Abbreviation disambiguation is an important sub-domain of WSD, and in this paper we try to construct a co-occurrence knowledge base for realizing fast abbreviation disambiguation, since speed is essential in applications such as question answering and machine translation. In our proposed method, named entities in context of abbreviations are essential for this disambiguation task, and the final experimental results show that our method can effectively realize the mentioned aim.

Fast diffusion of information makes microblogging an efficient platform for seeking information, and the most convenient way for a user to get useful information is following others and in real time the updates of the followed users will be presented automatically. Deciding to follow or not to follow a user is usually based on this user's tweet content, because users usually try to find friends who post information relevant to their interests. Since reading through all tweets of a user is very time-consuming, we need to design a convenient user summarization form. In this paper, we design a model for summarizing users with their most representative tweets. The experimental results on Sina-weibo, one of the most popular microblogging sites in China, show our model can get a better performance than baseline methods.

A common capping agent for gold nanorods, Cetyl trimethylammonium bromide (CTAB), is particularly problematic for biological studies because of its cytotoxicity. Several procedures have been developed to remove the CTAB from the surface of the gold nanorods, but most are lengthy, involving many steps, and use expensive reagents. Here, we present a simple, one-pot method for the complete removal of CTAB from the surface of gold nanorods, so that particles can be more effectively utilized in biological in vivo studies. The procedure involves first adding sodium borohydride to remove the CTAB, quickly followed by a replacement ligand, such as mercaptoundecanoic acid (MUA). Both the CTAB removal and MUA replacement were monitored by FTIR, surface enhanced Raman spectroscopy (SERS) and X-Ray Photoelectron Spectroscopy (XPS) and compared to commercially available citrate-capped gold nanorods. The procedure presented herein is shown to be as effective at removing CTAB and replacing it with MUA as commercially available gold nanorod samples.

Sideslip-induced asymmetrical vortices are critical to the performance of canard-configuration aircraft. In this paper, a canard-configuration model was found to roll around a nonzero trim angle in a free-to-roll experiment, indicating a loss of lateral static stability. This loss was also evidenced by the positive slope of the rolling-moment versus sideslip curve. To reveal the underlying mechanism of this phenomenon, we focused on sideslip effects, taking surface-pressure measurements and conducting PIV (particle image velocimetry) tests. At the attack angle of 16°, sideslip causes inward extension of the windward low-pressure area on the main wings, which leads to a decrease in rolling moment. The inferred cause is the inward movement of the windward reattachment point. At the attack angle of 35°, complex multi-vortex structures were analyzed using PIV for three forms of the model: with all components; without canard; with neither canard nor strake. The effects of sideslip on vortex flow at high attack angle were then studied. As sideslip angle changed from -1° to 1°, sideslip promotes the breakdown of windward vortices, causing a sharp decrease in windward suction. Subsequently, as sideslip angle changed from 1° to 4°, the backward movement of the breakdown point and an increase in strength of vortices are observed on the leeward side, which coincides with an increase in both leeward suction and the rolling moment. As the sideslip angle continues to increase, the inboard vortex on the leeward side rises and becomes weak, which leads to a decrease in leeward suction, and hence, the recovery of lateral static stability. Moreover, the coiling of leeward vortices weakens under sideslip.Sideslip-induced asymmetrical vortices are critical to the performance of canard-configuration aircraft. In this paper, a canard-configuration model was found to roll around a nonzero trim angle in a free-to-roll experiment, indicating a loss of lateral static stability. This loss was also evidenced by the positive slope of the rolling-moment versus sideslip curve. To reveal the underlying mechanism of this phenomenon, we focused on sideslip effects, taking surface-pressure measurements and conducting PIV (particle image velocimetry) tests. At the attack angle of 16°, sideslip causes inward extension of the windward low-pressure area on the main wings, which leads to a decrease in rolling moment. The inferred cause is the inward movement of the windward reattachment point. At the attack angle of 35°, complex multi-vortex structures were analyzed using PIV for three forms of the model: with all components; without canard; with neither canard nor strake. The effects of sideslip on vortex flow at high attack...

We propose a method for generation of tunable three-dimensional (3D) helical lattices with varying helix pitch. In order to change only the lattice helix pitch, a periodically varying phase along the propagation direction is added to the central beam - one of the interference beams for lattice construction. The phase periodicity determines the helix pitch, which can be reconfigured at ease. Furthermore, a helical lattice structure with an interface (domain wall) is also achieved by changing the phase structure of the lateral beams, leading to opposite rotating direction (helicity) on different sides of the interface. When a Gaussian beam is used to probe the bulk lattice, it can evolve into a spiral beam with its helicity varying in accordance with that of the lattice. Probing along the interface with two dipole-like optical beams leads to unusual propagation dynamics, depending on the phase and size of the two beams. This approach could be further explored for studies of nonlinear interface solitons and topological interface states. In addition, the helical lattices may find applications in dynamical multi-beam optical tweezers.

