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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.

Objectives To evaluate the effectiveness of a prevention strategy against the spread of SARS-CoV-2 infection among dental hospital staff over a 3-month period. Materials and methods The effectiveness of the prevention strategy, which adopted healthcare staff protective measures, including patient triage and correct usage of personal preventive equipment, was evaluated by SARS-CoV-2 detection and serological testing. Patients who visited the Affiliated Stomatology Hospital, Zhejiang University School of Medicine, Hangzhou, China, between January 31 and March 1 (lockdown period) and March 2 and April 27 (reopening period) in 2020 and in the same period in 2019 were included in the study. Patients’ diagnosis, age, gender, and several undergoing aerosol-generating procedures during the study period were collected from the hospital’s database. Corresponding data were compared year-on-year (2020-on-2019). A total of 757 hospital staff underwent SARS-CoV-2 detection and serological testing on April 28–29, 2020. Results During the lockdown and reopening period in 2020, the number of hospital visits was dramatically decreased to about 6% and 58%, respectively, compared with the same period in 2019. However, emergency visits were increased 16- and 6.4-fold. A total of at least 6654 patients (13.58%) underwent aerosol-generating procedures during the study period in the year 2020. All hospital staff were negative according to SARS-CoV-2 detection and serological testing (IgG, IgM) data. Conclusion During the study period in 2020, the total number of hospital visits dramatically reduced but emergency visits significantly increased. The prevention strategy implemented successfully prevented SARS-CoV-2 infection spread among healthcare workers in a dental hospital. Clinical relevance The prevention strategy indicated patient triage and how to adopt preventive measures for controlling SARS-CoV-2 spread among healthcare workers. These data can be used as a reference for other sectors suffering from the COVID-19 pandemic. Supplementary Information The online version contains supplementary material available at 10.1007/s00784-021-03886-9.

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.

There is an obvious aerodynamic interference problem that occurs for a quad tilt rotor in near-ground hovering or in the conversion operating condition. This paper presents an aerodynamic interference test of the quad tilt rotor in a wind tunnel. A 1:35 scale model of the quad tilt rotor is used in this test. To substitute for the ground, a moveable platform is designed in a low-speed open-loop wind tunnel to simulate different flight altitudes of the quad tilt rotor in hovering or forward flight. A rod six-component force balance is used to measure the loads on the aircraft, and the flow field below the airframe is captured using particle image velocimetry. The experimental results show that the ground effect is significant when the hover height above the ground is less than the rotor diameter of the quad tilt rotor aircraft, and the maximum upload of the airframe is approximately 12% of the total vertical thrust with the appearance of obvious fountain flow. During the conversion operating condition, the upload of the airframe is reduced compared with that in the hovering state, which is affected by rotor wake and incoming flow. The aerodynamic interference test results of the quad tilt rotor aircraft have important reference value in power system selection, control system design, and carrying capacity improvement with the advantage of ground effect.

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.

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 rapid development of the Internet industry, from a global perspective, the risks brought by network security are becoming increasingly prominent, and continue to penetrate into political, economic, cultural, social, national defense and other fields. Network security has attracted more and more researchers’ attention. This paper first analyzes the two types of network protcol attacks, reviews the development history and current status of off-path attacks, analyzes and summarizes the domestic and foreign literature from the morris TCP injection attacks inwa 1985 to the present. Finally, relying upon the reviewed work, we prospect the future development direction and research focus of off-path attacks.

A method for the generation of tunable multi-degree-of-freedom rotations of vector beams on demand along a propagation direction is theoretically proposed. This generation can be achieved by a suitable vector superposition of three monochromatic non-coplanar beams, including a plane wave with elliptical polarization and two Bessel–Hermite–Gauss (BHG) beams with orthogonal polarization, the parameters of which were systematically chosen to obtain the different longitudinal characteristics of the field, i.e., the state of polarization (SoP), phase, and intensity. On one hand, both the incidence angles of the two BHG beams and the additional phase of the plane wave affect the rotation of the beam intensity and phase, but the incidence angle does not affect the rotation of the SoP. Moreover, the additional phase can lead to a change of the rotation angle of the SoP. On the other hand, the weight coefficients of the two BHG beams periodically change the beam intensity distribution along the propagation direction. Interestingly, the beam is non-diffracting, which means that energy is only exchanged internally and is conserved as a whole. This approach may find applications in dynamic multi-beam optical tweezers, atom guiding, materials processing, microscopy, and optical communications.

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.

Membrane distillation (MD) is a membrane-based thermal separation process. Vapor pressure difference between both sides of the membrane is the driving force for mass transfer of volatile compounds via the gas phase. A hydrophobic porous membrane is generally used as a barrier to isolate the feed from the volatiles permeated across the membrane. Although MD is a thermally energy-intensive process, it can be coupled with low-grade/waste heat sources to increase the overall thermal energy utilization efficiency or reduce thermal pollution. In this chapter, five aspects of MD were studied: • Configurations of MD and their applications in wastewater and water treatment • MD performance enhancement and employment scope broadening by membrane material and structure modifications • MD commercialization • Treatment cost analysis • Conclusion and future trends

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.

Unmanned Aerial Vehicles (UAVs) can extract energy to improve their range and endurance due to thermal updrafts in the environment via static soaring. In this paper, a soaring control strategy is improved based on multi-hole probe technology. A vertical wind speed estimation method based on the multi-hole probe is proposed to design thermal updraft identification, mode switching logic, and the soaring controller. Turn logic is used to determine the correct turn direction for UAVs when a thermal updraft is detected. A simulation environment containing a six-degree-of-freedom glider model and a thermal updraft model is described. The induced roll effect caused by the asymmetric vertical velocity distribution of thermal updraft is included in the simulations. The results show an improved soaring capability from the proposed soaring strategy. Thus, the proposed method based on a multi-hole probe is more accurate and robust, and the turn logic allows a glider to enter a thermal updraft more quickly. The more energy a glider can obtain from thermal updraft enables a lower soaring speed during static soaring.

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.

We investigate the “inverted” solitons in spin-orbit-coupled Bose-Einstein condensate with one-dimensional spatially periodic Zeeman field. Soliton existence depends on the exact invert for the condensate components in the spatially periodic Zeeman field. And the position and the total pseudomagnetization density of the solitons can be controlled by the spatially periodic Zeeman field. Simulated results show that the inverted solitons can be stable for the interatomic attractive interactions.

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.

We report on the existence and stability of fundamental and out-of-phase dipole gap solitons in parity-time (PT)-symmetric mixed linear-nonlinear optical lattices with a fourth-order diffraction. These solitons exist in the semi-infinite gap. For fundamental gap solitons, they can bifurcate from the higher edge of the first Bloch band, solitons are stable in the low power region. For dipole gap solitons, they cannot bifurcate from the higher edge of the first Bloch band, they can stably exist in the moderate power region. The coupling constant of the fourth-order diffraction can influence the stability of these gap solitons.

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 ...

Controlled orientation and alignment of rod‐shaped plasmonic nanoparticles are of great interest for many applications. Herein, it is demonstrated that the nonlinear optical response of gold nanorod suspensions is dynamically controlled by electric field‐induced orientation. Merely by switching incident light polarization, the longitudinal and transverse surface plasmon resonance (SPR) absorption peaks are modulated with opposite trends, and the resulting optical nonlinearity is revealed from self‐trapping of plasmonic resonant solitons. Moreover, even with a very low concentration of fluorescent molecules, a significant increase in the fluorescent signal is observed with a transmittance‐type volume detection scheme. Such an enhancement is attributed to a combined action of optical force‐induced nonlinearity and electric field‐induced nanorod orientation, as explained by the theoretical analyses. Herein, new possibilities for engineering nonlinear plasmonic soft matter and detecting low‐concentration (yet a large total number of moleculesas needed) fluorescent samples are brought out.