We investigate Airy-soliton interactions in self-defocusing media with PT potentials in one transverse dimension. We discuss different potentials in which the interacting beams with different phases are launched into the media at different separation distances. During interactions, there exist a primary collision region and a relaxation region accompanied by continuous interaction with the dispersed Airy tail. In the relaxation region, the beams exist soliton-like and breathers-like propagation. The beam width and mean power are influenced by initial separation, phase shift and modulation depth of PT potentials. Especially, the collision distance decreases with the spatial beam separation and the mean power possesses sinusoidal dependence on the phase shift., 16 pages, 5 figures

In a photoelectrochemical (PEC) cell for water splitting, the critical issue is charge separation and transport, which is usually completed by designing semiconductor heterojunctions. TiO2 anatase-rutile mixed junctions could largely improve photocatalytic properties, but impairs PEC water splitting performance. We designed and prepared two types of TiO2 heterostructures with the anatase thin film and rutile nanowire phases organized in different sequences. The two types of heterostructures were used as PEC photoanodes for water splitting and demonstrated completely opposite results. Rutile nanowires on anatase film demonstrated enhanced photocurrent density and onset potential, whereas strong negative performance was obtained from anatase film on rutile nanowire structures. The mechanism was investigated by photoresponse, light absorption and reflectance, and electrochemical impedance spectra. This work revealed the significant role of phase sequence in performance gain of anatase-rutile TiO2 heterostructured PEC photoanodes.

Plasma-based flow control is one of the most promising techniques for aerodynamic problems, such as delaying the boundary layer transition. The boundary layer’s characteristics induced by AC-DBD plasma actuators and applied by the actuators to delay the boundary layer transition on airfoil at Ma = 0.3 were experimentally investigated. The PIV measurement was used to study the boundary layer’s characteristics induced by the plasma actuators. The measurement plane, which was parallel to the surface of the actuators and 1 mm above the surface, was involved in the test, including the perpendicular plane. The instantaneous results showed that the induced flow field consisted of many small size unsteady vortices which were eliminated by the time average. The subsequent oil-film interferometry skin friction measurement was conducted on a NASA SC(2)-0712 airfoil at Ma = 0.3. The coefficient of skin friction demonstrates that the plasma actuators successfully delay the boundary layer transition and the efficiency is better at higher driven voltage.

The effects of the arrangement position and control parameters of nanosecond dielectric barrier discharge (NS-DBD) plasma actuators on lift enhancement for flying wing aircraft were investigated through wind tunnel experiments at a flow speed of 25 m s−1. The aerodynamic forces and moments were obtained by a six-component balance at angles of attack ranging from −4° to 28°. The lift, drag and pitching moment coefficients were compared for the cases with and without plasma control. The results revealed that the maximum control effect was achieved by placing the actuator at the leading edge of the inner and middle wing, for which the maximum lift coefficient increased by 37.8% and the stall angle of attack was postponed by 8° compared with the plasma-off case. The effects of modulation frequency and discharge voltage were also investigated. The results revealed that the lift enhancement effect of the NS-DBD plasma actuators was strongly influenced by the modulation frequency. Significant control effects were obtained at f = 70 Hz, corresponding to F + ≈ 1. The result for the pitching moment coefficient demonstrated that the plasma actuator can induce the reattachment of the separation flows when it is actuated. However, the results indicated that the discharge voltage had a negligible influence on the lift enhancement effect.

Chemical vapor deposition (CVD) is an attractive technique for the metallization of organic thin films because it is selective and the thickness of the deposited film can easily be controlled. However, thermal CVD processes often require high temperatures which are generally incompatible with organic films. In this paper, we perform proof-of-concept studies of photochemical CVD to metallize organic thin films. In this method, a precursor undergoes photolytic decomposition to generate thermally labile intermediates prior to adsorption on the sample. Three readily available Ru precursors, CpRu(CO)2Me, (η3-allyl)Ru(CO)3Br, and (COT)Ru(CO)3, were employed to investigate the role of precursor quantum yield, ligand chemistry, and the Ru oxidation state on the deposition. To investigate the role of the substrate chemistry on deposition, carboxylic acid-, hydroxyl-, and methyl-terminated self-assembled monolayers were used. The data indicate that moderate quantum yields for ligand loss (φ ≥ 0.4) are required for ruthenium deposition, and the deposition is wavelength dependent. Second, anionic polyhapto ligands such as cyclopentadienyl and allyl are more difficult to remove than carbonyls, halides, and alkyls. Third, in contrast to the atomic layer deposition, acid-base reactions between the precursor and the substrate are more effective for deposition than nucleophilic reactions. Finally, the data suggest that selective deposition can be achieved on organic thin films by judicious choice of precursor and functional groups present on the substrate. These studies thus provide guidelines for the rational design of new precursors specifically for selective photochemical CVD on organic substrates.