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.

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...

A new dynamic test mechanism has been developed in the unsteady low-speed wind tunnel at Nanjing University of Aeronautics and Astronautics to enhance the abilities of experiments in the unsteady flow cases. The structure of the new test mechanism is described in detail in this paper and the equations used to control the performance of test model’s motions are also listed here. Then a wing-body model was tested in the new test system for the first time, including the forced oscillation tests and free-to-roll test at high angle of attack region. The test results are also discussed.

We investigate the nonlocal gray solitons in parity-time (PT)-symmetric potentials with spatially modulated nonlinearity. If the nonlinear modulated function (nonlinear potential) is real, the coefficient of the function can control the grayness and the existence domain of these gray solitons. Especially, if the coefficient of the nonlinear modulated function is below a threshold, the gray solitons will be changed into anti-dark solitons. The effects of the degree of the nonlocality and the imaginary part of the PT-symmetric potentials on the grayness and the existence of the gray solitons are also discussed. If the nonlinear modulated function is also PT symmetric, the imaginary part of the function will obviously affect the existence and stability of the nonlocal gray solitons.

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.

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.

We study the existence of discrete solitons in saturable nonlinearity media with parity-time symmetric lattices. We find that there exist two kinds of discrete solitons, they share the same parameters but different energy flows. The degree of saturable nonlinearity can influence the properties of such discrete solitons. Stable discrete solitons are found near the anti-continuum limit.

We report the fabrication of 2D ZnIn2S4 nanosheet/1D TiO2 nanorod heterojunction arrays by a facile hydrothermal process and their use as photoelectrodes in a photoelectrochemical (PEC) cell for high-performance solar water splitting. The morphology, microstructure, and phase of pristine TiO2 and 2D ZnIn2S4 nanosheet/1D TiO2 nanorod heterojunction arrays were characterized in detail. PEC measurements showed that 2D/1D heterojunction arrays offered enhanced photocurrent density (3 times higher than that of pristine TiO2), negatively shifted onset potential from 0.05 to -0.53 V, and high light on/off cycle stability. Electrochemical impedance investigation attested to a significant improvement of the interface electron transfer kinetics in this heterojunction, thus facilitating electron-hole separation, transfer, and collection, which resulted in enhanced PEC properties.

An array PSJA is tested in this paper by using high-speed phase-lock schlieren system. The characteristic of the transient flow field is studied. The experiment shows that a series of high-speed blast waves spreads outward after discharge. These blast waves, attenuated to the local sound speed, form a wavefront, which continues to influence the flow field. Due to the interaction between each blast wave and the squeeze from previous blast waves, the subsequent blast waves' impact range is limited and form “jet-like” phenomenon. A little later, there comes a high-speed jet to continuous influence the flow field.

We investigate numerically that a finite Airy-Gaussian (AiG) beam varies its trajectory and shape in the defected photonic lattices. The propagation properties and beam self-bending are controlled with modulation depth and period of the photonic lattices, positive and negative defects, beam distribution factor and nonlinearity change. For positive defects, the pseudo-period oscillation and localization of the AiG beam may be formed under a certain condition, while the beam is diffused for negative defects. Moreover, the solitons may appear during the propagation process when the self-focusing nonlinearity is introduced., 15 pages, 8 figures

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.

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.

We investigate numerically surface-wave solitons occurring at the interface between semi-infinite linear and thermal nonlinear optical media, with the refractive index of the linear medium being greater than that of the nonlinear medium (in the absence of light). We find that the threshold energy flows of the existence of the surface solitons depend on the linear refractive index difference of the two media. Their fitting empirical formula has been obtained. Furthermore, we elucidate that the optical beams propagating in thermal nonlinear optical media, either as a single surface soliton or as a dipole surface soliton, can be attracted to the surface, even when launched from far away.

Target irradiation uniformity is very important in laser-produced plasmas experiments. The wavelength dependence of the irradiation uniformity is investigated in the joint scheme using a lens array (LA) and the technique of smoothing by spectral dispersion (SSD). It is proved that, for the long wavelength laser, lateral thermal conduction smoothing within the target is quite effective, while for the ultraviolet laser, SSD is the main smoothing mechanism. So SSD and other temporal smoothing methods are very necessary in producing uniform irradiation with laser beam of short wavelength.

Classical electromagnetic theory is applied to determine the eigenvalue equation and the fields of the allowed guided modes in a symmetric metal-clad planar uniaxial crystal waveguide for an arbitrary orientation of the optical axes. There are different hybrid guided modes in the different uniaxial crystals. For each mode, the conditions for their existence, the dispersion equation, and the accuracy of the solutions of the modal fields are analytically discussed. We report the propagation conditions and the asymmetry of various electric field distributions of the single modes.

Recent fruitful progresses on brain science have largely broadened our understanding of the cerebrum. These great works led us to propose a computational cognitive model based on a graphical model that we carried out before. The model possesses many attractive properties, including distinctive knowledge representation, the capability of knowledge accumulation, active (top-down) attention, subjective similarity measurement, and attention-guided disambiguation. It also has “consciousness†and can even “think†and “make inference.†To some extent, it works just like the human brain does. The experimental evidence demonstrates that it can give reasonable computational explanation on the human phenomenon of forgetting. Although there are still some undetermined details and neurobiological mechanisms deserving consideration, our work presents a meaningful attempt to give further insights into the brain’s functions.

In this paper, the influences of strake wing on unsteady characteristics of aircraft at high angle of attack during rolling oscillation, yawing oscillation, and coupled motion at different frequencies is investigated by using a forced oscillation test rig. The experiments include dynamic force and flow field measurements. As the results show, the rolling moments are affected by the vortices generated by the strake wing. The rolling moment is large and shows strong hysteresis both in the rolling and yawing oscillations. The value of the rolling moment coefficient is small in the coupled motion. The change of the rolling moment is related to the unsteady development of the strake vortices. The characteristics are almost the same for the yawing moment, which may mainly be affected by the sideslip angle. This paper is for the aerodynamic configuration design and the flight control design using flow control method.

We investigate light-beam propagation along the interface between linear and nonlinear media with parity–time symmetry. A novel class of two-dimensional localized surface modes (LSMs) is found analytically and numerically. If the potential is parity–time invariant along the direction parallel to the interface between the two media, stable LSMs can exist. Otherwise, if the potential is parity–time invariant along the direction perpendicular to the interface between the two media, there are no stable LSMs.

As one of the most important methods of vulnerability mining, the technology of fuzzing is developing rapidly and widely used during vulnerability analysis of various kinds of software. Nowadays, with the widespread craze of Android phones, the security of Android operating system has drawn more and more attention. However, fuzzing technology of Android is still in the beginning and professional fuzzing products of Android are unavailable. In this article, a fuzzing method of Android browser based on bitmap structure is presented. The result of experiment proves that this method is efficient in triggering Android browser crashes and can help with further work of analysis and exploitation.

User generated social annotations provide extra information for describing document contents. In this paper, we propose an effective method to model the categorization property of social annotations and explore the potential of combining it with classical language models for improving retrieval performance. Specifically, a novel TR-LDA model is presented to take annotations as an additional source for generating document contents apart from the document itself. We provide strategies for representing and weighting the categorization property and develop an efficient inference algorithm, where space saving is taken into account. Experiments are carried out on synthetic datasets, where documents and queries come from the standard evaluation conference TREC and annotations come from the website Delicious.com. Our results demonstrate the effectiveness of the proposed method on the ad-hoc retrieval task, which significantly outperforms state-of-art baselines.